Position Control of a Hydraulic Servo Cylinder Using a Backstepping-Based Sliding Mode Approach

In this paper, a cascaded nonlinear control design for the position of a hydraulic servo cylinder is presented that is based on a control-oriented mathematical model of the test rig. The difference pressure is controlled in the inner loop, whereas the position control is addressed in the outer control loop. Additionally, the outer positioin control loop is extended by a combination of feedforward friction compensation and an observer-based disturbance compensation to improve the position tracking behaviour. Thereby, the benefits of both measures can be exploited: fast reaction and robustness w.r.t. remaining parameter uncertainties and inaccuracies in the friction model. As the system states are measurable, a reduced-order disturbance observer is designed. The efficiency of the overall control structure and the impact of the individual control actions are pointed out by experimental results obtained at a test rig at the Chair of Mechatronics, University of Rostock.