GB2180994A - Particulate spacers for touch sensitive overlay panel applications - Google Patents

Abstract

Fine particles (53) sized to be within a predetermined size range, are deposited on, and thereafter adhere in random distribution to, one of two adjacent surfaces, serving to keep the surfaces uniformly spaced apart except when an external force causes them to make local contact. The particles are conveniently applied in the form of a spray of a suspension of particles and a fluid carrier material, preferably water with alumina particles, or an aqueous solution of a chloride salt of an-alkaline earth metal such as calcium, potassium or sodium when small glass beads are used as the particles. Brown alumina particles (approximately 96% Al2O3) in the size range 3-50 microns, so utilized, are found well suited as parallel surface spacers in optically transparent touch sensitive overlay (TSO) panels. Particle distribution densities in the range 300-1,000 particles per inch are satisfactory for TSO panels,with the higher particle density requiring a higher actuation pressure to be applied. Applicable to contact-making or optical touch sensitive switch panels. <IMAGE>

Description

SPECIFICATION Particutatespacersfortouchsensitive overlay panel awlicaffons NICAL FIELI) These invention rePalssg.enerally to the provision of particulate spacers, of small dimensions, for placement between andinornrealEy parallel layers in atouch sensitive overlay (TSO) assembly to prevent contact between the layers until art external force, e.g., pressure by a finger, is provided to obtain such a contact deliberately at a predetermined location.

BACKGROUND OF THE INVENTION A great variety of apparatus is currently in use in which various operations are performed by the application of external force, e.g., by a user's finger, to obtain optical or electrical contact between two adjacent, closely spaced apartflexible layers to generate signals which are generallyprocessedfurth- er by an external electrical circuit. Examples of these include elevatorfloorselection buttons, certain computerterminals, and, lately, touch sensitive overlay screens that permitthe user of a computer monitorto manipulate records stored within the computer.

When a touch sensitive overlay (TSO) assembly is utilized with a computer monitor, in a manner that requires that light be transmitted through multiple transparent layers so that the user may manipulate data stored within the computer, it has become increasingly importantthat spacing apart of adjacent optically transparent, and sometimes also electrically conductive, layers within the TSO assembly be achieved by optically non-intrusive means. One approach is to provide small plastic non-conductive bumps or points, as best seen in Figures 1 and 2, between adjacent pressure-sensitive electrically conductive layers to separate them. Such plastic spacer bumps are usually distributed in a uniform manner and are visible, and therefore are intrusive to the user.

An example of such an approach is found in U.S.

Patent No.4,423,299, issued to Gurol et al in 1983, for a "Touch Sensitive Transparent Switch Array".

As an even more general proposition, even for light-opaque adjacent closely spaced layers, e.g., a touch sensitive key-board face lighted from the user's side, it may be very desirable to ensure either electrically conductive or non-conductive separation in a predetermined manner.

A need, therefore, exists fora simple, inexpensive solution to the problem of separating two normally parallel layers by a predetermined distance without eliminating the facility for an external force to cause the surfaces te move closerto each othertothereby obtain a positionatly determinable contact between them. When the layers to be separated are electrically conductive, the separation between them must be provided electrically non-conductively.

DISCLOSURE OF THE INVENTION Accordingly, it is an object ofthis invention to provide easily applied and inexpensive means for separating two adjacent, closely spaced, essentially parallel surfaces by a predetermined small distance.

It is another object of thins invention to provide means for electrically non-conductively separating two electrically conductive surfaces of opticallytrans- parent adjacent layers in a TSO assembly.

It is yet another object ofthis invention to separate by a small predetermined distance two adjacent, normally parallel, surfaces of two adjacent layers in a TSO assembly such that a predetermined pressure applied by a user to one side of the assembly will effectuate positionally determinable contact betweenthe two adjacent surfaces.

It is a further object ofthis invention to provide an optically non-intrusive means for separating two adjacent, closely spaced, normally parallel surfaces spaced apart so that a controlled pressure by a user can generate in acoupledelectrical circuit a signal indicative of the location atwhich the pressure is applied.

It should be understood that "opticallytransparent" is a term that comprehends "translucent" as well as "partially transparent and partially opaque", both physically and temporally (e.g., when a liquid crystal display is included).

These and other objects of the invention may be achieved by depositing fine particles of a suitable material, in a predetermined area density and within a predetermined particle size range, onto one ofthe two adjacent surfaces oftwo adjacent iayers. The material ofthe particles preferably is optionally non-intrusive, chemically inert, and relatively inexpensive to apply foruse.Asuitable materialforthis purpose is brown alumina particles, which may be readily sprayed in suspension in water onto a surface to be treated. The water evaporates and leaves behind a random distribution ofthe particles which, when an adjacent surface is juxtapased therewith, keepsthesurfaces separated by a small predetermined distance char acts sized bathe largest of said particles.Pressure by a user onto the layer bearing one of the separated surfaces permits contact between the adjacent surfaces on either side of the particles without any deleterious effects on eitherthe surfaces or, in the preferred embodiment, on electrically conductive very thinfilms which may be vacuum deposited onto the flexible surfaces. Small glass beads, suspended in a chloride solution of an alkali earth metal, likewise, provide satisfactory separation. The carrier fluid evaporates in each case and leaves behind a suitable random distribution of the opticaily non-intrusive fine particles which adhere to the surface onto which they were sprayed, for location thereafter between the adjacent electrically conductive layers.While the true cause responsibleforthe desired adherence ofthe fine particles to the surface they are sprayed on is not fully understood, it is believed that this adherence is due to small or molecular bonding forces otherwise known as van der Waal's forces. Thus the particles do not depend on pressure by one ofthe spaced-apart surfaces acting against the other surface to maintain the particulate distribution in place. It is believed that the fluid carrier also serves to avoid or preventthe exertion of der Walls' forces between particles, thus providing the desired random distribution of particles adhering to the sprayed-on surface.

BRIEF DESCRIPTION OF THE DRA WINGS Figure lisa plan view of a typical, flat, conventional TSO assembly, in which is visible through the transparent layers a regular pattern of dots represent- ing the plastic spacers between two closely spaced layers which, in this case, have electrically conductive adjacent surfaces.

Figure 2 is a cross section normal to the plan view of Figure 1, ofthe same conventional TSO assembly, to displaythe multitudinous layers contained therein.

Figure 3 is a schematic illustration of a conventional spray apparatus from which a suspension ofthe particles and fluid carrier material is sprayed onto a surface.

Figure 4 is a schematic enlarged representation of the random distribution of particles within the selected size range onto a surface.

Figure 5 is a cross sectional view normal to the view ofthe view of Figure 4, showing the two adjacent surfaces separated by simultaneous contact on opposite sides of a random distribution ofthe larger particles deposited therebetween.

The same numbers are used to identify like elements, or parts of elements, in each ofthe drawings andforpurposesofreference elsewhere.

BESTMODE FOR PRACTICING THE INVENTION The description belowfocuses on the use of non-conductive fine particulate spacers between adjacent closely spaced-apart essentially parallel surfaces and on a method for obtaining satisfactory distributions of such particles forthis purpose. In the preferred embodimentthe spaced apart surfaces have selective- ly oriented electrically conductive zones between which electrical contact is possible underthe action of an external force. Figure lisa plan view of a conventional flat, generally rectangular,TSO panel 11 which is electrically connected at its periphery by wires in sets 12 and 13to a decoder ci rcu it 14which is most likely to be connected to a computer (not shown for simplicity).Persons skilled in the art will recognize that other geometries involving closely spaced apart surfaces, e.g., with cylindrical orspherical shapes, are feasible and at times even desirable. The geometry of the surfaces generally, or the particular use thereof, in no way detracts from the usefulness ofthis invention as taught here.

Touch sensitive panels need not necessarily have electrically conductive surfaces to allow determination of the point of contact underthe action of an externally applied force, e.g., by means of a stylus or a user's finger. Examples ofthe use of touch sensitive panels based on photo-voltaic modes of operation, e.g., not utilizing electrically conductive contactable surfaces, are to be found in U.S. Patent No. 4,484,179 to Kasday,titled "Touch Position Sensitive Surface", and in IBM Technical Disclosure Bulletins: Vol. 24 No.

6November1981, titled "Optical Overlay Input Device for a Cathode RayTube", and Vol. 26 No. 6 November 1983, titled "Optical Keyboard Device and Techni que", respectively. The principal need in both types of touch sensitive panels, i.e., those with and without electrically conductive adjacent contactable surfaces, is to maintain normal separation ofthe adjacent surfaces until an externally applied force causes them to contact, and then to establish the location ofthe point of contact by processing a signal produced as a result of such contact. Persons skilled in the artwill readily appreciate that such adjacent surfaces need not necessarily be flat and also that one or both may even be optically non-transparent at selected locations.These, however, are variations on a theme and the present invention, as disclosed herein, will serve to keep such adjacent surfaces apart in predetermined separation regardless ofthe mode by which the signals are generated, transmitted or processed subsequently. Clearly, if electrically conductive su rfaces are to be separated physically by small such particles or beads, as taught and claimed herein, then such particles or beads must be electrically nonconductive. The preferred embodiment discussed herein is one in which electrically conductive surfaces are separated; however, persons skilled in the art will readily appreciate the very broad scope of application ofthe invention.

Figure 2 is a vertical cross section ofthe panel of Figure 1 in a direction normal to the panel plane.

Atypical TSO panel of the conventional sort, as best seen in Figure 2, contains a top flexible optically transparent layer 1 5 that has an exterior upper surface 16 and a lower surface 17.To lower surface 17, is attached a thin electrically conductive film 18, general ly by vacuum deposition, of a predetermined pattern of electrica I ly conductive metal, that has a lower surface 19. Depending on the application athand,the use of metallic oxides, mixtures of metals, or of metal and metallic oxide may be found desirableforsuch an electrically conductive predetermined pattern.There is a second optically transparent flexible layer 20, normally parallel to layer 15, that has a top surface 22 and a bottom surface 21.To surface22 is applied, again preferably byvacuum deposition of metal, a predetermined pattern of electrically conductive material 23 having a top surface 24. As Figure 2 shows, a conventional approach for assuring a predetermined separation of the two electrically conductive surfaces 19 and 24 is to provide a predetermined pattern (as best seen in Figure 1) of electrically non-conductive bumps such as 25. These bumps 25, shown in Figure 2 as based on the lowerlayer20, are in physical contact with surface 19 ofthe upper electrically conductive film 18.Underneath layer 20, in some conventional TSO panels, is yet another layer 32 which typically is not electrically conductive and serves to defeat the formation of Newton rings when layer 20 rests against a generally clear backing plate 30 having an uppersurface31.

Figure 3 schematically depicts the application, by means of a conventional spray apparatus 51 through a spray nozzle 52, of a spray 55 which results in the deposition of larger particles 53 and smaller particles 54, within a predetermined size range for such particles, onto the upper surface 24 of an electrically conductive pattern 23 deposited on the top surface of an opticallytransparent layer 20. Persons skilled in the artwill recognizethatforsuch a TSO panel to work satisfactorily where the operator has to be able to see whatisbehindthe panel, aswhen such an assembly is positioned directly in front of a computer optical monitor, electrically conducting metal deposits 18 and 23 generally are extremely thin, probably only a few atoms thick.At such minute thicknesses, with highly conductive metals such as gold deposited thereon in a vacuum deposition process of known type, the electrically conducting layer is so thinthat most of the light incident on the transparent layer beneath it is transmitted th rough.

The spray 55 contains not onlythe particles 53 and 54 within the specified size range but also contains a fluid such aswaterto hold the particles in suspension during the spraying action. Research shows that brown alumina (approximately 96% Awl203) in the size range 3-50 microns, preferably suspended in water, provides the desired effect. Other comparable electrically non-conductive and chemically inert, and therefore stable, materials include white alumina and small glass beads. An aqueous solution of a chloride of an alkaline earth metal, such as potassium, sodium, or calcium, is found to be particularly effective as a fluid carrierfor particles such as glass beads.While it is not completely understood what processes and molecular level forces are involved, it is found that upon drying out ofthe carrier the particles have a tendency to adhere very firmly to typically suitable optically transparent materials such as acrylic plastics, glass, Mylar (TM) and polycarbonates, aswell astovery thinly deposited conductive metal or oxide films as are produced by the typical vacuum deposition process.

persons skilled in the art will, of course, appreciate that a sprayed on deposition of fine particles onto a surface that has a predetermined pattern of electrical ly conductive zones will adhere to notonlythe electrically conductive zones but also to the nonconductive areas therebetween.

Afterthe spraying on of particles and the subse quentdrying ofthecarriermaterialtheparticle covered surface is juxtaposed with a second layer which also has a predetermined pattern of electrically conductive zones. By proper selection of particles within the size range it is possible thus to ensure that the electrically conducting surfaces, while very close to each other, normally remain separated by an amount determined by the size ofthe largest particles which are in simultaneous contact with both the adjacent surfaces.As discussed above, it is found that once the particles have been deposited onto one surface they do not move therefrom. Itshould also be understood that it is preferable thatthe largest particles make simultaneous contact between the adjacent surfaces, although the smaller particles will remain in adherence to the surface onto which they were initially sprayed. This is best seen in Figures which is a cross sectional view normal to the surface shown in Figure 4. It is easily seen here howthe largest particles contact the electrically conducting surface 19 ofthe upper layer and the comparable electrically conducting surface 24 ofthe lower layer, with the smaller particles interspersed among the larger particles.

A userwho applies an external localized force to surface 16 (See Figure 2) will thereby cause layer 15 to deflect inward and closer to layer 20. Ifthe applied pressure is large enough then, despite the presence of particles 53and 54 in the small gap,the electrically conductive surface 19 will make localized contact with electrically conductive surface 24 and thereby complete a portion ofthe external circuit and generate a useful signal indicative, generally, ofthe location at which the force is applied. Experiments showthat particles in the 3-50 micron size range do not have any deleterious effect on the conductive layers 18 and 23, nor do they cause any damage to the flexible optically transparent layers 15 and 20.Furthermore, it is found thatforpractical purposes brown alumina particles in the sub 100 micron range are impossibleto see by an unaided eye in a TSO assembly.

It is found that a desirable density for distribution of the particles in the 3-50 micron size range is in the range 300-1,000 particles per square inch. For valuers below 300 particles per square inch there is the risk of intermittent and irregular shorting out between the electrically conductive surfaces. For distribution densities greaterthan 1,000 particles per square inch it is necessaryto apply a higher actuation pressure in orderto obtain electrical contact locally. Persons skilled intheartwill immediatelyrecognizethatitis thus possible to regulatethe actuation pressure for a TSO panel by controlling the predetermined density of distribution of particles of a given size range. This, therefore, becomes a useful design factor rangefor such elements.

As described above, th rough experimental studies it has been verified that fine particles in a predetermined denisty of distribution, and within a predetermined size range, can be used most effectively to separate two electrically conductive surfaces that are also optical Iy transpa rent, without a ny deletrious effects over prolonged use. Furthermore, as previously indicated, persons skilled in the art may find thatfor particular applications it may be preferable to utilize white alumina, small glass beads, or other comparable chemically inert and stable particles which have the added inherent advantage of being physically stable at or above the temperature at which typical computer equipment and monitors are operated.

The spray deposition of the suspension of fine particles and a carrier fluid may be obtained either by conventional hand operated atomizertype spray devices or, for more precise, sophisticated, and economicallyfeasible processes, be achieved by computer controlled or mechanized spraying devices of a conventional nature.

It should be apparent from the preceding that the invention may be practiced otherwise as specifically described and disclosed herein, and may be used with equal efficacy in applications wherein the separated contactable surfaces are not electrically conductive.

Modifications may, therefore, be made to the specific embodiments disclosed here without departing from the scope of this invention and are intended to be included within the claims appended below.

Claims (45)

1. An apparatus in which two closely spaced apart normally parallel layers of materials are moved closer relative to each other to establish local contact between them underthe action of an external force, comprising: a first layer, of a first material, comprising a first surface and a parallel second surface; a second layer, of a second material comprising a third surface and a parallel fourth surface; and particles sized within a predetermined size range, disposed between said first and second layers such that said particles are randomly distributed in a predetermined density and a portion thereof are in simultaneous contact with said second andthird surfaces thereof respectively.

2. An apparatus according to claim 1, wherein: saidfirstsurface is the touch surface of a touch sensitive overlay panel;

3. An apparatus according to claim 1, wherein: said particles are sized in the range 3-50 microns.

4. An apparatus according to claim 1,wherein: said particles are randomly distributed in a density in the range 300-1,000 particles persquare inch.

5. An apparatus according to claim 1 wherein: said particles comprise brown alumina.

6. An apparatus according to claim 1,where: said particles comprise glass beads.

7. A method for non-conductively spacing apart two adjacent surfaces, of normally parallel layers, which make local physical contact underthe action of an external force, comprising the steps of: depositing on a first one of said surfaces particles randomly sized within a predetermined size range and randomly distributed in a predetermined area density; and juxtaposing said first and second of said two surfaces in said apparatus such that a portion of said particles deposited on said first surface make simultaneous contact with both said first surface and said second surface.

8. An method according to claim 7, wherein: said depositing step comprises spraying onto said first surface a suspension of said particles in a fluid carrier material.

9. An method according to claim 7, wherein: said depositing step comprises spraying onto said first surface a suspension of brown alumin particles in water.

10. An method accordingto claim 7, wherein: said depositing step comprises spraying onto said first surface a suspension of glass beads in an aqueous solution of a chloride salt of an alkaline earth metal.

11. An method according to claim 7, wherein: said predetermined size range is 3-50 microns.

12. An method according to claim 7, wherein: said predetermined area density is in the range 300-1,000 particles per square inch.

13. An apparatus in which two closely spaced apart light transmitting and normally parallel layers are moved closer relative to each other to establish local contact between them underthe action of an external force, comprising: a first layer, of a firsttransparent material, comprising a first surface and a parallel second surface; a second layer, of a second transparent material comprising a third surface and a parallel fourth surface; and particles sized within a predetermined size range, disposed between said first and second layers such that said particles are randomly distributed in a predetermined density and a portion thereof are in simultaneous contact with said second and third su rfacesthereof respectively.

14. An apparatus according to claim 13, wherein: saidfirsttransparent material is Mylar(TM).

15. An apparatus according to claim 13, wherein: said first surface is the touch surface of a touch sensitive overlay panel.

16. An apparatus according to claim 13, wherein: said particles are sized in the range 3-50 microns.

17. An apparatus according to claim 13, wherein: said particles are randomly distributed in a density in the range 300-1,000 particles per square inch.

18. An apparatus according to claim 13, wherein: said particles comprise brown alumina.

19. Anapparatus according to claim 13, wherein: said particles comprise glass beads.

20. A method for spacing apart two adjacent surfaces, of normally parallel layers, which make local physical contact under the action of an external force, comprising the steps of: depositing on a first one of said surfaces particles randomly within a predetermined size range and randomly distributed in a predetermined area density; and juxtaposing said first and second of said two surfaces in said apparatus such that a portion of said particles deposited on said firstsurface make simultaneous contact with both said first surface and said second surface.

21. A method according to claim 20, wherein: said depositing step comprises spraying onto said first surface a suspension of said particles in a fluid carrier material.

22. Amethod accordingto claim 20, wherein: said depositing step comprises sparying onto said first surface a suspension of brown alumina particles in water.

23. A method according to claim 20, wherein: said depositing step comprises spraying onto said first surface a suspension of glass beads in an aqueous solution of a chloride salt of an alkaline earth metal.

24. Amethodaccordingto claim 20, wherein: said predetermined size range is 3-50 microns.

25. A method according to claim 20, wherein: said predetermined area density is in the range 300-1,000 particles persquare inch.

26. An apparatus in which two closely spaced apart light transmitting, electrically conducting and normally parallel layers of transparent material are moved closer relative to each other to establish local electrical contact between them underthe action of an external force, comprising: a first layer, of a first electrically non-conductive trasparent material, comprising a first surface and a parallel second surface; a first electrically conductive material, of optically transparent thickness, attached to said second surface in a first set of zones of predetermined shape, size and orientation; A second layer, of a second electrically nonconductive transparent material comprising a third surface and a parallel fourth surface;; a second electrically conductive material, of opticai- lytransparentthickness, attached to said third surface in a second set of zones or predetermined shape, size and orientation; and electrically non-conductive particles sized within a predetermined size range, disposed between said first and second sets of electrically conductive zones such thatthe largest of said particles are randomly distributed in a predetermined density and a portion thereof are in simultaneous contact with at least one zone from each of said first and second sets of zones.

27. An apparatusaccording to claim 261wherein: said first transparent material is Mylar (TM).

28. An apparatus according to claim 26, wherein: said first surface is contacted to move said first set of zonestoward said second set of zones to establish local electrical contact between a respective zoone from each set.

29. An apparatus according to claim 28, wherein: said first surface is the touch surface of a touch sensitive overlay panel.

30. An apparatus according to claim 26, wherein: said first and second electrically conductive materials are gold.

31. An apparatus according to claim 26, wherein: saidfirstelectricallyconductivematerial comprises a metallic oxide.

32. An apparatus according to claim 26, wherein: said first electrically conductive material comprises at least one metal.

33. An apparatus according to claim 26, wherein: electrical pathways are provided linking at least one zone from each of said first and second sets of zones to an electrical circuit.

34. An apparatus according to claim 26, wherein: said particles are sized in the range3-50 microns.

35. An apparatus according to claim 26 wherein: said particles are randomly distributed in a density in the range 300-1,000 particles per square inch.

36. An apparatus according to claim 26, wherein: said particles comprise brown alumina.

37. An apparatus according to claim 26, wherein: said particles comprise glass beads.

38. A methodfor non-conductively spacing apart two electrically conducting surfaces, of normally parallel layers, which make local physical contact under the action of an external force, comprising the steps of: depositing on afirst one of said electrically conducting surfaceselectrically non-conducting particles randomly sized within a predetermined size range and randomly distributed in a predetermined area density; and juxtaposing said first and second of said two surfaces in said apparatus such that a portion of said particles deposited on said first surface make simultaneous contact with both said first surface and said second surface.

39. A method according to claim 38, wherein: said depositing step comprises spraying onto said first surface a suspension of said particles in a fluid carrier material.

40. A method according to claim 38, wherein: said depositing step comprises spraying onto said first surface a suspension of brown alumina particles in water.

41. Amethod according to claim 38,wherein: said depositing step comprises spraying onto said first surface a suspension of glass beads in an aqueous solution of a chloride salt an alkaline earth metal.

42. A method according the claim 38, wherein: said predetermined size range is 3-50 microns.

43. A method according to claim 38, wherein: said predetermined area density is in the range 300-1,000 particles persquare inch.

44. An apparatus, substantially as hereinbefore described with reference to Figs. 3-5 oftheaccompan- ing drawings.

45. A method of spacing aparttwo adjacent surfaces, substantially as hereinbefore described with reference to Figs. 3-5 of the accompanying drawings.