Design and Preliminary Evaluation of a 3-DOF Powered Prosthetic Wrist Device

Abstract

Though the human wrist greatly benefits manipulation by orienting the hand, recreating its functionality in anthropomorphic proportions proves to be difficult. As a result, upper limb amputees who desire wrist functionality must often use often passive single degree of freedom devices to attempt to recover some of this missing ability. In this work, the authors present the preliminary design and kinematic testing of a 3 DOF actuated wrist prosthesis. The device is capable of 90 degrees of circumduction (combined flexion and abduction), and continuous rotation in pronation. The circumducting portion of the wrist is composed of a parallel mechanism, while the pronation drive is a belt-driven serial mechanism. The circumducting DOFs are actuated via nonbackdrivable linear DC motors, and the gear ratio and friction of the pronation mechanism make it nonbackdrivable under reasonable loads as well. The architecture of this wrist was chosen such that when the device is integrated into a transradial socket, the motors could be placed on the socket periphery, allowing amputees with long residual limbs to use the wrist without significantly offsetting the terminal device. Benchtop evaluation of the wrist device is performed to evaluate the speed of the wrist in actuation from the neutral position to a variety of flexion and abduction positions, as well as to evaluate its pronation speed. We find the wrist performs rather near to the ideally expected speed values.