| U-shaped assembly line comes from the lean manufacturing system of Toyota in Japan,which has been widely used worldwide.U-shaped assembly line production in the form of segmentation is also relatively common,because each production unit is composed of one worker and several pieces of equipment,and this type of unit production is also known as the production mode of "one person and multiple processes".Segmentation is one type of organization.A split assembly line contains multiple systems of one person and multiple processes at the same time.In this mode,the behavior of workers is very important.Whether the change of speed or the error of operation will seriously affect the efficiency and quality of the entire production system.Psychological load evaluation is the key to improve production line efficiency.Therefore,this study conducted practical operation experiments on segmented assembly line to analyze the psychological load of the subjects,which is of great significance to the operation safety of the production line and the assignment of work tasks,and to ensure the operation safety and task assignment.Firstly,in order to explore the influence of psychological load on the operation process of segmented assembly line,subjective scale,heart rate tester and flash fusion frequency were used as measurement tools.After the training,15 subjects were recruited and carried out three operational tests with different task difficulty.Polar Team Pro was used to measure the subjects’ heart rate changes,and after the test,bright spot scintillometer was used to measure the changes of fatigue state of the subjects,and three subjective scales including NASA-TLX,SWAT and CH were filled in to score the psychological load.The results showed that subjective score,heart rate and flash fusion frequency tended to increase with increasing difficulty.Secondly,in order to better study the human behavior in the experiment,the human behavior model is constructed.The main constituent factors of human behavior model are analyzed,the body fatigue,work pressure,the work error rate and other related factors are defined,and the fuzzy mathematics is used to quantify the body fatigue and work pressure.Finally,the influence coefficient of working speed and error rate was calculated according to the experimental process data,and the range of working speed under different task difficulties was finally determined to provide evaluation indexes for the psychological load model.Then,in order to provide reference for the early warning of high psychological load of segmented assembly lines,a psychological load model was constructed to screen the operators with low psychological load for task allocation.Principal component analysis was used to reduce the dimension of subjective index,subjective score comprehensive index,number of job errors,key error rate,missing report rate,test time and working speed considering working pressure,fatigue and personal errors was determined.The psychological load in segment-type assembly line operation was modeled based on GBDT-LR algorithm.The results show that the recognition degree and recall rate of psychological load model are high,F1 value and AUC value also perform well,which are 96.6% and 98.7%.Finally,in order to balance the psychological load of workers and improve the production efficiency of enterprises,a task allocation model is constructed.The concept of job competency index was put forward,and on this basis,a task assignment model was established with the optimization objectives of minimum task completion cost,shortest task completion time and lowest load.The task assignment was realized on U-shaped production line according to the standard working time,and the effectiveness of the three models was verified by an example.There are 34 figures,53 tables and 125 references in this thesis. |
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