Sliding mode control for an electrohydraulic actuator system with discontinuous non-linear friction

This paper considers the application of a sliding mode controller (SMC) to a high-precision electrohydraulic actuator (EHA) system with non-linear discontinuous friction effects. An important consideration in such systems is the oscillations that occur in the system response owing to friction for small input signals at cross-over regions where the velocity changes sign. A new model for a high-precision hydrostatic actuation system is developed to investigate the effects of discontinuous and non-linear friction. This model is used in the development of a sliding mode control strategy. A significant result from this study is that the SMC can suppress such oscillations. In addition, the paper uses a linear quadratic approach for defining a discrete-time sliding surface for non-linear systems. A comparative study involving the application of the proposed SMC versus a gain-scheduled proportional controller is presented.