GB2038096A

GB2038096A - Electric switches

Info

Publication number: GB2038096A
Application number: GB7849116A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1978-12-19
Filing date: 1978-12-19
Publication date: 1980-07-16

Abstract

An electric switch comprising a first contact in the form of a bowed metal strip (1) constrained at each end with a push button (3) placed above and supported by the strip and a second contact strip (4) placed below and transverse the strip. Downward movement of the push button causes a resilient collapse of the centre portion of the bowed strip to make contact with the transverse strip. Means (5) to limit the downward movement of the push button are provided. A matrix array may be formed by single long strips secured at intervals to provide a number of bound sections and cooperating with rows of transverse strips. <IMAGE>

Description

SPECIFICATION Electric switches This invention relates to electric switches, particularly to switches suitable for use in a matrix arrangement, e.g. for a telephone keylock.

Switches for assembly in a matrix arrangement require a simple construction utilising as few different components as possible.

According to the present invention there is provided an electric switch comprising a flat strip of resilient material constrained at its ends to form an upwardly bowed member under which at least one of a pair of electrical contacts is disposed at a distance substantially not lower than the ends of the bowed member, and an operating member disposed above the centre of the bowed member, the operating member having its lower end shaped whereby downward movement of the operating member deforms the bowed member so as to introduce a reverse bowing of the central portion of the bowed member to cause the latter to make contact with the electrical contact.

In one embodiment of the invention the other of the pair of electrical contacts is provided on the underside of the bowed member.

In yet another embodiment of the invention the electrical contact disposed below the bowed member is provided on a resilient strip transverse the bowed member.

The above and other features of the invention will now be described with reference to the accompanying drawings, in which: Figures 1 and 2 illustrate a switch in the unoperated and operated condition respectively, and Figure 3 illustrates the construction of a matrix arrangement of switches.

The switch in Figs. 1 and 2 consists of a flat strip 1 of spring metal, e.g. phosphor bronze, which is bowed by being constrained at each end at an angle 0, by means of shaped mounting pieces 2 to which the ends of the strip 1 are firmly secured, for example by rivetting. Above the centre of the bowed strip 1 and supported by it there is an operating member 3 that is part of a keytop (not shown). This operating member has a rounded surface of radius r. Underneath the centre of the bowed strip 1 there is a second flat metal strip 4 running transversely. When the operating member is depressed the bowed strip has a collapsing snap action by virtue of the geometry of the strip and the member, so that the central region of the bowed strip is now bowed in the reverse direction and makes contact with the second strip 4.The latter is deflected until the operating member movement is stopped by a stop 5. The collapsing snap action of the switch and the operating force of the member (e.g. a push button) can be varied by varying either the angle 8 or the radius r, or both. In the extreme case the radius r can be increased to infinity, although it is desirable to have rounded corners in this case to prevent excessive wear between the operating member and the strip. To increase the contact force between the strips the transverse strip 4 can be preformed (predeflected) and bifurcated to improve contact reliability. This contact is normally arranged to occur at a position that gives the greatest possible time of closure consistent with the collapsing snap action of the bowed strip.

It is to be noted that several variations on the above are possible within the scope of the invention. For example, the function of the stop 5 being primarily to limit the movement of the operating member once contact has been established it is not necessary for the stop to be in the position shown in Figs. 1 and 2. It can be provided in the construction of the keytops itself. In another configuration the second flat strip 4 can be omitted, the stop 5 carrying a metal contact on its upper surface. The bowed strip 1 need not be of metal but can be made of a reilient plastics material provided on its underside with a metallic coating. In so far as the geometry of the various parts is concerned it is obvious that the uppermost position of the transverse strip 4 is limited by the necessity for at least a minimum clearance between the two strips.

The lowest position of the strip 4 should be approximately level with the ends of the bowed strip 1, for if it is any lower there is a danger that the strip 1 will not revert to its original bowed position when the operating pressure is removed from the member 3.

Fig. 3 shows how a matrix switch array can be constructed. A single long strip 11 can be secured at intervals to provide a number of bowed sections 12, each of which is provided with its own operating member 1 3. Several of the strips 11 are fixed in parallel, spaced apart to make up the array. The transverse strips provide either single contacts 1 4a, one to a bowed section, or double contacts 1 4b in which the two ends of one strip provide a common contact for corresponding bowed sections in two adjacent strips 11. Two or more strips 1 4a or 1 4b can be placed one above the other to be operated in the manner of a conventional contact set such as is well known in the switch or relay arts.

1. An electric switch comprising a flat strip of resilient material constrained at its ends to form an upward bowed member under which at least one of a pair of electrical contacts is disposed at a distance substantially not lower than the ends of the bowed member, and an operating member disposed above the centre of the bowed member, the operat

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electric switches This invention relates to electric switches, particularly to switches suitable for use in a matrix arrangement, e.g. for a telephone keylock. Switches for assembly in a matrix arrangement require a simple construction utilising as few different components as possible. According to the present invention there is provided an electric switch comprising a flat strip of resilient material constrained at its ends to form an upwardly bowed member under which at least one of a pair of electrical contacts is disposed at a distance substantially not lower than the ends of the bowed member, and an operating member disposed above the centre of the bowed member, the operating member having its lower end shaped whereby downward movement of the operating member deforms the bowed member so as to introduce a reverse bowing of the central portion of the bowed member to cause the latter to make contact with the electrical contact. In one embodiment of the invention the other of the pair of electrical contacts is provided on the underside of the bowed member. In yet another embodiment of the invention the electrical contact disposed below the bowed member is provided on a resilient strip transverse the bowed member. The above and other features of the invention will now be described with reference to the accompanying drawings, in which: Figures 1 and 2 illustrate a switch in the unoperated and operated condition respectively, and Figure 3 illustrates the construction of a matrix arrangement of switches. The switch in Figs. 1 and 2 consists of a flat strip 1 of spring metal, e.g. phosphor bronze, which is bowed by being constrained at each end at an angle 0, by means of shaped mounting pieces 2 to which the ends of the strip 1 are firmly secured, for example by rivetting. Above the centre of the bowed strip 1 and supported by it there is an operating member 3 that is part of a keytop (not shown). This operating member has a rounded surface of radius r. Underneath the centre of the bowed strip 1 there is a second flat metal strip 4 running transversely. When the operating member is depressed the bowed strip has a collapsing snap action by virtue of the geometry of the strip and the member, so that the central region of the bowed strip is now bowed in the reverse direction and makes contact with the second strip 4.The latter is deflected until the operating member movement is stopped by a stop 5. The collapsing snap action of the switch and the operating force of the member (e.g. a push button) can be varied by varying either the angle 8 or the radius r, or both. In the extreme case the radius r can be increased to infinity, although it is desirable to have rounded corners in this case to prevent excessive wear between the operating member and the strip. To increase the contact force between the strips the transverse strip 4 can be preformed (predeflected) and bifurcated to improve contact reliability. This contact is normally arranged to occur at a position that gives the greatest possible time of closure consistent with the collapsing snap action of the bowed strip. It is to be noted that several variations on the above are possible within the scope of the invention. For example, the function of the stop 5 being primarily to limit the movement of the operating member once contact has been established it is not necessary for the stop to be in the position shown in Figs. 1 and 2. It can be provided in the construction of the keytops itself. In another configuration the second flat strip 4 can be omitted, the stop 5 carrying a metal contact on its upper surface. The bowed strip 1 need not be of metal but can be made of a reilient plastics material provided on its underside with a metallic coating. In so far as the geometry of the various parts is concerned it is obvious that the uppermost position of the transverse strip 4 is limited by the necessity for at least a minimum clearance between the two strips. The lowest position of the strip 4 should be approximately level with the ends of the bowed strip 1, for if it is any lower there is a danger that the strip 1 will not revert to its original bowed position when the operating pressure is removed from the member 3. Fig. 3 shows how a matrix switch array can be constructed. A single long strip 11 can be secured at intervals to provide a number of bowed sections 12, each of which is provided with its own operating member 1 3. Several of the strips 11 are fixed in parallel, spaced apart to make up the array. The transverse strips provide either single contacts 1 4a, one to a bowed section, or double contacts 1 4b in which the two ends of one strip provide a common contact for corresponding bowed sections in two adjacent strips 11. Two or more strips 1 4a or 1 4b can be placed one above the other to be operated in the manner of a conventional contact set such as is well known in the switch or relay arts. CLAIMS

1. An electric switch comprising a flat strip of resilient material constrained at its ends to form an upward bowed member under which at least one of a pair of electrical contacts is disposed at a distance substantially not lower than the ends of the bowed member, and an operating member disposed above the centre of the bowed member, the operat ing member having its lower end shaped whereby downward movement of the operating member deforms the bowed member so as to introduce a reverse bowing of the central portion of the bowed member to cause the latter to make contact with the electrical contact.

2. A switch according to claim 1 wherein the one of the pair of electrical contacts is provided on a resilient flat strip running transverse the bowed member.

3. A switch according to claim 1 or 2 wherein the other of the pair of.electrical contacts is provided on the underside of the bowed member.

4. A switch according to claim 2 or 3 wherein the bowed member is made of a flat strip of spring metal.

5. A switch according to any preceding claim wherein the one of the pair of contacts is provided by a flat strip of spring metal.

6. A switch according to claim 1 wherein the one of the pair of contacts is mounted on a stop member disposed below the bowed member to limit the movement of the operating member.

7. An electrical switch substantially as described and shown in Figs. 1 and 2 of the accompanying drawings.

8. A matrix array of electric switches each of which is according to any one of claims 1-7 wherein a plurality of parallel, spaced apart flat strips are each constrained at intervals to provide two or more bowed sections of the same strip, each bowed section forming the bowed member of one switch provided with an individual operating member and pair of electrical contacts.

9. A matrix switch array substantially as described and shown in Fig. 3 of the accompanying drawings.