Bandwidth expansion of a pressure control system for pneumatic anti-vibration apparatuses in presence of dead time

This paper considers the pressure control of air springs used for a pneumatic anti-vibration apparatus (AVA), which isolates vibration transmitted to semiconductor lithography equipment. In the control of the pneumatic AVA, pressure feedback is often employed so as to keep the inner pressure of air springs constant. By expanding the bandwidth of pressure control system, fast response can be obtained, though this bandwidth is restricted due to anti-resonance and resonance in a pneumatic system. To eliminate the anti-resonance and resonance, relative displacement derivative (RDD) positive feedback control has been presented. However, previous RDD positive feedback control cannot be implemented under the condition where the dead time of air springs exists. In order to compensate effects of the dead time, a Smith predictor is utilized. Through experiments, it is shown that in the presence of the dead time, the anti-resonance and resonance can be eliminated by means of the RDD positive feedback control combined with Smith prediction. The bandwidth of the pressure control system increases with the gain of pressure PI compensator. Furthermore, effects of proposed approach on vibration transmissibility are investigated. Although the vibration transmissibility is the performance metric for the development of the pneumatic AVA, the case where the dead time is present was not sufficiently considered. In this paper, it is shown that the vibration transmissibility changes in accordance with the dead time.