GB2174844A

GB2174844A - Multi-contact key

Info

Publication number: GB2174844A
Application number: GB08610341A
Authority: GB
Inventors: Roger Meleard; Michel Pioger
Original assignee: MEKTRON FRANCE SA
Current assignee: MEKTRON FRANCE SA
Priority date: 1985-05-02
Filing date: 1986-04-28
Publication date: 1986-11-12
Also published as: IT8620112A1; FR2581475A1; FR2581475B3; GB2174844B; IT8620112A0; IT1190309B; SE460569B; SE8601989L; GB8610341D0; DE3614873A1; SE8601989D0

Abstract

A multi-contact key for providing successive contact making includes superimposed first and second insulating sheets (10, 12), each provided with a first conducting circuit (18, 22) facing each other, and an intermediate insulating sheet (16) placed between the sheets and provided with an opening (26) at the position of the conducting circuits. The sheets, (10, 12) each include a second conducting circuit (20, 24) which extends around the first circuit (18, 22), but which is electrically insulated from it while a diaphragm (28) is placed next to one of the first or second sheets and has a first protuberance (30) at the position of the first circuits (18, 22) and a second protuberance (32) surrounding the first protuberance (30) and arranged at the position of the second circuits (20, 24). The arrangement allows the first circuits (18, 22) to make before the second circuits (20, 24) when the switch is actuated. <IMAGE>

Description

SPECIFICATION Multi-contact key with delayed contacts The present invention relates to a multi-contact key with delayed contacts.

Single contact keys are known, from document FR-A-8301779, which comprise a first insulating sheet provided with a first conducting circuit on one of its surfaces, a second sheet made from insulating material provided with a first conducting circuit on one of its surfaces, the said first and second sheets being superimposed so that the said first conducting circuits are facing each other, an intermediate sheet made from insulating material placed between the said first and second sheets and provided with an opening at the position of the conducting circuits to enable the making, by pressure, of a mechanical and electrical contact between these conducting circuits.

In certain applications, for example in telephony or in the data processing field, it is desirable to make two successive contacts with a single brief pressure.

These contacts must also always be made in the same order. In order to produce such keys, known as multi-contact keys, there has, up to the present time, simply been provided a stack of two single contact keys of the type described in the quoted document.

In other words, known multi-contact keys include a first pair of sheets, each with an electrical contact, arranged facing each other and separated by a first intermediate sheet with an opening at the position of the contacts and a second pair of sheets adjacent to the first pair with electrical contacts facing each other, aligned with those of the first sheet and also separated by a second intermediate sheet with an opening. This stratified structure of six superimposed layers has therefore been designed with the intention of making a first electrical contact in the first pair of sheets, followed by the making of the electrical contact in the second pair of sheets by increasing the applied pressure.

This type of multi-contact key, however, has several disadvantages. In fact, being formed from six superimposed layers, the whole structure must be squashed in order to ensure the making of both contacts, which requires a certain manual force.

Also, this structure does not provide sufficient guarantee that both contacts will always be made in the same order. In fact, it is possible, for example as a result of a reduction in the mechanical strength of one of the layers and/or an eccentric pressure on the structure, that the contacts are not delayed, i.e. they are made simultaneously or they are made in the reverse order from that which was intended. It is evident that if this phenomenon should occur, the keys, or the keyboard which they form, becomes useless.

The object of the present invention is to provide a multi-contact key that is simpler and more reliable from the functional point of view, as well as a keyboard formed from such multi-contact keys.

Viewed from one aspect the invention provides a multi-contact key with delayed contacts comprising a first insulating sheet provided with a first conducting circuit on one of its surfaces, a second insulating sheet provided with a first conducting circuit on one of its surfaces, the said first and second sheets being superimposed so that the said first conducting circuits are facing each other, an intermediate insulating sheet placed between the said first and second sheets and provided with an opening at the position of the conducting circuits to enable the making, by pressure, of a mechanical and electrical contact between said first conducting circuits, wherein the first and the second sheets each include a second conducting circuit which extends around the first circuit but which is electrically insulated from it, said second circuits being arranged facing each other and said opening in the intermediate sheet being sufficiently large to enable mechanical and electrical contact between the second conducting circuits, there being provided a diaphragm adjacent to one of the first or second sheets and having a first protuberance at the position of the first circuits and a second protuberance surrounding the first protuberance and being arranged at the position of the said second circuits, the said protuberances being pointed towards the adjacent sheet.

The first conducting circuits are preferably two pads of conducting ink corresponding with each other, whereas the second circuits are two rings of conducting ink also corresponding with each other and coaxial with the said pads and having corresponding openings to allow the passage of electrical contacts to the central pads.

In an advantageous embodiment, the said first protuberance is formed from a dome capable of a tactile inversion towards the outside under the effect of pressure, while the second protuberance extends in the form of an annular rim around this dome.

Preferably there is provided a surface layer adjacent the other of the first or second sheets, on the opposite side with respect to the diaphragm and provided with a protuberance at the position of the first and second circuits, pointed away from these circuits and provided on its inside surface with a contact stud directed towards the first circuit of the adjacent sheet.

This protuberance is preferably also capable of tactile inversion towards the inside under the effect of manual pressure.

Preferably a plurality of such keys may becom- bined in a keyboard.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a cross-section through an embodiment of a multicontact key, Figure 2 shows the key of Figure 1 under the effect of pressure making the first electrical contact.

Figure 3 shows the key of Figure 1 under the effect of pressure making the first and second electrical contacts, and Figure 4 shows a perspective view of the first and second sheets with their conducting circuits and the intermediate sheet.

The stratified structure of Figure 1 includes two sheets made from insulating material 10,12 arranged on either side of an intermediate sheet 16.

The first sheet 10 includes a first conducting circuit 18 and a second conducting circuit 20 both insulated from each other and produced by depositing a conducting ink. Similarly, the second sheet 12 includes a first conducting circuit 22 and a second conducting circuit 24 also insulated from each other and produced by depositing a conducting ink.

Circuits 18 and 22 of the first sheet 10 have the same shape and the same size as the corresponding circuits 22,24 of the second sheet and the two sheets 10,12 are arranged such that circuits 18 and 20 are facing circuits 22 and 24 respectively.

In a preferred embodiment the conducting circuits have the shapes shown in Figure 4 in which circuits 18 and 20 are visible by transparency. Circuits 18 and 22 are each in the form of a pad provided with a connecting terminal 18a, 22a. Asfor circuits 20, 24, these are each in the form of a ring each surrounding the central pad 18 and 22 with the exception of the section enabling the passage of terminals 18a and 22a. The rings 20 and 24 are also provided with connecting terminals 20a and 24a.

The three sheets 10, 12 and 16 are thin flexible diaphragms, preferably made from synthetic material such as, for example, polyester having a thickness in the order of 1/10 mm. In the figure these sheets are shown separated from each otherfor reasons of clarity but it is obvious that in practice they are in mutual contact, for example stuck to each other.

The intermediate sheet has an opening 26 at the position of the conducting circuits. This opening 26 has a diameter greater than that of the conducting rings 20 and 24 in order to allow mechanical contact between the pads 18 and 22 on the one hand and between the rings 20 and 24 on the other hand.

Outside of one of the sheets 10, 12 for example below sheet 12, there is a diaphragm 28 which has, at the position of the conducting pad 22 a protuberance in the form of a dome 30 whose centre and peak are pointed towards the pad 22. This dome is produced from a semi-rigid material which allows, in a way that is known in itself, under the action of a pressure on the centre of the dome, a tactile reversal, i.e. an inversion of the dome that is capable of being felt, towards the outside and therefore, in the example shown, towards the bottom.

Around this dome 30 is an annular rim 32, whose diameter corresponds with that of the conducting ring 24 and which is arranged opposite that ring. In a preferred embodiment, the height of this rim 32 can be double the thickness of the diaphragm, whereas the height of the dome 30 can be three times the thickness of that diaphragm.

Below the diaphragm 28 there can be provided a rigid support, not shown in the figure.

On the opposite side from diaphragm 28, in the example shown under sheet 10, there is a surface layer 34. This layer 34 also has, at the position of the conducting circuits immediately below, a protuberance 36 in the form of a dome or section of a core pointing towards the outside of the structure.

On the inside, this protuberance 36 includes a contact stud 38 extending the entire height of the protuberance 36 and pointed towards the conducting pad 18 of sheet 10. The layer 34 can, like the diaphragm 28, be thermo-formed and the protuberance 36 is also capable of tactile reversal under the effect of manual pressure. Symbols used to identify the key can be located on the outside of protuberance 36.

The functioning of the multi-contact key can be seen in Figures 2 and 3. A manual pressure on the dome 36 enables, under the effect of the contact stud 38, the making of the electrical contact between the central pads 18 and 22. The making of this contact is perceptible by the click caused by the reversal of the dome 36. At this moment there is not yet contact between rings 20 and 24. An additional pressure on the dome 36 causes the reversal of the lower dome 30 and finally the second electrical contact between rings 20 and 24 at the moment when they are pushed onto the rim 32. It should be noted that the reversal of the dome 30 causes a slight raising of the rim 32 or, at least, a certain force in the direction of the sheet 12 such that the second electrical contact is made by the pressures exerted on either side of sheets 10 and 12.

It should be noted that the layer 34 with the protuberance 36 is not in principle necessary for the making of the two successive contacts, this being also capable of being produced by a presure on sheet 10 in the position of the pad 18. However, the presence of the two domes 30 and 36 and, more particularly, their tactile reversal with a perceptible click enables the moment at which the two contacts are made to be noted and provides a guarantee that both contacts have been made.

The advantage of the system, at least in its preferred forms, with respect to the state of the art is that the time-delayed contacts are always made in the same order. It is impossible for the contact between rings 20 and 24 to be made before or at the same time as that between pads 18 and 22.

The structure is also simpler insofar as it comprises only four or five superimposed layers whereas keys according to the state of the art must comprise 6 or 7. Also, the pressure necessary for the making of the two contacts, particularly of the second contact at the position of the conducting rings 20 and 24 is lower than the pressure necessary to make the contacts in known multi-contact keys.

For reasons of simplicity, the figures only show the basic component of the invention, i.e. a single multi-contact key. It is however obvious that a keyboard may be provided having a stratified structure as shown in the figures but provided with a certain number of multi-contact keys such as described above.

Finally, it should be noted that the invention is not limited to multi-contact keys provided for the making of two successive contacts. In particular the structure could be extended to the making of three successive contacts. For this purpose it would be sufficient to provide around each of the rings 20,24 a second conducting ring concentric with respect to the pads and rings 20 and 24. The diaphragm 28 should then contain a second rim corresponding with this additional conducting ring and extending around rim 32 at a height lower than rim 32.

Claims

1. A multi-contact key with delayed contacts comprising a first insulating sheet provided with a first conducting circuit on one of its surfaces, a second insulating sheet provided with a first conducting circuit on ne of its surfaces, the said first and second sheets being superimposed so that the said first conducting circuits are facing each other, an intermediate insulating sheet placed between the said first and second sheets and provided with an opening at the position of the conducting circuits to enable the making, by pressure, of a mechanical and electrical contact between said first conducting circuits, wherein the first and the second sheets each include a second conducting circuit which extends around the first circuit but which is electrically insulated from it, said second circuits being arranged facing each other and said opening in the intermediate sheet being sufficiently large to enable mechanical and electrical contact between the second conducting circuits, there being provided a diaphragm adjacent to one of the first or second sheets and having a first protuberance at the position of the first circuits and a second protuberance surrounding the first protuberance and being arranged at the position of the said second circuits, the said protuberances being pointed towards the adjacent sheet.

2. A key according to claim 1, wherein each said first conducting circuit comprises a pad of conducting ink and each said second circuit comprises a ring of conducting ink coaxial with a respective pad and an opening to enable the passage of an electrical contact to a respective pad.

3. A key according to claims 1 or 2, wherein said first protuberance is a dome capable of a tactile inversion towards the outside under the effect of pressure and the second protuberance extends in the form of an annular rim around said dome.

4. A key according to any of claims 1 to 3, comprising a surface layer adjacent the other of the said first or second sheets on the opposite side with respect to the said diaphragm and provided with a protuberance at the position of the said first and second circuits, pointed away from said circuits and provided on its inside surface with a contact stud directed towards the first circuit of the adjacent sheet.

5. A key according to claim 4, wherein said protuberance is capable of tactile inversion towards the inside under the effect of manual pressure.

6. A key according to any preceding claim wherein said protuberances and said rim are thermoformed in flexible membranes.

7. A key according to any preceding claim, wherein said insulating sheets and said intermediate sheet are formed from flexible layers of synthetic material.

8. A multi-contact key substantially as hereinbefore described with reference to the accompanying drawings.

9. A keyboard comprising a plurality of multicontact keys according to any preceding claim.