Smith predictor-based time delay compensation for attitude control of pneumatic anti-vibration apparatuses with two degrees-of-freedom

Pneumatic anti-vibration apparatuses (AVAs), which have air springs, are needed for the precision positioning of wafer stages in lithography equipment. However, the difference of time delays in the response of the air springs causes the undesirable rotational motion of an isolated table. This paper considers the attitude control of the AVA including difference time delays. To avoid the rotation of the isolated table, a Smith predictor is employed. It is verified that this approach can be used for the AVAs with mode control, which is often used in vibration isolation systems for semiconductor manufacturing. The overshoot of the rotational angle of the isolated table can be further reduced by shaping the reference trajectory.