Thumb CMC(Carpometacarpal) joint for the prosthetic hand with a realistic motion

Abstract

Thumb has the most important and featured movement of our hand. Due to Carpometacarpal (CMC) joint with two degree of freedom, the thumb could oppose to the other fingers. Therefore in prosthetic hands, the thumb is the most important but difficult part to develop. There have been various mechanism for an artificial thumb. However most of them used single or series of pin joint mechanism to conduct the dexterous motion of the human thumb. In this study, we developed the novel thumb mechanism with the single saddle joint. In addition, to mimic the realistic motions of the human thumb, the saddle joint with the tilted axis was suggested. With this tilted saddle joint, the developed mechanism shows similar motions to the human thumb. It has two degree of freedom in flexion/extension and abduction/adduction direction, and has coupled internal rotation motion too. Also, expect for the motions in flexion/extension and abduction/adduction, the other motions are strictly constrained including the coupled internal rotation. Therefore the developed CMC joint mechanism has high resistance against the external forces. By applying this CMC joint mechanism to the thumb partial prosthetics, the realistic thumb motion is achieved.