Reaction force exposure for tightening tool users: A psychophysical based experimental study of electric right-angle nutrunners

Reaction forces from nutrunner tools constitute a risk of developing MSDs. However, recommendations for sustainable reaction force levels are lacking. The aim of this study was to inform recommendations regarding reaction load exposures from right-angle nutrunners. Through a psychophysics approach, experienced assembly workers subjectively assessed reaction loads when using a nutrunner in six combinations of tool tightening strategy, work-pace and screw-joint stiffness. Electromyography, tool and joint parameters were measured. Regardless of tightening strategy, joint stiffness and work-pace combinations, no large differences in acceptable tightening torque, peak reaction force, and handle displacement were observed. However, acceptable jerk and impulse differed substantially between the TurboTight (R) (high-acceleration) and QuickStep (R) (conventional) tightening strategies. Although the TurboTight (R) strategy overall showed reduced peak muscular activities compared to the QuickStep (R), the participant-rated acceptable torque levels were similar, plausibly due to TurboTights' high jerk levels. Jerk and impulse are hypothesized to influence the perception of reaction loads.

Automated summary

This study aimed to assess the reaction load exposures from right-angle nutrunners and provide recommendations for reaction force levels. The subjective assessments from experienced assembly workers showed no significant differences in acceptable tightening torque, peak reaction force, and handle displacement regardless of tightening strategy, joint stiffness, and work-pace combinations. However, significant differences in acceptable jerk and impulse were observed between the TurboTight and QuickStep tightening strategies. These findings suggest that acceleration and impulse have an impact on the perception of reaction loads.