Dynamic Characteristics of Hydrostatic Air Bearing Spindle with Two Circumferential Grooves and Discrete Feeding Hole Restrictions.

Abstract

This paper describes the design method and fabricated result of a hydrostatic air bearing spindle which has both high static stiffnesses and high damping ratios at resonance frequencies. The air bearing spindle designed by the proposed design method is composed of two thrust bearings of 110mm outer diameter and 55mm inner diameter and one radial bearing of 50mm length and 50mm diameter. The developed air bearing spindle has a high static stiffness of 500N/μm in the thrust direction, 110N/μm in the radial direction and 3.9×105Nm/rad in the angular direction under the supply pressure of 0.49 MPa. Dynamic stiffnesses measured by the experimental modal analysis method are, respectively, found to be 1.8, 2.6 and 2.2 times the above-described static stiffnesses in each direction. These static and dynamic stiffnesses are found to be in a fairly good agreement with theoretical ones. Damping ratios are, respectively, 0.039, 0.035 and 0.055 in the thrust, radial and angular directions, which are roughly 50 percent larger than the theoretical ones.