Commutation of a universal motor operating in brake mode

Details Commutation of a universal motor operating in brake mode Commutation of a universal motor operating in brake mode

1994-08-25

1997-10-14

Dougherty, Thomas M.

Electrical generator or motor structure

Dynamoelectric

Rotary

310 68A, 310 93, 310184, 388932, H02K 1100

Patent

active

056775865

ABSTRACT:
A universal motor (18) for a power tool (10) has a stator assembly (22) and an armature (24). The stator assembly includes a plurality of interconnected field windings (28-34) to which current is supplied to run the motor. The armature has a commutator (36) including brushes (40a, 40b) for circulating current through the armature. To quickly and safely brake the motor, without excessively damaging the brushes, a switch (16) is interposed between an AC power source for the motor and the armature. In one embodiment, the switch shorts the armature during braking. In this embodiment, the switch includes sets (56, 58, 60) of electrical contacts by which the inner field windings (28, 30) are connected in series with the outer filed windings (32, 34); and the field windings are series connected with the armature. When the motor is braked, the switch is moved to a position opening the electrical connection between the power source and the outer field winding, while maintaining the electrical connection with the inner field windings. The switch includes electrical contacts across which the armature is connected when the motor is braked. The armature is shorted across these electrical contacts to help brake the motor.

REFERENCES:
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patent: 4451752 (1984-05-01), Tahara et al.
patent: 4743815 (1988-05-01), Gee et al.
patent: 4891562 (1990-01-01), Nuckolls et al.
patent: 4912378 (1990-03-01), Vukosvic
patent: 4967464 (1990-11-01), Stephens
patent: 5063319 (1991-11-01), Mason et al.
patent: 5099184 (1992-03-01), Hornung et al.
patent: 5294874 (1994-03-01), Hessenberger et al.
patent: 5444318 (1995-08-01), Stumpf

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