Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-06-12
2003-08-19
Lam, Thanh (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S049030, C310S089000, C310S091000, C029S596000, C029S598000
Reexamination Certificate
active
06608416
ABSTRACT:
The present application is based on Japanese Patent Application No. 2001-178404, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a relatively small-sized motor, such as a motor for feeding an optical pickup in an optical disk drive apparatus or the like, and a method of manufacturing the same, and more particularly to a technique for improve the accuracy of such a motor.
In many cases, high dimensional accuracy and rotational accuracy are required for small-sized motors depending on their applications. For instance, in a motor for feeding an optical pickup in an optical disk drive apparatus or the like, there is a need to move the optical pickup smoothly, and it is required that the stopping position accuracy is to be high. Referring now to
FIG. 4
, a description will be given of an example of a conventional motor of this type.
In
FIG. 4
, a stator portion of the motor includes a stator set consisting of a stator core
1
and drive coils
3
each wound around a bobbin
13
circumscribing this stator core
1
as well as a stator set consisting of a stator core
2
and drive coils
4
each wound around a bobbin
19
circumscribing this stator core
2
. These two stator sets are fixed by being superposed in the axial direction. This motor is a stepping motor, and each of the stator cores
1
and
2
has a plurality of pole teeth arranged at equal intervals in a cylindrical shape on its inner peripheral side. An outer side surface of a bent side
10
a
at one end side of a frame
10
, which is formed in a U-shape with both end faces bent orthogonally in the same direction and with a long bottom, is fixed to an end face on an axially outer side of the stator core
1
.
A hole with a diameter of &phgr;B is formed in a bent side
10
b
at the other end side of the frame
10
, and a bearing
11
, which consists of an outside-diameter portion having the same diameter as the aforementioned &phgr;B and an outside-diameter portion larger than the same, has its outside diameter &phgr;B portion fitted and fixed in this hole from the inner side of the frame
10
. The bearing
11
has a recess for receiving one end portion of an output shaft
6
, and has a semispherical recess for receiving an approximately half of a steel ball
12
in a bottom of this recess. A conical recess provided at a distal end of the output shaft
6
is fitted over the steel ball
12
fitted in the semispherical recess.
The bent side
10
a
at the one end side of the frame
10
is also provided with a hole with substantially the same diameter &phgr;D as the aforementioned diameter &phgr;B, and the output shaft
6
is passed through this hole. One end side of the output shaft
6
is formed as a small-diameter portion
6
a
, and this small-diameter portion
6
a
is inserted in holes defining inner peripheral sides of the stator cores
1
and
2
. The inside diameter &phgr;C of the stator cores
1
and
2
is larger than the diameters &phgr;B and &phgr;D of the holes formed in the bent sides
10
a
and
10
b
of the frame
10
. A slide bearing
8
whose outside diameter is substantially the same as the aforementioned inside diameter &phgr;C is fitted on an inner periphery of a bearing member fixed to an end face of the stator core
2
having the inside diameter &phgr;C, such that the slide bearing
8
is slidable along the inner periphery of the bearing member.
The slide bearing
8
has a recess on its inner end side, and an approximately half portion of a steel ball
7
is thrust into this recess, while the remaining approximately half portion of the steel ball
7
is fitted in a conical recess formed in an end face of the small-diameter portion
6
a
which is the one end side of the output shaft
6
. The slide bearing
8
has its proximal portion urged in a direction in which it enters an inner periphery of the stator core
2
by a leaf spring
9
fixed to an outer end of the stator core
2
. The steel ball
7
presses the output shaft
6
by this urging force to cause the steel ball
12
at the distal end of the output shaft
6
to be pressed against the bearing
11
. Thus the output shaft
6
is rotatably supported by the bearings
8
and
11
via the steel balls
7
and
12
, and the load in the direction of thrust is thereby received. A hollow cylindrical magnet
5
is fitted and secured on an outer peripheral side of the small-diameter portion
6
a
of the output shaft
6
, and the output shaft
6
and the magnet
5
constitute the rotor of the motor.
Magnetic poles are formed in the magnet
5
at equal intervals in the circumferential direction, and as the drive coils
3
and
4
are alternately energized by a power supply in the form of pulses, the rotor rotates through predetermined angles. A lead screw is formed on the output shaft
6
between the bent sides
10
a
and
10
b
of the frame
10
, and as a portion of an object to be driven, such as an unillustrated optical pickup, or a member substantially integrated therewith, is engaged with this lead screw, the object to be driven is moved back and forth along the output shaft
6
in correspondence with the rotation of the output shaft
6
.
The above-described motor is a compact motor with an outside diameter of 6 mm or less in the case of driving an optical pickup, or one with a width of 6 mm or thereabouts in the case of an oval motor. With such a small-sized motor, since there is a need to make smaller the air gap between the inner periphery of the stator and the outer periphery of the rotor magnet
5
, high accuracy of concentricity is required for respective component units. However, a further increase in the accuracy of individual components involves higher cost, which is undesirable since a highly sophisticated production technique is required.
In addition, to obtain concentricity for the main body portion of the motor and the output shaft
6
, during assembly a pin gage is inserted through a hole defining an inner periphery of the main body portion of the motor and the holes formed in the bent sides
10
a
and
10
b
of the frame
10
, and the main body of the motor and the frame
10
are fixed in a state in which the relative positional offset, inclination, and a deviation in concentricity are eliminated. However, since the inside diameter of the main body portion and the diameter of the holes formed in the bent sides
10
a
and
10
b
of the frame
10
differ, as described above, a pin gage having a step needs to be used correspondingly. As such, however, if the pin gage is provided with a step, there is a possibility that the pin gage itself loses its concentricity between the large-diameter portion and the small-diameter portion. Hence, there is a drawback in that the concentricity of the pin gage is reflected as it is on the concentricity of the main body portion of the motor and the output shaft, so that the concentricity varies.
In particular, with the motor for feeding an optical pickup in an optical disk drive apparatus, the span of the bent sides
10
a
and
10
b
of the frame
10
is 50 to 60 mm or thereabouts and is thus long. Therefore, if the frame
10
is inclined even slightly when it is fixed, the position for supporting the distal end of the output shaft becomes offset by a large degree, so that unless the hole diameter on the distal end side of the frame is measured directly to control concentricity, the accuracy of concentricity required for this type of motor cannot be ensured.
SUMMARY OF THE INVENTION
The invention has been devised in view of the above-described conventional art, and its object is to provide a motor which has a motor body and a frame for holding its output shaft, and which makes it possible to obtain concentricity of the motor body and the output shaft with high accuracy and minimize the clearance between the stator and the rotor, as well as a method of manufacturing the same.
(1) In accordance with the invention, there is provided a method of manufacturing a motor including a cylindrical rotor having a magnet, a stator having a cyli
Kabushiki Kaisha Sankyo Seiki Seisakusho
Lam Thanh
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