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Brushless-motor

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Brushless motor

Details

Inventors: Ushiro, Tatsuzo; Karube, Yukuo;
Assignee: Canon Kabushiki Kaisha (Tokyo, JP); Canon Seiki Kabushiki Kaisha (Tokyo, JP)
Primary Examiner: Skudy; R.
Assistant Examiner:
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto

A brushless motor includes a rotor having a multipolar magnet with n-number of magnetic poles and a stator yoke having a plurality of field coils disposed at a position opposing the multipolar magnet. The stator yoke of the brushless motor is provided with a magnetic-resistance varying portion to improve the smoothness of rotation of the rotor.

DETAILED DESCRIPTION It is therefore a first object of the present invention to provide a motor in which it is possible to reduce the aforementioned torque ripples.
It is a second object of the present invention to provide a brushless motor having a construction such as that described illustratively in the related art in which motor a magnet and field coils are respectively disposed on a rotor yoke and a stator yoke in a flat manner and in face-to-face relationship with each other, the yoke for forming a magnetic circuit for magnetic flux being provided with a construction for generating cogging torque which acts to compensate for torque ripples.
It is a third object of the present invention to provide a flat-type brushless motor having a magnetic-resistance varying portion formed in a yoke member for generation of cogging torque.
A first feature of the present invention resides in a three-phase brushless motor comprising a rotor yoke having a multipolar magnet with n-number of magnetic poles; a stator yoke arranged to cause the rotor yoke to rotate about its axis; and at least three ridges disposed on the surface of the stator yoke which opposes the multipolar magnet and around the circumference of the stator yoke at a pitch equivalent to an electric angle of 60.
degree.
.
A second feature of the present invention resided in a three-phase brushless motor comprising a rotor yoke having a multipolar magnet with n-number of magnetic poles; a stator yoke arranged to cause the rotor yoke to rotate about its axis; and at least three holes formed in the surface of the stator yoke which opposes the multipolar magnet, the at least three holes being coaxial with the circumference of the stator yoke and being disposed at a pitch equivalent to an electric angle of 60.
degree.
.
A third feature of the present invention resides in a brushless motor comprising a rotor having a permanent magnet magnetized alternately in N and S polarities around the circumference thereof; a plurality of armature coils disposed in face-to-face relationship with the permanent magnet in a number which corresponds to the number of phases; an armature yoke for fixedly supporting the armature coils; and a magnetic-resistance varying portion for generating a cogging-torque wave form which is of a phase opposite to that of the wave form of torque ripples generated by the brushless motor

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