Output feedback tracking control of electro-hydraulic servo systems

This paper presents a model-free robust/adaptive control scheme for tracking control of electrohydraulic servo systems using output feedback only. The Taylor expansion theory is used to enable the proposed controller to identify and feedback linearize the dynamics of a system online, and to compensate parameter variation and various disturbances in real time. As a result, the closed-loop system of the complicated electrohydraulic system behaves as a simple linear dominated system plus a small uncertainty residual. By properly designing the adaptive law of the robust gain, asymptotic stability and satisfactory performance of the closed-loop system can be achieved. The details of controller design and stability analysis are presented in the paper. The controller has been implemented on a plastic injection moulding machine to control the position of the mould-supporting movable platen. The results from experiments indicate that the proposed controller performs much better than the conventional PID feedback controller