This paper presents a combined scheme of identification and robust torque control for rotary hydraulic actuators. The composite controller consists of a dynamic feedback linearizing inner loop cascaded with an optimal l1 - H feedback outer loop. The proposed controller allows the actuator to generate any desired torque irrespective of the actuator motion. In fact, the controller reduces significantly the impedance of the actuator as seen by its external load, making the system an ideal source of torque suitable for any robotics and automation applications. A through-out analysis relating to the stability of the internal unobservable dynamics is presented. An identification method to extract the parameters of nonlinear model of actuator dynamics and to estimate a bound for modeling uncertainty used for synthesize of the outer optimal controller, is presented. The theoretical results of the paper are illustrated experimentally on the pitch actuator of the Titan II, Schilling industrial robot.

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