U.S. patent application number 10/318789 was filed with the patent office on 2005-05-12 for machine for polishing the surface of a work piece.
This patent application is currently assigned to Eastman Kodak Company. Invention is credited to Meissner, Stephen C..
Application Number | 20050101232 10/318789 |
Document ID | / |
Family ID | 34549075 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050101232 |
Kind Code |
A1 |
Meissner, Stephen C. |
May 12, 2005 |
Machine for polishing the surface of a work piece
Abstract
A machine for polishing a surface of a work piece has a
precision sub-aperture polishing element. The polishing element has
a compliant, toroidal polishing member mountable to a support
member. A circumferential portion of the polishing member extends
uniformly beyond the peripheral surface of the support member and
forms a clearance with the work piece surface during polishing
operations.
Inventors: |
Meissner, Stephen C.; (West
Henrietta, NY) |
Correspondence
Address: |
Thomas H. Close
Patent Legal Staff
Eastman Kodak Company
343 State Street
Rochester
NY
14650-2201
US
|
Assignee: |
Eastman Kodak Company
|
Family ID: |
34549075 |
Appl. No.: |
10/318789 |
Filed: |
December 13, 2002 |
Current U.S.
Class: |
451/278 |
Current CPC
Class: |
B24B 13/01 20130101 |
Class at
Publication: |
451/278 |
International
Class: |
B24B 007/00 |
Claims
What is claimed is:
1. A machine for polishing a work piece surface, comprising a
polishing element for polishing the work piece surface, said
polishing element having a compliant, toroidal polishing member
mountable to a support member, said compliant, toroidal polishing
member having a circumferential active polishing surface extending
beyond a peripheral surface of said support member for engaging
said work piece surface; and, a drive means operably associated
with said polishing element for rotating said polishing element in
contact with said work piece surface.
2. The machine recited in claim 1 wherein said compliant, toroidal
polishing member comprises a material selected from the group
consisting of an elastic solid material, a polymeric material, and
a mixture thereof.
3. The machine recited in claim 2 wherein said polymeric material
is selected from the group consisting of: polyurethane,
chloroprene, fluorocarbon, fluorosilicone, ethylene propylene, and
nitrile.
4. The machine recited in claim 2 wherein said polymeric material
is nitrile.
5. The machine recited in claim 2 wherein said active polishing
surface of said toroidal, polishing member is at least partially
conformable with a surface of said work piece surface being
polished.
6. The machine recited in claim 1, wherein said support member is
mounted to said compliant, toroidal polishing member with an
adhesive bonding material.
7. The machine recited in claim 1 wherein said support member is
mounted to said compliant, toroidal polishing member by chemical
bonding.
8. The machine recited in claim 1 wherein said support member is
mounted to said compliant, toroidal polishing member by thermal
bonding.
9. The machine recited in claim 1 wherein said support member is
mounted to said compliant, toroidal polishing member by mechanical
bonding.
10. The machine recited in claim 1 said active polishing surface
has a Shore A hardness in the range of about 40-95.
11. The machine recited in claim 1 wherein said compliant, toroidal
polishing member has a substantially elongated shape along a radial
axis.
12. The machine recited in claim 1 wherein said compliant, toroidal
polishing member has a substantially elongated shape along an axial
axis.
13. The machine recited in claim 1 wherein said compliant, toroidal
polishing member has a substantially square shape with rounded end
edge portions.
14. The machine recited in claim 1 wherein said work piece surface
is an optical surface.
15. The machine recited in claim 1 wherein said work piece surface
is ceramic.
16. The machine recited in claim 1 wherein said work piece surface
is a metal.
17. The machine recited in claim 1 wherein said work piece surface
is a vitreous material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is related to U.S. application Ser.
No. ______, filed ______, by Stephen C. Meissner, and entitled,
"Sub-Aperture Compliant Toroidal Polishing Element," and U.S.
application Ser. No. 10/241,144, filed Sep. 11, 2002, by Stephen C.
Meissner, and entitled, "Dual Motion Polishing Tool."
FIELD OF THE INVENTION
[0002] The invention relates generally to the field of optical
manufacturing processes, and in particular to polishing of optical
surfaces. More specifically, the invention relates to a
high-precision polishing tool for polishing an optical quality
surface onto a substrate.
BACKGROUND OF THE INVENTION
[0003] In manufacturing of optical components, lenses, molds and
the like, preliminary operations, such as grinding or diamond
turning, are performed to generate an optical surface on a raw
blank of material. These preliminary operations provide the general
form of the component, but leave surface defects that include
turning grooves, cutter marks, and sub surface damage. A final
polishing step is required to remove these surface and sub-surface
defects. Polishing is typically accomplished in a variety of ways
depending upon the material and the form of the surface, i.e.,
plano form, spherical form, or aspherical form.
[0004] Skilled artisans will appreciate that work piece surfaces
having either a piano and spherical form are typically polished
using "full-aperture" or "full-surface" tools. Full aperture tools
tend to cover over 80% of the work piece surface during polishing.
These tools are constructed in a variety of ways, including
traditional "pitch" and more recent pad-type. "Pitch" polishing
tools are comprised of a soft flow-able material, such as pitch or
bees wax, which is used to create a mold of the optical
surface.
[0005] Referring to FIG. 1, a typical prior art full aperture
"pitch" polishing tool 10 has a plurality of grooves 12 to aid in
the movement of polishing fluid at the interface of work piece
surface (not shown). Polishing tool 10 has a support surface 14
attachable to a shank 16. Shank 16 defines an arbor for holding the
polishing tool 10 for operation in a working unit. In operation,
polishing tool 10 is held against the work piece (not shown) with
an applied force and the two components, i.e., work piece and
polishing tool 10, are moved relative to one another in the
presence of a free abrasive polishing compound, such as cerium
oxide, to achieve polishing.
[0006] Referring to FIG. 2, a typical full-aperture pad polishing
tool 20 has of a pad mounting surface 22 for receiving a polishing
pad 24 thereon. The polishing pad 24 is typically attached to the
pad mounting surface 22 via an adhesive or via friction grip as
disclosed in U.S. Pat. No. 4,274,232 issued to Wylde on Jun. 23,
1981, titled "Friction Grip Pad."
[0007] Those skilled in the art will appreciate that polishing
aspheric surfaces using full-aperture tools involves much iteration
to rebuild or reshape the polishing tool slowing the polishing
process considerably. Therefore polishing of aspheric surfaces is
commonly restricted to sub-aperture methods using existing
ring-tools or small-area tools. Sub-aperture methods using
ring-tools or small-area tools rely on a polishing tool that
contacts less than 50% of the work piece surface at one time. Ring
tools, as disclosed in U.S. Pat. No. 4,768,308 issued to Leland G.
Atkinson, III, et al. on Sep. 6, 1998, titled "Universal Lens
Polishing Tool, Polishing Apparatus And Method Of Polishing," have
a diameter that is comparable to or larger than the radius of the
work piece and contact the work piece surface over an area that is
much larger than that for a small-area tool. Small-area tools
contact only a small area of the work surface at a time and create
an interfacial contact area that is on the order of 99% smaller
than the area of the work piece surface.
[0008] Moreover, it is well known that sub-aperture small-area
tools may be outfitted with a variety of polishing head shapes,
including spherical (as shown in FIG. 3), but may also include
conical, cylindrical, and flat along with a polishing pad. In FIG.
3, a sub-aperture tool 30 includes an arbor 32 fixedly attached to
a spherical polishing head 34. It should be noted that the
spherical polishing head 34 may be substituted with one of the
aforementioned polishing heads of a different geometrical shape.
Sub-aperture ring-tools may be considered a variation on the
small-area tool with the polishing head being of ring-shaped
configuration with surface contact during polishing being from 3%
to 50% of the work piece surface.
[0009] It is further known that sub-aperture tools are commonly
made from materials, such as felt, wood, cast iron, lead, and woven
polymers, that allow free-abrasive particles to become imbedded
within the material so that relative motion is generated between
the abrasive particles and the part. Such materials allow free
abrasive particles to imbed themselves within this carrier,
allowing the tools to wear which is a detriment when trying to
control material removal precisely. The concept of a compliant tool
that does not allow free abrasive particles to imbed themselves and
therefore is resistant to wear, provides advantage in precision
polishing.
[0010] One precision polishing method, Elastic Emission Machining
(EEM) uses this concept where a polishing tool (with a spherical or
flat configuration) is made from an elastic solid. This tool is
precisely controlled to maintain a minute gap between itself and
the part surface within a temperature-controlled bath of
free-abrasive slurry. The tool is rotated at high speed and is
driven to traverse the part surface creating a hydrodynamic bearing
at the tool-part interface gap. This situation allows abrasive
particles to be projected against the surface being conditioned
with sufficient energy to cause elastic penetration and subsequent
precision material removal.
[0011] As with any method that uses a rotating tool, the area at
the tool's center of rotation remains stationary--creating a "dead
zone." As the radial distance from the center of rotation
increases, the tangential velocity also increases. Therefore, when
polishing with sub-aperture tools, the greatest removal and
subsequent benefit comes from a contact point radially distant from
the tools center of rotation. For spherical or conical polishing
tools, the tool must be tipped at an angle to provide needed
tangential velocity. In order to generate productive velocities for
polishing, spherical and conical polishing tools either need to be
rotated at very high speeds or tipped at a large angle or a
combination of the two. When very small tools are used, a
combination of the two is required to gain maximum benefit.
[0012] Referring to FIGS. 4-7, limitations exist when attempting to
polish deep concave surfaces, where a large angle would restrict
the polishing capability of the tool. For example, using a tool
with a spherical tip, an impractical angle of nearly 60 degrees
would be required to achieve the same surface speed as a toroidal
tip of the same overall diameter. FIG. 4 illustrates this example,
where the arbor 32 of the spherical tipped tool interferes with the
curved surface 40 of the part 42. Similar limitations exist for
cylindrical and "flat" sub-aperture tools. As depicted in FIGS. 5,
6, and 7, cylindrical and "flat" sub-aperture tools 46 having arbor
32 and polishing surface 48 do not conform to curved surfaces 40 of
the work piece or part 42 well and therefore restrict their
application for polishing these surfaces. The cylindrical
sub-aperture tool 46 allows minimum tilt while allowing maximum
tangential velocity to be achieved, however, the contact area is
crescent-like and tends to be non-uniform in this configuration,
which is detrimental to precision polishing. If used without any
tilt, benefits are realized from the maximized diameter, but fluid
flow is restricted and the ability to polish severe or steep
aspheres is limited.
[0013] Therefore, the need persists in the art for a precision
polishing element for polishing optical surfaces without adversely
affecting the quality of the surface.
SUMMARY OF THE INVENTION
[0014] It is, therefore, an object of the invention to provide a
precision polishing tool capable of uniformly polishing optical
surfaces.
[0015] Another object of the invention is to provide a sub-aperture
tool that minimizes tilt limitations and conforms to the surface of
the work piece to be polished.
[0016] The present invention is directed to overcoming one or more
of the problems set forth above. Briefly summarized, according to
one aspect of the present invention, a precision polishing element
for polishing a work piece surface has a compliant, toroidal
polishing member mountable to a support member. The compliant,
toroidal polishing member has an active polishing surface extended
uniformly beyond a peripheral surface of the support member for
engaging the work piece surface.
[0017] The tool disclosed provides greater advantage for
free-abrasive type polishing operations, like EEM, due to the
toroidal geometry. The toroidal shape allows shallow contact angles
to be used, providing significant practical advantage for polishing
steep concave surfaces. The toroidal shape is also advantageous due
to the low axial profile, while providing radial distance to
maximize tangential speed for material removal. The shape of the
toroid also provides a uniform geometry that allows for polishing
fluid to be transported along the circumference, providing the
necessary flow required for polishing. In addition, the contact
area generated at the tool-part interface tends to be very uniform
and consistent, appearing oval in shape, which is essential for
deterministic polishing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other objects, features, and advantages of the
present invention will become more apparent when taken in
conjunction with the following description and drawings wherein
identical reference numerals have been used, where possible, to
designate identical features that are common to the figures, and
wherein:
[0019] FIG. 1 is an isometric view of a prior art polishing
tool;
[0020] FIG. 2 is an isometric view of a prior art polishing tool
with a polishing pad;
[0021] FIG. 3 is an isometric view of a prior art sub-aperture
polishing tool with a spherical polishing head;
[0022] FIG. 4 shows the interference condition when a spherical
sub-aperture polishing tool used in prior art, angled at nearly 60
degrees from vertical to achieve satisfactory surface speed for
productive material removal, engages a concave surface;
[0023] FIG. 5 shows a sub-aperture pitch/pad polishing tool used in
prior art, engaged with a concave surface;
[0024] FIG. 6 shows a sub-aperture pitch/pad polishing tool used in
prior art, engaged with a convex surface;
[0025] FIG. 7 shows a sub-aperture cylindrical polishing tool used
in prior art, engaged with a convex surface;
[0026] FIG. 8 illustrates the first example of the embodiment of
the compliant toroidal polishing tool according to the
invention;
[0027] FIG. 9 is a close up view of the toroidal polishing tip of
the compliant toroidal polishing tool according to the
invention;
[0028] FIG. 10 illustrates the second example of the embodiment of
the polishing tool according to the invention;
[0029] FIG. 11 is an exploded view of the third example of the
embodiment of the polishing tool according to the invention;
[0030] FIG. 12 is an exploded view of the fourth example of the
embodiment of the polishing tool according to the invention;
[0031] FIG. 13 is a close up view of the compliant toroidal
tip;
[0032] FIG. 14 is a cross-sectional view of the polishing tip
showing a circular cross section of the compliant toroidal tip;
[0033] FIG. 15 is a cross-sectional view of the polishing tip
showing an oval cross-section of the compliant toroidal tip with
the long side of the oval aligned perpendicular to the arbor
axis;
[0034] FIG. 16 is a cross-sectional view of the polishing tip
showing an oval cross-section of the compliant toroidal tip with
the long side of the oval aligned parallel to the arbor axis;
[0035] FIG. 17 is a cross-sectional view of the polishing tip
showing a square cross-section with rounded corners of the
compliant toroidal tip;
[0036] FIG. 18A illustrates a typical clearance condition when a
compliant toroidal polishing tool is used in service; and
[0037] FIG. 18B illustrates the polishing tool of the invention in
contact with the work piece.
DETAILED DESCRIPTION OF THE INVENTION
[0038] Turning now to the drawings, and in particular to FIGS.
8-13, the compliant toroidal polishing element 50 of the invention
is illustrated. Broadly defined, compliant toroidal polishing
element 50 includes a support member, or mounting arbor 52, and a
compliant toroidal polishing tip 54 mounted to the mounting arbor
52. Compliant toroidal polishing tip 54 preferably has a
circumferential active polishing surface 57 extending substantially
symmetrically beyond the peripheral surface of the mounting arbor
52 for engaging the curved surface 40 of work piece 42. Work piece
42 may comprise a variety of materials including metallic
materials, ceramic materials, and vitreous materials. According to
FIGS. 9-12, the mounting arbor 52 may be constructed simply as a
solid (as shown) or hollow cylinder. Referring to FIG. 11, the
mounting arbor 52 is preferably constructed with additional
features, such as a locating shoulder 51 for advantage in tool
holding and repetitive placement. Mounting arbor 52 has a distal
end 56 with support surface 58 for supporting compliant toroidal
polishing tip 54. Upon support surface 58, a centering boss 60 may
be mounted which aids in providing concentric alignment of toroidal
polishing tip 54 during attachment. If provided, centering boss 60
projects normally from support surface 58 of distal end 56.
Toroidal polishing tip 54 of toroidal geometry is then attached
centrally to the support surface 58, whereby the toroidal polishing
tip 54 is concentric with the diameter of the mounting arbor 52.
According to FIG. 13, the toroidal polishing tip 54 may have an
alignment port 70 concentric with its outside diameter intended to
mate with centering boss 60 (FIG. 12) if provided on mounting arbor
52 to provide concentric alignment and to aid in attachment.
[0039] Attachment of the toroidal polishing tip 54 to the arbor 52
may be accomplished in a variety of ways including adhesive,
chemical, thermal, or mechanical bonding. Once joined, the
compliant toroidal polishing tool 50 of the invention is ready for
use.
[0040] Referring again to FIGS. 9 and 10, an important feature of
compliant toroidal polishing element 50 is the compliant toroidal
tip 54. The compliant toroidal tip 54 may be manufactured from a
variety of compliant polymers such as, but not limited to,
polyurethane, chloroprene, fluorocarbon, fluorosilicone, ethylene
propylene, and nitrile. We prefer using nitrile because of its
compliant properties. For advantageous sub-aperture deterministic
polishing in the presence of free-abrasive lapping compound, the
hardness of the compliant toroidal polishing tip 54 needs to be in
the range of 40-95 on the Shore A scale.
[0041] Referring to FIGS. 14-17, the shape of toroidal polishing
tip 54 may deviate from a pure toroid and still provide advantage
in polishing. According to FIG. 14, toroidal tip 54 has a
substantially circular shape. According to FIG. 15, toroidal tip 54
has a substantially horizontally oriented oval shape. According to
FIG. 16, toroidal tip 54 has a substantially vertically oval shape.
According to FIG. 17, toroidal tip 54 has a substantially square
shape with rounded corners 59. If used, centering boss 60 should be
made so arbor material does not extend beyond the boundary of the
toroidal polishing tip 54 to avoid risk of damage to part surface
when polishing.
[0042] According to FIG. 18A, in operations, compliant toroidal
polishing element 50 is mounted in a rotary polishing machine 80
for polishing a work piece. As shown in FIG. 18B, the polishing
surface 57 engages curved surface 40 of work piece 42 for
polishing. An important advantage of compliant toroidal polishing
element 50 is that a clearance 64 is formed between the mounting
arbor 52 and the curved surface 40 of the work piece 42. Experience
suggests that compliant toroidal polishing element 50 should be
angled at about 30 degrees from a centerline extending normally
through the curved surface 40 for most efficient operation.
According to our experience, this arrangement produces satisfactory
surface speed for productive material removal during polishing.
[0043] The invention has been described with reference to a
preferred embodiment. However, it will be appreciated that
variations and modifications can be effected by a person of
ordinary skill in the art without departing from the scope of the
invention.
Parts List
[0044] 10 full-aperture pitch polishing tool
[0045] 12 grooves
[0046] 14 support surface
[0047] 16 shank
[0048] 20 full-aperture pad polishing tool
[0049] 22 pad mounting surface
[0050] 24 polishing pad
[0051] 30 sub-aperture tool
[0052] 32 arbor
[0053] 34 spherical polishing head
[0054] 40 curved surface
[0055] 42 work piece
[0056] 46 sub-aperture tool
[0057] 48 polishing surface
[0058] 50 compliant toroidal polishing element
[0059] 51 locating shoulder
[0060] 52 mounting arbor
[0061] 54 polishing tip
[0062] 56 distal end
[0063] 57 polishing surface
[0064] 58 support surface
[0065] 59 rounded corners
[0066] 60 centering boss
[0067] 64 clearance
[0068] 70 alignment port
[0069] 80 rotary polishing machine
* * * * *