Hydraulic actuator control based on continuous higher order sliding modes

This paper presents the robust trajectory tracking of a hydraulic cylinder using an output feedback sliding mode technique. The proposed control scheme relies only on measuring the position of the cylinder rod. A robust, exact, finite-time observer of the output's derivatives is provided to attain the control goal. Then, a continuous third-order sliding mode controller for the system with relative degree three is designed using the estimated derivatives. It is shown that the separation principle can be used for the closed-loop system, which includes the higher-order sliding mode observer and the controller. The paper includes experimental results on a hydraulic setup in which a second energized cylinder is also connected in an antagonistic way to produce external dynamic disturbances and demonstrate the control method's feasibility and robustness.