A variable structure controller for a cost-effective electrostatic suspension system

In this paper, the variable structure controller, which is designed considering the damping force and the nonlinear dynamic characteristic of an electrostatic suspension system, is used to suspend a 4-inch silicon wafer by electrostatic forces. The controller consists of a sliding mode controller that is used in the local existence region of a sliding mode and a relay feedback controller playing the role of a swing up controller. In order to highlight the performance of the proposed controller, the simulation and experimental results are shown. The performance of the controller is compared with that of the delay controller proposed in previous research. Experimental results show that a 4-inch silicon wafer has been stably suspended at a gap length of 300 µm in an atmospheric environment with very small steady-state vibrational amplitude. Simulation and experimental results shown that the variable structure controller is more effective than the delay controller for suppressing gap fluctuation when large damping forces are exerted on a suspended object.