Optimal design and control of 6 degrees of freedom active vibration isolation system using voice coil motor

Abstract

This paper represents a design and control of an Active Vibration Isolation System (AVIS). AVIS is widely used to isolate disturbance for precision measuring instruments like an AFM, STP and interferometer. These instruments are sensitive to disturbances that transmitted from ground and direct disturbance caused by environments in all six degree of freedom. The amplitude of vibration in low frequency region with micro-meter level hinders precision and accuracy of instruments. AVIS needs an actuator in order to actively isolate a 6 D.O.F vibration such as a VCM. The proposed VCM actuator is composed of permanent magnet array and coils. The permanent magnet array produces magnetic flux which can generate actuating force to isolate disturbances. Firstly, the proposed VCM actuator is designed and modelled. It uses back steel yoke and the Halbach magnet array to reinforce magnetic flux density. The Halbach magnet array has been developed in order to increase a flux density comparing with conventional NS magnet array. Secondly, in case of AVIS, payload is changed according to the types of instruments which can be isolated from other disturbance. Therefore, actuator should maintain uniform performance through payload change. The proposed AVIS is satisfied this condition through relative relation between the Halbach magnet array and coils in the VCM actuator. The length of coils is longer than magnet array so that VCM actuator handles different coil position according to payload variation. The optimal design procedure, to accomplish maximum force density, is performed considering constraints and cost function. It can generate uniform force for variable payloads. The AVIS needs two types of the proposed actuator, which are classified as direction of generated force like a horizontal and vertical actuator. Depending on actuator type, each of optimal procedures has different design variables. Finally, the proposed AVIS is manufactured and controlled. The manufactured AVIS is evaluated the isolation performance at 20Kg mass payload.