Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-06-08
2002-10-22
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C370S902000
Reexamination Certificate
active
06469410
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement in an outer rotor type disc driving spindle motor on which a plurality of discs such as magnetic discs are to be laminated and mounted.
2. Description of the Related Art
A rotor diameter of an outer rotor type disc driving spindle motor is increased due to its structure. An inertia moment is increased so that a rotational non-uniformity is reduced. Accordingly, the outer rotor type disc driving spindle motor is suitable as a magnetic disc driving motor to be used, for instance, as a memory medium for a computer.
There has been provided conventionally a disc driving spindle motor on which a plurality (about ten) of magnetic discs are able to be loaded in lamination in a magnetic disc driving device called “1.6 Inch-Height” with 40.6 mm in total height.
Such a conventional spindle motor for driving a disc is shown in FIG.
4
.
As shown in
FIG. 4
, in an outer rotor type disc driving spindle motor, a rotor
3
(hub) having magnets
3
a
that face a stator
2
having coils
2
a
(stator coils) are located outside the stator
2
fixedly supported to a shaft. The energization of the stator
2
to cause rotation of rotor
3
(hub) by interaction of the stator
2
with magnets
3
a
is caused by controlled electrical signals provided on wires to coil windings.
In such a conventional spindle motor for driving a disc, the rotor
3
and the stator
2
are provided with the following support structure.
The rotor
3
is formed to have a substantially cylindrical drum portion
3
b
in which an axial dimension is set so that a plurality (predetermined number, e.g., ten in this case) of discs (not shown) may be laminated in the axial direction and loaded on its outer circumference. Then, the rotor
3
is rotatably supported on the shaft
1
through an upper bearing
4
located on an opening surface
3
c
on the upper side and a lower bearing
5
located at an opening surface
3
d
on the lower side of the drum portion
3
b
of FIG.
4
.
In this case, a substantially annular bush
6
is interposed between opening ends of the lower opening surface
3
d
and the lower bearing
5
. Accordingly, the lower end portion of the rotor
3
is supported by the lower bearing
5
through the bush
6
. The hub is indirectly supported by the bearing
5
via a bush
6
.
The stator
2
is disposed between the upper and lower bearings
4
and
5
. In this stator
2
, the axial dimension S
2
is set to be substantially the same as the axial dimension M
2
of the magnets
3
a
.The stator
2
is fixedly supported on the shaft
1
over the range of the full axial dimension S
2
.
Incidentally, reference character
1
a
denotes a tubular hole formed in the shaft
1
and
2
a
1
denotes a lead wire connected to a coil end of the stator coils
2
a
.This lead wire
2
a
1
is inserted into the tubular hole
1
a
to be guided to the outside of the rotor
3
(drum portion
3
b
). Reference numeral
7
denotes a frame for holding and fixing the shaft
1
, and the frame
7
is located so as to cover the bush
6
.
Any one of the bearings
4
and
5
is a radial bearing as shown in FIG.
4
.
The magnet
3
a
is made of magnet material having a magnetic energy product of 160 kJ/m
3
that is a typical example of this type motor. The magnet
3
a
is fixed to an inner wall of the drum portion
3
b
of the rotor
3
with an axial dimension that is close to the full length between the upper and lower bearings
4
and
5
.
However, the prior art suffers from the following disadvantages.
Since the stator
2
is interposed between the upper and lower bearings
4
and
5
, the lead wire
2
a
1
from the stator coils
2
a
has to be led to the outside of the rotor
3
through the tubular hole la of the shaft
1
. For this reason, it is necessary to perform the processing of the shaft
1
, the insertion of the lead wire
2
a
1
through the tubular hole
1
a
, and the like, thereby increasing both the part cost and the assembling work cost. Also, the structure itself in which the stator
2
is interposed between the upper and lower bearings
4
and
5
causes labors for assembling the stator
2
to be increased.
Since the bush
6
is interposed between the lower bearing
5
and the rotor
3
, the assembling precision and hence the rotational precision would be degraded. It gives trouble to enhance the precision. In addition, since the bush
6
is an expensive and precise part, the part cost and the assembling work cost are both increased.
In particular, such a complicated structure, in which the annular hole
1
a
is formed in the shaft
1
, the lead wire
2
a
1
is passed through the annular hole
1
a
, and the bush
6
is provided in addition to the frame
7
, results in more difficulty and causes a cost increase in the assembly.
Incidentally, it is possible to solve the above mentioned problem by disposing the stator
2
under the lower bearings
4
and
5
by providing the stator
2
outside (on the side of the opening surface
3
d
on the lower side of the drum portion) rather than between the upper and lower bearings
4
and
5
. This will now be explained.
In the motor shown in
FIG. 4
, assume that the relationships, L:S
2
=1:0.38 and L:B
2
=1:0.66, are established where L is the length of the shaft
1
(nearly equal to the total motor length) and B
2
is the distance between the bearings
4
and
5
.
Keeping the shaft length L intact, i.e., under the condition that the motor is not enlarged, the value S
2
to the value L (the dimension in the axial direction of the stator) and the distance between the bearings
4
and
5
(referred to as B
3
for the sake of explanation although not shown) are sought in the case where the stator
2
is shifted from the distance between the bearings
4
and
5
to the outside. Then, the relationship, L:S
2
=1:0.38, is unchanged but the relationship, L:B
3
=1:0.22, is established.
Since the axial dimension S
2
of the stator is too large, the ratio of the dimension B
3
between the bearings
4
and
5
to the shaft length (nearly equal to the total motor length) is extremely small at 0.22. For this reason, the center between the bearing
4
and
5
is remarkably eccentric from the center of gravity of the rotor
3
on which the discs are mounted, as a result of which the bearing load is displaced to adversely affect the rotational precision or the service life of the bearings.
It is basically preferable that the discs be located in a place corresponding to a position between the bearings
4
and
5
. If the distance (ratio) between the bearings
4
and
5
is reduced, the number of the discs that may be mounted is also reduced. Accordingly, it is preferable that the ratio L:B of the distance B between the bearings
4
and
5
to the dimension L be large, and in general, the ratio is needed to be about 0.5 at the minimum.
However, as described above, such a simple method to shift the stator
2
from the space between the bearings
4
and
5
to the outside is not actually adopted because the ratio is extremely small at 0.22. Accordingly, the above-described problems could not yet solved in the state of the art.
SUMMARY OF THE INVENTION
In order to solve the problems inherent in the above-described prior art, an object of the present invention is to provide a spindle motor for driving discs, which may reduce the part cost and the assembling work cost and enhance the assembling precision and the rotational precision.
In order to attain this and other objects, according to a first aspect of the present invention, there is provided an outer rotor type disc driving spindle motor in which a rotor having a magnet facing a stator having a coil and supported to a shaft is located outside of the stator, characterized in that: the rotor is formed to have a cylindrical drum portion to have an axial dimension so that a predetermined number of discs may be laminated in the axial direction and mounted around an outer circumference of the rotor, the rotor being rotatably mounted on the
Le Dane Dinh
Minebea Co. Ltd.
Oliff & Berridg,e PLC
Waks Joseph
LandOfFree
Spindle motor for driving disc does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Spindle motor for driving disc, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spindle motor for driving disc will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2968730