Position Error Reduction of the Actuator Using the Sliding Mode Controller with Variable Boundary Layer Thickness

Sliding mode control with nonlinear interpolation in the boundary layer is investigated. A hyperbolic tangent function is used for nonlinear interpolation in the boundary layer and its parameter is tuned by a fuzzy controller. The fuzzy controller that takes both the sliding variable and the measure of chattering as its inputs guides online the shape of the hyperbolic tangent function through tuning the parameter of the function. Owing to the decreased thickness of the boundary layer, the proposed method has better tracking performance than the conventional linear interpolation method. To demonstrate its performance, the proposed control algorithm is applied to the electro-hydraulic servo system which is composed of a double ended hydraulic cylinder driven by a direct drive valve