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Time-Optimal Control of an Electrostatic Suspension for 4-inch Silicon Wafer

A simple method to levitate an object without any contacts which is based on controlling a switching voltage incorporating with a time-optimal controller is presented in the paper. The main features of the electrostatic suspension system with time-optimal control are: simple and reliable, cost-effective and possibly implemented in (ultra) high vacuum environment. The switched-voltage control operates as a relay feedback control. Only a dc high-voltage power supply, instead of dc high-voltage amplifiers, can deliver constant voltages to an arbitrary number of stator electrodes. Although limit cycles or sustained oscillations due to the property of the relay exist in the suspension processing, a good performance in terms of position control can be obtained. Simulation and experimental results carried out for a 4-inch silicon wafer will clearly demonstrate the effect of the proposed control structure to levitate the wafer stably at the desired gap of 300 mum.