Observer-based sliding mode control of hydraulic cylinders in the presence of unknown load forces

A laboratory hydraulic setup consisting of a coupled actuating and load cylinder is investigated in order to emulate real world working conditions of heavy equipment such as excavators and loaders. An observer-based control scheme is proposed to regulate the position of the actuating cylinder. It relies on on-line identification of unknown parameter as well as reconstruction and compensation of unknown load forces, such that the performance of the closed position feedback loop is superior compared to classical control strategies. The applied method exploit ideas of variable structure systems in the design of both, the observer and the parameter identification scheme.