Performance evaluation and analysis of a vertical type absolute displacement sensor

In the field of vibration control, accelerometers are widely used as feedback sensors. On the other hand, it is desirable to use a velocity sensor or a displacement sensor without integral operators. Effects of damping and a skyhook spring are obtained by velocity and displacement feedback, respectively. Due to this, an absolute displacement sensor has proposed as a feedback sensor for semiconductor exposure apparatuses. The proposed displacement sensor has the same mechanical structured having a detector and pendulum as a commercial velocity sensor. In authors´ previous works, the proposed sensor has been successfully applied as feedback and feedforward sensors. However, detection bandwidth is limited due to mechanical resonances called high frequency dynamics. In this paper, we consider the suppression of high frequency resonance. At first, the modal analysis of the vertical type displacement sensor is conducted in order to investigate vibration modes. Then, the shaking test is also conducted by using the pneumatic active anti-vibration apparatus with the proposed sensor. Finally, we evaluate the performance of the apparatus under the condition that the vertical type displacement sensor is used for feedback control.