Dynamic magnetic information storage or retrieval – Head mounting – For moving head into/out of transducing position
Reexamination Certificate
2000-11-30
2003-03-18
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head mounting
For moving head into/out of transducing position
Reexamination Certificate
active
06535358
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive comprising a plastic molded crash stop with embedded magnet for latching an actuator arm.
2. Description of the Prior Art
A computer system usually includes one or more disk drives for economical, non-volatile data storage.
FIG. 1
shows an exploded view of a disk drive
2
comprising a base
4
for housing a disk
6
and a head
10
attached to a distal end of an actuator arm
8
. A spindle motor
12
rotates the disk
6
about its axis, and a voice coil motor (VCM)
14
rotates the actuator arm
8
about a pivot
16
in order to position the head
10
radially over the disk
6
. A crash stop
18
is provided which facilitates latching the head
10
in a park position while the disk drive
2
is powered down in order to protect the data recorded on the disk
6
as well as prevent damage to the head
10
. In the disk drive of
FIG. 1
, the head
10
is parked on a landing zone on the inner diameter (ID) of the disk
6
. Alternatively, the head
10
may be parked on a ramp located at the periphery of the disk
6
(a.k.a., ramp loading/unloading).
FIG. 2
illustrates the orientation and operation of the crash stop
18
with respect to the actuator arm
8
. The actuator arm
8
comprises a tang
20
attached to a base end and positioned between a first arm
22
A and second arm
22
B of the crash stop
18
. The second arm
22
B presents a physical barrier to the tang
20
so as to limit the stroke of the actuator arm
8
, thereby preventing the head
10
from exceeding a radial limit (e.g., the edge of the disk
6
). The first arm
22
A comprises a latch with a magnet for latching the tang
20
to the first arm
22
A, thereby safely parking the head
10
(e.g., on the inner diameter of the disk
6
). In order to prevent damaging the head
10
, the force from the magnetic latch should be strong enough to prevent the actuator arm
8
from unlatching even if the disk drive
2
is subjected to an external, physical shock. In addition, it is desirable to achieve a single-point contact between the latch and the tang
20
to attenuate vibrations in the actuator arm
8
which can damage the head
10
due to the head
10
striking the surface of the disk
6
(a.k.a., head-slap).
FIG. 3A
illustrates a prior art crash stop
18
and cylindrical latch
24
disclosed in U.S. Pat. No. 5,703,735 which provides a single-point contact with the tang
20
.
FIG. 3B
illustrates a cross-sectional view of the cylindrical latch
24
as comprising a cylindrical magnet
26
having a steel post
28
disposed axially through the magnet
26
. The magnet
26
is enclosed in a steel casing
30
which prevents the tang
20
from striking the magnet
26
and releasing contaminates into the disk drive. The post
28
comprises a dome-shaped top surface
28
A which provides a single-point contact for the tang
20
which mitigates head-slap.
The strength of the magnetic force generated by the magnet
26
decreases exponentially as the distance between the magnet
26
and the tang
20
increases. The steel post
28
acts as a magnetic flux conductor for conducting the magnetic flux (shown as dashed circles in
FIG. 3B
) between the north and south poles of the magnet
26
and away from the VCM
14
, thereby allowing the use of more powerful magnets without interfering with the operation of the VCM
14
. However, because the steel post
28
attracts the magnetic flux away from the tang
20
, the magnetic force decreases sharply as the distance between the magnet
26
and tang
20
increases. This is illustrated in
FIG. 6
which shows the sharp exponential decrease in the magnetic latching force
32
as the distance between the magnet
26
and the tang
20
increases. Thus, in order to exploit the maximum latching power of the magnet
26
it is important to manufacture the steel post
28
and casing
30
with tight tolerances. If the top surface
28
A of the steel post or casing
30
are manufactured too thick, it may result in insufficient latching force leading to drive failure. The multiple part count together with the tight tolerance imposed on the steel post
28
and casing
30
, as well as the need to properly align and attach the latch
24
to the crash stop
18
, increases the cost and decreases the manufacturing yield of the disk drive. In addition, fretting corrosion may occur due to the tang
20
contacting the steel post
28
which can release contaminates into the disk drive.
U.S. Pat. No. 5,822,155 teaches a latch comprising a magnet contained within a steel cup, wherein the sides of the steel cup conduct the magnetic flux between the north and south pole of the magnet and away from the VCM
14
, thereby allowing the use of a more powerful magnet without interfering with the operation of the VCM
14
. In one embodiment, a plastic, dome-shaped bumper is attached to the top of the cup and over the magnet which reduces fretting corrosion and facilitates a single-point contact with the tang
20
. However, manufacturing a cup by attaching a plastic bumper increases the expense of the latch, and the latch must still be properly aligned and attached to the crash stop
18
which increases the manufacturing cost of the disk drive. Further, if the plastic bumper is manufactured too thick, the latching force may be to small due to the sharp exponential decrease in the latching force inherent with the steel cup design.
U.S. Pat. No. 6,028,744 teaches a latch made in part out of injection molded plastic with an embedded magnet, wherein the thickness of the plastic is more readily controllable so as to attain the desired force/distance distribution with respect to the tang
20
. However, the latch disclosed in the '744 patent comprises several parts, including a magnetic plate extension mounted to the base of the disk drive with a “floating” plastic nest having the embedded magnet placed over the magnetic plate. This multiple-part design is more difficult and expensive to manufacture, as well as properly align within the disk drive. Further, the latch disclosed in the '744 patent does not facilitate a single point contact with the tang
20
.
Another problem inherent in prior art latch designs is that the maximum latching force may exceed the maximum torque of the VCM
14
. Thus, even though the prior art latch designs provide a high latching force at a short distance between the magnet and the tang
20
as illustrated in
FIG. 6
, thereby providing sufficient latching energy to retain the actuator arm
8
in the latched position in the presence of a physical shock, the maximum latching force may exceed the maximum torque of the VCM
14
preventing the tang
20
from unlatching during spin-up. Thus, the prior art latch designs may prevent the use of a less efficient, but less expensive VCM
14
, such as the VCM disclosed in the above-referenced U.S. patent application entitled “DISK DRIVE EMPLOYING A VOICE COIL MOTOR COMPRISING A YOKE FOR GENERATING A UNIDIRECTIONAL MAGNETIC FLUX AND A VOICE COIL PARTIALLY INTERACTING WITH THE UNIDIRECTIONAL MAGNETIC FLUX”.
There is, therefore, a need for a more cost effective latch for use in a disk drive which mitigates fretting corrosion, provides a single point contact with a tang, has a more gradual force/distance distribution in order to relax the manufacturing tolerances, and exhibits a lower maximum latching force to facilitate the use of less efficient VCMs while providing adequate protection against physical shocks.
SUMMARY OF THE INVENTION
The present invention may be regarded as a disk drive comprising a base, a disk, an actuator arm comprising a tang attached to a base end of the actuator arm, a head attached to a distal end of the actuator arm, a voice coil motor for rotating the actuator arm about a pivot to position the head radially over the disk, and a crash stop comprising injection molded plastic formed into a body piece having a protruding first arm and a protruding sec
Hauert Serge
Watson Scott E.
Kim Esq. W. Chris
Renner Craig A.
Shara, Esq. Milad G.
Sheerin, Esq. Howard H.
Western Digital Technologies Inc.
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