| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem in the conventional motors used for a disc device or a general machine, such that even though a rotor hub is fixed to the outer ring of a ball baring in a form that the inside peripheral face of the rotor hub which has a disc presser mounting hole 12, etc., at its top end face engages with the outside peripheral face of the outer ring of the ball bearing, the circumferential stress of the inside peripheral face of the rotor hub becomes nonuniform due to the mounting hole 12, and this causes nonuniform stress distortion in the outer ring of the ball bearing 7 and deterioration of NRRO in rotation and also may cause noise and vibration at rotation if left intact. SOLUTION: New holes 14 are arranged at equal intervals between the mounting holes 12, and the rigidity in the inside peripheral direction of the rotor hub is substantially equalized in the circumferential direction. Hereby, the outer ring of the ball bearing 7 receives equal stress in circumferential direction from the rotor hub, and it can maintain its cylindrical form, NRRO is improved, and it can reduce noise and vibrations at motor operation, too.
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