Stepping motor structure

Claim 2

A stepping motor comprising: a stator fixedly mounted on a shaft, said stator comprising a spider having a plurality of spokes radially extending outward from the shaft, operating windings disposed on said spokes and effective when energized to generate magnetic flux in said spokes, the direction of flux being radial, an enlarged pole piece section at the outer end of each of said spokes, said sections each being provided with a plurality of radial teeth, a rotor surrounding and substantially enveloping said stator, said rotor comprising a cylinder having a plurality of teeth on the inner surface thereof corresponding in dimension to the teeth of said stator, the teeth on said stator and the teeth on said rotor being skewed or advanced with respect to one another by one quarter of a pole pitch, said rotor being mounted for rotation on said shaft, a permanent magnet flux source for providing an operating flux bias for said motor, said magnet comprising a circular magnet member concentric with said shaft and said rotor, and flux focusing means associated with said magnet for directing the flux from said magnet in a preferred path including said rotor and said stator.

Claim 3

A stepping motor as claimed in claim 1, in which said permanent magnet comprises a ring-shaped magnet concentric with said shaft, and located at the closed end of said rotor, and said flux focusing means comprises a tapered cylindrical member extending axially from said magnet to said spider.

Claim 4

A stepping motor comprising a stator fixedly mounted on a shaft, said stator having a first and a second spider, each comprising a plurality of spokes radially extending outward from the shaft, said spiders being disposed at opposite ends of the motor, operating windings disposed on said spokes and effective when energized to generate magnetic flux in said spokes, the direction of flux being radial, an enlarged pole piece section at the outer end of each of said spokes, said sections each being provided with a plurality of radial teeth, a rotor surrounding and substantially enveloping said stator, said rotor comprising a cylinder having a plurality of teeth on the inner surface thereof corresponding in dimension to the teeth of said stator, said rotor being mounted on bearings at opposite ends of said motor for rotation on said shaft, a permanent magnet flux source for providing an operating flux bias for said motor, said magnet comprising a circular magnet member concentric with said shaft and said rotor, and flux focusing means associated with said magnet for directing the flux from said magnet in a preferred path including said rotor and said stator, said flux focusing means comprising a circular magnetic element fitting between said magnet and said shaft, said permanent magnet and said focusing means being disposed centrally on said shaft with respect to said first and second spiders.

Claim 5

A stepping motor comprising a stator fixedly mounted on a shaft, said stator having a first and a second spider, each comprising a plurality of spokes radially extending outward from the shaft, said spiders being disposed at opposite ends of the motor, operating windings disposed on said spokes and effective when energized to generate magnetic flux in said spokes, the direction of flux being radial, an enlarged pole piece section at the outer end of each of said spokes, said sections each being provided with a plurality of radial teeth, a rotor surrounding and substantially enveloping said stator, said rotor comprising a cylinder having a plurality of teeth on the inner surface thereof corresponding in dimension to the teeth of said stator, said rotor being mounted on bearings at opposite ends of said motor for rotation on said shaft, a permanent magnet flux source for providing an operating flux bias for said motor, said magnet comprising a circular magnet member concentric with said shaft and said rotor, and flux focusing means associated with said magnet for directing the flux from said magnet in a preferred path including said rotor and said stator, said flux focusing means comprising a circular magnetic element fitting between said magnet and said shaft, said permanent magnet and said focusing means being disposed centrally on said shaft with respect to said first and second spiders.

Claim 6

A stepping motor as claimed in claim 3, in which said permanent magnet is radially magnetized.

Claim 7

A stepping motor as claimed in claim 3, in which the teeth on said stator teeth and said rotor teeth are skewed or advanced with respect to one another by an even fraction of a pole pitch.

Claim 8

A stepping motor as claimed in claim 5, in which the fraction is one-quarter of a pole pitch.

Claim 9

A stepping motor as claimed in claim 3, in which the outer surface of said rotor is provided with load engaging means.