Dynamics of Power Hand Tools on Operator Hand and Arm Stability

Abstract

Threaded fastener tightening was studied to determine effects of tool dynamics (torque and build-up time) and workstation configuration (orientation, horizontal distance and height) on operator kinematics and ability to stabilize a right-angle power hand tool. Hand velocity, hand displacement, tool torque, and spindle angle were recorded during tool operation. Four subjects participated. Workstation factors and tool dynamics had significant effects on hand stability. The magnitude of hand velocity and displacement was significantly greater for (1) vertical work surfaces compared to horizontal work surfaces; (2) vertical work surfaces higher than 90 cm above the ground; (3) horizontal work surfaces 90 cm above the ground; (4) increasing torque levels, and (5) long torque build-up times. Subjective ratings of perceived exertion were greater for increasing torque levels, long build-up times, and increasing workstation heights. Perceived exertion was significantly related to hand velocity and displacement ( p<0.05), however, the strength of the correlation was small (R2 ranged between 0.01 and 0.10).