U.S. patent application number 17/448569 was filed with the patent office on 2022-02-03 for curved eye protection shield for welding protection.
The applicant listed for this patent is 3M Innovative Properties Company. Invention is credited to Britton G. Billingsley, Laurent Froissard, Kenneth Jarefors, Kristina M. Magnusson.
Application Number | 20220031514 17/448569 |
Document ID | / |
Family ID | 1000005854250 |
Filed Date | 2022-02-03 |
United States Patent
Application |
20220031514 |
Kind Code |
A1 |
Magnusson; Kristina M. ; et
al. |
February 3, 2022 |
CURVED EYE PROTECTION SHIELD FOR WELDING PROTECTION
Abstract
A curved eye protection shield for welding protection. The eye
protection shield has an electrically switchable darkening filter
and a protective cover. The darkening filter has eye facing major
inner and outer surfaces, and the protective cover has major inner
and outer surfaces. The protective cover is provided for
arrangement on the inner surface of the darkening filter. The inner
and outer surface of the darkening filter are equidistant, whereas
the inner and outer surface of the protective cover are
non-equidistant. The invention is advantageous in that it provides
an eye protection shield having a minimized refractive power.
Inventors: |
Magnusson; Kristina M.;
(Djurmo, SE) ; Jarefors; Kenneth; (Falun, SE)
; Froissard; Laurent; (Cottage Grove, MN) ;
Billingsley; Britton G.; (St. Paul, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M Innovative Properties Company |
St. Paul |
MN |
US |
|
|
Family ID: |
1000005854250 |
Appl. No.: |
17/448569 |
Filed: |
September 23, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
16098155 |
Nov 1, 2018 |
11129748 |
|
|
PCT/US2017/030344 |
May 1, 2017 |
|
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17448569 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 9/06 20130101; A61F
9/067 20130101; A61F 9/061 20130101 |
International
Class: |
A61F 9/06 20060101
A61F009/06 |
Foreign Application Data
Date |
Code |
Application Number |
May 4, 2016 |
EP |
16168229.9 |
Claims
1. A curved eye protection shield for welding protection,
comprising an electrically switchable darkening filter and a
protective cover, wherein the protective cover is removably
attached to the darkening filter, the darkening filter having a
refractive power, an eye facing major inner surface and, opposite
thereof, a major outer surface, and the protective cover having a
major inner surface and, opposite thereof, further a major outer
surface, wherein one of the inner and outer surface of the
protective cover faces the respective outer or inner surface of the
darkening filter, and wherein the inner and outer surface of the
protective cover are shaped to compensate for the refractive power
of the darkening filter.
2. The curved eye protection shield of claim 1, wherein an absolute
value of a total refractive power of a combination of an inner
protective cover, the darkening filter and an outer protective
cover is lower than the absolute value of each of the inner
protective cover, the darkening filter and the outer protective
cover individually.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/098,155, filed Nov. 1, 2018, now allowed;
which is a US 371 application of International Application No.
PCT/US2017/030344, filed May 1, 2017; which claims priority to EP
Application Serial No. 16168229.9, filed May 1, 2016, the
disclosures of which are incorporated by reference in their
entirety herein.
FIELD OF THE INVENTION
[0002] The invention relates to a curved eye protection shield for
welding protection, and in particular to a curved eye protection
shield which comprises an electrically switchable darkening filter
having two equidistant major surfaces, and a protective cover
having two non-equidistant major surfaces.
BACKGROUND ART
[0003] 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-state.
[0004] 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
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.
[0005] 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 eliminate this
action since the welding shield can be left in position
continuously.
SUMMARY OF THE INVENTION
[0006] The invention relates to a curved eye protection shield for
welding protection. The eye protection shield comprises an
electrically switchable darkening filter and a protective cover.
The darkening filter has an eye facing major inner surface and a
major outer surface. The inner surface and the outer surface of the
darkening filter are opposite of each other, meaning facing in
opposite directions. Further, the protective cover has a major
inner surface and further a major outer surface. The inner surface
and the outer surface of the protective cover are opposite of each
other, meaning facing in opposite directions. The protective cover
may be arranged relative to the darkening filter directly on or
spaced adjacent the outer surface of the darkening filter, or on or
spaced adjacent the inner surface of the darkening filter.
Accordingly, the outer surface of the protective cover faces the
inner surface of the darkening filter or, alternatively, the inner
surface of the protective cover faces the outer surface of the
darkening filter. The inner and outer surface of the darkening
filter are equidistant, whereas the inner and outer surface of the
protective cover are non-equidistant. The electrically switchable
darkening filter therefore has two equidistant major surfaces, and
the protective cover has two non-equidistant major surfaces.
[0007] Because the inner and outer surface of the darkening filter
being equidistant the portion of the darkening filter formed by the
inner and outer surface has a uniform thickness (defined between
the inner and outer surface of the darkening filter). Further,
because the inner and outer surface of the protective cover being
non-equidistant the portion of the protective cover formed by the
inner and outer surface has a non-uniform thickness (defined
between the inner and outer surface of the protective cover).
[0008] The invention is advantageous in that it provides for a
curved eye protection shield having no or a minimized refractive
power. Further, the invention allows for compensating a refractive
power of a curved darkening filter. The invention further provides
for a maximized convenience for a wearer of a welding protector
having a curved darkening filter, in providing an eye protector
with minimized refractive power.
[0009] For the purpose of the present specification the term
"equidistant" refers to two curves or surfaces which extend at the
same distance relative to each other along their length or across
their areas, respectively. For example, two equidistant planes are
parallel to each other.
[0010] Preferably the darkening filter is switchable between a
light-transmission-state in which a substantial portion of light
can pass through the darkening filter and a dark-state in which a
substantial portion of light is blocked from passing through the
darkening filter. In the light-transmission-state the transmittance
of the darkening filter may be within a range of about 1% to about
20%, in more particular within a range of about 5% to about 10%,
whereas in the dark-state the transmittance of the darkening filter
may be within a range of about 0,0005% to about 0.1%.
[0011] In one embodiment the inner and outer surface of the
darkening filter are cylindrical and concentric relative to each
other. The inner and outer surface of the darkening filter
preferably form surfaces of a portion of the darkening filter which
serve for the user, for example a welder, to see through during
use. This portion of the darkening filter therefore may also be
referred to as the "see-through portion of the darkening filter".
The darkening filter may have further portions, such as one or more
structures for stiffening the darkening filter or for mounting the
darkening filter within the eye protection shield, for example.
Such further portions are typically not used for seeing through and
further may not have equidistant inner and outer surfaces.
[0012] Preferably, the inner and outer surface of the protective
cover are cylindrical. However, the cylinder shape of both, the
inner and outer surface of the protective cover, are preferably in
an off-center relationship to each other. The cylindrical shape of
the inner and outer surface of the protective cover may have the
same radius. Again, the inner and outer surface of the protective
cover preferably form surfaces of a portion of the protective cover
which serve for the user, for example a welder, to see through
during use. This portion of the protective cover therefore may also
be referred to the "see-through portion of the protective cover".
The protective cover may have further portions, such as one or more
structures for stiffening the protective cover or for mounting the
protective cover within the eye protection shield, for example.
Such further portions are typically not used for seeing
through.
[0013] In a further embodiment the protective cover is pre-shaped
so that the outer surface of the protective cover corresponds in
shape to the inner surface of the darkening filter. Further, the
protective cover may be pre-shaped so that the outer surface of the
protective cover corresponds to a proportionally reduced shape of
the inner surface of the darkening filter. Such a proportionally
reduced shape may be provided to account for a space between the
darkening filter and the protective cover. For example, the radius
of the outer surface of the protective cover may be smaller than
the radius of the inner surface of the darkening filter. Further,
the darkening filter and the protective cover may be arranged
relative to each other such that the inner surface of the darkening
filter and the outer surface of the protective cover are
concentric. Accordingly, the space between the inner surface of the
darkening filter and the outer surface of the protective cover has
a uniform thickness.
[0014] In an alternative embodiment, the protective cover is
pre-shaped so that the inner surface of the protective cover
corresponds in shape to the outer surface of the darkening filter.
Further, the protective cover may be pre-shaped so that the inner
surface of the protective cover corresponds to a proportionally
enlarged shape of the outer surface of the darkening filter. Such a
proportionally enlarged shape may be provided to account for a
space between the darkening filter and the protective cover. For
example, the radius of the inner surface of the protective cover
may be greater than the radius of the outer surface of the
darkening filter. Further, the darkening filter and the protective
cover may be arranged relative to each other such that the outer
surface of the darkening filter and the inner surface of the
protective cover are concentric. Accordingly, the space between the
outer surface of the darkening filter and the inner surface of the
protective cover has a uniform thickness.
[0015] For example, the protective cover may be molded (for example
injection molded) from an optically clear plastic material. The
inner and outer surface of such a molded protective cover
preferably naturally has the cylindrical shape, in particular
without being under mechanical tension.
[0016] In one embodiment the protective cover has a first thickness
adjacent a margin and a second thickness in the middle between two
opposite margins. The margins preferably refer to lateral margins
of the see-through portion. The lateral ends of the see-through
portion are opposite ends in a horizontal dimension of the eye
protection shield. The term "horizontal" refers to a dimension of
the eye protection shield that is defined by a parallel to the
centers of the wearer's eyes, when the eye protection is worn by a
wearer. Further the eye protection shield has a vertical dimension.
The term "vertical" refers to a dimension perpendicular the
horizontal dimension and perpendicular to the optical axis of the
wearer's eyes in a straight view orientation. The first and second
thickness each are preferably uniform along the vertical
dimension.
[0017] The second thickness is preferably greater than the first
thickness. The thickness of the protective cover gradually
increases from the first toward the second thickness. The second
thickness may be within a range of about 1 mm to 3 mm, preferably
1.7 mm or about 1.7 mm.
[0018] In one embodiment the cylindrical shape of the inner and
outer surface of the protective cover are based on the same radius.
The radius may be within a range of 70 mm to 150 mm, more
preferably within a range of 80 mm to 100 mm, most preferably 85 mm
or about 85 mm. Further, the center axes of the cylindrical shape
of each the inner and outer surface of the protective cover are
preferably parallel offset from each other on a normal on the inner
and outer surface. Preferably the offset is within a range of 0.5
mm to 3 mm, more preferably 1.7 mm or about 1.7 mm.
[0019] In one embodiment the protective cover is removably attached
to the darkening filter. The darkening filter and the protective
cover are preferably arranged with a (preferably uniform) space
between the inner surface of the darkening filter and the outer
surface of the protective cover. Alternatively, the darkening
filter and the protective cover are arranged with a (preferably
uniform) space between the outer surface of the darkening filter
and the inner surface of the protective cover. The eye protection
shield may comprise a spacer for providing such a space. The spacer
may be formed by one or more protrusions (for example a
circumferential rim or circumferentially distributed pins) that
is/are arranged adjacent a margin of the inner or outer surface of
the darkening filter or adjacent a margin of the inner or outer
surface of the protective cover. Further, the protective cover may
be mounted in a welding protector in which also the darkening
filter is integrated. The protective cover may in this embodiment
mounted at a space relative to the darkening filter. Alternatively,
the darkening filter and the protective cover may, for example, be
bonded to each other by an optically clear adhesive.
[0020] For the purpose of the present specification any surface of
the spacer does not form part of the inner or outer surface of the
darkening filter and/or the protective plate, although the spacer
may be monolithically formed with the darkening filter and/or the
protective cover.
[0021] In one embodiment the protective cover is made of a plastic
material selected from among polycarbonate (PC), polymethyl
methacrylate (PMMA), polystyrene (PS) and styrene acrylonitrile
copolymer (SAN). Preferably, the protective cover is molded, in
particular injection molded, in the cylindrical shape. In more
particular, the protective cover may be molded, in particular
injection molded, such that the inner and outer surface are in the
cylindrical shape. In a further embodiment the darkening filter
comprises liquid crystals arranged in direct contact between a
first and second alignment layer, the first and second alignment
layer being arranged on a first and a second transparent electrode
layer, respectively, and the first and second transparent electrode
layer are arranged on a first and a second transparent layer,
respectively, and wherein the first and a second transparent layer
are each provided with a polarizer. The first and second
transparent layer, first and second electrode layer and first and
second alignment layer form a liquid crystal cell. In a preferred
embodiment the eye protection shield comprises two liquid crystal
cells arranged in optical sequence. This means that a light beam
impinging on perpendicular on the eye protection shield passes both
liquid crystal cells at least in the light-transmission-state. In
such an embodiment one polarizer may be arranged between the two
liquid crystal cells and the so formed sandwich of the two liquid
crystal cells may be arranged between further two polarizers.
Accordingly, such an embodiment has three polarizers and two liquid
crystal cells. This is advantageous to provide a maximized
darkening effect in the dark-state and a sufficient light
transmission state in the light-transmission-state.
[0022] The eye protection shield is preferably connected to a
sensor and a control circuit. In particular, the control circuit is
preferably electrically connected to the first and second electrode
layer of the liquid crystal cell for powering liquid crystal cell
dependent on a signal provided by the sensor. The control circuit
may for example apply a voltage to the first and second electrode
layer for causing the liquid crystals to orient in a particular
orientation, or switch off the voltage so that the liquid crystals
reset to their preferred orientation provided by the first and
second alignment layer. Thereby the darkening filter is switched
between the light-transmission-state or the dark-state. Preferably,
the sensor, the control circuit and the darkening filter cooperate
such that light of a certain minimum intensity received by the
sensor causes the darkening filter to switch in the dark-state, and
light of an intensity below that minimum intensity causes the
darkening filter to switch in the light-transmission-state.
[0023] In a further embodiment the eye protection shield has a band
pass filter for attenuating the infra-red (IR) and ultra-violet
(UV) wavelength components from high-intensity incident light. The
band pass filter can be an interference filter that reflects the IR
radiation and absorbs the UV-A, -B and -C components of the
incident light.
[0024] In one embodiment the curved eye protection shield the
protective cover is an "inner protective cover". The inner
protective cover is arranged with the outer surface facing the
inner surface of the darkening filter. Alternatively, the
protective cover may be an "outer protective cover". The outer
protective cover is arranged with the inner surface facing the
outer surface of the darkening filter. It is noted that the
invention encompasses an eye protection shield having both, an
inner and an outer protective cover. In other words, the presence
of an inner protective cover does not exclude the additional
presence of an outer protective cover.
[0025] In such an embodiment the outer protective cover may have
non-equidistant inner and outer surfaces as described above or
equidistant inner and outer surfaces as described in the
following.
[0026] Accordingly, in one embodiment the eye protection shield
further (in addition to the inner protective cover having
non-equidistant inner and outer surfaces) has an outer protective
cover being arranged on or adjacent the outer surface of the
darkening filter. The outer protective cover may be provided to
protect the darkening filter from dust and splashes of hot or
glowing material during welding. Preferably, the outer protective
cover is removably attached to the darkening filter. Therefore, the
outer protective cover can be replaced if necessary. The outer
protective cover may have a major inner surface and, opposite
thereof, a major outer surface. The inner and outer surface of the
outer protective cover may be equidistant. In other words, a
thickness defined between the inner and outer surface of the outer
protective cover is preferably uniform. The inner and outer surface
of the outer protective cover preferably form surfaces of a portion
of the outer protective cover which serve for the user, for example
a welder, to see through during use. This portion of the outer
protective cover therefore may also be referred to the "see-through
portion of the outer protective cover". The outer protective cover
may have further portions, such as one or more structures for
stiffening the outer protective cover or for mounting the outer
protective cover within the eye protection shield, for example.
Such further portions are typically not used for seeing through and
further may not have equidistant inner and outer surfaces.
[0027] Alternatively, in one embodiment the eye protection shield
further (in addition to the outer protective cover having
non-equidistant inner and outer surfaces) has an inner protective
cover being arranged on or adjacent the inner surface of the
darkening filter. Again, the inner protective cover may be provided
to protect the darkening filter from dust and splashes of hot or
glowing material during welding. Preferably, the inner protective
cover is removably attached to the darkening filter. Therefore, the
inner protective cover can be replaced if necessary. The inner
protective cover may have a major inner surface and, opposite
thereof, a major outer surface. The inner and outer surface of the
inner protective cover may be equidistant. In other words, a
thickness defined between the inner and outer surface of the inner
protective cover is preferably uniform. The inner and outer surface
of the inner protective cover preferably form surfaces of a portion
of the inner protective cover which serve for the user, for example
a welder, to see through during use. This portion of the inner
protective cover therefore may also be referred to the "see-through
portion of the inner protective cover". The inner protective cover
may have further portions, such as one or more structures for
stiffening the inner protective cover or for mounting the inner
protective cover within the eye protection shield, for example.
Such further portions are typically not used for seeing through and
further may not have equidistant inner and outer surfaces.
[0028] The refractive power for the purpose of the present
specification is measured in accordance with Standards EN 166:2001
(E) and EN 167:2001 (E).
[0029] In a further aspect the invention relates to a welding
protector. A welding protector may be a welding mask or welding
helmet, for example. The welding protector preferably comprises the
curved eye protection shield of the invention and a non-transparent
head protection shield. The head protection shield preferably at
least comprises a face protection portion. The head protection
shield may comprise a further portion for protecting further parts
of a wearer's head. The head protection shield preferably forms a
window which is closed by the curved eye protection shield.
[0030] In a further embodiment the welding protector further
comprises a headband for retaining the welding protector on a
wearer's head. The head protection shield is preferably pivotally
suspended relative to the headband. Thus, the head protection
shield can be swiveled between a lower position in which the head
protection shield protects a wearer's face, eyes and eventually
further parts, and an upper position in which the head protection
shield is lifted away from the wearer's face. Therefore, a wearer
does not need to put off the welding protector for accessing her or
his face, for example.
[0031] In a further aspect the invention relates to a method of
retrofitting a welding protector which has a curved eye protection
shield. The eye protection shield comprises an electrically
switchable darkening filter having an eye facing major inner
surface and, opposite thereof, a major outer surface. The inner and
outer surface of the darkening filter are equidistant. The method
comprises the steps of (i) providing a protective cover having a
major inner surface and further a major outer surface, wherein the
inner and outer surface of the protective cover are non-equidistant
(as specified herein), and (ii) mounting the protective cover
relative to the darkening filter such that the outer surface of the
protective cover faces the inner surface of the darkening filter or
such that the inner surface of the protective cover faces the outer
surface of the darkening filter.
BRIEF DESCRIPTION OF THE FIGURES
[0032] FIG. 1 is a perspective view of a welding protector
according to an embodiment of the invention; and
[0033] FIG. 2 is a top view on an eye protection shield according
to an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0034] FIG. 1 shows a curved eye protection shield 1 for welding
protection. The eye protection shield 1 has an electrically
switchable darkening filter 10, an inner protective cover 20 and an
outer protective cover 30.
[0035] The darkening filter 10 is an automatic darkening filter, in
the example is based on a liquid crystal cell. The darkening filter
10 is electrically switchable between a light-transmission-state
and a dark-state. When switched in the dark-state, the darkening
filter 10 blocks a significant amount of light from being
transmitted therethrough. This enables a user to observe a welding
arc by seeing through the darkening filter 10 without risking to be
exposed to harmful light radiation from the welding arc. In the
light-transmission-state the darkening filter 10 permits a
significant amount of light to be transmitted therethrough. Thus,
the darkening filter 10 in the light-transmission-state allows the
user to see under ambient light conditions (in the absence of the
welding arc).
[0036] The darkening filter 10 has an eye facing major inner
surface 11 and, opposite thereof, a major outer surface 12.
Further, the inner protective cover 20 has a major inner surface 21
and further a major outer surface 22. The inner protective cover 20
is provided for arrangement on or next to the inner surface 11 of
the darkening filter 10. In the example the inner protective cover
20 is attached at a space relative to the inner surface 11 of the
darkening filter 10. Several ways of attaching the inner protective
cover 20 to the darkening filter 10 are possible, for example by
individually mounting the darkening filter 10 and the inner
protective cover 20 in a welding protector (not illustrated).
[0037] The inner and outer surface 11, 12 of the darkening filter
10 are equidistant. In the example, the inner and outer surface 11,
12 of the darkening filter 10 each have a cylindrical shape.
Therefore, the equidistant inner and outer surface 11, 12 are
concentric relative to each other. Due to the curvature of the
cylindrical shape the darkening filter 10 has a certain refractive
power with respect to a wearer viewing through the darkening filter
10. This is because light passing through the darkening filter 10
at angles other than perpendicular to the inner and outer surface
11, 12 are deflected by the darkening filter 10.
[0038] The inner and outer surface 21, 22 of the inner protective
cover 20 are non-equidistant. In particular the inner and outer
surface 21, 22 are shaped to compensate for the refractive power of
the darkening filter 10. In the example, the inner and outer
surface 21, 22 are each cylindrical but not concentric. In
particular, the inner and outer surface 21, 22 are in an off-center
relationship relative to each other. The centers of the inner and
outer surface 21, 22 of the inner protective cover 20 are offset
relative to each other in a dimension perpendicular to the inner
and outer surface 21, 22. Further, the inner and outer surface 21,
22 are arranged such that the center of the outer surface 22 is
arranged between the center of the inner surface 21 and the inner
protective cover 20. Accordingly, the inner and outer surface 21,
22 extend non-equidistant relative to each other, in a manner
providing a refractive power that compensates for the refractive
power of the darkening filer 10.
[0039] The outer protective cover 30 in the example has a major
inner and a major outer surface 31, 32 which extend equidistant to
each other. In particular, the inner and outer surface 31, 32 are
cylindrical and concentric relative to each other. In another
example the outer protective cover 30 may extend non-equidistant to
compensate for a refractive power of the darkening filter 10. In
still another example the refractive power of the darkening filter
10 may be compensated by a combination of both, the inner and outer
protective cover 20, 30.
[0040] The outer surface 12 of the darkening filter 10 is based on
a cylindrical shape which is defined by a radius of 90.1 mm and the
inner surface 11 of the darkening filter 10 is based on a
cylindrical shape which is defined by a radius of 89 mm. The inner
and outer surface 11, 12 of the darkening filter 10 are concentric.
The refractive power of the darkening filter 10 is -0.044 l/m. The
inner and outer surface 21, 22 of the inner protective cover 20,
are each based on a cylindrical shape which is defined by a radius
R of 85 mm. The inner and outer surface 11, 12 are in an off-center
relationship to each other with the offset D of the off-center
relationship being 1.7 mm. Accordingly, the maximum thickness T1 is
1.7 mm. T2 indicates an area in which the inner protective cover
has a smaller thickness than 1.7 mm. The refractive power of the
inner protective cover 20 in the example is 0.051 l/m. Further, in
this embodiment the outer surface 32 of the outer protective cover
30 is based on a cylindrical shape which is defined by a radius of
91 mm and an inner surface 31 of the outer protective cover 30 is
based on a cylindrical shape which is defined by a radius of 90.25
mm. The inner and outer surface of the outer protective cover are
concentric. The refractive power of the outer protective cover is
-0.034 l/m. The combination of the inner protective cover 20, the
darkening filter 10 and the outer protective cover 30 (as
illustrated) thus has a total refractive power of -0.027 l/m. The
absolute value of the total refractive power of the combination of
the inner protective cover 20, the darkening filter 10 and the
outer protective cover 30 is lower than the absolute value of each
of the inner protective cover 20, the darkening filter 10 and the
outer protective cover 30 individually.
[0041] Other dimensions are possible as appropriate. The refractive
power of the eye protection shield or its components may be
calculated in accordance with Gullstrand's afocal lens formula:
1 f = ( n - 1 ) .function. [ 1 R 1 - 1 R 2 + ( n - 1 ) .times. d nR
1 .times. R 2 ] , ##EQU00001##
In which "n" is the refractive index of the material of the eye
protection shield and its components, R1 is the radius of the outer
surface, R2 is the radius of the inner surface and d is the
thickness of the eye protection shield or its components. It is
noted that R2 for the eye protection shield or its components is a
negative value because it refers to the radius of a concave
surface, whereas R1 refers to the radius of a convex surface.
* * * * *