Magnetic Marker Detection Method and Detection System

Abstract

To provide a detection method for a magnetic marker, having high detection reliability.SOLUTION: A detection system 1 for detecting a magnetic marker arranged on a runway while a vehicle including magnetic sensors C1 to C15 travels on the runway, includes a magnetic generation source detection circuit 121 that detects a magnetic generation source that can be the magnetic marker, an intersection identification circuit 125 that determines intersections with a road surface in an applying direction of magnetism when the vehicle passes through a predetermined section to which the magnetic generation source belongs, and a determination circuit 127 that determines whether or not the magnetic generation source is the magnetic marker according to the degree of scattering of the intersections.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method and a detection system for detecting magnetic markers disposed on a road surface of a vehicle.

Background Art

[0002] Conventionally, a magnetic marker detection system for vehicles for using magnetic markers disposed on a road for vehicle control has been known (see, for example, Patent Document 1). By using such a magnetic marker detection system, for example, if magnetic markers disposed along a lane can be detected, various driving supports such as automatic steering control, lane departure warning, and autonomous driving can be realized.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the above-described conventional magnetic marker detection system has the following problems. That is, there is a problem that the detection reliability of magnetic markers may be impaired due to various external magnetic fields acting on a magnetic sensor or the like. For example, vehicles traveling side by side or passing vehicles can also be sources of external magnetic fields.

[0005] The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a method and a detection system for detecting magnetic markers with high detection reliability.

Means for Solving the Problems

[0006] One aspect of the present invention is a method for detecting a magnetic marker disposed on a road surface while a vehicle equipped with a magnetic sensor is moving on the road surface, The magnetic sensor is a sensor that can acquire at least a measurement value capable of specifying the acting direction of magnetism, a first process of processing the measurement value obtained by the magnetic sensor to detect a magnetic source that may be the magnetic marker, a second process of obtaining an intersection with the road surface for the acting direction specified by the measurement value obtained by the magnetic sensor when the vehicle passes through a predetermined section to which the magnetic source detected by the first process belongs, and a third process of determining whether the magnetic source detected by the first process is a magnetic marker according to the degree of dispersion of the intersections obtained by the second process, are included in a method for detecting a magnetic marker.

[0007] One aspect of the present invention is a system for detecting a magnetic marker disposed on a road surface while a vehicle equipped with a magnetic sensor is moving on the road surface, wherein the magnetic sensor is a sensor that can acquire at least a measurement value capable of specifying the acting direction of magnetism, a first circuit that processes the measurement value obtained by the magnetic sensor to detect a magnetic source that may be the magnetic marker, a second circuit that obtains an intersection with the road surface forming the road surface for the acting direction specified by the measurement value obtained 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 third circuit that determines whether the magnetic source detected by the first process is a magnetic marker according to the degree of dispersion of the intersections obtained by the second circuit, are included in a magnetic marker detection system.

Advantages of the Invention

[0008] The present invention is an invention for reliably detecting a magnetic marker disposed on a road surface while a vehicle equipped with a magnetic sensor is traveling. In the present invention, based on the measured values by the magnetic sensor, first, a magnetic source that may be a magnetic marker is detected. Then, for the acting direction of the magnetism derived from this magnetic source, the intersection with the road surface is obtained. In the present invention, depending on the degree of dispersion of these intersections, it is determined whether the magnetic source detected as described above is a magnetic marker or not.

[0009] According to the present invention, by paying attention to the degree of dispersion of the intersections between the acting direction of the magnetism acting on the magnetic sensor from the magnetic source and the road surface, the possibility of misdetecting a magnetic source other than the magnetic marker can be reduced, and the magnetic marker can be detected with high reliability.

Brief Description of the Drawings

[0010]

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Mode for Carrying Out the Invention

[0011] The embodiments of the present invention will be specifically described using the following examples. (Example 1) This example relates to a detection method and a detection system 1 for detecting the magnetic marker 10 disposed on a road. This content will be described with reference to FIGS. 1 to 14.

[0012] This example relates to a detection system 1 of the magnetic marker 10 that can be combined with a driving support system 5S enabling lane-keeping driving as shown in FIGS. 1 and 2. The driving support system 5S includes a vehicle ECU 50 that controls a steering actuator (not shown) for steering the steering wheel, a throttle actuator for adjusting the engine output, and the like. The vehicle ECU 50 controls the vehicle 5 so as to make the lateral displacement amount with respect to the magnetic marker 10 approach zero, thereby realizing lane-keeping driving.

[0013] The detection system 1 in this example is a system that detects the magnetic marker 10 using a sensor array 11 in which magnetic sensors Cn are arranged in a straight line. This detection system 1 includes a detection unit 12 that processes the magnetic measurement values of each magnetic sensor Cn to detect the magnetic marker 10. Hereinafter, after briefly describing the magnetic marker 10, the sensor array 11 and the detection unit 12 that constitute the detection system 1 will be described.

[0014] (Magnetic Marker) The magnetic marker 10 (Figs. 1 to 3) is a road marker arranged, for example, every 2 m along the center of the lane 100 forming the road surface of the vehicle 5. This magnetic marker 10 has a columnar shape with a diameter of 20 mm and a height of 28 mm, and can be accommodated 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, which is a magnetic material, is dispersed in a polymer material as a base material. Note that a resin mold layer may be provided on all or part of the surface of the magnetic marker 10, which is the ferrite plastic magnet itself.

[0015] The maximum energy product (BHmax) of the ferrite plastic magnet forming the magnetic marker 10 is 6.4 kJ / cubic meter. And the magnetic flux density at the end face of the magnetic marker 10 is 45 mT (millitesla). Here, as the vehicle 5 using the magnetic marker 10, various vehicle types such as passenger cars and trucks can be considered. The mounting height of the magnetic sensor Cn (sensor array 11) depends on the ground clearance for each vehicle type, and a range of 90 to 250 mm is assumed. The magnetic marker 10 can act on magnetic fields with a magnetic flux density of 8 μT at a height of 250 mm, which corresponds to the upper limit of the range assumed as the mounting height of the magnetic sensor Cn.

[0016] (Sensor Array) The sensor array 11 is a rod-shaped unit in which 15 magnetic sensors C1 to C15 are arranged in a straight line as shown in FIGS. 1, 2, and 4. The intervals between the 15 magnetic sensors C1 to C15 are equally spaced at 10 cm. The sensor array 11 is attached inside, for example, the front bumper of the vehicle 5 in a posture along the vehicle width direction. The sensor array 11 is configured to include a combination of 15 magnetic sensors Cn (n is an integer from 1 to 15) and a signal processing circuit 110 incorporating a CPU or the like (not shown) (FIG. 4).

[0017] The magnetic sensor Cn is a sensor that detects magnetism by utilizing the known MI effect (Magneto Impedance Effect) that the impedance of a magnetosensitive body such as an amorphous wire changes sensitively according to an external magnetic field. The magnetic sensor Cn detects a magnetic component acting along a magnetosensitive body such as a linear amorphous wire and outputs a sensor signal representing the magnitude of the magnetic component. In the magnetic sensor Cn, two linear magnetosensitive bodies are incorporated so as to be orthogonal to each other. The magnetic sensor Cn can detect two-directional magnetic components along each magnetosensitive body respectively.

[0018] The magnetic sensor Cn is a highly sensitive sensor with a magnetic flux density measurement range of ±0.6 mT and a magnetic flux resolution of 0.02 μT within the measurement range. As described above, the magnetic marker 10 can act on magnetism with a magnetic flux density of 8 μT or more in the range of 90 to 250 mm assumed as the mounting height of the magnetic sensor Cn. Any magnetic marker 10 that acts on magnetism with a magnetic flux density of 8 μT or more can be reliably detected using the magnetic sensor Cn with a magnetic flux resolution of 0.02 μT.

[0019] In the sensor array 11 of this example, each magnetic sensor Cn is incorporated so that the axial directions of the two linear magnetosensitive bodies (amorphous wires) coincide with each other. And the sensor array 11 is attached to the vehicle 5 so that each magnetic sensor Cn can detect magnetic components acting in the traveling direction and the vertical direction.

[0020] The signal processing circuit 110 (Fig. 4) is a circuit that performs signal processing such as noise removal and amplification on the sensor signals of each magnetic sensor Cn. The signal processing circuit 110 takes in the sensor signals of each magnetic sensor Cn every time the vehicle 5 advances by a predetermined amount (e.g., 5 cm), converts them into magnetic measurement values, and externally outputs them as the output signals of the sensor array 11. The output signals of the sensor array 11 are 15-channel signals for each magnetic sensor Cn representing magnetic measurement values (magnetic measurement values in the traveling direction and magnetic measurement values in the vertical direction).

[0021] (Detection unit) The detection unit 12 (Fig. 4) is a circuit that executes arithmetic processing for detecting the magnetic marker 10. The detection unit 12 has a circuit board (not shown) on which a CPU (central processing unit) that executes various operations, memory elements such as a ROM (read only memory) and a RAM (random access memory), etc., are mounted.

[0022] In the storage area of the RAM, a work area for storing the time-series magnetic measurement values for each magnetic sensor Cn is provided. The detection unit 12 uses this work area to store the time-series magnetic measurement values during the movement period of the vehicle 5 over a past predetermined distance (e.g., 10 m). The time-series magnetic measurement values are a combination of the magnetic measurement values in the traveling direction and the magnetic measurement values in the vertical direction.

[0023] A signal line of a vehicle speed sensor (not shown) provided in the vehicle 5 is connected to the detection unit 12. The vehicle speed sensor is a sensor that outputs a pulse signal every time the wheels rotate by a predetermined amount. Examples of the predetermined amount include a predetermined angle such as 1 degree, 10 degrees, 30 degrees, etc., and a predetermined distance such as 1 cm, 5 cm, 10 cm, etc. The detection unit 12 in this example controls the sensor array 11 so that magnetic measurement values can be acquired every time the vehicle 5 advances 5 cm. Note that it is also possible to control the sensor array 11 so that magnetic measurement values can be acquired, for example, at a frequency of 3 kHz.

[0024] The detection unit 12 reads the magnetic measurement values for each magnetic sensor Cn stored in the work area of the above-mentioned RAM, and executes a process for detecting the magnetic marker 10. The detection unit 12 executes the process 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. When the magnetic marker 10 is detected, it also includes the amount of lateral displacement with respect to the magnetic marker 10.

[0025] The detection unit 12 has functions as the following respective circuits (means). (a) Magnetic source detection circuit 121: A circuit (first circuit, first process) that processes the magnetic measurement values by a magnetic sensor to detect a magnetic source that may be the magnetic marker 10. (b) Lateral displacement amount measurement circuit 123: A circuit that measures the amount of lateral displacement, 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 process) that obtains the intersection with the road surface 100S for the magnetic vector specified by the magnetic measurement values acquired by the magnetic sensor when the vehicle passes through a predetermined section to which the magnetic source belongs. (d) Determination circuit 127: A circuit (third circuit, third process) that determines whether or not the detected magnetic source is the magnetic marker 10 according to the degree of dispersion of the intersections obtained by the intersection identification circuit 125. The determination circuit 127 performs threshold processing on the variance, which is an index value representing the degree of dispersion of the intersections, to determine whether or not it is the magnetic marker 10.

[0026] Regarding the processing flow executed by the detection system 1 configured as described above, it will be described with reference to the flowcharts of FIGS. 5, 7, 10, and 12. FIG. 5 is a flowchart 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 flowchart of the process in which the detection unit 12 as the lateral displacement measurement circuit 123 measures the lateral displacement amount of the vehicle 5 with respect to the magnetic source. FIGS. 8 and 9 are reference diagrams in the description of FIG. 7. FIG. 10 is a flowchart of the process in which the detection unit 12 as the intersection identification circuit 125 obtains the intersection of 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 flowchart of the process in which the detection unit 12 as the determination circuit 127 determines whether the detected magnetic source is the magnetic marker 10. FIGS. 13 and 14 are reference diagrams in the description of FIG. 12. Hereinafter, the content of each process by the detection system 1 will be described mainly based on the operation of the detection unit 12.

[0027] The detection unit 12 as the magnetic source detection circuit 121 takes in the magnetic measurement values of each magnetic sensor Cn of the sensor array 11 every time the vehicle 5 advances 5 cm (step S101 in FIG. 5). Note that the detection unit 12 detects that the vehicle 5 has advanced 5 cm in response to the capture of the pulse signal by the vehicle speed sensor, and inputs a data request signal to the sensor array 11. The data acquired by the detection unit 12 from the sensor array 11 as described above are the magnetic measurement values in the traveling direction and the vertical direction by each magnetic sensor Cn.

[0028] The detection unit 12 writes the magnetic measurement values (traveling direction and vertical direction) of each magnetic sensor Cn acquired from the sensor array 11 into the work area (the storage area of the RAM) at any time. At this time, while the latest magnetic measurement value is newly stored, the oldest magnetic measurement value is erased. As a result, for each magnetic sensor Cn, the time-series magnetic measurement values (traveling direction and vertical direction) over a past predetermined period (in this example, the moving period corresponding to a moving distance of 10 m) are stored and held in the work area (S102).

[0029] When the vehicle 5 passes the magnetic marker 10, the detection unit 12 obtains a magnetic total value, which is the sum of the time-series magnetic measurement values in the traveling direction by each magnetic sensor Cn at each time point (S103). When the vehicle 5 passes the magnetic marker 10, this magnetic total value changes over time as illustrated in FIG. 6. The horizontal axis in FIG. 6 indicates the time direction corresponding to the traveling direction, and the vertical axis indicates the magnitude of the magnetic total value.

[0030] The magnetic total value, which is the sum of the magnetic measurement values in the traveling direction at each time point, gradually increases as it approaches the magnetic marker 10, that is, as time progresses, and becomes a positive peak at a position in front of the magnetic marker 10. Further, as it approaches the magnetic marker 10, this magnetic total value gradually decreases, becomes zero when the magnetic sensor Cn is located directly above the magnetic marker 10, and the acting direction of the magnetism is reversed. Then, as the magnetic sensor Cn moves away from the magnetic marker 10, that is, as time progresses after passing the magnetic marker 10, the magnetic total value gradually increases in the negative direction and reaches a negative peak. Further, when moving away from the magnetic marker 10, the absolute value of this magnetic total value gradually decreases and approaches zero. That is, the magnetic total value, which is the sum of the magnetic measurement values in the traveling direction at each time point, exhibits a curve in which two positive and negative peaks are adjacent to each other with the magnetic marker 10 in between as shown in FIG. 6. This curve includes a zero cross Zc that intersects zero with a steep slope at a position directly above the magnetic marker 10.

[0031] The detection unit 12 determines whether or not it has detected the zero cross Zc for the time change of the magnetic total value in FIG. 6, for example (S104). When the zero cross Zc has been detected (S104: YES), the detection unit 12 determines that the magnetic source has been detected (S105).

[0032] When a magnetic source is detected (step S105 in FIG. 5), the detection unit 12 as the lateral displacement measurement circuit 123 executes the process of FIG. 7 for measuring the lateral displacement amount of the vehicle 5 with respect to the magnetic source. First, the detection unit 12 reads out the vertical magnetic measurement values of the respective magnetic sensors Cn when the sensor array 11 is located directly above the magnetic source (the position corresponding to the zero cross Zc in FIG. 6) from the work area of the RAM (S201).

[0033] When the sensor array 11 is located directly above the magnetic source, the distribution of the vertical magnetic measurement values of the respective magnetic sensors Cn becomes the distribution shown in, for example, FIG. 8. The horizontal axis in FIG. 8 indicates the vehicle width direction, and the vertical axis indicates the magnitude of the magnetic measurement value. The graduations 1 to 15 on the horizontal axis indicate the positions of the magnetic sensors C1 to C15. Note that the figure is an illustration when the magnetic source is the magnetic marker 10.

[0034] When the magnetic source is the magnetic marker 10, the magnetic measurement values of the respective magnetic sensors Cn are distributed along a curve close to the normal distribution indicated by the broken line in FIG. 8. The peak of the curve indicated by the broken line appears corresponding to the position of the magnetic marker 10. In the example of the figure, it is an illustration when the magnetic marker 10 as the magnetic source is located around the middle between the magnetic sensor C9 and the magnetic sensor C10. Note that FIG. 9 to be described later corresponding to FIG. 8 is also an illustration when the magnetic source is the magnetic marker 10.

[0035] The detection unit 12 generates, for example, the distribution of the magnetic gradient in the vehicle width direction of FIG. 9 by obtaining the difference between the magnetic measurement values of adjacent magnetic sensors (magnetic difference value) with respect to the distribution of the magnetic measurement values in FIG. 8 (S202). The horizontal axis in FIG. 9 indicates the position in the vehicle width direction, and the vertical axis indicates the intensity of the magnetic gradient in the vehicle width direction, that is, the magnitude of the magnetic difference value.

[0036] The distribution of the magnetic gradient (magnetic difference value) in the vehicle width direction follows a curve where positive and negative peaks adjacent to each other, as indicated by the dashed line in FIG. 9 for example. In this curve, depending on which side of the magnetic sensor it is with respect to the magnetic source, whether it is a positive magnetic difference value representing a gradient where the magnitude (intensity) of the magnetic field increases, or a negative magnetic difference value representing a gradient where the magnitude of the magnetic field decreases, is swapped. And in this curve, a zero crossing Zc where the positive and negative of the magnetic difference value reverse occurs corresponding to the position of the magnetic source.

[0037] The detection unit 12 obtains an approximate curve (for example, 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 crossing Zc. The position of the magnetic source in the vehicle width direction can be identified as the position corresponding to the zero crossing Zc of the approximate curve. Note that when the magnetic source is not the magnetic marker 10, it may occur that the zero crossing Zc cannot be identified. In such a case, it may be good to determine that the magnetic source is not the magnetic marker 10 because the zero crossing Zc cannot be identified.

[0038] The detection unit 12 measures, as the lateral displacement amount of the vehicle 5, the deviation in the vehicle width direction of the magnetic source with respect to the position at the center of the sensor array 11 (in this example, the position of the magnetic sensor C8) (S203). For example, in the case of FIG. 9, the zero crossing Zc of the approximate curve is located around C9.5, which is around the middle between C9 and C10. Since the interval between the magnetic sensors C9 and C10 is 10 cm, the lateral displacement amount of the vehicle 5 with respect to the magnetic source is (9.5 - 8) × 10 cm = 15 cm based on C8 located at the center of the sensor array 11 in the vehicle width direction.

[0039] Furthermore, the detection unit 12 selects a magnetic sensor that passes closest to the magnetic source generation point (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 generation point out of magnetic sensors C9 and C10. If the distances to the magnetic source generation point are about the same, either of magnetic sensors C9 and C10 may be selected. Alternatively, both magnetic sensors C9 and C10 may be selected to obtain the average of the magnetic measurement values.

[0040] Subsequently, the detection unit 12 as the intersection identification circuit 125 sets, as a predetermined section, a range of 1 m before and after centered on the position of the magnetic source generation point in the traveling direction (the position corresponding to the zero cross Zc in FIG. 6) (step 301 in FIG. 10). Then, the detection unit 12 refers to the work area of the above RAM and sequentially reads out the magnetic measurement values (the magnetic measurement value in the traveling direction, the magnetic measurement value in the vertical direction) acquired by the magnetic sensor selected in step S204 in FIG. 7 in the predetermined section (S302). Here, as the order of reading out the time-series magnetic measurement values, the order may be from the one with an older measurement time point, that is, the one located upstream in the traveling direction, or from the one with a newer measurement time point, that is, the one located downstream in the traveling direction.

[0041] The detection unit 12 identifies, as shown in FIG. 11, a magnetic vector, which is a 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 predetermined section (S303). In FIG. 11, the width direction of the paper surface corresponds to the traveling direction. The line indicated by R in the figure shows 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 is acquired. In FIG. 11, these measurement positions are shown as ○ marks on the line R. The direction of each magnetic vector indicates the acting direction of the magnetic field at the corresponding measurement position. Also, the length of each magnetic vector indicates the magnitude (intensity) of the magnetic field acting at the corresponding measurement position.

[0042] For each magnetic vector starting from each measurement position (the position indicated by the ○ mark in FIG. 11) belonging to a predetermined section, the detection unit 12 obtains the intersection point with the road surface 100S (S304) and sequentially stores the position of the intersection point (S305). In the example shown in FIG. 11, the intersection point between the magnetic vector and the road surface 100S is indicated by an × mark. The position of each × mark is specified by the position in the traveling direction.

[0043] The detection unit 12 repeatedly executes the above-described processes of steps S302 to S305 until all the magnetic measurement values whose measurement positions belong to a predetermined section are read out (S306: NO). The detection unit 12 terminates the process in response to the reading of all the magnetic measurement values whose measurement positions belong to a predetermined section (S306: YES).

[0044] Subsequently, the detection unit 12 as the determination circuit 122 evaluates the degree of dispersion of the intersection points stored in step S305 of FIG. 10 and determines whether the magnetic source is the magnetic marker 10 (FIG. 12). The detection unit 12 first obtains the average position of the intersection points (S401). Note that the position of each intersection point is a one-dimensional position on the road surface directly below the movement path of the magnetic sensor that is the output source of the magnetic measurement value. The average position of the intersection points is also this one-dimensional position on the road surface.

[0045] The detection unit 12 obtains the variance, which is an index value representing the degree of dispersion of the intersections (S402). The variance (S2), which is a statistical value, can be obtained by the following formula. Here, let the position of each intersection be xi and the average position of the intersections be xav. (Equation 1) TIFF0007698192000001.tif19167

[0046] The detection unit 12 performs threshold processing on the variance obtained in step S402 (S403, threshold judgment). If the variance (S2) is less than the threshold (within the threshold is also acceptable) (S403: YES), it is determined 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 greater than or equal to the threshold (exceeding the threshold is also acceptable) (S403: NO), it is determined that this magnetic source is the source of external magnetic interference and is not the magnetic marker 10 (S414).

[0047] Note that it is also possible to perform threshold processing on the standard deviation (S), which is the square root of the variance (S2). The standard deviation (S) is a statistical value representing the degree of dispersion such that 68.3% of the intersections belong to the range of ±S centered on the average position. The smaller the value of the variance (S2) or the standard deviation (S), the lower the degree of dispersion, and the larger these values, the higher the degree of dispersion.

[0048] Here, the state of dispersion of the intersections derived from the magnetic marker 10 and the state of dispersion of the intersections derived from the external magnetic source will be compared and explained. The magnetic marker 10 is a magnetic source with a diameter of 20 mm and a very small size in the traveling direction. On the other hand, when, for example, the steel frame of a bridge or a parallel vehicle serves as the magnetic source, the size in the traveling direction is likely to be large.

[0049] FIG. 13 and FIG. 14 are diagrams illustrating the state in which the intersections obtained by the process of FIG. 10 are scattered in the traveling direction. The horizontal axis of the figure represents the traveling direction. The bar graph represents the frequency of intersections located at the corresponding positions. FIG. 13 is an illustration when the magnetic generation source is the magnetic marker 10, and FIG. 14 is an illustration when a bridge or a parallel vehicle is detected as the magnetic generation source.

[0050] As is clear from the comparison between FIG. 13 and FIG. 14, when the magnetic marker 10 is the magnetic generation source, the frequency distribution at the measurement time point 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, in the case of a magnetic generation source of disturbance, the frequency distribution at the measurement time point is far from the normal distribution and spreads to both sides, and the value of the standard deviation (S), which is the square root of the variance (S2), is large. According to the threshold determination in step S303 in FIG. 12, a frequency distribution such as that in FIG. 14 with a large variance (S2) and standard deviation (S) can be excluded, and the magnetic marker 10 can be determined with high certainty.

[0051] As described above, according to the detection system 1 of this example, by paying attention to the degree of dispersion of the intersections between the magnetic vector representing the acting direction of the magnetic field around the magnetic generation source and the road surface 100S, the possibility of erroneously detecting magnetic generation sources other than the magnetic marker 10 can be reduced, and the magnetic marker 10 can be detected with high certainty.

[0052] In this example, the variance, which is an index value representing the degree of dispersion of the intersections in the traveling direction, is the subject of threshold determination. Instead of or in addition to this, the variance of the intersections in the vehicle width direction may be the subject of threshold determination. If it is a magnetic sensor capable of measuring the magnetic field acting in the vehicle width direction in addition to the vertical direction, for example, regarding the intersections related to the magnetic vectors acting on each magnetic sensor when the sensor array 11 is located directly above the magnetic marker 10, the variance in the vehicle width direction can be obtained.

[0053] It is also possible to employ a magnetic sensor capable of detecting the acting direction of magnetism in a three-dimensional space. In this case, it is advisable to determine whether it is the magnetic marker 10 according to the degree to which the intersection point of the magnetic vector acting on the magnetic sensor and the road surface 100S is two-dimensionally scattered on the road surface.

[0054] Note that if the angle formed by the magnetic vector (acting direction) with respect to the road surface 100S is small, there is a possibility that the error in obtaining the intersection point becomes excessive. Therefore, it is also possible to exclude from the target for obtaining the dispersion the magnetic vectors (acting directions) whose angles with this road surface 100S are less than or equal to a predetermined angle. Note that the angle formed by the movement vector (acting direction) with respect to the road surface is, for example, the angle indicated by θ in FIG. 11. Also, if the magnitude of the magnetism acting on the magnetic sensor is small, there is a possibility that the error in obtaining the intersection point becomes excessive. Therefore, it is also possible to exclude magnetic vectors whose magnitude of magnetism is less than or equal to a predetermined value from the target for obtaining the dispersion.

[0055] It is also possible to evaluate the shape of the locus 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 determine whether it is the magnetic marker 10. When the magnetic source is the magnetic marker 10, the magnetic vector rotates like the hand of a clock around the magnetic marker 10. Also, since the length of the magnetic vector, that is, the magnitude of the magnetism, becomes larger as it is closer to the magnetic marker 10, the locus formed by 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 locus formed by the end point of the magnetic vector by an ellipse or a normal distribution shape and obtain the error between the approximate shape and the actual locus. It is also possible to handle this error as an index value and perform threshold processing to determine whether it is the magnetic marker 10. Furthermore, it is also possible to standardize the rotation of the magnetic vector centered on the magnetic marker 10 and determine whether it is the magnetic marker 10.

[0056] Furthermore, not only for the magnetic sensor passing directly above the magnetic marker 10, but also for the magnetic vector formed by the magnetic measurement values obtained by each magnetic sensor of the sensor array 11, it is also good to evaluate the shape of the locus of the end point. The end point of the magnetic vector acting on each magnetic sensor has a shape close to an ellipsoid (upper part) or a two-dimensional normal distribution shape. Similar to the above, it is also good to obtain the error between the approximate shape and the surface formed by the actual locus, and determine whether it is the magnetic marker 10 by threshold processing.

[0057] As described above, specific examples of the present invention have been described in detail as in the embodiments. However, these specific examples merely disclose an example of the technology included in the claims. Needless to say, the claims should not be construed in a limited manner by the configuration, numerical values, etc. of the specific examples. The claims include technologies obtained by variously modifying, changing, or appropriately combining the specific examples using known technologies and the knowledge of those skilled in the art.

Explanation of Reference Numerals

[0058] 1 Detection system 10 Magnetic marker 11 Sensor array 12 Detection unit 121 Magnetic source detection circuit 123 Lateral displacement measurement circuit 125 Intersection identification circuit 127 Judgment circuit Cn Magnetic sensor 5 Vehicle 5S Driving support system 50 Vehicle ECU

Claims

1. A method for detecting a magnetic marker disposed on a road surface while a vehicle equipped with a magnetic sensor is moving on the road surface, comprising: the magnetic sensor being a sensor capable of acquiring at least a measurement value capable of specifying the acting direction of magnetism; a first process of processing the measurement value obtained by the magnetic sensor to detect a magnetic source that may be the magnetic marker; a second process of obtaining an intersection with the road surface for the acting direction of the magnetism with respect to the magnetic sensor when the vehicle passes through a predetermined section to which the magnetic source detected by the first process belongs; a third process of determining whether the magnetic source detected by the first process is a magnetic marker according to the degree of dispersion of the intersections obtained by the second process. A method for detecting a magnetic marker that executes the above processes.

2. The method for detecting a magnetic marker according to Claim 1, wherein the third process is a process of obtaining an index value representing the degree of dispersion of the intersections and determining the presence or absence of the magnetic marker by threshold processing on the index value.

3. The method for detecting a magnetic marker according to Claim 1 or 2, wherein in the second process, acting directions with an angle formed with the road surface being equal to or less than a predetermined angle or less than the predetermined angle are excluded, and intersections with the road surface are obtained for acting directions with an angle formed with the road surface being equal to or greater than a predetermined angle or exceeding the predetermined angle.

4. The method for detecting a magnetic marker according to any one of Claims 1 to 3, wherein the magnetic sensor can acquire, as the measurement value, the magnitudes of magnetic components acting along at least two intersecting directions.

5. A system for detecting a magnetic marker disposed on a road surface while a vehicle equipped with a magnetic sensor is moving on the road surface, comprising: the magnetic sensor being a sensor capable of acquiring at least a measurement value capable of specifying the acting direction of magnetism; a first circuit that processes the measurement value obtained by the magnetic sensor to detect a magnetic source that may be the magnetic marker; a second circuit that obtains an intersection with the road surface of the road surface for the acting direction 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; a third circuit that determines whether the magnetic source detected by the first circuit is a magnetic marker according to the degree of dispersion of the intersections obtained by the second circuit. A detection system for a magnetic marker including the above circuits.

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