GB2039417A

GB2039417A - Contact pad switch

Info

Publication number: GB2039417A
Application number: GB7941424A
Authority: GB
Original assignee: MAAG GUMMI
Current assignee: MAAG GUMMI
Priority date: 1978-12-01
Filing date: 1979-11-30
Publication date: 1980-08-06
Also published as: GB2039417B; DE2945707C2; CH645205A5; DE2945707A1

Abstract

A contact pad switch (1) has a spring part (3) integral with a base foil (2) and a hollow body (10) with resilient walls (11) arranged on the spring part (3) and joined via a pressure plate 8 which carries a contact plate (9) and in the rest position lies at a distance (a) from a contact plane (4), the free end face of the hollow body (10) supporting a button (13) on an annular projection (14). The button (13) has a post (16) which in the rest position lies a distance (b) from the pressure plate (8) and on pressing the button (13) this traverses a path (a + b). The sequence for traversing both partial paths (a) and lb) as well as the force profile on pressing the button can be influenced as desired by varying the shapes of the hollow body (10) and the spring part (3). <IMAGE>

Description

SPECIFICATION Contact pad This invention relates to contact pads such as are used in electrical and electronic apparatus.

Contact pads are known which consist of an elastomeric base comprising at least one contacting element having a resilient part integral with the base and a contact plate arranged relative to the spring part, and wherein the spring part in the rest position defines a hollow space extending above a contact plane, the space thus having resilient walls, and wherein the resilient part includes a pressure plate bearing the contact plate on one side of the hollow space at a distance from the contact plane.

By the term contact pad a contacting device is to be understood in which one or more contacting elements are arranged in an elastomeric foil, e.g. of rubbery plastics, the resilient parts of which constitutu an integral part of the plastics foil. As material for the plastics foil and the spring part normally an elastomer is used, preferably silicone rubber. The spring part constitutes in the rest position an elevated portion which surrounds a hollow space and it bears on the side of the hollow space a little contact plate. If now the contact pad is laid e.g. on to a carrier with a printed circuit, then the contacting elements can be arranged in suitable positions so that they overlie contact areas on the printed circuit.

Thus, in the rest position, the little contact plates lie at a distance above the contacts on the printed circuit. On operating a contacting element, its resilient portion is compressed and by this deformation a returning force is generated which after release of the contacting element brings the little contact plate again into the rest position. The deformation of the spring parts, which as already mentioned consists likewise of the elastomer of the plastics foil, determines the lifetime of the contact element and indeed it is dependend upon the size of the deformation i.e.

on the stroke of the contacting element. For practical embodiments the distance of the little contact plate from the contact position and accordingly the stroke of the contacting element amounts to about 0.5 to 1.5 mm. Using this stroke several million operations can be carried out before defect of the resilient part arise.

The stroke for the contact element of pressure pads is too small for certain applications, for which reason it has been proposed, by corresponding increase in the size of the spring part surrounding the hollow space, to increase the distance of the contact plates from the contact positions and accordingly the stroke of the switching element. This however has as a result a notable diminution of the lifetime of the spring part. For this reason a pressure pad which has contact elements with an increased stroke cannot be used for a whole number of areas of application e.g. in communications technology such as telephones and teleprinters. A further disadvantage consists in the fact that because of its larger stroke an increase in the diameter of the spring part is unavoidable, by which the minimum distance between two adjacent contact elements is correspondingly increased.

According to the present invention there is provided a contact pad consisting of an elastomeric material comprising at least one contact element which element has a spring part integral with the contact pad and a contact plate arranged relative to the spring part, wherein the spring part in the rest position defines a hollow space extending over a surface against which the contact pad may be placed, the space having resilient walls and the spring part also comprises a pressure plate carrying the contact plate on one side of the hollow space at a distance from the plane of the surface, and wherein on the pressure plate there is arranged a hollow body provided with resilient wall parts on the free end face of which a push button is supported.

In this way, an increase of the contact stroke of the contact elements is achieved without lessening the life of the elements relative to that of the known contact elements and without increasing the diameter of the spring part.

The total stroke of the contact element consists of two partial strokes, the stroke of the spring part on the one hand and the stroke of the hollow body on the other hand, by means of which a high life-time for the contact element is guaranteed.

The invention is illustrated by way of example with reference to the accompanying drawings which show several exemplary embodiments as follows: Figure lisa section through a first embodiment of a contact element of a contact pad of the invention, in the rest position; Figure 2 is a section as in Figure 1 but with the contact element located in the contacting position; Figure 3 is a section through a further embodi mentofthe contact element through further embodiment of the contact element of a contact pad;; Figures 4-8 are sections through a partly illustrated contact element of a contact pad with various shapes of a hollow body provided with spring walls, and Figure 9 is a section through a partly illustrated contact element with a further embodiment of its spring part connected with the base plate of the contact pad.

The contact elements illustrated in Figures 1 to 3 are part of a contact pad which consists of a base foil 2 and a resilient section 3 connected integally with the base foil 2 of the contact element 1. The base foil 2 lies on a base plate 4 which for example consists of an insulator and is the carrier for a printed circuit.

The contact element 1 lies in this case above a contact position of the circuit. Accordingly one or several contact elements 1 can be arranged on the base foil 2 in any arrangement. The base foil 2 has on its base plate side grooves 5 which connect the hollow spaces 6 under the sections 3 of the contact element 1 together as connection channels and also connect the hollow spaces 6 with the exterior air so that on pressing down the contact element 1 the air can escape from the reducing hollow space 6.

The section 3 is composed of resilient walls 7 and a pressure plate 8. The pressure plate 8 carries on the side of the hollow space 6, contact plate 9 which on pressing the switch element 1 contacts the contact positions (not shown) arranged on the base plate 4 after travelling the distance a between the position of the contact plate 9 in the rest position and surface of the base plate 4.

As is evident from Figures 1 to 3 there is arranged on the side of the pressure plate 8 remote from the hollow space 6a hollow body 10 having at least partly resilient wall parts 11; conveniently the hollow body 10 consists of the same material as the base foil 2 and spring plate 3. The hollow body 10 consists a hollow space 12 which is covered by a button 13 which has a annular projection 14, the projection 14 appropriately lying against a cover 15 e.g. of plastics.

A post 16 arranged on the end of the button 13 towards the hollow space lies at a distance b from the pressure plate 8 in the rest position.

The contact element described accordingly has two resilient stages one lying over the other: the resilient wall 7 of the spring part 3 and resilient wall part 11 of the hollow body 14. Correspondingly the stroke of the button 13 to effect contact of the contact positions by the contact plate 9 consists of both partial strokes a and b. In Figure 2 the contact element 1 is illustrated in the contact position. The post 16 lies against the pressure plate 8 i.e. the button 13 has traversed the stroke b. Furthermore the contact plate 9 lies on the base plate 4 i.e. contact plate 9 and accordingly also the button 13 have traversed also the stroke a. On traversing the partial strokes a and b both the spring part 3 and also the hollow body 10 are deformed, see Figure 2.The spring part 3 forms a fold position 17 e.g. a wavy zone, for forming which an additional force must be exercised on the button 13. There thereby arises the action of a press button. As illustrated in Figure 1 it is taken that on pressing down the button 13 first the hollow body 10 transforms on traversing partial stroke b into the position shown dashed. For the deformation of the spring part 3 on traversing partial stroke a then a somewhat greater force is necessary.

The force profile can however be matched within wide limits to the particular requirements. Thus Figures 1 and 2 show a recess 18 in the projection 14 on the side toward the hollow body 10, by means of which the deformation of the hollow body 10 and accordingly the pressure of the button 13 can be influenced. The pressure profile can however be influenced also in other fashions, particularly by giving a particular shape to the hollow body 10 or to the spring part 3. In Figures 4 to 8 various shapes of hollow bodies of contact elements are illustrated.

Figure 4 shows a barrel shaped hollow body 10 while hollow body 10 according to Figures 5 and 6 consists of a simple and double bellows. The hollow body 10 according to Figure 7 has a cylindrical shape and that according to Figure 8 is a hyperboloid shape. In the case of the hollow body 10 according to Figure 3 the resilient wall parts 11 have the shape of a truncated circular cone onto which a circular cylindrical part is joined. The wall part 11 deforms accordingly in similar fashion to the resilient wall 7 of the spring part 3. Obviously it is also possible to form the spring part 3 otherwise than a trucated circular cone.

Figure 9 shows a barrel-shaped wall 7 for spring part 3.

The pressure profile of button 13 can also be influenced by differing wall thicknesses. By the combination of the shape of the spring part 3 of the hollow body 10 and of the wall thicknesses of these two parts any desired stroke for the button 13 e.g. for keyboards from about 2 - 10 mm can be achieved. In this connection it is important that by splitting up the button stroke into the part strokes a and b there is a diminution of wear and accordingly a corresponding increase of the lifetime achieved. While maintaining this, the force profile i.e. the rise in force on pressing down the button 13 can be matched within wide limits when simple or double pressure action can be achieved. Also the pressure action can be achieved before or after touching of the contact position by the contact plate 9.By the numerous possibilities noted it is achieved that the elements of the contact pad mentioned can also be introduced into areas which have previously been closed to such elements.

The distance b between the post 16 and the pressure plate 8 can also be achieved in that the post 16 can be arranged on the pressure plate. This distances is then defined by the distance between the post 16 connected to the pressure plate 8 and the end face of the button 13. It is however important that by means of the arrangement of the hollow body on the pressure plate 8 the possibility is given, with the aid of post 16, of varying as desired the size of one partial stroke b and accordingly of influencing the pressure profile at the button 13.

The button 13 is taken in Figures 1 and 2 as a cylindrical body which projects through the cover 15.

If guidance of the button 13 in the cover 15 is necessary then suitably a collar may be provided on the top cover 15. If the button 13 is not to be able to turn then the cross section of the button 13 can be square of rectangular. The end of the button 13 projecting above the cover 15 or the collar 19 can be shaped as desired e.g. as a press button or press pad with or without an inscription.

Plastics are suitable for the individual parts of the pressure pad, wherein the base foil 2, the spring part 3 and the hollow body 10 can be made of an elastomer e.g. silicone rubber. The base plate 4, the button 13 and the cover 15 can be manufactured for example from a mouldable plastics material while the contact plate 9 can be manufactured e.g. from a conductive silicone rubber.

Claims

1. A contact pad consisting of an elastomeric material comprising at least one contact element which element has a spring part integral with the contact pad and a contact plate arranged relative to the spring part, wherein the spring part in the rest position defines a hollow space extending over a surface against which the contact pad may be placed, the space having resilient walls and the spring part also comprises a pressure plate carrying the contact plate on one side of the hollow space at a distance from the plane of the surface, and wherein on the pressure plate there is arranged a hollow body provided with resilient wall parts on the free end face of which a push button is supported.

2. A contact pad according to claim 1 wherein arranged on the button or on the pressure plate there is a post projecting into the hollow body, the distance of which from the pressure plate or from the button respectively constitutes part of the stroke of the push button stroke.

3. A contact pad according to claim 1 or 2 wherein the push button has an annular projection on which the free front face of the hollow body is supported.

4. A contact pad according to claim 3 wherein the projection has on its side turned towards the hollow body an annular aperture which extends over the free front face of the hollow body.

5. A contact pad according to any one of claims 1 to 4 wherein the hollow body has differing wall thickness over its length.

6. A contact pad according to any one of claims 1 to 5 characterised in that the resilient parts of the hollow body in the contacting position constitute at least one fold position e.g. a wavy zone.

7. A contact pad according to any one of claims 1 to 6 wherein the deformation pressure for the hollow body for overwhelming the partial stroke is different from that of the resilient walls of the spring part for overwhelming the partial stroke.

8. A contact pad according to any one of claims 1 to 6 wherein the spring part and the hollow body are formed from different elastomers.

9. A contact pad substantially as hereinbefore described with reference to the accompanying drawings.