Rotational assembly for disc drive device having small...

Details Rotational assembly for disc drive device having small... Rotational assembly for disc drive device having small...

1998-03-27

2001-01-09

Davis, David (Department: 2754)

Dynamic magnetic information storage or retrieval

Record transport with head stationary during transducing

Disk record

Reexamination Certificate

active

06172847

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a disc drive device used in information equipment and audio-video equipment, and in particular in optical disc units and magnetic disc units.
BACKGROUND OF THE INVENTION
Heretofore, disc drive devices have been constructed e.g. as shown in FIG.
1
. Such a disc drive unit is typically used for a spindle motor.
More specifically, the disc drive device has a rotational assembly
10
on which a disc (not shown) can be mounted, a shaft
1
on which the rotational assembly
10
is rotatably supported by means of two ball bearings
23
, and a base
7
to which the lower end of the shaft
1
is secured The rotational assembly
10
and the disc mounted thereon are rotatably driven by a motor M which is disposed between the base
7
and the rotational assembly
10
. The motor M has a rotor
8
secured to the rotational assembly
10
, and a stator
9
secured to the base
7
with the rotor
8
and stator
9
radially opposed to each other.
The rotational assembly
10
comprises a hub in tie case of the spindle motor.
With the magnetic disc units, however, due to the development of high recording densities, it is desirable that the deviation of non-repetitive runout (NRRO) in the disc drive device used in the magnetic disc units be small. The term “non-repetitive runout” is also referred to as “non-repeatable runout”.
With the conventional disc drive device, as shown in
FIG. 1
, the deviation of non-repetitive runout (NRRO) needs to be small with the ball bearings
23
. However, since the ball bearings
23
have vibration due to rolling of the balls and vibration due to errors in the shape of the bearing members, even with improved manufacturing accuracy, it is difficult to keep the deviation of non-repetable runout below a specified value.
FIG. 2
shows another example of the conventional disc drive devices, that is a spindle motor, which uses hydrodynamic fluid bearings with small deviation of non-repetitive runout, for both a radial bearing and a thrust bearing. In this example, the rotational assembly includes a shaft
1
and a hub
40
.
A sleeve
6
is fitted into the base
7
to which the motor M is mounted, and provided with a cylindrical bole, the inner peripheral surface of which is formed with a radial bearing face
6
a
. The radial bearing face
6
a
of the sleeve
6
and the outer peripheral surface of the shaft
1
cooperate to form a radial hydrodynamic fluid bearing. On the other hand, the lower end face
1
a
of the shaft
1
and the upper surface
58
a
of the thrust bearing
58
cooperate to form a thrust hydrodynamic fluid bearing to support the thrust load.
Although such hydrodynamic fluid bearings make small the deviation of non-repetitive runout, there is a drawback that the shaft
1
with the hub
40
can easily come off the sleeve
6
if it receives shock or load from outside in the direction where the shaft comes off Therefore, in the example of
FIG. 2
, a stopper
60
is mounted to the hub
40
in an interference relation with a flanged portion
6
b
of the sleeve
6
. However, it is troublesome to provide such a stopper
60
. And during transportation, the stopper
60
sometimes bumps the axially opposing flange portion
6
b
of the sleeve
6
causing abrasion debris.
SUMMARY OF THE INVENTION
An object of the present invention is, in view of the above problems, to provide a disc drive device wherein the deviation of non-repetitive runout is small, the starting torque is small, and the introduction of lubricant and the assembly are simple.
Another object of the present invention is to provide a spindle motor in which the deviation of non-repetitive runout is small, and can be placed in an inverted state and has good shock resistance.


REFERENCES:
patent: 4706143 (1987-11-01), Asada et al.
patent: 4972283 (1990-11-01), Kim
patent: 5453892 (1995-09-01), Hasegawa et al.
patent: 5581425 (1996-12-01), Choi
patent: 5754374 (1998-05-01), Kim
patent: 63-94327 (1988-06-01), None
patent: 6-178497 (1994-06-01), None
patent: 7-310739 (1995-11-01), None
patent: 9-149586 (1997-06-01), None

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