Abstract
Recently, gas bearings have been used in high speed spindles and in ultra precision cutting machines. It is known that the bearing performances are defined in stiffness and damping, and when the disturbance force acts on the shaft, the shaft response is predicted by damping factors of the bearing system and frequency ratio. In this paper, the journal center locus is measured in two cases : one is when the radial and the tangential electromagnetic forces act on the shaft twice and the other, four times, at every rotational cycle time at 10000 rpm and 30000 rpm, and theoretical calculations and experimental results are compared. Following conclusions are obtained : (1) The time of shaft convergence is shorter under low supply pressure than under high supply pressure. (2) The amplitude of shaft vibration becomes small when frequency ratio is greater than 2-3. (3) When high frequency external forces act on the shaft at every rotational cycle time, if the radial damping factor (ξr) gets to over 0.3 and the tangential damping factor (ξt) over 0.5, the shaft comes to the steady state within 2-3 periods of rotational cycle time at 30000 rpm.
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