An active device
using electromagnetic forces was constructed and examined for the purpose of
minimizing the resonance in air mounts of clean rooms. The air mounts are
vulnerable to low-frequency resonance due to heavy weight and low stiffness. A
hybrid structure of the active device, composed of pneumatic and
electromagnetic parts, was developed and tested. The
pneumatic parts in the device support heavy weights under the air mounts, and
the electromagnetic parts reduce the resonance. The electromagnetic
parts are composed of dual stators and an armature, which surround the
pneumatic parts. The resonance can decrease when electromagnetic forces are
generated in the gaps between the stators and the armature. Four active devices
were installed under a 3-ton surface plate for a vibration test apparatus. The
vibration was detected by eddy-current sensors. Discrete P Control logic was
based on displacement, and embedded in a C6713 DSP. The results from impact
tests show that the peak magnitude in the resonance frequency can be reduced to –10 dB.
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