Design and control of a six degree of freedom active vibration isolator using voice coil motor

Abstract

Nanomanufacturing technology largely depends on precise and accurate measurement in the nanometer level. Precision measuring instruments with nanometer resolution are almost always susceptible to disturbance transmitted mainly from ground vibration as well as other sources such as acoustic noise and direct mechanical vibrations due to the moving parts of the measuring instrument itself. The amplitude of such vibration typically in the sub-micrometer region and of low frequency is well enough to distract both precision and accuracy of the measuring instruments. Even though the instrument itself is designed to handle such disturbances, researchers in this field are still in need of a smart way to properly eliminate this problem so that they can make their measurement results more trustworthy. Many researches have so far been carried out in the field of isolation of instruments from such disturbance sources. Main principle is to provide stiffness and damping in the path of vibration from ground to instrument such that the isolator works like a low-pass filter which attenuates relatively high frequency disturbances. Commercial isolation systems use different approaches such as passive, active or semi- passive. In this paper the proposed solution is to use a hybrid active-passive vibration isolation system between the instrument and ground to eliminate vibration transmitted from ground as well as direct disturbances transmitted from the moving parts of the instrument to the support plate of the payload in all six degrees of freedom. The reason behind this hybrid solution is to take advantage of both the passive as well as active stage. Both the natural frequency as well as high frequency response is first improved through the dynamics of the passive system which provides high attenuation rate. Then the active stage works on the system to reduce the corner frequency so that low frequency attenuation is achievable and also the resonance amplitude is controllable....