Note: Descriptions are shown in the official language in which they were submitted.
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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
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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.,
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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
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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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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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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.
