JP2005157901A - Vehicle detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicle detection device capable of certainly deciding a traffic lane with a simple configuration. <P>SOLUTION: This vehicle detection device has: a plurality of magnetic sensors 1a, 1b disposed inside respective traffic lanes 21a, 21b of a road 22 having the plurality of traffic lanes 21a, 21b; and a traffic lane decision part 24 deciding whether a vehicle 5a passes on the desired traffic lane 21a or not, according to whether or not a value Ia-βIb obtained by subtracting a value βIb obtained by multiplying an output Ib of the magnetic sensor 1b of the adjacent traffic lane 21b by a prescribed ratio β from an output Ia of the magnetic sensor 1a of the desired traffic lane 21a is larger than a value obtained by multiplying an output Ib of the magnetic sensor 1b of the adjacent traffic lane 21b by a prescribed ratio γ. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a vehicle detection device that detects a vehicle traveling on a road and is used for measuring a traffic flow rate, and more particularly to a magnetic field sensitive vehicle detection device that determines passage of a vehicle from a change in magnetic field by the vehicle.

  If a magnetic field is detected at a certain point in the vicinity of the road, a certain value that is constant in time is obtained. This is due to geomagnetism. When a vehicle that is a lump of magnetic material passes on the road, magnetic flux concentrates on the magnetic material, so that the magnetic field at the point changes with time. When the vehicle is magnetized, the magnetic field is stronger if the direction of magnetization is the same as the direction of geomagnetism, and the magnetic field is weaker if the direction of magnetization is opposite to the direction of geomagnetism. It changes a lot. Patent Documents 1 to 4 describe such a magnetic field sensitive vehicle detection device.

  In Patent Documents 1 and 2, two magnetic sensors are installed at an interval in the longitudinal direction of a road, and a pair of a maximum value and a minimum value of a magnetic sensor output due to the passage of one vehicle is detected to pass the vehicle. And the moving direction and speed of the vehicle are detected from the phase difference between the outputs of the two magnetic sensors.

  In Patent Literature 3, two magnetic sensors are embedded at intervals in the longitudinal direction of the road, and the timing of binarizing the magnetic sensor output is devised to identify the passage of two consecutive vehicles. Yes.

  In Patent Document 4, magnetic sensors are respectively installed in the sky between the center in the width direction of one side lane of a road having two adjacent lanes and the lane boundary line and between the center in the width direction of the opposite lane and the lane boundary line. The sensitivity axis of each magnetic sensor is made to face each other or obliquely downward, and the two magnetic sensors detect the lane by sensing the change in the magnetic field due to the vehicle with one side only and the other side only. Yes.

JP-A-6-325288 Japanese Patent No. 2729977 JP 2001-076119 A Utility Model Registration No. 2524593

  In Patent Documents 1 to 3, even if only a vehicle passing through a desired lane among roads having a plurality of lanes is detected, the magnitude of the output of the magnetic sensor depends on whether the vehicle is strongly magnetized or not. Because of the difference, the difference in distance from the magnetic sensor to the vehicle cannot be determined by the magnitude of the output of the magnetic sensor, and even a vehicle that passes through another lane is erroneously detected as passing through the lane. That is, the accuracy of detecting the vehicle is low. For this reason, there is a problem that the traffic volume is counted more than the actual traffic volume.

  In Patent Document 4, although the lane can be discriminated, the magnetic field change due to the vehicle in the adjacent lane must be blocked only by the direction of the sensitivity axis of the magnetic sensor, so the location and posture of each magnetic sensor are set strictly. There is a need to.

  Accordingly, an object of the present invention is to provide a vehicle detection device that solves the above-described problems and can reliably determine a lane with a simple configuration.

  In order to achieve the above object, the present invention provides a plurality of magnetic sensors arranged in each lane of a road having a plurality of lanes, and outputs from a magnetic sensor of a desired lane to an output of a magnetic sensor of an adjacent lane. A lane determining unit that determines whether or not the vehicle has passed the desired lane depending on whether or not a value obtained by subtracting a value multiplied by the ratio is greater than a value obtained by multiplying the output of the magnetic sensor of the adjacent lane by a predetermined coefficient; It is provided.

  The ratio may be obtained in advance as a ratio of the temporal maximum value of the magnetic sensor output of the adjacent lane to the temporal maximum value of the magnetic sensor output of the desired lane during a period in which the vehicle has passed through the desired lane. .

  The present invention exhibits the following excellent effects.

  (1) The lane can be reliably determined with a simple configuration.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, the vehicle detection device according to the present invention includes two magnetic sensors 1a and 1b arranged in each lane of a road 22 having lanes 21a and 21b. These magnetic sensors 1a and 1b can be embedded under the road surface, attached to a gantry straddling the road, attached to the back of the viaduct, or attached to the back of the floor plate of the shield tunnel. A vehicle traveling on the lane 21a is referred to as a vehicle 5a, and a vehicle traveling on the lane 21b is referred to as a vehicle 5b.

  Here, as shown in FIG. 2, the magnetic sensors 1 a and 1 b are embedded under the road surface 23. Each of the magnetic sensors 1a and 1b has a sensitivity axis direction (indicated by an arrow) perpendicular to the road surface 23 (y-axis direction). The sensitivity axis (also referred to as the detection axis) is the direction in which the magnetic field is felt most strongly. By keeping the sensitivity axis perpendicular to the road surface 23, the magnetic sensors 1a and 1b are respectively directly above the vehicles 5a and 5a. The magnetic field by 5b is detected most strongly, and only the upward vector component can be detected from the magnetic field by vehicles 5b and 5a passing diagonally upward. The magnetic sensors 1a and 1b are disposed at substantially the center of the lanes 21a and 21b, respectively.

  As shown in FIG. 3, the vehicle detection device according to the present invention includes a lane determination unit that determines whether or not the vehicle has passed through its own lane for each lane in addition to the two magnetic sensors 1 a and 1 b described above. 24. The lane determination unit 24 includes multipliers 2a and 2b that multiply the output of the magnetic sensor of the adjacent lane by a predetermined ratio, arithmetic units 3a and 3b that subtract the multiplication value from the output of the magnetic sensor of the own lane, and this subtraction. Judgment that outputs a vehicle detection signal by determining whether the vehicle has passed through the own lane based on whether the value is greater than a value obtained by multiplying the output of the magnetic sensor of the adjacent lane by a predetermined coefficient or a predetermined threshold value And 4a and 4b. When the own lane is the lane 21a, the multiplier 2a multiplies the output Ib of the magnetic sensor 1b of the adjacent lane 21b by the ratio β to obtain a multiplication value βIb, and the calculator 3a multiplies from the output Ia of the magnetic sensor 1a of the own lane 21a. The value βIb is subtracted to obtain a subtraction value Ia−βIb, and the determination unit 4a determines whether the subtraction value Ia−βIb is greater than a value obtained by multiplying the output Ib of the magnetic sensor 1b of the adjacent lane 21b by a predetermined coefficient γ or a threshold value. It is determined whether the vehicle has passed through its own lane. When the own lane is the lane 21b, the multiplier 2b multiplies the 1a output Ia of the magnetic sensor of the adjacent lane 21a by the ratio α to obtain a multiplication value αIa, and the computing unit 3b multiplies from the output Ib of the magnetic sensor 1b of the own lane 21b. The value αIa is subtracted to obtain a subtraction value Ib−αIa, and the determiner 4b determines whether the subtraction value Ib−αIa is greater than a value obtained by multiplying the output Ia of the magnetic sensor 1a of the adjacent lane 21a by a predetermined coefficient δ or a threshold value. It is determined whether the vehicle has passed through its own lane.

  First, changes in the output of the magnetic sensor 1 due to the vehicle 5 passing through the vicinity of the magnetic sensor 1 will be described with reference to FIGS. As shown in FIGS. 4 (a) and 4 (b), the vehicle 5, which is a lump of magnetic material, is magnetized in the front-rear direction (x-axis direction based on the road) due to the characteristics of the structure. There are many cases. In addition, even if the vehicle 5 is not magnetized, the magnetism concentrates on the magnetic material, so that an influence equivalent to that of being magnetized is given to the surrounding magnetic field. Note that the strength of magnetization of the vehicle 5 does not depend on the size of the vehicle 5 or the type of vehicle, depending on the magnetic substance content of the vehicle 5 and the history of magnetization.

  Assuming that the vehicle 5 is a virtual magnet 7, the virtual magnet 7 is a bar magnet having both poles at the ends and parallel to the x axis, and the distance from the magnetic sensor 1 is t and y axes in the z axis direction. H in the direction. FIG. 5 shows the magnetic field that the virtual magnet 7 brings to the magnetic sensor 1 after removing the vehicle 5 and the road surface 23 from FIG.

  As shown in FIG. 5A, when the magnetic field generated when the virtual magnet 7 is directly above the magnetic sensor 1 (dotted circle) is H, the magnetic sensor 1 at an angle θ looking down from the virtual magnet 7. A magnetic field r is generated at the inner point P. As shown in FIG. 5B, the magnetic field H generated at the point P in the magnetic sensor 1 is a combination of the magnetic field Hs due to the S pole of the virtual magnet 7 and the magnetic field Hn due to the N pole. These relationships are given by:

  As the vehicle 5 moves forward, the distance d between the midpoint of the virtual magnet 7 in the front-rear direction and the magnetic sensor 1 changes continuously. Since the magnetic field Hs and the magnetic field Hn are functions of the distance d, the intensity changes as the distance d changes. This intensity change can be drawn as an intensity change waveform with respect to the elapsed time. FIG. 6 shows a change waveform of the strength of the magnetic field H in the y-axis direction when the speed of the vehicle 5 is constant. The horizontal axis represents the elapsed time, and the vertical axis represents the magnetic field strength when the magnetic field strength (due to geomagnetism) when there is no vehicle is zero.

  4 to 6 are as conventionally known. Since the method of detecting the passage of the vehicle from the time waveform of FIG. 6 is conventionally known, the description thereof is omitted here.

  Next, how the magnetic field in the direction perpendicular to the road surface is distributed in the lane crossing direction at a certain time T will be described. 7A shows an arrangement when the vehicle 5a passes through the right lane 21a in FIG. 1, and FIG. 7B shows an arrangement when the vehicle 5b passes through the left lane 21b in FIG. FIG. 7C shows the magnetic field strength distribution in each case. In FIG. 7C, the horizontal axis represents the crosswise center of the right lane 21a as 0 and represents the distance in the crossing direction from the crosswise center, and the vertical axis represents the magnetic field strength of the magnetic field generated by the vehicle. The magnetic field strength when there is no vehicle is 0.

  As shown in the distribution 71a of FIG. 7C, when the vehicle 5a travels on the right lane 21a, the center in the transverse direction has the strongest magnetic field, and on both sides of the center in the transverse direction, depending on the distance from the center in the transverse direction. The magnetic field is weak in a curve. Further, as shown in the distribution 71b, when the vehicle 5b travels on the left lane 21b, a point about 3.5m from the center in the cross direction (the center in the cross direction of the lane 21b) has the strongest magnetic field, and both sides of the point Then, the magnetic field weakens in a curve according to the distance from that point. That is, if a large number of magnetic sensors are arranged with minute intervals in the direction crossing the road, the distribution 71a or the distribution 71b can be observed by the lane through which the vehicle passes.

  FIG. 7C shows the time T when the magnetic field intensity reaches the maximum value in FIG. 6 when viewed on the time axis. The spatial maximum value of the magnetic field intensity is 1 at any time in FIG. The distribution profile is the same.

  In the present invention, the magnetic sensor 1a is installed in the lane 21a, and the magnetic sensor 1b is installed in the lane 21b. Now, assuming that the right lane 21a is the own lane and the vehicle 5a passes through the own lane, the magnetic field intensity at the point of 0 m, which is the installation point of the magnetic sensor 1a, in the distribution 71a of FIG. The output Ia of the magnetic sensor 1a is similar to that shown in FIG. At this time, since the magnetic field intensity at the point of about 3.5 m, which is the installation point of the magnetic sensor 1b in the distribution 71a, is 0.6, the output Ib of the magnetic sensor 1b is similar to FIG. Change over time. The ratio of the maximum value 0.6 of the output Ib of the magnetic sensor 1b in the adjacent lane to the maximum value 1 of the output Ia of the own-lane magnetic sensor 1a is 0.6. Therefore, 0.6 is previously set as the ratio β in the multiplier 2a.

  On the other hand, paying attention to the distribution 71b of FIG. 7C, when the left lane 21b is the own lane and the vehicle 5b passes through the own lane, the magnetic field at the point of 0 m, which is the installation point of the magnetic sensor 1a in the distribution 71b. Since the intensity is 0.6, the output Ia of the magnetic sensor 1a is similar to that in FIG. 6 and changes over time with a maximum value of 0.6. At this time, since the magnetic field intensity at the point of about 3.5 m, which is the installation point of the magnetic sensor 1b in the distribution 71a, is 1, the output Ib of the magnetic sensor 1b is similar to FIG. do. The ratio of the maximum value 0.6 of the output Ia of the magnetic sensor 1a in the adjacent lane to the maximum value 1 of the output Ib of the magnetic sensor 1b in the own lane is 0.6. Therefore, 0.6 is preset as the ratio α in the multiplier 2b.

  When the vehicle 5a passes through the right lane 21a in this state, the output Ia of the magnetic sensor 1a is 1, and the output Ib of the magnetic sensor 1b is 0.6. The multiplier 2b multiplies the magnetic sensor 1a output Ia = 1 by a ratio α = 0.6 to obtain a multiplication value 0.6. The arithmetic unit 3b subtracts the multiplication value 0.6 from the output Ib = 0.6 of the magnetic sensor 1b to obtain a subtraction value 0. Since the subtraction value 0 is smaller than the threshold value, the determiner 4b determines that the vehicle has not passed through the own lane (left lane 21b). The multiplier 2a multiplies the 1b output Ib = 0.6 of the magnetic sensor by the ratio β = 0.6 to obtain a multiplication value of 0.36. The calculator 3a subtracts the multiplication value 0.36 from the output Ia = 1 of the magnetic sensor 1a to obtain a subtraction value 0.64. Since the subtraction value 0.64 is larger than the threshold value, the determiner 4a determines that the vehicle has passed the own lane (right lane 21a).

  Conversely, when the vehicle 5b passes through the left lane 21b, the output Ia of the magnetic sensor 1a is 0.6 and the output Ib of the magnetic sensor 1b is 1, and as a result of calculation similar to the above, the right lane 21a Is not passed, and it is determined that the vehicle has passed the left lane 21b.

  Thus, the vehicle detection apparatus of the present invention determines whether or not a value obtained by subtracting a value obtained by multiplying the output of the magnetic sensor of the adjacent lane by the predetermined ratio from the output of the magnetic sensor of the desired lane is greater than the predetermined threshold. By determining whether or not the vehicle has passed the desired lane, it can be accurately detected that the vehicle has passed the desired lane.

  In the above embodiment, the road 22 is a one-way two-lane road, but the present invention can also be applied to a two-way two-lane road. The present invention can also be applied to multi-lane roads of two or more lanes. If a magnetic sensor is installed in each lane, and a multiplier, a calculator, and a judgment device are provided, the lanes of all lanes are A determination of whether or not has passed is obtained.

  In the above example, it is assumed that the vehicle has traveled in the center of the lane, but actually, the vehicle may travel closer to the center in the lane. The lane width is 3.5 m and the vehicle width is about 1.5 m. If the vehicle 5a travels near the adjacent lane, the horizontal distance between the vehicle 5a and the magnetic sensor 1b is given by 3.5 / 2 + 1.5 / 2, which is 2.5 m, and the distance between the vehicle 5a and the magnetic sensor 1a is The horizontal interval is 1 m. Therefore, the output of the magnetic sensor 1b is 0.75 times the maximum value of the magnetic fluctuation caused by the vehicle. On the other hand, the output of the magnetic sensor 1a is 0.95 times the maximum value of the magnetic fluctuation caused by the vehicle. When this maximum value is 1, the output of the arithmetic unit 3b is 0.75−0.6 × 0.95 = 0.13. Therefore, in order to prevent erroneous detection, the threshold value is set to the larger one of the 0.13 value of the output value of the opposing magnetic sensor or the value that provides a sufficient S / N.

It is a top view of the road which has arrange | positioned the magnetic sensor which shows one Embodiment of this invention. It is sectional drawing of the road in the AA 'line of FIG. It is a block block diagram of the vehicle detection apparatus which shows one Embodiment of this invention. It shows the magnetization of the vehicle, (a) is a front view, (b) is a side view. It represents the vector of a magnetic field, (a) is a front view, (b) is a side view. It is a wave form diagram which shows the time change of the intensity | strength of the magnetic field at the time of vehicle passing. (A), (b) is sectional drawing of the road which shows a measurement condition, respectively, (c) is a wave form diagram which shows magnetic field strength distribution in which the magnetic field of a road surface perpendicular direction distributes to a lane crossing direction.

Explanation of symbols

1a, 1b Magnetic sensor 2a, 2b Multiplier 3a, 3b Operation unit 4a, 4b Judgment unit 5, 5a, 5b Vehicle 21a, 21b Lane

Claims (2)

  A plurality of magnetic sensors arranged in each lane of a road having multiple lanes, and a value obtained by subtracting a value obtained by multiplying the output of the magnetic sensor of the adjacent lane by a predetermined ratio from the output of the magnetic sensor of the desired lane A vehicle detection apparatus comprising: a lane determination unit that determines whether or not the vehicle has passed through the desired lane based on whether or not the output of the magnetic sensor of the lane is greater than a value obtained by multiplying a predetermined coefficient. The ratio is obtained in advance as a ratio of the temporal maximum value of the magnetic sensor output of the adjacent lane to the temporal maximum value of the magnetic sensor output of the desired lane during a period in which the vehicle passes through the desired lane. The vehicle detection device according to claim 1.

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