Patent ID: 6051898
Filing Date: 2000-04-18
Classification: H02K

Abstract:
An outer rotor composite type three-phase stepping motor comprising: a stator consisting of two stator elements each having twelve stator magnetic poles extending outwardly radially with Ns pieces of pole tooth formed on a tip end of each stator magnetic pole, and a permanent magnet held by the two stator elements,an annular rotor of magnetic material arranged so as to face to an outer periphery of the stator through an air gap, Nr pieces of pole tooth being formed on an inner periphery of the rotor,exciting windings wound around each stator magnetic pole of the stator elements, said exciting windings consisting of one set of three-phase windings wound around every other stator magnetic poles among the twelve stator magnetic poles, and another set of three-phase windings wound around remaining six stator magnetic poles among the twelve stator magnetic poles, a mechanical degree angle formed between the adjacent magnetic poles in the twelve magnetic poles being changed between (30.degree.-.theta.s) and (30.degree.+.theta.s) alternately, where Nr is a number of rotor pole teeth, ns is an integer not less than 1, and .theta.s is a step angle of (30.degree./Nr)/k, where k is an integer number not less than 1.