FR2576449A1 - Keyboard with integral control elements with predetermination of the law for pressurising their electroconductive element, and method of manufacturing this keyboard - Google Patents

Abstract

The subject of the present invention is a keyboard with control keys 1c. The keyboard according to the invention includes a means providing a deformable link between the electroconductive element or a control key and the body 4c of each key, which consists of a shroud 10 having the form of a hollow body provided with a thin bottom delimiting with the key body an air-filled space which allows the bottom of the shroud to move upwards when the corresponding key is actuated. Application to apparatuses including a control keyboard with keys or the like.

Description

 The present invention relates to control keyboards, of the type comprising control elements, such as keys or the like, integrated in a membrane, in particular made of elastomer, and having an extended contact stroke of which the law of placing can be pre-established. pressure of the electroconductive element of the membrane on the keyboard printed circuit.

 The invention also relates to a method for manufacturing the aforementioned keyboard.

 In the prior art, two families of keys are encountered - the "single stroke" keys, and - the "extended stroke" keys.

 With regard to the "single stroke" key technology, this leads to contacts of electroconductive pads / tracks which are often random, mainly due to a non-parallel approach between the electroconductive pad of a key and the tracks. electrically conductive circuit board underlying the keyboard, which can lead to a complete absence of electrical contact.

 The uncertainty in establishing this electrical contact, which is often unacceptable in the case of professional-class keyboards, is essentially due to the design of the keyboard, in particular the system for centering the keys relative to the front face of the keyboard. and drawing the electrically conductive tracks of said printed circuit.

 With regard to the "extended stroke" keys, which are double-veil keys and which have greater reliability in terms of the abovementioned electrical contact (compared to the "single stroke" keys), these are outside the scope of the present invention since they are not keys of the so-called integrated type (in the keyboard membrane).

 The object of the present invention is therefore to provide a control keyboard, of the type comprising control elements integrated in a membrane, in particular an elastomer, which respond better to the necessities of practice than keyboards aiming at the same aim previously. known, in particular in that the reliability of the electrical contact between the electroconductive element of a key and the corresponding tracks of the printed circuit of the keyboard is significantly improved, and in that one can even pre-establish the law of pressurization of the electroconductive element on said printed circuit.

 Another object of the invention is to provide a method of manufacturing the keyboard according to the invention.

The subject of the present invention is a control keyboard, of the type comprising control elements such as keys or the like integrated into a membrane, in particular made of elastomer or any other thermoplastic material, which membrane - comprises a flat part and body of keys, who are provided
at their lower part of an electrically conductive element and
which protrude from said flat part, to which they
are attached via a deformable veil
main comer of molding, and - is supported by a printed circuit on which are
deposited electrically conductive tracks, which keyboard is characterized in that it comprises means ensuring a deformable connection between said electrically conductive element and the corresponding key body.

 According to a preferred embodiment of the keyboard according to the invention, the means for connecting said electroconductive element to the corresponding key body is constituted by a secondary deformable veil, in particular also made of elastomer, which has the shape of a hollow body provided with '' a thin bottom and a side wall, also thin, which delimit by cooperation with the underside of said touch body a space, filled with air, allowing the upward movement of the bottom of the secondary veil following the deformation of the latter by pressing the corresponding button.

 According to a preferred arrangement of this embodiment, the electroconductive element is constituted by an electroconductive insert which is secured to the bottom of the secondary web, in particular during molding.

According to an advantageous variant of this arrangement, the electroconductive element is constituted by the secondary deformable veil itself or at least by the bottom or a portion of this bottom, which are made conductive of electricity by introduction of an electroconductive charge. suitable trice, in particular constituted by carbon black or carbon fibers
According to another advantageous arrangement of this embodiment, the secondary deformable veil comprises an annular flange which projects outwards from its wall, preferably at the opening of said hollow body.

 According to another advantageous embodiment of the keyboard according to the invention, said electroconductive insert and / or the bottom of said deformable web are provided with vents.

The present invention also relates to a method of manufacturing a control keyboard of the type comprising control elements such as keys or the like integrated into a membrane, in particular made of elastomer or any other thermoplastic material, which membrane - comprises a part plane and key bodies, which are
with an electro element at their bottom
conductor and which protrude from said planar part,
which they attach via a
main deformable web from molding, and - is supported by a printed circuit on which are
of electroconductive tracks, which method is characterized in that the electroconductive element of said membrane is produced separately from the other parts of the membrane, and in that it is then connected to said key body by means ensuring a deformable connection, according to the foregoing provisions.

According to a preferred embodiment of the method according to the invention, it comprises the following successive steps - molding of said key body, using a first
mold in two parts, lower and upper, - molding of said secondary deformable web, said element
electroconductive being constituted by an electro insert
conductor or by this same veil or at least its bottom or
part of this bottom, using a second mold in
two parts, lower and upper, - overmolding of the flat part and the main veil of the
keyboard membrane with key body and veil
secondary thus formed, by cooperation of the party
upper and lower part of said first and
second mold, respectively.

According to an advantageous variant of this embodiment, it comprises the following successive steps - molding of the entire keyboard membrane, - molding of said secondary deformable veil, said element
electroconductive being constituted by an electro insert
conductor or by the secondary veil itself or at least
its bottom or a portion of this bottom, - assembly of the membrane and the secondary veil as well
formed by any suitable means, in particular by bonding
Or other.

 In addition to the foregoing provisions, the invention also comprises other provisions, which will emerge from the description which follows.

The invention will be better understood with the aid of the additional description which follows, which refers to the appended drawings in which - Figure 1 schematically illustrates in particular the
membrane of a keyboard with so-called single stroke keys "
integrated into this membrane, - Figure 2 illustrates in planes (s, f) and (s, r) the
qualitative patterns of the forces f and the resistance of
contact r as a function of displacement s corresponding to
actuation of a key of the type shown in the figure
1, the diagrams (s, f) and (s, r) being associated between
them, - Figures 3 and 4 correspond to Figures 1 and 2 in
the case of a keyboard membrane with so-called "d stroke" keys
extended ", - Figures 5 (a and b) schematically represent two
embodiments of keyboard membranes according to the invention, - Figures 6 (a, b and c) schematically
alternative embodiments of the secondary veil
according to the invention, FIG. 7 compares qualitatively the shape of the force
f in the plane (s, f) in the case where said secondary veil
is provided with vents relative to the absence of vents, - Figures 8a, 8b and 8c schematically show views
in section relating to three successive stages of a process
for manufacturing the membrane according to the invention, corresponding to
as shown in Figure 5a.

 It should be understood, however, that these drawings and the corresponding descriptive parts, are given solely by way of illustration of the subject of the invention, of which they do not in any way constitute a limitation.

 Before describing the invention in detail, it is useful to recall the notion of "ergonomics" of a keyboard key and how electrical contact is established between the electroconductive element of the key body and the corresponding electroconductive tracks deposited. on the keyboard's underlying printed circuit.

Let us first refer to a "single stroke" keypad (see Figure 1) integrated into a membrane3a obtained by molding an elastomer (silicone, for example) or any other thermoplastic material, which includes - a key body 4a, which may or may not be marked, on its
upper part, - said electrically conductive element, which is notably constituted
killed by an electrically conductive patch-5, often performed
using an elastomer of the same kind as the body of
button 4a but doped with capable electroconductive charges
to make it conductive of electricity, - a deformable part 6, known as the touch screen, the
design (dimensions, shapes, etc.) conditions
the "ergonomics" of the corresponding key la, - a relatively rigid lower flat part 7, in
which are integrated the keys la, and - a printed circuit 8, on which are arranged said
electrically conductive tracks 9.

 The curve represented in FIG. 2 corresponds to the recording made by a dynamometer (not shown) coming to press on the key body 4a. A measuring cell (not shown) records the force f exerted by the dynamometer descending at constant speed.

We can distinguish two zones I and II,
In zone I, only the veil 6 offers resistance to displacements: more precisely, the veil is first of all subjected to a prestress, with the force f rising until it reaches the value fN, so-called nominal activation force (see point A of curve a). At this moment the veil flexes and the key body 4a sets in motion until it comes into contact, via its pad 5, on the printed circuit 8: we are on the point
C of curve a which defines the start of zone II.

 In zone II, the curve a having the shape a2 corresponds to the difference between the force exerted by an operator (cf. curve b) and the restoring force of the deformed veil 6 (cf. curve a1): this difference is called "contact force" exerted on the pad 5 and corresponds to the restoring force of the elastomeric key body 4a, namely the reaction of the printed circuit 8 which manifests itself when the pad 5 is in contact with this circuit.

 The curve a1, which corresponds to the restoring force of the veil and which is drawn in dotted lines, represents the appearance that the curve a would have if the veil 6 was alone.

The hatched area to the right of point C between curves a1 and a2 represents the work done
1 by said contact force.

 In FIG. 2, the diagram (s, f) has been associated with the diagram (s, f) representing the variation of the resistance r of the pad / track contact as a function of the displacement s: we see that in correspondence of the point C of the curve (s, f), the curve (s, r) has a vertical asymptote with respect to which one can define a "random contact zone" in which the contact resistance is above a determined value rc.

 This contact resistance r is influenced by certain parameters, the main ones of which are the shape of the patch and that of the electroconductive tracks.

 That said, it should be pointed out that the contact stroke sc, namely the diagram (s, f) - is all the more reduced when the contact body is massive and the restoring force of the veil is large.

 It is true that to reduce the risk of a random docking between the patch and the corresponding tracks, it would be possible to adopt a design of strongly nested tracks, in particular by electrolytic offset of these tracks on said printed circuit (preferably copper, but one can also use tin tin etc ...); however, the coating processes by electrolytic deposition tend to be replaced more and more, for economic reasons, by the processes of screen printing (inks, carbons, silver, etc ...), which involves an imprecision of deposition such that the design of the electroconductive tracks of the printed circuit is ultimately coarse and essentially results in a change - without elimination - of the hazard terms.

 It is to improve the reliability of the contact that, in the prior art, a key profile, called "extended stroke", has been designed (cf. FIG. 3 and the reference lb), which makes it possible to increase the contact stroke (see Figure 4). The contact force (which also in this case is given by the difference between the force exerted by an operator and the restoring force of the veil) is in particular equal to the deformation force of the secondary veil 6 ~, which is defined by the presence, in the membrane 3b, namely in the touch body 4b, of a flange 2 for applying force on the main veil 6a. The action of the veil 6b ctinsnce to manifest itself when the pellet comes contact on the printed circuit (see point C 'of shape a'1 and curve a'3 in Figure 4) and ends when the upper part of the elastomeric key body 4b comes into contact with a system of activation which is applied to said flange 2 and which is constituted, for example, by a plastic cap (not shown): it can therefore be seen that a "long stroke" key is in no case usable when the bodies of keys are integrated in the keyboard membrane. (Also in this cash the hash surface urea in FIG. 4 and lying between curves a'1 and a'2, corresponds to the work carried out by the contact force in the case of a "long stroke" key).

 The present invention aims to extend to the keys integrated in a membrane, in particular an elastomer, the principle of increasing the contact stroke which is the basis of said keys "with extended stroke".

 For this purpose, a means is used which ensures a deformable connection between the electroconductive element and the corresponding key body.

 Figures 5 and 6 show a non-limiting example of this deformable connecting means which is constituted by a secondary web 10 in the form of a hollow body provided with a thin bottom 11 and a side wall 12, also thin, which delimit, by cooperation with the lower face 13 of the key body 4c, a space 14 (filled with air) which allows the displacement of the bottom 11 of the veil 10, following the deformation of the latter by actuation of the corresponding button.

With regard to the electroconductive element, this consists - preferably by an insert 15 (cf. FIG. 6c) and
secured, particularly during molding, with the bottom 11 of the
veil 10, - either constituted by veil 10 itself or at least by
its bottom 11 (cf. FIG. 6a) or a portion 11a of this
background (cf. Figure 6b), in particular by introduction into
the mass of 11 elastomer constituting the web 10 of a
suitable electroconductive charge, especially black
or carbon fibers.

 The secondary web 10 may advantageously comprise, in each case, an annular flange 16 (cf. FIG. 5a) which projects outwards from the wall 12 of the web and which is arranged in particular at the opening 17 of the hollow body 10.

 The appropriate dimensioning of the electrically conductive insert 15 or of said electrically conductive portion of the base 11, in particular in terms of shape and thickness, makes it possible to pre-establish the law of pressure rise of the electrically conductive element on the printed circuit 8.

 More precisely, when by pressing the key ic according to the invention the electroconductive element comes into contact with the printed circuit 8, the deformable veil 10 ensures a progressive pressurization of the electroconductive element on this printed circuit, which increases the contact stroke and self-stabilizes the electrically conductive element on the circuit.

 It is advantageously possible to subsequently increase the contact stroke of the keys according to the invention, by providing vents (not shown) in the electrically conductive element and / or in the bottom of the deformable web 10: in fact, in this way, the air located in the space 14 freely escapes through these vents promoting greater deformation of the web 10, namely of its bottom 11.

FIG. 7 makes it possible to compare qualitatively the stroke of contact s' without vents with the stroke of
c contact s "c with vents (see curves a * 2 2 and ae2, respectively).

Figures 8a, 8b and 8c schematically show the successive phases of a preferred manufacturing process, relating to the keyboard membrane illustrated in Figure 5a (presence of an annular flange). In this case, the manufacturing process comprises the following successive steps - molding of the key body 4b using a mold 18 in
two parts A * and C * (cf. Figure 8a) ;; - molding of the secondary deformable veil 10, the electric element
troconductive being constituted by an insert 15 or by the veil
itself or at least its bottom or a portion of this bottom,
using a mold 19 in two parts C * and D *,
(see Figure 8b) - overmolding of the main wall 6 and the flat part 7
keyboard membrane 3c with veil 10 and body
key 4- thus formed by cooperation of the parties
A * and D * of molds 18 and 19.

This method has the advantage of being able to mold the key body and the remaining portion of the membrane separately (flat part and main veil), which makes it possible to use, if necessary, for the key body a material having the same nature but greater hardness compared to the material used for said remaining portion of the keyboard membrane: the result is easier centering relative to the front face (not shown) of the keyboard -
As regards the method of manufacturing the keyboard membrane illustrated in FIG. 5b, it comprises the following successive steps: - molding of the entire membrane (key body,
main wall and flat part), - molding of secondary wall 10 (as in the process
previous), - assembly of the membrane and the secondary veil by all
suitable means known per se, such as bonding or the like.

 As is apparent from the above, the invention is in no way limited to those of its modes of implementation, embodiment and application which have just been described more explicitly; on the contrary, it embraces all the variants which may come to the mind of the technician in the matter, without departing from the framework, or the scope, of the present invention.

Claims (9)

 1.- Control keyboard, of the type comprising control elements such as keys (1c) or the like integrated into a membrane (3c), in particular made of elastomer or any other thermoplastic material, which membrane - comprises a flat part (7) and key bodies  (4c), which are provided at their lower part with a  electrically conductive element and which protrude from said  flat part, to which they are attached by the intermediary  diary of a main deformable veil (6) from  molding, and - is supported by a printed circuit (8) on which are  deposited electrically conductive tracks (9), which keyboard is characterized in that it comprises means ensuring a deformable connection between said electrically conductive element and the corresponding key body (4c).  2.- control keyboard according to claim 1, characterized in that the means for connecting said electroconductive element to the corresponding key body (4c) consists of a secondary deformable veil (10), in particular also made of elastomer, which has the form of a hollow body provided with a thin bottom (11) and a side wall (12), also thin, which delimit by cooperation with the lower face (13) of said key body (4c) a space (14), filled with air, authorizing the upward movement of the bottom of the secondary wall following the deformation of the latter by actuation of the corresponding key.  3.- control keyboard according to claim 2, characterized in that the electroconductive element is constituted by an electroconductive insert (15) which is secured to the bottom (11) of the secondary web (10), in particular during molding.  4.- control keyboard according to claim 2, characterized in that the electroconductive element is constituted by the secondary deformable veil itself (10) or at least by the bottom (it) or a portion (lia) of this bottom , which are made electrically conductive by the introduction of an appropriate electroconductive charge, in particular consisting of carbon black or carbon fibers.  5.- control keyboard according to claim 2, characterized in that the secondary deformable veil (10) has an annular collar (16) which projects outwards from its wall (12), preferably at the level of the opening (17) of said hollow body (10).  6.- control keyboard according to any one of claims 2 to 5, characterized in that said electroconductive insert (15) and / or the bottom (11, lita) of said secondary deformable veil (10) are provided with vents.  7.- Method of manufacturing a control keyboard of the type comprising control elements such as keys (ic) or the like integrated into a membrane (3c), in particular of elastomer or of any other thermoplastic material, which membrane - comprises a flat part (7) and key bodies (4c),  which have an element at their bottom  electrically conductive and which protrude from said part  plane, to which they attach via  a main deformable web (6) from molding, and - is supported by a printed circuit (8) on which are  deposited from the electroconductive tracks (9), which method is characterized in that the electroconductive element of said membrane (3c) is produced separately from the other parts of the membrane, and in that it is then connected to said key body (4c ) by a means ensuring a deformable connection according to claims 1 to 6.  8.- Method according to claim 7, characterized in that it comprises the following successive steps - molding of said key body (4c), using a first  wheel (18) in two parts (A *, B *), lower and upper, - molding of said secondary deformable web (10), said  electrically conductive element consisting of an insert  electrically conductive (15) or by this same veil (10) or  minus its bottom (11) or a portion (lia) of this bottom,  using a second mold (19) in two parts (C *, D *),  lower and upper, - overmolding of the flat part 17) and of the main veil  (6) the keyboard membrane (3c) with the key body  (4c) and the secondary web (10) thus formed, by cooperate  ration of the upper part (A *) and the lower part  lower (D *) of said first and second mold (18, 19),  respectively.  9.- Method according to claim 7, characterized in that it comprises the following successive steps: - molding of the entire keyboard membrane (3c),  molding of said secondary deformable web, said element  electroconductive being constituted by an electro insert  conductor (15) or by the secondary web itself (10)  or at least its bottom (11) or a portion (lia) of this bottom, - assembly of the membrane (3c) and the secondary web (10)  thus formed by any appropriate means, in particular by  collage or whatever.