Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1989-04-25
1991-04-23
Stephan, Steven L.
Electrical generator or motor structure
Dynamoelectric
Rotary
310261, H02K 2114
Patent
active
050102664
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a structure of a rotor of a radial type synchronous motor wherein the rotor core is held between permanent magnets, and more particularly, to a rotor structure whereby slot ripple is reduced.
BACKGROUND ART
Torque fluctuation, that is, slot ripple, occurs during the rotation of a rotor due to the presence of slots in a stator in a synchronous motor provided with a stator having slots for a winding, and a rotor having permanent magnets. This is due to a change in clearance between the rotor and the stator in correspondence with an angular position of the rotor, because of the slots in the stator, and a consequent change of density of magnetic flux. A slight fluctuation of feed velocity occurs when an electric motor having slot ripple is used, for example, in a feed mechanism of a machine tool, and thus the finished accuracy of a workpiece is poor.
To solve the above problem, the applicant disclosed, in Japanese Unexaminated Patent Publication No. 63-178750, a rotor structure wherein the rotor is divided into a plurality of unitary rotor elements arranged along an axis thereof, and each unitary rotor element is fixed at a first angular position or a second angular position separated from the first angular position by a prescribed angle.
Seventy two slot ripples occur in one rotation of a rotor of, for example, an eight pole-synchronous motor having thirty six slots, and in this case, the angular difference between the above-mentioned first and second angular positions is 2.5 degrees, but an angular error of as much as one degree can occur during the manufacture and assembly of a rotor. In the above-mentioned rotor having two angular positions, when the error angle is 2.5 degrees, each slot ripple caused by a relative position between the stator slots and each unitary rotor element fixed at the first or second angular position has the same phase, and thus a slot ripple similar to a ripple in the prior art rotor not having a skew structure in which each angular position is shifted, occurs. Although the error in the angle between the two angular positions in a skew rotor is not necessarily exactly 2.5 degrees, the effect obtained by adopting the skew structure is substantially lost when an angular error of as much as one degree occurs
DISCLOSURE OF THE INVENTION
To solve the above problem, an object of the present invention is to provide a rotor structure wherein each unitary rotor element is fixed exactly at a predetermined first or second angular position.
Therefore, according to the present invention, there is provided a rotor structure of a synchronous motor having a rotor core held between permanent magnets, wherein each of a plurality of unitary rotor elements constituting a rotor is arranged at one angular position or at another angular position around a central axis of the rotor in correspondence with a period of a slot ripple of the motor; an angular difference between the two angular positions is an angle corresponding to a half wave of the slot ripple; end portions of permanent magnet elements and rotor core elements, which elements constitute the unitary rotor element in each angular position, provide recesses and projections in a direction parallel to the central axis; and an end plate member is engaged with the recesses and projections formed by the permanent magnet elements and the rotor core elements.
Each of two groups of unitary rotor elements in two angular positions constituting a rotor is held exactly at a respective prescribed angular position by the end plate member having projecting portions and recessed portions engaged with the recesses and the projections provided by end portions of the permanent magnet elements and the rotor core elements of the unitary rotor element, whereby slot ripple is considerably reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a is a schematical general plan view of a rotor according to the present invention; this figure does not fully show details of the end plate member. FIG. 1b shows a partial enla
REFERENCES:
patent: 4196366 (1980-04-01), Schiethart
patent: 4700096 (1987-10-01), Epars
patent: 4823038 (1989-04-01), Mizutani et al.
patent: 4906882 (1990-03-01), Erndt et al.
Fanuc Ltd
Rebsch D. L.
Stephan Steven L.
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