GB1455704A - Electric stepping micromotors - Google Patents

Abstract

1455704 Electric motors FRESARD FRERES 10 Dec 1973 57080/73 Heading H2A An electric stepping micromotor comprises a rotor 10 including a peripherally slotted, non- magnetic support disc 11 carrying, in the slots, 2p inserts 18 of permanent magnetic material magnetized in alternate axial directions, and a stator 20 including a flat cylindrical casing 21, 22 of non-magnetic material, the internal face of each end wall of which is covered with a flat annular disc 24, 25, of non-permanent magnetic material carrying flat coils 26, 27 distributed in circular symmetry, the coils being arranged in mutually opposite relationship on either side of the rotor and being electrically interconnected to form a winding which, in use, is supplied with alternate polarity pulses and produces 2p axial magnetic fields in alternately opposite directions. The rotor support disc 11 and the stator casing 21, 22 may be made of light, non-magnetic alloy or synthetic resin. There are eight rotor inserts in the embodiments disclosed, the inserts preferably being made of a cobalt-rare earth compound, e.g. a cobalt-samarium compound. The rotor may be retained in any one of eight angular positions by an annular stator member 28 of magnetic material notched to form eight projections. The rotor shaft 13 is coupled to an output shaft through gearing 15, 16 providing an output speed of 1 r.p.m., the motor being suitable for use in a wrist watch. In a modification, Figs. 3, 4 (not shown), the notched member 28 is omitted and the two stator discs 24, 25 are notched to form eight projections on each.