Macro-scale investigation of high speed gas bearings for MEMS devices

Abstract

A macro-scale experimental test facility for investigating high-speed gas bearings for MEMS devices such as the MIT Micro-Engine is presented along with results from subsequent experiments. It is shown that the bearings required by such MEMS devices fall outside the usual range of design parameters for conventional gas lubrication systems. Due to the unorthodox design of the bearings, a new "hybrid" mode of operation is introduced along with the traditional hydrodynamic regime. The new hybrid mode is exploited to implement a novel in-situ rotor balancing scheme which enables hydrodynamic operation. Analysis for both modes of operation is presented along with experimental results. A high-order, efficient scheme for computing both the steady and unsteady hydrodynamic properties of the fully coupled, rotor/gas film dynamical system is presented along with comprehensive calculations for this class of plain, cylindrical, gas journal bearing. The scheme is then used to perform a generalized eigenvalue analysis on the compressible, unsteady system which reveals a new type a hydrodynamic instability. From a fundamental understanding of the bearing physics, strategies for operating MEMS devices with this class of bearing are deduced and minimum requirements for the accompanying measurement systems are established. Ancillary issues such as axial equilibrium of the rotor are discussed in detail.