A design of electrostatic suspension system based on delay controller

The position control of silicon wafer in the contacless electrostatic suspension system based on a delay controller is presented in this paper. The stability of the controller is completely analyzed. Sufficient conditions for stability including time delay and initial value of the suspended object are found. The critical time delay, maximum admissible value of time delay ensuring the stability of the system, which is depended only on suspended gap of the levitated object, is also shown in this paper. By using this control scheme, the amplitudes of vibration of suspended object are extremely reduced. In addition, the delay controller is a kind of switched-voltage control scheme, which uses only two high-voltage power supplies to apply a DC voltages of positive or negative polarity to the electrode unit instead of employing high voltages amplifiers that are costly and bulky. Therefore, the cost of the suspension system is reduced significantly compared with conventional systems. This system can be used to handle objects in vacuum environment.