GB1582947A

GB1582947A - Electrical switches

Info

Publication number: GB1582947A
Application number: GB3653676A
Authority: GB
Original assignee: Thales Research and Technology UK Ltd; Racal Research Ltd
Current assignee: Thales Research and Technology UK Ltd; Racal Research Ltd
Priority date: 1977-07-21
Filing date: 1977-07-21
Publication date: 1981-01-21

Description

(54) IMPROVEMENTS IN AND RELATING TO ELECTRICAL SWITCHES (71) We, RACAL RESEARCH LIMITED, a British Company, of Western Road, Bracknell, Berkshire, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to electrical switches and switching keyboards.

According to the invention, there is provided a switching keyboard having an array of electrical switch units, each switch unit having a pair of movable contacts and a pair of fixed contacts, the movable contacts of all the switch units being formed from a single sheet of resilient electrically conductive material which has been slotted to define pairs of outwardly directed leaves which pairs respectively form the movable contacts of the switch units and pairs of inwardly directed leaves for controlling the movement of the respective pairs of outwardly directed leaves into and out of engagement with the fixed contacts, and control means for each pair of inwardly directed leaves, each control means constraining its pair of inwardly directed leaves apart to define two stable positions for the inwardly directed leaves and biasing the inwardly directed leaves into one of the two stable positions and being operable to move the inwardly directed leaves into the other stable position against the bias whereby to make or break contact between the movable and fixed contacts.

According to the invention, there is also provided a switching keyboard having an array of electrical switch units, each switch unit having a pair of movable contacts and a pair of fixed contacts, the movable contacts of all the switch units being formed by a single sheet of resilient electrically conductive material which has been slotted to define respective pairs of inwardly and outwardly directed leaves, biasing means for each pair of inwardly directed leaves tp urge the facing edges of the leaves apart and so cause the leaves of the pair to bend out of the plane of the sheet in order to increase the spacing between the said facing edges, the inwardly directed leaves thus being capable of having two stable positions one on each side of the plane of the sheet and performing a snap action in moving between the two positions, each pair of inwardly directed leaves being coupled to its associated pair of outwardly directed leaves to displace the outwardly directed leaves between a first position in which the outwardly directed leaves cause the movable contacts to contact the fixed contacts and a second position in which the outwardly directed leaves cause the movable contacts to break contact with the fixed contact in response to the snap action movement of the inwardly directed leaves from one stable position to the other stable position A switching keyboard embodying the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which: Figure lisa plan view of the keyboard; Figure 2 is a plan view of an array of snapaction movable contact sets of the keyboard; Figure 3 is a section through the keyboard on the line III-III of Figure 1 Figure 4 is a fragmentary plan view of a single switch unit of the keyboard; and Figures 5 and 6 are sections taken in the line A-A of Figure 4 with the switch unit in different operative positions.

As shown in Figures 1 and 3, the switching keyboard includes a housing 10 which is closed off by a coverplate 12 fastened by suitable means.

The cover plate 12 has a 4 x 5 array (in this example) of apertures 16 in each of which is captively mounted a switch button 17 which is capable of limited vertical movement.

Legends, for example, numerals, are provided on the cover plate 12 to identify each switch button 17 and, therefore, each of the twenty switch units now to be described.

As shown in more detail in Figure 3, the keyboard includes a matrix 18 of movable contacts supported in the housing 10 and suspended above its floor 10a by a predetermined distance. The matrix 18 provides a 4 x array of pairs of movable contacts, each formi part of one of the switch units, and each pair is coupled to a specially shaped control spring 20 - shown in more detail in Figure 5.

Each control spring has two feet 20a, 20a resting on the floor 10a and a neck portion 20b imprisoned between its corresponding pair of movable contacts.

Located above the matrix 18 is a printed circuit board 22. The printed circuit board 22 has a plurality of apertures through which the heads of the control springs 20 project. The printed circuit board 22 carries on its underside an array of pairs of fixed contacts corresponding to the array of pairs of movable contacts of the matrix 18.

A sheet 24 of flexible material such as a plastics membrane, covers both the printed circuit board 22 and the heads of the control springs 20. The sheet 24 may be preformed with an array of bulges, each one corresponding to a head of a respective one of the control springs 20 so that where the heads of the control spring 20 distort the adjacent portions of the sheet 24, there is relatively little downward force imparted to the spring by the sheet because the bulges have been preformed.

A peripheral spacer 26 is provided between the matrix 18 and the printed circuit board 22 to ensure a predetermined spacing between them.

The matrix 18 is more clearly shown in Figure 2. The matrix is formed from a sheet of beryllium copper by cutting various slots therein to form a plurality of movable contact set units. Each contact set unit of the matrix is formcd by an 'I' shaped slot 38 partially enclosed by slots 40, 40A forming a pair of square brackets. The result is to provide a pair of inwardly facing leaves 30 and 32 and a pair of outwardly facing leaves 34 and 36, together with supporting arms 37, 38 (see Figure 4 which shows to an enlarged scale one of the matrix units). Further slots 41 are provided between adjacent rows of matrix units to reduce the extent to which any bending movement to which the two pairs of leaves may be subjected is transmitted to the units in adjacent rows.

As already mentioned, each movable contact set of the matrix includes a pair of movable contacts and these are formed by the leaves 34 and 36. Each unit is coupled to a corresponding one of the control springs 20 and this is achieved by the inwardly facing leaves 30 and 32 engaging opposite sides of the neck of the spring 20, the head of the spring 20 being forced through the gap between the leaves 30 and 32 which open out to allow the passage of the head therethrough and thereafter under their own resilience move towards each other again to engage the neck of the control spring, and thus improson the control spring. The gap between the two leaves 30 and 32 when in their relaxed state (that is, when they lie in the plane of the matrix) is arranged to be narrower than the width of the neck of the control spring. Accordingly the leaves will tend to bend outwardly from the plane of the matrix until the gap between them equals the width of the neck of the control spring (which is of course compressed to an extent dependent on its resilience). As a result, the leaves 30 and 36 have two stable postions, one on each side of the sheet from which they are formed.

This provides the basis of the snap action of each switch unit of the keyboard.

Because the feet of the control spring rest on the floor 10a and the gap between the matrix and the floor is arranged to be smaller than the vertical distance between the neck and the feet of the control spring, the control sprint will be under stress and so normally be forcing the leaves 30 and 32 into their stable position on the opposite side of the plane of the matrix to the floor 10a.

Because they are coupled to the inwardly facing leaves 30 and 32, the outwardly facing leaves 34 and 36 will tend to move in the opposite sense to the inwardly facing leaves owing to the curvature which the inwardly facing leaves adopt when displaced to their stable positions. Thus when the inwardly facing leaves 30 and 32 are moved upwardly (see Figure 5), the outwardly facing leaves 34 and 36 move downwardly and when the inwardly facing leaves 30 and 32 are moved downwardly (see Figure 6), the outwardly facing leaves 34 and 36 move upwardly.

The operation of each switch unit of the keyboard will now be described with reference to Figures 4 and 5.

When the assembled switch unit of the keyboard is unactuated, its components adopt the positions shown in Figure 5.

In Figure 5, the leaves 30 and 32 are urged into their upper stable position by the spring 20 and accordingly the movable contacts formed by the outwardly facing leaves 34 and 36 are urged into a lower position away from corresponding fixed contact members 44 and 46.

If now the head of one of the control springs 20 is moved downwardly as by an operator pushing down on the corresponding switch button 17, the facing edges of the leaves 30 and 32 are also moved downwardly and in doing so move closer together and compress the neck of the control spring 20, against the latter's resilience. When the facing edges of the leaves 30 and 32 have passed through the plane of the matrix they will snap into their lower stable position and in doing so will snap the leaves 34 and 36 into an upper position in which they engage the respective contacts 44 and 46. The contacts 44 and 46 are thus bridged and current can now flow between the contacts 44 and 46 through the leaves 34 and 36 (via appropriate external connections not shown).

It will be appreciated that when the control spring 20 is displaced downwardly, its feet will tend to slide along the floor 10a splaying the legs of the spring apart, thus augmenting the resilience of the spring in opposing the compressing action on the neck of the facing edges of the leaves 30 and 32. This increases the forces to which the leaves 30 and 32 are subjected and so improves the snap action effect, giving a sharper and more positive switching action.

When the control spring is released, it will under its own resilience return to the position shown in Figure 5 and on returning will move the leaves 30 and 32 back to their upper stable position. As a result the leaves 34 and 36 are returned to their lower position and disengage the fixed contacts 44 and 46.

The opening and closing of the switch takes place positively and so a hesitant finger on the switch is unlikely to produce unwanted intermittent switching actions. Furthermore, the spring 20 and the contact arms 34, 36 are preferably mutually designed to give an increased hysteresis action in that the vertical position of the neck 20 at which the snap-on operation of the contact arms takes place is different from the vertical position at which the snap-off operation takes place. This helps to ensure that jitter of the operator's finger does not cause unintended switch operation. The hysteresis is enhanced by the slots 41 (Figure 2) which enable the portion of the sheet 18 corresponding to each switch unit to move vertically slightly when the switch unit is operated, so that, in effect, the reference plane about which the switch operation takes place moves slightly in a vertical direction.

Each control spring is symmetrical, particularly around the neck region, to ensure that the two facing leaves maintain a symmetrical relationship at all times, especially when moving between the two stable positions, so as to produce a positive snap action.

In a modification, the cover plate 12 is not provided with the captive buttons 17 but instead merely has apertures into which extend the heads of the control springs 20 (covered with the membrane 24). The keyboard is therefore operated by the operator pressing directly on the covered control springs through the apertures in the cover plate. In this modification, the membrane 24 may be made of rubber.

WHAT WE CLAIM IS: 1. A switching keyboard having an array of electrical switch units, each switch unit having a pair of movable contacts and a pair of fixed contacts, the movable contacts of all the switch units being formed from a sing]e sheet of resilient electrically conductive material which has been slotted to define pairs of outwardly directed leaves which pairs respectively form the movable contacts of the switch units and pairs of inwardly directed leaves for controlling the movement of the respective pairs of outwardly directed leaves into and out of engagement with the fixed contacts, and control means for each pair of inwardly directed leaves, each control means constraining its pair of inwardly directed leaves apart to define two stable positions for the inwardly directed leaves and biasing the inwardly directed leaves into one of the two stable positions and being operable to move the inwardly directed leaves into the other stable position against the bias whereby to make or break contact between the movable and fixed contacts.

2. A keyboard according to Claim 1 or 2, in which each pair of inwardly and associated outwardly directed leaves is formed by an Ishaped slot partially enclosed by squarebracket-shaped slots.

3. A keyboard according to Claim 1 or 2, in which each control means is a spring member having a portion held captive between and under resilient compression from the corresponding two inwardly directed leaves, the spacing between the inwardly directed leaves when in a relaxed condition being smaller than the thickness of the said portion when the spring is in a relaxed state.

4. A keyboard according to Claim 3, in which the spring force exerted on the inwardly directed leaves by the said portion is increased when the spring member is displaced to urge the inwardly directed leaves into the other stable position.

5. A switching keyboard having an array of electrical switch units, each switch unit having a pair of movable contacts and a pair of fixed contacts, the movable contacts of all the switch units being formed by a single sheet of resilient electrically conductive material which has been slotted to define respective pairs of inwardly and outwardly directed leaves, biasing means for each pair of inwardly directed leaves to urge the facing edges of the leaves apart and so cause the leaves of the pair to bend out of the plane of the sheet in order to increase the spacing between the said facing edges, the inwardly directed leaves thus being capable of having two stable positions one on each side of the plane of the sheet and performing a snap action in moving between the two positions, each pair of inwardly directed leaves being coupled to its associated pair of outwardly directed leaves to displace the outwardly directed leaves between a first position in which the outwardly directed leaves cause the movable contacts to contact the fixed contacts and a second position in which the outwardly directed leaves cause the movable contacts to break contact with the fixed contacts in response to the snap action movement of the inwardly directed leaves from one stable position to the other stable position.

6. A keyboard according to Claim 5, in 'which ^ncll b basin means comprises a respect- ive bifurcated leaf spring positioned between the facing edges of the respective pair of in wardly directed leaves so that the facing edges of the leaves respectively make contact with

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the legs of the spring apart, thus augmenting the resilience of the spring in opposing the compressing action on the neck of the facing edges of the leaves 30 and 32. This increases the forces to which the leaves 30 and 32 are subjected and so improves the snap action effect, giving a sharper and more positive switching action. When the control spring is released, it will under its own resilience return to the position shown in Figure 5 and on returning will move the leaves 30 and 32 back to their upper stable position. As a result the leaves 34 and 36 are returned to their lower position and disengage the fixed contacts 44 and 46. The opening and closing of the switch takes place positively and so a hesitant finger on the switch is unlikely to produce unwanted intermittent switching actions. Furthermore, the spring 20 and the contact arms 34, 36 are preferably mutually designed to give an increased hysteresis action in that the vertical position of the neck 20 at which the snap-on operation of the contact arms takes place is different from the vertical position at which the snap-off operation takes place. This helps to ensure that jitter of the operator's finger does not cause unintended switch operation. The hysteresis is enhanced by the slots 41 (Figure 2) which enable the portion of the sheet 18 corresponding to each switch unit to move vertically slightly when the switch unit is operated, so that, in effect, the reference plane about which the switch operation takes place moves slightly in a vertical direction. Each control spring is symmetrical, particularly around the neck region, to ensure that the two facing leaves maintain a symmetrical relationship at all times, especially when moving between the two stable positions, so as to produce a positive snap action. In a modification, the cover plate 12 is not provided with the captive buttons 17 but instead merely has apertures into which extend the heads of the control springs 20 (covered with the membrane 24). The keyboard is therefore operated by the operator pressing directly on the covered control springs through the apertures in the cover plate. In this modification, the membrane 24 may be made of rubber. WHAT WE CLAIM IS:

1. A switching keyboard having an array of electrical switch units, each switch unit having a pair of movable contacts and a pair of fixed contacts, the movable contacts of all the switch units being formed from a sing]e sheet of resilient electrically conductive material which has been slotted to define pairs of outwardly directed leaves which pairs respectively form the movable contacts of the switch units and pairs of inwardly directed leaves for controlling the movement of the respective pairs of outwardly directed leaves into and out of engagement with the fixed contacts, and control means for each pair of inwardly directed leaves, each control means constraining its pair of inwardly directed leaves apart to define two stable positions for the inwardly directed leaves and biasing the inwardly directed leaves into one of the two stable positions and being operable to move the inwardly directed leaves into the other stable position against the bias whereby to make or break contact between the movable and fixed contacts.

the two legs of the spring and so that the head of the spring from which the legs bifurcate lies on one side of the sheet and the distal ends of the legs lie on the other side of the sheet, whereby the resilience of the legs urges the facing edges of the inwardly directed leaves apart and tends to hold the inwardly directed leaves in the one of the said two stable positions in which they lie on the same side of the plane of the sheet as the head of the spring, means for exerting pressure on the head of each spring whereby to move the spring in the direction towards the opposite side of the plane of the sheet, and thus to move the facing edges of the inwardly directed leaves in the same direction, and thereby snap the inwardly directed leaves into their other stable position, and means for displacing the legs of the spring apart, in response to such movement of the spring, whereby to increase the spring forces directed outwardly against the facing edges of the inwardly directed leaves by the legs of the spring so that the spring resiles into its previous position when the pressure on its head is removed.

7. A keyboard according to Claim 6, in which the means for exerting pressure on the head of each spring comprises a relatively rigid cover for the sheet and defining positions each corresponding with a respective one of the springs, and means at each said position for enabling an operator's finger pressure to be exerted onto the head of the spring.

8. A keyboard according to Claim 7, in which a flexible membrane is interposed between the sheet of resilient conductive material and the relatively rigid cover, and covers the heads of the springs, and in which the means at each position on the relatively rigid cover for enabling the operator's finger pressure to be exerted on the head of the corresponding spring comprises an aperture.

9. A keyboard according to Claim 8, includ ing a switch button positioned in each said aperture and constrained therein for limited movement in response to the operator's finger pressure.

10. A keyboard according to any one of Claims 6 to 9, in which the means for moving the legs of each spring apart comprises a base plate on which the distal ends of the legs of each spring stand so as to be splayed apart by the movement of the spring in response to said finger pressure on its head.

11. A switching keyboard, substantially as described with reference to the accompanying drawings.