Realization of a Zero-compliance System by Using Displacement Cancellation Control

A control method for achieving zero compliance to direct disturbance is proposed for a vibration isolation system. The structure of the proposed zero-compliance system is as follows. A middle mass is suspended by a spring from the base. The isolation table is suspended and moved by a linear actuator that is fixed to the middle mass. When direct disturbance acts on the isolation table, the middle mass begins to move in the same direction as the disturbance. The actuator operates to move the isolation table in the opposite direction to cancel the displacement of the middle mass to the base. To verify the effectiveness of this principle, a single-axis apparatus was fabricated. In this apparatus, the isolation table and the middle mass are guided to move horizontally to study characteristics without the influence of gravity. A voice coil motor (VCM) is installed between the isolation table and the middle mass, and integral-proportional-derivative (I-PD) control is implemented to achieve displacement cancellation control. Another VCM is installed between the middle mass and the base, and PD control is implemented for realizing the prescribed stiffness and damping. The efficacy of the designed control system is confirmed experimentally.