GB2090979A - Proximity control switching panels - Google Patents

Abstract

A proximity control switching panel including a plurality of capacitors each comprising a command electrode plate and at least one slave electrode plate arranged in capacitive relation, and achieving a high degree of standardisation while allowing for different user requirements, comprises capacitors (12, 13) including command (11) and slave (3, 4) electrode plates respectively deposited on front (10) and rear (1) dielectric sheets. At least the front sheet (10) and the command electrodes (11) are light-transmitting, and a dielectric indexing sheet (8) carrying switch-identifying indicia (9), each located in register with a capacitor (12 or 13), is sandwiched between the front (10) and rear (1) sheets. The indicia (9) may be formed by printing. In other embodiments all the electrode plates are light-transmitting, being deposited on opposite faces of a single transparent sheet behind which is located a dielectric indexing sheet bearing the indicia. In either case, the whole panel, apart from printed portions of the indexing sheet, may be transparent. A screening electrode (2) may be provided and the panel may be bonded together using an adhesive bead (14) and/or adhesive laminating film. <IMAGE>

Description

SPECIFICATION Proximity control switching panels This invention relates to a proximity control switching panel including a plurality of capacitors each comprising a command electrode plate and at least one slave electrode plate arranged in capacitive relation.

In one form, a switch on a panel of the type referred to comprises a dielectric sheet having on one face a command electrode plate and on its other face a slave electrode plate in register with the command electrode and connected to a switching circuit. In use the slave electrode plate is charged so that when the command electrode plate is touched or closely approached by a finger for example, the slave electrode plate emits a control signal to the switching circuit. In other arrangements, such a switch has two slave electrode plates of which one is chargeable and the other is arranged to emit a control signal to the switching circuit.

Control panels bearing such switches are being used for an increasingly large number of purposes.

The following are given merely as examples: calculator, typewriter and telephone keyboards; domestic cooker, television and sound reproduction apparatus controls; display panel readout controls; elevator controls.

It will be apparent that these different control panels require different labelled arrangements of the switch or switches which they contain. It will also be apparent that for series mass production it is desirable to standardise the type of control panel produced to as great an extent as is compatible with customer requirements and this is the principal object of the present invention.

According to the present invention there is provided a proximity control switching panel including a plurality of capacitors each comprising a command electrode plate and at least one slave electrode plate arranged in capacitive relation, characterised in that said panel includes a plurality of said capacitors and said command and said slave electrode plates are light-transmitting plates deposited on opposite sides of a light-transmitting dielectric sheet and in that behind said sheet there is a dielectric indexing sheet which is printed to exhibit a plurality of switch-identifying indicia, a said indicium being located in register with each of at least some of said capacitors.

When making switching panels in accordance with the invention, it is possible to achieve a very high degree of standardisation in manufacture. It is possible to select a pattern for the array of switching capacitors so that switching panels for use with different circuitry can all be made identical as regards their electrode plates and the transparent dielectric sheets on which they are deposited, and different indexing sheets can be incorporated in the panels according to customer requirements.

Thus for example, switching capacitors may be arranged in a four-square matrix. If such a switching panel is to be incorporated in a telephone for "touch dialling", an appropriate indexing sheet could be printed with indicia representing the ten digits to register with ten of the switching capacitors, and the telephone manufacturer would connect the ten indexed capacitors to appropriate switching circuitry. On the other hand, a switching panel incorporating an identical array of switching capacitors could be incorporated in a calculator. In that case, the calculator manufacturer might require the indexing sheet to be printed with indicia representing the ten digits, the decimal point, and the add, subtract, multiply, divide, and equals functions.Thus the only change in the panel manufacturing process which is required when making panels for these different purposes is substitution of the indexing sheet. This is a very simple operation.

By proper selection of the pattern of the array of switching capacitors, it is possible, from a standardised production, to obtain switching panels bearing fractions or multiples of the number of capacitors deposited in a standard array. This may be done by dividing the standard array or by juxtaposing two or more such arrays as the case may be. In each case it is again easy to adapt the indexing sheets to customer requirements.

A further advantage of using indexing sheets which are separate from the capacitor-bearing sheets is that deposition of the indicia does not interfere with the process used to deposit the electrode plates.

In preferred embodiments of the invention, at least some of said capacitors comprise two slave electrode plates, namely a chargeable slave electrode plate and a discharging slave electrode plate, since this simplifies the required switching circuitry.

According to a second aspect of the invention, there is provided a proximity control switching panel including a plurality of capacitors each comprising a command electrode plate and at least one slave electrode plate arranged in capacitive relation, characterised in that said panel includes a plurality of said capacitors of which the command and slave electrode plates are respectively deposited on front and rear dielectric sheets, at least the front sheet and the command electrodes being iight-transmitting, and in that between said front and rear sheets there is sandwiched a dielectric indexing sheet which carries a plurality of switch-identifying indicia, a said indicium being located in register with each of at least some of said capacitors.

In addition to the advantages recited hereinbefore in respect of the first aspect of the invention, a panel according to the second aspect of the invention has the further advantage of being easier to manufacture, because the electrode plates may be deposited on a single surface only of their respective sheet.

In embodiments of the invention in its second aspect, said indicia may be applied to the indexing sheet in any convenient manner, but it is preferred that said indexing sheet is printed to exhibit said indicia.

Deposition of the command electrode plates of a panel according to the second aspect of the invention is simplified when they are deposited on a single surface of a sheet as is preferred.

In some embodiments of either aspect of the invention, each said capacitor includes a single slave plate for connection to switching circuitry, but as with the first aspect, so with the second, in preferred embodiments, each of at least some of said capacitors comprises two slave electrode plates, namely a chargeable slave electrode plate and a discharging slave electrode plate.

In embodiments of the second aspect of the invention, all said chargeable slave electrode plates are preferably deposited on a single surface of a sheet. Likewise all said discharging slave electrode plates are preferably deposited on a single surface of a sheet.

In some preferred embodiments of the second aspect of the invention, said chargeable slave electrode plates and said discharging slave electrode plates are deposited on at least two different sheet surfaces. Such surfaces may be opposite surfaces of a single sheet or surfaces of two or more different sheets. This facilitates the arrangement of conductors connected to the electrode plates.

In other preferred embodiments of the second aspect of the invention, all said slave electrode plates are deposited on a single surface of a sheet.

This has the advantage that all those electrode plates can be formed at one and the same time.

Again in embodiments of the second aspect of the invention it is preferred that all electrode plates and all sheets on which they are deposited are light-transmitting. This makes the electrodebearing sheets suitable for incorporating in a switching panel together with an indexing sheet having at least one light-transmitting portion in register with a said capacitor so as to enable an indication of operation of such switching capacitor to be given by a light which may be located behind the panel.

In some preferred embodiments of either aspect of the present invention, said indexing sheet has at least one light-transmitting portion in register with a said capacitor.

As an alternative, or in addition, said indexing sheet preferably includes a light-transmitting display section. This is especially valuable in the cases of for example calculators and telephone keyboards associated with an encoded memory bank. In such cases a display device may be located behind the panel to display the progress of a calculation or a telephone number recalled from memory as the case may be.

Advantageously, the or at least one said electrode-bearing sheet is of glass.

The indexing sheet is preferably of plastics material, for example a polyester such as polyethylene terephthalate. Said indexing sheet is preferably between 50 jum and 120 ym in thickness. This range meets requirements for the usual printing techniques, and reliable operation of the capacitor switches is not hindered in cases where the indexing sheet is located between electrode-bearing sheets.

Each of the electrode plates is preferably formed by a deposit of SnO2 or In203 which is optionally doped to enhance its conductivity. Such deposits can be hard and abrasion resistant while being substantially transparent.

In order to prevent spurious switching, it is advantageous to provide a shielding electrode behind the electrode plates.

In some preferred embodiments of the invention, the sheets of the panel are laminated together. This can be done very conveniently by using double faced adhesive film. Alternatively or in addition, one sheet of the panel may be larger than the others which are assembled thereto to leave a rebate which accommodates a bead of adhesive material bonding the panel sheets together.

Preferred embodiments of the invention will now be further described by way of example with reference to the accompanying drawings in which Figures 1 and 2 are cross sectional views through two embodiments of the invention, Figure 3 is a plan view of an insulating substrate carrying chargeable and discharging electrodes, Figure 4 is a plan view of an indexing substrate which could be used with a switching panel incorporating the substrate of Figure 3, and Figures 5 and 6 are partial sectional views of a third and a fourth embodiment of the invention.

In Figure 1, a glass sheet 1 has an optional tin oxide coating 2 applied to the whole of one face thereof to serve as a screening electrode and on its other face it carries two pairs of slave electrode plates, each pair consisting of a chargeable electrode 3 and a discharging electrode 4. These electrodes are also of tin oxide, doped as necessary. The discharging electrodes 4 are individually connected by conductors 5 (which may also be of tin oxide) to terminals 6 each of which is formed by a body of enamel applied to an end portion of the respective conductor 5. The terminals 6 are located at side margins of the panel for connection to associated circuitry. The chargeable electrodes 3 are connected to a common potential source (not shown).

The face of the substrate which bears the slave electrodes, 3, 4 may optionally be covered by a thin transparent plastic film, for example applied by spraying to prevent condensation on that face from adversely affecting operation of the switches.

Figure 3 illustrates an arrangement in which a sixteen switch panel has a single terminal 7 for connection to the potential source. Sixteen chargeable electrodes 3 are connected to their common terminal 7, and their sixteen associated discharging electrodes 4 are connected via conductors 5 to individual terminals 6 for the connection of operating circuitry.

The positions of some command electrodes 11 are indicated in dotted lines.

In Figure 1, an indexing sheet 8 of dielectric material, for example a plastics such as polyethylene terephthalate is laid over the first electrode-bearing sheet 1 and has areas bearing indicia 9 located in register with the electrode plates 3, 4. The indexing sheet 8 is of smaller size than the first electrode-bearing sheet 1 to leave a rebate around its periphery. A second glass sheet 10 which is transparent and of the same size as the indexing sheet 8 is laid over that sheet so that transparent command electrode plate deposits 11, for example of doped tin oxide, are located in registrer with the indicia and chargeable and discharging electrodes 3, 4 to form capacitors 12, 1 3.The rebate formed by the margin of the first sheet 1 and the edges of the indexing sheet 8 and second electrode-bearing sheet 10 contains a bead 14 of adhesive material to hold the sheets of the panel together.

In operation of the switch panel illustrated in Figure 1, the chargeable slave electrodes 3 are connected to a pulse generator while the discharging slave electrodes 4 are individually connected to a detector circuit. If a command plate 11 is touched, or in some cases even approached closely, for example by a finger, the capacitance between the three electrode plates will be modified. This will accordingly modify the pulse signal delivered by the discharging slave electrode plate 4, and this modification is detected to give a signal which can be amplified as necessary to control a switching circuit to perform a desired function. In cases in which it is not actually necessary to touch the electrodes 1 the sheet 10 on which they are deposited may if desired be reversed so that the electrodes 11 are beneath the surface of the panel.

In order to deposit a plurality of SnO2 electrodes on a dielectric sheet in a predetermined pattern in the formation of a capacitive touch control switch panel, the following process may be adopted. A silk-screen stencil is prepared, and a negative masking pattern of Wiederhold's WIEDOPRINTAL (Trade Mark) ink is printed on one side of a vitreous or ceramic sheet. The sheet is then conveyed through a heating station, in which the masking ink is baked to leave a dry powdery adherent masking residue, and thence to a coating station where it is sprayed with a solution of SnCI4 in known manner. When the SnCI4 solution contacts the heated sheets it is pyrolised to give a uniform overall coating of SnO2 80 nm thick.After cooling, the masking residue and overlying regions of SnO2 are removed by brushing to leave a positive patterned SnO2 coating on one side of the sheet. The process is then repeated using another silk-screen stencil to provide a positive patterned SnO2 coating on the other side of the same sheet or on a different sheet as required to form the required array of capacitors.

In a modified process, both sides of a sheet are masked and the sheet is then baked, and SnO2 coatings are formed on both sides of the sheet in a single stage of the process by a high frequency cathode sputtering technique.

Figure 2 shows a similar panel which has been assembled in a slightly different way. The only difference of substance is that the adhesive bead 14 of Figure 1 has been dispensed with, and the indexing sheet 8 and second electrode-bearing sheet 10 are laminated to each other and to the first electrode-bearing sheet 1. This is done by using double sided adhesive films 1 5 available under the trade name Mac Bond.

A panel according to Figure 1 and having an array of capacitor switches as illustrated in Figure 3 may be used in a calculator in which the various switches would be arranged to enter numbers in a display, carry out one or more of the four major arithmetical operations and give an answer. All the sixteen switch capacitors can be used to this effect. The sheet 1 will be larger than illustrated in Figure 3 to provide a place for a display. The display can be mounted upon the sheet 1 by any known means.

Figure 4 illustrates an indexing sheet suitable for use in a panel for such a calculator.

The substrate 8 is made of a film of clear plastics material such as polyester. This film bears indicia 9 which may be made of different colours or colour shades. The remaining space between the indicia 9 and around a section 17 marked "display" is covered by an opacifying coating. The indicia and the opacifying coating are applied to the polyester film by a printing technique such as off-set printing. The plastics film 8 may for example by 50 ,um to 120 ym in thickness.

The display section 1 7 remains transparent. In the calculator, this section is to be located in register with a display device (not shown) while the indicia 9 will be in register with the switching capacitors as above described. Furthermore, a small portion 1 6 of the indexing sheet 8 which is to be located in register with a switching capacitor may be left transparent if desired so that a signal light can be flashed on to indicate that any key has been touched.In the indexing sheet illustrated, only those areas of the indexing sheet 8 which are to register with a switching capacitor which governs a function which will not immediately modify the display, that is to say the decimal point, divide, multiply, subtract and add functions, are provided with such a transparent portion 1 6. The use of signal lights in conjunction with suitable circuitry for capacitive switches associated with those indicia can thus provide a positive indication that the desired function has in fact been keyed in.

Such a positive indication in respect of the otherswitches will normally be provided by an immediate modification of the display in response to switching.

A panel as described with reference to Figures 1 and 3 may also be used as a telephone keyboard. For this purpose, only ten of the sixteen switching capacitors will be connected to the external circuitry and indexed. Use can be made of an indexing sheet as illustrated in Figure 4 but wherein only the indicia corresponding to the digits 1 to 9 and 0 appear. These indicia will be placed in register with the selected switch capacitors. The area around the indicia 9 corresponding to the said ten digits is opacified as described above. The remaining sets of electrodes are not connected in circuit, so that they do not form active switches. As the electrode plates are mde of a transparent coating the non-selected switch capacitors will in practice be invisible to the user as they are not indexed.Of course if it is desired to provide some additional facility such as entering into or reading from a coded memory bank of frequently used telephone numbers or to provide for recalling an operator or for switching to an extension then the appropriate number of sets of electrodes can be connected to the desired circuitry and appropriate indicia provided.

In such a variant, the display panel 1 7 would sometimes be omitted, and if that were done it would be preferable to provide a light-transmitting portion such as 1 6 in register with each selected switching capacitor.

From a comparison of those two examples of use it will be apparent that the same array of electrodes has been used for the manufacture of the panels. A standardised process may be used for depositing the electrode plates on their substrates. This is of particular interest when a coating is deposited by pyrolysis of metal compound on a hot substrate such as heated glass. The control of the process is simplified. Only the indexing sheet has to be substituted in the panel. As those indexing sheets are obtained by a printing technique it is quite easy to modify the indicia as to their location, colour, pattern, etc., without those modifications affecting the more complicated process used for depositing the electrodes as would be the case if the indicia were to be applied to one of the sheets bearing the electrodes.

Figure 5 illustrates a further modification of the embodiments shown in Figures 1 and 2 in which similar elements are again given similar reference numerals. The principal difference between the embodiments of Figures 1 and 5 is that in Figure 5, the chargeable slave electrodes 3 are deposited on a surface of a sheet 1 A which is different from the surface on which the discharging slave electrodes 4 are deposited. In Figure 5, the sheet 1 A is a sheet of glass intermediate in size, and located between the sheet 1 on which the discharging slave electrodes 4 are deposited and the indexing sheet 8. The chargeable slave electrodes 3 are connected to a common terminal 7.

The sheets of the switch panel of Figure 5 may be bonded together by a bead of adhesive analogous to that shown at 14 in Figure 1 and/or by using three sheets of double faced adhesive film (compare film 1 5 of Figure 2).

Figure 6 illustrates an embodiment of the invention in which all the electrode plates 3, 4, 11 are carried by the same dielectric sheet 10 which is of clear glass. As before, the discharging slave electrodes 4 are connected by conductors 5 to terminals 6 at the sides of the panel, but in this case those conductors and terminals are applied to glass substrate 10. An indexing sheet 8 bearing printed indicia 9 is laminated to the glass sheet 10 by an adhesive film 15, and a support sheet 18 is in turn laminated to the indexing sheet 8, again by an adhesive film 1 5.

Claims (23)

1. A proximity control switching panel including a plurality of capacitors each comprising a command electrode plate and at least one slave electrode plate arranged in capacitive relation, characterised in that said panel includes a plurality of said capacitors (12, 13) and said command (11) and slave (3, 4) electrode plates are lighttransmitting plates deposited on opposite sides of a light-transmitting dielectric sheet (10) and in that behind said sheet there is a dielectric indexing sheet (8) which is printed to exhibit a plurality of switch-identifying indicia (9), a said indicium being located in register with each of at least some of said capacitors (12, 13).

2. A panel according to Claim 1, wherein at least one said capacitor (12, 13) comprises two slave electrode plates (3, 4).

3. A proximity control switching panel including a plurality of capacitors each comprising a command electrode plate and at least one slave electrode plate arranged in capacitive relation, characterised in that said panel includes a plurality of said capacitors (12,13) of which the command (11) and slave (3, 4) electrode plates are respectively deposited on front (10) and rear (1, 1 A) dielectric sheets, at least the front sheet ( 0) and the command electrodes (11) being lighttransmitting, and in that between said front (10) and rear (1, 1A) sheets there is sandwiched a dielectric indexing sheet (8) which carries a plurality of switch-identifying indicia (9), a said indicium (9) being located in register with each of at least some of said capacitors (12, 13).

4. A panel according to Claim 3, wherein said indexing sheet (8) is printed to exhibit said indicia (9).

5. A panel according to Claim 3 or 4, wherein all said command electrode plates (1 1 ) are deposited on a single surface of a sheet (10).

6. A panel according to any of Claims 3 to 5, wherein each of at least some of said capacitors (12, 13) comprises two slave electrode plates (3, 4) namely a chargeable slave electrode plate (3) and a discharging slave electrode plate (4).

7. A panel according to Claim 6, wherein all said chargeable slave electrode plates (3) are deposited on a single surface of a sheet (1 or 1 A).

8. A panel according to Claim 6 or 7, wherein all said discharging slave electrode plates (4) are deposited on a single surface of a sheet (1).

9. A panel according'to any of Claims 6 to 8, wherein said chargeable slave electrode plates (3) and said discharging slave electrode plates (4) are deposited on at least two different sheet surfaces.

10. A panel according to any of Claims 3 to 8, wherein all said slave electrode plates (3, 4) are deposited on a single surface of a sheet (1).

11. A panel according to any of Claims 3 to 10, wherein all electrode plates (3, 4, 11) and all sheets (1, 1 A, 10) on which they are deposited are light-transmitting.

12. A panel according to any of Claims 1, 2 and 11, wherein said indexing sheet (8) has at least one light-transmitting portion (16) in register with a said capacitor (12 or 13).

13. A panel according to any of Claims 1, 2, 11 and 12, wherein said indexing sheet includes a light-transmitting display section (17).

14. A panel according to any preceding claim, wherein the or at least one electrode-bearing sheet (1, 1A, 10) is of glass.

1 5. A panel according to any preceding claim, wherein said indexing sheet (8) is of plastics material.

1 6. A panel according to Claim 15, wherein said indexing sheet (8) is of a polyester.

1 7. A panel according to any preceding claim, wherein said indexing sheet (8) is between 50 ym and 120 ,um in thickness.

18. A panel according to any preceding claim, wherein each said electrode plate (3, 4, 11) is formed by a deposit of SnO2 or In203 which is optionally doped to enhance its conductivity.

19. A panel according to any preceding claim, wherein a shielding electrode (2) is provided behind the electrode plates (3, 4, 1 1).

20. A panel according to any preceding claim, wherein the sheets (1, 1 A, 8, 10) thereof are laminated together.

21. A panel according to Claim 20, wherein such lamination is effected using double-faced adhesive film (15).

22. A panel according to any preceding claim, wherein one sheet (1) of the panel is larger than the other sheets (8, 10) which are assembled thereto, to leave a- rebate which accommodates a bead (14) of adhesive material bonding the panel sheets together.

23. A proximity control switching panel substantially as herein described.