JP7698192B2 - Magnetic marker detection method and detection system - Google Patents

Description

The present invention relates to a method and system for detecting magnetic markers installed on a vehicle path.

Magnetic marker detection systems for vehicles that use magnetic markers placed on roads for vehicle control have been known for some time (see, for example, Patent Document 1). If such a magnetic marker detection system could be used to detect magnetic markers placed along lanes, for example, it would be possible to realize various driving assistance functions, such as automatic steering control, lane departure warning, and automatic driving.

JP 2005-202478 A

However, the above-mentioned conventional magnetic marker detection system has the following problem. That is, there is a problem that the reliability of detection of the magnetic marker may be compromised due to various disturbance magnetic fields acting on the magnetic sensor, etc. For example, vehicles running alongside each other or vehicles passing each other can also be sources of disturbance magnetic fields.

The present invention was made in consideration of the above-mentioned problems in the conventional technology, and aims to provide a method and system for detecting magnetic markers with high detection reliability.

One aspect of the present invention is a method for detecting a magnetic marker disposed on a road while a vehicle equipped with a magnetic sensor is moving on the road, the method comprising the steps of:
The magnetic sensor is a sensor capable of acquiring a measurement value capable of identifying at least a direction of magnetic action,
a first process for processing measurements by the magnetic sensor to detect a magnetic source that may be the magnetic marker;
a second process for determining an intersection point with a road surface in a direction of action specified by a measurement value acquired by the magnetic sensor when a vehicle passes through a predetermined section including the magnetic source detected by the first process;
The magnetic marker detection method includes a third process of determining whether or not the magnetic source detected by the first process is a magnetic marker depending on the distribution of the intersections obtained by the second process.

One aspect of the present invention is a system for detecting a magnetic marker disposed on a road while a vehicle equipped with a magnetic sensor is moving on the road, the system comprising:
The magnetic sensor is a sensor capable of acquiring a measurement value capable of identifying at least a direction of magnetic action,
a first circuit for processing measurements by the magnetic sensor to detect magnetic sources that may be the magnetic marker;
a second circuit that determines an intersection point between the action direction, which is specified by the measurement value acquired by the magnetic sensor when the vehicle passes through a predetermined section to which the magnetic source detected by the first circuit belongs, and a road surface that forms the surface of the road;
The magnetic marker detection system includes a third circuit that determines whether the magnetic source detected by the first processing is a magnetic marker based on the degree of dispersion of the intersections determined by the second circuit.

The present invention is an invention for detecting magnetic markers placed on the road surface with high reliability while a vehicle equipped with a magnetic sensor is traveling. In this invention, a magnetic source that may be a magnetic marker is first detected based on the measurement value by the magnetic sensor. Then, the intersection point with the road surface is obtained for the direction of magnetic action originating from this magnetic source. In this invention, depending on the degree of dispersion of these intersection points, it is determined whether the magnetic source detected as described above is a magnetic marker or not.

According to the present invention, by focusing on the degree of dispersion of the intersection points between the direction of magnetic field acting on the magnetic sensor from the magnetic source and the road surface, it is possible to reduce the risk of erroneous detection of magnetic sources other than magnetic markers, and to detect magnetic markers with high reliability.

FIG. 4 is a front view showing a state in which a vehicle detects a magnetic marker. FIG. 2 is a top view showing a vehicle traveling on a lane on which magnetic markers are provided. FIG. FIG. 1 is a diagram showing the configuration of a marker detection system. FIG. 4 is a flowchart showing a process for detecting a magnetic source. 13 is a graph showing the change over time in the magnetic total value, which is the sum of the magnetic measurement values in the direction of travel by each magnetic sensor when the sensor array passes directly above the magnetic marker. FIG. 4 is a flowchart showing a process for measuring the amount of lateral deviation of a vehicle relative to a magnetic marker. 13 is a graph illustrating the distribution of magnetic measurement values in the vertical direction by each magnetic sensor when the sensor array is positioned directly above a magnetic marker. 13 is a graph illustrating the distribution of the transverse magnetic gradient in the vehicle width direction when the sensor array is located directly above the magnetic marker. 5 is a flowchart showing a process for determining an intersection point between a magnetic vector representing the direction of magnetic action on a magnetic sensor and a road surface. FIG. 2 is an explanatory diagram of the intersection of a magnetic vector, which represents the direction of magnetic action, with the road surface. FIG. 11 is a flow diagram showing the process of determining whether a magnetic source is a magnetic marker. 1 is an explanatory diagram showing how the intersections of a magnetic vector, which represents the direction of magnetic action of a magnetic marker on a magnetic sensor, and the road surface are dispersed in the direction of travel. An explanatory diagram showing how a magnetic vector, which represents the direction of magnetic action exerted on a magnetic sensor by a magnetic source larger than a magnetic marker, intersects with the road surface in the direction of travel.

The embodiment of the present invention will be specifically described using the following examples.
Example 1
This example relates to a detection method and detection system 1 for detecting a magnetic marker 10 placed on a road. The contents of this example will be described with reference to FIGS.

This example is an example of a detection system 1 for a magnetic marker 10 that can be combined with a driving assistance system 5S that enables lane-keeping driving, as shown in Figures 1 and 2. The driving assistance system 5S includes a vehicle ECU 50 that controls a steering actuator (not shown) for steering the steering wheels, a throttle actuator for adjusting engine output, and the like. The vehicle ECU 50 controls the vehicle 5, for example, to bring the amount of lateral deviation from the magnetic marker 10 closer to zero, thereby realizing lane-keeping driving.

The detection system 1 in this example is a system that detects a magnetic marker 10 using a sensor array 11 in which magnetic sensors Cn are arranged in a straight line. This detection system 1 is equipped with a detection unit 12 that detects the magnetic marker 10 by processing the magnetic measurement values of each magnetic sensor Cn. Below, we will provide an overview of the magnetic marker 10, and then explain the sensor array 11 and detection unit 12 that make up the detection system 1.

(Magnetic marker)
The magnetic marker 10 (FIGS. 1 to 3) is a road marker that is placed, for example, every 2 m along the center of the lane 100 that forms the path of the vehicle 5. The magnetic marker 10 is columnar, with a diameter of 20 mm and a height of 28 mm, and can be placed in a hole provided in the road surface 100S. The magnetic marker 10 is a ferrite plastic magnet in which magnetic powder of iron oxide, a magnetic material, is dispersed in a polymeric material that is a base material. It is also possible to provide, for example, a resin molded layer on all or part of the surface of the magnetic marker 10, which is the ferrite plastic magnet itself.

The maximum energy product (BHmax) of the ferrite plastic magnet that constitutes the magnetic marker 10 is 6.4 kJ/cubic meter. The magnetic flux density at the end face of the magnetic marker 10 is 45 mT (millitesla). Here, various types of vehicles, such as passenger cars and trucks, can be considered as vehicles 5 that use the magnetic marker 10. The mounting height of the magnetic sensor Cn (sensor array 11) depends on the ground clearance of each vehicle type, and is expected to be in the range of 90 to 250 mm. The magnetic marker 10 can apply a magnetic field with a magnetic flux density of 8 μT at a height of 250 mm, which is the upper limit of the range of expected mounting heights for the magnetic sensor Cn.

(Sensor Array)
1, 2 and 4, the sensor array 11 is a rod-shaped unit in which 15 magnetic sensors C1 to C15 are arranged in a straight line. The 15 magnetic sensors C1 to C15 are spaced at equal intervals of 10 cm. The sensor array 11 is attached, for example, to the inside of the front bumper of the vehicle 5, in an orientation along the vehicle width direction. The sensor array 11 includes a combination of 15 magnetic sensors Cn (n is an integer from 1 to 15) and a signal processing circuit 110 incorporating a CPU and the like (not shown) (FIG. 4).

The magnetic sensor Cn is a sensor that detects magnetism by utilizing the well-known MI effect (Magneto Impedance Effect), in which the impedance of a magnetically sensitive body such as an amorphous wire changes sensitively in response to an external magnetic field. The magnetic sensor Cn detects magnetic components acting along a magnetically sensitive body such as a linear amorphous wire, and outputs a sensor signal that represents the magnitude of the magnetic component. Two linear magnetically sensitive bodies are incorporated in the magnetic sensor Cn so that they are perpendicular to each other. The magnetic sensor Cn can detect magnetic components in two directions along each magnetically sensitive body.

The magnetic sensor Cn is a highly sensitive sensor with a magnetic flux density measurement range of ±0.6 millitesla and a magnetic flux resolution of 0.02 microtesla within the measurement range. As described above, the magnetic marker 10 can exert a magnetic flux density of 8 μT or more in the range of 90 to 250 mm, which is the assumed mounting height of the magnetic sensor Cn. A magnetic marker 10 that exerts a magnetic flux density of 8 μT or more can be detected with high reliability using the magnetic sensor Cn, which has a magnetic flux resolution of 0.02 μT.

In the sensor array 11 of this example, each magnetic sensor Cn is assembled so that the axial directions of the two linear magnetic sensors (amorphous wires) are aligned. The sensor array 11 is attached to the vehicle 5 so that each magnetic sensor Cn can detect magnetic components acting in the direction of travel and in the vertical direction.

The signal processing circuit 110 (Figure 4) is a circuit that performs signal processing such as noise removal and amplification on the sensor signal of each magnetic sensor Cn. The signal processing circuit 110 captures the sensor signal of each magnetic sensor Cn every time the vehicle 5 moves a predetermined distance (e.g., 5 cm), converts it into a magnetic measurement value, and outputs it to the outside as an output signal of the sensor array 11. The output signal of the sensor array 11 is a 15-channel signal for each magnetic sensor Cn that represents the magnetic measurement value (magnetic measurement value in the traveling direction and magnetic measurement value in the vertical direction).

(Detection unit)
The detection unit 12 (FIG. 4) is a circuit that executes calculation processing to detect the magnetic marker 10. The detection unit 12 has a circuit board (not shown) on which a CPU (central processing unit) that executes various calculations, memory elements such as a ROM (read only memory) and a RAM (random access memory), and the like are mounted.

The RAM memory area is provided with a work area for storing the time series of magnetic measurement values for each magnetic sensor Cn. The detection unit 12 uses this work area to store the time series of magnetic measurement values over a period of time during which the vehicle 5 moved a predetermined distance in the past (e.g., 10 m). The time series of magnetic measurement values is a combination of magnetic measurement values in the traveling direction and magnetic measurement values in the vertical direction.

The detection unit 12 is connected to a signal line of a vehicle speed sensor (not shown) equipped on the vehicle 5. The vehicle speed sensor is a sensor that outputs a pulse signal every time the wheel rotates a predetermined amount. The predetermined amount can be, for example, a predetermined angle such as 1 degree, 10 degrees, or 30 degrees, or a predetermined distance such as 1 cm, 5 cm, or 10 cm. The detection unit 12 in this example controls the sensor array 11 so that magnetic measurement values can be obtained every time the vehicle 5 moves 5 cm. It is also possible to control the sensor array 11 so that magnetic measurement values can be obtained at a frequency of, for example, 3 kHz.

The detection unit 12 reads out the magnetic measurement values for each magnetic sensor Cn stored in the work area of the RAM, and executes processing to detect the magnetic marker 10. The detection unit 12 executes processing every time the vehicle 5 advances (moves) 5 cm, and inputs the detection result of the magnetic marker 10 to the vehicle ECU 50. The detection result of the magnetic marker 10 includes information on whether or not the magnetic marker 10 has been detected, and, if the magnetic marker 10 has been detected, includes the amount of lateral deviation relative to the magnetic marker 10.

The detection unit 12 has the functions of the following circuits (means).
(a) Magnetic source detection circuit 121: A circuit that processes magnetic measurement values obtained by a magnetic sensor to detect a magnetic source that may be a magnetic marker 10 (first circuit, first processing).
(b) Lateral deviation amount measuring circuit 123: A circuit for measuring the lateral deviation amount, which is the lateral deviation of the vehicle 5 with respect to the magnetic source.
(c) Intersection identification circuit 125: A circuit (second circuit, second processing) that determines the intersection between the magnetic vector identified by the magnetic measurement value obtained by the magnetic sensor and the road surface 100S when the vehicle passes through a specified section to which the magnetic source belongs.
(d) Judgment circuit 127: A circuit (third circuit, third processing) that judges whether or not the detected magnetic source is a magnetic marker 10 based on the degree of dispersion of the intersections determined by the intersection identification circuit 125. The judgment circuit 127 applies threshold processing to the variance, which is an index value representing the degree of dispersion of the intersections, to judge whether or not it is a magnetic marker 10.

The flow of the process executed by the detection system 1 configured as above will be described with reference to the flow diagrams of FIG. 5, FIG. 7, FIG. 10, and FIG. 12. FIG. 5 is a flow diagram of the process in which the detection unit 12 as the magnetic source detection circuit 121 detects a magnetic source. FIG. 6 is a reference diagram in the description of FIG. 5. FIG. 7 is a flow diagram of the process in which the detection unit 12 as the lateral deviation amount measurement circuit 123 measures the lateral deviation amount of the vehicle 5 relative to the magnetic source. FIG. 8 and FIG. 9 are reference diagrams in the description of FIG. 7. FIG. 10 is a flow diagram of the process in which the detection unit 12 as the intersection identification circuit 125 determines the intersection between the magnetic vector acting on the magnetic sensor and the road surface 100S. FIG. 11 is a reference diagram in the description of FIG. 10. FIG. 12 is a flow diagram of the process in which the detection unit 12 as the determination circuit 127 determines whether the detected magnetic source is a magnetic marker 10 or not. FIG. 13 and FIG. 14 are reference diagrams in the description of FIG. 12. Below, we will explain the details of each process performed by the detection system 1, focusing mainly on the operation of the detection unit 12.

The detection unit 12, which serves as the magnetic source detection circuit 121, captures the magnetic measurement values of each magnetic sensor Cn of the sensor array 11 every time the vehicle 5 moves 5 cm (step S101 in FIG. 5). The detection unit 12 detects that the vehicle 5 has moved 5 cm in response to the capture of a pulse signal by the vehicle speed sensor, and inputs a data request signal to the sensor array 11. As described above, the data that the detection unit 12 acquires from the sensor array 11 are the magnetic measurement values in the traveling direction and the magnetic measurement values in the vertical direction by each magnetic sensor Cn.

The detection unit 12 writes the magnetic measurement values (travel direction and vertical direction) of each magnetic sensor Cn obtained from the sensor array 11 to a work area (storage area of RAM) as needed. At this time, the latest magnetic measurement value is newly stored, while the oldest magnetic measurement value is erased. As a result, for each magnetic sensor Cn, the time series magnetic measurement values (travel direction and vertical direction) over a predetermined period of time in the past (a movement period corresponding to a movement distance of 10 m in this example) are stored and held in the work area (S102).

The detection unit 12 calculates a magnetic total value, which is the sum of the magnetic measurement values at each point in time for the time series of magnetic measurement values in the traveling direction by each magnetic sensor Cn when the vehicle 5 passes through the magnetic marker 10 (S103). When the vehicle 5 passes through the magnetic marker 10, this magnetic total value changes over time as shown in FIG. 6. The horizontal axis of FIG. 6 indicates the time direction corresponding to the traveling direction, and the vertical axis indicates the magnitude of the magnetic total value.

The magnetic total value, which is the sum of the magnetic measurement values in the direction of travel at each time point, gradually increases as the magnetic marker 10 is approached, i.e., as time progresses, as shown in FIG. 6, and reaches a positive peak just before the magnetic marker 10. As the magnetic sensor Cn approaches the magnetic marker 10, the magnetic total value gradually decreases, and when the magnetic sensor Cn is located directly above the magnetic marker 10, the magnetic action direction is reversed. As the magnetic sensor Cn moves away from the magnetic marker 10, i.e., as time progresses after passing the magnetic marker 10, the magnetic total value gradually increases to the negative side, reaching a negative peak. As the magnetic sensor Cn moves away from the magnetic marker 10, the absolute value of the magnetic total value gradually decreases and approaches zero. In other words, the magnetic total value, which is the sum of the magnetic measurement values in the direction of travel at each time point, exhibits a curve with two positive and negative peaks adjacent to each other across the magnetic marker 10, as shown in FIG. 6. This curve includes a zero cross Zc that crosses zero with a steep slope at a position directly above the magnetic marker 10.

The detection unit 12 determines whether or not a zero cross Zc has been detected for the time change of the magnetic sum value in FIG. 6, for example (S104). When the zero cross Zc has been detected (S104: YES), the detection unit 12 determines that a magnetic source has been detected (S105).

When a magnetic source is detected (step S105 in FIG. 5), the detection unit 12, which serves as the lateral deviation measurement circuit 123, executes the process shown in FIG. 7 to measure the lateral deviation of the vehicle 5 relative to the magnetic source. The detection unit 12 first reads out from the work area of the RAM the magnetic measurement values in the vertical direction of each magnetic sensor Cn when the sensor array 11 is located directly above the magnetic source (the position corresponding to the zero cross Zc in FIG. 6) (S201).

When the sensor array 11 is located directly above the magnetic source, the distribution of the magnetic measurement values in the vertical direction of each magnetic sensor Cn is, for example, as shown in Figure 8. The horizontal axis of Figure 8 indicates the vehicle width direction, and the vertical axis indicates the magnitude of the magnetic measurement value. The scale of 1 to 15 on the horizontal axis indicates the positions of the magnetic sensors C1 to C15. Note that this figure is an example in which the magnetic source is a magnetic marker 10.

When the magnetic source is a magnetic marker 10, the magnetic measurement values of each magnetic sensor Cn are distributed along a curve close to a normal distribution shown by the dashed line in Figure 8. The peak of the dashed curve appears corresponding to the position of the magnetic marker 10. The example in the figure is an example of a case where the magnetic marker 10, which is the magnetic source, is located approximately halfway between magnetic sensors C9 and C10. Note that Figure 9, which corresponds to Figure 8 and will be described later, is also an example of a case where the magnetic source is a magnetic marker 10.

The detection unit 12 obtains the difference (magnetic difference value) between the magnetic measurement values of adjacent magnetic sensors for the distribution of magnetic measurement values in Figure 8, thereby generating a distribution of the magnetic gradient in the vehicle width direction, for example, as shown in Figure 9 (S202). The horizontal axis of Figure 9 indicates the position in the vehicle width direction, and the vertical axis indicates the strength of the magnetic gradient in the vehicle width direction, i.e., the magnitude of the magnetic difference value.

The distribution of the magnetic gradient (magnetic difference value) in the vehicle width direction is, for example, a distribution along a curve with adjacent positive and negative peaks, as shown by the dashed line in Figure 9. In this curve, depending on which side of the magnetic sensor in relation to the magnetic source, the positive magnetic difference value indicates a gradient where the magnitude (strength) of the magnetic field increases, and the negative magnetic difference value indicates a gradient where the magnitude of the magnetic field decreases. In this curve, a zero cross Zc, where the positive and negative magnetic difference values are reversed, occurs corresponding to the position of the magnetic source.

The detection unit 12 obtains an approximation curve (e.g., the dashed curve in FIG. 9) of the distribution of the magnetic gradient (magnetic difference value) in the vehicle width direction, and identifies the zero cross Zc. The position of the magnetic source in the vehicle width direction can be identified as the position corresponding to the zero cross Zc of the approximation curve. Note that if the magnetic source is not the magnetic marker 10, there may be cases where the zero cross Zc cannot be identified. In such cases, it may be possible to determine that the magnetic source is not the magnetic marker 10 because the zero cross Zc cannot be identified.

The detection unit 12 measures the deviation of the center position of the sensor array 11 (the position of magnetic sensor C8 in this example) in the vehicle width direction from the magnetic source as the lateral deviation of the vehicle 5 (S203). For example, in the case of FIG. 9, the zero cross Zc of the approximation curve is located at about C9.5, halfway between C9 and C10. Since the distance between magnetic sensors C9 and C10 is 10 cm, the lateral deviation of the vehicle 5 from the magnetic source is (9.5-8) x 10 cm = 15 cm, with C8, which is located in the center of the sensor array 11 in the vehicle width direction, as the reference point.

Furthermore, the detection unit 12 selects the magnetic sensor that passes close to the magnetic source (S204). In the example of FIG. 9 where the zero cross Zc is located around C9.5, the closest magnetic sensor is magnetic sensor C9 or C10. The detection unit 12 selects the magnetic sensor that is closer to the magnetic source, between magnetic sensors C9 and C10. If the distances to the magnetic source are about the same, either magnetic sensor C9 or C10 may be selected. Alternatively, both magnetic sensors C9 and C10 may be selected and the average of the magnetic measurement values may be calculated.

Then, the detection unit 12 as the intersection identification circuit 125 sets a range of 1 m before and after the position of the magnetic source in the traveling direction (the position corresponding to the zero cross Zc in FIG. 6) as a predetermined section (step 301 in FIG. 10). Then, the detection unit 12 refers to the work area of the RAM and sequentially reads out the magnetic measurement values (magnetic measurement values in the traveling direction, magnetic measurement values in the vertical direction) acquired in the predetermined section by the magnetic sensor selected in step S204 in FIG. 7 (S302). Here, the order in which the time-series magnetic measurement values are read out may be from the oldest measurement time point, i.e., the measurement position located upstream in the traveling direction, or may be from the newest measurement time point, i.e., the measurement position located downstream in the traveling direction.

The detection unit 12 identifies the magnetic vector, which is the composite vector of the magnetic measurement value GL in the traveling direction and the magnetic measurement value GV in the vertical direction for each measurement position belonging to a specified section, as shown in FIG. 11 (S303). In FIG. 11, the width direction of the paper corresponds to the traveling direction. The line indicated by R in the figure indicates the line through which the target magnetic sensor passes, and the distance between the line R and the road surface 100S corresponds to the mounting height of the sensor array 11. The starting point of each magnetic vector is at the measurement position, which is the position of the magnetic sensor when the corresponding magnetic measurement value was obtained. Note that in FIG. 11, these measurement positions are indicated by circles on the line R. The direction of each magnetic vector indicates the direction of magnetic action at the corresponding measurement position. Also, the length of each magnetic vector indicates the magnitude (strength) of the magnetic field acting on the corresponding measurement position.

The detection unit 12 determines the intersections between the magnetic vector, which starts at each measurement position (positions indicated by circles in FIG. 11) belonging to a specific section, and the road surface 100S (S304), and stores the positions of the intersections sequentially (S305). In the example shown in FIG. 11, the intersections between the magnetic vector and the road surface 100S are indicated by crosses. The positions of the crosses are determined by the position in the direction of travel.

The detection unit 12 repeats the above steps S302 to S305 until all magnetic measurement values in which the measurement position belongs to the specified section have been read (S306: NO). The detection unit 12 ends the process when all magnetic measurement values in which the measurement position belongs to the specified section have been read (S306: YES).

Then, the detection unit 12 as the judgment circuit 122 evaluates the degree of scattering for the intersections stored in step S305 of FIG. 10, and judges whether the magnetic source is the magnetic marker 10 or not (FIG. 12). The detection unit 12 first obtains the average position of the intersections (S401). Note that the position of each intersection is a one-dimensional position on the road surface directly below the movement path of the magnetic sensor that outputs the magnetic measurement value. The average position of the intersections is also a one-dimensional position on this road surface.

The detection unit 12 calculates the variance, which is an index value representing the degree of scattering of the intersections (S402). The variance (S2), which is a statistical value, can be calculated by the following formula: Here, the position of each intersection is xi, and the average position of the intersections is xav.
(Equation 1)

The detection unit 12 performs threshold processing on the variance found in step S402 (S403, threshold judgment), and if the variance (S2) is less than the threshold (or within the threshold) (S403: YES), it determines that the magnetic source detected in step S105 in FIG. 5 is the magnetic marker 10 (S404). On the other hand, if the variance (S2) is equal to or greater than the threshold (or above the threshold) (S403: NO), it determines that this magnetic source is a source of disturbance magnetic field and not a magnetic marker 10 (S414).

It is also possible to apply threshold processing to the standard deviation (S), which is the square root of the variance (S2). The standard deviation (S) is a statistical value that indicates the degree of dispersion, with 68.3% of the intersections falling within a range of ±S centered on the average position. The smaller the value of the variance (S2) or standard deviation (S), the lower the degree of dispersion, and the larger these values, the higher the degree of dispersion.

Here, we will explain the scattering of intersections originating from the magnetic marker 10 by comparing it with the scattering of intersections originating from a magnetic disturbance source. The magnetic marker 10 is a magnetic source with a diameter of 20 mm, which is very small in size in the direction of travel. On the other hand, if the magnetic source is, for example, the steel frame of a bridge or a vehicle running parallel to it, there is a high possibility that the size in the direction of travel will be large.

Figures 13 and 14 are diagrams illustrating how the intersections found by the process of Figure 10 are scattered in the direction of travel. The horizontal axis of the figures represents the direction of travel. The bar graphs represent the frequency of intersections located at corresponding positions. Figure 13 is an example of a case where the magnetic source is a magnetic marker 10, and Figure 14 is an example of a case where a bridge, a vehicle traveling parallel to the vehicle, etc. are detected as the magnetic source.

As is clear from a comparison between Figures 13 and 14, when the magnetic marker 10 is the magnetic source, the frequency distribution at the time of measurement is close to a normal distribution centered on the average position, and the value of the standard deviation (S), which is the square root of the variance (S2), is small. On the other hand, when the magnetic source is an external disturbance, the frequency distribution at the time of measurement is far from a normal distribution and spreads out on both sides, and the value of the standard deviation (S), which is the square root of the variance (S2), is large. By using the threshold judgment in step S303 in Figure 12, it is possible to eliminate the frequency distribution in Figure 14, which has a large variance (S2) and standard deviation (S), and the magnetic marker 10 can be determined with high certainty.

As described above, the detection system 1 of this example focuses on the degree of dispersion of intersections between the road surface 100S and the magnetic vector representing the direction of magnetic action around the magnetic source, thereby reducing the risk of erroneous detection of a magnetic source other than the magnetic marker 10, and enabling detection of the magnetic marker 10 with high reliability.

In this example, the variance, which is an index value that indicates the degree of dispersion of intersections in the direction of travel, is used as the subject of threshold judgment. Alternatively, or in addition, the variance of intersections in the vehicle width direction may be used as the subject of threshold judgment. If the magnetic sensor is capable of measuring magnetism acting in the vehicle width direction in addition to the vertical direction, for example, the variance in the vehicle width direction can be obtained for intersections related to magnetic vectors acting on each magnetic sensor when the sensor array 11 is located directly above the magnetic marker 10.

It is also possible to use a magnetic sensor that can detect the direction of magnetic action in three-dimensional space. In this case, it is possible to determine whether or not the intersection of the magnetic vector acting on the magnetic sensor and the road surface 100S is a magnetic marker 10 depending on the degree to which it is scattered two-dimensionally on the road surface.

If the angle of the magnetic vector (direction of action) with respect to the road surface 100S is small, there is a possibility that the error when determining the intersection will be excessive. Therefore, it is also good to exclude magnetic vectors (directions of action) whose angle with the road surface 100S is less than or equal to a predetermined angle from the targets for determining the variance of the intersection. Note that the angle of the movement vector (direction of action) with respect to the road surface is, for example, the angle indicated by θ in FIG. 11. Furthermore, if the magnitude of the magnetism acting on the magnetic sensor is small, there is a possibility that the error when determining the intersection will be excessive. Therefore, it is good to exclude magnetic vectors whose magnitude of the magnetism is less than or equal to a predetermined value from the targets for determining the variance.

It is also possible to evaluate the shape of the trajectory of the end point of the magnetic vector (the tip of the arrow representing the magnetic vector in FIG. 11) acting on the magnetic sensor passing directly above the magnetic source, and to determine whether or not it is a magnetic marker 10. If the magnetic source is the magnetic marker 10, the magnetic vector rotates like the hands of a clock around the magnetic marker 10. In addition, since the length of the magnetic vector, i.e., the magnitude of the magnetism, increases the closer it is to the magnetic marker 10, the trajectory of the end point of the magnetic vector becomes an ellipse (upper part) centered on the magnetic marker 10 or a shape close to a normal distribution shape. Therefore, it is also possible to approximate the trajectory of the end point of the magnetic vector by an ellipse or a normal distribution shape, and to obtain the error between the approximate shape and the actual trajectory. It is also possible to treat this error as an index value and perform threshold processing to determine whether or not it is a magnetic marker 10. Furthermore, it is also possible to index the rotation of the magnetic vector around the magnetic marker 10 to determine whether or not it is a magnetic marker 10.

Furthermore, it is also good to evaluate the shape of the trajectory of the end point of the magnetic vector formed by the magnetic measurement values of each magnetic sensor of the sensor array 11, not just the magnetic sensor passing directly above the magnetic marker 10. The end point of the magnetic vector acting on each magnetic sensor will be an ellipsoid (upper part) or a shape close to a two-dimensional normal distribution shape. As above, it is also good to find the error between the approximate shape and the curved surface formed by the actual trajectory, and use threshold processing to determine whether or not it is a magnetic marker 10.

Although specific examples of the present invention have been described in detail as examples above, these specific examples merely disclose examples of the technology encompassed by the scope of the claims. Needless to say, the scope of the claims should not be interpreted in a limited manner based on the configurations or numerical values of the specific examples. The scope of the claims encompasses technology that is a variety of modifications, changes, or appropriate combinations of the specific examples using publicly known technology or the knowledge of those skilled in the art.

REFERENCE SIGNS LIST 1 Detection system 10 Magnetic marker 11 Sensor array 12 Detection unit 121 Magnetic source detection circuit 123 Lateral deviation amount measurement circuit 125 Intersection identification circuit 127 Determination circuit Cn Magnetic sensor 5 Vehicle 5S Driving assistance system 50 Vehicle ECU

Claims (5)

A method for detecting a magnetic marker disposed on a road while a vehicle equipped with a magnetic sensor is moving on the road, comprising the steps of:
The magnetic sensor is a sensor capable of acquiring a measurement value capable of identifying at least a direction of magnetic action,
a first process for processing measurements by the magnetic sensor to detect a magnetic source that may be the magnetic marker;
a second process for determining an intersection point between the direction of magnetic field acting on the magnetic sensor and a road surface when the vehicle passes through a predetermined section including the magnetic source detected by the first process;
A method for detecting a magnetic marker, which executes a third process of determining whether the magnetic source detected by the first process is a magnetic marker depending on the degree of dispersion of the intersections obtained by the second process. A magnetic marker detection method according to claim 1, in which the third process is a process of determining an index value representing the degree to which the intersections are dispersed, and determining the presence or absence of the magnetic marker by threshold processing of the index value. A method for detecting a magnetic marker according to claim 1 or 2, in which the second process excludes action directions whose angles with the road surface are equal to or less than a predetermined angle, and finds intersections with the road surface for action directions whose angles with the road surface are equal to or greater than the predetermined angle. A method for detecting a magnetic marker according to any one of claims 1 to 3, in which the magnetic sensor is capable of acquiring the magnitude of a magnetic component acting along at least two mutually intersecting directions as the measurement value. A system for detecting a magnetic marker disposed on a road while a vehicle equipped with a magnetic sensor is moving on the road, comprising:
The magnetic sensor is a sensor capable of acquiring a measurement value capable of identifying at least a direction of magnetic action,
a first circuit for processing measurements by the magnetic sensor to detect magnetic sources that may be the magnetic marker;
a second circuit that determines an intersection point between the action direction, which is specified by the measurement value acquired by the magnetic sensor when the vehicle passes through a predetermined section to which the magnetic source detected by the first circuit belongs, and a road surface that forms the surface of the road;
A magnetic marker detection system including a third circuit that determines whether the magnetic source detected by the first circuit is a magnetic marker based on the degree of dispersion of the intersections determined by the second circuit.

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