Application of displacement cancellation control to vibration isolation system

A control method achieving infinite stiffness to direct disturbance is applied to a vibration isolation system. The structure of the studied vibration isolation 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 vibration acts on the isolation table, the middle mass is displaced in the same direction of the force. 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 is fabricated. In this apparatus, the isolation table and the middle mass are guided to move horizontally for studying the characteristics without the influence of gravity. This apparatus uses two linear DC motors. One is installed between the isolation table and the middle mass and implemented with a PD controller for realizing a prescribed stiffness. The other is installed between the middle mass and the base, and implemented with an I-PD controller for realizing displacement cancellation. The efficacy of the control method is confirmed experimentally.