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 feedback outer loop. The proposed controller allows the actuator to generate 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 many robotics and automation applications. The stability analysis of 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 synthesis of the outer optimal controller, is also presented. The theoretical results of the paper are illustrated experimentally on pitch actuator of the Schilling industrial robot.
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