A New Anthropomorphic Thumb Configuration With Passive Finger Torsion

The unique position of the thumb and joint configuration make the human hand dexterous in manipulating objects and using tools. The thumbs design is significant for the development of prosthetic hands that aim to restore the motor function. In this paper, a novel thumb configuration is proposed, in which we use two coupled motions in the trapeziometacarpal joint to simulate the whole fingers torsional motion accompanying the abduction/adduction of the human thumb. This passive torsional motion increases the contact surface during dynamic gripping. It also improves the direction of the fingertips on the abdomen during gripping to increase the stability of the fine grip. The detailed structure and kinematic analysis are given in this work, a prototype of prosthetic hand that equipped with this kind of thumb is also developed. The simulation results about opposition test show that the prosthetic thumb developed based on the proposed design method has a natural behavior similar to the human thumb.