Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1992-04-03
1993-01-05
Ro, Bentsu
Electricity: motive power systems
Induction motor systems
Primary circuit control
318772, H02P 736
Patent
active
051774232
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a winding arrangement in an AC motor capable of varying the rotating speed in a wide range from a low rotating speed to a high rotating speed without significantly varying the output. The AC motor can be applied as a spindle motor capable of providing a high power over a wide range of rotation speeds.
BACKGROUND ART
In a C-axis control of the angular position of the spindle motor of a machine tool for a contour machining, the spindle must be smoothly rotated at a very low rotating speed and the spindle motor must deliver a high output, and during a usual machining, the spindle motor must be operated at a high rotational speed and deliver a high output.
The conventional machine tool is provided with two motors, namely, one for low-speed machining and the other for high-speed machining, to meet those two requirements, but such a drive system of the conventional machine tool is costly and requires a large floor space. Another system employs belts and gears to maintain a high output for machining over a range of from a low-speed to a high-speed, which also requires an increased floor space.
DISCLOSURE OF THE INVENTION
Accordingly, an object of the present invention is to provide an AC motor capable of maintaining a high output over a wide range of rotational speeds and able to use less floor space.
In view of the above object, the present invention provides a winding arrangement in an AC motor, comprising power-carrying windings respectively for phases, each of the windings including a plurality of sets of coils held in slots of the AC motor for a corresponding phase. The ends of each set of coils are connected to a plurality of terminals for the corresponding phase, and the connection between the terminals and a power source is changed by a switching device.
Since the coils for each phase held in the slots are connected to the terminals, the number of coils in each slot can be decided by selectively connecting the terminals for each phase to the power source by the switching device, whereby the output of the AC motor can be held substantially constantly in a desired range of rotational speed, and the rotational speed can be varied continuously in a range of from a low rotational speed to a high rotational speed, while maintaining a high output.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration of a typical winding arrangement in a first embodiment according to the present invention;
FIG. 2 is a diagrammatic view showing the arrangement of windings for one of a plurality of phases in connection with the slots;
FIG. 3 is an illustration of a typical winding arrangement in a second embodiment according to the present invention; and
FIG. 4 is an illustration of a typical winding arrangement in a third embodiment according to the present invention; and
FIG. 5 is a graph showing the output characteristics of an AC motor incorporating a winding arrangement according to the present invention.
BEST MODE OF CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. FIG. 1 shows star-connected U-, V- and W-windings for a three-phase AC motor; and FIG. 2 shows a winding for phase U in an actual arrangement in connection with slot position denoted by reference numerals 1, 2, 3 and the like. The U-, V- and W-windings are joined electrically at a neutral point XYZ. Since the U-, V- and W-phase windings have the same construction, only the U-phase winding will be described hereinafter.
Both ends of the U-phase winding are connected, respectively, to the neutral point XYZ and a terminal U1. In this example, the AC motor is assumed to be provided with thirty-six slots. A wire starting from the terminal U1 is passed through the slots 1, 12, 2, 11, 3 and 10, in that order, to form a coil X1 for a first set, and then through the slots 19, 30, 20 29, 21 and 28, in that order, to form another coil X2 for the first set. The slots are arranged sequentially along a circular d
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Hayashi Yoshiyuki
Kimijima Masami
Nakamura Kosei
Numai Kazuhisa
Fanuc Ltd.
Ro Bentsu
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