Modeling of an Electrostatic Micromotor Based on a Levitated Rotor

This paper presents a mathematical model developed for an electrostatically levitated micromotor in which the ring-shaped rotor is levitated by electrostatic force in five degrees of freedom (DOFs). A glass/silicon/glass sandwich structure is utilized in this electrostatic micromotor, which is based on the technology of micro-electro-mechanical systems (MEMS). In the center of ring-shaped cavity formed by ICP between the top and bottom glass plates, the rotor is levitated by the five DOFs position servo system and driven by speed control system. In this paper, the mathematical model for the motion control of the rotor in five DOFs is developed. This model describes the capacitances and electrostatic forces between the rotor and associated electrodes, and moments of two rotations about the x, y-axis. The rotational torque model governing the rotor’s rotational speed is also described. In order to obtain the analytical nonlinear models for error analysis, these integral equations are expanded using the Taylor’s series. Moreover the finite element model and its simulation results are obtained by using ANSYS. In terms of comparison between the simulated results and the nonlinear models, the modeling accuracy of the micromotor can be evaluated. Furthermore, the error characteristics of the linearized models via rotor displacement are analyzed. Thus, position sensing and control of both the rotor’s motion, and the rotational speed, can be achieved based on these linearized models of electrostatically levitated micromotors.