| 摘要 |
PURPOSE:To reduce the irregularity of a torque in a motor by reducing a magnetic interference between upper and lower groups. CONSTITUTION:A rotor magnet 15 is composed by securing a concentric cylindrical magnet 22 through a collar of nonmagnetic material, such as plastic to a rotor shaft 14. N-, S-poles are alternately magnetized at a predetermined circumferential pitch at the magnet 22, and a nonmagnetized region 23 of predetermined width is formed at the axial center of the magnet 22. Thus, a magnetic interference between an upper group and a lower group can be reduced by the region 23 near the vicinity of the bent part of a yoke to reduce the irregularity of a torque between upper and lower exciting coils, thereby alleviating a vibration noise.
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