Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention is a touch panel device which electrically
indicates the X-Y coordinates of contact of an operator's finger on it
and is sensitive to pressure only. Frequently, information is displayed on a
substrate beneath the touch panel as well. The coordinates of a contact
can be related to the displayed information thus providing for inter-
active communication between the operator and the device of which the
touch panel forms a part.
The prior art includes a variety of techniques for sensing the
location of contact on a surface. The most similar device of which the
inventors are aware is the stretched drumhead type of membrane. This de-
vice employs a membrane spaced from a flat substrate and which can be
deflected to cause conductors carried on it to contact those on the sub-
strate. Another device is disclosed in an article entitled "CRT Touch
Panels Provide Maximum Flexibility in Computer Interaction"~
Control Engineering~ July 1976, pp. 33-34. This article discloses a
curved flexible plastic sheet carrying small wires. The sheet can be
deflected to cause these wires to come into contact with an orthogonal
set of similar wires mounted immediately below. Spacers separate the sets
of wires. United States Patent 3,760,360 discloses a quite similar de-
20 vice embodied in a flat panel but having no capability of interactivelydisplaying information. United States Patent 3,495,232 discloses a some-
what simpler embodiment of a similar device. United States Patent
3,921,167 discloses a panel locati~r-sensitive to the approach of an exter-
nal probe sensing change in capacitance.
The touch panel covers a rigid substrate, whose face has a pre-
determined radius of curvature ranging from infinite (flat) to 25 inches
or less, and comprises in part a resilient membrane of a contour confor-
ming to the substrate face and attached about its periphery thereto. A
group of discrete conductive strips adheres to the substrate on the sur-
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face facing the membrane. A second group of discrete conductive stripswhich flex with the membrane and which cross the first, is carried by the
membrane on its surface facing the substrate. External pressure on a local
area of the membrane forces one or more conductive strips on the membrane
into electrical contact with one or more conductive strips on the substrate.
By detecting which strips are in contact with each other, the approximate
coordinates of the pressure point on the membrane can be determined. To
prevent shorting between strips of each group when no external pressure is
present, any one of several means can be used. In one embodiment, a thin,
transparent insulating grid is interposed between the two groups of conduc-
tive strips. A piezo-resistant coating on the surfaces of at least one
group of strips also appears to function satisfactorily. When a curved
substrate is used, a third anti-short means involves making the radius of ~;
curvature of the membrane somewhat smaller than the substrate~s. It appears
that the natural resllience of the membrane is sufficient to support the
conductive strips carried by it spaced from the substrate's conductive
strips with no interposed element.
In one preferred embodiment, the rigid substrate comprises a
curved CRT faceplate or screen, with a resilient membrane curved to conform
to the CRT screen. The conductive strips both on the substrate and the
membrane are sufficiently thin so as to be transparent and permit viewing
of information displayed on the CRT screen. Being transparent, the conduc-
tive strips can be relatively wide with respect to the spacing between
adjacent ones on the same surface and thus permit a larger area of contact~
The anti-short means comprise an insulating grid preferably formed of one
of several photo-resist polym~ now available, thus allowing the grid to
be formed in situ on either the substrate or the membrane by masking and
exposing to light, followed by the appropriate chemical process. Such
photo-resist materials at the small thicknesses contemplated are substan- -
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tially transparent.
Accordingly, one purpose of this invention is to provide a passive
surface sensitive to low pressure from a finger or stylus.
A second purpose is to provide a touch panel permitting the viewing
of a display beneath it.
Another purpose is to provide a touch panel which can be easily
integrated with existing display designs.
Thus, in accordance with one broad aspect of the invention, there
is provided a transparent switch matrix to be carried on the face of a rigid
insulator substrate having a predetermined radius of curvature, and compris-
ing:
a) a plurality of spaced apart transparent conductive first strips
firmly adhering to the face of the substrate;
b) a transparent resilient membrane having an undistorted contour
substantially alike the predetermined contour, and attached about its peri-
phery to the face of the substrate in a position matching the membrane con-
tour to the substrate contour and spaced apart from the first strips thereon
in a predetermined area of the membrane;
c) a plurality of transparent, flexible, spaced apart conductive
second strips firmly adhering to the resilient membrane surface facing the
substrate, each of said second strips located in the area spaced apart from
the first strips and thinner than the spacing therefrom, and each of said
second strips crossing at least two first strips; and
d) an insulating grid interposed between the first and second
strips, and having, within each crossover area between the first and second
strips, a plurality of gaps permitting electrical contact between a first
and second strip responsive to manual pressure at each said crossover area,
said insulating grid being formed of insulating photo-resist material.
In accordance with another broad aspect of the invention there is
provided a method of forming a transparent switch matrix to be carried on the
face of a rigid insulator substrate having a predetermined radius of curva-
ture, said method comprising:
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a) adhering a plurality of spaced apart transparent conductive
first strips to the face of the substrate;
b~ coating the conductive strips covered substrate with a photo-
resist material;
c) exposing the photo-resist material to a light pattern corres-
ponding to a preselected grid pattern;
d) developing the photo-resist material;
e) removing chemically the photo-resist material between the
individual grid lines;
f) adhering a plurality of transparent, flexible, spaced apart
conductive second strips to a surface of a resilient membrane having an
undistorted contour substantially alike the predetermined contour; and
g) attaching the membrane about its periphery to the face of the
substrate in a position matching the membrane contour to the substrate con-
tour and spaced apart from the first strips thereon in a predetermined area
of the membrane, each of said second strips being located in the area spaced
apart from the first strips and thinner than the spacing therefrom, and each
of said second strips crossing at least two first strips.
The invention will now be further described in conjunction with
the accompanying drawings, in which:
Figure 1 is a plan view of a corner portion of a typical touch
panel assembly, flat or curved, embodying the invention.
Figure 2 is a cross section of a curved embodiment of the touch
panel displayed in Figure 1 and incorporating a membrane having a slightly
smaller radius of curvature than the substrate.
Figure 3 is a blowup of a portion of Figure 2 detailing the re-
lationship of the two sets of conductor strips and the insulating grid
- ~when present). ~-
Figure 4 is a blowup of a portion of Figure 3 showing in still
greater detail the relationship of the two sets of conducting strips and
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the insulating grid.
Figure 5 is a blowup of a portion of Figure 2 employing a piezo-
resistant anti-short means.
In all of these drawings scale between the various parts is not
always consistent as this simplifies understanding. Suitable dimensions for
the elements of the structure are set out below as needed.
The corner portion of the preferred embodiment shown in Figure 1
comprises a base or substrate 10 which may be flat or, as in Figure 2,
curved. Substrate 10 must have an insulating surface. Y conductive strips
20-24 comprise transparent coated areas firmly adhering to the surface of
substrate 10 facing the viewer. In a typical application substrate 10 can
at least partly comprise a CRT screen. It may not be convenient to directly
apply conductive strips to a CRT screen or other substrate, but rather form
them on a clear plastic sheet 55, curved if intended to conform to a curved
CRT screen, which is then glued or otherwise attached to substrate 10.
Leads 40-44 are attached to ends of strips 20-24 respectively so as to make
electrical contact between them and external support electronics. In a
typical device, each of conductive strips 20-24 is .5 in. wide and is
separated from adjacent strips by .005 in. gaps. Strips 20-24 are in one
embodiment preferably formed from indium oxide, tin oxide, or a combination
OI both oxides. The strips are easily formed by coating the entire face
of substrate 10 with the conductive material using standard techniques.
Standard etching technique using photo-resist material then forms the
narrow gaps between adjacent strips.
In one embodiment of this invention, insulating grid 45 forms the
next layer of the panel, overlaying at least a portion of conductive strips
20-24, and usually covers strips 20-24 uniformly. When such an insulating
grid is used, it can be most easily formed from widely available and well
known transparent photo-resist material which is itself inherently non-
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conductive. The areas to be covered by insulating grid 45 are covered with
the photo-resist material, an appropriate mask is placed on these areas, the
; resist is exposed according to usual procedures, and the unexposed photo-
resist is removed with standard chemical procedures. A suitable grid 45
comprises a crosshatch of lines or strips formed of the photo-resist mate-
rial, where each line is .005 in. wide (w in Figure 4) and all lines, in
both the vertical and horizontal directions are on .025 in. centers (s in
Figure 3). Thickness of insulating grid 45 can vary depending on the pres-
sure desired to form contact, but a nominal value of 0.0001 in. appears to
be suitable for the 0.003 MYLAR (reg. trademark of Dupont Corp.) polyester
membrane described below. In general, a ratio of from 1:5 to 1:100 for the
width w of the insulating grid lines to the centerline spacing s of adjacent
pairs is suitable for this grid thickness. The width w of individual lines
should never exceed a few thousandths of an inch. Insulating grid 45 can ~ -
also be formed on membrane 11 after strips 12-16 are formed as described
below.
Resilient insulating membrane 11 forms the tactile surface which
the operator presses at a desired point to create an electrical contact
indicating the coordinates of the pressure point. Membrane 11 carries con-
ductive strips 12-16 on its surface facing substrate 10~ which strips are
formed before attaching membrane 11 to substrate 10. Strips 12-16 must be
flexible enough to easily bend with membrane 11. Transparent polyester film
of 0.003 in. thickness with a transparent conductive gold film on one sur-
face available from Sierracin Corp., 12780 San Fernando Road, Sylmar, CA,
91342 is suitable, as well as other thicknesses to at least 0.007 in.
Conductive strips 12-16 are conveniently formed by removing (through
etching) narrow strips of gold in parallel lines from such a film. Typical
; dimensions of the gold-free lines defining gold strips 12-16 are 0.002 in.
on .5 in. centers. Vent 50 allows membrane 11 to assume its natural shape
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more quickly after pressure on it by allowing air to rapidly flow into the
space between membrane 11 and substrate 10. It may be desirable to place a
filter in vent 50 to prevent the entrance of dirt. This vent prevents the
slow return of membrane 11 to its natural shape when deflected over a large
area at one instant. It also prevents shorts caused by changes in ambient
atmospheric pressure.
If substrate 10 is curved, it is necessary to mold membrane 11 and
strips 12-16 already formed on it to a smooth contour which conforms to
substrate 10. ~embrane 11, after etching of the gold layer to form conductive
strips 12-16, is formed into a shape substantially conforming to the topology
of substrate 10. If substrate 10 is curved it is preferable that the curva-
ture of membrane 11 when unstressed be slightly greater than that of sub-
strate 10. When substrate 10 comprises a typical curved CRT implosion shield,
curvature is approximately spherical with a radius of approximately 20-30 in.
In such a case membrane 11 preferably is molded to a radius of curvature of
from 1-4 in. less than that of substrate 10. The slightly greater curvature
prevents strips 12-16 on membrane 11 from being drawn down tightly onto
strips 20-24 and possibly shorting to them. Further, such dimensioning is
essential if anti-short means other than grid 45 are employed on a curved
substrate, as described infra. Membrane 11 is securely fastened around its
periphery to substrate 10 by tape strips 54 in such a position that con-
ductive strips 12-16 pass across each of conductive strips 20-24 and are
spaced therefrom by grid 45 and the natural tendency of membrane 11 to
assume its molded-in spherical shape when unstressed. Conductive strips
12-16 are connected to leads 32-36 by a conductive adhesive. Leads 32-36
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may be formed in situ on substrate 10 at the same time conductive leads
20-24 are formed. The support electronics can thus be easily connected to
strips 12-16. Spacer 53 (Figure 2), though often not essential, can be em-
ployed advantageously in certain cases to prevent shorting around the peri-
phery of membrane 11, particularly if anti-short means other than grid 45
are used. Spacer 53 need not be placed on strips 20-24 and may extend to the
edge of membrane 11.
In operation, a contact between any one of conductive strips
20-24 and any one of conductive strips 12-16 can be made by gentle finger or
stylus pressure on membrane 11 above the desired point of intersection.
Because of the relatively wide contact surfaces the pressure point need not
precisely in the center of the desired intersection. With either insulating
grid 45 or the other anti-short means described nfra, gentle finger
pressure forms an essentially zero resistance contact between the two
selected strips. The wide contact surfaoes also add reliability in forming
each contact between the strips.
Figure 5 discloses one alternative to ins~lating grid 45 as the
anti-short means. The aforementioned gold covered polyester film from
Sierracin Corp. is available optionally with a "proprietary ceramic coating
which serves to increase visible light transmission and to provide a
measure of mechanical protection to the conductive metal deposit".
(Sierracin Corp. brochure entitled Sierracin_Intrex (TM) Electricall
Conductive Film Components.~ This coating has been determined to have a
piezoresistant characteristic of high resistance under very light pressure,
and a very low resistance under pressure no heavier than that generated by
gentle finger pressure. In Figure 5~ coatings 51 and 52 indicate use of
this alternative. As now available, both coating 51 and 52 must be present
to yield sufficiently high resistance at very low pressures to allow
functioning as an anti-short means. It is probable that a coating 51
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thicker than now available would allow omission of coating 52. As previous-
ly mentioned, when no insulating grid 45 is used, spacer 53 may be necessary
to prevent shorting adjacent the edges.
Another means for preventing shorting between the X and Y conductor
strips 12-16 and 20-24 is available for use with a substrate 10 having a
finite radius of curvature. ~y selecting membrane ll's radius of curvature
smaller than substrate 10's (for membr-Qnes mounted on substrate lO's convex
side, of course), as shown in Figure 2, the natural resiliency of membrane
11 and its arched shape supports X strips 12-16 in spaced ~elationship with
Y strips 20-24 and prevents their shorting absent external pressure.
Although a wide variety of radius of curvature will undoubtedly work, it is
known that a substrate of 25 in. radius of curvature and a .003 in thick
polyester membrane molded with a form having a 22 in. radius of curvature
are satisfactory. As shown in Figures 1 and 2, it is desirable with this
anti-short means, to bond the periphery of membrane 11 to substrate 10 out-
side Y strips 20-24 to increase the clearance between the peripheral X and
Y strip~ areas. Spacer 53 may also be used for this purpose. It is likely~
although not confirmed, that use of membrane 11's natural resiliency and
curvature to provide the necessary anti-short spacing between X and Y strips
requires a greater difference in radihc of curvature for substrate 10 and
membrane 11 than do the previously mentioned anti-short means. Thus, while
a 3 in. smaller radius works with a 25 in. substrate radius in all 3 cases,
a 1 in. difference or less may well be satisfactory when grid 45 or piezo- -
resistant coating 51 is used.
During the manufacture of this apparatus, it is important that
the surfaces of strips 20-24 and 12-16 be relatively free of dust and other
foreign matter during attachment of membrane 11 to substrate 10. However,
the relatively wide contact areas between crossing strips does tolerate a
small amount of such foreign matter, particularly as long as the foreign
~J màtter is non-conductive. 9 ~ -
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