U.S. patent application number 10/319785 was filed with the patent office on 2004-01-29 for method and system for gram load stabilization by repetitive mechanical back bending of a head suspension assembly.
This patent application is currently assigned to KR Precision Public Company Limited. Invention is credited to Thaveeprungsriporn, Visit.
Application Number | 20040016277 10/319785 |
Document ID | / |
Family ID | 30772666 |
Filed Date | 2004-01-29 |
United States Patent
Application |
20040016277 |
Kind Code |
A1 |
Thaveeprungsriporn, Visit |
January 29, 2004 |
Method and system for gram load stabilization by repetitive
mechanical back bending of a head suspension assembly
Abstract
A method for stabilizing gram load of a head suspension
assembly. The invention includes a mechanical back bending process.
After forming, the suspension is subjected to residual stress.
During mechanical back bending of the load beam, the applied stress
is in the opposite direction of the forming operation.
Subsequently, the resultant residual stress around the pre load
area is reversed and acted against the pre-existing residual stress
remaining from the forming operation. The net effect is a reduction
and/or the elimination of residual stress altogether. Depending on
the pre-load geometry and desired spring force, the degree of back
bending is varied. Typically, a one-time back bending is not
sufficient to stabilize the spring region at a microstructure
level. It has been demonstrated that such repetitive back bending
operation can effectively bring mobile dislocations into
equilibrium, and thus reduce or eliminate the hysteresis loop.
Inventors: |
Thaveeprungsriporn, Visit;
(Ayutthaya, TH) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
KR Precision Public Company
Limited
Ayutthaya
TH
|
Family ID: |
30772666 |
Appl. No.: |
10/319785 |
Filed: |
December 12, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60398962 |
Jul 25, 2002 |
|
|
|
Current U.S.
Class: |
72/31.1 ;
G9B/5.153; G9B/5.231 |
Current CPC
Class: |
G11B 5/6005 20130101;
G11B 5/4833 20130101 |
Class at
Publication: |
72/31.1 |
International
Class: |
B21C 051/00 |
Claims
What is claimed is:
1. A process for manufacturing a disk drive apparatus, the process
comprising: providing a load beam in a head suspension assembly,
the load beam having a spring region; forming a pre-load region in
the spring region by causing a bend in a first direction in the
spring region within the load beam, the bend including a residual
stress within a vicinity of the spring region; and redistributing
the residual stress in the spring region by causing a counter bend
in a second direction in the spring region, whereupon the first
direction is counter to the second direction.
2. The process of claim 1 wherein the redistributing is provided by
at least one counter bend in the second direction; wherein the
forming of the pre-load region mechanically bends the spring region
in the first direction.
3. A method for manufacturing suspension assemblies for hard disk
drives, the method comprising: providing a suspension including a
pre-load region, the pre-load region including a residual stress
within a vicinity of the pre-load region; determining a degree of
back-bending beyond z-height desired to compensate for the residual
stress in the pre-load region; and performing a back bending
process on the pre-load region of the suspension to release a
portion of the residual stress in the pre-load region.
4. The method claim in 3 wherein the back bending process is
provided more than one time.
5. A suspension assembly for hard disk drives, the suspension
assembly comprising: a suspension member including a pre-load
region; whereupon the pre-load region is free from a residual
stress within a vicinity of the pre-load region.
6. The assembly of claim 5 wherein the residual stress is caused by
manufacturing the pre-load region.
7. The assembly of claim 5 wherein the pre-load region comprises a
bent region in a first direction.
8. The assembly of claim 7 wherein the pre-load comprises a re-bend
region, the re-bend region being counter to the bend region.
9. A process for manufacturing a disk drive apparatus, the process
comprising: providing a load beam in a head suspension assembly,
the load beam having a spring region; forming a pre-load region in
the spring region by causing a bend in a first direction in the
spring region within the load beam, the bend including a residual
stress within a vicinity of the spring region; and redistributing
and/or relieving the residual stress in the spring region by
causing a counter bend in a second direction in the spring region,
whereupon the first direction is counter to the second
direction.
10. The process of claim 1 wherein the redistributing and/or
relieving is provided by at least one counter bend in the second
direction; wherein the forming of the pre-load region mechanically
bends the spring region in the first direction.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The application claims priority of U.S. Provisional
Application No 60/398,962 filed Jul. 25, 2002, commonly assigned,
and in the name of Visit Thaveeprungsriporn, which is incorporated
by reference for all purposes.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
[0002] Not applicable
REFERENCE TO A "SEQUENCE LISTING," A TABLE, OR A COMPUTER PROGRAM
LISTING APPENDIX SUBMITTED ON A COMPACT DISK.
[0003] Not applicable
BACKGROUND OF THE INVENTION
[0004] The present invention relates to memory storage devices.
More particularly, the invention provides an apparatus and method
for stabilizing a load of the head suspension assembly of a
magnetic disc drive. Preferably, the apparatus and method utilizes
cyclic cold working for such stabilization by back bending a
portion of the pre-loaded suspension assembly.
[0005] Head suspension assemblies have been commonly used in rigid
magnetic disk drives to accurately position the read and write head
in close proximity to the spinning storage medium. Such assemblies
include a base plate, a load beam and a flexure (gimbal) to which a
slider is to be mounted. The slider support the read/write head and
possess special aerodynamic shape allowing the head to fly over the
air bearing created by the rotating disk. The load beam is
generally composed of an actuator mounting section, a spring and a
rigid region. The spring region gives the suspension a spring force
or preload counteracting the aerodynamic lift force created by the
spinning medium during reading/writing. The flexure is mounted at
the distal end of the load beam and support the slider allowing
this one to have pitch and roll movement in order to follow the
irregularities of the disk surface.
[0006] A conventional manufacturing method for such suspension is
composed of steps including: etching, trace mounting, forming,
stabilization, gram adjust, pitch and roll adjust, detab, cleaning,
packaging, and possibly others. From a thin sheet of stainless
steel, a strip of pre-shaped suspensions are formed by chemical
etching. Next the trace or circuit, giving electrical connectivity
to the head is mounted. Each flat strip is then fed to the gram
load adjustment machine. The method forms the spring region (e.g.,
large bending) giving a large initial gram load. Such forming
method is generally realized by stamping, rolling, or coining and
results in a non-equilibrium microstructure of the spring region. A
phase of stabilization of the spring region is often necessary.
Generally, the use of heat treatment is employed to re-distribute
the stress in stainless steel. Then the suspension's gram load is
often fine adjusted, which gives the suspension its nominal
preload. Such fine adjustment is mainly accomplished by mechanical
bending and/or laser irradiation, which is described in U.S. Pat.
No. 5,682,780. Once the gram load has been adjusted, the suspension
is fed to the pitch and roll adjustment apparatus, then the
suspension are separated from the strip, cleaned, and individually
packed. Unfortunately, numerous limitations exist with the
convention methods. As merely an example, the fine adjustment of
the suspension is often difficult to perform in an accurate and
efficient manner. These and other limitations are described
throughout the present specification and more particularly
below.
[0007] From the above, it is seen that an improved method for
manufacturing disk drive apparatus is desirable.
SUMMARY OF THE INVENTION
[0008] According to the present invention, techniques related to
memory storage devices are provided. More particularly, the
invention provides an apparatus and method for stabilizing a load
of the head suspension assembly of a magnetic disc drive.
Preferably, the apparatus and method utilizes cyclic cold working
for such stabilization by back bending a portion of the pre-loaded
suspension assembly.
[0009] As the storage density of magnetic disks increases, the
flying height of actual disks drive is quickly decreasing, making
suspension gram load a desirable parameter of the suspension. This
gram load need to have a reduce deviation or a minimum deviation
from the target spring force during long term operation especially
in high temperature and humidity environment.
[0010] Furthermore, to pre-form the spring force on the load beam,
the pre-load area is mechanically bent by stamping, rolling or
coining. This mechanical deformation generates non-uniform stress
distribution across the load beam thickness, which needs to be
properly re-distributed; otherwise, a long-term relaxation is
expected causing a decrease in gram load affecting the fly height
performance. The prior art practice has been to subject the
stainless steel to a temperature between 250 and 350 Degrees
Celsius for a period of time. The entire heat-treating process
however takes much longer time to accommodate the pre-heating and
cooling steps resulting in a significant loss in cycle time and
productivity. Furthermore, recent models of suspension also has a
trace gimbal attached to the suspension which comprises of
polyimide cover layer and multi-metal layers of gold, nickel and
copper, New feature such as visco-elastic damper and laminated load
beam are also developed. The use of heat treatment is not a
preferred choice due to concerns regarding the structural integrity
of the polyimide and the possibility of copper and nickel
migration. The present invention proposes a replacing stabilization
method based on cyclic mechanical back bending of the spring region
and describes the associated apparatus.
[0011] The present invention provide the manufacturer a way to
ensure better quality gram load adjustment for a lower cost by
proposing a alternative solution to the heat-based gram load
stabilization.
[0012] In a specific embodiment, the invention provides a process
for manufacturing a disk drive apparatus. The process includes
providing a load beam in a head suspension assembly. The load beam
has a spring region. The method forms a pre-load region in the
spring region by causing a bend in a first direction in the spring
region within the load beam. The bend includes a residual stress
within a vicinity of the spring region. The method also includes
releasing the residual stress in the spring region by causing a
counter bend in a second direction in the spring region, whereupon
the first direction is counter to the second direction.
[0013] In an alternative specific embodiment, the invention
provides a method for manufacturing suspension assemblies for hard
disk drives. The method includes providing a suspension including a
pre-load region, which has a residual stress within a vicinity of
the pre-load region. The method determines a degree of back-bending
beyond z-height desired to compensate for the residual stress in
the pre-load region. The method also includes performing a back
bending process on the pre-load region of the suspension to release
a portion of the residual stress in the pre-load region.
[0014] In an alternative specific embodiment, the invention
includes a suspension assembly for hard disk drives. The suspension
assembly includes a suspension member including a pre-load region;
whereupon the pre-load region is free from a residual stress within
a vicinity of the pre-load region.
[0015] Other and further features as well as advantages
characterizing the invention will appear from the following
detailed description and associated drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a simplified isometric view of the suspension
assembly 10 according to an embodiment of the present
invention.
[0017] FIG. 2 is a simplified profile view of a suspension assembly
10 according to an embodiment of the present invention.
[0018] FIG. 3 is a simplified flow diagram of the full suspension
manufacturing according to an embodiment of the present
invention.
[0019] FIG. 4 is a simplified flow diagram of the gram load
adjustment process according to an embodiment of the present
invention.
[0020] FIG. 5 is a simplified comparison of the gram load loss over
100 cycles between a heat treated suspension and a non heat treated
suspension according to an embodiment of the present invention.
[0021] FIG. 6 is a simplified comparison of the gram load loss over
100,000 cycles between a heat-treated, a non heat-treated and a
back bended suspension according to an embodiment of the present
invention.
[0022] FIGS. 7 and 8 are more detailed isometric views of back
bending stabilization station 601 according to an embodiment of the
present invention.
[0023] FIG. 9 is a more detailed side view of the clamping
apparatus 640 according to an embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] According to the present invention, techniques related to
memory storage devices are provided. More particularly, the
invention provides an apparatus and method for stabilizing a load
of the head suspension assembly of a magnetic disc drive.
Preferably, the apparatus and method utilizes cyclic cold working
for such stabilization by back bending a portion of the pre-loaded
suspension assembly.
[0025] FIG. 1 is a simplified isometric view of the suspension
assembly 10 according to an embodiment of the present invention.
FIG. 2 is a simplified profile view of a suspension assembly 10
according to an embodiment of the present invention. These diagrams
are merely illustrations, which should not unduly limit the scope
of the claims herein. One of ordinary skill in the art would
recognize many other variations, modifications, and alternatives.
As shown, a head suspension assembly (HSA) 10 is formed with a
flexure 11, an air bearing slider 12 mounted on the flexure 11, a
load beam 13, a base plate 14, among other elements. The load beam
13 has a mounting region 15 on its proximal end and a flexure
mounting region 17 on its distal end. The base plate 14 is
typically welded on the mounting region 15 and ensures rigidity of
the mounting. The load beam comprises also a spring region 16
between its proximal and distal region. The spring region 16 gives
the suspension the ability to maintain, a precise distance between
the head and the media to be read (fly height) by giving the beam a
pre load force counteracting the air bearing created by the
spinning medium. This preload is called gram load of the
suspension. Further details of manufacturing the suspension are
provided throughout the present specification and more particularly
below.
[0026] FIG. 3 shows a simplified flow diagram of the suspension
manufacturing. This diagram is merely an illustration, which should
not unduly limit the scope of the claims herein. One of ordinary
skill in the art would recognize many other variations,
modifications, and alternatives. From a thin sheet of stainless
steel, the general shapes of the suspension are etched by
photochemical etching 100. Then different stamping operations 200
are carried out (reinforcement shapes, dimple and load/unload tab
formation). Next is the welding assembly of the base plate, load
beam and gimbal 300. To enable the reading and writing function of
the head, a flexible polyamide and copper electric circuit (trace)
is attached to the head 400. At this stage the suspension is given
an initial pre load by rolling or coining forming 500. Once pre
formed the suspension gram load is fine adjusted 600. The last
operations are pitch and roll adjustment 700, detab (separation)
800, cleaning and packing 900. The gram load adjustment process is
provided in more detail below.
[0027] FIG. 4 gives a detailed flow diagram of the gram load adjust
machine with its four stations. This diagram is merely an
illustration, which should not unduly limit the scope of the claims
herein. One of ordinary skill in the art would recognize many other
variations, modifications, and alternatives. After forming the
suspension is first presented to the stabilization station 601. At
this stage the suspension is cyclically back bended in order for
the residual stress present in the spring region 16 and due to the
forming to be redistributed and/or relieved. Details are given
throughout the present specification but more particularly in a
later section. Once stabilized the suspension gram load is measured
on the station 602. This station can be any conventional or
specific known apparatus for gram load measurement. This initial
measurement is used to determine the parameter of the gram load
adjustment station 603 (bending angle for cold working adjustment
and/or irradiation time for laser adjustment). Once adjusted to its
nominal gram load the suspension is fed to the last gram load
measurement station 604 which valid or reject the suspension.
[0028] As a part of customer specifications for gram load
reliability test, suspensions must generally exhibit a low change
in gram-load during usage. FIG. 5 shows a comparison of gram load
change over 100 cycles between heat-treated and non heat-treated
suspension. The heat-treated parts demonstrate almost no change in
gram-load while the no-heat treated parts experience a slight loss
in gram-load. The loss is most pronounced during the first 20
cycles and stabilized afterwards.
[0029] FIG. 5 also demonstrates that a stabilization (heat
treatment in this case) is necessary to avoid gram load loss during
usage. The disclosed invention proposes a new stabilization
process. A cyclic back bending of the suspension load beam is
proposed in replacement to the costly and time-consuming heat
treatment stabilization.
[0030] FIG. 6 gives a comparison of the gram load loss over 100,000
cycles for a non-stabilized, a heat-treated and a back bended
suspension (5 times back bending). After improving and/or
optimizing the algorithm and amount of deflection during cyclic
cold working, it has been shown that there is no noticeable
difference between the heat-treated parts and cyclically
cold-worked parts. Several reliability tests including gram-load
change versus z-height adjusts, gram-load distribution, thermal
shock test, and resonance performance shown that cyclic back
bending can efficiently replace heat treatment stabilization.
[0031] FIGS. 7 and 8 are detailed isometric views of the mechanical
stabilization station 601. The embodiments of the stabilization
station 601 include a walking beam 610, a clamping device 640 and a
back bending apparatus 670. The walking beam 610 (not completely
represented) index feed the suspensions to the station 601. This
device can be any known walking index feeder.
[0032] The clamping device 640 is composed of an upper clamp 641, a
linear actuator 643 and a plurality of clamping pins 642. The upper
clamp 641 is mounted on the linear actuator 643 through to the
holder 644. The upper clamp 641 had a plurality of holes 647 (FIG.
9) positioned in alignment with the plurality of clamping pins 642.
The linear actuator 643 is used for lowering and raising the upper
clamp 641 during clamping and unclamping operations. The linear
actuator 643 is attached to the station base (not represented)
thanks to the holder 625. The plurality of clamping pins 642 is
attached to the linear actuator 671 through the holders 645 and
646. The plurality of clamping pins 642 is mounted on springs 648
in order to allow the pins 646 to retract when touching the base
plate 14 as well as maintain the clamping force during back bending
operation. Details of this device are given on FIG. 9.
[0033] The bending apparatus 670 includes a linear actuator 671, a
holder 672 and a bending arm 673. The bending arm 673 is attached
to the moving part of the actuator 671 through the holder 672. The
bending arm is composed of a roll 678 having a length equivalent to
five suspensions width and a roll holder 674. The linear actuator
671 is used for raising and lowering the bending arm during back
bending. The linear actuator 671 is attached to the station base
(not represented) by to the holder 675 and 676.
[0034] The holder 676 and 625 as well as the walking beam 610 are
mounted on a common base not shown on FIG. 7 and 8.
[0035] The multiple back bending operation is composed of several
steps. First, the walking beam 610 presents the suspensions to be
stabilized into the clamping assembly. After the base plate has
been aligned with the plurality a pins 642 and the upper clamp 641
by the walking beam 610, the upper clamp 641 is driven to close
position shown of FIG. 9b. The actuator 671 is driven to
simultaneously raise the plurality of pins 642 and the bending roll
678. The plurality of pins 642 clamp the base plate 14 of the fives
suspension to be back bended. At the same time the bending roll 678
applies a bending force on the suspension load beam 13 in an
opposite direction than the forming operation. The roll 678 is kept
in high position during a short time then lowered while the
suspensions 10 are released from the clamping system 640. Once the
operation terminated the walking beam 610 move the strips 20 of one
suspension and the cycle start again.
[0036] The clamping and bending apparatus respectively 640 and 670
are designed to clamp and back bend five suspension at the same
time. The feeding being incremental, one suspension will be back
bended five times. Indeed a one time back bending is not sufficient
to stabilize the gram load at a microstructure level. Experiments
have proven that five is the optimum number of back bending needed
for best stabilization according to a specific embodiment.
[0037] One of ordinary skill in the art would recognize many other
variations, modifications, and alternatives. The above example is
merely an illustration, which should not unduly limit the scope of
the claims herein. It is also understood that the examples and
embodiments described herein are for illustrative purposes only and
that various modifications or changes in light thereof will be
suggested to persons skilled in the art and are to be included
within the spirit and purview of this application and scope of the
appended claims.
* * * * *