Device for measuring force on a complex surface

Abstract

Force measuring device on a complex surface The present description relates to a conformable force measuring device, intended to be subjected simultaneously to compressive forces and bending forces, the device comprising sensors (11, 12) arranged on either side of a substrate (100), the sensors comprising an organic piezoelectric layer (120) arranged between a first electrode (110) and a second electrode (130), the sensors (11, 12) being arranged opposite one another, so as to form a bimorph (10), the sensors being connected to electrically conductive tracks (200) intended to be connected to measuring devices, the organic piezoelectric layers (120) of the sensors (11, 12) being polarized and the sensors (11, 12) being intended to be electrically connected to the measuring devices so as to cancel either the compressive forces or the bending forces. Figure for abstract: Fig. 6

Description

Title of the invention: Device for measuring force on a complex surface Technical field

[0001] The present description relates generally to force measuring devices, and in particular to force measuring devices on complex and / or deformable surfaces. Prior art

[0002] Piezoelectric sensors can be used to measure forces, including compressive forces. Generally, the sensor is positioned on a surface so that the mechanical stress is not only uniform across the surface of the sensor but also unidirectional in the direction transverse to the sensor. Thus, it is possible to have a proportionality between the electrical charge Q generated by the sensor and the force F applied.

[0003] For planar surfaces, the sensors may comprise rigid inorganic piezoelectric materials such as ceramics.

[0004] For some applications, the surfaces are non-planar and / or deformable and the sensors must be flexible. For these applications, flexible sensors comprising a piezoelectric polymer thin film are generally used.

[0005] For example, in the article by Hong et al. (Hong, Y. et al. “Highly anisotropic and flexible piezoceramic kirigami for preventing joint disorders”. Sci. Adv. 7, eabf0795 (2021)), a flexible sensor is presented. The sensor is made from a nylon textile in the form of a honeycomb. The textile is coated with a solution of [Pb(Zr0.52 Ti0.48)O3]. After evaporation of the solvent, a gel forms around the nylon. Then PDMS is added to form a polymer matrix. Finally, silver nanowire electrodes are formed. Two 1.5cm x 1.5 cm sensors thus fabricated are positioned one above the other to form the final device. This device is flexible and can be used on the skin. It is used to determine the direction of bending applied to the sensor. For example, when positioned on a person's neck or shoulder, different deformations can be detected. There is no compression measurement.

[0006] The article by Lin et al. (Lin, W. et al. “Skin-Inspired Piezoelectric Tactile Sensor Array with Crosstalk-Free Row+Column Electrodes for Spatiotemporally Distin-guishing Diverse Stimuli”. Adv. Sci. 8, 2002817 (2021)) presents a flexible device comprising several piezoelectric sensors. The sensors comprise PVDF layers arranged between PDMS films. The number of electrical connections corresponds to the sum of the number of rows and the number of columns. The different stresses are tested one by one. The device makes it possible to differentiate the amplitude, positions and various external stimuli in real time (bending, compression and shear). Compression causes a bending deformation of the piezoelectric film.

[0007] There is no simple theoretical model for relating the electrical charge generated by the piezoelectric to the bending stresses when the device is subjected to both bending and compressive forces.

[0008] Indeed, when the conformable sensor is positioned on a complex surface, the flexural deformation of the sensor generates electrical charges which disturb the charges generated by the force which must be measured. If this force is too weak (in particular less than 100 kPa) and the flexural deformations are too large, it is then not possible to measure the force.

[0009] As an example, [Fig.l] represents tests of piezoelectric force sensors. The graph referenced (a) represents a force applied in compression on a non-conformable sensor pressed against a rigid surface. The graph referenced (b) represents the response of the sensor. The signal is easy to interpret: a first peak appears when the force is applied and a second peak opposite the first is visible, this peak is characteristic of the release after the application of the force. The graph represented (c) represents the response of a conformable sensor taking the shape of the surface on which the force is applied. The sensor is therefore subjected to bending and compression: the signal is chaotic with numerous peaks and cannot be interpreted. Summary of the invention

[0010] There is therefore a need to provide a measuring device making it possible to measure compressive forces (even weak ones), or even bending forces, when it is placed on a complex and / or deformable surface and when it is subjected to both bending and compressive forces.

[0011] This object is achieved by a conformable force measuring device, intended to be subjected simultaneously to compressive forces and bending forces, the device comprising a substrate having a first face and a second face, at least one first sensor arranged on the first face of the substrate and at least one second sensor arranged on the second face of the substrate, the sensors comprising an organic piezoelectric layer arranged between a first electrode and a second electrode, the sensors being arranged opposite one another, so as to form a bimorph. The sensors are connected to electrically conductive tracks intended to be connected to measuring devices. The organic piezoelectric layers of the sensors are polarized in an identical or opposite manner.

[0012] Advantageously, the sensors are covered by a stack successively comprising a first dielectric layer, a ground plane and a second dielectric layer.

[0013] Advantageously, the ground plane is made of carbon and / or in that the first dielectric layer and the second dielectric layer are made of ED AG or PVDF.

[0014] Advantageously, the substrate is a PEN or PI substrate.

[0015] Advantageously, the substrate comprises two support substrates, for example made of TPU, assembled to each other by an adhesive element.

[0016] Advantageously, the first face of the substrate is covered by a first matrix of sensors and the second face of the substrate is covered by a second matrix of sensors, the first matrix and the second matrix being arranged opposite each other.

[0017] According to this advantageous variant, on the one hand, the first electrode of each sensor of the first matrix can be connected to an individual electrically conductive track and, on the other hand, all the second electrodes of the sensors of the first matrix can be connected to a common electrically conductive track and, on the one hand, the first electrode of each sensor of the second matrix can be connected to an individual electrically conductive track and, on the other hand, all the second electrodes of the sensors of the second matrix can be connected to another common electrically conductive track.

[0018] This object is also achieved by a force measurement system comprising a conformable device intended to be subjected simultaneously to compressive forces and bending forces, the device comprising a substrate having a first face and a second face, at least one first sensor arranged on the first face of the substrate and at least one second sensor arranged on the second face of the substrate, the sensors comprising an organic piezoelectric layer arranged between a first electrode and a second electrode, the sensors being arranged opposite one another, so as to form a bimorph. The system further comprises measuring devices electrically connected to the sensors to measure the signals from the sensors.The organic piezoelectric layers of the sensors are polarized and the sensors are electrically connected to the measuring devices so as to cancel either the compressive forces or the bending forces, and measure, respectively, either the bending forces or the compressive forces applied to the device.

[0019] Advantageously, the polarization of the sensors is opposite, in that the sensors are connected to the measuring devices in opposite manner and in that the signals measured by the measuring devices are added, whereby the bending forces are canceled and the compression forces are measured.

[0020] Advantageously: - the polarizations of the sensors are identical, the sensors are connected to the measuring devices in an identical way and the signals measured by the measuring devices are added together, or - the polarizations of the sensors are opposite, the sensors are connected to the measuring devices identically and the signals measured by the measuring devices are subtracted, or - the polarizations of the sensors are identical, the sensors are connected to the measuring devices in opposite directions and the signals measured by the measuring devices are subtracted, whereby the bending forces are cancelled out and the compressive forces are measured.

[0021] This aim is also achieved by a method for measuring compressive and flexural force, comprising the following steps: - provide a force measurement system comprising a conformable device intended to be subjected simultaneously to compressive forces and bending forces, the device comprising a substrate having a first face and a second face, at least one first sensor arranged on the first face of the substrate and at least one second sensor arranged on the second face of the substrate, the sensors comprising an organic piezoelectric layer, arranged between a first electrode and a second electrode, the sensors being arranged opposite one another, so as to form a bimorph, the system further comprising measuring devices electrically connected to the sensors, for measuring the signals from the sensors, the organic piezoelectric layers of the sensors being polarized and the sensors being electrically connected to the measuring devices so as to cancel either the compressive forces or the bending forces, - simultaneously apply compressive and bending forces to the measuring device, - add or subtract the signals measured by the measuring devices, so as to cancel either the compressive forces or the bending forces, and thus measure, respectively, either the bending forces or the compressive forces applied to the device.

[0022] Advantageously, the device comprises a first matrix of sensors on the first face of the substrate and a second matrix of sensors on the second face of the substrate, the first matrix and the second matrix being arranged opposite one another.

[0023] Advantageously, the sensor(s) of the first face have an opposite polarization. upon polarization of the sensor(s) of the second face, the sensor(s) of the first face are electrically connected to first charge amplifiers, the sensor(s) of the second face are electrically connected to second charge amplifiers, the electrical connections to the first charge amplifiers and the electrical connections to the second charge amplifiers being opposite, the signals from the sensors being added to eliminate the signal of the bending forces and obtain the signal of the compression forces.

[0024] Advantageously, on the one hand, the first electrode of each sensor of the first matrix is ​​connected to an individual electrically conductive track, itself electrically connected to a charge amplifier, and, on the other hand, all the second electrodes of the sensors of the first matrix are connected to a common electrically conductive track, electrically connected to the ground of one of the measuring devices, and, furthermore, on the one hand, the first electrode of each sensor of the second matrix is ​​connected to an individual electrically conductive track, itself electrically connected to a charge amplifier, and, on the other hand, all the second electrodes of the sensors of the second matrix are connected to a common electrically conductive track, electrically connected to the ground of one of the measuring devices. Brief description of the drawings

[0025] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0026] [Fig.l], previously described, represents graphs corresponding to tests of piezoelectric force sensors for sensors of the prior art;

[0027] [Fig.2] represents, schematically and in top view, a measuring device comprising a substrate, each face of which is covered by a sensor according to a particular embodiment of the invention;

[0028] [Fig. 3] represents, schematically and in top view, a measuring device comprising a substrate, each face of which is covered by a matrix of sensors according to another particular embodiment of the invention;

[0029] [Fig.4] represents, schematically and in section, a measuring device according to another particular embodiment of the invention;

[0030] [Fig.5] represents, schematically and in section, a measuring device according to another particular embodiment of the invention;

[0031] [Fig.6] represents, schematically and in section, a measuring device according to another particular embodiment of the invention;

[0032] [Fig.7] shows, schematically and in section, a measuring device according to another particular embodiment of the invention;

[0033] [Fig.8A], [Fig.8B], [Fig.8C] and [Fig.8D] represent, respectively, schematically and in section, unitary devices on convex, concave or complex surfaces as well as a matrix device on a complex surface;

[0034] [Fig.9A], [Fig.9B] and [Fig.9C] represent, schematically and in different sections, a measuring device positioned in a heart valve comprising an anterior leaflet (AL) and a posterior leaflet (PL), according to different particular embodiments of the invention;

[0035] [Fig. 10] schematically represents a compression test for the calibration of the sensors according to another particular embodiment of the invention;

[0036] [Fig. 1 1] schematically represents a conformability test in flexion and compression, according to another particular embodiment of the invention;

[0037] [Fig.l2A] is a graph representing the response of two sensors (denoted C1 and C2) positioned on each side of the same substrate for a compression test, for the calibration as represented in [Fig. 10];

[0038] [Fig.l2B] is a graph representing the response of the two sensors C1 and C2 for a bending-only test;

[0039] [Fig. 13] is a graph representing the response of the two sensors C1 and C2 for a conformability test in bending and compression as shown in [Fig. 11]

[0040] [Fig. 14] and [Fig. 15] are photographs of different measuring devices according to different particular embodiments of the invention;

[0041] [Fig. 16] and [Fig. 17] are photographic images of the device of [Fig. 15] on complex surfaces; and

[0042] [Fig. 18] is a photographic image of several types of piezoelectric sensors printed according to different particular embodiments of the invention. Description of the embodiments

[0043] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0044] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed.

[0045] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by through one or more other elements.

[0046] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made unless otherwise specified to the orientation of the figures.

[0047] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0048] We will now describe the device in more detail with reference to Figures 2, 3, 4, 5, 6 and 7.

[0049] The piezoelectric devices for force measurement are devices comprising at least two organic electronic sensors 11, 12 arranged on either side of a substrate 100. The first face 100a of the substrate 100 is covered by at least one first sensor 11 and the second face 100b of the substrate 100 is covered by at least one second sensor 12. The first sensor 11 is arranged opposite the second sensor 12 in order to form a bimorph 10.

[0050] The invention is fundamentally distinguished from the prior art by the use of a conformable device having at least two sensors 11, 12 arranged symmetrically on either side of the substrate 100 and of which the sensors 11, 12 have a particular polarization and a particular connection, whereby the signal of the forces in compression or the signal of the forces in bending can be canceled, and a measurement of the force is thus obtained, respectively, either in bending or in compression. In particular, the device makes it possible to obtain a precise measurement of a compressive force by eliminating, thanks to the principle of the piezoelectric bimorph, the generated bending signal.

[0051] By arranged opposite one another, we mean that the alignment is perfect or that there is a maximum of 50 pm of misalignment between the electrodes of the two sensors 11, 12.

[0052] The substrate is a flexible substrate. By flexible, it is meant that the element can deform reversibly.

[0053] Advantageously, a substrate having an elasticity of less than 8 GPa and a flexural rigidity of less than 10 4 N / m will be chosen. Preferably, all the layers of the device have an elasticity of less than 8 GPa and a flexural rigidity of less than 10 4 N / m.

[0054] The device is conformable, i.e. it can take the form of a complex surface (i.e. deformable and / or non-planar, for example having concave areas and / or convex areas) to measure the forces exerted on it. The device is also lightweight and can be carried by a person.

[0055] With this force measuring device, it is possible to differentiate the forces in compression and bending forces when the device is subjected to both forces simultaneously.

[0056] Preferably, the first face 100a of the substrate 100 is covered by a first group of sensors 11 and the second face 100b of the substrate 100 is covered by a second group of sensors 12.

[0057] The first group of sensors comprises the same number of sensors as the second group of sensors. In other words, the first face 100a and the second face 100b are covered by the same number of sensors.

[0058] Each sensor 11 of the first group of sensors is arranged opposite a sensor 12 of the second group of sensors.

[0059] The sensors 11, 12 of the same face can be arranged in line or in the form of a matrix ([Fig.3]).

[0060] For example, a line may include between X and Y sensors.

[0061] By between X and Y, it is meant here and hereinafter that the limits are included.

[0062] The matrices are matrices of nxm sensors with n and m positive integers, greater than or equal to 2, and preferably between 2 and 10. For example, as shown in [Fig.3], this is a matrix of 4 x 7 sensors.

[0063] For matrices having common electrodes (n+m electrodes), larger matrices can be used (e.g. up to 50 rows / columns).

[0064] This matrix form makes it possible to have several sensors arranged side by side on the same face of a substrate 100. Each sensor 11, 12 has an identical sensor placed symmetrically on the other side of the substrate 100 in order to form bimorphs 10. This embodiment is particularly advantageous because it makes it possible to measure forces at several points in space and thus to produce a map of the forces on a surface.

[0065] The sensors 11, 12 comprise at least one flexible piezoelectric polymer film 120 (also called a flexible organic piezoelectric layer or electroactive layer). Each piezoelectric polymer film 120 is disposed between a first electrode 110 and a second electrode 130.

[0066] The sensor 11, 12 may comprise a single electroactive layer 120 or several electroactive layers 120 (two or three electroactive layers for example). When the sensor comprises several electroactive layers 120, the sensor is formed from a stack comprising an alternation of piezoelectric layers 120 and electrodes 110, 130. The stack begins and ends with an electrode.

[0067] Preferably, each sensor 11, 12 comprises a single piezoelectric polymer film 120, disposed between a first electrode 110 (also called lower electrode) and a second electrode 130 (also called upper electrode).

[0068] Each piezoelectric layer 120 has a thickness, for example, between 1 and 11 pm, preferably between 2 and 5 pm, for example 3 pm. Such thicknesses make it possible to obtain layers 120 having good flexibility.

[0069] Preferably, each piezoelectric layer 120 is an organic piezoelectric layer. Each piezoelectric layer preferably comprises a polymer matrix made of PVDF, a PVDF copolymer or a PVDF terpolymer. It may be a copolymer of vinylidene fluoride and at least one other monomer copolymerizable with VDF. Advantageously, the copolymer comprises at least 50 mol%, preferably at least 70 weight%, even more preferably at least 90 mol% of VDF.

[0070] By way of illustration, the copolymerizable monomer(s) are, for example, chosen from chlorotrifluoroethylene (CTFE), chlorofluoroethylene (CFE), hexafluoropropylene (HFP), trifluoroethylene (VF3), methyl methacrylate (MMA), tetrafluoroethylene (TFE), and perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE).

[0071] For example, the copolymer is a copolymer of poly(vinylidene fluoride-trifluoroethylene) PVDF / TrFe, also noted P(VDF-TrFe) or PVDF-CTFE.

[0072] It can also be a terpolymer. For example, a PVDF / CTFE / CFE terpolymer will be chosen.

[0073] According to another embodiment variant, the polymer is not a ferroelectric polymer: it may be PVDF-HFP.

[0074] According to another embodiment variant, the polymer is polylactic acid (also noted PLA or PLLA).

[0075] Preferably, the piezoelectric films 120 are piezoelectric polymers chosen from PVDF, P(VDF-TrFE) and PLLA.

[0076] Each organic piezoelectric layer 120 may be a composite material. For example, the layer 120 may comprise, in addition to a piezoelectric or non-piezoelectric polymer matrix, piezoelectric particles and / or PEDOT:PSS particles. The particles will be small enough not to alter the roughness.

[0077] For example, the ferroelectric particles are made of BaTiO3 (BTO), PZT (lead zirconate titanoate), AIN, ZnO, or even SBN (Sr-Ba-Nb oxide) or SBT (Sr-Ba-Ti oxide).

[0078] For example, the piezoelectric films 120 are formed from composite materials comprising, for example, a polymer (piezoelectric type PVDF, or non-piezoelectric type TPU, PDMS, PVDF HFP) and piezoelectric nanoparticles or nanofibers (PVDF, PZT, BaTiO3, AIN).

[0079] The piezoelectric films 120 are polarized under an electric field such that, in the final device, the polarization direction of the piezo film(s) electrical of the sensors 11 positioned on the first face 100a of the substrate 10 is identical or opposite to the polarization direction of the sensors 12 positioned on the second face 100b of the substrate 100. By way of illustration, the arrows in FIGS. 4 and 6 represent opposite polarization directions.

[0080] The piezoelectric films 120 are arranged between electrodes 110, 130. The electrodes 110, 130 are flexible electrodes.

[0081] The electrodes 110, 130 have, for example, a thickness of between 0.1 and 3 μm, preferably between 0.5 and 1.5 μm, for example 1 μm.

[0082] Preferably, the electrodes 110, 130 are made of an electrically conductive polymer or a metal such as gold. Electrically conductive polymers have a better interface with the P(VDF-TrFE). Preferably, it is PEDOT-PSS (poly(3,4-ethylenedioxythiophene).

[0083] The sensors 11, 12 may be covered by a stack comprising one or more dielectric layers 140, 160 and / or a ground plane 150 (figures 6 and 7).

[0084] Preferably, the ground plane 150 is arranged between the two layers of a dielectric material 140, 160.

[0085] The ground plane 150 is flexible. It has a thickness of between 3 pm and 10 pm, for example 5 pm.

[0086] The ground plane 150 makes it possible to greatly reduce measurement noise, improve measurement accuracy and therefore open up the field of applications more widely.

[0087] The ground plane 150 is preferably printed. It is integrated into the device during its manufacture by printing.

[0088] To make the ground plane 150, any flexible conductive ink can be used.

[0089] The ground plane 150 is preferably made of carbon. Carbon is very conductive and has good biocompatibility, which is advantageous in the case where it is in contact with the human body because it is one of the layers closest to the external environment.

[0090] Alternatively, the ground plane 150 may be gold.

[0091] The lower dielectric layer 140 serves to electrically isolate the sensors 11, 12 from the ground plane 150. The upper dielectric layer 160 serves to protect the sensors 11, 12 from the outside (humidity, mechanical wear...).

[0092] The dielectric layers 160 are also flexible. They have a thickness between 3 µm and 10 µm, for example 5 µm.

[0093] The dielectric layer 140 between the electrode and the ground plane is thick enough not to crack during polarization and not too thick so as not to stiffen the sensor. Thicknesses of 30 µm can be used.

[0094] The dielectric material has few constraints. Preferably, a printable and crosslinkable material will be chosen. For example, it can be crosslinked non piezoelectric or FED AG. Preferably, EDAG is preferred because, at the time of printing, it does not contain a solvent that can damage the lower layers (unlike the TEP solvent of PVDF which damages silver).

[0095] Despite the superposition of the materials, the assembly formed by the sensor 11, 12, the dielectric layers 140, 160 and the ground plane 150 remains very thin. In particular, it has a total thickness of less than 100 μm.

[0096] The shape and size of the sensor 11, 12 can be varied as long as the two double-sided sensors have the same shape and size. They can be adapted to the intended application.

[0097] For the sensors 11, 12, a size will be chosen that is neither too small to facilitate the alignment of the two sensors facing each other, nor too large to avoid the presence of slight defects in the sensor. Indeed, the defects can cause an asymmetry between two sensors positioned facing each other, which can lead to a different electrical response and therefore hinder the proper functioning of the sensor.

[0098] For example, the largest dimension of the sensors 11, 12 (length, width, side or diameter in particular) is between 2 mm and 3 cm, preferably between 0.5 and 3 cm, and even more preferably between 1.5 and 2.5 cm.

[0099] To make denser matrices, reduce the probability that a sensor has a defect that could create an asymmetry in the double-sided and / or to have a uniform compressive stress over the entire surface of the sensor, sensors having a larger dimension between 2 and 5 mm will be preferred.

[0100] The distance between two sensors 11, 12 is, for example, between 0.1 and 5 mm, preferably between 0.5 and 2 mm.

[0101] The different sensors 11, 12 may have the same dimensions or different dimensions. The sensors positioned opposite each other will nevertheless have the same dimensions.

[0102] The sensors 11, 12 may have the same shape or different shapes.

[0103] They may be, for example, square, rectangular or circular. Preferably, they are circular.

[0104] Simple shapes (round or rectangular) will be preferred for ease of manufacture. Preferably, they have a round shape because the axial symmetry of this geometry also slightly facilitates the alignment of the face-to-face sensors. In addition, in the case of matrices with a high density of sensors 11, 12, the round shape leaves a little more space for the electrical tracks, for example in silver, and thus facilitates manufacture.

[0105] The materials forming the different sensors 11, 12 may be identical or different. Preferably, they are identical. Even more preferably, each sensor 11, 12 comprises electrodes 110, 130 made of PEDOT-PSS and a piezoelectric layer 120 made of P(VDF-TrFe).

[0106] The substrate 100 is a flexible substrate.

[0107] The substrate 100 serves as a mechanical support for the manufacture and use of the device.

[0108] It plays an essential role in the conformability of the device.

[0109] The substrate 100 may be made of polyimide (PI), poly(ethylene naphthalate) (PEN), polyethylene terephthalate (PET), thermoplastic polyurethane (TPU) or polydimethyl-siloxane (PDMS).

[0110] The thickness of the substrate 100 is, for example, between 10 and 500 μm, preferably between 20 and 250 μm.

[0111] The flexural rigidity of the substrate 100 depends on its modulus of elasticity and its thickness, each of which must have a sufficiently low value for the substrate 100 to be flexible.

[0112] Flexibility can be defined by means of the flexural rigidity of the substrate according to the following equation:

[0113] p — with Y the modulus of elasticity of the substrate, e its thickness and v its co Poisson efficiency

[0114] The substrate 100 is considered flexible if D < 10 4 Nm. Preferably, D = 105 Nm is chosen.

[0115] For illustration purposes, the flexibilities of different substrates 100 have been calculated and listed in the following table:

[0116] [Tables 1] Substrate Elastic modulus (MPa) Thickness (pm) Flexural stiffness (Nm) Conformable Glass 55,000 1,100 7 No PEN 4,000 125 7.10 4 No PI 5,000 25 7.106 Yes TPU 50 100 5.106 Yes PDMS 1,100 1.107 Yes

[0117] The thickness of the substrate 100 depends on the material chosen. For example, for PI, PEN, PET, a thickness less than 50 pm can be chosen, for TPU a thickness less than 250 pm and for PDMS a thickness less than 500 pm.

[0118] TPU is advantageously used because under high mechanical stress TPU has the advantage of not breaking / tearing, but rather of deforming plastically, which is a considerable advantage for in vivo applications.

[0119] As shown, for example, in Figures 4 and 6, the substrate 100 may be a one-piece support substrate (i.e. the substrate is formed from a single piece).

[0120] As shown for example in Figures 5 and 7, the substrate 100 may be formed from two support substrates 101, 102 assembled to each other, for example by means of an adhesive element 103, for example an adhesive film or a layer of glue, preferably deposited by screen printing. The two support substrates 101, 102 are preferably identical.

[0121] Thus, the sensors 11, 12 can be printed on two different substrates 101, 102 which are then assembled together. Indeed, it can be difficult to carry out a printing technique on two sides of the same substrate for certain thicknesses and / or certain materials such as TPU.

[0122] Preferably, an adhesive film is used. The adhesive film has little or no inhomogeneities in its thickness and does not require a solvent.

[0123] This is a double-sided adhesive. The double-sided adhesive may be a polyimide tape, for example a tape marketed under the name Kapton.

[0124] For medical applications, an adhesive will be chosen which does not lose its adhesion properties in the target environment, and in particular which does not lose its adhesion properties with humidity.

[0125] The two support substrates 101, 102 can also be assembled with a three-layer comprising a thin substrate (typically having a thickness of less than 50 μm) arranged between two so-called transfer adhesive tapes. The substrate is for example a PI substrate. It preferably has a thickness between 10 μm and 50 μm, for example 25 μm. The adhesive tapes are preferably resistant to temperature and to immersion in water. For example, the adhesive tape marketed by 3M under the reference VHB will be chosen.

[0126] The device comprises electrical connection means 200 arranged to route the electrical signal from the sensors, preferably to amplifiers 301, 302, then to measuring devices, preferably electronic measuring devices. Voltage measuring devices can also be used. Preferably, the two measuring devices are identical for each sensor.

[0127] The measuring devices electrically connected to the sensors make it possible to measure the signals from the sensors (11, 12).

[0128] The connection is preferably made by means of electrical tracks 200 (i.e. electrically conductive tracks). The tracks 200 can be printed on the substrate.

[0129] Any highly conductive ink that can be printed with a fairly fine resolution (typically the track width is less than 100 pm for high density matrices) can be used.

[0130] The tracks 200 may be made of a metal (gold for example), an electrically conductive polymer material. For example, the electrically conductive polymer material is PEDOT:PSS. It may also be a polymer in which electrically conductive particles, for example carbon particles, are dispersed. Silver may also be used in the form of ink, preferably formulated with a solvent-resistant polymer matrix (for example with a silicone, TPU or acrylate base).

[0131] Preferably, a silver-type ink (in particular a silicone matrix with silver particles) is used for the electrical connections between the sensor and the measuring electronics.

[0132] In the case of gold electrical connections 200, highly conductive tracks are obtained. These tracks are also biocompatible. The thickness of such tracks is preferably less than 200 nm to obtain flexible tracks. The thickness is preferably between 10 nm and 200 nm, for example 100 nm.

[0133] Gold can be deposited by photolithography, which makes it possible to achieve very high resolution and thus obtain matrices with a high density of sensors.

[0134] Preferably, gold is used with a PI substrate, which is resistant to the solvent used during photolithography (typically acetone).

[0135] Preferably, each sensor 11, 12 of the same face has an individual electrode and all the sensors 11, 12 of the same face share a common electrode connected to ground. For example, for a matrix n rows xm columns, there are anxm + 1 electrodes. Thus each sensor 11, 12 can be connected to a charge amplifier 301, 302. The charge amplifiers convert the electrical charges generated by the sensor into a proportional voltage signal.

[0136] For example, the first electrode 110 of each sensor 11 of the first matrix is ​​connected to an individual electrically conductive track 200 and, on the other hand, all the second electrodes 120 of the sensors 11 of the first matrix are connected to a common electrically conductive track 200. This makes it possible to reduce noise. According to another example, on the one hand, the second electrode 120 of each sensor 11 of the first matrix is ​​connected to an individual electrically conductive track 200 and, on the other hand, all the first electrodes 110 of the sensors 11 of the first matrix are connected to a common electrically conductive track 200.

[0137] The same applies to the second matrix.

[0138] Alternatively, it is possible to have n + m connections 200, that is to say that on one side all the sensors on the same row share a common electrode, and on the other side all the sensors on the same column share a common electrode. However, this configuration does not allow the signal from each sensor to be decorrelated individually.

[0139] According to an alternative embodiment, instead of connecting each sensor (or each row or each column) to a different charge amplifier, it is possible to short-circuit the lower electrodes of the two sensors and thus connect them to a single charge amplifier. The electrical charges are naturally summed. By dividing the signal by 2, the average of the signals is obtained. The signal corresponds to the sum of the signals from the sensors because the signal from each sensor can no longer be isolated.

[0140] Depending on the polarization direction and how the sensors are electrically connected to the measuring devices, it is possible to have several configurations. The signals of the sensors 11 of the first face 100a of the substrate 100 and the signals of the sensors 12 of the second face 100b of the substrate 100 can be either added or subtracted.

[0141] For example, to keep a signal in compression, the different possible configurations are listed in the following table 2:

[0142] [Tables2] Sensor polarizations Connecting sensors to measuring devices Operation to be performed to eliminate bending opposites opposites sum identical identical sum opposites identical subtraction identical opposites subtraction

[0143] Opposite polarization means that the sensor(s) on the same face of the substrate have a polarization opposite to the polarization of the sensor(s) on the other face of the substrate. Such polarization is represented by the arrows in [Fig.4].

[0144] By opposite connection of the sensors to the measuring devices (and to the charge amplifiers) is meant that the sensor(s) on the same face of the substrate are connected to the measuring devices in the opposite way to the way in which the sensor(s) on the other face of the substrate are connected to the measuring devices. For example, [Fig.6] shows two charge amplifiers connected in the opposite way.

[0145] The first configuration is the most optimal. This is the configuration shown in [Fig.6] (the arrows representing the direction of polarization of the piezoelectric layers 120). It makes it possible in particular to reduce noise by connecting the upper electrodes (closer to the external environment) to ground.

[0146] For some applications, it may be interesting to eliminate the compression and retain the bending. In this case, referring to Table 2, it is sufficient to reverse the operation performed on the 2 signals (i.e. subtract instead of adding, add instead of subtracting).

[0147] We will now describe in more detail the method of manufacturing such a device.

[0148] The device can be made as follows:

[0149] a) depositing several electrically conductive zones on a first face 100a of a substrate 100, the electrically conductive zones forming first electrodes 110,

[0150] b) forming piezoelectric layers 120 on the electrically conductive areas,

[0151] c) forming second electrodes 130 on the piezoelectric layers 120,

[0152] d) optionally, successively forming a first dielectric layer 140, a ground plane 150 and a second dielectric layer 160,

[0153] e) repeating steps a), b), c) and where appropriate d) on the second face 100b of the substrate 100.

[0154] It is also possible to carry out step a) on the first face 100a and on the second face 100b, then step b) on the first face 100a and on the second face 100b, then step c) on the first face 100a and on the second face 100b, then, if necessary, step d) on the first face 100a and on the second face 100b.

[0155] According to an alternative embodiment, steps a), b), c) and possibly d) are carried out on a first support substrate 101, step e) is carried out on a second support substrate 103 then the support substrates 101 and 103 are assembled by means of an adhesive element 102.

[0156] In step b), the piezoelectric material layer 120 can be deposited by "spin coating" (whirling coating). Other types of localized depositions can be used such as screen printing or spraying or even inkjet printing. Preferably, the piezoelectric layer 120 is deposited by screen printing. In one pass, the deposited thickness is between 1 and 20 µm. It is possible to stack several layers by screen printing up to the desired final thickness.

[0157] Steps a), b) and c) can be repeated to form several electroactive layers 120 intercalated between two electrodes 110, 130, according to the following sequence: N x (electrode / composite / electrode).

[0158] The method also comprises a step of crystallization (or alignment of the dipoles) of the layer of piezoelectric material, to improve its piezoelectric performance. This irradiation is for example implemented with UV flash light, with a flash duration, or pulse, of between approximately 500 ps and 2 ms, a fluence (energy delivered per unit area) of between approximately 15 J / cm2 and 25 J / cm2, and with light of wavelength of between approximately 200 nm and 380 nm. The number of flashes, or pulses, of UV light produced during this irradiation varies according to the thickness over which the piezoelectric material must be crystallized. For example, for a thickness of P(VDF-TrFe) equal to about 2 pm, the irradiation can be implemented with a fluence equal to about 17 J / cm2, a pulse duration equal to about 2 ms and a number of pulses equal to 5.

[0159] The piezoelectric material, having possibly undergone a previous crystallization, is then subjected to annealing, for example, carried out at approximately 130°C for approximately 60 min, to finalize the total crystallization of the piezoelectric material.

[0160] The crystallization of the piezoelectric material can therefore be carried out in two stages: firstly, irradiation by UV light pulse to properly crystallize the second face of the layer of piezoelectric material in order to increase its thermal conductivity, then thermal annealing completing the crystallization for the remainder of the piezoelectric material not crystallized by the previous irradiation.

[0161] When the piezoelectric material is a P(VDF-TrFe)-based copolymer, a step of polarizing the piezoelectric material is carried out before its use. This step can be carried out, for example, by applying a direct electric voltage to its terminals, via the electrodes, in order to improve the piezoelectric coefficient of this material. This polarization is carried out only once for the entire lifetime of the piezoelectric material. This polarization by electric field can be carried out at room temperature or hot (up to approximately 100°C). When the polarization is carried out at room temperature, it is possible to apply a direct voltage up to approximately 150V / pm of thickness of the piezoelectric layer for a duration, for example, of between a few seconds and a few minutes. For example, a voltage of 120V / pm will be applied for 20s.When the polarization is carried out hot, for example at a temperature of about 90°C, a direct voltage for example between about 50 V and 120 V per micron of thickness of the piezoelectric layer can be applied for a duration for example between about 1 min and 5 min. The temperature is then lowered until it reaches room temperature, then the electric field applied to the piezoelectric material, via the applied direct voltage, is stopped. Such polarizations allow the PVDF to achieve piezoelectric coefficients between about 10 and 40 pC / N.

[0162] The molecules inside the piezoelectric layer remain oriented in this way, even when the material is no longer subjected to this electric field. The material can be polarized in this way by applying an initial polarization voltage to the terminals of the electrodes. A thickness of piezoelectric material less than or equal to approximately 3 μm will preferably be chosen in order to promote the polarization of the piezoelectric material of this capacity, and the level of the electric voltage applied between the electrodes to achieve the initial polarization of the piezoelectric material (when the piezoelectric material must be initially polarized).

[0163] For example, we will aim for an ideal remanent polarization of 8 pC / cm2.

[0164] Annealing is advantageously carried out at the end of the process, or between the different stages. The annealing is, for example, at a temperature between 100°C and 150°C, preferably around 100°C to remove residual traces of solvent and / or finalize the crystallization of the piezoelectric material.

[0165] Each sensor 11, 12 of the device is preferably printed by screen printing on a substrate 100. The printing manufacturing method makes it possible to simplify and reduce the cost of the manufacturing process.

[0166] All sensors on the same side of the substrate can be printed at the same time.

[0167] As mentioned previously, the sensors can be printed on each side of the same substrate 100 or printed on two different support substrates 101, 102 which are then assembled with an adhesive element 103 (a glue or a double-sided adhesive for example).

[0168] When assembling the support substrates 101, 102, care will be taken to align them so that they are superimposed and that the bimorph principle works correctly. For example, for this, it is possible to print the two sensors 11, 12 on the same face of a substrate so that they are perfectly symmetrical along an axis. Then, a double-sided adhesive 103 is placed on the other side of the substrate 100. The substrate 100 is then folded along this axis of symmetry: the sensors 11, 12 are glued and superimposed.

[0169] The electrically conductive tracks 200 are preferably obtained by screen printing for silver after the formation of the sensors. If the tracks are made of gold, they can be deposited by evaporation or sputtering and then etched by photolithography before the formation of the sensors so as not to damage them. The tracks are advantageously formed before the double-sided assembly.

[0170] The device is used to measure compressive or bending forces.

[0171] To carry out a measurement, the lower electrodes 110 of each sensor are each connected to a measuring device, and preferably to a charge amplifier 301, while the upper electrodes 130 and the ground planes 150 are connected to the ground of the measuring electronics (the connections of the sensor(s) of the first face are therefore opposite the connections of the sensor(s) of the second face of the substrate). In this precise configuration, when the device is subjected to a compressive stress, the two sensors 11, 12 will produce an identical signal; when the device is subjected to a bending stress, the two sensors 11, 12 will produce an opposite signal. It is then possible to numerically calculate the average of the two signals to measure only the compression signal and eliminate the bending signal.

[0172] The method for measuring force in compression and bending comprises the steps following: - providing a conformable device comprising a substrate 100, having a first face 100a and a second face 100b, at least one first sensor 11 arranged on the first face 100a of the substrate 10 and at least one second sensor 12 arranged on the second face 100b of the substrate 10, the sensors 11, 12 being arranged opposite one another, the two sensors 11, 12 being polarized and electrically connected so as to cancel either the compressive forces or the bending forces, - applying compressive and bending forces to the device, - adding or subtracting the signals from the piezoelectric sensors 11, 12 so as to obtain either a compressive signal or a bending signal, and thus determining the compressive force or the bending force applied to the device.

[0173] In fact, even with a rigorous and controlled manufacturing method, it can be difficult to obtain two or more perfectly identical sensors assembled on both sides. The sensors can then have a slightly different response in bending. It is then possible that calculating the average of their signal will not be enough to completely eliminate the bending signal. The greater the bending, the more inaccurate the compression measurement will be, to the point of becoming uninterpretable. It is possible to correct this asymmetry by adding a digital gain in the software which is in addition to the measurement electronics. Indeed, when a bimorph device is stressed in a bending direction, whatever the radius of curvature, the difference in response between sensors remains identical.For example, in a bending direction, a first sensor can generate 30% less load than a second sensor, so it is sufficient to add a gain x0.7 to the second sensor so that the two sensors have an identical response and can thus completely eliminate the bending signal. However, this signal difference between sensors can vary depending on the bending direction. So for example, for a unitary conformable device (a single bimorph sensor 10), if the measurement is carried out on a convex surface ([Fig.8A]) it may be necessary to apply a gain x0.7 to the second sensor 12, while on a concave surface it will be necessary to apply a gain x0.9 to the first sensor 11. For more complex surfaces ([Fig.8C]), it may be difficult to find a simple correction factor since the surface has convex and concave areas.In this configuration, a device having a matrix, composed of several bimorph sensors 10, is particularly interesting since it allows the complex surface to be fictitiously divided into several concave or convex sub-surfaces ([Fig.8D]). Thus, each sensor is locally deformed only in a single bending direction, and the digital gain correction method can be applied to each bimorph 10.

[0174] Various embodiments and variations have been described. The person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art.

[0175] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.

[0176] Generally speaking, the invention makes it possible to measure compression forces with a flexible sensor even when the surface of the sensor is deformed (i.e. the surface is not flat during the measurement) or when it deforms during the measurement (for example when the sensor is placed on a flexible surface which will deform during the application of the force).

[0177] The invention is particularly interesting for the medical field. The device can be used to measure the force on a biological tissue, generally flexible and with a complex surface.

[0178] This invention is particularly aimed at medical applications, especially that of the mitral valve.

[0179] In particular, it can be used to measure coaptation forces in a heart valve in order to verify the correct closure of the heart valve, in particular during surgeries. The device previously described is particularly interesting for such applications because it makes it possible to match the curved shape of the valves which are flexible and to ignore the bending.

[0180] For example, Figures 9A, 9B, and 9C depict conformable measuring devices in a closed heart valve (mitral valve) consisting of an anterior leaflet (AL) and a posterior leaflet (PL) in different views.

[0181] The use of a device having sensor matrices is advantageous for having a mapping of the forces over the entire coaptation surface.

[0182] The device can also be placed directly on the skin which is flexible and which deforms greatly in bending. It can be used as pulse sensors, swallowing sensors, breathing sensors, or touch sensors on the body (touch sensors measuring the force between the skin and an external object).

[0183] The sensors are conformable and the elimination of the bending signal allows for quantitative analysis of the measured signal.

[0184] The device is also interesting for applications outside the medical field.

[0185] For example, the device can measure the pressure in a tire. The two-sided device makes it possible to measure the pressure variation in the tire without being influenced by rolling. Indeed, the surface of a tire deforms in flexion during rolling, a pressure variation corresponds to a compressive stress.

[0186] The device can also be used to measure a force on a textile material. The device can be integrated directly onto a textile without modifying its flexibility and allowing the measurement of compressive forces.

[0187] Illustrative and non-limiting example of a particular embodiment

[0188] The device described herein is made to measure, for example, coaptation forces in the mitral valve. The device is a unitary device (two sensors facing each other), but it could be a matrix device or a linear device. All sensors on the same side of the substrate could be printed at the same time.

[0189] The sensors are screen printed on a TPU substrate with a thickness of 100 μm (for example, marketed under the reference Intexar TE-1 IC by DuPont). A layer of PEDOT:PSS (marketed by Heraeus) is printed first to form the first electrode. Then, an annealing at 135°C for 30 minutes is carried out to evaporate the solvent (final thickness approximately 1 μm). The piezoelectric material, P(VDF-TrFE) 80 / 20 marketed by the company Arkema Piezotech, is printed and then an annealing for 3 minutes is carried out at 135°C under vacuum (thickness 3 μm). The upper electrode in PEDOT:PSS is then deposited in the same way as the lower electrode. Silver tracks (Taiyo) are also printed. The tracks have a thickness of approximately 10 μm. Then a 10-minute annealing at 135°C is carried out. These tracks allow the sensor to be connected to the measuring electronics.Then the first layer of dielectric is printed (marketed under the reference Loctite ED AG PF 455B). Exposure under a mercury lamp (UV) allows the layer to crosslink (layer thickness approximately 10 pm).

[0190] For example, for a speed of 10 m / min, three passes and 35% of the power (for a conventional mercury insolation lamp), the following fluences (energies delivered per unit of area) were used:

[0191] [Tables3] mJ / cm2 W / cm2 UVA 430 248 UVB 257 155 UVA2 98 61 UVV 340 195

[0192] Depending on the Young's modulus of the substrate, it is possible to modify this fluence range between 100 and 500mJ / cm2. UVA and UVB correspond to the major part of the crosslinking energy.

[0193] If the substrate has a Young's modulus of less than 0.5GPa, as is the case for a TPU substrate, a fluence of approximately 150 mJ / cm2 is sufficient and allows to avoid creating too many constraints in the piezoelectric layer (which could affect ferroelectric performance).

[0194] The ground plane is then printed. This is a layer of 10 pm carbon, marketed by the DuPont company under the reference PE 671, then an annealing is carried out for 10 minutes at 135°C. The thickness can be between 1 and 20 pm and preferably around 5 pm.

[0195] Finally, the second dielectric layer is deposited in the same manner as the first.

[0196] Once two identical sensors are printed in the same way on two separate substrates, they are laser cut with the same geometry. Then, the substrates are bonded, using the precision of the cutting for alignment. Bonding is carried out using a three-layer adhesive obtained from a 25 μm thick polyimide film onto which an adhesive marketed by the company 3M under the reference VHB has been transferred on each side.

[0197] The sensors are then polarized. The first sensor is connected to a voltage source via its electrodes. A first low DC voltage (electric field in the piezoelectric material ~ 30 V / pm) is applied for 3 minutes to evacuate a maximum of electrical charges from the sensor. It is then possible to carry out a first voltage increase in AC at 10 Hz (from approximately 30 V / pm up to 120 V / pm) to eliminate certain defects in the sensor. The same voltage increase is then carried out again but at 1 Hz to finalize the alignment of the dipoles. The same polarization process is repeated for the second sensor, taking care to connect the lower and upper electrodes to the outputs of the voltage source in the same configuration as for the first sensor.

[0198] For measurements, each lower electrode of each sensor is connected to a charge amplifier (DDC118 with 2 kHz sampling). The upper electrodes and the ground planes are connected to the ground of the measurement electronics.

[0199] A program, for example a python program, allows you to visualize the response of the two charge amplifiers, to apply a 20 Hz low-pass filter to eliminate the noise, and to calculate the average of the two signals.

[0200] To calibrate the device in compression, it is placed on a rigid glass plate with a double-sided adhesive (for example a double-sided adhesive sold under the reference “Sticky double face 9030 W” by the company Teraoka). Then, a flat indenter is pressed perfectly parallel to the surface of the sensor with different forces ([Fig. 10]).

[0201] To test the correct operation of the device (elimination of bending), the device is placed between two curved pieces having complementary shapes to fit into each other, and pressed with different forces ([Fig. 11]). To fit the curved shape, the sensors are subjected to bending and compression when the parts are pressed against each other.

[0202] The response of the sensors in compression on the one hand and in bending on the other hand was studied (figures 12A and 12B).

[0203] The compression signal is very clear ([Fig.l2A]). In compression the two sensors have a similar response.

[0204] The bending signal can be cancelled ([Fig.l2B]).

[0205] The mixture of the two stresses (bending and compression) results in a disturbed signal for the two sensors taken individually ([Fig. 13]). However, the average of the two signals makes it possible to eliminate the bending signal and to obtain only a compression signal as during the compression calibration test. It is thus possible to go back to the value of the force applied between the two parts.

[0206] Different devices have been realized. [Fig. 14] represents a 4x7 sensor matrix on a convex surface. [Fig. 15] represents a 4x7 sensor matrix covered by an encapsulation layer with long connections. Figures 16 and 17 represent the device of [Fig. 15] on complex surfaces.

[0207] [Fig. 18] shows several types of piezoelectric sensors printed on a 38 cm by 32 cm substrate.

Claims

Claims

1. A conformable force measuring device, intended to be subjected simultaneously to compressive forces and bending forces, the device comprising a substrate (100) having a first face (100a) and a second face (100b), at least one first sensor (11) arranged on the first face (100a) of the substrate (100) and at least one second sensor (12) arranged on the second face (100b) of the substrate (100), the sensors (11, 12) comprising an organic piezoelectric layer (120) arranged between a first electrode (110) and a second electrode (130), the sensors (11, 12) being arranged opposite one another, so as to form a bimorph (10), the sensors being connected to electrically conductive tracks (200) intended to be connected to measuring devices, the organic piezoelectric layers (120) of the sensors (11, 12) being polarized in the same or opposite way.

2. Device according to claim 1, characterized in that the sensors (11, 12) are covered by a stack successively comprising a first dielectric layer (140), a ground plane (150) and a second dielectric layer (160).

3. Device according to one of claims 1 and 2, characterized in that the ground plane is made of carbon and / or in that the first dielectric layer (140) and the second dielectric layer (160) are made of ED AG or PVDF.

4. Device according to any one of claims 1 to 3, characterized in that the substrate (100) is a PEN or PI substrate.

5. Device according to any one of claims 1 to 3, characterized in that the substrate (100) comprises two support substrates (101, 102), for example made of TPU, assembled to each other by an adhesive element (103).

6. Device according to any one of the preceding claims, characterized in that the first face (100a) of the substrate (100) is covered by a first matrix of sensors and the second face (100b) of the substrate (100) is covered by a second matrix of sensors, the first matrix and the second matrix being arranged opposite each other.

7. Device according to the preceding claim, characterized in that, on the one hand, the first electrode (110) of each sensor (11) of the first matrix is connected to an individual electrically conductive track (200) and, on the other hand, in that all the second electrodes (120) of the sensors (11) of the first matrix are connected to a common electrically conductive track (200) and in that, on the one hand, the first electrode (110) of each sensor (12) of the second matrix is connected to an individual electrically conductive track (200) and, on the other hand, in that all the second electrodes (120) of the sensors (12) of the second matrix are connected to another common electrically conductive track (200).

8. Force measurement system comprising a conformable device intended to be subjected simultaneously to compressive forces and bending forces, the device comprising a substrate (100) having a first face (100a) and a second face (100b), at least one first sensor (11) arranged on the first face (100a) of the substrate (100) and at least one second sensor (12) arranged on the second face (100b) of the substrate (100), the sensors (11, 12) comprising an organic piezoelectric layer (120) arranged between a first electrode (110) and a second electrode (130), the sensors (11, 12) being arranged opposite one another, so as to form a bimorph (10), the system further comprising measuring devices electrically connected to the sensors (11, 12) for measuring the signals of the sensors (11, 12), the layers organic piezoelectrics (120) of the sensors (11, 12) being polarized and the sensors (11,12) being electrically connected to the measuring devices so as to cancel either the compressive forces or the bending forces, and measure, respectively, either the bending forces or the compressive forces applied to the device.,

9. System according to claim 8, characterized in that the polarization of the sensors (11, 12) is opposite, in that the sensors are connected to the measuring devices in opposite ways and in that the signals measured by the measuring devices are added, whereby the bending forces are canceled and the compressive forces are measured.

10. System according to claim 8, characterized in that: - the polarizations of the sensors (11, 12) are identical, the sensors are connected to the measuring devices in such a way identical and the signals measured by the measuring devices are added together, or - the polarizations of the sensors (11, 12) are opposite, the sensors are connected to the measuring devices in an identical manner and the signals measured by the measuring devices are subtracted, or - the polarizations of the sensors (11, 12) are identical, the sensors are connected to the measuring devices in opposite directions and the signals measured by the measuring devices are subtracted, whereby the bending forces are cancelled out and the compressive forces are measured.

11. A method for measuring compressive and flexural force, comprising the following steps: - providing a force measurement system comprising a conformable device intended to be simultaneously subjected to compressive forces and bending forces, the device comprising a substrate (100) having a first face (100a) and a second face (100b), at least one first sensor (11) arranged on the first face (100a) of the substrate (100) and at least one second sensor (12) arranged on the second face (100b) of the substrate (100), the sensors (11, 12) comprising an organic piezoelectric layer (120), arranged between a first electrode (110) and a second electrode (130), the sensors (11, 12) being arranged opposite one another, so as to form a bimorph (10), the system further comprising measuring devices electrically connected to the sensors (11, 12), for measuring the signals of the sensors (11, 12), the organic piezoelectric layers (120) of the sensors (11, 12) being polarized and the sensors (11,12) being electrically connected to the measuring devices so as to cancel either the compressive forces or the bending forces, - simultaneously apply compressive and bending forces to the measuring device, - add or subtract the signals measured by the measuring devices, so as to cancel either the compressive forces either the bending forces, and thus measure, respectively, either the bending forces or the compressive forces applied to the device.

12. Method according to claim 11, characterized in that the device comprises a first matrix of sensors on the first face (100a) of the substrate (100) and a second matrix of sensors on the second face (100b) of the substrate (100), the first matrix and the second matrix being arranged opposite each other.

13. Method according to one of claims 11 or 12, characterized in that the sensor(s) (11) of the first face (100a) have a polarization opposite to the polarization of the sensor(s) (12) of the second face (100b), in that the sensor(s) (11) of the first face (100a) are electrically connected to first charge amplifiers (301), the sensor(s) (12) of the second face (100b) are electrically connected to second charge amplifiers (302), the electrical connections to the first charge amplifiers (301) and the electrical connections to the second charge amplifiers (302) being opposite, the signals from the sensors being added to eliminate the signal of the bending forces and obtain the signal of the compression forces.

14. Method according to claims 12 and 13, characterized in that, on the one hand, the first electrode (110) of each sensor (11) of the first matrix is connected to an individual electrically conductive track (200), itself electrically connected to a charge amplifier, and, on the other hand, in that all the second electrodes (120) of the sensors (11) of the first matrix are connected to a common electrically conductive track (200), electrically connected to the ground of one of the measuring devices, and in that, on the one hand, the first electrode (110) of each sensor (12) of the second matrix is connected to an individual electrically conductive track (200), itself electrically connected to a charge amplifier, and, on the other hand, in that all the second electrodes (120) of the sensors (12) of the second matrix are connected to an electrically common conductor (200),electrically connected to the ground of one of the measuring devices.,

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