A setting method of a feedthrough term for pneumatic isolation tables considering difference between bandwidth of pressure fluctuation and mechanical resonance

This paper considers the trade-off between flow disturbance attenuation and transmissibility reduction for pneumatic isolation tables. In the active control of the pneumatic isolation table, compressed air is supplied to air springs. However, the pressure of the compressed air fluctuates. This pressure fluctuation, which is called flow disturbance, causes the vibration of the isolation tables. Since the pressure fluctuation is periodic, repetitive control is utilized so as to compensate for the flow disturbance. The feedthrough term in a repetitive controller is usually designed as a static compensator. Although the flow disturbance is further attenuated by increasing the gain of the static compensator, the transmissibility becomes large in the frequency region of mechanical resonance of the isolation tables. Therefore, this paper focuses on the setting of the feedthrough term. In the proposed approach, a dynamic compensator is adopted as the feedthrough term instead of the static compensator. Two break-point frequencies of the dynamic compensator are tuned on the basis of the bandwidth of the pressure fluctuation and the mechanical resonance. It is shown that, by using the proposed setting method, the flow disturbance can be attenuated and the peak of the transmissibility can be reduced.