A biomechanical and psychophysical examination of fastener initiations in automotive assembly

A psychophysical and electromyographical methodology was utilized to examine 24 female subjects while performing fastener initiation (FI) tasks on a simulation device. Three wrist postures (neutral, flexed and extended) and two fastener sizes (large: 10 mm depth×20 mm diameter; small: 5 mm×10 mm) were examined. The number of FIs per minute and the number of efforts per FI were the kinematic dependent variables, and posture and fastener size were found to have significant effects on both (p<0.05p<0.05). Maximal acceptable frequencies (MAF) of FI were calculated to be those acceptable to 75% of the female subjects. These ranged from a low of 6.1/min (extended wrist, small fastener) to a high of 7.4/min (neutral wrist, large fastener). EMG data showed a significant effect of posture for the FCU and Thenar muscles. The ECU was found to have the highest activity of all muscles regardless of the condition.Relevance to industryThe current study provides recommended TLV guidelines for MAFs for the common manufacturing task of FIs. These guidelines can be used to both protect worker health and safety and insure manufacturing quality with tasks involving hand starts of fasteners.