AU601417B2 - Improved keypad - Google Patents

Description

ORIGINA.

This document contains the amendments made under Secton 4 and is correct for printing COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-1969 60141I COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED "IMPROVED KEYPAD" The following statement is a full description of this invention, including the best method of performing it known to us:i 1. i. i 1 _~(IIIO-^--LIIIUYII~ I This inventJ n relates to an improved keypad and will be described with reference to a keypad for a telephone.

In recent years push buttons have replaced the rotary dial in most subsets. Push buttons are fairly complicated mechanical devices which usually incorporate a return spring, electrical contacts and suitable mounting arrangements.

A recent development has been the membrane keypad which basically consists of a pair of membranes one of which has a first array, e.g. columns and the other of which has a second array, e.g. rows of contact pads which can be used to uniquely identify a desired "button". The membranes are separated by a spacer having holes corresponding to the "button" locations.

When a "button" is pushed the conductive tracks on the upper membrane are brought into contact with those of the lower membrane so there is a change in the electrical resistance between the row and column involved. The upper membrane must have some resilience, and while the lower membrane may S also be flexible, it is preferable that its tracks be rigidly mounted so the lower membrane may be placed on or replaced by a fairly rigid substrate.

One feature of the new generation telephone is the use of microi200 processors to incorporate a number of features in the subset. One such feature is a memory to store frequently called numbers. Some phones have S provision to write the allocated number to be called in proximity to the related button. However the numbers and destinations or purpose associated t with some of the buttons may change from time to time. To overcome this problem it is proposed to have a removable designation card carrying the designation of some or all of the buttons. This card is thin and sufficiently flexible to be slid under a transparent flexible cover of the membrane keypad so that the designations align with the "button" locations.

This invention proposes a membrane keypad comprising a substantially 31( ",Oplanar, flexible upper membrane containing a first array of contact pads on 2 L 4 r _il a first side thereof, and a substantially planar lower member being rigidly mounted and having a second array of contact pads on a first side thereof the pads of the second array being aligned with corresponding pads of the first array to form contact pad pairs, a first spacer member between the upper membrane and the lower member and having a plurality of holes corresponding to the location of the contact pad pairs, the first and second arrays being contained in a first contact pad area the keypad including a membrane keypad comprising a substantially planar, flexible upper membrane containing a first array of contact pads on a first side thereof, and a substantially planar lower member being rigidly mounted and having a second array of contact pads on a first side thereof, the pads of the second array being aligned with corresponding pads of the first array to form contact pad pairs, a first spacer member between the upper membrane and the lower member and having a plurality of holes corresponding to the location of the contact pad pairs, the first and second arrays being contained in a first a contact pad location, the keypad including at least one remote button posio c' tion comprising a flexible arm extending from and integral with the upper membrane or lower member respectively, said flexible arm having at the free-end thereof a second contact pad location on which is disposed a pair °o .20 of bridgeable contact pads connected to a pair of conductor leads carried on said flexible arm, the pair of bridgeable contact pads being operably located above a first bridging contact at the second contact pad location and spaced from the first bridging contact by a second spacer member at the second contact pad location. The invention will be described with reference to the accompanying drawings, in which:- Fig. 1 shows an exploded partial view of a keypad to which the invention is applicable; Fig. 2 is a similar view of a further suitable keypad; Fig. 3 shows a membrane incorporating the remote contact zone and $Tg flexible arm of the invention; Fig. 4 a and b show variations thecontact pad conductor patterns; Fig. 5 shows an integral membrane with 2 contact pad arrays; Fig. 6 is a schematic view of an arrangement of the remote Rwitch.

Fig. 1 is a partial exploded view showing a membrane keypad incorporating the replaceable designation card.

The top cover 1 is flexible and has transparent windows, Wn, corresponding to button positions. This sits on a spacer 2 which conforms to the perimeter of 1 but is open ended on one side to allow insertion of the designation card 3. Card 3 is sufficiently rigid to allow it to be pushed into place in the space provided under cover 1 by spacer 2. This space is 0 1 a 3 4

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in practice a push-fit with card 3 to ensure sufficient friction to retain the card in place during normal operation. Card 3 and cover 1 are sufficiently flexible to allow operation of the membrane contacts below.

Under card 3 is the upper membrane 4 which has an array of columns (or rows) of conductive pads on its under surface. A further spacer 5 having spaces which conform to the boundaries of each button location and substantially enclose the conductive pads for each button on the upper and lower membranes. Membrane 6 has rows (or columns) of conductive pads arranged to correspond with associated pads or membrane 4. According to an embodiment of the invention, membrane 6 may in fact be replaced by a more rigid substrate. One embodiment is the use of a PCB as the lower substrate. One pad or alternatively two isolated pads may be formed on the PCB for each switch while the flexible membrane carries the mating (or bridging) pad. This results in a rigid keypad and, where the PCB has two pads per switch, the need for connection to the thin film may be eliminated. Further, the spacer 5 may be integrated into this substrate with the lower pads incorporated in shallow recesses formed thereby. The spacers may also have notches through which the conductive paths may be led. Optionally the bottom membrane or substrate 6 may have an adhesive layer on its underside to facilitate mounting.

A disadvantage of the membrane keypad is that the user can not confidently determine whether the "button" has been actuated. One method of overcoming this drawback is the use of an audible feedback signal generated by the circuitry when a button is operated. The autobank system uses such an arrangement. This arrangement requires circuitry to detect the button operation and to generate a signal to be fed to an electro-acoustic transducer.

In Fig. 2 a clicker plate 8 has been added. This plate comprises a thin resilient plate of e.g. rubber, plastics or metal, the plate has 64, (dimples or domes corresponding with the locations of the buttons. The pur- Uz 01 pose of these domes is to provide tactile feedback to the operator as they collapse when the button is depressed so the operator can "feel" the operation of the button. If the clicker plate is sufficiently stiff it will also produce a "click" as the button is operated giving acoustic as well as tactile feedback. A spacer 9 is also associated with the clicker plate 8.

If the clicker plate 8 and spacer 9 are mounted above the membrane 14 it may be covered by an additional flat flexible membrane 10 to ensure that the card 3 does not catch on the domes of plate 8 when the card is being pushed into place.

If the clicker plate 8 is mounted under membrane 6 (which must be flexible in such a case) the additional membrane 10 should not be required.

In this case the clicker plate may provide suf'ficient rigidity to act as a substrate for membrane 6 but tolerances may become critical as the domes could act against the pads of membrane 6 to cause contact with thp pads on membrane 14 if spacer 9 is not sufficiently thick.

As shown in Fig. 3 the invention proposes the addition of remote switching facilities by the addition of a button location attached to the membrane by a flexible arm. As the conductive tracks and membrane are flexible it is proposed to use the same Cacilitiec for switching at a lo- 2P cation remote from the keypad. Indeed it is not necessary for the remote ''location to be in the samne plane as the keypad. One such application is the use of a membrane switch as a gravity switch. A remote pad attached to and part of the membranes 4/6 is located to be actuated by the hook switch by a flexible strip of the membrane. As shown in Fig. 3 the additional strip projects from the main keypad membranes and contains one or more additional pads. If the pads are not capable of carrying telephone line current the gravity switch pads 4' 4.1 YU-e~-I could actuate an electronic line switch such as disclosed in patent application No. 59803/86.

Fig. 6 is a schematic view of one possible arrangement of the remote contact. A first flexible arm 13 terminating in a contact zone 10 is associated with a further spacer 12. The spacer 12 has an appropriate hole (not shown) under contact pad 10. The flexible arm 10 may carry either a single conductor track or a pair of conductor tracks each terminating in an appropriate contact pad area at 10. If only 1 conductor track is applied to arm 13, then a second arm 11 may be provided with a mating contact zone on the other side of the hole in spacer 12.

If two conductor tracks are applied to arm 13 then arm 11 can be dispensed with and the contact zones can be, e.g. as shown in Fig. 4a or 4b.

In this case the hole in spacer 12 would be a blind hole with a shorting contact zone applied to the base of the hole.

It should be noted that the flexible arm allows the remote contact zone to be in a different plane from the main key pad and it may be in a non-parallel plane in relation to the main keypad.

One application of the remote contact is as the electrical contact for a telephone gravity switch. A spring loaded mechanical switch arm may be arranged to operate the contact when the handset is lifted.

In an alternative embodiment, instead of having the row and column layout, one of the membranes may comprise a pair of pads which may comprise two sets of fingers which are interleaved or two sets of interwoven spirals (Fig. 4a and while the other membrane may contain a bridging pad to interconnect the two pads of the first membrane. The advantage of this is that all the active leads which must be taken off the keypad can be contained on one membrane and this simplifies connections between the membrane and the rest of the telephone circuit.

A further embodiment achieves a similar advantage by printing both the ,~upper and lower pad layouts on a single piece of membrane. The pad layouts .u ppe i--iii~ r I are aligned when the membrane is folded over the spacer. This again allows the connection point to be on one side only, (see Fig. A further improvement is the addition of an earth plane in front of the switches and the membrane to act as a static electricity screen to prevent damage to the equipment by static discharge which may occur for instance when a user has nylon carpet. The static shield may be a complete planar screen or it may consist of a grid or of rows of conductive paths which are connected. The screen also serves as a radio frequency shield.

One method of eliminating the need for an ohmic connection from the static shield to earth is by the use of capacitive coupling. This is achieved by having at least areas (on earth grid) on the membrane to be shielded which underlie at least some of the conductive areas of the electrostatic shield to give capacitance coupling. Coupling may optionally be enhanced by having a reduced space between thle screen and at least some of the corresponding capacitance layers. Static discharge tends to follow the path of least resistance and since the active keypad areas have additional impedance interposed between the pads and earth, the discharge will S preferably be via the earth grid on the membrane.

In some instances it may be preferred to have the static screen in physical contact with the earth grid on the membrane in one or more places.

The use of the static screen may be extended to serve a dual purpose by replacing the upper membrane. A particular application of this is where S the lower circuit contains both pads and the upper membrane acts as a shorting pad. This has the advantage of reducing the number of layers required to make up the keypad.

A further method of achieving a single-sided connection is by welding the upper and lower membranes together so that the leads from the membrane without the connection are Joined to tracks on the other membrane which lead to the connector.

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u .ar- 31 L i _i ul rr .I A technique which has proved useful in preparing the membranes particularly where there are complicated patterns is the use of multi-layer printing of tracks and insulation. By this technique a first conductor pattern may be laid down and coated with an insulator layer. The insulator layer is provided with windows so a further set of conductors may be printed onto the insulator and make contact with the first layer at the desired points. This then allows the use of "flying-leads" on the membrane.

The technique of leaving windows in the insulation is also applicable to the welding technique mentioned above.

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Claims (7)

1. 2. A membrane keypad as claimed in claim 1 wherein the first and sec- ond array are formed on the same side of a single membrane, which is folded along a fold line to align the contact pad pairs. o" 3. A keypad as claimed in any one of claims 1 or 2, including an electrostatic shield between the operator and the contact pad pairs.
2. 4. A keypad as claimed in claim 3, wherein the electrostatic shield is I capacitively connected to earth. 0 0 A keypad as claimed in claim 3, wherein the electrostatic shield is ohmically connected to earch.
3. 6. A keypad as claimed in any one of claims 1 to 5 wherein air chan- nels interconnect the holes of the first spacer. 08 L1 d W r_
4. 7. A membrane keypad as herein described with reference to the accom- panying drawings.
5. 8. A keypad as claimed in claim 1, wherein the lower member is a rigid substrate.
6. 9. A keypad as claimed in claim 8, wherein the first spacer is incor- porated in the substrate. A telephone including a keypad as claimed in any one of the preced- ing claims.
7. 11. A telephone as claimed in claim 10 wherein the remote button posi- tion is actuable by a gravity switch. DATED THIS THIRTIETH DAY OF MAY, 1990 STANDARD TELEPHONES AND CABLES PTY. LIMITED 0 0 R, Ro 4a 9 i i I C, I O t" 0 I