FR2993407A1 - Piezoelectric sensor for use in vehicle, has soleplate comprising set of terminals that is arranged to allow establishment of electrical connection with terminals coupled to another sole of latter piezoelectric sensor - Google Patents

Abstract

The invention relates to a piezoelectric detector comprising a sole (21), a piezoelectric device carried by said sole, a mechanical connection between a measuring face (17) arranged to be able to receive a pressure force and the sole and adapted to transmit the forces of pressure imparted on the face (17) of measurement to the piezoelectric device. The sole (21) is provided with means (35, 36, 37) for assembling at least one other sole plate (21) of another adjacent analog piezoelectric detector, to allow the soles of several detectors to be assembled with the faces. of measurement that are adjacent to each other. The soleplate (21) has at least one series of terminals (24) arranged to provide electrical connection to a series of terminals (24) mated with another flange of another adjacent analog piezoelectric detector. The invention extends to a sensor provided with a plurality of detectors according to the invention assembled juxtaposed on a common support.

Description

The invention relates to a piezoelectric detector, and a sensor 5 for passing a moving vehicle comprising a plurality of piezoelectric detectors associated with a common support intended to be implanted on the ground in the form of a piezoelectric detector. through a passageway of said vehicles. US 5461924 discloses a measuring rail for installation across a passageway for dynamic detection of reaction forces acting on the surface, such as, for example, speed or the like. This rail incorporating in particular a tubular force transmission structure incorporating sensitive elements in the form of piezoelectric plates, all electrically connected to the same electrical conductor delivering the electrical charges provided by the piezoelectric plates to a same processing unit arranged to the outside of the rail on one side of the passageway. Such a rail has no reliability, the different piezoelectric plates can not present by construction strictly the same sensitivity, not providing each of the calibrated signals and influencing each other. US 5265481 also discloses a passage sensor in the form of an elongated hollow beam incorporating a plurality of piezoelectric plates electrically connected in pairs in parallel to a same external unit for processing the signals delivered by the plates. A preamplifier may be provided connected to each of the piezoelectric plates, or to each group of piezoelectric plates so as to compensate for variations in sensitivity. Again, in addition to the fact that this sensor does not have the required reliability, the different piezoelectric plates influencing each other, the electrical connection and the mounting of different piezoelectric plates and electronic circuits inside of this sensor are particularly complex and expensive. US 5942681 discloses a truck tire pressure track 30 comprising a plurality of force measuring elements, each force measuring element comprising an upper rolling plate, a lower plate, and a structure tubular transmission of forces connecting the upper rolling plate to the lower plate via a network of crystals as sensitive elements. A collector channel is provided in the soleplate of each detector for the passage of individual signal lines to outdoor data acquisition unit. Here again, the variations in sensitivity between the sensitive elements are not compensated, and the assembly and the electrical connection of all the different detectors to form the same rail are complex, long and expensive. The invention therefore aims to overcome these disadvantages by providing a piezoelectric detector whose mechanical assembly and electrical connection during its integration into a sensor system are simple, reliable, fast and inexpensive. The invention also aims at providing such a piezoelectric detector capable of providing calibrated detection signals which are devoid of drift and which have a precisely determined and constant sensitivity, so that the detection signals thus delivered are directly exploitable in combination with signals detectors delivered by other detectors of the same nature. The invention also aims at providing such a detector which makes it possible to provide signals with high accuracy, undisturbed by the deformations of the peripheral environment close to the detector, or by the non-vertical components of the pressure forces applied to the detector. . It also aims at providing a sensor for moving vehicles comprising a plurality of such a detector according to the invention, simple, inexpensive, easy and quick to assemble and set up in a passageway. The object of the invention is also to propose such a rolling vehicle passage sensor capable of delivering signals of high accuracy (in particular less than 5%, in particular of the order of 2%) and of high reliability. allowing in particular to determine load values with a sufficiently good precision to determine from these values whether the vehicle meets a predetermined regulatory constraint or not.

More particularly, the invention aims to provide such a piezoelectric sensor and such a sensor for determining sufficiently accurately selected load values among the axle load, the instantaneous speed of the vehicle, the total weight of the vehicle. The invention also aims at providing such a sensor for delivering, in a sufficiently precise and reliable manner, dimensional data of the vehicle, in particular chosen from the width of each wheel, the distance between the axles (the wheelbase), the track (distance between the two wheels of the same axle), the distinction between a narrow tire and a wide tire, the distinction between twin wheels and single wheels, and the detection of underinflation. The invention also aims at providing such a sensor which is less sensitive to integration defects in a passageway. The invention also aims at providing a piezoelectric detector and a sensor that can be fully calibrated at the factory before being mounted in a passageway. To this end, the invention relates to a piezoelectric detector comprising: a sole, a measurement face arranged to be able to receive a pressure force, a piezoelectric device carried by said soleplate comprising at least one piezoelectric sensitive element, a mechanical assembly between said measurement face and said soleplate and adapted to transmit the pressure forces imparted on said measurement face to each piezoelectric sensitive element; - an electrical connection circuit connected to the piezoelectric device arranged to receive the electrical signals, called signals detection device, issued by the latter, characterized in that: - said sole is provided with means for assembling at least one other sole of another adjacent piezoelectric detector, said connecting means being adapted to allow the assembly soles of several piezoelectric detectors with the measuring faces that i adjoin, - said connecting circuit comprises at least one series of terminals arranged to allow to establish an electrical connection with a series of conjugate terminals of another sole of another adjacent piezoelectric detector. A detector according to the invention can therefore be easily assembled to at least one similar adjacent detector (that is to say equipped with conjugated assembly means) in a simple manner, the electrical connection between the different adjacent detectors being ensured also by easy and fast way.

Advantageously and according to the invention, said assembly means and each series of terminals are arranged so as to establish an electrical contact with a series of terminals of another sole of another analogous piezoelectric detector adjacent to the effect -particularly by the sole effect- of the mechanical assembly of the two soles by said assembly means. In addition, advantageously and according to the invention, said assembly means are rigid assembly means able to position and maintain in place the soles relative to each other by simple relative engagement. In particular, said rigid assembly means of the soles of detectors between them can be implemented by a single movement, without requiring the addition of additional fasteners (screws, bolts, rivets ...) or additional assembly steps (welding, gluing, ...). Such rigid and fast assembly means according to the invention can be the subject of a large number of alternative embodiments, for example: conjugated rabbets; groove (s) and tongue (s) (or false tongue (s)); tenon (s) and mortise (s); dovetail (s) and / or similar forms; with elastic, reversible or irreversible interlocking ... According to a possible embodiment, the rigid assembly means comprise at least one lug integral with a soleplate of a detector adapted to be engaged in a conjugate through-light integral with another sole of another adjacent detector. Advantageously, said light has a counterbore and the lug has an end extending into this counterbore (preferably without exceeding it), end which can be crushed hot, for example by bouterollage (preferably without protruding boss by relative to the surface of the sole). Any other embodiment can nevertheless be envisaged alternatively or in combination. Preferably, especially in the case where the detector is integrated in a moving vehicle passage sensor, said assembly means are irreversible assembly means. Nothing prevents, in particular in other applications, to provide on the contrary means for assembling the detectors between them which are reversible, that is to say, removable. In addition, advantageously a detector according to the invention is adapted to ensure electrical continuity on the same electrical conductors between a plurality of adjacent detectors of which it is part. Thus, a detector according to the invention is also advantageously characterized in that said soleplate comprises first terminals extending on a first side of the soleplate for connection to a first other soleplate or a signal processing circuit, and second terminals on a second side of the sole opposite the first side, for connection to a second other sole or a signal processing circuit, and in that each first terminal is electrically connected to each second terminal-particularly by a track conductive extending from one side to the other of the sole-. Thus, a plurality of detectors according to the invention assembled juxtaposed two by two to each other and electrically connected to each other are connected in an electrical circuit in series to one or more electrical lines (conductors), each line can in particular serve channel for a digital bus, or conductor for an analog signal and / or a power supply. In particular, advantageously and according to the invention, the sole has a base in the general shape of quadrilateral-in particular rectangle-, and has two sets of terminals, one on each side of two opposite sides of said quadrilateral base. Advantageously and according to the invention, each series of terminals comprises at least two-in particular three-electrical conductors isolated from each other.

Furthermore, advantageously and according to the invention the terminals of each series of terminals are formed of flat conductive tracks able to form an electrical connection by superposition and contact with terminals conjugate a series of terminals of another sole. Nothing prevents to also provide relief shapes and / or concave to improve the electrical contact between superimposed terminals.

Several embodiments of a detector according to the invention are possible with respect to each piezoelectric sensitive element and said electrical connection circuit. In a first economical embodiment, each piezoelectric sensitive element of the piezoelectric detector is directly electrically connected to said electrical connection circuit and to the series of terminals of the latter, in order to deliver the detection signals in the form of electric charges. In this embodiment, the electrical connection circuit may comprise only two phases, and each series of terminals may comprise only two terminals, one corresponding to the ground (or to a negative electrode of each piezoelectric sensitive element), the other corresponding to the detection signals which are piezoelectric signals delivered in the form of electric charges by a positive electrode of each piezoelectric sensitive element. The different analog piezoelectric detection signals of the different detectors connected in series with each other can be collected on a centralized electronic processing circuit, for example placed at the end of a rail of a moving vehicle passage sensor. In a second variant of possible embodiment of a detector according to the invention, the latter incorporates an electronic circuit for processing the piezoelectric signals delivered by each piezoelectric sensitive element.

In particular, a detector according to the invention is also advantageously characterized in that it comprises an electronic circuit comprising a charge amplifier and a drift compensation circuit for outputting a controlled detection signal on a predetermined constant value independently. possible untimely variations in the value of the piezoelectric signals. In particular, advantageously and according to the invention, this electronic circuit can be in accordance with WO 2012031964 and / or FR 2969279, modified to present a digital output and / or supplemented at least by an analog / digital conversion module adapted to transform the analog output voltage in a digital signal. It further preferably comprises at least one memory adapted to store the digital values of the measured voltage. In this second embodiment, a detector according to the invention is also characterized in that said electronic circuit is adapted to deliver detection signals in the form of digital data on the tracks and at said terminals of the detector. In this variant, each series of terminals also advantageously comprises three conductors, two of which are used for the transmission of the detection signals (in particular in the form of digital data representative of an output voltage) according to a digital serial link protocol, the third conductor being used to supply the power supply of the electronic circuit. Thus, each series of terminals and the corresponding tracks act as a digital serial bus, for example of the UART and / or LIN and / or CAN type. In this second variant in particular, a detector according to the invention is also advantageously characterized. in that it comprises a central receiving housing of an electronic circuit electrically connected to each piezoelectric sensitive element and delivering a detection signal whose value is representative of the pressure force undergone by the measuring face. Furthermore, advantageously a detector according to the invention is also characterized in that each piezoelectric sensitive element is disposed in said assembly in an annular geometry with respect to a support plane face.

More particularly, advantageously and according to the invention in that it comprises a single piezoelectric sensitive element in the form of a block of polycrystalline piezoelectric synthetic material, in particular in the form of an annular plate (washer) of such a material. This piezoelectric washer can be interposed between two also annular electrodes, one of which is connected to the ground of said electronic circuit, and the other, positive, is connected either directly to one of the tracks (first variant mentioned above), or said electronic circuit input of the charge amplifier to deliver the piezoelectric signals (second variant above) .. Furthermore, advantageously and according to the invention, the detector is extra flat. In particular, advantageously and according to the invention, said mechanical assembly of a detector according to the invention comprises an elastically deformable device -particularly an axially flexible peripheral sleeve-adapted to subject each piezoelectric sensitive element to a compression prestress in one direction measuring device normal to said measuring face, and this elastically deformable device has a height in said measurement direction 10 smaller than its largest dimension orthogonal to said measurement direction, in particular less than 15 mm -notably between 3 mm and 10 mm Similarly, a detector according to the invention is also advantageously characterized in that it has a height between the measuring face and the sole, which is smaller than the dimensions of the detector parallel to the measuring face. For example, this height between the measurement face and the soleplate is advantageously of the order of 10% to 20%, for example of the order of 12% to 15%, of the dimensions of the detector parallel to the measuring face. A detector according to the invention can be used advantageously in any situation and in any orientation, for measuring the pressure forces in a measuring direction. Nevertheless, a detector according to the invention is more particularly (although not exclusively) advantageous with the measurement face of the horizontally oriented rolling plate, said measurement direction being vertical, and even more particularly in the context of measuring the pressure. vertical movement exerted by a vehicle wheel on a passageway. The invention thus extends to a sensor provided with a plurality of piezoelectric detectors according to the invention assembled juxtaposed on a common support. The invention also relates more particularly to a sensor for moving vehicles, comprising a plurality of piezoelectric detectors 30 associated with a common support intended to be implanted on the ground across a vehicle passageway, each piezoelectric detector being adapted to supplying an electrical signal, said detection signal, representative of the pressure force exerted on this piezoelectric detector by the passage of a vehicle wheel, each piezoelectric detector comprising at least one piezoelectric sensitive element interposed in an assembly suitable for submitting each element piezoelectric sensitive to a vertical compression prestressing and to transmit to each piezoelectric sensitive element the compression forces generated by the passage of a vehicle wheel, - said common support comprising a rigid flat upper face, said base, carrying at least one row of piezoelectric detectors juxtaposed next to each other on the base, characterized in that each piezoelectric detector is in accordance with the invention. Advantageously and according to the invention, each piezoelectric detector comprises a clean rolling plate (that is to say, specific to this piezoelectric detector) having an upper planar face, called measuring face, arranged to receive the entire effort passing a wheel of a vehicle rolling above-especially on this rolling plate, and for transmitting these forces to each piezoelectric sensing element of said piezoelectric detector. Furthermore, said assembly means are adapted so that said rolling plate of each piezoelectric detector is distinct and remote from the rolling plates of the piezoelectric detectors which are adjacent to it and to which they are assembled, so that each piezoelectric detector receives exclusively the piezoelectric detector. the force resulting from the passage of a wheel of a vehicle running above the above-especially on the rolling plate of this piezoelectric detector. More particularly, advantageously and according to the invention, the rolling plate of each piezoelectric detector has a width (dimension parallel to the longitudinal direction of the common support) of less than 10 cm. Advantageously and according to the invention, this width is greater than 1 cm. For example, this width is between 4 cm and 6 cm, in particular of the order of 5 cm. According to an advantageous embodiment of the invention, the rolling plate of each piezoelectric detector is of square shape. Furthermore, advantageously and according to the invention, the rolling trays of the different piezoelectric detectors juxtaposed on the base are separated from each other in the longitudinal direction of the beam by a non-zero distance as small as possible, in particular less than 2 cm, for example advantageously of the order of 1 mm. In addition, advantageously and according to the invention, the piezoelectric detectors are separated from each other by a filler material having negligible compressive strength compared to that of each piezoelectric detector. This results in particular that the detectors are mechanically independent of each other, and therefore provide reliable and accurate results.

Advantageously, a sensor according to the invention is also characterized in that the measurement faces of the piezoelectric detectors are of rectangular shape and of the same dimensions, the different piezoelectric detectors being juxtaposed on the base parallel to one another by forming a tiling of a free upper face of the sensor comprising at least one row of piezoelectric detectors intended to extend across the passageway, and in that the piezoelectric detectors juxtaposed are electrically connected to each other in pairs the along a row through the series of terminals of the piezoelectric detectors which extend parallel to said row. The series of terminals, in particular the conductive tracks, are parallel to one of the sides of the measurement faces of the detectors, and to the longitudinal direction of said row. In addition, a sensor according to the invention is also characterized in that said rigid planar base is formed of an upper face of a beam having a longitudinal direction intended to be arranged across said passageway, in that it comprises at least one row of piezoelectric detectors juxtaposed in alignment along said rigid planar base, one side of the rectangular measurement faces of the piezoelectric detectors being parallel to said longitudinal direction of the beam forming the base. Advantageously in a sensor according to the invention, said elastically deformable device of each piezoelectric detector has a total height less than its total length - in particular of the order of 10% to 20%, for example of the order of 12% to 15% of its total length - in the direction of passage of a vehicle wheel. Advantageously and according to the invention, each piezoelectric detector comprises a soleplate of its own (that is to say distinct from the soleplate of each other adjacent piezoelectric detector), and said soleplate of each piezoelectric detector is superimposed on the baseplate. and assembled at mounting to that of the adjacent detector (s). The invention thus makes it possible to propose a sensor which is particularly simple and fast to produce with precision, the electrical connection being as simple and quick to establish along the sensor, by simple assembly of the detectors on the common support, possibly with a step of finalization of this assembly (bouterollage for example) and a step of finalizing the electrical connection (welding or crimping the terminals in contact, for example). Advantageously and according to the invention, the different piezoelectric detectors of a sensor according to the invention are identical to each other and in accordance with the invention. They can therefore in particular be mass-produced at a lower cost, and the manufacture of the sensor according to the invention is itself particularly simple since it is sufficient to juxtapose and assemble identical detectors one beside the other on a same base.

Moreover, each piezoelectric detector can be prefabricated and precalibrated during manufacture (at the factory) so that a detection signal can be delivered accurately and reliably, that is to say whose value is strictly proportional to the force of the detector. pressure exerted on the rolling platform, independently of the temperature, the shear forces or the dynamic forces exerted. According to an advantageous embodiment, a sensor according to the invention is also characterized in that it comprises a single row of piezoelectric detectors juxtaposed on the base. In a variant, a sensor according to the invention comprises at least two parallel rows of piezoelectric detectors juxtaposed on the base.

In addition, advantageously a sensor according to the invention comprises an electronic circuit for processing the detection signals from the different piezoelectric detectors, and said electronic processing circuit is adapted to produce digital data representative of the pressure force measured by each piezoelectric detector. , the speed of passage of each wheel of the vehicle, and the weight of the vehicle transmitted at each wheel of the vehicle. The calculation of the passage speed and the weight of the vehicle can be easily obtained in the embodiment in which the sensor according to the invention comprises several parallel rows of detectors juxtaposed on the same base, so that each wheel of a vehicle rolling rolls successively on several piezoelectric detectors (of several successive rows). Nevertheless, this calculation can also be obtained with other configurations, for example with a single row of piezoelectric detectors oriented non-orthogonal to the longitudinal direction of the passageway, so that each wheel of a vehicle comes into contact with several piezoelectric sensors of the sensor according to the invention, which are thus offset in the longitudinal direction of the passageway. The invention also relates to a piezoelectric detector and a sensor characterized in combination by all or some of the characteristics mentioned above or below.

Other objects, features and advantages of the invention will become apparent on reading the following non-limiting description which refers to the appended figures in which: FIG. 1 is a diagrammatic exploded perspective view of a detector piezoelectric according to one embodiment of the invention, - Figures 2a, 2b, 2c are partial schematic views in longitudinal vertical section, according to different sectional planes, of a detector of Figure 1, during a step of The assembly of the latter, the rolling plate and the assembly base being in particular not shown, - Figure 3 is a partial schematic view in longitudinal vertical section of the detector of Figure 1 in the fully assembled state FIG. 4 is a partial schematic view in partial transverse vertical section of a sensor according to one embodiment of the invention provided with a row of piezoelectric detectors 5a and 5b are partial diagrammatic views in longitudinal vertical section, according to different sectional planes, of a sensor according to FIG. 4 illustrating FIGS. 1 to 3 and set up in a vehicle passageway. respectively the detail of the electrical connection, respectively the mechanical assembly, between two adjacent detectors, - Figure 6 is a schematic perspective view partially exploded of a sensor according to the invention. A sensor according to the invention (FIGS. 4 to 6) comprises a beam 11 intended to be placed across a passageway for moving vehicles so that the sensor has a free upper face 12 on which the wheels of the vehicles roll. along the said route.

This beam 11 is preferably rigid, that is to say adapted to undergo substantially no deformation under the effect of the passage of the heavier vehicles considered, for example up to 40t in the case of roads or motorways. It should be noted, however, that the invention makes it possible to dispense with the mechanical characteristics of the beam 11, which may be made of inexpensive material, for example aluminum alloy, steel or polymeric rigid synthetic material and / or composite. The beam 11 has a flat horizontal top face, said base 13, on which are juxtaposed piezoelectric detectors 14 mechanically independent of each other (besides the fact that they are carried by the same rigid base 13), so as to form a paving said upper face 12 of the sensor according to the invention. The beam 11 is preferably formed of a profile having a hollow cross section as in the example shown in the figures, but which may alternatively be a cross section I, H or polygonal or full cross section. It should be noted in particular that the use of a hollow beam 11 allows the insertion of accessories, for example a main signal processing circuit, into the central volume of the beam by an open longitudinal end of the latter. as described below. Each piezoelectric detector 14 (FIGS. 1 to 3) comprises at least one piezoelectric sensitive element 15 capable of delivering a signal of electrical charges as a function of the compressive forces it undergoes, for example and preferably a block of piezoelectric synthetic material such as a lead free polycrystalline ceramic. Each piezoelectric sensitive element 15 is interposed in a proper assembly on the one hand to subject each piezoelectric sensitive element 15 to a vertical compression prestress, and on the other hand to transmit to each piezoelectric sensitive element 15 the compression forces generated by the passage of a vehicle wheel above the piezoelectric detector 14. Each piezoelectric detector 14 is adapted to deliver an electrical signal, said detection signal, representative of the pressure force exerted on this piezoelectric detector 14 by the passage of a wheel of vehicle. In the embodiment shown, this detection signal is developed and delivered by an electronic printed circuit 18 integrated in each piezoelectric detector 14. This electronic printed circuit 18 is electrically connected to each piezoelectric sensitive element 15 to receive load signals.

In the preferred embodiment shown, each piezoelectric detector 14 comprises at least one-in particular a single-piezoelectric sensitive element 15 in the form of a flattened annular washer (crown) symmetrical about a vertical axis 19 (orthogonal to the base). 13), which makes it possible in particular to provide a hollow receiving cavity central space for said electronic circuit 18. This central space is preferably then filled with at least one layer of soft synthetic protective material-in particular silicone- covering and protecting the electronic circuit 18 vibrations and moisture. This embodiment is particularly advantageous in that it makes it possible to optimize the quantity of piezoelectric material necessary and sufficient for the sensitivity of the piezoelectric detector 14, the geometry of the assembly and the overall bulk of the piezoelectric detector 14 which is particularly compact in the horizontal directions and thin (extra flat), with regard to its performance, especially in sensitivity. It should be noted in this regard that a small thickness of the piezoelectric detector 14 is particularly advantageous, in particular to avoid signal disturbance by the shear effects in the horizontal directions and / or the deformations induced on the passageway by the wheels of the vehicle before they arrive above the sensor, and adjacent detectors. Each piezoelectric detector 14 comprises a clean rolling plate 16 having an upper planar face, called measuring face 17, arranged to receive fully the force resulting from the passage of a wheel of a vehicle running above this plate 16 of rolling and in contact with this measurement face 17, and for transmitting this force to each piezoelectric sensitive element 15 of said piezoelectric detector. When the detector is integrated in a sensor set up in a passageway, the measurement face 17 is horizontal (parallel to the base 13) and forms a part of said free upper face 12 of the sensor. The rolling plate 16 of each piezoelectric detector 14 is distinct and remote from the rolling platens 16 of the other piezoelectric detectors 14 which abut it, so that each piezoelectric detector 14 receives exclusively the force resulting from the passage of a wheel of a rolling vehicle. above the rolling plate of this piezoelectric detector 14. A piezoelectric detector according to the embodiment shown comprises a molded plastic part 26 forming: - a soleplate 21 for supporting the piezoelectric washer 15, - a sleeve 22 elastically deformable device in compression / vertical traction, - and, from the end of the sleeve 22 opposite the sole 21, and extending radially outwardly, a base plate 32 receiving the tray 16 rolling.

The synthetic material making it possible to produce this part 26 is chosen so as to be sufficiently hard and rigid to be able to form a suitable support for the piezoelectric washer (in particular by supporting a compression prestressing of the latter substantially without deformation, and more generally the forces pressure experienced by this piezoelectric washer). It is also chosen so as to obtain the appropriate mechanical properties of the elastically deformable peripheral sleeve 22, taking into account the shape imparted to this sleeve. In practice, excellent results have been obtained with a synthetic material selected from the group consisting of polyetheretherketone (PEEK) and liquid crystal polymers (LCP). The soleplate 21 in particular forms a support face 30 in the lower part of the sleeve 22, this support face 30 being adapted to receive and support the piezoelectric washer 15 via an electrode 29 also made of electrically conductive material general crown similar to that of the piezoelectric washer. In this embodiment, the piezoelectric washer 15 is surmounted by a second upper electrode 28, also in the general shape of a ring. Preferably, the support face 30 is formed from the bottom of a peripheral groove formed in recess in the sole 21 in the lower part of the sleeve 22 to ensure proper centering and retention of the piezoelectric washer and electrodes 28, 29. The printed electronic circuit 18 is fixed on the central portion 31 of the sole 21 in a central housing circumscribed by the piezoelectric washer and the electrodes 28, 29. This circuit 18 is positioned in the center of the housing by means of studs projecting from the sole plate, cooperating with recesses formed at the periphery of the circuit 18. This printed circuit 18 carries in particular an integrated circuit 38 adapted to perform electronic functions, especially as mentioned below. The upper and lower electrodes 28 and 28 have tabs 48 and 49 respectively for connection to the printed circuit 18, so that the electrical charges delivered by the piezoelectric washer 15 are transmitted to the printed circuit board 18. In addition, the central portion 31 of the sole 21 is provided with recesses through its thickness for the passage of tabs 27 connecting conductive tracks 24 which extend under the sole 21.

After placing the various elements mentioned above in the piece 26, the piezoelectric washer 15 is compressed by screwing a ring 33 of pressure in the sleeve 22 (Figure 14). This pressure ring 33 has a thread 41 external to its upper part, adapted to cooperate with a thread 40 formed inside the upper part of the sleeve 22. The pressure ring 33 extends downwards from this thread 41 with dimensions such that it does not come into contact with the inner wall of the sleeve 22. The crown 33 of pressure has a lower face 53 in the form of a flat ring adapted to be superimposed on the upper electrode 28. The pressure ring 33 is provided with shapes 34 such as radial slots to allow its screwing and clamping with the aid of a suitable tool. The tightening torque imparted to the pressure ring 33 makes it possible to calibrate the compression preload of the piezoelectric washer. It should be noted in this respect that the adjustment of this compression prestressing can easily be carried out by simple measurement of the electrical detection signals delivered by the electronic circuit 18, so that their value corresponds to a predetermined value corresponding to the prestressing. desired compression. The pressure ring 33 preferably has a central bore 43 therethrough for subsequently introducing said layer 23 of waterproof and insulating filling material, for example silicone, which allows to seal and protect in this bore 43, the printed circuit 18 and the integrated circuit 38 that it carries. This bore 43 is then itself closed by placing an upper plug 42 having an upper plate 44 of generally square shape extending radially beyond the pressure ring 33, the corners of this plate 44 being endowed of through-holes 45 into which pins 46 integral with the upper plate 32 of the molded part 26 can be introduced. The rolling plate 16 is then overmoulded on the assembly previously formed so as to cover the peripheral edges of the plate 32, the ring 33 of pressure, the cap 42, and to be rigidly attached thereto. This overmolding of the rolling plate 16 is made of a synthetic material suitable for forming a leveling and wear layer - in particular a rigid resin layer (for example chosen from an epoxy resin filled with silica, a polyamide, a polyamide charged with glass fibers) -. The upper plate 32 of the molded part 26 advantageously has, in addition to centering pins 39, forms which promote the securing of the overmolded rolling plate 16, for example slots at its edges and / or angles. The rolling plate 16 is of generally parallelepipedal shape, and has an upper free planar face forming the measurement face 17 receiving the pressure forces exerted along the axis 19 of symmetry of the detector, which corresponds to the vertical when the detector is integrated in a sensor 10 for moving vehicles. A lower assembly base 25 is overmoulded under and around the sole 21 and tracks 24, this assembly base 25 having, at its two opposite ends at the longitudinal ends of the tracks 24, assembly rabbets 36, respectively 37, adapted to allow rapid assembly of two similar detectors according to the invention next to one another, with an electrical connection of the tracks 24 of the two detectors established by the simple effect of this assembly. However, there is nothing to prevent an additional step, for example welding or crimping, to ensure the electrical connection. In the example shown, a first rabbet 36 is formed at a first end (on the right in FIG. 1) of the assembly base 25, this first rabbet 36 having a horizontal upper free face on which holes 35 open. A second rabbet 37 is provided at a second end (on the left in FIG. 1) of the assembly base 25, opposite the first rabbet, this second rabbet 37 having a horizontal lower free face from which lugs 47 extend downwardly. so as to be able to enter the holes 35 of a first rabbet 36 of another adjacent detector. The first rabbet 36 is furthermore provided with a central recess 46 in which ends of the tracks 24 extend so that these ends may be slightly deformed in bending under the effect of the pressure of the assembly and the ends of the tracks of another adjacent detector. The second rabbet 37 is adapted to extend above and on each side of the end of each track 24, to electrically isolate it. It should be noted that the overmolding 25 is made around the sole 21 so that the sole 21 has a lower face 56 having at least portions slightly projecting downwards relative to the lower face 57 of the base 25. Otherwise said, the overmolded base 25 extends integrally above said portions of the lower face 56 of the sole 21. In this way, the detector 14 rests on the base 13 of the beam 11 with the lower face 56 of the sole 21 in contact with the base 13, the base 25 not itself being in contact with this base 13. Thus, the reaction of the beam 11 is directly transmitted to the sole 21 supporting the piezoelectric sensitive element 15, and therefore to the molded part 26 forming the sole 21, the sleeve 22, and the plate 32 receiving the rolling plate 16. In the example shown, said portions of the lower face 56 projecting downwards to come into contact with the base 13 are q four crown portions globally angularly complementary to each other, and separated in pairs by transverse radii and ribs covering the tracks 24 to electrically isolate them. To guarantee a good electrical contact and to improve the electrical connection, each track 24 is advantageously provided on at least one of its ends with a connection boss 58, for example by stamping and / or adding electrically conductive fuse material ( for example, tin alloy) for hot welding of the ends of superimposed tracks. Such fuse electrically conductive material facilitating welding can be added to each end of the tracks, or over their entire surface.

In the example shown, the detector comprises three parallel tracks 24 electrically insulated from each other, one of which serves to supply power to the printed circuit 18 and its components, while the other two are used for the transmission of detection signals delivered by the printed circuit 18 (one of these two tracks transmitting the detection signal as digital data, the other track corresponding to the electrical ground and / or zero). The ends of the tracks 24 thus constitute, on each side, a series of terminals making it possible to establish an electrical connection with a series of conjugate terminals of another adjacent analog piezoelectric detector. FIG. 3 represents a piezoelectric detector according to the invention after the assembly of its various constituent elements.

The rolling plate 16 of each piezoelectric detector 14 has a width (dimension parallel to the longitudinal direction of the base 13 and the beam 11) of less than 10 cm, for example between 4 cm and 6 cm, in particular advantageously order of 5 cm. The width of each rolling plate 16 is preferably less than the width of a vehicle wheel intended to be detected by a sensor according to the invention, so that a wheel which passes on such a sensor is necessarily detected by several separate piezoelectric detectors 14. The trays 16 of rolling of the different piezoelectric detectors 14 juxtaposed on the base 13 of a sensor according to the invention are separated from each other in the longitudinal direction of the beam 11 by a separation distance which is different from zero, the different piezoelectric detectors 14 do not touch each other and are thus mechanically independent of each other with respect to the forces applied to the rolling plates, but this separation distance is preferably as small as possible, in particular less than 2 cm, for example between 1 mm and 10 mm. Advantageously, the separation distance is less than half the width of a rolling plate 16. In the case of a sensor comprising several parallel rows of piezoelectric detectors, the piezoelectric detectors 14 are also separated from each other by a non-zero separation distance in the horizontal direction orthogonal to the longitudinal direction of the beam 11 which corresponds to the longitudinal direction of the passageway when the sensor according to the invention is placed with the beam 11 orthogonal to the latter. More generally, a piezoelectric detector 14 of a sensor according to the invention is separated from all the other piezoelectric detectors 14 which adjoin it with such a non-zero separation distance and as small as possible. Preferably, this separation distance is the same in all directions, but nothing prevents, if the need arises, to achieve a different tiling, with separation distances that vary in the direction between the piezoelectric detectors 14 which are adjacent. The detection signals delivered by the different piezoelectric detectors 14 are thus totally independent of one another.

In order to form a sensor according to the invention, in a first step, a plurality of detectors 14 according to the invention are juxtaposed in pairs by assembling them, in the inverted position, the measurement faces 17 resting on a plane floor. The lugs 47 of a detector are introduced into the conjugate holes of an adjacent detector to effect mechanical assembly, the ends of the tracks 24 of the two adjacent detectors being superimposed and in electrical contact with one another. Preferably, the lugs 47 of the second rabbet 37 are also gripped, the latter being adapted to have an end extending in a suitable recess (FIG. 5b) of the conjugate holes of the first rabbet 36. preferably a weld at the ends of the tracks 24 in contact, by melting the bosses 58, then pouring an insulating material 55 (for example an insulating epoxy resin) in the residual cavities left by the assembly and arranged for this purpose in each base 25, to ensure sealing and electrically isolate definitively the electrical connections of the tracks 24 in particular on the side of the lower face of the detector. At this stage, the different detectors 14 juxtaposed in the same row are assembled to each other in pairs in a rigid manner and normally irreversible, and are electrically connected by this simple assembly. The different tracks 24 of each detector establish an electrical connection between the different detectors 14 juxtaposed from one end to the other of the sensor by simply assembling the detectors together. These tracks 24 thus form an electrical connection circuit of the detectors which are thus mounted and electrically connected in series with each other on the beam 11. The soles 21 of the different piezoelectric detectors 14 are then rigidly fixed to the base 13 , For example by gluing and / or screwing and / or crimping, ... In the variant shown of the invention, the beam 11 is provided with lateral rails or upper lateral wings defining stirrups 54 facing each other adapted to receive the 21 and the base 25 of each piezoelectric detector 14 so that the base 25 is clamped by the latter so as not to be dissociated from the base 13. At least one of the stirrups 54 (the one shown in FIG. left in the example of Figure 4) is adapted to be deformed plastically at each base 25, after placement between the stirrups, so as to fix rigidly to the base 13. In addition to these possible brackets 54, the piezoelectric detectors 14 are carried by the base 13 of the beam 11 and therefore extend completely upwards (in the normal operating position) above the base 13 and the beam 11. To assemble the beam 11 to the row of detectors 14 previously assembled juxtaposed to each other and which are still returned to said flat floor, the beam 11 is placed with the base 13 turned on the free faces of the bases 15 25 of the different detectors, and one of the sides of the pedestals 25 is inserted into one of the stirrups 54 curved hook (stirrup formed by the profile, shown on the right in Figure 4). The other yoke 54 is not curved and allows the introduction of the bases 25 between the two stirrups 54. This crimp 54 is then crimped (as shown on the left in FIG. 4) to bend it around the bases. 25 and 20 trap the detectors 14 between the stirrups 54. At one of the longitudinal ends of the sensor, the latter advantageously comprises a main electronic processing circuit 60 receiving the different detection signals, and connected to the tracks 24 of the last detector mounted at this longitudinal end of the sensor. In the subsequent step of the sensor mounting method according to the invention, therefore, the main processing circuit 60 is introduced inside a longitudinal end of the beam 11, and the main circuit 60 is electrically connected to the main circuit 60. three tracks 24 of the last detector present at this longitudinal end. To do this, an end flange 62 made of insulating material is fixed to the longitudinal end of the beam 11, this end flange housing a connector 61 adapted to be fixed and welded to the ends of the tracks 24 (by welding their bosses 58), this connector 61 being connected by leads 65 to the main circuit 60 treatment. The assembly is plugged by an end cover 63. The main processing circuit 60 has an output port to which is connected an Ethernet cable 59 which extends inside the beam 11 all the way to the opposite longitudinal end thereof at which this Ethernet cable 59 emerges by a light formed in the lateral part of the beam 11. This Ethernet cable can be connected to a computer unit adapted to exploit the digital data delivered by the main processing circuit 60. In a subsequent step, a molding form is placed around the side walls of the sensor bearing on the lateral faces of the beam 11 which are slightly protruding laterally with respect to the lateral faces of the rolling plate 16. With the aid of this formwork, a filler material 15 is molded around the lateral faces of the sensor, and in all the spaces separating the different piezoelectric detectors 14 of the sensor according to the invention. This filling material is chosen so as to have negligible compressive strength with respect to that of each piezoelectric detector 14 and also a modulus of elasticity in compression that is negligible compared to that of each piezoelectric detector 14, especially less than 50. MPa. It may in particular be chosen from synthetic materials that can be molded, in particular from a silicone and a rubber. This filling material is in any case chosen so as to preserve the mechanical independence of the different piezoelectric detectors 14 from each other. In other words, it must not form any connection between the different trays 16 of rolling, so that a tray 16 for rolling a piezoelectric detector 14 can undergo a vertical force so that the piezoelectric detector 14 delivers a signal of detection of the corresponding force, without any of the other adjacent piezoelectric sensors 14 deliver any detection signal and is influenced by this effort. It should be noted that the fact that the detectors are extra flat also largely contributes to achieving this independence between adjacent detectors.

This filling material 50 is thus molded around the upper part of the beam 11 and all the piezoelectric detectors 14, including the spaces which separate them from each other. This filling material 50 may in particular be chosen from synthetic materials that can be molded, for example a silicone. This gives a sensor ready to be integrated in a passageway, as shown in FIG. 6. For the integration of such a sensor according to the invention in a roadway (road, highway, taxiway, airport runway ...), a transverse groove is formed in the track, then a volume 52 of resin -particularly a silica-filled epoxy resin- is deposited at the bottom of the groove, then the sensor is put in place with the lower portion of the beam 11, including the filler material 50, which is embedded in said resin mass prior to curing. Preferably, the volume 52 of epoxy resin is in sufficient quantity to occupy the entire volume of the groove which is not occupied by the sensor itself. The tracks 24 of the two or two adjacent two adjacent detectors according to the invention form an electrical connection circuit for the different piezoelectric devices of the detectors. This electrical connection circuit is arranged at least to receive the different detection signals emitted by the different detectors, and to transmit them (via the main processing circuit 60 in the embodiment shown), in particular outside each detector. , and outside the sensor, for their treatment and / or operation. This electrical connection circuit has parallel tracks 24, each track being electrically connected to each electronic circuit 18 of each detector, at least one of the tracks 24 having the function of transmitting the detection signal of the piezoelectric detectors 14 of the sensor, so that all the detection signals are delivered in a serial link to the main electronic signal processing circuit 60, placed at one end of the base 13 intended to be itself located on one side of a signal path. passage.

The electronic circuit 18 of each piezoelectric detector 14 is adapted to provide a detection signal in the form of digital data representative of a voltage proportional to the vertical force experienced by the piezoelectric detector 14, without drift. For this purpose, it comprises, for example, a charge amplifier and a closed-loop compensation circuit. It is in practice formed of a disc-shaped electronic printed circuit housed in the center of the piezoelectric sensitive element 15 and receiving an integrated circuit (ASIC, FPGA, ...). In particular, advantageously and according to the invention, this electronic circuit may be generally in accordance with WO 2012031964 and / or FR 2969279, modified to present a digital output and / or supplemented in particular by an analog / digital converter, a microcontroller and a memory recording each measured value of the voltage constituting the detection signal. The electronic circuit 18 is also adapted to be able to supply each value of the detection voltage in the form of a digital signal on an output port of the circuit 18 comprising two terminals, one of which for the ground or reference of the zero is connected. to one of the tracks 24, and the other allows the transmission of the digital bits according to a serial protocol, for example of the UART type, and the communication according to a protocol for example of the LIN type ("Local Interconnect Network") and is connected at another of the tracks 24. Such an electronic circuit 18 outputs a detection signal in the form of a numerical value proportional to the pressure experienced by the piezoelectric detector 14, and which is independent of the temperature, the pyroelectricity phenomena being permanently automatically compensated in real time. It is possible to extract from each of the detection signals 25, in particular: the maximum value Fmax of the force measured by the piezoelectric detector 14, the values of different times ti for which the measured force corresponds to a predetermined proportion of the maximum value Fmax, 30 - statistical parameter values such as the standard deviation or the symmetry coefficient, - the weight of a wheel reduced to a unit speed, that is to say the value of JFdt. The weight P of the vehicle can then be calculated according to the formula: P = (v / D) JFdt D being the characteristic distance of the rolling plate 16 of each piezoelectric detector 14 in the direction of displacement of the wheel, that is to say orthogonal to the beam 11. In addition, the detectors being independent, they make it possible to precisely determine the duration of passage of each wheel on the sensor, and to deduce a possible under-inflation of one of the wheels, and this without measuring the internal pressure of the tires. Indeed, a duration of passage of a wheel on the sensor larger than the other durations of passage of the other wheels is representative of under-inflation. These values can be calculated by said main detection signal processing circuit 60 which receives these in digital form, on the serial link formed by the assembly of the different detectors. An example of the communication protocol between the electronic circuits of each detector 14 and this main circuit 60 through tracks 24, which constitute a bus, may be as follows. The main circuit 60 is adapted to be able to sequentially continuously solicit the different electronic circuits 18 of the different piezoelectric detectors 14 of the entire sensor, or only part of the latter, to require the transmission of measured voltage values and / or stored by these different electronic circuits 18. When a variation of the value of the detection voltage is or has been measured by a detector 14, the microcontroller of its electronic circuit 18 is adapted to address in response a message corresponding to the main circuit 60. The latter then interrogates this electronic circuit 18 to ask him to communicate the value of the voltage thus measured, and possibly other previously measured values, and / or values measured over a certain predetermined time range. The invention may be the subject of numerous variants with respect to the preferred embodiments described above and shown in the figures.

In particular, in a simplified and economical variant of the invention, each detector does not incorporate an electronic circuit for processing the signals delivered by the piezoelectric sensitive element, the electrical charges delivered by each piezoelectric sensitive element of the different detectors 5 juxtaposed on a beam to form the same sensor is instead directly transmitted (via a circuit board only connector office) in the form of an analog signal by the tracks 24 to a single electronic circuit placed at the longitudinal end of the sensor. This common electronic circuit, which then comprises a charge amplifier and preferably a drift compensation circuit, processes the electrical charges thus recovered from the different piezoelectric sensitive elements to generate a value representative of the passage of a vehicle, which can be delivered on a three-conductor cable, for example a shielded twisted pair. Furthermore, the mechanical assembly and electrical connection structures may be the subject of various alternative embodiments fulfilling the same functions; the elastically deformable device of the detector may be formed other than a sleeve, for example a plurality of elastic springs or resilient blades or pads of elastic material, connecting the rolling plate and the sole, uniformly distributed at the periphery.

A detector according to the invention is extremely simple to assemble and integrate into a multi detector system, reliable, accurate, precalibrated, robust and insensitive to external disturbances. It may also be the object of other applications, in particular for the precise and reliable measurement of high-value pressure forces, possibly with relatively large parasitic horizontal components and / or in severe environments, for example on public works sites, on board an aircraft or space systems, in connection with machining centers or other machine tools ... A sensor according to the invention may advantageously have a larger number of rows of detectors for example three or four rows 30 or more. These rows can be arranged on the same rigid common base, whose width is adapted to receive the different rows of piezoelectric detectors juxtaposed, the whole being integrated in one piece in a passageway. Such a sensor comprising several rows may in particular be used in passageways likely to undergo severe deformation. Indeed, the fact of multiplying the rows makes it possible to ensure that one and the same wheel of the vehicle is, at least at a given moment, entirely supported by the sensor according to the invention, without being in contact with any portion of the coating. road. Thus, regardless of the quality of the integration of the sensor with respect to the road surface, initially because of the wear of the latter, the quality of the detection remains good and reliable. Such a multi-row sensor may also be used for other applications, for example as a low speed vehicle weigh scale.

Claims (8)

CLAIMS1 / - Piezoelectric detector (14) comprising: - a sole (21), - a measurement face (17) arranged to be able to receive a pressure force, - a device (15, 28, 29) piezoelectric carried by said sole ( 21) comprising at least one piezoelectric sensitive element (15), - a mechanical connection between said measurement face (17) and said sole (21) and adapted to transmit the pressure forces imparted on said measuring face (17) to each piezoelectric sensitive element (15), - an electrical connection circuit connected to the piezoelectric device arranged to receive the electrical signals, called detection signals, delivered by the latter, characterized in that: - said sole (21) is provided with means (35, 36, 37, 47) to at least one other sole plate (21) of another adjacent piezoelectric detector, said assembly means (35, 36, 37, 47) being adapted to allow the assembling s emelles (21) of several piezoelectric detectors with the measuring faces (17) which are adjacent, - said connecting circuit comprises at least one series of terminals (24) arranged to allow to establish an electrical connection with a series of terminals (24) conjugate another sole (21) of another adjacent piezoelectric detector. 2 / - Detector according to claim 1 characterized in that said means (35, 36, 37, 47) of assembly and each series of terminals (24) are arranged to establish an electrical contact with a series of terminals ( 24) of another sole plate of another similar piezoelectric detector adjacent by the effect of the mechanical assembly of the two flanges by said assembly means (35, 36, 37, 47). 3 / - Detector according to one of claims 1 or 2 characterized in that said means (35, 36, 37, 47) of assembly are means of assemblagerigide able to position and hold in place the soles (21) the ones compared to the others by simple relative engagement. 4 / - Detector according to one of claims 1 to 3 characterized in that said means (35, 36, 37, 47) assembly are irreversible assembly means. 5 / - Detector according to one of claims 1 to 4, characterized in that said sole (21) comprises first terminals (24) extending on one side of the sole (21) for connection to a first other soleplate or to a signal processing circuit, and second terminals (24) on a second side of the outsole opposite the first side, for connection to a second other soleplate or a signal processing circuit, and in that each first terminal is electrically connected to each second terminal. 6 / - Detector according to one of claims 1 to 5, characterized in that the terminals of each series of terminals are formed of flat conductor tracks (24) able to form an electrical connection by superposition and contact with similar terminals d a series of terminals of another sole. 7 / - Detector according to one of claims 1 to 6, characterized in that it comprises a central receiving housing of an electronic circuit (18) electrically connected to each piezoelectric sensitive element (15) and delivering a signal of detection whose value is representative of the pressure force undergone by the face (17) of measurement. 8 / - Detector according to one of claims 1 to 7, characterized in that each series of terminals (24) comprises at least two-in particular three-electrical conductors isolated from each other. 9 / - Detector according to one of claims 1 to 8 characterized in that each element (15) sensitive piezoelectric is disposed in said assembly in an annular geometry with respect to a face (30) of support plane. 10 / - Detector according to one of claims 1 to 9 characterized in that it comprises a single element (15) piezoelectric sensitive in the form of a block of polycrystalline piezoelectric synthetic material.11 / - Detector according to one of claims 1 to 10, characterized in that it has a height between the face (17) of measurement and the sole (21), which is smaller than the dimensions of the detector parallel to the face (17) of measurement. 12 / - Passenger vehicle passage sensor, comprising a plurality of piezoelectric detectors (14) associated with a common support (11) intended to be implanted on the ground across a vehicle passageway, each detector (14) piezoelectric sensor being adapted to deliver an electrical signal, said detection signal, representative of the pressure force exerted on this piezoelectric detector by the passage of a vehicle wheel, each piezoelectric detector comprising at least one piezoelectric sensitive element (15) interposed in an assembly adapted to subject each piezoelectric sensing element to vertical compression prestressing and to transmit to each piezoelectric sensitive element the compression forces generated by the passage of a vehicle wheel, said common support (11) comprising a face flat rigid upper, said base (13), carrying at least one row of detents Piezoelectric actuators (14) juxtaposed next to one another on the base (13), characterized in that each piezoelectric sensor (14) is according to one of claims 1 to 11. 20 13 / - Sensor according to claim 12, characterized in that the measuring faces (17) of the piezoelectric detectors (14) are of rectangular shape and of the same dimensions, the different piezoelectric detectors (14) being juxtaposed on the base (13) parallel to one another in parallel with each other. forming a tiling of a free upper face (12) of the sensor comprising at least one row of 25 piezoelectric detectors for extending across the passageway, and in that the piezoelectric detectors (14) juxtaposed are electrically connected to each other in pairs along a row through the series of terminals (24) of the piezoelectric detectors which extend parallel to said row. 30 14 / - Sensor according to one of claims 12 or 13, characterized in that said rigid planar base (13) is formed of an upper face of a gutter (11) having a longitudinal direction intended to be arranged across said passageway, in that it comprises at least one row of piezoelectric detectors (14) juxtaposed in alignment along said rigid flat base (13), one side of the rectangular measurement faces (17) of the detectors (14). ) piezoelectric being parallel to said longitudinal direction of the beam (11) forming the base (13). 15 / - Sensor according to one of claims 11 to 14 characterized in that the detectors (14) piezoelectric are separated from each other by a material (50) filling having a compressive strength 10 negligible compared to that of each detector (14) piezoelectric.