A 3 DOF model for an electro magnetic air mount

A model with three degrees of freedom is proposed as a means for controlling for controlling micro vibrations in semiconductor manufacturing. The model was derived from an assumption based on small and low frequency vibrations. The coordinates of the 3 DOF was composed of a vertical position, pitch, roll and a proof term. The coordinates of the 4 variables can be calculated from the 4 positions in an isolator. This coordinate can be written as a 4 × 4 matrix, which possesses inversive full rank. The proposed algorithm was applied to an electro-magnetic isolator. The active isolator consisted of a heavy surface plate, sensors, electro-magnetic actuators, amps, air springs and a DSP controller. The electro-magnetic actuator was installed in a pneumatic chamber of the individual air spring. The active isolator was experimentally used as a base structure under the semiconductor manufacturing machines. The performance of the 3 DOF model was compared with that of a 1 DOF model in an impact test. The settling time was reduced to 25% in the experiment.