Coplanar interdigital electrode capacitive transducer, liquid sensing mat, vehicle seat

Abstract

The invention relates to a capacitive transducer (2) with coplanar interdigital electrodes suitable for detecting a liquid in a motor vehicle seat; said capacitive transducer (2) comprising a first electrode (4) and a second electrode (6), the first electrode and the second electrode each comprising a rod (8, 12) and branches (10, 14) integral with the rod; the branches (10) of the first electrode being interposed between the branches (14) of the second electrode, a branch (10) of the first electrode being spaced from an adjacent branch (14) of the second electrode by a distance (d) of between 50 micrometers and 250 micrometers; said first electrode (4) and the second electrode (6) each comprising between 2 and 9 branches. Figure to be published with the abstract: Figure 1

Description

Title of the invention: Capacitive transducer with coplanar interdigital electrodes, liquid detection mat, vehicle seat Technical field of the invention

[0001] The present invention relates to the field of liquid detection in the foam of a vehicle seat, in particular a motor vehicle seat. In particular, the invention relates to a capacitive transducer with coplanar interdigital electrodes, a liquid detection mat and a vehicle seat. State of the prior art

[0002] In the automotive field, occupancy sensors are generally used to manage the deployment of a safety airbag. Many occupancy sensors are based on capacitive technology. However, when a vehicle seat has become wet, capacitive occupancy sensors may detect an occupied state by mistake or communicate erroneous information about the category of people occupying the seat. Presentation of the invention

[0003] To overcome this drawback, the present invention has the first aim of proposing a capacitive transducer capable of detecting a liquid.

[0004] The second aim of the present invention is to propose a capacitive transducer capable of detecting both the presence of liquid and the presence of an occupant seated on the seat or of an object placed on the seat.

[0005] Advantageously, such a capacitive transducer is capable of performing a self-diagnosis on the reliability of its determination of seat occupancy.

[0006] The third aim of the present invention is to propose a mat for detecting the presence of liquid on a seat.

[0007] The fourth object of the present invention is to propose a seat comprising a capacitive transducer capable of detecting a liquid or a capacitive transducer capable of detecting both a liquid and an occupant or an object. Summary of the invention

[0008] The present invention relates to a capacitive transducer with coplanar interdigital electrodes suitable for detecting a liquid in a motor vehicle seat; said capacitive transducer comprising a first electrode and a second electrode, the first electrode and the second electrode each comprising a rod extending in a longitudinal direction and branches integral with the rod, the branches extending in a transverse direction; the branches of the first electrode being separated from each other by the same first distance, the branches of the first electrode being interposed between the branches of the second electrode, characterized in that a branch of the first electrode is spaced from an adjacent branch of the second electrode by a distance of between 50 micrometers and 250 micrometers; said first electrode and the second electrode each comprising between 2 and 9 branches. Advantageously, this capacitive transducer is suitable for quickly detecting the presence of liquid.

[0009] The features set out in the following paragraphs may optionally be implemented. They may be implemented independently of one another or in combination with one another: - the rod of the first electrode comprises an additional rod portion which extends in the longitudinal direction, and additional branches integral with the additional rod portion; the additional branches extending in a transverse direction, the additional branches being separated from each other by the same second distance, the second distance being greater than the first distance; said capacitive transducer further comprising a third electrode comprising a rod and branches integral with said rod, said rod of the third electrode extending in a longitudinal direction; the branches of the third electrode extending in a transverse direction; the branches of the third electrode being separated from each other by the second distance, the branches of the third electrode being interposed between the additional branches of the first electrode. Advantageously, this capacitive transducer is suitable for quickly detecting both the presence of liquid and the presence of an occupant seated on the seat or an object placed on the seat. - The additional branches of the first electrode have free ends, and wherein a free end of an additional branch of the first electrode is spaced from a portion of the stem of the third electrode arranged opposite it, by a spacing of between 250 micrometers and 1000 micrometers, and preferably between 300 micrometers and 500 micrometers. - The third electrode has between 20 and 100 branches and the first electrode has between 20 and 100 additional branches. - The additional branches of the first electrode and the branches of the third electrode have a dimension in the longitudinal direction between 300 micrometers and 500 micrometers. - The rod of at least one electrode among the first electrode, the second electrode and the third electrode, has a dimension in the transverse direction between 50 micrometers and 1000 micrometers, and preferably between 50 micrometers and 250 micrometers. - The stem of at least one electrode among the first electrode, the second electrode and the third electrode, has a depth of between 5 micrometers and 100 micrometers, and preferably between 7 micrometers and 20 micrometers, the depth being measured in a direction perpendicular to the longitudinal direction and to the transverse direction. - The additional branches of the first electrode, the branches of the second electrode and the branches of the third electrode have a depth of between 5 micrometers and 100 micrometers, and preferably between 7 micrometers and 20 micrometers, the depth being measured in a direction perpendicular to the longitudinal direction and to the transverse direction. The invention also relates to a liquid detection mat for a vehicle seat, in particular a motor vehicle seat, the mat comprising at least one flexible support, a capacitive transducer with coplanar interdigital electrodes shaped according to the characteristics mentioned above. The invention also relates to a set of a first and a second capacitive transducer with coplanar interdigital electrodes, in which the first capacitive transducer with coplanar interdigital electrodes is shaped according to the characteristics mentioned above, and in which the second capacitive transducer with coplanar interdigital electrodes comprises an electrode and an additional electrode, the electrode and the additional electrode each comprising a rod and branches secured to the rod, the branches extending perpendicular to the rod, the branches of the additional electrode being separated from each other by the same second distance, the second distance being greater than the first distance, the branches of the electrode being interposed between the branches of the additional electrode. Advantageously, this set of capacitive transducers makes it possible to detect the presence of liquid and the presence of an occupant or an object on the seat.

[0010] According to one embodiment, the electrode and the additional electrode each comprise between 20 and 100 branches in which the second distance is between 300 micrometers and 500 micrometers.

[0011] Finally, the invention also relates to a vehicle seat, in particular a motor vehicle seat, comprising a backrest, a seat articulated to the backrest, a capacitive transducer with coplanar interdigital electrodes shaped according to the characteristics mentioned above or a set of a first and a second capacitive transducer with coplanar interdigital electrodes shaped according to one of the characteristics mentioned above. Brief description of the figures

[0012] [Fig-1] is a diagram showing in front view a capacitive transducer with coplanar interdigital electrodes according to a first embodiment of the invention;

[0013] [Fig.2] is a diagram showing a front view of part of a transducer capacitive with coplanar interdigital electrodes according to a second embodiment of the invention;

[0014] [Fig.3] is a diagram showing a front view of a liquid detection mat comprising a capacitive transducer with coplanar interdigital electrodes as illustrated in [Fig.2];

[0015] [Fig.4] is a diagram showing, in perspective view, a vehicle seat comprising capacitive transducers with coplanar interdigital electrodes as illustrated in [Fig.2];

[0016] [Fig.5] is a diagram showing in front view a set of AC transducers coplanar interdigital electrode drivers of an assembly according to the invention. Detailed description of the invention

[0017] The capacitive transducer 2 with coplanar interdigital electrodes according to the present invention is capable of detecting that a liquid has penetrated into the foam of a motor vehicle seat.

[0018] The capacitive transducer 2 with coplanar interdigital electrodes according to a first embodiment of the invention has been shown schematically in [Fig.l]. It is described in connection with an orthonormal trihedron (X, Y, Z).

[0019] It comprises a first electrode 4 suitable for being connected to a voltage source 5 and a second electrode 6 suitable for being connected to a first ground 7.

[0020] The voltage source 5 generates a voltage between 5 and 12 volts and, preferably, a voltage equal to 5 volts.

[0021] The first electrode 4 comprises a rod 8 and branches 10 secured to the rod. The branches 10 extend perpendicular to the rod, at a distance from each other in a comb-shaped configuration. The adjacent branches 10 of the first electrode are separated from each other by the same distance, called the first distance DI. They are distributed along the rod with the exception of a lower end portion 11 of the rod.

[0022] The second electrode 6 is similar to the first electrode. In particular, it comprises a rod 12 and branches 14. The rod 12 extends parallel to and opposite the rod 8 of the first electrode. In the embodiment shown in [Fig.l], the first electrode 4 comprises five branches. Alternatively, the first electrode 4 may comprise between 2 and 9 branches.

[0023] The second electrode 6 preferably comprises the same number of branches 14 as the number of branches 10 of the first electrode.

[0024] Preferably, the branches 14 of the second electrode are spaced from each other by the same distance. This distance is equal to the first distance D1. The branches 14 of the second electrode are offset relative to the branches 10 of the first electrode so that the branches 14 of the second electrode are interposed between the branches 10 of the first electrode. Thus, each branch 10 of the first electrode is arranged between and at an equal distance d from two branches 14 of the second electrode. In particular, a branch 10 of the first electrode is spaced from an adjacent branch 14 of the second electrode by a distance d of between 50 micrometers and 250 micrometers.

[0025] The branches 10 of the first electrode have free ends 17. A free end 17 of a branch of the first electrode is spaced from a rod portion of the second electrode disposed opposite thereto, by a first spacing SI between 50 micrometers and 250 micrometers. This first spacing SI is measured in the transverse direction X. Preferably, this first spacing SI is identical to the distance d between a branch 10 of the first electrode and an adjacent branch 14 of the second electrode, the distance d being measured in the longitudinal direction Y. The same first spacing SI is also provided between the ends 19 of the branches 14 of the second electrode and a rod portion of the first electrode disposed opposite each of them.

[0026] The rod 8 of the first electrode is identical to the rod 12 of the second electrode. Only the rod of the first electrode is described in detail below.

[0027] The rod 8 extends in a longitudinal direction Y. In the embodiment shown, the rod 8 has a rectangular section. The rod 8 has a dimension ed in the transverse direction X of between 50 micrometers and 1000 micrometers, and preferably between 100 micrometers and 1000 micrometers. More preferably, the dimension ed is between 250 micrometers and 500 micrometers. Advantageously, the rod 8 has a dimension ed equal to 300 micrometers.

[0028] The rod has a depth h of between 5 micrometers and 100 micrometers. The depth h is measured in a direction Z perpendicular to the longitudinal direction Y and to the transverse direction X. Preferably, the depth of the rod is between 7 micrometers and 20 micrometers. Advantageously, the depth of the rod is equal to 10 micrometers. Alternatively, the section of the rod may be circular, trapezoidal or any other shape. In the embodiment shown, the branches 10 of the first electrode are identical to the branches 14 of the second electrode.

[0029] The branches 10 of the first electrode and the branches 14 of the second electrode have the same section as the rod 8. Thus, the dimension ed of a branch 10, 14 in a longitudinal direction Y has the same length as the dimension ed of a rod in the transverse direction X.

[0030] Preferably, the dimension ed along the longitudinal direction Y of a branch 10, 14 is between 300 micrometers and 500 micrometers. Alternatively, the dimension ed of a branch 10, 14 in a longitudinal direction Y has a length different from the dimension ed of a rod in the transverse direction X.

[0031] The depth h of the branches 10, 14 in the Z direction is identical to the depth h of the rods in the Z direction. Thus, the branches 10, 14 have a depth h of between 5 micrometers and 100 micrometers, and preferably between 7 micrometers and 20 micrometers. Advantageously, the depth of the branches 10, 14 is equal to 10 micrometers. Finally, the branches 10, 14 have a dimension 1 in the transverse direction X between 3 millimeters and 25 millimeters, and preferably between 7 and 15 millimeters.

[0032] Alternatively, the length of the branches 14 along the transverse direction X of the second electrode is different from the length of the branches 10 of the first electrode along the same direction.

[0033] With reference to [Fig.2], a capacitive transducer 16 with interdigital electrodes co planar according to a second embodiment is partially shown. This capacitive transducer 16 is adapted to measure both the presence of a liquid and to detect the presence of an occupant seated on the transducer or of an object placed on the transducer.

[0034] This capacitive transducer 16 comprises a first electrode 4, a second electrode 6 and a third electrode 18.

[0035] The first electrode 4 is similar to the first electrode of the transducer according to the first embodiment except that the rod 8 comprises an additional rod portion 20 which extends in the longitudinal direction Y and that this additional rod portion 20 comprises additional branches 22. In particular, the first electrode comprises between 20 and 100 additional branches.

[0036] The additional branches 22 are identical to the branches 10 described in connection with the first embodiment except that the additional branches 22 are separated from each other by the same second distance D2. The second distance D2 is greater than the first distance DI defined between two adjacent branches 10 of the first electrode. The second distance D2 is between 250 micrometers and 500 micrometers.

[0037] The other technical elements of the first electrode 4 of the transducer according to the second embodiment are identical to the technical elements of the first electrode 4 of the transducer according to the first embodiment. They bear the same references and will not be described a second time.

[0038] The second electrode 6 of the capacitive transducer according to the second embodiment is identical to the second electrode 6 according to the first embodiment. The dimensions and the positioning of the first electrode 4 relative to the second electrode 6 is identical to that described in connection with the first embodiment. The third electrode 18 comprises a rod 24 which extends in a longitudinal direction Y and which is connected to a second ground 9.

[0039] The dimensions of the rod 24 are identical to the dimensions of the rod 8 of the first electrode. The rod 24 comprises a rod portion 26 provided with branches 28 integral with the rod and a rod portion 29 without branches. The rod portion 26 and the branches 28 are arranged opposite the additional rod portion 20 and the additional branches 22. The branches 28 extend in a transverse direction X. The branches 28 are separated from each other by a distance equal to the second distance D2. The branches 28 of the third electrode are interposed between the additional branches 22 of the first electrode 4.

[0040] The dimensions of the branches 28 of the third electrode are identical to the dimensions of the branches 10 of the first electrode except for the fact that the dimension along the transverse direction X of the additional branches 22 and of the branches 28 is greater than the dimension 1 of the branches 10 along the same direction.

[0041] The additional branches 22 of the first electrode comprise free ends 30. A free end 30 of an additional branch of the first electrode is spaced from the rod portion 26 of the third electrode arranged opposite the latter, by a second spacing S2 having a length of between 250 micrometers and 1000 micrometers, and preferably between 300 micrometers and 500 micrometers.

[0042] This second spacing S2 is measured along the transverse direction X. This second spacing S2 has a length identical to the distance between an additional branch 22 of the first electrode and an adjacent branch 28 of the third electrode 18. The same second spacing S2 also separates the ends 32 of the branches 28 of the third electrode and the additional rod portion 20 of the first electrode arranged opposite them.

[0043] The present invention also relates to a mat 34 for detecting the presence of liquid in the foam of a vehicle seat, in particular a motor vehicle. With reference to [Fig. 3], the liquid detection mat 34 comprises a first flexible support 36, a second flexible support 38 fixed on the first flexible support and capacitive transducers 16 with coplanar interdigital electrodes according to the second embodiment carried by the second flexible support 38.

[0044] The first flexible support 36 may be a woven or non-woven support in natural fibers or synthetic fibers. It may also be made of plastic. In the illustrated embodiment, the first flexible support 36 is perforated to allow the passage of air from a seat ventilation system.

[0045] The second flexible support 38 may be made of a resin or a plastic material such as thermoplastic polyurethane known by the acronym TPU, polyethylene terephthalate known by the acronym PET, polycarbonate known by the acronym PC or polymide known by the acronym. The capacitive transducers 16 with interdigital electrodes and conductive tracks 40 are fixed on the upper face of the second flexible support. The capacitive transducers 16 are produced by electronic printing or by sewing.

[0046] Advantageously, this liquid detection mat is capable of detecting both the presence of liquid and the presence of an occupant or an object on it. According to an embodiment not shown, the liquid detection mat 34 is identical to the liquid detection mats shown in [Fig. 3] except that it comprises capacitive transducers 2 with coplanar interdigital electrodes according to the first embodiment instead of the capacitive transducers 16 with coplanar interdigital electrodes according to the second embodiment. The detection mat according to this embodiment only detects the presence of liquid and not the presence of an occupant on the seat. The present invention also relates to a vehicle seat 42, in particular a motor vehicle seat. The seat 42 comprises a backrest 44, a seat 46 articulated to the backrest, and capacitive transducers 16 with coplanar interdigital electrodes shaped as mentioned above and illustrated in [Fig. 2]. The capacitive transducers 16 are arranged on the foam of the seat. A cover with a thin layer of foam is arranged on the seat and covers the capacitive transducers 16. The capacitive transducers 16 are each connected, by electrical wires not shown, to a ground, to a voltage source and to an electronic unit. The electronic unit is for example constituted by a processor or an integrated circuit generally called ASIC. The electronic unit is capable of measuring a potential difference across the terminals of the first electrode 4 and the second electrode 6, as well as the potential difference between the first electrode 4 and the third electrode 18. In [Fig. 4], the capacitive transducers 16 with interdigitated electrodes are represented schematically by squares.

[0047] Alternatively, the seat comprises capacitive transducers 2 with coplanar interdigital electrodes shaped as mentioned above and illustrated in [Fig.l]. In this case, capacitive transducers 2 with coplanar interdigital electrodes are only suitable for detecting the presence of liquid. In addition, the seat may comprise other occupancy detection sensors.

[0048] The present invention also relates to an assembly 49 comprising a first capacitive transducer 2 with coplanar interdigital electrodes as illustrated in [Fig. 1] and a second capacitive transducer 48 with coplanar interdigital electrodes as illustrated in [Fig. 5]. The first capacitive transducer 2 is identical to the capacitive transducer described in connection with [Fig. 1]. The same technical elements have the same references and will not be described a second time.

[0049] The second capacitive transducer 48 with coplanar interdigital electrodes comprises an electrode 47 and an additional electrode 50.

[0050] The electrode 47 is identical to the third electrode 18 described in connection with [Fig. 2] except that the portion of rod 29 without branches is shorter. The same technical elements have the same references and are not described a second time. The electrode 47 is connected to a ground 7. The additional electrode 50 comprises a rod 52 and branches 54 secured to the rod 52. The branches 54 extend perpendicular to the rod 52. The branches 54 of the additional electrode 50 are separated from each other by the second distance D2. The second distance D2 is greater than the first distance DI. The branches 28 of the electrode 47 are interposed between the branches 54 of the additional electrode. The ends 32 of the branches 28 of the electrode 47 are arranged at a distance equal to the length of the second spacing S2 of the rod 52 of the additional electrode 50 in the transverse direction X. The ends 32 of the branches 28 of the electrode 47 are arranged at a distance equal to the second spacing S2 of the rod 52 of the additional electrode 50. The ends 56 of the branches 54 of the additional electrode 50 are arranged at a distance equal to the second spacing S2 of the rod 24 of the electrode 47. The additional electrode 50 is connected to a voltage source 5. The electrode 47 and the additional electrode 50 each comprise between 20 and 100 branches. The second distance D2 is between 300 micrometers and 500 micrometers.

[0051] According to a variant not shown, the occupancy detection mat illustrated in [Fig.3] comprises an assembly comprising an assembly 49 as illustrated in [Fig.5] in place of each capacitive transducer 16. According to a variant not shown, the seat 42 illustrated in [Fig.4] comprises a assembly 49 as illustrated in [Fig.5] in place of each capacitive transducer 16.

[0052] According to a variant not shown, the vehicle seat comprises a detection mat according to the invention covered with a seat covering.

Claims

Claims

1. Capacitive transducer (2, 16) with coplanar interdigital electrodes suitable for detecting a liquid in a motor vehicle seat; said capacitive transducer (2, 16) comprising a first electrode (4) and a second electrode (6), the first electrode and the second electrode each comprising a rod (8, 12) extending in a longitudinal direction (Y) and branches (10, 14) integral with the rod, the branches extending in a transverse direction (X); the branches (10) of the first electrode being separated from each other by the same first distance (Dl), the branches (10) of the first electrode being interposed between the branches (14) of the second electrode, characterized in that a branch (10) of the first electrode is spaced from an adjacent branch (14) of the second electrode by a distance (d) of between 50 micrometers and 250 micrometers;said first electrode (4) and the second electrode (6) each comprising between 2 and 9 branches.;

2. Capacitive transducer (16) according to claim 1, wherein the rod (8) of the first electrode (4) comprises an additional rod portion (20) which extends in the longitudinal direction (Y), and additional branches (22) integral with the additional rod portion (20); the additional branches (22) extending in a transverse direction (X), the additional branches being separated from each other by the same second distance (D2), the second distance (D2) being greater than the first distance (D1); said capacitive transducer (16) further comprising a third electrode (18) comprising a rod (24) and branches (28) integral with said rod, said rod (24) of the third electrode extending in a longitudinal direction (Y); the branches (28) of the third electrode extending in a transverse direction (X);the branches (28) of the third electrode being separated from each other by the second distance (D2), the branches (28) of the third electrode being interposed between the additional branches (22) of the first electrode.;

3. A capacitive transducer (16) according to claim 2, wherein the additional branches (22) of the first electrode comprise free ends (30), and in which a free end (30) of an additional branch of the first electrode is spaced from a rod portion (26) of the third electrode arranged opposite the latter, by a spacing (S2) of between 250 micrometers and 1000 micrometers, and preferably between 300 micrometers and 500 micrometers.

4. A capacitive transducer (16) according to any one of claims 2 and 3, wherein the third electrode (18) comprises between 20 and 100 branches (28) and the first electrode (4) comprises between 20 and 100 additional branches (22).

5. Capacitive transducer (16) according to any one of claims 2 to 4, in which the additional branches (22) of the first electrode and the branches (28) of the third electrode have a dimension (ed) in the longitudinal direction (Y) of between 300 micrometers and 500 micrometers.

6. Capacitive transducer (16) according to any one of claims 2 to 5, in which the rod (8, 12) of at least one electrode among the first electrode (4), the second electrode (6) and the third electrode (18), has a dimension (ed) in the transverse direction (X) of between 50 micrometers and 1000 micrometers, and preferably of between 50 micrometers and 250 micrometers.

7. Capacitive transducer (16) according to any one of claims 2 to 6, wherein the stem (8, 12, 24) of at least one electrode among the first electrode, the second electrode and the third electrode, has a depth (h) of between 5 micrometers and 100 micrometers, and preferably between 7 micrometers and 20 micrometers, the depth being measured in a direction (Z) perpendicular to the longitudinal direction (Y) and to the transverse direction (X).

8. Capacitive transducer (16) according to any one of claims 2 to 7, in which the additional branches (22) of the first electrode, the branches (14) of the second electrode and the branches (28) of the third electrode, have a depth (h) of between 5 micrometers and 100 micrometers, and preferably between 7 micrometers and 20 micrometers, the depth (h) being measured in a direction (Z) perpendicular to the longitudinal direction (Y) and to the transverse direction (X).

9. A liquid detection mat (34) for a motor vehicle seat, the mat (34) comprising at least one flexible support (36), a capacitive transducer with coplanar interdigital electrodes (2, 16) shaped according to any one of claims 1 to 8.

10. Assembly (49) of a first (2) and a second (48) capacitive transducer with coplanar interdigital electrodes, in which the first capacitive transducer with coplanar interdigital electrodes (2) is shaped according to claim 1 and in which the second capacitive transducer (48) with coplanar interdigital electrodes comprises an electrode (47) and an additional electrode (50), the electrode (47) and the additional electrode (50) each comprises a rod (24, 52) and branches (28, 54) integral with the rod, the branches extending perpendicularly to the rod, the branches of the additional electrode (50) being separated from each other by the same second distance (D2), the second distance (D2) being greater than the first distance (D1), the branches (28) of the electrode (47) being interposed between the branches (54) of the additional electrode (50).

11. An assembly (49) according to claim 10, wherein the electrode (47) and the additional electrode (50) each comprise between 20 and 100 branches wherein the second distance (D2) is between 300 micrometers and 500 micrometers.

12. Motor vehicle seat (42) comprising a backrest (44), a seat (46) articulated to the backrest, a capacitive transducer (2, 16) with coplanar interdigital electrodes shaped according to any one of claims 1 to 8 or a set (49) of a first (2) and a second (48) capacitive transducers with coplanar interdigital electrodes shaped according to one of claims 10 and 11.

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