U.S. patent application number 10/963189 was filed with the patent office on 2005-04-14 for tool, apparatus, and method for precision polishing of lenses and lens molds.
Invention is credited to Bechtold, Michael J..
Application Number | 20050079812 10/963189 |
Document ID | / |
Family ID | 34425744 |
Filed Date | 2005-04-14 |
United States Patent
Application |
20050079812 |
Kind Code |
A1 |
Bechtold, Michael J. |
April 14, 2005 |
Tool, apparatus, and method for precision polishing of lenses and
lens molds
Abstract
A tool for polishing objects having a wide variety of materials
and shapes including precision optical surfaces, injection mold
inserts, and thin film coating dies. The tool has an elastic solid
bladder with a curved surface, upon which is disposed an abrasive
band. The curved bladder surface is produced by compressing the
bladder between two parallel plates. The apparatus comprises a
multi-axis computer controlled machine to which the tool is
attached.
Inventors: |
Bechtold, Michael J.;
(Ontario, NY) |
Correspondence
Address: |
HOWARD J. GREENWALD P.C.
349 W. COMMERCIAL STREET SUITE 2490
EAST ROCHESTER
NY
14445-2408
US
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Family ID: |
34425744 |
Appl. No.: |
10/963189 |
Filed: |
October 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10963189 |
Oct 12, 2004 |
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10863702 |
Jun 8, 2004 |
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10863702 |
Jun 8, 2004 |
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10439833 |
May 16, 2003 |
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Current U.S.
Class: |
451/504 |
Current CPC
Class: |
B24B 13/06 20130101;
B24B 13/01 20130101 |
Class at
Publication: |
451/504 |
International
Class: |
B24B 001/00 |
Claims
I claim:
1. A polishing tool comprising: a) a mandrel having a drive shank
at a proximal end thereof, a threaded shank, a mandrel shank, and a
flange at a distal end thereof; b) a solid elastic annular bladder
comprising a bore, an outer surface, a lower surface, and an upper
surface, said bladder disposed upon said mandrel with said lower
surface of said bladder in contact with said flange of said mandrel
and said mandrel shank passing through said bore in said bladder;
c) a compression flange comprising a compression washer and a
compression collar, said compression washer comprising a lower
surface in contact with said upper surface of said bladder, and
said compression collar comprising a bore slidingly engaged with
said threaded shank of said mandrel; and d) a compression nut
threadedly engaged with said threaded shank of said mandrel,
wherein when said compression nut is tightened upon said threaded
shank, said solid bladder is compressed between said flange of said
mandrel and said compression washer, causing said outer surface of
said bladder to have an arcuate shape.
2. The polishing tool as recited in claim 1, wherein said arcuate
shape of said bladder resulting from said solid bladder being
compressed between said flange of said mandrel and said compression
washer is further ground to a different arcuate shape.
3. The polishing tool as recited in claim 2, wherein said different
arcuate shape is a spherical shape.
4. The polishing tool as recited in claim 1, wherein said solid
elastic annular bladder consists essentially of an elastomer.
5. The polishing tool as recited in claim 4, wherein said elastomer
is selected from the group consisting of gum rubber, nitrile
rubber, and polyurethane.
6. The polishing tool as recited in claim 4, wherein said elastomer
has a Shore A durometer of between about 10 and about 90.
7. The polishing tool as recited in claim 6, wherein said elastomer
has a Shore A durometer of about 40.
8. The polishing tool as recited in claim 1, wherein said solid
elastic annular bladder consists essentially of an elastomeric
closed cell foam.
9. The polishing tool as recited in claim 1, wherein said
compression collar of said compression flange comprises an inner
stop, and said mandrel comprises a shoulder stop, and wherein when
said compression nut is tightened upon said threaded shank, said
inner stop of said compression collar contacts said shoulder stop
of said mandrel.
10. The polishing tool as recited in claim 1, further comprising
means for locking said compression flange to said mandrel.
11. The polishing tool as recited in claim 10, wherein means for
locking said compression flange to said mandrel comprises a
setscrew in said compression collar engaged with said mandrel.
12. The polishing tool as recited in claim 1, further comprising a
polishing band engaged with said outer surface of said bladder.
13. The polishing tool as recited in claim 12, wherein said
polishing band comprises an outer surface impregnated with abrasive
particles.
14. The polishing tool as recited in claim 13, wherein said
abrasive particles are selected from the group consisting of ceria,
alumina, silica, diamond, and mixtures thereof.
15. A polishing tool comprising: a) a mandrel having a drive shank
at a proximal end thereof, a threaded shank, a mandrel shank, and a
flange at a distal end thereof; b) a solid elastic annular bladder
comprising a bore, an outer surface, a lower surface, and an upper
surface, said bladder disposed upon said mandrel with said lower
surface of said bladder in contact with said flange of said mandrel
and said mandrel shank passing through said bore in said bladder;
c) a compression flange comprising a compression washer and a
compression collar, said compression washer comprising a lower
surface in contact with said upper surface of said bladder, and
said compression collar comprising a bore slidingly engaged with
said threaded shank of said mandrel; d) a polishing band engaged
with said outer surface of said bladder; and e) a compression nut
threadedly engaged with said threaded shank of said mandrel,
wherein when said compression nut is tightened upon said threaded
shank, said solid bladder is compressed between said flange of said
mandrel and said compression washer, causing said outer surface of
said bladder and said polishing band to have an arcuate shape.
16. The polishing tool as recited in claim 15, wherein said
polishing band comprises an outer surface impregnated with abrasive
particles.
17. A polishing tool comprising: a) a mandrel having a drive shank
at a proximal end thereof, a threaded shank, a mandrel shank, and a
flange at a distal end thereof; b) a solid elastic annular bladder
comprising a bore, an outer surface, a lower surface, and an upper
surface, said bladder disposed upon said mandrel with said lower
surface of said bladder in contact with said flange of said mandrel
and said mandrel shank passing through said bore in said bladder;
and c) means for compressing said lower surface of said bladder
toward said upper surface of said bladder, thereby causing said
outer surface of said bladder to have an arcuate shape.
18. The polishing tool as recited in claim 17, wherein said means
for compressing said lower surface of said bladder toward said
upper surface of said bladder comprises a compression flange
comprising a compression washer and a compression collar, said
compression washer comprising a lower surface in contact with said
upper surface of said bladder, and said compression collar
comprising a bore slidingly engaged with said threaded shank of
said mandrel; and a compression nut threadedly engaged with said
threaded shank of said mandrel.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application is a continuation-in-part of copending
patent application U.S. Ser. No. 10/863,702, filed on Jun. 8, 2004,
which is a continuation-in-part of copending patent application
U.S. Ser. No. 10/439,833, filed on May 16, 2003, the disclosures of
which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] A polishing tool for correcting surface errors, and for
polishing objects comprising a wide variety of materials and shapes
including precision optical surfaces and injection mold
inserts.
BACKGROUND OF THE INVENTION
[0003] This invention relates to tools, an apparatus, and a method
for correcting figure errors, and for polishing a wide variety of
materials and shapes including but not limited to precision optical
surfaces, injection mold inserts, thin film coating dies, and the
like. The method of the present invention provides for improving
and further finishing of any surface, ranging from a relatively
rough ground surface to a polished surface.
[0004] Typically the part being finished according to the present
invention is measured with a coordinate measurement machine (CMM),
a surface profilometer, an interferometer, microscope or some other
measuring instrument capable of giving surface roughness and or
profile data. The data from such measurement and analysis is then
entered into a machine process-controlling computer that then
manipulates the data into process parameters for improving or
polishing the desired component by a polishing machine of the
present invention. One or more iterations of the process of the
present invention may be required to achieve the desired results.
In the preferred embodiment, a polishing tool comprising an
inflatable bladder is attached to and driven by the tool spindle of
the polishing machine. The part to be improved or polished, whether
spherical, aspherical or parabolic in shape, is placed into the
work piece spindle of the polishing machine. If such part is not
axially symmetrical, it may be held in a braked position in the
work piece spindle, or held in a fixture on a table of the machine.
The polishing tool is then compressed against and traversed in a
path over the component. Several variables are able to be
controlled as process parameters, so that the desired finishing
results are achieved.
[0005] In another preferred embodiment, the polishing tool further
comprises actuation means to extend and/or position and/or compress
the inflatable bladder or other compliant part with respect to the
part to be improved or polished. Such actuation means may comprise
one or more linear actuating devices such as e.g., air operated or
hydraulically operated cylinders.
[0006] The present invention provides a method and apparatus for
which the main goal is to polish out and remove defects left from a
preceding grinding operation or to improve the accuracy of a
workpiece such as a lens, mirror, insert for an injection mold, or
coating die, such accuracy being relative to the intended use of
the workpiece; and also to improve the economy of the polishing
process.
[0007] In the following specification, for the sake of linguistic
simplification, only optical components, also known as precision
optics or optics generally, are typically mentioned as the
workpiece. However, it is to be understood that all lenses,
spherical and aspherical, conformal optics, mirrors, plano shapes,
injection mold components, coating dies, and other articles of
manufacture that require highly polished accurate surfaces are also
included in the description, and are to be considered as being
within the scope of the present invention. Materials that may be
finished using the method and apparatus of the present invention
include, but are not limited to brittle amorphous materials such as
e.g., glass, ceramics, infrared materials such as quartz, and the
like. Also included are metals such as e.g., tool steel, stainless
steel, and the like; crystalline materials such as e.g. silicon;
and any other workpieces requiring high finish and form
specifications.
[0008] Currently, many optical lenses are made beginning with a
"blank" starting part (such blank part being an approximately
formed and generally roughly finished piece) in several processing
steps. The process steps typically include fine grinding, followed
by conventional polishing techniques wherein the surface roughness
and surface accuracy of the lens is significantly improved. This
prior art process is sufficient for many conventional low-precision
lenses, but when the desired lens has a shape that is not spherical
or plano and/or where such conventional methodologies cannot be
applied e.g., aspherics, or where the lens has very high accuracy
requirements, such prior art process is not sufficient. In such
circumstances, the method and apparatus of the present invention is
advantageous.
[0009] In particular, several prior art procedures are known to the
applicants as being used to fabricate precision optics. One of
these procedures is known in the art as small spot tool polishing,
wherein a pencil like polishing tool (typical 5 to 15 millimeters
in diameter) is used, such tool comprising a polishing medium of
polyurethane, felt, pitch or some other combination of polishing
material bonded thereto, and typically known as a foil.
[0010] In one specific embodiment of the small spot tool polishing
process, a polishing tool, rotating around the axis thereof, is
mounted to a robotic arm and is traversed by such arm across the
lens surface, or alternatively, such tool is built into a computer
numerically controlled (CNC) polishing machine. During the process
a polishing suspension is applied, while the polishing tool is
traversed across the lens surface through a predetermined typically
computer controlled path. Depending on the correction geometry
required, different volumes of material are abraded, or polished,
from the lens surface. The robotic arm of the correction machine is
programmed in such a way that the polishing tool is moved with
different dwell times at different positions as such tool passes
over the lens. Thus, when more material must be removed at a
particular location, the dwell time is increased, and vice versa.
During the polishing process, the lens may be rotate around its
axis, or be it may be fixed in specific positions if the robotic
arm of the correction machine has such capability.
[0011] In the small spot procedure there are several disadvantages.
The polishing tool wears quickly due to its small diameter, which
results in the distinct disadvantages of a) typically very long
polishing cycles; and b) because of quicker degradation of the
small polishing foil it is much more difficult and costly to
develop accurate corrective polishing routines. Another
disadvantage is due to the small spot diameter of the tool.
Material removal rates are typically very slow, since the
performance is directly proportional to the size of the surfaces
that are in contact during the polishing routine.
[0012] Another known finishing/polishing procedure is known as
magnetorheological finishing (MRF). With the use of the MRF
process, marked improvements in surface roughness and accuracy can
be achieved. In general, the MRF process produces better results
than small spot polishing. Reference may be had e.g., to U.S. Pat.
Nos. 5,795,212, 6,106,380 (deterministic magnetorheological
finishing), 5,839,944 (apparatus deterministic magneto-rheological
finishing), 5,971,835 (system for abrasive jet shaping and
polishing of a surface using a magnetorheological fluid),
5,951,369, 6,506,102 (system for magnetorheological finishing of
substrates), and 6,267,651 and 6,309,285 (magnetic wiper). The
entire disclosure of each of these United States patents is hereby
incorporated by reference into this specification.
[0013] With the MRF procedure a polishing suspension is used, which
contains particles that can be magnetized and therefore under the
effect of strong electromagnets can be solidified. A polishing
suspension is applied sequentially on the outside surface of a
cylinder rotating around its horizontal axis. The polishing
suspension is disposed in a thin band upon the outside surface of a
rotating cylinder, and is conveyed to a location where a strong
magnetic field is focused. This field is created by magnets
surrounding both sides of the wheel. Under the influence of the
magnetic field, the polishing suspension increases in viscosity
until it is substantially an abrasive solid, thereby forming a
stiff polishing body, which becomes the polishing tool. Thus within
this area i.e., in the upper apex of the polishing tool, a lens may
be polished by such solidified MRF fluid. As the wheel rotates the
polishing suspension leaves the contact area of the lens and the
magnetic field, and is then vacuumed/wiped off of the wheel and
continuously recirculated.
[0014] During the MRF polishing process, the lens rotates. The lens
carrier with the lens can be placed by means of a tilting device
and an assigned axis control at angles to the vertical axis. With a
large angle of inclination, the edge of the lens touches the
polishing tool, while with a small angle of inclination the center
of the lens comes into contact with the polishing tool.
Additionally the lens carrier is guided in such a way that it also
can execute vertical movements. With a rotating lens, the angles of
inclination are continually varied; such variation is accomplished
with the use of virtual pivot point computer controlled motion that
combines the two linear and one rotary axes and thus keeps the lens
in consistent contact with the polishing tool. A spiral develops on
the lens that is the trajectory of the point of contact between the
solidified polishing suspension and the lens surface.
[0015] The different material removals necessary for the correction
of the lens geometry are implemented as follows: The dwell time of
the point of contact on a certain area on the lens surface can be
varied by appropriately controlling the courses of motion. Since
the material removal is proportional to the dwell time, the desired
corrections can be achieved. The polishing suspension in its
"firmness" can be influenced by variation of the magnetic field
strength. This further enables different material removal rates. A
further correction option results by varying the depth of
submergence of the lens into the polishing suspension.
[0016] Although the MRF process has many attributes, such process
also has some distinct disadvantages as follows: 1) Cost-effective
polishing of deviations is limited to errors of less than 200
nanometers only. This is a result of the lack of "stiffness" of the
magnetically stiffened polishing suspension and the ability to
shear/polish features greater in magnitude. 2) There is a very high
capital cost of entry into the MRF technology. The process entails
very complex technology, which also increases the cost of
operation. It is also necessary to continuously change the MRF
polishing suspension, which is very expensive because of its
proprietary nature. 3) Parts made of magnetic materials are not
able to be polished with this process, as the workpiece will become
magnetized and not release the magnetic process fluid. 4) Small
concave parts cannot be polished due to the configuration and size
of the MRF polishing wheel.
[0017] Reference may be had to German patent DE003 1057 of R.
Mandler, the disclosure of which is incorporated herein by
reference. There is disclosed in such patent a method for polishing
of lenses and mirrors for high resolution optics. The lens/mirror
is polished conventionally and measured by interferometric means to
map the surface and to determine how much material needs to be
removed and from where. The lens is supported on a rotating holder
with two degrees of movement, while the polishing wheel is
supported with axial adjustment. The polishing wheel has a flexible
rim inflated with a variable internal pressure to adjust the
hardness of flexible rim/tire. Mandler relies upon changes in
pressure on a polyurethane foil to impact removal rates and
finishing qualities. Although as stated therein, the apparatus of
Mandler can change the pressure during the process, such process
does not have the ability to change to softer media, such as felt
or other softer synthetic materials as is disclosed and claimed in
this application. Mandler also discloses only a 3-axis process,
whereas embodiments of the present invention include control and
operation with respect to five or more axes.
[0018] With the method and apparatus of the present invention, many
of the disadvantages of the aforementioned techniques are
non-existent, or rendered insignificant. It is therefore an object
of this invention to provide an apparatus for precision polishing
of objects comprising a wide variety of materials and shapes.
[0019] It is a further object of this invention to provide a
versatile and adjustable tool for precision polishing of objects
comprising a wide variety of materials and shapes.
[0020] It is another object of this invention to provide a method
for precision polishing of objects comprising a wide variety of
materials and shapes.
[0021] It is an object of this invention to provide a method and
apparatus for precision polishing of objects that is simple and has
a low operating cost.
[0022] It is an object of this invention to provide a method, a
tool, and an apparatus that in having the ability to remove low,
mid, and high spatial surface errors, reduces the requirements of
the pre-fine grind tolerances, which in turn reduces the
requirements of the fine grinding apparatus.
[0023] It is an object of this invention to provide a method and
apparatus for precision polishing of objects that has a high rate
of material removal.
[0024] It is an object of this invention to provide a tool for
precision polishing of objects that has high longevity and
stability of operation.
[0025] It is an object of this invention to provide a method, a
tool, and an apparatus that has the ability to perform polishing of
object surfaces that are deeply concave in shape.
SUMMARY OF THE INVENTION
[0026] In accordance with the present invention, there is provided
a polishing tool comprising a mandrel having a drive shank at a
proximal end thereof, a threaded shank, a mandrel shank, and a
flange at a distal end thereof; a solid elastic annular bladder
comprising a bore, an outer surface, a lower surface, and an upper
surface, said bladder disposed upon said mandrel with said lower
surface of said bladder in contact with said flange of said mandrel
and said mandrel shank passing through said bore in said bladder; a
compression flange comprising a compression washer and a
compression collar, said compression washer comprising a lower
surface in contact with said upper surface of said bladder, and
said compression collar comprising a bore slidingly engaged with
said threaded shank of said mandrel; and a compression nut
threadedly engaged with said threaded shank of said mandrel,
wherein when said compression nut is tightened upon said threaded
shank, said solid bladder is compressed between said flange of said
mandrel and said compression washer, causing said outer surface of
said bladder to have an arcuate shape.
[0027] In accordance with the present invention, there is provided
a polishing tool comprising a mandrel having a drive shank at a
proximal end thereof, a threaded shank, a mandrel shank, and a
flange at a distal end thereof; a solid elastic annular bladder
comprising a bore, an outer surface, a lower surface, and an upper
surface, said bladder disposed upon said mandrel with said lower
surface of said bladder in contact with said flange of said mandrel
and said mandrel shank passing through said bore in said bladder; a
compression flange comprising a compression washer and a
compression collar, said compression washer comprising a lower
surface in contact with said upper surface of said bladder, and
said compression collar comprising a bore slidingly engaged with
said threaded shank of said mandrel; a polishing band engaged with
said outer surface of said bladder; and a compression nut
threadedly engaged with said threaded shank of said mandrel,
wherein when said compression nut is tightened upon said threaded
shank, said solid bladder is compressed between said flange of said
mandrel and said compression washer, causing said outer surface of
said bladder to have an arcuate shape.
[0028] In accordance with the present invention, there is provided
a polishing tool comprising a mandrel having a drive shank at a
proximal end thereof, a threaded shank, a mandrel shank, and a
flange at a distal end thereof; a solid elastic annular bladder
comprising a bore, an outer surface, a lower surface, and an upper
surface, said bladder disposed upon said mandrel with said lower
surface of said bladder in contact with said flange of said mandrel
and said mandrel shank passing through said bore in said bladder;
and means for compressing said lower surface of said bladder toward
said upper surface of said bladder, thereby causing said outer
surface of said bladder to have an arcuate shape.
[0029] The tools, apparatus, and method of the present invention
are advantageous because they are simple and lower in cost compared
to other approaches, and it can be adapted for the polishing of a
variety of materials and shapes, particularly those objects having
deeply concave shapes. As a result of the invention, articles of
manufacture such as precision optics, injection mold inserts, and
thin film coating dies can be polished with high precision at a
high throughput and low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The invention will be described by reference to the
following drawings, in which like numerals refer to like elements,
and in which:
[0031] FIG. 1 is a schematic representation of one preferred
polishing apparatus of the present invention;
[0032] FIG. 2A is a cross-sectional view of one preferred polishing
tool of the present invention;
[0033] FIG. 2B is a side elevation view of the polishing tool of
FIG. 2A, in the process of polishing a convex lens;
[0034] FIG. 3 is a cross-sectional view of another preferred
embodiment of a polishing ring disposed upon the polishing tool of
FIG. 2A;
[0035] FIG. 4 is a cross-sectional view of one preferred embodiment
of a polishing ring disposed upon the polishing tool of FIG.
2A;
[0036] FIG. 5 is a flowchart depicting a method of assembly of the
preferred polishing tool of FIG. 2A;
[0037] FIG. 6 is a flowchart depicting a method of preparing the
preferred apparatus of FIG. 1 for a polishing operation; and
[0038] FIG. 7 is a flowchart of a complete method of polishing an
optic using the apparatus and polishing tool of the present
invention.
[0039] FIG. 8A is a cross-sectional view of another preferred
polishing tool of the present invention;
[0040] FIG. 8B is a side elevation view of the polishing tool of
FIG. 8A, in the process of polishing a concave lens;
[0041] FIG. 9 is a schematic representation of another preferred
polishing apparatus for polishing concave spheres, aspheres, convex
spheres, or other conformal shapes;
[0042] FIG. 10 is a first perspective view of another preferred
polishing tool of the present invention comprising single cylinder
actuation means to extend and/or position the inflatable bladder or
other compliant part with respect to the part to be improved or
polished;
[0043] FIG. 11 is a side elevation view of the polishing tool of
FIG. 10;
[0044] FIG. 12 is a top view of the polishing tool of FIG. 10;
[0045] FIG. 13 is a second perspective view of the polishing tool
of FIG. 10, taken from the plate side of the polishing tool;
[0046] FIG. 14 is a first perspective view of another preferred
polishing tool of the present invention comprising twin cylinder
actuation means to extend and/or position the inflatable bladder or
other compliant part with respect to the part to be improved or
polished;
[0047] FIG. 15 is a side elevation view of the polishing tool of
FIG. 14;
[0048] FIG. 16 is a top view of the polishing tool of FIG. 14;
[0049] FIG. 17 is a second perspective view of the polishing tool
of FIG. 14, taken from the plate side of the polishing tool;
[0050] FIG. 18A is a cross-sectional elevation view of the
polishing tool of FIG. 14, shown disengaged with a deeply concave
object to be polished;
[0051] FIG. 18B is a cross-sectional elevation view of the
polishing tool of FIG. 14, shown engaged from a deeply concave
object to be polished;
[0052] FIG. 19 is a perspective view of a first preferred polishing
apparatus of the present invention comprising a polishing tool
having actuation means to extend and/or position the inflatable
bladder or other compliant part with respect to the part to be
improved or polished;
[0053] FIG. 20 is a perspective view of a second preferred
polishing apparatus of the present invention comprising a polishing
tool having actuation means to extend and/or position the
inflatable bladder or other compliant part with respect to the part
to be improved or polished;
[0054] FIG. 21 is a perspective view of a third preferred polishing
apparatus of the present invention comprising a polishing tool
having actuation means to extend and/or position the inflatable
bladder or other compliant part with respect to the part to be
improved or polished;
[0055] FIG. 22A and FIG. 22B are schematic representations of means
for engaging a polishing foil of the polishing tools of FIGS. 10-13
and FIGS. 14-18B;
[0056] FIG. 23A is a perspective view of a solid bladder polishing
tool of the present invention depicted in an uncompressed
state;
[0057] FIG. 23B is a perspective view of a solid bladder polishing
tool of the present invention depicted in a compressed state;
[0058] FIG. 24 is an exploded perspective view of the solid bladder
polishing tool of FIG. 23A, exploded along the axis 23A-23A;
[0059] FIG. 25A is a side cross-sectional view of a solid bladder
polishing tool of the present invention depicted in an uncompressed
state, with the polishing foil absent;
[0060] FIG. 25B is a side cross-sectional view of a solid bladder
polishing tool of the present invention depicted in an compressed
state, with the polishing foil absent;
[0061] FIG. 26A is a side view of a solid bladder polishing tool of
the present invention depicted in an uncompressed state; and
[0062] FIG. 26B is a side view of a solid bladder polishing tool of
the present invention depicted in an compressed state.
[0063] The present invention will be described in connection with
certain preferred embodiments, however, it will be understood that
there is no intent to limit the invention to the embodiments
described. On the contrary, the intent is to cover all
alternatives, modifications, and equivalents as may be included
within the spirit and scope of the invention as defined by the
appended claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0064] For a general understanding of the present invention,
reference is made to the drawings. In the drawings, like reference
numerals have been used throughout to designate identical elements.
In describing the present invention, the following term(s) have
been used in the description:
[0065] As used herein, the term figure error (or form error) is the
measured global deviation from the desired surface shape e.g., a
sphere, asphere or polynomial geometric shape.
[0066] As used herein, form error is a low frequency error.
Traditionally in optics, irregularity and power are the two
specifications that need to be considered. Irregularity is the
deviation from a perfect surface. Power is the resulting average
surface dimensions e.g., radius of curvature.
[0067] As used herein, the term zonal enhancement is meant to
indicate a correction of the figure error, which is located
symmetrically or asymmetrically at one specific location (zone) on
the work piece. For example, if a cylindrical disc was the
workpiece, a zonal error would be in one sector of the disc, or in
a specific band or ring on the disc, or other rotationally
symmetrical part.
[0068] As used herein, the terms spot, high, mid- and low spatial
frequencies in reference to errors in a surface to be polished are
meant to indicate the following. Low spatial frequencies are errors
that appear only once to a few times across a particular surface.
Mid-spatial frequencies are errors that occur many times across a
surface of a part, generally have a periodic spacing of between 80
microns and 3 mm, and are typically caused by cutter marks due to
machine or tool vibrations. High spatial frequencies are errors
that happen on a microscopic scale, which may appear thousands of
times across the surface of a part, and have a periodic spacing of
less than 80 microns.
[0069] As used herein, the term polishing, when used in reference
to a workpiece to be finished, is meant to indicate a
chemo/mechanical process that ablates material from a surface.
[0070] As used herein, the term correction of form, or form error
modification correction, when used in reference to a workpiece to
be finished, is meant to indicate the same as has been defined for
figure error.
[0071] As used herein, the term figure, when used in reference to a
workpiece to be finished, is meant to indicate polishing in a
correction for error in the figure and or form, which are the
same.
[0072] As used herein, the term surface roughness, when used in
reference to a workpiece to be finished, is meant to indicate high
frequency errors, which are typically the result of brittle
fracture regime (e.g.microcracks).
[0073] FIG. 1 is a schematic representation of one preferred
polishing apparatus of the present invention. Referring to FIG. 1,
polishing apparatus 100 is configured for polishing convex spheres,
aspheres, shallow concave spheres, or other conformal shapes.
Polishing apparatus 100 comprises a base 102 that supports Y-axis
linear slide 104, the motion of which is bi-directional along
Y-axis 105 (directed perpendicular to the plane of FIG. 1). Linear
slide 106, the motion of which is bi-directional along X-axis 107,
is mounted upon Y-axis linear slide 104. These linear slides 104
and 106 are both computer numerically controlled (CNC) positioning
devices, providing programmable motion in the X-Y plane.
[0074] Workpiece spindle 108 is mounted upon linear slide 106, such
that the motion of spindle 108 is bidirectionally programmable
along axis 109, which is parallel to X-axis 107. Thus spindle 108
is movable by computer control along axis 109, depending on the
requirements or the polishing process. Rotatable workpiece chucking
device 110 is attached to end of workpiece spindle 108. The
workpiece 10 to be polished is engaged and held by chuck 110 and
rotated by spindle 108 around the central rotary axis thereof.
[0075] Apparatus 100 further comprises vertical slide 120 attached
to polishing machine column 122, which is joined to base 102. The
motion of vertical slide 120 is bi-directional along Z-axis 121.
Polishing tool spindle 124 is attached to the Z-axis slide 120. The
rotational speed (RPM) of this spindle is varied by the computer
depending on the desired removal rate of material from workpiece
10. Apparatus 100 further comprises a rotatable chucking device 126
attached to the end of polishing tool spindle 124, in which
polishing tool 128 of the present invention is inserted and
rotated. Polishing tool 128 is provided in a variety of shapes,
sizes, and materials (e.g. see polishing tool 200 of FIG. 2A and
2B), as will be described subsequently in this specification.
[0076] In summary, there are three linear and one rotary axis
drives in this configuration, all of which are computer controlled
to allow for a deterministic polishing process, to be described
subsequently in more detail in this specification.
[0077] Referring again to FIG. 1, in the preferred embodiment,
apparatus 100 further comprises a fluid delivery system 130 for
delivery of a homogeneous liquid or a liquid slurry. In some
embodiments, delivery system 130 delivers a liquid containing
finely divided solid particles, and as such is considered a slurry,
a suspension, or a particulate dispersion. Such particles are
preferably abrasive polishing particles with a hardness sufficient
to wear a typical optical material such as e.g. glass. Such
particles may comprise e.g., silica, alumina, ceria, diamond, and
the like, and mixtures thereof. Many other hard, abrasive
particulate materials such as e.g., carbides, nitrides, etc. will
be apparent to those skilled in the art.
[0078] In other embodiments, delivery system 130 delivers a
homogeneous liquid substantially free of solid particles. Suitable
liquids may be e.g. water, water soluble oils or lubricants (such
as e.g. glycerine), hydrocarbon oils, silicone oils, and the like.
The selection of a particular homogeneous liquid or a particulate
slurry will depend upon the particular optical part being polished,
and upon the desired end results.
[0079] Referring again to FIG. 1, slurry or fluid delivery system
130 comprises a reservoir (not shown), a slurry/fluid mixer 132,
and a slurry/fluid pump 134. Slurry/fluid delivery system 130 is
used to supply an abrasive slurry/fluid (not shown), which is
delivered through conduit 136 and directed by nozzle 138 upon the
polishing tool 128 and workpiece 110, at the area of contact there
between.
[0080] FIG. 2A is a cross-sectional view of one preferred polishing
tool of the present invention used in apparatus 100 of FIG. 1,
according to the methods of the present invention. Referring to
FIG. 2A, polishing tool 200 comprises a main body or bladder
mandrel 202 having a shank 201 at a proximal end 224 thereof, and a
flange 211 at a distal end thereof, around which a bladder 204 is
disposed and sealably engaged therewith. Compression washers 206
and 207 are disposed on both sides of bladder 204, and are held in
place by locking nuts 208 and 209, respectively. Nuts 208 and 209
and washers 206 and 207 provide sealing means in that nuts 208 and
209 and washers 206 and 207 hold bladder 204 tightly against flange
211 of mandrel 202. In the preferred embodiment, lips 246 and 248
of bladder 204 are disposed and held firmly in grooves 242 and 244
of mandrel 202, so that bladder 204 is sealed to mandrel 202.
[0081] End 210 of mandrel 202 has an axial bore 212 disposed
therein, which is connected to at least one radial bore 214, or
preferably a plurality of radial bores 214 extending to a cavity
216 disposed in the perimeter 218 of mandrel 202. Such axial bore
212 and radial bores 214 form a continuous passageway such that
cavity 216 is in communication with the atmosphere outside of tool
200. Thus axial bore 212 and radial bores 214 allow the cavity 216
to be filled and pressurized with a fluid delivered through
inflation device 220, which is disposed and sealed in axial bore
212 at the end 210 of mandrel 202.
[0082] Polishing tool 200 further comprises a ring assembly 230 of
polishing material disposed around the outer perimeter of bladder
204. FIG. 3 is a cross-sectional view of one preferred embodiment
of a polishing ring disposed upon the polishing tool of FIG. 2A.
Referring to FIG. 3, ring assembly 230 is a dual ring assembly
comprising a backer ring 232 of material, over which is disposed
abrasive ring 234 comprised of a polishing medium adhered thereto.
The resulting polishing ring assembly 230 is disposed around the
perimeter of and contiguous with bladder 204. In one preferred
embodiment, backer ring 232 consists essentially of a band of
poly(ethylene terephthalate) having a thickness of between about 50
microns and about 1000 microns, and a width of between about 2
millimeters and about 30 millimeters.
[0083] Abrasive ring 234 is made of a material of sufficient
structural strength to withstand the high shear and tensile forces
during polishing, and to resist degradation through exposure to the
polishing/lubricating fluid, such as e.g. polyurethanes of various
durometers; and various types of felt, cork, and metal and/or resin
bond diamond, alumina, and/or zirconium, with a multitude of
different types of backings and patterns therein. Abrasive ring 234
preferably has a thickness of between about 1 millimeter and about
5 millimeters, and a width of between about 2 millimeters and about
30 millimeters.
[0084] FIG. 4 is a cross-sectional view of another preferred
embodiment of a polishing ring disposed upon the polishing tool of
FIG. 2A. Referring to FIG. 4, ring 230 simply comprises a single
ring 236 of polishing material disposed around the perimeter of
bladder 204. The embodiment of FIG. 4 is used when ring 236 is of
sufficient structural strength so as to be able to perform the
particular polishing process without the use of a supporting ring
disposed contiguously with such ring, as was depicted in FIG. 3. In
one preferred embodiment, single ring 236 consists essentially of
polyurethane, and has a thickness of between about 1 millimeter and
about 5 millimeters, and a width of between about 2 millimeters and
about 30 millimeters.
[0085] FIG. 2B is a side elevation view of the polishing tool of
FIG. 2A, in the process of polishing a convex lens. Referring to
FIGS. 2A and 2B, polishing ring assembly 230 (also known as the
foil) is disposed around the outer perimeter of bladder 204 and
held in place while bladder 204 is pressurized with a fluid. In
operation, polishing tool 200 comprising polishing ring assembly
230 is rotated and engaged with lens 10 such that polishing ring
assembly 230 provides a shearing and polishing action upon the
surface of lens 10. It will be apparent that the pressure that is
applied to bladder 204 will determine the curvature and firmness of
the outer surface of polishing ring assembly 230 during a polishing
operation.
[0086] Referring again to FIG. 2A, and in one preferred embodiment,
bladder 204 has a shape and cross sectional profile that is
substantially similar to that of a tire. Bladder 204 is preferably
made of a compliant, flexible elastic material that is wrapped or
attached at its periphery to the perimeter 218 of mandrel 202.
Suitable materials for bladder 204 are e.g., natural or synthetic
rubber, silicone, or polyurethane, with a wall thickness of
approximately 1 millimeter.
[0087] The tire-shaped bladder 204 may have a variety of specific
cross sectional shapes. Before inflating bladder 204 with either
air or some other fluid, polishing foil 203 is disposed around or
applied to the bladder tool to act as the polishing medium. In one
further embodiment, polishing foil 230 is made of polyurethane, and
the abrasive polishing medium is provided in a liquid slurry that
is pumped onto workpiece 10 and polishing foil 230, as described
previously. Alternatively, abrasive particles may be embedded in
the polishing foil. Suitable abrasive particles include particles
made by the Rhodes Corporation, or by the Minnesota Mining and
Manufacturing Company (3M). or it may actually be a product that
has In a further embodiment, abrasive particles in the shape of
miniature pyramids of polishing medium such as e.g., alumina in
varying grit sizes is used. Such products will require that only
water be added to wet the polishing medium (the dry powder.)
[0088] In another embodiment, foil 230 comprises a backer ring of
poly(ethylene terephthalate) (PET) or similar material to allow
softer polishing ring media to be used without tearing or pulling
apart, yet maintaining the flexibility required for fine polishing.
Bladder 204 of tool 200 is then inflated to a specific pressure
depending on the polishing results desired. In such an embodiment,
foil 230 is held in position upon bladder 204 by the expansion
pressure of the bladder 204 being inflated; thus no adhesive or
mechanism is required to bond foil 230 to bladder 204. Such a
configuration enables a simple and rapid change of foil polishing
media.
[0089] In operation of apparatus 100 of FIG. 1, to which is fitted
polishing tool 200 of FIG. 2A, several factors will affect the
accuracy and removal rates of the polishing process: the size and
shape of bladder 204, the composition of the polishing medium, the
composition of the polishing slurry, and the pressure applied to
the bladder 204 and also the type of fluid used to inflate the
bladder. These latter variables are related to the tool itself
(with the exception of slurry composition). Also affecting the
accuracy and removal rates of the polishing process included in
this invention are variables of the apparatus, such as e.g.,
example spindle speeds, axis feed rates and polisher path
modifications.
[0090] It will be apparent that a variety of fluids may be used to
pressurize bladder 204 of polishing tool 200, and that the physical
properties of such fluids, as well as the pressure of such fluids
also will affect the accuracy and removal rates of the polishing
process. The fluid may be selected so as to beneficially affect the
polishing process. In one simple and thus preferred embodiment, air
is used as the bladder inflation fluid. In another embodiment, a
much more dense fluid, i.e. a liquid, such as water is used as the
bladder inflation fluid. In such an embodiment, the effective
pressure of the outer wall of the bladder is a function of not only
the inflation pressure, but also the rotational speed. Such
rotational speed provides an additional pressure component due to
the centrifugal force exerted by the fluid, in proportion to the
square of the rotational speed. Such pressure is analogous to the
pressure at the base of a column of liquid acted upon by
gravity.
[0091] In a further embodiment, a viscous liquid, such as a
hydraulic oil is used as a bladder inflation fluid. The viscosity
of such a viscous liquid is preferably between about 10 centipoise
and about 100,000 centipoise, and more preferably between about 20
centipoise and about 1000 centipoise. The higher viscosity of such
fluid also affects the accuracy and removal rates of the polishing
process, because at the contact area of the bladder with the
workpiece, the bladder is deformed; hence the fluid disposed within
the bladder must undergo viscous flow in this region. Thus a higher
viscosity fluid has a greater resistance to deformation, and also
being non compressible and thus can provide a beneficial polishing
effect. In yet another embodiment, the use of a viscous fluid
provides vibration damping to the process, thereby rendering such
process more precise, stable, and reliable. In further embodiments,
non-Newtonian fluids are used such as. e.g. a shear thinning fluid,
or a shear thickening fluid. In other embodiments, fluids for which
the rheology may be varied by exposure to an electric or magnetic
field may be used.
[0092] Referring again to FIG. 2A, in one embodiment, inflation
device 220 is a simple, inexpensive check valve. In a preferred
embodiment, inflation device is a valve stem, commonly used for the
inflation of tubeless tires. In another embodiment, axial bore 212
is sealed, and mandrel 202 of tool 200 is provided with a second
axial bore 222 disposed through the opposite end 224 of mandrel
202. In such an embodiment, axial bore 212 is supplied with
pressurized fluid from a fluid supply means (not shown) in real
time during the polishing process. Such fluid supply means is
commonly used as a coolant supply to a machine tool and is well
known in the art of machine tools. Thus the pressure within bladder
204 may be varied and/or pulsated during the polishing process, by
the delivery or withdrawal of bladder inflation fluid as indicated
by arrow 225.
[0093] It is to be understood that many multi-axis CNC machine
tools are known in the art, which can be suitably configured to use
the polishing tool and the methods of the present invention. The
particular configuration of machine tool will depend upon the
material properties, size, and shape of the starting blank and the
desired finished end product. The present invention is not limited
only to the use of the machine tools described herein. For example,
such a machine tool could comprise from between two computer
controlled axes up to as many as five or six computer controlled
linear and/or rotary axes.
[0094] Referring again to FIG. 1, polishing tool 200 and workpiece
10 to be polished are typically inserted into separate spindles 124
and 108 of a multi-axis CNC machine tool. Machine tool apparatus
100 could have a configuration as shown in FIG. 1, or a
configuration similar to that of a lathe, mill or some other
customized arrangement of the axes, depending upon the part to be
polished. Work piece spindle 108 may also be programmed to maintain
constant surface speed and also to do zonal enhancements that are
especially necessary when there are axial asymmetries in the part.
It is to be understood that many different machine variations are
possible, and that axes and spindles can be configured in a
multitude of combinations/permutations to suit any workpiece shape
that needs to be polished. The configuration of the different
machine axes and spindles can be in any order as required to enable
actuation of the polishing tool over the surface of the workpiece
to be polished. Accordingly, all such configurations are to be
considered within the scope of the present invention.
[0095] During the polishing operation, the polishing slurry/fluid
suspension is fed between the polishing tool 200 and the work piece
10 by slurry delivery system 130. Depending on the results
required, the axis traverse feedrates (i.e. the velocities of the
linear slides), the workpiece rotational speed in revolutions per
minute (RPM) and tool spindle rotational speed in RPM, and the tool
path variation in three dimensional space are adjusted via
automated computer control.
[0096] In one embodiment, the pressure (and thus the "firmness") of
bladder 204 of polishing tool 200 is preset, and maintained
constant during the polishing operation. Depending on the bladder
shape, the bladder material properties, the bladder inflation
pressure, and the hardness/density of polishing foil 230, a
specific pretest is performed in order to characterize the
polishing spot profile. As used herein, the term spot profile is
meant to indicate the indentation resulting from contacting a test
workpiece with polishing tool 200 or 300 by moving the otherwise
stationary test workpiece into contact with the polishing tool 200
or 300, thus leaving a depression, indentation, or "footprint" in
the part the test is performed in a standard manner, with the
workpiece moved against the tool with a specified displacement for
a specified period of time. The resulting volume of the indentation
per unit time period it the material removal rate.
[0097] Thus the shape and size of the area produced when the
polishing tool is pressed into the test piece for a given period of
time is the spot profile. This spot profile is then used in the
generation of the time dependent trajectory of the polishing tool
over the surface of the workpiece that is required to achieve the
desired polishing results. This time dependent trajectory is also
known in the art as the tool path and dwell times used in
polishing. With the profile characterized, high, mid and low
spatial features can be greatly improved through adjustments of the
polishing variables, tool rpm, workpiece rpm, axes feedrates, and
compression factor. As used herein, the term compression factor is
meant to indicate the compressive force applied by the polishing
tool against the workpiece, such force being the combination of
force due to bladder pressure, and force due to the trajectory of
the tool against the workpiece.
[0098] Referring again to FIG. 1, the work piece spindle 108 holds
workpiece 10, i.e. the optic or other part to be finished. Work
piece spindle 108, and/or polishing spindle 124 as described are
attached to computer controlled linear or rotary slides 104, 106,
108, and 120 so that any path or desired motion and dwell times of
the polishing tool 200 over the workpiece 10 can be achieved. As
described previously, workpiece spindle 108 also acts as a servo
controlled positioning axis, the motion of which may be controlled
in coordination with the described linear and rotary motions such
that any non-axially symmetric irregularities, zonal enhancements,
in the workpiece 10 may be also corrected with the polishing method
of the present invention. Polishing tool spindle 124 is controlled
via a motor and spindle drive (not shown) such that the rotation
speed in RPM is variable, and may be adjusted during the polishing
process, depending on the process and workpiece requirements.
[0099] As was described previously, there are machine
configurations for apparatus 100 that can be provided, depending on
the workpiece shape and size, and the desired finished workpiece
results. The motions of these axes may be combined so as to not
only provide straight, linear, or arcuate motions of the polishing
tool 200, but also to provide zigzag, sinusoidal, rotary or other
programmable oscillations, in order to achieve the amount of
material that is to be removed and to achieve the resulting surface
quality.
[0100] Based on the configuration of the machine 100, the spindles
and linear and/or rotational slides thereof, and the type/form or
the polishing tool(s) to be used, there are various steps required
in the process of the present invention, which results not only in
the polishing of the workpiece, but also the correction of the
surface errors/form of the workpiece.
[0101] In general, the pre-machined (i.e. unfinished) workpiece may
be measured with a surface profilometer, an interferometer, a CMM
or any other type of measuring device capable of analyzing the
geometric shape, in order to quantitatively define the basic
starting condition of the workpiece. This information is required
to begin the process of improving the components surface roughness,
mid-spatial frequency (waviness) and figure. After the analysis,
the acquired data on the workpiece is then communicated into the
computer control on the machine. This information, along with the
software built into the computer control, calculates the process
parameters/motion control required giving the desired workpiece
improvements.
[0102] The polishing tool spot size and shape is either known based
on a library of predetermined empirical parameters obtained
experimentally, or it is analyzed through a series of tests. The
polishing tool spot size and shape is then sent to the CNC
controller. This data is the additional information needed to
develop the required polishing tool path motion and speed, and
spindle rotational and linear speeds to achieve the desired process
results. It is to be understood that the polishing spot size may be
affected by the size, shape, material properties, and fill pressure
of the bladder, fluid type of the filled bladder, and the polishing
foil material properties.
[0103] A more detailed description of methods for using the
polishing tools and the apparatus of the present invention will now
be described. It is to be understood that the steps in the
following descriptions are illustrative of some embodiments of
methods, but that the order of the steps described herein may be
changed, while still achieving substantially the same end results.
Thus, such variations in the methods described herein are to be
considered within the scope of the present invention.
[0104] A first preferred step, based upon experience and knowledge
of the finishing process and the previously described data obtained
on the unfinished part, is to assemble and fit a polishing tool to
the polishing apparatus. FIG. 5 is a flowchart depicting a method
of assembly of the preferred polishing tool of FIG. 2A in the
apparatus of FIG. 1. Referring to FIG. 5, FIG. 1, and FIG. 2A, tool
setup process 410 begins with step 412, wherein polishing tool 200
sans polishing ring assembly 230 is fitted in holding chuck 126 of
spindle 124. Subsequently in step 414, polishing ring assembly or
foil 230 is selected and fitted to bladder 204 of polishing tool
200. Bladder 204 is inflated to hold polishing ring assembly 230 in
place thereupon in step 416. A measurement of the center height of
polishing ring 230 is made with suitable measuring means such as
e.g., a dial indicator, a caliper, a micrometer, and the like in
step 418. With steps 412-418 completed, tool setup process 410 is
complete. Alternatively or additionally, an alignment fixture may
be used to aid in proper position/alignment of the foil and or
reinforcement ring
[0105] The overall preparation/setup of the polishing apparatus
then follows. FIG. 6 is a flowchart depicting a method of preparing
the preferred apparatus of FIG. 1 for a polishing operation.
Referring to FIG. 6, and FIG. 1, apparatus or machine setup process
420 begins with step 422, installing the completed polishing tool
assembly 200 in chuck 126 of spindle 124. (Step 422 is performed in
the event that tool 200 was removed from spindle 124 in order to
make the measurement 418 of tool setup process 410 of FIG. 5, or if
tool 200 was setup separately from machine 100.)
[0106] Machine setup process 420 continues with step 424, in which
the polishing tool dimensional data obtained in measurement step
418 is entered into the CNC process controller of machine 100. The
unfinished optic or other workpiece to be polished is then placed
into holding chuck 110 of spindle 108 in step 426. The data
obtained from measurements made on the unfinished optic that have
been described previously are also entered into machine 100 in step
428. In step 430, an analysis of the spot size/removal function of
the polisher on the optic is performed, or such data from a
previously described library of tool functions is entered into the
CNC process controller. In step 432, the CNC process controller is
further programmed with polishing tool and polishing medium
parametric data such as removal function, polishing spot size,
polishing tool medium/material type, polishing tool
dimensions/shape, polishing tool bladder pressure, optic/workpiece
starting and finished dimensions, and polishing slurry
type/composition.
[0107] With all of the relevant data programmed into the CNC
process controller, the deterministic path of the polishing tool
200 on the optic 10 is calculated by such controller in step 434.
In performing machine setup process 420, depending on the shape and
size of the workpiece 10, coordinate offsets will be established in
all of the programmable axes 104, 106, 108, and 120, so as to
provide the CNC controller of machine 100 the information/location
of part 100 such machine 100 will begin the polishing process at
the correct location on workpiece 10. At this point, with machine
setup 420 complete, some test probing of the workpiece 10 and/or
the polishing tool 200 may be implemented to confirm that such
starting location is correct. Once the CNC controller of machine
100 has defined/confirmed the "part zero" or starting position of
polishing tool 200 upon workpiece 10, the polishing process may
begin.
[0108] FIG. 7 is a flowchart of a complete method of polishing an
optic using the apparatus and polishing tool of the present
invention. Referring to FIG. 7, tool setup process 410, and machine
setup process 420 are performed according to the foregoing
descriptions of FIG. 5 and FIG. 6. Subsequently, in step 440, the
optic polishing cycle is performed, wherein a computer developed
path of polishing tool 200 upon workpiece 10 is performed. As
described previously, the workpiece spindle 108 and polisher
spindle 124 are placed in rotary and linear motion along one or
more of axes 105, 107, 109, and 121, depending on the desired
results. Note that in some embodiments the part may not be attached
to a rotating spindle and may be held in a stationary position,
while polishing tool is actuated over the surface thereof.
[0109] In some circumstances, more than one bladder-polishing tool
may be required to achieve the desired results in polishing
workpiece 10. Accordingly, in one embodiment (not shown), machine
100 is provided with automatic tool changers, to change between
multiple polishing tools during the process. In another embodiment
(not shown) multiple spindles are provided on machine 100, wherein
a first polishing tool on a first spindle performs part of the
polishing operation, a second polishing tool on a second spindle
performs part of the polishing operation, and so forth, to the
extent that multiple tools and spindles are provided on machine
100.
[0110] In the preferred embodiment of polishing cycle 440, but not
in all embodiments, at such time when the spindles 108 and 124 have
started, but before any motion of tool 200 along axes 105, 107,
109, and 121, there is provided and injection or pumping of a
specific polishing slurry or other fluid at the contact location of
polishing tool 200 with workpiece 10, which enhances the polishing
action or removal rates of material from workpiece 10. As described
previously, the path of the polishing tool 200 over the workpiece
10 may include straight, linear, arcuate zigzag, sinusoidal,
rotary, spiral, or other programmable motions so as to enhance the
removal rate of material from workpiece 10.
[0111] In performing polishing cycle 440 of process 400 of FIG. 7,
there are several process parameters that will affect the removal
rates and figure enhancement:
[0112] 1. The rotational speed of the workpiece spindle 108 may be
controlled to give the effect of constant surface speed of
workpiece 10 similar to that of current CNC lathe technology, so as
to maintain a constant removal rate of material from the workpiece
10. Such control of spindle speed eliminates the effect of the
decreasing or increasing diameter of the contact circle made by the
polishing tool 200 upon the rotating workpiece 10, as it will be
apparent that the surface speed at the extremity (i.e. maximum
diameter) of the rotating workpiece is much greater than the
surface speed near the center of the workpiece. As the polishing
tool 200 approaches the center of the workpiece 10, the surface
speed approaches zero; thus such a variation in surface speed may
be compensated for by varying the rotational speed of workpiece
spindle 108.
[0113] 2. The speed/position of workpiece 10 may also be controlled
so as to improve rotational asymmetries of the workpiece during the
polishing cycle 440. For example, if there is an asymmetry that
requires more removal in a specific area of workpiece 10, then the
part spindle may slow or even stop in this area so as to allow more
removal by polishing tool 200. Alternatively, the opposite
situation may occur wherein less material removal is required and
the workpiece 10 may speed up during polishing in this area to
minimize the removal. In other terms, the dwell time of the
polishing tool 200 upon the workpiece 10 is adjusted to selectively
decrease or remove rotational asymmetries.
[0114] 3. The "stiffness" of the polishing tool may be preset based
upon the inflation pressure within the bladder 204 of tool 200.
Depending on how "hard" or "soft" bladder 204 is made by inflation
pressure, the removal function of tool 200 will be affected.
Typically a stiffer polishing tool (i.e. higher inflation pressure)
will be used where higher removal functions are required such as in
processes where form error modification of workpiece 10 is needed.
Likewise, less inflation pressure will be applied to bladder 204 in
a final finishing process where the best possible surface finish is
required, at the expense of a lower material removal rate. In a
further embodiment described previously, inflation pressure may be
varied in real time during the polishing cycle 440.
[0115] 4. The compression factor may also be controlled in the
polishing cycle 440. Control of the compression factor is achieved
through the CNC program wherein the path the polishing tool 200 is
moved in a less compressed or more compressed path ("tighter" or
"looser path") over the part, thereby affecting its removal
function and rate.
[0116] 5. The tightness of the zigzag or circular motion of the
polishing tool 200 in its path over the workpiece 10 may also be
adjusted and varied throughout the polishing cycle 440. In one
embodiment, the compression factor is held constant while the
zigzag or circular motion of the polishing tool 200 is varied.
Circular and other motions such as e.g., zigzag, provide better
surface finish i.e. polish without leaving artifacts from the
tool/abrasive slurry in the surface i.e., grooving.
[0117] 6. The composition, Theological properties, PH,
concentration, and flow rate of polishing slurry delivered to the
polishing tool/workpiece during the process may be varied to affect
removal rates and surface roughness.
[0118] 7. The size, shape, and material properties of the bladder
204 of polishing tool 200 significantly affects the process results
and capabilities depending on the workpiece 10 to be polished.
[0119] 8. The material that the bladder is wrapped with (the foil
230) is another variable, which will also affect the material
removal and finishing characteristics during polishing cycle
440.
[0120] 9. The physical properties of the fluid medium used to
pressurize bladder 204 of tool 200 may be varied. Such physical
properties include specific gravity, shear viscosity, and
extensional viscosity. Variation of such properties between the
basic choice of a liquid or a gas is at least several orders or
magnitude. However, there is significant variation between liquids,
and there is opportunity for further control based on the use of
non-Newtonian liquids, such as shear or extensional thickening
liquids, shear or extensional thinning liquids, visco-elastic
liquids, and/or magneto-rheological liquids.
[0121] Using variations of the process parameters described in 1-9
above, the removal rates, the surface roughness, mid spatial
frequency errors and figure error will be optimized during
polishing cycle 440. Upon completion of polishing cycle 440, the
machine 100 of FIG. 1 is stopped. Referring again to FIG. 7, and
continuing again with process 400, the profile of the polished
optic or other workpiece is measured in step 450, according to
methods previously described. A decision is made at step 455,
wherein if the optic 10 is acceptable against specifications, it
proceeds through a step 490 of final measurement/quality control,
and/or packaging, and shipping.
[0122] If such optic is not acceptable against specifications,
steps are taken to prepare for another polishing cycle 440. Such
steps include step 460, reprogramming of the CNC controller;
optional step 470 of setting up/installing/and/or changing to a new
polishing tool; and step 480, calculation of a new deterministic
path for the next polishing cycle 440. The second polishing cycle
then proceeds as previously described, and further iterations of
steps 450-480 and 440 occur until the optic is polished to a
condition that is acceptable against specifications, at which time
step 490 is performed.
[0123] Included within the scope of the present invention is
another embodiment of a polishing tool for the polishing of concave
surfaces. FIG. 8A is a cross-sectional view of such a preferred
polishing tool. Referring to FIG. 8A, polishing tool 300 comprises
a mandrel 302 within which is disposed a groove 303 around the
outer periphery of a flange 305 formed at one end of mandrel 302.
Tool 300 further comprises a dome-shaped bladder 304, having a lip
307 that is disposed in groove 303 of mandrel 302. Compression
washer 306 is fitter over the shank 301 of mandrel 302 and disposed
against lip 305 of bladder 304. Locking nut 308 is threadedly
engaged with a corresponding threaded portion of shank 301, such
that locking nut 308 compresses lip 305 of bladder 304 into groove
303 of mandrel 302, thereby sealing bladder 304 to mandrel 302.
Bladder 304 sealed to flange 305 of mandrel 302 thus forms a cavity
316 therebetween. Suitable materials for bladder 304 are e.g.,
natural or synthetic rubber, silicone, or polyurethane.
[0124] Numerous other embodiments of tool 300 are possible, wherein
bladder 304 is formed such that bladder 304 fully encloses the
outer surface 309 of the distal end of mandrel 302. In one
embodiment, bladder 304 is conical, as indicated by dotted lines
311. In other embodiments, bladder 304 may have a parabolic shape,
a hyperbolic shape, or combinations and transitions between
hemispherical, conical (linear), hyperbolic, and parabolic surfaces
at different radial zones along the surface of bladder 304. Thus
bladder 304 may have a precisely hemispherical shape, a precisely
conical shape, or a generally curved or domed shape formed by some
combination of these various surface definitions. It will be
apparent that even in the instance of a conically shaped bladder
304, that such bladder will likely be formed with a slight radius
at the apex of such cone.
[0125] Mandrel 302 is further provided with an axial bore 312
disposed from the outer end 324 of shank 301 through the center of
flange 305, such that the outer end 324 of mandrel 302 is in
communication with cavity 316. Polishing tool 300 further comprises
an inflation device 320 such as e.g., a check valve, or a tire
valve stem, for providing a means to pressurize cavity 316 and
maintain pressure therein, as previously described for tool 200 of
FIG. 2A. Cavity 316 may be pressurized with any suitable fluid such
as the liquids or gases previously described in this specification.
In a further embodiment, axial bore 312 is connected during the
polishing process to an adjustable pressure source, so that the
pressure within cavity 316 may be varied in real time during the
polishing operation, as described previously in this
specification.
[0126] It will be apparent that in embodiments in which a
relatively dense fluid, i.e. a liquid is used, and in which an
elastic bladder is used, that the overall profile of the bladder,
and therefore the spot size, can be varied as a function of
polishing tool rotational speed. At relatively low rotational
speed, a bladder with a substantially hemispherical shape will
maintain such shape. As rotational speed is increased, the
centrifugal force acting on the liquid contained in the bladder
will deform the bladder into a flattened dome profile having a
large radius of curvature near the center of the bladder, and a
small radius of curvature near the lip 303 of the bladder. Such a
feature can be used in the process of the present invention,
wherein the polishing spot size is rendered adjustable as a
function of rotational speed.
[0127] Referring again to FIG. 8A, polishing tool 300 further
comprises a first ring or dome 332 of backing material disposed
over the outer wall of bladder 304, and a second ring or dome 334
of polishing material adhered to dome 332, thereby forming a dual
or composite ring or dome. In one embodiment, only a single ring or
dome of material is used as the polishing medium, as described and
shown for FIG. 4. Polishing tool is thus used in substantially the
same manner as described for polishing tool 200 of FIG. 2A
previously in this specification, with polishing tool 300 being the
preferred tool for the polishing of concave surfaces. FIG. 8B is a
side elevation view of the polishing tool of FIG. 8A, in the
process of polishing a concave lens. Referring to FIG. 8B, it can
be seen that the axis of rotation of polishing tool 300 is
preferably disposed at an obtuse angle 50 with respect to the axis
of rotation of concave lens 20, in order to achieve the desired
contact between polishing surface 334 of toll 300 and concave
surface 22 of lens 20.
[0128] FIG. 9 is a schematic representation of another preferred
polishing apparatus for polishing concave spheres, aspheres, convex
spheres, or other conformal shapes, such as lens 20 of FIG. 8B.
Referring to FIG. 9, apparatus 150 is in one embodiment
substantially similar to apparatus 100 of FIG. 1, with the main
difference being provisions to contact the polishing tool with the
concave surface of the workpiece. In order to accomplish this, the
first preferred provision is the use of tool 300 of FIG. 8A, having
a hemispherical, domed, or conical shape. A second preferred
provision is in apparatus 150 wherein a B axis 152 directed
into/out of the plane of FIG. 9 is provided, upon which polishing
tool spindle 124 is mounted, and upon which polishing tool spindle
124 is bidirectionally rotatable, as indicated by arcuate arrow
154. Such a provision enables polishing tool 300 to be moved as
indicated by arcuate arrow 156 into a position wherein the axis of
rotation of polishing tool 300 is disposed at an obtuse angle 50
with respect to the axis of rotation of concave workpiece 20, as
indicated in FIG. 8B. Such motion enables the polishing foil 334 of
polishing tool 300 to contact the concave surface of a workpiece
such as a concave lens or an asphere without having another portion
of the polishing tool colliding with such workpiece.
[0129] It is to be understood that the machine 100 of FIG. 1, and
the machine 150 of FIG. 9 that are provided to execute process 400
of FIG. 7, using tools 200 of FIG. 2A and tool 300 of FIG. 8A may
have many different configurations. Axes types, spindle types,
layout, size, provision of an automatic tool changer, and overall
cost are just a few of the variables that could affect the desired
design. While only show two specific possible machine
configurations and specific possible tooling configurations are
described in this specification and shown in FIGS. 1 and 9, it is
to be further understood that many multi-axis CNC machine tools are
known in the art, which can be suitably configured to use the
polishing tools 200 and 300 and the process 400 of the present
invention.
[0130] The overall computerized polishing process 400 using the
apparatus 100 and polishing tool 200 of the present invention has
many distinct advantages over prior art figure/polishing
enhancement techniques, which are as follows:
[0131] 1. There are numerous options available with respect to size
and shape of the bladder attached to the tool, such as a tire
shape, hemisphere shape, domed shape, conical shapes, cylindrical
shape, and the like. The shape of the bladder chosen depends on the
part geometry and the desired process results. There are also
options available in the choice of material composition and
properties of the bladder. These options of size, shape, and
material composition render the process of the present invention
very versatile.
[0132] 2. Bladder inflation pressure is easily adjusted before the
process begins and for many polishing process requirements, no
pressure modification is required during the polishing process. In
the event that it is desirable to adjust bladder pressure during
the polishing process, a polishing tool and apparatus can be made
to provide such additional process versatility.
[0133] 3. The method of inflating the bladder into the polishing
foil makes replacement of the foil very simple, and typically no
adhesive or mechanisms are required for attaching the foil to the
bladder. Adhesive is only required to attach the foil to the PET
ring.
[0134] 4. In using the polishing tools of the present invention,
many types of materials may be wrapped around the bladder, thus
allowing for the use of a wide variety of polishing foil media.
Polishing foils may be made of e.g. polyurethanes, felts,
synthetics, corks, leathers, and many other materials, depending on
the desired polishing results. The foils may be impregnated with
cerium, diamond, alumina, pitch, etc.
[0135] 5. The preferred method of placing the ring or foil upon the
bladder also allows for modification of the shape of the foil or
ring, i.e. the width, radius/contour or thickness thereof.
[0136] 6. In the preferred embodiment, the poly(ethylene
terephthalate) ring that the foil may be attached to has not only
great strength but also long lasting flexibility, which greatly
extend the life of the polishing tool.
[0137] 7. The concept of the bladder tool allows for flexibility so
that the polisher can conform to a variety of workpiece surface
geometries and still maintain contact/polishing action upon such
surfaces.
[0138] 8. In contrast to small spot polishing tools, the bladder
polisher of the present invention will last and hold its shape much
longer in operation. A polishing ring of material, and not just
single spot develops the spot in the polishing tool and the process
of the present invention, so the polishing surface area of the tool
is greatly increased.
[0139] 9. The compression amount and spot size of the polishing
tool can be easily adjusted by modifying the computer program to
move the tool closer or further from the part in its path over such
part.
[0140] 10. Because of the variety of shapes and types of materials
that the various components of the polishing tool can be made from,
the polishing process of the present invention has the flexibility
to repair figure errors in a workpiece, and also achieve the
highest surface quality requirements of such workpiece.
[0141] 11. In instances where the process may require one or more
polishing tools to achieve the final results, this is easily
accomplished with known machine tool automatic tool changing
technology or multiple spindle technology, depending on the
configuration of the particular machine.
[0142] 12. The powerful computer control algorithms provide the
machine operator with a variety of flexible programs which,
depending on desired results, can be easily modified and
implemented, such as e.g., zigzag, circular, orbital, elliptical
tool paths.
[0143] 13. Polishing of steels and other metallic components,
especially those used in injection molds, and thin film coating
dies can be done without the current technological limitations of
prior art polishing processes.
[0144] In another preferred embodiment, the polishing tool further
comprises actuation means to engage and/or extend and/or position
and/or compress the inflatable bladder or other compliant part, and
any polishing foil disposed thereupon, with respect to the part to
be improved or polished. Such actuation means may comprise one or
more linear actuating devices such as e.g., air operated or
hydraulically operated cylinders.
[0145] FIG. 10 is a first perspective view of one such preferred
polishing tool of the present invention comprising single cylinder
actuation means to extend and/or position the inflatable bladder or
other compliant part with respect to the part to be improved or
polished. FIG. 11 is a side elevation view of the polishing tool of
FIG. 10; FIG. 12 is a top view of the polishing tool of FIG. 10;
and FIG. 13 is a second perspective view of the polishing tool of
FIG. 10, taken from the plate side of the polishing tool.
[0146] Referring to FIGS. 10-13, polishing tool 500 comprises a
base 502 to which various components are affixed. In the preferred
embodiment, base 502 comprises a rigid plate of material such as
steel, aluminum, or fiber reinforced polymer. Other base materials
and or structures, such as a frame structure may be suitable, with
the operative requirement being that the base is rigid enough to
hold components attached thereto in sufficiently precise
dimensional relationships so as to enable the overall precision
polishing operation to be performed; and that the base is provided
with provisions to enable the attachment of components thereto.
[0147] Toward the proximal end 504 of base 502, drive wheel 510 is
operatively joined or attached to rotatable shaft 512, which is
disposed in a housing 514 joined to base 502. Housing 514 is
preferably joined to base 502 by threaded fasteners (not shown)
engaged with tapped holes (not shown) therein, or by other suitable
means. Rotatable shaft 512 is preferably disposed within means for
enabling precise rotation, such as e.g., a bushing, or more
preferably, bearings 516.
[0148] Tool 500 further comprises a polishing wheel 520, which is
joined to linkage 530. Linkage 530 is operatively attached to
actuating means 540, such that actuating means 540 actuates linkage
530, and thus moves polishing wheel 520, as indicated by
bidirectional arrow 599. This motion of polishing wheel 520 serves
to engage a polishing foil with a portion of the perimeters of
polishing wheel 520 and drive wheel 510; such engagement will be
described subsequently in this specification.
[0149] In the preferred embodiment depicted in FIGS. 10-13,
actuating means 540 is a linear actuator, and in particular,
actuating means 540 a pressure driven cylinder 542. Linkage 530 in
this embodiment is a clevis 532 that is operatively joined to
cylinder rod 544. Polishing wheel 520 is joined to clevis 532 by
shoulder bolt 534, which passes through a hole in the center of
wheel 520, and engages with nut 536. The position of wheel 520 is
preferably maintained constant within clevis 532 by the use of
spacing washers 535 and 537. In a further embodiment (not shown),
polishing wheel 520 is provided with at least one bushing or
bearing to minimize wear, friction and heat buildup, and to provide
precise positional control in the event that polishing wheel is
operated at high speeds.
[0150] Referring again to FIGS. 10-13, cylinder 542 is joined to
base 502 at its proximal end by a shoulder bolt 547, which passes
through bracket 543, and which is engaged with threaded hole 508 in
base 502. Cylinder 542 is properly spaced out from base 502 by the
use of jig bushing 546, through which bolt 547 also passes.
Cylinder 542 is further joined to base 502 at its distal end by
mounting nut 548, which is threadedly engaged with the housing 545
of cylinder 542, and also engaged with bracket 550. Bracket 550 is
fastened to the distal end 506 of base 502 by threaded fasteners
552 and 554, which are engaged with tapped holes therein.
[0151] Cylinder 542 is thus rigidly secured to base 502, and thus
in the operation of the tool 500 (to be described subsequently in
this specification), cylinder 542 linearly actuates polishing wheel
520 as indicated by bidirectional arrow 599. To accomplish such
actuation, cylinder 542 is operatively connected to a pressurized
fluid supply at ports 556 and 558 in the housing 545 thereof,
preferably provided through flexible hoses (not shown). Such fluid
supply is selectable and switchable, i.e. fluid pressure may be
applied at port 556 and fluid vacuum may be applied at port 558 to
actuate wheel 520 away from distal end 506 of base 502 and toward
the work piece 112 (see FIG. 18A), and fluid pressure may be
applied at port 558 and fluid vacuum may be applied at port 556 to
actuate wheel 520 toward distal end 506 of base 502 and away from
the work piece 112. Such fluid cylinder actuating devices are well
known. In addition, the pressurized fluid supply (not shown) may
provide a pressurized gas such as air (i.e. cylinder 542 is an air
cylinder), or pressurized fluid supply may provide a pressurized
liquid such as a hydraulic oil (i.e. cylinder 542 is a hydraulic
cylinder).
[0152] It will be apparent that actuating means 540 may comprise
suitable linear actuators other than fluid pressure driven
cylinders; many other linear actuators, such as rodless cylinders,
stepper motors and other electromechanical actuators are well known
and are to be considered within the scope of the present invention.
Such linear actuators may be further provided with position sensing
means, and/or position control means, and communication means for
control thereof by an external process controller.
[0153] Tool 500 further comprises a polishing foil 680 (see FIG.
14), which is engaged with a portion of the perimeters of drive
wheel 510 and polishing wheel 520. Polishing foil 680 thus has the
function of a drive belt, rotationally coupling drive wheel 510 and
polishing wheel 520 as indicated by arrows 598 and 597. (It will be
apparent that the rotational direction could be the opposite of
that depicted by arrows 598 and 597.) For the sake of simplicity of
illustration, polishing foil 680 is not shown in FIGS. 10-13.
Polishing foil 680 is shown in FIGS. 14-18B in the two-cylinder
embodiment depicted therein.
[0154] Polishing foil 680 is also shown in FIGS. 22A and 22B, for
the purpose of illustrating the manner of engagement thereof with
drive wheel 510 and polishing wheel 520, and for illustrating the
preferred properties of polishing foil 680.
[0155] FIG. 22A and FIG. 22B are schematic representations of means
for engaging a polishing foil of the polishing tool 500 of FIGS.
10-13. FIG. 22A depicts such engagement means in the retracted, or
unengaged position, and FIG. 22B depicts such engagement means in
the deployed, or engaged position. It is to be understood that the
following description is also applicable to the polishing tool 600
of FIGS. 14-18B.
[0156] Referring to FIG. 22A, it can be seen that engagement means
540 comprising cylinder 542 is in the retracted position, as
indicated by the short length of cylinder rod 544 that is visible
therein. In the embodiment depicted in FIG. 22A and 22B, polishing
foil 680 comprises an assembly similar to that described for ring
assembly 230 of tool 200 of FIGS. 2A, 2B, 3, and 4, having a belt
682 of material and an abrasive ring 684.
[0157] Belt 682 is formed of an elastic material. In one
embodiment, belt 682 consists essentially of a band of
poly(ethylene terephthalate) having a thickness of between about 50
microns and about 2000 microns, and a width of between about 7
millimeters and about 125 millimeters. In another embodiments, belt
682 consists essentially of elastomers such as e.g., gum rubbers,
polyurethane, silicone and the like. Many other belt materials may
be suitable, with the operative requirement being that belt 682
have sufficient elasticity to stretch when rod 544 of cylinder 542
is deployed as shown in FIG. 22B, and that the outer surface of
belt 682 is engageable with the inner surface of abrasive ring 684,
either by friction, or by engagement features in the surfaces
thereof, or by other means.
[0158] The abrasive ring 684 of foil 680 is made of a material of
sufficient structural strength to withstand the high shear and
tensile forces during polishing, and to resist degradation through
exposure to the polishing/lubricating fluid, such as e.g.
polyurethanes of various durometers; water resistant high strength
cloth materials, and various types of felt, cork, and metal.
Abrasive ring 684 further comprises abrasive particles embedded
therein, or coated on the outer surface thereof, such as e.g. resin
bonded diamond, alumina, and/or zirconium and the like. Abrasive
ring 684 may have an inner surface having different types of
backings, and/or patterns for engagement with belt 682.
[0159] Abrasive ring 684 preferably has a thickness of between
about 1 millimeter and about 5 millimeters, and a width of between
about 7 millimeters and about 125 millimeters. Additional operative
requirements of abrasive ring 684 are that it have a greater
circumference than belt 682, and that it is substantially
inelastic, or significantly less elastic than belt 682, in order to
enable proper engagement therewith.
[0160] The engagement of belt 682 with abrasive ring 684 is now
described. Referring again to FIGS. 22A, belt 682 has been
stretched at least slightly, and has been fitted such that belt 682
is engaged with portions of the perimeters of drive wheel 510 and
polishing wheel 520. Belt 682 is thus under some tension, and when
drive wheel 510 rotates as indicated by arrow 597, belt 682 is
displaced as indicated by arrows 594, thereby resulting in rotation
of polishing wheel 520 as indicated by arrow 598.
[0161] As can be seen in FIG. 22A, with rod 544 of cylinder 542
retracted, abrasive ring 684 is not engaged with belt 682, as
indicated by gap 683 that is present between belt 682 and ring 684.
Referring to FIG. 22B, when the rod 544 of cylinder 542 is
deployed, polishing wheel 520 is displaced away from cylinder 542.
Belt 682, being of an elastic material, stretches to the extent
required to accommodate such displacement of wheel 520. Abrasive
ring 684, however, being of a relatively inelastic material
compared to belt 682, has not stretched, and has instead become
engaged with belt 682 by friction, and/or by engagement features
disposed on the contiguous surfaces thereof.
[0162] The rotation of drive wheel 520 in such circumstances thus
results in the displacement of abrasive ring as indicated by arrows
593. Essentially, the actuation of cylinder 542 as indicated by
arrow 599, in combination with the components attached thereto,
acts as a clutch mechanism to engage and drive abrasive ring
684.
[0163] In another embodiment, polishing foil 680 may be formed as a
unitary structure in a manner similar to ring 230 of FIG. 4 as
described previously, but having both the required properties of a
drive belt for engagement with wheels or pulleys, and an abrasive
belt for polishing or more substantial surface removal, as well as
having the requisite elastic properties as previously described.
The applicant believes that the belt and ring structure is
preferred, as such components are more easily and inexpensively
provided, and such structure enables simple and rapid changeover
between belts comprised of various abrasive media, either manually,
or by automatic tool changing means.
[0164] In order to have good function as a drive belt engaged with
wheels, polishing foil 680 may be provided with features known in
drive belt art, such as grooves (not shown) on the inner surface
thereof (mated with corresponding grooves in wheels 510 and 520);
or teeth (not shown) on the inner surface thereof (mated with
corresponding teeth in wheels 510 and 520 as is done with timing
belts and pulleys); or knurling or other textures on the inner
surface thereof. Drive wheel 520 may further be provided with rims
extending radially outward from the edges thereof for improved belt
retention, as is commonly done with drive pulleys.
[0165] Polishing foil 680 may vary in length from about 4 inches
for tools having pulleys on the order of 0.25-0.5 inches in
diameter to about 50 inches for tools having pulleys on the order
of 8 inches in diameter. The rotational speed of drive wheel 510 is
provided such that the surface speed of polishing foil 680 is
between about 2 and about 1000 inches per second, depending upon
the particular polishing application. Polishing foil 680 may
further comprise fiber reinforcements disposed therein, and may
comprise woven or cloth-like material, provided that sufficient
elasticity is provided as described herein.
[0166] Referring once again to FIGS. 10-13, tool 500 further
comprises a dowel pin 559 extending outwardly from and joined to
base 502 by engagement with a threaded hole therein, or by an
interference fit with a hole therein, or by other suitable means
such as e.g. welding or adhesive. Dowel pin 559 is utilized to
attach and/or stabilize tool 500 when it is engaged with drive
means such as a CNC machine and used to polish an object. The
details of such use will be described subsequently in this
specification with reference to FIGS. 19-21. Tool 500 is preferably
used in a multi-axis CNC apparatus for the polishing of objects;
however, tool 500 may be engaged with a variety of more simple or
more complex drive means, and used for many other surface polishing
or surface abrasion applications. In one embodiment, tool 500 may
simply be provided with an air motor or electric motor attached
thereto as drive means, and placed in contact with the object to be
worked.
[0167] Thus tool 500 may be fabricated at a variety of scales,
depending upon the particular application, and in particular, the
size, shape, and degree of finishing required of the part to be
worked. The diameters of drive wheel 510 and polishing wheel 520
may vary from about 0.25 inches to about 8 inches. The scale of the
other components, i.e. base 502, cylinder 542, and linkage 530
would be sized as required to operate drive wheel 510 and polishing
wheel 520 and the foil 680 engaged therewith. For example, cylinder
542 may be provided with a bore of between about 0.1 inch and about
three inches.
[0168] Although it appears in the embodiment shown in FIGS. 10-13
that the diameters of drive wheel 510 and polishing wheel 520 are
approximately equal, this is not an operating requirement. To the
contrary, in some applications, it is advantageous to either
increase the rotational speed of polishing wheel 520 or decrease
the speed of polishing wheel 520 with respect to drive wheel 510,
by providing polishing wheel 520 with a different diameter than
drive wheel 510. The ratio of polishing wheel diameter to drive
wheel diameter may vary from as much as about 1:10 to about 10:1,
depending upon the application.
[0169] Polishing foil 680 may vary in width from about 0.25 to
about 5 inches. The corresponding widths of drive wheel 510 and
polishing wheel 520 thus vary in a similar manner in order to
properly engage with and drive polishing foil 680.
[0170] The length of actuation stroke of means 540 (indicated by
arrow 599) may vary from about 0.1 inch to about 3 inches,
depending upon the scale of tool 500, and upon the degree of
elasticity provided in polishing foil 680.
[0171] Referring again to FIGS. 10-13, and in the preferred
embodiment depicted therein, polishing wheel 520 is preferably
provided with a generally arcuate surface 521, and more preferably
a spherical surface. Polishing foil 680, which is under tension
from the action of actuation means 540, conforms to this surface
521 as it wraps around the perimeter of polishing wheel 520 during
a polishing operation. This wrapping action results in better
tracking of polishing foil 680 on polishing wheel 520. In addition,
the radius of curvature and/or the curvature profile (spherical,
elliptical, hyperbolic, etc.) of arcuate surface 521 partially
determines the tool spot size during a polishing operation. Tool
spot size has been described previously in this specification.
[0172] Referring to FIG. 12, in a further embodiment, wheel 520 is
provided with a cavity 522 formed within the interior thereof, and
a passageway 524 from the exterior of wheel 520 to cavity 522.
Cavity 522 may thus be pressurized with various fluids during a
polishing operation, as described previously in this specification
with reference to tool 200 of FIGS. 2A and 2B, and tool 300 of
FIGS. 8A and 8B. Passageway 524 may be further provided with an
inflation device, such as inflation device 220 of FIG. 2A. In one
embodiment, inflation device 220 is preferably a simple,
inexpensive check valve. In a preferred embodiment, inflation
device is a valve stem, or the inner workings thereof commonly used
for the inflation of tubeless tires. Alternatively, inflation
device may comprise a miniature check valve, such as one of many
manufactured and sold by the Lee Company of Westbrook, Conn.
[0173] Polishing wheel 520 may be formed of suitable elastomers
such as rubber, polyurethane, or silicone, or a harder or higher
durometer polymer. The selection of material for polishing wheel
520 will depend upon whether or not polishing wheel 520 is provided
with a cavity therein for pressurization, the extent to which such
cavity may be pressurized and thus deformed, and the desired tool
spot size during the polishing operation. These variables have been
described in detail in this specification with regard to tool 200
of FIGS. 2A and 2B, and are also generally applicable to polishing
wheel 520. In the preferred embodiment, polishing wheel 520
comprises a hub of solid material such as e.g. a plastic, ferrous,
or non-ferrous metal (optionally including a bearing or bushing),
and an exterior portion of elastomer (optionally including a
pressurizable cavity therein), upon the perimeter of which is
engaged the polishing foil. In the embodiment wherein polishing
wheel does not include a pressurizable cavity therein, and is
instead a solid elastomeric material, it is preferable that such
elastomeric material be of a durometer between about 10 and about
90, with the particular durometer depending upon the polishing
application.
[0174] In other embodiments, and depending upon the particular
object to be polished or otherwise finished, polishing wheel may be
formed with a plano (cylindrical) surface, or a convex surface.
Polishing wheel 520 may also be formed with circumferential grooves
on surface 521, or axial grooves (such as e.g. a timing pulley),
and/or a texture such as knurling. These various surfaces may be
employed to improve the tracking and/or traction between polishing
wheel 520 and foil 680, thereby preventing slippage therebetween.
These various surfaces may be further employed advantageously in
that such surfaces may be used to cause high frequency vibrations
of polishing wheel 520 and foil 680 against the part to be
finished, thereby enhancing the polishing effect of tool 500.
[0175] FIG. 14 is a first perspective view of another preferred
polishing tool of the present invention comprising twin cylinder
actuation means to engage the polishing foil, and to extend and/or
position the inflatable bladder or other compliant part, and the
polishing foil disposed thereupon, with respect to the part to be
improved or polished. FIG. 15 is a side elevation view of the
polishing tool of FIG. 14; FIG. 16 is a top view of the polishing
tool of FIG. 14; and FIG. 17 is a second perspective view of the
polishing tool of FIG. 14, taken from the plate side of the
polishing tool. It will be apparent that much of the structure of
the embodiment depicted in FIGS. 14-17 is substantially the same as
the embodiment depicted in FIGS. 10-13, with the main difference
being the provision of twin cylinder actuation means in the
embodiment of FIGS. 14-17. Accordingly, in the following
description, only the twin cylinder actuation means will be
described in detail, with the remaining structure and function of
tool 600 of FIGS. 14-17 being as described for tool 500 of FIGS.
10-13.
[0176] Referring to FIGS. 14-17, tool 600 comprises base 602, drive
wheel 610 joined to shaft 612, polishing wheel 620, dowel pin 659,
and polishing foil 680. Tool 600 further comprises actuation means
640, which further preferably comprises a first linear actuator and
a second linear actuator. The first linear actuator is preferably a
cylinder 642, and the second linear actuator is preferably a
cylinder 662. First cylinder 642 is operatively connected to
polishing wheel 620 by clevis 632, and thus provides linear
actuation of polishing wheel as indicated by bidirectional arrow
699, in a manner similar to that described previously for tool 500
of FIGS. 10-13.
[0177] Second cylinder 662 is joined at the proximal end thereof by
shoulder bolt 667, which passes through bracket 663 and spacer 666,
and which is threadedly engaged with a tapped hole in base 602.
Second cylinder 662 also provides linear actuation of rod 664 and
clevis 633 inwardly and outwardly from cylinder body 665 as
indicated by bidirectional arrow 696. Since cylinder 662 is
rotatable about shoulder bolt 667, this linear actuation of clevis
633 results in motion of the distal end of cylinder 642, and clevis
632 and polishing wheel 620 along a generally arcuate path as
indicated by bidirectional arrow 695. This arcuate motion enables
polishing wheel 620 and polishing foil 680 to be more effectively
engaged with and compressed against the object to be polished, as
will be subsequently explained with reference to FIGS. 18A and
18B.
[0178] Referring again to FIGS. 14-17, clevis 633 is joined to
cylinder rod 664 and also to lock plate 670 by shoulder bolt 672.
Lock plate 670 is also joined to the body 645 of cylinder 642, and
lock plate is movably joined to base 602 by shoulder bolt 674,
which passes through slotted opening 676 in lock plate 670.
Referring to FIGS. 15A and 15B in particular, FIG. 15A depicts the
position of polishing wheel 620 with cylinder 662 fully retracted.
FIG. 15B depicts the position of polishing wheel 620 with cylinder
662 fully deployed. It can be seen that lock plate 670 is displaced
downwardly and outwardly resulting from the freedom of motion along
slot 676, resulting in the arcuate motion of polishing wheel 620
and foil 680 as indicated by arcuate arrow 695. It will be apparent
that many other combinations of a second linear actuator joined to
a first linear actuator by a movable bracket, hinge, or other means
can provide a suitable arcuate motion of polishing wheel 620, and
thus all such combinations of linear actuators are comprehended
within the scope of the present invention.
[0179] It is also noted that in the embodiment of tool 600 depicted
in FIG. 17, although port hole 607 in plate 602 is depicted as
being circular, port hole 607 may be oblong in the vertical
direction, or of larger diameter. This variation in shape may be
necessary because the arcuate motion of polishing wheel 620 as
indicated by arrow 655 in FIG. 15B that results when cylinder 662
is deployed. This deployment and retraction of cylinder 662 causes
the rod end of cylinder 642 to pivot up and down vertically as
described previously. Since there is provided hydraulic fittings
(not shown) connected to cylinder 642 through holes 607 and 609,
and since the fittings and hose (not shown) connected to cylinder
662 through hole 607 has some significant amount of vertical
travel, it may be necessary to enlarge or make oblong shaped hole
607, in order to provide operating clearance for such fittings
and/or hose to move within hole 607 when cylinder 662 is
deployed.
[0180] In a further embodiment, there is provided the tool of FIGS.
14-17, but with a simple pivotable link (not shown) in place of
cylinder 642. In such an embodiment, there is preferably used a
polishing foil 680 that is unitary in construction and that is
elastic, such that polishing foil 680 is stretched over drive wheel
610 and polishing wheel 620, and engaged therewith. Thus first
linear actuation means 640 comprising cylinder 642 is not provided.
In the operation of such a tool, cylinder 642 provides the arcuate
motion of polishing wheel 620, with wheel 620 pivoting along an
arcuate path defined by the rigid link (not shown) provided in lieu
of cylinder 642. (Substantially the same result could be obtained
if cylinder 642 of tool 600 of FIG. 14 were locked in a fixed
position, such that cylinder 642 would function as a rigid
link.)
[0181] FIG. 18A is a cross-sectional elevation view of the
polishing tool of FIG. 14, shown disengaged with a deeply concave
object to be polished; and FIG. 18B is a cross-sectional elevation
view of the polishing tool of FIG. 14, shown engaged from a deeply
concave object to be polished. Referring to FIG. 18A, it can be
seen that cylinder 662 is fully retracted as depicted in FIG. 15A,
and that polishing wheel 620 and foil 680 are not in contact with
object 112, there being a gap 114 between the inner surface 116 of
object 112 and polishing foil 680. Referring to FIG. 18B, it can be
seen that when cylinder 662 is subsequently fully deployed as
depicted in FIG. 15B, polishing wheel 620 and foil 680 move along
an arcuate path and make contact with object 112.
[0182] The fluid pressure applied to cylinder 642 and to cylinder
662 are among the parameters that determine the amount of force
applied by polishing wheel 620 and foil 680 to the object 112, and
which thus determine the tool spot size. Other parameters that
determine such force and tool spot size are as described previously
in this specification for tool 200 of FIGS. 2A and 2B, and tool 300
of FIGS. 8A and 8B.
[0183] In addition to the polishing tools described herein, and in
accordance with the present invention, there is provided an
apparatus for polishing objects comprising a computer numerically
controlled (CNC) machine in which is fitted one of the tools of the
present invention as depicted in FIGS. 10-18A. Various embodiments
of such apparatus are depicted in FIGS. 19, 20, and 21.
[0184] FIG. 19 is a perspective view of a first preferred polishing
apparatus of the present invention comprising a polishing tool
having actuation means to extend and/or position the inflatable
bladder or other compliant part with respect to the part to be
improved or polished. FIG. 20 is a perspective view of a second
preferred polishing apparatus of the present invention comprising a
polishing tool having actuation means to extend and/or position the
inflatable bladder or other compliant part with respect to the part
to be improved or polished. FIG. 21 is a perspective view of a
third preferred polishing apparatus of the present invention
comprising a polishing tool having actuation means to extend and/or
position the inflatable bladder or other compliant part with
respect to the part to be improved or polished.
[0185] Referring to FIGS. 19-21, each of the apparatus therein are
described with respect to the orthogonal x axis 107, y axis 105,
and z axis 121 depicted therein. CNC machine 1000 is similar to
that depicted in polishing apparatus 100 of FIG. 1, comprising a
base 102 that supports Y-axis linear slide 104, the motion of which
is bi-directional along Y-axis 105 as indicated by arrow 999.
Linear slide 106, the motion of which is bi-directional along
X-axis 107 as indicated by arrow 998, is mounted upon Y-axis linear
slide 104. These linear slides 104 and 106 are both computer
numerically controlled (CNC) positioning devices, providing
programmable motion in the X-Y plane.
[0186] CNC machine 1000 further comprises vertical slide 120
attached to polishing machine frame or plate 123, which is joined
to base 102. The motion of vertical slide 120 is bi-directional
along Z-axis 121 as indicated by arrow 997. CNC machine 1000 is
preferably provided with rotary axis 151, which is mounted upon
vertical slide 120, and which is rotatable around B axis 152
(parallel to Z-axis 121) as indicated by bidirectional arrow 154.
Polishing tool spindle 124 is attached to rotary axis 151. CNC
machine 1000 further comprises a rotatable chucking device 126
attached to the end of polishing tool spindle 124, in which the
drive shaft 612 polishing tool 600 of the present invention is
inserted and rotated. Polishing tool 600 is positionable in a
variety of orientations, several of which are depicted in FIGS.
19-21, depending upon the particular object to be polished.
Polishing tool 600 is further affixed by a linkage (not shown),
which attaches to pin 659 and which is joined to spindle 124,
thereby immobilizing base 602 and preventing overall rotation of
tool 600 by spindle 124. Thus only the drive shaft 612 of tool 600
is rotatable by spindle 124, while the remainder of tool 600 is
held in position relative to object 112 to be polished.
[0187] Referring now only to FIG. 19, and in the embodiment
depicted therein, apparatus 1010 comprises CNC machine 1000 further
comprised of a work piece spindle 108 mounted upon linear slide
106. The motion of spindle 108 is bidirectionally programmable
along axis 109, which is parallel to X-axis 107. Thus spindle 108
is movable by computer control along axis 109, depending on the
requirements or the polishing process. The motion of object 112 in
the X-Y plane with respect to tool 600 is programmable, and is
performed by slides 104 and 106.
[0188] Rotatable work piece chucking device 110 is attached to end
of work piece spindle 108. The work piece 112 to be polished is
engaged and held by chuck 110 and rotated by spindle 108 around the
central rotary axis 109 thereof as indicated by arrow 996. This
rotary motion of object 112 results in the surface motion thereof
being orthogonal to the motion of the polishing foil 680 (see FIG.
14) of tool 600. In this manner, such orthogonal motion of the
object surface with respect to the foil substantially eliminates
any "grooving" effect in the object surface by the polishing
foil.
[0189] Referring now only to FIG. 20, and in the embodiment
depicted therein, apparatus 1020 comprises CNC machine 1000 further
comprised of a work piece spindle 162 mounted upon linear slide
106. Apparatus 1020 is similar to apparatus 1010 of FIG. 19, with
the differences being in the orientation of the object 112 and the
use of various slides and spindles to provide the relative motion
between tool 600 and object 112. Spindle 162 is a vertically
disposed spindle, the central axis 169 of which is parallel to
Z-axis 121. Rotatable work piece chucking device 164 is attached to
end of work piece spindle 162. The work piece 112 to be polished is
engaged and held by chuck 164 and rotated by spindle 162 around the
central rotary axis 169 thereof as indicated by arrow 995.
[0190] The motion of spindle 162 is bidirectionally programmable
along the X axis 107 and the Y axis 105, both of which are
perpendicular to the central axis of rotation 169 of object 112. To
provide motion of tool 600 toward and away from object 112 in the
direction of Z axis 121, rotary axis 151 and spindle 124 are
rotated 90 degrees clockwise from their respective positions in
FIG. 19, and slide 120 is used to move tool 600 axially in the Z
direction.
[0191] Referring now only to FIG. 21, and in the embodiment
depicted therein, apparatus 1030 is substantially the same as
apparatus 1020 depicted in FIG. 20 in terms of components.
Apparatus 1030 differs in setup in the position of spindle 162 on
slide 106, and in the extent of rotation of rotary axis 151 and
spindle 124, such rotation being about 30 degrees clockwise from
their respective positions in FIG. 19. In addition, spindle 162 is
locked, thereby preventing rotation of object 114, since object 114
is not axisymmetric. In the embodiment depicted in FIG. 21, object
114 is an equilateral prism, which thus requires the rotation of
rotary axis 151 and spindle 124 of about 30 degrees. During the
polishing operation, prism 114 is moved in the X and Y directions
by the motion of slides 106 and 104 respectively, thereby moving
prism in the X-Y plane with respect to tool 600. Tool 600 is moved
in the Z-direction by slide 120, thereby enabling the foil 680 (see
FIG. 14) of tool 600 to traverse up and down the sloped face 115 of
prism 114.
[0192] In a further embodiment, the CNC machine 1000 is programmed
to articulate tool 600 over the surface 115 of object 114 in a more
complex path in X-Y-Z space. For example, tool 600 may be generally
advanced along a linear path, but with a circular motion
superimposed on such linear path. Such a tool path is known in the
art as a trichordal path. Alternatively, and as described
previously for the embodiments of FIGS. 1-9, such tool paths may
include arcuate, zigzag, sinusoidal, or other combinations of
motion so as to enhance the removal rate of material from object
114, and to prevent the occurrence of any "grooving" effect in the
object surface during the polishing thereof.
[0193] It will be apparent that many other apparatus configurations
are possible in fitting the tools of the present invention to CNC
machines to polish and/or grind and/or otherwise finish objects.
Such CNC machines may have more or fewer linear and rotational
actuators as required by the particular application.
[0194] It will be further apparent that the polishing methods
described herein and depicted in FIGS. 5, 6, and 7 for the
operation of apparatus 100 of FIG. 1 and apparatus 150 of FIG. 9,
using tool 200 of FIG. 2A and tool 300 of FIG. 8A are readily
adaptable to tool 500 of FIGS. 10-13 and tool 600 of FIGS. 14-17,
when such tools are fitted to apparatus 1010, 1020, or 1030 of
FIGS. 19-21 respectively. In general, such methods may in some
embodiments only differ by the setups of the particular tools 500
and 600, and in the additional control required of the linear
actuating means, such as the fluid pressure provided to cylinder
542 (see FIG. 10) or cylinders 642 and 662 (see FIG. 14).
[0195] It will be apparent that there are many other apparatus
configurations comprising actuation means that can increase the
separation distance between two wheels, thereby providing increased
tension of a belt engaged therewith; or that can increase the belt
path length therearound (such as by an idler pulley), thereby
providing increased tension of a belt engaged therewith, and that
such actuation means are considered within the scope of the present
invention. It will be apparent that there are many other apparatus
configurations comprising actuation means that can adjust the
position of a first wheel engaged to a second wheel by a belt,
either along an arcuate path or a linear path or a combination
thereof, and that such actuation means are also considered within
the scope of the present invention.
[0196] In accordance with the present invention, another tool is
provided that may perform similar polishing operations as those
tools shown in FIG. 2A-FIG. 4 and described herein. This tool
shares the common principle of providing a force from within a
flexible tool material which results in the formation of a curved
surface of an elastomeric bladder. A polishing foil is disposed
upon the bladder, and polishing of an object is performed by the
tool at the point of contact of the foil on the curved surface with
the surface of the object. Instead of using the force of a
pressurized fluid within a cavity inside the bladder to produce the
curved surface, there is provided an axial compressive force upon
the bladder, which causes such bladder to be deformed outwardly
orthogonally in the radial direction, thereby producing a curved
surface that can be used for polishing in substantially the same
manner as has been described herein for the tools shown in FIG.
2A-FIG. 4.
[0197] FIG. 23A, 25A, and 26A are a perspective view, a side
cross-sectional view, and a side view, respectively, of a solid
bladder polishing tool of the present invention depicted in an
uncompressed state; and FIG. 24 is an exploded perspective view of
the solid bladder polishing tool of FIG. 23A, exploded along the
axis 23A-23A. Referring to FIGS. 23A, 24, 25A, and 26A, tool 700
comprises a main body or bladder mandrel 710 having a drive shank
712 at a proximal end 711 thereof, and a flange 718 at a distal end
719 thereof, upon which solid bladder 730 is disposed and engaged
therewith. Mandrel 710 further comprises a bladder shank 714
extending upwardly from flange 718, and a threaded shank 716
extending downwardly from drive shank 712, joining bladder shank
714 at stop shoulder 715.
[0198] Solid bladder 730 has a generally annular shape and is
fitted over mandrel 710 such that when assembled, bladder shank 714
of bladder mandrel 710 is disposed within inner bore 732 of solid
bladder 730. Upper surface 734 and lower surface 736 of solid
bladder 730 are in contact with the lower surface 742 of
compression washer 740 and upper surface 717 of flange 718,
respectively.
[0199] Compression collar 750 is slid over drive shank 711 of
mandrel 710, and is positioned along mandrel 710 proximate to
threaded shank 716; however, compression collar 750 is not engaged
with the threads of threaded shank 716. Nut 760 is engaged with the
threads of threaded shank 716 of mandrel 710, thereby applying an
axial force against compression collar 750, and compression washer
740. Thus nut 760 can be tightened so that compression washer 740
and flange 718 of mandrel 710 to apply a compressive force against
solid bladder 730 as indicated by arrows 799 and 798 (see FIG.
25B), thereby enabling the engagement of bladder 730 with polishing
band 770, as will be explained presently. For the sake of
simplicity of illustration, it is noted that polishing band 770 of
tool 700 is not shown in FIG. 25A.
[0200] The assembly and preparation of tool 710 for polishing use
will now be described. Such assembly and preparation is best
understood with reference to FIG. 24 and FIGS. 23B, 25B, and 26B,
which are a perspective view, a side cross-sectional view, and a
side view, respectively, of a solid bladder polishing tool of the
present invention depicted in a compressed state. Referring to
FIGS. 25A and 25B, and beginning with the tool 700 assembled in an
uncompressed state as shown in FIG. 25A, nut 760 is tightened,
driving compression washer 740 toward flange 718 of mandrel 710, as
indicated by arrows 799 and 798. Concurrently, inner shoulder 755
of compression collar 750 is also driven toward stop shoulder 715
of mandrel 710, as indicated by arrow 797. Nut 760 is tightened,
preferably by engaging a first wrench (not shown) with nut 760 and
a second wrench (not shown) with a wrench flat 729 provided in stub
728 of mandrel 710 (see FIG. 26B) until inner shoulder 715 seats
upon stop shoulder 755 and is stopped thereby, as depicted in FIG.
25B. This feature of tool 700 enables a highly reproducible
compressive force to be applied to solid bladder 730 when tool 700
is disassembled and reassembled.
[0201] Solid bladder 730 is made of a highly elastic incompressible
solid. Solid bladder preferably consists essentially of an
elastomer having a Shore A durometer of between about 10 and about
90. Solid bladder 730 may be made of any suitable material which,
when subjected to a compressive force, undergoes elastic
deformation in a direction substantially orthogonal to such
compressive force. For example, solid bladder 730 may consist
essentially of gum rubber, nitrile rubber, or polyurethane. In a
further embodiment, solid bladder 730 may consist essentially of an
elastomeric closed cell foam.
[0202] In one preferred embodiment, solid bladder 730 is made of
nitrile rubber having a Shore A durometer of about 40. Accordingly,
when solid bladder 730 is compressed between compression washer 740
and flange 718 of mandrel 710 as indicated by arrows 799 and 798,
the outer surface 739 of solid bladder 730 bulges outwardly as
indicated by arrows 796. Referring now to FIGS. 26A, at the
beginning of final assembly of tool 700 for use in polishing,
polishing band 770 is slid over solid bladder 730. Polishing band
770 slides over uncompressed and/or semi-compressed solid bladder
730 with a generally loose sliding fit. When solid bladder 730 is
compressed as indicated in FIG. 26B, solid bladder 730 expands
radially outwardly as indicated by arrows 796, and engages tightly
with polishing band 770, stretching polishing band 770 into the
arcuate shape of outer surface 739 of solid bladder 730 (see FIG.
25B).
[0203] The outer surface 739 of solid bladder 730 assumes a
generally arcuate shape simply due to the axial compression
thereof, and the resulting radial expansion thereof. However, to
achieve optimum polishing results of optics and the like, it is
preferable that the arcuate surface 739 of compressed solid bladder
730 be ground or otherwise formed to a specified arcuate shape. To
perform such a forming process, tool 700 is assembled as just
previously described, with solid bladder 730 in compression and
polishing band 770 not fitted to solid bladder 730. Setscrew 759 in
compression collar 750 is fitted and tightened such that setscrew
759 engages in slot 713 in threaded shank 716 of mandrel 710 to the
position indicated by engaged setscrew 759A shown in phantom in
FIG. 25B. This engagement of setscrew 759 in slot 713 prevents the
rotation of compression collar 750 on mandrel 710 during grinding
and during a polishing operation.
[0204] The assembled tool 700 is then fitted into a precision lathe
or other surface grinding machine, and arcuate surface 739 of solid
bladder 730 is ground to a desired shape. In one preferred
embodiment for the polishing of optics, arcuate surface 739 is
ground to a spherical shape. By way of illustration, solid bladder
730 may have an uncompressed radius 795 of about 3.1 inches, a
thickness of about 1 inch, and when compressed, a spherical arcuate
surface 739 with a radius of about 4 inches and a thickness of 0.75
inches. It is to be understood that this radius of about 4 inches
describes the radius of curvature of the surface 739 in the x-z
through y-z planes, with z being the central axis 23A-23A (see FIG.
24) of tool 700, rather than the radius 795 of solid bladder
730.
[0205] After surface 739 of solid bladder 730 is ground to the
desired arcuate shape, tool 700 is removed from the surface grinder
machine for the fitting of a polishing band to surface 739. To
accomplish this, setscrew 759 in compression collar 750 is loosened
slightly to allow setscrew 759 to slide in the axial direction
(along axis 23A-23A) in slot 713 in threaded shank 716 of mandrel
710. Nut 760 is then loosened, and setscrew 759 slides in slot 713
until setscrew 759 butts up against the upper end 721 of slot 713.
With setscrew 759 fitted in compression collar 750 and engaged with
upper end 721 of slot 713, further axial travel of compression
collar 750 is stopped.
[0206] Therefore, even if nut 760 is released further, solid
bladder 730 remains in a state of semi-compression from that point
on. Solid bladder 730 is thus preferably never totally released
from its compression by compression washer 740 and flange 718 of
bladder mandrel 710 after the finish grind is completed. A
polishing band is then fitted around solid bladder 730, and nut 760
is retightened, engaging polishing band 770 with solid bladder 730,
and forming polishing band 770 to the desired arcuate shape.
Because of the provision of inner stop 755 in compression collar
750, which stops against shoulder stop 715, solid bladder 730 is
compressed reproducibly to the same extent as when it was ground to
the desired arcuate shape, and thus the curvature of arcuate
surface 739 and polishing band 770 disposed thereupon is accurately
reproduced.
[0207] Referring again to FIGS. 24 and 25B, as a final step in the
assembly of tool 700 with polishing band 770, setscrew 759 in
compression collar 750 is tightened such that setscrew 759 engages
in slot 713 in threaded shank 716 of mandrel 710 to the position
indicated by engaged setscrew 759A shown in phantom in FIG. 25B. In
one preferred embodiment, compression collar 750 and compression
washer 740 are provided as a single unitary part, i.e. as a
compression flange 750/740. Such a compression flange 750/740 is
locked to said mandrel and prevented from rotation by engaged
setscrew 759A during operation. Since solid bladder 730 is highly
compressed and thus frictionally engaged with flange 718,
compression washer 740, and bladder shank 714, solid bladder 730
and polishing band 770 engaged therewith are also prevented from
slipping during the use of tool 700 for a polishing operation.
[0208] It will be apparent that numerous other suitable means for
locking the compression collar 750 or the combined collar
750/washer 740 as a compression flange 750/740 to mandrel 710 can
be provided alternatively or additionally, such as e.g. a pin
passing through collar 750 and threaded shank 716, or the keying of
the shank 716 and the bore of collar 750, and the disposition of a
piece of keystock in a key slot in one of shank 716 or the bore of
collar 750. The arrangement depicted in the Figures herein is
preferred, because it provides both rotational locking, and limited
travel to maintain the bladder in semi-compression after precision
grinding, while a polishing band is fit thereto.
[0209] In general, suitable materials for polishing band 770 are as
described previously in this specification for the polishing tools
described and shown in FIGS. 2A-4. As used herein, the terms
"polishing foil" and "polishing band" are used interchangeably. In
a further embodiment, rather than a polishing band, there is
provided a solid bladder 730 impregnated with abrasive particles
such as e.g., diamond particles, such that the solid bladder
performs both the function of deformability to some extent to
define the spot size during polishing, and abrasiveness to effect
material removal during polishing.
[0210] It will be apparent that numerous other suitable means for
compressing the lower surface 736 toward the upper surface 734 of
solid bladder 710 and causing the outer surface 739 of said bladder
to have an arcuate shape may be provided. For example, one may
provide a pin cam assembly, or an assembly wherein a compression
collar is rotated a small angular displacement such as a
quarter-turn, compressing bladder 730 and then locking in place.
Such assemblies may make use of one or more springs. In another
embodiment, compression may be provided by one or more coil springs
disposed on a shank portion of mandrel 710, with a circular disc
and keepers engaged with such shank, in much the same way that
valves are held in an automotive cylinder head.
[0211] It is, therefore, apparent that there has been provided, in
accordance with the present invention, a tool for polishing objects
comprising a wide variety of materials and shapes including
precision optical surfaces and injection mold inserts. While this
invention has been described in conjunction with preferred
embodiments thereof, it is evident that many alternatives,
modifications, and variations will be apparent to those skilled in
the art. Accordingly, it is intended to embrace all such
alternatives, modifications and variations that fall within the
spirit and broad scope of the appended claims.
* * * * *