U.S. patent application number 13/713331 was filed with the patent office on 2014-06-19 for curved automatic-darkening filter.
This patent application is currently assigned to 3M INNOVATIVE PROPERTIES COMPANY. The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Britton G. Billingsley, Kenneth Jarefors, Kristina M. Magnusson, Joy L. Manske, Larissa Zuravskaja.
Application Number | 20140168546 13/713331 |
Document ID | / |
Family ID | 50930477 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140168546 |
Kind Code |
A1 |
Magnusson; Kristina M. ; et
al. |
June 19, 2014 |
Curved Automatic-Darkening Filter
Abstract
An automatic-darkening filter 10, 10' that comprises a first
polarizer 14, a second polarizer 18, a first liquid-crystal cell
16, and a sensor 64. The first polarizer 14 has a first
polarization direction, and the second polarizer 18 has a second
polarization direction. The liquid crystal cell 16 is disposed
between the first and second polarizers 14, 18 and contains first
and second optically-transparent, flexible, glass layers 40 and 42
with the liquid crystal layer 48 being located between these
layers. The sensor 64 detects incident light and causes a signal to
be sent, which causes molecular rotation within the liquid crystal
layer. The inventive automatic-darkening filter is beneficial in
that overall product weight can be reduced and the view field can
be increased.
Inventors: |
Magnusson; Kristina M.;
(Djurmo, SE) ; Billingsley; Britton G.; (St. Paul,
MN) ; Jarefors; Kenneth; (Borlange, SE) ;
Zuravskaja; Larissa; (Borlange, SE) ; Manske; Joy
L.; (Menomonie, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Assignee: |
3M INNOVATIVE PROPERTIES
COMPANY
ST. PAUL
MN
|
Family ID: |
50930477 |
Appl. No.: |
13/713331 |
Filed: |
December 13, 2012 |
Current U.S.
Class: |
349/14 ; 349/13;
349/25; 349/96 |
Current CPC
Class: |
A41D 13/1184 20130101;
B32B 38/1866 20130101; B29C 66/81421 20130101; B32B 2551/00
20130101; B32B 37/153 20130101; G02C 7/101 20130101; B29C 65/1406
20130101; B29C 66/81471 20130101; B29C 65/4845 20130101; G02F
1/13439 20130101; G02F 2001/1398 20130101; B29C 66/836 20130101;
G02F 1/1333 20130101; B29C 66/81264 20130101; G02F 1/1341 20130101;
G02F 1/13471 20130101; G02F 2201/56 20130101; B23K 9/322 20130101;
B29C 66/301 20130101; A61F 9/067 20130101; G02F 1/1396 20130101;
G02F 1/133305 20130101; G02F 1/13318 20130101; G02F 1/133528
20130101; A61F 9/023 20130101 |
Class at
Publication: |
349/14 ; 349/96;
349/25; 349/13 |
International
Class: |
G02F 1/13 20060101
G02F001/13; A41D 13/11 20060101 A41D013/11; G02F 1/139 20060101
G02F001/139 |
Claims
1. A switchable filter that comprises: (a) a first polarizer having
a first polarization direction; (b) a second polarizer having a
second polarization direction, which may be the same or different
from the first polarization direction; and (c) a first
liquid-crystal cell disposed between the first and second
polarizers, the liquid crystal cell containing first and second
optically-transparent flexible glass layers that are curved and
that have a first liquid crystal layer located between them.
2. The switchable filter of claim 1, wherein the switchable filter
has a viewing area of at least 100 cm.sup.2.
3. The switchable filter of claim 1, wherein the switchable filter
has a viewing area of at least 125 cm.sup.2.
4. The switchable filter of claim 1, further comprising a band pass
filter that attenuates IR and UV wavelength components of incident
light.
5. The switchable filter of claim 1, wherein the thickness of the
flexible glass layers is 10 to 200 micrometers.
6. The switchable filter of claim 1, wherein the thickness of the
flexible glass layers is 30 to 150 micrometers.
7. The switchable filter of claim 1, wherein the thickness of the
flexible glass layers is 75 to 125 micrometers.
8. The switchable filter of claim 1, wherein the flexible glass
layers have a curvature exhibiting a radius of 5 to 30
centimeters.
9. The switchable filter of claim 8, wherein the flexible glass
layers have a non-constant radius.
10. The switchable filter of claim 9, wherein the flexible glass
layers are parabolic, catenary, epicycloidal, or free form.
11. The switchable filter of claim 1, wherein the flexible glass
layers have inwardly facing surfaces that have transparent
conductive electrode layers.
12. The switchable filter of claim 1, wherein the curvature of the
first and second flexible glass layers each have a radius of 7 to
20 centimeters.
13. An automatic darkening filter that comprises the switchable
filter of claim 1 and further comprises: (d) a control circuitry;
and (e) a sensor that detects incident light and that causes a
signal to be sent to the switchable filter via the control
circuitry, which signal causes molecular rotation within the liquid
crystal layer.
14. The automatic darkening filter of claim 13, further comprising:
a third polarizer having a third polarization direction, which may
be the same or different from the first and second polarization
direction; and a second liquid-crystal cell disposed between the
second and third polarizers, the second liquid-crystal cell
containing third and fourth optically-transparent curved, flexible
glass layers and having a second liquid crystal layer being
disposed between the third and fourth flexible glass layers.
15. The automatic darkening filter of claim 14, wherein the third
polarizer has a polarization direction similar to the first
polarizer, and wherein the first liquid-crystal cell is a twisted,
nematic, liquid-crystal cell.
16. The automatic darkening filter of claim 13, wherein the first
liquid-crystal cell contains nematic molecules and has a twist
angle of 1 to 100 degrees.
17. The automatic darkening filter of claim 13, wherein the first
and second flexible glass layers of the first liquid-crystal cell
have electrodes that provide an electric field between the first
and second flexible glass layers in response to an activation
signal, each of the first and second flexible glass layers have
mutually facing surfaces that have an alignment layer that defines
first and second alignment directions, respectively.
18. The automatic darkening filter of claim 13, wherein the
automatic darkening filter is configured in concave curved
configuration, which is electrically switchable to a dark
transmission state over substantially its entire area.
19. The automatic darkening filter of claim 13, wherein the
automatic darkening filter has a viewing area between 10 cm.sup.2
and 600 cm.sup.2.
20. The automatic darkening filter of claim 19, wherein the
automatic darkening filter has a viewing area exceeding 125
cm.sup.2.
21. The automatic darkening filter of claim 13, wherein the
curvature of the first and second flexible glass layers has a
radius of 5 to 20 centimeters.
22. The automatic darkening filter of claim 13, wherein the
automatic darkening filter has a curvature that is not a constant
radius and is selected from the group consisting of parabolic,
catenary, epicycloidal, and free form.
23. The automatic darkening filter of claim 13, wherein the
thickness of the first and second optically-transparent, flexible,
glass layers is 10 to 200 .mu.m.
24. The automatic darkening filter of claim 13, wherein the
thickness of the first and second optically-transparent, flexible,
glass layers is 30 to 150 .mu.m.
25. The automatic darkening filter of claim 13, wherein the
thickness of the first and second optically-transparent, flexible,
glass layers is 75 to 125 .mu.m.
26. The automatic darkening filter of claim 14, wherein the first,
second, third, and fourth optically-transparent, flexible, glass
layers are assembled within a frame.
27. A welding shield that comprises: a protective shell that has an
opening into which the automatic-darkening filter of claim 13 is
disposed.
28. The welding shield of claim 27, wherein the automatic-darkening
filter has a curvature that has a radius of about 5 to 20
centimeters.
29. Goggles that comprise the automatic darkening filter of claim
13.
Description
[0001] The present invention pertains to a curved light filter that
changes from a light-transmission-state to a
dark-transmission-state in response to incident light. The curved
switchable filter has at least one liquid-crystal layer disposed
between thin, flexible, glass substrates.
BACKGROUND
[0002] Automatic darkening filters commonly have a switchable
filter that automatically changes from a light-transmission-state
to a dark-transmission-state in response to incident light. The
switching is generally achieved through use of a photodetector that
is located on, or as part of, personal protective equipment. The
photodetector recognizes the presence of the incident
light-to-be-filtered, and an electronic module generates a control
voltage that, when applied to the switchable filter, causes the
filter to change from the light-transmission-state to the
dark-transmission-state.
[0003] Automatic light filters have been designed which contain
liquid-crystal cells located between polarizing films. U.S. Pat.
No. 4,240,709 to Hornell describes a switchable filter that has a
single-twisted, nematic, liquid-crystal cell sandwiched between a
pair of mutually crossed polarizers. The liquid-crystal cells are
generally flat, optically-transparent, glass substrates that
include transparent electrode and alignment layers. The
liquid-crystal molecules orientate themselves in a particular
direction when a voltage is applied across the liquid-crystal cell
under the control of an electronic module. Many commercially
available products use this kind of switchable filter.
[0004] The use of an automatic-darkening filter in a protective
shield gives significant ergonomic benefits. Previously welders,
for example, had to "nod" their welding shield down when they
struck the welding arc to ensure that their eyes were protected
from the torch light. Automatic welding filters eliminated this
action since the welding shield could be continuously placed in the
down position. As a result, weld pattern quality has been generally
improved because more accurate electrode placement can be achieved.
Productivity improvements also have been noted since grinding and
rework have been correspondingly reduced.
[0005] Existing flat-glass automatic darkening filters can,
however, add considerable weight to the final product (such as
welding shield), which in turn, can create stress and tension in
the user's neck and shoulders. The rectangular configuration of the
typical glass sandwich construction also tends to limit the
wearer's field of view. Known welding filters have been generally
limited to rectangular constructions because of difficulties in
scribing and breaking the rigid glass substrates.
GLOSSARY
[0006] The terms set forth below will have the meanings as
defined:
[0007] "Automatic darkening filter" means a device that attenuates
light in response to an input from the light itself and without an
input from a person;
[0008] "Band pass filter" means a device that allows light of a
certain range of frequency(s) to pass therethrough but rejects the
passage of light of other frequencies;
[0009] "Curved" means not following a straight line when viewed in
cross-section;
[0010] "Deformation" with respect to a glass layer means being able
to be bent 5 millimeters (mm) over a cantilevered distance of 50 mm
from the fixed point without fracture;
[0011] "Electric field" means a region surrounding an electric
charge, which region can generate a force that can be exerted upon
charged particles or molecules;
[0012] "Flexible" means being able to withstand deformation into a
curved shape without breaking;
[0013] "Glass" means an inorganic amorphous non-crystalline solid
material that is capable of transmitting visible light;
[0014] "Glass layer" or "glass sheet" means glass that has
dimensions that are substantially greater in width and length than
in thickness;
[0015] "Juxtaposed" means to place side by side but not necessarily
in contact with each other;
[0016] "Liquid crystal layer" means a layer that has molecules in a
liquid phase which molecules have some orientational order with
respect to each other and have the ability to align in response to
an electric field;
[0017] "Low twist" means having a twist angle of less than 90
degrees;
[0018] "Nematic molecules" means molecules that exhibit parallel
axes in response to an electric field;
[0019] "Optically-transparent" means that visible light can pass
therethrough sufficiently to see the desired image on the opposing
side of the structure;
[0020] "Orthogonal" means at right angles thereto;
[0021] "Polarize" means to cause light to vibrate in a definite
pattern;
[0022] "Polarizer" means having the ability to polarize visible
light;
[0023] "Polarization direction" means an orientation resulting from
the polarization of light;
[0024] "Rotate" means to change orientation;
[0025] "Sensor" means a device that can detect the presence of a
defined light source and that can send a signal to another
device;
[0026] "Signal" means an electrical quantity such as voltage;
and
[0027] "Twist angle" means an angular difference in orientation
between two surfaces.
SUMMARY OF THE INVENTION
[0028] The present invention provides a switchable filter that
comprises a first polarizer, a second polarizer, and a first
liquid-crystal cell. The first polarizer has a first polarization
direction, and the second polarizer has a second polarization
direction. The second polarization direction may be the same or
different from the first polarization direction. The liquid-crystal
cell is disposed between the first and second polarizers. The
liquid crystal cell contains first and second
optically-transparent, flexible, glass layers and has a liquid
crystal layer located between the first and second curved,
optically-transparent flexible glass layers.
[0029] The inventive switchable filter is beneficial in that
overall product weight can be reduced relative to known
commercially-available products. Reductions in weight are achieved
by the, low weight of the flexible glass layers. These flexible
layers tend to be thinner than the flat glass substrates that have
been used in previous conventional products. Further, the inventive
switchable filter can be fashioned to have a non-rectangular shape,
which improves the user's view field. The user can be provided with
an expanded peripheral range of vision in both the horizontal and
vertical dimensions. The switchable filter also may be configured
in various shapes, for example, to follow the contours of the
wearer's face and to accommodate goggles or eye glasses.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is an exploded view of a curved, switchable filter 10
according to the present invention;
[0031] FIG. 2 shows an exploded view of a curved, switchable filter
10' according to the present invention.
[0032] FIG. 3 is a schematic cross-section of a curved
liquid-crystal cell 34 that may be used in a switchable filter
according to the present invention;
[0033] FIG. 4 is a block diagram of the switchable filter 10 (or
10') disposed in an automatic filter darkening apparatus 60
according to the present invention;
[0034] FIG. 5 is a perspective view of welding helmet 68 according
to the present invention;
[0035] FIG. 6 is a perspective view of protective shield 72 in
accordance with the present invention; and
[0036] FIG. 7 shows a perspective view of protective goggles 76 in
accordance with the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0037] In the practice of the present invention, flexible glass
layers define an enclosed area where liquid-crystal molecules are
free to rotate under the influence of an electric field to produce
a light-filtering effect. The use of flexible glass layers in the
manufacture of a switchable filter enables the components of the
switchable filter to be laminated together in curved form. This
assembly enables a larger viewing area to be achieved for the same
(or even less) weight.
[0038] FIG. 1 shows a curved, switchable, filter 10 where an
outermost component of the filter 10 is a band pass filter 12 that
serves to attenuate the infra-red (IR) and ultra-violet (UV)
wavelength components from a high-intensity incident light. The
band pass filter 12 can be an interference filter that reflects the
IR radiation and absorbs the UV-A, -B and -C components of the
incident light. The band pass filter 12 also may be a combination
of separate IR and UV reflecting and/or absorbing filters. The
curved, switchable filter 10 also includes a first polarization
filter 14, a first optically-rotating liquid-crystal cell 16, and a
second polarization filter 18. The polarization filters 14 and 18
have substantially orthogonal polarization directions, where the
polarization direction of the first polarization filter 14 is
approximately 90.degree. to the polarization direction of the
second polarization filter 18 but in a parallel place. The first
optically-rotating, liquid-crystal cell 16 may be a twisted,
nematic, liquid-crystal cell located between the first and second
orthogonally-related polarization filters 14 and 18. In parallel
alignment with these components is a second liquid-crystal cell 20,
disposed between a pair of polarization filters 18 and 22. The
polarization filters 18 and 22 each have substantially parallel
polarization directions. The parallel polarization directions
enable the cell to be dark when no voltage is applied and light
when there is voltage. The default dark-state provides a safety
function that notifies the user that the product is turned "off".
Each of the liquid crystal cells 16 and 20 are provided with
connectors 24 and 26, respectively, by which control voltages can
be applied to these cells. The application of a voltage to
connectors 24 creates an electric field between the flexible glass
layers of the liquid-crystal cell 16. The nematic, liquid-crystal
molecules align with the electric field perpendicular to the
defining surfaces that enclose the major sides of the cell. This
perpendicular alignment, rather than a parallel one, in the excited
cell achieves a darkened state. Thus, when a control voltage is
applied to the liquid-crystal cell 16, a filter effect is achieved.
The liquid-crystal cell controls the polarization of the light, and
the light becomes absorbed by the polarizer. The degree of rotation
of the nematic molecules may be controlled by varying the control
voltage, and thus the corresponding filter effect also may be
controlled. The result is that the liquid-crystal cell 16 is in a
light transmission state in the absence of an applied voltage and
is in a dark transmission state in the presence of the applied
voltage. The voltage levels may be different for varying cell
designs, depending on the liquid crystal materials used, cell gap
geometries, etc. In use, the light transmission state corresponds
to any of welding shades 2 to 4, and the dark transmission state,
which can be user-selectable, corresponds to any of welding shades
7 to 14. The welding shades have been defined in eye protection
standards ANSI 287.1:2010 and 169:2001--see also EN 379:2003.
[0039] FIG. 2 shows an exploded view of a curved,
automatic-darkening filter 10' that comprises the liquid-crystal
cells 16, 20, and 28. The first liquid-crystal cell 16 is disposed
between the first and second polarization filters 14 and 18, the
second liquid-crystal cell 20 is disposed between first and third
polarization filters 18 and 22, and the third liquid-crystal cell
28 is disposed between polarization filters 30 and 14. The two
liquid crystal cells 16 and 28 may be substantially identical, but
they are generally rotated about 180.degree. with respect to each
other, to give less optical variation for different viewing angles.
The application of a voltage to connectors 24 and 32 creates an
electric field between transparent conductive electrodes. The
nematic, liquid-crystal molecules align with the electric field
perpendicular to the surfaces that enclose the molecules to cause
the cells to restrict light transmission. The alignment directions
of the liquid crystal cells 16 and 28 are arranged substantially
parallel to and oriented asymmetrically with respect to one
another. The advantages of positioning two substantially-identical,
liquid-crystal cells together, such that the face-to-face molecule
alignment directions are substantially perpendicular, compensates
for an angular dependency of the filtering effect. Variations in
shade (improved homogeneity) in the dark state may be achieved
using offset polarizers, that is polarizers offset by about 1 to 20
degrees--see U.S. Pat. No. 7,884,888 to Magnusson et al. The offset
polarizers may eliminate an uneven shade of the viewing area caused
by variations in cell-gap geometry, unwanted birefringence in the
adhesive layers of the construction, and different viewing
angles.
[0040] FIG. 3 shows a liquid-crystal cell 34 such as the first,
second, and third cells 16, 20, and 28. The laminar construction
contains two optically-transparent flexible glass layers 40 and 42.
The present invention can be implemented using a variety of such
glass layers. The thickness of each of the layers may be about 10
micrometers (.mu.m) to 200 .mu.m, more typically about 30 to 150
.mu.m, and still more typically about 75 to 125 .mu.m. The flexible
glass layers 40 and 42 may be supplied in sheet or roll form. The
curved layers 40, 42 typically have a radius of less than infinite
curvature, typically about 5 to 30 centimeters (cm), more typically
about 7 to 20 cm. The curvature also may exhibit a non-constant
radius, for example, it may be parabolic, catenary, epicycloidal,
and free form. On the inwardly facing surfaces of the
optically-clear glass layers 40 and 42 are transparent conductive
electrode layers 44 and 46, respectively, (e.g., indium tin oxide
layers). By applying a voltage to the electrodes 44 and 46, an
electric field is created across the liquid-crystal layer 48 to
shift the orientation of the liquid crystal molecules. Juxtaposed
against the electrodes 44 and 46 are alignment layers 50 and 52,
respectively, for instance, a polyimide layer that has been treated
mechanically, such as by brushing or rubbing, in specific alignment
directions. The alignment layers 50 and 52 are spaced apart using
equally sized spacers 54, inside the cells. The cell edges can be
sealed using an edge adhesive 56, such as Norland 68, available
from Norland Products, Cranbury, N.J. Before the cell is completely
sealed, the nematic molecules 58 are pumped into the gap 48 between
the layers 50 and 52. The alignment layers 50 and 52 force the
liquid-crystal nematic molecules 58 to take specific angular
positions at the surfaces so that the molecules are twisted through
their respective twist angle between these surfaces. The rotational
condition of the nematic liquid-crystal 58 permits or blocks
light-transmission through the cell. The liquid crystals used may
be of the nematic type with a .DELTA.n (difference between the
refractive index of ordinary and extraordinary light rays) of about
08 to 14 sandwiched between the two optically-clear flexible glass
layers 40 and 42. The gap between layers 50 and 52 typically is
about 3-5 .mu.m. The optically-transparent flexible glass layers 40
and 42 used in the present invention generally have a
substantially-uniform optical transmission, typically greater than
80% in the wavelength range of 380 nanometers (nm) to 750 nm. The
glass layer may be formed by an overflow downdraw method to have a
thickness as indicated above. The composition of the glass layer
may be various glass compositions of silicate glass and the like,
such as silica glass and borosilicate glass. A non-alkali glass may
include glass that does not substantially contain an alkali
component, specifically, glass containing an alkali metal oxide of
1000 parts per million (ppm) or less (preferably, of 500 ppm or
less, and more preferably, of 300 ppm or less). The glass layer may
have a protective sheet juxtaposed against it. When winding the
glass layer, the protective sheet prevents occurrence of the flaws,
which is caused by contact of one part of the glass layer with
another. The protective sheet absorbs external pressure applied to
the glass roll. The thickness of the protective sheet may be from
10 .mu.m to 2000 .mu.m. The protective sheet may be an ionomer
film, a polyethylene film, a polypropylene film, a polyvinyl
chloride film, a polyvinylidene chloride film, a polyvinyl alcohol
film, a polypropylene film, a polyester film, a polycarbonate film,
a polystyrene film, a polyacrylonitrile film, an ethylene vinyl
acetate copolymer film, an ethylenevinylalcohol copolymer film, an
ethylene-methacrylic acid copolymer film, a nylon film (polyamide
film), a polyimide film, cellophane or other buffer materials made
of resins. Conductivity may be imparted to the protective sheet by
adding a component for imparting the same, such as polyethylene
glycol, into the protective sheet. In a case where the protective
sheet is made of inserting paper, it is possible to impart the
conductivity by adding conductive fiber. Further, it is possible to
impart the conductivity also by laminating a conductive layer, such
as an indium-tin-oxide (ITO) film, on a surface of the protective
sheet. See U.S. Pat. No. 8,241,751 to Tomamoto et al.; see also
U.S. Pat. No. 7,735,338 to Mueller et al. and U.S. Patent
Application Publication 2011/0059296. An example of a
commercially-available flexible glass is Schott D263T glass.
[0041] Liquid crystal cells 16, 20, and 28 may be a twisted,
nematic, liquid-crystal cell type cell that provides a "fail-safe"
intermediate transmission state in the case of electronic module
failure. An automatic darkening filter that has low-twist,
liquid-crystal, cells is described in U.S. Pat. No. 6,097,451 to
Palmer et al.; see also U.S. Pat. No. 5,825,441 to Hornell et al.
The twisted, nematic, liquid-crystal cell may have a twist angle of
less than 100 degrees, typically zero or 1 to 99 degrees. The
liquid-crystal cell also may have a low twist angle of 1 to 85
degrees. More specifically, the twist angle of a low-twist,
liquid-crystal, cell may be about 30 to 70 degrees. A "fail-safe"
liquid crystal cell is in many ways similar in design to the
low-twist, liquid-crystal, cell, but its operation is different
because it is sandwiched between parallel polarizers, as opposed to
crossed or orthogonal polarizers. Liquid crystal cell 20 is in a
dark transmission state (a nearly optically-opaque state in which
the majority of the incident light is blocked) when no voltage is
applied to the connectors 26. Liquid crystal cell 20 may become
optically transparent when a certain voltage is applied.
[0042] FIG. 4 is a block diagram of an automatic darkening filter
(ADF) 60. Automatic darkening filter 60 includes a curved
switchable filter 10 (or 10') that has offset polarizers of the
type described above with respect to FIGS. 1 and 2. Switchable
filter 10 is mounted in protective headgear 62 that would be worn
by the user during a welding procedure or other situation where
protection of the type provided by switchable filter 10 is desired.
ADF 60 also includes a sensor 64 for detecting light incident upon
the front surface of filter 10, such as a welding arc. The sensor
detects incident light and causes a signal to be sent which causes
molecular rotation within the liquid crystal layer. The sensor 64
may be provided with a polarizing member that precludes non-normal
light from activating the sensor. Such a device prevents light from
other welding torches and sensors from reaching the sensor--see
U.S. Pat. No. 6,934,967 to Migashita et al. Control circuitry 66
receives signals from the sensor 64 pertaining to the presence or
absence of incident light and causes corresponding control voltages
to be applied to filter 10, thus controlling the degree of shade
provided by filter 10. When the presence of a welding arc or other
source of incident light is detected by sensor 64, for example,
control circuitry 66 may cause a control voltage to be applied to
liquid-crystal cells 16 and 20 (FIGS. 1 and 2) while eliminating
the voltage to guest-host cell 28 (FIG. 2). This causes the filter
60 to darken and protect the user from the glare of the incident
light. In the absence of a welding arc or other source of incident
light, control circuitry 66 may reduce or eliminate the applied
voltage to liquid crystal cells 16 and 20, thus causing the filter
to become more open to light. This increase in light transmittance
enables a welder, for example, to perform a welding operation and
also to perform tasks outside the welding area without removing the
protective facemask or helmet. In addition, the filter construction
described herein results in increased homogeneity in the dark state
as seen by the user over a large angular range. The switchable
filter 10, sensor 64, and control circuitry 66 are typically
supported on a protective headgear as a unit, typically a
replaceable unit that is mounted in the shell directly in front of
the wearer's eyes when the helmet is worn by the user. The unit may
take the form of a rectangular (or other shaped) frame or housing
that supports the filter, sensor, and circuitry. Examples of helmet
shells may be seen, for example, in U.S. Pat. Nos. 6,185,739,
5,533,206, 5,191,468, 5,140,707, 4,875,235, and 4,853,973. The
welding helmets also can have clean air supplied to their interior
and thus may include a face seal to separate a breathing zone from
the ambient air. An example of such a face seal is shown in U.S.
Pat. No. 7,197,774 to Curran et al.; see also U.S. Design Pat. Nos.
D517,744, D517,745, D518,923, D523,728, and D532,163; and U.S.
Patent Publication Nos. 2006-0101552, and 2006-0107431.
[0043] FIG. 5 is a perspective view of a welding helmet 68 that has
a helmet body 70 that contains an automatic-darkening filter
apparatus 60 mounted within an opening in the helmet body 70. The
helmet body 70 may include a crown member that engages the wearer's
head when the device 68 is being donned. An example of a suitable
crown member is described in U.S. Pat. No. 7,865,968 to Lilenthal
et al.; see also, U.S. Patent Application 2010/229286 A1 to Ahlgren
et al. The automatic-darkening filter apparatus 60 includes curved
automatic darkening filter 10 that is placed in position to
intercept electromagnetic radiation (e.g., visible light, UV light,
IR, etc.). The automatic-darkening filter 60 may be positioned in
the shield body 70 so that it is directly in front of the wearer's
eyes when the shield is worn by the user. The automatic-darkening
filter 60 may include an electronic control unit 66 (FIG. 5) for
receiving and controlling the various signals to the curved
automatic welding filter 10 and, more particularly, liquid crystal
cells 16, 20 and 28, via connectors 24, 26 and 32, respectively
(FIG. 2)--see for example, U.S. Patent Application No. US2010265421
(Sundell). The electronic control unit also may include an input
detector that is capable of detecting at least an input from the
presence of high intensity light. The detector may be located
physically close to some or all of the other components (hardware,
etc.) of automatic darkening filter apparatus 60 or may be located
physically remote from some or all of these components. The
detector can be implemented using various photodetector devices and
technologies. Alternatively, an input that indicates the presence
of high-intensity light can be generated from an electronic control
unit in response to an activation signal generated by, for example,
a welding tool or torch--see WO2007/047264 to Garbergs, et al.
[0044] FIG. 6 is an embodiment of the present invention where the
curved, switchable filter 10 of the present invention, is mounted
in a suitable face-covering apparatus 72. The switchable filter 10
can be mounted to the face-covering apparatus such that it is
rotatable about pivot point 73. Alternatively, the curved automatic
welding filter 10 may be mounted in an automatic-darkening filter
apparatus disposed in a set of goggles 76 as depicted in FIG.
7.
[0045] Switchable filters of the present invention may be curved
about one, two, or three axis. Typically a switchable filter used
in a welding helmet (FIG. 5) would be curved about one or two axes.
The physical properties of the flexible glass layers allow for
curved switchable filters to be manufactured which have a radius of
curvature of about 5 cm to 20 cm, and a viewing area of about 10 to
600 square centimeters (cm.sup.2), more typically 30 cm.sup.2 to
250 cm.sup.2. Conventional welding filters typically have a viewing
area of about 50 to 100 cm.sup.2. The present invention may enable
switchable filters having a viewing area of at least 100 cm.sup.2
to 125 cm.sup.2 to be provided.
[0046] The automatic darkening filter apparatus of the present
invention can be used in connection with industrial operations, for
example welding (e.g. arc welding, torch welding, acetylene
welding), cutting (e.g. laser cutting, acetylene cutting), brazing,
soldering and the like. They also can be used in connection with
medical procedures involving high intensity light (e.g. laser
surgery, hair removal, tattoo removal, light-curing of dental
resins, etc.) and other uses as well. One or more
automatic-darkening filter apparatuses may be provided in any other
suitable equipment or articles and for other applications. For
example, an automatic-darkening filter apparatus may be supplied as
part of protective eyewear rather than a full-face coverage helmet.
Alternatively, an automatic darkening filter apparatus may be
provided in a hand-held device, or in a window or aperture allowing
inspection of a room, enclosure, machinery space, etc., in which
high intensity light may be present.
EXAMPLE
Liquid Crystal Cell Assembly
[0047] A curved liquid crystal cell for an automatic welding filter
was made in the following manner.
[0048] The starting flexible glass layer was a 0.1 mm thick D263T
glass from Schott Glass of Schott Glas Export, GmbH, located at
Rheinallee 145, 55120 Mainz, Germany. The glass was sputter
deposited with indium tin oxide (ITO). The conductivity of the
coated ITO was roughly 100 ohm/square. The ITO glass was coated
with a thin layer of polymide polymer. A commercially-available
polyimide alignment material was coated onto the glass using a spin
coating technique. The dried coating thickness was between 80
nanometers (nm) and 200 nm. The thin polymide layer was aligned by
brushing it with using a rotating felt cloth. This brushed
polymide, ITO/glass piece was cut into pieces for the top and
bottom portion of the liquid crystal cell. A first piece (top) of
glass was rotated 90.degree. from the orientation of the second
(bottom) piece of glass to provide proper alignment.
[0049] The curved, liquid-crystal cell was formed using a metal
cylinder that had a radius of approximately 90 millimeters (mm) as
the template. The bottom portion of the cell, the ITO glass having
the rubbed polyimide coating, was taped to the metal cylinder using
3M Magic Tape.TM.. An edge adhesive (UV curing Norland 68 optical
adhesive) was applied to the bottom portion using a syringe and
needle. A twisted, nematic, liquid-crystal mixture was combined
with 1% by weight of 4 micrometer (.mu.m) ceramic spacer beads. The
liquid crystal/spacer bead mixture was placed on the bottom portion
of the cell using a pipette. The top portion of the cell was
attached to the bottom portion at the leading edge using 3M
Removable Tape.TM.. A polyester film, that was attached to the
metal cylinder on one end, was used to wrap and curve the top
portion of the cell onto the bottom portion. A rubber roll was used
to compress the top portion onto the bottom portion. Tension was
maintained on the polyester film to keep the components of the cell
in close contact. Using a UV light source for 5 minutes, the UV
curing edge adhesive was then cured. The completed cell was then
removed from the cylinder by removing the polyester film and pieces
of tape. Polarizing films were attached to the bottom and top
portions using a pressure-sensitive adhesive. The polarizing films
were orthogonal to each other and corresponded to the alignment
that was rubbed into the polyimide layer. Copper tape, with
conductive adhesive, was attached to the ITO on the top portion,
and another piece of copper tape with conductive tape was attached
to the ITO on the bottom portion. A 10 volt potential was placed
across the cell through the copper tape. The cell switched from a
light state to a dark state when the voltage was applied. The
dimensions of the finished cell were approximately 75 mm wide and
75 mm long (5625 mm.sup.2; 56.25 cm.sup.2) with a curvature that
was slightly less than the 100 mm radius of the original
cylinder.
[0050] This invention may take on various modifications and
alterations without departing from its spirit and scope.
Accordingly, this invention is not limited to the above-described
but is to be controlled by the limitations set forth in the
following claims and any equivalents thereof.
[0051] This invention also may be suitably practiced in the absence
of any element not specifically disclosed herein.
[0052] All patents and patent applications cited above, including
those in the Background section, are incorporated by reference into
this document in total. To the extent there is a conflict or
discrepancy between the disclosure in such incorporated document
and the above specification, the above specification will
control.
* * * * *