Schematic Models for Production Engineering 3031336887, 9783031336881

Citation preview

Ricardo Seidl da Fonseca

Schematic Models for Production Engineering

Schematic Models for Production Engineering

Ricardo Seidl da Fonseca

Schematic Models for Production Engineering

Ricardo Seidl da Fonseca Austrian Senior Experts Pool - ASEP Vienna, Austria

ISBN 978-3-031-33688-1 ISBN 978-3-031-33689-8 (eBook) https://doi.org/10.1007/978-3-031-33689-8 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

To my wife, Cristina, children, and grandchildren.

Preface

The present book is centered on the conceptualization and analysis of schematic models used in Methods Engineering, as an area of knowledge of production or industrial engineering, but with wider application in almost all branches of engineering, regarding the use of these methods for design and simulation. With the growing automation of production and the introduction of robotics and the “Internet of machines,” more than ever the use of schematic models is expected to be essential to achieve quality and safety in production projects, whether manufacturing, industrial processes, or services. Indeed, technological development in the industry and service sectors records and indicates a growing effort to standardize and automate the production process. In this context, schematic methods can be essential tools for the study and analysis of the production process, its representation and simulation, as well as for the implementation of new systems and their maintenance. The work containing an updated version of a representative set of schematic models serves as both didactic reference for students and technical support for professionals in the field. In production engineering, the work aims to be used in the knowledge areas of production management, ergonomics and work safety, facilities planning, production automation, production planning and control. The work realizes a review of the most successfully used schematic models for work methods study in the traditional and modern industry and proposes their extension to the Industry 4.0 context. Indeed, the work intents to build a bridge linking the traditional industry, still prevalent in most countries, to the implementation of digitalizing, computer intensive, automation, and robotization technologies, which are the characteristics of the Industry 4.0 concept. Vienna, Austria

Ricardo Seidl da Fonseca

vii

viii

Preface

Acknowledgments The author wishes to express his appreciation to Prof. Itiro Iida for his support and inspiration from the origin of this work and to the Brazilian Association of Production Engineering (ABEPRO) and Prof. Francisco Soares Másculo for the encouragement to publishing this book.

Introduction

The work belongs to the study of work methods applied in a conscious and organized way in the performance of economic productive activities. The theme of concentration here is the schematic models used by the designer of methods to represent and enable action on real work situations. The treatment given to the models in this context consists of: (a) classify, regroup, and name the most widespread and used models; and (b) analyze and conceptualize each distinct model. The first treatment aims to bring together in a single text a representative number of schematic models of Methods Engineering, mentioned according to different classifications and names in the most significant specialized works. The second treatment offers a form of common understanding to the various models, since in the works available, most of the models are formalized differently and partially. The text structure comprises a conceptual presentation of models (Chap. 1); a conceptualization of the work study (Chap. 2), which defines its scope and interrelationships, and its field and criteria for action; and a conceptualization of Methods Engineering (Chap. 3), where its field and design instruments are defined, and particularly the schematic models of representation and analysis. The core of the work is Chap. 4, in which ten most significant schematic models are presented. Each model is analyzed according to a common structure, divided into conceptualization of the model, constructive conception, criteria for improvement of work situations, typical and extensive uses of the model, and the possibilities of manipulation in order to allow the visualization of possible improvements in situations of work. Finally, examples are presented to demonstrate the proposed design of each schematic model. The content of the book, in addition to texts with didactic purposes, presents a total of 75 figures, containing selected classic examples and others prepared by the author, showing in detail the design and formalization of schematic methods and related topics.

ix

Contents

1 Model Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Models in Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 3 4

2 Concept of Work Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Work Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Work Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Development Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Productivity Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 6 6 8 9 12

3 Concept of Methods Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Basic Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Responsibilities for Work Methods Projects . . . . . . . . . . . . . . . . . . . . 3.3 Techniques for Designing Work Methods . . . . . . . . . . . . . . . . . . . . . . 3.4 Methods Engineering Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13 13 15 15 16 18

4 Analysis of Schematic Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Purpose and Content of Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Glossary of Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Classification and Characteristics of Schematic Models . . . . . . . . . . 4.4 Analysis of Schematic Models Presentation . . . . . . . . . . . . . . . . . . . . 4.4.1 Interrelationship Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1.1 Transport Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1.2 Table of Preferred Interconnections . . . . . . . . . . . 4.4.2 Information Distribution Table . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3 Process Flow Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3.1 Single Flow Diagram . . . . . . . . . . . . . . . . . . . . . . . 4.4.3.2 Assembly Flow Diagram . . . . . . . . . . . . . . . . . . . . 4.4.3.3 Manufacturing and Assembly Flow Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19 19 21 25 28 28 34 41 49 50 67 71 73

xi

xii

Contents

4.4.4

4.4.5 4.4.6

4.4.7 4.4.8 4.4.9

4.4.10

References

4.4.3.4 Productive Sectors Flow Diagram . . . . . . . . . . . . 4.4.3.5 Complex Procedure Flow Diagram . . . . . . . . . . . 4.4.3.6 Chronological Flow Diagram . . . . . . . . . . . . . . . . 4.4.3.7 Business Process Diagrams (BPD) . . . . . . . . . . . Map Flow Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.4.1 Bidimensional Map Flow Diagrams . . . . . . . . . . 4.4.4.2 Three-Dimensional Map Flow Diagram . . . . . . . Chronologic Assembly Diagram . . . . . . . . . . . . . . . . . . . . . . Simultaneous Activities Diagram . . . . . . . . . . . . . . . . . . . . . . 4.4.6.1 Person-Machine Diagram . . . . . . . . . . . . . . . . . . . 4.4.6.2 Team Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.6.3 Production Line Diagram . . . . . . . . . . . . . . . . . . . Route Frequency Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cyclegraph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sensory-Motor Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.9.1 Sensory-Motor Diagram for Manual Work . . . . . 4.4.9.2 Sensory-Motor Diagram for Work with Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . Manual Activity Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.10.1 Manual Activity Diagram for Operations . . . . . . 4.4.10.2 Manual Activity Diagram for Operations and Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.10.3 Manual Activity Diagram for Operations, Transport and Delays . . . . . . . . . . . . . . . . . . . . . . . 4.4.10.4 ASME Manual Activity Diagram . . . . . . . . . . . . 4.4.10.5 Fundamental Manual Activities Diagram . . . . . . 4.4.10.6 Chronological Manual Activity Diagram or SIMO Diagram . . . . . . . . . . . . . . . . . . . . . . . . . .....................................................

87 90 93 96 101 107 109 111 115 122 127 129 136 143 150 152 154 157 163 164 167 167 172 175 183

About the Author

Prof. Dr.–Ing. Ricardo Seidl da Fonseca is International Senior Researcher and Adviser on strategic decision-making. He is member of the Austrian Senior Experts Pool - ASEP, based in Vienna, Austria. He acted as University Professor at the Federal University of Rio de Janeiro, Production Engineering Department (COPPE/ UFRJ). He is Former Senior Officer at the United Nations Industrial Development Organization (UNIDO), where he acted as Unit Chief of the Business, Investment, and Technology Branch. He held a position of Visiting Scholar at the George Washington University’s Institute for International Science and Technology Policy. He acted as Doctorant and Researcher at the Technical University of Munich, Institute for Machine-Tools and Business Science, Germany. He is a senior specialist in industrial engineering; work study and methods; science, technology and innovation policy; project finance; public–private partnerships; and foresight.

xiii

List of Figures

Fig. 1.1 Fig. 1.2 Fig. 2.1 Fig. 2.2 Fig. 3.1 Fig. 4.1 Fig. 4.2 Fig. 4.3 Fig. 4.4 Fig. 4.5 Fig. 4.6 Fig. 4.7 Fig. 4.8 Fig. 4.9 Fig. 4.10 Fig. 4.11 Fig. 4.12 Fig. 4.13 Fig. 4.14 Fig. 4.15 Fig. 4.16 Fig. 4.17 Fig. 4.18 Fig. 4.19 Fig. 4.20 Fig. 4.21 Fig. 4.22 Fig. 4.23 Fig. 4.24 Fig. 4.25

Models concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Model building cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coverage levels of production systems . . . . . . . . . . . . . . . . . . . . . Productivity development and the role of work study . . . . . . . . . Classification of methods engineering models . . . . . . . . . . . . . . . Characterization of models’ names . . . . . . . . . . . . . . . . . . . . . . . . System representation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . From-to matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Triangular matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of using the interrelationship table . . . . . . . . . . . . . . . . . Example of a From-To Table with entry and exit of items . . . . . . Multi-column flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transport moment definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of transport movement evaluation . . . . . . . . . . . . . . . . . Examples of connection classes . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of use of the table of preferential interconnections . . . . Example of the related graphics of importance . . . . . . . . . . . . . . . Example of network analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Symbology used for flow diagrams . . . . . . . . . . . . . . . . . . . . . . . . Example of a summary table for flow diagram . . . . . . . . . . . . . . . Summary sheet of multiple singular flowcharts . . . . . . . . . . . . . . Example of single flow diagram—dimple format . . . . . . . . . . . . . Example of a single flow diagram—standardized format . . . . . . . Construction of assembly flowchart . . . . . . . . . . . . . . . . . . . . . . . . Assembly flowchart example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of convention for process inputs . . . . . . . . . . . . . . . . . . . Example of manufacturing and assembly flow diagram construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Repetition or loop indication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indication of reprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indication of material removal . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 4 7 10 17 21 29 31 31 32 35 36 37 38 45 46 47 47 55 61 68 69 70 71 72 76 77 79 79 80 xv

xvi

Fig. 4.26 Fig. 4.27 Fig. 4.28 Fig. 4.29 Fig. 4.30 Fig. 4.31 Fig. 4.32 Fig. 4.33 Fig. 4.34 Fig. 4.35 Fig. 4.36 Fig. 4.37 Fig. 4.38 Fig. 4.39 Fig. 4.40 Fig. 4.41 Fig. 4.42 Fig. 4.43 Fig. 4.44 Fig. 4.45 Fig. 4.46 Fig. 4.47 Fig. 4.48 Fig. 4.49 Fig. 4.50 Fig. 4.51 Fig. 4.52 Fig. 4.53 Fig. 4.54 Fig. 4.55 Fig. 4.56 Fig. 4.57 Fig. 4.58 Fig. 4.59 Fig. 4.60 Fig. 4.61 Fig. 4.62 Fig. 4.63

List of Figures

Indication of an independent decision . . . . . . . . . . . . . . . . . . . . . . Indication of dependent decision . . . . . . . . . . . . . . . . . . . . . . . . . . Indication of state change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indication of crossing of lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indication of the document title . . . . . . . . . . . . . . . . . . . . . . . . . . . Indication of termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indication of distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indication of data transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indication of corrections and reiterations . . . . . . . . . . . . . . . . . . . Example of a person process flow diagram . . . . . . . . . . . . . . . . . . Example of material process flowchart . . . . . . . . . . . . . . . . . . . . . Example of productive sectors flow diagram . . . . . . . . . . . . . . . . Indication of alternative actions . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of a complex procedure diagram . . . . . . . . . . . . . . . . . . Chronological flow diagram basic formats . . . . . . . . . . . . . . . . . . Example of chronological flow diagram for single form . . . . . . . Example of chronological flow diagram for multiple forms . . . . Example of business process diagram . . . . . . . . . . . . . . . . . . . . . . Example of a bidimensional map flow diagram of route . . . . . . . Example of a map flow diagram of activities . . . . . . . . . . . . . . . . Example of three-dimensional map flow diagrams of activities and route . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of chronological assembly diagram . . . . . . . . . . . . . . . . Basic shape of the diagram of simultaneous activities . . . . . . . . . Types of graphic symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of person-machine diagram construction . . . . . . . . . . . . Representation and diagram of pit stop team in a car endurance racing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of a production line diagram . . . . . . . . . . . . . . . . . . . . . . Example of a route frequency table . . . . . . . . . . . . . . . . . . . . . . . . Example of route frequency diagram for operator movements in a plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of route frequency diagram for bench operator . . . . . . . Construction of an electronic device for variable electrical power interruption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Examples of cyclegraph and chronocyclegraph using photographic technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Symbology of the activities of perception . . . . . . . . . . . . . . . . . . . Example of sensory-motor diagram for manual work . . . . . . . . . Schematic definition of the person-machine system . . . . . . . . . . . Person-machine relationship scheme . . . . . . . . . . . . . . . . . . . . . . . Example of sensory-motor diagram for working with equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of a manual activity diagram for operations . . . . . . . . .

80 81 81 82 82 83 83 84 84 85 86 89 91 92 93 94 95 100 108 109 110 114 117 118 127 130 136 139 142 143 147 150 151 154 155 155 156 165

List of Figures

Fig. 4.64 Fig. 4.65 Fig. 4.66 Fig. 4.67 Fig. 4.68 Fig. 4.69 Fig. 4.70

Example of a manual activity diagram for operations and transports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of a diagram of operations, transport and delays . . . . . . Example of ASME diagram—simple . . . . . . . . . . . . . . . . . . . . . . Example of ASME diagram—form . . . . . . . . . . . . . . . . . . . . . . . . Definition and representation of “therbligs” . . . . . . . . . . . . . . . . . Example of a fundamental manual activities diagram using “therbligs” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of SIMO diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xvii

166 168 170 171 173 180 183

List of Tables

Table 2.1 Table 4.1 Table 4.2 Table 4.3 Table 4.4 Table 4.5 Table 4.6 Table 4.7 Table 4.8 Table 4.9 Table 4.10 Table 4.11 Table 4.12 Table 4.13

Aspects related to productivity development . . . . . . . . . . . . . . . Glossary of the analyzed models . . . . . . . . . . . . . . . . . . . . . . . . . Classification and functional characteristics of schematic models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Components, flows, and relationship factors . . . . . . . . . . . . . . . Example of weight assignment for transport difficulty . . . . . . . Summary transport table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of transport difficulty definition . . . . . . . . . . . . . . . . . . Example of a transport table . . . . . . . . . . . . . . . . . . . . . . . . . . . . Information distribution table basic design . . . . . . . . . . . . . . . . . Example of the use of information distribution table . . . . . . . . . Definition of perceptual activities . . . . . . . . . . . . . . . . . . . . . . . . Hands micro-movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Definition of effective and ineffective activities . . . . . . . . . . . . . Suggestions for improvements of fundamental activities . . . . .

11 22 26 30 35 35 39 42 50 51 153 153 175 176

xix

List of Boxes

Box 4.1 Box 4.2 Box 4.3

Magnitude Account (Mag Count Chart) . . . . . . . . . . . . . . . . . . . . . Mathematical Calculations of Costs for Determination of the Optimum Number of People and Machines . . . . . . . . . . . . . Mathematical Calculations for Chronocyclegraph Analysis . . . . .

37 125 148

xxi

Chapter 1

Model Concept

CONCEPT: A model is a reasoning scheme that enables the human mind to understand and act on an aspect of the real world, through its reproduction and interpretation in terms of a known reference framework. When facing a certain real fact, one tries to express it in a way that is known and can be better acted upon, without the need to get directly involved with the real fact, which is sometimes impossible, uneconomical, or dangerous. For example, in order to study the conditions under which the embankment and widening of an ocean beach should be carried out, a reduced-scale three-dimensional model of the entire affected coast can be constructed. With it, several alternatives for landfill and containment are tested, and thus, the best solution is determined, according to certain parameters, easily controlled by the model. Without a similar resource, it could lead to very high costs, errors, and huge risks. The model is scientific reasoning par excellence. In other words, a portion of reality is taken, which is reproduced according to known facts, as part of a space whose laws of formation are known, and the behavior of some chosen variables is studied. It is observed that this reasoning scheme is not new to people. From an early age, people already have contact with models, whether the spoken language is a representation of thoughts, or toys reproducing some components of the real world. And the manipulation of these models undoubtedly taught a lot about their correlates of reality. Throughout life, the use of models continues to appear quite frequently. Much of the teaching process is based on analogies, physical models, graphs, formulas, abstract models, etc. In relationships with other people, often one uses language models, analogies to guide a discussion or drawings to explain a fact. Thus, it can be concluded that the use of models is of vital importance in any perception of the problems of reality that need to be understood and acted upon, because in addition to being almost a “natural” way for people to reason, they

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 R. Seidl da Fonseca, Schematic Models for Production Engineering, https://doi.org/10.1007/978-3-031-33689-8_1

1

2

1 Model Concept

allow a freer, more flexible, and more precise manipulation of the facts and variables involved. According to Buffa (1969, p. 23), “in fact, clear thinking requires a knowledge of the nature and use of models.” A model is not just a representation of reality but also an interpretation of reality. It is a representation because it is always an abstraction at some level of the actual fact or situation of which certain aspects one wish to study. In this case, it works as a kind of translation of phenomena, from a vast and partially unknown universe to another, more restricted and better-known universe. The construction of models is oriented in order to make it possible to explain the behavior of some, but not all, aspects of the actual fact or situation. That is, it should emphasize the aspects considered most important in the case under study and ignore or consider irrelevant those of lesser significance. Thus, an interpretation of reality will be made, as there will always be intentionality and non-neutrality, in the selection of study aspects by those who build or work the model. To avoid mistakes or inconsequence, when building or working with models, one should always define and, if possible, clearly explain the assumptions that guide the thought when focusing on the study theme of the model in question. Models are used to, through a reproduction or interpretation in terms of a controllable universe, understand the real, to act on this understanding of the real, to then act on the real, and finally, closing a cycle, to understand the action performed over the real (Fig. 1.1).

Fig. 1.1 Models concept

1.1 Models in Engineering

3

1.1 Models in Engineering Engineering models follow the general conceptualization of models, but they have some specific characteristics and language. In these models, the explanatory aspects of the real event are considered as variables; the relationship of these variables must meet a certain and defined function; the fulfillment of such function is the objective of the study or project, and consequently of the model, the relationship of variables oriented toward the fulfillment of a given function and objective establishes a relationship structure; the set of variables, relationship of variables, function and objective, and relationship structure as well constitute a system; the various possible alternative forms of functional relationship of the variables, and, as a result, the various possible systems generate and are affected by different behaviors of the variables; as a consequence of that, they will meet, to a greater or lesser degree, the function and objective; the behavior of variables and systems are evaluated according to the degree of compliance with the function and objective, defining performance standards. Another important specificity is that the engineering models aim to permit and enable an immediate action upon the reality. Thus, the use of engineering models will be focused on acting upon the real and acting on the understanding of the action performed upon the real (as shown in Fig. 1.1). The effort of understanding the real and acting on the understanding of the real will be provided through scientific or technological models according to the aspects of the real highlighted in the study. For example, to understand a machine, models from physics, chemistry, and mathematics are used; as for the understanding of a work system are applied models of sociology, economics, psychology, physiology, and ergonomics. The engineering action upon a real subject almost always aims to create a new fact, based on preexisting situations, whether it is a construction based on materials or an operational system based on functions. So, it can be said that engineering work is basically a project design work. And this gives the engineering models another basic characteristic, which is forecast. In fact, this predictive characteristic is the main reason for the use of models in engineering projects, as they allow testing a given project design through its reproduction in a controllable and evaluable context, instead of creating or modifying the real situation and then evaluating it, which could be dangerous, difficult, or uneconomical. Thus, it can be considered that engineering models must be (a) less complex than the real situation; (b) belonging to a known, controllable, and evaluable context; (c) they must allow a clear correlation and evaluation of the highlighted variables, in regard to performance standards; (d) guiding the action to be carried out upon the real subject; and (e) allow predicting with some accuracy what happens or could happen in the real situation. A model that does not meet these conditions can lead to serious errors or restrictions. Furthermore, any single model may not consist the only way to represent or interpret a given real fact, considering that several different models can be used and combined to understand it. The most familiar type is the three-dimensional scale

4

1 Model Concept

Fig. 1.2 Model building cycle

model, such as prototype and mock-up. However, a wide variety of models is available such as descriptive and verbal models; graphic representations, as diagrams, graphs, photos, films, drawings, copies, forms, or computer simulation models as well as several others that will be classified and analyzed in detail in the two following sections of this work. Engineering models can be used to guide and represent a design, enable evaluations, represent an operating procedure, gather information, record behaviors, or as a means of communication and language. The models, however, shall not be passive instruments, requiring a built-in systematic reevaluation, which permits comparing systematically the results forecast by them against those actually produced. This systematic reevaluation will determine its accuracy and reliability (Fig. 1.2). An example from Buffa (1969, p. 23) facilitates the understanding of these concepts: “A model is always an abstraction to some degree of the real-life thing or process for which we want to predict performance. For example, the aerodynamicist (sic. airplane aerodynamics designer) uses models and a wind tunnel to study his design. Bei no means does the model attempt to duplicate all characteristics of the design. Although factors of shape, weight, strength of parts, temperature, and so on are all important in determining how well the plane design may perform, the engineer is studying aerodynamic performance wherein shape is the main characteristic. Therefore, his model accurately replicates shape and ignores other factors. The model that is used allows ease of measurement, the manipulation of variables at will, etc., and all at fairly low cost. To attempt similar study with real planes would not only be costly and hazardous, it probably would not yield as much information. By abstracting from real-life situation, the aerodynamist can focus his attention on something simpler and not lose much by the fact that many details have been ignored.”

Reference Buffa ES (1969) Modern production management, 3rd edn. Wiley, New York

Chapter 2

Concept of Work Study

This chapter seeks to define where the central theme of the book fits—the schematic models of Methods Engineering—in the context of knowledge related to the study of work as a component of production systems. From the structure of productive systems, which deal with the generation, supply, and maintenance of material goods that human societies need, the text highlights the work systems. More specifically, human work systems are focused. In the concept used here, it is considered that human work systems are studied by a wide body of knowledge about nature, the human being itself and the material transformed by human beings, defined as the work study or ergology. Among this very comprehensive field of study, which relates to almost the entire universe of human knowledge, the present text is restricted to the study of the physical execution of work and finally to the study of the performance on the ways or methods of executing it, i.e., Work Methods Engineering. From this area, some instruments used to guide and check the projects of working methods are taken: the schematic models. Work study—refers to the study of human work systems as a component of production systems. Ergology—consists of the in-depth study of work, encompassing the analysis of all the variables that interact with the work phenomenon, in a multi-disciplinary approach that mobilizes the areas of economics, ergonomics, psychology, linguistics, philosophy, sociology and law to analyze the universe of work.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 R. Seidl da Fonseca, Schematic Models for Production Engineering, https://doi.org/10.1007/978-3-031-33689-8_2

5

6

2 Concept of Work Study

2.1 Work Systems The components of the productive systems that perform the dynamic part of production are the work systems, mobilizing people, animals, machines, and processes, which directly provoke the transformation of material goods and information. The passive part of production is attributed to components that do not act directly in the transformation of material goods and information, such as buildings, land, access roads. In this line, Nadler (1963, p. 37) defines work systems as follows: “Work systems refers to the whole complex of physical, mechanical, electrical, chemical and human activities (in other words, all the technical competences) required to process any material or information to its the desired state of product or service.” Thus, it can be defined that work systems are made up of three basic subsystems: • human work system; • system of work of produced goods (consisting, in principle, of all artificial instruments produced, such as tools, machines, and equipment); and • nature’s work systems (consisting of all-natural resources that cause man-made transformations on material goods, such as hydraulic, electric, nuclear, chemical energy, domestic animals, agriculture). This text is part of the study of human work systems as indicated below. Human work systems are made up of all forms of intentional, organized and interrelated participation of people in productive systems. The participation of people in production systems can be defined according to three basic types of activities: • direct productive activities; • indirect productive activities or direct support; and • organizational activities. Considering the automation of production, the use of robots to replace or expand human work and the application of artificial intelligence for decision processes and communication between equipment, this text encompasses, when relevant, the extension or expansion of human work with these facilities.

2.2 Work Study The term work study is therefore referred in this text to the study of human work systems, oriented toward those three types of basic activities mentioned above. The British Standards Institution (1959, 1979) defines work study as: “A generic term for those techniques which are used for the understanding of human work in all its contexts, and which systematically lead to the investigation of all factors which affect the efficiency and economy of the situation under study, in order to effect improvements.”

2.2 Work Study

7

Using this definition in a broader conception, it can be established that the study of work involves two levels of action: (1) analysis and synthesis of laws and principles that create knowledge about work systems, such as certain branches of sociology, psychology, physiology, economics, law, politics, anthropology, physics, chemistry, process engineering, administration, etc. (2) design of work systems based on such knowledge in order to systematically find better and more improved viable solutions, such as certain branches of production engineering, ergonomics, occupational medicine, methods engineering, statistics, and mathematics. As for the scope of the work study, one can consider all levels of the productive system that have a human work system as a component. For operational purposes, five basic levels of coverage are defined relative to levels of production systems: • • • • •

macroeconomic; sectoral, regional, or professional groups; company, plant or group of firms; departments or functional groups; workstation.

Figure 2.1 provides a visualization of the scale of coverage levels, according to the average number of persons involved at each level. This broad conception of the work study characterizes a body of knowledge formed by different branches of almost all sciences, arts and technologies related to the understanding and development of productive activity organized by human, entitled ergology. One key component of the work study dedicated to the design of work systems constitutes the Methods Engineering. It is up to Methods Engineering to design the ways in which individuals or groups of persons perform work in an organized manner, at the various levels of production systems. In short, Methods Engineering focuses on specifying how persons physically performs work. Fig. 2.1 Coverage levels of production systems

8

2 Concept of Work Study

2.3 Development Criteria Work studies shall observe certain development criteria, which define the study objectives. Considering the performance of production systems, the immediate criterion for study should be productivity, that is, by achieving the highest possible production with the least expenditure of resources. For human work systems, the productivity criterion implies orienting the study to enable the highest possible production with the least expenditure of human productive capacity. The ideal goal of a study in this way is to make the best application of human work capacities used in the intentional and organized production of goods and services. The concept of productivity presented here suggests two basic orientations: resource balance and non-waste. Therefore, the guiding criterion of the work study is the enhancement of the productivity of production systems. In this context, productivity is defined as an efficiency ratio between: a. indices of output and input of a production system, that is, the production obtained, and the resources used to obtain it; or b. the actual and projected indices referring to a given characteristic of a productive system. Some productivity measures used at each level of scope of the work study are listed below (Sevá 1974). A. Macroeconomic level Indexes: O (output)—physical performance of production: total amount of production per period. Ex. 15 million coffee bags a year, 300 thousand cars a month. Y (income)—economic performance of production: total value, gross or net, of production in the period. Ex. Gross Domestic Product (GDP) of 1.80 trillion dollars in 2015. L (labor force)—physical performance of the workforce: total person-hours effectively used in the period. Measurement: O/L—physical productivity of labor, in units of physical product per unit of manhours. Ex. 20 barrels of oil per man/hour. Y /L—economic productivity of labor in monetary unit per man/hour. Ex. net product per industrial worker = US$ 20.000 per year. B. Sectors level

2.4 Productivity Development

9

Indexes (for sector j). Oj —sectoral product. Y j —sectoral income. L j —sectorial labor employment. Measurement: Oj /L j —physical productivity of sectoral labor, in units of physical product per unit of man-hours. Y j /L j —economic productivity of sectorial labor in monetary units per man/hour. C. Enterprise level (for enterprise i of sector j) Measurement: Y ij /L ij —average economic productivity of employer in monetary units per man/ hour. D. Workstation level Measures of efficiency of a given operator: ep = actual/projected quantity of products = net production efficiency. eq = actual/projected quality level = production quality efficiency. er = actual/projected use of resources = logistic or use of resources efficiency. et = actual/projected time or pace = time or pace efficiency.

2.4 Productivity Development A productivity level is directly linked to a technology level used in the production system. In order to develop the productivity of a production system, that is, increasing from a productivity level at a given moment to a higher level after a certain period of time, it is necessary to further develop the technology used, and consequently, the productive system itself. Observing the development of a production system together with the development of the technology used and the productivity of the system, it is verified that the following facts occur: • Extra financial investment resources are injected into the system aimed at transforming the system’s conditions from that initial moment onwards. • Workspace and equipment, labor qualification, and production organization are increased, improved, or elaborated.

10

2 Concept of Work Study

Fig. 2.2 Productivity development and the role of work study

Given that the realization of these facts depends on the mobilization of intentional and organized human participation, thus defining a work system, one can represent the effort of work study for the development of productivity as indicated in Fig. 2.2. Some aspects related to the development of the productivity of human work systems are listed in Table 2.1, integrating the factors workspace and equipment, labor qualification, and production organization.

2.4 Productivity Development

11

Table 2.1 Aspects related to productivity development Action upon

Means of increment, improvement and elaboration

Work study

Methods study

Workspace and equipment

• Process design • Product design • Physical arrangement • Work environment • Equipment, machines, and tools • Architecture • Location • Facilities • Technical standards • Standardization • Quality • Numeric control equipment • Automation and robotization

• • • •

• Sequences, flows, movements • Location of resources and physical facilities • Tooling • Safety equipment • Control, automation, and robotization • Logistics • Workplace architecture, lighting, ventilation, colors, sensors

• Division of work • Education • Standard and quality of life • Control procedures • Participation • Working conditions • Personnel administration

• Training • Wages rates • Psychology and sociology of work • Anthropometry • Medicine, hygiene and safety • Labor law • Methods Engineering • Time and movement study • Work evaluation • Work measurement • Technical education • Information systems

Labor qualification

• •

•

•

Plant layout Anthropometry Ergonomy Hygiene and safety Operational methods Maintenance, transport and movements Design of equipment, machines, and tools Human control of equipment and facilities

• Means of training • Job specialization and job enlargement • Work rhythm and time • Task specification • Intercommunication • Fatigue study • Personnel selection • Remuneration rates

(continued)

12

2 Concept of Work Study

Table 2.1 (continued) Action upon

Means of increment, improvement and elaboration

Work study

Methods study

Production organization

• Administration • Division of labor • Controlling • Management • Production relations • Remuneration • Personnel policy • Legal conditions • Automation and artificial intelligence

• Supervision • Formal and informal groups • Leadership • Incentives • Motivation • Delegation of responsibilities • Discipline • Sociology and psychology of work

• Production delivery • Preparation and chronological planning of resources and works • Production scheduling • Team building • Quality enhancement

References British Standards Institution—BSI (1959, 1979). Glossary of terms in work study. BS 3138. British Standards House, London Nadler G (1963) Word design. Richard D. Irwin, Homewood Sevá Filho AO (1974) Introdução à Administração do Trabalho, mimeo. COPPE

Chapter 3

Concept of Methods Engineering

3.1 Basic Concepts Methods Engineering is responsible for designing the ways in which people or groups of people perform their parts of work in a productive system. In other words, designing how human work is realized. As automated equipment, robots, or facilities acting with artificial intelligence replace or expand human work, Methods Engineering has its scope extended as well. Methods study is characterized as an engineering for aiming at a direct action on the objective reality. At Maynard (1963, pp. 2–3) is defined that “Methods Engineering is that aspect of industrial engineering which is concerned with the planning of more effective working methods.” Krick (1962, p. 81) states that: “Methods Engineering is concerned with integration of the human being into a productive system.” The International Labour Office, OIT-ILO (1973) defines that: “Methods study is the systematic recording, analysis and critical examination of existing and proposed ways of performing work, and the development and application of simpler and more effective methods, and to reduce costs.” “The objectives of the methods study are to improve processes and procedures; improve the layout of the factory, workshop and workplace, as well as the design of equipment and facilities; economize human effort and reduce unnecessary fatigue; improve the use of materials, machines and labor; create better material working conditions.” The design of how people or groups of people perform or will perform their work is done by creating a new work situation or improving an existing work situation, according to a key development criterion, considered in this text as productivity. The creation of a new work situation seeks to guarantee in its formulation the highest possible level of productivity within the boundary conditions. Based on the evaluation of an existing work situation and verifying that predicted goals were not achieved or within a broad effort to develop the productive system, the need to improve the work

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 R. Seidl da Fonseca, Schematic Models for Production Engineering, https://doi.org/10.1007/978-3-031-33689-8_3

13

14

3 Concept of Methods Engineering

situation arises. The exercise to improve working methods may entail, in addition to changes in the existing one, changes in boundary conditions. Boundary conditions, or project constraints, for the design of work methods are due to the work content and the work environment. And these two vectors of study and project, in fact components of the general work study, define the action field of Methods Engineering. Ultimately, from a given work content, Methods Engineering determines how to execute that content within a given work environment. Work content refers to specifying the type of human work involved in a work situation and what work is performed by the person or set of people involved. The specification of the work content is based on a division of labor between people and between people and machines, which defines the attributions of each element or set. This division of labor, and consequently the content of work, is guided and limited by technological, economic, and sociological criteria. The work environment refers to the entire factors complex that involves the work situation, consisting of physical environments (equipment, buildings, climate, ventilation, hygiene and safety, products, etc.), psychological environments (tensions, motivation, interests, dependencies, etc.), sociological (groups, classes, communication, conflicts, leadership, commands, etc.), economic (technology, state of maintenance, remuneration, etc.), and political (representations, laws, responsibilities, etc.). Since these boundary conditions influence and are affected by the design of the working methods, it will also be the responsibility of Methods Engineering to consider both the work content and the work environment. There is also an interdependence between the content, the method and the environment. Below are indicated examples of this content-method-environment interdependence: Example 1—The product design (physical environment) practically determines and is constrained by the defined production process (content); the production process demands and is limited by alternative work methods; the work method, according to cost criteria, sequences, movements, execution difficulties, will, in turn, reorient or change the product design. Example 2—The social organization (sociological environment) defines and is structured by a division of labor (content); the division of labor defines and is reinforced, or even challenged, by the ways of performing the various tasks (method); the actual realization the work may lead to reorganizations or changes in the social organization. Typical problems of work methods design are: (1) physical movement and transport of people, materials, and information within a production system, involving flow and sequencing problems; (2) physical positioning of work systems components; (3) ideal or optimal composition of the environmental factors involved in the execution of the work (e.g., physical dimensions, human relations, colors, lighting, hygiene, and safety); (4) training and qualification of human elements or teams in the organized execution of work; (5) specification and dimensioning of tasks and working hours; (6) control, evaluation, and valuation of work execution.

3.3 Techniques for Designing Work Methods

15

3.2 Responsibilities for Work Methods Projects Work methods projects should be part of the normal planning activities for the implementation, maintenance, and development of any work system, at any level of scope. The responsibility for the projects may fall on the following professionals, group of professionals or entities: • Operators and workers—the executors of the production process themselves can be directly responsible for the design of working methods according to development criteria. Work study and work methods design techniques can form part of vocational training curricula (both technical schools and higher education) or even on-the-job training. • methods, work, and production engineers—with the responsibility of advising managers and workers in the application and dissemination of methods design techniques and in advising on complex projects. • ergologists and work study scholars—working in the various branches of knowledge linked to the work study, such as sociologists, economists, engineers, administrators, and others, with the responsibility of acquiring, developing, and disseminating knowledge about work systems. • administrators and directors—responsible for ensuring planning and control over the execution of human work within the related production systems. In a broader sense, all members of production systems and society are somehow responsible for establishing the methods for the physical execution of work. This is because the ways of working define and represent the standard of life and culture, and the very structuring of society.

3.3 Techniques for Designing Work Methods In the context of Methods Engineering, a series of techniques are available aiming to guide and improve the design of work methods. The most used are: (1) Problem-solving methodology—methodological processes developed from techniques to increase the creativity of the human mind, oriented toward the discovery of a range of alternative solutions to defined problems. (2) Project methodology—methodological processes developed for the execution of engineering projects. The most used methodologies are the Cartesian type ones, which divide the project into successive phases (see Krick 1962, p. 89): formulation (description of the problem and project objectives), analysis (collection and investigation of data, restrictions and criteria related to the project), search for solutions ( definition of alternative solutions or guidelines for the project), evaluation of solutions (judgment of alternative solutions, under the criteria and objectives of the project), project specification (outlining and presentation of

16

3 Concept of Methods Engineering

the proposed solution), and implementation and monitoring (actual application phase of the proposed solution). A referential project methodology is the logical framework, which identifies and aligns goals, objectives, inputs, and outputs. (3) Modeling techniques—consisting of the use of engineering models for the study, analysis, simulation, representation, and evaluation of work methods projects. The central core of this text (Chap. 4) presents and analyzes some of the most used schematic models in Methods Engineering.

3.4 Methods Engineering Models In general, human work situations involve numerous variables, making their understanding and elaboration quite complex. In this sense, the study and design of work methods require the construction and manipulation of models to reduce the universe of variables and lower the complexity of the study and still reach feasible solutions. Representing work systems by models is often more technically viable, economical, fast, and safe, for manipulation and experimentation than acting on the real work situation. In cases where there is a complex or dangerous relationship between operators and the work situation or intricate technological processes, the use of models is essential. On the other hand, the models, by providing a concentrated view of the structure and formalization of the subject studied, allow designers and other professionals involved to have a common understanding of the work situation they observe or participate in. The objectives of the models developed for the study and projects of work methods are: (a) collection, organization, and presentation of data and information on the work situation; (b) support in analyzing data and information, and the work situation itself; (c) support in the development of new or improved methods; (d) support for the general or specific understanding of the work situation; (e) assistance in promoting and accepting innovations and improvements in the work situation for the people involved; (f) support to the control mechanisms on the work situation or execution. To meet these objectives, there are a large number of models, which can be classified according to some functional characteristics, such as: structure of model construction, highlighted variables, type of record of the work situation, object of focused study, scope level of the study, type of work situation project, and administrative use of the model. The identification of the different models according to the abovementioned classification is presented below (Fig. 3.1). Among the types of models defined regarding their constructive structure, the present text is dedicated to schematic models.

3.4 Methods Engineering Models

17 • Statistical • Mathematical • Physical • Analog and physical simulation • Descriptive

Regarding the constructive structure

• Pictorial • Schematic • Graphic, symbols and tables • Economic and cost

• Time • Distance Quantitative

• Costs • Frequency • Flow density

Regarding the variables

• Precedence relation Qualitative

• Interrelation • Functionality • Location

• Function • Input • Output Regarding the type of record

• Work sequence or flow • Equipment or work environment • Repetitive work • Non-repetitive work • Research work • Human

Regarding the study object

• Machine • Material • Information

Fig. 3.1 Classification of methods engineering models

18

3 Concept of Methods Engineering • Macroeconomic - countries and macroregions • Sectoral, regional, group of enterprises, professional groups

Regarding the coverage level

• Plant, company, industrial process • Department or functional groups • Workstation • Work bench

• Complete manufacturing cycle • Plant layout (material transportation) Regarding the project type

• Plant layout (workers movements) • Material transportation • Workstation layout • Teamwork or automatic machine operation • Operators movements at the workstation • Decision

Regarding the administrative use

• Planing • Behaviour • Control

Fig. 3.1 (continued)

Schematic models are drawings with diagrammatic form that represent the real fact through graphic conventions and symbols. In Chap. 4, ten schematic models are presented, considered the most important ones for the study and design of work methods. The classification scheme presented above is used in Table 4.2 to indicate the characteristics of each schematic model analyzed in the present text.

References Krick EV (1962) Methods engineering: design and measurement of work methods. Wiley, New York, London, p 1962 OIT-ILO (1973) Introducción al Estudio del Trabajo, Oficina Internacional del Trabajo (OIT-ILO). Jornal de Genéve Maynard HB (1963) Industrial engineering handbook, 2nd edn. McGraw-Hill Book Company Inc., New York, Toronto, London, p 1963

Chapter 4

Analysis of Schematic Models

4.1 Purpose and Content of Analysis This chapter, which is the core of this work, presents a detailed analysis of ten main schematic models and 24 subtypes. Based on research carried out in the specialized texts of work study, the most known and used schematic models in the scope of Methods Engineering were selected and analyzed. The main objectives of the analysis are: (a) To gather in a single text a representative group of schematic models of current use in Methods Engineering, giving them a common conceptual and analytical treatment. This objective was motivated by the fact that no researched text presents the complete set of models, and each text highlights and analyzes only certain aspects of the presented models. Thus, the work carried out consisted of: grouping and classifying the models presented in the researched texts; unifying and making compatible the various aspects analyzed by each of these texts, of each class and type of model; making own considerations about each class and type of model, complementary to the researched models, or the development of new aspects and even new classes or types of models; defining the different types of models and their subtypes, assigning them names (chosen in the researched texts or suggested by the author) that best indicate the distinction made (presented in item 4.2); and finally, integrating the analysis according to a common presentation structure for all models. (b) To widen the scope of the study of models, and consequently of Methods Engineering to other levels of reach, work situations, production systems and approaches to manipulating the models. This objective derives from the observation that the researched authors limit the use of these models and of Methods Engineering, to the study at the workbench, workstation and, at most, plant

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 R. Seidl da Fonseca, Schematic Models for Production Engineering, https://doi.org/10.1007/978-3-031-33689-8_4

19

20

4 Analysis of Schematic Models

levels1 ; industrial work situations, whether in factories or offices; or production planning and control. The present work incorporates the application of schematic models for automated processes, the use of industrial robots as well as orders and decisions with artificial intelligence. The analysis work to meet this objective consists in: (a) introducing the consideration of other levels of scope of work situations as indicated below: • countries and major regions; • region, sector, group of companies, professional group; • plant and process, company; • department, functional group; • workstation and group or team; • workbench.

(b) extending the use of schematic models to non-industrial work situations,2 such as handicrafts, services, agriculture, domestic work, sports, creative activities; (c) seeking to direct the focus of the study of methods toward other objectives, such as increasing productivity, improving working conditions, increasing safety of equipment and workplaces, adapting the work situation to the operator and ergonomics conditions, and raising the possibility of the study of methods being self-developed by the worker (or by groups of workers), as a mechanism for work enhancement and not just an instrument for production control. In short, the text aims to relate the use of schematic models with modern administrative concepts, such as the system approach, self-management, job enlargement, automation, and robotics.

1

The limitation of the study of work to bench and station levels made by the authors surveyed (such as: Barnes, Nadler, Fields, Whitmore, Maynard, Buffa, Morris) is due to the fact that they are mostly linked to the Scientific Management Movement of Frederick Taylor, who understands the productive system as formed by workstations with defined and specialized functions, within the classical or neoclassical economic concept. 2 The limitation to industrial works in the original applications can be explained by the fact that most of the authors of primary reference refer to countries and times where there was a great predominance and development of the industrial sectors of the economy, implying a great cultural influence and technical concern with this theme.

4.2 Glossary of Names

21

4.2 Glossary of Names The present work assigns standard names to the analyzed models, which best define them according to the proposed grouping of model types and the distinction of subtypes. Some names just follow the researched texts and others are suggested by the author. The distinctions used for the basic characterization of the model standard name are indicated in Fig. 4.1. With the aim of correlating the names found in the various texts with the given standard name, a glossary table is presented in Table 4.1, where the original sources are also indicated.

Diagram: symbolic drawing

Table: matricial records

to from A B C D

Graph: plotting curves referred to two or three coordinate axes

Fig. 4.1 Characterization of models’ names

A

B

C

D

22

4 Analysis of Schematic Models

Table 4.1 Glossary of the analyzed models Proposed name in English

Names in English, Spanish, Portuguese

Sources

Interrelationship table

From-to chart

Fields (1969)/87

Link diagram

Fields (1969)/87

Cross chart

Muther (1955)/184

Travel chart

Fields (1969)/87

Transport table

Nadler (1970) /270 Whitmore (1970)/222 Movement matrix

Fields (1969)/87

Trip frequency chart

Krick (1962)/106

Table of preferred interconnections

Cross chart

Muther (1955)/184

Information distribution table

Information distribution chart

Nadler (1970)/255

Process flow diagram

Outline process chart

Fields (1969)/42 Morris (1969)/35 Whitmore (1970)/180

Singular flow diagram

Flow process chart

Fields (1969)/42

Process chart

Close (1960)/117

Flow process chart

Buffa (1969)/165 Close (1960)/129 Fields (1969)/50 Muther (1955)/79 Nadler (1970)/247 Whitmore (1970)/184

Product process chart

Nadler (1970)/247

Operation process chart

Buffa (1969)/164 Close (1960)/139 Muther (1955)/335 Karger (1966)/96

Assembly flow diagram

Process chart

Barnes (1963)/21

Assembly process chart

Barnes (1963)/30

Operation flow chart

Close (1960)/135

Assembly chart

Buffa (1969)/159 Nadler (1970)/245

Gozinto chart Manufacturing and assembly Flow process chart flow diagram

Buffa (1969)/159 Fields (1969)/54 (continued)

4.2 Glossary of Names

23

Table 4.1 (continued) Proposed name in English

Names in English, Spanish, Portuguese

Sources Morris (1969)/33 Muther (1955)/337 Karger (1966)/488

Assembly process chart

Barnes (1963)/30

Operation process chart

Buffa (1969)/164 Close (1960)/139 Krick (1962)/96

Operation flow chart

Close (1960)/135

Arrow diagram

Whitmore (1970)/317

Amplified flow process chart

Whitmore (1970)/185

Form process chart

Nadler (1970)/254

Operational sequence diagram

Nadler (1970)/343

Procedure chart

Fields (1969)/60

Forms distribution diagram

Krick (1962)/422

Procedure flow chart

Close (1960)/140

Chronologic flow diagram

Multi-column flow process chart

Maynard (1963)/2–33

Business process diagram

BPMN Process diagram

OMG (2014)/8

Diagrama de Processo de Negócio

Valle and Oliveira (2016)0

Business process model

Debevoise and Geneva (2008)/ 20

Flow diagram

Muther (1955)/193

Productive sectors flow diagram

Complex procedure flow diagram

Map flow diagram

Krick (1962)/122 Diagrama de recorrido

OIT-ILO (1973) /112

Bidimensional map flow diagram of route

Flow or workplace diagram

Nadler (1970)/346

Diagrama de los movimientos del operario

OIT-ILO (1973)/146

Bidimensional map flow diagram of activities

Flow diagram

Barnes (1963)/22 Close (1960)/130 Fields (1969)/83 Whitmore (1970)/191 Krick (1962)/122

Three-dimensional map flow Flow diagram diagram

Buffa (1969)/84 (continued)

24

4 Analysis of Schematic Models

Table 4.1 (continued) Proposed name in English

Names in English, Spanish, Portuguese

Sources

Chronologic assembly diagram

Diagrama de montagem

Reichert (1967)/125

Simultaneous activities diagram

Multiple activity chart

Close (1960)/222 Fields (1969)/62 Morris (1969)/77 Whitmore (1970)/188 Krick (1962)/103

Person-machine diagram

Activity chart

Buffa (1969)/373

Multi-activity chart

Nadler (1970)/334

Man–machine chart

Barnes (1963)/38 Fields (1969)/64 Krick (1962)/98

Man and machine chart

Nadler (1970)/335

Man and machine process chart

Karger (1966)/490

Man–machine multiple activity Whitmore (1970)/189 chart

Team diagram

Diagrama de proceso hombre-maquina

Niebel (1970)/135

Gang process chart

Karger (1966)/493

Gang chart

Morris (1969)/37

Multiple activity chart

Krick (1962)/102

Multiman chart

Nadler (1970)/335

Diagrama de proceso de grupo Niebel (1970)/141 Production line diagram

Multiple activity chart

Krick (1962)/103

Route frequency diagram

String-diagram

Whitmore (1970)/190 Nadler (1970)/250

Cyclegraph

Trip frequency diagram

Krick (1962)/105

Chronocyclegraph and cyclegraph

Fields (1969)/83 Nadler (1970)/189 Whitmore (1970)/215 Krick (1962)/153 (continued)

4.3 Classification and Characteristics of Schematic Models

25

Table 4.1 (continued) Proposed name in English

Names in English, Spanish, Portuguese

Sources

Sensory-motor diagram

Sensorimotor process chart

Nadler (1970)/346

Manual activity diagram

Left- and right-hand operator process chart

Barnes (1968)/493

Right and left hand chart

Close (1960)/184

Work place chart

Close (1960)/184

Operator chart

Close (1960)/184

Operation chart

Buffa (1969)/367

Diagrama bimanual

OIT-ILO (1973)/164

Manual activity diagram for operations

Two-handed operator chart

Morris (1969)/40

Manual activity diagram for operations and transport

Right and left hand chart

Barnes (1963)/50

Operation chart

Buffa (1969)/371

Manual activity diagram for operations, transport and delays

Gráfico de operações

Starr (1971)/391

ASME manual activity diagram

Two-handed operator process chart

Fields (1969)/64

Two-handed operator chart

Whitmore (1970)/185

Two-handed therblig chart

Fields (1969)/66

Left-hand right-hand chart

Krick (1962)/110

Therblig chart

Nadler (1970)/333

Simo chart

Barnes (1963)/65

Fundamental manual activities diagram

Chronologic manual activity diagram or Simo diagram

Buffa (1969)/369 Fields (1969)/68 Whitmore (1970)/187 Krick (1962)/100 Operation time chart

Nadler (1970)/345

Micromovigrama

Krick (1971)/102

Note: The sources associated with the names in the glossary table indicates where the original sources are cited.

4.3 Classification and Characteristics of Schematic Models Table 4.2 shows the selected schematic models following the classifications presented in Sect. 3.4 as well as their applicable functional characteristics.

Function Input Ouput Work sequence or flow Equipment or work environment Repetitive work Non repetitive work Reserch work

Functionaly Location

Interrelation

Time Distance Costs Frequency Flow density Precedence

MODELS CLASSIFICATIONS

Variables

Quantitative

x

x

X X X X

X X

X X

X

X X x

X X X

Interrelationship table

X X

X

X

x x

x

x

x x

x

x

x

x x

x

x

x x x x

x

x

x x

x

x

x x

x

x

Process flow diagram

x

x

x x x x

x x x

x

X

X

x

X

X x

X

x

x

X

x x

x

x

Map flow diagram

Table 4.2 Classification and functional characteristics of schematic models

Registry type

Qualitative

Transport table

Table of Preferred interconnection

Information distribution table Singular flow diagram Assembly flow diagram Manufactoring and assembly flow diagram

Productive sectors flow diagram Complex procedure flow diagram Chronologic flow diagram Business process diagram Bidimensional map flow diagram of activities Bidimensional map flow diagram of route

x

x

x

x x

x

x

x

Three-dimensional map flow diagram

X X

X

X

X x

x

Chronologic assembly diagram

x x

x

x X

X

x x

x

x x

x

x

x

x

x

Simultaneous activities diagram

Person-machine diagram

Team diagram Production line diagram

x x

x

x

x

x X

x

Route frequency diagram

x

x

x

x

x

x

Cyclegraph

x

x

x

x

x

x x

Cyclegraph

Chronocyclegraph

x x x

x

x x

x x x

x

x X

diagram

Sensori motor

Sensorimotor diagram for manual work Sensorimotor diagram for work with equipment

x

x

x

Manual activity diagram for operations

x

x

x

x

x

x

x

x

x

x

x

x

x

(continued)

x

x

x

Manual activity diagram

Manual activity diagram for operation and transportation Manual activity diagram for operation, transportation and delays

ASME manual activity diagram Fundamental manual activities diagram

Simo diagram

26

4 Analysis of Schematic Models

Use

Project type

Coverage level

Study object

Human Machine Material Information Macroeconomic – countries/ macroregions Sectoral/regional/ group of enterprises/ professional groups Plant/company/ industrial process Department or functional groups Workstation Work bench Complete manufacturing cycle Plant layout (material transportation) Plant layout (workers movements) Material transportation Workstation layout Teamwork/automatic machine operation Operators movement at the workstation Decision Planning Behavior Control

Table 4.2 (continued)

X

X

x

X

X

X

x

x x x

x

x

x

x

x

x

x x

x

x

x

x

x

x

x

x

x

x

x

x

x

x x

x

x

x

x

x

x

x

x x

x

x

x

x

x

x

x

x x

x

x

x x

x

x

x

x

x

x x

x

X

x

X

X

X x

x

x

X

x

x

x

x

x

x

x

x x

x

x

X

x

X

x

x

x

X

X

x

X

x x x x

X

X

X

X

X X X X

X X X X X

x

X

x

X

X

X

X

X

X

X

x X

X

x

x

x

x

x

x

x

x

x

x x

x

X

X

X

X

X

X

X X

x x x

x

x

x x

x x x

x

x

x

x x

x x x

x

x

x x

x

x

x

x

x

x

X

x x x

x

x

x

x x x

x

x

x x

x

x

x x x

x

x

x x

x

x x x

x

x x

x

x x x

x

x

x x

x

x x x

x

x

x

x x x

x

x

x

x x x

x

x

x

x x x

x

x

x

x x x

x

x

x

x x x

x

x

x

4.3 Classification and Characteristics of Schematic Models 27

28

4 Analysis of Schematic Models

4.4 Analysis of Schematic Models Presentation The presentation structure of the analysis of the models is divided in five study aspects, such as: Conceptualization—definition of the conceptual aspects that guide the design of the model. Criteria—listing the criteria that guide the studies of the development of the work situation represented by the model. Construction—explanation of the basic construction details of the model. Uses—indication of the uses of the model, both in terms of typical work situations and in terms of their role within the work methods study. Manipulation—indication of the methods designer’s ways of acting, following the information visualized by the model, both upon the represented work situation and upon the model itself. In order to illustrate the respective text, at the end of the analysis of each type of model, is giving an Example and a drawing of the corresponding model. The presentation sequence follows the classification according to the coverage levels, from macro to workbench application: (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

Interrelationship Table; information distribution table; process flow diagram; map flow diagram; chronological assembly diagram; simultaneous activities diagram; route frequency diagram; cyclegraph; sensorimotor diagram; manual activity diagram.

4.4.1 Interrelationship Table Conceptualization The Interrelationship Table records the relationship of transit or exchange that exists between each pair of components of a production system during a given period of time. For the present approach to the design of the Interrelationship Table, it is firstly necessary to conceptualize system, component, flows and relationship of transit or exchange.

4.4 Analysis of Schematic Models Presentation

29

Fig. 4.2 System representation. Note A, B, C = components. f AB , f AC , f BC , f CB = internal flows. Input, output = flows exchanged with the outside

System is an integrated unit organized according to a structure, defined by a set of components that interact through flows among each other in a space of action limited by borders (internal flows) and between elements external to these borders (flows exchanged with the outside), as represented in Fig. 4.2. In methods study, the interest is focused on production systems, at their various levels of scope. Thus, the system under study can be a work center or person-machine, machine-machine, person-person systems, a department, a facility or a group of production facilities. The objective of any production system is the use of production factors for the generation of goods and/or services. The organizational structure of the production system encompasses location, positioning and physical arrangement of components, relationships and communications, production orders, activities sequence, task distribution, production planning and control, work methods. The components of the production system are the work units that perform the productive activities, assuming different and complementary functions in the system. Depending on the level of coverage of the system, the components can be persons, equipment and tools, benches and machines, workstations and complete equipment, sections and groups of machines, departments, plants or group of plants. The integration, interdependence, and interaction of the components are done by the flows and the relationships between them, dictated by the structure, objective, and functionality of the system. The flows of the production system, within the registration scope of the Interrelationship Table, are constituted by the items exchanged in a given direction between the pairs of components, being basically persons, materials or products, forms, and information. Each type of item establishes a network of flows in the production system. Depending on the objective of the study, a certain item is chosen to be observed, becoming the object of study of the Interrelationship Table. The Table is especially useful in recording and analyzing processes with a large number of different items in transit, for example, in a factory that produces hundreds different pieces a day.

30

4 Analysis of Schematic Models

The Interrelationship Table allows to exclusively record the transit relationships between pairs of components. Transit relationship is understood here as the relationship established by the transmission or exchange of elements between pairs of productive units. This relationship is generated by the operation of the production system integrated by those components. The elements transmitted or exchanged can be material (product, persons, forms) or communication (words, signals, streams, e-files, data). Thus, for example, two machines are connected through the passage of semi-finished products from one to the other; or two persons interact through the exchange of oral orders or written reports. This relationship is expressed by a value, defined by the character of the flows exchanged, by the type and importance of the items in transit and by the relationship between the components defined by the organizational structure. In order to analyze the transit relationship, depending on certain aspects that one wishes to highlight in the work situation, the determination of the value of the relationship is made according to relationship factors. The choice of factor depends on the variable (or variables) to be isolated and on the possibility of observing the case under study. The relationship factors can be quantitative or qualitative. Among the quantitative factors, the normally used are distance, route frequency, number of units, volume, weight and cost. And when qualitative factors are priorities, the factors used are characteristics of the transport route, preferences, dangerousness, difficulty and precision. Qualitative factors are valued through classification into levels of importance or “weights”. It can also be considered an isolated factor, a group of factors, or a combination. The most used combinations are weight × distance = transport moment, volume × distance × importance, number of items × specific weight, and number of items × transport difficulty. Table 4.3 summarizes these abovementioned aspects. Table 4.3 Components, flows, and relationship factors Components

Flows

Relationship factors

Person, equipment, and tools Tables, benches, and machines Workstations and complete equipment Sections and groups of machines Departments Plants or group of plants

Material: product, people, papers Communication: words, signals, streams, e-files, data

Quantitative factors: distance, route frequency, number of units, volume, weight and cost Qualitative factors: priorities, characteristics of the transport route, preferences, dangerousness, difficulty, and precision

4.4 Analysis of Schematic Models Presentation

31

The usual form of graphic record of the Interrelationship Table is a matrix table, which can be organized according to two graphic concepts: From-To Matrix and Triangular Matrix. When there is interest in making explicit the direction of the flow exchanged between the pairs, a From-To Matrix is used. In this case, the items allocated above the main diagonal are related to flows in a forward direction in relation to the order in which the components were written in the table; items below the main diagonal are related to flows in the backward direction (Fig. 4.3) When the direction of the flow is difficult to be defined or there is no interest in making it explicit, or even when what needs to be shown is the total number of items exchanged, the table is represented in a Triangular Matrix (Fig. 4.4) When the transit relationship between the pairs is associated with the idea of physical movement, that is, a dynamic concept, the model is known as Travel Chart or Transport Table. When the associated concept is static, such as functional or formal contacts, the model is called Cross-Chart or Table of Preferred Interconnections. Fig. 4.3 From-to matrix

To

From A B C D

Fig. 4.4 Triangular matrix

A

B

C

D

32

4 Analysis of Schematic Models

The Transport Table records the movement of certain elements, which can be materials, persons or information between the pairs of a group of work centers. For example, the number of documents that pass through a commercial bank among its employees. The Table of Preferred Interconnections shows the types of connections that exist between the pairs of a group of work centers or persons classified according to levels of importance, necessary for the system to work or to meet a formal scheme, for example, the operational relationship between employees in an emergency health center. Note that there is no fixed boundary between the fields of use of these two types of Interrelationship Table. One can even use both or switch from one to the other in certain cases. For example, as shown in Fig. 4.5, an exercise might start with recording with a system diagram (or a flow intensity diagram) the number of documents in transit within an office among employees for one week (1), then representing the flows between pairs using the Transport Table (2), further the numerical totals can be separated into bands and classified according to levels of importance (3), and finally, the preferential interrelationship level of each pair of employees (4) can be defined. It is important to emphasize that the Interrelationship Table is an instrument for analyzing symptoms, which allows estimating the possibility of advantageous changes in the present or projected situation; however, the model alone does not

Fig. 4.5 Example of using the interrelationship table

4.4 Analysis of Schematic Models Presentation

33

lead reaching optimal solutions, requiring in addition the use of mathematical optimization techniques. In other words, the table points out deficiencies or possibilities for improvement, according to predefined concepts. The viable changes in the work situation are processed, and this new situation is recorded. The analysis of the table and application of efficiency criteria feeds back the process. The Interrelationship Table takes on an outstanding importance with the advent of just-in-time plant supply schemes, which is a production management system that determines that everything must be purchased, produced, transported, and finally delivered at the exact moment of its entry on the production lines. The Table is also an instrument used in the determination of optimal industrial location. In economic planning, it helps in the construction of input–output matrices. Another important use is for social networks analysis and representation. General Constructive Conception To begin the study of a production system using the Interrelationship Table, it is necessary to define the system’s level of coverage and define all the components or work centers involved. In order to facilitate registration, components shall be identified by a code of letters or numbers. Then, the exchanged flows will be observed and analyzed. This preliminary study aims to clarify the character of the flows, that is, to identify whether the items exchanged are persons, materials, information or contacts, and which are their transit directions. If there is more than one network of flows, they will be identified and observed separately. If a flow network is made up of a large variety of items in transit, one should choose a representative number that is easier or more economic to observe. For the survey of each flow network, a system diagram can be used, like the one shown in Fig. 4.2. The collection of data on flows can be done directly or indirectly. In the direct survey, the analyst is placed in a strategic position of observation and records the items in transit; or tracks each item in transit through the work centers; this survey is generally done by continuous observation, during the cycle or a sample time period. In studies with a large volume of data or with a very long work cycle period, the sampling technique is used. For indirect surveying, filming, routine or fabrication sheets, travel frequency diagram, and other similar means may be used. From this survey, it is determined which traffic relations exist in the system, and among these which transit relations are interesting to study in more detail. Depending on the relationship to be studied and the economic and technical restrictions regarding the observation and collection of data about the flows, the most representative traffic relationship factor is chosen. If the chosen transit ratio factor provides a quantitative value to the flow and is related to a physical movement, the Transport Table will be used. If the factor values the flow in qualitative terms and is related to formal or functional links, the Table of Preferred Interconnections will be used. Finally, the choice of matrix type for registration is made. Thus, when possible and there is interest in representing the flow direction, the From-To Matrix is used. If it is not possible, technically or economically, or there is no interest in representing

34

4 Analysis of Schematic Models

the direction of flow, or even what is interesting is to record the total value of the transit ratio between the pairs, the Triangular Matrix is used. In general, as indicated earlier, the From-To Matrix is more appropriate for the construction of the Transport Table, and the Triangular Matrix for the Table of Preferred Interconnections.

4.4.1.1

Transport Table

The Transport Table is used to study some aspects related to the physical movement of items between pairs of work centers in a production system. Such aspects are the physical arrangement of the work centers, the transport routes and information channels, the balancing of the workload of the centers, and the processing sequence. Depending on the specific use, the Table shall follow defined approaches in terms of criteria, construction, and manipulation. As the assignment of values to flows depends on the basic sequence of physical movement between pairs of components, and the graphic allocation of the record of these values in the From-To Matrix depends on the sequence in which the components are arranged in the Table, a one-to-one relationship is established between the work situation and the record in the Table. Therefore, it is possible to use manipulation techniques on the Table, to look for better solutions for the work situation.3 Construction Once the traffic relationship factor is chosen, the value of the relationship between each pair of system components can be determined. In the From-To Matrix, the components or work centers, identified by means of a code of letters or numbers, are listed in the first row and column in the same order of the chosen sequence, thus defining the coordinate axes “From” and “To”. Note that the Transport Table requires a clear definition of the sequential order in which the components are physically arranged, or the main transit sequence. In the Table, the components are registered according to such determined sequence, which can be the existing one or a proposal. At the intersections of the “From” and “To” coordinates, the values of the traffic relationship between the corresponding pairs are recorded. Thus, in each intersection, the total value of the physical movement is registered “From” a component “To” another component, which define the graphic location of the related intersection. The intersections arranged on the main diagonal of the matrix would indicate the physical movement of a component toward itself, and since this movement does not occur, such intersections are filled in bold. As already mentioned, the values recorded above the main diagonal indicate positive or forward flow (in relation to the

3

Author’s Note: as in general, the Transport Table is built according to a From-To Matrix, and the values of the traffic relations are most quantitative, the present text considers only this conception. Singular conceptions will be mentioned as an extension of possibility.

4.4 Analysis of Schematic Models Presentation Fig. 4.6 Example of a From-To Table with entry and exit of items

To From

35 A

B

C

D

X

0 0 reception X - expedition

A B C D

chosen sequence) and the values recorded below the main diagonal indicate returns, or negative or backward flow. To show what goes in and out of the system, it is necessary to add an intersection in the “From” line at the beginning of the sequence representing the exterior or reception; and add in the line “To” an intersection at the end of the sequence representing the outside or the expedition. The From-To Table thus takes the form shown in Fig. 4.6. The transit ratio factors used in the Transport Table are primarily distance, frequency, volume, weight, number of units, and cost. A combination of these factors can also be used, such as distance × weight = transport moment. Other factors can still be defined, by attributing levels of importance or quantitative “weights” to the basic factors, to establish the relative magnitude of the problem of movement of each distinct item, for example, in relation to transportation difficulties, as exemplified in Table 4.4. The data for the construction of the Transport Table are preliminarily gathered in a summary table like Table 4.5, or in a multi-column flowchart (Fig. 4.7).

Table 4.4 Example of weight assignment for transport difficulty

Difficulty of moving each item

“Weight”

Extremely large and heavy items

4

Heavy and bulky items

3

Moderate size

2

Small, stockable items

1

Very small items

1/2

Source Muther (1955, p. 189)

Table 4.5 Summary transport table

Product

Factor: Quantity

Workstation: Sequence

a

20

A–C–D

b

35

A–D–E

c

100

d

500

C–D–B–A–D–E

e

30

A–B–C–D–E–D

B–C–A–D–E

36

4 Analysis of Schematic Models

Fig. 4.7 Multi-column flowchart

Prod uct Quan tity Unit

A

a

b 20

1

35 1

d

100

500

3

4

1

B C

2

D

3

E

c

e

2

1 4

3

5

2

1 2

3

2

30

3 5

4

6

5

Uses The main types of Transport Tables used are analyzed below according to the aspect of the work situation that is to be studied, related to the physical movement between pairs of production units. (1) Physical Arrangement (Lay-out) The Transport Table is used in the study of the physical arrangement of the component units of a production system, in the sense of indicating the most advantageous relative proximities in terms of a given efficiency criterion. The criteria are generally to minimize total transport time, reduce returns, minimize moves, and minimize material handling. The manipulation of the Table seeks to decrease the value of the transit relationships between the pairs, and to allocate the highest values close to the main diagonal. For Table manipulation, the basic reference is the main diagonal. This is because the further away from the main diagonal is the intersection with the value of the transit ratio between the respective pairs, the further away these two components are in the physical arrangement of the plant. Thus, the Table itself provides a notion of transport moment. Graphically, the idea given by the Table to the transport moment can be represented as indicated in Fig. 4.8. It would be desirable for all components that have some transit interrelationship to be placed adjacent to each other in the plant. As this is generally impossible, an arrangement is sought in which the components with higher values of transit ratio are adjacent and the others in positions such that the total movement is minimal. To make it easier to compare alternative solutions, one can use a percentage efficiency ratio, such as: efficiency % of layout = actual movement/ideal movement where the ideal movement would be the hypothesis that all components with traffic interrelationship are adjacent. Thus, in relation to the Table, the most advantageous arrangement will have the highest values on the diagonal line immediately above the main diagonal.

4.4 Analysis of Schematic Models Presentation

37

V = Value of the transit ratio (weight, volume, number of items). d = Distance between the pair. V x d = transport moment The criterion is to minimize the total transport moment, or minimize Σ Vi x di + Σ Vk x dk (objective function) Fig. 4.8 Transport moment definition

The determination of the distance factor of the transport moment of each arrangement solution can be done by direct measurement of the real length of the paths, by the scale measurement of the straight line between the centers of the physical areas of the productive units, or by the attribution of “weights” or levels to each diagonal of the Table as a function of its distance parallel to the main diagonal. Transport moments relative to returns (or backward movement direction) can be given additional “weight” (Fig. 4.9). When moving items have different transport characteristics, a “weighting” scheme is used that takes into account the relative difficulties of transporting each one; this technique is called magnitude account (shown in Box 4.1). Box 4.1 Magnitude Account (Mag Count Chart) According to Nadler (1970, pp. 237–238), this technique of establishing factors of importance aims to determine the magnitude or relative magnitude of the transport difficulties of a group of parts that pursue different physical and transport characteristics. The basic idea is to classify a group of parts, moving in a production facility, by applying different “weights” to the transit ratio, which take into account the difficulty of transporting each part. The resulting classification can be used (a) to single out items of greatest magnitude to be taken as representative of a large set or to be considered first in the design of the transportation system, or (b) to correct all items according to a chosen pattern.

38

4 Analysis of Schematic Models

Magnitude accounting uses the technique of dividing factors into levels and assigning a scale of points to each level. Density, shape, risk of damage, and contact condition can be considered. Definition of the unit of magnitude: 1 mag is related to a physical item of reasonably solid, compact, clear, and firm nature, not likely to be damaged in handling. Its size should be such that it can be held conveniently in a hand (Nadler 1970, p. 237) (

B +C + D+ E Mag count = A + A N

)

A = number of units of the product B, C, D, E = values for the factors that influence the specific situation N = number of factors used. Table 4.6 shows an example of magnitude definition for transporting parts or components.

p = additional return weight (in this case it follows a linear arithmetic progression; it can also follow other functions). E.g.: ∑ Transport Moment = 10 x 3 +5 x 2 + 8 x (2 + 1) = 64 (making p = 1). Fig. 4.9 Example of transport movement evaluation

Highly flat and stackable or fully nestable (flat sheets)

Shape

Risk of Damage

Condition

B

C

D

E

Partially nestable

Light and fairly bulky

−1

Not Susceptible to susceptible at practically no all (scrap iron) damage (castings)

Readily stackable or nestable (pad of paper, soup bowls)

Very light and empty (bulky sheet metal)

−2 Fairly heavy and dense (cored castings)

+1

Clean and firm

Not susceptible to much damage (measured and cut wood)

Very heavy and dense (die black, lead)

+3

+4

Very susceptible to some. Susceptible to much damage

Highly susceptible to some of susceptible to damage (glass)

Long and slim Long, slim, and Extra-long and (tubes, short curved or curved or bars) extra-long especially long

Heavy and dense (solid castings and forgings)

+2

Oily or flimsy. Covered with Awkward to grease, handle slippery, and very awkward to handle

Susceptible to some damage by crushing, breaking or scratching

Basically, Oval, round or square rectangular or elongated

Base – reasonably solid (block of any wood)

0

Source Three new tools for better plant layout, Factory, Vol. CXVIII, No. 6 (June 1960), pp. 101-3, at Nadler (1970, Fig. 11.3, p. 238); copyright by John Wiley & Sons, Inc.

−3

Bulkiness or density

Factor

Table 4.6 Example of transport difficulty definition

4.4 Analysis of Schematic Models Presentation 39

40

4 Analysis of Schematic Models

The technique of handling the Transport Table for the study of plant layout can be summarized as follows: • • • • • • •

calculate the values of the traffic relations and compute them in the Table; determine the solution’s efficiency; detect improvement points, by observing the Table; modify the plant’s physical arrangement; calculate values of the traffic relations and efficiency of the new solution; compare the efficiencies of feasible solutions; choosing the most efficient feasible solution.

The Table is particularly useful when the production process encompasses a large number of items, and it is not possible “a priori” to establish an overall processing sequence; in this case, an attempt is made to determine a physical layout of the productive units involved, which best meets the total number of items in processing or a representative sample of the total. (2) Production Line Balancing The Transport Table allows a preliminary study of the distribution of workloads across the productive units that operate according to a work method. In this application case, the basic relationship factor is the number of items in processing. The construction of the Table for this purpose requires the attachment of columns totaling the movements “From” and “To”. Thus, the possible analyzes to be made from the record of a given work situation through the Transport Table are: • verification of the balance of the workload allocated to the set of productive units involved: this verification is carried out by comparing the totals of items recorded in the total column “From”, which shows the sum of the items that leave each production unit; in order for the load to be balanced, the totals assigned to each unit must be equivalent; the indicated imbalances should be reviewed using one of the production line balancing techniques; • verification of individual workloads: this observation aims to highlight the existence of overload in some production unit, generating work accumulation in this unit; verification is carried out by comparing the total number of items that enter and leave each unit, recorded in the total columns “From” and “To”; there is overload, or backlog, if the number of items entering is greater than the number of items leaving; if this occurs, the production capacity of the overloaded unit must be increased, by improving the work method used in it, increasing the speed or rhythm of work of the machine and/or operator, multiplying the number of production units for this activity, or forecasting overtime; when the two totals are equal,

4.4 Analysis of Schematic Models Presentation

41

one should ask about the possibility of increasing their demanded production, with the aim of reaching the unit’s maximum production capacity. (3) Transport Routes or Information Channels The quantitative record provided by the Transport Table can be used as a summary or data collection for the dimensioning of the capacity or constructive specification of the transport routes and information channels, such as aisle width, appropriate flooring type, transport equipment type, communication equipment type, communication line capacity, digital connection volume. It can also be used to highlight the most important routes to focus especial attention on them. (4) Sequence of Flows The comparison of Transport Tables that record the same work situation in different observations (such as: projected with real, or verification, at subsequent times, of the implemented method) allows observing the occurrence of any change in the sequences of the flows of the items in processing. The deviations visible in the Table are returns or “by-pass”. The Table also serves to establish an overall standard flow for facilities that produce a large number of items, with different individual flows. To determine this pattern sequence, the movement of all items or a random sample is recorded. The chain of pairs with the highest concentration of movements between them defines the standard sequence. Example The example below shows a Table From-To applied to a multi-product workshop specialized in producing several types of gears in “on order” basis. The raw material is provided in the form of castings, forgings, and cut pieces of the bar-stock, as well as drawings, technical specifications, and the requested quantity. The raw material could be cast iron, steel, bronze, or plastics. The Table registers the traffic volume between the different machinery and workbenches for manufacturing 50 types of gears (Table 4.7).

4.4.1.2

Table of Preferred Interconnections

Given a structure, organizational, or functional, of a productive system, the Table records and analyzes the preferential links established between the pairs of components involved in the work situation. These relationships, identified as preferential links, depend only on the structure of the production system, not changing for the different alternative work situations (as in the relationships defined by the Transport Table), with the relative arrangement of the components, with the sequence of physical movement, and sometimes with the traffic intensity.

Source By the Author, following the model proposed by Muther (1955. Fig. 14.8a, p. 186)

Table 4.7 Example of a transport table

42 4 Analysis of Schematic Models

4.4 Analysis of Schematic Models Presentation

43

Thus, there is a univocal relationship between the production system and the record in the Table. Therefore, the Table handling cannot be used to search for better solutions. The action is only carried out on the work situation, trying to meet the preferential connections indicated in the best possible way. The aspects of the work situation analyzed by the Table of Preferred Interconnections are the physical arrangement of the components and the transport routes and information channels. For the construction of the Table, it is not necessary to establish defined sequences of physical movement. The basic record of the Table is a qualitative value, which can be expressed in relation to a scale of levels or “weights”, or by graphic signs, which defines the preferential links established between each pair of components. In general, the value recorded refers to the sum of flows exchanged between the pairs, due to the relationship under study; in this case, it is not important to define the directions of the flows. Based on the general constructive conception of the Table of Preferred Interconnections described above, the Triangular Matrix is the most suitable record form for this scheme. In the study of the work situation done with the Table of Preferred Interconnections, the analyzed and recorded flows can be information, communications, formal or informal contacts, functional actions, and even physical movements; however, the relationships defined by the flows between the pairs must be valued according to qualitative criteria, establishing a scale of preference between these relationships. The choice of the criterion and the scale of preference is the initial step for the construction of the Table of Preferred Interconnections. For example, in studying the physical arrangement of components, one can use the criterion of relative proximity and employ the preference scale below: • must be adjacent

5

• essential proximity

4

• important proximity

3

• not essential to be close

2

• must not be adjacent

1

• must not be close to

0

The attribution of qualitative values to relationships between pairs can be done, (a) by direct framing in the established preference scale, based on empirical knowledge or on identified reasons, such as the following group of reasons that explain the classification of an interconnection according to the previous scale:

44

• • • • • •

4 Analysis of Schematic Models

a lot of personal contact; too much information transfer; use of common team; intermittent contact; free access to the street; avoid chemical contamination.

Or (b) by the quantitative assessment of the flows exchanged, observed during a representative period of time, with the quantitative values divided into levels of importance and converted into a qualitative classification, for example, measuring the flows of formal contacts between pairs of office workers, during a week (still with reference to the physical arrangement study with the criterion of relative proximity): 1–5

1

6–20

2

21–100

3

101–300

4

In the study of the Table of Preferred Interconnections, it is difficult, if not impossible, to establish a criterion of percentage efficiency, to judge alternative solutions applicable to the work situation; in general terms, the best solution is the one that best meets the preferential connections. Note: For considerations on the construction and use of the Table of Preferred Interconnections, in the present text, reference is made only to the basic registration scheme, i.e., the Triangular Matrix. Uses (1) Physical Arrangement (Layout) The Table of Preferred Interconnections records the qualitative assessment of the importance or convenience of placing each component of a work center adjacent, close or far from each of the others in the physical arrangement of the plant, according to a preference scale. The work center can be a group of facilities in a geographic region, departments in a facility, or even handheld devices on a bench. The most used traffic relationship factors in the study of the physical arrangement are priorities, danger, difficulty, type of road or channel, type of transport equipment. In the process of improving the work situation, existing or projected, based on the information in the Table, an attempt is made to solve the most important and essential problems of approximation and separation. The criterion for acting at the work situation is to bring together the components that have priority connections and to separate, or even isolate, the components between which it is not desirable to have a connection. When the object of study is material, product, or forms, the construction of the schema is made from counting or registering quantitative data of the movement of items between the pairs of components involved; then, the quantities relative to each pair are grouped and classified into levels of importance, constituting a

4.4 Analysis of Schematic Models Presentation

45

preference scale, of a qualitative nature. In cases where the collection of quantitative data is difficult to solve, or when it is economically unjustifiable, the qualitative classification of the movement between the pairs is subjectively made by consensus of people familiar with the work situation or by the designer. When the object of study is persons or groups of persons constituting a work system, the preferential links established between pairs are generally formal or informal contacts and exchanges of information. In this case, the classification of links is guided by the relative importance of these links to the functionality of the system. As examples of preference scales for the study of physical proximity and move, one can have: • absolutely essential closeness

5

• particularly important proximity

4

• important closeness

3

• ordinarily close

2

• not important proximity

1

• undesirable proximity

0

or • large movement record

3

• average movement

2

• small movement

1

• null movement

0

To help the search for physical arrangement alternatives for a work situation, it is suggested to use a graphic scheme that allows better visualization of the connection classes between the pairs, grouping the components that have the same connection class. In the drawing below, the lines joining the components keep reference to the connection class they represent (Fig. 4.10). A

B B

D

essential

C

important

F G

H

Fig. 4.10 Examples of connection classes

P

not important

46

2.

4 Analysis of Schematic Models

Traffic Routes or Information Channels

In this case, the record in the Table is the classification or definition of the preferred type of traffic lane or information channel, which connects each pair of components of a work system. The study carried out based on this record is to verify or define the technical specifications of the road or channel, according to its main use. The observation of the Table also allows highlighting the possibility of combining, replacing or eliminating routes or channels. Example The example shows a Table of Preferred Interconnections used in planning the layout of the service and administrative areas of a bank branch, to define the needs of physical proximity of each pair. The Table reflects the importance of proximity between each pair of operational areas due to the expected volume of people moving between them (Fig. 4.11). The graphics of importance below indicates visually the strengths of the interrelations among the operational units (Fig. 4.12)

A - Entrance and exit B - Reception C - Automatic teller machines D - Attendance boxes E - Account Managers

Proximity 3 3 2

2 2

1

1

3

3

0

2 2

1

0 X

0

X

1

X

0

J - Meal room 0

K - Technical control room 0

L - Stockroom 0

M - Personnel toilets 1

N - Area and coffee machine

0 0

0 2

3

0

X

0

0

3

0

0

3

3

O - Waiting room

X

3

P - Meeting room

Fig. 4.11 Example of use of the table of preferential interconnections

3

0 2

0 0

0

1 3

2

3

1

3

2

0

2

X

1

3

X

2

X 2

0

X

0 1

2

X

0

X

2

X

X

3

0

1

0

0

0

Undesirable

X

0

2

3

Not important

0

0

2

1

0

0

0 0

2

X

X

I - General manager

X 1

0

H – Safe room

X

2

Desirable

0

0

0

3

Important

X

3

0

1

3

0

X

3

3

G - Rental safes

1

X

3

X

2

0 0

1 2

0

3 0

F - Security

Weight

Fundamental

X

4.4 Analysis of Schematic Models Presentation

47

B A

I F

C

K L

G D

H

M

N E J

O P Fig. 4.12 Example of the related graphics of importance

3.

Social networks analysis

The Table of Preferred Interconnections can be used as a basis for recording and analyzing the interactions between the persons responsible for the functioning of a productive system, forming social networks. For the analysis of social networks, formalizations and algorithms are available that identify and calculate their properties and structure, such as nodal degree, density, reachability, critical parts (bridge and cut points), connectivity, centrality (closeness and betweenness), and K-core. For further

SO JW

LZ

NB VL

KK

AR JS

JD

SC

Fig. 4.13 Example of network analysis

48

4 Analysis of Schematic Models

reference, see Wasserman and Faust (1994), Borgatti et al. (2018) and Dorogovtsev et al. (2006). As an example, the analysis of a social network formed by researchers of a certain scientific topic acting as co-authors of a set of selected articles is carried out below. The table and diagram of interconnections K-core among these researchers are presented in Fig. 4.13. Note that in this case, due to the requirement to use the selected algorithm,4 the From-To Matrix has a special format, as shown below. The initial analysis of this social network indicates that it appears to be quite cohesive, where all components are related to each other, and the AR researcher has a central role (centrality) in the network structure. From (source)

To (target)

Articles

NB

SC

1

NB

JD

1

NB

KK

1

NB

VL

1

NB

SO

1

NB

AR

1

NB

JS

1

NB

JW

1

NB

LZ

1

SC

JD

4

SC

KK

4

SC

SO

1

SC

AR

1

SC

JS

1

SC

JW

1

SC

LZ

1

JD

KK

1

JD

VL

1

JD

SO

1

JD

AR

2

JD

JS

2

JD

JW

1

JD

LZ

1

KK

VL

1

KK

SO

1

KK

AR

1 (continued)

4

For the construction of the example presented, the Gephi algorithm was used (www.gephi.org, 2022).

4.4 Analysis of Schematic Models Presentation

49

(continued) From (source)

To (target)

Articles

KK

JS

1

KK

JW

1

KK

LZ

1

VL

SC

1

VL

SO

1

VL

AR

1

VL

JS

1

VL

JW

1

VL

LZ

1

AR

JS

4

AR

JW

1

AR

LZ

1

JS

LZ

2

JW

LZ

1

4.4.2 Information Distribution Table Processing services and information systems that make up a productive unit use a series of forms, printed or digital, which individually record a group of information. The systems for processing the forms and handling the information recorded are generally quite complex. The design of these systems, which is the attribution of the methods study, requires a treatment with models to make their visualization and manipulation simpler. After the processing service and/or information system have been designed or surveyed, and the forms used have been determined, it is necessary to study the format and types of information contained in each form. The design criteria for the forms of these systems is basically to avoid recording unnecessary information and the excessive duplication of recording information in multiple forms. It is therefore necessary for the design of form systems to identify the sources of information supply, determine all the information required from each source by the processing service and/or information system under study, and organize the rational distribution of this information among the various forms. It is evident that in the survey of a system of forms already in operation, the investigation process is inverse to that of the project. For the study and implementation of digital forms systems, the Information Distribution Table constitutes an initial stage.

50 Table 4.8 Information distribution table basic design

4 Analysis of Schematic Models

Required information on form Info 1 Info 2 Info 3 …

Form a √

Form b √

… √

√

√

√ √

…

The schematic model consists of a double-entry table, listing on one line the various forms of the processing service and/or information system under study and on √the other line the information required from a certain source. By using a checkmark ( ) or a binary pair (0–1, I–X) to indicate common intersections, the such a table provides a visual understanding of what information is required at the various forms. Table 4.8 shows its basic design. Example The example analyzes the distribution of information in forms and documents required by a university to process the hiring of faculty. The source of information in this case is the candidate lecturer and the forms are the standardized ones to be filled in by the candidate and the documents requested (Table 4.9).

4.4.3 Process Flow Diagram Conceptualization The process flow diagram has the objective of schematically representing the production process through the sequences of activities of transformation, examination, handling, movement, and storage that the flow of production items goes through. The model exclusively records fixed, deterministic activity sequences. The distinct activities are represented in the model by graphical symbols and the flow of items between successive activities by segments that join the corresponding symbols. This schematic model allows for a general and compact understanding of the production process, by highlighting and identifying the constituent steps and their order of execution. The basic visual information given by the diagram (process steps and order of execution) can include other information that allows a clear understanding of the process, such as execution location, productive unit, activity duration times, distances moved, activity costs. This information can be organized according to a number of different concepts. The constructive concepts and different flow diagram symbology depend on the specificity of the process under study, the type of object of study, and the set of required information.

Portrait

Blood type

Issue date

Profession or professional category

Gender

Marital status

Nationality

Birthplace

Date of birth

City and State

Address

Registration number

Name

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√ √

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

√

(continued)

√

√

Identity Professional Driver’s Diploma Declaration Non-accumulation Work Medical Personal Professional Conflict Proof of card license license of assets hours examination data data of residence interest √ √ √ √ √ √ √ √ √ √ √

Information Forms and documents

Table 4.9 Example of the use of information distribution table

4.4 Analysis of Schematic Models Presentation 51

Tax registration

Bank account

Physical and mental fitness

Position, function or activity

Working hours

Discipline

Department

Goods or assets

Military situation

√

√

√

√

√ √

√ √

√

√

√

√

√

√

√

Identity Professional Driver’s Diploma Declaration Non-accumulation Work Medical Personal Professional Conflict Proof of card license license of assets hours examination data data of residence interest √

Information Forms and documents

Table 4.9 (continued)

52 4 Analysis of Schematic Models

4.4 Analysis of Schematic Models Presentation

53

Basic flow diagram types are: (1) (2) (3) (4) (5) (6) (7)

single flow diagram; assembly flow diagram; manufacturing and assembly flow diagram; productive sectors flow diagram; complex procedure flow diagram; chronological flow diagram; business process diagram—BPD.

When studying the production process through the flow diagram, it needs to be specified in terms of the type of work processed and its level of coverage. Such specificities will determine different forms of flow diagram representation and related symbology. For the purpose of classification according to the type of work, four basic types are defined: manufacturing work, bureaucratic work, transport work, and mobile service work. Such work is considered to be carried out by people or machines. It is understood such definitions as: • manufacturing work, where material units are transformed into products; • bureaucratic work which covers the procedures of handling written or digital information; • transport work, where single movement of material units can be observed, changing their position in space; • work of mobile services; it is characterized by the need to move the production unit to carry out observation actions, inspections, maintenance, or even transformations on the matter that do not imply necessarily in the production of products. As examples of this last class, it could be cited routine aircraft take-off and landing, routine for receiving and transporting emergency patients, and routine factory preventive maintenance. The flow diagram model is most suitable for studying work methods at the plant or department level. The symbology usually employed, which is presented in this text, has been established according to those levels. For higher or lower coverage levels, it is necessary to reformulate the meanings of symbols and graphic conventions. This is done, for example, for the manual activity diagram. The object of study of the flow diagram can be either the item in production or the productive unit that performs the processing. Thus, the flows represented in the diagram, which define the flow diagram in terms of the object of study, can be: • as to the item produced: – material or product flow; – form or information flow. • as for the production unit: – person flow; – machine flow or transport equipment flow.

54

4 Analysis of Schematic Models

Thus, the production process can be represented by the flow diagram in terms of the processing steps that the product or material undergoes, the formal handling of data or information, the activities of the operator or the activities of the manufacturing or transportation equipment. The diagram, however, only admits the registration of just one object of study, which must be previously chosen in accordance with the objective of using the model. When understanding and studying a process requires representing more than one object, it is necessary to build separate diagrams. For example, when the process is recorded in terms of the product, the activities performed by the operator or equipment will not be presented. Care must be taken during the registration or analysis of the model, to keep the focus of attention on the chosen object, avoiding inadvertently changing the object. As for the choice of the set of information to be represented, it will depend on each case studied, and one should only take care that the set is coherent with the desired use for the model. It should be noted that the flow diagram follows the systemic conception of the process, and it is possible to identify in the diagram a productive system made up of components, such as: activities; flows (of items or of a production unit); boundaries (as limited to an object of study, a department or plant and within a period of time); and structure (mainly formed by the work process and methods and the production facilities). The survey of constructive data for the process flow diagram is done (a) by direct continuous observation or filming, following the object through processing, and identifying the successive steps and related information; or (b) from the process record, i.e., the manufacturing or assembly routines sheets, operator work orders, and machine load sheets. These sheets summarize, in the form of tables or written descriptions, the production process, specifying for each item processed, the manufacturing, assembly and handling activities required in the execution sequence, the work methods, equipment, special tools, accessories, and templates. Estimation or recording of the times of activities, production costs, the place of execution are usually also added to these sheets. The basic constructive concept of flow diagram is to understand and represent the process as if the item being processed or the processing unit “flows” through a logical sequence of productive activities. The graphical expression of this basic concept consists of flow lines of a type-item, on which the graphical symbols identifying the activities are drawn, arranged according to the processing sequence. In other words, the logical sequence of the productive activities constituting the process is presented in the flow diagram, listing the identifying symbols according to the order of occurrence and connecting them by straight lines, which represent the item’s flow. Note that the segments of flow lines between the symbols can indicate either physical movement or transport, or just the passage from one activity to the next. Each of the constructive concepts of the different types of process flow diagram follows the abovementioned basic concept, only introducing additional schematic information, altering the graphic organization of the scheme, and employing specific symbology.

4.4 Analysis of Schematic Models Presentation

55

The different activities of the process, referred to a given level of coverage, are identified in the diagram by a graphical symbol. Depending on the degree of detail of the study, the type of information required, and the type-item observed, different sets of symbols were established. The use or creation by the designer of the symbols used in the flow diagram should be guided by the fact that the smaller the number of symbols, the easier it will be to build and understand the scheme; a very small number of symbols can, however, lead to difficulty in grouping and classifying different activities. Figure 4.14 presents the most commonly used symbology in the flow diagram. To enrich the basic visual information of the flow diagram (symbols, sequence and lines of flows) about the process, annotations can be made next to the symbols, which indicate other important characteristics of the symbolized activities or elements. Such annotations can be written in the form of short descriptions or in coded digits. The characteristics of the process activities, usually introduced in the flow diagram, are numbering of activities; nature of activity (e.g., drilling, reading); duration time; physical location where it is carried out; identification of the production unit (e.g., number and name of the machine or operator); relate cost center; classification of the task (manual, automatic, with the aid of equipment, etc.); traveled distances. A suggestion for coding the symbols of processing activities is to use separate numbering series for each type of activity. This artifice allows the direct indication of the total number of activities of each type in the graphic scheme. Symbol

Activity Operation

Transportation

Inspection

Activity definition An operation occurs when an object is intentionally changed in any of its physical or chemical characteristics, is assembled or disassembled from anther object, of is arranged or prepared for another operation, transportation, inspection, or storage. An operation also occurs when information is given or received or when planning or calculating takes place. A transportation occurs when an object is moved from one place to another, except when such movement are a part of the operation or are caused by the operator at the workstation during an operation of an inspection An inspection occurs when an object is examined for identification or is verified for quality or quantity in any of its characteristics.

Fig. 4.14 Symbology used for flow diagrams

Use Material Equipment Forms

56

4 Analysis of Schematic Models Delay

Storage

Combined activity

Number 1

Source

Symbol

Activity Operation

A delay occurs to an object when conditions except those which intentionally change the physical or chemical characteristics of the object, do not permit or require immediate performance of the next planned action. A storage occurs when an object is kept and protected against unauthorized removal. When it is desired to show activities performed either concurrently or by the same operator at the same workstation, the symbols are combined (for example operation and inspection ASME (1947, 1952)

Number 2

Source

Activity definition Change of any physical or chemical characteristic of an object in a workplace (such as shape, size, colour, assembly, disassembly, etc.) Comparison of some feature of an object with a quantity standard Comparison of some characteristic of an object with a quality standard Moving an object from one job site to another, between operating, inspection, delay, or storage activities Retention of an object after an activity when the following activity does not start immediately, in the workplace or in an appropriate place, and whose removal does not require formal authorization or control Retention of an object in a certain location, for whose removal there is a need for formal authorization or control Nadler (1970 pp. 334)

Symbol

Activity

Activity definition

Use

Operation with machine

Changing some physical or chemical characteristic of an object performed by machinery or equipment with or without the use of labour Changing some physical or chemical characteristic of an object by a human operator, with or without hand tools Comparison of some characteristic of an object with a standard of quality or

Material Equipment Forms

Inspection for quantity Inspection of quality Transportation

Delay

Storage

Manual Operation Inspection with device

Fig. 4.14 (continued)

Use Material Equipment Forms

4.4 Analysis of Schematic Models Presentation

Visual inspection Mechanical transportation Manual transportation Storage

57

quantity, performed with the help of evaluation equipment Inspection performed by direct visual assessment Moving an object from one location to another carried out by or with the help of transport equipment Transport performed by a human operator without the aid of transport equipment Retaining an object at a certain location

Number 3

Source

IDEG-RJ (Instituto de Desenvolvimento Econômico e Gerencial)

Symbol LL

Activity Operation with labour

Us e Material Equipment Forms

M

Operation with modification

Us e Person Equipment

Number 4

Source

Activity definition Expenditure of labour or cost on product at one workplace which does not add value to the product Modification or any change at all (changing shape or size, machining, permanent assembly or disassembly, etc.) of product at one workplace Modifications can be performed using machines and/or labour and do not necessarily add value to the product Comparison of product with a standard of quantity or quality at one workplace Changing in location of product from one workplace to another workplace Delay, waiting or banking of product when no special order or requisition is required to perform next activity Delay, waiting or banking of product when a special order or requisition is required to perform next activity Nadler (1970 pp. 248)

Symbol

Activity Operation

Activity definition Doing something at one workplace

Verification

Comparing the product or service to a standard of quality or quantity Change in location without load from one workplace to another or taking more than one step at one workplace Change in location with load from one workplace to another Waiting, or idleness, or any activity which is not necessary for the method of work on the operation being modelled

Verification Move Temporary storage Controlled storage

Move without load Move with load Delay

Fig. 4.14 (continued)

58

4 Analysis of Schematic Models

Hold

Maintaining an object in a fixed position

Interval

Productive activity but not for the job being modelled Nadler (1970 pp. 331)

Number 5

Source

Symbol

Activity Issuance

Number 6

Source

Activity definition Indicates the origin of the issue of a form when filled in in N copies with initial or starting information Indicates modification or addition of information to a form previously issued Checking or verifying the information contained in the form, usually by comparing it with another source Temporary or permanent filing of the form Reichert (1967)

Symbol

Activity Operation

Activity definition Changing or adding information to a form

Document

Identifying or titling a form

Decision

When a point occurs from which alternative processing follows

File

Temporary or permanent retention in an appropriate location with known access to a form Indicates the form's exit point from a file for querying, processing, or transport

N Action Inspection

Archive

Exit file

Number 7

Symbol

Connection between operations

Indicates that the operations are interrelated

Material or part Assembly or finished product Source

Indicates that the form refers to a component from a set Indicates that the form refers to a set

Activity Origin

Activity definition Indicates the origin of the record, i.e., the occurrence of the first time that information of any kind is placed in a form Indicates that additional information is recorded in the form already issued

Additions to the record Fig. 4.14 (continued)

U se Form

Use Form

IDEG-RJ (Instituto de Desenvolvimento Econômico e Gerencial) Use Form

4.4 Analysis of Schematic Models Presentation Handling

Inspection

Movement TO Delay (archive or destruction)

Relationship

Number 8

Source

Symbol

Activity Origination and number issued Operation

2

Temporary storage Controlled storage Disposal Information transmission Source of information Source

Reading or removal of information on form for use by someone of some machine When information is obtained from sources other than another form Nadler (1970 pp. 256)

Move

Categories

Indicates non-productive operations on the form, such as sorting, separating copies, eliminating or deleting The record is checked for accuracy and when errors are found, the form needs to be corrected, accepted, rejected or reprocessed Used to indicate physical or digital movement of the form between work centres Indicates stop or inactive delay of the form, which can be temporary (for example, waiting to resume processing) or permanent (file or trash) This convention on the flow line indicates that there is a relationship between different forms, where the action on one influence the action on the other (for example, taking information from form 1 to record it in form 2) Close (1960 pp. 140) Activity definition Form being made out at one workplace (Number in centre represents number of copies made) Modification of, or addition to, form at one workplace Comparison of form with other information to ascertain correctness of form Change in location of form from one workplace to another Delay or waiting of form, where no special order is required to perform next activity Delay or waiting of form, where special order is required to perform next activity Form destroyed

Verification

Number 9

59

Symbol

Flow objects

Fig. 4.14 (continued)

Element Events

Element definition Situations occurring in the process

U se Form

Use Material, Operator,

60

4 Analysis of Schematic Models

Activities

Tasks performed Equipment, inside a process Form Decision-makers Point where the flow is controlled

Connection Objects

Sequence flow

Message flow

Association

Artefacts

Data

Groups

Annotations Groupings

Pool

Rays or swimming lanes

Number 10

Source

Indicates the order of the elements of the process Indicates the exchange of information among participants Associates the flow objects and artefacts with the process flow Indicates how data is requested or produced by activities Indicates completion of documentation or analysis Additional Information Defining entities or processes Subdivisions existing in entities or processes

OMG (2011;2014)

Fig. 4.14 (continued)

For the construction of the process flow diagram,5 it is possible to define a basic sequence of construction steps valid for the general case and for the specific flow diagram types: (1) determine the level of coverage and degree of detail of the study; (2) define the study object, whose processing flow will be raised, as well as the type of process work;

5 For drawing flow diagrams using a computer, both simple tools, for example, MS PowerPoint, MS Word, Google/diagrams.net, and online, for example, draw.io or Lucidchart (2022), are available. For online workflow management, more sophisticated tools can be employed, e.g., Pipefy (2022).

4.4 Analysis of Schematic Models Presentation

61

(3) choose well-defined and easily identifiable points of beginning and end, in order to certainly cover the entire process under study. Usually for manufacturing work, the diagram represents the process from the entry of raw materials into the plant, following all the processing until the formation of the finished unit, ending in its packaging, storage or even shipping; (4) survey the processing flow, defining the steps and activities, and their sequential orders. Take care not to change the object of study during the survey of the processing; (5) collect additional data and characteristics of the process and corresponding activities; (6) choose or create the most suitable symbology; (7) schematically reconstitute the process, through the lines of flow and symbols. In general, in order to facilitate the reconstitution of the process, the graphic record starts from the end to the beginning of the process, i.e., from the last activities to the first ones; (8) add to the basic scheme, the supplementary information that is desirable; (9) check the record’s accuracy; (10) compute and summarize the most important information, according to the evaluation criteria used in the case, in a summary table. Note: In order to facilitate the computation of data for the analysis of the diagram, or the comparison between alternative solutions, it is convenient to attach a summary

Activity type

Symbol

Activity No

Operation Inspection Delay Storage Transport Types of transportation

Manual Cart Forklift Overhead crane

TOTALS Fig. 4.15 Example of a summary table for flow diagram

Time

Distance

62

4 Analysis of Schematic Models

table to each flow diagram. This table summarizes the characteristics of the represented process, according to the evaluation criteria employed. Such characteristics can be types of activities, number of activities, types of transport, number of transports, processing or transport times, distances covered, costs, quantities produced. Figure 4.15 shows a simple summary table example. The primary objective of production processes is to increase product value. The relative value of the product can be regarded as monetary, utility, esteem, artistic, mystical, psycho-social, or survival.6 In order to increase the value of the product, it is necessary to employ material efforts and resources, such as human or machine work, inputs, energy, and capital. All these efforts and resources generate monetary costs in terms of time, personal, social, and nature’s wear and tear. In relation to work methods, activities that imply an increase in the value of the product are thus defined as productive activities (or value-generating activities); and those that do not contribute directly to this increase in value, defined as nonproductive activities. From the above, it can be inferred that the basic criterion that guides the study of improvement of production processes, with regard to work methods, consists of: improving and developing productive activities; eliminating, reducing, or rationalizing non-productive activities; and reducing production costs. For example, in the development or evaluation of the physical arrangement, the criterion is improvement of physical flow. This means improving the processing sequence in order to reduce inefficiency due to returns or queues. The criteria for comparing alternative solutions for the work situation, from the visual and computational analysis of the information gathered in the process flowchart, are: (a) (b) (c) (d)

smallest total number of activities; fewer non-productive activities; less total processing time; lowest cost generated by the production per item produced.

Manipulation The study of manipulation of the flow diagram and the work situation it portrays revolves around the consideration of productive and non-productive activities, and the costs generated by production. Within the model’s basic coverage levels (plant and department), the productive activities are active operations and inspections. Active operations are activities that directly lead to changes in the form, chemical composition or physical condition of the input or product in order to increase its value, and/or that meet the objectives of 6

As all categories of value can be converted “in principle” into monetary value, the reasoning in the present work will always be referred to in these terms. This is reinforced by the fact that the organized production of goods and services is always closely related and conditioned by the monetary values involved. The same is true for the cost factor.

4.4 Analysis of Schematic Models Presentation

63

the production organization. Inspections or examinations considered as productive activities are those that carry out a control over production, in order to guarantee the increase in value by quality control or achieving the quantity demanded in the expected time. Non-productive activities, in the case of the process flow diagram, are storage and transportation. In general, the storage of material, product or form, within the production system, in addition to not adding value to the items, constitutes immobilized capital and implies additional investments in physical space. In the context of the methods study, stocks, both initial and final, as well as intermediate or in process, entail the need for supplementary projects of transport system and loading and unloading methods. Controlled stocks also require the design of a control and release system. It should be noted that in the study of methods, the designer’s interest is focused on the existence and location of stocks to balance and organize production; the dimensioning of the size of the stocks is up to the production planning and control (PPC) study, which determines the economic production batch, which must take into account the cost of handling the material, and direct labor or idle machines. Transports that consist only of moving items in process also add nothing to the value of the moved item and generate additional costs. Transport is only considered a productive activity when transporting is the objective of the organization, as for example in the bus or truck companies. Production costs are affected by processing time, by the deployment and use of production capacities and by the physical flow of materials and/or operators. Based on these considerations, it is possible to formulate some basic actions on the work situation or project guided by the diagram records: (a) designing the work process or method so that its sequence of activities has a greater number of active operations, since only they contribute to the evolution of the raw material or product from its initial state to the desired final state; (b) question if each active operation and if the projected or existing inspection activities are necessary and compatible with the desired increase in value; (c) study whether the projected or existing stock policy is the most appropriate from the point of view of handling and controlling stocked items; consider just-in-time scheme; (d) try to eliminate, as far as possible, without harming the balance of production, the intermediate stocks, questioning the need, and methods of control over stocks; (e) reduce transport distances by bringing sections or workstations closer together in the physical arrangement; increase the efficiency of transport, providing for movement in the largest possible batches and using faster transport equipment with greater load capacity; (f) combine activities of different types, such as operate-on-the-move, inspect-onthe-move, stock-on-the-move, operate-inspect, etc.; combine activities of the same type (e.g., punching and folding operations performed simultaneously in the same pressing);

64

4 Analysis of Schematic Models

(g) employing the full capacity of the production units, enabling the production or handling of the largest number of items at a time (e.g., providing dies to stamp the maximum number of parts within the capacity of a press stroke, or training the inspector to examine the largest possible batch with a given margin of error); (h) rearrange the sequence of activities, in order to avoid inefficiency due to returns or queues, or to allow a more continuous flow. It is important, however, that when it has been possible to eliminate all unnecessary activities and make all possible gains with combinations of activities, changes in the sequence of procedures and other manipulation actions guided by the flow diagram the doubt remain whether the necessary activities are carried out in the best-known way. To continue the improvement study, it is then necessary to move to the next lower level of coverage, which considers each activity as a productive system. The schematic models that can be used for this are manual activity diagrams, sensorymotor diagram, and cyclegraph. Uses The function of the schematic representation of the process flow diagram is to allow the designer to formulate the problem, solve it, present and install the solution. In order to fulfill this function, some specific, distinct and triggering application of a problem-solving process can be defined for the flow diagram: (1) Schematically recording the sequence of activities that are components of a production process. This record consists of the collection, organization, and visualization of events and related information that occur during the process, defining a logical sequence of processing. (2) Assisting the process analysis. The schema itself, by graphically separating and identifying the component parts and stages of the process, already constitutes a process analysis. This analysis has the objective of understanding the general process through the understanding of what its constituent parts are, how they work and how they interact. (3) Helping develop better work methods. For this purpose, the model is used in the representation of the various solutions generated in the work methods design. Thus, it allows the analysis of each one of the solutions, so that the designer understands it and seeks to improve it, and the comparison of the set of solutions in order to highlight the best ones. During the development of work methods solutions, their study through the flow diagram helps to visualize the effects that would come from changes in parts of the process on other points or elements. The improvement study is done on two levels by: (a) analyzing the general processing, seeking to develop the set of activities and their sequencing in a way that is most coherent with the objectives of the production process and the production resources in question; and (b) identifying the particular activities that could be submitted to a more detailed analysis.

4.4 Analysis of Schematic Models Presentation

65

(c) Present a condensed visualization of the process. The fact that the graphic scheme represents the operation of the entire process in a condensed way makes it a good means of communication for those involved in the process, whether in the design, “sales”, implementation, maintenance, or redesign phases. For each of these purposes, it is advisable to consider a visual programming that highlights the most important information in the case in focus. The flow diagram is used in almost all phases of the project, evaluation, and monitoring of production facilities, from the design phase of the production processes involved, through the selection of equipment-machinery-labor, the work methods, automation and robotics, the integration of artificial intelligence, control and feedback procedures, bureaucratic procedures, physical arrangement, to the architecture of physical spaces. The most common use of the flow diagram is to study the physical arrangement of production facilities. It is almost a rule to start a layout study by surveying the process flow diagram. This is because the scheme clarifies what type and what importance have the physical interrelationships between the production units of an installation, whether persons, machines, equipment, workstations, sections, or departments. And not only in the initial approach to the study of the physical arrangement, the flow diagram is shown to be a very useful reasoning resource, but also during the development of solutions, in the study of possible improvements, in the evaluation and “sale” of the project, in the planning of physical changes in the facilities, in the implementation schedule, and in the control of the implemented plan in the operating regime. In the case of the study and analysis of continuous processes (basically chemical and metallurgical processes), mechanized or automated processes, and manufacturing processes of a specific product in large quantities, there is a direct relationship between the flow diagram and the physical arrangement of the installation. This is because, in order to avoid or minimize the occurrence of unnecessary returns, queues, crossings, and movements, their workstations, equipment, and production departments must have a physical layout according to the sequential ordering of the process, represented in the flow diagram. Another relevant use of the model for studies of production systems with such characteristics is in the identification of the control points and facilities needed for the process. In the design phase of the production process, the flow diagram provides elements for decisions regarding the production units to be employed to carry out its stages: whether person and/or machine, which professional, which machine, which equipment and infrastructures are required. The model can also suggest the first ideas for the design of work methods, both at the level of the whole process and for each element or step. In the study of work methods, the flow diagram basically serves to separate and identify, among the actions or events that occur on the flow of items being processed, those that result from the action of the human element. The different actions of

66

4 Analysis of Schematic Models

the human element, constituents of the process, distinguished in the analysis of the flow diagram, are dimensioned and methodized separately and, further, integrated in order to form a general work method for the process. This methodization of the performance of the human element in the production process, thus defining a work method, aims to raise awareness and forecast their performance and establish more economical ways of acting (such as less human effort, greater use of their mental and physical faculties, lower production costs, greater speed, less risk of errors and accidents). This procedure can provide the basis to improve or facilitate human work using automated or robotic activities, and even to replace it. The record of defined and established work methods can be done by human process flow diagram, or other models, such as manual activity diagram, orders or service sheets, sensory-motor diagram, etc., according to the type of work involved and the study’s level of scope. The most practical classification, however, regarding the use of the process flow diagram, refers to the type of item whose flow is registered, whether is a person, machine, product, forms, or information. The record item is chosen according to which project factors one wants to analyze. The classification referring to the type of constructive conception of the model also defines fields of use for the flow diagram. These types, as already presented above, are: single, assembly, manufacturing and assembly, productive sectors, complex procedure, chronological, and business process. In the present book, a special treatment is given to each of these types, in which their employment distinctions are more clearly defined. As for restrictions on the use of the process flow diagram, they are summarized as follows: (1) The flow diagram represents the process by recording the evolutions, changes, or actions suffered by only one of the types of elements participating in the process, whether person, machines, products, forms, information, etc. For a complete view of the process, it would be necessary to create flow diagrams for each element involved. It is therefore necessary for the designer to keep in mind that each flow diagram suggests design factors directly related to the registered element, i.e., to the object of study chosen for registration. (2) The model alone has more direct application to the systematic study of stable processes, which obey a sequence of deterministic steps. It is clear that such a statement does not detract from its use as an instrument for surveying unknown processes or with random sequences, requiring, however, a subsequent sample study, to define a representative behavior of the process. (3) The process flow diagram as presented in this book fits better at plant and department coverage levels. For levels above or below, the conceptual assumptions are valid; however, the symbology and organization of the other schematic information must be reformulated.

4.4 Analysis of Schematic Models Presentation

4.4.3.1

67

Single Flow Diagram

This concept of process flow diagram is characterized by representing the sequence of processing activities of a single item. Single item here defines the object-item that, during the period of observation of the production process in which it is involved, does not suffer component integrations or disintegrations. It is an antonymous definition of a composite item, made up of component sub-items, which in the production process are either integrated or disintegrated into it. In the case of composite items, one can use single flow diagram to separately record the processing of each component sub-item, not worrying about recording the joins or disjunctions. Still in this case, the single flow diagram is used to get an approximate idea of the process, registering only the processing of the main component and considering the integrations or disintegrations as actions performed on it. This approximate version of the process is very useful at the beginning of the development study of alternative solutions, to have a first idea of the overall process, by recording the main sequence of activities. For the record of this approximate version, it is customary to symbolize only operations, and eventually inspections, constituting an “outline process flow diagram”. The characterization of the single item obviously depends on the study’s level of coverage. At the lowest level, it will be either a single product or form, or a single person or piece of equipment. Increasing the coverage level, it can become a product group or a team, for example, and so on, but always with the restriction that integrations or disintegrations of components to it do not occur or are not considered. The most appropriate record for the single flow diagram is the work method of a person, who is the object of study. In that case, the typical situations are: (a) operator moving from one workstation to another, at each one performing productive actions, following a service routine; (b) operator performs a series of activities in the same workstation following a service routine. Such considerations are valid for the case of the object of study to be a device that acts similarly to the situations mentioned above for the human operator. When the object of study is a product or form, they will rarely meet the uniqueness constraint, except in the case of the approximate version of the process. The constructive conception of the single flow diagram is the simplest of the process flow diagrams, consisting of a single flow line on which the symbols representing the events that occurred to the object-item of study during the recorded processing are drawn (see Fig. 4.17).

68

4 Analysis of Schematic Models

In comparison with the other flow diagram conceptions, presented in the next chapters, in this case, there are no entry or exit lines of component items but only a continuous line from the beginning to the end of the recorded process. For its construction, it is enough to choose a set of symbols, best suited to the type of study during recording processing and refer them to that symbology. It should be noted that any of the single flow diagrams will have a similar graphic constitution, as the scheme is a simple ordering of symbols on a continuous line. It is also possible to facilitate the drawing of the scheme, using printed standardized forms (see Fig. 4.18), for a given symbology. The symbols are already drawn on these forms, simply joining them according to the sequence of activities of the process being recorded. To make better use of the printed form, it is interesting to organize a format that allows for the inclusion of other desirable information, in addition to symbols, such as a forecast for recording some alternative methods, a summary description of the activity symbolized, quantities, weights, costs, savings, type of equipment, digits of identification of work centers or items handled, etc. When studying a group of products or single forms that are processed in the same set of work centers, a suitable representation usually consists of drawing the various flow diagrams in a common matrix table items x work center. This scheme (Fig. 4.16) is very useful in studying the layout of facilities that process various products (or forms).

Product Work station

a

b

A

1

1

B C

2

2 3

3

Fig. 4.16 Summary sheet of multiple singular flowcharts

d 1

1 2

D E

c

4

3

2 5

4.4 Analysis of Schematic Models Presentation

69

Examples The examples below show the single flow diagram for a human operator, performing a tune-up service of a gasoline engine in a car maintenance workshop. The single flow diagram is presented in two formats, simple and standardized. Example 1 Simple format (Fig. 4.17).

Fig. 4.17 Example of single flow diagram—dimple format

70

4 Analysis of Schematic Models

Example 2 Standardized format (Fig. 4.18).

Fig. 4.18 Example of a single flow diagram—standardized format

4.4 Analysis of Schematic Models Presentation

4.4.3.2

71

Assembly Flow Diagram

The assembly flow diagram represents the assembly (or disassembly) process of a composite item, through a schematic indication of the sequence in which its components and sub-assemblies are integrated (or disintegrated). In the diagram, these integrations (or disintegrations) of the component parts of the composite item are performed over a main component, sub-assembly or body. The part considered to be the main part is the one that receives the others, or it is the part that undergoes the greatest number of productive activities, or the part that is most manipulated or transported. It should be noted that the assembly flow diagram is exclusively limited to the assembly process, which can be part of a more complete production process, involving an earlier phase of manufacturing the components and a later stage of dispatching the composite item produced. The basic visual information of this scheme is: • • • •

the sequence of assembly of the main body and of the component sub-assemblies; which components make up sub-assemblies; the relationship between components in the assembly process; the entry points of each component and sub-assembly into the main assembly.

The design of this schema, as shown at Fig. 4.20, is more appropriate for product, and eventually forms, as object of study. The constructive form of the scheme (in the case of assembly) consists of a vertical column, where the assembly of the main body is registered, to which horizontal lines are connected that indicate the entry of each component and sub-assembly in the assembly process (Fig. 4.19). As in principal this scheme is used to have a general idea of the assembly process, without great details, it is customary to use only the operation and inspection symbols, and when important, delay. Fig. 4.19 Construction of assembly flowchart

Component entry Assembly process

Subassembly entry

72

1 3 4

4 Analysis of Schematic Models CAN

10 5 2 7 8 9

12 11

ASSEMBLE CELL BOTTOM & SIDES TO CAN

2

ASSEMBLE SECTION IN CAN

3

SOLDER WIRE LEADS

4

ASSEMBLE TOP SECTION OF CELL TO CAN

5

ASSEMBLE COVER SUBASSEMBLY TO CAN

CELL BOTTOM & SIDES

SECTION, ALU FOIL

S1 6

1

FLAT LEADS WIRE LEADS (2) TOP SECTION OF CELL

WIND & INSERT WIRE LEADS IN SECTION

COVER MICARTA WASHER CORK WASHER STUD

INERTEEN

TERMINAL

S2

1

DRY TEST

6

SOLDER

7

CLEAN

8

IMPREGNATE WITH INERTEEN

9

SOLDER TERMINALS AND VENT HOLE

10

CLEAN

2

TEST FOR LEAKS

3

ELECTRIC TEST

4

FINAL INSPECTION

Fig. 4.20 Assembly flowchart example. Source Buffa (1969, p. 161, Fig. 27); copyright @ 1969 by John Wiley & Sons, Inc.

4.4 Analysis of Schematic Models Presentation

73

Note that the diagram only shows the sequence of occurrence of successive assemblies; the study or record of how the assemblies are performed, that is, of the assembly work methods, is done at a level of scope below, with more detailed models, such as p. ex. the manual activities diagram or service orders. In the case of assembly, the graphic construction of the flow diagram starts from the end of the process (assembled item) and continues reconstituting the successive integrations of components and sub-assemblies into the main body, until the beginning of the process (component entries). In the dismantling record, construction is carried out in reverse, that is, from the beginning to the end. The common constructive idea is to start from the most aggregated set to the most disaggregated set, from the compound to the components, similarly to a diffusion process. The typical situation of using the assembly flow diagram is in the study of the work of assembly lines. For single-product assembly lines with large-scale production, the flow diagram directly indicates the physical arrangement of assembly stations and intermediate storage and holding centers. Example The example below shows the material flow diagram for the process of assembling a capacitor (Fig. 4.20)

4.4.3.3

Manufacturing and Assembly Flow Diagram

Conceptualization The manufacturing and assembly flow diagram provides a schematic view of composite item processing, which involves fabrication, manufacturing, handling, and assembling component parts processes. In summary, the scheme shows the way in which various components are processed and assembled to form a complete product. The model shows the sequences of parts processing activities, the formation of sub-sets or sub-assemblies, the points of introduction of purchased parts or whose processing is considered external to the process in record, in the sub-assemblies, and in the main assembly. The main set can be depending on the type of registered flow as follows: (a) For materials or products, it is the basic component that receives all other parts, sub-sets and sub-assemblies, in order to constitute the final product. (b) For forms or information, it is the most important document or copy. It should be noted that if this distinction is not possible, the appropriate flow diagram conceptions will be, in this case, the sector flow diagram or the complex procedure flow diagram. (c) For the human element, the manufacturing and assembly flow diagram only applies when there is a team working on the same flow of materials, products, forms or information. The main set in this case will be the operator that performs activities on the basic component of the final product.

74

4 Analysis of Schematic Models

(d) For manufacturing and transportation equipment, the same considerations above to the human element apply. It is clear that the manufacturing and assembly flow diagram can be characterized as proper to the registration of material and product flows due to the restrictions on the use for other types of flow.7 In this kind of flow diagram, a special distinction is made between the productive activities model and the complete model. Indeed, two types of manufacturing and assembly flow diagram are defined, as distinguished by the degree of explicitness of the activities, as follows: (1) Manufacturing and assembly flow diagram for productive activities In this diagram, only the activities that change the value of the input or product or constitute the main purpose of the productive organization, are represented. In general, such activities are active operations and inspections. The diagram for productive activities is known by Methods Engineering technicians by the name of “operation process chart”, thus defined by ASME, in the case of material flow: “An operation process chart is a graphic representation of the points at which materials are introduced into the process, and the sequence of inspections and all operations, except those involved in material movement. It may include any other information considered desirable for analysis, such as time required and location” (ASME 1947, point 13). (2) Complete manufacturing and assembly flow diagram The complete flow diagram records all the activities that comprise the process, whether productive or non-productive. The complete flow diagram can be considered as an expansion of the flow diagram for productive activities. Between the two types, a slight difference in the field of application can be distinguished. While the productive activities model could be used to present the main production process of complex products, the complete flow diagram would apply to the more detailed study of the most critical parts or sub-assemblies. Uses The manufacturing and assembly flow diagram is useful in depicting the following situations: (a) when many parts are processed separately and are gradually assembled and processed together, in sub-sets, or in a final set; (b) when a product or material is dismantled, and the component parts are then separately processed. This would be the case, for example, for the processing of beef animals;

7

In the present text, reference is made basically to the flows of materials and products, leaving the other types of records as extensions of the diagram, taking into account, however, the imposed restrictions.

4.4 Analysis of Schematic Models Presentation

(c)

75

when it is necessary to show divisions in the processing flow, for example, activities on different lanes of an office form. In the study of work methods, manufacturing and assembly flow diagram is used

to: (a) provide a compact overview of the entire production system (machines, facilities, quantities, materials) and the production process of complex items. This to determine how to aggregate the groups of similar activities in workstations-type and how to organize the physical relationship between them, in order to allow the best flow of the materials in process; (b) assist in the study of physical arrangement and installation of equipment and machinery. In case the productive system processes a single product, or a product with importance (quantity, weight, or cost) highlighted in relation to the others, its flow diagram shows an ideal physical distribution of the equipment in the plant, unless there are aggregations of activities similar to the same workstations; (c) make it possible to graphically record the workflow of the digital forms system for the study of replacing paper forms and files, improving digital systems in operation, improving workflow management and process automation, and evaluating solutions alternatives according to digital technology advances; (d) specify the production system, as a means of communication and marketing (“sale”) to the people involved; (e) programming the sector for receiving materials purchased outside, and the intermediate storage and waiting for the materials manufactured; (f) educational help, providing operators and designers with a global view of the productive system in which they participate, in order to awaken a critical and creative attitude of action on the organization and constitution of the system. Manipulation From the schematic record, one can analyze and evaluate the productive system in order to highlight points of action for improvements. For this purpose, a list of points of analysis should be organized, according to the scope of the study of the work in question. An example on listing for a general assessment of the process would be: (1) verify that the overall process is compatible with the item’s production objectives; (2) verify that the purpose of each productive activity is compatible with the production objectives of the item; (3) check the design and drawing of the composite item and its component parts, in relation to tolerances and specifications, materials, manufacturing processes, assembly process, work method; (4) check the production equipment in relation to type of tooling, tooling preparation process, working conditions for the operator, physical distribution in the plant, environmental disturbances, risks, and hazards;

76

4 Analysis of Schematic Models

(5) verify that the transport equipment meets the characteristics of the flows, such as weight, quantity, physical condition, material damage and risks, speed, risks of accidents to personnel; (6) check the system’s general safety and hygiene conditions. Obviously, the set of information recorded in the scheme must meet and be consistent with the process evaluation listing. If this is only answered in part by the flow diagram analysis, it is necessary to use other models more representative of the system. Construction The most appropriate source for surveying and collecting constructive data for the manufacturing and assembly flow diagram are the manufacturing and assembly sheets or orders. This model is even considered as a schematic summary of the manufacturing and assembly sheets for the entire process. When these are not available, the way is to carry out the survey by continuous direct observation, following the evolution of the items in the workplace, which for very complex products it is not an easy job. In the case of a project, one should try to prepare the manufacturing and assembly sheets of the process as far as possible. The constructive conception of the graphic scheme consists of a main processing flow line to which the various branches of secondary processing lines are connected, according to the order of integration. The sequences of processing activities that take place on each part, sub-set or main set, are represented by the arrangement of symbols on vertical flow lines. The input of materials to be processed or purchased outside, or whose processing is considered external to the process under study, is represented by horizontal lines that meet vertical lines at the points of use of the corresponding materials. When it occurs that a certain sub-set or processed part is used at more than one point in the process, its processing line connected to the first point of use is represented only once in the diagram. The other inputs to the process are indicated in the same way as for purchased material; to facilitate visual recognition between the purchased material input and the processed part with more than one use, some differentiating graphic convention can be used, such as (Fig. 4.21): material purchased

part processed with more than one input Fig. 4.21 Example of convention for process inputs

4.4 Analysis of Schematic Models Presentation

77

In the design shown below, the main processing line is drawn on the right side of the diagram. The secondary processing lines are shown to the left of the main sequence, with the lines corresponding to the materials that subsequently enter the process indicated far more to the left. Schematically, one can show this general conception of the diagram, as follows (Fig. 4.22):

part processed

material purchased

material purchased

part processed

sub-assembly or sub-set processed material purchased part processed with more than one input

sequences or processing steps

material purchased

main assembly processing

part processing

material purchased

part processing

material, part or sub-set supplied to the process

Fig. 4.22 Example of manufacturing and assembly flow diagram construction. Source ASME (1947, 1952, Fig. 1), Maynard (1963, pp. 2–22, Fig. 3.1) and revised by the Author

To start the diagram construction, it is necessary to determine or choose the main set, whose processing will be indicated in the main flow line. This determination or choice can be made based on three alternative criteria: (a) identify the basic component of the product, which receives the other component parts or sub-sets; (b) identify the component on which the largest number of processing activities occurs; (c) in the case of a study of the physical arrangement of a progressive assembly line, identify the component of greater volume or greater weight, which receives the other smaller or lighter components. Such criteria are also valid for determining secondary sub-sets.

78

4 Analysis of Schematic Models

Based on the scope and degree of detail of the study, the type of workflow observed and the type of manufacturing and assembly flow diagram, the group of symbols to represent the processing activities of each component is chosen (see Fig. 4.14). In the case of the flow diagram for productive activities, in general, only symbols of operations and inspections are used; in the complete flow diagram all symbols of the chosen group are used. When the construction data collection is provided by the manufacturing and assembly sheets, the construction of the diagram is facilitated if the process is reconstituted in the opposite direction to the sequence of occurrence of the processing activities, that is, from the final product to the component raw materials. In this case, the construction proceeds with the reconstitution of the processing of the main assembly, starting from the last activity recorded in the corresponding manufacturing and assembly sheet, followed by the successively previous activities. After all the activities performed on the main set have been symbolized, the entries of purchased materials and processed parts or sub-sets are indicated. The leftmost vertical line is reserved for the processed part or sub-set that enters the main set last. This same procedure for reconstituting the main set processing is applied to the other component sub-sets. The beginnings of the representation of all processing, that is, input of raw material or component, must be aligned at the top of the diagram. The drawing of the processing sequence of each part begins with the arrow indicating the raw material input. At the head of the vertical column corresponding to each part, the name and number of the part, the quantity required, and important specifications are usually indicated, by short description or code. Other information about characteristics of processing activities, considered important for the understanding and analysis of the represented process, can be added by means of annotations along with the corresponding symbols, in the form of brief descriptions or coded digits. Additional constructive conventions8 : (a) Numbering It is suggested to use a series of numbers for each type of symbolized activity. This provides immediate information on the quantity of each type of activity. One can also use a coded number that indicates, in addition to the activity number, other information, such as the sector or workplace where it is carried out, distance moved, whether carried out by person or machine, etc. (b) Repeated activities When processing activities or groups of activities that are repeated several times, a graphical indication is used to avoid unnecessarily stretching the diagram. This indication is a “loop” with information on the number of repetitions (Fig. 4.23). 8

The constructive conventions for flow diagrams presented by Figs. 4.23, 4.24, 4.25, 4.26, 4.27, 4.28, 4.29, 4.30, 4.31, 4.32, 4.33, 4.34 and 4.38 have been collected and adapted from different authors such as Fields, Maynard, Nadler and Niebel.

4.4 Analysis of Schematic Models Presentation

79

repeat n times

Fig. 4.23 Repetition or loop indication

(c) Reprocessing Sometimes, an inspection indicates the need to reprocess the part or sub-assembly. This decision is represented by a closed “loop” (Fig. 4.24).

NO YES

Fig. 4.24 Indication of reprocessing

(d) Removal of material. It is the opposite indication of material input. This occurrence is generally due to the removal of excess material or packaging, templates, and auxiliary fixings; or even the rejection of defective items without recovery, which will constitute scrap (Fig. 4.25).

80

4 Analysis of Schematic Models

Fig. 4.25 Indication of material removal

(e) Alternative Processes (e.1) Independent decision It occurs when, after a certain point, the process can proceed according to several different activity sequences, simultaneously or not. This convention also applies to the representation of disassembles (Fig. 4.26). Fig. 4.26 Indication of an independent decision

(e.2) Decision dependent The alternative routes in this case are mutually exclusive. From a certain point, usually after an inspection, the process goes through one of the alternative sequences, depending on a decision pattern (Fig. 4.27).

4.4 Analysis of Schematic Models Presentation

81

Fig. 4.27 Indication of dependent decision

NO 1

NO 2 YES

(f) Change of state When there is a change in the physical state of the material being processed, it is necessary to indicate this in the diagram, to foresee changes or special care in the handling or transport of the material. The graphic indication consists of a double bar that interrupts the flow line, with information on the type of change that has taken place (Fig. 4.28). Fig. 4.28 Indication of state change

change of state

(g) Crossing lines The diagram should be constructed in such a way that horizontal and vertical flow lines do not intersect. For very complex items, where this is not possible, the normal convention for crossing flows applies (Fig. 4.29).

82

4 Analysis of Schematic Models

Fig. 4.29 Indication of crossing of lines

Flow Diagram for Office Procedure For the study of office procedures where the observed flow consists of forms or information, the same design and constructive scheme of the manufacturing and assembly flow diagram can be used, except for certain changes in symbology and additional constructive conventions. In terms of symbology, any of the groups presented in the general study (see item 4.4.3) can be used for forms or information. Additional constructive conventions are as follows: (a) Document title For easier reading of the schema, it is advisable to identify each document with a title placed in a rectangle at the beginning of the representation of the corresponding processing sequence (Fig. 4.30). Fig. 4.30 Indication of the document title

Form XPT

(b) Representation limits Form processing is generally too complex and extensive. When the designer is interested in studying only a part of the process, or when the representation of the entire process results in a very large and intricate diagram, it is necessary to limit the representation to a certain area of the entire diagram.

4.4 Analysis of Schematic Models Presentation

83

To indicate the limitation made to the representation of the process, it is used to draw a horizontal line on the flow line, after the last activity symbolized. This indicates that the study ended at that point, but the corresponding form processing continues (Fig. 4.31). Fig. 4.31 Indication of termination

(c) Distribution Processing the form is similar to disassembling products. This is because, during the procedure, multiple copies are generated, which follow separate sequences. The multiplication of forms in several copies and their distribution by different procedures is represented in the schema with a convention similar to the one used for alternative processing with independent decision (Fig. 4.32). Fig. 4.32 Indication of distribution

84

4 Analysis of Schematic Models

(d) Information transfer During form processing, information or data are transferred from one form to another. This occurrence can be represented on the diagram by a dashed line joining the symbols of the corresponding read and compile operations in each form involved; whenever possible, the symbols of the operations of each transfer should be horizontally aligned (Fig. 4.33). Fig. 4.33 Indication of data transfer

Reading

compilation data X

compilation data Y

(e) Corrections and reiterations Expected error corrections or reiterative processing of data are indicated in the diagram by convention similar to that used for reprocessing in the flow diagram for materials and products (Fig. 4.34). Fig. 4.34 Indication of corrections and reiterations

Corrections YES

4.4 Analysis of Schematic Models Presentation

85

Examples Example 1 Shows the person process flow diagram (manufacturing and assembly) for the process of producing a master’s thesis at a university by a student (Fig. 4.35). TUTOR

EXAMINATION BOARD

Chooses the themes of his/her research field

STUDENT

Attends the introductory seminar and study the subject

Application for thesis Evaluation of the themes from his/her field of study

Definition of possible theses on these themes

Proposal of themes to students

Examines the material, its consistency and importance

Checks the available in that field and type of relevant contribution

Prepares the minutes of observations, criticisms and recommendations

Choice of tutor Selection of 2 or 3 topics in the chosen area Analysis of theses made in these matters Choice of thesis topic Bibliographic research Request to the library

LIBRARY

Reading the material

Receives orders from books, articles and copies

Tutor

Checks availability on library and in the bibliographic bases

Tutor

Applies for loans or copies of other bases

Analysis of the bibliographic research Research and thesis script

Research work Tutor

Prepares copies

Computer

Data analysis

Realizing seminar 1

Registers the loans

Material to the board Tutor

Final treatment of research and data

Final analysis of variables and parameters

DESIGNER Receives editing request of text and drawings

Text writing

Elaboration of illustrations

Prepares text and drawings

Editing request Final joining of material Realizing seminar 2 Tutor

Examination board

Fig. 4.35 Example of a person process flow diagram

Correction with board inputs

Thesis defense and delivery

86

4 Analysis of Schematic Models

Example 2 Shows the material flow diagram for the manufacturing and assembly process of a hand drill (Fig. 4.36).

Fig. 4.36 Example of material process flowchart. Source Krick (1962 p. 96, Fig. 22); copyright @ 1962 by John Wiley & Sons, Inc.

4.4 Analysis of Schematic Models Presentation

4.4.3.4

87

Productive Sectors Flow Diagram

The productive sectors flow diagram model has the objective, while schematically presenting the flow of material, information, person or equipment through a sequence of production activities, to make explicit the allocation of each activity to the sector responsible for its execution. Sector means here the functional subdivisions of a productive unit, involved in a given production process. The definition of the productive unit and its sectors will depend on the level of coverage where the study is focused (e.g., plant → departments, department → sections or groups of people or equipment, operator → members of the human body, machine → devices or tools). In this way, in addition to the basic information of the process flow diagram, this format shows where each phase or even each processing activity is performed. This additional graphic information is obtained by drawing the flow diagram (also using symbols-activities and lines-flow) on a matrix table, where the columns are the productive sectors, and the lines the description of each activity. For the construction of the sectors flow diagram, individual flow diagrams (singular, assembly or manufacturing and assembly) must first be prepared for each sector or for each isolated item in flow9 and then join them in the sectors x activities matrix, recording the events according to the sectors where they occur. It should be noted that all the sectors listed in the columns must: to be of the same level of coverage; to be subdivisions of the same productive unit; and being involved in the same production process. The drawing of each symbol must be horizontally aligned with the description of the respective activity, made on the right or left margins of the matrix board (see Fig. 4.37). In order to speed up the understanding of the record, making its analysis easier, one should try to align the flow on the main diagonal of the matrix. The sectors model, or matrix, or even multi-columns, should be used whenever it is necessary to show in a condensed way the flow of items in production through different productive sectors. For this type of information, only the map flow diagram (item 4.4.4) provides greater clarity, as it indicates the occurrence of flows on the physical arrangement of the production facility; however, due to the matrix form, the sectors flow diagram can aggregate a greater amount of information.

9

Thus, in the case of products, a flow diagram for each component; for forms, for each copy; in the case of a team, for each individual; in the case of groups of equipment, for each equipment.

88

4 Analysis of Schematic Models

The most suitable use for the productive sectors flow diagram is in the study of forms processing. This is because it constitutes one of the models that best represents formal systems of paper or digital flow, such as bureaucratic routines and information systems, due to the fact that the logic of these systems fundamentally depends on where they are manipulated or who acts on them.10 In the case of forms as object of study, the basic scheme shows the work centers participating in the system, documents, information, and data added to or removed from each document, the origin, distribution, and final destination of each document. This information is particularly valuable for the process of digitizing or automating the form or information processing system. The manipulation of the diagram in the study of improvements in a registered processing follows some basic guidance, such as: • By going through the descriptions of the events and respective symbols in the horizontal lines of the matrix, it is possible to verify if all the activities performed are really necessary and if there is the possibility of being added, eliminated, or modified, and even if any activity should be studied in more detail. • Analysis in the direction of vertical lines allows verifying if the activities are compatible with the sectors involved and if there is no duplication or redundancy of activities or processes. It is worth mentioning that the sectors flow diagram is essentially a manufacturing and assembly flow diagram, drawn against the sectors x activities matrix. In this way, the considerations and conventions established for those models are also valid here. Example In the example below (Fig. 4.37), a record is shown through the sectors flow diagram, of a form flow in an industrial production planning and control (PPC) system. The PPC system is required to integrate scheduling, dispatch (shipment), inspection, quality management, inventory management, supply management, and equipment management.

10

In item 4.4.2, conceptual considerations on forms and information distribution are made.

Fig. 4.37 Example of productive sectors flow diagram

Note: Symbology: Figure 4.14, Number 9, Nadler (1970) Glossary: PPC - Production Planning and Control OM - Order Management Dept. SO – Sales Order OS – Order of Service in1, in2 – internal notification prs – production release sheet bom – bill of materials PO – purchase order qcb – quality control bulletins

4.4 Analysis of Schematic Models Presentation 89

90

4.4.3.5

4 Analysis of Schematic Models

Complex Procedure Flow Diagram

The complex procedure flow diagram scheme aims to enable the concentrated schematic representation of a complex and long production process. Complex procedure defined here is characterized by being constituted of several sequences of activities executed in parallel, with strong relationship between them. A long process is defined as a process consisting of a large number of productive activities. The productive processes that best meet such characterization, and therefore indicated to be represented with this model are chemical-industrial processes, metallurgical processes, automated and/or robotic manufacturing, and bureaucratic procedures. In the study of methods, greater interest falls on the bureaucratic procedure, since in the chemical, metallurgical, or automated/robotized process, in general the human element enters only in the supervision and control activities or command activation, and the main productive activities are performed by equipment. Moreover, work methods in this case are more strongly determined by the chemical-industrial, metallurgical, and automation technologies employed than by alternative modes of human work organization. In bureaucratic procedures, however, Methods Engineering is used from the formulation of the process logic to the specification of the components of the workstations. Even if bureaucratic processing activities are digitized, automated, or robotic, the methods designer is still responsible for formulating the process logic. In this way, the model can be specialized, within the scope of Methods Engineering, for the study of complex bureaucratic procedures, be it a long process of records, transport (or digital submissions) and archiving over forms, files, and multi-copies. For this scheme, the basic constructive conception of the process flow diagram is valid, differing only in being drawn with the flow lines running horizontally and in the use of additional graphical conventions. The horizontal arrangement of the flow lines is due to the fact that, in general, for the design of the flow diagram of complex and long processes, it is usually necessary to use continuous sheets or records, with horizontal unfolding. In the printed version of the template, the vertical or horizontal arrangement of the stream depends on the type of computer printer available to plot the layout. The construction of the model begins with a survey of the single flow diagrams of each item (in this case, each form and each copy of the multi-copies), then joining them by the junctions and relationships of their flows. The groups of symbols that are most suitable for this format are the numbers 6, 7, 8, and 9 (8 is better), indicated in Fig. 4.14. Additional conventions are as follows: (a) Relationship (^ v > ) or (----) indicates that there is a relationship between different forms or copies, where the action on one form influences or implies

4.4 Analysis of Schematic Models Presentation

91

an action on the other (e.g., removing information from one form to register in another form). (b) When forms or copies in operations, transports (or digital submissions). or filings are joining, the correspondent symbols are linked by a vertical line (perpendicular to flow lines and representing a simultaneity relationship). (c) Alternative actions (IF) as indicated below (Fig. 4.38):

IF

YES NO

Fig. 4.38 Indication of alternative actions

Regarding the criteria and manipulations of this model, the basics of the process flow diagram and of the study of form systems are valid as defined in item 4.4.2. As for its use, as already seen, the complex procedure flow diagram is especially suited to the study and recording of complex bureaucratic processes that use a system of forms and multiple copies. In this sense, this model serves to guide the study of replacing physical processing of forms or information with digital processing, reducing or eliminating the circulation of paper. For chemical, metallurgical, and automated/robotized processes (or processes with similar characteristics), this model can be used to represent the process for illustrative purposes and to identify human work points, whether of supervision, control, triggering of equipment commands or maintenance. In order to study the participation of human labor in these processes, methods that better deal with the person-machine relationship are used, which are presented later in this text. Example In the example below (Fig. 4.39), the processing of a delivery request to the warehouse of a commercial company is represented through the complex procedure diagram.

Separate No 4 copy

Checked and approved by foreman

No 2 Lemon

Out mail

Filed by serial number

TO

Stores

TO

Delay

TO Ordering department with material

Place Order on clerk material

TO

Record Office

Material control card Check stock Insert number, unit Remove In code No 3 unit mail designation copy Delay

Clear from file

Destroy

Filed

Out mail

Place in binder

Remove copy No 2

Post

Accounting department

File

TO

TO

Stores

Pull

Relation

Delay/Arquive

Inspection

Move

Handling

Destroy

Permanent file

Adding to the record

Origin

Out mail

TO

Post

Fig. 4.39 Example of a complex procedure diagram. Symbology Fig. 4.14, Number 8, Close (1960). Source Close (1960 p. 144, cart 6.11); copyright @ 1960 by John Wiley & Sons, Inc.

No 4 Pink

No 3 Blue

No 210A Written by dept. clerk

No 1 White

Cost ledger

92 4 Analysis of Schematic Models

4.4 Analysis of Schematic Models Presentation

4.4.3.6

93

Chronological Flow Diagram

The chronological flow diagram aims to provide a schematic view of temporal and chronological relationships between productive activities over a flow of items in processing. In this process flow diagram format, the graphic scheme indicates the evolution of the flow of items in processing through the sequenced activities of a production process, against the instants and time periods elapsed in the execution of these activities. In the chronological flow diagram, the flow lines and the activity symbols are drawn at a matrix of sectors (work centers) versus time or events versus time and in some cases sectors and events versus time (Fig. 4.40). Note that the information events are the description of the productive activities. In this format, as in the complex procedure flow diagram, flow lines run horizontally. The basis of the constructive conception of this model is that the horizontal spacings between the symbols-activities are proportional to the temporal relationships between the beginnings of execution of the symbolized activities. The time scale is graduated (in second, minute, hour, day, …) according to the length of the process represented. For its construction, the single flow diagrams of each item in processing are initially prepared, later joining them in the chronological matrix according to the temporal relationships between the beginning of execution of activities (horizontal spacing between symbols) and the simultaneity relationships between activities (alignment vertical of symbols). As for the type of records, three versions of the chronological flowchart are distinguished: (1) following a single item from work center to work center (a single person, equipment, form or copy, or material)—in this case, it consists only of the single item flow diagram, mounted against the matrix sectors (and/or events) versus time; (2) registration of a system of forms with multi-copies, or of processing composite products are respectively the complex procedure flow diagram and manufacturing and assembly flow diagram, drawn at the matrix sectors (and/or events) versus time;

Fig. 4.40 Chronological flow diagram basic formats

sectors

sectors or events

flow

flow

events

time

time

Fig. 4.41 Example of chronological flow diagram for single form. Source By the Author, following the model proposed by Maynard (1963, pp. 2–36, 2–37, Fig. 3.10)

94 4 Analysis of Schematic Models

Fig. 4.42 Example of chronological flow diagram for multiple forms. Source by the Author, following the model proposed by Maynard (1963 pp. 2–32, 2–33, Figs. 3–7)

4.4 Analysis of Schematic Models Presentation 95

96

4 Analysis of Schematic Models

(3) record of teamwork—consists of the single flow diagram for each team member, arranged in parallel horizontally, mounted against the matrix operators versus time, respecting the chronological order, the beginnings of execution and the simultaneity relationships between their activities. This representation is similar to the simultaneous activities diagram (item 4.4.6). In this format, in addition to the criteria and basic manipulations of the process flow diagram, an improvement study could be carried out in order to reduce the time spent on activities and sequences, and on the entire process. Within the scope of Methods Engineering, the chronological flow diagram is used in the study of times and movements and in the study of process programming. Example Example 1 Shows a chronological flow diagram of sectors versus time for a form to follow the processing of Bill of Lading (B/L) for an overseas transportation of industrial goods (Fig. 4.41). Example 2 Shows a chronological flow diagram sector versus time for a multicopy form system to follow a recruitment process for a new engineer at a high-tech corporation (Fig. 4.42).

4.4.3.7

Business Process Diagrams (BPD)

Conceptualization With the advent of digital facilities and resources for process management, new concepts and instruments have emerged to be applied in a broad and compatible way at the various levels of the company, whether in administration, finance, quality management, software development, services, production, manufacturing, and automation. In this context, business process diagrams allow the graphical representation and modeling of the different operational processes of a company, both existing and proposed, to enhance their analysis, elaboration, efficiency measurement, and presentation. As an updated version of a process flow diagram, the schematic basis of business process diagrams can, in principle, adopt a variety of graphical notations like those presented in this chapter at Fig. 4.14. In the meantime, the Business Process Modeling Notation (BPMN) is presented as a solution to unity and standardize the graphical construction of process models, proposed and maintained by the international entity that regulates technological standards, the Object Management Group—OMG (OMG 2014).

4.4 Analysis of Schematic Models Presentation

97

The BPMN standard has consolidated the various notations employed in business process diagrams such as UML, IDEF, EPC, BPMS, ADF, ebXML BPSS11 (see Briol 2008). The UML standard is most commonly used in the software industry and IDEF in engineering design. The notation used in the BPDs allows the graphic representation of activities, tasks, roles, and responsibilities of the participants and the workflow or operational flow of a business process. The notation attempts to define the basic elements of the process, such as: • • • •

inputs and outputs; used resources; order of execution of the activities or the workflow; events that determine and lead the process.

in addition to helping standardize the process modeling to facilitate its understanding and reproduction by different participants and users of the business process being studied or presented. Assessment Criteria In evaluating the performance of a business process under study and for designing future processes, the criteria to be followed shall observe, according to Bianchini (2016) “to look for improvement opportunities that would allow to increase operational efficiency, productivity, and customer satisfaction; reduce service costs and deadlines and rationalize the use of resources; to eliminate or reduce rework, redundancies, and waste; encourage creativity, motivation, and integration among employees” (Valle and Oliveira 2016, p. 192). Construction According to Bitencourt (2009), “the participants of the business processes may be people or groups of people, information systems or another process. These participants are represented within the BPMN diagram by a metaphor of pools and lanes where exchanges of services, products, values, transactions, information and knowledge between customers, suppliers and organization partners are identified”. Business process diagrams (BPD) using the BPMN notation are built according to four basic categories of elements, as shown below. (1) Flow objects •

Events are key elements of the process and directly affect the process flow, defined as beginning, intermediate, or end. The start event is represented by a circle with a single border, the intermediate one with a double border and the end event with a strong border. To facilitate its graphic characterization,

Abbreviations: UML = Unified Modeling Language; IDEF = Integrated Definition); EPC = Event-driven Process Chain; BPMS = Business Process Management System; ADF = ActivityDecision Flow Diagram; ebXML BPSS = Electronic Business extensible Markup Language Business Process Specification Scheme.

11

98

4 Analysis of Schematic Models

inside the circle different symbols can be added, such as message, time, exception, compensation, connector, rule, end, etc. (see Valle and Oliveira 2016, p. 86). • Activities are the distinct works (step by step) performed in a business process, which can be indicated as tasks (or actions) or sub-processes (collapsed or expanded). The graphic representation is a rectangle with sweetened edges. Symbols or markers are added for sub-processes, to highlight associations, loop, offset, links, etc. (see Valle and Oliveira 2016, p. 81). • Decisions (connectors or gateways) used to control the divergence or convergence of the flow sequence, and to determine decisions and milestones for bifurcation, merging, and union of trajectories. They are represented by diamonds and inside them signs can be placed indicating, for example, if the decision is based on data or events. (2) Connection objects The flow objects are interconnected by lines, creating the basic structure of the process diagram skeleton. Three connection objects are identified: •

Sequence flow used to show the order (or sequence) in which the activities are executed in a process, represented by an arrow with a direction head. • Message (or information) flow used to indicate the exchange of messages or information between participants who send and receive them. The message flow representation is a dashed arrow with a direction head and an origin head. • Association is used to associate data, text, and other artifacts with the flow objects, showing the inputs and outputs of these elements in carrying out the activities. It is represented by a dotted line. (3) Groupins •

Pool identifies a participant in a business process. It is represented by a rectangle (graphic container) for the positioning of the corresponding elements of the process diagram. • Rays or swimming lanes are sub partitions of a pool used to organize and categorize the activities assigned to each component of the pool.

(4) Artifacts Artifacts are used to provide additional or explanatory information about process elements. Three standard artifacts are highlighted, such as: •

Data objects are used to indicate what data or information is required or produced by activities. They are connected to related activities through associations. • Groups indicate whether documentation or analysis grouping has occurred. They are represented by a rectangle with dashed borders.

4.4 Analysis of Schematic Models Presentation

•

99

Annotations allow the introduction of additional texts to clarify certain diagram elements. They are represented by a rectangle for text with a linking line with the corresponding element.

A set of symbols from the BPMN scheme is shown in Fig. 4.14, number 10. Depending on the category and complexity of modeled processes, there is a large number of complementary symbols, as shown in the BPMN Quick Guide (www. bpmn.org). Uses The business process diagram applying the BPMN notation can be used in the modeling of a wide range of processes, such as administrative, financial, operational, quality assurance, software, or service development. The model associated with digital tools or suites can be used in the design, analysis, simulation, monitoring, and optimization of these processes. Manipulation The BPD modeling exercise starts with the definition of the business process to be represented. In this context, a process is an articulated set of a series of steps and controls carried out by an organization or through several organizations and which constitutes a flow of information, materials and services. This concept can range from macro processes of a company to work processes carried out by only one person. A BPD model can represent three basic process types, namely: • Private or internal business processes, which are performed within a single organization. The process flow is contained within a pool and must not go outside the boundaries of this Pool. • Public business processes, which show the interactions between the process flow of one entity (i.e., a private process) with the process flow(s) of other external entity(ies). The graphic design exclusively represents the activities that carry out some type of communication between the entities involved, in addition to the connections between activities that define the execution of the process. • Collaboration business process, which represents interactions between process flows from two or more entities. In this modeling, are exclusively portrayed the activities of the distinct processes where messages or information between the activities involved are exchanged. The construction, modeling, manipulation, and automation of process diagrams rely on the availability of digital programs, from the simplest dedicated only to graphic design to the most complex, following cycles or business process management (BPM) systems, such as for example MS Visio; iGrafix; Aris; IBM Websphere; Bizagi Modeler, Studio and Automation (see Valle and Oliveira 2016). Example The BPD template below represents the processing of a package to be sent by courier, visualizing customer, and postmaster activities at the delivery counter. The graphic model was built using the Bizagi Modeler software (https://www.bizagi.com) (Fig. 4.43).

Fig. 4.43 Example of business process diagram

100 4 Analysis of Schematic Models

4.4 Analysis of Schematic Models Presentation

101

4.4.4 Map Flow Diagram Conceptualization The map flow diagram represents the physical movement of an item through the processing centers located in the physical arrangement of a production facility, following a fixed sequence or routine. The physical path or route of the item, which can be a product, material, form, or person, is drawn, by means of graphic lines with an indication of the direction of movement, on the scale floor plan of the installation involved. The map flow diagram allows the methods designer to study together the physical movement conditions that follow a given production process, the available or necessary spaces, and the relative locations of the work centers. The model thus provides a compact and global view of the existing or proposed process in terms of its physical occupation in the production facility. When there is interest in analyzing and highlighting the types of activities carried out in the work centers through which the items in processing pass, graphic symbols are drawn on the flow lines, next to each work center, that define the activities performed there. The most common symbols are those of ASME (see Fig. 4.14, number 1), for operation, storage, delay, inspection, and transport activities. In this case, the diagram is called map flow diagram for activities. When the interest is focused only on the evolution of the processing sequence in the physical installation, being not important to differentiate the activities carried out in the work centers, only flow lines are drawn with arrows indicating the direction of movement, representing the route followed by the item from a work center to another one in accordance with the routine sequence. With this configuration, the diagram is called a map flow diagram of route. The scheme can be designed in two or three dimensions. The two-dimensional diagram consists of the floor plan top view presenting the physical trajectory traveled on a single pavement or floor of the productive building. The three-dimensional diagram serves to represent the trajectory through different floors; in this case, the floors are drawn in perspective and superimposed according to the relative arrangement in the building. The graphical lines are drawn in perspective and the trajectory traveled in the vertical plane is also represented. The model is a useful supplement to the process flow diagram, and it is essential when physical movement is an important factor in the process, involving large distances or spaces traveled. In conjunction with the flow diagram, it shows the sequence, physical positioning of activities, and direction of movement, of the stages of the productive task. It helps to better explain the activities and their sequence recorded in the process flow diagram and to highlight more clearly the importance and difficulties inherent in carrying out each activity or moving the item, in relation to the physical layout and dimensions of the facility and equipment.

102

4 Analysis of Schematic Models

In the study of methods improvement, the model is more adequately applied to the plant coverage level. For other coverage levels, such as workstation and bench, the model lends itself more to understanding or presenting the work situation. The most appropriate work situations for the use of the map flow diagram model are those in which the process follows a pattern of execution and regular or routine movement and only a single item in processing is studied. To represent the evolution of more than one item, it is necessary to use graphical differentiations, choose the most important or representative ones to be observed, or build a diagram for each item. Uses The current use of the map flow diagram is in the study of improvement of the physical arrangement of productive facilities or “layout”. This can be done both in the design phase, showing the physical dispositions proposed in the alternative solutions, and in revisions of the distributions of the existing equipment in the facilities. Another application is in the study of transportation systems in productive facilities. The model is also used as a registration document for the proposed method, for its presentation or implementation. In developing the general work method of the production facility, the model allows the visualization of the relative locations of equipment and facilities, the transportation system, temporary and permanent storage areas, inspection, and workstations. Construction The preliminary step in the construction of the map flow diagram is the definition and drawing in plan of the detailed physical arrangement of the work centers involved in the processing under study. Note that the detailing must be compatible with the adopted level of coverage. The survey of the constructive data of the diagram can be done by direct observation (for the current work situation), from the manufacturing sheets or description of routines, by semi-structured interviews or from the process flow diagram. These data are sequence of processing, identification of process activities, and determination of work center locations where these activities are performed. The process flow that passes through the work centers that perform the processing is drawn on the physical arrangement plant. The flow line is usually continuous, following the process from start to finish. In the map flow diagram of activities, a graphic convention is adopted that identifies the activities performed during processing, which are drawn on the flow line, next to the corresponding work center. In the map flow diagram of route, the flow line contains only the indication, by means of arrows, of the direction of movement. In order to facilitate and improve the assumptions about the work situation to be made from the flow diagram, the plan must be drawn to scale and preferably on a

4.4 Analysis of Schematic Models Presentation

103

reticulated background, which allows for a better view of areas and distances. At the facility or even departmental level, 1:50 and 1:100 scales are suitable for the drawn or printed version. In the digital version, depending on the software used, such as the different AutoCAD versions (computer-aided design software), one can have a very detailed view of the plant and components, with the advantage of manipulation and search for optimized and varied solutions. In the plan, the location of the workstations involved, the storage and waiting areas, machines, equipment, benches, tables, corridors, doors, passages, and service areas shall be represented. In addition to these operational elements, care must be taken to represent the fixed or irremovable devices and conditions in the plant, which constitute a restriction to changes in the physical arrangement or in the flow; such elements may be columns and structural components, heavy equipment with its own foundation, external roads, walls, etc. It is advisable to use a graphical means of highlighting fixed elements. The graphical tracing of the flow lines can meet a different color code or shape. This distinction applies in cases of: (a) representing the flows of various items in the same drawing; (b) showing the flow of alternative methods (e.g., current and proposed) in the same drawing; (c) distinguishing the participation of different work centers; (d) highlighting a particular sequence or activity to consider. In the study of the transport system, graphic conventions are adopted in the tracing of the processing flow line. Conventions in layout design can also be used to indicate limitations on movement and performance of transport equipment in relation to areas of the facility. In this study, it is convenient to add information on the characteristics of the equipment to the flow line, such as number of transported items, type of packaging, transport speed, risks involved, etc. Criteria (1) Physical Arrangement By means of the map flow diagram, the study to upgrade the work method focused on improving the physical arrangement of the productive units has as its basic criterion the increase in the efficiency of the processing flows. In other words, the physical arrangement is better when it entails more efficient processing flows. It should be noted that the analysis of the physical arrangement by the map flow diagram is carried out from the flow point of view alone. This means carrying out the analysis under only two of the criteria for analyzing the physical arrangement: the principle of obedience to the flow of activities and the principle of minimum distance. For a more complete study of the represented arrangement, one should check the alternative solutions with the other principles, such as integration, use of space, satisfaction and security, and flexibility (see Kehl and Iida 1970, pp. 7 and 8). Otherwise, one could design, for example, an optimized arrangement in terms of the most efficient flow, which could be extremely unsafe or uncomfortable, such as when

104

4 Analysis of Schematic Models

placing adjacent chemical treatment sections with high environmental pollution and assembly sections with large numbers of people. Another aspect possibly not considered by the analysis of the physical arrangement with the map flow diagram is the economic factor. So, for example, for heavy equipment or with critical installation conditions, the change of location can cost much more than the possible gain in flow improvement. The criteria for comparing solutions can be shorter total distance traveled, fewer activities of each type, more direct and trouble-free flow. (2) Transport System The basic criterion of the transport system specification study for the production process made with the map flow diagram is to increase the efficiency of the flow of the items being processed. Thus, the transport system is better when it makes it possible the transportation activities to flow more efficiently. Also, in this case, the analysis of alternative solutions will be based on the transport flow alone. In order to avoid the sub-optimization induced by the model, one must always keep in mind, when looking for the most adequate transport system, the other aspects to be considered, such as safety, limitations due to the floor and the structure of the building, limitations to the speed of transportation due to item characteristics. The criteria for comparing alternative solutions for transport systems are total transport speed and number of transported items (total and of each batch). Manipulation (1) Physical Arrangement The manipulation of the map flow diagram to improve the physical arrangement consists of analyzing the registered solution, seeking to identify certain problems or typical defects in the arrangement. Next, the causes of the identified problems are determined, and an attempt is made to eliminate them by modifying the physical layout. The design of the map flow diagram of the new solution, and subsequent analysis and eventual modification, causes a reiterative process of improvement that shall tend toward an optimized solution. The process described above allows improving and perhaps optimizing a basic solution, used as a starting solution. When, however, it is desired to generate original solutions, it should not be used because it restricts the designer’s creativity by fixing a given solution. In this case, independent solutions for the arrangement should be sought from the basic design problem. After designing the various viable alternative arrangements, the map flow diagram is drawn for each arrangement, following a representative item. Finally, the analysis of each map flow diagram is performed, and the arrangements are compared according to the flow efficiency criteria.

4.4 Analysis of Schematic Models Presentation

105

Typical problems and mismanagement related to the flow of items in the physical arrangement of a production system are: (a) Unnecessary or dispensable activities The classes or types of production activities can be identified in two categories: • value activities—they are those that increase the value of the product, such as operations and inspection; • non-valuing activities—they do not increase the value of the product, such as transport, storage, and delay. The last two also generate additional costs, as they represent idle capital. The analysis and contestation of each activity that is part of the production process represented in the map flow diagram will focus on the second category, seeking to reduce or eliminate them. (b) Possibility of grouping and combining activities This analysis focuses on operation and inspection activities. Here, it means to grouping and placing related activities adjacent. Another concern is to combine activities in order to be carried out in the same workstation or bench, or by the same operator. Note: These two analyses above are possible only when using the map flow diagram of activities. (c) Long move between activities An attempt should be made to reduce movement distances, especially those that are noted as excessively long in the map flow diagram. Long moves increase processing time, which can mask possible improvements achieved in the workplace. Distances walked by production personnel should be minimized. Whenever possible, efforts are made to combine the moves with other activities. Thus, it is possible to operate in motion (e.g., continuous painting, where the conveyor belt passes inside the oven), inspect on the move (quality control follows the transport of the product) or even store and delay while moving (e.g., the paint drying during transport to another section). When long moves are unavoidable, it is necessary to study the best transportation system to be utilized. (d) Changes in the direction of flow, returns and flow crossings The most direct flow should be planned for greater productivity. Changes in direction, returns, and flow crossings disturb the movement of items, introducing inefficiency, risks, and disruption to processing. (e) Mismatch of flow direction in relation to its magnitude or frequency Production frequency and volume (number of items) should govern the flow pattern whenever possible. Thus, the following extreme situations shall be avoided:

106

4 Analysis of Schematic Models

• large volume of items, or high production work areas with processing flow following long routes through secondary circulation corridors; • small volume of items, or low production work areas with a straight-line processing flow through the main circulation corridor. (f) Points of traffic congestion This analysis is carried out by superimposing the map flow diagrams of the various items being processed in the same physical arrangement. It serves as data for dimensioning the circulation routes. (g) Location of the stock areas in relation to the work areas and the receiving and shipping areas. The model allows to visualize the distribution flows between loading docks-receiving-stock, stock-work areas-stock and stock-shipping-loading docks. Regarding these flows, the physical arrangement must meet the following conditions as far as possible: • The material arriving at the factory must be stored directly at the place of use. However, bulky materials can disturb the work area or movement; another restriction to this optimal condition is dictated by the need for safety or strict control of the material. • Processes or work centers that involve heavy or difficult-to-move parts should be located as close as possible to receiving and shipping areas. (2) Transport system The manipulation of the model in the case of transport system specification consists of analyzing the material or people movement flows in order to design the most appropriate transport routes and equipment. In this analysis, the designer’s interest is focused on the transportation activities. The analysis is carried out seeking to identify the most important characteristics of the movement flows, which may influence the choice of each type of road or transport equipment. The purpose of this study is to determine the methods of movement and transport, the number of items moved at a time, the types of roads and equipment used, and the transport speeds. For more responsible projects, the best solutions for the transport system can be tested by setting up a physical arrangement in three dimensions on a reduced scale to simulate the different alternatives. Using AutoCAD software allows for the search for optimized solutions.

4.4 Analysis of Schematic Models Presentation

4.4.4.1

107

Bidimensional Map Flow Diagrams

Bidimensional Map Flow Diagram of Route The map flow diagram of route has the purpose of analyzing the directional path of items in processing, without worrying about the activities carried out at the workstations they pass through. It is strictly used to visualize crossflows, long paths and inefficient trajectories, or the degree of physical occupation of the facility with the observed items. The designing of the scheme is carried out by following the item(s) under study through the layout of the production section, showing its passage from one workstation to another to fulfill the processing routine with a continuous line with indication of the direction of motion. The data collection can be direct, observing the evolution of the item on the spot, or indirect, based on the formal specification of the procedure, which can be presented by a process flow diagram, manufacturing sheets, bureaucratic routines, or description with interviews. Example The example below shows the physical processing of a personnel document in a public office. The process starts with the delivery by the user of a standardized form with the requested information and ends with the delivery of the document to the user. The process consists of attaching documents, filling in forms, archiving, official signatures, and records (Fig. 4.44).

Bidimensional Map Flow Diagram of Activities The map flow diagram of activities is intended to graphically present the sequence of activities carried out in the various workstations, distributed in the physical facilities of a productive sector, for the processing of one or more items that follow a fixed routine. The model is concerned with studying operations, transport, delay, inspection, and storage activities, and basically uses ASME graphic symbols (see Fig. 4.14, number 1). The design of the scheme is based on the process flow diagram and the location of the stations where the activities in the plant layout are carried out. In this case, the joint presentation of the model with the process flow diagram is very valuable for the global visualization of the process and installations.

108

4 Analysis of Schematic Models

Convention: solid line with arrows indicating direction. Fig. 4.44 Example of a bidimensional map flow diagram of route

Example Below shows the manufacturing process of seamed galvanized steel pipes. It is a continuous process, with each item going through the same sequence of operations, changing only the pipe gauge. Transports are made by overhead crane and transfer mechanisms. The process can be divided into two phases: the mechanical transformation phase (cutting, forming, welding, and threading) and the chemical treatment phase (deoxidation, degreasing, and zinc plating) (Fig. 4.45).

4.4 Analysis of Schematic Models Presentation

109

Convention: activities indicated with ASME symbols with numbering:

operations

inspection

storage

delay

transport

Flow: continuous line

Fig. 4.45 Example of a map flow diagram of activities

4.4.4.2

Three-Dimensional Map Flow Diagram

The three-dimensional map flow diagram is used to present the sequence of steps or activities of processing one or more items in a facility physically distributed over several floors. Items may be manufacturing objects or printed forms or even persons in routine circulation.

110

4 Analysis of Schematic Models

For the multi-story case, this diagram gives a better overview of the process in the building than the two-dimensional schematic models, showing in addition the vertical transport flow.

PROCESS FLOW DIAGRAM

CUTTING

OFF ICES

NUMBERING

COUNTING

R RO

OMS

PACKING

LOC KE

FINAL STORAGE

DISCHARGE FRONT DESK TO DEPOSIT MAIN DEPOSIT OF MATERIAL TO THE FIRST FLOOR PRINT FOR INTAGLIO PRINT INTAGLIO PRINT TO INSPECTION

INSPECTION AND COUNTING

INSPECTION

INTAGLIO PRINT

O FF

ICES

INTERMEDIATE STORAGE

LOCKE

R RO O MS

PRINTING

TO SECOND FLOOR PREPARATION NUMBERING TO THE CUT CUTTING TO THE COUNTING COUNTING TO PACKAGING PACKING TO STORAGE

FRONT DESK MAIN DEPOSIT OF MATERIAL MAIN OFFICE

FINAL STORAGE TO THE GROUND FLOOR EXPEDITION LOADING

EXPEDITION LOADING FLOW OF PERSONNEL FLOW OF MATERIAL

Fig. 4.46 Example of three-dimensional map flow diagrams of activities and route

4.4 Analysis of Schematic Models Presentation

111

Also, in this case, the joint presentation with the process flow diagram is quite useful. Example The example shows the flow of activities for printing bank notes on a three-story graphic (map flow diagram of activities) and the movement of people to reach the installation’s work sections (map flow diagram of route) (Fig. 4.46).

4.4.5 Chronologic Assembly Diagram Conceptualization The chronological assembly diagram schematically records the duration times of the coordinated sequences of production and assembly activities of a set of materials, parts and sub-assemblies, components of a complex product. The visual scheme shows the junction points of the components and the start and finish times of processing each component and the final product. In the standard diagram, only the times of production activities directly linked to the product, such as manufacturing and assembly operations, machine preparation, inspection, and transport, are indicated. In this model, activities dependent on factors external to production or factors of uncertainty, such as delays, storage, breakdown, and maintenance of machines, person-work or person-machine interactions, etc., are not considered. The times recorded are generally: setup time + manufacturing time + transport time + assembly time + inspection time. In cases of greater detail, project times, drawing, technical specifications, packaging, and others can be computed. This standard design aims to arrange and coordinate the sequences of production activities for each component so that the total processing time is as short as possible depending on the capabilities of the available productive resources. Such resources are human workload, machine load, working hours, speed of transportation equipment, etc. Thus, the concept of the standard diagram suggests that, for a given set of available production resources, it is possible to establish a coordinated scheme for the processing activities (manufacturing and assembly) of a complex product with minimized duration. The ideal scheme (which does not take into account activities dependent on factors external to production or uncertainty) serves as a basis for evaluating the “performance” of the actual scheme of an existing process or proposed alternatives. The actual scheme incorporates the times of all activities that took place. The complex product, object of study of the chronological assembly diagram, can be a material good or a service, formed by a set of components that are joined to constitute a unit, for example, electronic device, automobile, airplane, book, and engineering project.

112

4 Analysis of Schematic Models

In graphic terms, chronological assembly diagram presents the same information as the manufacturing and assembly flow diagram, plus an explicit indication of the duration of activities. Construction The schematic model is built on a graph with two coordinate axes. The horizontal axis is the time scale, and the vertical axis is the listing of components (materials, parts, and sub-assemblies). The manufacturing and assembly activities are represented by horizontal lines proportional to the duration. A horizontal line is drawn for each component at the height of its name in the vertical listing and graduated into segments according to the duration of activities, in the component processing sequence. One can add other vertical columns with information on quantity per product, total quantity, supplier, etc. On the segments of the horizontal lines, the work centers corresponding to the activities represented can be indicated. The left endpoints of each horizontal line indicate the exact start-up times of the components’ production. The junction points are connected by vertical lines and indicate the corresponding assembly start times. The drawing of the horizontal lines of the scheme is done from right to left, that is, reconstituting the process in the opposite direction of the time scale. Thus, it starts with tracing the process line of the final product, then the lines of sub-assemblies and other components. The data on the parts and materials and the sequences of activities can be collected through a specific table or through the manufacturing and assembly flow diagram of the product under study. Processing times are calculated based on the capacities of productive resources and the amount of production demanded. This data can be arranged in a load (or Gantt) chart. The constructive design of the diagram allows the use of electronic processing. This technique is valid, and sometimes, it is the only viable one for the study of products made up of a large number of components. In this case, a network algorithm or PERT/CPM can be used. Further, software like MS Project can facilitate the calculations and even simulation of alternative solutions. Uses In the scope of Methods Engineering, the chronological assembly diagram is used in the study of the variable time in the processing of complex products and in the determination of the points and moments of junction of the components. The diagram is suitable for the following typical cases: (1) Determination of critical components in terms of processing time This technique consists of determining the “critical path” of the scheme, that is, the series of component processing that ties the critical timing of the process and fixes the total time frame. The methods of the manufacturing and assembly processes

4.4 Analysis of Schematic Models Presentation

113

of critical components receive special treatment in the study of improvements. The diagram serves to highlight only the critical components and processes, and the study of the methods must be done through other specific models, such as the map flow diagram or route frequency diagram for transport methods, the manual activity diagram for the manual assembly operations, and others as required. (2) Evaluation of processing alternatives in terms of duration When the execution time is important in the establishment of the work method, the “performance” of the existing or projected alternatives can be compared with the optimal standard scheme, defined for a given set of available productive resources. In this case, the study aims to choose the shortest duration alternative. (3) Programming of the Method In the final stage of specifying the method to be implemented, the diagram is used to highlight critical times and establish delivery dates. It has a special use in the study of methods in “job shop”, where it is necessary to quickly establish the deadlines for calculating the cost of orders. The diagram can also be used in establishing the schedule for implementing the method. By the way, the diagram was created and developed as an instrument for Programming and Production Control (PPC). Evaluation Criteria The chronological assembly diagram allows evaluating the work method applied for manufacturing and assembling a complex product as a function of the total processing time. According to the diagram evaluation criterion, the best method among alternatives is the one that requires the least processing time. The duration times of processes or activities decrease when the capacities of the production resources employed increase, that is, the number of machines, the number of personnel, the transport speed, etc., increase. Further study of these changes depends on additional information and modeling. Manipulation The study of the work method firstly focuses on the identification, elimination or reduction of the times of external factors or uncertainty, considered undesirable in this approach, in order to define an ideal scheme for the work method under study. The elaboration of the coordinated processing scheme must be consistent with the capacities of the available production resources. Thus, it is necessary to verify if the load of each work center supports the execution of the activities assigned to it in the work method, within the predicted time. It should be noted that the optimal

114

4 Analysis of Schematic Models

method could indicate the execution of two or more activities simultaneously by the same work center. Example The example illustrates a chronological assembly diagram for a washbasin mixer (Fig. 4.47).

Parts Main body Cartridge mixer Screw Fixing nuts Rubber ring/joint Metal support Handle Aerator Flexible pipes

Units 1 1 1 1

Work time foundry chrome plating threading setting purchase setting purchase setting purchase

2

1 2

subassembly setting purchase setting purchase

2

1

subassembly

foundry

threading milling

final assembly packaging

chrome plating threading setting purchase

Fig. 4.47 Example of chronological assembly diagram. Source By the Author, following the model proposed by Starr (1971, p. 449)

4.4 Analysis of Schematic Models Presentation

115

4.4.6 Simultaneous Activities Diagram Conceptualization The simultaneous activities diagram represents the coordinated work of a set of productive units, through a graphic scheme that registers the sequence of activities of each unit and the simultaneity relationship between activities or events of interacting units. The model is more suitable for the study of work methods that meet the characteristics of coordinated, cyclical or repetitive work, and composed of intermittent activities. Coordinated work characterizes the type of job done by a group of units that perform interdependent and coordinated tasks among themselves, to achieve a common goal; and where a general work method can be identified. It should be noted that in carrying out a complete group cycle, the units can fulfill one or more individual cycles. The representation of activities and the level of detail in the diagram is a function of the duration of the full cycle. Eventually, non-repetitive or non-cyclical work methods can be represented by the model, which, however, require precise coordination between service units when they are carried out. In general, the sequence of activities of each unit is characterized as intermittent. Thus, a unit executes a productive activity, stops and waits for the interference of another unit or the completion of another sequence of activities. Production units can be persons, machines, equipment, or processes. The registration of the activity sequences of each unit can be done by an occurrence listing or with a graphic form proportional to a time scale. The list identifies the simultaneous activities with graphic symbols arranged on the same horizontal line and the passage from one horizontal line to another indicates that there was a change in the activity of some productive unit. The graphic design proportional to a time scale also provides visual information on the duration of each activity and more accurately indicates the simultaneity relationships. This scheme makes it easier to highlight the relative importance of each activity as a function of time and the percentage relationship between working time and idle time for each unit; in addition to providing a better picture of the relationship between the activities of the units at a given moment. This design is mandatory when one of the production units controls the cycle time or when there is a cycle time control device. In this case, the work is coordinated as a function of that element. The duration times of the activities indicated in the diagram are real or estimated, depending on the work measurement technique appropriate for the case under study. A basic assumption of this model is that the activity duration time and the cycle time remain constant from cycle to cycle. This is not the case in practice, neither for machine or equipment times nor for human service time. Variations in machines are due to speed changes, occasional breaks, variation in physical characteristics of raw material; for the human operator, service time fluctuates with fatigue, own rhythm, motivation, and training. In order to avoid erroneous conclusions, this model should only be used in the study of work methods in which variations in time from cycle to cycle can be considered negligible.

116

4 Analysis of Schematic Models

The relationship of simultaneity that exists at certain moments, between activities or events of some of the units of the group, occurs due to the coordination among these units, necessary for the accomplishment of the common work. This coordination then generates interrelationships or interdependencies at the individual work methods of each unit. The concurrent activities or events can be supportive or parallel. Support activities, carried out by a unit, are those that enable or assist the work of another unit. There is direct interference of support activities in the work of interdependent units. In parallel activities, there is no interference, but the simultaneous execution is dictated by savings or for the viability of a following support activity. From the conception of support and parallel activities, it is possible to establish a simple classification for the component activities of a coordinated work of several productive units, which identifies them as: independent, combined and waiting. This classification is sufficient and adequate for most cases framed by the simultaneous activities diagram. However, for studies that demand a greater degree of detail, the ASME, Nadler symbols or even “therbligs” classifications can be used (see Fig. 4.14). The identification of classes of activities in independent, combined, and waiting meets the following characterizations: (1) Independent activity The activity is carried out by only one of the productive units, without interference from another unit and without interfering with the activities of the others, for example, a machine operator inspecting the final product. (2) Combined activity It occurs when the execution of the activity by one of the productive units requires the interference or the concurrence of other unit(s), or when the unit performs an activity that interferes with the work of the others. In this case, the activities of two or more units are combined to carry out a common service, for example, a machine being manually driven by the operator. (3) Waiting When there is an inactivity of any production unit; it usually occurs when the unit waits for interference from another unit to start its work again, for example, the operator performs a maintenance service, which prevents the machine from running. This classification allows, in the analysis of coordinated work, to differentiate when the units work independently and when the work of one unit depends on another. The coordination between the work methods of each unit depends only on the combined activities. Independent activities can be rearranged within the individual method without influencing the other methods of the units in the group. This concept, which guides the manipulation of the diagram, greatly facilitates the study of complex coordinate tasks. As in any process made up of separable stages, the sequence of individual activities and the interdependence and simultaneity relationships between the activities of the group of productive units meet a basic precedence relationship. This basic provision, which guides the coordination and sequencing of the activities of the group, must

4.4 Analysis of Schematic Models Presentation

117

undergo a critical evaluation in the study phase to eliminate dubious, unreal, and unnecessary precedence. The schematic model of the simultaneous activities diagram admits four different conceptions: person-machine diagram, team diagram, production line diagram, and SIMO diagram. The person-machine diagram represents the coordinated work of one or more persons employed in operating one or more machines. This model consists of a scheme of simultaneous activities accompanied by a mathematical calculation, which make it possible to determine the technically and economically feasible optimal number of machines and persons. The team diagram represents the coordinated work of a group of persons who together perform a service. It is employed with the aim of better combining and integrating the group’s activities. The production line diagram represents the sequences of activities of persons, machines or processes, which perform an in-line processing within a common cycle time. In this case, the objective is to equilibrate the assignments of each production unit in order to balance the line. The SIMO diagram, or Micromovigram, represents the coordinated activities of the hands of the operator performing manual work. This model aims to evaluate manual work against the principles of economy of motion. By a criterion of level of coverage, this model fits better in the study of diagrams of manual activities. Construction The constructive conception of the model is that the sequences of activities demanded from each production unit during the realization of a complete cycle of coordinated work are represented in vertical columns arranged side by side. The information contained in the diagram is arranged according to the orientation shown in Fig. 4.48: 2

(Production Units)

simultaneity of activities

n Activities sequence

1

(Activities duration time)

Fig. 4.48 Basic shape of the diagram of simultaneous activities

118

4 Analysis of Schematic Models

(A)

(B)

Fig. 4.49 Types of graphic symbols

The graphical representation of the activity sequences of each production unit can be made by two alternative conceptions (Fig. 4.49): (A) The vertical columns are divided into segments representing the activities. The nature or class of activities is highlighted by filling in the segments according to a hatching or coloring convention. (B) Graphic symbols are drawn on vertical flow lines that indicate the nature or class of activities Graphic symbols and conventions are relative to any of the activity classifications. The information about the duration of the activities can be explicit included or not in the graphic design of the scheme. In the first case, the diagram has a time scale, and the graphic representation of activities is proportional to the corresponding duration times. In the segment scheme (A), the height of the segment is proportional to the respective activity duration. In the symbols scheme (B), the symbol is placed at the initial instant of the activity, with the distance between two consecutive symbols being proportional to the activity duration of the first one. The total height of columns is proportional to the full cycle time. In the second case, the activities of each productive unit, simultaneous and of equal duration, are represented on the same horizontal alignment, by either segments or symbols. In this conception, when there is any change in the activity of some unit, this new activity is represented on the next line, while remain represented the other units’ simultaneous activities. Note that in both cases, the horizontal alignment indicates the simultaneity relationship.

4.4 Analysis of Schematic Models Presentation

119

As this is the most important information in the diagram, its determination and representation must respect the exact and complete simultaneity. In the timeproportional diagram, the simultaneity relationship between activities is reported on the time scale, thus being established more precisely. All vertical columns representing the activity sequences of production units must cover a complete cycle of the global work. For the recording of repetitive or cyclic jobs, the start and end points of the cycle can be arbitrarily set up or, when possible, identified with the natural starting and ending points of the job. It should be noted that the global work cycle can contain several cycles, complete or not, of the sequence of activities of some component unit. A concise or coded description of the corresponding activities is given next to the segments or symbols in the diagram. The methodology for determining the constructive data of the diagram consists of identifying the nature, class, and sequence of activities of each productive unit, establishing the duration times of activities and the cycle, and identifying the simultaneity relations between the activities of the units of the group. The diagram can be constructed to represent an existing method or methods under development in the search for alternatives. For existing methods, or projected methods that can be piloted or simulated, the analysis is done through direct observation, filming or sampling. The choice of the technique for obtaining information is guided by the time needed or difficulty of observation and the potential savings of the work being studied. Direct observation is appropriate for short work cycles, assemblies with few units, easily perceived concurrency relationships, and for products or methods of low economic importance. In these cases, a good perception of detail is possible. Time is determined by chronometer. Filming the work method can be done at normal speed or low speed. Filming at normal speed is used for short cycle jobs, methods, or products of high economic importance, or when the set has many production units, and the simultaneity relationships are quite complex. With frame-by-frame projection, fine detail is achieved. Low-speed filming, or “memo-motion”, is used for long cycle work (hours or days), but there is a loss in detail. Times are determined by fixing the filming speed, by a micro-chronometer included in the frame or by electronic counting in the case of digital videos. Job sampling is recommended for very long cycle jobs (weeks or months) or where filming is not feasible for technical and/or economic reasons. The loss of detail in this case is large and the time determination obeys statistical confidence criteria. The duration time of each activity should be the standard time, which includes acceptable processing tolerances. For persons, these tolerances take into account fatigue, unavoidable delays, accident risks and physiological needs. For machines, it takes into account unavoidable mis adjustments, speed variation, changes in the physical characteristics of the processed material, etc. It should always be remembered that the construction and manipulation of the diagram assumes by hypothesis that the times remain constant from cycle to cycle, thus restricting themselves to work methods that admit this approximation.

120

4 Analysis of Schematic Models

The diagram must be accompanied by a summary table with total idle time, service time, and preparation time, with respective percentages in relation to cycle time. In summary, the simultaneous activity diagrams will have the following constructive characteristics in the basic design: (a) The activities performed by the productive units of a group are represented in columns, one for each unit, and graphically proportional to the respective time spent. (b) It is considered, in the representation, three types of activities: independent, combined, or waiting. (c) The simultaneity must be fully respected in the graphic representation. (d) A summary table accompanies the scheme that shows the calculated percentages of utilization for each unit and for the whole. It is possible to distinguish general uses, criteria, and manipulation procedures, and common to simultaneous activity diagrams, although each specific type of diagram (person-machine, team and production line) has its own applications, criteria and manipulation, due to its link to study techniques of different work methods. Uses The simultaneous activity diagram serves two main purposes: (1) study the methods, sequences, and individual activities of productive units that carry out coordinated work together; (2) study the relationship between the activities of the productive units, in order to carry out the coordination of work. The diagram is used mainly in the study of improvement of work methods, serving as an “assessment tool” for alternative methods. In the study of improvements, the scheme can assist in the design of the stations and the work center, in the identification of critical activities that require more detailed study, in the design and evaluation of operational efficiency of auxiliary equipment. Other uses of the scheme are in the presentation and establishment of work standards and in training operators and analysts. Criteria In the study of improvement of work methods, the diagram allows considering a series of criteria to increase the production efficiency of the group of productive units. Depending on the problem at hand, some of these criteria are chosen. Increased production efficiency means higher production with lower resource consumption. The production considered by the diagram refers to the quantity of items produced in a period of time, or the work execution time; the resources in this case are the number of productive units, the production capacity of the units per period of time, and the available time of work.

4.4 Analysis of Schematic Models Presentation

121

The series of criteria is the following: (1) to minimize the percentage of idle time, real or expected, for the productive units and for the whole group; (2) maximize the percentage of useful time, real or expected, for the production units and the whole group; (3) minimize total group cycle time; (4) determine the adequate number of productive units forming the group; (5) use the maximum production capacity of the units and the whole group; (6) maximize production rate (number of items produced per period of time) and productivity (quantity of productive resources per production rate). Manipulation The means available to the general technique of the simultaneous activity diagram to increase the production efficiency of the group of units is to improve the sequence of individual activities and to improve the coordination among the productive units. The mechanisms of action in the work situation, existing or projected, that can lead to changes and interpreted by the model as improvements are listed below, composing a general manipulation procedure: (1) eliminate or combine activities that are identified as non-essential; (2) change the individual work methods of the productive units, for simpler and/or shorter alternatives; (3) establish the basic precedence relationship of individual activities and coordinated ones; (4) arrange (or rearrange) the activities of each production unit in a sequence that allows for a better integration with the other units of the group and reduces idle, individual and total times; (5) fill the remaining idle time with extra or support activities. The specific types of diagrams of simultaneous activities follow this general procedure, incorporating other mechanisms of their own. The most outstanding visual information on the diagram is the relative amount of idle times. In this way, the interpretation of the work situation by the model is more sensitive to improvements that occur in this area, being, therefore, the most appropriate one to start the study carried out by the diagram. An important constraint to consider in re-arrangement attempts is the redistribution of activities among the units of the group, as the tasks to be assigned to each unit depend on the acceptability of the related unit to the requested type of work. Such acceptability is due to technological reasons in the case of machines, and to technical reasons (such as aptitude, training, experience, anthropometric measurements, limits of physical, and mental capacities…), as well as to psychological and sociological reasons in the case of humans.

122

4.4.6.1

4 Analysis of Schematic Models

Person-Machine Diagram

The simultaneous activities diagram of human person and machine12 schematically represents the sequences of activities of one or more operators related to the control process or service of one or more machines, during a complete production cycle. The diagram is accompanied by a mathematical calculation to determine the economic performance of the represented work method. The model, composed of the graphic scheme and the mathematical calculation, aims to show the operational and economic consequences of the expansion or diversification of the work of machine operation by a person or a team, so that one can decide which is the appropriate (or optimal) number of machines assigned to each person (or each team). The principle of this study is based on the fact that during the service cycle of automatic or semi-automatic machines, the operator is idle for a good part of the cycle time, thus opening up the possibility of his/her simultaneous use in the operation of another similar machine(s) or in another service. This model fits into the design of the simultaneous activities diagram. Multiple operation of several machines by one person can, however, generate idle time for the machines. As the costs of person and machine idle times are generally different, it is necessary to calculate the total cost of each alternative, hence the inclusion of the mathematical calculation mentioned above. With the graphic scheme, the operational viability of each group formed by a given number of persons and machines is examined, and the optimal coordination between their activities is studied. This part of the study is made by trying arrangements at the simultaneous activities diagram. After solving the production scheme for each alternative, its cost amount is calculated, which will serve as a base criterion for the evaluation of viable alternatives. The study of the person-machine diagram, also known as coupling of machines, is only possible when the machine does not require constant attention from the operator during the production period and that the absence or delay of the operator in servicing the machine does not lead to accidents, damage to the equipment, reduced product quality, or complications in another work center. The machine must automatically control the end of processing. In the typical and most appropriate case for the study of the person-machine diagram, the machine is prepared, loaded, and turned on by the operator, performs the production service requiring no or partial attention from the human element, and turns off when the service is complete to wait to be unloaded. This is the case of numerical control machines. This concept can be extended to similar situations such as the use of industrial robots. Thus, in general, this study is used only in the work with automatic or semiautomatic machines, producing, in a cyclical and repetitive regime, a large number of products per unit of time. It has also been used in the design of machines and

12

The general term “person”, in the presentation of this model, follows an expression widely used in practice, of a generic order meaning human element or operator. The term “machine” in this study means equipment with a service time control device.

4.4 Analysis of Schematic Models Presentation

123

equipment, and in their “sale”, to emphasize better execution of the work at lower cost compared to another competing project. The possibility for a person to operate more than one machine is taken with some resistance by labor representatives due to safety issues, multiple generation of errors, exploitation of labor. Labor problems can be mitigated if safety is not compromised, and the enlargement of work reduces monotony and allows for an increase in pay. The criteria for improving the coordinated work method of machine operation by person are decreasing machine idle time, decreasing human element idle time, increasing the number of machines allocated to each person, decreasing cycle time, and increasing total units produced per unit time. With the graphic scheme and the mathematical calculation, the best combination of meeting these criteria is sought, with the objective of increasing the overall efficiency of the system and increasing production savings. In the construction of the graphic scheme, it is more appropriate for the study of the person-machine relationship to trace it with columns and segments proportional to a time scale. The classification of activities into independent, combined, and waiting is sufficient for the person-machine diagram, identifying them within the diagram specificity: (a) Independent activities—person or machine works without interference • Person—activities not related to machine operation. For example: receiving or preparing the raw material; inspect finished product; gather technical data; go from machine to machine. • Machine—effective production activities without human attention. (b) Combined activities—person and machine work together. Here, in the graphic design, the activities of preparing, loading, unloading and cleaning the machine can be differentiated. • Person—the human element acts directly on the machine. For example: regulate and feed the machine and operate it with manual control. • Machine—activities that require services from the operator, or work in combination with other equipment. E.g.: machine being regulated, programmed, fed, unloaded, or controlled. (c) Waiting—idle time of person or machine, where there is no productive activity. E.g.: machine off waiting to be unloaded; person waiting for machine to finish working. The study of the work method through the person-machine simultaneous activities model follows three phases: (1) Preliminary study—examination of the working conditions The first step in this phase is to check if the operator is really idle at some point in the cycle, that is, if there is activity independent of the machine. As already seen, if there

124

4 Analysis of Schematic Models

is no machine-independent activity, the study with the person-machine diagram does not apply. It then seeks to improve the machine’s preparation, loading, and unloading methods, increasing the machine’s speed or capacity to the economic limit, and other improvements that increase the machine’s efficiency. Then, a study is carried out to improve the physical arrangement and the possibility of using auxiliary equipment, transport, or pre-production; and when feasible, from the machine design itself. These studies, which can be carried out with other specific models, aim to reduce the cycle time and increase the operator’s useful work efficiency. This can lead to increased operator idle time, which may make it possible to operate other machine(s). (2) Determination of the optimum number of people and machines This phase, which is the study of the model itself, consists of two steps: the study of the schematic model and the calculation of the cost amount. The first step consists in the schematic representation of several alternatives of person-machine sets, and in the manipulation of each schema, trying to coordinate the interdependent activities of the units of the set, in order to make the coordinated work method operationally viable and meet the criteria for improvement. Model manipulation consists in the systematic study of the arrangement of the sequences of activities in relation to the individual work method and that of the group. In order to reduce the machine’s waiting time, one should try to make the independent activities for the set simultaneous, for example, allocating the entire operator-independent service exactly in the period of independent machine operation. In the second step, the calculation of the total costs of each alternative is made. For the method of calculation, see mathematical model in Box 4.2. The comparison of operational and economic conditions, and the consideration of the important intangible variables involved, enables the analyst to determine the optimal number of persons and machines used in the execution of the work under study. (3) Subsequent study—use of residual idle times In the conclusion phase of the study, the aim shall be to reach the full use of the productive capacities of the set of persons and machines foreseen in the selected alternative. In general, the operational-economic optimum number of units in the set for the execution of a given job does not necessarily imply that both persons and machines are always busy. Thus, the total occupation of the productive units’ working time will only be possible with the introduction of extra services during idle times. The extra services that the operator can perform are prior positioning of the material or activities that facilitate the programming and loading of the machine, inspection of raw material and/or product, maintenance of equipment, collection of technical and statistical data, sharpening or preparing tools, services at another workstation. Machine idle times can support maintenance, inspection, cleaning, and even processing of another product.

4.4 Analysis of Schematic Models Presentation

125

It is clear that this phase of the study is only justified when the residual idle times are considerable and/or their costs are high. The solution developed by the study of the person-machine model is an ideal theoretical situation. This is because it takes into account only the potential productive capacities of the human and machine elements, although the objective working conditions may change or make it impossible to fully comply with the projected scheme. Deviations introduced in the theoretical model are generally due to occasional disturbances and defects in the equipment; variations in machine operating time caused by the heterogeneity of the raw material; fluctuations in energy supply, etc.; and variations in the physical condition of the human operator, beyond the predicted pattern, introduced by fatigue, personal vital rhythm, physiological needs, changes in mental and social behavior, training and learning, etc. The method selected and represented by the diagram, being seen as an ideal standard of efficiency, is very useful in the measurement and evaluation of practical results, in the process of developing and improving work methods by inducing the concept of full use of resources in the mind of the designer, and in the training of operators. In summary, the idea of the person-machine model is to obtain the work method that provides the best use of the productive capacities of the persons and machines employed in a facility. This is achieved by decreasing or eliminating higher cost idle time, and making the most of the remaining idle time, according to the basic question of “how many machines can each person or team operate?”. Box 4.2 Mathematical Calculations of Costs for Determination of the Optimum Number of People and Machines (1) Total cycle idle cost → C idT ($/cycle) C idT = total idle cost per cycle ($/cycle) np = number of people per workstation nm = number of machines per workstation C idp = hourly cost of person idleness ($/h) C idm = hourly cost of machine idleness ($/h) tidp = person idle time per cycle (h/cycle) t idm = machine idle time per cycle (h/cycle) i = person i j = machine j. C idT =

n ∑ 1

C idp i × t idp i +

n ∑ 1

C idm j × t idm j

126

4 Analysis of Schematic Models

(2) Total hourly production → P T (pieces/h) P T = total units produced per unit of time P cycle = production per cycle (pieces/h) t cycle = total cycle time (h/cycle) P Tj =

P cycle j t cycle j

(pieces/h) → per machine P 'T =

n ∑ P cycle j t cycle j 1

(pieces/h) → per workstation N m = total number of machines involved in the study P ''T =

N ∑ P cycle j t cycle j 1

(pieces/h) → for the total number of machines involved in the study (3) Total direct cost → CT ($/product) CT = direct cost per unit of product, for the total number of persons involved in the study C opp = hourly operating cost of people ($/h)—person working C opm = hourly operating cost of machines ($/h)—service machine k = cycle k t cycle k = total cycle time t opp = person operating time per cycle t opm = machine operating time per cycle Note: t cycle k = topp + t idp or t cycle k = t opm ∑k ∑n CT =

1

(

)

n=1 C opp × t opp + C idp × t idp i + P ''T

∑n

+ t idm (

(

)

n=1 C opm × t opm + C idm × t idm j

+

Δ P ''T

)

4.4 Analysis of Schematic Models Presentation

127

Δ = constant for a given number of persons and machines, and production level Δ = other direct production costs (salary supplements, depreciation of the machine, maintenance, raw materials, energy, etc.) and indirect production costs (rents, facilities, administration). Note: In order to compare the alternatives studied with the person-machine diagram, in general, Δ can be considered constant for all alternatives and not include it in the calculations However, it should be always checked if this is possible The example below shows the study to use operator idle time to increase the number of machines under his/her control, from one machine in position (a) to three machines in position (c) (Fig. 4.50).

1

person machine

S

2 3

idle

0

S

F

minutes

minutes

0

(b)

1 2 3 4

4 Cycle time = 4.0 min Person operating time = 1.5 min Person idle time = 2.5 min Machine operating time = 4.0 min

(c)

1 2 person machine machine

S1 S2

S

S F

idle

0

F

F

minutes

(a)

1 2

1 2 3 person machine machine machine

S

S1 S2

F

3 4 4,5

S3

idle

F idle S

F idle

F

S

Cycle time = 4.0 min Topp = 3.0 min

Cycle time = 4.5 min Topp = 4.5 min

Tocp = 1.0 min

Tocp = 0

Topm = 6.0 min

Topm = 13.0 min

Tocm = 0

Tocm = 1.5 min

Machine idle time = 0 F = machine running

S = machine service (loading and unloading)

Fig. 4.50 Example of person-machine diagram construction. Source Krick (1962, p. 98, Fig. 23); copyright @ 1962 by John Wiley & Sons, Inc.

4.4.6.2

Team Diagram

The team simultaneous activities diagram represents, with a graphical scheme, the interrelationship of the individual sequences of activities of the components of a team, during the common work, in which the execution time and the strict coordination between the activities of the components are important.

128

4 Analysis of Schematic Models

The definition of team that best meets the model’s design is where the team is characterized by the combination of efforts of its components, which simultaneously perform interdependent tasks, to enable the accomplishment of a complex work. The interdependence of team members’ tasks is due to the fact that the activities of one component interfere with the activities of another to support or complement the execution of the individual task. In general, the components work together around the same work center, during the time the service is being carried out. The division of tasks between the components is made according to a criterion of capacity limit or work specialization of each component. The team’s components are generally human workers and may eventually involve equipment, automated devices, and industrial robots. The team diagram is used to simplify the study of the coordinated activities of a team that are too complex to be understood by direct observation or other models, such as a team flow diagram, memo-motion movie, or description. The diagram is especially appropriate in the case of teamwork that needs a method that precisely coordinates the activities of its components, and that allows the execution of the service in the shortest time possible. Typical cases include the firefighters team preparing to respond to a call, the surgeon and assistants, flight crew on landing and take-off, maintenance and emergency repair group of petrochemical plants and other continuous industrial chemical processes, airport aircraft fueling and maintenance staff, car racing pit stop crew, and most mobile industrial maintenance crews. The teamwork included in this study can be cyclical and repetitive, or occasional, and with short cycle or execution time (seconds, minutes, or a few hours). The diagram is used as an operational instrument for the organization of teamwork, aiming to coordinate interdependent activities according to simultaneity relationships and to equitably balance the workload of the components. The most appropriate classifications of activities for this diagram are the simultaneous activity diagrams (independent, combined and waiting) and the Nadler symbols (operation, transport with and without load, waiting, hold), as shown in Fig. 4.14, number 5. The basic criteria of method improvement by team diagram are to reduce the total working time and reduce the number of team components. The reduction of the cycle or work execution time is done by the operational manipulation of the diagram, which follows the general procedure of simultaneous activities diagrams, that is, identifying activities according to the proper classification, reducing or eliminating idle time, rearranging the sequences of individual activities in order to simplify work methods and better integrate interdependent activities, use auxiliary equipment or devices, etc. Reducing the number of components is done by dispensing the completely idle components. This study can be carried out to firstly verify if there is the possibility of using more components than necessary and consists of transferring the activities of a component with idle time, which is considerable in relation to the total time, to other components of the team until that one becomes completely idle. However, this can only be done when it is possible in practice to transfer activities, in view of

4.4 Analysis of Schematic Models Presentation

129

capacity and specialization restrictions. In some cases, the idle component can be used as an occasional replacement for other components in order to better balance the productive capacity and other physical requirements for the team. When the team is made up only of human workers and there is no device to control the cycle ∑ or execution time, the assumption that the elementary times (and total, where elements = total) are constant probably does not occur in practice nor within of the acceptable limits of variation. This instability occurs because the time relationship between the team members does not only depend on the workload assigned to each one, but also on the speed and rhythm of the workers, the methods used, the degree of motivation and application to the service and, when and how much each one chooses to attend to their tolerances of fatigue, personal needs and breaks, as well as the team’s integration as a social group. Due to the instability of the times, in some cases it is not justified to use the graphical design proportional to the time scale to construct the diagram. The diagram that simply represents the simultaneity relations would be more adequate. It should be noted that when the team included in the study do not have great inequality between the salaries of their members, the calculation of the costs of the alternatives is not necessary. However, when it is the case, the procedure of calculation of the person-machine diagram could be used. Example The car racing pit crew needs to carry out maintenance tasks during car stops in a precise, coordinated and time-saving manner, following a pit strategy. Pit stop procedure consists of refueling, changing all four tires, refilling engine oil and gearbox oil, checking and tuning the engine, and instructing the driver (or changing drivers in the case of endurance racing) (Fig. 4.51).

4.4.6.3

Production Line Diagram

The scheme represents the distribution of product or service processing tasks among a set of workstations that operate according to the production line technique. The workstation can be made up of one or more production units, such as person and/or equipment. The basic characteristic of the production line technique is that the workstations simultaneously execute progressive stages of processing, where each station specializes in the execution of a certain stage, forming a portion of the product or service. In progressive stages, each station performs a step further in the production process than the previous station. The last station of the line concludes the product or service. The term production line is due to the fact that when connecting the stations by a graphic line according to the production sequence, in general, there will be a single continuous line. The product flows through such line, being completed progressively at each step. In the ideal case, the stations are physically arranged along the production line and the movement of the product along the line is carried out by continuous

130

4 Analysis of Schematic Models

Fig. 4.51 Representation and diagram of pit stop team in a car endurance racing

transportation systems, such as conveyor belts, rollers, overhead cranes. In this situation, the processing speed of the line is equal to or dependent on the speed of the transportation facility. A second characteristic of the production line is that the workstations work independently. There is no interference between activities of different stations of the line.

4.4 Analysis of Schematic Models Presentation

131

The independence between the tasks of the stations can be increased by the introduction of intermediate stocks to supply each station. When this practice is not possible, a relationship of dependence is created between the stations, regarding only on the start and end times and the speed at which individual tasks are performed. This production technique has yet another characteristic, as it establishes that the quantities of components or parts of the product or service produced in each stage are equivalent. This means that the number of components produced in each step must be such that, as output of the line, there is only and exactly a certain number of finished products. In other words, there should be no components at the output of the line that cannot form complete products. The production line technique is an alternative way of organizing mass production work of products or services. In this case, the problem of producing a large number of identical items is solved by assigning to each workstation the formation of a portion or component of the product in progressive, highly repetitive and short cycle steps. This technique can be considered an artifice that shortens the general production cycle of each complete product, thus achieving a higher production rate (products/ time unit) and, in general, higher productivity (production resources employed per production rate). The highly specialized and highly repetitive character of the task, when performed directly by a human element, can make the act of producing monotonous and tiring; in addition, the line work rhythm may be different from each person’s normal rhythm. These negative injunctions can lead to unfavorable working conditions, reflecting both in the direct formation of the product, introducing errors and accidents, as well as in the psychological and social environment by the generation of conflicts. In practice, for the worker, such injunctions are eventually mitigated by economic rewards, included in the negotiations of wage rates. However, this same character induces quite mechanized activities, composed of easily identifiable work elements, which can be fully reproduced by automated devices and mechanisms, such as industrial robots. Indeed, the technique of production line, due to the very rational framework and study of production work, can be used as a way of automatization and automation, as it allows a detailed understanding of the participation of productive mechanisms, whether of the human element or machine. The production line technique provides production management with technical advantages, such as ease of learning and execution by a trained human operator or automated mechanisms, ease of control and measurement, use of standardization, ease of equipment and labor replacements, etc.; it also provides economic advantages due to economies of scale in repeatability, at lower labor costs. The processes that best serve and exemplify the conception of in-line production are product assembly work. The difference between line production and team production is that on the line, the processing product passes from one station to another and the sequences of individual activities are independent of each other, while in the team scheme, the production units move around the processing product and their sequences of individual activities are interdependent.

132

4 Analysis of Schematic Models

There is a relationship of simultaneity between the tasks of the stations on the line because they must start and end at the same time; that is, the individual execution times must be approximately equal and simultaneous. The type of work that is coordinated and organized according to the production line technique fits perfectly into the design of the simultaneous activities diagram. The scheme applied to the production line is a useful instrument in the study of improvement of work methods organized according to this technique, constituting an approach that uses the criteria of the simultaneous activities diagram and the criteria of the line balancing technique. The most appropriate construction of the diagram for studying line balance is the time-scaled segment scheme. The production line schema can be used in method pattern establishment and assignment; as an instrument for recording and measuring work being carried out; training workers and analysts; and digital programming of automated mechanisms. As a result, the construction of the diagram of elements or segments, with or without a time scale, depends on the characteristics of each study. Line Balancing In the study of improvements and increase in the efficiency of work methods, the diagram can be used, as an auxiliary or recording instrument, in production line balancing techniques. Line balancing consists of organizing, equilibration, and adjusting the workstation assignments of a production line, by distributing equivalent workloads, so that the set meets the desired production rate (time/items or items/time) with maximum efficiency. Workload distribution refers to the number of items produced and the execution time. The balancing technique means determining the exact quantity of items produced at each stage so that the production line results in only the desired rate of complete products, determining the “standard” time for each stage, and distributing, coordinating, and grouping the stages at different workstations so that the cycle times of the stations are minimal and approximately equal to each other and the overall cycle time. A step can be a work element, a task, or a set of tasks assigned to a workstation, depending on the scope of the study. In general, the distribution of tasks or work elements to productive units must comply with some basic restrictions, such as the precedence relation, the work field, and the indivisibility of work elements. The precedence relationship between the steps is determined by the basic sequence of processing that indicates which tasks or elements must be completed before each step begins. This relationship depends on: (a) the functional arrangement of the line, (b) the physical, technical and constructive characteristics of the product, (c) the physical space, facilities and technologies available, and (d) the production processes available. The precedence relationship can be represented schematically by a precedence graph or a precedence matrix. The field of work restricts the operational versatility of workstations in the sense that there is a specialization according to the identification of distinct activity groups.

4.4 Analysis of Schematic Models Presentation

133

In other words, the identification of distinct activity groups within a production process defines fields of work that are performed by specialized stations. Thus, an activity, identified to a work field, should only be allocated to certain stations on the line. The distinction between fields of work can be made according to similarity of task, equipment, technical knowledge of the human operator, competence, and working conditions. In some balancing problems, the subdivision or analysis of tasks is limited by indivisible elements, depending on technical or economic criteria. Such elements must be fully executed by only one workstation and within the cycle time. A set of restrictions on the distribution of tasks is relative to a particular work situation. Changes in the work situation can imply changes in the restrictions on the distribution of tasks. As the greater the number of constraints, the less likely alternative solutions will be, the analyst should seek to act on the work situation in order to change or eliminate excessive, inconsistent, or inconvenient constraints. This study includes changes in product design, quantity to be produced, quality levels, processing technology, etc. Balancing Problems There are three typical formulations for balancing problems: (1) Given the overall cycle time and the time of the individual steps, determine the number of production units (e.g., workers) needed for each step, in order to meet a given production schedule. (2) Given the desired overall cycle time, minimize the number of workstations. (3) Given the number of workstations, distribute and allocate the work elements to them, within certain established restrictions, in order to minimize the cycle time. For simple production lines, with few stations and many restrictions, the balance study can be done manually, using the precedence chart, mathematical calculations, summary tables, and the production line diagram. The diagram is employed to represent the solution or plot the data for calculation. For more complex lines, with many stations and few restrictions, the number of viable solutions can be considerable, thus requiring electronic processing. To compose the balancing program, the precedence matrix, the positional weights table, the calculation program, and summary tables format and the production line diagram are used. The diagram serves there to represent the solutions in graphic form, which can be traced by computer. Balancing Mechanisms The balancing study is done based on some criteria and model manipulations, which work as mechanisms to balance the line. Depending on the balancing problem, some mechanisms are chosen and combined to form an appropriate technique.

134

4 Analysis of Schematic Models

The following are the basic mechanisms and mathematical relationships used in the balancing technique: (1) Definition, analysis, and challenge of the restrictions of the precedence relationship, fields of work and indivisibility of elements. This preliminary study aims to determine, respectively, the basic sequence of processing, the really distinct specializations and the greatest degree of detail feasible. From the setting of the restrictions to be obeyed, the study of the distribution and combination of elements, tasks, or steps is made, in order to form the workstations of the line. (2) The basic balancing criterion is to increase production line efficiency. Line efficiency, or productivity, is a function of the number of items produced and lead time. The line is more efficient, the greater the number of complete items produced in relation to installed capacity or desired production rate, and the lower the sum of the idle times of the stations in relation to the sum of the total execution times. Thus, maximizing the efficiency of the line is to maximize the ratio of quantity of complete items produced/productive capacity and to minimize the ratio of idle time/total time. (3) The evaluation of the duration times of elements and tasks aims to obtain standard times, and the measurement reliability level must be compatible with the balancing precision. The choice of the time study technique must therefore take into account this compatibility. In addition, the variability of operator and machine times must always be kept in mind, either to predict the possible degree of accuracy of the study, or to avoid critical or rigid situations. Only when there is an external control of the rhythm of the line (as for example, the transport between stations made by a continuous mechanical belt) can it be approximated in practice to the consideration of constant times. Otherwise, the variation of the rhythm of each station causes the execution time to fluctuate and consequently the idle time. In general, the balancing calculations do not consider this variability but set standard times. An ideal or theoretical behavior is thus determined for the line and in practice a behavior oscillating around this pattern is expected. In a balanced production line, the individual cycle time is always equal to or less than the cycle time of the line. The minimum cycle time of the line is equal to the cycle time of the slowest station (with the longest cycle time) which is the limiting station. When the line cycle time is fixed by some device or external event, stations may have individual times below and/or above the line time. This is the case for processing linked to fixed-rhythm processes, such as chemical processes or processes that rely on continuous conveyors. For stations with time below the cycle time, resulting in idle time, it is sought to combine them, in order to constitute a station with a time that is closer to the line’s cycle time. When it is not possible to group stations in full, idle times can be reduced by redistributing tasks.

4.4 Analysis of Schematic Models Presentation

135

For stations with excess time, the cycle time can be shortened by the following mechanisms: (a) increase the number of production units that make up the station, thus increasing the station’s productive capacity; (b) allocate part of the activities of the station with excess time to others with idle time; (c) improve the work method of the station with excess time; (d) when the excess time is very large, the task is divided by so many identical stations, so that the cycle of each is approximately equal to the cycle of line. Mechanisms to increase and decrease the cycle time of stations are also employed to reduce or eliminate individual idle times and balance the idle times of the set. These mechanisms act on the productive capacity of the production unit and/or workstation. The application of these mechanisms is always conditioned to task distribution restrictions. (4) Determining the quantity of component items to be produced at the stations depends on the production capacity of each production unit to perform each step, and the number of complete items desired. In general, there should be no incomplete items left over. This practice is only used when there is an interest in storing semi-finished products, for extra supply in production or for sale. Such a policy could also be included as a balancing mechanism. As the production capacities of the stations generally differ, the quantity of items produced is limited by the least productive station. Increasing the production of the line consists of increasing the capacity of the least productive station(s) by activating the following mechanisms: (a) (b) (c) (d)

increase the number of productive units that are part of the station; multiplying the number of identical stations to the least productive one(s); improve the work method of the station; run the station overtime to accumulate production.

To balance the production line and not reduce its efficiency may be necessary to reduce the individual production capacity of some workstations. This is done by allocating more tasks to stations with more capacity than demanded. Note: For a better understanding of the line balancing techniques, see: Close (1960, p. 200); and Niebel and Freivalds (2009, p. 45). Example The example below shows the simultaneous activity diagram for a bicycle final assembly line, with five workstations along the assembly conveyor (Fig. 4.52).

136

4 Analysis of Schematic Models Stations along assembly conveyor 1 0

Minutes

1

4

5

Mount

Pedals

Handle bars

Adjust rear wheel

Front fender

3

3

Seat Lamp

2

2

Invert Rear fender

Sprocket assembly

Reflector Idle Idle

Idle

Rear wheel, carrier and chain

Stand Chain guard

Front wheel

Lubrification

Inspect Idle

Idle

4

Fig. 4.52 Example of a production line diagram. Source Krick (1962, p. 103, Fig. 26); copyright @ 1962 by John Wiley & Sons, Inc.

4.4.7 Route Frequency Diagram Conceptualization The route frequency diagram records the movement paths, described by one or more items in transit between components of the physical arrangement of a productive unit, during the execution of a task or a set of tasks, observed in a representative period of time. The model consists of a scaled floor plan of the physical arrangement of the productive unit involved in the processing under study, on which are traced the actual trajectories of the observed movement activities. In this model, the other activities involved in the processing performed at the work points are not represented, but only the activities of movement or transport between one point and another. The visual information provided by the diagram is the magnitude ratio of the frequencies with which the various sectors or circulations of the physical arrangement, involved in the task under study, are covered. This type of flow diagram is especially suitable for the study of tasks that do not have a single and deterministic processing sequence, and where the movementtransport factor has a great influence on the relationship between work method and physical arrangement. This is the case, for example, of a production unit that processes a variety of products, aggregated in the same class of importance, that follow different manufacturing processes; therefore, even though each product may have a fixed and repetitive sequence, and efficient working method and physical arrangement for one or more processes, it will not necessarily be efficient for all

4.4 Analysis of Schematic Models Presentation

137

processes. Thus, the route frequency diagram helps the determination of a work method and a physical arrangement that equally meet the range of processes, from the point of view of the movement-transport factor. The diagram also applies when the movements are random. The moving item can be a human person, material or transportation equipment. Two or three of these items may be involved and combined in the same movement. In these cases, it is important to clearly define the object of study or to represent its trajectories with graphic symbols or different colors. The lines drawn in the diagram generally represent a sample of the actual trajectories described by the item(s) over the period of total duration of the task(s). This is because in most cases to which this model is applied, the duration of the cycle is too long, making full registration unfeasible; and also, the movements of the item(s) may occur according to random distributions, which requires extracting sample data. Sampling is done by determining a representative time period for observing the task. That is, the observation time must allow the recording of a sample of the trajectory that represents the most likely occurrence. This period will then depend on the degree of variability and the total duration of the task. The basic diagram is only for recording trajectories described in a single plane. Three-dimensional trajectories require special handling, or the use of more appropriate models, such as three-dimensional wire (physical model) or cyclegram. CAD software can be very helpful for complex work methods and/or trajectories. The characteristics of the motion trajectory represented in the diagram are the frequency of travel between the pairs of components of the physical arrangement, and the total or partial distances covered. Frequency of travel between two points is the number of times an element travels the physical distance that separates them. The evaluation of the frequency of travel between the pairs of components is done by counting the lines of flow. The quantitative value of the travel frequency defines the intensity of movement or transport flow existing between the component pairs. In case there are differences in traffic conditions, the value of the flow intensity can be restated by correction factors or “weights”. The value of the flow intensity or even the visual analysis of the diagram allows locating the points of concentration of movements or transports. For the determination of the distances covered, two resources are available: mathematical calculation and string diagram. The mathematical calculation follows the equation below: Dp =

n ∑

f i j × di j

2

where: Dp = distance traveled when moving between n components f i j = frequency of travel between components i and j (flow line count) di j = distance of the route between i and j (measurement on a scaled plant).

138

4 Analysis of Schematic Models

As a simple solution, the string diagram consists of following the evolution of movement trajectories in the scaled plan by means of a continuous wire or string that, after defining the start and end points of the representative trajectory, is rectified and measured directly. The model admits almost the whole range of coverage levels framed in the study of methods (bench, workstation, process, plant, plant group, or region). Thus, the unit may be an assembly bench, whose components are the containers, jigs, fixtures, and tools arranged on the bench, and the moving items are the operator’s hands. It could be a warehouse whose components are storage locations, and the moving item, a forklift. For a group of plants, the model can be used to analyze a just-in-time parts supply scheme. The unit can also be the region where an aviation company operates, whose components are the airports in which it operates, and the moving items, the company’s aircrafts. The design of the route frequency diagram admits the system concept. Thus, a system can be defined by the components of the productive unit involved in the accomplishment of a given task, by the transport flows formed in moving the item(s) in transit and by the boundaries of the physical area of movement and observation time; and this system being organized according to a work method and physical arrangement. The systemic conceptualization of the route frequency diagram establishes a close similarity with system diagrams. However, the flow intensity diagram (see Fig. 4.5) does not explain the relative dispositions and physical sizes of the components, paths and work area; and the trajectories of movement are understood as flows with quantitative value of intensity. Moreover, the flow intensity diagram can assist in the construction or analysis of the route frequency diagram. Construction The construction of the diagram is made from the survey and scale drawing of the physical arrangement of the work area involved in the studied process, including the physical restrictions to movement. A continuous line is traced on this drawing, which follows the trajectory of the item(s) under study, during the pre-set time period. The representative line of the trajectory can be a graphic trace or a wire. The model that represents the trajectory with wire is called a string diagram and can be seen as a simple and rudimentary device for measuring the length of the trajectory. For the construction of the string diagram, the floor plan is placed on a plank of soft material and pins or nails are placed at the points corresponding to service locations and traffic restrictions and at points of change of direction. The trajectory is reconstructed with a malleable wire, connecting the pins corresponding to the points visited, from the beginning to the end of the route. Removing the wire from the pins and measuring it with a scale, the travel distance of the trajectory under study is determined. When it is desired to represent and highlight the trajectories of several items on the same drawing, the diagram is constructed with lines of different colors or styles. The coherent choice of the observation time period should aim at the largest representativeness of the sample. Whenever possible, statistical sampling techniques should be used.

4.4 Analysis of Schematic Models Presentation

139

Fig. 4.53 Example of a route frequency table

In the representation of the components and physical restrictions of the production facility, the exact places of visit must be determined, and an identification code established. There are four techniques for surveying and register the trajectory in the sequence of occurrence: (1) (2) (3) (4) (5)

pairs with transit; route frequency table; direct drawing on the plant; filming “memo-motion”; digital monitoring with positioners or transponders.

The technique of pairs with transit is a simple listing of the pairs of components between which the item under study moves, in the sequence of the trajectory. E.g.: A–B B–E E–G G–Z Z–A The route frequency table is a “from-to” matrix where the movements between the pairs of listed components are recorded (Fig. 4.53). The direct tracing technique is only possible for short observation periods and easily surveyed trajectories. The “memo-motion” filming technique consists of filming the task at low speed (50 to 100 frames/min) and surveying the trajectory by projecting the film at normal speed. The shooting speed must match the speed of the movement. The use of this technique is only justified when it is not easy or desirable to directly observe the task visually, for example, when the observation period is quite long. The technique of tracking the transported or moving object, or the transport equipment through a transponder associated with radio-frequency identification (RFID— radio-frequency identification) or with markers and computation graphics for tracing the trajectories are sophisticated and precise techniques. It should be used for products and processes with a value compatible with the costs of the technology involved.

140

4 Analysis of Schematic Models

Uses The main use of the route frequency diagram is to record alternative solutions for work methods that involve intense movements between work centers without defined or easily identifiable trajectories. This record can be used to compare and judge alternative solutions or even visualize possibilities for improving the work method. The diagram only serves to record solutions being executed or simulated. Another design situation that can be used with the diagram is when one is studying the movement of several items that follow predetermined individual processing sequences. Due to the simplicity of its visual information, it is a great resource for the presentation and “sale” of the proposed method. In order to illustrate the possibilities of using the route frequency diagram in the study of work methods, some typical applications, industrial or otherwise, are listed below: (1) operator who supplies and controls two or more machines with random cycle times; (2) “office boy” who delivers to and collects papers from the desks of an office; (3) conveyor or forklift that delivers and collects material at a job shop’s workplaces; (4) bench operator that performs tasks with variable work sequence and time cycle; (5) operators who move at irregular intervals between points in the work area, with or without material, for example, the case of manufacture with a fixed product (ships, bulky or heavy products, turbines, etc.); (6) stores or warehouses in which a variety of materials are stocked and removed from shelves or storage locations; (7) laboratory operators, where a test routine occurs at irregular intervals; (8) dimensioning of passages or aisles in a shopping center; (9) choice and specification of transport equipment from a package distributor warehouse. (10) operator in kitchen, laundry, bakery, cafeteria. Criteria The critical examination of the relationship between work method and physical arrangement represented in the model in terms of the demanded physical movements is made from the verification of the most frequently used routes, the points of concentration of movements and the distances covered.

4.4 Analysis of Schematic Models Presentation

141

The most frequent routes are those with more lines in the diagram. The study to improve the work method and physical arrangement obeys the following evaluation criteria: (1) minimization of the total distance covered; (2) minimization of the path distances between the pairs of components; (3) adequacy of the passages, corridors or sectors of movement, depending on the intensities of the flows of movement; (4) adequacy of transport systems and equipment, depending on travel distances and transport flows intensities. Manipulation In general, the route frequency diagram is used as a tool for analyzing the symptoms of problems in a work method in progress. In the study of improvement of the method, the causes of inefficiency due to handling or transport are indicated in the diagram. Then, it is sought to act in the work situation to eliminate or mitigate the observed inefficiencies. In this way, some alternative solutions are generated, which are put into practice and recorded again with the diagram. The comparison of alternative solutions against the evaluation criteria highlights the best solutions. It is important to take into account, however, that this technique is generally based on a random sample, thus subjecting the comparison data to a margin of error. As a basis, differences in savings of around 5% are in principle not significant, and only differences above 20% should be considered. The use of statistical techniques in obtaining the sample can determine confidence intervals and tolerances with more precision. The minimization of distances is done by approaching in the physical arrangement the pairs of work centers and visit points that have a higher frequency of travel between them, or by changing the work method or the transport system, in order to reduce travel frequencies. The adequacy of the passages, corridors, and sectors of movement is done in an attempt to avoid congestion, crossings of flows, or incompatible flows in the same direction (e.g., fast forklifts on the personnel access walkways). This adequacy also includes the specification of the roads and paves and the dimensioning of the widths and heights of the passages. The adequacy of transport systems and equipment aims to specify them in order to meet the required transport conditions and reduce travel frequencies. Note that the study with this model needs direct action on the work situation, on the physical arrangement and the work method, in order to obtain the comparison results. This could entail restrictions on its use, due to eventual technical and economic difficulties to carry out such exercise.

142

4 Analysis of Schematic Models

Examples Example 1 Shows the route frequency diagram for the flow of a person during a meal preparation process, in the kitchen area (Fig. 4.54).

Fig. 4.54 Example of route frequency diagram for operator movements in a plant. Source Krick (1962, p. 105, Fig. 27); copyright @ 1962 by John Wiley & Sons, Inc.

Example 2 Shows the path frequency diagram for the movements of an operator’s hands on the workbench, during the cycle of the assembly process of an electronic device (Fig. 4.55).

4.4 Analysis of Schematic Models Presentation

143

Fig. 4.55 Example of route frequency diagram for bench operator. Source Fields (1969, p. 108 Fig. 9.6); copyright @ 1969 by The Orion Publishing Group

4.4.8 Cyclegraph Conceptualization For the study of certain operations that are formed by a cyclic series of movements of the hands or limbs of the operator’s body, it is important to determine the type and extent of the trajectory they travel through space. The extent and difficulties encountered in traversing trajectories in space are the major causes of increased physical fatigue for the operator and the risk of accidents, in addition to lengthening the cycle time. These conditions are affected by the distribution of items handled on the workbench or work area, existing obstacles to go around, placement in extreme locations within normal reach, the need for sudden changes of direction implying rapid deceleration and acceleration of moving parts. In this regard, the cyclegraph model provides a representation of the trajectory traveled in space by members or parts of the operator’s body during the execution of a cyclic series of productive activities within a restricted work area. Cyclegraph is usually presented by a picture showing the place or workbench with the trajectories of the cycle movements superimposed. It can still show the operator in one or more of the positions taken.

144

4 Analysis of Schematic Models

Construction There are different techniques for the construction of this model, which are manual drawing, photography, stereoscopic photographs, videogrammetry, digital graphics, or three-dimensional models. The manual drawing of the trajectory by direct observation is employed when the trajectory is very simple, not justifying the use of more sophisticated and expensive techniques; also, when the trajectory is long or dispersed over a very wide area that makes it difficult to frame a photograph or the lines are blurred; and even when the angle of shot of the scene makes, it impossible to use a photo or video camera, due to materials or protrusions that block the view of the entire trajectory. In order to record the trajectories using the photographic technique, small light sources are attached to the limb (or limbs) whose movement is to be studied, and a photographic register is exposed in a camera with an open shutter during the complete activity cycle. The moving lamps impress the register along luminous lines. If the lamps remain lit with a constant luminous intensity throughout the cycle, continuous lines are recorded; in that case, the model is called a cyclegraph. If, by means of mechanical or electronic apparatus, an intermittent variation in the intensity of the light source is imposed in order to reach maximum and minimum brilliance with a certain frequency, the trajectories will be recorded as dashed lines; the model thus constructed is called a chronocyclegraph. This artifice of using flashing lights with a controlled frequency allows extracting from the model information about movement characteristics, such as cycle duration time (hence the prefix “chrono”), speeds, accelerations, and decelerations. These indications may show points of hesitation or contour difficulties inherent to the method and/or the physical arrangement used in the task. The light lines can be rectangular in shape if the intensity changes are instantaneous and take on a pear shape if the increase in intensity is instantaneous and the decrease is slow. In this case, the tip of the pear-shaped spots indicates the direction of movement. The construction technique of the cyclegraph model with stereoscopic photography consists of photographing the evolution of the lamps in movement in space by means of two cameras simultaneously, forming between their main axes an angle congruent with the angle of vision of the human eyes; the two photos related to the recorded cycle are placed on a special reading device, which gives the viewer an illusion of three dimensions. A more advanced technique is replacing light bulbs with “transponders” or markers connected to a digital algorithm. New techniques for work measurement represent novel generation of digital architectures, applying motion capture technologies (MOCAP) and customized algorithms to offer a digital representation of the human body or parts at the working situation under study. From any of these graphic records of the trajectory, three-dimensional models can be constructed. The most rustic is the three-dimensional wireframe model, and the more sophisticated ones use computer-aided extended reality graphics.

4.4 Analysis of Schematic Models Presentation

145

Uses The cyclegraph model for the study of movements by recording the trajectory of the operator’s limbs is mainly used in jobs with short highly repetitive cycles or jobs that require quick or skillful movements. Cyclegraph and chronocyclegraph models can be used in the field of work methods studies for the following objectives: (1) Recording, analyzing, and improving existing working method This study is of assistance both in the case of tasks carried out with unrestricted movement, where there are no fixed devices or physical arrangement of elements that regulate the form of the movements (e.g., folding plants or towels) as well as tasks that require the manipulation of a series of elements laid out in the workplace. In this case, the model may show the wrong placement of machine controls and an inadequate way of activating levers and handles. It can also be used to judge the solution given for the physical arrangement of containers and hand tools on the service bench. Examples of the above mentioned tasks are the work of driving machine-tools, surgical operations, small parts assembly, and office services. (2) Experimentation and testing of new method to be deployed When it is possible to simulate the method designed in an experimental stage, the model is an immediate test for the judgment of flaws and project qualities. (3) Operator training Once an improved method of carrying out the work has been chosen, the operator must know the details and be trained in this method. The cyclegraph record, whether drawn, photograph, computer graphic, or three-dimensional, provides an accurate idea of the work method to be followed. In the training phase, its most useful application is to verify the operator’s learning, as the record of each training phase allows checking the progress and the moment in which the trajectories become uniform and according to the projected method. It can also be used to train specialists in work methods, helping to promote a behavior aimed at observing the form and character of the movements involved and not just the duration of the task. (4) Marketing or “selling” of the proposed method The model allows for a quick comparison between alternative methods, clearly demonstrating the superiority of one method over another. Disadvantages The limitations that the cyclegram models are subject to are: (1) It is restricted to the study of short cycles, limited workspace, and not too complex body movements.

146

4 Analysis of Schematic Models

(2) The placement of lamps and wires or markers in the operator’s body limbs can cause difficulties and restrictions to their movements, and with that distortion of the method, requiring the operator to have an acclimatization period before recording. (3) For a normal photographic record, it is necessary to reduce the amount of light in the environment, possibly influencing the work method of the operator and the trajectory itself. (4) By using photograph technique, mathematical manipulations are difficult to be made, such as establishing an equation of motion for the cycle, which could lead to gross errors. Only computer-aided models can allow more accurate trajectory, velocity, and acceleration calculations. Criteria The characteristics of a trajectory of motion are length, duration, shape, correction from obstructions or changes in direction, and variation of speeds along the path. Box 4.3 presents the possible calculations of those characteristics. The criteria for improving the work method employed are reduction of operator fatigue, reduction of accident risks and reduction of cycle time. Under these criteria, the defining characteristics of the trajectory must be analyzed and evaluated. Technical Specifications The traditional photographic technique for recording a cyclegraph or chronocyclegraph consists of exposing a photographic record, in a camera with the shutter open, to the evolution of light sources, fixed to the operator’s limbs, in space, during the performance of a complete cycle of tasks (see, Fields 1969, p. 83; Nadler 1970, p. 189; Maynard 1963, pp. 2–70). The cyclegram record only requires that the lamps remain lit with constant intensity during the cycle. For the chronocyclegram record, it is necessary to use a special apparatus that produces the intermittent variation of the intensity of the light source with controlled frequencies. The device that regulates the dotted tracing of the trajectory in the photograph can have two different operating concepts: by using a rotating shield in front of the camera lens or by interruption of the electrical energy supply to the lamps, either by means of a mechanical drive or electronic circuit. The rotating shield is driven by an electric motor, of variable and controllable speed, and consists of a disk with transparent sectors and opaque sectors. The unit for intensity variation of the lamps by interruption of electrical energy can use mechanical or electronic drive. The mechanical switch consists of a small electric motor with variable and controllable speed, which rotates an eccentric rotor that operates in the opening and closing of a plate in order to control the discharge of electric energy from a capacitor to the lamps. The electronic interruption unit is made up of three sub-circuits: a relaxation oscillator, a multivibrator (“flip-flop”) and a drive, as indicated in Fig. 4.56.

4.4 Analysis of Schematic Models Presentation

Power

Relaxation oscilator

Flip-flop

147

Driver

Lamps Fig. 4.56 Construction of an electronic device for variable electrical power interruption

Brief description: The relaxation oscillator is responsible for generating the signal that orders the switching off and on of the lamps. To increase the duration of the pulses, a multivibrator-bistable is used, triggered by the pulses generated by the relaxation oscillator. In the collector of one of the transistors of the multivibrator is generated a waveform capable of excite lamps, however of small power. To amplify the power a “driver” is used for the lighting of the lamps with the aid of a power transistor. The camera is positioned at a distance that allows the entire working area to be framed. The lamps are attached, by means of adhesive tape or elastic bands, to the parts of the operator’s body whose movement is to be recorded and it is ensured that the evolution of the lamps remains visible through the photographic frame during the entire cycle. The wires must be arranged in a way that does not restrict the operator’s movements. The lens focus is adjusted exactly in the light bulb evolution region. The aperture will depend on the lighting level of the environment, but the picture should not lose its sharpness. In the case of the chronocyclegram record, the intensity variation unit must be regulated according to the operation rhythm. For fast-paced movements, the frequency of the lamps should be in the range of 20–25 “flashes” per second and for slow-paced movements in the range of 5–10 “flashes” per second. But the correct frequency must be determined by successive tests, and the use of digital cameras allows for immediate verification of results. The operator, when reaching the position of completion of the cycle, must maintain it so that a second exposure can be carried out using the “flash” (or adequate lighting) that allows superimposing the recorded trajectory, the scene of the workplace and operator, in order to see the relationship between these elements. Note that for this second exposure, the aperture and speed of the camera must be corrected to the new lighting level. The superposition of the two exposures can be done directly by the camera or later by digital photoshop. With the use of infrared filters, it will be possible to record photographs under normal lighting conditions, avoiding the alteration of the operator’s movements due to the darkening of the workplace. When there is a possibility that the trajectories of the moving parts may intersect or overlap, causing confusion in the registration, it is interesting to use different colored lamps for each moving part under study.

148

4 Analysis of Schematic Models

The stereoscopic photography technique also makes it possible to better distinguish the various trajectories traced in space, due to the depth effect. The recording is done using special stereoscopic cameras or two common cameras, which take the pictures simultaneously from viewpoints that correspond to the visual angle of the human eye. Box 4.3 Mathematical Calculations for Chronocyclegraph Analysis The mathematical calculations for the study and analysis of chronocyclegraphs can determine time of cycle, velocities and accelerations between two points, and trajectory length. (1) Time of cycle

sec

frequency

sec

n 1 s Cycle time: t = × n = f f ⎧ 1 ⎪ ⎪ ⎪ ⎨ f = time elapsed between two consecutive light points f = frequency on lighting of the lamps (flash/s) ⎪ ⎪ ⎪ ⎩ n = number of points of light in a cycle (2) Velocity between two luminous points The speed of movement between two points of the trajectory can be evaluated if the evolution of the lamp is made in a plane parallel to the photographic film plane, and it is possible to photograph a scale placed on the same plane of evolution. In case the velocity is considered constant during the cycle, the velocity between any two points will be: Velocity between two luminous points

4.4 Analysis of Schematic Models Presentation

(3)

149

di j di j × f vi j = = ( cm/s) ti j ni j ⎧ ⎪ ⎨ di j = distance between the points i and j ti j = time between points i and j ⎪ ⎩ n i j = number of luminous points between points i and j 10 cm × 25 flashes/s = 50 cm/s Ex.: v1−5 = 5 flashes Acceleration

Taking into account the same considerations made for calculating the velocity, the acceleration between any two points will be: acceleration between two luminous points ) vi j di j × f 2 ( cm/s2 = ai j = 2 ti j ni j Ex.: a1−5 =

10 cm × (25flashes/s)2 = 250 cm/s2 (5flashes)2

(3.1) In the case where there is a variation of velocity along the trajectory, it is possible to determine a distribution of velocities and accelerations by calculating the values for each two consecutive points, approaching the concept of velocity and instantaneous acceleration. di,i+1 (cm/s) 2 ) vi, j+1 ( cm/s2 = 4

Vi,i+1 = ai,i+1

Novel technologies have been developed and applied to introduce digitalization hardware and software for the study of work methods, especially for analyzing human body movements. Videogrammetry using markers at the human body, one or more video cameras for movement tracking, and image digital processing constitutes one alternative for tracing and analyzing cyclegraphs, and complex body motions as well (see Machado et al. 2012). Motion capture (MOCAP) technologies build the fore front of digital motion analysis, which can be explored by the methods engineer both to trace cyclegraphs through computer graphics or even to carry out the work study more in deep as with the information provided by this model. The use of depth multi-cameras13 for markerless motion capture allows to tracing complex trajectories of operators’ members. 13

Depth-sensing camera is used to automatically detects and measures distance between two objects.

150

4 Analysis of Schematic Models

For more detail on the MOCAP techniques see Ferrari et al. (2018, Faccio et al. (2019). Example The example shows pictures of a cyclegraph and a chronocyclegraph for an assembly work done by photographic technique as described above (Fig. 4.57).

Fig. 4.57 Examples of cyclegraph and chronocyclegraph using photographic technique. Source Fields (1969, Figs. 7.5 and 7.6, p. 86); copyright @ 1969 The Orion Publishing Group

4.4.9 Sensory-Motor Diagram The human operator, to perform a manual task or act on equipment controls, uses three basic functions: • The function of perception, or input, which gathers information or stimuli about the state of the material or equipment handled, through the sense organs and forwards them to the brain. • The processing function, or control, where the central nervous system computes and processes the received information, makes decisions and communicates them to the motor system. • The motor function, or output that, from specific activation of the motor system, produces a muscular activity of applied force or movement on the material or equipment handled.

4.4 Analysis of Schematic Models Presentation

151

Motor activity models are only concerned with representing and analyzing the results of motor function, such as the manual activity diagram, the human process flow diagram, the person-machine diagram, and others. In this case, however, a complete view of the performance of the human element in the execution of a productive task is not achieved, as their psycho-perceptive activities will not be represented there. Nonetheless, in the study of certain works carried out with the concurrence of the human operator, it is necessary to determine the mental load demanded and establish the perceptual and psychic activities involved, highlighting the human senses at stake. The sensory-motor diagram is a type of psycho-sensory model, which schematically represents the process of perceptual activities and its relationship with the motor activities developed in the execution of work by human operators. For the construction of the model, each movement element relevant to the task under study is examined to determine whether perceptual processes are being used, and what are the perceptual activities involved and related to the motor process. Conscious awareness or perceptual activities can be divided into the following classes (Fig. 4.58): • Plan (

)

There is a planning activity when the operator has to think about choosing between alternatives. This occurrence is detected when the work method varies from cycle to cycle in some important way, implying the planning of the next action. • Control ( ) The activity of controlling is necessary when some movement of the operator cannot be done in a natural way (such as ballistic movement of the hand to reach an object) and each variation of movement requires a feedback of stimuli between the central nervous system and the part of the body on the move. This activity usually occurs when an unusual level of precision and/or care is required, implying continuous sensorial control. • Initiate ( ) and stop ( ) Conscious initiation and/or termination activities are necessary when the start and/ or end of the task depends on an external signal, an indication of equipment “performance” or an operator decision. Perceptual activities Plan Control Check Initiate Stop

Short description When choice exists in performance of motion When care or accuracy required When outcome is in doubt When external signal or performance is given When external signal of performance is given

Symbols

Fig. 4.58 Symbology of the activities of perception. Source Nadler (1970, p. 346, Table 15.4)

152

4 Analysis of Schematic Models

• Check (

)

The conscious activity of checking exists whenever the task’s output element raises some doubt as to expected results. This occurrence can be detected by examining the possibilities of the action or product going wrong, within the criteria for elaborating the task under study, implying verification. The recording of the work method through the sensorial-motor diagram can be used in three types of study: method improvement, ergonomic research, and operator training. In the study of improvement of the work method used in the execution of a certain task, the objective to be reached will depend on the character of the work. If this is repetitive, the objective is to decrease the total fatigue of the operator. Whether it is intermittent or single, the goal is to increase the effectiveness of the mental load expended, to make the method more accurate. For the reduction of fatigue caused by psycho-sensory activities, the criterion should be to detect and try to suppress the activities of controlling and planning; in that order are the ones that cause the most mental fatigue. It should be noted, however, that the elimination of these activities entails a job, for the human operator, which is highly mechanized and repetitive. This could generate feelings of monotony and boredom in the operator, and consequently mental fatigue as well. In this way, an adequate balance of planning and checking activities must be provided, so that, on the one hand, it facilitates the execution of the task; on the other hand, it enriches the operator’s participation in the work. To increase the effectiveness of the mental load, it must be verified whether the activities of controlling, planning, and checking are coherent with the limits of human capacity to exercise them. In ergonomics research, it is used to control the psychomotor influence of the operator on the variable method of operation. The sensory-motor diagram allows standardizing the behavior of operators according to a psycho-physiological scheme, so that an adequate balance of fatigue and attention can be established within the statistical sample surveyed. In operator training, the construction of the diagram is a first step toward the development of a learning plan with a system approach. Among the various possibilities of construction, two are most used: the diagram for manual work and the diagram for work with equipment.

4.4.9.1

Sensory-Motor Diagram for Manual Work

This model is an operator process flow diagram, similar to the manual activity diagram, differing only in the inclusion of a column for the representation of the perception process related to the motor process of the operator’s limbs. It is used when the elaboration of the item is carried out directly by the hands – (and/or feet) of the operator, aided or not by tools or working instruments, usually on a bench. Its construction aims to determine the existing relationships between manipulation activities and demanded psycho-sensory activities.

4.4 Analysis of Schematic Models Presentation

153

Table 4.10 Definition of perceptual activities Human organs or senses involved in perceptual activities

Central

Memory (M) Decision (D)

Sensory

Eye (Y) Ear (E) Nose (N) Tact (T) Kinesthetic (K)—sense of perception of muscle movement

Table 4.11 Hands micro-movements Motion

Symbol

Definition

Reach

R

Movement of hand or finger without load

Grasp

G

Movement involved in securing control of an object with fingers

Move

M

Movement of hand or fingers under load

Position

P

Movements involved in aligning, orienting, and joining objects

Release

RL

Relinquish control of an object previously grasped in fingers

Turn

T

Movement requiring rotation of the forearm about its axis

Delay

D

Hesitation of hand while awaiting termination of some act or event

Hold

H

Act of supporting and object with the hand while work is performed on object

Source Krick (1962, p. 93, Table 3); copyright @1962 by John Wiley & Sons, Inc

The scheme is built by observing the movements of each hand, classifying them according to any of the symbols presented in the study of the manual activity diagram, listing them in the respective columns. It is then determined which psycho-sensory activities are involved in each motor activity (plan, control, check, initiate, stop) and to which human organs or senses are responsible (Table 4.10). For studies dedicated to microscopic analysis of manual operations, a special hands micro-movements description can be used, as indicated in Table 4.11. Example The example shows the sensor-motor diagram for registration of an operation of welding with an oxyacetylene torch on junctions of a chassis (Fig. 4.59).

154

4 Analysis of Schematic Models

Fig. 4.59 Example of sensory-motor diagram for manual work. Source By the Author following the model proposed by Nadler (1970, p. 347, Fig. 15.9)

4.4.9.2

Sensory-Motor Diagram for Work with Equipment

The model is similar to the person-machine diagram, being more complete, as it encompasses the relationship between the equipment and the operator’s psychosensory system, in addition to the motor response system. The operation of an equipment or machine by a human operator defines the existence of an integrated system, the person-machine system, which is governed by an exchange of information flows between these components. Regarding the object of study of the model, the human operator receives a flow of input information from the equipment, which is perceived by his/her organs or perception sensors, and sent to the central nervous system, which processes the information related to the work situation; at the end of this processing, the operator makes decisions and, through the brain, communicates them to his/her motor system, which in turn transforms these decisions into a flow of information to the controls of the machine (Fig. 4.60). The sensory-motor diagram is necessary when it is desired to schematically explain the three functions performed by the human operator (perception, processing, and motor) in jobs in which the equipment performs the productive operations and the operator only drives it, and it is important to determine the mental load expended by the human operator (Fig. 4.61).

4.4 Analysis of Schematic Models Presentation

155

controls equipment input

X

display equipment

X

muscle command action

equipment output action of perception

control information output

operator

information input

Fig. 4.60 Schematic definition of the person-machine system. Source Seidl da Fonseca (1975, p. 206, Fig. 5)

Display Output

Observation information

Central nervous system

Mechanisms Controls Machine

Perception function

Action information

Motor system Person

Fig. 4.61 Person-machine relationship scheme

For the construction of the diagram, each stage of the operation cycle is observed and, by means of special symbology, indicated in the respective columns, which are the human organs or senses, and which machine elements are used in their execution. Example The example shows a sensory-motor diagram built to determine and standardize the sensory and motor activities required in the execution of a standard part machining on a lathe, for a sample of operators employed in an ergonomic research to determine the sensitivity of a machine tool regarding anthropometric variations. In this case, the information represented in the diagram are movements, number of feedbacks, mental workload, estimated time per cycle, elements used in the personmachine system, and work position (Fig. 4.62).

156 Maschine

WORK ON THE INTERFACE

Op erat or

Display 1

2

3

C o nt ro l 4

5

I

II

S en so ry III

Hand

Eye

Central Ear

M

D

Feed back

MOVEMENTS TO REACH THE INTERFACE

4 Analysis of Schematic Models

MOV. RH TO START SWITCH LEVER ACTION MOV. RH/LH TO LONGITUDE CONTROL

NO YES

LONGITUDE CONTROL ACTION MOV. RH TO SPEED CONTROL SPEED CONTROL DRIVE MOV. LH TO TRANSVERSAL CONTROL TRANSV. CONTROL ACTION MOV. RH/LH TO LONGITUDE CONTROL LONGITUDE CONTROL ACTION MOV. RH/LH TO TRANSV. CONTROL TRANSV. CONTROL ACT.(ADJUS TMENT) MOV. LH TO DRAG PLATE DRAG PLATE ACT. MOV. RH/LH TO LONGITUDE CONTROL LONGITUDE CONTROL ACTION MOV. RH/LH TO TRANSV. CONTROL

NO

TRANSV. CONTROL ACT.

YES

NO

YES

Fig. 4.62 Example of sensory-motor diagram for working with equipment. Source Ureta (1973); copyright 1973 by Lucio Ureta

4.4 Analysis of Schematic Models Presentation

157

4.4.10 Manual Activity Diagram Conceptualization The schematic representation of the method used by a human operator in manual, repetitive work with cycle time not controlled by equipment, performed at a fixed location, can be done by the manual activity diagram. This model covers the study of micro-activities and micro-movements, restricted to the normal area of reach of the operator sitting or standing in a fixed position, usually in front of a bench, machine tool or control panel. The model is more appropriate for tasks with short cycle times (two minutes or less). Manual work consists of a series of intentional and coordinated activities carried out by members of the operator’s body to carry out a productive operation, such as assembling small sets of parts, carrying out medical operations, creating an art object, doing a craft work, writing texts or filling forms, repairing electronic devices or watches, etc. Among manual works, the ones with a repetitive cycle fit the most into the model, characterized by tasks that are performed in the same way over and over a considerable period of time. In this class are most traditional mass production tasks of industrial goods and services. With the advancement of automation, the use of industrial robots, 3D printers and artificial intelligence, manual tasks performed by human operators can be replaced, supplemented, or even completely reformulated. The diagram presented here can still be used to guide the process of automation, robotization, and other advanced industrial production and service technologies. Generally, manual operation is part of a production process, consisting of a sequence of operations, transport and waiting. Thus, the focus of the manual activity diagram is a sub-set of the study of the production process, which uses models such as flow diagram, map flow diagram, chronological assembly diagram. In other words, the level of coverage of the model is the smallest of the scale, that is, at the bench level. The diagram supports recording the activities of several operator members engaged in a task simultaneously, such as hands, feet, knees, shoulders, head, ears, and eyes. It is usually interesting to record only the activities of the operator’s hands, as the greatest workload is usually concentrated on the tasks addressed by the present model.14

14

The manual activity diagram is ultimately a simultaneous activities diagram by schematic conception. In the present text, however, even if the concept and basic criteria of the simultaneous activities diagram are also considered valid for this diagram, it deserves a separate study due to the particular focus of the two diagrams. The way of looking at the work situation through these models, as well as the level of scope and the object of study, differ greatly. For example, while in the simultaneous activities diagram the concern is to coordinate the work of two or more productive units, in the manual activity diagram, the study focuses exclusively on the productive unit human operator, who seeks to self-coordinate the work of its members.

158

4 Analysis of Schematic Models

The factors studied by the model are the members activity with a significant performance; characterizing and classifying activities; the relationship of simultaneity between the activities of each member; and eventually the execution times for each activity. The characterization and classification of activities, with the consequent graphic symbology, directly depend on the degree of detail of analysis desired in the study. Thus, as the level of detail increases, the subdivision of the task into micro-activities and also the number of distinct activity classes will increase. The degree of analysis detail chosen for the construction of the model is determined by the nature of the work, demanded precision of movements and activities, degree of cycle repeatability, cycle duration, the number of operators involved, the risk of accidents and, especially, the potential economy in simplifications. Six different types of manual activity diagrams can be distinguished, depending on the classification of activities used, in an increasing degree of analysis detail: (1) (2) (3) (4) (5) (6)

manual activity diagram for operations; manual activity diagram for operations and transport; manual activity diagram for operations, transports and delays; ASME manual activity diagram; fundamental manual activities diagram; chronological manual activity diagram or SIMO diagram.

These models are presented in detail in the next sections. Among them only the SIMO diagram takes into account the duration of activities, incorporating a time scale into the schematic layout. For most real-world tasks, diagram detail for operations, transports, and delays is sufficient. The use of the most refined techniques is only justifiable when the determining factors of the analysis’s detail are critical; that is, when the work is complex, with high-precision, highly repetitive, high risks involved, and cost savings are significant. Construction The manual activity diagram is a schematic model of the detail of a simple operation performed by an operator employing coordinated and/or simultaneous activities of hands or other limbs. The graphical aspect of the diagram suggests that it is formed by detailed process flow diagram for each hand,15 interconnected by simultaneity relations. The definition of the degree of detail coherent with the desired analysis determines the diagram type. Each method studied is broken down into fundamental activities for each hand separately, according to classification, nomenclature, and symbology, related to the type of diagram chosen. The schematic outline is constructed by drawing on the columns or parallel lines of flow associated with each hand, the indicative symbols of the activities, ordered according to the work sequence.

15

From here on, the idea of extending the diagram to other members in action is implicit.

4.4 Analysis of Schematic Models Presentation

159

Symbols for simultaneous activities on both hands are placed on the same line perpendicular to the corresponding flow lines. A summary description of the activity is made next to the symbols, according to the nomenclature of the type diagram. When a change in the activity of one or both hands occurs, the new activity is register in the next line, respecting the simultaneity relations between the activities of the two hands. Except in the SIMO diagram, the passage from one line to another is not associated with the duration of the activities. In the SIMO diagram case, the distance between the different lines of activities is proportional to their duration. In the other diagram types, if necessary, the time of the corresponding activity is indicated next to its symbol. The survey of the task and the constituent micro-activities can be carried out by direct observation or with the help of photographs, cinematographic films, or digital videos, recorded at normal or high speed. The use of film or video in this model should be considered under a criterion of economic feasibility or when direct observation is not possible. High-speed filming, which allows for the “slow motion” effect, is only justified in the construction of SIMO diagrams and only in critical cases. When technically feasible, movements can be recorded using motion capture techniques and computer graphics analysis. In this case, its greatest utility is to allow a better elaboration of the work study or to define a basis for the substitution by artificial facilities. The choice of the start and end points of the task must allow their easy identification and be consistent with the natural evolution of the cycle. This choice, and the observation of the task for recording, are only made after the work has entered the normal regime; that is, the operator has been trained in the task. The diagram can be accompanied, for better understanding and evaluation, of the workplace design and a summary table. The service station drawing shall show the physical arrangement of work elements (such as fixtures, tooling, jigs, controls, sensors, and displays), transport equipment, operator position, and important dimensions. The table plots the observed number of each type of activity, according to the classification used. Use The basic use of the model is associated with the idea of improving the efficiency of the human operator’s repetitive manual movements and activities. The types of work to which the diagram is most often applied are small parts assembly or inspection tasks, packaging, machine control operations. Further, it is highlighted some specific uses for the diagram, in the study of productive operations that meet the previously established conceptualization: (1) Systematic evaluation of existing method or in project The diagram can be applied as an auxiliary instrument in the search for the best method for a set of manual activities. In such study, the diagram is used to make a direct comparison between the alternative methods, evaluating them and highlighting

160

4 Analysis of Schematic Models

possible improvements according to criteria of simplification and economy, such as the “principles of motion economy” (see Barnes 1968, Chap. 17). It is important to emphasize, however, that when used to improve an existing method, due to the diagram enabling a critical evaluation of the represented method, it may inhibit the designer’s creativity. This is because the detail of the record made leads to a fixation on the starting method, which normally limits the search for innovative solutions. The procedure that perhaps provides greater creative freedom and, with it, the discovery of original and possibly more effective solutions, is first to develop alternative methods based on improvement principles or criteria and then to compare the resulting manual activity diagrams. (2) Analysis of equipment controlled by human operator The use of the diagram in this case consists of the study of manual controls of equipment to verify if the operation activities are balanced regarding the use of the set of members of the human body. It also allows highlighting possible simplifications and savings. However, the sensory-motor diagram should be used for a more accurate analysis, encompassing the displays, dials, screens and other information devices of the equipment (see Sect. 4.4.9.2). Another use of the diagram is to simplify and reduce the operator’s time of action. This use aims to reduce machine idle times, due to waiting for the operator to complete the task. (3) Aid in operator learning The use of the manual activity diagram as an element of technical education to workers, employees and artisans, together with the concepts of methods study, helps the operator to form a behavior of attention to the micro-movements and microactivities of his/her body in the performance of manual work. It allows identifying movements and critical situations with risk of accidents or ergonomic dysfunctions. Further, it also helps to emphasize and fix the principles of economy of movements. The ease of construction and critical analysis of the diagram allows the operator to self-organize his/her work method better. (4) New operator training The diagram is a useful instrument in the process of training and adapting operators to new services. It serves to transmit, as the instruction sheets, the established work procedure and to monitor the evolution of the operator’s performance. It can also serve as a record of a standardized method to help avoiding deviations from the accepted optimal standard. Further, it is also a means of aiding in the teaching of special skills. (5) Estimate standard times The construction of the manual activity diagram is the first step of the time predetermination methods – PMTS (MTM, MTS, MTA, etc. (see Fields 1969, p. 71). The estimation of standard time for manual operations, without the use of direct measurement, is important in the design of new ventures to set initial prices of products and

4.4 Analysis of Schematic Models Presentation

161

other planning conditions. It is also useful when it is not possible or convenient to make the direct measurement of times. (6) Marketing or “selling” the production process project The constructive characteristics of the manual activity diagram make it possible to directly emphasize the qualities and merits of a method among others. The diagram is used as an illustrative and/or recording document in the presentation of a production process project, for those who will judge, implement, and use the proposed work methods. Criteria The analysis and improvement criteria relating to the manual activity diagram aim to guide the search for simplifying, safe and economic solutions for the manual work situation, which express an increase in efficiency. The criteria to increase the efficiency of manual work are: (1) balancing the workload of the group of involved body members; (2) attending to simultaneity relationships, through the proper sequencing of the movements and activities of each member; (3) elimination or reduction of non-productive activities and movements; (4) reduced time for each movement and activity, and cycle time; (5) decreased difficulty in performing the task; (6) reduction of operator fatigue; (7) eliminating hazardous situations; (8) reduction of labor costs on the product or service executed. Meeting these criteria, with more emphasis on some, as well as the establishment of supplementary criteria, should be governed by the specific work situation and the type of diagram used. Manipulation The objectives of the manual activity diagram in the study of improvement of the work situation are: (1) (2) (3) (4) (5) (6) (7)

study balancing workload between hands; determine activities that are marginal to the task; discover the causes of abnormal operator placements and positions; reveal seeking, hesitant and reaching movements; discovering inappropriate locations of tools, controls, materials or equipment; analyzing the type and sequence of movements and activities; improve the layout of the work area.

In order to improve the manual work situation, according to the objectives mentioned above and meeting the improvement criteria, some sets of principles for analyzing and manipulating the diagram and the work situation have been elaborated. In light of these principles, which are nothing more than optimizing suggestions, and also the creative ideas of the designer or the operator himself, both the work situation

162

4 Analysis of Schematic Models

and the diagram that represents it are studied. The diagram points out symptoms of inefficiencies and risks as well as possibilities for improvement, allowing action to be taken in the design of the work situation, seeking to apply the principles and innovative ideas. New viable solutions are then represented by the diagram and compared under the improvement criteria. In the iterative process, new analyses of the most efficient solutions are carried out, still seeking possible improvements. Such iterative process may be limited, however, by economic criteria. Below is a set of analysis and manipulation principles: • eliminate unnecessary movements and activities and arrange the remaining necessary movements in a better sequence; • eliminate the activities of holding or retaining with the hands, designing jigs or devices that perform this function; • design symmetrical sequences for both hands; • reduce total activities; • project each micro-activity to be more easily performed by the operator or automated device. Method design scholars such as Barnes, Buffa, Gilbreth, and Maynard have established lists of “principles of motion economy”. These principles, however, are more applicable in manual work that predominantly requires hand and limb movement activities during its execution. The principles of economy of motion suggest an integral treatment for the components of the worksite system, such as operator movements and activities, materials, tools, devices, jigs, transportation equipment, and operator working conditions. Below is a list of 20 principles, adapted by the author from the originals proposed by the scholars cited above. (1) start and finish each micro-movement simultaneously with both hands; (2) use simultaneous hand and arm movements in symmetrical and opposite directions; (3) using manual movements of the lowest rank (automatic or reflexive movements that require little or no conscious mental effort to execute or control) compatible with satisfactory task performance; (4) maintain the trajectory of movements within the normal working area; (5) avoid sudden changes of direction, projecting smoothly curved trajectories and approximately parabolic shape for the movements; (6) use gliders for small objects whenever possible, avoiding picking up and transporting; (7) locate tools and materials in proper sequence, in fixed positions; (8) use the minimum number of micro-movements in order to get the shortest time; (9) use rhythm and automaticity in micro-movements, to increase production and reduce muscle fatigue; (10) relieve the hands of work that can be done with the feet, through pedals;

4.4 Analysis of Schematic Models Presentation

163

(11) avoid holding or retention activities, by using devices or jigs in this function, leaving the hands to manipulate the parts and use the tools; (12) design automatic or foot-operated ejectors to remove finished parts; (13) use gravity feeding and removal whenever possible; (14) decrease transport distances for moves with load, keeping materials close to the operator, using gravity-fed receptacles; (15) pre-position the tools for quick use; (16) pre-position the product for the next operation; (17) locate machine controls near the operator and in functional groups for ease of operation; (18) design the manipulation of controls to be compatible with popular stereotypes and uniform for the entire equipment; (19) design the height of the workplace to allow for sitting and standing work interchangeably whenever possible. Use a chair with adjustable dimensions for height, seat and back that are appropriate for the task and provide good comfort; (20) provide pleasant working environmental conditions and within the comfort range of the individual, considering lighting, temperature, humidity, dust, fumes, noise level, ventilation, color scheme, order, and other ergonomic aspects. It is important to note that for tasks with long continuous time, it should be avoided to make the work schedule too rigid and automated, causing highly monotonous routines for the operator. It should also be noted that the practice of the abovementioned principles could result to the human operator an excessive specialization in highly mechanized tasks, requiring little technical knowledge and almost no commitment of his mind at work. Such facts lead, as a consequence, to an impediment to their technical and mental development, and to an inevitable devaluation of their participation in the production process, resulting in ease of replacement, low salary and alienation. It is precisely in these activities considered inappropriate or devaluing the performance of the human operator that the possibilities of using automated or robotic facilities can be concentrated. A valuable contribution, however, of these principles is the concept of physical order and tidiness of work practice.

4.4.10.1

Manual Activity Diagram for Operations

The diagram for operations is the lowest-detailed variant of analysis. This type meets the need for representation and analysis of tasks consisting of simple activities and without great importance in terms of savings potential. In this case, no distinction is made between the micro-activities, all defined as operations.

164

4 Analysis of Schematic Models

For the construction of the diagram, the task is subdivided into easily perceptible activities, being identified by the respective hand. Activities are recorded in the work sequence and all symbolized as operations on the flow lines relative to each hand. The graphic symbol used is a numbered circle. For activities performed simultaneously by both hands, the same number is given, and their symbols are horizontally aligned. Another convention adopted is the junction of the parallel lines of flow from each hand, at the beginning and end of the cycle, thus identifying these points. The most straightforward analysis criteria are to reduce total activities and cycle duration, and to examine the compatibility of simultaneous activities. It is used when the rough visualization of the method is sufficient for both analysis and communication. It can also be the first step of a more detailed study. Convention:

Operation number 1. Parallel flow lines for each member of the operator under study. Example The example shows the manual assembly process for a washbasin mixer (see Fig. 4.47). The schema only records assembly operations (Fig. 4.63).

4.4.10.2

Manual Activity Diagram for Operations and Transport

This variant already distinguishes between the activities involved in a manual task as operations and transport. In this model, activities are recorded where the hands perform some direct action, such as grasping, positioning, using, or releasing, which will be identified as operations; and activities that involve changing the position of the hands in relation to the work area, identified as transport. Two symbols are used in the graphic construction: a small circle indicating transport and a larger circle indicating operation. Inactive periods are indicated by the continuous vertical line. This distinction of activities already allows the analyst to use the economy of moves approach. In this case, the visual information given by the diagram regarding the simultaneity of hand movements is clearer, as is the number of unnecessary activities, the class in which transports are allocated “a priori”. Another focus of savings is the inactivity represented by the vertical lines between operations or movements.

4.4 Analysis of Schematic Models Presentation

165

Fig. 4.63 Example of a manual activity diagram for operations. Source By the Author, following the model proposed by Morris (1969, p. 40, Fig. 6.4)

166

4 Analysis of Schematic Models

operation

transport

Example The example below shows the recording, by a manual activity diagram for operations and transports, of two methods of assembling clamps: the first with asymmetrical movements, and the second with symmetrical movements and with the placement of the nuts through rotating sockets (Fig. 4.64).

Fig. 4.64 Example of a manual activity diagram for operations and transports. Source Diagram with asymmetrical movements (Method 1): Source: Barnes (1968, p. 116, Fig. 72); copyright @1968 by John Wiley & Sons, Inc. Diagram with symmetrical movements (Method 2) by the Author

4.4 Analysis of Schematic Models Presentation

4.4.10.3

167

Manual Activity Diagram for Operations, Transport and Delays

This model introduces the explicit record of delays, or elements of inactivity, over the previous one. Delays are sub-classified into retention or waiting. Retention defines the act of holding an object in a fixed orientation or position to allow work to be done on the object; it is usually a case of holding the object with one hand and using a tool in the other. Waiting defines the element in which an idle hand occurs, to wait for the performance of an activity by the other or by some external agent, or for having finished its list of tasks in the cycle. The graphic symbol used for retention is inverted delta, with the waiting symbol being double dash. In addition to this distinction, the model separates the transports in which the hand is carrying an object, from the simple movements of changing the position of the hand to reach the places where the elements are arranged on the workbench. They are defined as transport with load and transport without load respectively. The graphical transport symbol is a small circle, with the transport with load symbol drawn with a dash in the middle. The use of this subdivision allows for a more critical analysis of the transports performed.

operation transport without load transport with load retention waiting or inactivity

Example The example below presents a diagram of operations, transport, and delays to the assembly work of a clamp tooth plate for fastening parts for free ends of toothed belts for bidimensional drive (Fig. 4.65).

4.4.10.4

ASME Manual Activity Diagram

The ASME diagram analyzes manual activities of operation, transport or movement, inspection, retention, and delay. The classification and symbols used in this model are from the American Society of Mechanical Engineers (ASME) standard. In this case, however, there are slight changes in the meaning of some elements, in relation

168

4 Analysis of Schematic Models

Fig. 4.65 Example of a diagram of operations, transport and delays

4.4 Analysis of Schematic Models Presentation

169

to the classic definition used in process flow diagrams (flow diagram and map flow diagram). The inspection element refers to the rare micro-activity where the operator’s hand performs a tactile examination of the manipulated part. It should be noted that the model’s study focus is on a sequence of activities that is part of a more comprehensive routine; that is, manual activity is often a sub-set of a process-level routine. Thus, the model can be used to define the elements of a quality control task, for example, measurement and fit checking of a casting, machined or assembled part. The storage element indicates that the hand is holding or retaining a piece, in a fixed position. The delay element indicates situations of waiting or idle. The transport element includes, without differentiating, transport with load and without load. Non-purpose hand movements are classified as delay. The straight line between two symbols indicates that the previous activity continues to be carried out. This usually happens when one of the hands carries out a series of activities while the other is still or holding. As in the case of the single process flow diagram, two types of construction for the schematic model are usual. A construction is made with a blank or checked background, aligning the symbols of the sequences of activities of each hand, according to vertical lines of straight and continuous flows, and parallel for each member (Fig. 4.66). In this case, it is customary to use separate numbers for each activity class and for each member of the operator under study; this provides direct information on the activity type totals. A printed form can be used, on which are drawn the five symbols and all activity description lines for each hand. The record is made by identifying the symbols related to each activity described and joining them through a continuous line. Thus, activity profiles are drawn for each member of the studied operator (Fig. 4.67). The ASME diagram, as well as the diagram of operation, transport and delay, is sufficient for most manual activities in manufacturing processes. In relation to the diagram of operation, transport and delay, the ASME diagram introduces the characterization of the inspection activity but does not differentiate the types of transport, with or without load. Direct critical examination of the diagram to improve the method implies eliminating the activities of holding for both hands, designing templates and proper devices, and eliminating the delay activities. In addition, design a movement model that focuses the use of the hands entirely on the manual processing, and a symmetrical sequence for both hands. The design of the method must, however, meet the general criteria for the study of manual activities, ergonomic conditions and accident risk analysis.

170

4 Analysis of Schematic Models CUSTOMER

STAMP

COMPUTER

PAID CHECKS BOX

KEYBORD

CASHIER

LEFT HAND

WAITING

CASH DRAWER

RIGHT HAND

REACH THE CHECK AT THE COUNTER RECEIVE THE CHECK BRING THE CHECK TO THE COUNTERTOP PLACE THE CHECK ON THE COUNTERTOP

REACH THE KEYBOARD

REACH THE KEYBOARD

TYPE THE CUSTOMER DATA INTO THE COMPUTER

TYPE THE CUSTOMER DATA INTO THE COMPUTER

VERIFY THE SIGNATURE AND THE BALANCE IN THE ACCOUNT

VERIFY THE SIGNATURE AND THE BALANCE IN THE ACCOUNT

MAKE THE CALCULATIONS

MAKE THE CALCULATIONS

TYPE THE WITHDRAWAL AND CHECK THE NEW ACCOUNT BALANCE

TYPE THE WITHDRAWAL AND CHECK THE NEW ACCOUNT BALANCE

REACH THE CHECK AT THE COUNTERTOP

REACH THE STAMP

HOLD THE CHECK

TAKE THE STAMP AND APPLY IT TO THE CHECK INITIAL ON THE CHECK

REACH THE CASH DRAWER

REACH THE CASH DRAWER

GET THE NOTES

GET THE NOTES

TAKE THE NOTES TO THE COUNTERTOP

TAKE THE NOTES TO THE COUNTERTOP

ACCOUNT AND VERIFY THE MONEY PAYABLE

ACCOUNT AND VERIFY THE MONEY PAYABLE

TAKE THE REST IN THE DRAWER

BRING PAYMENT TO THE COUNTER

WAITING

PAY THE CUSTOMER REACH THE CHECK AT THE COUNTERTOP HOLD THE CHECK TAKE THE CHECK TO THE PAID CHECK BOX PUT THE CHECK IN THE BOX

Fig. 4.66 Example of ASME diagram—simple

4.4 Analysis of Schematic Models Presentation

171

Fig. 4.67 Example of ASME diagram—form. Source Close (1960, p. 196, cart 8.8); copyright @ 1960 by John Wiley & Sons, Inc.

172

4 Analysis of Schematic Models operation transport or motion tactile inspection delay retention

Example Example 1 Shows the diagram of manual activities of the operation of paying checks by a commercial bank teller. Example 2 Shows the form record of the two-handed working method of an operator performing an inspection on electric spot-welding units. The test consists of inserting the units in the sockets (TE and TD) of the meter and verifying that the value indicated on the displays is within the standard. The tested feature is the omics resistance.

4.4.10.5

Fundamental Manual Activities Diagram

The fundamental manual activities diagram lends itself to the analysis of human operator manual tasks with a high degree of detail. To meet the refinement of detail, the subdivision of the task is done according to an established set of distinct categories of fundamental micro-activities. Fundamental micro-activities are understood as the tiny elements that subdivide into the smallest possible portions the manual tasks performed by the operator’s members and which are observable in any type of manual work. Fundamental microactivities, also known as “therbligs”16 or fundamental movements, are productive or service elements. The identification and standardization of the different fundamental activities defines a kind of alphabet, which aims to make it possible for any manual task to be reconstituted by a composition of the basic micro-elements. This “assembly” of the task by basic elements is advantageous in the design of new work methods. Basically, for activities performed by the human operator’s hands, 18 “therbligs” are identified. Each “therblig” is associated with a standard name, abbreviations, a special graphic symbol and a color tone. Color coding is especially important in SIMO diagram construction (Sect. 4.4.10.6 ahead). In addition to those listed in Fig. 4.68, other types can be developed for the other body members, such as defining speech activities or eye movement in more specific inspection. 16

The term “therblig” is an anagram of the name of a pioneer of the study of micro-activities, Frank B Gilbreth (Gilberth 1911), who researched the basic fundamental activities.

4.4 Analysis of Schematic Models Presentation Nr.

Symbol

Name

Abrev.

Colour

173 Description

1

GRASP

G

Dark red

Grasping an object with empty hand

2

HOLD

H

Gold

Holding an object

3

SEARCH

SH

Black

Attempting to find and object using the eyes and hands

4

SELECT

ST

Light gray

Choosing among several objects in a group

5

POSITION

P

Dark blue

Positioning an object in a defined location

6

PLAN

PN

Dark brown

Deciding on a course of action

7

AVOIDABLE DELAY

AD

Light yellow

Waiting withih worker‘s control which causes idleness

8

UNAVOIDABLE DELAY

UD

Dark yellow

Waiting due to factors beyond worker‘s control

9

PRE-POSITION

PP

Light blue

Positioning and object for the next operation

10

TRANSPORT EMPTY

TE

Light green

Reaching for an object with an empty hand

11

TRANSPORT LOADED

TL

Dark green

Moving an object using a hand motion

12

REST

R

Orange

Resting to overcome fatigue, pausing motions of hands

13

INSPECT

I

Light brown

Determining quality of an object using hands and/or exes

14

RELEASE LOAD

RL

Light red

Releasing control of an object

15

USE

U

Purple

Manipulating a tool during a work task

16

ASSEMBLE

A

Dark violet

Joining parts together

17

DISASSEMBLE

DA

Light violet

Separating components that were joined

18

FIND

FI

Dark grey

A momentary mental reaction at the end of a search

Fig. 4.68 Definition and representation of “therbligs”. Source By the Author, based on Fields (1969, p. 66, Fig. 6.4); copyright @ 1969 The Orion Publishing Group

It is worth to note that in this model, activities are viewed differently from other manual activities diagrams. This is because the analysis and classification is based on fundamental elements of the activities of the operator’s body members, which are identified based on the objective of the activity performed, rather than on process elements, which represent what happens with the tools or materials handled. The refinement of detail achieved with the fundamental activities diagram only makes its use justifiable in highly repetitive manual operations with high savings potential, in high-precision activities (such as surgical operations) or in work study laboratory, and automation and robotization research. The survey of the constituent elements of the task, for the construction of the diagram, can be done by means of direct visual observation, photographic, video or digital techniques. Direct visual observation should be made about the normal method of performing the task, as changing the pace or speed of execution alters the composition of microactivities. It is good to emphasize this fact because it would seem advantageous to observe the task, to execute it slowly, which could lead to registry distortions. The slow execution, however, is valid in training tasks that involve delicate handling or highlighting key points. The instructor in this case must be aware of the possibility of involuntary alteration of the method.

174

4 Analysis of Schematic Models

The study of micro-activities with the use of films or digital sensors (transponders or markers), due to the possible high cost, in general, only justifies for jobs with many activities, where the duration and repeatability are large. It is also used when the human eye is not capable of following and perceiving the fundamental activities of the operator’s members employed in the task, given a quick sequential execution. The graphic construction of the fundamental manual activities diagram follows the same basic idea as its similar ones: • vertical parallel columns to record the activities of each operator’s hand17 ; • when simultaneous two-handed activities occur, the symbols are placed in the same respective horizontal line; • the change of activity is simply indicated by moving to the next line, regardless of a time scale; • the occurrence of blank lines in the column of one of the hands, where symbols are not drawn, indicates that the last recorded activity is still in execution. In addition to the common uses of manual activity diagrams, the fundamental activity diagram has special application in the study of simplification of highprecision tasks, in the training of operators, instructors, and designers of methods, and, mainly, in the predetermination of standard times. In obtaining predetermined times for task cycle duration, the fundamental activity diagram is used as an auxiliary instrument. The diagram analyzes and records the task through the fundamental micro-elements. One of the time predeterminations models18 is applied to it, which convert each activity category, considering the influencing factors (particular conditions of execution of activities), into synthetic time units. For critical examination, the fundamental micro-activities are divided, according to Niebel (1967, p. 172) into effective and ineffective. Effective activities directly execute the task and ineffective activities do not affect the physical evolution of work. Effective ones are sub-classified into physical and objective; ineffective ones into sensorial (or mental) and delays (Table 4.12). The criteria for improving work methods are to reduce and make effective activities more efficient and eliminate the ineffective activities. Thus, if the set of projected activities consists only of effective elements (physical and objective) the execution of the task is more efficient, from a mechanical point of view. This is advantageous as it makes possible the automation or robotization of the task at a later stage. However, if the designed method must be performed by a human operator, meeting these criteria can lead to excessively monotonous work. In that case, one should seek to balance and enrich the service with higher-level mental or sensorial activities. 17

Maintaining the validity of the record by the diagram of other body members involved in the execution of the task. 18 Synthetic time predetermination models (or Predetermined Motion Time Systems—PMTS) are part of the motion time study where several models have been developed, such as MTM (MethodsTime Measurement), MTS (Motion-Time Standards), Work Factor, MTA (Motion-Time Analysis), BMTS (Basic Motion-Time Study) and DMT (Dimensional Motion Times).

4.4 Analysis of Schematic Models Presentation Table 4.12 Definition of effective and ineffective activities

Effective activities

175

Physical

Grasp Transport Pre-position Release Hold Change direction

Objective

Use Assemble Disassemble

Ineffective activities Sensorial or mental Search Relation Position Inspect Find Plan Delays

Unavoidable delay Avoidable delay Rest

In Table 4.13, suggestions for improvements are indicated on each elementary activity. Example The example shows a fundamental manual activities diagram for a process of removing the scrap of a die casting bathroom faucet body by means of a double puncher. The faucet body is placed in a positioning devise, and the puncher is manually activated to hammer out the scrap (Fig. 4.69).

4.4.10.6

Chronological Manual Activity Diagram or SIMO Diagram

The SIMO diagram consists of the schematic record of the micro-activities that are part of the manual task as a function of the elementary duration times, in order to establish an exact simultaneity relationship between the activities performed by the hands and other involved members of the operator. The model is distinguished from other manual activity diagrams by introducing the time variable explicitly in the graphic design. The visual information on the magnitude of the elementary times spent allows for the relative importance of each micro-activity in the set to be highlighted. This data is especially important in the study of improvement of the work method and its possible automation or robotization. In the classic form of the SIMO diagram, the task is analyzed by means of photographic, film, video, or computational techniques and is subdivided into elements

176

4 Analysis of Schematic Models

Table 4.13 Suggestions for improvements of fundamental activities No.

Fundamental micro-activities (“therbligs”)

Definition

Improvement

1

Grasp

The act of establishing contact with and controlling an object; it may consist of finger contact, grasping with fingers, or with the whole hand

Design the objects’ containers and locations so that they are easier to grasp

2

Hold

The act of holding or supporting a stationary object with the hand, under control, supported or not, for a certain period of time; usually one hand holds the object for the other to perform an operation

It must be eliminated, designing a device that holds the object in the desired position, or that allows supporting the object; bear in mind that the hand is seldom an efficient means of holding objects firmly

3

Search

The act of seeking to locate objects; it can be done by the hands with the touch, or with the aid of the eyes; this element terminates when the object is found or focused

It should be eliminated whenever possible; workstation design must provide for fixed locations for each component so that the trained operator knows in advance where each one is

4

Select

The act of choosing and separating by hand, by touch or with the help of the eyes, one or more objects from a similar group

It must be eliminated, by means of an appropriate design of the containers that allow prior separation and scheduled delivery of the desired number of objects at a time

(continued)

4.4 Analysis of Schematic Models Presentation

177

Table 4.13 (continued) No.

Fundamental micro-activities (“therbligs”)

Definition

Improvement

5

Position

The act of rotating Placing the object in the desired position can be or orienting an improved by designing guides or adjusting and object to fit it into a inputting facilities defined placement or location; it is often a precise act and requires mental and physical control

6

Plan

Mental process of setting up a program or scheme of action; or deciding between alternatives on next actions

It can be eliminated or reduced by identifying possible doubts and hesitations during the work cycle and operator training; on the other hand, inclusion in the “planning” cycle can reduce the monotony of work

7

Avoidable delay

Hand inactivity during the work cycle, due to an interruption of work by the operator, intentional or unintentional, that is not a necessary part of the cycle

Only the operator is responsible for this delay and can be avoided In most cases, it should be regarded as an occasional element; when frequent, the cause must be looked for in the operator’s method or procedure

8

Unavoidable delay

Inactivity of the hand during the work cycle, outside the operator’s control; the interruption of work in this case may be foreseen and necessary to attend to the process or some impediment

To eliminate these delays, it is necessary to re-study the process or the work method employed

(continued)

178

4 Analysis of Schematic Models

Table 4.13 (continued) No.

Fundamental micro-activities (“therbligs”)

Definition

Improvement

9

Pre-position

The act of placing This manual action can be replaced by an object in pre-positioning devices like guides, conveyors, advance in a and feeders determined location to be grabbed and held when necessary, in the evolution of the work cycle

10

Transport empty

The act of moving the hand (or other limb) without load or resistance to movement from one point of the workplace to another during the cycle

The time of this movement depends on the distance covered by the hand; in general, it is not possible to eliminate, and should seek to reduce movement distances by locating the components closer to each one at the workstation

11

Transport loaded

The act of moving an object or load with the hand, or against resistance; can be carry in air or pushing

The timing of this movement depends on distance, weight or resistance, and type of movement; it is usually difficult to eliminate, and the movement time can be reduced, trying to shorten the distances covered, relieving the load and improving the type of movement through gravity fall or the use of conveyors or sliders

12

Rest

Delay or allowance of time for the operator to recover from the fatigue in the muscles of the hands, other limbs and sense organs, employed in the execution of the work cycle

This delay must be foreseen whenever the repetitiveness or the workload implies cumulative fatigue for the operators; their fatigue can be mitigated by adapting the work method to the use of their muscles, sense organs and body positions; other factors that influence are the environmental working conditions (lighting, ventilation, temperature, noise, humidity) and the physical dimensions of the workplace (height and reachable areas, dimensions of seats and benches, distances between the components handled); whenever possible, devices should be used to move stationary loads and perform highly repetitive and mechanized activities (continued)

4.4 Analysis of Schematic Models Presentation

179

Table 4.13 (continued) No.

Fundamental micro-activities (“therbligs”)

Definition

Improvement

13

Inspect

The act of comparing, testing, or examining some feature of an object, in relation to a pattern, with the hands by touch or the sense organs; in general, it involves a mental reaction

The time it takes the inspection depends on the level of investigation and the difficulty of the decision; whenever possible, use pass-no-pass gauges and better technical conditions for carrying out the inspection; if it is economically or technically justifiable do use automatic devices

14

Release load

The act of giving In general, there is no need for improvement up control of the due to the short time of this element; whenever object by the hands possible use expulsion devices or sliders and try to foresee releasing the object during a movement

15

Use

The act of controlling an object (generally a tool or manual device) to perform productive work, resulting in changes in the characteristics of the product or material handled

The duration of this activity depends on the type of operation, precision and quality of service, the method, tools and devices used, and the skill of the operator; on these factors, the search for improvement is carried out

16

Assemble

The act of assembling parts

It depends on the method of assembly and the design of the object to be assembled

17

Disassemble

The act of separating parts

It depends on the disassembly method and the design of the object to be disassembled

18

Find

Mental reaction resulting from successful search for objects with hands

It depends on the work method and the product or service design

by the classification of fundamental micro-activities (“therbligs”). Thus constructed, the diagram constitutes the most refined model for the study of micro-activities, regarding the degree of detail and degree of precision. The other classifications of micro-activities, mainly operations-transport-delay and ASME, can be used in the construction of SIMO diagram. However, the imprecision of these classifications may invalidate the application of the time scale in some cases.

180

4 Analysis of Schematic Models

Fig. 4.69 Example of a fundamental manual activities diagram using “therbligs”

The graphic format of the SIMO diagram is similar to that of the simultaneous activities diagram, changing only the level of coverage. The basic idea is that the representation of the micro-activities keeps a direct proportionality relationship with the respective duration times. For this purpose, the parallel vertical columns of each member involved are divided into sections whose size is proportional to the duration of the micro-activity they represent. In other words, the horizontal lines that indicate the activity change are separated according to a time scale. It should be noted that in the other diagrams of manual activity previously presented, the distance between the lines is constant, not depending on the time elapsed in the execution of the activities.

4.4 Analysis of Schematic Models Presentation

181

When constructed for the study of an existing method, the analysis of microactivities and the evaluation of elementary times can be done by direct visual observation or by means of photographic or computational technique. The analysis of micro-activities usually follows the classification of fundamental micro-activities (or “therbligs”), as it is more coherent with the degree of detail provided by the SIMO diagram. The evaluation of elementary times by visual observation is carried out with stopwatches or electronic time counters. Direct visual observation requires that the analyst is quite familiar with distinguishing and identifying micro-activities, and that there is no possibility for the operator to considerably vary the work method with the cycles. The evaluation of the elementary times per filming is done using the techniques of the micro-chronometer or the frame count. The micro-chronometer technique consists of filming the task by placing a special clock on the scene frame; the joint projection of the evolution of the task and the clock allows identifying the microactivities and measuring the respective duration times. Such clock, called a microchronometer, is divided into intervals in “wink” units equal to 1/2000 of a minute, which constitutes the normal threshold of perception of movement by the human eye. The frame counting technique implies using special camcorders that have a constant speed controller and a frame per minute counter; the frame-by-frame projection of the film makes it possible to identify the distinct micro-activities of each member, and the counting of the number of frames in which each distinct micro-activity appears being performed, from the beginning to the end, is converted into the duration of the micro-activity. The analysis of micro-activities is obviously more accurate when done through filming, where it is possible to examine the task in detail, looking at the film frame by frame, as described above. When required, viable and available the use of motion capture techniques and computer graphics analysis can reach a very precise micro-motion study and facilitate the construction of the SIMO diagram with fine degree of detail. In the study of method in design or as an alternative to other techniques presented, the elementary times can be evaluated by techniques of predetermination of times. It is important to note that the evaluation of the elementary times and the cycle time is only complete with the determination of the standard times. For this, it is necessary to use work measurement techniques, which effect the correction of times and the depersonalization of the task, when considering the pace factor, personal tolerances, fatigue, environmental conditions, and other influencing factors. For the study of work methods, however, it is sufficient in most cases to simply determine the normal time (observed time corrected in relation to a work rhythm established as normal).

182

4 Analysis of Schematic Models

The visual identification of the sections that subdivide the columns related to the operator’s members according to the component micro-activities, can be done by color coding or by graphic lines. Next to each section is drawn the symbol and other corresponding information. The SIMO diagram, due to its high degree of detail and the additional work of time measurement, is only justified in cases where the defining factors of the degree of detail are critical, in special projects or in research. Or even when the time variable influences with high relative importance, it clearly shows where there is unnecessary inactivity or sequences of chronologically exaggerated activities. Typical cases of using the SIMO diagram are: • situations where a large number of operators perform the same repetitive task over a long period of time; • design and development of high-precision equipment, which is affected by the human element’s operating method; • training in tasks where it is necessary to be highly aware of the activities and movements carried out, in terms of looking for possible savings and controlling risks of accidents or mistakes. Convention: • Activity change boundaries are graded proportionally to the duration of activities, according to a time scale. • Symbology and coding—according to the fundamental manual activities diagram, and eventually, other manual activity diagrams. Example The example shows the SIMO diagram of an operation of assembling the camshaft of an internal combustion engine with a head cam on an assembly line for automobile engines (Fig. 4.70).

References

183

Fig. 4.70 Example of SIMO diagram. Source Krick (1962, pp. 100, Fig. 24); copyright @1962 by John Wiley & Sons, Inc.

References ASME (1947, 1952) Operation and flow process charts. ASME Standard. The American Society of Mechanical Engineers, University of Michigan Libraries, New York Barnes RM (1963) Work methods manual, 9th edn. Wiley, New York Barnes RM (1968) Motion and time study. Design and measurement of work, 6th edn. Wiley. New York Bianchini W (2016) Melhoria dos processos de retaguarda; in Valle, Oliveira Bitencourt M (2009) Modelagem de Processos com BPMN. Projeler, http://www.projeler.com.br/ download/pdf/artigo_bpmn_projeler_mauricio_bitencourt.pdf. Visited on 22 Nov 2022 Borgatti SP, Everet MG, Johnson JC (2018) Analyzing social networks. Sage Publications BPMN Quick Guide (www.bpmn.org). Visited on 29.11.2022

184

4 Analysis of Schematic Models

Briol P (2008) BPMN, the business process modeling notation handbook, 1st edn. Lulu.com. 12 Apr 2008 Buffa ES (1969) Modern production management, 3rd edn. Wiley, New York Close GC (1960) Work Improvement, 1st edn. Willey, New York Debevoise T, Geneva R (2008) The microguide process modeling in BPMN. Booksurge Dorogovtsev SN, Goltsev AV, Mendes JFF (2006) K-core organization of complex networks. Phys Rev Lett 96:040601 Faccio M, Ferrari E, Gamberi M, Pilati F (2019) Human factor analyser for work measurement of manual manufacturing and assembly processes. Int J Adv Manuf Technol. https://doi.org/10. 1007/s00170-019-03570-z Ferrari E, Gamberi M, Pilati F, Regattieri A (2018) Motion analysis system for the digitalization and assessment of manual manufacturing and assembly processes. IFAC-PapersOnLine 51(11):411– 416 Fields A (1969) Method study, 1st edn. Cassel & Company Ltd., London Gilbreth FR (1911) Motion study. D. Van Nostrand Co., New York, p 1911 Karger DW, Bayha FH (1966) Engineered work measurement, 2nd edn. Industrial Press Inc., New York Kehl SAP, Iida I (1970) Arranjo Físico, DEP/USP. São Paulo Krick EV (1962) Methods engineering: design and measurement of work methods. Wiley, New York, London Krick EV (1971) Métodos e Sistemas. 1ª edição. Livros Técnicos e Científicos Editora Ltda., Rio de Janeiro Machado FD, Comunello E, Fernandes AMR (2012) Análise do Movimento Humano por Videogrametria. In: Simpósio de Excelência em Gestão e Tecnologia. Universidade do Vale do Itajaí Maynard HB (1963) Industrial engineering handbook, 2nd edn. McGraw-Hill Book Company Inc., New York, Toronto, London Morris JW (1969) Principles of work study, 1st edn. William Heinemann Ltd., London, p 1969 Muther R (1955) Practical plant layout, 1st edn. McGraw Hill Book Company Inc., New York Nadler G (1970) Work design a system concept. Revised edition. Richard D. Irwin Inc., Homewood, Illinois, p 1970 Niebel BW (1967) Motion and time study. Richard D. Irwin Inc., Homewood Niebel BW (1970) Ingenieria Industrial – Estudio de Tiempos y Movimientos- 1ª edicion, Representaciones y Servicios de Ingenieria, SA. Mexico Niebel BW, Freivalds A (2009) Ingenieria Industrial. Métodos, estándares y diseño del trabajo. 12. Edición. The McGraw Hill Companies, Inc. 2009 OIT-ILO (1973) Introducción al Estudio del Trabajo, Oficina Internacional del Trabajo (OIT-ILO), Jornal de Genéve OMG (2011) Business process model and notation (BPMN), Object Management Group, version 2.0, OMG document number: formal/2011-01-03. http://www.omg.org/spec/BPMN/2.0 OMG (2014) Business process model and notation—BPNM, Object Management Group, version 2.0, Jan 2014. www.omg.org/spec/BPMN/2.0.2. Visited on 22 Nov Reichert G (1967) Estudo e medida do trabalho. Mimeo. Departamento de Engenharia de Produção, USP. São Paulo Seidl da Fonseca R (1975) Sistema home-máquina – uma proposta de conceituação. Arquivos Brasileiros de Psicologia Aplicada 27(1):202–210 (Rio de Janeiro, Brasil) Starr MK (1971) Administração da Produção – Sistemas e sínteses. 1ª edição. Editora Blücher Ltda. São Paulo Ureta LHH (1973) Análise ergonômica de um sistema hombre-máquina. MSc thesis. COPPE/UFRJ, 1973 Valle R, Oliveira SB (2016) Análise e Modelagem de Processos de Negócio: foco na notação. BPMN, Editora Atlas

References

185

Wasserman S, Faust K (1994) Social network analysis: methods and applications. Cambridge University Press, Cambridge Whitmore D (1970) Work study and related management services, 2nd edn. William Heinemann Ltd., London