Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-10-16
2004-08-24
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S184000
Reexamination Certificate
active
06781260
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a permanent magnet type rotary machine and, more particularly, relates to a hybrid (HB) type permanent magnet rotary machine or stepping motor for use in an office automation equipment or the like.
2. Description of the Prior Art
A three-phase permanent magnet type stepping motor is smaller in vibration than a two-phase permanent magnet type stepping motor. A number of transistors used in a bipolar type driving circuit of the three-phase stepping motor is six, whereas a number of transistors used in a bipolar type driving circuit of the two-phase permanent magnet type stepping motor is eight. Accordingly, the three-phase motor is better than the two-phase motor in general viewpoint. However, even in the three-phase motor, a number of harmonics are included in a field magnetic flux formed by the permanent magnet due to a number of pole teeth so that vibrations and noises are generated, even if a number of rotor pole pairs is increased, though the precision of the positioning and the fluctuation of rotation at the low speed of the motor are enhanced. A number multiplied by three, such as 3, 6, 9 or 12 etc. may be considered as a number of stator main magnetic poles of the three-phase motor. As inexpensive three-phase motors, three stator main magnetic poles are used in view of the simplicity in construction. Further, it is preferable to reduce the number of the stator main magnetic poles in order to increase the torque, because an interlinkage magnetic flux per one main magnetic pole is increased if the number of the main magnetic poles is reduced. A total quantity of magnetic flux &PHgr; of a permanent magnet type rotor in case of the three-phase motor having six stator main magnetic poles is the same with that in case of the three-phase motor having three stator main magnetic poles, if the permanent magnet type rotors are the same with each other. It is assumed that a turn number N of the winding for each phase of the motor having six stator main magnetic poles is the same with that of the motor having three stator main magnetic poles, that a torque per one phase, an interlinkage magnetic flux per one stator main magnetic pole, and a turn number of the winding per one stator main magnetic pole of the motor having six stator main magnetic poles are represented by T6, &PHgr;/6 and N/2, respectively, and that a torque per one phase, an interlinkage magnetic flux per one stator main magnetic pole, and a turn number of the winding per one stator main magnetic pole of the motor having three stator main magnetic poles are represented by T3, &PHgr;/3 and N, respectively. In the motor having six stator main magnetic poles, one phase is composed of two stator main magnetic poles, so that following equation (1) can be obtained.
T
6
=k
(&PHgr;/6)(
N/
2)
I×
2
=k
(&PHgr;
NI/
6) (1)
Where, I represents a current.
In the motor having three stator main magnetic poles, one phase is composed of one stator main magnetic pole, so that a following equation (2) can be obtained.
T
3
=k
(&PHgr;/3)
NI×
1
=k
(&PHgr;
NI/
3) (2)
It is apparent from the comparison of the two equations (1) and (2) that the torque of the motor having three stator main magnetic poles is larger than that of the motor having fix stator main magnetic poles.
U.S. Pat. No. 5,289,064 corresponding to the Japanese patent No. 3,140,814 discloses such conventional rotary machine.
In case that the conventional rotary machine having three stator main magnetic poles and a hybrid type (HB) rotor, an unbalance electromagnetic force in the radial direction is generated when the rotary machine is energized, so that harmonic waves are generated and thus a cogging torque is increased if the number of the rotor teeth is large, and that the vibrations and the cogging torque may be increased due to the unbalance electromagnetic force and the eccentricity in the air gap. Accordingly, it is required to improve the rotary machine in the property and the cost.
In the widely used two-phase rotary machine, the number of stator main magnetic pales is eight, and no unbalance electromagnetic force is generated. However, if the number is four, the construction of the rotary machine and the winding work of the winding become simple, so that the cast can be reduced. A torque T8 obtained in case that the number of the stator main magnetic poles is eight can be expressed by an equation (3).
T
8
=k
(&PHgr;/8)(
N/
4)
I×
4
=k
((
&PHgr;NI/
8) (3)
A torque T4 obtained in case that the number is four can be expressed by an equation (4)
T
4
=k
(&PHgr;/4)(
N/
2)
I×
2
=k
(
&PHgr;NI/
4) (4)
As apparent from the comparison of the two equations (3) and (4), the torque T4 is larger than the torque T8, however, in case that the number is four a radial unbalance electromagnetic force is generated between the stator and the rotor, so that the vibration and noise are increased and that the precision of the positioning is deteriorated.
In the widely used five-phase rotary machine, the number of stator main magnetic poles is ten, and no unbalance electromagnetic force is generated. However, if the number is five, the construction of the rotary machine and the winding work of the winding become simple, so that the cost can be reduced. Further, the torque of the motor having five stator main magnetic poles is larger than the torque of the motor having ten stator main magnetic poles, however, a radial unbalance electromagnetic force is generated between the stator and the rotor, so that the vibration and noise are increased and that the precision of the positioning is deteriorated.
That is, an air gap between the rotor an the stator becomes uneven, because a small air gap between an outer ring of a bearing and a bracket, as well as a small air gap between an inner surface of a bearing and an outer periphery surface of a shaft are varied, so that a cogging torque and a vibration when the motor is energized are increased, and that the noise are generated. The air gap in the permanent magnet type HB rotary machine is normally small as about 50×10
−6
m, so that if the air gap becomes uneven by a small fluctuation of the bearing, the vibration and the noise become large. The mechanism to generate the unbalance electromagnetic force will be explained with reference to the conventional example.
U.S. Pat. No. 5,289,064 discloses the three-phase rotary machine having three stator main magnetic poles and a HB type rotor, the number Nr of the rotor teeth being 3n±1, where n is a positive integer. In order to simplify the explanation, the pole pair number of the rotor is determined as one. In such a case that Nr=3n±1, n=0, and Nr=1, the vertically sectional side view of the rotary machine can be shown as
FIG. 7
, and the relation between the stator and the rotor of the three-phase rotary machine when it is energized ban be shown as
FIG. 8
showing a vertical section of the rotary machine. As shown in
FIG. 7
, a permanent magnet
5
is magnetized in the axial direction of a rotary shaft
4
so as to form two poles. In
FIG. 7
, a reference numeral
1
denotes three stator main magnetic poles extending radially from an annular magnetic yoke,
2
denotes a HB type magnetic rotor,
3
denotes three-phase stator windings, each wound around each of stator main magnetic poles,
6
and
7
denote front and back brackets of non-magnetic material such as aluminum, respectively, and
8
denotes bearings. The S pole of the rotor
2
is attracted upwards and the N pole of the rotor
2
is attracted downwards, so that the rotary shaft
4
receives a moment force, and if any air gap exists between the rotary shaft
4
and the bearing
8
, the air gap between the stator magnetic pole
1
and the rotor
2
becomes uneven.
FIG. 9
shows vectors showing components of upper and lower directions of the unbalance force shown in FIG.
8
. In
FIG. 9
, F
Boyle Fredrickson Newholm Stein & Gratz S.C.
Japan Servo Co. Ltd.
Nguyen Tran
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