Device and method for detecting the approach and/or contact, and the pressure of an object in relation to a detection surface

Abstract

A device for detecting an object with respect to a detection surface including at least one measurement electrode and at least one guard electrode separated by a distance (D) that is elastically modifiable locally by a load exerted by the object on the detection surface; and structure for electrical polarization of the electrodes (V, E) arranged in order to: (i) apply to the measurement and guard electrodes one and the same first alternating electrical potential (V.sub.g) so as to measure a first signal relating to an electrode-object capacitance (C.sub.eo); and (ii) apply between the measurement and guard electrodes an alternating electrical potential difference (V1), so as to measure a second electrical signal relating to an electrode-guard capacitance (C.sub.eg). A detection method utilizing the present detection device is also provided.

Claims

1. A device for detecting an object with respect to a detection surface, the device comprising: at least one measurement electrode; at least one electrode, called a guard electrode; a measurement electronics for measuring a signal with respect to an electrical capacitance of said at least one measurement electrode; said at least one measurement electrode and said at least guard electrode being separated by a distance (D) that is elastically modifiable locally, by a load exerted by the object on the detection surface; and means for electrical polarization of said at least one measurement electrode and said at least one guard electrode, arranged to: apply to the at least one measurement electrode and the at least one guard electrode: a first alternating electrical potential (Vg), or a plurality of second substantially identical, alternating potentials; wherein the first alternating electrical potential and the second alternating potentials are different from a ground potential (G), so as to measure a first signal with respect to a capacitance (Ceo), called electrode-object capacitance, between said at least one measurement electrode and the object; and apply, between the at least one measurement electrode and the at least one guard electrode, an alternating electrical potential difference (VI), so as to measure a second signal with respect to a capacitance (Ceg), called electrode-guard capacitance, between said at least one measurement electrode and the at least one guard electrode, wherein the means for electrical polarization of the electrodes comprises: at least one electrical source and at least one electrical switch; or at least two electrical sources.

2. The device according to claim 1, wherein the means for electrical polarization of the electrodes are arranged so as to generate the first alternating electrical potential (V.sub.g) and the electrical potential difference (V1) satisfying at least one of the following criteria: the first alternating electrical potential (V.sub.g) and the electrical potential difference (V1) comprise respectively at least one frequency component at a different frequency; and the first alternating electrical potential (V.sub.g) and the electrical potential difference (V1) comprise signals that are orthogonal to one another.

3. The device according to claim 1, further comprising measurement electronics with at least one demodulation means utilizing at least one of the following elements: a synchronous demodulator; an amplitude detector; and a digital demodulator.

4. The device according to claim 3, further comprising a first demodulation means exploiting the first alternating electrical potential (V.sub.g) to determine the first signal, and a second demodulation means exploiting the alternating electrical potential difference (V1) to determine the second signal.

5. The device according to claim 1, wherein the means for electrical polarization of the electrodes are arranged to generate the alternating electrical potential difference (V1) with an amplitude different from the amplitude of the first alternating electrical potential (V.sub.g).

6. The device according to claim 1, wherein the means for electrical polarization of the electrodes comprise at least one of the following switches: a first switch arranged to make it possible to apply to the at least one guard electrode and to the at least one measurement electrode, either the ground potential (G) or the first alternating electrical potential (V.sub.g); and a second switch arranged to make it possible to apply between the at least one guard electrode and the at least one measurement electrode, either the alternating electrical potential difference (V1), or a zero or substantially zero potential difference.

7. The device according to claim 1, further comprising at least one calculation module configured to: determine a distance or a contact between the object and the detection surface as a function of the first signal; or determine a load or a pressure applied by the object on the detection surface as a function of the second signal.

8. The device according to claim 1, wherein said at least one measurement electrode and said at least one guard electrode are separated by a layer that is elastically compressible, comprising or formed by a dielectric material.

9. The device according to claim 1, wherein said at least one measurement electrode is placed on, or in, or under, a support, produced from a flexible material, such as a fabric, placed above and at a distance from said at least one guard electrode, and deforming at least locally when a load is exerted on said support.

10. The device according to claim 1, further comprising several measurement electrodes.

11. The device according to claim 10, further comprising one or more guard electrodes arranged according to at least one of the following configurations: at least one of the guard electrodes, placed opposite to each of said at least one measurement electrode; for each said at least one measurement electrode, said at least one guard electrode placed opposite said at least one measurement electrode; and for each said at least one measurement electrode, a plurality of guard electrodes placed opposite said at least one measurement electrode.

12. The device according to claim 1, further comprising at least one second guard electrode polarized at a potential identical to the potential of said at least one measurement electrode.

13. The device according to claim 1, further comprising a plurality of measurement electrodes, and an electrode switch making it possible to selectively connect at least one of said measurement electrodes, called “active electrode”, to the measurement electronics, said electrode switch also being arranged to polarize the other measurement electrodes of said plurality of measurement electrodes, at the same electrical potential as the active electrode.

14. The device according to claim 1, wherein the measurement electronics comprise a circuit utilizing an operational amplifier with an impedance comprising a feedback capacitive component, said at least one measurement electrode being connected to the negative input of said operational amplifier.

15. The device according to claim 14, wherein the circuit utilizing an operational amplifier is supplied by an electrical supply referenced to the first alternating electrical potential (V.sub.g).

16. A detection layer, for an item of equipment, equipped with a device according to claim 1.

17. An item of equipment, equipped with a detection device according to claim 1.

18. A method for the detection of an object with respect to a detection surface utilizing a detection device the method comprising at least one iteration of the following steps: a first step of detecting at least one of an approach and a contact of the object with respect to the detection surface comprising the following operations: applying to at least one measurement electrode and at least one guard electrode: a first alternating electrical potential (V.sub.g), or second alternating potentials that are substantially identical; wherein the first alternating electrical potential and the second alternating potentials are different from a ground potential (G); measuring a first signal with respect to a capacitance (C.sub.eo), called electrode-object capacitance, between said at least one measurement electrode and the object; a second step of detecting pressure of the object on the detection surface comprising the following operations: applying, between said at least one measurement and said at least one guard electrode, an alternating electrical potential difference (V1); and measuring a second signal with respect to a capacitance (C.sub.eg), called electrode-guard capacitance, between said at least one measurement and said at least one guard electrode.

19. The method according to claim 18, wherein the detection device comprises a plurality of measurement electrodes, the second detection step being carried out only in an area of the detection surface in which the object was detected during the first detection step.

20. The method according to claim 18, further comprising a calibration step comprising: detecting at least one of the approach and the contact; and detecting pressure, in the absence of a detected object, to determine the electrode-guard capacitance called “calibration capacitance”.

21. The method according to claim 20, further comprising a step of functional verification comprising a comparison of an electrode-guard calibration capacitance with a nominal electrode-guard capacitance or a range of nominal electrode-guard capacitances.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other advantages and characteristics will become apparent on examination of the detailed description of non-limitative examples and from the attached drawings in which:

(2) FIG. 1 is a diagrammatic representation of the electrical principle of a first non-limitative embodiment example of a device according to the invention;

(3) FIG. 2 is a diagrammatic representation of the electrical principle of a second non-limitative embodiment example of a device according to the invention;

(4) FIG. 3 is a diagrammatic representation of the electrical principle of a third non-limitative embodiment example of a device according to the invention;

(5) FIG. 4 is a diagrammatic representation of the electrical principle of a fourth non-limitative embodiment example of a device according to the invention;

(6) FIG. 5 is a diagrammatic representation of the electrical principle of a fifth non-limitative embodiment example of a device according to the invention;

(7) FIGS. 6-8 are diagrammatic representations of different configurations of electrodes that can be implemented in a device according to the invention;

(8) FIG. 9 is a diagrammatic representation of a non-limitative embodiment example of a device according to the invention with a plurality of measurement electrodes;

(9) FIG. 10 is a diagrammatic representation of a non-limitative embodiment example of a device according to the invention with a plurality of individually controlled guard electrodes.

DETAILED DESCRIPTION

(10) It is well understood that the embodiments that will be described hereinafter are in no way limitative. In particular, variants of the invention may be envisaged comprising only a selection of characteristics described hereinafter, in isolation from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention with respect to the state of the prior art. This selection comprises at least one, preferably functional, characteristic without structural details, or with only a part of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention with respect to the state of the prior art.

(11) In particular, all the variants and all the embodiments described may be combined together if there is no objection to such combination from a technical point of view.

(12) In the figures, elements that are common to several figures retain the same reference.

(13) FIG. 1 is a diagrammatic representation of the electrical principle of a first non-limitative embodiment example of a detection device according to the invention.

(14) The device 100, represented diagrammatically in FIG. 1, is intended to detect the approach, the contact and the pressure exerted by a control object 102 on a detection surface 104.

(15) To this end, the device 100 comprises at least an electrode 106, called measurement electrode, placed level with, or opposite, the detection surface 104, and an electrode 108, called guard electrode, placed opposite the measurement electrode 106 according to the face thereof opposite to the detection surface 104, and at a distance from this measurement electrode 106.

(16) In the embodiments shown, the detection surface 104 is represented by a face of the measurement electrode or electrodes 106, preferably covered with a thin layer of electrically insulating material (polyimide, insulating varnish, etc.) in order to avoid short-circuits with the control object 102.

(17) The device 100 also comprises an electronic circuit which can be represented in the form of an operational amplifier (OA) 110, whose output is looped on its negative input by an impedance 112, which can be for example a capacitor, a capacitor combined with a resistor, or a capacitor combined with a reset or discharge switch. In the example shown, the impedance 112 is formed by a capacitor C.

(18) The device 100 also comprises a first electrical source E, which supplies a first alternating potential V.sub.g. The first electrical source E is also called guard electrical source, and the first alternating potential V.sub.g is also called guard potential V.sub.g, for reasons that will be explained hereinafter. This first alternating potential V.sub.g, or guard potential V.sub.g, is different from a ground electrical potential, referenced G, corresponding to the general ground potential of the system (which can be for example earth). The first electrical source E is connected at the input to the ground potential G and at the output in particular to the guard electrode 108.

(19) It should be noted that the control object 102, by definition, is normally polarized at the ground potential G, directly or indirectly by resistive or capacitive coupling. Of course, it is not necessary for the object to be perfectly polarized at this ground potential G. In order for it to be detected, it is simply necessary for it to be polarized at a potential different from the guard potential V.sub.g.

(20) In the embodiments shown, the operational amplifier (OA) 110 is referenced to the guard potential V.sub.g. To this end, it is supplied by an electrical supply source (not shown) that is also referenced to the guard potential V.sub.g.

(21) Alternatively, the operational amplifier (OA) 110 can be referenced to the ground potential, while being supplied by an electrical supply source (not shown) referenced to the electrical ground potential G.

(22) The voltage V.sub.s present on the output of the OA 110 is referenced to the guard potential V.sub.g.

(23) In order to obtain a voltage V.sub.s referenced to the general ground potential G, the device comprises a module 114 shown in the form of a differential amplifier 114, electrically referenced to the general ground potential G, and connected at the input respectively to the output of the OA 110 and to the guard potential. Thus an image signal of V.sub.s is obtained at the output of this differential amplifier 114, referenced to the general ground potential G.

(24) In the example shown, the device 100 also comprises a second electrical source V, placed between the positive input of the OA 110 and the guard source E, and supplying an alternating electrical potential difference V1.

(25) In this embodiment, the measurement electrode 106 is connected to the negative input of the OA 110, and the guard electrode 108 is connected at a point between the guard source E and the second source V.

(26) Due to the very high impedance and open-loop gain of the OA 110, it can be considered that the measurement electrode 106 connected to the negative input of the OA 110 is polarized (with respect to the ground potential G) at an electrical potential corresponding to the sum of the guard potential V.sub.g (or of the first alternating electrical potential V.sub.g) and the alternating electrical potential difference V1.

(27) The guard electrode is polarized at the guard potential or first alternating electrical potential V.sub.g.

(28) The measurement electrode 106 is arranged such that the distance D between the measurement electrode 106 and the guard electrode 108 can be elastically modified, locally, by a load exerted by the control object 102 on the detection surface 104. In particular, when a load is applied on the detection surface 104, the measurement electrode 106 moves closer to the guard electrode 108. To this end, the measurement 106 and guard 108 electrodes are placed on either side of (or in) a layer 118 formed by an elastically compressible dielectric material, such as for example foam or plastic or also a liquid dielectric.

(29) Under these conditions, the approach and the contact of the control object 102 with the detection surface 104 can be detected and/or measured by measuring a value representative of a capacitance C.sub.eo, called electrode-object capacitance, formed between the measurement electrode 106 and the control object 102. Once in contact with the detection surface 104, the load exerted by the control object 102 can be detected and/or measured by measuring a value of a capacitance C.sub.eg, called electrode-guard capacitance, formed between the measurement electrode 106 and the guard electrode 108.

(30) In both cases, it is possible to link the measured capacitances by using the parallel-plate capacitor law, respectively to a distance between the measurement electrode and the object and a distance between the measurement electrode and the guard electrode. The load can thus be calculated from the variation in the measured thickness of the dielectric material 118.

(31) The signal V.sub.s measured at the output of the OA 110 comprises a combination of a first signal V.sub.sa, and a second signal V.sub.sp which depend respectively on the electrode-object capacitance C.sub.eo, and a sum of the electrode-object and electrode-guard C.sub.eg capacitances:

(32) $\begin{array}{cc}{V}_s=V_{\mathrm{sa}}+V_{\mathrm{sp}}& \left(1\right)\\ \mathrm{with}& \\ V_{\mathrm{sa}}=V_g\frac{C_{\mathrm{eo}}}{C}& \left(2\right)\\ \mathrm{and}& \\ V_{\mathrm{sp}}=V1.Math.\left(1+\frac{C_{\mathrm{eo}}+C_{\mathrm{eg}}}{C}\right)& \left(3\right)\end{array}$

(33) According to a mode of implementation, a first electrical potential V.sub.g and a potential difference V1 are generated with different fundamental frequencies sufficiently spaced apart in order to be capable of being separated by demodulation and/or by filtering. These signals can be for example sinusoidal or square. In this case, the first and second signals V.sub.sa and V.sub.sp obtained also have different fundamental frequencies. It is then possible to obtain the respective amplitude of these first and second signals V.sub.sa and V.sub.sp by demodulating the signal V.sub.s around, respectively, the fundamental frequency of the first electrical potential V.sub.g for the first signal V.sub.sa, and the fundamental frequency of the potential difference V1 for the second signal V.sub.sp. It is then possible to deduce from the amplitude of these signals, respectively, the electrode-object capacitance C.sub.eo and the sum of the electrode-object and electrode-guard capacitances C.sub.eo+C.sub.eg, thus the electrode-guard capacitance C.sub.eg. Thus there is obtained simultaneously, a first signal with respect to the value of the electrode-object capacitance C.sub.eo, and a second signal with respect to the value of the electrode-guard capacitance C.sub.eg.

(34) To this end, the device 100 comprises two synchronous demodulators 115 which carry out the functions of multiplication of the signal V.sub.s originating from the OA 110 with respectively, a carrier signal corresponding to the first electrical potential V.sub.g, and a carrier signal corresponding to the potential difference V1, then low-pass filtering.

(35) These demodulations of first and second signals V.sub.sa and V.sub.sp at different frequencies can also be carried out with an asynchronous demodulator comprising rectification followed by a low-pass filter.

(36) Preferably, the signal V.sub.s is pass-band filtered around, respectively, fundamental frequencies of the first and second signals V.sub.sa and V.sub.sp before demodulation.

(37) According to other modes of implementation, a first electrical potential V.sub.g and a potential difference V1 can be generated in the form of signals that are orthogonal to one another (i.e. the scalar product of which is zero). Such signals can be generated for example in the form of phase quadrature signals (for example sinusoidal or square), or in the form of binary sequences constituting orthogonal base signals.

(38) In this case, it is possible to demodulate the first and second signals V.sub.sa and V.sub.sp, as previously with synchronous demodulators 115, by using respectively, a carrier signal corresponding to the first electrical potential V.sub.g, and a carrier signal corresponding to the potential difference V1, then low-pass filtering. More generally, if the first signal V.sub.sa is demodulated with a carrier signal orthogonal to the second signal V.sub.sp and vice-versa, it is possible to obtain their respective amplitudes without crosstalk.

(39) Of course, these demodulation operations can be carried out in an analogue manner, with analogue electronics components, and/or digitally, with a FPGA, a microprocessor, etc. They can for example be carried out by digitizing the analogue signals (for example the signal V.sub.s) then carrying out the demodulation operations by calculation with an FPGA or a microprocessor.

(40) It is also possible to implement the device 100 with the guard source E and the second source V turned on alternately (and thus one at a time). In this case, measurements are taken alternately at the output of the OA of a signal V.sub.s that corresponds respectively to the first signal V.sub.sa or to the second signal V.sub.sp, depending on the source that is turned on. It is then possible to demodulate this signal V.sub.s as previously with two demodulators 115, or to use only a single demodulator, switching the carrier signal so that it corresponds to that of the turned on source.

(41) It should be noted that a voltage source, such as the first electrical source E or the second electrical source V, behaves as a short-circuit when switched off.

(42) In this mode of implementation, it is also possible to implement a guard electrical source E and a second source V that use the same excitation frequency or generate a signal of the same shape, which simplifies the detection electronics.

(43) It is also possible to keep the guard source E permanently turned on but to turn on the second source V only periodically, or only when an object 102 is detected in contact with or in proximity to the detection surface 104, based on the measurement of the electrode-object capacitance C.sub.eo. This makes it possible to measure the electrode-object capacitance C.sub.eo under better conditions, more accurately, and limiting the risks of crosstalk, in particular when the objects 102 are distant and therefore this electrode-object capacitance C.sub.eo is very low. When the objects 102 are in proximity to or in contact with the detection surface 104, the electrode-object C.sub.eo and electrode-guard C.sub.eg capacitances are measured simultaneously (or sequentially) as described above.

(44) It should be noted that the guard electrodes 108 fulfil the following functions: For measuring the electrode-object capacitance C.sub.eo, the guard electrodes 108 protect the measurement electrodes 106 from parasitic capacitive coupling with the environment by being polarized at the same potential as the measurement electrodes 106, at least from the point of view of the demodulation with respect to the first alternating electrical potential. It should be noted that this holds true even when the second source V is turned on, inasmuch as it supplies an alternating potential difference V1 orthogonal to the first alternating electrical potential, or with different frequencies. To this extent, the first alternating electrical potential is a guard potential; For measuring the electrode-guard capacitance C.sub.eg, the guard electrodes 108 are at a potential different from the measurement electrodes 106, with a difference corresponding to the alternating potential difference V1. This allows a capacitance C.sub.eg to develop, which can be measured with a demodulation based on the alternating potential difference V1.

(45) FIG. 2 is a simplified diagrammatic representation of the electrical principle of a second embodiment example of a device according to the invention.

(46) The device 200, shown in FIG. 2, comprises all the elements of the device 100 in FIG. 1.

(47) In the device 200, unlike the device 100, the second electrical source V is connected to the guard electrode 108, and not to the measurement electrode 106, via inputs of the OA 110 as shown in FIG. 1. The positive input of the OA 110 is connected to the guard potential V.sub.g. The second electrical source V is also referenced to the guard potential V.sub.g.

(48) The functioning of the device 200 is essentially similar to that of the device 100.

(49) When the first electrical source E and the second electrical source V are turned on and respectively generate the guard potential (or first alternating electrical potential) V.sub.g and the alternating electrical potential difference V1, a measurement is taken at the output of the operational amplifier (OA) 110 of a signal V.sub.s, corresponding to the sum of two signals V.sub.sa and V.sub.sp representative respectively of the electrode-object capacitance C.sub.eo, and la electrode-guard capacitance C.sub.eg:

(50) $\begin{array}{cc}{V}_s=V_{\mathrm{sa}}+V_{\mathrm{sp}}& \left(4\right)\\ \mathrm{with}& \\ V_{\mathrm{sa}}=V_g\frac{C_{\mathrm{eo}}}{C}& \left(5\right)\\ \mathrm{and}& \\ V_{\mathrm{sp}}=-V1\frac{C_{\mathrm{eg}}}{C}& \left(6\right)\end{array}$

(51) It should be noted that in this embodiment of the device 200, the signal V.sub.sp representative of the electrode-guard capacitance C.sub.eg does not depend on the electrode-object capacitance C.sub.eo, as in the case of the device 100. This is an advantage of this embodiment.

(52) The signal V.sub.s can be demodulated as explained with respect to the device 100, with one or two demodulators 115. In particular, all the demodulation methods explained with respect to the device 100 are applicable to the device 200.

(53) As explained above, the device 200 can therefore be implemented with the first electrical source E and the second electrical source V turned on or activated simultaneously, provided that the first alternating electrical potential V.sub.g and the alternating electrical potential difference V1 generated are orthogonal signals or have different frequencies. It is thus possible to demodulate the signals V.sub.sa and V.sub.sp in parallel with two demodulators 115 as explained above. In this case the first signal with respect to the value of the electrode-object capacitance C.sub.eo and the second signal with respect to the value of the electrode-guard capacitance C.sub.eg are obtained.

(54) The device 200 can also be implemented by alternately turning on only the first electrical source E, then the second electrical source V. In this case, the first alternating electrical potential V.sub.g and the alternating electrical potential difference V1 generated can be, as above, orthogonal signals or have different frequencies, but they can also have the same frequency or the same shape. Two signals representative respectively of the electrode-object capacitance C.sub.eo and the electrode-guard capacitance C.sub.eg are then measured alternately or sequentially.

(55) As described with respect to the device 100, it is also possible to keep the first electrical source E permanently turned on but to turn on the second electrical source V only periodically, or only when an object 102 is detected in contact with or in proximity to the detection surface 104, based on the measurement of the electrode-object capacitance C.sub.eo. This makes it possible to measure the electrode-object capacitance C.sub.eo under better conditions, more accurately, and limiting the risks of crosstalk, in particular when the objects 102 are distant and therefore this electrode-object capacitance C.sub.eo is very low. When the objects 102 are in proximity or in contact with the detection surface 104, the electrode-object C.sub.eo and electrode-guard C.sub.eg capacitances are measured simultaneously (or sequentially) as described above.

(56) FIG. 3 is a simplified diagrammatic representation of the electrical principle of a third embodiment example of a device according to the invention.

(57) The device 400, shown in FIG. 3, comprises all the elements of the device 100 in FIG. 1. It comprises in particular a first electrical source E connected at the input to the ground potential G and at the output in particular to the guard electrode 108. It also comprises a second electrical source V, placed between, on the one hand, the guard electrode 108 and the output of the first electrical source E, and on the other hand, the positive input of the OA 110.

(58) The device 400 also comprises a first switch 402 placed at the output of the first electrical source E. This first switch 402 is controlled by the control module 116 and makes it possible to connect the guard electrode 108: in a first position, to the output of the first electrical source E; and in a second position, to the ground potential G.

(59) The device 400 also comprises a second switch 302 placed at the output of the second electrical source V. This second switch 302 is also controlled by the control module 116 and makes it possible to connect the positive input of the OA 110: in a first position, to the guard electrode 108; and in a second position, to the output of the second electrical source V.

(60) It should be noted that the device 400 is functionally equivalent to the device 100 in the case where the first electrical source E or the second electrical source V are turned on or off, respectively.

(61) The first switch 402 is placed so as to connect or disconnect the first electrical source E, or more specifically the output of this first electrical source E, to/from the rest of the circuit, while arranging, when the first electrical source E is disconnected, to connect the guard electrode 108 to the ground potential G (as if the first electrical source E was turned off). It thus makes it possible to avoid turning this first electrical source E on and off at a high rate.

(62) Similarly, the second switch 302 is placed so as to connect or disconnect the second electrical source V, or more specifically the output of this second electrical source V, to/from the rest of the circuit, while arranging, when the second electrical source V is disconnected, to connect the input of the OA 110 to the guard electrode 108 (as if the second electrical source V was turned off). It thus makes it possible to avoid turning this second electrical source V on and off at a high rate.

(63) All the modes of implementation described with respect to the device 100 in FIG. 1 are applicable to the device 400.

(64) However, of course, the device 400 is particularly well adapted to performing sequential measurements, with the first electrical source E and the second source V activated alternately (and thus one at a time). In this case, measurements are taken alternately, at the output of the OA, of a signal V.sub.s that corresponds respectively to the first signal V.sub.sa or to the second signal V.sub.sp, depending on the source that is activated. It is then possible to demodulate this signal V.sub.s as above with two demodulators 115, or to use only a single demodulator 115 as shown in FIG. 3 by switching the carrier signal (for example with the control module 116) so that it corresponds to the one with the activated source.

(65) Thus, for measuring the first signal V.sub.sa, the first switch 402 is switched in order to connect the guard electrode 108 to the output of the first electrical source E, and the second switch 302 is switched in order to connect the positive input of the OA 110 to the output of the first electrical source E (or to the guard electrode 108). For measuring the second signal V.sub.sp, the first switch 402 is switched in order to connect the guard electrode 108 to the ground potential G, and the second switch 302 is switched in order to connect the positive input of the OA 110 to the output of the second electrical source V.

(66) According to a variant, the device 400 can comprise a first switch 402 and no second switch 302. In this case, the second source V is still inserted in the circuit. Of course, it can be turned on or off as described above.

(67) According to a variant, the device 400 can comprise a second switch 302 and no first switch 402. In this case, the first source E is still inserted in the circuit. Of course, it can be turned on or off as described above.

(68) FIG. 4 is a simplified diagrammatic representation of the electrical principle of a fourth embodiment example of a device according to the invention.

(69) The device 500, shown in FIG. 4, comprises all the elements of the device 200 in FIG. 2. It comprises in particular a first electrical source E connected at the input to the ground potential G and at the output to the positive input of the OA 110. It also comprises a second electrical source V, placed between, on the one hand, the output of the first electrical source E, and on the other hand, the guard electrode 108.

(70) The device 500 also comprises a first switch 402 placed at the output of the first electrical source E. This first switch 402 is controlled by the control module 116 and makes it possible to connect the positive input of the OA 110: in a first position, to the output of the first electrical source E; and in a second position, to the ground potential G.

(71) The device 500 also comprises a second switch 302 placed at the output of the second electrical source V. This second switch 302 is also controlled by the control module 116 and makes it possible to connect the guard electrode 108: in a first position, to the positive input of the OA 110; and in a second position, to the output of the second electrical source V.

(72) It should be noted that the device 500 is functionally equivalent to the device 200 in the case where the first electrical source E or the second electrical source V are turned on or off, respectively.

(73) The first switch 402 is placed so as to connect or disconnect the first electrical source E, or more specifically the output of this first electrical source E, to/from the rest of the circuit, while arranging, when the first electrical source E is disconnected, to connect the positive input of the OA 110 to the ground potential G (as if the first electrical source E was turned off). It thus makes it possible to avoid turning this first electrical source E on and off at a high rate.

(74) Similarly, the second switch 302 is placed so as to connect or disconnect the second electrical source V, or more specifically the output of this second electrical source V, to/from the rest of the circuit, while arranging, when the second electrical source V is disconnected, to connect the guard electrode 108 to the positive input of the OA 110 (as if the second electrical source V was turned off). It thus makes it possible to avoid turning this second electrical source V on and off at a high rate.

(75) All the modes of implementation described with respect to the device 200 in FIG. 2 are applicable to the device 500.

(76) However, of course, the device 500 is particularly well adapted to performing sequential measurements, with the first electrical source E and the second source V activated alternately (and thus one at a time). In this case, measurements are taken alternately, at the output of the OA, of a signal V.sub.s that corresponds respectively to the first signal V.sub.sa or to the second signal V.sub.sp, depending on the source that is activated. It is then possible to demodulate this signal V.sub.s as above with two demodulators 115, or to use only a single demodulator 115 as shown in FIG. 4 by switching the carrier signal (for example with the control module 116) so that it corresponds to the one with the activated source.

(77) Thus, for measuring the first signal V.sub.sa, the first switch 402 is switched in order to connect the positive input of the OA 110 to the output of the first electrical source E, and the second switch 302 is switched in order to connect the guard electrode 108 to the output of the first electrical source E (or to the positive input of the OA 110). For measuring the second signal V.sub.sp, the first switch 402 is switched in order to connect the positive input of the OA 110 to the ground potential G, and the second switch 302 is switched in order to connect the guard electrode 108 to the output of the second electrical source V.

(78) According to a variant, the device 500 can comprise a first switch 402 and no second switch 302. In this case, the second source V is still inserted in the circuit. Of course, it can be turned on or off as described above.

(79) According to a variant, the device 500 can comprise a second switch 302 and no first switch 402. In this case, the first source E is still inserted in the circuit. Of course, it can be turned on or off as described above.

(80) FIG. 5 is a simplified diagrammatic representation of the electrical principle of a fifth embodiment example of a device according to the invention. The device 600, shown in FIG. 5, comprises all the elements of the device 500 in FIG. 4 for example. It differs however in that: it does not comprise a second electrical source V, nor a second switch 302; the guard electrode 108 is connected at all times to the output of the first electrical source E and receives the potential V.sub.g supplied by this first electrical source E.

(81) The device 600 comprises a first switch 402 placed at the output of the first electrical source E, and downstream of the guard electrode 108. This first switch 402 is controlled by the control module 116, and makes it possible to connect the positive input of the OA 110: in a first position, to the output of the first electrical source E, and to the guard electrode 108; and in a second position, to the ground potential G.

(82) This embodiment is very simple inasmuch as it comprises only one source, the first electrical source E. On the other hand, it only allows sequential measurements of the first signal with respect to the value of C.sub.eo and of the second signal with respect to the value of C.sub.eg.

(83) For measuring the first signal with respect to the value of C.sub.eo, the control module 116 controls the first switch 402 in order to connect the positive input of the OA 110 to the first electrical source E: in this position the guard electrode 108 and the measurement electrode 106 receive the first potential V.sub.g.

(84) For measuring the second signal with respect to the value of C.sub.eg, the control module 116 controls the first switch 402 in order to connect the positive input of the OA 110 to the ground potential G: the guard electrode 108 is then at the first potential V.sub.g and the measurement electrode 106 at the ground potential G. In other words, in this configuration, an alternating electrical potential difference V1 corresponding to the first potential V.sub.g is applied between the measurement electrode 106 and the guard electrode 108.

(85) In this embodiment, the measurement of the first signal provides the following signal at the output of the OA:

(86) $\begin{array}{cc}{V}_{\mathrm{sa}}=V_g\frac{C_{\mathrm{eo}}}{C}& \left(7\right)\end{array}$

(87) And the measurement of the second signal provides the following signal at the output of the OA:

(88) $\begin{array}{cc}{V}_{\mathrm{sp}}=-V_g\frac{C_{\mathrm{eg}}}{C}& \left(8\right)\end{array}$

(89) It is then possible to demodulate the first signal V.sub.sa and the second signal V.sub.sp with a demodulator 115, while using the same carrier signal (for a synchronous demodulator).

(90) According to a variant of the device 600 (not shown) the switch 402 can be placed between the guard electrode 108 on the one hand, and the source E and the ground potential on the other hand, by connecting the positive input of the OA 110 to the source E at all times.

(91) In this case, the first switch 402 makes it possible to connect the guard electrode 108: in a first position, to the output of the first electrical source E, and to the positive input of the OA 110; and in a second position, to the ground potential G.

(92) In this configuration, the measurement electrode 106 is always polarized at the first potential V.sub.g via the positive input of the OA 110.

(93) Each of the devices described can also comprise at least one calculation module (not shown in the figures) configured in order to: determine a distance, a contact or semi-contact between the object 102 and the detection surface 104 as a function of the first measured signal; and/or determine a load applied by said object 102 on the detection surface 104 as a function of the second measured signal.

(94) FIG. 6 is a diagrammatic representation of a first configuration of electrodes which can be implemented in a device according to the invention.

(95) In the configuration 700, represented in FIG. 6, the device can comprise a plurality of measurement electrodes 106.sub.1-106.sub.N, and a single guard electrode 108 common to all of the measurement electrodes 106.sub.1-106.sub.N, In the configuration shown, this guard electrode 108 is placed opposite the face of the measurement electrodes 106.sub.1-106.sub.N opposed to the detection surface 104.

(96) FIG. 7 is a diagrammatic representation of a second configuration of electrodes which can be implemented in a device according to the invention.

(97) In the configuration 800, shown in FIG. 7, the device can comprise a plurality of measurement electrodes 106.sub.1-106.sub.N and an individual guard electrode, respectively 108.sub.1-108.sub.N, for each measurement electrode 106.sub.1-106.sub.N. In the configuration shown, these guard electrodes 108.sub.1-108.sub.N are placed opposite the face of the measurement electrodes 106.sub.1-106.sub.N opposed to the detection surface 104.

(98) FIG. 8 is a diagrammatic representation of a third configuration of electrodes which can be implemented in a device according to the invention.

(99) In the configuration 900, represented in FIG. 8, the device comprises a plurality of measurement electrodes 106.sub.1-106.sub.N and an individual guard electrode, respectively 108.sub.1-108.sub.N, for each measurement electrode 106.sub.1-106.sub.N.

(100) It also comprises second guard electrodes 902 preferably placed in one and the same plane as the guard electrodes 108.sub.1-108.sub.N. These second guard electrodes can be produced in the form of a single guard plane 902, or in the form of separate electrodes connected to one and the same potential.

(101) These second guard electrodes 902 are kept at the potential of the measurement electrodes 106, or at least at a potential identical or substantially identical to the potential of the measurement electrodes 106. They thus make it possible to form a guard for these measurement electrodes 106, including during the measurements of the second signal with respect to the value of C.sub.eg, while avoiding the development of parasitic capacitances between these electrodes 106 and their environment. To this end, in the embodiments described with respect to FIG. 1 to FIG. 5, the second guard electrodes 902 are electrically connected to the positive input of the OA 110. Thus, they “follow” the potential imposed on the inputs of the OA 110 and on the measurement electrodes 106 in all the measurement configurations.

(102) FIG. 9 is a diagrammatic representation of a non-limitative embodiment example of a device according to the invention with a plurality of measurement electrodes.

(103) It shows an example configuration 1000 making it possible to take measurements sequentially with a plurality of measurement electrodes 106. This configuration 1000 is described based on the configuration 200 in FIG. 2, with the understanding that it can be implemented with all the embodiments described above.

(104) The device comprises a plurality of measurement electrodes 106.sub.1-106.sub.N connected respectively to an electronic electrode switch (switch) 1001 by connecting tracks 1002.

(105) The electrode switch 1001 is connected at the output to the measurement input (negative input) of the OA 110. It makes it possible to select a measurement electrode 106.sub.1-106.sub.N with which the measurements of the first and second signal are carried out as described above. This electrode switch 1001 is also arranged so that each measurement electrode 106.sub.1-106.sub.N is connected, either to the measurement input of the OA 110 in order to constitute an active (measuring) electrode, or to a potential that is identical or substantially identical to that applied to the active electrode or electrodes. Preferably, a single active electrode is selected at a time.

(106) In all the embodiments presented, the measurement electrodes 106.sub.1-106.sub.N which are not active are connected by the electrode switch 1001 to the positive input of the OA 110, which as explained above is at the same potential as the active measurement electrode 106.

(107) The fact of polarizing the measurement electrodes 106.sub.1-106.sub.N which are not active at a potential identical or substantially identical to that applied to the active electrode or electrodes makes it possible to avoid any crosstalk between the selected measuring electrode or electrodes and the non-measuring electrodes. The non-measuring electrodes which are thus at the guard potential participate in the optimization of the reach of the measuring electrode or electrodes for proximity detection by creating a maximum guarded surface.

(108) The device also comprises a plurality of guard electrodes 108.sub.1-108.sub.N placed respectively opposite the measurement electrodes 106.sub.1-106.sub.N. These guard electrodes 108.sub.1-108.sub.N are interconnected by a connecting track 1003 which makes it possible to connect them to the electronics. According to the embodiment in question, and as described above, the guard electrodes 108.sub.1-108.sub.N are thus all connected to the second electrical source V as shown, or:

(109) to the output of the first electrical source E (configuration 100, 600);

(110) to the switch 302 (configurations 500);

(111) to the switch 402 (configuration 400).

(112) The surface, the overlap coverage and the form of these electrodes 108.sub.1-108.sub.N can comprise a wide variety of configurations, as a function of the applications: larger, identical or smaller than the measurement electrodes 106.sub.1-106.sub.N, arranged so as to overlap partially one or more measurement electrodes, in the form of solid or openwork surfaces or tracks or having any forms whatsoever.

(113) Alternatively, as explained above, the guard electrodes 108.sub.1-108.sub.N can be produced in the form of a guard plane, or a single guard electrode 108.

(114) Optionally, the device also comprises a second guard electrode 902 in the form of a guard plane 902 placed between the guard electrodes 108.sub.1-108.sub.N. This second guard electrode is connected, as described above, to the positive input of the OA 110, in order to be kept at the same potential as the active measurement electrode or electrodes 106.sub.1-106.sub.N.

(115) This second guard electrode 902 for example offers a significant advantage with respect to the connection between the detection surface 104 and the electronics, by eliminating the capacitive leaks from this connection (said connection can be a cable, an extension of the active surface, a flexible connection, a printed circuit element, etc.).

(116) FIG. 10 is a diagrammatic representation of a non-limitative embodiment example of a device according to the invention with a plurality of measurement electrodes and a plurality of guard electrodes.

(117) It shows an example embodiment 1100 which makes it possible to control the guard electrodes selectively.

(118) This embodiment 1100 is similar to the embodiment 1000, therefore only the differences will be detailed here.

(119) The configuration 1100 implements a second electrical source V intended to be connected to the guard electrode 108, as for example in the embodiment 200.

(120) The device comprises a plurality of measurement electrodes 106.sub.1-106.sub.N connected respectively to an electronic electrode switch (switch) 1001 by connecting tracks 1002. The electronic electrode switch (switch) 1001 functions as explained in the embodiment 1000.

(121) The device also comprises a plurality of guard electrodes 108.sub.1-108.sub.N placed respectively opposite the measurement electrodes 106.sub.1-106.sub.N. These guard electrodes 108.sub.1-108.sub.N are individually connected by connecting tracks to a guard electrode switch 1101 the operation of which is explained hereinafter. The measurement electrodes 106.sub.1-106.sub.N and the guard electrodes 108.sub.1-108.sub.N are represented diagrammatically in a cross section view. They are placed on either side of a layer 118, formed by an elastically compressible dielectric material.

(122) Optionally, the device also comprises second guard electrodes 902 placed between the guard electrodes 108.sub.1-108.sub.N. These second guard electrodes are connected, as described above, to the positive input of the OA 110, in order to be kept at the same potential as the measurement electrode or electrodes 106.sub.1-106.sub.N.

(123) According to the embodiment shown, the guard electrodes 108.sub.1-108.sub.N have a dimension (for example width and/or length) less than the dimension of the measurement electrodes 106.sub.1-106.sub.N opposite, so that a measurement electrode is facing several guard electrodes.

(124) The guard electrode switch 1101 is connected to the output of the second electrical source V. It makes it possible to apply selectively the potential difference V1 generated by the second electrical source V to a particular guard electrode 108.sub.1-108.sub.N. This electrode switch 1001 is also arranged so that each guard electrode 108.sub.1-108.sub.N is connected, either to the second electrical source V in order to constitute an excited guard electrode, or to a potential that is identical or substantially identical to that applied to the measurement electrode or electrodes. Preferably, a single excited guard electrode is selected at a time.

(125) According to an example mode of implementation, during the measurement of the second signal in order to obtain the electrode-guard capacitance C.sub.eg (and therefore the load): A measurement electrode 106.sub.1 is selected, with the electrode switch 1001 (the active measurement electrode); A guard electrode 108.sub.1, present opposite the active measurement electrode, is selected with the electrode switch 1001 (the excited guard electrode); A measurement of the second signal is carried out in order to obtain the electrode-guard capacitance C.sub.eg between the active measurement electrode and the excited guard electrode.

(126) If the measurement electrodes 106.sub.1-106.sub.N are deformable, it is thus possible to obtain a measurement of load with a spatial resolution that corresponds to the spatial dimension of the guard electrodes 108.sub.1-108.sub.N, and that is therefore better than the spatial resolution achievable with the measurement electrodes 106.sub.1-106.sub.N.

(127) This embodiment therefore has the advantage of allowing a better spatial resolution for measurement of the electrode-guard capacitance C.sub.eg than for measurement of the electrode-object capacitance C.sub.oe. It is thus possible to retain measurement electrodes 106.sub.1-106.sub.N with a more extensive surface area, allowing a better sensitivity for the distance measurements with a reasonable spatial resolution, and a finer spatial resolution for the load measurements, for which the spatial resolution is important.

(128) In this configuration, it is possible to have several guard electrodes 108.sub.1-108.sub.N connected together, each being opposite a different measurement electrode 106.sub.1-106.sub.N. Inasmuch as the measurement electrodes 106.sub.1-106.sub.N are “polled” sequentially, the same spatial resolution is obtained for the load or pressure measurements, while still limiting the number of tracks or channels necessary for the guard electrode switch 1101.

(129) According to embodiments, the guard electrodes 108.sub.1-108.sub.N, can extend opposite several measurement electrodes 106.sub.1-106.sub.N, at least in one direction. In this case, in the perpendicular direction, they can: extend according to one single measurement electrode (thus with a dimension substantially equal to that of the measurement electrodes); extend according to several measurement electrodes (thus with a dimension greater than that of the measurement electrodes); or, as described above, have a dimension less than that of the measurement electrodes, so as to have several guard electrodes opposite one measurement electrode.

(130) This makes it possible in particular to limit the number of channels necessary for the guard electrode switch 1101 without excessively degrading the spatial resolution of the measurement of load, which is determined by the overlap surface area between the active measurement electrode (as selected by the electronic electrode switch 1001) and the excited guard electrode (as selected by the guard electrode switch 1101).

(131) The guard electrode switch 1101 can also be utilized with all the configurations that implement a second electrical source V intended to be connected to the guard electrode 108, as for example in embodiments 200 and 500. When a switch 302 intended to connect or disconnect the second electrical source V is utilized, the guard electrode switch 1101 is inserted between the guard electrodes 108.sub.1-108.sub.N and this switch 302.

(132) According to embodiments, the device can comprise guard electrodes 108.sub.1-108.sub.N that are offset or partially overlap with respect to the measurement electrodes 106.sub.1-106.sub.N, and/or that extend respectively opposite several measurement electrodes 106.sub.1-106.sub.N, so as to allow the measurement of a shear displacement of the dielectric material 118 by measurement of a variation in the overlap surface area between at least one of said measurement electrodes 106.sub.1-106.sub.N and at least one of said guard electrodes 108.sub.1-108.sub.N. This arrangement makes it possible in particular to measure a tangential shear component of a pressure exerted on the detection surface 104. Of course, the device can also comprise guard electrodes 108.sub.1-108.sub.N respectively opposite a single measurement electrode 106.sub.1-106.sub.N, which are thus insensitive to this shear component (or vice-versa, measurement electrodes 106.sub.1-106.sub.N respectively opposite a single guard electrode 108.sub.1-108.sub.N). The tangential and perpendicular (or radial) components of a load exerted on the detection surface 104 can thus be deduced from measurements taken with a plurality of electrodes.

(133) For example, the device can comprise at least one guard electrode 108 opposite two neighbouring measurement electrodes 106. In the presence of pure shear displacement in the direction of overlap, the electrode-guard capacitance C.sub.eg between one of the measurement electrodes 106 and this guard electrode 108 increases due to the increase in the opposite surface areas, while the electrode-guard capacitance C.sub.eg between the other measurement electrode 106 and this same guard electrode 108 reduces.

(134) Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without exceeding the scope of the invention.