U.S. patent application number 10/132719 was filed with the patent office on 2003-01-23 for silicon rubber surfaces for biometric print tir prisms.
Invention is credited to Arnold, Joe F., Bardons, Charles P..
Application Number | 20030016427 10/132719 |
Document ID | / |
Family ID | 26963772 |
Filed Date | 2003-01-23 |
United States Patent
Application |
20030016427 |
Kind Code |
A1 |
Arnold, Joe F. ; et
al. |
January 23, 2003 |
Silicon rubber surfaces for biometric print TIR prisms
Abstract
Molded silicone rubber sheets with optical quality surfaces and
methods for making the same. The silicone rubber sheets are made by
molding liquid silicone rubber in a mold. In embodiments, the mold
forms parallel optical quality flat surfaces. In one embodiment, a
stiffening plastic is molded in the middle of the silicone rubber
sheet between the parallel optical quality flat surfaces. In
another embodiment, the mold forms one optical quality flat surface
while the surface parallel to the optical quality flat surface is
bonded to a prism.
Inventors: |
Arnold, Joe F.; (Palm Beach
Gardens, FL) ; Bardons, Charles P.; (Palm Beach
Gardens, FL) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX PLLC
1100 NEW YORK AVENUE, N.W., SUITE 600
WASHINGTON
DC
20005-3934
US
|
Family ID: |
26963772 |
Appl. No.: |
10/132719 |
Filed: |
April 26, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60286373 |
Apr 26, 2001 |
|
|
|
60292341 |
May 22, 2001 |
|
|
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Current U.S.
Class: |
359/831 |
Current CPC
Class: |
B32B 2038/0076 20130101;
G02B 1/10 20130101; B32B 25/08 20130101; B32B 17/063 20130101; G06V
40/1324 20220101; B29C 37/006 20130101; B32B 7/12 20130101; G02B
7/18 20130101; B32B 17/10 20130101; B32B 27/308 20130101; B32B
2323/04 20130101; B32B 27/322 20130101; B32B 2255/10 20130101; G02B
5/04 20130101; B32B 25/04 20130101; B32B 2319/00 20130101; B32B
2369/00 20130101; B29C 39/02 20130101; B32B 25/20 20130101; B32B
2327/18 20130101; B29C 37/0078 20130101; Y10T 428/31598 20150401;
B32B 27/365 20130101; B29K 2083/005 20130101; B29C 39/10
20130101 |
Class at
Publication: |
359/222 |
International
Class: |
G02B 026/08 |
Claims
What is claimed is:
1. A silicone rubber sheet, comprising: at least one layer of
silicone rubber compound; and at least one optical quality surface
attached to said at least one silicone rubber compound, wherein
said at least one optical quality surface is molded to said at
least one layer of silicone rubber compound.
2. The silicone rubber sheet of claim 1, wherein said at least one
layer of silicone rubber compound is comprised of one of liquid
silicone and liquid silicone diluted with a silicone thinner.
3. The silicone rubber sheet of claim 1, wherein said at least one
layer of silicone rubber compound is integrally molded to a surface
of a device.
4. The silicone rubber sheet of claim 3, wherein said device is a
TIR (Total Internal Reflection) prism.
5. The silicone rubber sheet of claim 2, wherein said silicone
rubber compound comprised of liquid silicone diluted with a
silicone thinner is diluted 10-40 percent.
6. The silicone rubber sheet of claim 1, wherein said at least one
layer silicone rubber compound includes a TIR platen surface that
is of optical quality.
7. The silicone rubber sheet of claim 1, wherein said at least one
layer of silicone rubber compound has an embedded layer of a stiff
plastic approximately midway of said at least one layer of silicone
rubber compound.
8. A method for making a silicone rubber sheet, comprising the
steps of: (1) preparing a liquid silicone compound; (2) out gassing
said liquid silicone compound; (3) pouring said liquid silicone
compound into one or more cavity molds; and (4) curing said liquid
silicone compound to generate said silicone rubber sheet.
9. The method of claim 8, further comprising the step of removing
said silicone rubber sheet from said mold.
10. The method of claim 9, further comprising the step of cutting
said silicone rubber sheet to defined dimensions for a defined
application.
11. The method of claim 8, wherein step (1) comprises the steps of:
(a) coating a surface of a prism with a binder; and (b) curing the
binder, wherein said silicone rubber sheet will be integrally
molded to the prism after step (4) is completed.
12. The method of claim 11, wherein step (a) further comprises the
step of coating said binder with a silicone sealer.
13. The method of claim 8, wherein step (1) comprises the steps of:
(a) applying a binder to a stiffening material; (b) curing said
stiffening material; (c) placing said stiffening material in a
tension device between said one or more cavity molds; and (d)
tensioning said stiffening material.
14. The method of claim 8, wherein step (1) comprises the step of
diluting liquid silicone with a silicone thinner solution.
15. A total internal reflective (TIR) platen for a biometric
imaging device, comprising: a silicone rubber compound; and a first
and second optical quality molded surface, wherein said first
optical quality molded surface provides for a TIR platen surface
and said second optical quality molded surface for making optical
contact with a prism.
16. The TIR platen of claim 15, wherein said silicone rubber
compound is integrally molded to said prism.
17. The TIR platen of claim 15, wherein said silicone rubber
compound includes a stiff plastic material in the middle of said
silicone rubber compound.
Description
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e) of U.S. Provisional Application No. 60/286,373, filed
Apr. 26, 2001, and U.S. Provisional Application No. 60/292,341,
filed May 22, 2001, which are incorporated by reference herein in
their entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to the field of
biometrics.
[0004] 2. Background Art
[0005] Biometrics is a science involving the analysis of biological
characteristics. Biometric imaging captures a measurable
characteristic of a human being for identity purposes. See, e.g.,
Gary Roethenbaugh, Biometrics Explained, International Computer
Security Association, Inc. (1998), pp. 1-34, which is incorporated
herein by reference in its entirety.
[0006] Fingerprint scanners and palm scanners are two types of
biometric imaging systems for acquiring fingerprint images and palm
print images, respectively. Many fingerprint and palm print
scanners include glass platens that result in latent prints. Latent
print images are images of prints that remain on the platen after a
person's finger or palm have been removed and may show up on
subsequent images of fingerprints or palm prints acquired
thereafter. To eliminate latent print images, glass platens have
been replaced by platens made of silicone rubber sheets.
[0007] Commercially available silicone rubber sheets are often
manufactured using a process known as calendaring. Calendaring is a
rolling process in which a machine with rollers, known as a
calendar, is used to form thin sheets from plastic, paper, or other
materials. For silicone rubber sheets, liquid silicone is poured on
rollers of the calendar with a catalyst and mixed. The rollers
rotate several times. As the temperature is changed from cold to
hot, the mixture begins to form a rubber sheet. The rubber sheet is
then passed through another set of rollers that are very hot. The
rubber sheet is then released and hardens almost instantly.
[0008] Silicone rubber sheets manufactured using calendaring often
have problems associated with them. For example, they may not be
completely flat, and often have inclusions and striations that
cannot be removed. The silicone rubber sheets may also be cloudy in
color. For many applications these characteristics may not be a
problem. But in applications where the silicone rubber sheets need
to be of optical quality, such as biometric imaging, commercially
available silicone rubber sheets produced from calendaring do not
provide adequate surface quality or finish to optimize image
enhancement.
[0009] Silicone rubber molding is another process used to produce
many products. However, conventional methods for molding silicone
rubber also do not provide the optical quality needed for biometric
imaging.
[0010] What is needed is an optical quality silicone rubber sheet
that provides adequate surface quality or finish to optimize image
enhancement. What is further needed is a method for making the
same.
BRIEF SUMMARY OF THE INVENTION
[0011] The present invention solves the above-mentioned needs by
providing silicone rubber sheets with optical quality surfaces and
methods for making the same. The silicone rubber sheets are made by
molding liquid silicone rubber in a mold. In embodiments, the mold
forms parallel optical quality flat surfaces. In one embodiment, a
stiffening plastic is molded in the middle of the silicone rubber
between the parallel optical quality flat surfaces. In another
embodiment, the mold forms one optical quality flat surface while
the surface parallel to the optical quality flat surface is bonded
to a prism during the molding process.
[0012] Further embodiments, features, and advantages of the present
invention, as well as the structure and operation of the various
embodiments of the present invention, are described in detail below
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
[0013] The accompanying drawings, which are incorporated herein and
form part of the specification, illustrate the present invention
and, together with the description, further serve to explain the
principles of the invention and to enable a person skilled in the
pertinent art to make and use the invention.
[0014] FIG. 1 is a diagram illustrating an optical quality silicone
rubber sheet for a biometric TIR prism.
[0015] FIG. 2 is a mold for making an optical quality silicone
rubber sheet according to an embodiment of the invention.
[0016] FIG. 3 is a method for making an optical quality silicone
rubber sheet according to an embodiment of the invention.
[0017] FIG. 4 is a diagram illustrating an optical quality silicone
rubber sheet that is bonded to a biometric TIR prism according to
an embodiment of the invention.
[0018] FIG. 5 is a mold for making an optical quality silicone
rubber sheet that is bonded to a biometric TIR prism according to
an embodiment of the invention.
[0019] FIG. 6 is a method for making an optical quality silicone
rubber sheet that is bonded to a biometric TIR prism according to
an embodiment of the invention.
[0020] FIG. 7 is a diagram illustrating an optical quality
reinforced silicone rubber sheet according to an embodiment of the
invention.
[0021] FIG. 8A is a side view of a mold for making an optical
quality reinforced silicone rubber sheet according to an embodiment
of the invention.
[0022] FIG. 8B is a top view of a mold for making an optical
quality reinforced silicone rubber sheet according to an embodiment
of the invention.
[0023] FIG. 9 is a method for making an optical quality reinforced
silicone rubber sheet according to an embodiment of the
invention.
[0024] FIG. 10A is an exemplary diagram illustrating an optical
quality reinforced silicone rubber sheet for a fingerprint
scanner.
[0025] FIG. 10B is an exemplary diagram illustrating an optical
quality reinforced silicone rubber sheet for a palm print
scanner.
[0026] The features, objects, and advantages of the present
invention will become more apparent from the detailed description
set forth below when taken in conjunction with the drawings in
which like reference characters identify corresponding elements
throughout. In the drawings, like reference numbers generally
indicate identical, functionally similar, and/or structurally
similar elements. The drawings in which an element first appears is
indicated by the leftmost digit(s) in the corresponding reference
number.
DETAILED DESCRIPTION OF THE INVENTION
[0027] The present invention provides optical quality silicone
rubber sheets and methods for making the same. The optical quality
silicone rubber sheets are produced using molding methods that
provide adequate surface quality or finish to optimize image
enhancement for many applications, such as biometric imaging.
[0028] Silicone Rubber Sheet
[0029] FIG. 1 is a diagram 100 illustrating an optical quality
silicone rubber sheet for a biometric TIR prism. FIG. 1 shows a
prism 102 and an optical quality silicone rubber sheet 104 attached
to prism 102. An enlarged view 108 of a portion 106 of silicone
rubber sheet 104 is also shown in FIG. 1. Enlarged view 108 shows
the components of silicone rubber sheet 104. The components of
silicone rubber sheet 104 include a silicone rubber compound 110
and two parallel optical quality molded surfaces 112.
[0030] In one embodiment, silicone rubber compound 110 is comprised
of liquid silicone. In another embodiment, silicone rubber compound
110 is comprised of liquid silicone diluted with a thinning
solution. The dilution may range from 10 to 40 percent.
[0031] At least one of the optical quality molded surfaces 112
enables optical contact with prism 102. In other words, when
silicone rubber sheet 104 is applied to the surface of prism 102,
silicone rubber sheet 104 adheres to prism 102 without any
separation between prism 102 and silicone rubber sheet 104. Quality
molded surfaces 112 have a surface flatness of 4 to 6 waves of
light per inch. In an embodiment, one of the quality molded
surfaces 112 is used to make optical contact with prism 102. The
other quality molded surface is used as a TIR (Total Internal
Reflection) platen surface.
[0032] The thickness of silicone rubber sheet 104 may range from 30
to 60 mils.
[0033] The thickness of silicone rubber sheet 104 is dependent on
the application in which it is used. For example, in the
application of biometric imaging, the thickness of silicone rubber
sheet 104 is dependent upon the size of prism 104.
[0034] The smaller the prism, the smaller the thickness of silicone
rubber sheet 104. The larger the prism, the larger the thickness of
silicone rubber sheet 104. For example, a fingerprint scanner may
use a smaller prism than a palm print scanner. The fingerprint
scanner with the smaller prism may therefore require silicone
rubber sheeting that is closer to the lower range of thickness,
that is 30 mils, while the palm print scanner with the larger prism
may require silicone rubber sheeting that is closer to the higher
range of thickness, that is 60 mils.
[0035] In an embodiment, RTV (Room Temperature Vulcanization)
liquid silicone manufactured by General Electric is used. RTV is a
very clear liquid silicone. RTV is comprised of two parts that when
mixed together cause it to vulcanize at room temperature. As its
name implies, RTV may be cured at room temperature. RTV is not
limited to curing at room temperature. RTV may also be cured by
heating to accelerate the curing process.
[0036] FIG. 2 is an exemplary mold 200 for making optical quality
silicone rubber sheet 104. Mold 200 is comprised of a mold cavity
202, a plurality of spacers 204, two plates 206, and two clamps
208. Spacers 204 are located at three edges of mold cavity 202. The
two plates 206 may be a glass or plastic plate for visibility. In
one embodiment, the two plates 206 are two pieces of float glass.
Float glass provides optically flat surfaces. In other words, the
surface flatness of float glass is within 4 to 6 wavelengths of
light per inch. In an embodiment, each float glass plate 206 may be
3/4 inch thick. The present invention is not limited to using float
glass. Other types of plates 206, such as plastics or optically
polished materials, may be used that allow for visibility, provide
for optically flat surfaces, and do not stick to rubber. For
example, such plastics as acrylic, polycarbonate, polypropolene,
polyethylene, teflon, etc. may be used if they meet the optically
flat standard of at least 4 to 6 wavelengths of light per inch.
[0037] Once the molding process for a given configuration is
developed, the molds may be made of opaque materials that are
compatible with silicone rubber.
[0038] The two plates 206 are separated by spaces 204. The
thickness of spacers 204 are equivalent to the desired thickness of
the silicone rubber sheet to be molded. Clamps 208 are U-shaped and
adjustable, and are used to hold the two pieces of float glass 206
together. Clamps 208 are applied with enough force to prevent
leakage of silicone rubber compound 110. Mold cavity 202 is used to
hold the liquid silicone compound for making silicone rubber sheet
104.
[0039] FIG. 3 is a method 300 for making optical quality silicone
rubber sheet 104 according to an embodiment of the invention. The
process begins with step 302, where the process immediately
proceeds to step 304.
[0040] In step 304, silicone rubber compound 110 is prepared. As
previously stated, silicone or RTV is in two parts and the two
parts must be mixed together.
[0041] In one embodiment, silicone rubber compound 110 is comprised
of 100 percent RTV. In another embodiment, RTV is diluted between
10 to 40 percent with Toluene to produce silicone rubber compound
110. Toluene is a solvent to silicone rubber and may be purchased
at any hardware store. General Electric recommends that Toluene be
used to thin RTV, if desired. The process then proceeds to step
306.
[0042] In step 306, silicone rubber compound 110 is out gassed.
Silicone rubber compound 110 is placed in a vacuum chamber to get
all of the entrapped air out of silicone rubber compound 110.
[0043] In step 308, silicone rubber compound 110 is injected into
mold cavity 202. The process then proceeds to step 310.
[0044] In step 310, silicone rubber compound 110 is cured in mold
cavity 202.
[0045] Mold 200 is placed into a temperature controlled oven.
Silicone rubber compound 110 is cured for a certain amount of time
at a specific temperature. Table 1 shows the recommended
temperature vs. cure time for curing silicone rubber compound 110.
The temperatures and cure times are recommended by General
Electric, the manufacturer of a specific variety of RTV.
1 TABLE 1 Temperature .degree. C. (.degree. F.) Cure Times 25 (77)
6 to 7 days 65 (149) 4 hours 100 (212) 1 hour 125 (257) 45 minutes
150 (302) 15 minutes
[0046] In one embodiment, silicone rubber compound 110 is cured for
1 hour at temperature 100.degree. C.(212.degree. F.). Other cure
times and temperatures shown in Table 1 may be used without
departing from the scope of the invention. At the end of the
desired cured time, mold 200 is removed from the temperature
controlled oven. Curing silicone rubber compound 110 causes the
float glass surface of plates 206 to be replicated on the surface
of silicone rubber compound 110 that forms a TIR surface for the
resulting silicone rubber sheet 104. The process proceeds to step
312.
[0047] In step 312, the mold is taken apart in order to remove
silicone rubber sheet 104. Clamps 208 are removed and plates 206
are separated. Silicone rubber sheet 104 is peeled from one of
plates 206. The plate 206 in which silicone rubber sheet 104 is
peeled from depends on which one of the two plates are easily
separated from silicone rubber sheet 104. The plate 206 that is
hardest to remove requires that silicone rubber sheet 104 be peeled
off. The process then proceeds to step 314.
[0048] In step 314, silicone rubber sheet 104 is cut to the desired
dimensions for its particular application. Silicone rubber sheet
104 may be cut with a die cutter. Other cutting devices may also be
used, such as an exacto knife, shears, etc. The process then
proceeds to step 316, where the process ends.
[0049] Integrally Molded Silicone Rubber Surface
[0050] Silicone rubber sheets 104 produced using molding process
300 provide optical clarity and flatness without striations
(induced stress in the silicone) and inclusions that result from
commercial silicone rubber sheets that are produced using the
calendaring process. Although silicone rubber sheet 104 produced
using molding process 300 provides a precise optical quality
silicone rubber layer, silicone rubber sheet 104 may be difficult
to install reliably and quickly on the surface of prism 102 without
inducing distortion and strain in the silicone layer and anomalies
in the interface between the surface of prism 102 and the silicone
rubber sheet 104. These distortions, strains, and anomalies may
cause unacceptable optical images. If the placement of silicone
rubber sheet 104 on prism 102 is anything except perfectly flat,
any distortions, strains, or anomalies will be displayed on an
image.
[0051] In another embodiment of the invention, in-situ molding on a
prism surface takes advantage of the precision qualities of the
molding process while avoiding installation problems that cause
distortion and strain in the silicone layer and interfacing
anomalies between the prism surface and the silicone rubber sheet.
FIG. 4 is a diagram illustrating an optical quality silicone rubber
sheet that is bonded to a biometric TIR prism according to an
embodiment of the invention. FIG. 4 shows prism 102 with an optical
quality silicone rubber sheet 402 bonded to prism 102 using a
binder. An enlarged view 406 of a portion 404 of silicone rubber
sheet 402 is also shown in FIG. 4. Enlarged view 406 shows the
components of silicone rubber sheet 402. The components of silicone
rubber sheet 402 include silicone rubber compound 110, one optical
quality molded surface 408, and a binder 410.
[0052] Quality molded surface 408 has a surface flatness of 4 to 6
waves of light per inch. Quality molded surface 408 is used as a
TIR (Total Internal Reflection) platen surface on which a biometric
image is formed. Binder 410 is the material used to bond silicone
rubber sheet 402 to the surface of prism 102. Thus, in this
embodiment, one does not have to attach or worry about attaching
silicone rubber sheet 402 to prism 102 because silicone rubber
sheet 402 is permanently bonded to the surface of prism 102.
[0053] In one embodiment, a liquid silicone primer, SS4120,
manufactured by General Electric, is used to bond silicone rubber
sheet 402 to prism 102. SS4120 is a very thin material with a
viscosity of alcohol. SS4120 has an approximate curing time of one
hour before one can use it. Other silicone primers that are clear
and remain clear after the primer cures may also be used.
[0054] FIG. 5 is an exemplary mold 500 for making optical quality
silicone rubber sheet 402 bonded to biometric TIR prism 102
according to an embodiment of the invention. Mold 500 is comprised
of a mold cavity 502, a plurality of spacers 504, two clamps 508,
and two plates 206 and 506, respectively. Plate 206 may be a glass
or plastic plate for visibility. In one embodiment, plate 206 is a
piece of float glass for providing an optically flat surface. Plate
506 may be any type of plate built to hold prism 102.
[0055] Spacers 504 are located along three sides of mold cavity
502. Spacers 504 are used to separate prism 102 from plate 206. The
thickness of spacers 504 are equivalent to the desired thickness of
the silicone rubber sheet to be molded. Clamps 508 are U-shaped and
adjustable, and are used to hold the two plates 206 and 506
together. Other types of clamps may be used to hold mold 500
together. Clamps 508 are applied with enough force to prevent
leakage of silicone rubber compound 110. Mold cavity 502 is used to
hold the liquid silicone rubber compound 110 for making silicone
rubber sheet 402.
[0056] FIG. 6 is a method for making an optical quality silicone
rubber sheet that is bonded to a biometric TIR prism according to
an embodiment of the invention. The process begins with step 602
and immediately proceeds to step 604.
[0057] In step 604, the surface of prism 102 is coated with a
liquid silicone primer or binder 410. A thin layer of silicone is
applied to the liquid silicone primer as a sealer. Then the liquid
silicone primer and thin layer of silicone are cured. In one
embodiment, curing time is one hour. Binder 410 enables silicone
rubber sheet 402 to adhere to prism 102. The process then proceeds
to step 606.
[0058] In step 606, silicone rubber compound 110 is prepared. As
previously stated, silicone is provided in two parts and the two
parts must be mixed together. As previously stated, the present
invention uses a liquid silicone, RTV, manufactured by General
Electric. In one embodiment, silicone rubber compound 110 is
comprised of 100 percent RTV. In another embodiment, silicone
rubber compound 110 is silicone, RTV, diluted with a thinner. One
embodiment dilutes the silicone with 10 to 40 percent of Toluene to
produce silicone rubber compound 110. The process then proceeds to
step 608.
[0059] In step 608, silicone rubber compound 110 is out gassed.
Silicone rubber compound 110 is placed in a vacuum chamber where
all of the entrapped air is removed from silicone rubber compound
110. The process then proceeds to step 610.
[0060] In step 610, silicone rubber compound 110 is injected into
mold cavity 502. The process then proceeds to step 612.
[0061] In step 612, silicone rubber compound 110 in mold cavity 502
is cured. Mold 500 is placed into a temperature controlled oven.
Silicone rubber compound 110 is cured for a certain amount of time
at a specific temperature. Table 1 shows the recommended
temperature vs. cure time for curing silicone rubber compound 110.
The temperatures and cure times are recommended by General
Electric, the manufacturer of RTV.
[0062] In one embodiment, silicone rubber compound 110 is cured for
1 hour at temperature 100.degree. C.(212.degree. F.). Other cure
times and temperatures shown in Table 1 may be used without
departing from the scope of the invention. At the end of the
desired cured time, mold 500 is removed from the temperature
controlled oven. Curing silicone rubber compound 110 causes the
float glass surface of plate 206 to be replicated on the surface of
silicone rubber compound 110. The replicated float glass surface
forms a TIR surface for the resulting silicone rubber sheet 402. In
biometric imaging applications, this surface is used as the TIR
platen surface. The process proceeds to step 614.
[0063] In step 614, prism 102, now having a bonded silicone rubber
sheet 402 adhered to it, is removed from mold 500. Clamps 508 are
removed and plate 206 is separated from silicone rubber sheet 402.
Prism 102 is then removed from plate 506. The process then proceeds
to step 616, where the process ends.
[0064] Reinforced Silicone Rubber Sheet
[0065] In one embodiment of the present invention, a plastic
stiffening material is embedded approximately in the center of two
layers of silicone to form a reinforced silicone rubber sheet. The
reinforcement serves to both prevent distortion strain during
application of the reinforced silicone rubber sheet and to assist
with application of the reinforced silicone rubber sheet by the
attraction of optically flat surfaces whose flatness is maintained
by the stiff reinforcement.
[0066] These factors, combined with the natural affinity of
silicone rubber to a smooth surface, allow adequate optical contact
to be achieved by simply placing the reinforced silicone rubber
sheet on an adequately clean surface. The attraction between the
silicone rubber, the stiff plastic material and glass causes the
reinforced silicone rubber sheet to make optical contact with a
clean surface, such as a TIR platen surface, almost entirely on its
own. When placed on a TIR platen surface, the reinforced silicone
rubber sheet becomes an image enhancing, resilient surface with no
optically degrading strains or interface irregularities being
induced or incurred.
[0067] FIG. 7 is a diagram illustrating an optical quality
reinforced silicone rubber sheet according to an embodiment of the
invention. FIG. 7 shows a prism 102 and an optical quality
reinforced silicone rubber sheet 702 attached to, yet separate
from, prism 102. An enlarged view 706 of a portion 704 of
reinforced silicone rubber sheet 702 is also shown in FIG. 7.
Enlarged view 706 shows the components of reinforced silicone
rubber sheet 702. The components of reinforced silicone rubber
sheet 702 include a stiff plastic material 708 positioned between
two layers of silicone rubber compound 110, two binder layers 710,
and two parallel optical quality molded surfaces 112. Binder layers
710 bind the two layers of silicone rubber compound 110 with stiff
plastic material 708. One of the two parallel optical quality mold
surfaces 112 is used to make optical contact with prism 102. The
other parallel optical quality mold surface 112 may be used as a
TIR platen surface on which a biometric image, such as a
fingerprint, a palm print, etc., is formed.
[0068] In an embodiment, polycarbonate may be used for stiff
plastic material 708. Polycarbonate is a high temperature plastic
having high strength. Polycarbonate is very clear, has a high index
refraction, and is readily available in thicknesses of 5 to 60
mils. Other types of stiff plastic material that bond to silicone
rubber and exhibit good optical quality may be used. Such plastics
may include acrylic, CR39, styrene, etc.
[0069] The overall thickness of reinforced silicone rubber sheet
702 is directly related to the size of the surface on which it is
to be applied. For example, on an approximately 3 by 2 inch surface
of a prism for a fingerprint scanner, the thickness may be in the
range of 25-30 mils. On an approximately 4 by 6 inch surface of a
prism for a palm scanner, the thickness may be in the range of
40-60 mils. Thus, the larger the surface on which reinforced
silicone rubber sheet 702 is to be applied, the larger the
thickness of reinforced silicone rubber sheet 702. In one
embodiment, the overall thickness of reinforced silicone rubber
sheet 702 may range from 25 to 100 mils. The thickness of stiff
plastic material 708 may range from 5 to 60 mils while the two
layers of silicone rubber compound 110 may range from 5 to 50 mils.
In one embodiment, the two layers of silicone rubber compound 110
and stiff plastic material 708 are of equal thickness. In another
embodiment, the thickness of stiff plastic material 708 may be 50
mils while each layer of silicone rubber compound 110 may be 25
mils. Yet, in another embodiment, the thickness of stiff plastic
material 708 may be 10-20 mils while one layer of silicone rubber
compound 110 may be 5-15 mils and the other layer of silicone
rubber compound 110 may be 10-30 mils.
[0070] FIG. 8A is a side view of an exemplary mold 800 for making
optical quality reinforced silicone rubber sheet 702 according to
an embodiment of the invention. Mold 800 comprises a base 802, a
first clamp 804 fixed to, and on one side of, base 802, a post 806
fixed to base 802 on the side opposite of first clamp 804, a spring
808, a moveable clamp 810, a pair of parallel plates 812, a pair of
clamps 814 on each side of parallel plates 812, a pair of parallel
mold cavities (not shown) for injecting silicone rubber compound
110, and spacers (not shown) located on each end of the pair of
mold cavities for indicating the thickness of the two layers of
silicone rubber compound 110. As previously indicated, the
thicknesses of the two layers of silicone rubber compound 110 may
not be equal.
[0071] Spring 808, clamps 804 and 810, and post 806 form a
tensioning device for tensioning stiff plastic material 708.
Parallel plates 812 may be glass or plastic plates for visibility.
In one embodiment, parallel plates 812 are pieces of float glass
for providing an optically flat surface. Clamps 814 are used to
hold the two pieces of float glass 812 together. Clamps 814 are
applied with enough force to prevent leakage of the two layers of
silicone rubber compound 110. The parallel mold cavities (not
shown) are used to hold the liquid silicone compound for making
reinforced silicone rubber sheet 702.
[0072] FIG. 8B is a top view of mold 800 for making optical quality
reinforced silicone rubber sheet 702. FIG. 8B indicates the
location of spacers 818.
[0073] FIG. 9 is a method for making an optical quality reinforced
silicone rubber sheet according to an embodiment of the invention.
The process begins with step 902, where the process immediately
proceeds to step 904.
[0074] In step 904, a binder is applied to a plastic stiffening
layer. In one embodiment, the binder is a silicone primer, SS4120,
manufactured by General Electric Company. Then a sealer coat of
silicone is applied. In one embodiment, the plastic stiffening
layer is dipped into the silicone. The plastic stiffening layer is
then cured for approximately 1 hour. The process then proceeds to
step 906.
[0075] In step 906, after curing, the plastic stiffening layer is
placed in the tensioning device of mold 800 between plates 812.
Each end of the plastic stiffening layer is attached to mold 800
via clamps 804 and 810. To prevent the silicone, in which the
plastic stiffening layer was sealed, from being attracted to plates
812 (wherein plates 812 are made of glass), enough tension must be
applied to the plastic stiffening layer to prevent it from
attaching itself to glass plates 812. Thus, the spring is used to
stretch the stiffening layer by a necessary amount to prevent the
stiffening layer from attaching itself to one of glass plates 812
and to maintain its position within mold 800. The process then
proceeds to step 908.
[0076] In step 908, silicone rubber compound 110 is prepared. As
previously stated, silicone or RTV is in two parts and the two
parts must be mixed together. In one embodiment, silicone rubber
compound 110 is comprised of 100 percent RTV. In another
embodiment, silicone rubber compound is comprised of RTV diluted
with a silicone thinner, Toluene. RTV may be diluted by 10 to 40
percent to produce silicone rubber compound 110. The process then
proceeds to step 910.
[0077] In step 910, silicone rubber compound 110 is out gassed.
Silicone rubber compound 110 is placed in a vacuum chamber to get
all of the entrapped air out of silicone rubber compound 110.
[0078] In step 912, the spacers are adjusted for the appropriate
thickness of the mold cavities. Silicone rubber compound 110 is
injected into the two mold cavities for mold 800. The process then
proceeds to step 914.
[0079] In step 914, silicone rubber compound 110 is cured in mold
800. Mold 800 is placed into a temperature controlled oven.
Silicone rubber compound 110 is cured for a certain amount of time
at a specific temperature as shown in Table 1.
[0080] In one embodiment, silicone rubber compound 110 is cured for
1 hour at temperature 100.degree. C.(212.degree. F.). Other cure
times and temperatures shown in Table 1 may be used without
departing from the scope of the invention. At the end of the
desired cured time, mold 800 is removed from the temperature
controlled oven. Curing silicone rubber compound 110 causes the
float glass surfaces of plates 812 to be replicated on each outside
surface of silicone rubber compound 110. The top surface of
silicone rubber compound 110 forms a TIR surface for the resulting
reinforced silicone rubber sheet 702. The bottom surface of
silicone rubber compound 110 enables reinforced silicone rubber
sheet 702 to make optical contact with a surface on which it
attaches. The process proceeds to step 916.
[0081] In step 916, mold 800 is taken apart in order to remove
reinforced silicone rubber sheet 702. Clamps 814, 804, and 810 are
removed and plates 812 are separated. The process then proceeds to
step 918.
[0082] In step 918, reinforced silicone rubber sheet 702 is cut to
the desired dimensions for its particular application. Silicone
rubber sheet 702 may be cut with a die cutter. Other cutting
devices may also be used, such as an exacto knife, shears, etc. The
process then proceeds to step 920, where the process ends.
[0083] FIG. 10A is an exemplary diagram illustrating a reinforced
silicone rubber sheet 1002 for a fingerprint scanner. Reinforced
silicone rubber sheet 1002 is comprised of two layers of clear
silicone rubber 1004 and one layer of clear polycarbonate 1006
inserted between the two layers of clear silicone rubber 1004. A
molded surface is formed on the outside surface of the two layers
of clear silicone rubber 1004. A primer/binder binds the inside
surface of the two layers of clear silicone rubber 1004 to the
layer of clear polycarbonate 1006. Reinforced silicone rubber sheet
1002 is approximately 3.24.+-.0.010 inches by 2.11.+-.0.010 inches
and has a thickness of approximately 30.+-.2 mils. Each layer of
clear silicone rubber 1004 is 7.5.+-.0.75 mils thick. The layer of
clear polycarbonate 1006 is 15.+-.0.75 mils thick. Notes for
reinforced silicone rubber sheet 1002 are found in Table 2.
[0084] FIG. 10B is an exemplary diagram illustrating a reinforced
silicone rubber sheet 1012 for a palm print scanner. Reinforced
silicone rubber sheet 1012 is comprised of two layers of clear
silicone rubber 1014 and one layer of clear polycarbonate 1016
inserted between the two layers of clear silicone rubber 1014. A
molded surface is formed on the outside surface of the two layers
of clear silicone rubber 1014. A primer/binder binds the inside
surface of the two layers of clear silicone rubber 1014 to the
layer of clear polycarbonate 1016. Reinforced silicone rubber sheet
1012 is approximately 5.75.+-.0.010 inches by 5.06.+-.0.010 inches
and has a thickness of approximately 45.+-.2 mils. The two layers
of clear silicone rubber 1014 are not of equal thickness. One layer
of clear silicone rubber 1014 is 10.+-.0.75 mils thick while the
other layer of clear silicone rubber 1014 is 20.+-.0.75 mils thick.
The layer of clear polycarbonate 1016 is 15.+-.0.75 mils thick.
Notes for reinforced silicone rubber sheet 1012 are found in Table
2.
2TABLE 2 NOTES 1. MOLDED OPTICALLY CLEAR SILICONE RUBBER WITH
REINFORCED LAYER OF CLEAR POLYCARBONATE FILM A) OPTICALLY CLEAR
SILICONE RUBBER: MECHANICAL PROPERTIES AFTER CURING: HARDNESS:
SHORE A DUROMETER: 44-46 TENSILE STRENGTH: 920 PSI ELONGATION: 120%
SHRINKAGE: 0.20% REFRACTIVE INDEX: 1.40 COEFFICIENT OF EXPANSION:
15.3 .times. 10.sup.-6 IN/IN/.degree. F. B) CLEAR POLYCARBONATE
FILM: GRADE: GRAPHICS QUALITY REFRACTIVE INDEX: 1.588 LIGHT
TRANSMISSION: 88% MINIMUM HARDNESS: ROCKWELL R 118 YIELD STRENGTH:
8.500 PSI ULTIMATE STRENGTH: 9.000 PSI COEFFICIENT OF EXPANSION:
37.5.sup.-6 IN/IN/.degree. F. VISUAL DEFECTS: NONE PERMITTED VISUAL
SCRATCHES: NONE PERMITTED C) PRIMER/BINDER: OPTICALLY CLEAR
PRIMER/BINDER WHICH WILL NOT REDUCE THE OPTICALLY CLEARNESS AND
TRANSMISSIVITY OF THE FINAL LAMINATE. A BOND STRENGTH OF 4-10 PSI
IN A PEEL CONFIGURATION AND 200- 800 PSI IN LAP SHEAR IS REQUIRED.
D) MOLDED SURFACES: TOOLING MOLD SURFACES MUST BE FLAT WITHIN 6-10
A PER INCH MAXIMUM, VISIBLE LIGHT AND HAVE A SURFACE QUALITY OF
80-50 (EQUIVALENT TO COMMERCIAL QUALITY FLOAT GLASS). E)
CLEANLINESS: MAINTAIN A CLASS 100 (M3.5) HEPA ENVIRONMENT
THROUGHOUT COMPLETE FABRICATION; MOLDING PROCESS, TRIMMING TO SIZE,
AND FINAL PACKAGING. F) ACCEPTANCE TESTS: VISUAL TEST: NO BUBBLES,
INCLUSIONS, OR STRIATIONS PERMITTED. TRANSMISSIVITY TEST PER (TBD)
METHOD: MINIMUM TRANSMISSIVITY OF (TBD) % OVER VISIBLE SPECTRUM.
FUNCTIONAL TEST: MOLDED SILICONE PAD (AFTER TRIMMING) MUST
OPTICALLY CONTACT, TO PRODUCE A VISUALLY TRANSPARENT INTERFACE WITH
A CLEAN GLASS SURFACE. THIS MUST OCCUR OVER 100% OF THE PAD SURFACE
AND WITHIN 30 SECONDS, AFTER PLACING PAD ON THE GLASS SURFACE,
WITHOUT ANY ADDITIONAL FORCE/PRESSURE OR WETTING AGENTS. GLASS
SURFACE MUST CONFORM TO THE SAME SPECIFICATIONS AS SPECIFIED FOR
THE MOLD SURFACES IN NOTE 1D. BOND TEST: (TBD) TEST METHOD TO
VERIFY PRIMER/BINDER BOND STRENGTH AS SPECIFIED IN SECTION 1C. 2.
APPLY PROTECTIVE FILM TO BOTH MOLDED SURFACES PRIOR TO TRIMMING PER
NOTE 3. 3. ALL EDGES TO BE CLEANLY TRIMMED WITHOUT DISTORTIONS,
BURRS, OR TRIMMING DEBRIS; TO INSURE FUNCTIONAL ACCEPTANCE TEST PER
NOTE 1F WILL BE MET. 4. PACKAGE INDIVIDUALLY TO MAINTAIN
CLEANLINESS, FLATNESS AND MOLDED SURFACE QUALITY. 5. SAMPLES MUST
BE APPROVED. 6. PRODUCTION LOT INSPECTION: AN AQL LEVEL SAMPLE WILL
BE PERFORMED BY THE QUALITY DEPT. TO VERIFY CONFORMANCE TO THE
ACCEPTANCE TESTS SPECIFIED IN NOTE 1F.
[0085] Although the present invention has been described using
silicone, the present invention may also be made using vinyl. In
another embodiment of the invention, color, such as a faint red or
blue, is added to the silicone rubber and/or stiffening layer to
provide an optical bandpass filter for improving ambient light. In
yet another embodiment of the invention, once the silicone rubber
sheet makes optical contact with a surface, such as, for example, a
prism surface, the silicone rubber sheet changes in color.
[0086] Conclusion
[0087] The present invention is not limited to the embodiment of a
biometric scanner. The present invention can be used with any
system that utilizes a silicone rubber sheet. The previous
description of the preferred embodiments is provided to enable any
person skilled in the art to make or use the present invention.
While the invention has been particularly shown and described with
reference to preferred embodiments thereof, it will be understood
by those skilled in the art that various changes in form and detail
may be made therein without departing from the spirit and scope of
the invention.
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