AU594368B2 - A contact mat for keyboards - Google Patents

Description

0 SPRUSON FtiRGUSON FORM 10 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FO)R OFFICE USE: g6 Class Int. Class Complete Specificaf-ion Lodged: AcceptLed: Published: '~'isd'cLtl~ ~.~.jtanSthe amencilll md undr Priority: Related Art: 0440 o 00 00 0 4000 04 0 0 010 *0 0 0 O 4~ 0 00 0 0 0000 0.1 0 0 0 001 C C 0-0.10 Name of Applicant: SIEMENS AKTIENGESELLSCHAFT Address of Applicant: Wittelsbacherplatz 2, D-8000 Munchen 2, Federal Republic of Germany Actual Inventor(s): HERBERT HOGER and ALFRED MURR Address for Service: Spruson Ferguson, Patent Attorneys, Level 33 St Martins Tower, 31 Market Street, Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: "A CONTACT MAT F:7OR KEYBOARDS" The following statement is a full descriptioni of this invention, including the best method of performing it known to us.

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Ps ABSTRACT OF THE INVENTION "A Contact Mat for Keyboards" The invention relates to a contact mat for keyboards which is relatively cheap to manufacture and in which the adhesive strength of each contact stud is increased. This is achieved by providing contact points for the contact mat in the form of at least one recess in each case, filled with a hardened liquid, hardenable, electrically conductive material such as a silicone resin.

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"A Contact Mat for Keyboards" The present invention relates to a contact mat for keyboards, which is made of an electrically non-conductive elastic material and which has a plurality of electrically conductive contact nipples 5 which correspond to the number of the keys and which are arranged above the conductor paths of a printed circuit board, or a contact foil, and act to bridge individual conductor paths to make a contact when a key is actuated.

Contact mats of this kind have been described in a large 10 number of Patent Specifications. On the operating side the side facing the keys in use), the mats have a number of deformable, elastic bellows members which corresponds to the number of keys, the bellows members executing a snap-like movement during depression of the key after a specific resistance has been overcome. On the side facing the contact points, the bellows members are provided with electrically-conductive studs to enable them to bridge individual conductor paths in the region of the contact point. Such contact studs can, for example, be prefabricated, and subsequently inserted into a tool and vulcanized onto the unvulcanized mat. Another possibility consists in a two-colour injection method using silicone rubber. Finally, it is conceivable to form the studs by printing the switching nipples with a conductive paste.

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7" -2- All these methods require a considerable outlay during production in order to achieve a high and constant quality.

It is an object of the present invention to provide a contact mat which requires a smaller outlay to produce, and in which the adhesive strength of the contact stud is simultaneously increased.

In accordance with the present invention there is disclosed a contact mat for a keyboard, said mat being made of an electrically non-conductive elastic material and having a plurality of electrically-conductive contact nipples corresponding in number and position to the keys of the keyboard, said contact nipples being arranged above the conductor paths of a printed circuit board, or a contact foil, and being arranged to bridge individual conductor paths to make a contact on actuation of a key, each of the contact nipples of the contact mat comprising at least one recess which is filled with an In situ hardened liquid, said liquid being a hardenable electrically-conductive material.

Layers of an electrically-conductive material can therefore be applied of a thickness depending on the size of the recess. The adhesive I itsr strength is substantially increased by the large surface areas of the surfaces of the recess which are in contact with the electricallyconductive material. Moreover, such a design can be easily effected using a dosing device and a high manufacturing quality can be achieved at the same time.

It is advantageous if the electrically-conductive material is a silicone rubber which can be easily processed.

The recess may have a concave cross-section. However it is

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4444i 4 4 '444 414 4 4 4444 4 14 4 44 4444 Ai 44 4 i 4 4444 4( 64 44 4 4 44 444, 4i 4 also conceivable to form the recess by the raising of an injection edge during the production of the contact mat, so as to achieve a contact surface which is as large as possible.

In order to form electrically separated circuits it may be desirable to provide two recesses formed by two grooves extending at a distance from one another.

The invention will new be further described with reference to the drawings, in which:- Figure 1 is a schematic perspective view of a bontact mat 10 according to the invention, viewed from the contact-making side; Figures 2 to 4 are similar schematic perspective views, partially cut-away, of different forms of contact-making region for use in the contact mat of Figure 1.

The contact mat illustrated in Figure 1 consists of a mat of 15 electrically non-conductive elastic material, such as rubber or a synthetic resin. On the one side the mat has deformable, elastic lifting bellows members 7 which when the mat is in use, are connected to individual keys and which act to effect the return of the keys inco their initial position on release of pressure. On the other 20 side (the contact-making side illustrated) contact-making elements 1, 2, 3, 4 are arranged in alignment with the keys.

Figure 2 shows a section of the contact mat in one contact-making region. The end face 5 of the bellows members 7 exposed at the contact-making face of the mat, has a recess 6 of approximately concave cross-section. An electrically-conductive I 1. 4 49.

-4material 13, which is mechanically strongly bonded to the material of the contact mat, is introduced into the recess 6. A key (not illustrated) can in use act on the bellows member and move it towards, for example, a printed circuit board. The contours of the bellows members are such that the bellows member in known manner executes a snap movement after it has moved through a specific distance.

Figurc 3 illustrates another embodiment. In this, the face of the bellows member has a disc-shaped recess 8 which is filled with an electrically-conductive material 9.

A further variant is illustrated in Figure 4. For electrical reasons, two switching functions, which are electrically separated 0 from one another, can be carried out in this case. For this purpose, the face 5 of the bellows member is provided with two recesses 10, 11 formed by two longitudinal grooves in the surface, the recesses being filled with an electrically-conductive material 12.

In all the embodiments, the electrically-conductive material 13, 9, 12 is produced by hardening in. 'situ a liquid, hardenable electrically conductive material, for example, a silicone rubber.

Claims (4)

1. 2. A contact mat as claimed in claim 1, wherein said hardenable electrically-conductive material is a silicone rubber.
2. 3. A contact mat as claimed in claim I or claim 2, wherein each said recess has a concave cross-section.
3. 4. A contact mat as claimed in claim 1 or claim 2, wherein the recess is formed by a raised injection edge formed during the production of the contact riat. A contact mat as claimed in claim 1, or claim 2, wherein each said contact nipple comprises two recesses formed by grooves extending at a spaced distance from one another.
4. 6. A contact mat substantially as hereinbefore described with reference to the drawings. i 7. A keyboard comprising a contact mat as claimed in any one of claims 1 to 6. -;DATED this FIRST day of DECEMBER 1989 Siemens Aktiengesellschaft Patent Attorneys for the Applicant SPRUSON FERGUSON