Rotary Actuators with Electrostatic Suspension

This paper studies two types of electrostatically suspended rotary actuators: electrostatically suspended variable- capacitance motors (ESVCM) and electrostatically suspended induction motors (ESIM). The ESVCM is an electrostatic stepping motor which features electrostatic suspension. Thus, ESVCM possesses the rotating and positioning ability of an ordinary stepping motor, in addition to providing contactless support by electrostatic suspension. To accomplish these two functions, a feedback control strategy and the operating principle of an ordinary electrostatic variable-capacitance motor are used. The ESIM is an induction motor where the rotor is suspended stably, like ESVCM, by actively controlling the electrostatic forces exerted on it. To implement a rotation, the operating principle of an ordinary electrostatic induction motor is used. In this paper, the working principle of the ESVCM and the ESIM, electrode design, a linear dynamic model of the suspension system, feedback control strategy and operating principle of rotation are described. Experimental results show that the rotor has been rotated with a speed of approximately 60 rpm while being suspended stably at a gap length of 300 µm.