EP0384874A2 - Device for the detection of passing vehicles on a road with a piezoelectric film - Google Patents

Abstract

The present invention relates to the production of a sensor consisting of a stack of strips of piezoelectric film (1), of a strip of piezoelectric film (2), and of a conductive strip (3) held between them and encased in a rubber-type flexible material, connected to electronics by means of a two-core cable. The sensor may be bonded in or on the carriageway, or mechanically held. Application to the detection of vehicles travelling over a carriageway. <IMAGE>

Description

The present invention relates to a passage detection device, its installation method and its applications to the detection of passage of vehicles, to the classification of vehicles, to dynamic weighing, to speed measurement; this device consists in part of one or more strips of piezoelectric film.

It is known to carry out metering, selection, speed, weighing, vehicle position measurements, fitted with wheels in contact with the ground, using a piezoelectric effect cable intended to deliver electrical signals to the detector. a measuring device. Generally such devices are placed in grooves made in the roadway and are therefore heavy to implement, and therefore expensive.

On the other hand, dynamic weighing devices using piezoelectric cables are complex to realize because the coating of the piezoelectric cable must be carried out so as to limit the effects of the piezoelectric coefficients of the longitudinal and transverse axes so as not to take take into account that the vertical component; in the case of the piezoelectric film, the shape is such that the transverse effect is reduced; the longitudinal effect is limited by a correct choice of the rigidity of the material supporting the film.

If the operating principles of a piezoelectric film system have already been stated, the actual implementation is very delicate and the products unreliable.

The present invention aims to propose the realization of the piezoelectric film detection device, simple to place on or in the roadway, or removable from a metal part sealed in the roadway. It relates to a device for detecting passage on a roadway of the type comprising a ribbon of piezoelectric film, characterized in that it consists of a slightly curved flat profile in which the piezoelectric film is located; said profile being made of flexible plastic material or rubber. The profile may also have the shape of a rectangular or trapezoidal tube, the upper face of which would be slightly curved. The profile may also have the form of a flexible mat in which would be placed several strips of piezoelectric film, associated or not with other sensors such as induction loops.

The present invention also relates to devices and methods of fixing in and on the roadway; the devices described above can either be glued to the surface of the road, or glued in an opening slightly larger than the profile, or mechanically mounted in a dovetail system provided for this purpose, or glued in a bleeding.

Other laying methods can consist of nailing sorts of jumpers or with nails, the profile comprising the piezo film ribbon (s) electric.

The present invention also aims to achieve a general purpose sensor mat characterized in that it comprises two piezoelectric tapes placed parallel to each other, at a perfectly known distance and an induction loop ; the assembly thus produced makes it possible to identify the axles belonging to a given vehicle as well as to weigh the axles by processing the signals from each of the two piezoelectric tapes.

Other characteristics and advantages will appear during the description which follows.

• * les figures 1 a et b sont des vues schématiques en coupe d'un dispositif suivant l'invention, pouvant être collé sur la chaussée.
• * les figures 2 a, b et c sont des vues schématiques en coupe d'autres variantes d'un dispositif suivant l'invention, pouvant être collés sur la chaussée.
• * les figures 3, 4, et 5, sont des vues schématiques d'autres dispositifs suivant l'invention, pouvant être collés sur la chaussée.
• * les figures 6 a et b sont des vues schématiques en coupe d'autres dis­positifs suivant l'invention, destinés à être insérés dans la chaussée.
• * les figures 7 a, b et c sont des vues de dessus d'une chaussée équipée de un ou plusieurs capteurs par voie de circulation, seul ou associé à une boucle à induction.
• * les figures 8 a et b montrent des exemples non limitatifs de pose par collage sur la chaussée.
• * les figures 9 a, b, c, et d, montrent des exemples non limitatifs de pose du système en insertion dans la chaussée.
• * la figure 10 est un schéma de principe d'un système de traitement du signal issu du capteur décrit ci-dessus, permettant de détecter et classer les essieux passant sur le capteur en plusieurs catégories de poids dynamique.

To the drawings given only as examples

• * Figures 1 a and b are schematic sectional views of a device according to the invention, which can be stuck on the floor.
• * Figures 2 a, b and c are schematic sectional views of other variants of a device according to the invention, which can be stuck on the floor.
• * Figures 3, 4, and 5 are schematic views of other devices according to the invention, which can be stuck on the floor.
• * Figures 6 a and b are schematic sectional views of other devices according to the invention, intended to be inserted in the roadway.
• * Figures 7 a, b and c are top views of a roadway equipped with one or more sensors per traffic lane, alone or associated with an induction loop.
• * Figures 8 a and b show non-limiting examples of installation by gluing on the floor.
• * Figures 9 a, b, c, and d show non-limiting examples of installation of the system for insertion into the roadway.
• * Figure 10 is a block diagram of a signal processing system from the sensor described above, for detecting and classifying the axles passing over the sensor in several dynamic weight categories.

In FIG. 1a, the sensor is constituted by a ribbon (2) of piezoelectric film preferably made of flexible polymer material, placed between a ribbon (1) of very rigid material in the axis of movement of the vehicles "L" but forming a spring in the axis perpendicular to the movement of the vehicle "l" and a ductile conductor (3) of sufficient thickness not to break during the passage of the vehicles. The conductor (3) will be held on the piezoelectric film (2) by a layer of conductive adhesive (4) previously deposited either on the piezoelectric film or on the conductor (3). The assembly thus formed is then embedded by molding, extrusion or other process in a material (5) of the elastomer, polyurethane resin or rubber type having a hardness greater than 50 ShA.

The size of the parts used to make the sensor allows to produce finished assemblies (7) several meters in length, a few millimeters thick and 40 to 80 mm wide.

As an example, we will use to make the support (1) a spring steel or steel blade to make the band saws 25 mm wide and a few tenths of a millimeter thick, to make ( 3 and 4) a self-adhesive copper strip a few tenths of a millimeter thick and 15 mm wide, to make (2) a piezoelectric PVDF film 20 mm wide and 40 μm thick.

The layer of steel used as a support for the piezoelectric film ribbon is intended to considerably improve the quality of the signal supplied by the sensor by limiting the dynamic effect of the vehicle in the direction of its movement by eliminating the deformation of the sensor in the longitudinal direction "L" to take into account only the force "P". The deformation along "l" will also be limited by the steel sheet (1). The deformation according to "P" is also limited by using for the coating (5) a flexible plastic material sufficiently hard to avoid the sinking of the metal and the punching of the resin. We will look for a natural or synthetic rubber or any other elastic material having a hardness greater than 50 ShoreA.

In order to avoid any electrical contact detrimental to the functioning of the system between the metal support (1) and the conductor (3), the widths of the strips will be decreasing (2), being wider than (3,) and (1) wider that (2), and vice versa.

The entire sensor is connected to the electronics by a cable with 2 shielded conductors (11), one of the conductors is connected by mechanical means or by welding to the steel blade (1), the other to the strip conductive (3).

FIG. 1b shows a variant of the device according to the invention in which the strips of metal (1), of piezoelectric polymer (2) and the conductor (3) are held together by a layer (6) of adhesive material or heat shrink. The assembly is then molded in the material (5) to obtain a strip (7) of several meters in length, a few millimeters in height, and a few centimeters in width. The signal is transmitted to the electronic system (12) by a 2-conductor cable (11).

In FIG. 2a which is a variant, the conductive strip forming a spring consists of a stack of a strip (18) made of non-conductive material, for example plastic reinforced or not reinforced with glass fiber or carbon covered with a thin layer of copper (15) or aluminum.

FIG. 2 b and c are other variants of the device where the metal reinforcements (1) and (3) are pressed onto the film (2) by the coating material (6) and molded in the resin and connected to the two conductor cable (11); a probe (16) measures the temperature of the profile core (7), its signal is transmitted by a cable with two shielded conductors (17) to the electronic system in order to be able to correct the response of the system as a function of temperature.

FIG. 3 is a variant in which the conductive metal strip (1) is slightly bent on the two largest sides for the dual purpose of increasing its rigidity and of avoiding mechanically injuring the coating (5) and the film ( 2).

FIG. 4 is a variant in which the mounting of decreasing width is reversed with respect to FIG. 1.

Figure 5 is a variant in which the conductive metal strip spring (1) is bent over its two long lengths, the conductive tape (3) consists of a steel tape also spring and provided with two longitudinal folds to avoid cut the piezoelectric film (2) and to participate in the stiffening of the profile (7).

Figures 6 a and b show alternative molding of the system. The sensor is constructed identically to that described above, but it is molded in the form of a rectangular or square parallelepiped (13) of approximately 30 x 30 m m and several meters in length. The surface (14) in contact with the tires can be flat or provided with a slight boss parallel to the greatest length. This version is intended to be inserted into the roadway as described below.

Figures 7 a, b and c show the main principles of the arrangement of piezoelectric sensors and in particular of those which are the subject of the invention, on the road, and the uses which can be made of them. In FIG. 7 a, a single sensor presented in a profile (7) or (13) is placed perpendicular to the traffic and connected to the detector (12) by the cable (11); such an arrangement makes it possible to count the axles, weigh the axles, discriminate the axles in several weight categories.

In FIG. 7b, two sensors presented in profiles (7) or (13) are placed parallel to each other perpendicular to the traffic, and connected by their cable (11) to the detectors (12). With such an installation, the speed of the vehicles can be measured; discriminate, count the axles and weigh them.

In FIG. 7c, the two sensors (7) or (13) are associated with an induction loop (21) and make it possible to determine all of the parameters of vehicle circulation by vehicle, speed, weight, distance between axles, vehicle class.

Figures 8a and b, given by way of non-limiting example, show two means of laying the profile (7) on the floor.

In FIG. 8A, the profile (7) is glued by any known adhesive means (9) to the surface (8) of the road (20).

In FIG. 8b, the profile (7) is covered by an adhesive sheet (10), whether or not recessed, which adheres both to the surface (8) of the roadway (20) and to the upper surface of the profile (7). by immobilizing it.

Figures 9a, b, c, and d are non-limiting examples showing means for fitting different forms of sensors for inclusion in the roadway.

In FIG. 9a, a section section (14) rectangular or square, is bonded by a suitable product (19) in a groove (21) formed in the roadway (20).

In FIG. 9b, the profile (13) has a boss of a few millimeters on the upper surface (14) and is bonded by a product (19) in a groove (21) formed in the roadway (20).

In FIG. 9c, the profile (13) has an upper surface (14) in the shape of a nail and is glued in the groove (21) and on the surface (8) by a suitable adhesive (19).

In FIG. 9d, the profile (13) is in the form of a trapezoid with a curved face (14); it is mounted in a support (22) sealed in the roadway (20) by lugs (25) or other systems, and held by two bars (23) forming a dovetail and blocking the profile by screwing (24) of the two bars on the part (22).

In FIG. 10 given solely by way of nonlimiting example, the signal from the sensor 7, conducted by the cable with two shielded conductors (11) has its impedance adapted by the circuit (26), the signal is then filtered (27 ) to eliminate any parasites or bounces of frequency greater than 100 Hz, then it is integrated by the circuit (28) to determine the area of the area surrounded by the signal, the value obtained is then compared by comparators (29 ) at thresholds set by potentiometers (31). The output of each comparator enters a monostable type circuit (30) generating a calibrated slot.

Claims (12)

1 / Device for detecting the passage of axles or wheels on a roadway, characterized in that it comprises 3 superimposed main tapes, of decreasing or increasing width respectively, a conductive strip making a spring (1), a piezo film tape -electric in plastic material (2), a conductive tape (3), the assembly being coated in a non-rigid plastic material (5), of shore hardness greater than 50 ShA, and connected to the outside by a two-wire cable shielded conductors (11). 2 / Device according to claim 1, characterized in that the conductive strip spring (1) is made of treated steel with a thickness between 2 and 8 tenths of a millimeter, flat or with two lateral folds parallel to the greatest length. 3 / Device according to claim 1, characterized in that the conductive strip spring (1) is made of reinforced plastic material or not coated by a means such as bonding, diffusion or other by a conductive layer. 4 / Device according to claim 1, characterized in that the piezo film ribbon (2) is made of flexible piezoelectric polymer type PVDF. 5 / Device according to claim 1, characterized in that the ribbon of conductive material (3) is copper. 6 / Device according to claim 1, characterized in that the conductive tape (3 ° is flat steel or with two lateral folds parallel to the greatest length. 7 / Device according to claim 1, characterized in that the layers 1. 2 and 3 are bonded together. 8 / Device according to claim 1, characterized in that the layers 1. 2 and 3 are pressed against each other using a thin coating (6) of adhesive type to the heat-shrinkable product or any other able to perform this function. 9 / Device according to claim 1, characterized in that the shape (7) of the molding in section is a trapezoid of very low height between 2 and 8 mm, of width between 40 and 100 mm and that it is glued on the surface of the roadway (8) by any known adhesives (9) deposited between the sensor (7) and the roadway (8) or by covering with a product (10) adhering both to the roadway (8) and to the profile (7). 10 / Device according to claim 1, characterized in that the sectional shape (13) of the molding is a rectangle, a square, or a trapezoid, possibly with a boss (14) and that it is glued or mechanically held in the roadway (20) by any known means. 11 / Device according to claim 1, characterized in that a temperature probe (16) is embedded in the resin (5) to allow compensation for variations in response of the system as a function of temperature. 12 / Apparatus according to claim 1 and following, characterized in that the signal it provides is processed electronically successively by an impedance matching (26), a filter (27), an integrator (28) followed by a battery comparators (29), allow dynamic weight thresholds to be selected, each one being followed by a monostable circuit (30) delivering a calibrated pulse.

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