Vibration control of an air type anti-vibration apparatus with two degrees-of-freedom using absolute displacement sensors: Feedback to voice coil motors

Accelerometers have been widely used in the field of vibration control. It is preferable to detect the velocity and displacement signals in addition to acceleration signal, because the direct feedbacks superior in robustness can be given to the control objects. Then, an absolute displacement sensor, which can simultaneously detect the acceleration, velocity, and displacement signals, was proposed, and each signal was fed back to an air type anti-vibration apparatus with one degree-of-freedom by using a voice coil motor. However, the apparatuses are connected each other in order to configure a large isolated table, and its vibration modes are selected and distributed in industrial applications. In this paper, an anti-vibration apparatus with two degrees-of-freedom is controlled by using the absolute displacement sensors. Since the bandwidth of the prototype sensors is not covered for the rotational vibration, the natural frequencies of the apparatus are shifted to be settled in the bandwidth. As results, the mechanical impedances of the apparatus are successfully manipulated by the direct acceleration, velocity, and displacement feedback.