Adaptive torque control of hydraulic actuators based on dynamic compensation

A systematic procedure is developed for the design of new adaptive robust torque tracking control for electro-hydraulic actuators with both parametric uncertainties and uncertain nonlinearities such as frictions. The dynamics of the electro-hydraulic actuators is assumed to be linearly parameterized about model parameters to develop the adaptive and robust control. The proposed algorithm is composed of the adaptive part for dynamic compensation and the robust part for overcoming the error of the estimated nonlinearities. The adaptation law is based on the previous Lyapunov analysis and the robustness to uncertain nonlinearities is obtained by a L₂-gain analysis for disturbance attenuation, which does not require the knowledge of the bound of the disturbance. There are two main advantages of the proposed algorithm which become significant during implementation. One advantage is that the accurate dynamic compensation is realized for the torque tracking. A second advantage of this method is that the uncertain nonlinearities, which is difficult for the use of the adaptation law, are considered and compensated for with the robust control using L₂-gain analysis. The controller shows the tracking accuracy in presence of both parametric uncertainties and uncertain nonlinearities.