Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2002-05-30
2004-01-20
Footland, Lenard A (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
C384S130000
Reexamination Certificate
active
06679632
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to an improved spindle motor design for a computer hard disk drive, and in particular to an improved lubricant retention design for a disk drive fluid dynamic bearing spindle motor.
2. Description of the Prior Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating.
A typical HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disks so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop directly over the desired track.
Typically, a plurality of the hard disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
FIG. 1
depicts a sectional side view of a conventional fluid dynamic bearing design for a spindle motor. One axial end of a shaft
11
(lower end in
FIG. 1
) is rigidly mounted to the mount flange
12
of the spindle motor. The other axial end of shaft
11
(upper end in
FIG. 1
) may be provided with optional internal threads so that the disk drive cover (not shown) can be attached to shaft
11
with a screw. The two zones of shaft
11
adjacent to the thrust plates
15
have precise diameters and provide stationary surfaces for the radial fluid dynamic bearings. Shaft
11
is located in a bearing sleeve
13
with the pair of thrust plates
15
therebetween. The flange at the top of sleeve
13
is used to center a disk clamp (not shown). Thrust plates
15
are fixed to shaft
11
and provide the stationary surfaces of the axial fluid dynamic bearing.
Still referring to
FIG. 1
, a small clearance is located between the outer diameter of thrust plates
15
and sleeve
13
. The clearance acts as a reservoir for excess lubricant, and helps to prevent the lubricant from escaping. If any excess lubricant escapes the reservoir, end seals
16
are provided to prevent the lubricant from escaping the spindle motor. Sleeve
13
provides the rotating fluid dynamic bearing surfaces for both the axial and radial bearings. The materials used to form shaft
11
, sleeve
13
, and thrust plates
15
and their surface treatments must be appropriate to survive wear and ensure reliable function of the disk drive.
As shown on the right sides of
FIGS. 2 and 3
, the center of the assembly is also provided with at least one lateral vent hole
19
which is interconnected to an axial vent hole
21
that extends through shaft
11
. Vent holes
19
,
21
are needed to equalize the atmospheric pressure exerted on both sides and both ends of the assembly.
When the assembly is subjected to non-operational vibration, such as during shipping or other handling when the disk drive is not in use, lubricant
17
migrates toward lateral vent hole
19
. A barrier film
20
is provided at lateral vent hole
19
on both shaft
11
and sleeve
13
in order to resist the flow of lubricant into lateral vent hole
19
. However, during extreme non-operation vibrational loads, such as high amplitude vibration encountered during transportation of the product, barrier film
20
is inadequate to impede the flow of lubricant
17
. Under such conditions, some of lubricant
17
can overcome barrier film
20
and enter vent holes
19
and
21
, thereby degrading the lubrication performance and causing contamination. Lubricant
17
that migrates into the vent holes
19
,
21
will not return to the bearing interface surfaces, which could result in failure of the bearing. Thus, an improved lubricant retention design for a fluid dynamic bearing in a spindle motor which overcomes the limitations of prior art designs is needed.
SUMMARY OF THE PRESENT INVENTION
One embodiment of a lubricant retention design for a fluid dynamic bearing design for a spindle motor is disclosed. A labyrinth gap is formed between the sleeve and the shaft of the bearing and is used in conjunction with a barrier film to impede the flow of lubricant into the lateral and axial vent holes during non-operational vibration, such as shipping and handling of the end product. In another embodiment of the present invention, a plug is located in the lateral vent hole. The plug has a very small passage that permits air to pass therethrough for atmospheric pressure equalization, but prevents the escape of lubricant into the vent holes. Alternatively, the plug may be formed from a non-wettable material such as porous foam or sintered material and provided with a larger opening. Yet another solution utilizes a combination of both the labyrinth and plug designs.
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Price Kirk B.
Stacer Daniel R.
Bracewell & Patterson L.L.P.
Footland Lenard A
Martin Robert B.
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