GB2156993A - Proximity control switches - Google Patents

Abstract

A proximity control switching key 1 is constituted by electrodes 2,3 of unequal area for example of tin oxide deposited on different faces 4, 5 of dielectric sheet material such as glass 6, 7. The pair of co-operating electrodes 2, 3 are deposited so that at least major portions thereof are out of register with each other on different sheet faces 4, 5 which are separated by a dielectric layer 7, and connector means are also deposited on the respective sheet faces 4, 5 for connecting those electrodes to control circuitry. In a variant, a keyboard for a proximity control switching panel includes a plurality of switching keys 1 comprising pairs of cooperating electrodes 2, 3 deposited on different faces 4, 5 of dielectric sheet material 6, 7. Such electrodes are arranged in rows and columns for co-operation with electrodes on the other sheet face to form a plurality of keys 1. Each such electrode 2, 3 is deposited so that at least a major portion of its area is out of register with its cooperating electrode, and the electrode-bearing sheet faces are again separated by a dielectric layer 7. Connector means are also deposited on the sheet faces 4, 5 for connecting each row of electrodes on one sheet face and each column of electrodes on the other sheet face to control circuitry. <IMAGE>

Description

SPECIFICATION Proximity control switches This invention relates to a proximity control switching key constituted by electrodes deposited on different faces of dielectric sheet material and includes keyboards incorporating such keys.

Keyboards incorporating such keys are well known, and their use for the control of many different kinds of equipment is increasing. Various constructions of such keys and keyboards are disclosed for example in British Patent Specifications Nos 2 060 895 and 2 061 004 to BFG Glass-group, and in No 2090979 to Glaverbel.

It is well known that certain problems arise in the manufacture of such keyboards, and in monitoring switching by keys they carry. The electrodes of the keys are usually deposited by a process involving a serigraphic step, whether by applying conductive material through a silk screen directly, or by applying a mask onto the dielectric sheet material through a silk screen and then applying a uniform coating of conductive material so that the required electrodes are left on removal of the mask. Such keys each comprise a pair of electrodes connected to control circuitry, and known keys are usually also provided with an additional floating electrode. Connexion of the electrodes to operating circuitry is simplified if connectors leading to terminals, for example at the edge of the keyboard, are formed at the same time and in the same way as the electrodes.It is usual for one electrode of each key to be connected to one or more terminals in turn connected to a common pulse source, while other electrodes are connected to a plurality of terminals in turn connected to detector circuitry. More often than not, each of such other electrodes is connected to a different terminal. It will be appreciated that this can result in a rather complicated pattern of electrodes and connectors deposited on the dielectric sheet material.

For reasons of economy in the detector circuitry, signals from those other electrodes are usually fed in sequence toa common threshold detector to monitor the condition of each key. This imposes certain constraints on the capacitances of the keys inters and as between their different operating states.

Because of the rather complicated pattern of electrodes and connectors deposited on the dielectric sheet material, and because it is generally desirable that the keyboard should be compact in size, it is necessary that electrodes and connectors should be deposited close together and this very often leads to undesired cross capacitances occurring between different electrodes and connectors, and this in turn can lead to spurious or irregular switching.

It is an object of the present invention to provide a key for such a keyboard in which the disadvantages referred to above are alleviated.

According to a first aspect of the present invention, there is provided a proximity control switching key constituted by electrodes deposited on different faces of dielectric sheet material, characterised in that such key comprises a pair of co-operating electrodes deposited so that at least major portions thereof are out of register witheach other on different sheet faces which are separated by a dielectric layer, and connector means also deposited on the respective sheet faces for connecting those electrodes to control circuitry, and in that one electrode of such pair has a smaller area than the other electrode of the pair.

A keyboard incorporating such a key should be used with the smaller of said electrodes to the front.

The adoption of the present invention affords a number of advantages which are of considerable practical importance. Because the electrodes and connector means are deposited on different sheet faces which are separated by a dielectric layer, they can be deposited in simpler patterns and with greater spacing between adjacent conductive elements. Conductive elements which cross over will be separated by the thickness of the dielectric layer between the two sheet faces. As a result of this undesired cross capacitances will be reduced, and as the pattern of deposition is simplified, pattern reproducibility as between successive keyboards will be improved. The front, over-coated electrode is smallerthan the other said electrode in order that capacitors formed by those respective electrodes and a conductor placed over the front of the key may have more nearly equal capacitances.For strict equality of capacitance, the areas of those two electrodes should be inversely proportional to their distances from the front of the keyboard. Making these capacitances more nearly equal allows the use of simpler and thus less expensive control circuitry.

In some embodiments of the invention, said key includes a floating electrode formed over said insultating means and in register with the other electrodes, but the provision of such a floating electrode is unnecessary for satisfactory operation of the key, and it adds to the cost of manufacture. It is accordingly preferred that such key comprises only two electrodes.

In preferred embodiments of the invention, said electrodes are formed by deposits of tin oxide. Tin oxide coatings, which may be doped to enhance their electrical conductivity, can be formed easily and economically on a variety of dielectric substrates.

In particular, tin oxide electrodes of the required conductivity can be made transparent, and this is of importance where the key itself is to be made transparent as is especially preferred. The adoption of this feature enables the use of keyboards incorporating such keys as facings for various types of equipment including variable displays, for example LED displays, which may for example be controlled by operation of the key or keys on the keyboard through which the display is to be viewed The use of keyboards as facings for various types of display equipment is described in our copending British Patent Application No.84 08375 (Publication No.GB A) of even date herewith filed under agents' reference 338 LAETARE, and the disclosure of that Application is specifically incorporated in this specification.

In general, tin oxide coatings have a refractive index of about 2, and this relatively high refractive index tends to give rather high reflection at the interface between the tin oxide coating and other material, for example a transparent sheet on which it is deposited or air to which it is exposed. In order that the display may be viewed without eye-strain caused for example by distracting reflective patterns across the keyboard, it is desirable that the visible light transmission and reflection properties of the keyboard over its area should conform to an acceptable criterion.

So as to go at least some way towards satisfying this desideratum, it is preferred to adopt one or more of the following optional features of the invention: i. at least one such electrode is deposited to a thickness in the range n x100 to n x 130nm, where n is 1 or3; ii. at least the smaller electrode is deposited to a said thickness in the range n x 100 to n x 130 nm, where n is 1 or 3; and iii. each electrode of said key is deposited to a thickness in the said range n x 100 to n x 130 nm, where n is 1 or 3.

Light reflection by the or each electrode plate which satisfies the required thickness criterion is reduced as compared with otherwise similar tin oxide electrode plates deposited to different thicknesses. Accordingly one or more such keys can be distributed across the keyboard in such a way as to give a less distracting reflecting pattern than has hitherto been possible. Tin oxide electrodes of such thicknesses have good optical and electrical properties for the purpose in view. The greatest benefit in respect of the thickness of the electrodes is achieved when n is 1 as is also preferred.

Preferably, said smaller electrode is covered by insulating means. The provision of said insulating means, which in use would be in front of the smaller electrode, will prevent direct electrical contact with the electrode which it over-coats but can easily be thin enough to allow a capacitive connexion to be made between that electrode and the other electrode of the key as desired for switching.

The insulating means may be substantially confined to one or more localised areas occupied by a said smaller electrode, or it may extend over sub stantiallythe whole area of the dielectric sheet material bearing the smaller electrode or electrodes.

Indeed, in some embodiments of the invention, said insulating means is in fact constituted by that dielectric sheet. In other embodiments of the invention, the insulating means is constituted by a polymeric layer, which may be applied as a film or in fluid form, for example a polypropylene film or a silicone based varnish, or by inorganic material, for example a sheet of thin glass or an inorganic dielectric coating.

Preferably, said insulating means comprises a coating of dielectric materials deposited over said smaller electrodes. Such a coating can be applied easily, and it avoids any requirement for a separate insulating sheet at the front of the key.

Further reduction of the difference in reflection as between portions of the dielectric sheet material bearing tin oxide electrodes and the remainder of the keyboard can be effected by adopting an additional feature which is particularly preferred, namely that such dielectric coating material has a refractive index in the range 1.3 to 1.6 inclusive. Tin oxide coatings generaly have a refractive index of about 2, as has been stated above. By overcoating those electrodes with a coating material having a refractive index approximately equal to the square root of the refractive index of tin oxide, it is found that the sum of the reflection at the tin oxide/coating interface and the reflection at the coating lair interface is reduced as compared with the reflection at a tin oxide lair interface.Accordingly, the adoption of this feature contributes to a reduction in the light reflected at the over-coated electrode, and gives an improvement in the uniformity of reflection from the keyboard even when the electrodes do not meet the thickness criterion set forth above.

Advantageously, such dielectric coating material is deposited to a thickness not exceeding 1 0lim, and preferably, each electrode of said key is so overcoated with a said dielectric coating.

Yet further reduction of the difference in reflection as between portions of the dielectric sheet material bearing tin oxide electrodes and the remainder of the keyboard can be effected by adopting another additional feature which is also particularly preferred, namely that the or each such dielectric overcoating has a thickness not exceeding 160nm. The adoption of this feature contributes to interference extinction of light reflected at the over-coated electrode, and again gives an improvement in the uniformity of reflection from the keyboard even when the electrodes do not meet the thickness criterion set forth above.It has been found that a said dielectric coating having such a thickness is particularly beneficial in reducing light reflection from the area of an underlying tin oxide coating over a wide range of thicknesses of tin oxide coating and no matter what the number of glass sheets or their thickness.

it is especially preferred that the or at least one said dielectric coating be of silica. Silica coatings are hard and abrasion resistant, and can readily be formed to a thickness of for example 1 00nm with a refractive index of about 1.41 by a dipping technique using a solution of tetramethylorthosilicate in methanol, or by the pyrolysis of silicon hydride in the presence of oxygen.

In some preferred embodiments of the present invention in which the electrodes are formed by deposits of tin oxide, each sheet face bearing one elctrode of said pair also bears an additional tin oxide deposit in register with and of substantially the same size and thickness as the other electrode of the pair. Because the two electrodes of the pair are located at different distances from the front of the key, and especially if the sheet faces on which they are deposited face in opposite directions, there will be differential reflection at those elecrodes. The pattern of relfection by the key or keys on a keyboard can be made more regular by incorporating such additional tin oxide deposits.

In some preferred embodiments of the invention, the rearmost additional tin oxide deposit is con nected to an earth terminal. This can provide a measure of shielding against electric fields generated by any apparatus located behind a keyboard bearing such a key.

Preferably, the or at least one said dielectric sheet is of glass.

Any such glass sheet used may be chemically tempered, and the or each such glass sheet preferably has a thickness of 1 .5mm or less.

Advantageously, the or each such electrodebearing glass sheet has been subjected to a dealkalising treatment. It has been found that a tin oxide coating having good mechanical and optical properties can more easily be obtained on a sheet of glass which has a low sodium content at least at its surface, and that when applied to such a sheet, the tin oxide coating is more adherent, so prolonging the useful life of the product. The adoption of this feature is also beneficial for giving a product having a relatively low diffuse transmission of light over the areas coated with tin oxide.

The present invention includes a keyboard for a proximity control switching panel including a plurality of switching keys deposited in common on one or more sheets of glass, characterised in that at least some of said keys are keys according to the first aspect of the invention as herein defined.

It is not essential that all the keys on such a keyboard should be as herein defined, but in preferred embodiments of keyboard according to the invention, all said keys are keys according to the first aspect of theinvention as herein defined.

The present invention in its second aspect has particular reference to a keyboard for proximity control switching which is especially advantageous both as regards ease of manufacture and as regards reliability in use, in view of the simplicity of the arrangement of electrodes and connectors of the control keys applied thereto.

According to the second aspect of the invention, there is provided a keyboard for a proximity control switching panel which includes a plurality of switching keys comprising pairs of co-operating electrodes deposited on dielectric sheet material, characterised in that each of two different dielectric sheet faces bears one elctrode of each said pair, in that such electrodes are arranged in rows and columns for co-operation with electrodes on the other shet face toform a plurality of keys, in that each such electrode is deposited so that at least a major portion of its area is out of register with its co-operating electrode, in that the elctrode-bearing sheet faces are separated by a dielectric layer, and in that connector means is also deposited on said sheet faces for connecting each row of electrodes on one sheet face and each column of electrodes on the other sheet to control circuitry. Advantageously, each electrode on one sheet face is of smaller area than its respective co-operating electrode on the other sheet face.

Preferably at least some and optimally all of said keys are keys according to the first aspect of the invention as herein defined.

The present invention will now be described in greater detail by way of example only, with reference to the accompanying diagrammatic drawings, in which Figures 1 to 3 are cross sectional views of parts of three different embodiments of keyboard incorporating keys according to the invention, Figure 4 is a plan view of the substrate of the keyboard of Figure 3 in the direction of the arrows IV, Figure 5 is a plan view of the substrate of the keyboard of Figure 3 in the direction of the arrows V Figure 6 is a cross sectional view of part of yet a further embodiment of keyboard incorporating keys according to the invention, and Figures 7 and 8 are views corresponding respectively to Figures 4 and 5, showing a different manner of arranging connectors on the keyboard.

In Figure 1 there is shown part of a keyboard incorporating two proximity control switching keys 1. Each proximity control switching key 1 isconsti- tuted by a pair of co-operating electrodes 2, 3 deposited on faces respectively 4, 5 of front and rear dielectric sheets 6, 7. In accordance with the first aspect of the inventions each key 1 comprises two electrodes 2, 3 deposited out of register with each other on different sheet faces 4, 5 which are separated by a dielectric layer, in this embodiment constituted by the rear dielectric sheet 7, and connector means (not shown in Figure 1) are also deposited on the respective sheet faces for connecting those electrodes to control circuitry.The electrodes 2 which are deposited on the front sheet 6 are of lesser area than the electrodes 3 which are deposited on what in use will be the rear face 5 of the panel illustrated in Figure 1.

The forward electrode-bearing sheet face 4 is covered by insulating means which in this embodiment is constituted by the front dielectric sheet 6.

Each of the dielectric sheets 6 and 7 is suitably made of glass.

Figure 2 shows part of a slightly modified panel in which like parts have been allotted the same reference numberals as in Figure 1. The main differences are firstly that the smaller, front electrodes 2 are deposited not on the rear face 4 of a front dielectric sheet 6, but rather on the front face 8 of the rear dielectric sheet 7, and secondly that the front sheet 6 is replaced by a film 9 of plastics material, for example of polypropylene.

In a further modification, the electrodes 2, 3 are formed by deposits of tin oxide, and each sheet face 5,8 bearing one elctrode of said pair also bears an additional tin oxide deposit 10, 11 shown in dotted lines which is in register with and of substantially the same size and thickness as the other electode 3, 2 of the pair. The rearmost additional tin oxide deposits 11 may be connected to an earth terminal (not shown).

Figure 3 shows part of another modified panel in which like parts have again been allotted the same reference numerals. As in Figure 2, the smaller, front electrodes 2 are deposited on the front face 8 of the dielectric sheet 7 whose rear face 5 bears the larger, rear electrodes 3.

In the embodiment shown in Figure 3, the front insulating means comprises a coating 12 of dielectric material deposited over the smaller electrodes 2. An optional dielectric coating 13 is also shown depo sited over the larger electrodes 3 at the rear of the panel. Instead of covering the whole surface of sheet 7, either dielectric coating can if desired by confined substantially to the areas of the electrodes.

Plan views of the different faces of the panel shown in Figure 3 form Figures 4 and 5.

Figure 4 illustrates one way in which rear electrodes 3 of a sixteen key panel may be connected to terminals 14 using connectors 15 deposited on the rear face 5 of the dielectric sheet, Figure 5 illustrates how the front electrodes 2 of that panel may be connected in common to terminals 16 using a connector network 17 deposited on front face 8 of the dielectric sheet.

From inspection of Figures 4 and 5, it will be apparent that the patterns of electrodes and connec torsthere shown are very much simplerthan would be necessary if all the electrodes and connectors were to be deposited on the same sheet face.

Figure 6 shows part of yet another modified panel in which like parts have again been allotted the same reference numerals. As in Figure 1, there are front and rear glass sheets respectively indicated at 6 and 7 on whose rear faces 4, 5 are respectively deposited smaller and larger electrodes 2,3. As in Figure 2, the electrodes 2,3 are formed by deposits of tin oxide, and each sheet face bearing one electrode of eahc pair also bears an additional tin oxide deposit 10, 11 shown in dotted lines which is in register with and of substantially the same size and thickness as the other electrode 3, 2 of the pair. An optional floating electrode 17 is provided on the front face of the front dielectric sheet 6.

Figures 7 and 8 show a modification of the arrangement of Figures 4 and 5 in accordance with the second aspect of this invention. From an inspection of Figures 7 and 8, it will be apparent that the various electrodes 2, 3 are arranged in four columns and four rows. In figure 7 the four electrodes 3 in each column are connected by connectors 15 to a common terminal 14a, 14b, 14c or 14d. In Figure 8 the four electrodes 2 in each row are connected by connectors 17 to a common terminal 16A, 16B, 16C or 16D. Potentials at the various terminals 14 and 16 can be compared to give an indication of a unique switching key which has been operated, and the control circuitry can than be arranged to effect the required switching function. Such comparison may be effected continuously, but is preferably cyclic.For example if in any given cycle the potential monitored at terminal 1 4b differs from that monitored at the other terminals 14, and the potential monitored at terminal 16C differs from that monitored at the other terminals 16, the control circuitry can be arranged to effect a switching function associated with the switching key located in column b, row C.

Any electrode-beaaring glass sheet such as 6 or 7 used in a panel according to the invention is preferably of dealkalised glass. Glass may be dealkalised by exposing itto an atmosphere containing an acid gas such as SO2, which can be formed in situ by passing SO2 over a suitable catalyst to reduce handling problems. As an alternative, dealkalisation can be effected by spraying the glass with a solution of HC1. The glass is preferably less than 1.5mm thick, and may for example be between 1.0mum and 0.4mm thick. The glass may be, and preferably is, chemically tempered.

Each electrode is preferably formed by a tin oxide deposit, preferably deposited to a thickness in the rangenxl00to nix130 nm,wheren is 1 or3, preferably 1. Any additional tin oxide deposit present (compare 10 and 11 in Figure 2) preferably has a like thickness.

Tin oxide electrodes or additional deposits may readily be formed in situ on a glass sheet by pyrolysis of a solution of tin tetrachloride in dimethyl formamide which contains triflouroacetic acid to give a flourine doped tin oxide coating whose thickness can readily be controlled to withinl2nm of 11 4nm and which has a resistivity within the range 45 to 60 Ohms per square. The pattern of the tin oxide deposit thus obtained can be controlled to define elctrodes, any required additional tin oxide deposits and any required connectors by previously applying a mask to the substrate to be coated using a serigraphic technique.

The dielectric coating 12 shown in Figure 3 preferably has a refractive index in the range 1.3 to 1.6 and a thickness not exceeding 1 0pom. In fact the coating 12 preferably has a thickness not exceeding 160nm, for example a thickness of 95 nm. Such a dielectric coating may also be applied to the keyboards shown in Figures 1 aand 2. The dielectric coating 13 also shown in Figure 3 preferably has similar properties.

A dielectric over-coating of silica, which is an especially suitable material to use in view of its hardness and in particular its refractive index, can readily be applied to a glass sheet by pyrolysis. A silica layer having a thickness of 95 nm and a refractive index of about 1.41 as is particularly preferred, and a resistance of about 108 Ohms per square can be formed by a vapour deposition technique using silicon hydride as coating precursor material.

Claims (25)

1. A proximity control switching key constituted by electrodes deposited on differnet faces of dielectric sheet material, charasterised in that such key comprises a pair of co-operating electrodes deposited so that at least major portions thereof are out of register with each other on different sheet faces which are separated by a dielectric layer, and connector means also deposited on the respective sheet faces for connecting those electrodes to control circuitry, and in that one electrode of such pair has a smaller area than the other electrode of the pair.

2. A key according to claim 1, wherein such key comprises only two electrodes.

3. A key according to claim 1 or 2, wherein said electrodes are formed by deposits of tin oxide.

4. A key according to claim 3, wherein the key is transparent,

5. A key according to claim 4, wherein at least one electrode is deposited to a thickness in the range n x 100 ton x 130 nm, where n is 1 or 3.

6. A key according to claim 5, wherein at least the smaller electrode is deposited to a said thickness in therangenx100tonx130nm,wherenis1 or3.

7. A key according to claim 6, wherein each electrode of said key is deposited to a thickness in thesaidrangenx100tonx130nm,wherenis1 or 3.

8. A key according to any of claims 5,6 and 7, wherein n is 1.

9. A key according to any preceding claim, wherein said smaller electrode is covered by insulating means.

10. A key according to claim 9, wherein each electrode of said key is covered by insulating means.

11. A key according to claim 9 or 10, wherein said insulating means comprises at least one coating of dielectric materila deposited over a said electrode.

12. A key according to any of claims 4 to 8 and to claim 11,wherein such dielectric coating material has a refractive index in the range 1.3 to 1.6 inclusive.

13. A key according to any of claims 4to 8 and to claim 11 or 12, wherein such dielectric coating material is deposited to a thickness not exceeding 10 > m.

14. A key according to any of claims 11 to 13, wherein the or each such dielectric over-coating has a thickness not exceeding 160nm.

15. A key according to any of claims 11 to 14, wherein the or at least one such dielectric overcoating is of silica.

16. A key according to any preceding claim, wherein said electrodes are formed by deposits of tin oxide, and wherein each sheet face bearing one electrode of said pair also bears an additional tin oxide deposit in register with and of substantially the same size and thickness as the other electrode of the pair.

17. A key according to claim 16, wherein the rearmost additional tin oxide deposit is connected to an earth terminal.

18. A key according to any preceding claim, wherein the or at least one said dielectric sheet is of glass.

19. A key according to claim 18, wherein the or each such glass sheet has a thickness of 1.5 mm or less.

20. Akeyaccodingtoclaim 18 or 19, wherein the or each such electrode-bearing glass sheet has been subjected to a dealkalising treatment.

21. A keyboard for a proximity control switching panel including a plurality of switching keys deposited in common on one or more sheets of glass, characterised in that at least some of said keys are keys according to any preceding claim.

22. A keyboard according to claim 21, wherein all its keys are keys accoding to any of claims 1 to 20.

23. A keyboard for a proximity control switching panel which includes a plurality of switching keys comprising pairs of co-operating electrodes deposited on dielectric sheet material, characterised in that each of two different dielectric sheet faces bears one electrode of each said pair, in that such electrodes are arranged in rows and columns for cooperation with electrodes on the other sheet face to form a plurality of keys, in that each such electrode is deposited so that at least a major portion of its area is out of register with its co-operating electrode, in that the electrode-bearing sheet faces are separated by a dielectric layer, and in that conneector means is also deposited on said sheet faces for connecting each row of electrodes onone sheet face and each column of electodes on the other sheet face to control circuitry.

24. A keyboard according to claim 23, wherein each electrode on oen sheet face is of smaller area than its respective co-operating electode on the other sheet face.

25. A keyboard according to claim 21 or 22 and to claim 23 or 24.