Pneumatic type anti-vibration apparatuses are used in the field of semiconductor manufacturing and precision measurement. The variation of the supplied air pressure from the air compressor causes the position fluctuation of the isolated table. A control method using a voice coil motor (VCM) as the actuator is proposed in this study to control the position fluctuation of the isolated table caused by the supplied air pressure. The feedforward compensator control scheme is used to provide a proper controlled signal to the VCM. According to the controlled signal, VCM exerts driving force in the opposite direction of the air spring expansion or compression to suppress the vibration of the isolated table.

The flow disturbance to a pneumatic vibration isolation table causes periodic fluctuation of the table. In current study, one cycle of flow disturbance is estimated offline using a disturbance observer. The time series data of one cycle estimated disturbance is then stored in the memory of digital signal processor. The program codes are prepared which can detect every cycle of the flow disturbance based on the threshold of table position. The estimated signal is then repeatedly injected from the memory through a compensator to the servo valve to suppress table fluctuation due to periodic actual flow disturbance. The effectiveness of this method is demonstrated by experimental results.

Pneumatic vibration isolation tables are used in the field of semiconductor manufacturing and precision measurement. The flow disturbance to the isolation table causes the fluctuation of the table. In order to control the flow disturbance, multi-connection air regulators are often used. However, the multi-connection air regulators lead to a pressure loss of the compressed air. Previously, we used two feedforward control methods which utilized a pressure sensor to measure the supplied air pressure and provide feedforward controlled signals to the actuators. One method used an air spring and the other used a voice coil motor (VCM) as the actuators. The current study proposes flow meter instead of pressure sensor for the feedforward control of the flow disturbance. Until now, a flow meter has been used for monitoring the supplied air flow to the pneumatic isolation table. The objective of this study is to utilize a flow meter in practical control of the flow disturbance. In addition to the control of flow disturbance, the proposed method is also used to control the disturbances caused by the reduced supplied flow and air flow drops.

To avoid a longer settling time of an isolation table, switching of the feedforward controller which is used for the control of supplied air's disturbances, is needed after starting and prior to stopping the table. However, this switching also causes the fluctuation of the table. In order to suppress the fluctuation of the table caused by switching, this study uses a difference operator before the feedforward compensator and the combination of feedforward and feedback loops. The effectiveness of this method is experimentally demonstrated.

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