| 摘要 |
PROBLEM TO BE SOLVED: To improve rotation accuracy of a motor by adhering and fixing an inner ring of a ball bearing to a shaft side, pressing in an outer ring to a motor hub side, and increasing thickness of the outer ring of at least one of vertically provided ball bearings. SOLUTION: In upper and lower ball bearings, an outer ring 3a of the upper bearing is thicker than an outer ring 3b of the lower bearing. Because a radial thickness T1 of an upper bearing press-in portion is larger than a radial thickness T2 of a lower bearing press-in portion, stresses applied to the bearing's outer ring are different from each other between the upper and lower press-in portions. Even slight thickening of the outer ring of upper ball bearing provides an effect, but preferably, the thickness is 1.5-2.5 times thicker than that of the lower ball bearing. Thus, rigidity can be improved, deformation can be prevented, and rotation accuracy of a motor can be improved by eliminating deformation of the ball bearing.
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