GB2272573A - Keypad assemblies - Google Patents

Abstract

A keypad assembly for an automatic teller machine (ATM) is constructed from a sub-assembly to which keys (22) are subsequently connected. The sub-assembly comprises a moulded body member (30) which defines a plurality of recesses (32) each receiving a respective key (22) having a key face (6) and a stem (23). Each key (22) is biased to a rest position by a spring (37) which clicks overcentre when the key (22) is depressed to provide feel to the operator. The spring (37) is held in each recess (32) by a key capture plate (38) having flanges (42) for engaging a waisted region (64) on the key stem (23). The key capture plate (38) and the spring (37) are retained within the respective recess (32) by a front plate (4). The sub-assembly also incorporates a sealing sheet (52) of compressible material interposed between the front plate (4) and the body member (30), and a membrane switch assembly (58, 60) fixed to the rear surface of the sub-assembly. Each key stem (23) extends through holes in the sealing sheet (52), the key capture plate (38), the spring (37) and the bottom of the recess (32). <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO KEYPAD ASSEMBLIES The present invention relates to keypad assemblies, to a sub-assembly therefor, and to a method of constructing a keypad assembly.

In this specification, the term "keypad assembly" is used to refer to an assembly comprising a plurality of individual keys, the keys being depressible to actuate pressure operable switch means arranged in cooperation therewith. Preferably, the pressure operable switch means comprises membrane switch means provided adjacent a rear surface of the keypad assembly from which stems of the individual keys project.

Such keypad assemblies are increasingly familiar and are utilised, for example, on automatic teller machines (ATM's). Because of their wide and increasing use, it is important that no radical departures in their size and shape be proposed and that the keypad assembly remains reliable. In this respect, existing keypad assemblies have generally been satisfactory.

However, the present invention seeks to improve existing keypad assemblies.

According to a first aspect of the present invention there is provided a sub-assembly for a keypad assembly as defined herein, the sub-assembly comprising a keypad body defining a front surface of the keypad assembly and having a rear surface which, in the keypad assembly, is adjacent to the pressure operable switch means thereof, wherein said keypad body comprises a plurality of recesses, each of said recesses being arranged to receive a respective key of said keypad assembly, and each said recess having a bore therein which opens into the rear surface of said keypad body, and further comprising key engaging means arranged in each said recess and arranged to engage and capture a respective key inserted into said recess.

Traditionally, keypad assemblies are manufactured by a process in which a complete assembly is built up sequentially. Whilst there is nothing wrong with such a process it does mean that the final function of the keypad assembly, including the required inscriptions on the keys, has to be known before the keypad assembly is manufactured.

By contrast, the present invention proposes the provision of a sub-assembly which, subsequently, is formed into a completed keypad assembly by the addition of an appropriate switch means and appropriately marked keys. This facilitates the manufacturing process considerably.

However, and very importantly, there is also no compromise on the standard of the final keypad assembly manufactured in this manner.

In a preferred embodiment, said sub-assembly further comprises pressure operated switch means arranged adjacent to said rear surface.

The switch means includes circuitry which is increasingly becoming standardised. Thus, in many cases the switch means may be included in the sub-assembly with no loss of flexibility. In this instance, the completed customised keypad assembly is formed simply by the addition of appropriately marked keys.

It is even more advantageous to provide sub-assemblies in which the switch means are already incorporated. If a stock of such sub-assemblies is held together with a wide range of keys, a large range of final assemblies can be offered to customers effectively from stock. Furthermore, as the keys are relatively low cost components there is generally no difficulty in keeping large quantities of different keys.

In a preferred embodiment, the front surface of the keypad assembly is provided by a front plate connected to a body member to form the keypad body. Appropriate fixing means are provided to hold the front plate on the body member.

Preferably, the front plate has a plurality of apertures therein, each aperture being aligned with a respective recess in said body member. It is prefered that said apertures have been formed by laser cutting. The front plate may be, for example, of stainless steel.

Conventionally, front plates of keypad assemblies are punched. It is preferred with the invention to laser cut the front plate, even though this is more expensive than punching, because this provides a clean cut with no burns or draws, and allows a thinner web betweenkeys.

In a preferred embodiment, the body member is moulded from a plastics material and defines said recesses and said rear surface. Preferably, the bore in each said recess is provided substantially centrally of a base surface of the recess.

In a preferred embodiment, spring means are retained in each said recess. The spring means are biassed outwardly of the recess, but are arranged to click into an overcentre position when pushed inwardly of the recess.

Preferably, said key engaging means in each said recess comprises a key capture plate having a substantially central, through bore. The key capture plate is preferably made of plastics material, the material and/or the shape of the plate or the bore being arranged to provide a degree of flexibility to the plate. The plate is positioned in the respective recess such that its through bore is aligned with the bore in the recess. In addition, key stem engagement means, such as one or more flanges, are provided on the periphery of the through bore of said key capture plate.

In a particularly preferred embodiment, the through bore in said key capture plate is substantially circular and is extended by lateral wing portions. The overall shape of the bore is chosen to provide the necessary flexibility to enable the engagement means to reliably engage the key stem. Preferably, the key stem engagement means comprise two axially extending flanges provided on opposed parts of the circular portion of said bore.

In a particularly preferred embodiment, each said key capture plate retains a respective spring means in its associated recess. In addition, the connection of the front plate to the base member holds the spring means and the key capture plates in the respective recesses.

In a particularly preferred embodiment, a sealing sheet is provided in the sub-assembly beneath the front plate thereof. The sealing sheet is appropriately provided with holes therein for the passage of key stems therethrough. The holes in the sealing sheet are substantially aligned with respective through bores in the key capture plates and respective bores in the associated recesses. The sealing sheet is arranged to seal the keypad assembly and is therefore made of a compressible material.

Where static electricity might be a problem, the sealing sheet is also arranged to be made of conductive material.

The present invention also extends to a keypad assembly comprising a sub-assembly as defined above, the keypad assembly further comprising a plurality of keys, each key being received in a respective recess such that a key stem thereof is engaged by said key engaging means, extends through the bore in the recess and projects relative to the rear surface of the sub-assembly, and the keypad assembly further comprising pressure operated switch means connected to said sub-assembly to be adjacent to said rear surface, said switch means being operable by the application of pressure to said keys.

In a preferred embodiment, said pressure operated switch means comprises a membrane switch assembly. For example, the membrane switch assembly may comprise a resilient and/or flexible sheet or pad provided to contact said rear surface, and a back plate having a membrane switch formed on one surface thereof, the back plate being fixed to said sub-assembly such that the membrane switch contacts the resilient and/or flexible sheet or pad and is thus operable by said keys.

According to a further aspect of the present invention there is provided a method of constructing a keypad assembly, the method comprising the steps of taking a subassembly as defined above, inserting a key in each said recess such that a key stem of the key extends through the bore of the respective recess and projects relative to the rear surface of the sub-assembly, and fastening pressure operated switch means on said sub-assembly adjacent to said rear surface, the pressure operable switch means being arranged to be actuated by said keys.

Preferably, each key is inserted in a respective recess such that a stem thereof is engaged by said key engaging means.

In a preferred embodiment, said pressure operated switch means comprises a membrane switch assembly. For example, the membrane switch assembly may comprise a resilient and/or flexible sheet or pad arranged to contact said rear surface, and a back plate having a membrane switch formed on one surface thereof, the back plate being fixed to said sub-assembly such that the membrane switch contacts the resilient and/or flexible sheet or pad.

In a preferred embodiment, said switch means may be fastened to said sub-assembly in advance. The sub-assembly with the switch means may then be stored until required.

A keypad assembly constructed from a sub-assembly as defined above, or a sub-assembly with the switch means, is particularly simple to manufacture and has the considerable advantage that the keys, and the particular pressure operable switch if required, are the last elements to be added to the final keypad assembly. This means that customisation of keypad assemblies is somewhat easier than heretofore and that large numbers of completed keypad assemblies do not have to be made and stored in order to meet demand in fast delivery times.

However, as well as being easier to manufacture and easier to customise, a keypad assembly of this aspect of the invention also has considerable advantages over existing keypad assemblies. The keypad assembly allows a relatively slim construction to be made, is operable reliably over a wide range of temperatures because it is well sealed against the ingress of water, and has a tactile operation which enables more satisfactory use.

The present invention also extends to a keypad assembly as defined herein, the keypad assembly further comprising respective spring means associated with each said key and arranged to bias said key outwardly of said keypad assembly to an initial, non-actuated position, wherein each said spring means is arranged to be clicked into an overcentre position upon operation of the respective key against the bias of said spring means.

The use of spring means arranged to be clicked into an overcentre position has the considerable advantage that the effect of the depression or actuation of a key can be felt.

That is, the keypad assembly is tactile. This is generally more satisfying to the user than pressing keys which give no feel or suggestion that anything has been actuated in response to their depression. In this respect, current ATMs, for example, emit a 'beep' on each successful actuation of a key, but this response is not helpful to those who are deaf.

Any appropriate spring means may be used to provide the overcentre operation. In a preferred embodiment, each said spring means comprises a plate spring having a central bore therethrough and being substantially convex over at least part thereof.

In an embodiment of this aspect of the invention, the keypad assembly comprises a sub-assembly formed of a front plate connected to a body member, said body member having a plurality of recesses in which each said key is received.

In a preferred embodiment, the body member is moulded from a plastics material and defines said recesses and said rear surface. Preferably, a bore is provided in each said recess substantially centrally of a base surface thereof.

In a preferred embodiment, the front plate has been laser cut from, for example, stainless steel. Appropriate fixing means hold the front plate on the body member.

In a preferred embodiment, said spring means are retained in each said recess. Preferably a key capture plate is provided in each said recess to engage a respective key therein. Each said key capture plate may also retain the respective spring means in the associated recess. In addition, the connection of the front plate to the base member holds the spring means and the key capture plates in the respective recesses.

Preferably, said key capture plate is preferably made of plastics material, the material or the shape of the plate being arranged to give a degree of flexibility to the plate. Each said plate. is provided with a through bore which is aligned with the bore in the base surface of the respective recess. In addition, key stem engaging means, such as one or more flanges, are provided on the periphery of the through bore of the key capture plate.

In a particularly preferred embodiment, the through bore in each said plate is extended by lateral wings, and.

said key stem engaging means are formed by axially extending flanges on the periphery of said bore.

In a particularly preferred embodiment, a sealing sheet is provided in the sub-assembly beneath the front plate thereof. The sealing sheet is appropriately provided with holes therein for the passage of key stems therethrough. The holes in said sealing sheet are substantially aligned with respective through bores in the key capture plates and respective bores in the recesses.

The sealing sheet is arranged to seal the keypad assembly and is therefore made of a compressible material.

Where static electricity might be a problem, the sealing sheet is also arranged to be conductive.

The present invention also extends to a keypad assembly as defined above comprising a sub-assembly as defined above.

It is important that a keypad assembly be operable over a wide range of temperatures, for example from -30 C to 500C. In order to be reliably operable at all temperatures it is essential that the keypad assembly be effectively sealed against the ingress of water. In existing keypad assemblies an individual seal is associated with each individual key. These seals do absorb moisture, and can prevent operation of the keypad in more severe climatic conditions.

In accordance with a still further aspect of the present invention there is provided a keypad assembly as defined herein, the keypad assembly further comprising a front plate having a plurality of apertures, each key of the keypad assembly having a key face which is arranged to be received in a respective aperture, and the keypad assembly also comprising a body member arranged to be connected to said front plate to form a keypad body, and wherein a sealing sheet of a compressible material is interposed between said front plate and said body member to seal said keypad assembly, said sealing sheet having a plurality of holes therein through which stems of respective keys extend whereby said sealing sheet is also interposed between said key faces and said body member.

The material of said sealing sheet may be chosen as required, it being necessary that it is compressible in order to provide a good seal and to sustain flexing over a wide temperature range without failure over a long life.

In a preferred embodiment, the sealing sheet is also conductive in order to provide discharge means for any static electricity. In a preferred embodiment, the sealing sheet is of a flexible, conductive plastics material.

It would be possible for the keypad to contact the sealing sheet directly. However, where the keys are punched out from, for example, stainless steel, they may well have sharp edges which may damage the sealing sheet.

Rather than seeking to smooth the edges, it is proposed that each key should be provided with a respective spacing pad which is interposed between the key and the sealing sheet. In a preferred embodiment, each said spacing pad is of a similar shape to that of the key and has a bore therethrough enabling the spacing pad to be slipped around the key stem and into contact with the rear surface of the key face.

In a particularly preferred embodiment, the spacing pad is made of the same material as that of the sealing sheet.

In an embodiment, the spacing pad is slightly smaller than the key face such that the key face projects beyond the spacing pad in four directions. This enhances the ability of the seal to flex when depressed.

Preferably, a keypad assembly in accordance with this aspect of the invention is as defined above, and comprises a sub-assembly as defined above.

Preferably, the keypad assembly comprises respective spring means associated with each said key and arranged to bias said key outwardly of said keypad assembly to an initial, non-actuated position, wherein each said spring means is arranged to be clicked into an overcentre position upon operation of the respective key against the bias of said spring means.

Embodiments of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a plan view of a keypad assembly of the invention, Figure 2 shows a longitudinal section of the keypad assembly of Figure 1, Figure 3 shows an exploded view of the keypad assembly of Figures 1 and 2, and Figures 4a, 4b and 4c show a plan view and sections on lines A-A and B-B of spring means for providing the keypad assembly illustrated with a tactile feel.

A keypad assembly 2, as illustrated in the drawings has many applications. Such keypad assemblies are particularly familiar when incorporated in automatic teller machines (ATMs) and are described herein below as used in such ATMs. However, it will be appreciated that a keypad assembly of the invention may be utilised in any appropriate environment.

As indicated in Figure 1, a keypad assembly 2 has a front plate 4, generally made of stainless steel, in which the faces 6 of twelve individual keys 22 are visible. In fact, the front plate 4 is provided with a plurality of apertures 8 (Figure 2) therein, and a respective key face 6 is arranged in each said aperture 8. Generally, the apertures 8 in the front plate 4 are formed by laser cutting techniques so that each key face is centralised in the respective aperture 8 which is accurately formed. The keys 22 are preferably made by punching. This provides a draw (not shown) which extends from the key face 6 to the front plate 4 which facilitates the provision of key faces 6 standing proud of the front plate 4. This is generally preferred for operational and aesthetic reasons, although, of course, the key faces 6 may be arranged to be flush with the front plate 4 if required.Similarly, it is also preferred that each key face 6 is larger than the respective aperture 8.

As described further below, depression of the key faces 6 is arranged to actuate switch means 10 carried by the keypad assembly 2. The switch means 10 (Figure 2) preferably comprises a membrane switch assembly supported by a keypad body 12 formed of the front plate 4 and a body member 30. The periphery of the body member 30 is larger than that of the front plate 4 whereby a mounting flange, indicated at 16, is defined to extend around the front plate 4 This mounting flange 16 enables the keypad assembly 2 to be appropriately mounted in an ATM (not shown) so that the front plate 4 with the key faces 6 therein is accessible. A gasket 15 (Figure 2) is preferably supported on the mounting flange 16 to facilitate its mounting in the ATM.Screw holes 18 are provided in the mounting flange 16, and in the gasket 15, and fixing screws for holding the keypad assembly 2 in the ATM pass through these screw holes.

The membrane switch assembly 10 is arranged to actuate appropriate electrical circuits and is connected thereto by way of a ribbon connector 19 and a connection block 20.

Figure 1 also shows an earth connection 21 which is generally made to a back plate of the keypad assembly 2.

It will be appreciated that operation of the electrical circuits is by depression of the key faces 6. In this respect, the application of pressure to the key faces acts to apply pressure to the membrane switch assembly 10 and thereby actuate the switch assembly in known manner. As can be seen in Figures 2 and 3, the keypad assembly 2 comprises a number of keys 22 each of which has a respective key face 6 which is connected to an extending key stem 23. Each key stem 23 is arranged to extend through the keypad assembly 2 to contact the switch assembly 10.

For ease of manufacture, and to enable the final keypad assembly to be customised as a last manufacturing stage, a keypad assembly 2 of the invention is constructed from a sub-assembly to which the keys 22 are subsequently connected. The sub-assembly comprises the keypad body 12 in which spring bias means and engaging means for the keys 22 are provided. The keypad body 12 comprises a body member 30 which is preferably moulded from plastics material. The body member 30 is moulded to define a plurality of recesses 32 each receiving a respective key 22. Each recess 32 has a base surface 34 and a peripheral wall 36 defining a substantially rectangular opening which is substantially aligned with a respective substantially rectangular aperture 8 in the front plate 4.

Spring means 37 are provided in each said recess 32 adjacent to the base surface 34 thereof. Generally, and as indicated in Figure 3, each spring means 37 is a generally convex, annular plate spring. The spring 37 is shown in Figures 4a to 4c and will be described further below with reference to those drawings.

The spring 37 is held within the respective recess 32 by way of key engaging means 38. Each said key engaging means comprises a key capture plate 38 of plastics material, preferably of the same material as that of the body 30, having a substantially central aperture 40 extending therethrough. As can be seen most clearly in Figure 3, which shows an exploded view of the keypad assembly 2, but only shows the recess 32, key capture plate 38 and other elements associated with a single one of the keys 22, extending flanges 42 are provided around the periphery of the aperture 40 of the key capture plate 38.

In the embodiment illustrated, the aperture 40 is a generally circular aperture extended by two or more cutout portions 44. The key capture plate 38, and hence the spring 37 are retained within the respective recess 32 of the body 30 by way of the front plate 4 which is fastened to the body 30 by appropriate fixing means, for example, screws and nuts, indicated at 50. Preferably, and as shown, the sub-assembly also incorporates a sealing sheet 52 of plastics material. This substantially rectangular sheet is laid over the body member 30 to extend over the openings of all of the recesses 32. A respective hole 54 is provided in the sheet 52 for each said recess 32 and further holes 56 are provided therein for the extension therethrough of the fixing means 50.The sealing sheet 52, which acts to seal the final keypad assembly, also acts to ensure that the key capture plate 38 and the springs 37 are appropriately retained within the sub-assembly.

The sub-assembly also comprises an appropriate membrane switch assembly 10 fixed to the rear surface of the sub-assembly. In this respect, the membrane switch assembly 10 preferably comprises a back plate 58 on which a membrane switch 60 is formed, the membrane switch 60 being connected to the ribbon connector 19. Preferably, the membrane switch assembly 10 also comprises a pressure pad 62, made of a flexible and resilient plastics material, which is interposed between the rear surface of the subassembly and the membrane switch 60 itself. In use, the pressure pad 62 equalises and applies pressure to the membrane switch 60 whilst protecting it from contact from the key stems 23.

We have seen that each key 22 comprises a key face 6 from a central area of which a respective stem 23 extends.

These stems 23 are generally circular in cross section and therefore able to extend through the circular bores and holes 54 and 40 provided in the sealing sheet 52 and in the respective key capture plate 38. It will also be seen from Figures 2 and 3 that each stem 23 has an appropriate waisted region 64 along the length thereof for engagement by the flanges 42 of the key capture plate 38.

When it is required to construct a keypad assembly, individual keys 22 with appropriate indications, such as numbers, on the front surfaces of the key faces 6, are pressed through the respective aperture 8 in the front plate 4 into appropriate engagement in the sub-assembly.

In this respect, as the key stem 23 is pushed into and through the key capture plate 38, the flanges 42 carried thereon are arranged to flex and to engage in the waisted portion 64 whereby the key 22 is reliably held in the appropriate recess 32. In this captured position, the stem 23 protrudes through a circular aperture 66 (Figure 2) provided in the base surface 34 of the respective recess 32. It will be seen that the respective spring 37 surrounds the key stem 23 and also engages the key capture plate 38. The spring 37 is arranged to bias the key 22 outwardly to its position in which the key face 6 is proud of the front plate 4.

When all of the keys 22 have been engaged in the keypad assembly 2 it is operational. In this respect, in known manner, pushing a key 22 causes it to be depressed relative to the keypad body 12 whereby its stem 23 actuates the membrane switch 60.

The depression of each key 22 is against the bias of the spring 37. As we shall see, this spring 37 is arranged when pressurised to click into an overcentre position so that the user can feel that the key face 6 has been depressed. When the pressure is removed from the key face 6, the spring 37 returns the key 22 to its original position.

It is possible to manufacture the keypad assembly 2 as described, that is, by inserting the keys 22 into an already constructed sub-assembly, because the peripheries of the key faces 6 can be accurately formed to be engaged within the apertures 8 of the front plate 4. In this respect, the accuracy which can be achieved with modern punching and laser cutting techniques is sufficient to make the key faces 6 effectively self-centring. This also enables circular cross section key stems 23 and correspondingly circular bores to be employed. Generally, in existing keypad assemblies, key stems have to be rectangular or square in cross-section to effectively centre the key faces 6 relative to apertures 8 in the front plate 4.

However, the punching technique can leave sharp edges on the peripheries of the key faces 6 and such edges can cut into the sealing sheet 52. Accordingly, and as shown, each key 22 is provided with a respective spacing pad 70.

This spacing pad 70 is generally of the same peripheral shape as the key face 6, although a little smaller, and has a central, substantially circular hole 72 through which the key stem 23 extends. It is generally preferred that the spacing pad 70 is mounted on each key 22 before the key is engaged with the sub-assembly. The spacing pad 70 is generally made somewhat smaller than the periphery of the key face 6 to provide the key face with enhanced flexibility when pressed, to thereby enhance the operation of the keypad assembly. The spacing pad 70 also lifts each key such that its face 6 is proud of the front plate 4.

As the sealing sheet 52 is interposed between the front plate 4 and the body member 30 it provides an extremely effective seal. In this respect, the only holes in the sealing sheet 52 are the holes 54 through which each key stem 23 extends and the holes 56 through which the fixing means 50 extend. The holes 54 and 56 are preferably sized so that they cling around the periphery of the key stems 23 and of the fixing means 50 extending therethrough to enhance the sealing effect. Furthermore, the engagement of the key capture plate 38 on the respective key stem 23 of each key 22 effectively sandwiches the sealing sheet 52 therebetween and also enhances the sealing effect.

Figures 4a to 4c show one embodiment of spring means to be mounted in each said recess 32 of the body member 30 to give the keypad assembly tactile characteristics. As can be seen in Figures 4a to 4c, the spring 37 is a generally annular spring having a substantially central, circular hole 74 therein. As is clearly shown in Figure 4b, the spring 37 has a generally convex shape, although it is substantially planar in its central region indicated at 76. However, along two diameters, as indicated in Figure.

4c, the periphery of the spring 37 is turned upwardly.

The spring 37 is, as described above, arranged to bias the respective key 22 outwardly. However, when the key 22 is pressed, against the force of the bias of the spring 37, the spring clicks into an overcentre position. This enables the user to feel that the key face 6 has been depressed. The upturned peripheral edges provided at parts of the spring 37 enable the spring to return to its original position upon the release of pressure therefrom.

The present invention has particular applicability to vandal resist keypad assemblies in which the accessible parts, that is, the key faces and the front plate, are made of metal of metallic compositions.

It will be appreciated that variations in and modifications to the present invention as described and illustrated herein may be made within the scope of this application.

Claims (42)

1. A sub-assembly for a keypad assembly as defined herein, the sub-assembly comprising a keypad body defining a front surface of the keypad assembly and having a rear surface which, in the keypad assembly, is adjacent to the pressure operable switch means thereof, wherein said keypad body comprises a plurality of recesses, each of said recesses being arranged to receive a respective key of said keypad assembly, and each said recess having a bore therein which opens into the rear surface of said keypad body, and further comprising key engaging means arranged in each said recess and arranged to engage and capture a respective key inserted into said recess.

2. A sub-assembly as claimed in claim 1, further comprising pressure operated switch means arranged adjacent to said rear surface.

3. A sub-assembly as claimed in claim 1 or claim 2, wherein the front surface of the keypad assembly is provided by a front plate connected to a body member to form the keypad body.

4. A sub-assembly as claimed in claim 3, wherein the front plate has a plurality of apertures therein, each aperture being aligned with a respective recess in said body member.

5. A sub-assembly as claimed in claim 4, wherein said apertures in said front plate have been formed by laser cutting.

6. A sub-assembly as claimed in any of claims 3 to 5, wherein said body member is moulded from a plastics material and defines said recesses and said rear surface.

7. A sub-assembly as claimed in any preceding claim, wherein spring means are retained in each said recess and are biassed outwardly of the recess, and wherein said spring means are arranged to click into an overcentre position when pushed inwardly of the recess.

8. A sub-assembly as claimed in any preceding claim, wherein said key engaging means in each said recess comprises a key capture plate having a substantially central through bore, wherein the material and/or the shape of the plate and/or of the bore is arranged to provide a degree of flexibility to the plate, and wherein each key capture plate is positioned in the respective recess such that its through bore is aligned with the bore in the recess.

9. A sub-assembly as claimed in claim 8, wherein key stem engagement means are provided on the periphery of the through bore of said key capture plate.

10. A sub-assembly as claimed in claim 9, wherein the through bore in said key capture plate is substantially circular and is extended by lateral wing portions, and wherein the key stem engagement means comprise two axially extending flanges provided on opposed parts of the circular portion of said bore.

11. A sub-assembly as claimed in any of claims 8 to 10, wherein each said key capture plate retains a respective spring means in its associated recess, and wherein the front surface of the keypad assembly is provided by a front plate connected to a body member, the connection of the front plate to the body member holding the spring means and the key capture plates in the respective recesses.

12. A sub-assembly as claimed in any of claims 8 to 11, wherein a sealing sheet is provided in the sub-assembly beneath the front plate thereof, the sealing sheet being appropriately provided with holes therein for the passage of key stems therethrough.

13. A keypad assembly comprising a sub-assembly as claimed in any preceding claim, the keypad assembly further comprising a plurality of keys, each key being received in a respective recess such that a key stem thereof is engaged by said key engaging means, extends through the bore in the recess and projects relative to the rear surface of the sub-assembly, and the keypad assembly further comprising pressure operated switch means connected to said subassembly to be adjacent to said rear surface, said switch means being operable by the application of pressure to said keys.

14. A keypad assembly as claimed in claim 13, wherein said pressure operated switch means comprises a membrane switch assembly.

15. A keypad assembly as claimed in claim 14, wherein said membrane switch assembly comprises a resilient and/or flexible sheet or pad provided to contact said rear surface, and a back plate having a membrane switch formed on one surface thereof, the back plate being fixed to said sub-assembly such that the membrane switch contacts the resilient and/or flexible sheet or pad and is thus operable by said keys.

16. A method of constructing a keypad assembly, the method comprising the steps of taking a sub-assembly as claimed in any of claims 1 to 12, inserting a key in each said recess such that a key stem of the key extends through the bore of the respective recess and projedts relative to the rear surface of the sub-assembly, and fastening pressure operable switch means on said sub-assembly adjacent to said rear surface, the pressure operable switch means being arranged to be actuated by said keys.

17. A method as claimed in claim 16, wherein each key is inserted in a respective recess such that a stem thereof is engaged by said key engaging means.

18. A method as claimed in claim 16 or claim 17, wherein said pressure operated switch means comprises a membrane switch assembly.

19. A method as claimed in any of claims 16 to 18, comprising the steps of forming a pre-assembly in which said switch means are fastened to said sub-assembly.

20. A keypad assembly as defined herein, the keypad assembly further comprising respective spring means associated with each said key and arranged to bias said key outwardly of said keypad assembly to an initial, nonactuated position, wherein each said spring means is arranged to be clicked into an overcentre position upon operation of the respective key against the bias of said spring means.

21. A keypad assembly as claimed in claim 20, wherein each said spring means comprises a plate spring having a central bore therethrough and being substantially convex over at least part thereof.

22. A keypad assembly as claimed in claim 20 or claim 21, wherein said keypad assembly comprises a sub-assembly formed of a front plate connected to a body member, said body member having a plurality of recesses in which each said key is received.

23. A keypad assembly as claimed in claim 22, wherein said body member is moulded from a plastics material and defines said recesses and said rear surface, and a bore is provided in each said recess substantially centrally of a base surface thereof.

24. A keypad assembly as claimed in claim 22 or claim 23, wherein the front plate has been laser cut, and wherein appropriate fixing means hold the front plate on the body member.

25. A keypad assembly as claimed in any of claims 22 to 24, wherein said spring means are retained in each said recess, and a key capture plate is provided in each said recess to engage a respective key therein, each said key capture plate also retaining the respective spring means in the associated recess, and wherein the connection of the front plate to the body member holds the spring means and the key capture plates in the respective recesses.

26. A keypad assembly as claimed in claim 25, wherein said key capture plate is made of plastics material, the material and/or the shape of the plate being arranged to give a degree of flexibility to the plate, wherein each said plate is provided with a through bore which is aligned with the bore in the base surface of the respective recess, and wherein key stem engaging means are provided on the periphery of the through bore of the key capture plate.

27. A keypad assembly as claimed in claim 26, wherein the through bore in each said plate is extended by lateral wings, and said key stem engaging means are formed by axially extending flanges on the periphery of said bore.

28. A keypad assembly as claimed in any of claims 22 to 27, wherein a sealing sheet is provided in the sub-assembly beneath the front plate thereof, the sealing sheet being appropriately provided with holes therein for the passage of key stems therethrough.

29. A keypad assembly as claimed in any of claims 20 to 28 comprising a sub-assembly as claimed in any of claims 1 to 12.

30. A keypad assembly as defined herein, the keypad assembly further comprising a front plate having a plurality of apertures, each key of the keypad assembly having a key face which is arranged to be received in a respective aperture, and the keypad assembly also comprising a body member arranged to be connected to said front plate to form a keypad body, and wherein a sealing sheet of a compressible material is interposed between said front plate and said body member to seal said keypad assembly, said sealing sheet having a plurality of holes therein through which stems of respective keys extend whereby said sealing sheet is also interposed between said key faces and said body member.

31. A keypad assembly as claimed in claim 30, wherein the material of said sealing sheet is compressible.

32. A keypad assembly as claimed in claim 30 or claim 31, wherein said sealing sheet is conductive.

33. A keypad assembly as claimed in any of claims 30 to 32, wherein said sealing sheet is of a flexible, conductive plastics material.

34. A keypad assembly as claimed in any of claims 30 to 33, further comprising a respective spacing pad provided for each key and interposed between the key and the sealing sheet.

35. A keypad assembly as claimed in claim 34, wherein each said spacing pad is of a similar shape to that of the key and has a bore therethrough enabling the spacing pad to be slipped around the key stem and into contact with the rear surface of the key face.

36. A keypad assembly as claimed in claim 34 or 35, wherein each spacing pad is made of the same material as that of the sealing sheet.

37. A keypad assembly as claimed in any of claims 34 to 36, wherein each spacing pad is slightly smaller than the key face such that the key face projects beyond the spacing pad in four directions.

38. A keypad assembly as claimed in any of claims 30 to 37, and comprising a sub-assembly as claimed in any of claims 1 to 12.

39. A keypad assembly as claimed in any of claims 30 to 38, wherein the keypad assembly comprises respective spring means associated with each said key and arranged to bias said key outwardly of said keypad assembly to an initial, non-actuated position, wherein each said spring means is arranged to be clicked into an overcentre position upon operation of the respective key against the bias of said spring means.

40. A sub-assembly for a keypad assembly substantially as hereinbefore described with reference to the accompanying drawings.

41. A method of constructing a keypad assembly substantially as hereinbefore described with reference to the accompanying drawings.

42. A keypad assembly as defined herein substantially as hereinbefore described with reference to the accompanying drawings.