Adaptive robust control of dynamic gas pressure in a vacuum servo system

This paper presents a system based on servo technology for controlling the dynamic gas pressure in a vacuum system. The electro-pneumatic proportional directional valve (EPPDV) is used as a control regulator, which places vacuum control techniques beyond the restrictions of point-to-point control. The two major components of the system, the chamber and the EPPDV are analyzed to derive a system mathematical model. Due to the air compression, valve leakage, there exist parametric uncertainties and uncertain nonlinearities in the vacuum system. An adaptive robust nonlinear controller is proposed to deal with these uncertainties effectively. The proposed controller employs on-line update of the uncertain parameters to improve the precision and utilizes the sliding mode control method to attenuate the effects of uncertain nonlinearities. In order to solve the conflicts between the sliding mode control design and the adaptive control design, the projection mapping is used so that the parameter estimates are kept within a certain range. The experimental results show that using EPPV as the regulator in a vacuum servo system is feasible, and the proposed controller is effective in dealing with the nonlinearity.