GB2178235A - Keypad - Google Patents

Abstract

The buttons of a bubble mat keypad are each provided with guide means to restric their freedom to tilt. The guide means may comprise a guide pin 16 and a guide socket 15, one rigidly fixed to the button 4, and the other rigidly fixed to the switch's base board 1. The guide member fixed to the baseboard 1 may be moulded integrally therewith. The guide means pass through an aperture in the bubble mat. The switch's static contacts may be separated by one or more of the conductive tracks connecting the various static switch elements. The switch's moveable contacts are so formed that when the switch is activated the moveable contacts contact the static contacts but not the conductive tracks there between. <IMAGE>

Description

SPECIFICATION Keypad One form of conventional keypad is that in which a flexible membrane or mat is supported with areas which form or carry a movable contact in spaced relationship to fixed contacts on a base member-often in the form of printed tracks. A flat membrane can be used, spaced by an apertured insulating layer, or a so-called bubble mat may be employed in which raised portions, or bubbles, are formed in an elastomeric mat; between the bubbles, the mat rests on the base. If the mat material is conductive, the movable switch contact can be formed integrally with the mat; otherwise a conductive pill is inserted. Commonly a keytop or button is provided, above the mat, as the actual actuating member.

One aspect of the present invention provides a keypad compising a base portion having fixed contacts thereon, a resilient support member supporting movable portions each forming or carrying a movable contact, and a key member on each of the raised portions, having, for each key, guide means extending through an aperture in the movable portion and comprising mutually engaging members secured to the key member and base portion respectively.

Another aspect of the invention concerns the arrangement of printed tracks on the base.

It can be applied to the keypad according to the first aspect of the invention, but may also be used in keypads not provided with keytops and/or guide mseans. Thus we also provide a keypad comprising a base portion having pairs of fixed contacts and interconnecting tracks thereon, and a plurality of resiliently supported movable contacts each movable when actuated to bridge the contacts of a pair, in which at least some of the interconnecting tracks pass between the fixed contacts of a pair and the corresponding movable contact is shaped so as when actuated to bridge those fixed contacts without touching the interconnecting tracks.

Some embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure la to id are cross-sections through part of a keypad according to one embodiment of the invention; Figure 2 is a plan view of two possible fixed contact configurations for the keypad of Fig. 1; Figure 3 is a plan view of the contact configurations for a second embodiment of the invention; Figures 4 and 5 are a cross-section and underneath plan view of the mat and moving contact of this second embodiment; and Figure 6 is an exploded, perspective view of this second embodiment.

Figure 7 is a plan view of a possible layout of conductive tracks for a large keypad such as a "QWERTY" keyboard.

Referring to Fig. 1, a keypad comprises a base member, printed circuit board 1, and overlying the board is an elastomeric "bubble" mat 2. The mat, of insulating material, has a number of raised portions 3, one for each key-though only one is shown on the drawing. The upper surface of the raised portion or bubble 3 is shaped to receive a button cap 4, whilst its lower surface carries a conductive pill 8 which forms the movable contact which, when the button cap 4 is depressed, is brought into contact with fixed printed contact pads on the circuit board 1.

As thus far described the keypad is of conventional construction. However, in order to stabilise the button cap 4 against any tendency to tilt, guide means are provided, comprising a guide sleeve 5 mounted in a hole in the board 1 and a guide pin 6 which slides in the sleeve 5 and is rigidly secured to (or integrally formed with) the button cap 4. The guide pin 6 passes through an aperture 7 formed in the top of the raised portion of the elastomeric mat 2.

As shown in Fig. 1 the guide pin is centrally disposed: clearly the usual arrangement of a centrally positioned conductive pill cannot be used, and instead a ring-shaped contact 8 is shown. Alternatively, three cylindrical pills might be symmetrically disposed about the central aperture.

Instead of having an inserted guide socket 5, an inserted guide pin 16, as shown in Fig.

1 b, can be used with a button cap 4 provided with an appropriate socket portion 15.

Where the fixed contact pads are provided on a moulded circuit board, the guide socket 5 or guide pin 16 can of course be integrally moulded with the rest of the board as shown in Figs. 1c and 1d respectively. As can cleariy be seen in Fig. Id, and the guide pins 16 may be provided with an axial bore through which the cap socket cavity may be vented.

Fig. 2 illustrates the way in which printed contact tracks 9,10 may be formed around the guide sleeve 5 to fit this geometry.

Another possible arrangement is depicted in Fig. 3 where printed contact pads 11, 12 and the guide sleeve 5 are positioned at the corners of an equilateral triangle. An off-centre contact pill 13 of elongate shape is then used, as illustrated in Figs. 4 and 5.

A particular feature of the variant shown in Figs. 3 to 5 is that, in order to facilitate connection to the switches of the keypad without recourse to double-sided (or multilayer) printed circuit techniques or the use of bridges, the passage of printed tracks (14) between the contacts of a given switch is permitted. The elongate conductive pill 13 permits contact to be made between the fixed contacts 11 and 12 despite the increased distance between them, and has two thicker end portions separated by a thinner central portion thereby avoiding accidental contact with the "through" tracks 14.

In manufacturing non-conductive mats of this type, conventionally the conductive pill is formed by inserting a portion of conductive rubber prior to final moulding. In practice, for ease of manufacture, it might be preferable to insert a flat disc- shaped piece, in a central location, the offset formation as indicated in Fig. 5 being moulded into it. Of course, where a conductive mat is used, the contact regions are simply moulded in.

An exploded view of one key of the keypad is shown in Fig. 6, whilst Fig. 7 shows a possible track layout of a 5XN keypad matrix.

In conventional keypads the keytops or buttons are retained by means of a frame, covering the bubble mat, and having apertures through which they project. Such frames also provide some measure of support for the keytops or buttons. The present invention enables the use of keypads with separate keytops without the need to use such a frame.

Where no frame is used, the keytops may be secured to the bubble mat by means of cooperating flanges and grooves, or by means of an adhesive.

As those skilled in the art will appreciate, the guide pins and sockets can be expected to provide relatively low friction engagement when moulded from conventional engineering plastics materials.

The guide pins and sockets may be of noncircular section and may have an angular cross-section to prevent rotation of the buttons. If the pins and sockets are of sufficiently large section, only a minimal gap need be provided between adjacent buttons when no frame is used.

Claims (9)

1. A keypad comprising a base portion (1) having fixed contacts thereon, a resilient support member (2) supporting movable portions (3) each forming or carrying a movable contact (8,13), and a key member (4) on each of the raised portions, characterised by, for each key, guide means extending through an aperture in the movable portion and comprising mutually engaging members secured to the key member and base portion respectively.

2. A keypad according to claim 1 characterised in that the movable contacts (13) are each movable when actuated to bridge the contacts of a pair of fixed contacts, interconnecting tracks (14) pass between the fixed contacts of at least one pair and the corresponding movable contact (13) is shaped so as when actuated to bridge those fixed contacts (11,12) without touching the interconnecting tracks.

3. A keypad as claimed in claim 1 or 2 wherein the guide means comprise a guide pin (16) slidably received within a guide socket (5,15), the pin or the socket being formed integrally with the base portion (1).

4. A keypad comprising a base portion (1) having pairs of fixed contacts (11,12) and interconnecting tracks (14) thereon, and a plurality of resiliently supported movable contacts (8) each movable when actuated to bridge the contacts of a pair, characterised in that at least some of the interconnecting tracks (14) pass between the fixed contacts of a pair and the corresponding movable contact (13) is shaped so as when actuated to bridge those fixed contacts (11,12) without touching the interconnecting tracks.

5. A keypad as claimed in any one of the preceding claims characterised in that the resilient support member has integrally-formed dome-like raised portions which form or carry the said movable contacts.

6. A keypad bubble mat comprising a plurality of integrally-formed, dome-like portions raised above the base layer of the mat, each of said portions having flexible sidewalls supporting an upper part, which upper part is provided on its lower surface with a conductive switch contact, characterised in that each of said raised portions is provided with a through aperture.

7. A keypad bubble mat as claimed in claim 6 wherein the conductive switch contact of at least one of the raised portions is in the form of a conductive pill having a higher conductivity than the rest of the mat, characterised in that said aperture extends through the conductive pill.

8. A keypad substantially as hereinbefore described with reference to and as illustrated in any one of Figs. 1a to 1d of the accompanying drawings.

9. A keypad substantially as hereinbefore described with reference to and as illustrated in one or more of Figs. 3 to 7 of the accompanying drawings.