EP0456325A1 - Device for the detection of data of passing vehicles on a road - Google Patents

Abstract

The invention relates to a device which records data about passing vehicles on a road (20) and consists of a piezoelectric cable (2) together with a system for rigidifying this cable and transmitting to it the stresses caused by the passing vehicles. This system is a cylindrical metallic tube (6) which has an inner diameter greater than the outer diameter of the piezoelectric cable (2) and which contains the piezoelectric cable along its axis. The space between the cable and the inner walls of the tube is filled with a compacted metal oxide powder (5), e.g. MgO. <??>This device can be installed in a groove (10) cut into the road (20), having a depth roughly equal to the outer diameter of the tube (6) and a lateral width slightly greater than this diameter. The device is mechanically fixed into the groove (10) in such a way that its upper surface is flush with the upper surface (1) of the road, e.g. by using wedges (7a, 7b) fixed to the road by bolts (8). <??>Application to the detection, counting, measurement of speed and weight, and classification, of vehicles in motion. <IMAGE>

Description

The invention relates to a device for detecting data relating to the passage of vehicles on a roadway, comprising a piezoelectric cable and means for making this cable rigid and transmitting to it the stresses produced by the passage of vehicles.

The invention finds its application in the detection of passage of vehicles, the counting, the measurement of speeds, the measurement of the weights of vehicles and their classification and this in all regions having various climatic conditions and in particular severe (very hot, temperate climate or very cold).

Patent FR 2 482 340 describes a device for detecting passage on a road, its laying method and its application to speed detection.

This device is partly made up of a piezoelectric effect cable. This cable is a shielded coaxial cable whose core and sheath are separated by a piezoelectric ceramic.

This device further comprises a rigid section having either the shape of a U or the shape of a rectangular quadrilateral whose upper face is curved. This profile is filled internally in a plastic form obtained hard by polymerization. The aim is to make the device rigid.

In a variant, this device is coated on the three faces not in contact with the vehicles, with a U-shaped envelope made of flexible or hard plastic, for example a resin loaded with elastomer, to absorb vibrations. This arrangement is carried out in the factory.

In either case, the method of laying the device in the pavement comprises forming a groove in the roadway, of dimensions slightly larger than those of the device. Then the bottom and sides of the groove are coated with a flexible plastic material absorbing vibrations and finally the device is placed in the coated groove so as to fix it, while making it protrude slightly from the upper surface of the roadway. The coating of the groove is not essential when the device already includes a plastic envelope made in the factory.

For speed measurement, two devices can be made so as to form two parallel rigid branches spaced by a predetermined fixed distance, and installed in two grooves in the roadway.

A disadvantage of the aforementioned device known from the prior art is that its manufacture uses plastics, which are organic materials and are particularly sensitive to temperature variations.

However, an object of the invention is the detection of the speed of vehicles, but also, in addition to counting, the detection of the weights of moving vehicles and their classification. The detection and analysis of this data is particularly important for the forecasting of new roads, new bridges, or pavements of all kinds, as well as for the forecasts concerning their maintenance.

If organic materials are used to make the detection devices, the measurements are not reliable as regards the detection of the weight of the vehicles, since these measurements depend on the climatic conditions. Depending on the case, these measures may be non-repetitive, or even impossible in regions where the climatic conditions are severe.

In addition, in the case where it is necessary to also use a plastic material to fix the device in the roadway, difficulties or impossibilities appear in regions where the climatic conditions are severe (scorching heat, extreme cold, very high humidity , great climatic differences between the seasons, or between days and nights, etc.).

An object of the present invention is to provide a device for detecting data relating to the passage of vehicles on a roadway, such as the detection of passage and the measurement of speed, as is done by the device known from the state of the technique, but also particularly data relating to the weight of moving vehicles to allow their classification.

The solution to this problem is to overcome the need to use organic materials, first in the manufacture of the detection device, and then in its method of installation in the pavement.

According to the invention, this problem is solved by means of a device as described in the preamble of claim 1, characterized in that the means consist of a cylindrical metallic tube of diameter greater than that of the piezoelectric cable, tube in the axis of which is arranged the piezoelectric cable, the space between the cable and the internal walls of the tube being filled with a compacted metal oxide powder.

The advantage which results from this device is that the rigid envelope is no longer a profile but a tube, still industrially easier and less expensive to manufacture.

Another advantage is that the compacted metal oxide powder transmits the required information very well to the piezoelectric cable, and is extremely less sensitive to climatic conditions than plastic.

Another advantage is that the device according to the invention has an improved longevity because it is mechanically practically insensitive to climatic conditions, and much less sensitive to mechanical degradation.

In addition, it is synergistically produced with the piezoelectric cable itself; the same techniques can be used to manufacture it, which is an economic advantage for the manufacturer who implements it.

Another object of the invention is to propose a simple and inexpensive installation method which is insensitive to climatic conditions.

According to the invention this method is characterized in that a groove is made in the upper covering of a road, this groove having a depth substantially equivalent to the outside diameter of the tube, and a transverse dimension slightly greater than this diameter, and in that the device is fixed in the groove by mechanical means.

In one implementation, this method is characterized in that the mechanical means consist of corners pressing on the upper part of the tube disposed in the groove, these corners being slid further between the tube and the vertical walls of the groove and fixed to the pavement by screws.

The advantage of this process is that it is very easy to implement. The groove does not need to have very strict dimensions. The means used are within the reach of a person skilled in the art of mechanics and not of a specialist in plastics. Considerable time is saved during installation: whereas it took 6 to 8 hours of laying work including the formation of a trench and the gluing of the known device, it now takes at most 3 hours to make the trench and fix the device by the corners. The device can be easily recovered if necessary. For example, if the sensor has any breakdown, or is accidentally damaged, it is easily exchangeable. It can also be simply retrieved and moved if you no longer wish to take measurements at a first location on the road, but take them at a second location. The first bleeding can then be filled or covered with a metal bar. Installation can be done anywhere and even under the most severe climatic conditions. And the measures are practically insensitive to said weather conditions. So not only passage detection, counting, speed measurement but also weight measurements and classification of vehicles are allowed by connecting the piezoelectric cable to a signal processing device of this cable.

• la figure 1a qui représente un dispositif de détection selon l'invention, en coupe transversale ;
• la figure 1b qui représente le même dispositif en coupe longitudinale ;
• la figure 2 qui représente un tel dispositif installé dans le revêtement supérieur d'une chaussée.

The invention will be better understood by means of the following description illustrated by the appended schematic figures including:

• Figure 1a which shows a detection device according to the invention, in cross section;
• Figure 1b which shows the same device in longitudinal section;
• FIG. 2 which represents such a device installed in the upper covering of a roadway.

• un câble à effet piézoélectrique 2, disposé sensiblement selon l'axe d'un tube cylindrique métallique 6 de diamètre interne supérieur au diamètre externe du câble piézoélectrique 2 ;
• un matériau de remplissage 5 disposé dans l'intervalle entre le câble piézoélectrique 2 et la paroi interne du tube 6, ce matériau 5 étant constitué par une poudre d'un oxyde métallique compactée.

As shown in FIG. 1a, in cross section and 1b in longitudinal section, the device for detecting data relating to the passage of vehicles on a road comprises:

• a piezoelectric effect cable 2, disposed substantially along the axis of a metallic cylindrical tube 6 with an internal diameter greater than the external diameter of the piezoelectric cable 2;
• a filling material 5 disposed in the gap between the piezoelectric cable 2 and the internal wall of the tube 6, this material 5 being constituted by a powder of a compacted metal oxide.

In a preferred implementation, resulting from tests which have given to date very good results in terms of measurements, ease of implementation, resistance to the aggressiveness of external agents, and longevity, we will choose to make the tube 6 an inexpensive, malleable metal, not degradable by oxidizing agents, such as aluminum, and, to make the filling material 5, a powder of magnesium oxide, or any other metal oxide which is easy to compress and transmitting the constraints well.

Preferably, a coaxial shielded cable 2 will be chosen as the piezoelectric cable, comprising a metallic core insulated from a metallic sheath by a ceramic material with piezoelectric effect. A piezoelectric cable which is particularly suitable for achieving the aims of the invention is the VIBRACOAX piezoelectric cable, Reference 30 P 1 C from the company THERMOCOAX (Suresnes - France).

As shown in FIG. 1b, the coaxial piezoelectric cable 2 is connected by a coaxial connector 12 to a coaxial transmission cable 11. Preferably, a reference cable RG 58 will be used in conjunction with the piezoelectric cable VIBRACOAX cited. Cu, from THERMOCOAX.

Each end of the tube 6 is preferably closed in a leaktight manner by plugs 10a, 10b, one of which for example 10b allows the transmission cable to pass through 11. A small thickness of filling material 5 separates the other end from the piezoelectric cable 2, not connected, of the second plug, for example 10a.

If the metal tube 6 is made of aluminum, the plugs will also preferably be made of aluminum.

Thus the detection device obtained is rigid, waterproof and the stresses are very well transmitted to the piezoelectric cable. It is also highly mechanical and allows electrical signals to be recorded from the cable, the characteristics of which are almost completely independent of climatic conditions, hot, cold, temperate or humid.

The manufacturing process of the data detector device is in total manufacturing synergy with the piezoelectric cable itself. This cable, if it is a vibracoax, is described and its manufacturing process given in patent FR 2 109 176 of October 1970.

This is a considerable advantage for industrial manufacturing to be able to manufacture the cable and the detection device by a process using the same techniques by the same tradesmen. There is a considerable reduction in costs, all the more so since the materials or starting materials for the implementation are also of reduced cost.

The method of manufacturing the detection device comprises the manufacture of a metal tube 6 said blank, of a malleable material, aluminum therefore having for this purpose very good properties, of diameter greater than the diameter of the finished device; the establishment of the cable 5, with its connector 12 and its connection cable 11; filling with the material 5 to 70% of its theoretical density, for example the magnesia oxide MgO; then reducing the diameter of the tube 6 by any technique known to those skilled in the art to produce this effect, such as hammering or rolling, until the device is obtained whose tube 6 has a reduced diameter and is perfectly rigid; finally the establishment of sealing plugs 10a, 10b.

• réalisation d'une rainure 10 dans la partie supérieure du revêtement de la chaussée 20. Cette rainure devra présenter une profondeur de l'ordre du diamètre externe du tube 6 du dispositif de détection et une dimension transversale un peu supérieure; la rainure 10 pourra présenter une section rectangulaire,
• la mise en place du dispositif de détection avec son câble de connexion 11 dirigé vers l'endroit localisé pour recevoir les appareils ou dispositifs de mesure et traitement du signal électrique provenant du câble piézoélectrique 2; le dispositif de détection est mis en place de manière à ce que le tube 6 repose sur le fond de la rainure 10 ; la partie supérieure du tube 6 est alors tangente à la surface supérieure 1 de la chaussée 20,
• la mise en place de coins 7a, 7b appuyant sur la partie supérieure du tube 6, pour le plaquer contre le fond de la rainure 10, ces coins étant glissés en outre entre le tube 6 et les flancs verticaux de la rainure 10,
• fixation des coins 7a, 7b à la chaussée 20 par exemple au moyen de vis traversant les coins et s'enfonçant dans la chaussée.

For the measurement of data relating to the passage of vehicles, the device is installed in the upper part of the pavement of a roadway. A method of installing this device, which makes it possible to properly transmit the stresses caused by the passage of vehicles, while overcoming climatic conditions, comprises the following operations, the result of which is illustrated in FIG. 2:

• making a groove 10 in the upper part of the covering of the roadway 20. This groove should have a depth of the order of the external diameter of the tube 6 of the detection device and a slightly greater transverse dimension; the groove 10 may have a rectangular section,
• the installation of the detection device with its connection cable 11 directed towards the localized location to receive the devices or devices for measuring and processing the electrical signal coming from the piezoelectric cable 2; the device detection is set up so that the tube 6 rests on the bottom of the groove 10; the upper part of the tube 6 is then tangent to the upper surface 1 of the roadway 20,
• the establishment of corners 7a, 7b pressing on the upper part of the tube 6, to press it against the bottom of the groove 10, these corners being slid in addition between the tube 6 and the vertical sides of the groove 10,
• fixing the corners 7a, 7b to the roadway 20 for example by means of screws passing through the corners and sinking into the roadway.

A certain number of corners are thus put in place to hold the detection device, in a purely mechanical manner, in the groove 10. The number of corners depends on the length L of the device (see FIG. 1b). The length of the device can be provided as required from 0.2 m to 4 m inclusive. In fact the length is not limited. These dimensions are given purely by way of example as being most probably useful in the near future.

• la détection du passage de véhicules,
• le comptage,
• la mesure des vitesses,
• la mesure des poids des véhicules en mouvement,
• le classement des véhicules.

Ainsi, le câble blindé à céramique piézoélectrique 2, et le dispositif 5, 6 qui l'entoure ne sont pas sensibles aux effets climatiques, et ils permettent la détection de signaux électriques donnant des informations plus complètes sur le passage des véhicules que les dispositifs connus incluant des matières plastiques.Once connected to an appropriate electronic data processing system, which is part of the knowledge of those skilled in the art of electronics or computer science, and does not form part of the invention, the device according to the invention allows:

• detection of the passage of vehicles,
• the counting,
• speed measurement,
• the measurement of the weights of moving vehicles,
• vehicle classification.

Thus, the shielded piezoelectric ceramic cable 2, and the device 5, 6 which surrounds it are not sensitive to climatic effects, and they allow the detection of electrical signals giving more complete information on the passage of vehicles than known devices. including plastics.

Claims (10)

Device for detecting data relating to the passage of vehicles on a roadway comprising a piezoelectric effect cable and means for making this cable rigid and transmitting to it the stresses produced by the passage of vehicles, characterized in that the means consist of a cylindrical metal tube with an internal diameter greater than the external diameter of the piezoelectric cable, tube in the axis of which the piezoelectric cable is disposed, the space between the cable and the internal walls of the tube being filled with a compacted metal oxide powder. Device according to claim 1, characterized in that the metal constituting the tube is aluminum (Al), and in that the metal oxide powder is a magnesia oxide powder (MgO). Device according to one of claims 1 or 2, characterized in that the piezoelectric cable is electrically connected to a coaxial connection cable, by a coaxial connector, connection cable intended to be connected by its other end to recording devices and for processing the electrical data of the piezoelectric cable. Device according to claim 3 characterized in that the metal tube is provided at its ends with sealing plugs, one of which lets a connection cable pass. Device according to one of the preceding claims, characterized in that it has a longitudinal dimension between 0.2 m and 4 m inclusive. Device according to one of Claims 1 to 5, characterized in that the piezoelectric cable is of the type comprising a metallic core, a metallic shield and a piezoelectric ceramic material arranged in a dense manner between the core and the shield. Method for producing a device according to one of claims 1 to 5, characterized in that the cable piezoelectric provided with electrical connection means is introduced into the external metal tube, the latter having a diameter much greater than the diameter of the piezoelectric cable, in that the gap between the internal walls of the tube and the piezoelectric cable is filled with powder d metal oxide, then in that the diameter of the external tube is reduced and the compacting of the powder is carried out in the same mechanical operation chosen for example from hammering, or mechanical rolling, followed by the fitting of the caps sealing, one of which lets the connection cable pass. Method for installing the device according to one of claims 1 to 6, characterized in that a groove is made in the upper covering of a road, this groove having a depth substantially equivalent to the outside diameter of the tube, and a transverse dimension slightly greater than this diameter, and in that the device is fixed in the groove by mechanical means, so that its upper surface is flush with the upper surface of the roadway. Method according to claim 8, characterized in that the mechanical means consist of corners pressing on the upper part of the tube arranged in the groove, these corners being slid further between the tube and the vertical walls of the groove and fixed to the pavement by screws. Use of a vehicle passage data detection device according to one of claims 1 to 6 for detecting the passage of vehicles, counting, measuring their speed, measuring their weight and classifying them by electronic data processing the piezoelectric cable.

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