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

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 g ) and the electrical potential difference (V 1 ) satisfying at least one of the following criteria:

the first alternating electrical potential (V g ) and the electrical potential difference (V 1 ) comprise respectively at least one frequency component at a different frequency; and

the first alternating electrical potential (V g ) and the electrical potential difference (V 1 ) 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 g ) to determine the first signal, and a second demodulation means exploiting the alternating electrical potential difference (V 1 ) 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 (V 1 ) with an amplitude different from the amplitude of the first alternating electrical potential (V 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 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 (V 1 ), 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 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 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 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 (V 1 ); and

measuring a second signal with respect to a capacitance (C 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.