| Flow line production is a highly efficient production organization form,but it can't meet the needs of multiple variety and middle or small batch production.Therefore,this kind of organization must be reformed.Some scholars have suggested that flow line manufacturing cell is a new production organization form with a broad prospect.Meanwhile,the more and more streamlined actions and the cycle time based on motion economical principle during traditional flow line production can increase mental workload.What's more,the high mental workload is harmful to workers' health and the maintenance of high production efficiency.Nowadays,in order to meet the personalized needs of customers,the multiple variety production organization form has been widely applied.Besides,the supply structure of the labor force has changed a lot.In this circumstance,the contradiction has been more and more outstanding.Most current studies focused on the problem of workers' physical workload,and few studies explored the workers' mental workload.Therefore,this study applied near-infrared spectroscopy to examine brain response in the prefrontal cortex(PFC)and the bilateral motor areas(MA)when workers completed repetitive assembly tasks with different workload levels.By this way,we can investigate the effects of works ‘mental workload,and the study results can provide important references for the work plan arrangement and the increase of production efficiency and safety.The purpose of this study is to investigate the effects of different workload on the mental workload and performance of workers.On the basis of the on-site survey in enterprises,experiments were carried out by simulating the carburetor assembly line in the laboratory.The laboratory simulation has the advantages of overcoming the difficulties of data acquisition,controlling the experimental variables and production conditions,and validating the optimization and improvement of the schemes.34 participants took part in the present study.By the time axis analysis,two kinds of workload tasks are developed(medium workload VS high workload).In order to explore the impact of fatigue on performance,participants received two tests of motion stability and working memory span before and after the assembly work.This study adopted NIRS_SPM?Matlab?ROI analysis and other methods to analyze the data.This study shows a decrease in motion stability which causes a higher activation in PFC and lower activation in the left motor area.The results suggest that repetitive assembly tasks induced both cognitive and physical loads to workers,and in turn may reduce their performance due to impaired ability of action control.The regular change patterns of the workers' mental workload with time is close to the "inverted U" pattern when they complete the assembly task with high workload.At the beginning of the assembly operation,the compensation process is temporary for the ability to perform competency compensation in order to complete the processing task.In the process,the mental workload of the participants increased first and then decreased,and their performance gradually increased.In the middle of the assembly operation,the participants' performance was at the best level and the mental workload reduced to a minimum.As time goes by,the participants began to feel tired.In the process,their mental workload increased and their performance declined.By correlation analysis,we find that the participants use the resource in left dorsolateral prefrontal cortex,bilateral primary motor cortex and motor cortex at the beginning of the task.Then,they use the resource in right dorsolateral prefrontal cortex and medial prefrontal cortex at the middle of the task.At last,they use the resource in medial prefrontal cortex.Therefore,Inverted-U theory is enriched.Thus appropriate management strategies should be made depending on the mental/physical loads of workers to improve their working efficiency and mental health and reduce potential industrial accidents. |
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