GB2025852A

GB2025852A - Improvements in or Relating to Keyboards for Actuating Push Switches

Info

Publication number: GB2025852A
Application number: GB7920552A
Authority: GB
Original assignee: Bizerba Werke Wilhelm Kraut GmbH and KG
Current assignee: Bizerba SE and Co KG
Priority date: 1978-06-13
Filing date: 1979-06-13
Publication date: 1980-01-30
Also published as: AT376325B; IT7922866A0; GB2025852B; CH646815A5; DE2825799C3; FR2428906A1; BE876925A; IT1114266B; NL7903919A; DE2825799B2; DE2825799A1; ATA361979A

Abstract

A keyboard is provided for actuating push switches 7, 8 of, for instance an electronic price computing weighing machine. Push elements 9, 10 and electrical components are disposed in a casing 2, 3, 4 which is covered by a flexible sheet 11. Push keys 15, 16 are associated with the push elements 9, 10 and actuate the push elements. The entire underside of each push key 15, 16 is in surface contact with the sheet 11. The push elements 9, 10 and the push keys 15, 16 are interconnected by components 14 which extend through the sheet 11 so that the sheet is clamped between the elements 9, 10 and the keys 15, 16. Each push element 9, 10 supports, on the same side of the sheet 11 thereof, a seal plate 12, 13 whose surface is at least as large as the push key underside. <IMAGE>

Description

SPECIFICATION Improvements In or Relating to Keyboards for Actuating Push Switches The invention relates to keyboards for actuating push switches. Such keyboards may be used for electronic, price computing weighing machines with push switches and may have push elements and electrical components disposed in a casing which is covered by a flexible sheet and push keys, associated with each push element and arranged to actuate the same and bearing in surface configuration by means of their underside on the said flexible sheet, the push elements and push keys being interconnected by a component which extends through the sheet so that the said sheet is clamped between the push element and the associated push key.

Keyboards for actuating push switches are generally used for electronic calculating machines, office machines, shop weighing machines or the like, so that by the operation of push switches and with the aid of the individual keys it is possible for instructions of the most diverse kind to be transmitted, for example to enter numbers, to select specific methods of operation and the like. If apparatus with such a keyboard is exposed in operation to severe ingress of dirt, for example in the case of electronic price computing weighing machines used in butchers shops or fishmongers shops, it is possible for the operation of such a keyboard to be substantially impaired. This is because dirt particles penetrate in the gaps between the keys and their cover and can thus cause the keys to jam.Liquid or fat entering between the keys and the cover can cause sticking of the keys which are thus rendered non-functional. Furthermore, operation of such keyboards is unhygienic.

It is therefore essential to ensure that the operation of the keyboard is not impaired by such dirt ingress and/or that the entire keyboard can be throughly cleaned in a simple manner. To this end it is already known to cover the entire keyboard by means of a transparent flexible sheet which protects the keys as well as the push switches against the ingress of dirt. To actuate the keys, they are depressed through the sheet. However, such a sheet becomes rough and opaque in a short time and must therefore be frequently exchanged. Furthermore, there is d risk in a keyboard of this kind of not correctly striking the desired key and accidentally simultaneously depressing an adjacent key.

To prevent this disadvantage it is also known ir such a construction to profile the sheet so that it has indentations which accommodate the keys.

The required inscription will then be provided on the outside of the sheet. However, this results in the same disadvantages as those of the embodiment described above; the sheet becomes rough and opaque in a short time and furthermore the inscription on the keys rapidly becomes illegible.

In another known construction, the soft flexible sheet which covers the casing is itself shaped in key configuration in the region of the push switches. However, in view of the necessary flexibility, soft materials must be used for manufacturing such sheets and the abovedescribed difficulties also result in this case: the keys wear rapidly, the inscription becomes illegible and dirt can lodge in cuts, notches and the like of the sheet. There is also a risk of damaging the sheet of soft material, for example with a knife or the like.

It is therefore obvious that a hygienic keyboard which can be readily kept clean is obtainable only if the keys are constructed of a material which is different, harder and more resistant than the material of the sheet which covers the casing.

In a known system of this kind the casing is associated with a cover which surrounds the flexible sheet and is provided with apertures, which guide the push key and which, on being depressed, bear on the sheet which covers the push switches and actuate the push switch push elements disposed therebelow through the sheet.

This prevents the ingress of dirt into the push switches but cleaning of such a keyboard is relatively awkward. Since the push keys must be retained in the cover so as not to drop out thereform when the cover is removed, it follows that it is very difficult to thoroughly remove the dirt which accumulates between the push keys and the cover in the narrow guide gap of the aperture. To this end it will at least be necessary to remove the push keys from the cover and to reinsert them after cleaning, a procedure which is very complicated and is carried out irregularly by the operating personnel, more particularly in the case of apparatus which must be cleaned daily, for example butchers shop weighing machines, sausage slicing machines and the like, so that the functionality of such a keyboard is endangered even after a short time.

As a remedy it has been proposed for the push keys to be fixedly connected to the sheet on the side thereof which is distal from the casing, more particularly by adhesive joining and welding and to construct the apertures in the cover plate only slightly larger than the push keys so that the aperture provides a lateral guide for the push keys. This permits a hygienic construction of the keyboard to be adopted but manufacture gives rise to difficulties since the connection between the keys on the one hand and the sheet on the other hand cannot always be made with the necessary accuracy. Furthermore, irregular elongation of the sheet in operation gives rise to the risk of the keys being displaced from their regular arrangement so that they bear and jam against the edges of the apertures in the cover plate which surrounds the keys.

On the other hand, the prior art discloses a contruction in which in the region of the push switch the sheet is provided with an opening through which extends a push key connected to push switch push element disposed therebelow.

In this construction however there is a risk of dirt ingressing through the openings in the sheet into the casing which accommodates the push switches and furthermore it is very difficult to clean the space between the push keys and the sheet.

German Offenlegungsschrift 64 99 44 also discloses a keyboard in which the push keys are connected to the push elements through an opening in the sheet and the sheet is clamped between a collar of the push element and the bottom edge of a tailpiece. The push key itself has the shape of a cap which is mounted on the shank formed by the push element and the tailpiece.

This results in a dead space beneath the capshaped push elements and above the sheets.

Accordingly, the risk of the ingress of dirt between the key and the sheet is increased in this known keyboard. Furthermore, cleaning is rendered exceptionally difficult since it is necessary for the cap-shaped push elements to be individually removed from their shanks.

According to the invention, there is provided a keyboard for actuating push switches, comprising by push elements disposed in a casing which is covered by a flexible sheet, there being provided push keys, which are associated with the push elements and which are arranged to actuate the push elements, bearing in surface contact by means of their underside on the said flexible sheet, the push elements and the push keys being interconnected by components which extend through the sheet so that the sheet is clamped between the push elements and the associated push keys, the entire underside of each push key bearing in surface contact on the flexible sheet and, on the side of the sheet nearer the push elements, each of the push elements supporting a seal plate the surface of which is at least as large as the surface of the push key underside.

It is thus possible to provide a keyboard of simple manufacture and having precise arrangement of the keys, which are constructed as separate components. The ingress of dirt into the keyboard, more particularly in the region between the push key and the film, may be substantially avoided.

The direct connection between the push keys and the push elements provides reliable guiding for the push keys thus substantially eliminating ail risk of maladjustment. Nevertheless, no ingress of dirt occurs in the region between the underside of the push key and the film since the film is clamped in surface configuration between the underside of the push key and the seal plate.

Since the seal plate surface has at least the same size as the underside of the push key, the latter bears firmly over its entire surface upon the film; spaces into which dirt can ingress are therefore substantially eliminated. The apertures required in the film are also substantially completely closed in sealing-tight manner on the one hand by the seal plate and on the other hand by the underside of the push key.

The push keys and the seal plates may be joined by a ratchet connection. The seal plates may have two substantially parallel webs which extend through an opening in the sheet, are provided with ratchet projections, can be resiliently thrust against each other and are arranged to engage in a ratchet opening which is provided in the push key under-side.

The direct connection between the push keys and the push elements dispenses with any further lateral guiding for the push keys but is nevertheless advantageous that the sheet be surrounded by a removable cover plate with apertures through which the push keys extend, the cover plate covering the sheet regions between the push keys. This reliably avoids substantially all damage to the flexible and easily damaged film.

This invention will be further described, by way of example, with reference to the accompanying drawings, in which- Figure 1 is a plan view of a keyboard with four keys; and Figure 2 is a longitudinal section along the line Il-Il of Figure 1.

Push switches 7, 8 with push elements 9, 10 of known construction are disposed on a casing floor 2, advantageously also constructed as a wiring or circuit board, in a casing 1 with the casing floor 2, lateral walls 3, 4 and flange-like edge strips 5 or 6 disposed at the free ends of the walls. The casing 1 is closed by a flexible sheet 11 which sealingly bears on the flange like edge strips 5 or 6 disposed at the free ends of the walls. The casing 1 is closed by a flexible sheet 11 which sealingly bears on the flange like edge strips 5 and 6 of the casing and is joined to the said edge strips.

On the side nearest to the sheet 11 the push elements 9 and 10 support seal plates 12 and 13 and are connected to ratchet projections 14 which extend through openings in the film or sheet 11. The push elements, the seal plate and the ratchet projections are advantageously of integral construction.

Push keys 1 5, 1 6 of wear-resistant material and having ratchet recess 1 7 are pushed over the ratchet projections 14 so that on the underside they bear in surface configuration on the film or sheet 11 and are resiliently thrust by the ratchet projections 14 against the seal plate 12, the film 11 being clamped in surface configuration between the push key underside and the seal plate.

The surface of the seal plate 12 which bears on the film is at least as large as the underside of the push key so that the seal plate is disposed opposite to the underside of the push key over the entire surface area thereof. A cover plate 18, which surrounds the edge strips 5 and 6 at the edges and is retained in this position in a manner not shown in the drawing, for example by a ratchet connection in which the free ends of the cover plate resiliently grip behind sloping edges of the flange-like edge strips 5, 6, is also provided.

The cover plate 18 has apertures 19, 20 through which the push keys 15, 1 6 extend. The apertures 19, 20 are only slightly larger than the push keys 1 5, 1 6 so that the film regions between the push keys 1 5 and 1 6 are substantially covered.

Excellent guiding of the push keys is ensured by virture of the positive connection between the push elements and the push keys so that jamming of the latter in the apertures of the cover plate can be reliably avoided. Although an opening in the film is necessary for the positive connection between the push elements and the push keys, there is substantially no risk of the ingress of dirt to the interior of the casing through the said opening in the film since the latter is sealed on one side by the seal plate and on the other side by the underside of the push keys. It is obvious that to this end the opening of the film will have a smaller cross-section than the seal plate and the underside of the push key.

No gap can form between the film and the underside of the push key due to the fixed, surface configuration contact of the underside of the push key so that no dirt can occur in this region.

The ratchet connection illustrated in the drawing between the push key and the seal plate represents one preferred kind of connection but other methods of connection are feasible, for example the push keys and the seal plates can be screwmounted to each other through the film.

Claims

1. A keyboard for actuating push switches, comprising push elements disposed in a casing which is covered by a flexible sheet, there being provided push keys, which are associated with the push elements and which are arranged to actuate the push elements, bearing in surface contact by means of their underside on the said flexible sheet, the push elements and the push keys being interconnected by components which extend through the sheet so that the sheet is clamped between the push elements and the associated push keys, the entire underside of each push key bearing in surface contact on the flexible sheet, and on the side of the sheet nearer the push elements, each of the push elements supporting a seal plate the surfaces of which is at least as large as the surface of the push key underside.

2. A keyboard as claimed in claim 1, in which the push keys and the seal plates are interconnected by means of ratchet connections.

3. A keyboard as claimed in claim 2, in which each of the seal plates has two substantially parallel webs which extend through an opening in the sheet, are provided with ratchet projections, can be resiliently thrust against each other, and are arranged to engage in a ratchet opening which is provided in the respective push key underside.

4. A keyboard as claimed in any one of the preceding claims, in which the sheet is surrounded by a removable cover plate with apertures through which the push keys extend, the cover plate covering the sheet regions between the push keys.

5. A keyboard for actuating push switches, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

6. An electronic apparatus including a keyboard as claimed in any one of the preceding claims.