Patent ID: 6707178
Filing Date: 2004-03-16
Classification: H02K

Abstract:
A permanent magnet type twelve-pole stepping motor of an inner rotor type, comprising:a stator comprising a yoke portion having substantially annular shape, a stator iron-core comprising magnetic material having twelve stator main poles that are directed from the inner circumferential surface of the yoke portion toward the center and each having four small teeth on the tip end thereof, and stator coils wound in the stator iron-core; and one of a hybrid type rotor rotatably supported by the stator through a predetermined air gap, having a cylindrical permanent magnet magnetized in a rotation axis direction that is sandwiched between a pair of rotors comprising magnetic material each having Nr pieces of pole teeth around the outer circumferential surface thereof at an equal pitch and the rotors being arranged such that the pole teeth are deviated with each other, and a permanent magnet type rotor having a cylindrical outer circumferential surface magnetized in a direction parallel to the rotation axis to form Nr pairs of N-pole and S-pole alternately; wherein said stator is formed as three-phase winding and second harmonic component, third harmonic component, fourth harmonic component and fifth harmonic component are removed by composing cogging torque of respective phases by a three-phase twelve-pole construction, and a mechanical deviation angle (&tgr;) between a pitch of the four small teeth in the stator and a pitch of teeth in the hybrid type rotor and permanent magnetic type rotor equals to (&pgr;/4Nr) radians so as to independently erase the second harmonic component, thereby the second harmonic component is doubly erased.