CA2090001A1

CA2090001A1 - Key button switches

Info

Publication number: CA2090001A1
Application number: CA 2090001
Authority: CA
Inventors: William W. Kidston; Roger M. De'ath; Donald E. Griffiths
Original assignee: Individual
Current assignee: McKechnie UK Ltd
Priority date: 1992-02-22
Filing date: 1993-02-19
Publication date: 1993-08-23
Also published as: GB9303386D0; JPH0668746A; EP0558239A1; GB2264393A

Abstract

Title:
IMPROVEMENTS IN OR RELATING TO KEY BUTTON SWITCHES
Abstract:
A key button structure for a keyboard of a data input device comprises a plastics base plate having an opening defining a switch site for a push button biassed to a raised inoperative position by a resiliently flexible elastomeric membrane integral with the base plate. Single and multi-button assemblies are disclosed in which the push button(s) are located on guide means integral with the base plate and the key button structure is secured to a carrier by attachment means Integral with the base plate.

Description

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0~ Thls Inventlon relates to keyboards for data Input devices such as telephones, calculators or the like and In partlcular, though not excluslvely keyboards Incorporating a push button swltch assembly.
05 It Is an object of the present Inventlon to provlde a key button structure for a push button swttch assembly of slmple constructlon.
Accordlng to the present Invention there Is provlded a key button structure for a swltch assembly comprislng a base plate havlng an openlng deflnlng a swltch slte, and a reslllently flexible membrane tntegral wlth the base plate and arranged to provlde a return sprlng functlon for a push button.
Preferably, the base plate has gulde means for locatlng the push button for axtal slldlng movement towards and away from the base plate.
Convenlently the gutde means Is posltloned around the marglnal edge of the opening and extends to one stde of the base plate for reception In a recess In the underslde of the push button.
Advantageously, the gulde means comprlses a plurality of gulde posts unlformly spaced around the marglnal edge of the openlng In the base plate.
In a preferred constructlon, there are four gulde posts for locatlon at respectlve corners of a square recess In the push button to engage adJolnlng slde walls along the outer corner edges of the gulde posts.
The push button may be retalned In a ralsed Inoperative or rest posltlon under the blasslng of the membrane by engagement wlth the guide means. For example, the push button may have retalner arms engageable wlth the gulde posts. The retalner arms may be releasable for detachlng the push button.
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01 A]ternatlvely, the push button may be retalned In the ralsed position under the blasslng of the membrane by engagement wlth a cover or case of the data Input devlce. For example, the push button may extend through an openlng tn the case for user 05 actuatlon and be retalned by engagement on the underslde of the case around the openlng.
The base plate may be adapted for securtng the key button structure to a circult board or slmilar substrate to allgn a switch devlce wlth the openlng In the base plate. For example, the base plate may have reslllent legs for engagement In allgned apertures In the clrcult board. The legs are preferably releasable for detachlng the key button structure.
A1ternatlvely, the base plate may be adapted for securlng the key button structure to a cover or case of the data Input devlce prlor to assembly to a clrcult board or the llke to allgn a switch devlce wlth the opentng In the base plate. For example, the base plate may have restllent tongues for engagement In an openlng In the cover or case through whlch the push button proJects for user access.
The swltch devlce may comprlse a pair of flxed swltch contacts on the clrcult board and a movable contact of electrlcally conductlve materlal secured to the underslde of the membrane.
Advantageously, the membrane Is arranged to seal the key button structure relatlve to the clrcult board around the openlng to protect the swltch devlce from Ingress of contamlnants.
In a preferred constructlon, the membrane Is of frusto-conlcal shape havlng a base seated around the openlng on the underside of the base plate and a ralsed platform at the apex engageable wlth the push button on the opposlte slde of the base plate.
Preferably, the base plate has stop means for llmltlng reslliently depression of the push button to lower the movable 2~

01 contact onto the fixed contacts. The stop means is preferably formed integrally with the membrane to secure non-releasably the membrane and the base plate.
In a preferred constructton, the base plate Is a moulding of G5 substantially rigld plastics such as polyphenylene sulphide and the membrane Is a moulding of elastomer such as slllcone rubber which is moulded onto the base plate so as to be permanently secured there~o.
The key button structure may be adapted for one push button by the provlslon of a stngle opening 7n the base plate.
Alternatlvely, the key button structure may be adapted for - several push buttons by the provlslon of a plurality of openlngs In the base plate with each openlng havlng an assoclated membrane integral wlth the base plate.
The invention will now be described in more detall, by way of example only, with reference to the accompanying drawings, wherein:-FIGURE l Is a sectional vlew of a switch assembly Incorporating a first embodiment of a key button structure accordTng to the Invention;
FIGURE 2 Is a section on the llne 2-2 of Flgure l;
FIGURE 3 Is a plan vlew of the base plate of the key button structure shown in Flgure l;
FIGURE 4 is a sectlon on the llne 4-4 of Figure 3;
FIGURE 5 Is a sectional vtew simtlar to Figure l showtng a modlfted key button structure;
FIGURE 6 Is a plan vtew of the base plate of the key button ~tructure shown In Figure 5;
FIGURE 7 Is a secttonal vlew slmtlar to Flgure l showtng another modlfted key button structure;
FIGURE 8 ts a sectlonal vtew of a swltch assembly Incorporattng a second embodlment of a key button structure accordtng to the tnventton; and .

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01 FIGURE 9 is a plan view of the base plate and integral membranes of the key button structure shown In Figure 8.
Flgures 1 to 4 of the accompanying drawings show a flrst embodiment of a key button structure Tn a switch assembly for a 05 data input device such as a telephone keyboard (not shown).
The key button structure comprises a plastics base plate 1, a resiliently flexTble elastomerTc membrane 2 and a plasttcs push button 3.
i The base plate 1 ts of generally square shape In plan vlew havTng a resTlTent leg 4 dependTng from each corner and a cTrcular hole 5 at the centre.
Upstanding from the base plate 1 adjacent to each corner are four guide posts 6 unTformly spaced around the margTnal edge of the hole 5.
The flexTble membrane 2 Ts of frusto-conTcal shape havTng an annular base 7 that seats around the hole 5 in a counterbore 5a on the unders7de of the base plate 1, and a platform 8 at the apex centrally posTtToned between the guTde posts 6 on the opposlte slde of the base plate 1.
The membrane 2 is moulded onto the base plate 1 and has formed Integrally therewTth on the upper surface of the base plate 1 at each corner, four pads 9 connected to ~he base 7 of ~he membrane 2 through respectTve orTfTces 10 in the base plate 1 to secure non-releasably the membrane 2 and base plate 1.
The button 3 Ts of square shape Tn plan vTew comprTsed of a top wa~l 11 and dependent slde walls 12 deflnTng a square ; recess 13 open to the underslde In whTch the gulde posts 6 are recelved.
; Each guTde post 6 Is posTtToned adJacent to a respecttve corner of the recess 13 and7 as best shown In FTgure 2, has radTused outer corner edges 6a engageable with adjoTnlng sTde walls 12 of the button 3 to locate the button 3 for axTal slidlng movement relatlve to the base plate 1 and prevent the button 3 tTltlng or rocking on the guide posts 6.

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01 The line contact between the .corner edges 6a of the guide posts 6 and side walls 12 of the button 1 facilltates axlal slidtng movement with mintmum frictional reslstance. FrTctional resistance may be further reduced by the selection of the 05 plastics materials for the base plate 1 and button 3.
Depending from the top wall 11 of the button 3 within the recess 13 are a centre post 14 of X-shape in transverse section that seats on the platform ~, and four retainer arms 15 uniformly spaced around the centre post 14 on the inside of the guide posts 6.
The guide posts 6 and retaTner arms 15 have opposed Internal and external chamfer faces 16 and 17 respectively that extend from the free ends and termlnate in respecttve undercut ledges 18,19.
The chamfer faces 16,17 co-operate to dtsplace the gutde posts 6 and retainer arms 15 radially for push fitting the button 3 on the gutde posts 6 until the ledges 18,19 engage with a snap actton ~o retatn the button 3 on the gutde posts 6 tn a ralsed tnoperatlve or rest posltlon under the blasslng of the flexlble membrane 2.
Cut-outs 20 tn the stde walls 12 of the button 3 provlde access between adjacent gutde posts 6 for tnsertton of a suttable tool (not shown) to release the retatner arms 15 for removtng the button 3 If requlred for repalr, replacement, etc.
The key button structure above-descrlbed provldes a sub-assembTy for securlng to a flat substrate such as a prlnted clrcult board 21 by Insertlng the dependent legs 4 of the base plate 1 through allgned apertures 22 In the board 21.
Each leg 4 has a foot 23 wlth an external ramp face 24 that 3 co-operates wlth the marglnal edge of the aperture 22 to dlsplace the leg 4 radially untll the foot 23 engages the underslde of the board 2t wlth a snap action to retaln the key button structure on the board 21.

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01 The key button structure may be detached from the board 21 if required for repair, replacement etc by releasing the feet 23 and withdrawing the legs 4 through the apertures 22.
Allgned with the hole 5 in the base plate l is a switch 05 device comprising a pair of fixed contacts 25 on the board 21 and a movable contact 26 of electrically conductive material on the underside of the platform 8 that ts spaced above the fixed contacts 25 in the inopera~ive or rest position of the button 3.
The movable contact 26 is lowered to engage and connect electrically the fixed contacts 25 by manual depression of the push button 3 against the biasslng of the membrane 2 which provides a spring function to return the button 3 to the inoperatlve or rest posltion on releaslng the button 3.
The base 7 of the membrane 2 seals the key button structure relatlve to the board 21 around the hole 5 to protect the swttch devtce from Ingress of contamtnants, and the pads 9 limit resiltently depresston of the button 3 for user comfort and to protect the swttch device from excesstve user actuation force i applied to the push button 3.
The data tnput device wtll typically have a pluralTty of separate key button structures secured to the circuit board 21 as above-described for performtng different functions wlth each button 3 arranged to project through an opentng 27 in an outer cover or case 28 for user access. The different functtons may be tdentifted by suttable indlcta on exposed surfaces of each button 3, for example the top wall ll.
As will be appreciated, the number and posttion of the key button structures can be adapted for dtfferent appltcattons as destred tn a stmple manner factlttating assembly of a wtde range of keyboards havtng dtfferent arrays of buttons ustng a common key button structure.
Referrlng now to Figures 5 and 6, a modlfted key button structure Is shown tn which ltke reference numerals are used to tndtcate parts correspondtng to the ftrst embodtment., , ' .

2~0~1 01 The key button structure provides a sub-assembly for securing to the outer cover or case 28 by four resilient tongues 29 upstanding from the marginal edges of the base plate l on each side. The tongues 29 are a push fit in and frictionally 05 engage the Inner end of the openlng 27 in the case 28 to locate and retain the key button structure for subsequent assembly of the case 28 onto the printed clrcult board 21.
When assembled, the key button structure Is loaded against the board 21 by engagement of the case 28 wlth the corner pads 9 at the tnner end of the openlng 27 so that the base 7 of the membrane 2 seals the key button structure relatlve to the board 21 around the hole 5 and the cut-outs 20 in the slde walls of the button 3 provlde clearance for the tongues 29 on depresslon of the button 3 to actuate the swltch devtce.
By securlng the key button structure to the case 28, the area of the clrcult board 21 that can be utillsed for clrcult connectlons ts increased as compared wlth the first embodlment in whlch the key button structure Is secured to the board 21.
Addltionally, as shown Tn Figure 6, the membrane base 7 Is arranged to ralse the underslde of the base plate l above the board 21 provldlng a clearance space 30 In which solder contacts 31 may be arranged thereby Increaslng further the area for maklng electrlcal contacts. Thls has advantages where avallable space is llmlted, for example for manufacture of small slze keyboards havlng a plurallty of closely arrayed push buttons.
Another modifled key button structure Is shown In Flgure 7 In which llke reference numerals are used to Indlcate parts correspondlng to the flrst embodlment.
The key button structure Is comprlsed of base plate 1 and membrane 2 releasably secured to the clrcult board by the dependent legs 4 of the base plate 1 and the push button 3 Is slldably mounted In the opening Z7 of the outer case Z8. The : . ~

209~001 01 push button 3 is retained in the raised posltlon under the biassing of the membrane 2 by engagement of an external projection 32 in an axtal guide slot 33 Tn the openlng 27.
Referring now to Flgures 8 and 9, a swTtch assembly 05 incorporating a second embodiment of a key button structure is shown Tn which like reference numerals in the series 100 are used to 7ndicate parts correspondlng to the first embodiment.
The base plate 101 has an open grid structure comprlsed of a square array of sixteen uniformly spaced circular holes 105 defined by ring elements 134 with interconnecting webs 135 Untformly spaced around the marginal edge of each hole are four guide posts 106 upstanding from the base plate 101 on which a respectlve push button 103 is located for axial slidlng movement.
Each button 103 is of square shape In plan view havlng a top wall 111 and dependent side walls 112 definlng a square recess 113 open to the underside in whlch the guide posts 106 are recelved.
Each guide post 106 Is positloned adJacent to a corner of the reoess 113 and has radiused outer corner edges 106a engageable with adjoinlng side walls 112 of the button 103 to locate the button 103 for axial sliding movement relatlve to the base plate 101 and prevent the button 103 tilting or rocking on the guide posts 106.
Each hole 105 is provtded with a resTliently flextble elastomerlc membrane 102 of frusto-conlcal shape having an annular base 107 that seats around the hole 105 In a counterbore 105a on the underslde of the base plate 101, and a platform 108 at the apex centrally positloned between the guide posts 106 on the oppodite side of the base plate 101.
Each membrane 102 is moulded onto the base plate 101 and has formed Integrally therewlth on the upper surface of the base plate 101, an annular pad 109 encircling the associated gulde .

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20~0~1 - 1 o -01 posts 106 and connected to the base 107 of the membrane 102 through orifices 110 in the base plate 101 to secure non-releasably the membrane 102 and base plate 101.
Upstanding from the base plate 101 adjacent to each corner 05 are four ptllars 136 for locatTng and securtng the base plate 101 to an outer case 128 having a matchlng array of slxteen openlngs 127 altgned wtth the buttons 103.
; Each button 103 ts retaTned on the gutde posts 106 tn a ralsed tnoperattve or rest posttton projecttng through the altgned opentng 127 under the btasstng of the assoctated membrane 102 by engagement of an external flange 137 wtth the understde of the case 128 around the opentng 127. Alternattvely, each button may be retatned tn the ratsed posttton by engagement wtth the gutde posts, for example by retatner arms stmllar to the ftrst and second embodtments.
The key button structure secured to the case 128 Is assembled onto a prtnted circutt board 121 to altgn each hole 105 tn the base plate 101 wtth a respecttve swttch devtce comprtstng a patr of ftxed swltch contacts 125 on the board 121 and a movable contact 126 secured to the underside of the platform 108 that ts spaced above the fixed contacts 125 tn the rest posttton of the assoctated button 103.
The switch devtces are selecttvely actuable by depresslon of the approprtate push button 103 to lower the movable contact 126 onto the ftxed contacts 125 agatnst the btasstng of the assoctated membrane 102 whtch provtdes a sprtng functton for ; returnlng the button to the inoperative posttton on releaslng the button 103.
The key button structure ts sealed relattve to the board 121 around each hole 105 by the base 107 of the assoctated membrane to prevent tngress of contamtnants and excesstve actuatlon forces are cushioned by engagement of the button 103 wtth the pad 109 for user comfort and to prevent damage to the swltch contacts 125,126.
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01 By uslng a common base plate for a plurality of buttons, thekey button structure can be adapted for dlfferent applIcations by changlng the buttons. It wlll be understood that the number and posltlon of the openings In the base plate may be altered to 05 provlde any deslred array of buttons for a gtven appllcatlon.
In the above-descrlbed embodlments, the base plate 1,101 Is convenlently a mouldlng of substantlally rlgld plastlcs such as polyphenylene sulphTde onto whlch the elastomerlc membrane(s) 2,102 is/are moulded to form an Integral sprlng unlt for the button(s) 3,103. Sultable elastomers for the membrane(s) 2,102 Include sillcone rubber and each push button 3,103 Is convenlently a mouldlng of substantially rlgld plasttcs such as acrylonltrlle butadlene styrene.
It wlll be understood that the Inventlon Is not llmlted to the embodiments above-descrlbed. For example, the actuatlon portlon of each push button may be rectangular or any other shape as deslred such as circular or oval. Thus, In the above embodlments, an actuatlon portlon of the desired shape may be provlded by an upstand on the top wall of the button arranged to proJect through the openlng In the case.
The base plate may be of rectangular or other sultable shape and/or the openlng(s) may be of circular or other sultable shape as deslred for a glven appllcatton.
The base plate may have a pluralIty of gulde posts or other sultable gulde means assoclated wlth each openlng for axlally locatlng the push button(s) wlth optlonal co-operatlng formatlons for retalnlng the push button(s) In a ralsed posltlon under the blasslng of the assoc7ated membrane. Where the base plate Is provlded wlth gulde posts, the number and arrangement may be chosen to sult the slze and shape of the openlng(s) In the base I plate and/or the recess In the button.
The base plate may be adapted for securing to the board or case by any sultable means. Where the base plate Ts provlded . .
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~0~01 01 with resllient legs, tongues or slmllar formatlons, the number and arrangement may be chosen to suit the slze and shape of the base plate. The formations may retaln the base plate by self-latchlng or frlctton engagement wlth the board or case as 04 desired.
The membrane(s) may be permanently secured to the base plate by any suitable formations providlng a mechanTcal key between the membrane(s) and the base plate. Alternatlvely, or additionally9 mould1ng of the membrane(s) onto the base plate may be controlled so that the the membrane(s) bond to the base plate.
The key button structure may be arranged for actuatton of any suitable switch device allgned with the hole(s) In the base plate and the Inventlon is not llmited to the exemplary switch device above-described.
It wlll be appreciated tha~ the integral sprlng unlt formed by ths base plate and membrane(s) has advantages for manufacture of keyboards incorporating the Invented key button strueture.
Thus, the number of separate components for assembly Is reduced and a common sprlng unlt may be used wlth dlfferent push button(s). Where provlded, the Internal gutde means posltively locates the push button throughout its travel and enables the overall helght to be reduced to a minimum producing a compact assembly sultable for a wlde range of appllcatlons wlth optlonal retentlon of the push button(s) on the gulde means provlding further assembly beneflts.
Other beneflts and adavantages of the tnvention wtll be apparent to those skllled In the art and the Inventlon Is deemed to Include all modlflcatlons and varlatlons wlthln the scope of the appendant clalms.

Claims

1. A key button structure for a switch assembly comprising a base plate having an opening defining a switch site, and a resiliently flexible membrane integral with said base plate and arranged to provide a return spring function for a push button.

2. A key button structure according to Claim 1 wherein said base plate has guide means for locating a push button for axial sliding movement towards and away from said base plate.

3. A key button structure according to Claim 2 wherein said guide means Is positioned around the marginal edge of said opening and extends to one side of said base plate.

4. A key button structure according to Claim 3 wherein said guide means comprises a plurality of guide posts spaced around the marginal edge of said opening in said base plate.

5. A key button structure according to Claim 4 wherein there are four guide posts for location at respective corners of a square recess in a push button to engage adjoining side walls along the outer corner edges of said guide posts.

6. A key button structure according to Claim 3 including a push button retained in a raised Inoperative position under the biassing of said membrane by engagement with said guide means.

7. A key button structure according to Claim 6 wherein said push button has retainer means engageable with said guide means.

8. A key button structure according to Claim 7 wherein said retainer means Is releasable for detaching said push button.

9. A key button structure according to Claim 1 wherein said base plate is adapted for securing to a carrier.

10. A key button structure according to Claim 9 wherein said base plate has integral attachment means for securing to a carrier.

11. A key button structure according to Claim 10 wherein said attachment means comprises a plurality of resilient formations.

12. A key button structure according to Claim 11 wherein said formations are self-latching.

13. A key button structure according to Claim 12 wherein said formations are releasable.

14. A key button structure according to Claim 1 wherein said membrane is adapted for actuating a switch aligned with said opening In said base plate.

15. A key button structure according to Claim 14 wherein said membrane is arranged to seal around said opening In said base plate.

16. A key button structure according to Claim 15 wherein said membrane is of frusto-conical shape having a base seated around said opening on the underside of said base plate and a raised platform on the opposite side of said base plate for engagement with a push button.

17. A key button structure according to Claim 1 wherein said base plate has stop means for limiting resiliently depression of a push button against the biassing of said membrane.

18. A key button structure according to Claim 1 wherein said base plate has a plurality of openings defining switch sites for a plurality of push buttons, and each opening has a respective resiliently flexible membrane integral with the base plate to provide a return spring function for a push button.

19. A push button switch assembly for a keyboard of a data input device comprises a base plate having an opening defining a switch site, guide means integral with said base plate and extending to one side thereof around the marginal edge of said opening, a push button located and retained on said guide means for axial sliding movement towards and away from said opening, a resiliently flexible membrane integral with said base plate and biassing said push button to a raised inoperative position, and said base plate having integral attachment means for securing to a carrier.

20. A push button switch assembly according to Claim 19 wherein said base plate has a plurality of openings defining a plurality of switch sites for a plurality of push buttons.