Electricity: motive power systems – Plural – diverse or diversely controlled electric motors – Plural – diverse or diversely controlled sources of armature...
Patent
1990-05-23
1992-09-15
Skudy, R.
Electricity: motive power systems
Plural, diverse or diversely controlled electric motors
Plural, diverse or diversely controlled sources of armature...
310106, 310276, 310254, 310269, H02P 736
Patent
active
051480905
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an AC servo motor of the variable reluctance type, more particularly it relates to an AC servo motor of the variable reluctance type which does not generate torque ripple.
BACKGROUND ART
In general, since a variable reluctance motor does not use magnets, as opposed to synchronous motors, it has a simple construction and may be cheaply fabricated. The method of use of this type of motor is as follows: The coil is wound around the poles of the stator; by passing a rectangular wave current, the poles of the stator are excited; the magnetic attraction force pulls the poles of the rotor and causes rotation.
Nevertheless, during rotation, a variable reluctance motor suffers from the problem of nonlinear changes in the magnetic permeance in accordance with the relative positions of the poles of the rotor and stator, and thus the generation of torque ripple. Further, rectangular wave currents include higher order high harmonics, and when the rotational speed becomes high, it is no longer possible to pass the required current due to the difference in the frequency response of the high harmonics. Therefore, it is difficult to use a variable reluctance motor for torque control, speed control, and position control.
DISCLOSURE OF THE INVENTION
Therefore, an object of the present invention is the provision of a variable reluctance motor able to be used as a servo motor free from the generation of torque ripple, thus solving the above problem.
In view of the above-mentioned object, there is provided a variable reluctance type AC servo motor characterized in that the number of salient poles of the rotor is n, the number of phases of at least three phases or more for exciting the salient poles of the stator is m, and the number of poles of the stator is r.multidot.m, the number of poles n being an integer, with the condition that r is not a whole multiple of the number r.multidot.m but is a whole multiple of the number r, the shape of the salient poles of the rotor changes sinusoidally in dimension in the longitudinal direction with respect to the direction position of the rotor, the shape of the salient poles of the stator is fixed in dimension in the longitudinal direction with respect to the circumferential direction position of the stator, the phase currents of the m phases exciting the stator poles are AC sine wave currents and have a period H2 two times the period of fluctuation of the magnetic permeance caused by rotation of the rotor, and the conductance phase between adjoining stator poles is shifted 2n.pi./(r.multidot.m) each in the phase of magnetic permeance fluctuation through the provision of current application means.
If the shape of the rotor poles is sinusoidal and the shape of the stator poles is band-like, i.e., rectangular, with a fixed width, the facing area of the rotor and stator during rotation of the rotor changes sinusoidally, whereby the magnetic permeance changes sinusoidally. In a motor of this construction, no torque ripple is generated if an alternating current with a period twice the period of fluctuation of the magnetic permeance is applied to the stator poles with the sine wave current shifted 2.pi./(r.multidot.m) each at the phases of the magnetic permeance fluctuation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematically expanded partial development of a portion of superimposed surfaces of rotor and stator poles of a motor according to the present invention;
FIG. 2 is a schematic horizontal sectional view of a motor according to the present invention;
FIG. 3a is a schematically expanded development of pole surface of a motor according to the present invention in an embodiment using four rotor poles and a three phase current;
FIG. 3b is a perspective view of a rotor of a motor of FIG. 3a;
FIG. 4 is a horizontal sectional view of a motor corresponding to FIGS. 3a, 3b which horizontal sectional view corresponds to the sectional position of the arrow line IV--IV of FIG. 3a.
FIG. 5a is an expanded partial development of pole su
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patent: 4698537 (1987-10-01), Byrne
patent: 4883999 (1989-11-01), Hendershot
patent: 4896088 (1990-01-01), Jahns
patent: 4933620 (1990-06-01), MacMinn
Nakamura Takeshi
Oku Hideaki
Fanuc Ltd.
Skudy R.
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