A Backstepping based Controller utilizing a Sliding Mode Disturbance Observer Applied to Hydraulic Servo Systems

Hydraulic servo systems are characterized by nonlinear dynamics that can render control design challenges. Controllers for a linearized model will typically be conservative, and the stability of the closed loop system, in the Lyapunov sense, may be difficult to prove. On the contrary, the backstepping technique can lead to control algorithms for which stability margins can be estimated. However, these tend to be complex algorithms that are difficult to apply. In this paper, the backstepping control design procedure is applied to a hydraulically actuated robot. A sliding mode disturbance observer is utilized to avoid the high complexity of the backstepping algorithm. The paper’s primary focus is hence on proving the stability of the proposed algorithm and its applicability to a laboratory setup. However, ways to improve performance are also discussed. Finally, results are presented where the designed controller is tested in both simulations and applied to the laboratory setup, and compared to linear controllers.