A robust nonlinear controller design for a pneumatic actuator

This paper presents a feedback linearization based variable structure controller for a pneumatically actuated system utilizing sliding mode observers. Using the robustness implications of the sliding mode control theory and the structural properties of pneumatically actuated systems, a nonlinear controller is designed to drive the output tracking error to zero in finite time. Strong robustness with respect to bounded modeling and parameter uncertainties is attained through compensation of the friction effect of the piston in the cylinder body. The controller and the observer are based on a third-order nonlinear state-space model of a pneumatic system which was developed, validated numerically with experimental data and presented by Acarman et al. (SAE, 2000-01). Simulation results are included to demonstrate the effectiveness of the designed observer and the good performance of the designed tracking controller.