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Electrical drive systems

Details

Inventors: Buckley, Maurice; Stone, Arthur; Murray, Aengus;
Assignee: Kollmorgen Technologies Corporation (Dallas, TX)
Primary Examiner: Ro; Bentsu
Assistant Examiner:
Attorney, Agent or Firm: Morgan & Finnegan

A direct current brushless electric motor has a rotor, and a stator with inwardly extending teeth, between each pair of which a winding slot is defined. The radially inward face of each tooth has a dummy slot shaped so the reluctance forces between rotor and stator due to the presence of the dummy slots are the same as those due to the winding slots. Motor control means incorporate a current feedback loop based on the incoming phase of each phase combination in the phase energization sequence in a driving mode and phase changeover may be initiated by Hall devices, two for each transition point, underlying the axial ends of the rotor magnets. The control means may incorporate a pulse width modulation power supply permitting the establishment of bias currents under motor standstill conditions.

DETAILED DESCRIPTION It is an object of the invention to provide a DC drive system having a low speed performance adequate for servo use.
In particular it is an object of the invention to minimize torque ripple in brushless drives and to provide smooth torque transitions.
It is a further object of the invention to provide a machine structure favourable to the elimination of cogging or reluctance torque.
Yet further aspects of the invention have as their object the reduction of heat generation in control systems and motors for DC drives of the kind to which the invention relates, and the extension of the speed range of such drives.
According to a first aspect of the invention there is provided a direct current electric motor comprising a winding portion having a plurality of winding slots and a field portion having a plurality of poles, at least one of said portions being mounted for displacement relative to the other of said portions, the winding portion having at least one dummy slot between at least one pair of adjacent winding slots, and said at least one dummy slot being shaped so that during relative displacement of the winding and field portions, the reluctance forces prevailing between said portions due to the presence of said at least one dummy slot are substantially the same as the reluctance forces prevailing between said portions due to the presence of the winding slots.
In a rotational embodiment, the invention provides a direct current electric motor comprising an armature portion having a plurality of winding slots and a field structure portion having a plurality of poles, at least one of said portions being mounted for displacement relative to the other, the armature portion having at least one dummy slot between at least one pair of adjacent winding slots, and said at least one dummy slot being shaped so that during relative displacement of the armature portion and the field structure portion, the reluctance forces prevailing between said portions due to the presence of said at least one dummy slot are substantially the same as the reluctance forces prevailing between said portions due to the presence of the winding slots

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