EtherCAT Implementation of a Variable-Stiffness Tendon Drive with Non-back-Drivable Worm-Gear Motor Actuation

Abstract

Here we present the design for a compliant actuator than makes use of agonistic-antagonistic tendons. Its novelty lies in its use of worm-gear motor drive and industrial EtherCAT control. We first describe a test rig to investigate variable-stiffness tendon drive for a single link and the construction of a corresponding EtherCAT controller. The tendon drive was based on the shoulder joint in the GummiArm and made use of tendons that exhibit a non-linear extension characteristic, so co-contraction increases joint stiffness. To ensures power was only needed when the arm is moving, low-cost worm-drive DC motors were used. An LQR observed-based controller was designed to realize angular position control of the link. The link controller was implemented using the custom-build EtherCAT panel. We present preliminary results of moving the joint link between angular target positions.