GB2072950A - A keyboard - Google Patents

Abstract

In a keyboard, a switch is provided by a base 1 with a switch contact face 3%. An insulating foil 4 overlies the base 1 and includes a second switch contact face 6% extending at least partly round an opening 7 in the foil 4. The switch contact faces 3% and 6% may be printed wiring elements as part of suitable circuits on the base 1 and foil 4. The foil opening 7 is aligned with the switch contact face 3% so that through a movable key part 9 with a conductive face 8, on depressing the part 9 the switch contact faces 3% and 6% are connected. Various arrangements of the 3% and 6% are described. <IMAGE>

Description

SPECIFICATION A keyboard Description The present invention concerns a keyboard, for example, a push-button keyboard for a calculator or the like. The invention is particularly concerned with a keyboard of the type having a base plate on which at least one electrically conducting first layer in the form of a wiring element having a first "switching contact face is positioned, with at least one insulating foil placed thereon, and at least one second conducting layer on the side of the insulating foil opposed to the base plate, the electrically conducting layer being in the form of a wiring element with a second switching contact face, the insulating foil having an opening over the first switching contact face.

Such type of keyboard has been put forward in the past, see German Offenlegungsschrift No. 2,448,587, and may have a first electrically conducting layer on a base plate and, on the conducting layer, an insulating layer with an opening over which there is a second conducting layer which can be moved, and over this there is a further insulating layer with an opening. Over this there is a third outwardly domed or curved flexible insulating layer which, where it is curved, may be forced inwards with a spring-like action so that the two conducting layers come into contact with each other through the opening in the first insulating layer, this producing the desired electrical contact. The German Offenlegungsschrift No. 2,448,587, discloses another possible construction in which the second conducting layer is fixed to the curved insulating layer.In a third construction disclosed, the first and the second conducting layers lie under the first insulating layer which has the opening, and a third conducting layer is fixed to the curved insulating layer so that, on forcing down the curved insulating layer the third electrical layer makes contact with the first and second conducting layers so that they are electrically joined together.

This prior art keyboard has to have more than one insulating layer, and this makes the keyboard expensive for the material costs while the process of manufacture is complex. Furthermore, the conducting layers that are placed one over the other and have to be contacted with each other in use have to be spaced apart at the opening so that any blows, vibrations or shaking effects to which the keyboard may be subjected are not responsible for undesired contacting. For this reason the first insulating layer has to be relatively thick.

Furthermore, on frequent use of the prior art keyboard, there is a danger of the development of hair cracks in the movable conducting layer so that the desired electrical connection can no longer be produced.

For this reason, one object of this invention is to provide an improved keyboard of the type described which, while being simple in design and taking up little space, provides trouble-free switching even after being used frequently.

For achieving this object and other objects, there is provided a keyboard of the type described wherein the second conducting layer is positioned on at least one insulating foil, that is to say one or more foils, and the switching contact face extends at least partly around the opening and over the second conducting layer, and there is a movable conducting switching or key face which is arranged in one position to make contact with the first and second switching contact faces to provide the desired electrical connection to each other.

By this invention the two conducting layers are separated by the relatively thin insulating foil, and the second insulating layer on the insulating foil is not stretched over the opening so that there is no danger of undesired contact on shaking, vibration, shock or other similar effects. Because the insulating foil may be very thin, the movable conducting switching or key face only requires a small change in form whilst ensuring high quality contact so that wear by frequent use is out of the question. Because the insulating foil is very thin, the assembly of the keyboard is small and compact.

One specially useful aspect is that at at least one of the openings, that is to say at one switching or key face connection, it is possible to have more than two conducting layers joined together. Accordingly, dependent on the number of the conductive layers to be joined, a number of switching contact faces may be provided on the base plate and/or the insulating foil in desired positions by using printed wiring elements in the form of segments. The faces may be in the part having the opening or, if they are on the insulating foil, they may be positioned at the edge of the opening.

Further useful aspects of the invention are described later herein.

The invention will now be described with reference to three exemplary embodiments shown in the accompanying drawings wherein: FIGURE 1 is a partly cut back plan view of part of a first embodiment of the keyboard of the invention.

FIGURE 2 is a section in the direction Il-Il of Figure 1.

FIGURE 3 is a plan view generally on the same lines as Figure 1 of a second embodiment of the keyboard.

FIGURE 4 is a section in the direction IV--IV of Figure 3.

FIGURE 5 is a plan view of a third embodiment of the keyboard with more than two conducting layers to be joined together.

FIGURE 6 is a section in the direction VI--VI of Figure 5.

In the Figures, similar parts are designated by the same reference numbers.

On an insulating base plate 1, made for example of paper-resin laminate, there is a first conducting layer 2 or printed wiring element ending at a round switching contact face 3. In practice there are a number of printed wiring parts with switching contact faces formed as a printed circuit. The first conducting layer may be produced in any known manner in the art as, for example, by etching, screen printing, or spraying onto the base plate. Over the base plate 1 with the conducting layer 2 there is an insulating foil 4. On the upper side of insulating foil 4, remote from base plate 1, there is a second conducting layer in the form of a printed wiring element 5 running into eye-like switching contact face 6. In practice it is possible to have a number of conductors with switching contact faces on the insulating foil 4.The second conducting layer may be produced on the insulating foil by any of the known ways noted.

The insulating foils are fixed to the base plate by contact pins or the like (not shown) which are arranged to provide electrical connections between the wiring elements as desired for the function of the keyboard.

The keyboard includes a movable conducting switching or key face (not shown in Figures 1 and 2, or Figures 3 and 4 as later referred to) which may comprise a flexible foil, rubber sheet, or separate pad, by which the switching function is obtained in use.

The insulating foil 4 is formed with an opening 7 extending over the switching contact faces 3 on the first conducting layer. The switching contact face 6 of the second conducting layer extends at least partly round the opening 7.

In the embodiment of Figures 1 and 2, the opening 7 is round like a circle. The switching contact face 3 is round as well and of generally same size as opening 7. There is a small degree of overlap, that is to say the opening 7 is somewhat smaller than the switching contact face 3 thereunder so that manufacturing or assembly tolerances are accommodated. The switching contact face 6 is, in the embodiment of Figures 1 and 2, in the form of a ring stretching as far as the edge of opening 7.

With reference to the embodiment shown in Figures 3 and 4, the opening 7 is semi-circular in shape. The switching contact face 3 of the conducting layer positioned on base plate 1 is under opening 7 and, is semi-circular. The switching contact face 8 on the insulating foil 4, is also semi-circular and is symmetrical with respect to switching contact face 3 in the assembly.

With reference to the embodiment shown in Figures 5 and 6, the opening 7 of insulating foil 4 is again in the form of a circle. On base plate 1, two separate wiring elements 2' and 2" are provided whose contact switching faces 3' and 3" are semi-circular and spaced apart laterally to some degree. However, the effective parts of the switching contact faces 3' and 3" lie beneath opening 7. On the insulating foil 4 there are two wiring elements 5' and 5" leading to the opening 7. The elements 5' and 5" terminate at segmental switching contact faces 6' and 6", which are also symmetrical with respect to the opening 7.

It will be seen from Figure 6 that the keyboard has a switch actuator part 9 having a conducting switching face 8 in its lower face. The switching face 8 and actuator part 9 are to some degree movable or flexible. When actuator part 9 is pushed downwards, the switching face 8 will make contact with the switching contact faces 3', 3", 6' and 6" so that they and the wiring elements 2', 2", 5' and 5" are electrically contacted together.

In place of the actuator part 9 it would furthermore be possible to have, by way of example, a flexible layer in the form of a foil or rubber sheet, which at least at the position wherein use switching contact faces to be joined together would have a conducting layer.

It will be appreciated that in a keyboard, a plurality of openings 7 may be provided in a selected array dependent on the function of the apparatus to be controlled or actuated by the keyboard.

It will be clear to the reader that the opening 7 may have any other shapes or forms different to those shown, the actual shape being selected for its function. In this respect, long and thin, or other elongate forms may be provided if a number of contact switching faces to be joined together are present in a single plane.

All measures and useful effects of the invention to be deduced from the specification, claims and the Figures, together with details of design and of configuration may be important for the invention separately or in any undesired combination.

Claims (15)

1. A keyboard having a base plate on which at least one electrically conducting first layer in the form of a wiring element having a first switching contact face is positioned, with at least one insulating foil placed thereon, and at least one second conducting layer on the side of the insulating foil opposed to the base plate, the electrically conducting layer being in the form of a wiring element with a second switching contact face, the insulating foil having an opening over the first switching contact face, characterised ln that the second conducting layer is positioned on at least one insulating foil, and the switching contact face extends at least partly round the opening and over the second conducting layer, and there is a movable conducting switching or key face which is arranged in one position to make contact with the first and second switch contact faces to provide the desired electrical connection to each other.

2. A keyboard as claimed in claim 1, characterised in that the second conducting layer is provided on each of the insulating foils by a printing or etching process or by spraying.

3. A keyboard as claimed in claim 1 or claim 2, characterised in that each of the insulating foils is fixed to the base plate.

4. A keyboard as claimed in claim 3, characterised in that the insulating foils are fixed to the base plate by contact pins.

5. A keyboard astlaimed in claim 4, characterised in that the contact pins are arranged to connect selected ones of the wiring elements of the first, second and any further conducting layer to each other.

6. A keyboard as claimed in any one of claims 1 to 5, characterised in that the switching contact face of the first conducting layer is congruent with respect to the opening (or the openings of a number of such layers) so that through the aligned openings in the foils, placed one over the other, switching functions may be produced between any selected conducting layers.

7. A keyboard as claimed in any one of claims 1 to 5, characterised in that the opening is circular.

8. A keyboard as claimed in any one of claims 1 to 5, characterised in that the opening is semicircular.

9. A keyboard as claimed in claim 7, characterised in that the switching contact face of the second conducting layer is of ring-shape extending around the opening.

10. A keyboard as claimed in any one of claims 1 to 9, characterised in that an opening has more than two associated switching contact faces that are of segmental shape and are on the base plate or the insulating foil.

1 A keyboard as claimed in any one of claims 1 to 10, characterised in that the conducting switching or key face extends over the switching contact faces next to an opening.

12. A keyboard as claimed in claim 11, characterised in that the conducting switching or key face is on a flexible layer.

13. A keyboard as claimed in claim 12, characterised in that the flexible layer is a rubber plate.

14. A keyboard as claimed in claim 11, characterised in that the conducting switching or key face is a movable actuator part.

15. A keyboard as claimed in claim 12, characterised in that the flexible layer is a foil with conducting parts.

1 6. A keyboard as claimed in claim 1 substantially as described above with reference to Figures 1 and 2, or Figures 3 and 4, or Figures 5 and 6.