State Space Analysis of Variable-Stiffness Tendon Drive with Non-back-Drivable Worm-Gear Motor Actuation

Here we investigate variable-stiffness tendon drive for a robot arm. The novel aspect of our design is that it makes use of non-back-drivable worm-gear motor actuation, so static arm configurations can be maintained at a desired stiffness level without requiring motor power. We first analyze a link that is driven via uni-directional agonistic-antagonistic non-linear elastic tendons and construct the state space model of the system. We then design an observer-based state feedback controller. This ensures the output link can track a reference input vector consisting of a desired joint angle as well as tendon extension realized by tendon co-contraction. We simulated the controller and plant in MATLAB and show examples of typical movement trajectories for angular control of the link.