Backstepping control of an electro-hydraulic servo system subject to disturbance and parameter uncertainty

This paper addresses the control of a hydraulic servo system rod subject to uncertainty in parameters and to an unknown but bounded disturbance. The proposed backstepping-based robust controller guaranties a uniformly ultimately bounded tracking error leading to practical stability of the closed loop system. Two schemes are proposed. First, a constant gain-based controller that achieves a good tracking accuracy with a steady state error in the millimeter range, but induces control input oscillations in transient. To improve such behavior, a second controller with time varying gain is proposed. Both controllers assure robustness against perturbations and uncertainties in the dynamics of the system. Numerical simulations illustrate the efficacy of the proposed scheme.