Hydrodynamic bearing and disk apparatus

Details Hydrodynamic bearing and disk apparatus Hydrodynamic bearing and disk apparatus

2002-06-13

2004-07-06

Davis, David (Department: 2652)

Dynamic magnetic information storage or retrieval

Record transport with head stationary during transducing

Disk record

Reexamination Certificate

active

06760187

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a hydrodynamic bearing to be used for an apparatus having a rotating mechanism, such as a disk recording/reproducing apparatus for recording and/or reproducing data while rotating a disk at a high speed.
Recently, in a disk recording/reproducing apparatus for recording and/or reproducing data while rotating the disk, the memory size greatly increases and the data transfer speed becomes very high. Therefore, it becomes necessary to provide mechanism for achieving a high speed and high precision rotation force in a rotating mechanism incorporated in such disk recording/reproducing apparatus. Accordingly, a high-speed rotatable hydrodynamic bearing which is constituted so as to support both ends of a main shaft, such as for example described in U.S. Pat. No. 5,504,637, is employed in a rotating mechanism of a disk recording/reproducing apparatus.
A conventional hydrodynamic bearing described in U.S. Pat. No. 5,504,637 is explained hereunder as an example of a prior art with reference to FIG.
10
.
FIG. 10
is a cross-sectional view showing a constitution in the vicinity of a main shaft in a conventional hydrodynamic bearing. In
FIG. 10
, an end portion (lower end portion in the drawing) of a fixed shaft
22
that is the main shaft is fixed to a base member
21
. A flange member
23
is fixed in the proximity of the other end portion of the fixed shaft
22
. A sleeve
24
and a rotor hub
25
are formed in one integral and is provided rotatable around the fixed shaft
22
. An outer circumferential end face of the flange member
23
is disposed inside of a stepped recess
25
A formed on the rotor hub
25
. A thrust plate
26
is placed so as to confront the upper face of the flange member
23
. The thrust plate
26
is fixed to the rotor hub
25
so that the thrust plate
26
can rotate around the fixed shaft
22
. Two sets of herringbone-shaped radial hydrodynamic pressure grooves
24
A and
24
B are formed on the outer circumferential surface of the fixed shaft
22
. And, herringbone-shaped thrust hydrodynamic pressure grooves
23
A are formed on the upper face of the flange member
23
, which is confronting the thrust plate
26
. Further on the lower face of the flange member
23
, thrust hydrodynamic pressure grooves
23
B are provided. The radial hydrodynamic pressure grooves
24
A and
24
B, as well as thrust hydrodynamic pressure grooves
23
A and
23
B are filled with lubricant
27
.
A rotor magnet
28
is attached to the rotor hub
25
formed in one unified body with the sleeve
24
. And, a motor stator
29
is attached to the base member
21
so as to confront the rotor magnet
28
.
In
FIG. 10
, a space shown by reference numeral
22
A is a ventilating path, which has a function for discharging air received in a clearance “H” in the proximity of the outer circumferential portion of the flange member
23
. A space shown by numeral
24
D in
FIG. 10
is also a ventilating path for discharging air received in a clearance “J” in the proximity of the lower inner circumferential portion of the flange member
23
.
Operations of the conventional hydrodynamic bearing constituted as above are described with reference to FIG.
10
.
When power is supplied to the motor stator
29
so that a rotative magnetic field is generated, the rotor magnet
28
starts to rotate along with the rotating members including the rotor hub
25
, sleeve
24
and the thrust plate
26
, etc. Concurrently, the herringbone-shaped radial hydrodynamic pressure grooves
24
A and
24
B collect the lubricant toward the central portion thereof. As a result a pressure is generated in a clearance between the outer circumferential surface of the fixed shaft
22
and the inner circumferential surface
24
C of the sleeve
24
, because the lubricant is squeezed into this clearance by pumping effect. Likewise, a pressure is generated around the herringbone-shaped thrust hydrodynamic pressure grooves
23
A and
23
B, by the pumping effect to squeeze the lubricant.
By such pressure generated by the lubricant
27
, the rotating members around the fixed shaft
22
rotate perfectly in non-contact state with the fixed shaft
22
. Consequently disks that are the recording mediums (omitted in the drawing) attached to the rotor hub
25
are driven to rotate together with the sleeve
24
. As a result, electric signal is recorded on or reproduced from the disk through a head (omitted in the drawing). Detailed description of operations for recording and reproducing to be performed here is omitted since they are similar to known recording and reproducing processes of a hard disk driving apparatus (HDD).
The conventional hydrodynamic bearing constituted as above has the following disadvantages.
As shown in
FIG. 10
, the lubricant
27
is applied to the thrust hydrodynamic pressure grooves
23
A as well as in the clearance “H” between the outer circumferential end face of the flange member
23
and the inner circumferential surface of the stepped recess
25
A. During the hydrodynamic bearing is at rest, the lubricant
27
contained in the clearance “H” moves toward a clearance “G” which is narrower than the clearance “H”, due to capillary action. The clearance “G” is located between the inner circumferential surface of the thrust plate
26
and the outer circumferential surface of the fixed shaft
22
. The lubricant
27
which has moved into the clearance “G” becomes in a visible state to stand up above the end of the clearance “G”, with the lapse of time. When power is supplied to the motor stator
29
and the rotor magnet
28
starts to rotate with the sleeve
24
, rotor hub
25
and thrust plate
26
under such a state. At the instant, the lubricant
27
in the clearance “G” instantly became lubricant drops
27
a
and
27
b
and splashes out of the hydrodynamic bearing as a result of centrifugal force. In
FIG. 10
, a mark “RH” shows a distance in a radial direction of the clearance “H” between the outer circumferential end face of the flange member
23
and the inner circumferential surface of the stepped recess
25
A. Also a mark “RG” shows a distance in a radial direction of the clearance “G” between the inner circumferential surface of the thrust plate
26
and the outer circumferential surface of the fixed shaft
22
. As shown in
FIG. 10
, the distance “RF” was greater than the distance “RG” (i.e., RH>RG) in a conventional hydrodynamic bearing.
In addition, in the conventional hydrodynamic bearing, the lubricant
27
is applied to the thrust hydrodynamic pressure grooves
23
A formed on the flange member
23
as well as to clearances “K” and “L” between the outer circumferential surface of the fixed shaft
22
and the inner circumferential surface of the sleeve
24
. Once the rotating members such as the rotor magnet
28
, sleeve
24
, rotor hub
25
and thrust plate
26
, etc. start rotating under such state, the lubricant
27
in the clearance “L” turns into overflow lubricant as a result of centrifugal force and starts to flow out (downward in
FIG. 10
) of the hydrodynamic bearing. In
FIG. 10
, a mark “RK” shows a distance in a radial direction of the clearance “K” between the outer circumferential surface of the fixed shaft
22
and the inner circumferential surface of the sleeve
24
, and a mark “RL” shows a distance in a radial direction of the clearance “L”. As shown in
FIG. 10
, the distance “RK” was greater than the distance “RL” (i.e., RK>RL) in the conventional hydrodynamic bearing.
As described above, the conventional hydrodynamic bearing has the disadvantage that the lubricant
27
flows out of the clearances “G” or “L”, amount of the lubricant
27
decreases, and therefore the lubricant
27
may finally become no longer effective. In addition, since the lubricant
27
splashes out of the apparatus, the lubricant
27
may adhere to other apparatus, thus causing unfavorable effect.
BRIEF SUMMARY OF THE INVENTION
Briefly stated, in one aspect, the present invention is a hydrodynamic bearing comprising a fixed shaft having one end fixed to a ba

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