Sliding Mode Control for a Model of an Electrohydraulic Actuator System with Discontinuous Nonlinear Friction

This paper considers the application of Sliding Mode Control (SMC) to a high precision hydrostatic actuation system with nonlinear discontinuous friction. An important consideration in such systems is the oscillations that occur in the system response due 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 assuming discontinuous and nonlinear friction in the actuator. 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 introduces for the first time, a linear quadratic approach for defining a discrete-time sliding surface for nonlinear systems. A comparative study involving the application of the proposed SMC versus a gain-scheduled proportional controller is presented. This comparison demonstrates the performance improvements resulting from the SMC and the added robustness of this strategy given large modeling uncertainties.