EP0770978A1 - Metallic mass detection system - Google Patents

Abstract

The system includes a magnetic detector (DEC1) sensitive to the direction of the magnetic field placed with a tube (TUB). The outside shape of the detector and internal section of the tube are such that the detector is able to slide along the tube but may not turn about the axis of the tube. The cross-section of the detector and the tube internally may be polygonal, or square. The tube is placed in an inaccessible position, or may be embedded in the surface of the road (R) for example, but access to the ends of the tube is retained for maintenance. A number of such detectors may be placed at intervals along the length of the tube (and consequently across the surface of the road).

Description

The invention relates to a system for detecting metallic masses and in particular vehicles. It is more particularly applicable to the detection and counting of vehicles on roadways as well as on car parking lots.

Different systems exist for detecting the passage or presence of vehicles. The most commonly used currently is based on the use of a conductive loop called an inductive loop to detect a metal mass. These loops are inserted on the surface of the road. For this, a groove a few centimeters deep is made in the pavement. The conductive wire is placed in the groove and a resin or other filling product immobilizes the wire in the groove. This system has several drawbacks. It requires interrupting the use of the roadway during the installation work of such a loop which is often difficult or expensive. In addition, the connecting thread must be close to the surface of the road. It is therefore vulnerable to the passage of vehicles and it is not uncommon for it to be rapidly deteriorated. In addition, during a repair of the road it is often torn off.

Other systems such as optical systems require aerial installations. They have the disadvantage of being subjected to bad weather or of being vulnerable to unfortunate or even malicious manipulation. Also known are ultrasonic or electromagnetic wave radar systems; but these systems are expensive installations.

The invention relates to a system the installation of which does not require traffic to be interrupted. In addition, the system of the invention is sheltered from bad weather and external damage. Finally, the sensor can be removed and replaced from the edge of the road, which greatly facilitates maintenance work.

• au moins un détecteur magnétique sensible à la direction du champ magnétique ;
• au moins un tube placé à proximité des masses métalliques à détecter dans lequel peut coulisser au moins un détecteur magnétique ;

caractérisé en ce que la section intérieure du tube perpendiculaire à l'axe du tube est de forme non circulaire et en ce que le détecteur possède des moyens complémentaires à cette section lui permettant de coulisser dans le tube mais lui interdisant de tourner autour de l'axe du tube.The invention therefore relates to a system for detecting metallic masses, comprising:

• at least one magnetic detector sensitive to the direction of the magnetic field;
• at least one tube placed near the metal masses to be detected in which can slide at least one magnetic detector;

characterized in that the inner section of the tube perpendicular to the axis of the tube is of non-circular shape and in that the detector has means complementary to this section allowing it to slide in the tube but preventing it from turning around the axis of the tube.

• la figure 1, un exemple de détecteur magnétique utilisé dans le cadre de l'invention ;
• les figures 2a à 2c, un exemple de système selon l'invention ;
• les figures 3, 4 et 5, des exemples de dispositions de l'invention transversalement à une chaussée de circulation ;
• les figures 6a à 6e, un système de détection à détecteurs multiples ;
• la figure 7, un système de détection applicable à une installation de parcs automobiles ;
• la figure 8, un système de détection applicable à une installation de péage pour détecter toute circulation en marche arrière d'un véhicule ;
• les figures 9a et 9b, un détecteur tridimensionnel de champ magnétique ;
• les figures 10 et 11, un système de multiplexage analogique des détecteurs ;
• les figures 12a, 12b, un système de multiplexage numérique des détecteurs ;
• les figures 13a, 13b, une variante du système de mise en place des détecteurs selon l'invention ;
• la figure 14, un arrangement de détecteurs pour la mesure de vitesse de véhicules.

The various objects and characteristics of the invention will appear more clearly in the description which follows and in the appended figures which represent:

• Figure 1, an example of a magnetic detector used in the context of the invention;
• Figures 2a to 2c, an example of a system according to the invention;
• Figures 3, 4 and 5, examples of arrangements of the invention transversely to a traffic pavement;
• FIGS. 6a to 6e, a detection system with multiple detectors;
• FIG. 7, a detection system applicable to a fleet installation;
• FIG. 8, a detection system applicable to a toll installation for detecting any reverse traffic of a vehicle;
• FIGS. 9a and 9b, a three-dimensional magnetic field detector;
• Figures 10 and 11, an analog multiplexing system of detectors;
• FIGS. 12a, 12b, a digital multiplexing system of the detectors;
• FIGS. 13a, 13b, a variant of the system for positioning the detectors according to the invention;
• FIG. 14, an arrangement of detectors for measuring vehicle speed.

The detection system according to the invention comprises a detector sensitive to the intensity and the orientation of the magnetic field. A detector placed at a determined point in space, for example in a roadway, is subjected to an ambient magnetic field. When a magnetic mass, such as an automobile, is approached to the detector, the configuration of the magnetic field lines is modified because the magnetic field tends to follow a path of greater magnetic permeability. In addition, an automobile may include magnetic masses. The direction of the magnetic field in the detector, and possibly its intensity is therefore changed and the magnetic detector detects this magnetic mass.

Sensors sensitive to the direction of the magnetic field are produced for example using an element based on magneto-resistive material, a simplified representation of which is given in FIG. 1. It mainly comprises an MR plate made of magneto-resistive material placed according to an xOy plan. Connection wires f1, f2 connected to two ends of the detector make it possible to measure the resistance of the wafer along the axis Ox. When the component of the magnetic field in the xOy plane and more precisely along the axis Oy varies, the resistivity of the magneto-resistive material varies and the measurement of the resistance of the MR plate gives an indication of the variation of the magnetic field.

It follows from the above that the orientation of the magneto-resistive plate MR is important. The invention therefore provides means for orienting in a determined manner and fixing the wafer in its environment. According to Figure 1, the wafer is placed in the DEC housing and is immobilized in this housing. The housing has means called "polarizing" in the art, to give it an orientation provided in advance.

FIG. 2a represents a system using a sensor sensitive to the orientation of the magnetic field such as that of FIG. 1. It has a TUB tube in which the DEC detector can slide. The tube TUB has means which cooperate with the keying device of the detector DEC so that the latter always has the same orientation in the tube, whatever its position along the axis of the tube.

The keying device of the DEC detector can be linked to its shape, for example parallelepiped. In Figure 2b there is shown an example that the tube has a square interior section and the detector has a square shape.

Thus the detector, once inserted with a suitable orientation in the tube, will keep this orientation when it is made to slide in the tube to bring it to the desired point of detection.

The invention is applicable to the detection of the passage of vehicles on a road. For this a hole is drilled in the roadway (see Figure 3), transverse to the direction of the roadway and parallel to the running surface of vehicles, 15 cm for example from the surface. A TUB tube is inserted into this hole and one or more detectors DEC1, DEC2 are inserted into the TUB tube.

The drilling of the hole parallel to the surface of the roadway is not always possible when there is, for example, no ditch on either side of the roadway, or at motorway toll stations. We then plan to drill a diagonal hole in the pavement (see Figure 4). The TUB tube is placed in this hole and a detector is inserted into the tube. The inclination of the hole and therefore of the tube is calculated so that the detector (s) according to their sensitivity can detect vehicles. The TUB tube can be placed in the roadway at a depth of between 1 cm and 1 meter. For installation at a depth of 1 cm, one can for example practice, in the roadway, a groove of the width of the TUB tube as shown in FIG. 2c. The TUB tube is then easily placed in the bottom of the groove and is covered with a filling material (bitumen or plastic material). It is shown that, placed about 1 meter deep, such a detector is still effective.

The same tube can contain several detectors. If the roadway has several traffic lanes, it is therefore possible to detect vehicles on the different lanes by having one detector per lane. There may also be more detectors than there are lanes for detecting vehicles traveling on two lanes. For example, as shown schematically in Figure 5, there is on each channel a detector in the middle of the channel and a detector at the separation limit of the channels.

This system is applicable in covered and / or underground car parking lots. In this case, we can plan to fix the tube at the ceiling of the parking lot which prevents work in the ground of the parking lot.

As shown in FIGS. 6a and 6b, it is also possible to have detectors close enough to detect twin wheels of trucks. Figure 6a is particularly applicable to a toll booth where each vehicle is channeled in its lane. We therefore know the passage area of vehicle wheels and in this area there is a detector at a pitch less than the width of a tire, every 15 cm for example to detect twin wheels of trucks.

FIG. 6b represents a profile of detection values provided by such a detection assembly which corresponds to the detection of a truck with twin wheels. The area "a" of the curve corresponding to the width of the truck. The zones "b0" and "b1" correspond to two spans of twin wheels and the zone "c" corresponds to the space between the two twin wheels.

Figures 6c and 6d correspond to the detection of a passenger car and according to the same principle the areas d, e0, e1, f correspond respectively to the width of the vehicle, the wheels and the space between wheels.

, $\overline{\text{d2}}$

, $\overline{\text{d3}}$

, $\overline{\text{d4}}$

.The analysis of the response of all the detectors makes it possible at any time to determine the type of vehicle detected. FIG. 6e represents a circuit for analyzing the signals d1, d2, d3, ... supplied by the various detectors D1, D2, D3, ... Dn. We can decide that beyond a first threshold dsl of detected signal, an analysis circuit provides the signals d1, d2, d3, d4, .. and that below this threshold, it provides the signals $\overline{\text{d1}}$

, $\overline{\text{d2}}$

, $\overline{\text{d3}}$

, $\overline{\text{d4}}$

.

In the case of FIG. 6b, the combination of the signals received will be: $$\overline{\text{d1}}\text{.d2.d3.d4.d5.d6.d7.d8.d9.d10.}\overline{\text{d11}}\text{.}\overline{\text{d12}}$$

In the case of Figure 6c, this combination will be: $$\overline{\text{d1}}\text{.}\overline{\text{d2}}\text{.d3.d4.d5.d6.d7.d8.}\overline{\text{d9}}$$

The system can therefore deduce the width of the vehicle as a function of the number of signals above the threshold ds.

et dans le cas de la figure 6d, on aura : $$\overline{\text{d1}}\text{.}\overline{\text{d2}}\text{.d'3.d4.d5.d'6.d7.d'8.}\overline{\text{d9}}$$

In addition, provision can be made that above a second threshold ds', signals of 1, 2, etc. are obtained. In the case of Figure 6b, we will therefore have the combination of signals: $$\overline{\text{d1}}\text{.d'2.d'3.d'4.d5.d6.d'7.d'8.d9.d'10.}\overline{\text{d11}}\text{.}\overline{\text{d12}}$$

and in the case of Figure 6d, we will have: $$\overline{\text{d1}}\text{.}\overline{\text{d2}}\text{.d'3.d4.d5.d'6.d7.d'8.}\overline{\text{d9}}$$

The system will thus make it possible both to know the width of the vehicle and to detect twin wheels.

The system observes the number of consecutive detectors which supply signals greater than the threshold ds' (for example, in FIG. 6b: of 2.d'3 on the one hand, and of 7.d'8 on the other hand ).

According to an alternative embodiment, a tube TUB1 can be arranged along the axis of circulation of a traffic lane and contain at least two detectors distant from each other of a length less than the normal length of a vehicle.

This can be useful for example in a parking lot to detect the presence of a vehicle. Due to irregularities in metallic masses, depending on the location of the vehicle, a detector may not detect metallic masses. For this, two detectors DEC1, DEC2 are provided, spaced about 50 cm to 2 m apart, arranged along the axis of the car park. Under these conditions, the detection logic circuit will supply the information in the event of detection. $$\text{d1.d2 + d1 + d2 (and) (or) (or)}$$

Such a system will thus make it possible, by interrogating the detectors, to identify the presence or not of a vehicle in a parking lot location.

The arrangement of two or more detectors along the axis of a lane can be useful in particular at toll stations to detect the direction of movement of vehicles. FIG. 8 thus represents a channel of a toll station and two detectors DEC1, DEC2. The two detectors DEC1, DEC2 are spaced apart by a distance preferably less than the length of a vehicle or, strictly speaking, slightly greater than the length of the vehicle. When a vehicle moves in the direction of the arrow, the DEC1 detector and then the DEC2 detector first detect its passage. At the various instants of passage of the vehicle, the signals are supplied successively according to the following sequences:
d1
d1, d2
then d2

On the other hand, if the vehicle reverses while it has entered the toll lane, the sequence of signals may be as follows:
d1
d1.d2
and again d1

The system is therefore able to detect a vehicle that is reversing after having entered a particular zone such as a toll zone. To do this, it records the last two sequences and each new sequence is compared to the oldest recorded sequence. If there is identity, the system deduces that the vehicle has backed up.

Alternatively, it is expected that the detector has three sensitive elements placed in perpendicular planes as shown in Figures 9a and 9b. According to Figure 9a, the sensitive elements are arranged in three planes perpendicular to each other. According to FIG. 9b, the two sensitive elements D1 and D3 are in the same plane (or in parallel planes) and are oriented to detect perpendicular magnetic field components. The sensitive element D2 is located along a plane perpendicular to that of the elements D1 and D3. Such a sensor is placed as described above in a tube buried in the roadway. It makes it possible to detect with great certainty the presence of a vehicle without being dependent on irregularities in the metal masses of the vehicle.

In the case where several sensors are inserted in series in the same tube, provision may be made to connect them by a rigid or semi-rigid cable which may be a cable containing wires for transmitting the detection signals of the sensors. Such an arrangement makes it possible to thread a series of detectors in series into the tube.

The collection and processing of signals provided by different sensors can be done analogically (Figure 10). An MUX multiplexer controlled by an "MUX command" successively transmits the various detection signals, by an amplification to a processing circuit which supplies detection information.

According to Figure 10, the different detectors are not physically arranged in series.

FIG. 11 represents an arrangement according to which several detectors are connected by separate wires to the multiplexing circuit MUX.

The collection and processing of signals can also be done digitally (Figures 12a, 12b).

In this case, the detectors must be placed in series in a tube or distributed at different points in an installation, they are addressed by the same series of wires of the transmission bus type (4 wires may be sufficient for a set of detectors ).

As shown in FIG. 12a, the MUX circuit successively transmits the addresses of the various detectors. For each address transmitted, a detector recognizes its address and sends back a signal indicating its detection state. The central processing circuit CC therefore successively knows the states of the various detectors and can carry out the detection processing operations described above.

A digital link between the detectors and the central processing circuit CC requires in each detector an electronic circuit CE capable of recognizing its address which the central circuit CC transmits to it and allowing it to connect to the bus to transmit its state.

FIG. 12b represents an exemplary embodiment of such a detector. It includes an INT interface circuit connected to the BUS transmission bus and allowing the connection of a local processing circuit CCL to the bus to allow reception of the information coming from the bus and to transmit in exchange, on this bus, the identity of the detector and the state of the detector. The DEC detector is connected to the local processing circuit by an amplifier.

Figures 13a and 13b show an alternative embodiment according to the invention for installing detectors in a tube. According to this system, a flexible strip REG is provided, the width L1 of which is slightly less than the horizontal interior width L2 of the tube TUB. The strip can thus be slid into the bottom of the tube while being guided laterally. One or more detectors DEC1, DEC2 are attached to the strip. This fixing can be done by any suitable means. In FIG. 13a, the detectors are fixed to the strip by means of adhesive tapes. Also, in FIG. 13a the detectors are represented in the form of housings. According to an alternative embodiment, the detectors could be fixed without a housing on the strip. For example, a printed circuit board carrying the sensitive element of the detector and its connection circuits could be glued directly to the strip.

Figure 13b highlights the fact that the strip can be flexible enough to allow its handling and insertion into the tube. However, unwound and flat in the tube, it has sufficient rigidity to be pushed into the tube. The length of the strip is calculated to allow the positioning of detectors in appropriate areas of the roadway.

For the installation of detectors in the tube, the detectors DEC1 and DEC2 are fixed on the REG strip at positions which correspond to their position in the roadway. The strip carrying the detectors is then slid into the tube by a sight OR provided in the roadway and detectors are in the positions provided in the roadway.

FIG. 14 represents an alternative embodiment according to which two tubes TUB1 and TUB2 are provided which are mutually parallel and transverse with respect to the longitudinal direction of the roadway. Each tube contains at least one detector per circulation channel. The distance D between the two tubes is such that each detector can detect the passage of a vehicle at clearly differentiated times. The electronic operating system of these detectors will then be equipped with a clock. The detection times of a vehicle by the two detectors of the vehicle lane will be recorded. A calculation circuit, making the ratio of the distance D of the two tubes and the difference in detection times, will make it possible to obtain the speed of the vehicle. For example, the distance D between two tubes can be 1 meter for example.

• Le tube utilisé est un tube de section parallélépipédique (rectangulaire ou carrée) tel qu'on en trouve dans le commerce. Il n'a pas besoin d'être conçu spécialement pour ce système ;
• La pose du tube dans la chaussée ne nécessite pas de précautions particulières autres que celles de le mettre à plat dans la chaussée sans moyens et indications d'orientation du tube et l'installateur n'a pas de précaution particulière à prendre lorsqu'il pose le tube dans la chaussée ;
  La forme carrée ou rectangulaire du tube est donc particulièrement intéressante. De plus, le tube peut être placé dans une saignée rectangulaire de la largeur du tube (voir figure 2c) pratiquée à la tronçonneuse dans la chaussée ;
• Le détecteur n'a pas besoin de moyens de guidage particulier. Il suffit qu'il soit dans un boîtier ayant des dimensions légèrement inférieures à la section intérieure du tube ou être sur une réglette de guidage ;
• La section rectangulaire ou carrée du tube présente l'avantage d'être mois sujette à déformation que toute autre forme

The invention generally has the following advantages:

• The tube used is a tube of rectangular (square or square) cross section as found commercially. It does not need to be designed specifically for this system;
• The laying of the tube in the pavement does not require any special precautions other than laying it flat in the roadway without means and indications of orientation of the tube and the installer has no particular precaution to take when laying the tube in the roadway;
  The square or rectangular shape of the tube is therefore particularly interesting. In addition, the tube can be placed in a rectangular groove the width of the tube (see Figure 2c) made with a chainsaw in the road;
• The detector does not need any particular guidance means. It suffices that it is in a housing having dimensions slightly smaller than the inner section of the tube or be on a guide strip;
• The rectangular or square section of the tube has the advantage of being less prone to deformation than any other shape

Claims (15)

Metal mass detection system, comprising: - at least one magnetic detector sensitive to the direction of the magnetic field; - at least one tube placed near the metal masses to be detected in which can slide at least one magnetic detector; characterized in that the inner section of the tube perpendicular to the axis of the tube is of non-circular shape and in that the detector has means complementary to this section allowing it to slide in the tube but preventing it from turning around the axis of the tube. Detection system according to claim 1, characterized in that the detector has a polygonal shape and that the tube has a similar section. Detection system according to claim 2, characterized in that the tube has a rectangular or square section. Detection system according to claim 1, characterized in that the tube is located in the ground on which vehicles move across the roadway or is fixed to the ceiling of a covered car parking area and / or underground. Detection system according to claim 4, characterized in that the position of the tube in the ground is at an angle or is parallel to the surface of the ground. Detection system according to claim 1, characterized in that the complementary means comprise a strip (REG) on which one or more detectors (DEC1, DEC2) are fixed, the strip being slid into the tube (TUB), its width (L1 ) being slightly less than the horizontal internal dimension (L2) of the section of the tube and its length being sufficient to place the detectors in determined positions in the tube. Detection system according to claim 4, characterized in that it comprises several detectors placed in the tube. Detection system according to claim 7, characterized in that the distance between two neighboring sensors is less or substantially equal to the normal width of a vehicle tire, so as to detect dual vehicle wheels. Detection system according to claim 8, characterized in that the detectors are placed in the tube by an inlet end of the tube and can be moved towards the opposite end of the tube, in that the housing of each detector allows passage detection wires from the inlet end of the tube to the detectors placed towards the opposite end and in that the detectors are connected by a cable allowing the distance between the various detectors to be kept constant. Detection system according to one of claims 1 or 4, characterized in that the tube is oriented parallel to the direction of movement of the vehicle and in that it comprises at least two detectors placed in the tube and spaced apart by a distance less than or slightly greater than the normal length of a vehicle and more than 50 cm. Detection system according to any one of the preceding claims, characterized in that each detector comprises a magneto-resistive sensitive element whose resistivity varies according to the value and the orientation of the magnetic field in the sensitive element. Detection system according to claim 5, characterized in that the tube is located in the ground at a depth of between 1 cm and 100 cm. Detection system according to claim 8, characterized in that it provides a first detection threshold (ds) for the detection of a vehicle, and a second detection threshold for the detection of the wheels of the vehicle. Detection system according to claim 1, characterized in that it comprises means for detecting the last two sequences of detection signals and for providing a signal (of indication of the vehicle backing up) when a third detected sequence of signals is identical to the first sequence of signals. Detection system according to claim 4, characterized in that it comprises at least two tubes (TUB1, TUB2) parallel to each other and transverse to the longitudinal direction of the roadway, each tube possibly containing at least one detector per circulation and the distance (D) between the two tubes being such that it allows a system Detector operating electronics identify the instants of detection of a vehicle by a detector of each tube and calculate the speed of the vehicle.

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