Note: Descriptions are shown in the official language in which they were submitted.
2 0 '~
(45 309 c) FLAT PI~ZOELECTRIC KEYBOARD
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention is directed to a flat key-
board comprising a base laminate or foil, respectively, a cover
laminate or foil, respectively, and piezoelectric elements
arranged between said laminates or foils, respectively, and
defining key locations of said keyboard, which piezoelectric
elements generate an electric signal upon mechanical bending of -
said elements almost without travel.
2. DESCRIPTION OF THE PRIOR ART
Such a keyboard is known e.g. from the European
Patent No. 210 386 (corresponding to U.S. Patent No.
4 857 887). In this keyboard a rigid~spacer laminate is pro-
vided between the base laminate and the cover laminate. The
: ,
spacer laminate is provided with recesses for receiving the
piezoelectric elements and has a thickness that corresponds to
the~thickness of the elements. This rigid spacer serves for
posit~ioning the piezoelectric elements, for separating the
conducting ætrips provided on the base and cover laminate, and
for reducing cross talk between adjacent keys.
: ~ : :: : :
~: :
2 2 ~ 3 ~
Such a spacer laminate leads to additional working
operations during manufacturing of the keyboard. Further, three
laminates and adhesive layers are necessary.
Piezoelectric keyboards are further known from U.S.
Patent No. 4,458,173 and No. 4,618,797 and from French Patent
Application No. 2 576 726.
SUNMARY OF THE INVENTION
It is therefore a general object of the invention
to provide a keyboard of the aforementioned type that does not
exhibit these disadvantages. Now, in order to implement this
and still further objects of the invention, which will become
more readily apparent as the description proceeds, the keyboard
is manifested by the features that the base and the cover
laminate are directly connected to each other and are forming
blister-like chambers between each other, each of said chambers
containing one of said piezoelectric elements.
By these features, the spacer laminate can be
eliminated without adversely affecting the function of the
keyboard. The keyboard can be manufactured with less working
operations and with less thickness.
::
: ' ~ : -
, ~ ' . ' , '
:, , :
-
2 $ ~ 't ~
BRIEF DESCRIPTION_OF_THE DRAWINGS
The invention will be better understood and objectsother than those set forth above will become apparent when
consideration is given to the following detailed description
thereof. Such description makes reference to the annexed
drawings, wherein:
Pigure 1 is a sectional vîew of a first embodiment
of the flat keyboard;
Figure 2 is a sectional view of a keyboard
according to Fig. 1 with an additional support plate;
Figure 3 is a schematic representation of a first
way to produce a keyboard according to the invention;
Figure 4 is a sectional view of another embodiment
of the flat keyboard with an additional support plate;
: Figure 5 is a sectional view of a third embodiment
of the~keyboard with additional support plate;
Figure 6 i8 a schematic representation of an
arrangement of the conducting strips;
Figure 7 is a sectional view of a keyboard
:according to the first embodiment with an additional rigid
: front panel;
m ~ Figure 8~is yet another embodiment of the keyboard
with a bulged out cover and base:laminate;
Figure 9 is an:embodiment of the flat keyboard,
:wherein the cover laminate is provided wlth recesses for the
;: ~
' ' ' ' , : '
.
,:
.. : .
'
4 2 ~
piezoelectric elements;
Figure 10 is a second schematic representation of
the production of a keyboard according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The general construction of the flat keyboard will
be explained first, with reference to Fig. 1. The use of the
terms cover laminate and base laminate in the following
description does not exclude that the keyboard can be used -
depending on the application - in inverted position, i.e. with
the base laminate forming the key area. Figure 1 shows a sec-
tional view of two ad~acent keys 1, 2 of the keyboard. The
keyboard i8 provided with a base laminate or base foil 3,
respectively, and a cover laminate or cover foil 4, respec- -
tively. These laminates enclose the piezoelectric elements 5
between them at each key 1, 2. The piezoelectric elements are
platelet shaped ceramic or~crystal elements. When stressed
méahanicaily, a voltage is generated between the upper and the
lower surface o~ the platelet, which voltage can be picked off
and can be detected as;key actuation signal by an interface
circuit, as well known. Each piezoelectric element 5 is mounted
on a~disc-like metal or~ceramic support 7, which support lends
mechanical stability to the element and serves at the same time
as the~lower contact surface for the element.
The piezoelectric elements are each provided with a
`
:
:' ' ' ' ~ . " " . . . '' '
contact layer 10 of conducting material on their upper sur-
faces. The lower contact surface 7 and the contact layer 10
each are in contact with conducting strips arranged on the
inner surfaces of the laminates or foils, respectively, as will
be described in detail below.
Either the cover laminate 4 or the base laminate 3
or both laminates can be bulged out at each key l, 2, so that
chambers 6 between cover laminate and base laminate are formed,
each for receiving a piezoelectric element. The dimensions of
these chamberæ conform essentially to the piezoelectric element
and its support 7 contained within the chamber. In the embodi-
ment of Fig. l, only the cover laminate 4 is provided with the
bulged out zones, so that the base laminate 3 is flat.
The base laminate 3 and the cover laminate 4 are
attached to each other between chambers 6, e.g. by means of an
adhesive layer 8 or by laminating or by lamination coating. The
chambers 6 are therefore blisters between the two foils 3, 4
attached to each other, the blisters containing the piezo-
electric elemQnts 5, 7. The actuation of the keys is neverthe-
le~s possible since the actuation occurs almost without tra~el
as will be described below.
Now, with reference to Fig. 2, the function of the
keyboard will be described in detail. The flat keyboard as
shown in Fig. 1 has been arranged on a support plate 9 by means
of a transfer adhesive 19 which has openings 14 at the key
locations. The transfer adhesive (e.g. the type no. 468 of the
r~ ~
3M Company) may have a thickness of approximately only 1/10
millimeter. The openings 14 make sure that the piezoelectric
elements S are bendingly stressed when the key is actuated. The
elements stressed in the bending mode but almost without
detectable travel generate a voltage signal that is used as the
key actuation signal. In Figure 2, the actuation force K on the
cover laminate 4 of key 2 is represented by an arrow. Since the
cover laminate abuts on the base laminate 4 in the intermediate
area between the keys and is attached to the base laminate, the
actuation force K will be completely absorbed by this inter-
mediate area, even if the cover laminate is a rather stiff
material. Accordingly, no crosstalk occurs between adjacent
keys 1, 2, even if these keys are located close together.
Since almost no travel occurs during actuation of
the keys, the stress on the cover laminate 4 is minimal.
As mentioned before, the cover laminate 4 may be
made of relatively stiff material. In such a case, the bulges
11 are permanently embossed in the cover laminate or foil 4,
respectively. If a relatively elastic laminate is used, the
bulges will form by elastic deformation of the laminate, as
shown in the examples o~ Fig. 4 and Fig. 8. In both cases, a
rounded, edgeless shape of the bulges 11 will reduce the
mechanical stress in this area.
Figure 4 shows an embodiment of the invention where
the element 5 and the metal support 7 have a convex shape. The
metal support 7 abuts on the laminate 3 only with its periphery
- . ~ '' '; ' ' .
. .
. . . ~
, .
~ ~ ~ 9 ~
and can be stressed to bend elastically in its center. Accord-
ingly, the piezoelectric element S is stressed in the bending
mode and generates a voltage signal. The signal is generated
even if there is almost no travel and, therefore, essentially
without a detectable depression of the bulge 11 of the cover
foil 4. The base laminate 3 is supported by a support plate 9
as has been described before, with the exception that no
openings 14 in a transfer adhesive layer are necessary with
this embodiment. It is therefore possible to make the base
laminate 3 itself in the form of a rigid support plate.
The same holds true for the embodiment of Figure 5.
In this embodiment the bending stress of the pie20electric
element 5 on the support 7 is caused by a knob 13 on the cover
laminate 4 and by a circular rest 12 on the base laminate 3.
To pick off the voltage generated across each
piezoelectric element 5 upon actuation of the keys, the contact
surfaces 7, 10 of the elements are connected by conducting
strips with an interface circuit. The conducting strips are
~arranged on the inner surfaces of the base laminate and the
cover laminate, as already mentioned. The conducting strips can
be formed, e.g. by a printing process, as is well known.
Figure 6 shovs such an arrangement of conducting
strips in the boundary plane of the base and the cover
:
laminate. The conducting strips shown as black, filled out
strips 15 are arranged on the cover laminate and the conducting
strips shown as double line 16, forming a common contact, are
': '' . ' :'
::
' . ', ' ' .' ' ,
2 ~
arranged on the base layer. As can be seen, the conducting
strips 15 on the cover laminate intersect the conducting strips
16 on the base laminate only at the keys, so that no short
circuit occurs, although all conducting strips are arranged in
the same plane.
The upper and lower contact surfaces 10 and 7,
respectively, of the piezoelectric elements are contacted at
the intersections.
If an insulating adhesive layer 8 is used between
laminates 3, 4, or if insulated strips 16 are used, an
arrangement of conducting strips is possible which intersect in
the boundary plane. The cover foil or the base foil can be a
metal foil in this case and can perform as common ground con-
tact 16 for all of the piezoelectric elements. In this case,
the metal foil has to be provided with an insulating layer
except at the key locations to avoid a short circuit with the
~conducting strips 15. The insulating layer may serve as
adhesive 8 between foils 3, 4 at the same time.
The cover laminate and the~base laminate may be
plastic foils ~or metal foils). The base laminate may have a
thickness of approximately 0.4 milllmeters and the cover
laminate of approximately 0.1 millimet~rs.
Figure 3 represents schematicalIy a first method
for joinlng laminates 3, 4 together to form a flat keyboard.
This method is suitable for relatively rigid, platelike
arrangements of limited size. First, the piezoelectric elements
- - - - .-
- .
., - .: , .
- - " . -- : . . - .
', ' '. : . . -:
, ~
2 ~ t~
5, already mounted on their supports 7, are arranged on the
base laminate. To this end, areas 17 on the base laminate are
left free of adhesive 8, if such adhesive is used. Afterwards,
the cover laminate 4 is pressed against the base laminate 3 by
means of a tool 18 (only represented schematically) which is
provided with recesses 19 corresponding to the bulges 11.
The tool 18 may be heatable so that the cover
laminate 4 and the base laminate 3 are laminated together by
pressure and heat.
The cover laminate may have been provided before-
hand with embossed bulges 11, or the bulges may be produced
only during the joining of cover and base laminates. If an
elastic cover laminate 4 is used, this element will elastically
stretch over the piezoelectric element (see e.g. Fig. 4). In
this way a small force acts permanently on the element which
insures good electrical contact of the element.
If the production process shown in Figure 3 is
carried out ln an atmosphere of inert gas, the blisters remain
filled with this gas, preventing oxidation of the contact
surfaces over a long time, insuring the faultless operation of
the keys.
Figure 10 represents schematically another produc-
tion process for producing flat keyboards continuously. The
base laminate and the cover laminate, which have been provided
with conductor strips by a printing process beforehand, are
joined together continuously~between two rollers 22, 23.
2 ~
Beforehand, an adhesive 8 has been applied to the base laminate
except at the areas 17. The piezoelectric elements 5 mounted on
their supports 7 are placed at these areas before joining the
laminates. The rollers 22, 23 are provided with corresponding
recesses 24, avoiding that a high pressure is exerted on the
elements 5 and that the elements 5 are damaged. Instead of
glueing the laminates together, the laminates may be heat
sealed.
By the described process a flat keyboard in the
form of a band is produced. Single keyboards may be cut from
the band. As can be seen in Figure 8, bulges 11 can be provided
on the base laminate as well as on the cover laminate. The
bulges 11 on the base laminate extend into the openings 14 of
the transfer adhesive layer 19.
The cover laminate may constitute directly the top
surface of the keyboard, especially if rather thick cover
laminates 4 are used.
If the keyboard has to have an essentially flat top
surface or an especially resistant top surface, a rigid front
panel 20 is mounted atop of the laminate 4, as shown in Figure
7. The~front panel may be a metal panel or a plexiglass panel
o 5 millimeter thickness, which is provided with recesses 21
at the keys 1, 2 receiving the bulges 11. The panel has thus a
reduced thickness of approximately 2 millimeters at the key
locations, providing weaker areas of the panel for transmitting
the key actuation force to the construction below.
, , ~,. . , ., . . :
,
2 ~
The front panel abuts with the weakened zones on
the bulges 11 and with the nonweakened zones on the cover
laminate areas between the k~ys. In this way, cross talk
between the keys is prevented in this embodiment as well. The
front panel embodiment secures the keyboard against damage,
especially against vandalism, but provides a keyboard with only
a small increase of total thickness. Instead of the panel 20, a
cover layer produced by using a sealing compound, e.g. resin,
may be used. In this way, the locally weakened zones above each
key are produced automatically when the compound is provided on
the cover laminate.
The front panel may conætitute the cover laminate 4
at the same time as shown in Figure 9. Recesses 25 in the bot-
tom surface of this front panel 4 are forming the chambers 6.
The flat keyboard as described is suitable for a
multitude of uses, especially where keyboards are subject to
high mechanical stresses and humidity. The sensitivity of the
travelless keys can be adjusted by selecting the thickness of
the cover laminates or front panels, respectively, and by the
interface circuit.
While there are shown and described present pre-
ferred embodiments of the invention, it is to be distinctly
understood that the invention is not limited thereto, but may
be otherwise variously embodied and practiced within the scope
of the following claims.
