Magnetic detection method and system

Abstract

Provided is a system capable of more accurately detecting an object to be detected. The method comprises: a step (S51, 52) in which a coordinate system is set in a detection region in which the object to be detected (MM) is estimated to be present, and detection magnetic field vectors at a plurality of measurement points in the coordinate system are measured by a movable first magnetic field sensor; a step (S53) for measuring or calculating the reference magnetic field vector in the coordinate system in the detection region; a step (S54) for calculating the vector difference between each detection magnetic field vector measured at the measurement point and the reference magnetic field vector; and a step (S55) for estimating the position of the object to be detected on the basis of the vector difference at each measurement point.

Description

Technical Field

[0001] The present invention relates to a magnetic detection method and a magnetic detection system for detecting a detection target object that cannot be visually seen, such as a magnetic body buried in soil or water, on the earth or in the universe, based on its magnetic components. Background Art

[0002] As a magnetic detection method for detecting the position and size of a detection target object including a magnetic body buried in the ground or sunk in water (including the sea), a method described in Patent Document 1 is known, for example. The magnetic detection method of Patent Document 1 is a method of synthesizing the output waveforms of a magnetic field sensor having a first coil and a second coil that is separately arranged in the axial direction of the first coil and has a winding direction opposite to that of the first coil. Based on the magnetic detection method of the device of Patent Document 1, as shown in Patent Document 1 Figure 6 An operator carries a magnetic field sensor in a detection area to detect a detection target object including a magnetic body existing in the ground. Prior Art Documents Patent Documents

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2023-007073 Summary of the Invention (Problems to be Solved by the Invention)

[0004] However, in the magnetic detection method of Patent Document 1, if there is a magnetic body other than the detection target object, it will be affected by it, and sometimes the detection target object cannot be accurately detected.

[0005] Therefore, an object of the present invention is to provide a magnetic detection method and a system that can more accurately detect a detection target object. (Technical Solution for Solving the Problems)

[0006] A magnetic detection method for detecting a detection target object including a magnetic body of the present embodiment. The magnetic detection method includes: a step of setting a coordinate system in a detection area where a detection target object is inferred to exist, and measuring the magnetic field vectors of a plurality of measurement points in the coordinate system by a movable first magnetic field sensor; a step of measuring a reference magnetic field vector in the coordinate system in the detection area; a step of calculating the vector difference between each magnetic field vector measured at the measurement point and the reference magnetic field vector; and a step of inferring the position of the detection target object based on the vector difference of each measurement point.

[0007] Preferably, the step of measuring the reference magnetic field vector includes: a step of setting one or more reference magnetic field sensors for measuring the reference magnetic field vector in the detection area and / or near the detection area. The reference magnetic field vector measured by a reference magnetic field sensor is regarded as the reference magnetic field vector, or the average value of the reference magnetic field vectors measured by two or more reference magnetic field sensors is regarded as the reference magnetic field vector. Furthermore, preferably, in the step of calculating the vector difference, the moments when the magnetic field vectors at multiple measurement points are measured by the first magnetic field sensor are synchronized with the moment when the reference magnetic field vector is measured by the reference magnetic field sensor.

[0008] A magnetic detection method for detecting a detection object including the magnetic body of the present embodiment. The magnetic detection method includes: a step of setting a coordinate system in a detection area where a detection object is inferred to exist, and measuring the detection magnetic field vectors at multiple measurement points in the coordinate system by a movable first magnetic field sensor; a step of calculating a reference magnetic field vector based on the detection magnetic field vectors measured by the first magnetic field sensor; a step of calculating the vector difference between each detection magnetic field vector measured at the measurement point and the reference magnetic field vector; and a step of inferring the position of the detection object based on the vector difference for each measurement point.

[0009] Alternatively, the magnetic field vectors at multiple points in the detection area may be measured by a movable second magnetic field sensor, and the average value of the magnetic field vectors at multiple points may be regarded as the reference magnetic field vector. In addition, the first magnetic field sensor and the second magnetic field sensor may be the same magnetic field sensor.

[0010] Alternatively, in the step of inferring the position of the detection object, for each measurement point, the S magnetic field vector of the detection object based on the S pole and the N magnetic field vector based on the N pole obtained by synthesizing the vector differences are calculated; the distances between the measurement point and other measurement points are calculated; and the position of the detection object is inferred based on the crossing angles of the S magnetic field vectors of the measurement point and other measurement points, the crossing angles of the N magnetic field vectors of the measurement point and other measurement points, and the distances. In addition, alternatively, in the step of inferring the position of the detection object, the position of the S pole of the detection object is inferred based on the crossing angle of the S magnetic field vectors of the measurement point and other measurement points and the distance; the position of the N pole of the detection object is inferred based on the crossing angle of the N magnetic field vectors of the measurement point and other measurement points and the distance; and the size of the detection object is inferred based on the positions of the S pole and the N pole.

[0011] A magnetic detection system for detecting a detection object including the magnetic body of the present embodiment has: a movable first magnetic field sensor that measures the detection magnetic field vectors of a plurality of measurement points in a coordinate system in a detection area where a detection object is inferred to exist; a reference magnetic field sensor that measures the reference magnetic field vector in the coordinate system in the detection area; a differential calculation unit that calculates the vector difference between each detection magnetic field vector measured at the measurement point and the reference magnetic field vector; and an inference unit that infers the position of the detection object based on the vector difference of each measurement point.

[0012] In addition, a magnetic detection system for detecting a detection object including the magnetic body of the present embodiment has: a movable first magnetic field sensor that measures the detection magnetic field vectors of a plurality of measurement points in a three-dimensional orthogonal coordinate system in a detection area where a detection object is inferred to exist; a calculation unit that calculates the reference magnetic field vector of the detection area based on the detection magnetic field vector of the first magnetic field sensor; a differential calculation unit that calculates the vector difference between each detection magnetic field vector measured at the measurement point and the reference magnetic field vector; and an inference unit that infers the position of the detection object based on the vector difference of each measurement point. (Advantages of the Invention)

[0013] The magnetic detection method of the present invention can detect the position of the detection object more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A diagram showing a magnetic detection system 100 that uses an unmanned aircraft flying in the air to detect a detection object. Figure 2 An image cross-sectional view of the geomagnetism in the case where there is a detection object including a magnetic body and in the case where there is no detection object including a magnetic body. Figure 3 A diagram showing a magnetic detection system 110 that detects a detection object by a vehicle traveling on land. Figure 4 A conceptual three-dimensional view of the reference magnetic field sensor 20 or the detection magnetic field sensor 30. Figure 5 In Figure 5 (A) is a flowchart of the magnetic detection method 1, Figure 5 (B) is a first example of calculating the reference magnetic field vector based on the detection magnetic field vector, Figure 5 (C) is a second example of calculating the reference magnetic field vector based on the detection magnetic field vector. Figure 6 A flowchart of the magnetic detection method 2. Figure 7A conceptual diagram showing the correlations of the measured detection magnetic field vector EF, reference magnetic field vector RF, magnetic field vector MF of the object MM to be detected, magnetic field vector MN generated by the N pole, and magnetic field vector MS generated by the S pole. It should be noted that Figure 7 It is a conceptual diagram when observing the location of Tokyo from the east side. Figure 8 In Figure 8 (A) of is a conceptual diagram showing the presence of the magnetic field vector MF of the object MM to be detected on the magnetic flux line based on the object MM to be detected. Figure 8 (B) of is a conceptual diagram for inferring the position and size of the object MM to be detected based on the magnetic field vectors MS and MN at the measurement points SU1 and SU2. It should be noted that Figure 8 (A) and (B) of are conceptual diagrams when observing the location of Tokyo from the east side. Detailed implementation mode

[0015] Hereinafter, the applicant will explain in detail the implementation mode of the present invention with reference to the attached drawings. It should be noted that in this specification and the attached drawings, for components having substantially the same functional configuration, the same reference numerals are given and repeated explanations are omitted. In addition, the drawings are not drawn according to the actual size.

[0016] <First Embodiment> <Outline 1 of the Magnetic Detection System> Figure 1 It is a conceptual diagram of the magnetic detection system 100 of the first embodiment, showing a state where an unmanned aircraft (generally called an aerial drone.) 45 flying in the air is used to detect an object MM to be detected including a magnetic body sunk in water WA. The magnetic detection system 100 includes one or more detection magnetic field sensors 30, and a computer 50 that calculates the detection magnetic field vector (hereinafter referred to as the detection magnetic field) in a three-dimensional orthogonal coordinate system (hereinafter called the coordinate system) from the detection magnetic field sensors 30. The detection magnetic field sensors 30 are mounted on the unmanned aircraft 45 so as to be able to move over the detection area where the object MM to be detected is inferred to exist. The details of the detection magnetic field sensors 30 will be described later.

[0017] It should be noted that the computer 50 does not need to be a computer configured on the ground surface SE, and can be a smart phone carried by an operator or a virtual computer in the cloud. In addition, the detection magnetic field sensors 30 may also include the computer 50 that calculates the detection magnetic field.

[0018] The unmanned aircraft 45 preferably flies in detection areas at different altitudes for the reference magnetic field vector (hereinafter referred to as the reference magnetic field) and the detection magnetic field. When detecting the detection object MM, the unmanned aircraft 45 flies on the plane 39 of the detection area at a height h0 relative to the water surface or the ground surface, and the detection magnetic field sensor 30 outputs the detection magnetic field (DX, DY, DZ). If there is no operator or obstacle, etc., the height h0 is preferably 0.5 m to 2 m above the water surface or the ground surface. It is preferable to fly as close as possible to the height of the detection object MM. This is because it is easier to be affected by the magnetic field of the detection object MM when approaching the detection object MM. In Figure 1 24 measurement points (detection points) SU are drawn in the detection area 39 at the height h0, but if the detection magnetic field sensor 30 sends the detection magnetic field at a sampling period of, for example, 1 second, the number of measurement points reaches tens of thousands.

[0019] The detection magnetic field of the detection magnetic field sensor 30 is sent to the computer 50 by wired communication or wireless communication. Even if the detection magnetic field sensor 30 has no communication function, the detection magnetic field can be stored from the detection magnetic field sensor 30 to a portable recording medium (SD (registered trademark) card, USB memory, etc.), and the operator connects the recording medium to the computer 50.

[0020] When flying the unmanned aircraft 45 in the reference magnetic field, it preferably flies in the detection area 35 at a height h5 relative to the water surface or the ground surface, and the detection magnetic field sensor 30 outputs the detection magnetic field for the reference magnetic field. Since the deformation based on the magnetic field of the detection object MM becomes smaller at the height h5, it is preferable to fly as high as possible, for example, at an altitude of more than 20 m. 24 measurement points SU are drawn in the detection area 35 at the height h5, but actually the number of measurement points reaches tens of thousands. It should be noted that Figure 1 both the detection area 35 and the detection area 39 are drawn as one area, but if it is a very large detection area, it can also be divided into multiple detection areas.

[0021] The computer 50 has: a reference magnetic field calculation unit 51 that calculates the reference magnetic field based on the detection magnetic field; a difference calculation unit 53 that calculates the vector difference between each detection magnetic field measured at the measurement point and the reference magnetic field; and a position inference unit 55 that infers the position and size of the detection object based on the vector difference for each measurement point. Furthermore, the computer 50 may also have a communication unit, etc.

[0022] (Related to geomagnetism) The applicant uses here Figure 2 to explain the change in the geomagnetism generated by the detection object MM. Similarly, the state in which the detection object MM sinks into the water WA is drawn, but in Figure 1 the same way, and Figure 2The cross-sectional image is drawn therein. Figure 2 In the figure, the parallel dotted lines drawn obliquely indicate the geomagnetism in a state where the influence of the detection object MM is small (or the state where the detection object MM does not exist), and the solid curve indicates the deformation of the magnetic field based on the detection object MM.

[0023] The detection magnetic field sensor 30 mounted on the unmanned aircraft 45 measures the detection magnetic field at the measurement point SU in the plane 39 of the detection area at the height h0 and outputs the detection magnetic field. In a state where the detection object MM does not exist, the output signal RF is an arrow (vector) drawn by a dotted line, which is a vector with almost constant direction and magnitude. Strictly speaking, the geomagnetism changes due to time, location, etc. On the other hand, in a state where the detection object MM exists, the output signal EF is drawn by a solid line, and the direction and magnitude of the output signal EF are vectors pulled by the detection object MM. In the present embodiment, the position and / or size of the detection object MM are inferred based on the vector difference between the reference magnetic field RF in a state where the influence of the detection object MM is almost non-existent or the influence of the detection object MM is reduced and the detection magnetic field EF in a state where the detection object MM exists.

[0024] The accuracy of inferring the position and / or size of the detection object MM is improved for the side with more measurement points SU of the vector difference between the reference magnetic field RF and the detection magnetic field EF. The plane 39 of the detection area at the height h0 includes not only one layer but also two layers including the plane 38 of the detection area at the height h1. If the number of layers is increased, the number of measurement points increases, and the accuracy of inferring the position and / or size of the detection object MM is further improved. It should be noted that Figure 1 and Figure 2 In the figure, it has been described on the premise that the height of the measurement point SU on the plane of the detection area is constant, but the height of the detection area can also vary for each measurement point. In addition, during flight, the unmanned aircraft 45 sometimes rotates around the roll axis, pitch axis, or yaw axis. At this time, the detection magnetic field sensor 30 also rotates around the roll axis, pitch axis, or yaw axis. As will be described later, it is preferable that the output signals (DX, DY, DZ) of the three axes of the detection magnetic field sensor 30 are corrected so as to be consistent with the set coordinate system.

[0025] It should be noted that in the first embodiment, the reference magnetic field RF is calculated based on the detection magnetic field in the detection area 35 at the height h5 and at multiple measurement points, but the reference magnetic field RF can also be calculated based on the detection magnetic field on the plane 39 of the detection area at the height h0.

[0026] In addition, in the first embodiment, although the reference magnetic field sensor 20 described in the following second embodiment is not prepared, one or more reference magnetic field sensors 20 may be prepared. The reference magnetic field sensor 20 can also be used to measure the reference magnetic field. Furthermore, the reference magnetic field can also be calculated based on both the reference magnetic field of the reference magnetic field sensor 20 and the detection magnetic field of the detection magnetic field sensor 30 mounted on the unmanned aircraft 45.

[0027] <Second Embodiment> <Outline of Magnetic Detection System 2> Figure 3 FIG. is a conceptual diagram of the magnetic detection system 110 according to the second embodiment, showing a state in which a vehicle 47 traveling on land is used to detect a detection object MM including a magnetic body buried in the ground. The magnetic detection system 110 includes: one or more reference magnetic field sensors 20; one or more detection magnetic field sensors 30; and a computer 50 that infers the position of the detection object MM based on the reference magnetic field of the reference magnetic field sensor 20 or the detection magnetic field of the detection magnetic field sensor 30. The detection magnetic field sensor 30 is mounted on the vehicle 47 so that it can move in the detection area where the detection object MM is inferred to exist. In other words, in the second embodiment, the reference magnetic field sensor 20 that was not prepared in the first embodiment is prepared. The computer 50 can also be a smartphone or a cloud computer, etc., as in the first embodiment.

[0028] The reference magnetic field sensor 20 outputs the reference magnetic field (DX, DY, DZ) every 1 second, for example. The reference magnetic field sensor 20 is disposed on the ground surface SE, for example, during the detection by the detection magnetic field sensor 30 mounted on the vehicle 47. When the detection area is narrow, one reference magnetic field sensor 20 may be set, and when the detection area is large, multiple reference magnetic field sensors 20 may also be set. In Figure 3 this case, four sensors from the reference magnetic field sensor 20-1 to the reference magnetic field sensor 20-4 are disposed at the vertices of a square with a 100 m interval on the ground surface SE, for example. It should be noted that the reference magnetic field sensor 20 may also be disposed within the detection area where the vehicle 47 moves, or may be disposed near the outside of the detection area. In addition, several reference magnetic field sensors 20 may be within the detection area, and the remaining reference magnetic field sensors 20 may be outside the detection area.

[0029] When the reference magnetic field sensor 20 is disposed on the ground SE, it can also be disposed obliquely according to the shape of the ground surface. As will be described later, the output signals (DX, DY, DZ) of the three axes of the four reference magnetic field sensors 20 are corrected so as to be consistent with the set coordinate system. The output signals (DX, DY, DZ) of the four reference magnetic field sensors 20 are sent to the computer 50 by wire communication or wireless communication. Even if the reference magnetic field sensor 20 does not have a communication function, the output signal can be transmitted from the reference magnetic field sensor 20 to a portable recording medium, and the operator connects the portable recording medium to the computer 50.

[0030] The reference magnetic field sensor 20 may also have the same configuration as the detection magnetic field sensor 30, and output output signals (DX, DY, DZ) every constant time (for example, every 1 second). Two or more detection magnetic field sensors 30 may also be mounted on the vehicle 47. In the case of mounting a plurality of them, it is preferable that the detection magnetic field sensors 30 be separated as much as possible. It should be noted that in the first embodiment, it is assumed that the vehicle 47 is a radio-controlled vehicle, and the operator may hold the detection magnetic field sensor 30 and walk instead of the vehicle 47.

[0031] In the second embodiment, an example in which four reference magnetic field sensors 20 are prepared is shown, but there may be no reference magnetic field sensor 20 as in the first embodiment. In the case of no reference magnetic field sensor 20, the reference magnetic field can also be obtained based on the detection magnetic field of one detection magnetic field sensor 30 obtained by the vehicle 47 moving around the ground surface of the detection area.

[0032] <Reference Magnetic Field Sensor (Detection Magnetic Field Sensor)> The reference magnetic field sensor 20 and the detection magnetic field sensor 30 may basically have the same structure, and therefore the applicant will mainly describe with the reference magnetic field sensor 20 as a representative.

[0033] Figure 4 The shown reference magnetic field sensor 20 is composed of a base portion 23 and a rod-shaped portion 21 mounted on the base portion 23. The rod-shaped portion 21 is formed in a shape where three rods cross toward an orthogonal coordinate system. The reference magnetic field sensor 20 may also include a fixing pile or the like for setting on a protection cover (not shown) or the ground surface. The rod-shaped portion 21 and the base portion 23 are preferably made of a non-magnetic material such as synthetic resin.

[0034] The reference magnetic field sensor 20 uses, for example, an electromagnetic coil as the magnetic field sensor 22 with sensitivity in a specific axial direction, and combines electromagnetic coils arranged in three axial directions. In other words, the rod-shaped portion 21 extending in the X-axis direction is provided with the X-axis electromagnetic coil 22X, the rod-shaped portion 21 extending in the Y-axis direction is provided with the Y-axis electromagnetic coil 22Y, and the rod-shaped portion 21 extending in the Z-axis direction is provided with the Z-axis electromagnetic coil 22Z. In particular, the magnetic field sensor is not limited to an electromagnetic coil, and a fluxgate-type magnetic field sensor or the like can also be used. The analog signals from the magnetic field sensors 22 of these respective axes are converted into digital signals via a low-pass filter, an A / D converter, etc., and are output as output signals (DX, DY, DZ). It should be noted that it is preferable that the output signals are output together with the measured time.

[0035] The reference magnetic field sensor 20 further includes a position / orientation detection unit 24, a communication unit 26, a clock, a battery, etc. The reference magnetic field sensor 20 may also include an arithmetic unit (CPU) that corrects the output of the reference magnetic field of the magnetic field sensor 22 to a set coordinate system.

[0036] The position / orientation detection unit 24 determines the position of the reference magnetic field sensor 20. In addition, in order to correct the coordinate system in the case of the direction change or inclination of the magnetic field sensor 22, the position / orientation detection unit 24 detects the orientation, etc. of the reference magnetic field sensor 20. The reference magnetic field sensor 20 provided on the ground surface SE or the like may sometimes be provided on, for example, an inclined ground surface SE. In addition, the detection magnetic field sensor 30 mounted on the vehicle 47 or the unmanned aircraft 45 changes its direction or rotates due to vibration or the like during movement. Therefore, the respective axial directions of the magnetic field sensor 22 do not necessarily face the X-axis direction, the Y-axis direction, and the Z-axis direction, and thus it is desirable to correct the output signals of these respective axial directions to the set coordinate system. The position / orientation detection unit 24 detects the position / orientation of the reference magnetic field sensor 20. Specifically, the position / orientation detection unit 24 includes a self-positioning device such as GNSS (Global Navigation Satellite System), camera measurement, or laser measurement. Furthermore, it may also include a self-positioning device such as an inertial device (a motion sensor composed of an acceleration sensor or a gyro sensor, etc.). It should be noted that in the case where the reference magnetic field sensor 20 does not have the position / orientation detection unit 24, the position / orientation of the reference magnetic field sensor 20 can also be measured by a measuring device (not shown) etc. to determine the position / orientation of the reference magnetic field sensor 20. In other words, the measuring device replaces the position / orientation detection unit 24. It is desirable that the signals of the position / orientation are output together with the measured time.

[0037] The communication unit 26 transmits the output signal of the magnetic field sensor 22, the position of the position / orientation detection unit 24, and the orientation signal to the computer 50 by wire / wireless. It should be noted that in the case where the reference magnetic field sensor 20 does not have the communication unit 28, the operator can also cause the output of the reference magnetic field to be transmitted from the reference magnetic field sensor 20 to a portable recording medium, and connect the portable recording medium to the computer 50.

[0038] For the reference magnetic field sensor 20 (detection magnetic field sensor 30) of the first embodiment and the second embodiment, in order to detect the intensity of a magnetic field that is very small relative to the geomagnetism, it is preferable that the sensitivity characteristics in the three axial directions of the magnetic field sensor can be accurately calibrated. Therefore, it is preferable that the sensitivities, offsets, and axis deviations in the three axial directions of the magnetic field sensor 22 are equal. In order to make the sensitivities, offsets, and axis deviations of these magnetic field sensors equal, it is desirable to incorporate a predetermined correction coefficient into the reference magnetic field sensor 20. The electromagnetic coil 22 of the reference magnetic field sensor 20 is placed on a rotating table (not shown) so as to coincide with the rotation axis of the rotating table by the correction coefficient. Moreover, the rotating table can also be rotated, the output of the reference magnetic field sensor 20 can be obtained, the correction coefficient that makes the variation of this output constant can be obtained, and this correction coefficient can be stored in a memory or the like.

[0039] <Magnetic Detection Method 1> Figure 5 (A) is a flowchart showing the magnetic detection method used in the magnetic detection systems of the first embodiment and the second embodiment. Figure 5 (A) is an example of the case where the magnetic detection system 100 or the magnetic detection system 110 does not include the reference magnetic field sensor 20. Therefore, if necessary, reference can be made to the one without the reference magnetic field sensor 20 drawn Figure 1 .

[0040] In step S51, the detection magnetic field sensor 30 mounted on the unmanned aircraft 45 or the vehicle 47 measures the detection magnetic field in the three axial directions (X, Y, Z) at each predetermined time (sampling period). Matching this measurement, the position / orientation detection unit 24 detects the position of the detection magnetic field sensor 30, and also detects how much the three axial directions of the detection magnetic field sensor 30 deviate from the set coordinate system (including the roll axis, pitch axis, or yaw axis in the three axial directions). It should be noted that the set coordinate system can also set, for example, the east direction (+y direction) of the earth, the north direction (+x direction), and the normal direction (z direction) of the plane including east, west, south, and north as three-dimensional orthogonal coordinates. Other arbitrary coordinate systems can also be set.

[0041] If referring to Figure 1, the detection magnetic field sensor 30 mounted on the unmanned aircraft 45 measures the detection magnetic field at the detection area 35 at the altitude h5 and at a plurality of measurement points SU (times t0, t1, …, t99). Then, the unmanned aircraft 45 moves to the altitude h0 and flies over the plane 39 of the detection area at the altitude h0, and the detection magnetic field sensor 30 measures the detection magnetic field at a plurality of measurement points SU (times t100, t101, …, t199). It should be noted that the unmanned aircraft 45 may first fly over the plane 39 of the detection area at the altitude h0 and then fly in the detection area 35 at the altitude h5 to measure the detection magnetic field. The detection magnetic field may also be measured by the detection magnetic field sensor mounted on another unmanned aircraft in the reference magnetic field.

[0042] In step S52, the detection magnetic field (times t0, t1, …, t100, …, t199) measured in step S51 is corrected to the set coordinate system based on the position / orientation detected by the position / orientation detection unit 24 provided in the detection magnetic field sensor 30. In other words, in steps S51 and S52, the detection magnetic field at the measurement points in the measurement coordinate system is measured.

[0043] In step S53, the reference magnetic field is calculated based on the corrected detection magnetic field. The calculation method is described in detail in Figure 5 (B) and (C) thereof.

[0044] In step S54, the differential calculation unit 53 calculates the vector difference between the detection magnetic field EF (coordinate correction completed) after step S52 and the reference magnetic field RF (coordinate correction completed) in step S53. This vector difference can be regarded as the object magnetic field vector generated by the detection object MM. The magnetic field vector generated only by this detection object MM is called the object magnetic field vector (hereinafter referred to as the object magnetic field) MF. In addition, the detection object MM including the magnetic body has an S pole and an N pole according to the geomagnetism.

[0045] In step S55, based on the vector difference (object magnetic field MF) obtained in step S54, the position inference unit 55 calculates the N magnetic field vector (hereinafter referred to as the N magnetic field) MN generated by the N pole of the detection object MM and the magnetic field vector generated by the S pole (hereinafter referred to as the S magnetic field) MS. Then, the position inference unit 55 calculates the distance LL between a certain measurement point SU and other measurement points SU. By calculating the N magnetic field MN, S magnetic field MS of a plurality of measurement points and the distance LL between these plurality of measurement points, the position inference unit 55 can infer the position and / or size of the detection object MM. The inference calculation of the position and size of the detection object MM is described later in Figure 7 and Figure 8 below.

[0046] It should be noted that in the above description, the detection magnetic field sensor 30 mounted on the unmanned aerial vehicle 45 measures the detection magnetic field in the detection area 39 at height h0 and the detection area 35 at height h5. However, it is also possible not to measure in the detection area 35 at height h5, but to calculate the reference magnetic field based on the detection magnetic field measured in the detection area 39 at height h0. However, this reference magnetic field is easily affected by the magnetic field generated by the detection object MM. In addition, the detection magnetic field sensor 30 may only perform step S51, and the computer 50 may calculate steps S52 to S55, or steps S51 to S55 may be calculated within the detection magnetic field sensor 30.

[0047] (Calculation of reference magnetic field based on time averaging) Figure 5 (B) in is the first example of calculating the reference magnetic field by the reference magnetic field calculation unit 51 based on the detection magnetic field measured by the detection magnetic field sensor 30. The first example is a method of averaging the detection magnetic fields measured at different times (t0 to t99) and taking the average value as the reference magnetic field. For example Figure 1 In, the unmanned aerial vehicle 45 flies from time t0 to time t99 over the entire area of the detection area 35 at height h5, and measures the detection magnetic field at each time. The reference magnetic field calculation unit 51 sets the reference magnetic field by averaging the 100 measured detection magnetic fields. It should be noted that in addition to averaging all the measured detection magnetic fields, when it is possible to clearly determine that the detection magnetic field includes abnormal signals, the reference magnetic field calculation unit 51 may also exclude these detection magnetic fields for averaging, or average the discrete detection magnetic fields such as at times t0, t9, t19... t99.

[0048] (Calculation of reference magnetic field based on spatial averaging) Figure 5 (C) in is the second example of calculating the reference magnetic field by the reference magnetic field calculation unit 51 based on the detection magnetic field measured by the detection magnetic field sensor 30. The reference magnetic field calculation unit 51 averages the detection magnetic fields measured at different positions and takes the average value as the reference magnetic field. For example, the reference magnetic field calculation unit 51 averages the detection magnetic fields at 24 points in the detection area 35 at height h5 shown in Figure 1 as the reference magnetic field.

[0049] (Calculation of reference magnetic field based on other methods) Although not particularly illustrated, especially when it is possible to be far from the ground or water surface (e.g., 100 m) as in the case of the unmanned aerial vehicle 45, the detected magnetic field measured only once by the detection magnetic field sensor 30 at 100 m can be used as the reference magnetic field. This is because if at a height of 100 m or more, it is almost not affected by the magnetic field of the detection target object MM buried in the ground or water.

[0050] <Magnetic detection method 2> Figure 6 It is a flowchart showing the magnetic detection method used in the magnetic detection systems of the first embodiment and the second embodiment. Figure 6 It is an example of the case where the magnetic detection system 100 or the magnetic detection system 110 includes the reference magnetic field sensor 20. Therefore, when necessary, reference can be made to the one Figure 3 .

[0051] In step S61, preferably, the reference magnetic field sensor 20 provided on the ground surface or the like measures the reference magnetic field in three axes (X, Y, Z) at each predetermined time (sampling period (t0 to t99)). Matching this measurement, the position / orientation detection unit 24 detects the position of the reference magnetic field sensor 20 and detects how much the three axes of the reference magnetic field sensor 20 deviate from the set coordinate system (including the roll axis, pitch axis, or yaw axis of the three axes). It should be noted that since the reference magnetic field sensor 20 is provided on the ground surface SE, the position / orientation detection unit 24 does not need to perform detection at each sampling period and can also be detected only once. If reference is made to Figure 3 , four reference magnetic field sensors 20 are provided near the outside of the detection area where the vehicle 47 travels, but the reference magnetic field sensor 20 can also be provided within the detection area.

[0052] In step S62, the reference magnetic field (time t0, t1... t99) measured in step S61 is corrected to the set coordinate system based on the position / orientation detected by the position / orientation detection unit 24 of the reference magnetic field sensor 20. In other words, in steps S61 and S62, the reference magnetic field of the set coordinate system is calculated.

[0053] In step S63, the reference magnetic fields (coordinate correction completed) output from the four reference magnetic field sensors 20 are averaged at each sampling period and regarded as the reference magnetic field. It should be noted that in the case where only one reference magnetic field sensor 20 is provided, this one reference magnetic field (coordinate correction completed) is regarded as the reference magnetic field for each sampling period. It is also possible to average the reference magnetic fields of all sampling periods regardless of the sampling period and regard it as the reference magnetic field.

[0054] In step S64, the detection magnetic field sensor 30 mounted on the unmanned aircraft 45 or the vehicle 47 measures the detection magnetic field in three axes (X, Y, Z) at each predetermined time (sampling period (t0 to t99)). Matching this measurement, the position / orientation detection unit 24 detects the position of the detection magnetic field sensor 30 and detects how much the three axes of the detection magnetic field sensor 30 deviate from the set coordinate system (including the roll axis, pitch axis, or yaw axis of the three axes). For the sake of explanation, step S64 is described after step S61, but since the geomagnetism changes over time, it is preferable to measure the detection magnetic field synchronously with step S61 (a difference in measurement times of less than 1 second is regarded as synchronization).

[0055] In step S65, the detection magnetic field measured in step S64 (times t0, t1...t99) is corrected to the set coordinate system based on the position / orientation detected by the position / orientation detection unit 24. In other words, in steps S64 and S65, the detection magnetic field of the measurement point in the measurement coordinate system is measured.

[0056] In step S66, preferably, the differential calculation unit 53 calculates the vector difference between the reference magnetic field RF in step S63 and the detection magnetic field EF after step S65 at each time (t0 to t99). Strictly speaking, the geomagnetism changes over time, so if the vector difference is calculated at each time, a high-precision vector difference can be obtained. This vector difference can be regarded as the object magnetic field vector generated by the detection object MM.

[0057] In step S67, based on the vector difference (object magnetic field MF) obtained in step S66, the position inference unit 55 calculates the N magnetic field MN generated by the N pole of the detection object MM and the S magnetic field MS generated by the S pole. Further, the position inference unit 55 calculates the distance LL between a certain measurement point SU and other measurement points SU. By calculating the N magnetic field MN, S magnetic field MS of multiple measurement points and the distance LL between these multiple measurement points, the position inference unit 55 can infer the position and size of the detection object MM. The inference calculation of the position and size of the detection object MM is described in Figure 7 and Figure 8 described later.

[0058] It should be noted that Figure 6 in the magnetic detection method 2 shown, the detection magnetic field output from the detection magnetic field sensor 30 is not used as the reference magnetic field. However, the average value of the reference magnetic field from the reference magnetic field sensor 20 and the detection magnetic field from the detection magnetic field sensor 30 can also be synthesized as the reference magnetic field.

[0059] (Position and size of the detection object MM) A method for inferring the position and / or size of the detected object MM inferred in steps S55 and S67 is described using Figure 7 and Figure 8 is explained.

[0060] Figure 7 and Figure 8 is an example of the case of magnetic detection at a position in Tokyo Metropolis, and is a conceptual diagram viewed from the east direction towards the west direction. The inclination of the geomagnetic field in Tokyo Metropolis is 49°, Figure 7 and Figure 8 is a top view drawn with an inclination of the geomagnetic field of 49° and a declination of 0°. The inclination and declination are explained in the lower left figure of Figure 7 .

[0061] Figure 7 and Figure 8 show examples of measuring the detected magnetic field EF at two measurement points SU1 and SU2. In addition, the detected object MM including the magnetic body is buried in the ground at a certain depth from the ground surface SE and has an S pole and an N pole based on the geomagnetic field. The reference magnetic field RF is at least one of the reference magnetic field calculated based on the detected magnetic field EF and / or the reference magnetic field output from the reference magnetic field sensor 20 as explained in the flowcharts of Figure 5 or Figure 6 .

[0062] In Figure 7 , the magnetic field vectors of the measurement points SU1 and SU2 are shown magnified within the range surrounded by a circle. The object magnetic field MF of the detected object MM is the vector difference (object magnetic field MF) obtained by subtracting the reference magnetic field RF from the detected magnetic field EF. This object magnetic field MF is the composite vector of the S magnetic field MS (double-dashed line) based on the S pole of the detected object MM and the N magnetic field MN (single-dashed line) based on the N pole. The position inference unit 55 calculates the S magnetic field MS and the N magnetic field MN based on the vector difference.

[0063] Figure 8 (A) is a conceptual diagram showing a magnetic flux line FL passing through the S pole and the N pole of the detected object MM. The object magnetic field MF exists on the magnetic flux line FL. Figure 8 In (A) of , for the sake of easy understanding, an example is shown where the magnetic flux line passing through the measurement point SU1 and the magnetic flux line passing through the measurement point SU2 exist on the same magnetic flux line FL. In many cases, generally, if the measurement points SU are different, different magnetic flux lines pass through.

[0064] Figure 8Part (B) of the figure is a conceptual diagram for inferring the position and size of the detection target object MM based on the N magnetic field MN and the S magnetic field MS. The position / orientation detection unit 24 provided in the detection magnetic field sensor 30 is used to detect the positions (X, Y, Z) of the measurement points SU1 and SU2. In other words, the position inference unit 55 can calculate the distance LL between the measurement point SU1 and the measurement point SU2. In addition, the position inference unit 55 can calculate the crossing angle between the S magnetic field MS (double-dashed line) based on the S pole of the measurement point SU1 and the S magnetic field MS (double-dashed line) based on the S pole of the measurement point SU2. Based on the crossing angle and the distance LL, the distance from the measurement point SU1 or the measurement point SU2 can be calculated. Thus, the position (X, Y, Z) of the S pole of the detection target object MM can be inferred. Similarly, the position inference unit 55 can calculate the distance from the measurement point SU1 or the measurement point SU2 according to the crossing angle between the N magnetic field MN (single-dashed line) based on the N pole of the measurement point SU1 and the N magnetic field MN (single-dashed line) based on the N pole of the measurement point SU2 and the distance LL. Thus, the position inference unit 55 can infer the position (X, Y, Z) of the N pole of the detection target object MM. In other words, the position inference unit 55 can infer the position of the detection target object MM as the position that equally divides the positions of the S pole and the N pole. It is also possible to infer the position of the S pole or the N pole as the position of the detection target object MM instead of the position that equally divides the positions of the S pole and the N pole.

[0065] In addition, since the distance between the position of the S pole and the position of the N pole of the detection target object MM can be calculated, the size of the detection target object MM can be inferred based on this distance. (Industrial Applicability)

[0066] In the first embodiment, a magnetic detection system using the unmanned aircraft 45 is described, and in the second embodiment, a magnetic detection system using the vehicle 47 that travels on land is described. Especially when detecting a detection target object MM in deep water (sea), an unmanned submarine (underwater drone) can be used. Even in water, the reference magnetic field can be measured by the reference magnetic field sensor 20 or the detection magnetic field can be measured by the detection magnetic field sensor 30. On the other hand, a position / orientation detection unit 24 such as GNSS cannot be used in water, so it is preferable to use at least one or more self-positionings such as acoustic positioning, laser measurement, and inertial devices. When GNSS is the position / orientation detection unit 24, it is preferable to make the position / orientation detection unit 24 float on the water. In addition, the magnetic field output signal of the reference magnetic field sensor 20 or the detection magnetic field sensor 30 in water is preferably output by acoustic communication, optical communication, or wired communication using a cable, etc.

[0067] In the first embodiment and the second embodiment, a method for detecting a detection target including a magnetic body on the earth has been mainly described. However, this embodiment can also detect a detection target in the universe such as the moon or Mars. For example, on the surface of a satellite or a planet, as described in the second embodiment, a detection magnetic field sensor 30 can be mounted on a rover that moves on the ground surface of the satellite or the planet to measure the detection magnetic field. In addition, the detection magnetic field sensor 30 can be mounted on a detector (suspended by a propeller or suspended by gas injection) that can fly at a very low altitude on the surface of a satellite or a planet to measure the detection magnetic field.

[0068] It should be noted that in the universe such as a satellite or a planet, GNSS cannot be used as the position / orientation detection unit 24, but at least one or more position / orientation detection units 24 such as camera measurement, laser measurement, and inertial devices can be used to detect the position / orientation of the reference magnetic field sensor 20 or the detection magnetic field sensor 30.

[0069] In the first embodiment and the second embodiment, a method for detecting a detection target including a magnetic body buried in soil or water has been mainly described. However, it is not limited to this. The system and method of this embodiment can detect detection targets that cannot be visually seen, such as detection targets covered by thick trees and detection targets that are difficult to find due to falling into gaps. In addition, the detection magnetic field sensor 30 can be moved around a human body, and the position of a capsule-type gastric camera can be detected based on the detection magnetic field. (Reference numeral description)

[0070] 100, 110: Magnetic detection system 20: Reference magnetic field sensor 24: Position / orientation detection unit 26: Communication unit 30: Detection magnetic field sensor 45: Unmanned aircraft 47: Vehicle 50: Computer EF: Detection magnetic field vector RF: Reference magnetic field vector MM: Detection target MF: Object magnetic field vector of the detection target MN: N magnetic field vector based on the N pole MS: S magnetic field vector based on the S pole SE: Ground surface SU (SU1, SU2): Measurement point.

Claims

1. A magnetic detection method for detecting a detection object including a magnetic body, the magnetic detection method comprising: Setting a three-dimensional orthogonal coordinate system as a coordinate system in a detection area inferred to have the detection object, and measuring magnetic field vectors at a plurality of measurement points in the coordinate system by a movable first magnetic field sensor; Measuring a reference magnetic field vector in the coordinate system in the detection area; Calculating a vector difference between each magnetic field vector measured at the measurement point and the reference magnetic field vector; and Inferring the position of the detection object based on the vector difference for each measurement point.

2. The magnetic detection method according to claim 1, wherein: The step of measuring the reference magnetic field vector includes: arranging one or more reference magnetic field sensors for measuring the reference magnetic field vector in the detection area and / or near the detection area, Regarding the reference magnetic field vector measured by one of the reference magnetic field sensors as the reference magnetic field vector, or regarding the average value of the reference magnetic field vectors measured by two or more of the reference magnetic field sensors as the reference magnetic field vector.

3. The magnetic detection method according to claim 2, wherein: In the step of calculating the vector difference, the time when the magnetic field vectors at a plurality of measurement points are measured by the first magnetic field sensor is synchronized with the time when the reference magnetic field vector is measured by the reference magnetic field sensor.

4. A magnetic detection method for detecting a detection object including a magnetic body, the magnetic detection method comprising: Setting a three-dimensional orthogonal coordinate system as a coordinate system in a detection area inferred to have the detection object, and measuring a detected magnetic field vector at a plurality of measurement points in the coordinate system by a movable first magnetic field sensor; Calculating a reference magnetic field vector based on the detected magnetic field vector measured by the first magnetic field sensor; Calculating a vector difference between each detected magnetic field vector measured at the measurement point and the reference magnetic field vector; and Inferring the position of the detection object based on the vector difference for each measurement point.

5. The magnetic detection method according to claim 4, wherein: Performing multi-point measurement of the magnetic field vector in the detection area by a movable second magnetic field sensor, and regarding the average value of the magnetic field vectors at multiple points as the reference magnetic field vector.

6. The magnetic detection method according to claim 5, wherein: The first magnetic field sensor and the second magnetic field sensor are the same magnetic field sensor.

7. The magnetic detection method according to claim 1 or 4, wherein: The step of inferring the position of the detection object includes: Calculating, for each measurement point, an S magnetic field vector of the detection object based on the S pole and an N magnetic field vector based on the N pole for synthesizing the vector difference; Calculating the distance between the measurement point and other measurement points; And Inferring the position of the detection object based on the crossing angle of the S magnetic field vectors of the measurement point and other measurement points, the crossing angle of the N magnetic field vectors of the measurement point and other measurement points, and the distance.

8. The magnetic detection method according to claim 7, wherein, in the process of inferring the position of the detection object, based on the cross angle and the distance of the S magnetic field vectors of the measurement point and the other measurement points, infer the position of the S pole of the detection object, based on the cross angle and the distance of the N magnetic field vectors of the measurement point and the other measurement points, infer the position of the N pole of the detection object, based on the positions of the S pole and the N pole, infer the size of the detection object.

9. A magnetic detection system for detecting a detection object including a magnetic body, the magnetic detection system having: a movable first magnetic field sensor that measures detection magnetic field vectors of a plurality of measurement points in a three-dimensional orthogonal coordinate system serving as a coordinate system in a detection area where the detection object is inferred to exist; a reference magnetic field sensor that measures a reference magnetic field vector in the coordinate system in the detection area; a differential calculation unit that calculates a vector difference between each detection magnetic field vector measured at the measurement point and the reference magnetic field vector; and an inference unit that infers the position of the detection object based on the vector difference of each measurement point.

10. A magnetic detection system for detecting a detection object including a magnetic body, the magnetic detection system having: a movable first magnetic field sensor that measures detection magnetic field vectors of a plurality of measurement points in a three-dimensional orthogonal coordinate system in a detection area where the detection object is inferred to exist; a calculation unit that calculates a reference magnetic field vector of the detection area based on the detection magnetic field vector of the first magnetic field sensor; a differential calculation unit that calculates a vector difference between each detection magnetic field vector measured at the measurement point and the reference magnetic field vector; and an inference unit that infers the position of the detection object based on the vector difference of each measurement point.

Images