ABSTRACT
The mathematical model of a hydraulically or pneumatically actuated system is highly nonlinear and time-varying. Several energy conversions are present (electro-mechanical to hydraulic or pneumatic pressure and then to mechanical motion). Generally the control of such systems has been first based on classical or PID feedback approaches [1, 2]. Next the intent was to enhance the control by use of state space design and adaptive control
[3, 4, 5, 6]. Standard or linearization-based control design methods have some drawbacks for pneumatic and hydraulic systems; this is due to the lack of knowledge of the model and parameters. The approximation by locally linear models is not applicable [7, 8]. Consequently the well known control methods like the computed torque or classic controllers are not directly applicable.
