Abstract
This paper discusses kinematics and control problems of a robot wrist mechanism with redundant muscles (actuators) . The redundancy enables us to reduce mechanical backlash, avoid near zero tendon forces, where the control accuracy goes down, and adjust the mechanical compliance. Because of the adjustability of the mechanical compliance, the wrist can adapt itself to changeable task environments easily and reduce vibrations by disturbances. On the other hand, high antagonistic forces and slacks cause the system to be unstable.
The wrist has a novel mechanism to overcome some problems in a conventional tendon-controlled mechanism. That is, nonlinear spring tensioners (NST) are inserted in a drive path to give the wrist more ability of adjustment of the mechanical compliance than a conventional tendon-controlled mechanism. Since desired mechanical compliance is easily realized by setting up the displacement of springs, the burden of controllers becomes very little. Therefore the wrist can perform with smaller stiffness and faster response than a conventional tendon-controlled mechanism.
In this paper, a control strategy for this mechanism is also discussed. Experimental results are given to show the efficiency of the tendon-controlled wrist mechanism with NST.
