Keyboard switch assembly having discrete helical conductors providing wiping action

Abstract

There is disclosed a keyboard in which each of the key contacts consists of a gold-coated wire contact with each end passing through a printed circuit board and soldered to one part of the circuit on the underside of the board and of a gold-coated plate contact with a base part mounted on the printed circuit board by lugs passing through the printed circuit board and soldered to another part of the circuit on the underside of the board and with a part cut in helical form and so deformed in an open spiral to form a resilient raised part directly above the wire contact. Each of the push buttons of the keyboard is circular with diametrical flanges extending outwardly and has a central stem which abuts the central part of the resilient raised part of the plate contact and an annular outer depending ring which surrounds the resilient raised part of the plate contact. On depression, the outer part of the spiral resilient raised part makes initial contact with the wire contact and, after further movement, the inner parts of the spiral resilient raised part make contact with the wire contact.

Description

A BRIEF SUMMARY OF THE INVENTION

This invention has reference to keyboards intended more particularly for use in electronic calculating machines and more especially for use in hand-held electronic calculating machines.

It is an object of the present invention to provide an improved keyboard.

It is another object of the present invention to provide a keyboard which will be of simple and robust construction yet able to be of a suitable size for use in a hand-held electronic calculating machine.

According to the present invention a keyboard comprises: a cover plate, a plurality of push buttons movably mounted within the cover plate, a base plate bearing a first set of contacts, each contact of this set each corresponding to one of the push buttons, and a plurality of contact plates, each contact plate co-operating with a corresponding button and a corresponding one of the first set of contacts; and wherein each one of the contact plates comprises a strip of electrically conducting material having at least one integral tag securing the strip to the base plate and a resilient part with a free end normally extending towards the corresponding push button but capable of being moved on depression of the push button towards the corresponding contact of the first set of contacts to make electrical connection therewith.

Preferably the base plate is a printed circuit board and has electrical connections extending from each contact of the first set of contacts and from each one of the contact plates to a connecting contact at the side of the printed circuit.

Conveniently the resilient part of the contact plate comprises an integral part of the contact plate cut out of the contact plate with a helical slot .

BRIEF DESCRIPTION OF THE DRAWINGS

A keyboard in accordance with the present invention will now be described by way of example with reference to the drawings:

FIG. 1 is a plan view of a calculating machine embodying the keyboard;

FIG. 2A is a view taken on the line A--A in FIG. 1;

FIG. 2B is an enlarged perspective view of the button contact assembly shown in FIG. 2A;

FIG. 3 is a view taken of the line B--B in FIG. 2; and

FIG. 4 is a plan view of the printed circuit board in the calculating machine.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to FIG. 1 of the drawings, there is shown a calculating machine of the hand-held type embodying a casing (1) having windows (2) behind which the displays are mounted. There are also shown three control switches (3). There is also shown the outer cover plate (4) of the keyboard. This cover plate includes 20 apertures and each of these apertures houses a push button (5). These push buttons are arranged in four banks of five buttons each. The buttons relate to the numbers 0-9 and additional control buttons relate to operative functions of the calculating machine.

Each of these buttons consists of a flat top surface on which is imprinted the number or other designation and on the under surface is an annular outer depending ring (5a) and a circular post (5b). Each of the push buttons has on its underside a pair of flanges which project outwardly in opposite directions along a diameter of the depending ring (5a) of the button. These flanges co-operate with complementary recesses in the housing of the cover plate to prevent the buttons rotating in the cover plate.

The under face of the cover plate bears a plurality of upright posts (not shown) which are screw threaded internally to receive screws for mounting the printed circuit board to be hereinafter described.

Referring to FIG. 2 of the drawings the calculating machine includes batteries (6) for driving the calculating machine and also includes an integrated circuit board (7) which includes the calculating circuitry of the calculating machine.

Beneath the banks of push buttons (5) is arranged a base plate in the form of a printed circuit board (8) more fully shown in FIG. 4. This printed circuit board comprises a sheet of electrically non-conducting material on the upper surface of which are mounted a first set of contacts in the form of a plurality of strips (9) of electrically conducting material set into the board. Each end of each of the strips (9) passes through the printed circuit board and on the rear side of the board is electrically connected, preferably by soldering to a connecting path which is joined to a contact (10) at the side of the board.

Mounted above each one of the contact strips is a resilient contact plate (11) consisting of a plate of gold plated nickel silver formed with a base part with a helical cut and so deformed in an open spiral to form a resilient raised part (11a) that the free end of the resilient part (11a) is located towards the under side of the corresponding push button (5). The depending ring (5a) surrounds the resilient part (11a) and the post 5b) engages the free end of the resilient part (11a). Each of the contact plates also bears a pair of lugs (12) each lug passing through the printed circuit board and serving to locate the contact plate in position on the printed circuit board. These lugs are electrically connected on the under side of the printed circuit board, preferably by soldering to a conducting path.

The method of manufacture of the contact plate on the printed circuit board is more fully described in our co-pending British application for patent No. 53001/73. In operation of the calculating machine the respective push buttons (5) when operated, cause a depression of the push button towards the printed circuit board. Downward movement of the button causes the end of the post (5b) to move downwardly the free end of the resilient part (11a) of the contact plate (11) and downward movement is transmitted to the remainder of the resilient part (11a) to cause the outer part of the resilient part to move downwards about the fixed contact (9) to make electrical contact therewith. After the initial contact, there is some lost motion and then inner resilient part (11a ) diametrically opposite to the outer part already in contact with the fixed contact (9) makes contact with the fixed contact (9) possibly simultaneously with the free end of the resilient part (11a) under the post (5b) abutting the fixed contact (9).

Preferably the fixed contact (9) is made of gold-plated phosphor bronze wire so that the contact between the resilient part (11a) and the fixed contact (9) is accompanied by a slight `wiping` action and the gold-to-gold contact mainly maintains the contact resistance to a consistently low value.

A major advantage of the keyboard is that, because of the combination of the helical form of contact plate (11) with the fixed contact (9) particularly in the form of gold-plated wire the keyboard is of reduced thickness.

Because of the shape of each of the push buttons (5) the button had a large bearing area so that during its movement the button does not wobble about and so jam. The anti-rotation flanges assist in preventing this wobble.

Claims

What I claim is:

1. A keyboard comprising a cover plate; a plurality of push buttons movably mounted within the cover plate; an insulating base plate spaced from the buttons bearing a first set of longitudinally directed fixed contacts on that side of the base plate facing said push buttons, each contact of this set located opposite one of the push buttons; and a plurality of contact plates, each contact plate affixed to said base plate in a position co-operating with a corresponding button and a corresponding one of the first set of contacts; wherein the contact plates each comprises a strip of electrically conducting material having at least one tag securing the strip to the base plate and a resilient part with a free end spaced away from said base plate to engage one said push button at a position normally extending towards the corresponding contact of the first set of contacts to make electrical wiping contact therewith when the push button is moved toward said base plate; and wherein the resilient part of the contact plate comprises an integral part of the contact plate cut out of the contact plate with a helical slot thereby forming a helically shaped conductor which engages said longitudinally directed fixed contact in a wiping action in at least two spaced positions on said helically shaped conductor when said push button is moved toward said base plate.

2. A keyboard according to claim 1, wherein each button has on its under surface an annular outer depending ring which surrounds the resilient part of the corresponding contact plate and a circular post which is concentric with the depending ring and which is in contact with the free end of the resilient part of the corresponding contact plate.