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Precision Trajectory Tracking Control of a Pneumatic Cylinder and Output Stiffness Regulation

Precision motion trajectory tracking control of a single rod pneumatic cylinder driven by two proportional pressure valves is considered. Rather severe nonlinearities and uncertainties exist in the dynamic modeling of the system. In order to guarantee both the transient performance and final accuracy, a nonlinear adaptive robust controller is developed. The proposed controller comprises a sliding mode controller (SMC) and an on-line recursive least squares estimator (RLSE). The RLSE is utilized to reduce the extent of parametric uncertainties, and the SMC is adopted to attenuate the effects of parameter estimation errors, unmodelled dynamics and disturbance. Since pressure in each cylinder chamber is controlled independently, output stiffness regulation can be achieved by changing the nominal control voltage. Several experiments are conducted to test the proposed control strategy, and the results well fulfill the design requirements.