The authors have developed an active microvibration control system using voice coil linear motors, air and piezoelectric actuators. This system is designed to reduce microvibration of the six degrees of freedom associated with rigid body modes of the vibration isolation table by giving feedback of the absolute displacement and absolute velocity of the table. To improve vibration isolation performance, a feed- forward control force is added to the sway components in each dimension. This system can also control bending modes of the table in the frequency range up to 200 Hz by applying a new proposed Virtual Tuned-Mass Damper theory, which is a type of the pole assignment method. In pole assignment problems, the semi-optimal pole is chosen by a Genetic Algorithm. As the result, the microvibration of the floor at around 0.5 cm/s$+2$/ and small earthquake at around 8 cm/s$+2$/ were reduced to about 1/100 in acceleration waveforms at the vibration isolation table. In comparison with the floor, the vibrations of the isolation table were decreased over the entire frequency range. This system showed good vibration control performance when an impact excitation was applied to the table directly. Vibrations were damped even within a time scale of around 0.1 sec. The resonance amplitudes around the bending modes of the table were reduced from 1/5 to 1/15 by the Virtual Tuned-Mass Damper method.
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