Dynamic magnetic information storage or retrieval – Head mounting – For shifting head between tracks
Reexamination Certificate
1999-08-13
2002-01-29
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head mounting
For shifting head between tracks
C384S296000
Reexamination Certificate
active
06342992
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates in general to hard disk drives and in particular to enhanced mechanical features on hard disk drive actuator pivot cartridges including contact pads that are axially inboard of the pivot bearings and a pivot sleeve with an enhanced wall thickness for improving the servo stability of the disk drive.
2. Background Art
Referring to
FIG. 1
, a conventional, prior art actuator pivot cartridge
11
for a hard disk drive has an outer, cylindrical housing or sleeve
13
with a bore
12
and axis
14
, an inner pivot shaft
15
, and a pair of bearings
17
. Shaft
15
rotates or pivots relative to sleeve and bearings
17
are mounted in counterbores
18
at the axial ends of sleeve
13
. Counterbores
18
have a larger diameter than that of bore
12
. Note that counterbores
18
only support the outer races of bearings
17
and that bore
12
is located radially outward of the center of the balls of bearings
17
. Sleeve
13
has a threaded radial mounting hole
23
that is centrally located between its axial ends.
Sleeve
13
also has a wall thickness
19
of approximately 2.0 mm. Thickness
19
is adequately sized to generally handle most loads exerted on cartridge
11
. However, thickness
19
is less than twice as thick as the wall thickness of the sleeve at counterbores
18
. Wall thickness
19
also provides ample clearance (about 1.0 mm) between bore
12
and the outer surface of shaft
15
. The external profile or cross-section of sleeve
13
is altered slightly at its axial ends with integrally formed, annular bosses or pads
21
that extend around its circumference. Pads
21
are provided as closely toleranced, highly repeatable contact surfaces for cartridges
11
as will be described below. If cartridge
11
had a smooth cylindrical exterior along its entire axial length, the tolerances of the contacting surfaces would be much more difficult to control. Pads
21
are substantially axially aligned with their respective bearings
17
and counterbores
18
.
A second prior art example is illustrated in
FIG. 1A
as cartridge
11
A. This example is more fully described in U.S. Pat. No. 5,446,608. Like cartridge
11
, cartridge
11
A has a sleeve
13
A with a bore
12
A and axis
14
A, a shaft, and a pair of bearings
17
A in counterbores
18
A. Sleeve
13
A has a conventional wall thickness
19
A of approximately 2.0 mm. Cartridge
11
A also has a pair of narrow pads
21
A that are located axially outward or “outboard” of bearings
17
A.
As shown in
FIGS. 2 and 3
, cartridge
11
or
11
A (only cartridge
11
is shown for simplicity) mounts in the cylindrical bore
25
of an actuator comb
27
. A scallop-shaped, undercut portion
29
extends axially along the inner surface of bore
25
for providing two axial “lines” of contact
30
for cartridge
11
. Cartridge
11
is secured from movement relative to comb
27
with a single screw
31
that extends through a radial hole in comb
27
into the undercut portion
29
. The outer surfaces of pads
21
make contact with lines
30
in bore
25
(FIG.
4
). Due to the axial end positions of pads
21
and the limited wall thickness
19
of sleeve
13
, cartridge
11
tends to bow slightly along axis
14
and distorts radially to form an ellipse (shown exaggerated for ease of understanding). Even a slight axial or radial distortion in cartridge
11
will decrease the servo stability, decrease servo performance, and increase the torsional resistance of bearings
17
due to the changes in bearing stiffness.
A disk drive with poor servo stability will generate an excess of hard errors. Instability can be characterized by measuring the plant transfer function of the drive and examining the relevant dynamic modes. Modes which are not at the proper gain or frequency are the sources of the instability. For example, at the “butterfly” mode (FIG.
5
), the heads
33
of the drive oscillate over the midpoint
35
of the unit in a uniform pattern. In the S-mode (FIG.
6
), the top, middle and bottom heads
37
oscillate about the midpoint
35
by a small amount, while the remaining heads
39
oscillate with greater magnitude.
The S-mode can be filtered out using a servo notch if it remains at a consistent frequency and gain. However, if the mode has a large gain or spread, or it is located at a frequency outside the servo notch zone, the mode will remain unfiltered and cause servo instability. These modes are very sensitive to the stiffness of the actuator mechanical system components, including the pivot cartridge, actuator comb, coil, head gimbal assembly (HGA), and their interfaces. Thus, an improved mechanical system with greater component stiffness is desirable to increase servo stability and performance of the disk drive.
SUMMARY OF THE INVENTION
A hard disk drive actuator pivot cartridge has a sleeve, a coaxial pivot shaft, and a pair of bearings therebetween. The bearings are located near the axial ends of the shaft. The sleeve has a wall thickness that is substantially greater than those of prior art sleeves. The sleeve also has a pair of annular pads that are located axially inward of the bearings. The cartridge mounts inside an actuator comb such that only the pads contact the bore of the comb. The axial location of the pads and the greater wall thickness of the sleeve significantly decrease the bending experienced by the cartridge when it is installed in the comb, and thereby increase the servo stability and performance of the disk drive.
REFERENCES:
patent: 5315465 (1994-05-01), Blanks
patent: 5446608 (1995-08-01), Sanada
patent: 5473489 (1995-12-01), Sanada
patent: 5675456 (1997-10-01), Myers
Albertson Eric Martin
Misra Ambrish
Prater Walter Lloyd
Radwan Hatem Radwan
Bracewell & Patterson L.L.P.
International Business Machines - Corporation
Martin Robert B.
Renner Craig A.
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