EP0317457A1 - Technical textile structure for the detection and conversion of a pressure variation into an electric signal - Google Patents

Abstract

The invention relates to a technical fabric with a piezoelectric effect. According to the invention, the fabric comprises a lap (5) for mechanical support and a plurality of piezoelectric cables (1) arranged parallel to one another, each piezoelectric cable being connected individually to the supporting lap. The invention is used particularly for peripheral and perimetric detection. <IMAGE>

Description

The present invention relates to a textile structure behaving as a sensor, and more specifically intended to capture and convert a pressure variation into an electrical signal.

The invention will be described and explained below, with reference to devices for detecting the presence or passage of an intruder, and in particular to peripheral or perimeter protection and security systems; but it should be understood that this is a particular field of application of the invention, but not exclusive, as will be stated at the end of the present description.

By variation in pressure is meant any variation in static pressure, caused for example by a jolt, shock, shock, or any other form of mechanical stress.

Such a pressure variation can also be caused by a noise, a sound, generating a difference in acoustic pressure.

According to patent EP-A-0146272, piezoelectric type sensors are already known, making it possible to transform a pressure variation into an electrical signal, and arranged in the form of a coaxial cable comprising:
- an internal conductive core, for example metallic, forming an electrode;
- An intermediate tube, in contact with the internal core, made of a piezoelectric material, for example a piezoelectric polymer, for example polyvinylidene fluoride;
- And an external conductive envelope, for example metallic, forming a counter-electrode, in contact with the intermediate tube.

Under the effect of a pressure variation applied to the coaxial cable defined above, an electrical signal is generated between the inner core and the outer shell, which can be processed for different purposes, for example to generate a signal alarm.

Such a piezoelectric cable has hitherto been used in a unitary manner, as a local and specific sensor. Thus, by drowning such a cable in a ground, for example in the roadway of a road, one can detect in a localized way the passage of a vehicle.

Such a unitary and localized implementation has significant drawbacks.

If a large area detection area is covered, by distributing therein a plurality of piezoelectric collection cables, one obtains respectively distinct and heterogeneous electrical signals; in fact, the response of the various corresponding sensors depends on the environment specific to each of them. The overall processing, for example electronic, of these different signals is difficult, if not impossible.

And, for a large detection area, the corresponding distribution of different filiform piezoelectric sensors proves incapable of compensating for the heterogeneities of the medium or the environment in which these sensors are arranged.

The present invention proposes to remedy the aforementioned drawbacks.

The invention relates to a piezoelectric type sensor, allowing the detection of a pressure variation over a relatively large surface, by obtaining an electrical signal relatively independent of the heterogeneity of the medium in which the detection surface is located. .

According to the present invention, the sensor consists of a technical textile structure comprising, on the one hand a ply of mechanical support wires, and on the other hand at least a plurality of piezoelectric cables of the coaxial type defined above, arranged in parallel and at a distance from each other in at least one direction of capture of the mechanical support ply. Each piezoelectric cable is individually linked to the mechanical support ply. And all the piezoelectric cables are connected, or arranged to be connected, in particular in parallel, to a single collector of an electrical signal.

The connection of each piezoelectric cable to the support ply can be obtained in different ways. It may for example be a connection with an adhesive, or an overall plastic coating, used in the final manufacturing phase, and providing complete privacy between the support ply and the coaxial cables.

Preferably, but not exclusively, it is a connection obtained during the process of manufacturing the piezoelectric fabric, with bonding threads, distinct from the weft and / or warp threads, finer than these last, and having no mechanical support function.

With the technical textile structure according to the invention, in connection with the parallel electrical arrangement of the various piezoelectric coaxial cables, a uniform response is obtained, relatively insensitive to local or point differences in the environment or the environment in which it is located. finds the surface sensor according to the invention.

It has also been discovered that a sensor according to the invention brings the following important and unexpected result:
- taking into account the connection between the piezoelectric cables and the mechanical support ply, any local variation in pressure is passed on step by step, that is to say from mesh to mesh of the support, and consequently on the neighboring cables
- We therefore obtain a response, not only from the cable subjected to a specific pressure stress, but also from others, and this in an omni-directional manner;
- there is therefore a real amplification of the point solicitation, passed on to the signal collector.

In addition, according to the invention, since the piezoelectric cables are in a way placed on the support ply, and therefore not integrated into the latter, they are not subjected to any stress, such as twisting or elongation, capable of modifying or alter their electrical response. The piezoelectric cables of the fabric according to the invention therefore have a direct electrical response, with respect to the pressure stresses received.

The invention also provides the following additional advantages.

A piezoelectric textile structure according to the invention, having its own mechanical resistance, does not require any intermediate support for its implementation. It can for example be used in natural soil, without significant preparation; a slight digging of the ground, corresponding to a cleaning or pickling on the surface, is enough to bury this structure in the vicinity of said surface. Likewise, this structure can be placed directly on a fence mesh.

The absence of such an intermediate support increases the sensitivity of the surface piezoelectric sensor according to the invention.

When buried in natural soil, the permeability of the piezoelectric tissue does not obstruct the flow of water, and this tissue contributes to the retention of natural soil.

The mode of electrical connection of the sensor according to the invention to the electrical signal processing system is greatly simplified, compared to a plurality of piezoelectric sensors, filiform, distinct and local. This observation also applies in the case of a sectorized sensor, as described below.

When a sensor according to the invention is buried in the ground, it prevents any digging on the part of an intruder or an animal, taking into account its own mechanical strength. This avoids any vacuum or cavity facing the coaxial cables, damping or even canceling the desired piezoelectric response.

• - la figure 1 représente une vue éclatée en pers­pective d'un cable piézo-électrique, tel qu'utilisé conformément à l'invention ;
• - la figure 2 représente, en vue de dessus, une structure textile technique conforme à l'invention, et le mode de connexion électrique de cette dernière ;
• - la figure 3 représente une vue en coupe selon la ligne III-III de la figure 2, du tissu représenté à cette dernière ;
• - la figure 4 représente de manière schématique un dispositif de détection de la présence ou du passage d'un intrus, assurant à la fois une protection périphérique et périmétrique, et faisant usage et application d'une structure textile selon les figures 2 et 3 ;
• -la figure 5 représente de manière schématique un tissu technique selon l'invention, sectorisé, c'est-­à-dire divisé en plusieurs zones distinctes de détec­tion ;
• - la figure 6 représente de manière schématique, en coupe, un dispositif de protection périphérique selon l'invention, utilisé et intégré dans une toiture ou terrasse ;
• - la figure 7 représente un exemple d'un système de traitement électronique du ou des signaux électriques générés par un capteur piézo-électrique selon l'invention.

The present invention is now described with reference to the accompanying drawings, in which:

• - Figure 1 shows an exploded perspective view of a piezoelectric cable, as used in accordance with the invention;
• - Figure 2 shows, in top view, a technical textile structure according to the invention, and the method of electrical connection thereof;
• - Figure 3 shows a sectional view along line III-III of Figure 2, of the fabric shown therein;
• - Figure 4 schematically shows a device for detecting the presence or passage of an intruder, providing both peripheral and perimeter protection, and making use and application of a textile structure according to Figures 2 and 3;
• FIG. 5 schematically represents a technical fabric according to the invention, sectorized, that is to say divided into several distinct detection zones;
• - Figure 6 shows schematically, in section, a peripheral protection device according to the invention, used and integrated in a roof or terrace;
• - Figure 7 shows an example of an electronic processing system of the electrical signal or signals generated by a piezoelectric sensor according to the invention.

According to FIG. 1, a piezoelectric cable (1) which can be used according to the invention comprises:
- an internal core and conductive of electricity, forming an electrode;
- an intermediate tube (3) of a piezoelectric material;
- an outer envelope (4) conductive of electricity, forming a counter-electrode.

The internal core, the intermediate tube, and the external envelope are in contact with each other, in an intimate manner.

In accordance with FIGS. 2 and 3, a technical textile structure according to the invention, having a role both to capture and convert a pressure variation into an electrical signal, comprises, on the one hand, a layer of threads (6) and (7) mechanical support, for example polyester, and on the other hand a plurality of piezoelectric cables, referenced (1a, 1b, 1c ...).

The support ply (5) comprises warp threads (6) arranged substantially in the same plane, as shown in FIG. (3), and weft threads (7), arranged transversely and perpendicularly on the chain wires (6). Relatively thin, continuous connecting wires (8) are inserted into the ply (5) in a binding direction, identical in this case to the chain direction. Each connecting wire (8) connects, by a movement of both translation and rotation, a weft thread (7) to the warp threads (6) arranged below and transversely. Thus, the mechanical support ply has good dimensional consistency and stability.

As shown in FIG. 2, the support ply (5) is perforated, according to a grid type texture, which means that there are gaps between the warp threads and the weft threads. Mechanical support plies, as previously defined, are for example manufactured and sold by the French company NOTEX, in Tarare in the Rhône.

Of course, the connection method described above can be achieved by linking the warp yarns to the weft yarns, contrary to the previous description.

The piezoelectric cables (1) are arranged parallel and at a distance from each other, in a direction of capture of the sheet, identical to the direction of the weft wires according to FIGS. 2 and 3. Each piezoelectric cable, by example (1a), is individually linked to the ply (5) of mechanical support, and more precisely, according to FIGS. 2 and 3, to an adjacent weft thread, for example (7a), and to the warp threads (6) arranged below and perpendicularly. To do this, a binding wire, for example (8a), identical to the connecting wires (8) described above, continuous, is inserted into the sheet (5), in the direction of capta tion, in this case the direction of the weft threads. Each binding wire such as (8a) connects by a movement, both in translation and in rotation, a piezoelectric cable (for example (1a)) or adjacent weft wire (for example (7a)), and to the lower chain threads (6).

A true crosslinking of the piezoelectric cables (1) is thus obtained with the support ply (5). The direction of capture, in this case that of the weft threads, corresponds to the direction of winding or unwinding of the piezoelectric textile structure.

As described above, the binding direction of all the weft yarns, whether it is the weft itself (7) or the piezoelectric cables (1), is identical to the direction of capture, whereby, at the manufacturing level, the connecting wires of the support ply (5) are not differentiated, and also serve as binding wires for piezoelectric cables (1).

As shown in Figure 2, all piezoelectric cables (1) are connected, in parallel, to a single collector (9) of the electrical signal.

The sensor described above can be arranged as a differential sensor, and to do this:
- a reference cable, for example (1a) is assigned to capturing the variations in permanent pressure of the environment;
- and two measurement cables, (1b, 1c) are assigned to capture instantaneous pressure variations, and greater than those of the environment;
- the collector (9) of the electrical signal is connected between the reference cable (1a) and the measurement cables (1b) and (1c), themselves arranged in parallel.

In accordance with FIG. 5, only the piezoelectric cables (1a) to (1d) have been shown, with the exception of the support ply described above. According to this same figure, the sensor described above can be sectorized, which means that the piezoelectric cables are distributed for example in two distinct sectors, in this case (1a) and (1b) on the one hand, and ( 1c) and (1d) on the other hand. The pair (1a / 1b) is connected to its own collector, and the same is true for the pair (1c / 1d). The reference (10) designates a system for processing the two separate electrical signals, collected as indicated above.

In accordance with FIG. 4, a piezoelectric textile structure as described above is used to detect the presence or the passage of an intruder, both horizontally and vertically.

According to this figure, posts (19) are embedded in a concrete screed (18), itself buried in natural soil (17). All these posts (19) support a fence grid (20), delimiting on one side the interior of an enclosure (on the left of FIG. 4), and on the other side the exterior of the same enclosure.

A first piezoelectric structure (11) is buried in the natural soil (17), inside the enclosure, in the vicinity of the fence, to generate an electrical signal, picked up at (12); such a signal will correspond to the passage of an intruder towards the fence.

A second piezoelectric structure (13) is arranged on the fence, on the other side of the grid (20), and follows the developed shape of the same fence. The structure (13) is buried at its lower part in the ground (17), and in particular embedded in the screed (18). Consequently, in (14), it is possible to collect a signal detecting the escalation or the attempted escalation of an intruder coming from inside the enclosure.

A third piezoelectric structure is supported by the grid (20), outside the fence, and is also embedded at its lower part in the ground (17) and the screed (18).

Consequently, in (16), one can pick up an electrical signal corresponding to the attempt to cross an intruder coming from outside.

FIG. 7 gives, by way of indicative example, and in no way limiting, a block diagram of a possible embodiment of an electronic system for processing the signals emitted by a piezoelectric sensor according to FIG. 5.

The pairs of piezoelectric wires (1a) - (1b) and (1c) - (1d) are connected in parallel in two separate areas and pass through coaxial sockets (PC) on ordinary intermediate coaxial cables (CO) to enter each on the grid of input field effect transistors (TEC1) - (TEC2) whose source is connected to 50 Hz rejection filters (F1) and (F2). It is considered that the domains (D1) and (D2) of the pairs of piezoelectric wires cannot be stressed at the same time.

The output of each of the filters (F1) and (F2) is connected in parallel to each of the inputs of an amplifier (AE) with zero adjustment (Z), the output of which is connected in series with another rejection filter on 50 Hz (F3) and an adapter amplifier (AA).

A Schmitt trigger (TS) connected to the amplifier output (AA), shapes small oscillations via a clipping circuit (E) to supply a light (V1) and sound (B1) signal , depending on the passing state of a door (ET).

A comparator amplifier (AC) with threshold adjustment (S), the other of the inputs of which is connected to the output of the adapter amplifier (AA), delivers voltages resulting from large oscillations, considered to be valid, to an integrating amplifier (AI), as well as a warning rocker (BA1) which supplies, via a flashing circuit (CL1), a light signal (V2) and, directly, an audible signal (B2).

The output of the integrating amplifier (AI) supplies a Vumeter (Vu) with scale contact (set at the top) through a calibrator circuit (CAL).

The Vumeter contact (CVu) is set to very large amplitudes and activates a rocker (BA2) supplying, via a flashing circuit, a light signal (V3) and a sound signal (B3) directly. An acknowledgment button (ACQ) acts on the elements concerned.

In accordance with FIG. 6, a piezoelectric textile structure (14) is integrated on the surface and outside of a construction, for example on a terrace or a roof. To this end, on a concrete screed (22), there is an elastomeric mat (23), therefore elastic. Next to this elastomeric mat is placed a piezoelectric textile (21), as defined above. Then, the piezoelectric textile (21) is covered with a sealing material (24). The sealing layer (24) consists of slabs of a waterproof material welded together, by a seal shown in reference (25).

The present invention, according to the preceding description, has been applied on the one hand to a peripheral protection device, by surface burial of the piezoelectric tissue, or integration into a terrace or a roof, and on the other hand to a perimeter protection, by applying piezoelectric fabric on one or both sides of a vertical fence, or of a wall, whereby any escalation or attempted escalation of an intruder can be detected.

With regard to fences, by an appropriate choice of particularly resistant mechanical support wires, the piezoelectric fabric according to the invention can be used directly as sensitive fence.

As regards the security of goods or people, the present invention can receive many other applications:
- by surface integration of the same technical fabric, in partitions, walls or ceilings;
- whether internal or external constructions or infrastructures;
- by arrangement like a net, above an empty space, such as an interior or exterior courtyard.

A technical fabric according to the invention can be immersed in a liquid medium, for example water, and serve as previously as a sensor.

Besides the security of goods and people, the invention can be applied to other fields, such as seismic detection, reception of ultra-sonic signals reflected by a target, etc.

Claims (18)

1 / Technical textile structure for capturing and converting a pressure variation into an electrical signal, characterized in that it comprises, on the one hand, a ply (5) of wires (6,7) of mechanical support, and d on the other hand at least a plurality of piezoelectric cables (1), arranged in parallel and at a distance from each other, in at least one direction of capture of the sheet, and individually linked to the mechanical support sheet, each piezo cable -electric comprising in a manner known per se an internal conductive core (2) forming an electrode, an intermediate tube (3) of a piezoelectric material, and an external conductive envelope (4) forming a counter-electrode, all cables piezoelectric being connected or being arranged to be connected to a single collector (9) of the electrical signal. 2 / Structure according to claim 1, characterized in that the ply (5) of mechanical support is perforated, in particular according to a texture of the grid type. 3 / Structure according to claim 1, characterized in that each piezoelectric cable (la) is linked to the sheet (5) of mechanical support by a continuous binding wire (8a), which is inserted into said sheet according to the direction of capture, and connects by a movement of both translation and rotation said cable to at least one wire (7a) of adjacent support. 4 / Structure according to claim 1, characterized in that the ply (5) of mechanical support comprises warp son (6) arranged in the same plane, and weft son (7) arranged transversely on the son of warp, while connecting wires (8), continuous, are inserted into the web, in at least one direction of binding, identical to the direction of weft or warp, and each connect by a movement of both translation and rotating a weft (7) or warp (6) thread to the warp (6) or weft (7) threads, respectively, arranged transversely. 5 / A structure according to claims 3 and 4, characterized in that the binding direction is identical to the capture direction, whereby the connecting son (8) of the mechanical support ply (5) serve as binding son ( 8a) piezoelectric cables (1). 6 / A structure according to claim 1, arranged as a differential sensor, characterized in that at least one reference cable (1a) is assigned to capture the permanent pressure variations of the environment, and at least one measurement cable ( 1b, 1c) is assigned to capture instantaneous pressure variations, and greater than those of the environment, the collector (9) of the electrical signal being connected between the reference cable and the measurement cable. 7 / A structure according to claim 1, sectorized, characterized in that the piezoelectric cables (1) are divided into separate sectors (1a, 1b) (1c, 1d), connected respectively to separate collectors. 8 / Device for detecting the presence or passage of an intruder, comprising a textile structure according to any one of claims 1 to 7, characterized in that it comprises, on the one hand, a support means (17, 20) of the developed surface of the structure piezoelectric textile, and on the other hand a system (10) for processing the collected electrical signal, in particular for generating an alarm. 9 / Device according to claim 8, characterized in that the piezoelectric textile structure (11) is buried in a natural soil (17), in the vicinity of the surface of the latter. 10 / Device according to claim 8, characterized in that the textile structure (21) piezoelectric is integrated on the surface in an interior or exterior construction (22). 11 / Device according to claim 10, characterized in that the piezoelectric textile structure (21) is arranged on a terrace (22) or a roof, and is itself coated with a sealing material (24). 12 / Device according to claim 11, characterized in that an elastic mat (23) is disposed between the terrace (22) or the roof, and the piezoelectric textile structure (21). 13 / Apparatus according to claim 8, characterized in that the textile structure (15) piezoelectric is disposed on a grid (20) for support, serving in particular as a vertical fence. 14 / Device according to any one of claims 8 to 13, characterized in that the system for processing the collected electrical signal essentially comprises at least one differential circuit capable of acting on amplifier-compactor circuits to trigger or not, depending on the data variations prerecorded corresponding to different stress states of the structure, alarm systems. 15 / Device according to any one of claims 8 and 14, characterized in that the piezoelectric wires of the structure are connected in parallel in two separate areas to attack the differential circuit. 16 / Device according to any one of claims 14 and 15, characterized in that the differential circuit comprises for each domain at least one field effect transistor (TEC1) - (TEC2) whose source is connected via '' a filter to an amplifier (AE), the output of which is connected in series to a filter (F3) and an amplifier-adapter (AA). 17 / Device according to any one of claims 14, 15 and 16, characterized in that a circuit for shaping a Schmitt trigger (TS) is connected to the output of the amplifier (AA) to supply or not through a clipping circuit (E), depending on the passing state or not of an electronic gate (ET), one of the alarm systems. 18 / Device according to any one of claims 14, 15 and 16, characterized in that the amplifier-comparator (AC) has one of its inputs connected to the output of the amplifier-adapter (AA) and delivers voltages to an amplifier-integrator (AI) and to a flip-flop (BA1) which supplies one of the alarm systems, the output of said amplifier-integrator (AI) supplying a control device (Vu), a contact of which is capable of actuating a rocker (BA2) subject to the amplifier-comparator (AC) to supply one of the other alarm systems.

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