FR2944351A1 - Device for detection of presence of user's finger at proximity of detection zone of capacitive-effect sensitive touch device, has conductive surface connected to conductive track using spacer that ensures electrical connection with surface - Google Patents

Abstract

The device has a support (7) including a conductive track (11) connected to an electronic circuit (4) used for measuring capacity variation. A conductive surface (3) is connected to the conductive track using a spacer (5), which is distinct from the conductive surface and the track, rests on the support, and is made of compressible conductive elastomer material. The spacer ensures electrical connection with the conductive surface while compensating height difference between an insulating body (2) of a sensitive touch device (1) and the support.

Description

The present invention relates to a device which makes it possible to detect, by capacitive effect, the presence of a conductive body in the vicinity of a determined detection zone. It relates in particular, but not exclusively, to a device for detecting the proximity of the end of a finger or a stylet with a detection zone consisting of a conductive surface 15 extending under an insulating body whose upper surface is the visible part of a touch pad.

It is known that there are sensitive keys each comprising an insulating body under which extends a conductive surface constituting a detection zone, which is connected to an electronic capacitance variation measuring circuit. In this way, the bringing together of a finger or more generally of a conducting body of the conductive surface causes a variation of the capacitance of the capacitor whose two armatures and the dielectric are constituted respectively by the finger, the conductive surface and the body. 25 insulation.

In addition, keyboards with touch sensitive keys of the above type are often associated with a display system which may consist of backlight illuminated LCDs, this display system and backlit means, which generally a thickness 1 of the order of two to ten millimeters, being disposed under said conductive surface.

However, the electrical connection between the conductive surface constituting a detection zone and the electronic circuit for measuring capacitance variation must be realized taking into account the height of this lighting system and this backlighting means, as well as the possible deformation of the sensitive keys during the contact of the finger of the user with the apparent face of said insulating body.

The invention therefore more particularly aims to solve this problem by proposing a device for detecting by capacitive effect the proximity of a conductive body of at least one determined detection zone, the latter being connected to an electronic measuring circuit capacitance variation so as to guarantee the electrical continuity and the absence of contact between the display system and the insulating body under which the detection zone extends.

For this purpose, it proposes a device for detecting by capacitive effect the proximity of a conductive body to a determined detection zone, this detection device comprising: at least one touch pad which comprises an insulating body under which extends a conductive surface constituting the detection zone; An electronic circuit for measuring capacitance variation connected to the conductive surface, this electronic circuit being included in a support; and characterized in that: • the conductive surface is integral with the insulating body; The support comprises at least one conductive track connected to the electronic circuit; The conducting surface is connected to a conductive track by means of at least one spacer, distinct from said conductive surface and from the conductive track, bearing on said support, constituted at least in part by a compressible conductive material, and which provides an electrical connection by contact with at least said conductive surface while compensating for any height differences between the insulating body and said support.

In this way, the compressibility of this electrical conductor ensures the electrical connection between the conductive surface and the electronic circuit while ensuring the absence of direct contact between the insulating body and a display system of the aforementioned type. In addition, advantageously, the sensitive key according to the invention makes it possible to satisfy the sealing and electrical isolation constraints.

In addition, advantageously, this device according to the invention makes it possible to separate the display function from the capacitive variation detection function. Indeed, the capacitive effect sensitive keys generally comprise a LCD (Liquid Crystal Display) type display device disposed under the insulating body, which comprises cells which are each framed by two longitudinally extending conductive surfaces, one of them being in contact with the insulating body. In this way, the contact of a finger or a conductive stylus with the apparent face of the sensitive key causes a variation of the electric field existing between these two conductive surfaces which are connected to an electronic circuit capable of detecting this variation. Thus, when the device according to the invention comprises a display system comprised in the space delimited by the insulating body and the electronic circuit, the latter does not participate in the capacitive variation detection function.

In addition, the device according to the invention advantageously allows a better ventilation of the display system which is no longer in direct contact with the insulating body.

According to a preferred embodiment of the invention, the armature constituted by said conductive surface is produced by the screen printing of a conductive ink which makes it possible to eliminate the presence of air between the insulating body and this conductive surface.

Advantageously, the touch pad is considered to be activated when the variation of capacity is greater than a predetermined threshold whose value has been defined so that the variation of capacity resulting from the contact of a finger of the user with the face apparent of the insulating body is greater than said threshold. Thus, preferentially, in the absence of contact with this apparent face, this threshold value is not exceeded, which makes it possible to avoid the inadvertent activation of the sensitive keys. The determination of this threshold is preferably established as a function of an average capacity value of the capacitor, which makes it possible to compensate for the dispersions due to the manufacture, to the evolution of the components over time, and to the environment (the temperature and humidity).

Embodiments of the invention will be described hereinafter by way of nonlimiting examples with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation, from the side, of the device according to the invention.

FIG. 2 is a diagrammatic representation, seen from above, of the device according to an alternative embodiment of the invention, the conductive surface comprising several sub-parts.

In this example, as shown in FIG. 1, the device according to the invention comprises: at least one sensing key 1 which comprises an insulating body 2 under which extends a conductive surface 3 constituting the detection zone ; An electronic circuit 4 for measuring capacitance variation connected to the conductive surface 3.

The insulating body 2 may consist for example of plastic material such as polycarbonate, or glass, the insulating body 2 being preferably made of a transparent material.

According to a preferred embodiment variant of the invention, as shown in FIG. 2, sensitive keys 1 each comprise a conductive surface 3 which comprises at least two sub-parts 3 ', 3 "extending over the In this way, the touch pad 1 is considered to be activated when the capacitance variation of the two capacitors corresponding respectively to the two sub-parts 3 ', 3 "is greater than a determined threshold, which reduces the risks of inadvertent activation of this key 1.

Advantageously, as shown in FIG. 2, the sensitive keys 1 can be arranged in a star 20 so as to constitute a potentiometer.

According to another alternative embodiment of the invention, as shown in FIG. 2, the sensitive keys 1 can be arranged in column 21, to which is associated an adjacent level indicator 22 (at each key 1 corresponds a level determined), this set constituting a bargraph.

Advantageously, the juxtaposition of sensitive keys 1 or sub-parts 3 ', 3 "3 of the aforementioned type can detect the movement of a conductive body 6, such as a finger.

Preferably, this conductive surface 3 is made by the screen printing of a conductive ink which makes it possible to eliminate the presence of air between the insulating body 2 and this conductive surface 3, which makes it possible to avoid deterioration of the performance of the dielectric 2 and to preserve the tightness of the touch pad 1.

In this way, when a conducting body 6, such as a finger of a user, approaches or is in contact with the visible face of the insulating body 2, the assembly comprising the touch pad 1 and the conductive body 6 constitutes a capacitor, the armatures and the dielectric being constituted respectively by the conductive body 6, the conductive surface 3 (or a sub-portion 3 ', 3 "of the conductive surface) and the insulating body 2, each of the sub-portions 3 ', 3 "constituting with the conductive body 6 and the insulating body 2, a capacitor.

Thus, for example, the contact of the end of a finger with a touch of 1 cm 2 causes, when the insulating body 2 has a few millimeters thick, a capacity variation of the order of 1 to 5 pics - Farads.

The capacitance variation resulting from the contact or the proximity of the conductive body 6 with the apparent face of the insulating body 2 is measured by the electronic capacitance measurement measuring circuit 4 which is constituted by a printed circuit which can be included in a support 7 , such as a housing.

This support 7 comprises at least one conductive track 11, in this case two tracks 11, connected to the electronic circuit 4, each of these tracks 11 extending so as to face the conductive surface 3 or a sub-surface. corresponding part 3 ', 3 "of the conductive surface 3.

This electronic circuit 4 can comprise in particular: • a central processing unit (CPU); Memory means such as volatile memory (RAM); • a clock.

The central processing unit of the electronic circuit 4 calculates said capacity variation and determines whether it is greater than a predefined threshold value. Thus, the sensitive key 1 is considered to be activated when the variation of capacity is greater than said predetermined threshold.

The threshold value may be predefined so that only the user's finger contact with the apparent face of the insulating body 2 causes a capacitance variation greater than this threshold value.

In addition, the device according to the invention may also comprise a display system 8 which may consist of liquid crystal cells (LCD: Liquid Crystal Display) illuminated by a backlighting means 10. This display system 8 and this backlighting means 10, which generally have a thickness of the order of two to ten millimeters, are arranged in the space between the insulating body 2 and the electronic circuit 4, the backlighting means 10 resting in the present case on the support 7 of the electronic circuit 20 4.

In addition, the conductive surface 3 and the electronic circuit 4 are connected by means of at least one spacer 5 made of a conductive and elastic material. In this case, each conductive surface 3 or each sub-part 3 ', 3 "of the conductive surface 3 is connected to the electronic circuit 4 by means of a spacer 5 oriented substantially perpendicular to the longitudinal axis of the insulating body 2 the upper and lower ends of each spacer 5 being respectively in contact with the conductive surface 3 or a respective sub-portion 3 ', 3 "of the conductive surface 3, and a respective conductive track 11 of the support 7 of the electronic circuit 4.

Preferably, each spacer 5 consists of a conductive elastomer with conductive strips that may be of the ZEBRA type, the compressibility and elasticity of which advantageously make it possible to compensate for any differences in height between the electronic circuit 4 and the insulating body 2, avoid any contact between the display system 8 and the insulating body 2, and dampen shocks resulting from a strike on the sensitive key 1.

In addition, the use of a conductive spacer 5 of the aforesaid type has the following advantages: the assembly of each spacer 5 is carried out by simply pressing the support 7 against the sub-parts 3 ', 3 "of the surface 3, the games being caught by the compression of said conductive strips, no parasite capacitance addition is created, the cost of producing the device according to the invention is optimized.

According to a preferred embodiment variant, the device according to the invention may also comprise guiding and fixing means 12 making it possible to hold the spacers 5 in position. These guiding and fixing means 12 may thus be arranged on both sides. other of each spacer 5 and be connected, by way of non-limiting example, at each of their ends to the support 7 and to the underside of the insulating body 2. These guide and fixing means 12 which are preferably constituted of plastic material, have a length less than that of the spacer 5 in the relaxed position and comprise at each of their ends a wedge (not shown) abutting against the support 7 and against the underside of the insulating body 2 when the spacer 5 is compressed, which makes it possible to control the depth of depression of the touch pad 1.

In addition, the device according to this alternative embodiment of the invention may comprise mechanical assembly means 13 connecting the insulating body 2 and the support 7, which make it possible to exert a pressure causing compression of the spacers 5, and ensuring thus the electrical contact with the conductive surface 3.

Claims (10)

Revendications1. Capacitive effect sensing device for the proximity of a conductive body (6) to a determined sensing area (3), said sensing device comprising: • at least one sensing pad (1) having an insulating body ( 2) under which extends a conductive surface (3) constituting the detection area; • an electronic circuit (4) for capacitance variation measurement connected to the conductive surface (3), this electronic circuit (4) being included in a support (7); and characterized in that: • the conductive surface (3) is integral with the insulating body (2); The support (7) comprises at least one conductive track (11) connected to the electronic circuit (4); The conductive surface (3) is connected to a conductive track (11) by means of at least one spacer (5), distinct from said conductive surface (3) and from the conductive track (11), resting on said support (7), formed at least in part of a conductive material, compressible, and which provides an electrical connection by contact with at least said conductive surface (3) while compensating for any differences in height between the insulating body (2) and said support (7). 25 2. Detection device according to claim 1, characterized in that the armature constituted by the conductive surface (3) is produced by the screen printing of a conductive ink which makes it possible to eliminate the presence of air between the insulating body (2). ) and this conductive surface (3). 10 30 3. Detection device according to one of claims 1 and 2, characterized in that each sensing pad (1) comprises a conductive surface (3) which comprises at least two sub-parts (3 ', 3 ") extending on the lower face of the insulating body (2), in this way the touch pad (1) is considered to be activated when the capacitance variation of the two capacitors corresponding respectively to the two sub-parts (3 ', 3 ") is greater than at a determined threshold, which reduces the risk of accidental activation of this key (1). 4. Detection device according to one of claims 1 to 3, characterized in that the electronic circuit (4) comprises: • a central processing unit (CPU); Memory means; • a clock; the variation in capacitance resulting from the contact or the proximity of the conductive body (6) with the apparent face of the insulating body (2) being measured by this electronic circuit (4) for measuring capacitance variation; the central processing unit of the electronic circuit (4) calculates said capacitance variation and determines whether it is greater than a predefined threshold value, the sensitive key (1) being considered to be activated when the variation in capacity is greater than said predetermined threshold; the electronic circuit (4) is constituted by a printed circuit included in the support (7). 25 5. Detection device according to claim 3 and 4, characterized in that the conductive track (11) connected to the electronic circuit (4) extends so as to be opposite the conductive surface (3) or a sub-surface area. corresponding portion (3 ', 3 ") of the conductive surface (3). 6. Detection device according to one of the preceding claims, characterized in that it comprises a display system (8) illuminated by a backlighting means (10), this display system (8) and this means of backlight (10) being arranged in the space between the insulating body (2) and the electronic circuit (4). 7. Detection device according to one of claims 3 to 6, characterized in that the upper and lower end of each spacer (5) is in contact respectively with a conductive surface (3) or a sub-part (3 ', 3 ") respectively of the conductive surface (3), and a respective conductive track (11) of the support (7) of the electronic circuit (4). 8. Detection device according to one of the preceding claims, characterized in that each spacer (5) consists of a conductive elastomeric conductive strips whose compressibility and elasticity can compensate for any difference in height between the circuit electronics (4) and the insulating body (2), and to avoid any contact between the display system (8) and the insulating body (2). 9. Detection device according to one of claims 3 to 8, characterized in that the assembly of each spacer (5) is effected by simply pressing the support (7) against the sub-parts (3 ', 3 " ) of the conductive surface (3), the games being caught by the compression of said conductive strips. 10. Detection device according to one of the preceding claims, characterized in that it comprises: • guiding and fixing means (12) for maintaining in position the spacers (5), these guiding and fixing means (12) being able to be arranged on either side of each spacer (5) and to be connected at each of their ends to the support (7) and to the lower face of the insulating body (2); and mechanical assembly means (13) connecting the insulating body (2) and the support (7), which make it possible to exert a pressure causing compression of the spacers (5), and thus ensuring electrical contact with the surface conductive (3).