Robot Reliability and Safety

B.S. DhillonRobot Reliabilityand SafetyWith 35 IllustrationsSpringer-VerlagNew York Berlin Heidelberg London ParisTokyo Hong Kong Barcelona Budapest

B.S. DhillonEngineering Management ProgrammeFaculty of EngineeringUniversity of OttawaOttawa, OntarioCanada KiN 6N5Printed on acid-free paper. 1991 Springer-Verlag New York, Inc.Softcover reprint of the hardcover 1st edition 1991All rights reserved. This work may not be translated or copied in whole or in part without thewritten permission of the publisher (Springer-Verlag New York, Inc., 175 Fifth Avenue, NewYork, NY 10010, USA), except for brief excerpts in connection with reviews or scholarly analysis.Use in connection with any form of information storage and retrieval, electronic adaptation,computer software, or by similar or dissimilar methodology now known or hereafter developedis forbidden.The use of general descriptive names, trade names, trademarks, etc., in this publication, even ifthe former are not especially identified, is not to be taken as a sign that such names, as understoodby the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone.Typeset by Asco Trade Typesetting Ltd., Hong Kong.9876 54 32 1ISBN-13 :978-1-4612-7814-6001: 10.1007/978-1-4612-3148-6e-ISBN-13 :978-1-4612-3148-6

This book is affectionately dedicatedto my son Mark

PrefaceRobots are increasingly being used in industry to perform various types oftasks. Some of the tasks performed by robots in industry are spot welding,materials handling, arc welding, and routing. The population of robots isgrowing at a significant rate in various parts of the world; for example, in 1984,a report published by the British Robot Association indicated a robot population distribution between Japan (64,600), Western Europe (20,500), and theUnited States (13,000). This shows a significant number of robots in use. Dataavailable for West Germany and the United Kingdom indicate that in 1977there were 541 and 80 robots in use, respectively, and in 1984 these numberswent up to 6600 and 2623, respectively. Just as for other engineering products,the reliability and safety of robots are important.A robot has to be safe and reliable. An unreliable robot may become thecause of unsafe conditions, high maintenance costs, inconvenience, etc. Robotsmake use of electrical, mechanical, pneumatic, electronic, and hydraulic parts.This makes their reliability problem a challenging task because of the manydifferent sources of failures. According to some published literature, the bestmean time between failures (MTBF) achieved by robots is only 2500 hours.This means there is definite room for further improvement in robot reliability.With respect to safety, there have been five fatal accidents involving robotssince 1978. A Swedish report stated that in Sweden there were 36 accidentsinvolving robots that caused human injury during the period 1979 to 1983.Furthermore, Japanese findings indicate that 8% of persons working withrobots have been injured, and as many as 36% of them have experienced anaccident of some sort. Because of such situations, the robot safety issue hasbecome of the utmost importance. Hence, one may say that robot reliabilityand safety are the most challenging problems to be dealt with, and this bookfocuses on both of these important areas.The main objective of this book is to be wide in scope, in particular withrespect to reliability. However, some areas of reliability, such as softwarereliability and fault tolerance, are not covered in depth due to several factors:space limitation, the size of computer software and hardware in robots inrelation to general computer systems, etc. Some general concepts presented invii

viiiPrefaceChapter 2 can be applied in the case of fault tolerance. For example, triplemodular redundancy (TMR) is probably the most discussed term in computerredundancy reliability, and is basically a special case of the k-out-of-n systemwith a voter. The k-out-of-n system is described in Chapter 2. In any case, forfurther studies of computer software and hardware reliability and other areas,the relevant references are cited at appropriate places in the text.This book is the result of filtering through almost all of the publishedliterature on robot reliability and safety, as is evident from the listed referencesin the book. The book is intended for readers such as practicing engineers andsenior undergraduate and graduate students with no previous knowledge ofthe subject. In general, emphasis is on the structure of concepts rather than onmathematical rigor and minute detail. The sources of most of the materialpresented are given in the references, ifthe reader wishes to delve deeper into aspecific area. The book contains over 750 references and approximately 40solved examples. The references will provide the reader with further information on relevant topics.Twelve chapters and an appendix constitute Robot Reliability and Safety.The purpose of Chapters 1 to 3 is to provide the necessary background to helpin understanding the remaining chapters of the book. Chapter 1 briefly discusses robots and robot reliability and safety histories, basic terms and definitions, and the scope of the book. Introductory aspects of general reliability andsafety are presented in Chapter 2. Chapter 3 consists of basic robotics; thisallows the reader to familiarize himselfjherself with the subject of robotics, orif he/she already possesses such a background on the said topic, to refreshhisjher memory. The topic of robot accidents is discussed in detail in Chapter4. This chapter covers subjects such as real-life examples of robot accidentsin Japan, Western Europe, and the United States; causes and characteristicsof robot accidents, effects of robot accidents, and robot accident analysis andprevention. Chapter 5 discusses various fundamental aspects of robot safety:Some of these are robot safety problems; the use of robots to promote safety;weak points in planning, design, and operations causing safety problems; themanufacturer's and user's role in robot safety; and robot safeguard methods.Several topics related to robot safety are discussed in Chapter 6: These includerobot safety education, safety considerations in robot testing and start-up,commissioning and acceptance, safety considerations in robot welding operations, robot safety in the automobile industry, robot safety standards, androbot safety research.Chapter 7 covers human factors in robotics. Human factors play an important role regarding robot reliability and safety. Topics such as robots versushumans, human factors' issues during the factory integration of robot systems,benefits and drawbacks ofrobotization from the standpoint of human factors,guidelines for safeguarding the operator and the teacher, human error datain robotics, and the mathematical modeling of robots with respect to humanerror are described. A mathematical model presented in this chapter is applicable when the robot system failure times due to humans or nonhumans are

Prefaceixexponentially distributed. If different human error rates occur during robotteaching, operation, and design, one should take an average of these threerates and then use the resulting figure in the derived model equations. However, if distinct probabilities are required for each of these three distinct modes,then the new equations can be developed in a similar manner.The subject of robot reliability is discussed in depth in Chapter 8. Manyreliability-related topics are covered in this chapter: robot-related failureterms, general categories of robot failures and their protection, selected references related to robot reliability, types of robot halts and warm restarts,hazard detector's fail-safe design, guidelines for developing a robot reliabilitystandard, robot reliability measures, and a reliability analysis of electric andhydraulic robots with the aid of block diagram and fault tree methods.Chapter 9 discusses the important subject of robot maintenance; this subjectis related to robot reliability, because poor maintenance leads to poor reliability. Failure data and analysis are discussed in Chapter 10, and are vitalfor robot-reliability analyses. This chapter covers many topics, some of whichare reliability-related data sources, failure data for selected items and tasks,and the hazard plotting method. Economics generally plays an importantrole in robot reliability and safety analyses; therefore, Chapter 11 is totallydevoted to this theme and discusses various aspects of robot economics. Thetopics covered are concerned with factors for installing robots, robot installation costs, robot economic techniques and methods for making robotfinancial decisions, robot life-cycle costing, and robot associated-cost estimation models. Robot testing is very important in the reliability evaluation ofrobots under development; thus, Chapter 12 discusses robot testing and thepertinent information related to robots. Some of the topics covered in thischapter are robot performance testing, robot reliability testing, robot specifications, and general information on robots. The appendix lists over 460references on robot reliability and safety and related areas.The author wishes to thank the editorial department at Springer-Verlag NewYork, Inc., for their close interest in this project. The author is indebted to hisrelatives, students, and friends for their interest, help, and encouragement inmoments of need. Last, but not least, I thank my wife, Rosy, for typing theoriginal manuscript and for her help in proofreading. During the preparation ofthe manuscript, her patience and tolerance were also appreciated.Ottawa, OntarioB.S. Dhillon

ContentsPrefaceviiCHAPTER 1Introduction1.1. History of Robots1.2. Brief History of Robot Reliability and Safety1.3. Terms and Definitions1.4. Scope of the BookSummaryProblemsReferences11234445CHAPTER 2Introduction to Reliability and Safety2.1. Introduction2.2. Reliability and Safety-Related Terms and Definitions2.3. Organizations Concerned with Reliability or Safety, or Both2.4. Reliability and Safety Periodicals and Conferences2.5. Reliability and Safety-Related Data Sources2.6. Selective Texts on Reliability and Safety2.7. Reliability2.8. CHAPTER 3Introduction to Robotics3.1. Introduction3.2. Some Attributes of Robots Available Commercially, Major Usersof Industrial Robots in Japan, and the United States' RobotEstimates by Application3.3. Robotics Research and Robot Application Areas3.4. Advantages of and Motivations for Using Robots, andArguments Against Robots3434353536xi

xiiContents3.5. Comparisons of Humans with Machines, Generations of Robots,and Robot Qualities Being Sought by Roboticists3.6. Areas of Commonly Asked Questions by Potential Robot Users,Factors for Using Robots Instead of Humans, and Rules andProcedures for Introducing Robots3.7. Robot Classifications, Production Robots, and Robot StructureCategories3.8. Robot Mechanical Design Decisions and Useful Guidelines,and Important Physical and Operational CharacteristicsVital for Robot Selection and Design3.9. Robot Public Relation 7CHAPTER 4Robot Accidents4.1. Introduction4.2. Real-Life Examples ofRobot Accidents4.3. Robot Accidents in Japan, Western Europe, and the United States4.4. Causes and Characteristics of Robot Accidents4.5. Effects of Robot Accidents and Periods Off Work Due toRobot Accidents4.6. Robot Accidents at Manufacturer and User Sites4.7. Robot Accident Analysis and 0656666CHAPTERSFundamentals of Robot Safety5.1. Introduction5.2. Robotic Safety Problems and Hazards, and the Use ofRobots to Promote Safety5.3. Weak Points in Planning and Design, and Operations CausingSafety Problems5.4. The Manufacturer's and User's Role in Robot Safety5.5. Safety Considerations in Robot Design, Installation,Programming, and Operation and Maintenance5.6. Robot Safeguard 83CHAPTER 6Topics in Robot Safety6.1. Introduction6.2. Robot Safety Education858585

Contents6. Considerations in Robot Testing and Start-Up,Commissioning, and AcceptanceSafety Considerations in Robot Welding OperationsRobot Safety in the Automobile IndustryStopping Grippers of Industrial Robots Not DroppingjThrowingWork Items When Experiencing Energy Loss or Not Grippingon the Return of EnergyRobot Standardization and Safety StandardsRobot Safety 89899CHAPTER 7Human Factors in uctionRobots Versus HumansHuman Factors' Issues During the Factory Integration ofRobotic SystemsBuilt-In Human Biases and Some Design Improvement Guidelinesfor Improving Robot Operator Comfort and ProductivityBenefits and Drawbacks of Robotization from the Standpoint ofHuman Factors and Rules of Robotics with Respect to HumansHumans at Risk from Robots and Guidelines for Safeguardingthe Operator and the TeacherHuman Factors' Considerations to Robotic SafetyTraining for Reducing Human Error in Robotics andHuman Error Data in RoboticsReliability Analysis of a Robot System with Human 9110111112117117118CHAPTER 8Robot Reliability8.1.8.2.IntroductionRobot-Related Failure Terms, Robot Failures, andLiterature on Robot Reliability8.3. General Categories of Robot Failure and Their Protection8.4. Types of Robot Halts and Warm Restarts8.5. Robot Effectiveness and Hazard Detectors Fail-Safe Design8.6. Robot Reliability Surveys and Guidelines for Developinga Robot Reliability Standard8.7. Robot Reliability Measures8.8. Reliability Analyses of Electric and Hydraulic 27129134146147147

xivContentsCHAPTER 9Robot ctionGeneral Maintenance Functions and Types of MaintenanceRobot Maintenance Needs and TypesRobot Parts and Special Tools for Maintenance and RepairRobot Warranty Coverage and Preventive Maintenance KitsRobot InspectionSome Guidelines for Safeguarding Robot Maintenance PersonnelSome Models Useful in Performing Robot 2153154157158166167167CHAPTER 10Failure Data and Analysis16910.1. Introduction10.2. Uses of Failure Data with Respect to Robots10.3. Failure Reporting and Documentation System for RobotslOA. Reliability Data Sources10.5. An Approach for Establishing an Event Data Bank, the Failure ReportForm, and Major Difficulties Associated with Failure Recording10.6. Robot Inspection and Repair Records10.7. Documents, Banks, and Organizations for Obtaining Failure Datafor Robot Reliability Studies10.8. Failure Data for Selected Items and Tasks10.9. Hazard Plotting 74174184189192193CHAPTER 11Robot 195196197202204205208208209IntroductionFactors for Installing Robots and Advantages of RobotizationCost ofInstalling Robots and Their Economic BenefitsBasic Robot Economic TechniquesMethods for Making Robot Financial DecisionsRobot Life Cycle CostingRobot Associated Cost Estimation ModelsSummaryProblemsReferencesCHAPTER 12Robot Testing and Information Related to Robots21012.1. Introduction12.2. Robot Performance Testing210210

Contents12. Reliability TestingSelective Mathematical ModelsRobot SpecificationsGeneral Information on 2225APPENDIXBibliography of Literature on Robot Reliability and Safetyand on Related Areas226A.I. IntroductionA.2. Robot Reliability and SafetyA.3. Robot MaintenanceA.4. Robot EconomicsA.5. Miscellaneous226226244246248Index251

standard, robot reliability measures, and a reliability analysis of electric and hydraulic robots with the aid of block diagram and fault tree methods. Chapter 9 discusses the important subject of robot maintenance; this subject is related to robot reliability, because poor maintenance leads to poor reli ability.