Hybrid actuator for robot manipulators: design, control and performance

A hybrid actuation method for robotic manipulators is proposed. The actuator employs a hybrid combination of DC servomotors and muscle-like bladder actuators. One DC motor-muscle actuator pair is arranged coantagonistically with an identical DC 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. DC servomotors are used to compensate for muscle actuator length changes, hence joint position is unaffected. High-gain servomotor 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 used to drive the final link. A control is formulated for this system to achieve, in addition to independent joint torsional stiffness and joint position control, approximately decoupled and linearized dynamics. A numerical simulation of this two-degree-of-freedom system is presented to verify the performance of the closed-loop system