Importance

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Abstract

A stepper motor includes a cylindrical rotor, a plurality of stators, a plurality of yokes, and a plurality of coils. The cylindrical rotor is made of a permanent magnet which has been magnetized radially. The rotor has two magnetized layers formed in an axial direction thereof. Each of the stators has a plurality of magnetic pole portions which are disposed such that they oppose an outer periphery of the rotor. The magnetic pole portions of the stators oppose one of the magnetized layers of the rotor. The plurality of yokes are made of a permeable material. The yokes are separated from the stators in the axial direction of the rotor. The end portions of the yokes oppose the other magnetized layer of the rotor. The plurality of yokes are shifted from the stators by a predetermined angle. The plurality of coils are disposed such that each coil excites a corresponding stator. By this arrangement, the diameter of the lens barrel of a camera containing such a stepping motor can be reduced and the output and efficiency of the stepper motor can be improved.

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First Claim