Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1995-03-20
1997-10-21
LaBalle, Clayton E.
Electrical generator or motor structure
Dynamoelectric
Rotary
310180, 310164, H02K 112, H02K 1904, H02K 2122
Patent
active
056799977
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a brushless DC motor, and more particularly to a brushless DC motor structure which excels in self starting reliability and has the rotational speed fluctuation reduced, and to a method for driving it.
BACKGROUND ART
Such a conventional radial gap type brushless DC motor has its rotor 51 consisted of a cup shaped back yoke 52, an annular permanent magnet 53 adhered to the inner wall of the back yoke, and a shaft, 55 inserted in a bush 54 at the center of the back yoke 52, as shown in FIG. 34. In the drawing, the reference numeral 56 represents a turn table.
A stator 57 consists of first and second stator yokes 58, 59 made of soft magnetic metal plate and a coil 60 disposed between the both stator yokes 58, 59 as shown in FIG. 35. These stator yokes 58, 59 have claw poles 58a, 59a which are pole pieces radially extended outward from the center and bent at right angles, and integrally formed rings 61, 62 at the center along the direction the claw poles 58a, 59a are bent. In the drawing, the motor is of four poles.
The first stator yoke 58 and the second stator yoke of the stator 57 are assembled with the coil 60 therebetween. A ring 61 and another ring 62 are joined to be magnetically connected to form a magnetic circuit. And, keeping a prescribed gap from the circumference of the permanent magnet 53 of the rotor 51, the claw poles 58a and the claw poles 59a of the first stator yoke 58 and the second stator yoke 59 are alternately disposed in the circumferential direction.
Further, a sleeve 63 is mounted within the ring 61 of the stator 57, and the shaft 55 of the rotor 51 is supported within the sleeve 63 via a bearing 64. At the bottom of the sleeve 63, a base plate 65 is fitted to support the stator 57, and a circuit substrate 66 is fixed to the base plate 65. In the drawing, the reference numeral 67 indicates a hole element which is a sensor for detecting magnetic pole of the rotor, and G indicates a gap.
In a conventional brushless DC motor, claw pole width a of one claw pole Xx is generally the same to claw pole width b of the other claw pole Yy as shown in FIG. 36 and FIG. 37(a), and claw pole pitch c from the one claw pole Xx to the other claw pole Yy is set to be equal to claw pole pitch d from the other claw pole Yy to the one claw pole Xx. In other words, claw poles having an equal claw pole width are combined at equal intervals. When a torque curve in this case is drawn (vertical axis: torque T, horizontal axis: machine angle .theta.), FIG. 37 (b) shows that when a cogging torque shown by a solid line (torque due to attraction by the magnet and stator yoke) reaches point B (unstable point: mark .DELTA.) at 180 degrees in electrical angle (for one magnetic pole in machine angle) from point 0 (unstable point: mark .DELTA.) via point A (stable point: mark o) in the rotation for one magnetic pole of the rotor, a negative torque works from point A and forward to generate a returning force to the rotor, and when the rotor is rotated in the opposite direction, a positive torque works to generate a force to point A. Suppose the position of the hole element is point C, polarity is switched at this point C, and the generated torque shown by a dotted line (torque which is generated when electricity is flown, and the sum of the excited torque and a cogging torque generated by the coil current) drops at point C as illustrated, generates a negative torque in the illustrated shaded area, and moves forward through point B. When the negative torque is generated, a dead point (point where self-starting is impossible) is always generated. This dead point is B in the drawing. The rotor stops at point A which is a stable point when the motor is under no load, but since it does not always stop at point. A when an external load is on the motor, the motor cannot rotate even when electricity is flown if the rotor stops at point B.
Generally, the motor is used as so-called actuator and under some load as described above. And, since the rotor does not always stop at so-called s
REFERENCES:
patent: 3857053 (1974-12-01), Yatsushiro et al.
patent: 4004168 (1977-01-01), Haydon
patent: 4656381 (1987-04-01), Komatsu
Ito Norio
Matsuzawa Kinya
Miyazawa Hiroshi
LaBalle Clayton E.
Seiko Epson Corporation
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