Abstract
Recently, in high technology industry, gas bearings have been used in high speed spindles owing to low friction, and in ultra precision cutting machines by the use of clean air. The pocketed orifices are adapted to their requirements, and it is known that the bearing performances are defined as stiffness and damping, and that the shaft movement is predicted by damping factor (ξ) of the bearing system. But it is not clear how the shaft movement is affected by their values. In this paper, journal center locus is measured when an impact force acts on the shaft, and theoretical calculations and experimental results are compared. Following conclusions are obtained : (1) A shaft movement behavior is affected by supply pressure, but when the bearing clearance is set to the optimum value (10 μm), damping factor gets to greater than 0.4 at any supply pressure. (2) When a disturbance force acts on the shaft at every rotational cycle time interval, if damping factor gets to greater than 0.2-0.3, the shaft comes to the steady state condition within 1-2 periods of rotational cycle time.
