Human performance in a knob-turning task

Knob turning is a common task that should influence the design of human-machine interfaces such as prosthetic arms, teleoperated robots, and virtual environments. This study examines the following metrics for a specified knob rotation: turning strategy, including arm motions used and number of grasps made, time used to complete the motion, and maximum applied forces and torques. The subjects' task was to rotate a one-degree-of freedom haptic knob at least 270 degrees for two angles of attack (hand parallel versus perpendicular to the plane of the knob), three knob sizes, and three motor gains. Results on the initial 260 degrees of rotation show that a more distal arm motion is used for a parallel angle of attack, decreased knob size, and increased gain. Further, a change in the angle of attack affects each metric, with the exception of the maximum z-axis force and the maximum lateral torque. A variation in the knob size modulates each metric, with the exception of the maximum z-axis torque and the maximum lateral force. A modification of the motor gain influences the outcomes of all of the metrics.