Magnetic marker detection method and detection system

Abstract

A detection system (1) whereby a vehicle, which comprises a sensor array (11) having magnetic sensors arranged in the width direction, detects a magnetic marker disposed on a travel route. The detection system includes: a differential circuit (121) that obtains the difference between magnetic measurement values for each combination of two separated magnetic sensors that are separated by a prescribed interval; an arithmetic circuit (123) that executes processing for detecting the position of a magnetic marker by processing the difference for each combination; and a settings circuit (125) that selectively sets a prescribed interval for obtaining the magnetic measurement value differences. Magnetic markers arranged on a travel route can be detected with high reliability, regardless of differences in installation height of the magnetic sensors on the vehicle side.

Description

[Technical Field]

[0001] The present invention relates to a detection method and a detection system for detecting magnetic markers arranged on a track. [Background technology]

[0002] Conventionally, a system for vehicles that uses magnetic markers placed on roads has been known (see, for example, Patent Document 1). This system is intended for vehicles equipped with magnetic sensors and aims to provide various driving assistance functions, such as automatic steering control and lane departure warning, that use the magnetic markers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-202478 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the conventional system has the following problem: The mounting height of the magnetic sensor varies depending on the vehicle model, which results in a large variation in the optimal specifications for processing the magnetic measurement values ​​obtained by the magnetic sensor.

[0005] The present invention has been made in consideration of the above-mentioned conventional problems, and aims to provide a detection method and detection system that can reliably detect magnetic markers placed on a roadway, regardless of variations in the mounting height of the magnetic sensor on the vehicle. [Means for solving the problem]

[0006] One aspect of the present invention is a method for a vehicle equipped with a sensor array in which magnetic sensors for acquiring magnetic measurement values ​​are arranged in a width direction to detect magnetic markers arranged on a roadway, the method comprising: a differential process for obtaining a difference between values ​​constituting the distribution or values ​​constituting a line representing the distribution for each combination of two positions spaced apart by a predetermined interval, based on the distribution of magnetic measurement values ​​of the plurality of magnetic sensors constituting the sensor array; a calculation process for detecting the magnetic marker or detecting the position of the magnetic marker using the difference for each combination obtained by the difference process as an input value; and a setting process for selectively setting the predetermined interval for obtaining the difference.

[0007] One aspect of the present invention is a system in which a vehicle equipped with a sensor array in which magnetic sensors for acquiring magnetic measurement values ​​are arranged in a width direction detects magnetic markers arranged on a roadway, the system comprising: a differential circuit that acquires, for each combination of two positions spaced apart by a predetermined interval, a difference between values ​​that constitute the distribution or values ​​that constitute a line representing the distribution, based on a distribution of magnetic measurement values ​​of the plurality of magnetic sensors that constitute the sensor array; an arithmetic circuit that executes arithmetic processing using the difference for each combination as an input value by the difference circuit to detect the magnetic marker or to detect the position of the magnetic marker; and a setting circuit for selectively setting the predetermined interval for obtaining the difference. [Effects of the Invention]

[0008] The present invention is a method or system for detecting a magnetic marker using the difference between magnetic measurement values ​​of two magnetic sensors among magnetic sensors arranged in a sensor array. One of the technical features of the magnetic marker detection method or detection system of the present invention is that the distance between the two magnetic sensors that acquire the difference can be selectively set.

[0009] If the mounting height of the sensor array differs, the magnitude of the magnetic field acting on the magnetic sensor from the magnetic marker will differ. For example, if the mounting height of the sensor array is lower, the magnetic field acting on the magnetic sensor from the magnetic marker will be stronger. Of the multiple magnetic sensors that make up the sensor array, the difference between the magnetic measurement value obtained by a magnetic sensor located near the magnetic marker and the magnetic measurement value obtained by a magnetic sensor located farther from the magnetic marker will also be larger as the mounting height of the sensor array is lower.

[0010] As in the present invention, by providing a process or circuit that selectively sets the distance between two magnetic sensors for obtaining the difference, it becomes possible to suppress the effects of differences in the mounting height of the sensor array. If the effects of differences in the mounting height of the sensor array can be suppressed, magnetic markers can be detected using a process with the same specifications regardless of differences in the mounting height of the sensor array. Using a process with the same specifications, magnetic markers can be detected with high reliability regardless of differences in the mounting height of the sensor array.

[0011] As described above, the magnetic marker detection method and detection system of the present invention are capable of detecting magnetic markers by processing with the same specifications, regardless of variations in the mounting height of the sensor array on the vehicle. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a front view of a vehicle equipped with a magnetic marker detection system according to a first embodiment. [Figure 2] FIG. 2 is an explanatory diagram showing a vehicle on a lane on which magnetic markers are provided in the first embodiment. [Figure 3] FIG. 2 is a perspective view of a magnetic marker according to the first embodiment. [Figure 4] FIG. 1 is a block diagram showing a system configuration of a magnetic marker detection system according to a first embodiment. [Figure 5] FIG. 4 is a flowchart showing the flow of a marker detection process in the first embodiment. [Figure 6] 6 is a graph showing the change over time in magnetic measurement values ​​in the traveling direction when passing through a magnetic marker in Example 1. [Figure 7] 10 is a graph showing the distribution of magnetic measurement values ​​in the vertical direction by each magnetic sensor when the sensor array is positioned directly above the magnetic marker in Example 1. [Figure 8] 10 is a graph showing the distribution of magnetic gradients (magnetic difference values) in the vehicle width direction when the sensor array is positioned directly above the magnetic marker in Example 1. [Figure 9] 10 is another graph showing the distribution of magnetic measurement values ​​in the vertical direction by each magnetic sensor when the sensor array is positioned directly above the magnetic marker in Example 1. [Figure 10] 10 is another graph showing the distribution of magnetic gradients (magnetic difference values) in the vehicle width direction when the sensor array is positioned directly above the magnetic marker in the first embodiment. [Figure 11] FIG. 10 is an explanatory diagram of a method for setting the distance between two magnetic markers in the third embodiment. [Figure 12] FIG. 10 is an explanatory diagram showing a sensor array in the fourth embodiment. [Figure 13] FIG. 10 is an enlarged view of a joint portion of the sensor array in the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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 magnetic markers 10 placed on a road. The details will be described with reference to FIGS.

[0014] 1 and 2, this example is an example in which the detection system 1 for the magnetic marker 10 is combined with a driving assistance system 5S that enables lane keeping driving. The driving assistance system 5S is configured to include a vehicle ECU 50 that controls a steering actuator (not shown) for steering the steering wheels, a throttle actuator for adjusting engine output, etc. The vehicle ECU 50 controls the vehicle 5, for example, to reduce the amount of lateral deviation from the magnetic marker 10 to close to zero, thereby realizing lane keeping driving.

[0015] The detection system 1 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 processes the magnetic measurement values ​​of each magnetic sensor Cn to detect the magnetic marker 10. 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.

[0016] (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 a lane 100 that forms the path of a vehicle 5. This magnetic marker 10 is columnar, 20 mm in diameter and 28 mm in height, and can be placed in a hole in the road surface 100S. The magnetic marker 10 is a ferrite plastic magnet in which iron oxide magnetic powder, a magnetic material, is dispersed in a polymeric material base material. It is also possible to provide, for example, a resin mold layer on all or part of the surface of the magnetic marker 10, which is the ferrite plastic magnet itself.

[0017] 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 5, such as passenger cars and trucks, are considered to be vehicles 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 expected range of mounting heights for the magnetic sensor Cn.

[0018] (sensor array) As shown in FIGS. 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 that extends along the vehicle width direction. The sensor array 11 includes a combination of 15 magnetic sensors Cn (n is an integer between 1 and 15) and a signal processing circuit 110 that incorporates a CPU and the like (not shown) (FIG. 4).

[0019] The magnetic sensor Cn is a sensor that detects magnetism by utilizing the well-known MI effect (Magneto Impedance Effect), which means that the impedance of a magnetically sensitive material 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 material such as a linear amorphous wire, and outputs a sensor signal representing the magnitude of the magnetic component. Two linear magnetically sensitive materials 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 material.

[0020] 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 mT within the measurement range. As described above, the magnetic marker 10 can act on a magnetic flux density of 8 μT or more within the assumed mounting height range of 90 to 250 mm for the magnetic sensor Cn. A magnetic marker 10 that acts on 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.

[0021] 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) 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 traveling direction and vertical direction.

[0022] The signal processing circuit 110 (FIG. 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 (for example, 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 (the magnetic measurement value in the traveling direction and the magnetic measurement value in the vertical direction).

[0023] (detection unit) The detection unit 12 (FIG. 4) is a circuit that executes marker detection processing, which is a calculation process for detecting the magnetic marker 10. The detection unit 12 has a circuit board 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.

[0024] A work area for storing time-series magnetic measurement values ​​for each magnetic sensor Cn is formed in the storage area of ​​the RAM. The detection unit 12 uses this work area to store time-series magnetic measurement values ​​over a period of time during which the vehicle 5 has traveled a predetermined distance (e.g., 10 m). The time-series magnetic measurement values ​​include magnetic measurement values ​​in the traveling direction and magnetic measurement values ​​in the vertical direction.

[0025] 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 wheel rotates a predetermined amount. The predetermined amount may 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 5 cm that the vehicle 5 moves. 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.

[0026] 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 marker detection processing, etc. The detection unit 12 executes the marker detection processing every time the vehicle 5 advances (moves) 5 cm, and inputs the detection results of the marker detection processing to the vehicle ECU 50. The results of the marker detection processing include information on whether or not a magnetic marker 10 has been detected, and, if a magnetic marker 10 has been detected, the amount of lateral deviation from the magnetic marker 10.

[0027] The detection unit 12 has the functions of the following circuits (means). (a) Differential circuit 121: A circuit that acquires a magnetic differential value, which is the difference between magnetic measurement values, for each combination of two magnetic sensors spaced apart by a predetermined distance from each other among the 15 magnetic sensors Cn that make up the sensor array 11. (b) Calculation circuit 123: A circuit that executes calculation processing using the magnetic difference value acquired by the difference circuit 121 as an input value. The calculation circuit 123 in this example executes calculation processing to detect the position of the magnetic marker 10 in the vehicle width direction by measuring the amount of lateral deviation of the vehicle 5 relative to the magnetic marker 10. (c) Setting circuit 125: A circuit that selectively sets the above-mentioned predetermined interval for acquiring the magnetic difference value.

[0028] The flow of the marker detection process performed by the detection system 1 configured as above will be described with reference to the flowchart in Fig. 5. This marker detection process is executed by the detection system 1 every time the vehicle 5 moves 5 cm. Below, the details of the marker detection process will be described, focusing mainly on the operation of the detection unit 12.

[0029] The detection unit 12 acquires the magnetic measurement value of each magnetic sensor Cn of the sensor array 11 every time the vehicle 5 moves 5 cm (S101). The detection unit 12 detects that the vehicle 5 has moved 5 cm in response to acquisition of a pulse signal from the vehicle speed sensor, and inputs a data request signal to the sensor array 11. As described above, the data acquired by the detection unit 12 from the sensor array 11 are the magnetic measurement value in the moving direction and the magnetic measurement value in the vertical direction of each magnetic sensor Cn.

[0030] The detection unit 12 writes the magnetic measurement values ​​(travel direction and vertical direction) of each magnetic sensor Cn acquired 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, a time series of magnetic measurement values ​​(travel direction and vertical direction) over a predetermined period of time in the past (in this example, a movement period corresponding to a movement distance of 10 m) is stored and held in the work area (S102).

[0031] The detection unit 12 calculates a magnetic total value, which is the sum of the magnetic measurement values ​​at each time point, for the time-series magnetic measurement values ​​in the traveling direction of 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.

[0032] As shown in FIG. 6, 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, 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 reaches zero when the magnetic sensor Cn is positioned directly above the magnetic marker 10. 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 in the negative direction and reaches a negative peak. As the magnetic sensor Cn moves further 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, forms a curve with two adjacent positive and negative peaks sandwiched between the magnetic marker 10, as shown in FIG. 6. This curve includes a zero crossing Zc, where the curve crosses zero with a steep slope directly above the magnetic marker 10.

[0033] The detection unit 12 determines whether or not a zero cross Zc has been detected with respect to the temporal change in the magnetic sum value in Fig. 6 (S104). If a zero cross Zc has been detected (S104: YES), the detection unit 12 determines that the magnetic marker 10 has been detected. Then, the detection unit 12 reads out from the work area the magnetic measurement value in the vertical direction of each magnetic sensor Cn when the sensor array 11 is positioned directly above the magnetic marker 10 (S105).

[0034] When the sensor array 11 is positioned directly above the magnetic marker 10, the distribution of magnetic measurement values ​​in the vertical direction of each magnetic sensor Cn is, for example, as shown in FIG. 7. The magnetic measurement values ​​of each magnetic sensor Cn are distributed along a curve that is close to a normal distribution, as shown by the dashed line in the figure. The peak of the curve shown by the dashed line appears corresponding to the position of the magnetic marker 10. The figure shows an example in which the magnetic marker 10 is located approximately halfway between magnetic sensors C9 and C10. Note that the horizontal axis in FIG. 7 and the following FIGS. 8 to 11 indicates the vehicle width direction, and the scales 1 to 15 indicate the positions of the magnetic sensors C1 to C15.

[0035] The detection unit 12 (setting circuit 125) selectively sets the interval (predetermined interval) between the two magnetic sensors for determining the magnetic gradient (magnetic difference value) in the vehicle width direction by a method described later (S106).Then, the detection unit 12 determines the magnetic difference value, which is the difference between the magnetic measurement values ​​in the vertical direction by the two magnetic sensors spaced apart at the interval set in step S106 (differential processing), thereby generating the distribution of the magnetic gradient in the vehicle width direction (S107).

[0036] The distribution of the magnetic gradient (magnetic difference value) in the vehicle width direction is, for example, as shown in Figure 8. The magnetic gradient in the vehicle width direction is distributed along a curve with adjacent positive and negative peaks, as shown by the dashed line in the figure. In this curve, depending on which side of the magnetic sensor is located relative to the magnetic marker 10, the positive magnetic difference value indicating a gradient where magnetism increases and the negative magnetic difference value indicating a gradient where magnetism decreases are reversed. 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 marker 10.

[0037] The detection unit 12 determines an approximation curve (e.g., the dashed curve in FIG. 8) of the distribution of the magnetic gradient (magnetic difference value) in the vehicle width direction, and identifies the zero cross Zc, thereby identifying the position of the magnetic marker 10 in the vehicle width direction. The position of the magnetic marker 10 in the vehicle width direction can be identified as the position corresponding to the zero cross Zc of the approximation curve.

[0038] 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) from the magnetic marker 10 in the vehicle width direction as the lateral deviation of the vehicle 5 (S108). For example, in the case of FIG. 8, the zero cross Zc of the approximation curve is located around C9.5, which is midway between C9 and C10. Because the distance between magnetic sensors C9 and C10 is 10 cm, the lateral deviation of the vehicle 5 from the magnetic marker 10 is (9.5-8) x 10 cm = 15 cm, with C8, which is located at the center of the sensor array 11 in the vehicle width direction, as the reference point.

[0039] When the detection unit 12 detects the magnetic marker 10 and measures the amount of lateral deviation as described above, it outputs a detection result including information indicating that the magnetic marker 10 has been detected and the amount of lateral deviation. The vehicle ECU 50 uses the detection result output by the detection unit 12 to realize driving assistance control such as lane keeping driving.

[0040] Next, the setting process (S106 in FIG. 5) by which the setting circuit 125 selectively sets the above-mentioned predetermined interval when calculating the magnetic gradient in the vehicle width direction will be described with reference to FIGS. 7 to 10. Here, the distribution in FIG. 9 corresponds to the distribution in FIG. 7. The distribution in FIG. 9 and the distribution in FIG. 7 differ in the mounting height of the sensor array 11. The distribution in FIG. 9 is a distribution when the mounting height of the sensor array 11 is higher than in the case of FIG. 7. The relationship between FIG. 9 and FIG. 10 is the same as the relationship between FIG. 7 and FIG. 8. FIG. 10 shows the distribution of magnetic difference values, which are the magnetic gradient in the vehicle width direction based on the magnetic measurement values ​​in FIG. 9.

[0041] The setting circuit 125 determines the numerical range R of the magnetic measurement value of each magnetic sensor Cn when the sensor array 11 is positioned directly above the magnetic marker 10 (see FIGS. 7 and 9). Specifically, the setting circuit 125 determines the maximum and minimum values ​​of the magnetic measurement value, and determines the numerical range R of the magnetic measurement value by subtracting the minimum value from the maximum value.

[0042] The setting circuit 125 sets the interval (predetermined interval) between the two magnetic sensors Cn for acquiring the magnetic gradient in the vehicle width direction narrower as the numerical range R of the magnetic measurement values ​​increases (for example, as shown in FIG. 7). Also, the setting circuit 125 sets the interval between the two magnetic sensors Cn wider as the numerical range R of the magnetic measurement values ​​decreases (for example, as shown in FIG. 9). In this example, the numerical range R@90 (simulation calculation value) when the mounting height of the sensor array 11 is 90 mm, which is the lower limit of the range, is used as a reference, and the predetermined interval for acquiring the magnetic gradient in the vehicle width direction is set as follows:

[0043] (1) When the numerical range R of the magnetic measurement value is R@90×80% or more. The predetermined interval is set to 10 cm, which is the interval between two adjacent magnetic markers. (2) When the numerical range R of the magnetic measurement value is greater than or equal to R@90×50% and less than R@90×80%. The predetermined spacing is set to 20 cm, which is the spacing between two adjacent magnetic markers. (3) When the numerical range R of the magnetic measurement value is less than R@90×50%. The predetermined interval is set to 30 cm, which is the interval between every two adjacent magnetic markers.

[0044] For example, in the distribution of magnetic measurement values ​​in Fig. 7, the numerical range R of the magnetic measurement values ​​is about 90% of R@90, which corresponds to the above case (1). In this case, the predetermined interval is set to 10 cm, and the difference in magnetic measurement values ​​between two adjacent magnetic sensors in the sensor array 11 is obtained (see Fig. 7), and the magnetic gradient (magnetic difference value) in the vehicle width direction is calculated (see Fig. 8).

[0045] On the other hand, for example, in the distribution of magnetic measurement values ​​in Fig. 9, the numerical range R of the magnetic measurement values ​​is about 60% of R@90, which corresponds to the above-mentioned case (2). In this case, the predetermined interval is set to 20 cm, and the difference in magnetic measurement values ​​is obtained for every two adjacent magnetic sensors in the sensor array 11 (see Fig. 9), and the magnetic gradient (magnetic difference value) in the vehicle width direction is calculated (see Fig. 10).

[0046] When the distribution of magnetic measurement values ​​in Fig. 7 is compared with the distribution of magnetic measurement values ​​in Fig. 9, the distribution in Fig. 7, in which the sensor array 11 is mounted at a lower height, has larger magnetic measurement values ​​and the peak of the approximation curve is higher. On the other hand, when the distribution of magnetic difference values, which are the magnetic gradient in the vehicle width direction in Fig. 8, is compared with the distribution of magnetic difference values, which are the magnetic gradient in the vehicle width direction in Fig. 10, there is no significant difference in the amplitude of the approximation curve. This is because the predetermined interval when acquiring the magnetic difference values ​​is selectively set according to the magnitude of the magnetic measurement values, thereby suppressing the degree of influence that differences in the magnitude of the magnetic measurement values ​​of each magnetic sensor Cn have on the magnetic difference values ​​(the differences in Figs. 7 and 9).

[0047] Here, in order to ensure the accuracy of the process of measuring the lateral deviation amount relative to the magnetic marker 10 as described above using the magnetic gradient in the vehicle width direction (for example, the magnetic difference value in Figures 8 and 10), it is important to ensure a certain degree of magnitude for the magnetic difference value that constitutes the magnetic gradient in the vehicle width direction. If the spacing between the two magnetic sensors for acquiring the magnetic difference value is set as described above, the magnitude of the magnetic difference value, which is the magnetic gradient in the vehicle width direction, can be ensured even if the mounting height of the sensor array 11 is low and the peak of the change curve of the magnetic measurement value of each magnetic sensor Cn is low and small (see Figure 9).

[0048] Furthermore, the similar distribution of the magnetic gradient (magnetic difference value) in the vehicle width direction is effective in improving the uniformity of the process for measuring the amount of lateral deviation using the magnetic gradient in the vehicle width direction, as described above. If the uniformity of the process for measuring the amount of lateral deviation is improved, the amount of lateral deviation can be measured with high accuracy regardless of differences in the mounting height of the sensor array 11.

[0049] As described above, one of the technical features of the detection system 1 of this example for processing magnetic measurement values ​​from each magnetic sensor Cn of the sensor array 11 attached to the vehicle 5 is that the spacing between two magnetic sensors that acquire the difference forming the magnetic gradient in the vehicle width direction is selectively set.

[0050] Selectively setting the distance between the two magnetic sensors for obtaining the difference makes it possible to suppress the influence of differences in the magnitude of the magnetic measurement values ​​caused by differences in the mounting height of the sensor array 11 (magnetic sensor). If the influence of differences in the mounting height of the sensor array 11 can be suppressed, the specifications for processing the magnetic measurement values ​​of the magnetic sensors can be made closer to common regardless of differences in the mounting height of the sensor array, thereby improving the detection accuracy of the magnetic marker 10.

[0051] In this example, the predetermined interval for calculating the difference is set to 10 cm in the width direction, which is the interval between adjacent magnetic sensors in the sensor array 11. In this example, a combination of two adjacent positions in the sensor array 11, which are spaced apart by a predetermined interval, is set, and the difference between the magnetic measurement values ​​of the adjacent magnetic sensors is calculated. The magnetic measurement values ​​of the magnetic sensors are values ​​that constitute the distribution of the magnetic measurement values ​​of the magnetic sensors. Note that instead of the configuration of this example, the predetermined interval may be set to the interval between two magnetic sensors spaced apart with one magnetic sensor therebetween, or the interval between two or more magnetic sensors spaced apart with two or more magnetic sensors therebetween.

[0052] Instead of the configuration of this example, the magnetic gradient in the direction of travel may be calculated from the time difference between time-series vertical magnetic measurement values. In this example, magnetic measurement is performed every 5 cm as the vehicle 5 moves. Therefore, the time-series vertical magnetic measurement values ​​are values ​​at each position every 5 cm in the direction of travel. When calculating the magnetic gradient in the direction of travel (magnetic difference value) from time difference, it is preferable to selectively set the predetermined interval for calculating the magnetic difference value to 5 cm, which corresponds to two time points that are adjacent in time, or 10 cm, which corresponds to two time points that are every other adjacent.

[0053] In this example, a process for measuring the lateral deviation of the vehicle 5 relative to the magnetic marker 10, i.e., a process for detecting the relative position of the magnetic marker 10 (relative to the vehicle 5) in the vehicle width direction, is illustrated as an example of a calculation process using the difference between magnetic measurement values ​​as an input value. As described above, the magnetic marker 10 may also be detected using the time difference between vertical magnetic measurement values ​​(magnetic gradient in the direction of travel) as an input value. Detecting the magnetic marker 10 using the magnetic gradient in the direction of travel corresponds to detecting that the vehicle 5 has reached the magnetic marker 10, i.e., that the relative position of the magnetic marker 10 (relative to the vehicle 5) in the direction of travel has become zero.

[0054] The calculation process for detecting magnetic markers may be a filter process for eliminating magnetic components of uniformly acting disturbances, such as geomagnetism. The technical concept of this example may be applied when calculating the difference between magnetic measurement values ​​as part of this filter process. In this case, the uniformity of the filter process specifications can be increased, making the filter characteristics closer to uniform, regardless of variations in the mounting height of the magnetic sensors, thereby improving the reliability of magnetic marker detection.

[0055] Example 2 This example is an example in which the method of setting the interval between two magnetic sensors when obtaining the difference between magnetic measurement values ​​is changed based on the configuration of the first embodiment.

[0056] (First setting method) The first setting method is a setting method in which the interval between two magnetic sensors that acquire a magnetic difference value, which is a magnetic gradient in the vehicle width direction, is changed according to the mounting height of the sensor array 11. The mounting height range of the sensor array 11 is 90 mm to 250 mm depending on the vehicle model. In the first setting method, this range is divided into three stages, and a predetermined interval is set for each stage. The mounting height of the sensor array 11 may be stored in advance as an installation specification, or may be measured using an ultrasonic sensor or the like. Measuring using a sensor makes it possible to appropriately respond to changes in vehicle height due to the weight of luggage carried in the vehicle or the number of passengers on board.

[0057] (1) First category The first section is a section where the mounting height is equal to or greater than 90 mm and less than 150 mm. The predetermined interval corresponding to the first section is 10 cm, which is the interval between two adjacent magnetic sensors in the sensor array 11.

[0058] (2) Second category The second section is a section where the mounting height is equal to or greater than 150 mm and less than 200 mm. The predetermined interval corresponding to the second section is 20 cm, which is the interval between every other two adjacent magnetic sensors in the sensor array 11.

[0059] (3) Third category The third section is a section for mounting heights of 200 mm or more and 250 mm or less. The predetermined interval corresponding to the third section is 30 cm, which is the interval between every third adjacent two magnetic sensors in the sensor array 11.

[0060] (Second setting method) The second setting method is a process of setting a predetermined distance between the two magnetic sensors so that when the sensor array 11 is positioned directly above the magnetic marker 10, the magnitude of the numerical range of the magnetic difference value obtained for each combination of two magnetic sensors approaches a predetermined value.

[0061] In this method, the distribution of magnetic difference values ​​(magnetic gradient in the vehicle width direction) for each combination of two adjacent magnetic sensors in the sensor array 11, the distribution of magnetic difference values ​​for each combination of two adjacent magnetic sensors that are every other sensor, and the distribution of magnetic difference values ​​for each combination of two adjacent magnetic sensors that are every third sensor are respectively obtained.

[0062] In the second setting method, a reference value for the maximum magnetic difference value is set, and in this setting method, the distribution in which the maximum magnetic difference value is closest to the reference value is selected from the above three types of magnetic difference value distributions and used for the measurement process of the lateral deviation amount, etc. The other configurations and effects are the same as those of the first embodiment.

[0063] Example 3 This example is an example in which the method of acquiring the difference, which is the magnetic gradient in the vehicle width direction, is changed based on the first embodiment, and the contents thereof will be described with reference to FIG.

[0064] In this example, the distribution of magnetic measurement values ​​of each magnetic sensor in the sensor array is replaced with an approximation curve (the curve shown by the dashed line in FIG. 11). In this example, when acquiring a magnetic differential value, which is the magnetic gradient in the vehicle width direction, the predetermined interval between two magnetic sensors is selectively set from a continuous range of intervals. In this example, it is assumed that the approximation curve of the distribution of magnetic measurement values ​​is composed of magnetic measurement values ​​from an infinite number of magnetic sensors.

[0065] Then, at the point of the greatest gradient on the approximation curve of the distribution of magnetic measurement values, the interval between the two positions is selected so that the difference between the two positions is a predetermined value. For example, in the example shown in FIG. 11, the two positions are two positions (e.g., 10.2 and 11.6) equally distant from the position with the greatest gradient (e.g., 10.9 on the horizontal axis in the figure). The predetermined range is 1.4, which is 11.6 minus 10.2. In this example, for the approximation curve of the distribution of magnetic measurement values ​​(see FIG. 11), the difference between the magnetic measurement values ​​is obtained for each combination of two positions that make up the interval selected above (the range of 1.4 in the case of FIG. 11).

[0066] In this example, an approximate curve is used as an example of a line representing the distribution of magnetic measurement values. The line representing the distribution may be a polygonal line that linearly connects two adjacent magnetic measurement values ​​that make up the distribution. The other configurations and effects are the same as those of the first embodiment.

[0067] Example 4 This example is an example that employs a sensor array that is capable of changing the interval between adjacent magnetic sensors, based on the configuration of Example 1. This will be described with reference to FIGS.

[0068] The sensor array 11 of this example has a multi-joint structure in which 28 links 111 are connected in series by 27 joints 113 as shown in Fig. 12. The links 111 are rod-shaped members with a rectangular cross section, and holes are provided at both ends for passing joint pins 115 (Fig. 13) through them. Each joint 113 is formed by connecting two links 111 with the joint pins 115. Note that a hole is also provided at a link end 118 located at the end of the sensor array 11, and a dummy joint pin 115 is passed through it.

[0069] In the sensor array 11, sliding pins 119 are provided to extend coaxially from two joint pins 115 at both ends of a link end 118 and from thirteen joint pins 115 at even-numbered positions counting from the link end 118. Furthermore, magnetic sensors (not shown) are provided at the other ends of these fifteen joint pins 115 opposite the sliding pins 119. The sensor array 11 is attached to the vehicle, for example, with the sliding pins 119 held and suspended in linear rail grooves 508 attached to the bottom surface of the vehicle.

[0070] Each joint 113 is provided with a biasing member (not shown) that biases the links 111 on both sides to narrow the angle between them. The biasing force of each joint 113 is uniform, so when the sensor array 11 is pulled from both sides, the angles between the links 111 at each joint 113 become uniform, which makes the spacing between adjacent joints 113 uniform and creates a uniform jagged wave shape across the entire sensor array 11. The sensor array 11 is attached to the vehicle with the 28 links 111 forming this uniform jagged wave shape.

[0071] When the sensor array 11 is suspended from the underside of the vehicle as described above, the 15 magnetic sensors arranged at the two link ends 118 at both ends and at the 13 even-numbered joints 113 counting from the link ends 118 face the road surface. As described above, each magnetic sensor is arranged on a joint pin 115 that is held in a linear rail groove 508 so that it can move back and forth, and the magnetic sensors are arranged in a straight line along this rail groove 508. Furthermore, because each link 111 of the sensor array 11 has a uniformly jagged wave shape as described above, the joint pins 115 on which the magnetic sensors are arranged are spaced evenly apart. Therefore, the magnetic sensors provided in the sensor array 11 are arranged at equal intervals along a straight line.

[0072] When mounting the sensor array 11 of this example on a vehicle, it is preferable to appropriately extend the sensor array 11 so that the spacing between the magnetic sensors is appropriate depending on the mounting height of the sensor array 11. This sensor array 11 can be applied to vehicles in which the mounting height of the sensor array 11 is low and the spacing between the magnetic sensors is narrow, and to vehicles in which the mounting height of the sensor array 11 is high and the spacing between the magnetic sensors is wide. In the case of this sensor array 11, when calculating the magnetic gradient in the vehicle width direction based on the magnetic measurement values ​​of each magnetic sensor, it is sufficient to calculate the difference between the magnetic measurement values ​​of two adjacent magnetic sensors.

[0073] Instead of this example, multiple magnetic sensors may be held along the axial direction of the central axis of a cylindrical helical spring. In this case, the spacing between the magnetic sensors can be adjusted by appropriately stretching the helical spring. A strip-shaped elastic member may be used instead of the helical spring. Note that a columnar elastic member may be used instead of the cylindrical helical spring. The other configurations and effects are the same as those of the first embodiment.

[0074] Although specific examples of the present invention have been described in detail as examples, these examples merely disclose examples of the technology encompassed by the claims. Needless to say, the scope of the claims should not be interpreted as being limited by the configurations, numerical values, etc. of the specific examples. The claims encompass technologies that are obtained by variously modifying, changing, or appropriately combining the specific examples using publicly known technology and the knowledge of those skilled in the art. [Explanation of symbols]

[0075] 1. Detection System 10 Magnetic Markers 11 Sensor Array 12 Detection Unit 121 Differential circuit 123 Arithmetic circuit 125 Setting circuit Cn magnetic sensor 5 vehicles 5S driving assistance system 50 Vehicle ECU

Claims

1. A method for detecting magnetic markers arranged on a roadway by a vehicle equipped with a sensor array in which magnetic sensors for acquiring magnetic measurement values ​​are arranged in a width direction, the method comprising: a differential process for obtaining a difference between values ​​constituting the distribution or values ​​constituting a line representing the distribution for each combination of two positions spaced apart by a predetermined interval, based on the distribution of magnetic measurement values ​​of the plurality of magnetic sensors constituting the sensor array; a calculation process for detecting the magnetic marker or detecting the position of the magnetic marker using the difference for each combination obtained by the difference process as an input value; a setting process for selectively setting the predetermined interval for acquiring the difference, A magnetic marker detection method, wherein the setting process can be performed while the vehicle is traveling, and the predetermined interval can be changed by the setting process while the vehicle is traveling.

2. In claim 1, the setting process changes the specified interval according to the numerical range of the magnetic measurement values ​​of the multiple magnetic sensors when the sensor array is positioned directly above the magnetic marker, and the larger the numerical range of the magnetic measurement values, the narrower the specified interval is, and the smaller the numerical range of the magnetic measurement values, the wider the specified interval is.

3. 2. The method according to claim 1, further comprising: measuring the height of the sensor array above ground; A magnetic marker detection method in which the setting process changes the predetermined interval according to the measurement value of the height above ground of the sensor array, making the predetermined interval narrower the lower the height above ground represented by the measurement value, and making the predetermined interval wider the higher the height above ground represented by the measurement value.

4. In claim 1, the setting process changes the specified interval according to the numerical range of the difference for each combination when the sensor array is positioned directly above the magnetic marker, and changes the specified interval so that the magnitude of the numerical range of the difference approaches a specified value.

5. According to any one of claims 1 to 4, the plurality of magnetic sensors are arranged at equal intervals in the sensor array, and the interval between two adjacent magnetic sensors is fixed; the setting process selects one of a distance between the two adjacent magnetic sensors, a distance between two magnetic sensors spaced apart with one magnetic sensor therebetween, and a distance between two or more magnetic sensors spaced apart with two or more magnetic sensors therebetween, and sets the selected distance as the predetermined distance; In the difference processing, the difference between the values ​​is obtained for each combination of two magnetic sensors located at the two positions.

6. According to any one of claims 1 to 4, the sensor array is configured such that the plurality of magnetic sensors are arranged at equal intervals, while the interval between two adjacent magnetic sensors is changeable; the setting process is a process of setting the predetermined interval by changing an interval between the two adjacent magnetic sensors in the sensor array; A magnetic marker detection method in which, in the difference processing, the difference in the values ​​is obtained for each combination of two adjacent magnetic sensors located at the two positions.

7. A method for detecting a magnetic marker according to any one of claims 1 to 4, wherein the line representing the distribution is an approximation curve of the distribution, and the two positions are positions on the approximation curve.

8. A system in which a vehicle equipped with a sensor array in which magnetic sensors for acquiring magnetic measurement values ​​are arranged in a width direction detects magnetic markers arranged on a road, a differential circuit that acquires, for each combination of two positions spaced apart by a predetermined interval, a difference between values ​​constituting the distribution or values ​​constituting a line representing the distribution, based on a distribution of magnetic measurement values ​​of the plurality of magnetic sensors that constitute the sensor array; an arithmetic circuit that executes arithmetic processing using the difference for each combination as an input value by the difference circuit to detect the magnetic marker or to detect the position of the magnetic marker; a setting circuit that selectively sets the predetermined interval for acquiring the difference; The setting circuit is configured to be able to selectively set the predetermined interval while the vehicle is traveling.

9. 7. The sensor array according to claim 6, wherein the sensor array holds the plurality of magnetic sensors so as to maintain the state in which the plurality of magnetic sensors are arranged at equal intervals, and includes a member that applies a biasing force to narrow the interval between two adjacent magnetic sensors, A method for detecting a magnetic marker, comprising: adjusting the distance between the two adjacent magnetic sensors by extending the sensor array in the width direction against the biasing force.

10. 9. The vehicle according to claim 8, further comprising a circuit for identifying a numerical range of magnetic measurement values ​​of the plurality of magnetic sensors when the sensor array is positioned directly above a magnetic marker according to the running of the vehicle, A magnetic marker detection system configured such that the setting circuit changes the predetermined interval according to the numerical range of the magnetic measurement values ​​of the multiple magnetic sensors when the sensor array is positioned directly above the magnetic marker, so that the larger the numerical range of the magnetic measurement values, the narrower the predetermined interval, and the smaller the numerical range of the magnetic measurement values, the wider the predetermined interval.

11. 9. The method according to claim 8, further comprising: a sensor for measuring the height of the sensor array above ground; A magnetic marker detection system configured such that the setting circuit changes the predetermined interval according to the measurement value of the height above ground of the sensor array, narrowing the predetermined interval as the height above ground represented by the measurement value decreases, and widening the predetermined interval as the height above ground represented by the measurement value increases.

12. 9. The method according to claim 8, further comprising: acquiring a magnitude of a numerical range of the difference for each combination when the sensor array is positioned directly above the magnetic marker as the vehicle travels; The magnetic marker detection system is configured such that the setting circuit changes the predetermined interval according to the magnitude of the numerical range of the difference for each combination when the sensor array is positioned directly above the magnetic marker, and sets the predetermined interval so that the magnitude of the numerical range of the difference is close to a predetermined value.

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