Theoretical analysis of a ball bearing used in HDD spindle motors for reduction of NRRO

In this paper, we theoretically analyzed the NRRO of the ball bearing caused by form errors of the inner and outer raceways and balls. The results are summarized as follows: (1) as for geometrical errors of the inner and outer raceways, it is possible to reduce the NRRO to less than 1 nm by choosing either 12 or 18 balls, even if the inner and outer raceways have harmonic undulation of less than the eleventh order; (2) the effect of the differences in ball diameter and ball form error on the NRRO monotonously decreases as the number of balls increases.