CA1298631C - Touch screen overlay with improved conductor durability - Google Patents
Touch screen overlay with improved conductor durabilityInfo
- Publication number
- CA1298631C CA1298631C CA000603520A CA603520A CA1298631C CA 1298631 C CA1298631 C CA 1298631C CA 000603520 A CA000603520 A CA 000603520A CA 603520 A CA603520 A CA 603520A CA 1298631 C CA1298631 C CA 1298631C
- Authority
- CA
- Canada
- Prior art keywords
- conductors
- overlay
- touch screen
- transparent
- flexible substrate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
- G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
- G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
- G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
- G06F3/047—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means using sets of wires, e.g. crossed wires
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K11/00—Methods or arrangements for graph-reading or for converting the pattern of mechanical parameters, e.g. force or presence, into electrical signal
- G06K11/06—Devices for converting the position of a manually-operated writing or tracing member into an electrical signal
Abstract
TITLE
TOUCH SCREEN OVERLAY
WITH IMPROVED CONDUCTOR DURABILITY
ABSTRACT OF THE DISCLOSURE
A touch screen overlay for use on the viewing surface of a visual display device formed from a flexible membrane laminate having improved conductor durability. The flexible laminate comprises first and second flexible substrates formed of transparent polyester material. An array of parallel transparent conductors is deposited on a surface of each flexible substrate. The two flexible substrates are joined together by an adhesive sheet of polyester material. The substrates are joined so that transparent conductors are deposited on the surface of each flexible substrate which faces away from the viewing surface when the overlay is attached to the visual display device. The two arrays, when so superimposed, form a grid-like pattern, separated by the thickness of the upper one of the flexible substrates and the adhesive sheet. A third flexible substrate also formed of polyester material covers the surface of the upper one of the other flexible substrates carrying the upper array of parallel conductors. The second and third flexible substrates are also joined by an adhesive sheet of polyester material. When the overlay is contacted either by finer touch or by a stylus, the transparent conductors located in tile laminated below the contact area will subjected substantially only to compression forces.
TOUCH SCREEN OVERLAY
WITH IMPROVED CONDUCTOR DURABILITY
ABSTRACT OF THE DISCLOSURE
A touch screen overlay for use on the viewing surface of a visual display device formed from a flexible membrane laminate having improved conductor durability. The flexible laminate comprises first and second flexible substrates formed of transparent polyester material. An array of parallel transparent conductors is deposited on a surface of each flexible substrate. The two flexible substrates are joined together by an adhesive sheet of polyester material. The substrates are joined so that transparent conductors are deposited on the surface of each flexible substrate which faces away from the viewing surface when the overlay is attached to the visual display device. The two arrays, when so superimposed, form a grid-like pattern, separated by the thickness of the upper one of the flexible substrates and the adhesive sheet. A third flexible substrate also formed of polyester material covers the surface of the upper one of the other flexible substrates carrying the upper array of parallel conductors. The second and third flexible substrates are also joined by an adhesive sheet of polyester material. When the overlay is contacted either by finer touch or by a stylus, the transparent conductors located in tile laminated below the contact area will subjected substantially only to compression forces.
Description
~;~9~3~L
TITLE
TOUCH SCREEN VVERLAY
~AÇKGROUND OF THE INVENTION
Field of the Invention This invention relates generally to touch screen overlays for use on the viewing surface of visual display devices 15 such as computer monitors and, more specifically, this invention relates to a laminate structure for such overlays with greatly improved durability and signal strength.
Description o~ the Prior Art 2û
Touch screen overlays have been used as interactive input devices at the display surface of computer monitors such as cathode ray tubes, gas panel displays, light-emitting diode arrays and other such types of visual display devices. Such 25 overlays have obvious advantages over conventional data input devices such as keyboards by enabling the user to interface more directly with the computer by interreacting directly with the monitor display. Such interaction may be by finger touch or by use of a stylus. The latter is preferable since it enables the 3 0 user to input data in various forms, including handwritten alphanumeric text and graphics.
One of the first interactive display devices utilized the light pen which has a photodetector near its tip. The light pen is manipulated by placing its tip in proximate contact-with a 35 computer monitor screen at a desired location. As the raster 129816;~
TITLE
TOUCH SCREEN VVERLAY
~AÇKGROUND OF THE INVENTION
Field of the Invention This invention relates generally to touch screen overlays for use on the viewing surface of visual display devices 15 such as computer monitors and, more specifically, this invention relates to a laminate structure for such overlays with greatly improved durability and signal strength.
Description o~ the Prior Art 2û
Touch screen overlays have been used as interactive input devices at the display surface of computer monitors such as cathode ray tubes, gas panel displays, light-emitting diode arrays and other such types of visual display devices. Such 25 overlays have obvious advantages over conventional data input devices such as keyboards by enabling the user to interface more directly with the computer by interreacting directly with the monitor display. Such interaction may be by finger touch or by use of a stylus. The latter is preferable since it enables the 3 0 user to input data in various forms, including handwritten alphanumeric text and graphics.
One of the first interactive display devices utilized the light pen which has a photodetector near its tip. The light pen is manipulated by placing its tip in proximate contact-with a 35 computer monitor screen at a desired location. As the raster 129816;~
scans the face of the monitor, the light dot it produces is detected by the light pen, thus enabling the computer to correlate the position of the pen with coordinates of the raster.
This type of interactive display device is not truly a touch sensitive one since it relies essentially on photodetection rather than touch. Light beam arrays interrupted by the presence of a finger or other intrusive object likewise rely principally upon photodeleclion rather than touch.
One torm of touch sensitive display uses a flexible, deformable membrane formed of a transparent laminate which is placed over the display surface of the computer monitor. The laminate generally comprises two conductor planes deposited on a flexible medium so that when the user mechanically displaces one of the conductor planes by a fin~er or stylus, the conductors are brought into electrica~ contact with the conductors in the second plane. The electrical resistance of the conductor plane is changed as a function of the position of the touch on the membrane. Appropriate electronics are provided to translate the resistance value into the position corresponding with the touch.
One version of such touch screen membranes is manufactured by the John Fluke Mfg. Co., Inc. and is typified in a number of patents assigned to this company, including U.S.
Patent No. 4,423,299 (Gurol et al) and U.S. Patent No.4,696,860 (D.L. Epperson). The touch screen display disclosed in the '299 patent uses a flexible membrane to support a first set of parallel transparent conductors. These conductors face a second set of parallel transparent conductors mounted on a backplate which is secured to the surface of the computer monitor. The second set of conductors faces upward away from the monitor while the first set faces downward toward the monitor. The conductors of one set run horizontally while those of the other set run vertically so when superimposed they form a ~rid. The different iayers are closely spaced apart and held together on the outer periphery by, for example, spring clips. Betweer~ the two sets of a conductors is an air gap. Along the outside edge of lZ9~3 each layer is a bus which interconnects the conductors supportedon that layer. In this manner, electrical signals from the conductors are transmitted to appropriate electronic equipment.
When pressure from a finger or stylus is applied to the flexible 5 membrane, the first set of conductors will be deflected downward across the air gap into contact with the second set of conductors mounted on the backplate along the surface of the monitor. Contact between these sets of conductors acts as a mechanical closure of a switch to complete an electrical circuit 10 which is detected by the electronic equipment through the respective buses at the edge of the panel, thus providing a means for detecting the location of the switch closure. To prevent inadvertent contact between the sets of conductors, both the '299 and '860 patents disclose uniformly distributing 1~ transparent beads or bumps of non-conductive material to keep the sets of conductors apart in the air gap except when pressed by the operator.
In the mechanically deformable type of membrane described in the aforenoted patents, the first set of conductors 20 in the top membrane layer must flex or bend in order to make physical contact with the the second set of conductors below.
The degree of such bending is reduced in a another type of membrane touch scrsen such as described in U.S. Patent No.
This type of interactive display device is not truly a touch sensitive one since it relies essentially on photodetection rather than touch. Light beam arrays interrupted by the presence of a finger or other intrusive object likewise rely principally upon photodeleclion rather than touch.
One torm of touch sensitive display uses a flexible, deformable membrane formed of a transparent laminate which is placed over the display surface of the computer monitor. The laminate generally comprises two conductor planes deposited on a flexible medium so that when the user mechanically displaces one of the conductor planes by a fin~er or stylus, the conductors are brought into electrica~ contact with the conductors in the second plane. The electrical resistance of the conductor plane is changed as a function of the position of the touch on the membrane. Appropriate electronics are provided to translate the resistance value into the position corresponding with the touch.
One version of such touch screen membranes is manufactured by the John Fluke Mfg. Co., Inc. and is typified in a number of patents assigned to this company, including U.S.
Patent No. 4,423,299 (Gurol et al) and U.S. Patent No.4,696,860 (D.L. Epperson). The touch screen display disclosed in the '299 patent uses a flexible membrane to support a first set of parallel transparent conductors. These conductors face a second set of parallel transparent conductors mounted on a backplate which is secured to the surface of the computer monitor. The second set of conductors faces upward away from the monitor while the first set faces downward toward the monitor. The conductors of one set run horizontally while those of the other set run vertically so when superimposed they form a ~rid. The different iayers are closely spaced apart and held together on the outer periphery by, for example, spring clips. Betweer~ the two sets of a conductors is an air gap. Along the outside edge of lZ9~3 each layer is a bus which interconnects the conductors supportedon that layer. In this manner, electrical signals from the conductors are transmitted to appropriate electronic equipment.
When pressure from a finger or stylus is applied to the flexible 5 membrane, the first set of conductors will be deflected downward across the air gap into contact with the second set of conductors mounted on the backplate along the surface of the monitor. Contact between these sets of conductors acts as a mechanical closure of a switch to complete an electrical circuit 10 which is detected by the electronic equipment through the respective buses at the edge of the panel, thus providing a means for detecting the location of the switch closure. To prevent inadvertent contact between the sets of conductors, both the '299 and '860 patents disclose uniformly distributing 1~ transparent beads or bumps of non-conductive material to keep the sets of conductors apart in the air gap except when pressed by the operator.
In the mechanically deformable type of membrane described in the aforenoted patents, the first set of conductors 20 in the top membrane layer must flex or bend in order to make physical contact with the the second set of conductors below.
The degree of such bending is reduced in a another type of membrane touch scrsen such as described in U.S. Patent No.
4,686,332 (Greanias et al), which is assigned to the IBM
25 Corporation. The structure of the touch screen described in this patent is fairly similar to that of the mechanically deformable screens described above, except that the air gap has ~een replaced with a very thin non-conductive adhesive layer. There is therefor no mechanical switch action such as described above.
3 0 Rather, ths conductors radiate electromagnetic signals out from the surface of the screen. These signals can be detected by a radialive pickup stylus. The presence of a finger can be detected by a change in the capacitance of the conductor array while the location of the stylus is determined by the signal strangth of the 1~9~ ;3~
electro-magnetic radiation emitted by individual ones of the conductors.
The structure of the overlay membrane disclosed in the '332 patent can be better understood with reference to FIGS.
25 Corporation. The structure of the touch screen described in this patent is fairly similar to that of the mechanically deformable screens described above, except that the air gap has ~een replaced with a very thin non-conductive adhesive layer. There is therefor no mechanical switch action such as described above.
3 0 Rather, ths conductors radiate electromagnetic signals out from the surface of the screen. These signals can be detected by a radialive pickup stylus. The presence of a finger can be detected by a change in the capacitance of the conductor array while the location of the stylus is determined by the signal strangth of the 1~9~ ;3~
electro-magnetic radiation emitted by individual ones of the conductors.
The structure of the overlay membrane disclosed in the '332 patent can be better understood with reference to FIGS.
5 8 and 12 of that patent. The air gap has been replaced by the non-conductive adhesive serving as an insulation layer 52. The overlay 20 in Fl(à 12 comprises two rnajor portions, an inner laminate 56 and an outer laminate 58 which are attached by an adhesive layer 52'. The inner larninate is applied over the outer 10 surface of the glass face of a computer monitor. The inner laminate also has an anti-newton ring coating 53 which is applied to the display side of the overlay to eliminate newton rings when the inner laminate comes into contact with the glass ~ace of the monitor and an electrostatic shield layer of 15 transparent conductive material which is grounded and serves to shield th~ conductors of the overlay from noise generated by the monitor. The inner laminate also contains inner substrate layer 50 which is an optically clear layer of polyethylene terephthalate onto which is sputtered transparent wire coatings 2 0 of indium tin oxide arranged as parallel vertical conductors facing out from the monitor display. The outer substrate layer 54 of the outer laminate 58 is substantially the same as the inner substrate 50. Indium tin oxide conductors are likewise deposiled on ~he outer substrate layer 54, but facing inward 25 toward the monitor display and oriented at right angles to the vertical conductors deposited on the inner substrate 50. The inner and outer substrates are disposed so that the respective sets of conductors formed thereon face sach other. Both the inner and outer substrates are coated on the face containing lhe 3 0 conductors with a thin insulation layer of ultraviolet initiated vinyl acrylic polymer, 52 and 52", respectively, and both are joined with adhesive layer 52' of the same composition as the insulation layers. When the inner and outer laminates are joined, layers 52, 52', and 52" become indistinguishable and can be 129~363~L
regarded structurally as a single thin insulating layer betweenthe facing sets of transparent conductors.
Touch screen overlays such as disclosed in the foregoing prior art patents are deficient in several important 5 respects. One is the durability o~ the laminate, particularly the transparent conductors. indium-tin-oxide (ITO) is typically used for the conductor wires because of its transparent and conductive properties. This compound is a ceramic material belonging to a class of the materials knoYvn as transparent 10 conducting oxides. Beiny ceramic, these materials are quite brittle and can readily crack under tensile forces. Cracking of conductor wires in touch screens is very serious since electrical conductivity and therefor signal transrnission will be lost. In the touch screen overlays of the above described prior art, the 15 transparent wire conductors formed on the outer membrane substrate and facing down toward the monitor screen undergo significant tensile forces when a stylus or other hard instrument is forced against the touch screen. This is particularly severe in the prior art touch screens which have an 20 air gap between the two sets of conductors since a large deflection of the top flexible membrane creates large tensile forces in the transparent conductors ~ormed on the inside surface of the membrane. The stylus forces the top flexible membrane downward so that contact is made between the upper 25 and lower conductors. This creates large tensile forces on the inner surface of the upper membrane which carry the first set of wire conductors. These tensile forces can cause the conductor wires to crack and lose their ability to conduct electricity. The touch screen will therefore fail in any area where such cracking 30 has occurred.
Cracking of the conductors due to such tensile forces is also a serious problem in touch screens such as disclosed in the aforenoted U.S. Patent 4,~86,332 where the air gap is replaced with the adhesive layer. While this relatively hard.
35 thin layer makes the touch screen more durable, experimental ~36;3 tests with a moving stylus has shown that cracking o~ the upper iT0 conductors still occurs. In fact, a stylus readily cracks the transparent IT0 conductors with only hand pressure. The tensile forces are so great at the centerline of the stylus that 5 elongation of the IT0 conductors is sufficient to cause considerable eracking problems and, therefor, failure of the touch screen.
While increasing the thickness of the outer substrate layer 54 in the touch screen overlay of the '332 patent would 10 improve conduc~or durability somewhat, this additional thickness would weaken conductor si~nal strength significantly.
The additional thickness would so attenuate the electromagnetic signals ernitte~ by the the transparent conductors that a change in capacitance due to finger touch could no longer be detected 15 effectively. The strength of the signal received by the stylus would also be weakened significantly.
Moreover, irrespec~ive of the thickness of the upper subtrate, there are significant ~i3nal losse~ in the touch screen overlay of the '332 patent due to the screening of the signal 20 from the lower conductors by the upper conductors. This is due to the close proxintity of the two sets of conductors in this prior art overlay, with the two sets ~f conductors facing one another and separated only by the adhesive layer. The electromagnetic signals emanating from the lower conductors are therefor 25 intercepted and absorbed by the upper conductors, thereby greatly attenuating the signal strength available for detection at the surface of the touch screen overlay.
Another disadvant~ye o~ the laminate touch screen disclosed in the aforenoted U.S. Patent No. 4,686,332 is due to 30 deficiencies o~ the adhesive layer 52, which is a thin layer of ultra~Jiolet light initiated vinyl acrylic polymer. This adhesive layer has been found to have 400r peel strength, due in part to the incompatibility of this adhesive with the base film supporting the transparent wires. The peel strength is also poor 3~ due to the inadequate cure of this adhesive because the 29~6 ultraviolet light needed to cure or initiate the acrylic polymer is readily adsorbed in the other substrates supporting the ITO
conductors. Another deficiency is that the adhesive layer, while transparent to light, does not readily lend itself to producing a 5 flat, distortion free touch screen overlay.
SUMMARY QF THE INVENTION
The present invention greatly improves the durability of touch screen overlays by providing a laminate structure which eliminates cracking of the transparent conductors when the overlay is subjected to the rubbing pressures exerted by a 15 stylus. The laminate structure of the present invention is also more durable ~ong term since fatigue stress is reduced.
Moreover, improved durability of the touch screen overlay is achieved without adversely affecting the signal strength of the lower set of transparent wire conductors In fact, the lower 20 conductor signal strength at the surface of the overlay is greatly improved.
The improved durability is achieved by reversing the dominate forces on the transparent conductors deposited on the top layer of the membrane laminate. In the prior art, these 25 conductors were subjected to tension which leads to cracking. In the laminate structure of the presen~ invention. These conductors are subjected principally to compression forces when a stylus rubs along the top of the touch screen overlay.
Transparent conducting oxides of ceramic material such as iTO
30 are quite brittle and readily erack under tension exerted by tensile forces. These materials, however, can withstand a significant amount of compressive forces.
The present invention makes use of this phenomenon by modifying the laminate structure so that both the upper and 3 5 lower set of transparent conductors are subjected principally to ~Z~i363~
\
regarded structurally as a single thin insulating layer betweenthe facing sets of transparent conductors.
Touch screen overlays such as disclosed in the foregoing prior art patents are deficient in several important 5 respects. One is the durability o~ the laminate, particularly the transparent conductors. indium-tin-oxide (ITO) is typically used for the conductor wires because of its transparent and conductive properties. This compound is a ceramic material belonging to a class of the materials knoYvn as transparent 10 conducting oxides. Beiny ceramic, these materials are quite brittle and can readily crack under tensile forces. Cracking of conductor wires in touch screens is very serious since electrical conductivity and therefor signal transrnission will be lost. In the touch screen overlays of the above described prior art, the 15 transparent wire conductors formed on the outer membrane substrate and facing down toward the monitor screen undergo significant tensile forces when a stylus or other hard instrument is forced against the touch screen. This is particularly severe in the prior art touch screens which have an 20 air gap between the two sets of conductors since a large deflection of the top flexible membrane creates large tensile forces in the transparent conductors ~ormed on the inside surface of the membrane. The stylus forces the top flexible membrane downward so that contact is made between the upper 25 and lower conductors. This creates large tensile forces on the inner surface of the upper membrane which carry the first set of wire conductors. These tensile forces can cause the conductor wires to crack and lose their ability to conduct electricity. The touch screen will therefore fail in any area where such cracking 30 has occurred.
Cracking of the conductors due to such tensile forces is also a serious problem in touch screens such as disclosed in the aforenoted U.S. Patent 4,~86,332 where the air gap is replaced with the adhesive layer. While this relatively hard.
35 thin layer makes the touch screen more durable, experimental ~36;3 tests with a moving stylus has shown that cracking o~ the upper iT0 conductors still occurs. In fact, a stylus readily cracks the transparent IT0 conductors with only hand pressure. The tensile forces are so great at the centerline of the stylus that 5 elongation of the IT0 conductors is sufficient to cause considerable eracking problems and, therefor, failure of the touch screen.
While increasing the thickness of the outer substrate layer 54 in the touch screen overlay of the '332 patent would 10 improve conduc~or durability somewhat, this additional thickness would weaken conductor si~nal strength significantly.
The additional thickness would so attenuate the electromagnetic signals ernitte~ by the the transparent conductors that a change in capacitance due to finger touch could no longer be detected 15 effectively. The strength of the signal received by the stylus would also be weakened significantly.
Moreover, irrespec~ive of the thickness of the upper subtrate, there are significant ~i3nal losse~ in the touch screen overlay of the '332 patent due to the screening of the signal 20 from the lower conductors by the upper conductors. This is due to the close proxintity of the two sets of conductors in this prior art overlay, with the two sets ~f conductors facing one another and separated only by the adhesive layer. The electromagnetic signals emanating from the lower conductors are therefor 25 intercepted and absorbed by the upper conductors, thereby greatly attenuating the signal strength available for detection at the surface of the touch screen overlay.
Another disadvant~ye o~ the laminate touch screen disclosed in the aforenoted U.S. Patent No. 4,686,332 is due to 30 deficiencies o~ the adhesive layer 52, which is a thin layer of ultra~Jiolet light initiated vinyl acrylic polymer. This adhesive layer has been found to have 400r peel strength, due in part to the incompatibility of this adhesive with the base film supporting the transparent wires. The peel strength is also poor 3~ due to the inadequate cure of this adhesive because the 29~6 ultraviolet light needed to cure or initiate the acrylic polymer is readily adsorbed in the other substrates supporting the ITO
conductors. Another deficiency is that the adhesive layer, while transparent to light, does not readily lend itself to producing a 5 flat, distortion free touch screen overlay.
SUMMARY QF THE INVENTION
The present invention greatly improves the durability of touch screen overlays by providing a laminate structure which eliminates cracking of the transparent conductors when the overlay is subjected to the rubbing pressures exerted by a 15 stylus. The laminate structure of the present invention is also more durable ~ong term since fatigue stress is reduced.
Moreover, improved durability of the touch screen overlay is achieved without adversely affecting the signal strength of the lower set of transparent wire conductors In fact, the lower 20 conductor signal strength at the surface of the overlay is greatly improved.
The improved durability is achieved by reversing the dominate forces on the transparent conductors deposited on the top layer of the membrane laminate. In the prior art, these 25 conductors were subjected to tension which leads to cracking. In the laminate structure of the presen~ invention. These conductors are subjected principally to compression forces when a stylus rubs along the top of the touch screen overlay.
Transparent conducting oxides of ceramic material such as iTO
30 are quite brittle and readily erack under tension exerted by tensile forces. These materials, however, can withstand a significant amount of compressive forces.
The present invention makes use of this phenomenon by modifying the laminate structure so that both the upper and 3 5 lower set of transparent conductors are subjected principally to ~Z~i363~
\
compression when a stylus is used. This is achieved in a preferred embodiment of the present invention by reversing the orientation of the upper set of conductors so that they face upward away from the monitor screen as do the lower set of 5 conductors. The present invention also thereby improves the signal strength of the lower conductors at the overlay surface by reducing the screening of the lower conductors by the upper conductors since the two sets of conductors are now further spaced apart in the new laminate structure.
BRIEF DESCRIPTION OF THE DRAWING~
The present invention may be more fully understood from the following detailed description thereof taken in connection with the accompanying drawings, which form a par of this application and in which:
FIG. 1 is a schematic illustrating the touch screen 20 overlay of the present invention in its intended environment at a computer workstation.
FIG. 2 illustrates a touch screen overlay having an improved bondply adhesive for laminating layers of the overlay together.
FIG. 3 is a diagrammatic illustration of the tension and compression forces exerted on a upper substrate of a prior art overlay.
FIG. 4 is a graph illustrating the relationship between conductor elongation due to tension and conductor failure due to cracking.
FIG. 5 is a graphic representation of computer modeling of strains in the touch screen overlay of FIG. 2 and comparing the same with the touch screen overlay of FIG. 6.
FIG 6 shows the new laminate structure of ~he touch screen overlay of the present invention.
-` lZ5~8~i3~L
g TAILED DESCRIPTION OF THE INVENT!QN
~;, The touch screen overlay of the present invention is designed for use w;th a personal computer or other type of computer terminal or workstation where an interactive input device which permits either ~inger touch or stylus cietection 10 input would be useful. Such a computer workstation is shown schematically in FIG.1 which includes a computer monitor such as a cathode ray tube (CRT) 12 and a control processor 22 which operates on stored program instructions and contains the electronics to provide detection of either finger touch location 15 or stylus ~ocation Ot boti).
The touch screen overlay 10 is attached by suitable means to the display screen of the CRT 12. A plurality of transparent conductors disposed vertically and horizontally in different layers of the overlay form a grid pattern of conductors 20 shown generally by reference number 11 in the overlay 10. The vertical conduGtors are connected to a horizontal bus 14 located in the non-viewing arsa ot CRT 12 along a side of the overlay layer carrying the vertical conductors. Likewise, the horizontal conductors are connected to a vertical bus 16 iocated in the non-25 viewing area of the CRT along a side of the overlay layer carrying the horizontal conductors. Electrical signals from the transparent conductors of the overlay are transmitted via these buses to a flexible circuit 18 which is connected to the control processor 22 via a cable and connectors shown generally as 20.
3 0 A stylus 24 capable of detecting electromagnetic radiation generated by the transparent conductors of the overlay 10 is also connected to the control processor 22. Tho stored program instructions and electronics of the control processor is able to correlate the signals from the styius 24 and from the 3 5 conductor grid to determine the horizontal and vertical position 291~363~
of the stylus anywhere along the viewing surface of the CRT and thereby display the movement of the stylus point on the CRT
screen. Electronics in the control processor 2Z is also able to detect the position of a finger touch through the change in capacitance between conductors at the corresponding location on the overlay 10.
FIG. 2 illustrates a touch screen overlay 10 which may be used with the system of FIG. 1 . The overlay 10 is similar to that described in the aforenoted US Patent No. 4,686,332, except that the vinyl acrylic layer of the prior art overlay has been replaced by a sheet adhesive or bondply. The overlay 10 comprises a lower substrate 32 formed from a sheet of polyester material such as polyethylene terephthalate, which is transparent and electrically insulative. The lower substrate 32 is fairly thin, on the order of about 5 mil or about 0.005 inches.
The lower substrate may be directly attached to the glass display surface 13 of the CRT 12 by, for example, a thin layer of transparent adhesive 33 havin~ a thickness of about 1 mil. An anti-newton ring coating and an electrostatic shield layer may also be included between the face of the CRT 12 and the lower substrate 32. On the upper surface (the side facing away from the CRT) of the lower substrate 32 is deposited either a horizontal or vertical array of transparent conductors 34. These conductors are typically deposited by magnetron sputtering a transparent conducting material, usually a ceramic material such as indiurn-tin-oxide (ITO). The thickness of each transparent conductor 34 is approximately 1000 angstroms. The ITO conductors are etched t~ provide approximately 25 mils wide line and are spaced approximately 125 mils center to center.
~he overlay 10 also comprises an upper substrate 36 formed of the same polyester material as the lower substrate 32. The upper substrate is somewhat thinner than the lower substrate, approximately on the order of 2 mils. On the lower surface of the upper substrate (the side facing toward the- CRT) 3~ is deposited an array of transparent conductors 38 similar to lZ91~3~3~
, 1 those deposited in the lower substrate, except that Qrientation of the array (horizontal or vertical) is opposite that of the lower substrate in order t~ present the grid-like structure referred to earlier. The upper s~rface o~ the upper substrate 36 7aces the 5 viewer and is contacted by the finger ~as shown in FIG 2) or by a stylus. This surface may be overcoated by an antiglare coat.
The upper and lower substrates 36,32 are joined together in a laminate by a sheet adhesive or bondply 40. The iatter is ~ ~hr~e-lay~r sandwich formed of a transparent 10 polyester base film ~2 of about 0.5 mils thick coated on both sides with a t,ansparent polyester based adhesive 44, each coating 44 being approxima1eJy also 0.5 mils thick. B~th the polyester b~e filrn 42 and the polyester-based adhesive coatinys 44 ar~ compatible wrth one another and can ~ cured by 15 means other than ultraviolet light, a major disadvantage encountered with the vin~,l acrylic adhesive used in the overlay of the aforenoted US Patent No. 4,686,332. The polyester adhesiv~ coatiny 44 is a heat setting adhesive. More~ver, the polyester based adhesives 44 of bondply 40 are compatible with 20 the polyester material of the upper and lower substrates 36,32 supporting the transparen~ conductor arrays. These adhesives can therefor be readily cured at elevated temperatures and applied pressure. ~t~e peel strength of the polyester-~ased adhe~i~s 44 is ~uperior ~o the vinyl acrylic materia~ used in the 2~ above described prior art overlay~ and the process for curing provides a transparent, flat and distortion-free touch screen ~isplay whi~t~ has ~ptic~l pro~erties superior to the Dverlay disclosed in the a~oren~ted US Patent No. 4,686,332.
An additiDnal advantage Df the bondply 40 is that 30 each o~ i~s lay~rs, incl~ding ttle polyester-based adhesive layers 44, c~me m she~t ~rm. ~his permils far easier proc~ssing and more c~n~rolJed thickness ~ the overall overlay laminats as compared with th~ earlier laminate wherein the vinyl acrylic adhesive must be applied in paste fDrm.
:
~ EL-4301 The improved laminate structure of the touch screen overlay 10 of FIG. 2 still sutfers from the conductor durability problem discussed earlier in connection with the prior art touch screens. The transparent wire conductors 38 disposed on the 5 lower surface of the upper substrate 36 are subjected to tensile forces created by the pressure exerted by a movin~ stylus on the top or writing surface of the upper substrate 36. Since these conductors are formed of a brittle ceramic material such as ITO, they readily crack vnder tensi~n, thereby interrupting electrical 10 conductivity and signai transmission in the overlay.
FIG. 3 diagrammatically ~llusttates the forces exerted on the upper substrate of the overlay laminate with an air gap between the two sets of conductor arrays. Transparent beads or bumps 35 maintain the air gap and separ~tion between 15 the two sets of conductors. The stylus 24 forces the top substrate 36 downward until contact is made between the upper transparent conductors 33 and the lower conductors 34 of the lower substrate 32. This do~nward deflection exerts both compressive and tensile forces on the upper substrate 36. As 70 seen in FIG. 3, the upper substrate 36 is in compression at or near the top surface and in tension at or near its lower surface.
These forces tend to cancel on~ another toward the middle of the substrate's thickness. Since the bottom surface (facing the CRT) of the upper substrate is where the prior art overlays deposited 25 the upper set of transparent conductors and since this surface is subjected to the largest tensile forces exerted on the upper substrate when contacted by stylus, the upper ITO conductors were very prone to cracking.
As noted earlier, cracking of ITO conductors due to 30 tensile forces at the lower surface of the upper substrate is also a serious problem for ~he touch screen overlays not ~sing an air gap for mechanical switch closure, such as the touch screen overlay disclosed in the aforenoted US Patent 4,686,332 and the improved version shown in FIG. 2 of the present application.
35 While the upper conductors do not deflect as much in the more 36~;~
durable overlay shown in FIG. 2, experimental tests have shown that cracking of the upper ITO conductors 38 still occurs with only hand pressure on a stylus. This can better be explained by reference to the graphs of FIGS. 4 and 5.
FIG 4 illustrates the relationship of ITO conductors subjected to elongation due to tensile forces to the ability of such conductors to transmit electrical signals. The y-axis represents the resistance of the ITO conductors normalized to the value at zero tensile stress (R/Ro). The x-axis represents 10 the percent elongation of the ITO wire conductor.
FIG 4 shows experinnental tests conducted on three diffsrent samples of ITO wire conductors deposited on 5 mil polyester substrates (shown in solid, dotted and dashed lines). What FIG.4 shows is that in all three samples, the resistance in the wire 15 conductor remains constant between 0 and about 1.5%
elongation, and the touch screen can function without loss of signal. Above about 1.5% elongation, resistance increases abruptly, indicating fracture and loss of signal strength. What is surprising is how ~ittle pressure need be exerted by the stylus 20 on the top surface of the upper substrate to place its lower surface, and the ITO wire conductors supported thereon, under sufficient tensile forces to exceed 1.5 % elongation. This becomes clearer by re~erence to FIG. 5.
The graph of FIG. 5 represents a computer modeiing 25 of strains in a touch screen using a stylus weighted to approximate hand pressure, which is about 1000 grams. The y-axis represents percent elongation of ITO wire conductors.
Above 0, lhere is positive % elongation due to tension. Below 0, there is negative % elongation due to compression. The x-axis 3 0 represents distance from the centerline of the stylus point extending out past the radius of the stylus point. The straight horizontal dashed line at approximately 0.0175 or 1.75%
elongation is chosen as representing the elongation point at which the ITO conductors have broken and failed. Curve A shows 35 the cornputer modeling of the touch screen overlay of FIG. 2. It ii3'~
is readily apparent that at or near the stylus centerline, the lower surface of the upper substrate 36 is being subj'ected to large tensile forces by the stylus, sufficient to cause over 4%
elongation in the ITO conductors 38 carried by this surface, or more than twice the % elongation necessary to crack the wire conductors while elongation and tension drop off dramatically away from the area of the stylus centerline. In fact, the computer model shows that the lower surface of the upper substrate 36 and the conductors 38 carried thereon may be subjected to compression at areas away from the stylus centerline. This is consistent with what should be expected away from the centerline where, as shown in FIG, 3, the forces along the lower surface of the upper substrate below the point of stylus deflection go from tension to compression and then 1~ back to neutral further away from the deflection point. The damage caused by the high tensile forces at or near the stylus centerline is, however, more than sufficient to cause significant conductor cracking and failure.
The touch screen overlay of the present invention solves these problems by modifying the structure of the overlay 10 of FIG. 2 so that the transparent wire conductors in the upper as well as lower conductor array are subjected principally to compression rather than tension. The lower array of conductors 34, because they are on the upper surface of the lower substrate 2~ 32 and face up away from the CRT 12, are in compression where the touch screen is contacted by the stylus. The improved Iaminate overlay of the present invention, shown generally as 50 in FIG. 6, accomplishes the same for the upper conductor array by essentially ~flipping" the layers of the laminate so that the ' 30 upper array ol conductors is on the top surface of the upper substrate and also faces upward.
FIG. 6 illustrates this flipped overlay laminate structure. The lower substrate 32 and lower array of ITO
conductors as well as their attachment to the CRT 12 remains essentially the same as in the overlay of FIG. 2. An anti-newton 91!3~;3 3L
ring coating and an electrostatic shield layer may likewise be included between the face of the CRT 12 and the lower substrate 32. The upper substrate, now referred ~o as 56, has been "flipped" so that the upper array of ITO conductors, now referred 5 to as 58, face upward away from the CRT. Upper substrate 56 is otherwise similar to the upper substrate 36 of FIG. 2, formed from sheet of polyester material such as polyethylene terephthalate about 2 mils thick. The ITO conductors 58 are likewise similar to the upper conductors 38 of FIG 2. The lower 10 substrate 34 and the upper substrate 56 are bonded together by a sheet of polyester based adhesive 54 which is similar to the adhesive sheet 44 of FIG. 2. The adhesive sheet 54 could alternatively be located only at the perimeter of the laminated structure in the non-viewing area, leaving the upper and lower 15 substrates 56,36 touching or separated by air in the viewing area. Adhesive sheet 54 may also be dispensed with entirely if the substrates 56,32 are clamped together at the edge of the overlay by other means such as disclosed in the air gap prior art overlays described earlier. The top surface of the upper 20 substrate 56, which faces the viewer, is covered with a sheet 60 of polyester material similar to substrates 32 and 56 of the overlay laminate. Cover sheet 60 is about 1 mil thick and is laminated to the upper substrate 56 by mearls of a second sheet of polyester adhesive similar to the one joining the lower and 25 upper substrates 32,56. Both adhesive sheets 54 are about 0.5 mils thick. The top surface of the cover sheet 60 may be coated by an antiglare hardcoat. Cover sheet 60 could alternatively be applied to the upper substrate 56 by other means, such as by spraying, screen printing, vapor deposition or the like, and may 3 0 be of minimal thickness sufficient to provide scratch protection.
Referring again to FIG. 5, curve B repres8nts a computer model of the flipped structure touch screen overlay of FIG 6. As is clearly evident, the ITO conductors are in compression at the stylus centerline since the elongation of the 35 upper conductors 58 is a negative 1.0%. This is a far cry from . .~ .~ . . .
~L~29~
the high tensile forces exerted on the upper conductors 38 of the overlay of FIG. 2. Since ITO and other transparent conducting oxides of brittle ceramic material can withstand a large amount of compression forces, the "flipped" structure of FIG. 6 5 represents a significant advance touch screen durability.
The flipped overlay laminate structure of FIG. 6 also minimizes lower conductor signal loss due to screening by the upper conductors. The lower conductor signal s~rength at the surface of the overlay is greatly improved since the upper 10 conductors 58 are further separated from the lower conductors 34 by the thickness of at least substrate 56, thus significantly diminishing the effect of screening by the upper conductors 58.
Because the thickness of the overlay, particularly between the lower conductors 34 and the overlay surface, has been reduced, 15 signal strength frorn both upper and lower sets of conductors has also been improved. Moreover, this new flipped structure is readily adaptable to even greater signal strength enhancement at the overlay surface because the cover sheet 60, which now does not support any transparent conductors, can be reduced to 20 minimal thickness sufficient only for scratch protection. This will further reduce attenuation of the electromagnetic signals emitted by both sets of conductors passing through this layer.
, Although specific embodiments of the invention been disclosed, it will be understood by those having skill in the art 25 that changes may be rnade to these embodiments without departing from the spirit and scope of the invention.
,.",,. ,- ... .
.. ..
BRIEF DESCRIPTION OF THE DRAWING~
The present invention may be more fully understood from the following detailed description thereof taken in connection with the accompanying drawings, which form a par of this application and in which:
FIG. 1 is a schematic illustrating the touch screen 20 overlay of the present invention in its intended environment at a computer workstation.
FIG. 2 illustrates a touch screen overlay having an improved bondply adhesive for laminating layers of the overlay together.
FIG. 3 is a diagrammatic illustration of the tension and compression forces exerted on a upper substrate of a prior art overlay.
FIG. 4 is a graph illustrating the relationship between conductor elongation due to tension and conductor failure due to cracking.
FIG. 5 is a graphic representation of computer modeling of strains in the touch screen overlay of FIG. 2 and comparing the same with the touch screen overlay of FIG. 6.
FIG 6 shows the new laminate structure of ~he touch screen overlay of the present invention.
-` lZ5~8~i3~L
g TAILED DESCRIPTION OF THE INVENT!QN
~;, The touch screen overlay of the present invention is designed for use w;th a personal computer or other type of computer terminal or workstation where an interactive input device which permits either ~inger touch or stylus cietection 10 input would be useful. Such a computer workstation is shown schematically in FIG.1 which includes a computer monitor such as a cathode ray tube (CRT) 12 and a control processor 22 which operates on stored program instructions and contains the electronics to provide detection of either finger touch location 15 or stylus ~ocation Ot boti).
The touch screen overlay 10 is attached by suitable means to the display screen of the CRT 12. A plurality of transparent conductors disposed vertically and horizontally in different layers of the overlay form a grid pattern of conductors 20 shown generally by reference number 11 in the overlay 10. The vertical conduGtors are connected to a horizontal bus 14 located in the non-viewing arsa ot CRT 12 along a side of the overlay layer carrying the vertical conductors. Likewise, the horizontal conductors are connected to a vertical bus 16 iocated in the non-25 viewing area of the CRT along a side of the overlay layer carrying the horizontal conductors. Electrical signals from the transparent conductors of the overlay are transmitted via these buses to a flexible circuit 18 which is connected to the control processor 22 via a cable and connectors shown generally as 20.
3 0 A stylus 24 capable of detecting electromagnetic radiation generated by the transparent conductors of the overlay 10 is also connected to the control processor 22. Tho stored program instructions and electronics of the control processor is able to correlate the signals from the styius 24 and from the 3 5 conductor grid to determine the horizontal and vertical position 291~363~
of the stylus anywhere along the viewing surface of the CRT and thereby display the movement of the stylus point on the CRT
screen. Electronics in the control processor 2Z is also able to detect the position of a finger touch through the change in capacitance between conductors at the corresponding location on the overlay 10.
FIG. 2 illustrates a touch screen overlay 10 which may be used with the system of FIG. 1 . The overlay 10 is similar to that described in the aforenoted US Patent No. 4,686,332, except that the vinyl acrylic layer of the prior art overlay has been replaced by a sheet adhesive or bondply. The overlay 10 comprises a lower substrate 32 formed from a sheet of polyester material such as polyethylene terephthalate, which is transparent and electrically insulative. The lower substrate 32 is fairly thin, on the order of about 5 mil or about 0.005 inches.
The lower substrate may be directly attached to the glass display surface 13 of the CRT 12 by, for example, a thin layer of transparent adhesive 33 havin~ a thickness of about 1 mil. An anti-newton ring coating and an electrostatic shield layer may also be included between the face of the CRT 12 and the lower substrate 32. On the upper surface (the side facing away from the CRT) of the lower substrate 32 is deposited either a horizontal or vertical array of transparent conductors 34. These conductors are typically deposited by magnetron sputtering a transparent conducting material, usually a ceramic material such as indiurn-tin-oxide (ITO). The thickness of each transparent conductor 34 is approximately 1000 angstroms. The ITO conductors are etched t~ provide approximately 25 mils wide line and are spaced approximately 125 mils center to center.
~he overlay 10 also comprises an upper substrate 36 formed of the same polyester material as the lower substrate 32. The upper substrate is somewhat thinner than the lower substrate, approximately on the order of 2 mils. On the lower surface of the upper substrate (the side facing toward the- CRT) 3~ is deposited an array of transparent conductors 38 similar to lZ91~3~3~
, 1 those deposited in the lower substrate, except that Qrientation of the array (horizontal or vertical) is opposite that of the lower substrate in order t~ present the grid-like structure referred to earlier. The upper s~rface o~ the upper substrate 36 7aces the 5 viewer and is contacted by the finger ~as shown in FIG 2) or by a stylus. This surface may be overcoated by an antiglare coat.
The upper and lower substrates 36,32 are joined together in a laminate by a sheet adhesive or bondply 40. The iatter is ~ ~hr~e-lay~r sandwich formed of a transparent 10 polyester base film ~2 of about 0.5 mils thick coated on both sides with a t,ansparent polyester based adhesive 44, each coating 44 being approxima1eJy also 0.5 mils thick. B~th the polyester b~e filrn 42 and the polyester-based adhesive coatinys 44 ar~ compatible wrth one another and can ~ cured by 15 means other than ultraviolet light, a major disadvantage encountered with the vin~,l acrylic adhesive used in the overlay of the aforenoted US Patent No. 4,686,332. The polyester adhesiv~ coatiny 44 is a heat setting adhesive. More~ver, the polyester based adhesives 44 of bondply 40 are compatible with 20 the polyester material of the upper and lower substrates 36,32 supporting the transparen~ conductor arrays. These adhesives can therefor be readily cured at elevated temperatures and applied pressure. ~t~e peel strength of the polyester-~ased adhe~i~s 44 is ~uperior ~o the vinyl acrylic materia~ used in the 2~ above described prior art overlay~ and the process for curing provides a transparent, flat and distortion-free touch screen ~isplay whi~t~ has ~ptic~l pro~erties superior to the Dverlay disclosed in the a~oren~ted US Patent No. 4,686,332.
An additiDnal advantage Df the bondply 40 is that 30 each o~ i~s lay~rs, incl~ding ttle polyester-based adhesive layers 44, c~me m she~t ~rm. ~his permils far easier proc~ssing and more c~n~rolJed thickness ~ the overall overlay laminats as compared with th~ earlier laminate wherein the vinyl acrylic adhesive must be applied in paste fDrm.
:
~ EL-4301 The improved laminate structure of the touch screen overlay 10 of FIG. 2 still sutfers from the conductor durability problem discussed earlier in connection with the prior art touch screens. The transparent wire conductors 38 disposed on the 5 lower surface of the upper substrate 36 are subjected to tensile forces created by the pressure exerted by a movin~ stylus on the top or writing surface of the upper substrate 36. Since these conductors are formed of a brittle ceramic material such as ITO, they readily crack vnder tensi~n, thereby interrupting electrical 10 conductivity and signai transmission in the overlay.
FIG. 3 diagrammatically ~llusttates the forces exerted on the upper substrate of the overlay laminate with an air gap between the two sets of conductor arrays. Transparent beads or bumps 35 maintain the air gap and separ~tion between 15 the two sets of conductors. The stylus 24 forces the top substrate 36 downward until contact is made between the upper transparent conductors 33 and the lower conductors 34 of the lower substrate 32. This do~nward deflection exerts both compressive and tensile forces on the upper substrate 36. As 70 seen in FIG. 3, the upper substrate 36 is in compression at or near the top surface and in tension at or near its lower surface.
These forces tend to cancel on~ another toward the middle of the substrate's thickness. Since the bottom surface (facing the CRT) of the upper substrate is where the prior art overlays deposited 25 the upper set of transparent conductors and since this surface is subjected to the largest tensile forces exerted on the upper substrate when contacted by stylus, the upper ITO conductors were very prone to cracking.
As noted earlier, cracking of ITO conductors due to 30 tensile forces at the lower surface of the upper substrate is also a serious problem for ~he touch screen overlays not ~sing an air gap for mechanical switch closure, such as the touch screen overlay disclosed in the aforenoted US Patent 4,686,332 and the improved version shown in FIG. 2 of the present application.
35 While the upper conductors do not deflect as much in the more 36~;~
durable overlay shown in FIG. 2, experimental tests have shown that cracking of the upper ITO conductors 38 still occurs with only hand pressure on a stylus. This can better be explained by reference to the graphs of FIGS. 4 and 5.
FIG 4 illustrates the relationship of ITO conductors subjected to elongation due to tensile forces to the ability of such conductors to transmit electrical signals. The y-axis represents the resistance of the ITO conductors normalized to the value at zero tensile stress (R/Ro). The x-axis represents 10 the percent elongation of the ITO wire conductor.
FIG 4 shows experinnental tests conducted on three diffsrent samples of ITO wire conductors deposited on 5 mil polyester substrates (shown in solid, dotted and dashed lines). What FIG.4 shows is that in all three samples, the resistance in the wire 15 conductor remains constant between 0 and about 1.5%
elongation, and the touch screen can function without loss of signal. Above about 1.5% elongation, resistance increases abruptly, indicating fracture and loss of signal strength. What is surprising is how ~ittle pressure need be exerted by the stylus 20 on the top surface of the upper substrate to place its lower surface, and the ITO wire conductors supported thereon, under sufficient tensile forces to exceed 1.5 % elongation. This becomes clearer by re~erence to FIG. 5.
The graph of FIG. 5 represents a computer modeiing 25 of strains in a touch screen using a stylus weighted to approximate hand pressure, which is about 1000 grams. The y-axis represents percent elongation of ITO wire conductors.
Above 0, lhere is positive % elongation due to tension. Below 0, there is negative % elongation due to compression. The x-axis 3 0 represents distance from the centerline of the stylus point extending out past the radius of the stylus point. The straight horizontal dashed line at approximately 0.0175 or 1.75%
elongation is chosen as representing the elongation point at which the ITO conductors have broken and failed. Curve A shows 35 the cornputer modeling of the touch screen overlay of FIG. 2. It ii3'~
is readily apparent that at or near the stylus centerline, the lower surface of the upper substrate 36 is being subj'ected to large tensile forces by the stylus, sufficient to cause over 4%
elongation in the ITO conductors 38 carried by this surface, or more than twice the % elongation necessary to crack the wire conductors while elongation and tension drop off dramatically away from the area of the stylus centerline. In fact, the computer model shows that the lower surface of the upper substrate 36 and the conductors 38 carried thereon may be subjected to compression at areas away from the stylus centerline. This is consistent with what should be expected away from the centerline where, as shown in FIG, 3, the forces along the lower surface of the upper substrate below the point of stylus deflection go from tension to compression and then 1~ back to neutral further away from the deflection point. The damage caused by the high tensile forces at or near the stylus centerline is, however, more than sufficient to cause significant conductor cracking and failure.
The touch screen overlay of the present invention solves these problems by modifying the structure of the overlay 10 of FIG. 2 so that the transparent wire conductors in the upper as well as lower conductor array are subjected principally to compression rather than tension. The lower array of conductors 34, because they are on the upper surface of the lower substrate 2~ 32 and face up away from the CRT 12, are in compression where the touch screen is contacted by the stylus. The improved Iaminate overlay of the present invention, shown generally as 50 in FIG. 6, accomplishes the same for the upper conductor array by essentially ~flipping" the layers of the laminate so that the ' 30 upper array ol conductors is on the top surface of the upper substrate and also faces upward.
FIG. 6 illustrates this flipped overlay laminate structure. The lower substrate 32 and lower array of ITO
conductors as well as their attachment to the CRT 12 remains essentially the same as in the overlay of FIG. 2. An anti-newton 91!3~;3 3L
ring coating and an electrostatic shield layer may likewise be included between the face of the CRT 12 and the lower substrate 32. The upper substrate, now referred ~o as 56, has been "flipped" so that the upper array of ITO conductors, now referred 5 to as 58, face upward away from the CRT. Upper substrate 56 is otherwise similar to the upper substrate 36 of FIG. 2, formed from sheet of polyester material such as polyethylene terephthalate about 2 mils thick. The ITO conductors 58 are likewise similar to the upper conductors 38 of FIG 2. The lower 10 substrate 34 and the upper substrate 56 are bonded together by a sheet of polyester based adhesive 54 which is similar to the adhesive sheet 44 of FIG. 2. The adhesive sheet 54 could alternatively be located only at the perimeter of the laminated structure in the non-viewing area, leaving the upper and lower 15 substrates 56,36 touching or separated by air in the viewing area. Adhesive sheet 54 may also be dispensed with entirely if the substrates 56,32 are clamped together at the edge of the overlay by other means such as disclosed in the air gap prior art overlays described earlier. The top surface of the upper 20 substrate 56, which faces the viewer, is covered with a sheet 60 of polyester material similar to substrates 32 and 56 of the overlay laminate. Cover sheet 60 is about 1 mil thick and is laminated to the upper substrate 56 by mearls of a second sheet of polyester adhesive similar to the one joining the lower and 25 upper substrates 32,56. Both adhesive sheets 54 are about 0.5 mils thick. The top surface of the cover sheet 60 may be coated by an antiglare hardcoat. Cover sheet 60 could alternatively be applied to the upper substrate 56 by other means, such as by spraying, screen printing, vapor deposition or the like, and may 3 0 be of minimal thickness sufficient to provide scratch protection.
Referring again to FIG. 5, curve B repres8nts a computer model of the flipped structure touch screen overlay of FIG 6. As is clearly evident, the ITO conductors are in compression at the stylus centerline since the elongation of the 35 upper conductors 58 is a negative 1.0%. This is a far cry from . .~ .~ . . .
~L~29~
the high tensile forces exerted on the upper conductors 38 of the overlay of FIG. 2. Since ITO and other transparent conducting oxides of brittle ceramic material can withstand a large amount of compression forces, the "flipped" structure of FIG. 6 5 represents a significant advance touch screen durability.
The flipped overlay laminate structure of FIG. 6 also minimizes lower conductor signal loss due to screening by the upper conductors. The lower conductor signal s~rength at the surface of the overlay is greatly improved since the upper 10 conductors 58 are further separated from the lower conductors 34 by the thickness of at least substrate 56, thus significantly diminishing the effect of screening by the upper conductors 58.
Because the thickness of the overlay, particularly between the lower conductors 34 and the overlay surface, has been reduced, 15 signal strength frorn both upper and lower sets of conductors has also been improved. Moreover, this new flipped structure is readily adaptable to even greater signal strength enhancement at the overlay surface because the cover sheet 60, which now does not support any transparent conductors, can be reduced to 20 minimal thickness sufficient only for scratch protection. This will further reduce attenuation of the electromagnetic signals emitted by both sets of conductors passing through this layer.
, Although specific embodiments of the invention been disclosed, it will be understood by those having skill in the art 25 that changes may be rnade to these embodiments without departing from the spirit and scope of the invention.
,.",,. ,- ... .
.. ..
Claims (14)
1. A touch screen overlay for use on the viewing surface of a visual display device comprising:
a first flexible substrate of transparent insulative material one surface adapted for attachment to the viewing surface of said visual display device;
a first set of transparent conductors formed in a parallel array on a second surface of said first flexible substrate, said second surface and the conductors thereon facing away from the viewing surface of said visual display device;
a second flexible substrate of transparent insulative material disposed at one surface thereof adjacent to the second surface of said first flexible substrate;
a second set of transparent conductors formed in a parallel array on a second surface of said second flexible substrate, said second set of transparent conductors also facing away from the viewing surface of said visual display device and having an orientation perpendicular to the first set of transparent conductors so that both sets form a grid-like pattern when superimposed, separated by at least the thickness of said second flexible substrate;
and coating means disposed adjacent to the second surface of said second flexible substrate, said coating means also facing a user and serving as the overlay surface for interactive input by means of finger touch or by stylus detection means, or both;
whereby when said coating means is contacted by either finger touch or a stylus detection means, the transparent conductors of both said first and second sets located below the area of contact will be subjected to substantially only compression forces due to any downward deflection on the overlay caused by said contact.
a first flexible substrate of transparent insulative material one surface adapted for attachment to the viewing surface of said visual display device;
a first set of transparent conductors formed in a parallel array on a second surface of said first flexible substrate, said second surface and the conductors thereon facing away from the viewing surface of said visual display device;
a second flexible substrate of transparent insulative material disposed at one surface thereof adjacent to the second surface of said first flexible substrate;
a second set of transparent conductors formed in a parallel array on a second surface of said second flexible substrate, said second set of transparent conductors also facing away from the viewing surface of said visual display device and having an orientation perpendicular to the first set of transparent conductors so that both sets form a grid-like pattern when superimposed, separated by at least the thickness of said second flexible substrate;
and coating means disposed adjacent to the second surface of said second flexible substrate, said coating means also facing a user and serving as the overlay surface for interactive input by means of finger touch or by stylus detection means, or both;
whereby when said coating means is contacted by either finger touch or a stylus detection means, the transparent conductors of both said first and second sets located below the area of contact will be subjected to substantially only compression forces due to any downward deflection on the overlay caused by said contact.
2. The touch screen overlay of claim 1 wherein said coating means is a third flexible substrate of transparent insulative material disposed at one surface thereof adjacent to the second surface of said second flexible substrate, the other surface of said third flexible substrate facing the user and serving as the overlay surface for interactive input.
3. The touch screen overlay of claim 2 wherein said first and second flexible substrates are attached to each other by means of a first adhesive sheet of transparent insulative material.
4. The touch screen overlay of claim 3 wherein said second and third flexible substrates are attached to each other by means of a second adhesive sheet of transparent insulative material.
5. The touch screen overlay of claim 4 wherein the material of each of said flexible substrates is polyethylene terephthalate.
6. The touch screen overlay of claim 4 wherein the material of said first and second adhesive sheets is a polyester based, heat curable adhesive which is compatible with the material of said flexible substrates.
7. The touch screen overlay of claim 1 wherein the transparent conductors are ceramic conducting oxides.
8. The touch screen overlay of claim 7 wherein the transparent conductors are composed of indium-tin-oxide.
9. The touch screen overlay of claim 1, further comprising:
a first bus means disposed along a side edge of said first flexible substrate for interconnecting the first set of transparent conductors on said first flexible substrate, and a second bus means disposed along a side edge of said second flexible substrate for interconnecting the second set of transparent conductors on said second flexible substrate.
a first bus means disposed along a side edge of said first flexible substrate for interconnecting the first set of transparent conductors on said first flexible substrate, and a second bus means disposed along a side edge of said second flexible substrate for interconnecting the second set of transparent conductors on said second flexible substrate.
10. Interactive input display apparatus comprising the the touch screen overlay of claim 9, and further comprising flexible circuit means for interconnecting the first and second sets of transparent conductors via the first and second bus means, respectively, to a control processor means, said stylus detection means also be connected to said control processor means whereby the position of the stylus detection means at the viewing surface of the visual display surface is displayed by correlating electromagnetic radiation emitted by the transparent conductors with signals detected by the stylus detection means.
11. The interactive input display apparatus of claim 10 wherein the position of a finger touch is detected by a change in capacitance detected by the transparent conductors of said first and second sets in the area below said finger touch, signals representing said capacitance change being transmitted via said conductors, bus means, and flexible circuit means to said processor control means.
12. The touch screen overlay of claim 2 wherein the other surface of the third flexible substrate is coated with an antiglare means.
13. The touch screen overlay of claim 1 wherein the first and second sets of conductors are spaced sufficiently apart to minimize the loss of signal at the overlay surface from the first set of conductors due to screening by the second set of conductors.
14. The touch screen overlay of claim 1 wherein the thickness of the overlay between the first set of conductors and the overlay surface is sufficiently minimized to enhance signal strengths from both the first and second set of conductors at the overlay surface.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/210,961 US4931782A (en) | 1988-06-24 | 1988-06-24 | Touch screen overlay with improved conductor durability |
| US210,961 | 1988-06-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1298631C true CA1298631C (en) | 1992-04-07 |
Family
ID=22785045
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000603520A Expired - Lifetime CA1298631C (en) | 1988-06-24 | 1989-06-21 | Touch screen overlay with improved conductor durability |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US4931782A (en) |
| EP (1) | EP0348229B1 (en) |
| JP (1) | JPH02118818A (en) |
| KR (1) | KR0146353B1 (en) |
| AT (1) | ATE104078T1 (en) |
| AU (1) | AU613568B2 (en) |
| CA (1) | CA1298631C (en) |
| DE (1) | DE68914342T2 (en) |
| HK (1) | HK1000387A1 (en) |
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-
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- 1989-06-21 CA CA000603520A patent/CA1298631C/en not_active Expired - Lifetime
- 1989-06-22 JP JP1160600A patent/JPH02118818A/en active Granted
- 1989-06-23 AU AU36769/89A patent/AU613568B2/en not_active Ceased
- 1989-06-23 DE DE68914342T patent/DE68914342T2/en not_active Expired - Lifetime
- 1989-06-23 KR KR1019890008824A patent/KR0146353B1/en not_active IP Right Cessation
- 1989-06-23 AT AT89306403T patent/ATE104078T1/en active
- 1989-06-23 EP EP89306403A patent/EP0348229B1/en not_active Expired - Lifetime
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1997
- 1997-10-21 HK HK97101978A patent/HK1000387A1/en not_active IP Right Cessation
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|---|---|
| KR900000760A (en) | 1990-01-30 |
| EP0348229B1 (en) | 1994-04-06 |
| US4931782A (en) | 1990-06-05 |
| JPH0587846B2 (en) | 1993-12-20 |
| DE68914342D1 (en) | 1994-05-11 |
| DE68914342T2 (en) | 1994-10-13 |
| HK1000387A1 (en) | 1998-03-13 |
| EP0348229A2 (en) | 1989-12-27 |
| JPH02118818A (en) | 1990-05-07 |
| AU3676989A (en) | 1990-01-04 |
| ATE104078T1 (en) | 1994-04-15 |
| KR0146353B1 (en) | 1998-09-15 |
| AU613568B2 (en) | 1991-08-01 |
| EP0348229A3 (en) | 1990-09-19 |
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