Influence of Unbalanced Electromagnetic Force and Air Supply Pressure Fluctuation in Air Bearing Spindles on Machining Surface Topography

Abstract

Air bearing spindles (ABS) can meet high accuracy demands for the precise rotation motion, which adopt air bearings to support spindle shaft, and the spindle shaft directly connects the motor rotor. The unbalanced electromagnetic force caused by motor rotor eccentricity (MRE) and air pressure fluctuation (APF) are two important influential factors to the dynamic performance of the spindle system and machining surface quality. This paper addresses the problems of measuring the MRE and APF in an ABS through testing machining surface topography. A permanent magnet synchronous motor (PMSM) was modelled by finite element simulation (FES). Through FES it found that the MRE between the motor rotor and stator hole produced a radial magnetic force (RMF), which could cause ABS to periodically vibrate in the axial direction. Besides, the change of the air supply caused the stiffness variation of ABS and result in the tilt error motions of the spindle shaft. A theoretical model of machining surface topography considering MRE and APF was then proposed for the first time, which revealed that the MRE and APF resulted in the periodic fluctuations of the machining surface topography. The overall surface topography then became grooved surfaces. The above findings were finally validated by measurement results of ultraprecision diamond turning experiments.