An electro-magneto-pneumatic spring for vibration control in semiconductor manufacturing

An active vibration isolator was developed for semiconductor manufacturing machines using electro-magnetic (EM) levitation force. The spring is composed of a pneumatic elastic chamber and a magnetic actuator. The actuator has a coil and a permanent magnetic plate and is installed inside of the chamber. The mechanical and electronic parts are designed to operate under a weight of 2.0 tons. An air mount is constructed for the experiment with a stone surface plate, 4 active air springs, 4 gap sensors, a DSP controller, a linear power amp and vibration measurement systems. The impulse response of the air mount was monitored before and after the active control. The time duration was reduced by 77% in the impulse response. The maximum peak in frequency domain was reduced by 62%. We also found that the active system can avoid the resonance caused by the natural frequency of the passive system.