Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-11-03
2001-11-27
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S112000, C310S257000
Reexamination Certificate
active
06323569
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a stepping motor, and particularly relates to a stepping motor comprising a stator provided with stator yokes each having magnetic pole teeth.
2. Related Art
Heretofore, a stepping motor is configured, for example, in such a manner as shown in
FIGS. 8 and 9
.
That is, as shown in
FIG. 8
, a stepping motor
1
includes a hollow cylindrical housing
2
having an open end, a bracket
3
for closing the open end of the housing
2
, a stator
4
provided along the inner circumferential surface of this housing
2
, and a rotor
5
supported rotatably by bearing portions
2
a
and
3
a
provided in the housing
2
and the bracket
3
respectively.
The above-mentioned housing
2
is made of metal material and provided with the bearing portion
2
a
in a position near the center of the closed end surface of the housing
2
.
The above mentioned bracket
3
is made of metal material and provided with the bearing portion
3
a
in a position near the center of the bracket
3
in the same manner as in the housing
2
.
As shown in
FIG. 9
, the above-mentioned stator
4
is constituted by a substantially cylindrical yoke unit
6
in which four stator yokes
6
a
to
6
d
each provided with a ring-like flange portion having an outer diameter substantially equal to the inner diameter of the housing
2
so as to be stored in the housing
2
are integrally molded with a bobbin
7
of resin, and coils
8
a
and
8
b
wound on coil winding portions defined by the stator yokes
6
a
and
6
b
and by
6
c
and
6
d
respectively. The stator
4
is stored and fixedly held in the housing
2
after the coils
8
a
and
8
b
have been wound.
The above-mentioned rotor
5
is constituted by a rotating shaft
5
a
rotatably supported by the above-mentioned bearing portions
2
a
and
3
a
, and a hollow cylindrical rotor magnet
5
b
fixedly held on the rotating shaft
5
a
. This rotor magnet
5
b
is formed to have an outer diameter slightly smaller than the inner diameter of a central hole of the yoke unit
6
. The rotor magnet
5
b
is magnetized circumferentially.
Here, the above-mentioned stator yokes
6
a
to
6
d
are configured, for example, as shown in FIG.
10
.
Since all the stator yokes
6
a
to
6
d
have the same shape, only the stator yoke
6
a
is shown in FIG.
10
.
In
FIG. 10
, the stator yoke
6
a
is made of conductive metal material, and constituted by a ring-like flange portion
6
e
and a large number of magnetic pole teeth
6
f
provided to erect vertically from an inner circumferential portion of this ring-like flange portion
6
e.
The four stator yokes
6
a
to
6
d
are combined so that the stator yokes
6
b
and
6
c
are put back to back with each other, and the magnetic pole teeth
6
f
of one pair of the stator yokes
6
a
and
6
b
are shifted in phase by a predetermined value from those of the other pair of the stator yokes
6
c
and
6
d
. In this state, the stator yokes
6
a
to
6
d
are stored in a mold for molding the bobbin
7
, so that the bobbin
7
of resin is integrally molded around the stator yokes
6
a
to
6
d
. The yoke unit
6
is completed thus.
In the illustrated case, the stepping motor
1
has a flange
9
on the closed end side of the housing
2
so as to be attached by means of screws or the like to an electronic equipment utilizing the stepping motor
1
.
According to the stepping motor
1
configured thus, when a driving current is made to flow into the respective coils
8
a
and
8
b
of the stator
4
, magnetic fields generated in the coils
8
a
and
8
b
interact with the magnetic field of the rotor magnet
5
b
through the respective stator yokes
6
a
to
6
d
of the yoke unit
6
. Then, the rotor
5
is driven and rotated intermittently by the effect of the magnetic pole teeth
6
f
of the respective stator yokes
6
a
to
6
d.
However, the stator yokes
6
a
and
6
d
located on the opposite ends are in tight contact with the end surface of the housing
2
or the surface of the bracket
3
while the stator yokes
6
b
and
6
c
located inside are in back-to-back contact with each other. Therefore, magnetic flux leaks out of the magnetic circuits constituted by the pair of stator yokes
6
a
and
6
b
and the pair of stator yokes
6
c
and
6
d
together with the coil
8
a
and
8
b
respectively so that magnetic interference is generated between the magnetic circuits.
Here, in the case where the stepping motor
1
is driven by so-called single-phase excitation, and when, for example, the rotor
5
stops sequentially at rotor stop positions shown by the symbols S
1
, S
2
, S
3
, S
4
. . . with respect to the magnetic pole teeth
6
f
of the stator yokes
6
a
to
6
d
as shown in
FIG. 11
, theoretically, the magnetic center is switched as shown by the symbols A, C, B and D.
However, when the above-mentioned leakage of magnetic flux is generated, for example, at the stop position S
2
, the magnetic flux of the stator yoke
6
c
slightly leaks also to the stator yoke
6
b
so that the magnetic center is slightly shifted from the position C toward the position B. Accordingly, the position where the rotor
5
stops actually is also shifted to the position B side.
Similarly, at the stop position S
3
, the magnetic flux of the stator yoke
6
b
slightly leaks also to the stator yoke
6
c
so that the effects of excitation of the yokes
6
b
and
6
c
are canceled with each other. Accordingly, the magnetic center is slightly shifted from the position B toward the position C. Accordingly, the position where the rotor
5
stops actually is also shifted to the position C side.
In order to reduce such shift of the stop position of the rotor
5
due to the leakage of magnetic flux, heretofore, there are a method in which the dimensions of the comb-like magnetic pole teeth
6
f
in each phase are changed to balance the magnetic force among the respective pole teeth portions
6
f
; a method in which the angle with which the stator yokes
6
b
and
6
c
are combined is slightly shifted from a theoretical angle in order to correct the stop position; and so on. However, since scattering of the magnetic force among the respective magnetic pole teeth
6
f
changes in accordance with the combination of the condition of winding of the coils, the intensity of the magnetic force of the rotor, and so on, it is difficult to correct the displacement of the stop position perfectly.
On the other hand, in the case where the stepping motor
1
is driven by so-called two-phase excitation, and when, for example, the rotor
5
stops sequentially at rotor stop positions shown by the symbols S
1
, S
2
, S
3
, S
4
. . . with respect to the magnetic pole teeth
6
f
of the stator yokes
6
a
to
6
d
as shown in
FIG. 12
, theoretically, the positions D and A are excited at the stop position S
1
so that the magnetic center coincides with the middle position between the positions D and A, that is, the stop position S
1
. Similarly, the positions A and C are excited when the rotor
5
stops at the stop position S
2
, the positions C and B are excited at the stop position S
3
, and the positions B and D are excited at the stop position S
4
, so that the magnetic centers in the respective cases theoretically coincide with the middle positions between the excited positions, that is, the stop positions S
2
, S
3
and S
4
, respectively.
However, when the above-mentioned leakage of magnetic flux is generated, for example, at the stop position S
2
, the magnetic force of the housing
2
is given to the stator yoke
6
a
so that the magnetic force in the position A becomes intensive more than that in the position C. As a result, the magnetic center is slightly shifted toward the position A. Accordingly, the position where the rotor
5
stops actually is also shifted on the position A side.
Similarly, at the stop position S
4
, the magnetic force of the bracket
3
is given to the stator yoke
6
d
so that the magnetic force in the position D becomes intensive more than that in the position B. As a resu
McGuireWoods LLP
Mullins Burton S.
NGB Corporation
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