Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1996-02-29
2001-11-20
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06700R
Reexamination Certificate
active
06320288
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a brushless DC motor having a plurality of position detectors for detecting the position of magnetic poles on a rotor, and more particularly to a brushless DC motor which improves the DC motor characteristic like the torque ripple characteristic and the rotation unevenness characteristic, etc. by arranging the position detectors.
2. Description of the Prior Art
The brushless DC motor for floppy disk drives of personal computers have Hall sensors using a Hall effect for detecting a roter position. The task of Hall sensors is a detection of a roter's position and maintenance of roter's rotation. This task is essential for producing an optimum commutating action. It is now understood that the action and its accuracy of positioning the position detectors directly affect the operational characteristics of the motor in that sense. However, the installation of the position detectors has been determined by consideration of the general principles and concepts in conventional brushless DC motors.
Particularly, a polyphase, multipole motor provides two or more combinations of location for installation of the position detectors according to the principles and concepts. It will thus take a considerable length of time and labor to determine the best of the combinations in applicable conditions.
It is known that the symmetrical arrangement of the position detectors is most commonly adopted in which the mechanical balance is maintained in a system of rotating action for minimizing deflecting and eccentric movements. For example, three of the position detectors in a conventional three-phase brushless DC motor, regardless of the number of poles, are mounted at equal angular intervals of 120 degrees as shown in FIG.
9
.
Such a known motor is usually designed to partially or entirely control the energization of its coils with analog voltage outputs of the position detectors. It's a big problem in the control method above that small and flat type motors easily structurally affect Hall output voltages to detect the rotor magnet position. In this common drive method, the outputs of the position detectors of phases should be uniform.
If not, the waveform of a coil driving signal produces a deviation from the timing of commutating or the amplitude in each commutating action. Accordingly, the rotor is varied in the torque depending on its rotational angle, thus increasing a nonuniformity of rotation.
SUMMARY OF THE INVENTION
The present invention is directed towards eliminating the foregoing drawbacks. It is an object of the present invention to provide an optimum arrangement of position detectors, which is inexpensive but hardly affected by intrinsic mechanical deflection, radial displacement on a rotary structure or motor, or by a secondary artifact or variation in the magnetic coupling resulting from the mechanical deflection or radial displacement.
For achievement of the above object of the present invention, a brushless DC motor with N phases (N≧2) is provided having position detectors of which signal outputs are indicative of the location of magnetic poles of a rotor and used for controlling the rotation for a constant speed. More particularly, it is characterized in that while any two adjacent position detectors are spaced from each other by a spatial angle &thgr;i [rad] about the center of the rotor, (1
)*(&thgr;i/2&pgr;)<KM is established where i=1 to N−1, 0<&thgr;i<2&pgr;/N, KM is the mechanical time constant of the motor (sec), and n is the number of revolutions (rps). The position detectors are consecutively arranged at equal intervals as located in their respective slots provided between stator magnetic poles. Preferably, the position detectors are Hall devices. Since the position detectors of different phases are spatially gathered in a small region, the magnetic imbalance resulting from mechanical deflection or radial displacement is attenuated. As a the result, a variation of the Hall voltage output of each position detector due to the magnetic imbalance will be minimized.
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Fujitani Sakae
Makino Kenichi
Ohyashiki Taketoshi
Suzuki Yuzuru
Minebea Co. Ltd.
Nguyen Tran
Staas & Halsey , LLP
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