Hybrid actuator for robot manipulators: Design, control and performance

Abstract

In this paper, a hybrid actuation method for robotic manipulators is proposed. The actuator employs a hybrid combination of D.C. servo motors and more recently developed muscle-like bladder actuators. One D.C. motor-muscle actuator pair is arranged co-antagonistically with an identical D.C. motor-muscle actuator pair to drive a manipulator joint. Through a suitable control applied to the hybrid actuator, independent control of joint torsional stiffness and joint position is made possible. When air pressure is varied in the muscle actuators, the muscle actuator stiffness and length change. In order to only affect the hybrid actuator stiffness with this pressure change, D.C. servo motors are used to compensate for muscle actuator length changes, hence joint position is unaffected. High grain servo motor control ensures a response to disturbances due almost solely to the muscle actuator stiffness characteristics. Dynamic equations of motion are developed for a two joint manipulator with a hybrid actuator to drive the final link. A control is formulated for this system to achieve, in addition to independent joint torsional stiffness the joint position control, approximately decoupled and linearized dynamics. A numerical simulation of these two degrees of freedom is presented to verify the performance of the closed-loop system.