U.S. patent number 3,892,947 [Application Number 05/446,151] was granted by the patent office on 1975-07-01 for electrically heated panel with anti-shock conductive strips.
This patent grant is currently assigned to Donnelly Mirrors, Inc.. Invention is credited to Roy D. Strengholt.
United States Patent |
3,892,947 |
Strengholt |
July 1, 1975 |
Electrically heated panel with anti-shock conductive strips
Abstract
An anti-fogging, electrically heated, frangible panel or
windowpane especially adapted to prevent electrical shocks to
persons who might come in contact therewith after fracture or
breakage. The pane includes an uncoated, insulating, marginal band
which extends completely around a transparent, electrically
conductive coating. An electric current conductive strip is adhered
in the marginal band and extends substantially completely around
the coating before contacting an edge thereof. Fracture or breakage
of any portion of the windowpane severs the conductive strip at
some point around the periphery of the pane preventing current flow
through the coating.
Inventors: |
Strengholt; Roy D. (Holland,
MI) |
Assignee: |
Donnelly Mirrors, Inc.
(Holland, MI)
|
Family
ID: |
23771497 |
Appl.
No.: |
05/446,151 |
Filed: |
February 27, 1974 |
Current U.S.
Class: |
219/522; 174/257;
219/203; 219/543; 338/309; 174/260; 219/541 |
Current CPC
Class: |
H05B
3/00 (20130101); H05B 3/84 (20130101); A47F
3/0434 (20130101) |
Current International
Class: |
A47F
3/04 (20060101); H05B 3/00 (20060101); H05B
3/84 (20060101); H05b 003/06 () |
Field of
Search: |
;219/203,522,541,543,544
;338/308,309 ;174/68.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mayewsky; Volodymyr Y.
Attorney, Agent or Firm: Price, Heneveld, Huizenga &
Cooper
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. In an anti-fogging, heated windowpane of the type including a
sheet of transparent glass having a pair of generally opposing,
planar surfaces, a peripheral edge having a plurality of edge
portions, and an electrically conductive, transparent coating
applied to a portion of one of said surfaces, the improvement
comprising the combination of an uncoated, insulating space
extending around the entirety of said one surface of said sheet
between the edge of said coating and said peripheral edge; a first
elongated strip of electrically conductive material applied to said
sheet within said uncoated, insulating space, said first strip
having a beginning end located adjacent one portion of said
peripheral edge of said sheet and extending around and being
insulated from substantially all of the total length of the edge of
said coating after which said strip includes a contact portion
which extends into electrical contact with a predetermined length
of a first portion of said edge of said coating; a second,
elongated strip of electrically conductive material applied to said
sheet in electric contact with a predetermined length of a second
portion of said edge of said coating; said second portion of said
coating edge and said second, elongated strip of electrically
conductive material being spaced across said coating a
predetermined distance apart from and in general opposition to said
first portion of said coating edge and said contact portion of said
first strip; electrical conduction means for conducting electricity
to said first strip and for grounding said second strip, said
conduction means engaging said first strip at said beginning end,
whereby an electrical current transmitted from said first strip
across said coating to said second strip for heating said coating
and said sheet is automatically shut off upon fracture of said
sheet anywhere along its length which causes a severance of said
first strip along its length.
2. The improvement of claim 1 wherein said sheet is rectangular;
said coating being rectangular with said coating edges extending
parallel to said peripheral edges of said sheet and spaced back
therefrom to define said insulated space, the edges of said coating
including two sets of parallel, opposing edges, the edges in each
of said sets being perpendicular to those of the other set; said
first strip extending around three entire edges of said coating and
substantially all of the fourth edge from said beginning end
location in said insulating space to a position immediately
adjacent said beginning end location, said contact portion of said
first strip extending into electrical contact with the entirety of
one of said coating edges in one of said sets from said position
immediately adjacent said beginning end location; said second strip
extending in electrical contact with the entirety of the remaining
edge of said coating in said one set of edges.
3. The improvement of claim 2 wherein said contact portion of said
first strip is parallel to, spaced from, and substantially
coextensive with the portion of said first strip extending along
said fourth edge of said coating.
4. The improvement of claim 1 wherein said first strip is
positioned generally midway between said coating edges and said
sheet peripheral edges in said insulated space except for said
contact portion thereof which extends out of said insulated space
into electrical contact with said first portion of said edge of
said coating.
5. The improvement of claim 1 wherein said first and second strips
comprise silver paste applied to said sheet in the desired
locations, said sheet with said paste being heated to bond the
paste to the sheet.
6. The improvement of claim 5 wherein said sheet of glass is
annealed glass prior to deposition of said silver paste thereon,
the heating of said sheet and paste causing said annealed glass to
become partially tempered and strengthened.
7. The improvement of claim 1 wherein said windowpane further
comprises partially tempered and strengthened glass.
8. An anti-fogging, electrically heated, panel comprising the
combination of a sheet of frangible material and electric current
conduction means for preventing the occurrence of electrical shocks
upon breakage of the panel; said current conduction means including
a layer of electrically conductive material applied to a portion of
at least one surface of said sheet and defining a marginal,
uncoated, insulating, electrically nonconductive band extending
around the entirety of said sheet between the edge of said layer
and the peripheral edges of said sheet, at least one elongated
strip of electric current conducting material applied to said sheet
within said marginal band and extending along said band
substantially completely around said layer from a first portion to
a second position immediately adjacent said first position, said
one strip including a contact portion extending from said second
position into electrical contact with a predetermined length of one
portion of said edge of said layer, another elongated strip or
electric current conducting material applied to said sheet in
electrical contact with a predetermined length of another portion
of said edge of said layer, said other elongated strip and other
portion of said layer edge spaced a predetermined distance across
said layer and generally opposing said one portion of said layer
edge and said contact portion of said one strip, and electrical
contact means for supplying electric current to said one strip at
said first position and for grounding said other strip whereby
current flow from said contact portion of said one strip across
said layer to said other strip for heating said panel is
automatically stopped upon fracture of said sheet causing severance
of at least one portion of said one strip along its length between
said first and second positions.
9. The panel of claim 8 wherein said one strip has a predetermined
uniform width dimension along its length; said second position
being spaced from said first position a distance no greater than
said width dimension.
10. The panel of claim 9 wherein the portions of said one strip
except for said contact portion are spaced from the edge of said
layer a distance at least as great as said width dimension of said
strip.
11. The panel of claim 9 wherein said electric current conducting
strips are silver paste applied to said uncoated, marginal band of
said sheet, said sheet and strips being heated to bond said strips
to said sheet.
12. The panel of claim 11 wherein said sheet is a sheet of annealed
glass prior to deposition of said silver paste thereon, the heating
of said sheet and paste causing said annealed glass to become
partially tempered and strengthened.
13. The panel of claim 8 wherein said panel further comprises
partially tempered and strengthened glass.
14. The panel of claim 8 wherein said contact portion of said one
strip is parallel to but spaced from another portion of said one
strip.
15. The panel of claim 8 wherein said layer is rectangular, said
generally opposing portions of said layer edge contacted by said
contact portion of said one strip and said other strip including a
pair of the edges of said rectangle which are parallel to and
opposite one another.
16. The panel of claim 15 wherein said one strip extends around
three entire edges and substantially all of the fourth edge of said
layer rectangle, said contact portion of said one strip extending
generally coextensively with, parallel to but spaced from a second
portion of said one strip, said second portion of said one strip
extending along said fourth edge of said layer rectangle within
said marginal band adjacent said fourth edge.
Description
BACKGROUND OF THE INVENTION
This invention relates to electrically heated frangible panels and
especially electrically heated, anti-fogging windowpanes. More
particularly, the invention relates to an electrically heated panel
or windowpane including conductive strips arranged to prevent
continued current flow and the occurrence of electrical shocks upon
fracture or breakage of the panel or windowpane.
Electrically heated panels and windowpanes adapted to prevent the
obstruction of vision due to fogging or the accumulation of
condensation are very well known. Typically, such windowpanes or
panels include transparent conductive coatings and conductive
strips or bus bars arranged to conduct electricity to such coatings
for heating the panel or windowpane. The conductive strips extend
into contact with an elongated edge portion of the conductive
coating such that electric current passes through the coating
substantially over the entire area of the coating to produce
uniform heating of the panel. A common use of such panels is in
refrigerator or freezer doors to provide a means for viewing
through the closed door even though a large temperature
differential exists which otherwise causes the formation of
condensation or fogging if the window were not heated.
A major problem encountered with such electrically heated
windowpanes and other frangible panels has been the substantial
shock hazard present in such windows upon their fracture or
breakage. Such problem results when the pane of glass only
partially breaks or fractures and the conductive strips allow the
conduction of electricity through the conductive coating on at
least a portion of the unbroken glass. Should a person come in
contact with the conductive coating during such time, the person's
body may act as a ground connection and the electrical current may
pass through him or her, possibly resulting in severe injury.
Several attempts have been made in prior panels to overcome this
substantial safety hazard. A first commonly known method is to
connect appropriate electrical or electronic circuitry in series
with the power supply supplying electrical current to the heated
panel. The circuitry is responsive to a drop in either current flow
or voltage which results from a partial breakage of the heated
panel. When the current or voltage is reduced, the circuitry
automatically opens shutting off the electricity. Not only does the
provision of such circuitry add to the cost of such panels, but its
reliability is often subject to question.
Another method is to position the electrical strips or bus bars
conducting electricity to the electrically conductive coating so as
to fracture and thus shut off current flow upon the breakage of the
glass. One such panel is disclosed in U.S. Pat. Stromquist et al.
No. 3,524,920. Although intended to prevent current conduction
after any fracture of the glass, it has been found that the panels
disclosed therein do not completely eliminate the shock hazards
described above. With such panes, it is possible that the glass
could fracture from the center of the pane outwardly through only a
portion of one of the bus bars, leaving another portion of that
same bus bar conducting electricity through a portion of the
conductive coating thereby producing a serious shock hazard.
Accordingly, the prior known electrically heated panels and
windowpanes have not completely overcome the hazard of electrical
shock present therein when the windowpane or panel is broken.
SUMMARY OF THE INVENTION
Accordingly, it is an object and purpose of the present invention
to provide an electrically heated frangible panel or windowpane
which substantially completely eliminates the possibility of shock
hazard upon breakage of the pane or panel without dependence upon
external circuitry or other components. The invention is especially
useful in refrigerator or freezer doors as a means for preventing
the accumulation of condensation or fogging on windows therein. The
invention provides an arrangement of electrical current conducting
strips designed to substantially completely and effectively break
the electrical current path and prevent current flow through an
electrically conductive coating on the window should breakage or
even partial fracture of the panel or window occur.
In the preferred embodiment, the invention includes a sheet of
transparent material, such as partially tempered or strengthened
glass, which is capable of withstanding the application of
sufficient heat to prevent fogging and condensation. The sheet
includes transparent, electrically conductive coating applied to a
portion of one surface thereof, the edges of the coating being
spaced back from the peripheral edges of the sheet providing a
marginal, insulating band or space extending completely around the
sheet. At least one electric current conductive strip or bus bar is
fused, bonded or otherwise adhered or applied to the marginal,
uncoated, insulating band. The conductive strip extends
substantially completely around the conductive coating to a
position immediately adjacent its beginning point, from which it
extends into electrical contact with the electrically conductive
coating. Another electric current conductive strip is positioned
across the electrically conductive coating on an edge thereof
generally opposing the portion of the first strip contacting the
coating to provide a current path which heats the conductive
coating and the sheet or glass to which it is applied. Should
breakage occur in any direction from the area of the glass covered
by the coating outwardly through even one peripheral edge of the
glass, the conductive strip extending around the glass will be
severed at a position prior to its contact with the electrically
conductive coating. Such severence prevents current flow through
the coating and eliminates any possible shock hazards. Accordingly,
effective use of the invention is dependent on nothing but the
arrangement of the conductive strip thereby eliminating the need
for any external circuit breakers, electronic circuitry, or the
like for completely safe operation.
These and other objects, advantages, purposes, and features of the
invention will become more apparent from a study of the following
description taken in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view of the present invention including an
insulated, electric current conductive strip extending
substantially completely around an electrically conductive,
transparent coating on a sheet of transparent material prior to its
conductive contact with the conductive coating; and
FIG. 2 is a broken, sectional view of the electrically heated panel
taken along plane II--II of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings in greater detail, FIG. 1 illustrates
the preferred embodiment of the electrically heated panel or
windowpane 10 including a sheet or plate of transparent material
12, a transparent, electrically conductive coating or layer 14, and
a pair of electric current conductive strips or bus bars 16 and 18.
In accordance with the concept of the present invention, the
conductive strips 16 and 18 are arranged such that strips 16 extend
substantially completely around the electrically conductive coating
14 before extending into contact therewith. Any fracture of the
transparent material will sever a portion of the strip or bus bar
16 prior to the location at which it extends into contact with the
coating. Electric current flow through the transparent electrically
conductive coating 14 is thus prevented in the event of
breakage.
The sheet or plate of transparent material 12 is a sheet of
annealed glass which becomes partially tempered or strengthened
after application of the coating 14 and strips 16 and 18 during
manufacture of the present invention. Sheet 12 has generally
opposing, planar surfaces 20 and 22 and a peripheral edge 24
extending therearound. Other glass, including glass which is either
annealed or fully tempered in its final form after application of
coating 14 and strips 16 and 18 herein, may also be used. Although
the material of the transparent sheet will typically be glass,
other materials such as silica, ceramics, heat-resistant synthetic
plastics, and other materials produceable in sheet form may be
utilized. Also, it is not necessary to the operation of the
invention that the sheet material be transparent although typically
its use will be in windows which must be transparent. The only
requirement is that the sheet material be capable of withstanding
the heat produced in the electrically conductive coating 14 without
deforming, melting, or softening.
Typically, the heat required to prevent fogging, misting, or
condensation is determined for the area in which the present
invention will be used. Then, the thickness of coating 14 is
designed to provide the wattage per square inch of coating area
required to produce such heat. Thereafter, a suitable sheet
material is chosen to withstand the heat required for the
particular application. Normally, the sheet will be glass which can
withstand great amounts of heat. Typically, the current required
for refrigeration applications is 5 to 20 watts per square foot at
110 volts. In applications where lower temperatures are encountered
such as in ship windows or the like, up to 400 watts per square
foot at 220 or 440 volts may be required. The coating thickness and
sheet material thus depend on the desired application. Variables
include the number of panels used, temperatures to be encountered,
and the like.
As is best seen in FIG. 2, the transparent, electrically conductive
coating 14 is applied or coated directly on the surface 20 of sheet
12 in only a portion of that surface area. In the embodiment shown
in the drawings, sheet 12 is rectangular in shape and coating 14 is
also applied in a rectangular area. Thus, coating 14 includes two
sets of parallel edges 26, 28 and 30, 32 extending parallel to the
peripheral edges 24 of sheet 12 but spaced inwardly therefrom. The
spacing of the edges 26, 28, 30, and 32 from the peripheral edges
24 defines an uncoated, insulated, nonelectrically conductive,
marginal strip or band 34 extending about the entire periphery of
sheet 12 and thus surrounding the coating 14. The insulating band
34 provides a barrier to the conduction of electricity thereby
limiting that condition to the coated area 14 on surface 20 of
sheet 12.
Coating 14 is typically applied in a layer several hundred
angstroms thick (typically 300-400 angstroms). The thickness, of
course, will depend on the wattage and heat desired to be produced
on sheet 12 as mentioned above. One of any or several types of
transparent coatings of various light transmissibility and
conductivity such as tin, tinindium or tin-zinc coatings, or
combinations thereof, may be used.
In accordance with the concept of the invention, the conductive
strip 16 is applied or coated substantially in the middle of the
marginal, uncoated band 34. Strip 16 includes a first portion 16a,
including beginning end 36, which extends parallel to coating edge
30. Similarly, portions 16b, 16c, and 16d extend along and parallel
to coating edges 28, 32, and 26 respectively. As a position
immediately adjacent the beginning end 36 of strip 16, a short
strip portion 16c extends perpendicularly to portion 16d into
portion 16f of strip 16. Strip portion 16f extends parallel to and
in electrical contact with the entirety of edge 26 of coating 14.
The strip 16 is normally applied first to sheet 12 so that coating
14 actually extends up and over strip portion 16f for effective
electrical contact (see FIG. 2). However, it is also possible to
apply coating 14 to the sheet first followed by application of the
strip 16 with portion 16f over the coating. Portion 16f is parallel
to portion 16d and is substantially coextensive therewith although
it is spaced and insulated therefrom by a portion of band 34.
Electric current conductive strip 18 is positioned across the
conductive coating 14 in general opposition to portion 16f of strip
16 such that electric current will flow from portion 16f through
coating 14 to strip 18 in the direction indicated in FIG. 1 at
substantially all portions of the coating.
In the preferred embodiment, short portion 16e of strip 16 is
spaced a distance less than or equal to the generally uniform width
of the entirety of strip 16 from beginning end 36. The spacing or
gap 38 between end 36 and portion 16e may be made smaller than the
strip width but it must be large enough to maintain sufficient
insulation such that no current will flow thereacross. The usual
electric current passes through strip 16 and coating 14 is small
enough to prevent the current from sparking or jumping across gap
38, i.e., approximately 5-20 watts per square foot at 110 volts, as
mentioned above. Portions 16a, 16b, 16c, and 16d are also spaced a
distance approximately equivalent to the width of the strip 16 from
edge 30, strip 18, edge 32, and edge 26, respectively. Thus, strip
16 extends substantially completely around the entire coating 14
after which it extends into contact with one edge portion of the
coating generally opposite the edge contacted by ground strip
18.
Preferably, strips 16 and 18 are formed by applying a paste of
silver, platinum, or other metals or conductive substances in the
strip configuration in the marginal band 34 after which the paste
is bonded or fused to the uncoated sheet surface 20 by the
application of heat in a furnace or the like. Such heat causes the
originally annealed glass sheet used in the preferred embodiment to
become partially tempered or strengthened. One of the many
conductive substances suitable for making the conductive strips 16
and 18 is silver paste which may be commercially obtained from E.
I. Du Pont de Nemours & Co. under the product designation
Conductive Silver No. 7713.
OPERATION
In operation, electric current is supplied to the strips or bus
bars 16 and 18 by electrical conduction means including a wire 42
connected in series with a power supply 44 and a switch 46 for
starting and stopping the current flow. The end of wire 42 is
soldered or otherwise secured in electrical connection with end 36
of strip 16. A ground wire 48 is soldered to one end of the ground
strip 18 to complete the circuit. It is important that the power
supply by connected to end 36 of strip 16 such that the current is
forced to flow substantially completely around the conductive
coating 14 in the various portions of strip 16 before passing
through coating 14.
Once switch 46 is closed, electric current flows through wire 42
and beginning end 36 of strip 16 through portions 16a, 16b, 16c,
16d, 16e, and 16f of strip 16. The current is conducted from strip
portion 16f through the electrically conductive coating 14 across
all portions thereof to opposing portions of the electrical ground
strip 18 such that the electrical potential or voltage between the
respective portions of strip 16f and strip 18 is generally the
same. Should the sheet of glass 12 be struck and fractured or
broken in any way, such as along any of the hypothetical cracks C
illustrated in FIG. 1, the portion of the electrically conductive
strip 16 through which the crack passes will be severed thereby
interrupting the current flow through the remainder of the strip 16
following the crack. Since the partially tempered or strengthened
glass preferably used in this type application will always crack
outwardly to at least one edge of the sheet, the electric current
conducting strip 16 will be severed at some portion prior to the
contact portion 16f thereby effectively preventing any current flow
through the conductive coating. The coating areas on the unbroken
portions of the glass or panel are thus isolated from electric
current upon the occurrence of virtually any breakage. Current flow
is prevented transversely from strip 16 at the point of severance
by the insulated spaces of the marginal band 34 on either side of
the strip. Also, the present panels or windows are typically used
alone or in multiple units wherein framing or other materials cover
and insulate conductive strip 16 around the periphery of sheet 12
to prevent direct contact with the strip in such marginal
areas.
Although it is conceivable that the sheet 12 could crack only
through gap or space 38 thereby allowing continued electric current
flow to coating 14, the chances of that occurrence are so small as
to be negligible. Although this is true for virtually any type of
transparent sheet material useful in this invention, it is
especially true with the originally annealed glass preferably used
herein. The manufacturing process used to produce this invention
results in the partial tempering or strengthening of the originally
annealed glass, as mentioned above. Such strengthened glass
typically fractures with a multiplicity of cracks in a "spider-web"
pattern or the like. A single crack of the type and size necessary
to pass only through gap 38 will, therefore, not normally
occur.
While one form of the invention has been shown and described, other
forms will now be apparent to those skilled in the art. Therefore,
it will be understood that the embodiment shown in the drawings and
described above is merely for illustrative purposes, and is not
intended to limit the scope of the invention which is defined by
the claims which follow.
* * * * *