Experimental modal analysis and shaking test of an absolute displacement sensor for suppression of high frequency dynamics

In the field of vibration control, accelerometers are widely used as feedback sensors. However, 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. Therefore, an absolute displacement sensor has proposed to be utilized as feedback sensors of semiconductor exposure apparatuses. The proposed displacement sensor has the same mechanical structured having a detector and pendulum as a commercial velocity sensor. In previous works, the proposed sensor is applied as feedback and feedforward sensors. However, detection bandwidth is limited due to mechanical resonances called high frequency dynamics. In this paper, causes of the resonances are identified and we carry out to suppress the resonances. At first, control structure and operating principle of the proposed sensor are described. Next, we carry out experimental modal analysis and suppress the resonances by using viscoelastic materials. Finally, we try addition of mass damper in consideration of vibration mode and suppress the same resonances, which are appeared in shaking test.