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Sensors 2017, 17(5), 1119; doi:10.3390/s17051119

Squeeze-Film Air Damping of a Five-Axis Electrostatic Bearing for Rotary Micromotors

Department of Precision Instrument, Tsinghua University, Beijing 100084, China
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Authors to whom correspondence should be addressed.
Academic Editor: Vittorio M.N. Passaro
Received: 16 April 2017 / Revised: 7 May 2017 / Accepted: 10 May 2017 / Published: 13 May 2017
(This article belongs to the Section Physical Sensors)
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Abstract

Air-film damping, which dominates over other losses, plays a significant role in the dynamic response of many micro-fabricated devices with a movable mass suspended by various bearing mechanisms. Modeling the damping characteristics accurately will be greatly helpful to the bearing design, control, and test in various micromotor devices. This paper presents the simulated and experimental squeeze-film air damping results of an electrostatic bearing for use in a rotary high-speed micromotor. It is shown that the boundary condition to solve the three-dimensional Reynolds equation, which governs the squeeze-film damping in the air gap between the rotor and its surrounding stator sealed in a three-layer evacuated cavity, behaves with strong cross-axis coupling characteristics. To accurately characterize the damping effect, a set of multiphysics finite-element simulations are performed by computing both the rotor velocity and the distribution of the viscous damping force acting on the rotor. The damping characteristics varying with several key structure parameters are simulated and discussed to optimize the device structure for desirable rotor dynamics. An electrical measurement method is also proposed and applied to validate the numerical results of the damping coefficients experimentally. Given that the frequency response of the electric bearing is critically dependent on the damping coefficients at atmospheric pressure, a solution to the air-film damping measurement problem is presented by taking approximate curve fitting of multi-axis experimental frequency responses. The measured squeeze-film damping coefficients for the five-axis electric bearing agrees well with the numerical solutions. This indicates that numerical multiphysics simulation is an effective method to accurately examine the air-film damping effect for complex device geometry and arbitrary boundary condition. The accurate damping coefficients obtained by FEM simulation will greatly simplify the design of the five-axis bearing control system and facilitate the initial suspension test of the rotor for various micromotor devices. View Full-Text
Keywords: squeeze-film damping; finite-element method; multi-physics simulation; electric bearing; MEMS micromotor; air-film damping measurement squeeze-film damping; finite-element method; multi-physics simulation; electric bearing; MEMS micromotor; air-film damping measurement
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Wang, S.; Han, F.; Sun, B.; Li, H. Squeeze-Film Air Damping of a Five-Axis Electrostatic Bearing for Rotary Micromotors. Sensors 2017, 17, 1119.

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