Stepping motor

• US 5,331,237 A
• Filed: 04/23/1993
• Issued: 07/19/1994
• Est. Priority Date: 04/28/1992
• Status: Expired due to Term

• Current Assignee: Minebea Kabushiki-Kaisha
• Original Assignee: Minebea Kabushiki Kaisha
• Inventors: Ichimura, Hirotaka
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US08/052,165
• Time in Patent Office: 452 Days
• Field of Search: 310/40 MM, 310/43, 310/44, 310/45, 310/49 R, 310/49 A, 310/89, 310/257, 310/258
• US Class Current: 310/44
• CPC Class Codes: H02K 1/02 characterised by the magnetic material
• CPC Class Codes: H02K 37/14 with magnets rotating within the armatures
• CPC Class Codes: H02K 5/02 Casings or enclosures characterised by the material thereof

Abstract

A small-sized stepping motor provided with can-type stator yokes and one flat-type stator yoke, all of which are injection molded of a composite powder (i.e., a mixture of a metal powder of a soft magnetic material, a powder of a thermoplastic synthetic resin). The injection molded stator yokes have a considerably large specific electrical resistance, and the stepping motor is free from various disadvantages resulting from a small specific electric resistance.

Claims

1. In a stepping motor comprising:

(a) a housing comprising a pair of can-type stator yokes each of which is provided with a toothed portion in an inner surface thereof for forming a plurality of magnetic poles;

(b) a rotor provided in said housing;

(c) a pair of coils disposed around said rotor in said housing; and

(d) a flat-type stator yoke provided with a toothed portion forming a plurality of magnetic poles which correspond to those of said toothed portions of said can-type stator yokes, said flat-type stator yoke being disposed in said housing;

the improvement comprising;

(e) both of said can-type stator yokes being injection molded yokes formed of an injection molded composite powder in which a metal powder of a soft magnetic material is mixed with a powder of a thermoplastic synthetic resin; and

(f) said flat-type stator yoke being a one-piece, integrated injection molded yoke formed of an injection molded composite powder in which a metal powder of a soft magnetic material is mixed with a powder of a thermoplastic synthetic resin which is the same as that of said can-type stator yokes, and said flat-type stator yoke being provided with its magnetic poles extending from opposite sides thereof and having its magnetic poles correspond to those of said can-type stator yokes.

2. The stepping motor as set forth in claim 1, wherein:

said metal powder is made of iron.

3. The stepping motor as set forth in claim 1, wherein:

said powder of thermoplastic synthetic resin of said composite powder which is molded into both of said can-type stator yokes and said flat-type stator yoke is made of polypropylene resins.

4. The stepping motor as set forth in claim 1, wherein:

said composite powder molded into both of said can-type stator yokes and said flat-type stator yoke is a mixture of an iron powder and a powder of polypropylene resins.