GB1562264A

GB1562264A - Electric switch matrix

Info

Publication number: GB1562264A
Application number: GB45785/77A
Authority: GB
Original assignee: Control Data Corp
Current assignee: Control Data Corp
Priority date: 1976-11-22
Filing date: 1977-11-03
Publication date: 1980-03-12
Also published as: AU3085177A; DE2751680A1; FR2371761B1; DE2751680C2; AU511354B2; FR2371761A1

Description

(54) ELECTRIC SWITCH MATRIX (71) We, CONTRCL DATA CORPORA TION, a corporation organised and existing under the laws of the State of Delaware, United States of America, of 8100-34th Avenue South, Minneapolis, Minnesota, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the follow ing statement:- This invention relates to electric switch matrices.

In general, a switch matrix or touch panel device indicates the X-Y coordinates of contact of an operator's finger on it and is sensitive to pressure only. Frequently, in formation is displayed on a substrate be neath the switch matrix. The coordinates of a contact can be related to the displayed information thus providing for interactive communication between the operator and an apparatus of which the switch matrix forms a part.

A variety of techniques are known for sensing the location of contact on a surface, such as, for example, a stretched drumhead type of membrane device. This device em ploys a membrane which is spaced from a flat substrate and which can be deflected to cause conductors carried on it to contact those on the substrate. Another known de vice is disclosed in an article entitled "CRT Touch Panels Provide Maximum Flexibility in Computer Interaction", Control En gineefing, July 1976, pp 33-34. This device consists of a curved flexible plastics sheet carrying a set of small wires. The sheet can be deflected to cause these wires to come into contact with an orthogonal set of similar wires mounted immediately below.

Spacers separate the two sets of wires. U.S.

Patent Specification No. 3,760,360 discloses a similar device embodied in a flat panel but having no capability of interactively displaying information. U.S. Patent Specification No. 3,485,232 discloses a somewhat simpler form of a similar device. U.S. Patent Specification No. 3,921,167 discloses a panel location-sensitive to the approach of an external probe sensing change in capacitance.

According to one aspect of the present invention there is provided an electric switch matrix comprising a plurality of spaced electrically conductive first strips fixed either to a face of a rigid electrically insulating substrate or to an electrically insulating layer itself fixed to a rigid substrate; a resilient insulating membrane having an undistorted topology substantially the same as the topology of the said face of the substrate, the membrane being attached only about its periphery to the face of either the substrate or the insulating layer into a position in which the topology of the membrane substantially matches the topology of the substrate, the membrane being spaced apart from the first strips in a predetermined area of the membrane; and a plurality of flexible spaced apart electrically conductive second strips fixed to a surface of the membrane facing the substrate, each of said second strips being located in the said predetermined area and being spaced from the first strips when the membrane is undistorted, each of said second strips crossing at least two first strips.

Preferably the first and second strips and the membrane are transparent.

In one embodiment the first strips are substantially parallel to each other and substantially orthogonal to the first strips.

The substrates may be convex, the membrane being slightly more convex than the substrate. Thus the substrates may be partspherical. The membrane may have a radius of curvature slightly smaller than that of the substrate. In this case the radius of curvature of the membrane, when undistorted, may be substantially 1 to 4 inches smaller than that of the substrate. The radius of curvature is, in one embodiment substantially 25 inches.

The membrane may comprise polyester film.

The insulating layer may be transparent.

The switch matrix may include an insulating grid interposed between the first and second strips, and having gaps within itself permitting electrical contact between a first and second strip responsive to manual pressure on their cross-over area occupied by the first strips. Preferably the insulating grid is transparent. The insulating grid may be formed of electrically insulating photoresist material.

In one embodiment the insulating grid has orthogonal lines, the ratio of the width of each line to the spacing between adjacent lines being the range of 1: 5 to 1:100.

Thus the width of each said line may be substantially 0.001 inches.

In an alternative embodiment a piezoresistant coating interposed between the first and second strips permits electrical conduction between a first and second strips responsive to manual pressure at their crossover area. The said coating may be a ceramic coating serving to increase visible light transmission. Each of the first and second strips may carry said coating.

The switch matrix preferably includes a vent for permitting air flow into the space between the membrane and the substrate.

According to a further aspect of the present invention there is provided a method of forming the insulating grid referred to above comprising coating the first strips and insulating layer with a photo-resist material, exposing the photo-resist material to a light pattern corresponding to a preselected grid pattern, developing the photoresist material, and removing the unexposed photo-resist material.

Switch matrices according to the present invention may provide a passive surface sensitive to low pressure from a finger or stylus and may allow a display to be viewed through them. Such switch matrices can be integrated with existing display designs.

The invention is illustrated merely by way of example, in the accompanying drawings in which: Figure 1 is a plan view of a corner portion of an electric switch matrix according to the present invention; Figure 2 is a cross section of the switch matrix of Figure 1; Figure 3 is a portion of Figure 2 on an enlarged scale showing details of the relationship between two sets of conductor strips and an insulating grid; Figure 4 is a portion of Figure 3 on an enlarged scale showing in still greater detail the relationship between the two sets of conductor strips and an insulating grid; and Figure 5 is a portion of Figure 2 on an enlarged scale illustrating the provision of piezo-resistant anti-short means.

In the drawings the scale between the various parts is not always consistent as this simplifies understanding. Suitable dimensions for the elements of the switch matrix are given in the following description as required; A corner portion of an electric switch matrix according to the present invention is shown in Figure 1. A base or substrate 10, which may be flat or, as shown in Figure 2, curved, has an electrically insulating surface. A set of Y-conductor strips 20-24 consists of transparent coated areas firmly adhering to the surface of the substrate 10 facing the operator. In a typical application the substrate 10 can be at least part of a CRT screen. It may not be convenient to apply directly the conductor strips to a CRT screen or other substrate, but rather form them on to a clear plastics sheet 55, curved, if intended to conform to a curved CRT screen, which is then glued or otherwise attached to the substrate 10. Electrical leads 40-44 are attached to the end of the conductor strips 20-24 respectively so as to make electrical contact between them and external support electronic circuitry. In a typical device, each of the conductor strips 20-24 is 0.5 inches wide and is separated from adjacent strips by gaps of 0.005 inches.

The conductor strips 20-24 are preferably formed from indium oxide, tin oxide or a combination thereof. The conductor strips are easily formed by coating the entire surface of the substrate with electrically conductive material using standard techniques, the gaps between adjacent conductor strips subsequently being formed by an etching technique using photo-resist material.

An insulating grid 45 overlays at least a portion of the conductor strips 20-24, and, usually, covers them uniformly. The insulating grid can most easily be formed from widely available and well known transparent photo-resist material which is itself inherently non-conductive. The areas to be covered by the insulating grid 45 are covered with the photo-resist material, an appropriate mask is placed on these areas, the photo-resist material is exposed to light using conventional techniques, and the unexposed photo-resist material is removed chemically. The insulating grid 45 comprises a crosshatch of lines or strips formed of the photo-resist material, where each line is 0.005 inches wide (with w in Figure 4) and all lines, in both the vertical and horizontal directions are on 0.025 inch centres (spacing s in Figure 3). The thickness of the insulating grid 45 can vary depending on the pres sure desired to form electrical contact, but a nominal value of 0.0001 inches appears to be suitable for a 0.003 MYLAR (Trade Mark) polyester membrane described below. In general, a ratio of from 1: 5 to 1: 100 for the width w to the spacing s is suitable for an insulating grid having a thickness of 0.003 inches. The width w preferably should never exceed a few thousandths of an inch. The insulating grid 45 can also be formed on a membrane 11 after a set of conductor strips 12-16 are formed as described below.

The membrane 11 is resilient and made of electrically insulating material and forms a tactile surface which the operator presses at a a desired point to create an electrical contact indicating the coordintaes of the pressure point. The membrane 11 carries the conductor strips 12-16 on its surface facing the substrate 10. The conductor strips 12-16 are formed before attaching the membrane 11 to the substrate 10, and must be flexible enough to bend easily with the membrane 11. The membrane 11 and the conductor strips 12-16 may be formed from transparent polyester film of 0.003 inches thickness with a transparent conductive gold film on one surface available from Sierracin Corporation, although other thicknesses up to at least 0.007 inches are suitable. The conductor strips 12-16 are conveniently formed by removing by an etching technique narrow strips of gold in parallel lines from such a film. Typical dimensions of the gaps between adjacent conductor strips 12-16 are 0.002 inches on 0.5 inch centres. A vent 50 allows the membrane 11 to assume its natural shape more quickly after release of applied pressure by allowing air to flow rapidly into the space between the membrane 11 and the substrate 10. It may be desirable to place a filter in the vent 50 to prevent dirt entering the switch matrix.

The vent 50 is particularly useful in preventing slow return of the membrane 11 to its natural shape when deflected over a large area at one instant and it also prevents shorting caused by changes in ambient atmospheric pressure.

If the substrate 10 is curved, it is necessary to mold the membrane 11 and the conductor strips 12-16 already formed on it to a smooth contour which conforms to the topology of the substrate 10. This in itself is not a trivial problem: the polyester film involved may be formed by the method described in our U. & Patent No. 4,117,608.

The membrane 11, after etching to form the conductor strips 12-16, is formed by the method of the above mentioned Patent into a shape substantially conforming to the topology of the substrate 10. If the substrate 10 is curved it is preferable that the curvature of the membrane 11, when unstressed, is slightly greater than that of the substrate 10. When the substrate 10 comprises a typical curved CRT implosion shield, the curvature is approximately part-spherical with a radius of approximately 20-30 inches. In such a case the membrane 11 preferably is moulded to a radius of curvature from 1-4 inches less than that of the substrate 10. The slightly greater curvature prevents the conductor strips 12-16 on the membrane 11 from being drawn down too tightly on to conductor strips 20-24 and the possibility of shortening them. Further, such dimensioning is essential if anti-short means other than the insulating grid 45 are employed on a curved substrate, as described infra.

The membrane 11 is securely fastened around its periphery to the substrate 10 by tape strips 54 in such a position that the conductor strips 12-16 pass across each of the conductor strips 20-24 and are spaced therefrom by the insulating grid 45 and the natural tendency of the membrane 11 to assume its unstressed condition. The conductor strips 12-16 are connected to leads 32-36 by an electrically conductive adhesive.

The leads 32-36 may be formed in situ on the substrate 10 at the same time as the conductor strips 20-24 are formed. The external support electronic circuitry can thus be easily connected to the conductor strips 12-16. A space 53 (Figure 2) although often not essential, is used in certain cases to prevent shorting around the periphery of the membrane 11, particularly if anti-short means other than the insulating grid 45 are used. The spacer 53 need not be placed on the conductor strips 20-24 and may extend to the edge of the membrane 11.

In operation, a contact between any one of the conductor strips 20-24 and any one of the conductor strips 12-16 can be made by gentle finger or stylus pressure on the membrane 11 above the desired point of intersection. Because of the relatively wide contact surfaces the pressure point need not be precisely in the centre of the desired intersection. With either the insulating grid 45 or the other anti-short means described infra, gentle finger pressure forms an essentially zero resistance contact between the two selected conductor strips. The wide contact surface also add reliability in forming each contact between the conductor strips.

Figure 5 discloses an alternative to the insulating grid 45 as the anti-short means.

The aforementioned gold covered polyester film from Sierracin Corporation is available optionally with a " proprietary ceramic coating which serves to increase visible light transmission and to provide a measure of mechanical protection to the conductive metal deposit" (Sierracin Corporation brochure entitled Sierracin Intrex (Trade Mark) Electrically Conductive Film Com- ponents). This coating has been determined to have a piezo-resistant characteristic of high resistance under very light pressure, and a very low resistance under pressure no heavier than that generated by gentle finger pressure. In Figure 5, coatings 51,52 indicate use of this alternative. As now commercially available, both coatings 51, 52 must be present to yield suffciently high resistance at very low pressures to allow functioining as an anti-short means. It is probable that a coating 51 thicker than that now commercially available would allow omission of the coating 52. As previously mentioned, when the insulating grid 45 is not used, the spacer 53 may be necessary to prevent shorting adjacent the edges.

Another means for preventing shorting between the conductor strips 12-16 and 20-24 is available for use with a substrate 10 having a finite radius of curvature. By selecting the radius of curvature of the membrane 11 smaller than that of the substrate 10 (for membranes mounted on the convex side of the substrate 10, of course), as shown in Figure 2, the natural resiliency of the membrane 11 and its arched shape supports the conductor strips 20-24 and prevents their shorting in the absence of external pressure. Although a wide variety of radii of curvature will undoubtedly work, it is known that a substrate of 25 inches radius of curvature and a 0.003 inch thick polyester membrane moulded with a form having a 22 inch radius of curvature are satisfactory. As shown in Figures 1 and 2, it is desirable to bond the periphery of the membrane 11 to the substrate 10 outside the conductor strips 20-24 to increase the clearance between the areas of the peripheral conductor strips. The spacer 53 may also be used for this purpose. It is likely, although not confirmed, that the use of the natural resilience is curvature of the membrane 11 to provide the necessary antishort spacing between the sets of conductor strips requires a greater difference in radii of curvature for the substrate 10 and the membrane 11 than do the other described arrangements to prevent shorting between the sets of conductor strips. Thus, while a 3 inch smaller radius works with a 25 inch substrate radius in all 3 cases, a 1 inch difference or less may well be satisfactory when the insulating grid 45 or the coatings 51,52 are used.

During the manufacture of the above described switch matrices it is important that the surfaces of the conductor strips 20-24 and 12-16 are relatively free from dust and other foreign matter during attachment of the membrane 11 to the substrate 10. However, the relatively wide contact areas between crossing conductor strips does tolerate a small amount of such foreign matter, particularly as long as the foreign matter is electrically non-conductive.

WHAT WE CLAIM IS: 1. A switch matrix comprising a plurality of spaced electrically conductive first strips fixed either to a face of a rigid electrically insulating substrate or to an electrically insulating layer itself fixed to a rigid substrate; a resilient insulating membrane having an undistorted topology substantially the same as the topology of the said face of the substrate, the membrane being attached only about its periphery to the face of either the substrate or the insulating layer in a position in which the topology of the membrane substantially matches the topology of the substrate, the membrane being spaced apart from the first strips in a predetermined area of the membrane; and a plurality of flexible spaced apart electrically conductive second strips fixed to a surface of the membrane facing the substrate, each of said second strips being located in the said predetermined area and being spaced from the first strips when the membrane is undistorted, each of said second strips crossing at least two first strips.

2. A matrix as claimed in claim 1 in which the first and second strips and the membrane are transparent.

3. A switch matrix as claimed in claim 1 or 2 in which the first strips are substantially parallel to each other and the second strips are substantially parallel to each other and substantially orthogonal to the first strips.

4. A switch matrix as claimed in the preceding claim in which the substrate is convex, the membrane being slightly more convex than the substrate.

5. A switch matrix as claimed in claim 4 in which the substrate is part-spherical.

6. A switch matrix as claimed in claim 5 in which the membrane has a radius of curvature slightly smaller than that of the substrate.

7. A switch matrix as claimed in claim 6 in which the radius of curvature of the membrane when undistorted is substantially 1 to 4 inches smaller than that of the substrate.

8. A switch matrix as claimed in claim 7 in which the radius of curvature of the substrate is substantially 25 inches.

9. A matrix as claimed in any preceding claim in which the membrane comprises polyester film.

10. A switch matrix as claimed in any preceding claim in which the insulating layer is transparent.

11. A switch matrix as claimed in any preceding claim including an insulating grid interposed between the first and second strips, and having gaps within itself permitting electrical contact between a first and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ponents). This coating has been determined to have a piezo-resistant characteristic of high resistance under very light pressure, and a very low resistance under pressure no heavier than that generated by gentle finger pressure. In Figure 5, coatings 51,52 indicate use of this alternative. As now commercially available, both coatings 51, 52 must be present to yield suffciently high resistance at very low pressures to allow functioining as an anti-short means. It is probable that a coating 51 thicker than that now commercially available would allow omission of the coating 52. As previously mentioned, when the insulating grid 45 is not used, the spacer 53 may be necessary to prevent shorting adjacent the edges. Another means for preventing shorting between the conductor strips 12-16 and 20-24 is available for use with a substrate 10 having a finite radius of curvature. By selecting the radius of curvature of the membrane 11 smaller than that of the substrate 10 (for membranes mounted on the convex side of the substrate 10, of course), as shown in Figure 2, the natural resiliency of the membrane 11 and its arched shape supports the conductor strips 20-24 and prevents their shorting in the absence of external pressure. Although a wide variety of radii of curvature will undoubtedly work, it is known that a substrate of 25 inches radius of curvature and a 0.003 inch thick polyester membrane moulded with a form having a 22 inch radius of curvature are satisfactory. As shown in Figures 1 and 2, it is desirable to bond the periphery of the membrane 11 to the substrate 10 outside the conductor strips 20-24 to increase the clearance between the areas of the peripheral conductor strips. The spacer 53 may also be used for this purpose. It is likely, although not confirmed, that the use of the natural resilience is curvature of the membrane 11 to provide the necessary antishort spacing between the sets of conductor strips requires a greater difference in radii of curvature for the substrate 10 and the membrane 11 than do the other described arrangements to prevent shorting between the sets of conductor strips. Thus, while a 3 inch smaller radius works with a 25 inch substrate radius in all 3 cases, a 1 inch difference or less may well be satisfactory when the insulating grid 45 or the coatings 51,52 are used. During the manufacture of the above described switch matrices it is important that the surfaces of the conductor strips 20-24 and 12-16 are relatively free from dust and other foreign matter during attachment of the membrane 11 to the substrate 10. However, the relatively wide contact areas between crossing conductor strips does tolerate a small amount of such foreign matter, particularly as long as the foreign matter is electrically non-conductive. WHAT WE CLAIM IS:

1. A switch matrix comprising a plurality of spaced electrically conductive first strips fixed either to a face of a rigid electrically insulating substrate or to an electrically insulating layer itself fixed to a rigid substrate; a resilient insulating membrane having an undistorted topology substantially the same as the topology of the said face of the substrate, the membrane being attached only about its periphery to the face of either the substrate or the insulating layer in a position in which the topology of the membrane substantially matches the topology of the substrate, the membrane being spaced apart from the first strips in a predetermined area of the membrane; and a plurality of flexible spaced apart electrically conductive second strips fixed to a surface of the membrane facing the substrate, each of said second strips being located in the said predetermined area and being spaced from the first strips when the membrane is undistorted, each of said second strips crossing at least two first strips.

second strip responsive to manual pressure on their cross-over area.

12. A switch matrix as claimed in claim 12 in which the insulating grid uniformly covers the area occupied by the first strips.

13. A switch matrix as claimed in claim 12 or 13 in which the insulating grid is transparent.

14. A switch matrix as claimed in claim 12 to 14 in which the insulating grid is formed of electrically insulating photoresist material.

15. A switch matrix as claimed in claims 12 to 15 in which the insulating grid has orthogonal lines, the ratio of the width of each line to the spacing between adjacent lines being in the range of 1: 5 to 1:100.

16. A switch matrix as claimed in claim 16 in which the width of each said line is substantially 0.001 inches.

17. A switch matrix as claimed in any of claims 1 to 11 including a piezo-resistant coating interposed between the first and second strips, and permitting electrical conduction between a first and second strip responsive to manual pressure at their crossover area.

18. A switch matrix as claimed in claim 18 in which said coating is a ceramic coating serving to increase visible light transmission.

19. A switch matrix as claimed in claim 1 & or 19 in which each of the first and second strips carry said coating.

20. A switch matrix as claimed in any preceding claim including a vent for permitting air flow into the space between the membrane and the substrate.

21. An electric switch matrix substantially as herein described with reference to and as shown in the accompanying drawings.

22. A method of forming the insulating grid of claim 12 comprising coating the first strips and insulating layer with a photoresist material, exposing the photo-resist material to a light pattern corresponding to a pre-selected grid pattern. developing the photo-resist materials, and removing the unexposed photo-resist material.

23. A method as claimed in claim 23 and substantially as herein described with reference to the accompanying drawings.