U.S. patent application number 12/792459 was filed with the patent office on 2011-02-10 for method and apparatus for reciprocal polishing.
Invention is credited to Zine-Eddine Boutaghou.
Application Number | 20110034107 12/792459 |
Document ID | / |
Family ID | 43535169 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110034107 |
Kind Code |
A1 |
Boutaghou; Zine-Eddine |
February 10, 2011 |
METHOD AND APPARATUS FOR RECIPROCAL POLISHING
Abstract
A polishing pad is located on a reciprocal motion generator. The
polishing pad includes a plurality of discrete fluid channels. An
abrasive article is located on the polishing pad. The abrasive
article is reciprocally energized relative to the work piece. A
fluid pressure in one or more of the discrete fluid channels is
altered to selectively deform the abrasive article to
preferentially remove material from the work piece.
Inventors: |
Boutaghou; Zine-Eddine;
(North Oaks, MN) |
Correspondence
Address: |
Clise, Billion & Cyr, P.A.
605 U.S. Highway 169, Suite 300
Plymouth
MN
55441
US
|
Family ID: |
43535169 |
Appl. No.: |
12/792459 |
Filed: |
June 2, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61232525 |
Aug 10, 2009 |
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Current U.S.
Class: |
451/5 |
Current CPC
Class: |
B24B 1/04 20130101; B24B
37/048 20130101; B24B 37/26 20130101 |
Class at
Publication: |
451/5 |
International
Class: |
B24B 49/00 20060101
B24B049/00 |
Claims
1. A polishing apparatus for polishing work pieces, the polishing
apparatus comprising: a reciprocal motion generator; a polishing
pad located on the reciprocal motion generator, the polishing pad
having a plurality of discrete fluid channels; an abrasive article
located on the polishing pad; and a controller fluidly coupled to
the discrete fluid channels and programmed to selectively alter a
fluid pressure in one or more of the discrete fluid channels to
selectively deform the abrasive article to preferentially remove
material from the work piece.
2. The polishing apparatus of claim 1 wherein the fluid channels
are configured in one of linear, curvilinear, or concentric
pattern.
3. The polishing apparatus of claim 1 further comprising sensors
adapted to monitor material removal from the work piece.
4. The polishing apparatus of claim 3 further comprising a
closed-loop control system for polishing the work piece.
5. The polishing apparatus of claim 1 further comprising a gimbal
assembly connecting the work piece bar to a support structure, the
gimbal assembly applying a preload that biases the work piece
toward the abrasive article.
6. The polishing assembly of claim 5 further comprising one or more
actuators configured to alter the pitch and roll of the work piece
relative to the abrasive article.
7. The polishing apparatus of claim 1 further comprising a
hydrostatic bearing assembly including a plurality of ports fluidly
coupled to a source of compress air, the ports oriented toward the
abrasive article to maintain a hydrostatic air bearing between the
work piece and the abrasive article.
8. The polishing apparatus of claim 1 wherein the abrasive article
is one of flexible, rigid or semi-rigid.
9. The polishing apparatus of claim 1 wherein the fluid channels
are configured to create a crown or camber on the work piece.
10. A method of polishing a work piece comprising the steps of:
locating a polishing pad on a reciprocal motion generator, the
polishing pad including a plurality of discrete fluid channels;
locating an abrasive article on the polishing pad; reciprocally
energizing the abrasive article relative to the work piece; and
selectively altering a fluid pressure in one or more of the
discrete fluid channels to selectively deform the abrasive article
to preferentially remove material from the work piece.
11. The method of claim 10 further comprising configuring the fluid
channels in one of a linear, a curvilinear, or a concentric
pattern.
12. The method of claim 10 further comprising: monitoring sensors
adapted to measure material removal from the work piece; and
altering the fluid pressure in one or more of the discrete fluid
channels in response to a signal from the sensors.
13. The method of claim 12 further comprising controlling fluid
pressure in the fluid channels in accordance with a closed-loop
control system.
14. The method of claim 10 further comprising: supporting the work
piece with a gimbal assembly; and applying a preload to bias the
work piece toward the abrasive article.
15. The method of claim 10 further comprising actuating one or more
actuators to alter the pitch and roll of the work piece relative to
the abrasive article.
16. The method of claim 10 further comprising creating a
hydrostatic bearing between the work piece and the abrasive
article.
17. The method of claim 10 further comprising the steps of
delivering a compressed gas to a plurality of ports on a work piece
holder to maintain a hydrostatic air bearing between the work piece
and the abrasive article.
18. The method of claim 10 further comprising altering the pressure
in one or more of the fluid channels to create a crown or camber on
the work piece.
19. The method of claim 10 wherein the work piece comprises one of
machined metal parts, silicon wafers, slider bars for hard disk
drives, lenses, or optical fibers.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefits of the filing date of
U.S. Provisional Patent Application Ser. No. 61/232,525 filed Aug.
10, 2009, which is entitled "Method and Apparatus for Ultrasonic
Polishing" which is hereby incorporated herein in its entirety by
reference.
FIELD OF THE INVENTION
[0002] The present invention is directed to a method and apparatus
for reciprocal or alternating polishing, and in particular,
user-controlled preferential material removal.
BACKGROUND OF THE INVENTION
[0003] Reciprocal excitation produces a relative motion responsible
for material removal at the interface between an abrasive article
and a work piece. The relative motion between the abrasive article
and the work piece causes asperities to interlock and high stresses
producing wear. During ultrasonic excitation a relative velocity is
produced between the abrasives and the work piece that varies from
zero to a maximum back to zero. The hydrodynamic film formed at the
interface is negligible promoting maximum wear at the
interface.
BRIEF SUMMARY OF THE INVENTION
[0004] The present invention is directed to an ultrasonic assembly
with user controlled preferential material removal. The present
ultrasonic polishing has wide application to polishing slider bars
for hard disk drives, optical fibers, lenses, and the like.
[0005] A series of air/fluid channels located behind an abrasive
article. The fluid pressure in the fluid channels can be changed to
deform the abrasive article, causing localized high stresses
between the abrasive article and a work piece. The localized high
stress preferentially removes more material from the work piece at
specific locations. Interference between the work piece and the
abrasive article is controlled by the magnitude of the air/fluid
pressure applied at the interface. An ultrasonic generator applies
ultrasonic energy to the abrasive article with negligible out of
plane motion.
[0006] The present invention is also directed to a method of
polishing a work piece. A polishing pad is located on an excitation
generator. The polishing pad includes a plurality of discrete fluid
channels. The excitations generated oscillate or energize the
abrasive article. An abrasive article is located on the polishing
pad. Fluid pressure in one or more of the discrete fluid channels
is selectively altered to selectively deform the abrasive article
to preferentially remove material from the work piece.
[0007] In one embodiment a series of air/fluid ports are fabricated
on the polishing pad to selectively deform the abrasive article,
thus increasing or decreasing interference between the polishing
article and the bar. This process may be very desirable for
controlled sensor material removal as is the practice in disk
drives, such as disclosed in U.S. Patent Application No.
2005/0071986 (Lackey et al.), which is hereby incorporated by
reference.
[0008] In another embodiment, a series of pressure hoses are
connected from the fixed base to the polishing pad to control the
pressure in each air/fluid channel. The spatial distance between a
series of sensors can be matched to the polishing plate channels to
produce customized stress management at each work piece sensor. If
the desired amount of wear is achieved at each sensor then the
pressure is removed from the pressure channel causing no
interference.
[0009] Reciprocal motion imparts interference between the work
piece and the abrasive article and minimizes formation of a
hydrodynamic film to maximize polishing and burnishing. Multiple
lubricant viscosities can be used without the concern of
interference mitigation due to hydrodynamic film formation. A
boundary lubrication regime is preferably maintained throughout the
polishing process.
[0010] Controlled interference between the abrasive article and the
work piece can be maintained using a hydrostatic air bearing and/or
preloaded gimbaled work piece holder. The work piece is presented
to the abrasive article is such a fashion that the cutting forces
emanating from the interaction are balanced and minimize chatter
and vibrations. The work piece holder maintains stability during
the polishing process.
[0011] Substrate actuation can impart preferred concave or convex
shapes (crown, camber, etc.) to the work piece. Compact lapping
tools capable of atomically smooth polishing bars. The floor space
required for housing this tool is extremely small compared to
spindle base lapping tools.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0012] FIG. 1 is a schematic sectional view of a reciprocal motion
assembly in accordance with an embodiment of the present
invention.
[0013] FIG. 2 is an exploded view of the reciprocal motion assembly
of FIG. 1.
[0014] FIG. 3 is a schematic illustration of a reciprocal motion
generator in accordance with an embodiment of the present
invention.
[0015] FIG. 4 is a schematic sectional view of a reciprocal motion
assembly with user-controlled preferential material removal in
accordance with an embodiment of the present invention.
[0016] FIG. 5 is an enlarged view of a polishing pad in accordance
with an embodiment of the present invention.
[0017] FIG. 6 is a schematic illustration of deformation of the
abrasive article in accordance with an embodiment of the present
invention.
[0018] FIG. 7 is a schematic illustration of a work piece being
polished using preferential material removal in accordance with an
embodiment of the present invention.
[0019] FIG. 8A is a schematic illustration of an alternate
polishing pad and method in accordance with an embodiment of the
present invention.
[0020] FIG. 8B is a schematic illustration of another alternate
polishing pad and method in accordance with an embodiment of the
present invention.
[0021] FIG. 9 is a perspective view of a polish pad with circular
fluid channels in accordance with an embodiment of the present
invention.
[0022] FIG. 10 is a gimballed work piece holder in accordance with
an embodiment of the present invention.
[0023] FIG. 11 is hydrostatic clearance control mechanism in
accordance with an embodiment of the present invention.
[0024] FIG. 12 is an exploded view of the clearance control
mechanism of FIG. 11.
DETAILED DESCRIPTION OF THE INVENTION
[0025] FIGS. 1 and 2 illustrate a reciprocal motion assembly 20
with a reciprocal motion generator 22 in accordance with an
embodiment of the present invention. An excitation platform 28 is
mounted to the ultrasonic generator 22. The excitation platform 28
includes a polishing pad 30 with an abrasive article 32 mounted
thereon. The abrasive article 32 can be attached to the polishing
pad 30 by a variety of techniques, including adhesives, vacuum,
mechanical fasteners, high friction interface, and the like.
[0026] A variety of abrasive articles are suitable for use with the
present a reciprocal motion assembly 20, such as for example,
abrasive charged polymers, diamond charged flexible plates,
diamond-like-carbon coated flexible plates, and the like. In one
embodiment, the abrasive article includes a DLC film with a
thickness of 50-200 nm with integrated cutting asperities with a
height of 5-50 nanometers to provide high stress sites, and a thin
film lubricant to provide boundary lubrication. Since deformation
of the abrasive article 32 is typically in the nanometer range, the
abrasive article 32 can be flexible, rigid, or semi-rigid.
[0027] FIG. 3 is a detailed illustration of the a reciprocal motion
generator 22 in accordance with an embodiment of the present
invention. Spring assembly 34 includes an X-springs 36 and a
Y-spring 38 attached to anchor pads 26 by spring anchors 40. The
anchor pads 26 retain the spring assembly 34 above the base 24 in a
cantilevered configuration. In the illustrated embodiment, the X-Y
springs 36, 38 for a generally rectangular shape with additional
spring anchors 42 at the corners.
[0028] Electro-mechanical system 48 including a moving base 44 with
a magnet that is actuated by alternating current applied to coil
46. Upon energizing of the coil 46, the springs 36, 38 are bent out
of plane, which causes the attached moving base 44 to undergo a
reciprocating motion. The motion of the moving base 44 can be
elliptical, orbital, circular, and the like. Additional coils 46
can optionally be provided to generate irregular motions.
[0029] FIGS. 4 and 5 illustrate an alternate reciprocal motion
assembly 50 with user-controlled preferential material removal in
accordance with an embodiment of the present invention. Polishing
pad 52 is mounted to ultrasonic generator 22 as discussed above.
The polishing pad 52 includes a plurality of discrete fluid
channels 54 fluidly coupled to one or more discrete ports 56. Each
of the ports 56 is fluidly coupled to pressure control ports 58 on
base 60 by one or more hoses 62. The fluid channels 54 can be
linear, curvilinear, circular, concentric, or any other suitable
configuration. The width and spacing between the fluid channels 54
can be regular or irregular. In one embodiment, abrasive article 64
is located directly on the fluid channels 54. In another
embodiment, an intermediate membrane 66 extends across the fluid
channels 54.
[0030] Controller 70 selectively adjusts fluid pressure in each of
the discrete fluid channels 54. Upon activation the controller 70
adjusts the fluid pressure in the fluid channels 54 to deform the
flexible abrasive article 64 and to increase or decrease
interference with the work piece 72 being ultrasonically polished
(see FIG. 7). The controller 70 can be hydraulic or pneumatic. In
alternate embodiments, the deformation of the abrasive article 64
can be electromechanical, electrostatic, or a variety of other
techniques.
[0031] FIG. 6 is a schematic side sectional view of the polishing
pad 52 and abrasive article 64 during reciprocal polishing in
accordance with an embodiment of the present invention. In the
illustrated embodiment, positive pressure is delivered to each of
the fluid channels 54 to deform the abrasive article 64 above the
surface of the polishing pad 52. Protrusions 65 of the abrasive
article 64 are exaggerated for illustration purposes. For most
applications, the protrusions 65 will have a height 67 of less then
one micrometer.
[0032] FIG. 7 illustrates the interference between a work piece 72
and the abrasive article 64 in accordance with an embodiment of the
present invention. In the illustrated embodiment, work piece 72 is
a slider bar containing a plurality of sliders 74A, 74B, 74C, 74D,
74E (collectively 74) for use in a hard disk drive. Each of the
sliders 74 includes one or more read/write heads and/or sensors 76.
In the illustrated embodiment, the amplitude of the ultrasonic
motion imparted by the reciprocal motion generator 22 is preferably
less than the size of the feature being polished, such as for
example the sensors 76, in order to maintain the position of the
protrusions 78 relative to the feature being polished.
[0033] Positive pressure is applied to fluid channels 54A, 54B, 54C
and 54E, while no pressure is applied to fluid channel 54D. The
present method and apparatus allows for selective polishing of the
individual sliders 74. The read/write heads and/or sensors 76 can
be adapted to provide a signal proportional to the progress of the
polishing operation. In one embodiment, the sensors 76 are height
sensors. Various control mechanisms are known for monitoring the
progress of the polishing process, such as the closed loop feedback
system disclosed in U.S. Patent Application No. 2005/0071986
(Lackey et al.), which is hereby incorporated by reference.
Consequently, controller 70 can be programmed to automatically
control the pressure in the fluid channels 54 in accordance with
the polishing requirements for the work piece 72.
[0034] FIG. 8A illustrates an alternate polishing pad 100 in
accordance with an embodiment of the present invention. The size
and shape of the fluid channels 102 can be engineered for specific
applications. The pressure in the fluid channels 102 can be
positive, negative, or neutral. Consequently, the present method
and apparatus can be used for polishing complex surfaces. For
example, negative pressure is applied to fluid channel 102B,
causing the abrasive article 104 to form a concave surface suitable
for polishing curvilinear work piece 106, such as for example
lenses, edges of fiber optics and the like. The abrasive article
104 can also be deformed to polish edges or fringes of a work piece
to create a crown or camber.
[0035] FIG. 8B illustrates an alternate polishing pad 120 in
accordance with an embodiment of the present invention. Instead of
deforming abrasive article 122 on the level of each fluid channel
124, the abrasive article 122 is deformed on a macro level. In the
illustrated embodiment, the abrasive article 122 assumes a
curvilinear shape, such as may be used for polishing lens 126 or
other optical elements.
[0036] FIG. 9 is a perspective view of an alternate polishing pad
140 with fluid channels 142 arranged concentrically in accordance
with an embodiment of the present invention. Each of the discrete
fluid channels 142 is fluidly coupled to one or more ports 144. The
concentric arrangement of the fluid channels 142 is particularly
useful for polishing circular objects, such as for example disks
for a hard disk drive or lens, such as illustrated in FIG. 8B. In
one embodiment, the work piece is rotated while engaged with the
abrasive article, with or without ultrasonic vibration.
[0037] Interference control between the work piece and the abrasive
article can be achieved using a variety of techniques, including
hydrostatic or hydrodynamic fluid bearings, and/or a gimballed
interface. Various methods and systems for interference control
suitable for use with the present reciprocal motion assembly are
disclosed in U.S. Provisional Patent Application Ser. No.
61/232,425, entitled Dressing Bar for Embedding Abrasive Particles
into Substrates, filed Aug. 8, 2009; Ser. No. 61/174,472, entitled
Abrasive Article with an Array of Gimballed Abrasive Members and
Method of Use, filed Jun. 30, 2009, all of which are hereby
incorporated by reference.
[0038] In one embodiment, the various work pieces discussed herein
are supported by a gimbal mechanism. FIG. 10 is an exploded view of
a work piece holder 150 that permits roll and pitch moments of work
piece 152 during the polishing process. Work piece 152 is attached
to gimbal mechanism 154. Spring assembly 156 includes dimple 158
that applies a point load to the gimbal mechanism 154.
[0039] FIGS. 11 and 12 illustrate a hydrostatic work piece holder
160 with an actuation mechanism 162 to bring the work piece 164 in
contact with the abrasive article (see FIG. 4) in accordance with
an embodiment of the present invention. A gimbal mechanism 166
holds the work piece 164. Pneumatic hoses 168 delivery externally
pressured bed through ports 172 to create a hydrostatic air bearing
between the abrasive article and the work piece holder 170. The
gimbal mechanism 166 allows for movement of the work piece 164 with
minimal bending and twisting during contact with the polishing
media. The hydrostatic air bearing is preferably greater than the
cutting forces, to stabilize the interface between the work piece
164 and the abrasive article.
[0040] Where a range of values is provided, it is understood that
each intervening value, to the tenth of the unit of the lower limit
unless the context clearly dictates otherwise, between the upper
and lower limit of that range and any other stated or intervening
value in that stated range is encompassed within the inventions.
The upper and lower limits of these smaller ranges which may
independently be included in the smaller ranges is also encompassed
within the inventions, subject to any specifically excluded limit
in the stated range. Where the stated range includes one or both of
the limits, ranges excluding either both of those included limits
are also included in the inventions.
[0041] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which these inventions belong.
Although any methods and materials similar or equivalent to those
described herein can also be used in the practice or testing of the
present inventions, the preferred methods and materials are now
described. All patents and publications mentioned herein, including
those cited in the Background of the application, are hereby
incorporated by reference to disclose and described the methods
and/or materials in connection with which the publications are
cited.
[0042] The publications discussed herein are provided solely for
their disclosure prior to the filing date of the present
application. Nothing herein is to be construed as an admission that
the present inventions are not entitled to antedate such
publication by virtue of prior invention. Further, the dates of
publication provided may be different from the actual publication
dates which may need to be independently confirmed.
[0043] Other embodiments of the invention are possible. Although
the description above contains much specificity, these should not
be construed as limiting the scope of the invention, but as merely
providing illustrations of some of the presently preferred
embodiments of this invention. It is also contemplated that various
combinations or sub-combinations of the specific features and
aspects of the embodiments may be made and still fall within the
scope of the inventions. It should be understood that various
features and aspects of the disclosed embodiments can be combined
with or substituted for one another in order to form varying modes
of the disclosed inventions. Thus, it is intended that the scope of
at least some of the present inventions herein disclosed should not
be limited by the particular disclosed embodiments described
above.
[0044] Thus the scope of this invention should be determined by the
appended claims and their legal equivalents. Therefore, it will be
appreciated that the scope of the present invention fully
encompasses other embodiments which may become obvious to those
skilled in the art, and that the scope of the present invention is
accordingly to be limited by nothing other than the appended
claims, in which reference to an element in the singular is not
intended to mean "one and only one" unless explicitly so stated,
but rather "one or more." All structural, chemical, and functional
equivalents to the elements of the above-described preferred
embodiment that are known to those of ordinary skill in the art are
expressly incorporated herein by reference and are intended to be
encompassed by the present claims. Moreover, it is not necessary
for a device or method to address each and every problem sought to
be solved by the present invention, for it to be encompassed by the
present claims. Furthermore, no element, component, or method step
in the present disclosure is intended to be dedicated to the public
regardless of whether the element, component, or method step is
explicitly recited in the claims.
* * * * *