INVESTIGATING THE EFFECTS OF PHYSICAL AND COGNTIVE DEMANDS ON QUALITY OF PERFORMANCE AND SUBJECTIVE RESPONSES UNDER PACING/TAKT TIME BY SHAKIL AHMED SHAIKH Thesis submitted to the University of Nottingham for the degree of Doctor of Philosophy 2015 Abstract Assembly work requires high levels of performance and quality but may involve complex cognitive and physical tasks. There is evidence that physical and cognitive workloads are not separate, but may interact. Work in exercise and simple physical tasks suggests that physical load may lead to changes in cognitive performance, and in perceived workload. The aim of this thesis is to examine physical and cognitive interactions that might affect assembly work. First, observation was undertaken in industry to identify the physical and cognitive factors relevant to examples of assembly lines. From this, a task analysis of a simulated assembly task was developed. Three experimental studies were conducted, based upon the simulated assembly task, in order to investigate three main assembly variables; working height, memory load and pacing. The first study showed that the number of completed assemblies was reduced when performed at higher pacing and while working at above shoulder height. The number of components dropped was higher when performed at above shoulder height. When the task was performed at elbow height ‘wait’ time increased as the beep time was found to be higher at elbow height than the above shoulder height, which led to increase wait time when performing the task at elbow height. Subjective measures (NASA TLX) showed that temporal demand and effort were reported as higher during high pacing. Perceived physical and temporal demand increased when working above shoulder height. An interaction on subjective measure was identified between pacing and working height. Performance of NASA TLX was found to be poor when performing the assembly operation at high pacing/Takt and above shoulder height as compared to working at high pacing/ Takt and elbow height. ii In the second study the experimental design was modified by changing the assembly order to variable assembly and consistent assembly, which represented single model assembly line (where only one type of assembly is being processed) and mixed model assembly line (different types of products being processed). Study 2 was found to be more mentally demanding due to task complexity. However, it was also found that completed assemblies were higher for the consistent assembly task. Subjective measures reported stress as being higher for higher pacing and variable assembly. The final study combined the variables from the first two studies as well as investigating different levels of memory load. Performance times for variable assembly were longer and resulted in less correct code responses. A higher memory load resulted in a higher performance time and lower correct code responses as well as fewer completed assemblies. An interaction between working height and perceived mental workload was found. Results showed that perceived temporal demand and perceived effort of NASA TLX were found to be higher when performing the assembly operation at elbow height and high memory as compared to the assembly operation performed at elbow height and low memory. It was also found that memory load affects perceived physical demand. For industry the findings suggest that in variable (mixed model) assembly different levels of pacing, working height and cognitive demands may affect workers’ performance both physically and mentally. Demands will be higher when working at variable assembly but also performance will vary where variable and consistent assembly are used together. The research also discusses theories that might be most useful for describing these effects. iii Acknowledgements First of all, Thanks to Allah Almighty for enabling me complete this research. I would like to offer my special thanks to my supervisors Dr. Sue Cobb, Dr. David Golightly, Dr. Christine Haslegrave and Dr. Joel Segal: I would not have been able to complete this work without their help and guidance. I would thank to my loving wife who encouraged me at every stage of my PhD work. Also thanks to my friends for having good companies and visits to different places of UK. Thanks to Sarah Sharples, Mirabelle DCruz, Richard Eastgate, Glyn Lawson, Alyson Langley and Harshada Patel who involved me in a ManuVAR project that gave some weight to my PhD. Thanks to Kirstie Dane and Anne Floyd for their administrative support. A great thanks to the Human Factors Research Group: Christmas parties and away days would always be the memorable events. iv Table of Contents Abstract ................................................................................................................... ii Acknowledgements ............................................................................................... iv 1 Introduction ................................................................................................... 1 1.1 Background .............................................................................................. 1 1.2 Research Aims and Objectives ............................................................... 5 1.2.1 Aim .................................................................................................... 5 1.3 Objectives ................................................................................................ 5 1.4 Organisation of thesis ............................................................................. 6 2 Literature Review .......................................................................................... 8 2.1 Introduction ............................................................................................. 8 2.2 Assembly tasks ........................................................................................ 8 2.2.1 Ergonomics Research into Assembly............................................ 10 2.2.2 Design for Assembly and assembly complexity ........................... 11 2.2.3 Summary ........................................................................................ 13 2.3 Physical characteristics related to assembly task ............................... 13 2.3.1 Physiology and anatomy of posture & task demands ................ 14 2.3.2 Anthropometrics of the work place ............................................. 15 2.3.3 Repetitive tasks.............................................................................. 18 2.3.4 Fatigue ............................................................................................ 19 2.3.5 Summary ........................................................................................ 21 2.4 Cognition and assembly tasks .............................................................. 21 2.4.1 Assembly complexity ..................................................................... 23 2.4.2 Mental Workload and assembly ................................................... 23 2.4.3 Summary ........................................................................................ 25 2.5 Pacing ..................................................................................................... 25 v 2.5.1 Effects of pacing/ Takt on physical and cognitive performance 26 2.5.2 Summary ........................................................................................ 28 2.6 Physical and Mental Workload Interaction ......................................... 28 2.7 Theoretical explanations of interactions ............................................. 30 2.7.1 Armstrong Model of WRULDs....................................................... 31 2.7.2 Single and Multiple Resource Models (MRM) ............................. 34 2.7.3 Summary ........................................................................................ 38 2.8 Research questions ............................................................................... 38 3 Familiarisation and understanding of assembly tasks............................. 41 3.1 Introduction ........................................................................................... 41 3.2 Background ............................................................................................ 42 3.3 Industry visits ......................................................................................... 44 3.3.1 Plant A - Automobile assembly ..................................................... 45 3.3.2 Plant B – Aero-engine assembly ................................................... 49 3.3.3 Plant C – Industrial vehicle assembly ........................................... 51 3.3.4 Plant D - Mineral equipment manufacture.................................. 53 3.4 Discussion .............................................................................................. 58 3.4.1 Developing a task analysis ............................................................ 61 3.5 Conclusion.............................................................................................. 67 4 Methodology ................................................................................................ 69 4.1 Introduction ........................................................................................... 69 4.2 Background ............................................................................................ 69 4.3 Experimental Setup ............................................................................... 71 4.4 Independent Variables .......................................................................... 79 4.4.1 Physical demand ............................................................................ 79 4.4.2 Cognitive Demand ......................................................................... 80 vi 4.4.3 Pacing ............................................................................................. 81 4.5 Dependent Variables............................................................................. 82 4.5.1 Objective measures - Performance .............................................. 82 4.5.2 Subjective measures - Physical and mental workload ................ 84 4.6 Relation with theory ............................................................................. 86 4.7 Summary ................................................................................................ 87 5 Study 1- Investigating effects of physical and cognitive demands under different pacing levels ......................................................................................... 89 5.1 Introduction ........................................................................................... 89 5.2 Experimental hypotheses ..................................................................... 90 5.3 Task Analysis .......................................................................................... 91 5.4 Method .................................................................................................. 93 5.4.1 Participants .................................................................................... 93 5.4.2 Experimental design ...................................................................... 93 5.4.3 Independent Variables .................................................................. 96 5.4.4 Procedure ....................................................................................... 98 5.4.5 Instructions to the participant ...................................................... 98 5.4.6 Dependent Measures .................................................................. 101 5.4.7 Statistical analysis ........................................................................ 101 5.4.8 Test for Assumptions ................................................................... 101 5.5 Results .................................................................................................. 102 5.5.1 Objective measures ..................................................................... 102 5.5.2 Subjective measures.................................................................... 112 5.6 Main findings of Study 1 ..................................................................... 123 5.7 Discussion of Experiment 1 ................................................................ 127 5.8 Summary .............................................................................................. 130 vii 6 Study 2 - Investigation of the effects of assembly order (Variable assembly and consistent assembly) in relation to cognitive and physical demands ............................................................................................................. 131 6.1 Introduction ......................................................................................... 131 6.2 Task Analysis ........................................................................................ 132 6.3 Experimental design ............................................................................ 134 6.3.1 Participants .................................................................................. 134 6.3.2 Independent Variables ................................................................ 134 6.3.3 Presentation of assembly order ................................................. 134 6.3.4 Dependent Variables ................................................................... 137 6.3.5 Procedure ..................................................................................... 137 6.3.6 Instructions to the participants .................................................. 139 6.3.7 Test for Assumptions ................................................................... 140 6.4 Results .................................................................................................. 140 6.4.1 Objective measures ..................................................................... 141 6.4.2 Subjective Measures ................................................................... 148 6.5 Main Findings of study 2 ..................................................................... 157 6.6 Discussion ............................................................................................ 161 6.7 Summary .............................................................................................. 164 7 Study 3 – Cognitive load and high pacing / Takt .................................... 166 7.1 Introduction ......................................................................................... 166 7.2 Experimental design and Task Analysis ............................................. 166 7.3 Method ................................................................................................ 170 7.3.1 Participants .................................................................................. 170 7.3.2 Procedure ..................................................................................... 170 7.3.3 Independent Variables ................................................................ 173 viii 7.3.4 Dependent Variables ................................................................... 175 7.4 Results .................................................................................................. 176 7.4.1 Test for assumption and results ................................................. 176 7.4.2 Objective measures ..................................................................... 177 7.4.3 Subjective Measures ................................................................... 183 7.5 Main findings of study 3 ..................................................................... 192 7.6 Discussion ............................................................................................ 195 7.1. Summary .................................................................................................. 197 8 Discussion ................................................................................................... 198 8.1 Introduction ......................................................................................... 198 8.2 Objective measures ............................................................................. 199 8.2.1 Effect of pacing on the objective measures .............................. 199 8.2.2 Effect of work height on the objective measures ..................... 201 8.2.3 Effect of memory on the objective measures ........................... 203 8.3 Subjective Measures ........................................................................... 205 8.3.1 Effects of pacing on the dimension of NASAL TLX..................... 205 8.3.2 Effects of work height on NASA TLX dimensions....................... 207 8.3.3 Effects of memory load on NASA TLX dimensions .................... 208 8.3.4 Fatigue .......................................................................................... 209 8.3.5 Stress and Arousal ....................................................................... 210 8.4 Interactions .......................................................................................... 210 8.4.1 Interaction between pacing and work height on number of completed assemblies................................................................................ 210 8.4.2 Interaction between pacing and work height on number of completed assemblies................................................................................ 211 ix 8.4.3 Interaction between pacing and assembly variability on number of completed assemblies ........................................................................... 212 8.4.4 Interaction between assembly variability and memory load on assembly time ............................................................................................. 213 8.4.5 Interaction between work height and memory load on number of dropped nuts and bolts ......................................................................... 214 8.5 Theory .................................................................................................. 214 8.6 Summary .............................................................................................. 219 9 Conclusion .................................................................................................. 221 9.1 Introduction ......................................................................................... 221 9.2 Contribution to aims and objectives .................................................. 221 9.3 Limitations and recommendations for Future work......................... 229 References........................................................................................................... 231 Appendix 1 Subject Information Sheet for Study 1 ....................................... 241 Appendix 2 Subject Information Sheet for Study 2 .......................................... 243 Appendix 3 Subject Information Sheet for Study 3 ....................................... 245 Appendix 4 General Well-Being Questionnaire................................................ 247 Appendix 5 Workload Check list ..................................................................... 248 Appendix 6 Physical Well-Being Checklist Questionnaire ............................ 250 Appendix 7 Stress and Arousal Checklist ....................................................... 252 Appendix 8 Observational Check list .............................................................. 254 Appendix 9 Observation Protocol for ManuVAR Tasks................................... 255 x