A Compliant Rolling Ellipsoidal Thumb Joint for the TU Hand

This work presents a compliant rolling ellipsoidal carpometacarpal (CMC) joint for the thumb of a robotic hand. This work is the first to introduce the biellipsoidal joint, a flexure hinge-based biomimetic thumb CMC joint. A model of this design is implemented in simulation and in experiment and compares the manipulability metrics, a quality metric for the end-effectors within robotic manipulators, across similar workspaces. Compliant mechanisms known as flexure hinges maintain the 3-D rolling of the ellipsoids rather than sliding or slipping. By comparing the results for the biellipsoidal joint with a gimbal joint, the relative size and location of the region of highest manipulability were found to be similar between CMC joint models, although the shape of this region varied somewhat from one to the other. The experimental comparison used tendon-displacement data generated from bio-inspired hardware prototypes of both the biellipsoidal CMC joint and gimbal CMC joint models for two similar robotic thumbs, whereas the analytical version used iterative forward kinematics to derive and compare the manipulability metric distributions.