JPH09211144A - Vehicle detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy and reliability of detection in a vehicle detection method for magnetically detecting vehicles by detecting a magnetic field generating from the vehicles with a magnetic sensor. SOLUTION: In or on the ground 14 whereon a vehicle 10 is passing in a width, a magnetic sensor 12 is arranged. The magnetic sensor 12 includes two or three magnetic detection elements having magnetic detection sensitivity in the longitudinal X-axis direction of the vehicle, the Z-direction vertical to the ground and Y-direction of the width of the vehicle. With these magnetic sensors, the intensity change of exterior magnetic field in two of X-axis and Z-axis directions or three directions by addition of the Y-axis direction is measured. From the base state without vehicles, detection of a vehicle is clone whether the sum of the absolute values of the intensity change in the exterior magnetic field in the two or three directions exceeds a prescribed threshold value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle detection method for detecting a vehicle such as an automobile, that is, the presence or absence of the vehicle or the passage of the vehicle. The present invention relates to a vehicle detection method for detecting a vehicle.

[0002]

2. Description of the Related Art Conventionally, a sensor for detecting a vehicle such as an automobile has been used in applications such as determining whether or not a vehicle is parked in a parking lot management system and measuring the traffic volume of the vehicle in a traffic management system.

Usually, a vehicle such as an automobile is magnetized by using a metal material such as a steel plate, which is easily magnetized. Therefore, by detecting a magnetic field generated from the vehicle by a magnetic sensor,
It is possible to recognize the presence or passage of a vehicle.

Conventionally, however, a loop coil type magnetic sensor has been used in a parking lot or the like to detect a vehicle. However, the sensor is large, and the magnetic field from the vehicle is detected only in one direction perpendicular to the ground. Therefore, the accuracy is not sufficient.

That is, when measuring the magnetic field generated from the bottom of the vehicle, the local magnetization of each of the body parts causes
The distribution of the magnetic field strength is considerably uneven, and a dead point that does not exceed the threshold value required for the vehicle detection determination occurs near the zero cross point where the magnetic field polarity reverses.

Therefore, under the present circumstances, the size of the sensor is increased, or the sensor is embedded in the ground a little deeper to reduce the influence of the locally magnetized parts and reduce the sensitivity. There was a problem in detection accuracy and reliability.

[0007]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is a vehicle detection method for magnetically detecting a vehicle by detecting a magnetic field generated from the vehicle with a magnetic sensor, which is highly reliable and reliable. The object is to provide a highly reliable vehicle detection method.

[0008]

In order to solve the above-mentioned problems, according to the present invention, a vehicle detection method for magnetically detecting a vehicle by detecting a magnetic field generated from the vehicle by a magnetic sensor, A magnetic detection element having magnetic field detection sensitivity in the longitudinal direction of the vehicle and a magnetic detection element having magnetic field detection sensitivity in the direction perpendicular to the ground (or further in the width direction of the vehicle) An external magnetic field in two directions (or three directions) of the longitudinal direction of the vehicle and the direction perpendicular to the ground (or the width direction of the vehicle). Of the strength of the external magnetic field in the two directions (or three directions) with reference to the absence of the vehicle, and whether the sum of absolute values of the strength of the external magnetic field exceeds a predetermined threshold value. It was adopted a method of performing detection.

Further, as a vehicle detection method when a magnetic sensor cannot be arranged on the ground or in the ground, a magnetic detection element having magnetic field detection sensitivity in the longitudinal direction of the vehicle outside the passage width of the vehicle and in the vehicle width direction are provided. A magnetic sensor including a magnetic detection element having a magnetic field detection sensitivity is arranged, and the magnetic sensor measures changes in the intensity of the external magnetic field in two directions, the longitudinal direction and the width direction of the vehicle, with reference to the absence of the vehicle. Also, a method of detecting a vehicle based on whether or not the sum of absolute values of changes in the intensity of the external magnetic field in the two directions exceeds a predetermined threshold value is adopted.

According to such a method, the sum of the absolute values of the intensity changes of the external magnetic field in the above-mentioned two or three directions is used to obtain the external magnetic field in each direction due to the local variation in the magnetization of the vehicle body parts. Compensates for the zero-cross point of the detection output of, and avoids erroneous detection due to the dead point near the zero-cross point in the conventional external magnetic field detection only in the 1-axis direction, which enables highly accurate vehicle detection and highly reliable vehicle detection. become.

The magnetic detection element of the magnetic sensor is a magnetic impedance element or a ring core as a small and highly sensitive element capable of simultaneously detecting biaxial or triaxial external magnetic fields at substantially the same point. A fluxgate type magnetic sensing element using is suitable.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] A first embodiment of the present invention will be described with reference to FIGS.

In the present embodiment, as shown in FIG. 1, on the ground 14 or the ground within the width through which the vehicle (automobile) 10 passes, the direction of the arrow (X) along the longitudinal direction of the vehicle 10 (X
A magnetic detection element having a detection sensitivity in the axial direction and a magnetic sensor 12 including the magnetic detection element having the detection sensitivity in the direction perpendicular to the ground surface 14 (Z-axis direction) are arranged to detect a vehicle.

The above two magnetic detection elements of the magnetic sensor 12 simultaneously detect and measure changes in the intensity of the external magnetic field in the X-axis direction and the Z-axis direction when the vehicle 10 passes through.
The vehicle detection is determined based on whether or not the sum of the absolute values of the intensity changes of the external magnetic fields measured in the X-axis direction and the Y-axis direction exceeds a predetermined threshold value based on the absence of the condition.

This vehicle detection method was derived from the following examination results.

First, as shown in FIG. 2, a magnetic detection element having detection sensitivity in the X-axis direction along the longitudinal direction of the vehicle 10 and a magnetic detection element in the X-axis direction are formed on the ground 14 within the width through which the vehicle 10 passes. A magnetic detection element having a detection sensitivity in the Y-axis direction in the width direction of the vehicle 10 which is perpendicular to the vehicle 10 and a Z direction which is a direction perpendicular to the ground
A magnetic sensor 12 including a magnetic detection element having a magnetic field detection sensitivity is arranged in the axial direction, and the vehicle 10 is mounted on the sensor 12.
Was moved, and the state of change in the external magnetic field strength in each axial direction detected and measured by the magnetic sensor 12 was examined. The amount of change in the external magnetic field strength is the detected value in the absence of the vehicle 10 as an initial value, and the amount of change from that value is displayed. A magnetic impedance element described later was used as the magnetic detection element. Note that the vehicle 10 used in the study was a manufacturer's 2
It is a door commercial vehicle.

The change in the magnetic field in each axial direction is shown in FIG.
As shown in (a), in the X-axis direction, a peak is once reached near the front end of the vehicle, zero crossing occurs, and the change of the magnetic field is reversed.
Then, after repeating the unevenness, a peak is formed after zero crossing again near the rear end of the vehicle, and then the change in the magnetic field is attenuated. The overall tendency of the magnetic field change in the X-axis direction is shown in FIG.
The tendency of the magnetic field distribution in the longitudinal direction of the bar magnet 16 shown in (a) is the same, and it is considered that a large magnet is formed in the longitudinal (front-back) direction of the vehicle 10. This tendency was also examined for other vehicle models, but it was almost the same.

Next, as shown in FIG. 2B, two small peaks can be seen in the data in the Y-axis direction, but it is presumed that this is probably due to the influence of the front and rear wheel axles.

Further, as shown in FIG. 2 (c), in the data in the Z-axis direction, the peak is reached near the front end of the vehicle, the zero cross is reversed on the way, the peak is formed again near the rear portion of the vehicle, and then the peak is attenuated. It is understood that there is. The overall tendency of the magnetic field change in the Z-axis direction is roughly the same as the tendency of the magnetic field distribution in the width direction of the bar magnet 16 shown in FIG. 3B, and the longitudinal direction of the vehicle 10 is the same as the data in the X-axis direction. This proves that a large magnet is formed in the direction.

Looking at the amount of change in the magnetic field, the maximum width is X
0.6 Gauss in the axial direction, 0.15 Gauss in the Y-axis, Z
It is about 0.8 Gauss in the axial direction. It can be said that the Y-axis direction has a small change and is not suitable for vehicle detection.

It can be seen that the data in the X- and Z-axis directions have a large change, but also have a zero cross and a small change region, and are not suitable for vehicle detection by themselves.

Therefore, it was examined whether or not the influence of the zero cross could be eliminated by combining the data in each axial direction.
As a result, the zero cross point point XA in the X-axis direction becomes Z
Looking at the data in the axial direction, it was found that peaks were shown as at point ZA, and other points were at point X.
It can be seen that B corresponds to point ZB and point XC corresponds to point ZC. That is, it can be inferred that when the magnetic field in the horizontal direction is zero, the probability that the vector of the magnetic field is oriented in the vertical direction is high. Therefore, FIG. 2D shows a graph in which the data in the X and Z axis directions are converted into absolute values and the sum of the two data is obtained.

From the data of FIG. 2D, the zero cross points of both are complemented, and a certain threshold value, for example, 0.1.
It turns out that the vehicle can be detected in a wonderfully wide range by cutting with Gauss.

When the practical resolution is several milligausses, the threshold value needs to be at least 0.05 gausses in consideration of noise and temperature characteristics.

The upper limit of the threshold value is about 0.2 gauss, considering that valleys can be formed in places like V1, V2 and V3 in the data of FIG. 2D.

It should be noted that although detection with only one magnetic sensor having a pair of magnetic detection elements having detection sensitivity in the X and Z axis directions is sufficiently reliable, noise etc. may occur depending on the installation location of the magnetic sensor. In some cases, the threshold value cannot be set low because it may be easily disturbed. In that case, as shown in FIG. 4, a plurality of magnetic sensors 12 having a pair of magnetic detection elements each having detection sensitivity in the X and Z axis directions are arranged along the longitudinal direction of the vehicle 10, and at least one magnetic sensor 12 is disposed. It is possible to increase the reliability of the threshold value by determining the vehicle detection based on whether the output of FIG. 2 (d) of the plurality of sensors exceeds a predetermined threshold value.

Although the change in the Y-axis direction data is small as described above and is not suitable for detection, if the change amount (absolute value) in the Y-axis direction is added to the X-axis and Z-axis direction data. ,
In some cases, it is possible to cover the dips in the valleys such as V1, V2, and V3 in FIG. 2D to some extent. Therefore, when a detection margin is desired, the Y-axis data is added to determine the vehicle detection. May be.

In the magnetic vehicle detection method described above,
It is necessary to select a suitable magnetic detection element.

For example, if the X-axis and Z-axis magnetic detection elements used are separated from each other, it may not be possible to complement the zero cross, so a small and integrated magnetic detection element is required. Further, when used near the ground, the temperature change is large, so an element having good temperature characteristics is required.
When the other items are also summarized, the conditions are as follows: -Resolution is 0.01 Gauss or more (milligaus order) -Elements are small and multiple elements can be installed close to each other.

Excellent in temperature characteristics.

Low power consumption.

Is raised.

First, a magneto-impedance element is given as a candidate. The magneto-impedance element is disclosed in JP-A-7-181239, and an element body as a magnetic body is composed of an amorphous wire or recently a magnetic thin film. When a high frequency current in the MHz band is applied to this element body, due to the magnetic impedance effect,
Impedance of element body is several tens% depending on external magnetic field
It changes and can be used to detect external magnetic fields.

The sensitivity of the magneto-impedance element is 10 ^-5.
It has a Gaussian sensitivity, is resistant to demagnetizing fields, and is very suitable for miniaturization. Therefore, if this element is adopted, an accuracy of about several milligauss can be obtained even in practical accuracy after the circuit is incorporated. Also, because of its size's resistance to demagnetizing fields, it is sufficient for the element to have a length of about a few mm, and even if it is incorporated into the sensor circuit, it fits within a size of several centimeters square, and at the same point, it is biaxial or triaxial. Directional magnetic field measurement is possible. Further, the element is used by being incorporated in an oscillation circuit, and low power consumption can be realized.

The magnetic field strength data shown in FIGS. 2 (a) to 2 (d) are obtained by using a Fe-Ta-C-based magnetic film on a glass substrate to measure a 0.5 × 3 × 1 mm size magneto-impedance element. It is measured by using a plurality of magnetic sensors. This magnetic sensor has an ultra-compact size, and it was possible to simultaneously measure two or three axes at the same point.

Another candidate is a fluxgate type magnetic detecting element using a ring core, which is a type generally used as a conventional orientation sensor. The fluxgate type sensor can secure a detection sensitivity of the order of 10 ^-5 Gauss, and there is no problem in sensitivity like the magnetic impedance element.

The Hall element is not suitable for the vehicle detection method according to the present invention because it has a sensitivity of 10 milligauss or less and a poor temperature characteristic.

[Second Embodiment] In the detection of a vehicle in traffic volume measurement or the like, there are cases where the magnetic sensor cannot be installed on the ground or cannot be buried in the ground. In that case, outside the width of the vehicle passing through. Measure the magnetic field from the side of the vehicle.

The vehicle detection method in this case is, as shown in FIG. 5, a magnetic detection element having a detection sensitivity in the arrow direction (X-axis direction) along the longitudinal direction of the vehicle 10 and the vehicle 10.
The magnetic sensor 12 including a magnetic detection element having a detection sensitivity in the width direction (Y-axis direction) is separated from the side surface along the longitudinal direction of the vehicle 10 by a predetermined distance d in the Y-axis direction outside the passage width of the vehicle 10. It is arranged at a position and the vehicle detection is determined by detecting the magnetic field from the side surface of the vehicle 10.

The above-mentioned set of magnetic detection elements of the magnetic sensor 12 simultaneously measure changes in the intensity of the external magnetic field in the X-axis direction and the Y-axis direction when the vehicle is passing, and when the vehicle is not present, reference is made to the X-axis direction. Vehicle detection is determined by whether or not the sum of absolute values of changes in the intensity of the external magnetic field in the Y-axis direction exceeds a predetermined threshold value.

The actual measurement data which is the basis for deriving this method is shown below.

First, as shown in FIG. 6, the X-axis along the longitudinal direction of the vehicle 10 is located at a position of a height of 50 cm at a distance of 1.5 m in the width direction of the vehicle 10 from the side surface along the longitudinal direction of the vehicle 10. Direction magnetic field detection sensitivity, magnetic field detection sensitivity in the vehicle width direction Y axis direction perpendicular to the X axis direction, magnetic field detection sensitivity in the Z axis direction perpendicular to the ground A magnetic sensor 12 including a detection element is arranged, and in front of the magnetic sensor 12 at a speed of 40 km / hour
0 was moved and the state of change of the magnetic field in each axial direction detected by the magnetic sensor 12 was examined. The amount of change in the magnetic field was set to the initial value when there was no vehicle, and the amount of change from that was displayed.

In this method, the magnetic sensor 12 and the vehicle 1
Unlike the case where the magnetic sensor is installed on the ground or underground under the vehicle body, the distance of 0 must be set large for safety, so the change in the external magnetic field strength in each axial direction is smaller than in the case of installation on the ground or underground. .

As shown in FIGS. 6A and 6B, the X axis,
It can be seen that the data of the magnetic field change in the Y-axis direction has almost the same tendency as the magnetic field distribution of the bar magnets shown in FIGS. 3 (a) and 3 (b). The reason why there is almost no fine unevenness is that the side surface of the vehicle body of the vehicle 10 is covered with the steel plate of the body and the distance between the vehicle 10 and the magnetic sensor 12 makes it less susceptible to local magnetization. . The Z-axis data has a small peak but very little change and need not be incorporated into the sensor output.

From the above tendency, the result of adding the absolute values of the changes in the magnetic fields in the X-axis and Y-axis directions is shown in FIG. 6 (d).
Similar to the first embodiment, the peak becomes large and the vehicle can be sufficiently detected even with the threshold value of 0.1 Gauss. The practical threshold setting range is 0.
A range of 05 Gauss to 0.15 Gauss is suitable.

Further, the side surface of the vehicle 10 and the magnetic sensor 12
As for the distance in the Y-axis direction, as shown in FIG. 7 with respect to the amount of change in the magnetic field, when it exceeds 2 m, it becomes difficult to obtain the amount of change in the magnetic field of 0.05 Gauss, and it becomes impossible to obtain a sufficient S / N.

Therefore, it is necessary to keep the distance between the magnetic sensor and the vehicle in the Y-axis direction to 2 m or less when the safety distance is 30 cm or more when moving at low speed.

When the vehicle and the magnetic sensors are used at a distance, as shown in FIG. 8, a plurality of magnetic sensors 12 are arranged along the longitudinal direction of the vehicle 10, and one or more magnetic sensors 12 are shown. If the vehicle is detected depending on whether the output of 6 (d) exceeds a predetermined threshold value, the reliability is further improved, and a margin can be obtained for the threshold value.

The “ground” in the above description of the embodiments is not limited to the ground, the road surface, and the ground of an outdoor parking lot, but the surface on which a vehicle runs or parks, such as the floor of a building in a multi-storey parking lot. Of course, including all, "underground" means those planes.

[0051]

As is apparent from the above description, according to the present invention, in a vehicle detection method for magnetically detecting a vehicle by detecting a magnetic field generated from the vehicle by a magnetic sensor, The intensity change of the external magnetic field in the direction perpendicular to the ground or in the width direction of the vehicle in two or three directions is measured, and the above-mentioned 2
Since the vehicle is detected depending on whether the sum of the absolute values of the changes in the intensity of the external magnetic field in the three or three directions exceeds a predetermined threshold value, the magnetic field due to the local variation in the magnetization of the body parts of the vehicle is detected. Erroneous detection due to dead point in detection can be avoided, highly accurate and reliable vehicle detection can be performed, for example vehicle detection for acquisition of vacant address information and parking time management in a large parking lot, It has an excellent effect that it can be suitably applied to vehicle detection for traffic volume measurement or vehicle detection on a railroad crossing for preventing a railroad crossing accident.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an arrangement of magnetic sensors and a magnetic field detection direction with respect to a vehicle in a first embodiment of a vehicle detection method according to the present invention.

FIG. 2 is an arrangement view of magnetic sensors and magnetic field detection directions in the embodiment, actual measurement data of intensity change of external magnetic field in the X-axis, Y-axis, and Z-axis directions, and intensity change of external magnetic field in X-axis and Z-axis directions. It is explanatory drawing and the graph which show the data of the sum of absolute values.

3A and 3B are an explanatory view and a graph showing a state of a magnetic field generated by a bar magnet and a magnetic field distribution in a longitudinal direction and a width direction of the bar magnet.

FIG. 4 is an explanatory diagram showing an arrangement when a plurality of magnetic sensors are used in the same embodiment.

FIG. 5 is an explanatory diagram showing the arrangement of magnetic sensors and the magnetic field detection direction with respect to the vehicle in the second embodiment.

FIG. 6 is an arrangement of magnetic sensors and a magnetic field detection direction in the embodiment, actual measurement data of intensity change of the external magnetic field in the X-axis, Y-axis, and Z-axis directions, and intensity change of the external magnetic field in the X-axis and Y-axis directions. It is explanatory drawing and the graph which show the data of the sum of absolute values.

FIG. 7 is a graph showing the relationship between the distance between the vehicle side surface and the magnetic sensor in the Y-axis direction and the magnetic field change amount in the same embodiment.

FIG. 8 is an explanatory diagram showing an arrangement when a plurality of magnetic sensors are used in the same embodiment.

[Explanation of symbols]

 10 Vehicle (automobile) 12 Magnetic sensor 14 Ground 16 Bar magnet

Claims (10)

[Claims] 1. A vehicle detection method for magnetically detecting a vehicle by detecting a magnetic field generated from the vehicle by a magnetic sensor, wherein magnetic field detection sensitivity is provided in a longitudinal direction of the vehicle on the ground or the ground within a passage width of the vehicle. A magnetic sensor including a magnetic detection element of the vehicle and a magnetic detection element having a magnetic field detection sensitivity in a direction perpendicular to the ground is arranged, and the magnetic sensor externally in two directions of a longitudinal direction of the vehicle and a direction perpendicular to the ground. It is characterized in that the change in the magnetic field strength is measured, and the vehicle is detected based on whether or not the sum of the absolute values of the change in the strength of the external magnetic field in the two directions exceeds a predetermined threshold value based on the absence of the vehicle. Vehicle detection method. 2. A vehicle detection method for magnetically detecting a vehicle by detecting a magnetic field generated from the vehicle by a magnetic sensor, wherein magnetic field detection sensitivity is provided in a longitudinal direction of the vehicle on the ground or the ground within a passage width of the vehicle. A magnetic sensor including a magnetic detection element having the magnetic detection element, a magnetic detection element having a magnetic field detection sensitivity in a direction perpendicular to the ground, and a magnetic detection element having a magnetic field detection sensitivity in the width direction of the vehicle is arranged, and the magnetic sensor is used to detect the vehicle. Of the absolute value of the intensity change of the external magnetic field in the three directions with reference to the absence of the vehicle, by measuring the intensity change of the external magnetic field in the three directions of the longitudinal direction, the direction perpendicular to the ground, and the width direction of the vehicle. A vehicle detection method characterized by detecting a vehicle depending on whether or not the sum exceeds a predetermined threshold value. 3. A plurality of the magnetic sensors are arranged along the longitudinal direction of the vehicle, and whether or not the sum of absolute values of changes in the external magnetic field strength measured by at least one magnetic sensor exceeds the threshold value. The vehicle detection method according to claim 1 or 2, wherein the vehicle is detected by the following method. 4. The threshold is 0.05 gauss to 0.2.
It is in the range of Gauss, It is characterized by the above-mentioned.
The vehicle detection method according to any one of items 1 to 7. 5. A vehicle detection method for magnetically detecting a vehicle by detecting a magnetic field generated from the vehicle by a magnetic sensor, wherein a magnetic detection element having magnetic field detection sensitivity in a longitudinal direction of the vehicle outside a passage width of the vehicle. And a magnetic sensor including a magnetic detection element having a magnetic field detection sensitivity in the width direction of the vehicle, the intensity change of the external magnetic field in the longitudinal direction and the width direction of the vehicle is measured by the magnetic sensor, A vehicle detection method, wherein a vehicle is detected based on whether or not the sum of absolute values of changes in the intensity of the external magnetic field in the two directions exceeds a predetermined threshold with reference to the absence of a vehicle. 6. A plurality of the magnetic sensors are arranged along the longitudinal direction of the vehicle, and whether or not the sum of absolute values of changes in the external magnetic field strength measured by at least one magnetic sensor exceeds the threshold value. The vehicle detection method according to claim 5, wherein the vehicle is detected by the following method. 7. The threshold value is 0.05 gauss to 0.1.
The vehicle detection method according to claim 5 or 6, wherein the vehicle detection range is within 5 gauss. 8. The distance between the side surface along the longitudinal direction of the vehicle and the magnetic sensor in the vehicle width direction is 30 cm or more and 2 m.
The vehicle detection method according to any one of claims 5 to 7, wherein the vehicle detection method is set within the following range. 9. The vehicle detection method according to claim 1, wherein a magnetic impedance element is used as a magnetic detection element of the magnetic sensor. 10. The vehicle detection method according to claim 1, wherein a fluxgate type magnetic detection element using a ring core is used as the magnetic detection element of the magnetic sensor.