| 摘要 |
A step motor is disclosed which comprises a rotor having four magnetic poles, a first magnetic pole which is excited by a first coil, a second magnetic pole which is excited by a second coil, and a third magnetic pole which is excited by the first and second coils. A gap (d) between the first or second magnetic pole and the rotor is so set that there occurs a magnetic attraction between a magnetic pole of the rotor and the first or second magnetic pole, and a gap (D) between the third magnetic pole and the rotor is formed lager than the gaps (d). When such a step motor is used in a shutter driving unit of a camera or the like, the open/closed state of the shutter can be surely kept even when no current is applied.
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