Development of electrostatic levitation motor for vacuum condition

To drive a motor in vacuum condition, many factors must be considered, such as friction and heat generation. Since typical electromagnetic motors structurally have problems of friction and heat generation, it is difficult to use them in vacuum condition. Besides, in some vacuum applications like EB lithography, SEM, and TEM, electromagnetic motors are unlikely to be used since existence of electromagnetic field is a fatal problem. We propose an application of non-contact levitation electrostatic motor using dual excitation multiphase electrostatic drive (DEMED) system to those fields. We have developed a direct drive high-power electrostatic linear motor called DEMED. DEMED is a linear synchronous motor that consists of pairs of thin plates, stator and slider, and possesses a power per weight ratio of 230 W/kg and acceleration of over 100 G in an open loop systems in dielectric liquid. These performances are higher than those of typical electromagnetic drives. In this paper non-contact levitation and driving control system for DEMED is proposed. A levitation motor using DEMED utilizes the same electrodes for both levitation and driving. For controlling attractive force, bias voltage is superposed onto driving voltage. We have fabricated prototype motor with 2-DOF and have realized levitation drive control. The fabricated motor was operated at a speed of 20 mm/s with keeping a levitation gap of 200 μm.