Kinematic Design of a Thumb Metacarpal for an Anthropomorphic Robotic Hand

This paper presents the kinematic design of a thumb metacarpal for a cable-driven anthropomorphic robotic hand. The general problem of finding the position and orientation of an axis around which a given vector is rotated from a position to another is first assessed. A particular case of this problem follows, in which the final direction of the vector has to be in opposition to the initial one, as for the adduction-opposition movement of the thumb. The configuration of the transmission system for the flexor tendon of the thumb is then established. This allows the calculation of the position and orientation of the deflecting pulley in the metacarpal, followed by the evaluation of the trajectory of the pulley system. Finally, a prototype of the thumb metacarpal is presented.