Underground target positioning method based on rotary permanent magnet type magnetic beacon

Abstract

The invention discloses an underground target positioning method based on a rotary permanent magnet type magnetic beacon, and belongs to the field of navigation, guidance and control. According to the invention, the problem of low precision of an existing positioning method caused by attitude errors in an underground positioning scene is solved. The method specifically comprises the following steps of: 1, respectively placing four same rotary permanent magnet type magnetic beacons at four points with known spatial positions, and respectively rotating the four magnetic beacons around a fixed shaft at a set rotating speed; 2, placing a magnetic sensor at an underground target point, and collecting mixed alternating magnetic field data under a sensor coordinate system by using the magnetic sensor; step 3, filtering the acquired mixed alternating magnetic field data by using a designed band-pass filter to obtain an alternating magnetic field vector of each rotating permanent magnet type magnetic beacon at the underground target point; constructing a positioning model according to the alternating magnetic field vector; and 4, obtaining an estimated target point position according to the positioning model. The method can be applied to underground target positioning.

Description

Technical Field

[0001] The present invention belongs to the field of navigation, guidance and control, and particularly relates to an underground target positioning method based on a rotating permanent magnet type magnetic beacon. Background Art

[0002] In recent years, with the continuous expansion and deepening of the industrial field, the navigation and positioning technology for underground scenarios has become increasingly important and has gradually become an indispensable core support force in many industrial application scenarios, especially in industries with extremely high accuracy requirements such as well digging and mining, and underground pipeline inspection and maintenance. However, due to their respective limitations, traditional navigation and positioning technologies cannot provide long-term and high-precision positioning services for underground unmanned equipment.

[0003] Ultra-low frequency magnetic field positioning systems have gradually become one of the research focuses for achieving high-precision and long-term stable positioning in satellite-denied scenarios such as underground and indoor due to their strong penetration, high anti-interference ability, and no cumulative error characteristics. In actual positioning scenarios, the attitude error between the magnetic beacon and the sensor relative to the reference coordinate system is the main factor affecting the positioning accuracy. Currently, most studies improve the positioning accuracy by compensating the attitude error of the sensor, often ignoring the attitude error of the magnetic beacon. However, when the road surface in the actual scenario is rough, the attitude error of the magnetic beacon will seriously affect the positioning accuracy.

[0004] In summary, in order to solve the problem of low positioning accuracy of existing methods, it is very necessary to propose a new positioning method to achieve high-precision and strong-robustness positioning services for underground scenarios. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem of low positioning accuracy caused by the attitude error between the magnetic beacon and the sensor relative to the reference coordinate system in the underground positioning scenario, and a method for underground target positioning based on a rotating permanent magnet type magnetic beacon is proposed.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: a method for underground target positioning based on a rotating permanent magnet type magnetic beacon, the method specifically includes the following steps:

[0007] Step 1: Place four identical rotating permanent magnet type magnetic beacons at four points with known spatial positions respectively, and record the position coordinates of the four magnetic beacons in the reference coordinate system as (x1, y1, z1), (x2, y2, z2), (x3, y3, z3) and (x4, y4, z4) respectively; the four magnetic beacons rotate around a fixed axis at rotational speeds n1, n2, n3 and n4 respectively;

[0008] Step 2: Denote the position coordinates of the underground target point in the reference coordinate system as (x, y, z). Place the magnetic sensor at the underground target point, and use the magnetic sensor to collect the hybrid alternating magnetic field data in the x b y b z b of the sensor coordinate system;

[0009] Step 3: Design band-pass filters according to the rotation frequencies of the four magnetic beacons respectively, and then use each designed band-pass filter to filter the hybrid alternating magnetic field data collected in Step 2 to obtain the alternating magnetic field vectors of each rotating permanent magnet type magnetic beacon at the underground target point

[0010] where, represents the components of the alternating magnetic field vector of the 1st magnetic beacon at the underground target point in the directions of each axis of the sensor coordinate system;

[0011] Then, according to and construct a positioning model;

[0012] Step 4: Obtain the estimated position of the target point according to the positioning model constructed in Step 3.

[0013] Furthermore, the rotational speeds n1 = 420 rpm, n2 = 660 rpm, n3 = 1020 rpm, n4 = 1380 rpm.

[0014] Furthermore, the according to and construct a positioning model, specifically:

[0015] Step 3-1: According to the magnetic dipole model, obtain the alternating magnetic field vectors of each rotating permanent magnet type magnetic beacon at the position of the target point in its own body coordinate system

[0016]

[0017] where t represents time;

[0018] M represents the magnitude of the magnetic moment of the permanent magnet;

[0019] μ represents the magnetic permeability of the medium;

[0020] f i represents the rotation frequency of the i-th magnetic beacon;

[0021] φ i represents the initial phase of the i-th magnetic beacon;

[0022] r irepresents the relative distance between the i-th magnetic beacon and the target point in the x i y i z i of the body coordinate system of the i-th magnetic beacon;

[0023] represents the pitch angle between the i-th magnetic beacon and the target point in the x i y i z i of the body coordinate system of the i-th magnetic beacon;

[0024] θ i represents the azimuth angle between the i-th magnetic beacon and the target point in the x i y i z i of the body coordinate system of the i-th magnetic beacon;

[0025] Step 32. Alternating magnetic field vector The expressions in the sensor coordinate system and the reference coordinate system are respectively:

[0026]

[0027] where, represents the expression of the alternating magnetic field vector in the sensor coordinate system;

[0028] represents the expression of the alternating magnetic field vector in the reference coordinate system;

[0029] represents the rotation matrix from the body coordinate system of the i-th magnetic beacon to the sensor coordinate system;

[0030] represents the rotation matrix from the body coordinate system of the i-th magnetic beacon to the reference coordinate system;

[0031] Step 33. The total magnetic field intensities of the i-th magnetic beacon in the body coordinate system, the sensor coordinate system, and the reference coordinate system are respectively:

[0032]

[0033] where: represents the total magnetic field intensity of the i-th magnetic beacon in the body coordinate system;

[0034] represents the total magnetic field intensity of the i-th magnetic beacon in the sensor coordinate system;

[0035] represents the total magnetic field intensity of the i-th magnetic beacon in the reference coordinate system;

[0036] From Equation (3), the total magnetic field intensity of the \(i\)-th magnetic beacon in different coordinate systems is the same, so the minimum value of the total magnetic field intensity of the \(i\)-th magnetic beacon in different coordinate systems is also the same;

[0037]

[0038] Among them, represents the minimum value of the total magnetic field intensity of the \(i\)-th magnetic beacon in the body coordinate system;

[0039] Then, according to and a non-linear equation system for estimating the target position is constructed:

[0040]

[0041] Furthermore, the rotation matrices \(C\) i g and \(C\) i b are respectively:

[0042]

[0043] Among them, \(\alpha\) i represents the heading angle of the body coordinate system of the \(i\)-th magnetic beacon relative to the reference coordinate system; \(\alpha\) b represents the heading angle of the sensor coordinate system relative to the reference coordinate system;

[0044] \(\beta\) i represents the pitch angle of the body coordinate system of the \(i\)-th magnetic beacon relative to the reference coordinate system;

[0045] \(\beta\) b represents the pitch angle of the sensor coordinate system relative to the reference coordinate system;

[0046] \(\gamma\) i represents the roll angle of the body coordinate system of the \(i\)-th magnetic beacon relative to the reference coordinate system;

[0047] \(\gamma\) b represents the roll angle of the sensor coordinate system relative to the reference coordinate system.

[0048] Furthermore, the specific process of Step 4 is:

[0049] Step 4-1. Let

[0050]

[0051] where \(i = 1, 2, 3, 4\);

[0052] Then, Equation (5) is simplified as:

[0053]

[0054] Subtract Equation ② to Equation ④ in Equation (10) from Equation ① respectively, and linearize the non - linear equation system of Equation (10) into:

[0055]

[0056] Step Four Two: Represent Equation (11) equivalently as AX = B, where A, X, and B are respectively:

[0057]

[0058] Step Four Three: Through matrix inversion, obtain the estimated result X of the target point position:

[0059] X = A -1 B (13).

[0060] Furthermore, the positions of the four magnetic beacons in the reference coordinate system satisfy that matrix A is non - singular.

[0061] Furthermore, in the non - linear equation system As prior information, it is determined by pre - calibration.

[0062] Furthermore, the prior information The calibration method is:

[0063] Construct an expression for the error e(K0):

[0064]

[0065] Wherein, represents the minimum value of the total magnetic field intensity measured at the l - th known point, represents the expression of the theoretical minimum value function of the total magnetic field intensity at the l - th known point, and K0 represents the estimation of the prior information;

[0066] Identify K0 in Equation (14) according to the magnetic field data collected at each known point, and take the identified K0 as the prior information

[0067] Even further, the least - squares method is used to identify K0 in Equation (14) according to the magnetic field data collected at each known point.

[0068] The beneficial effects of the present invention are:

[0069] Based on the magnetic dipole model, the present invention obtains the spatial magnetic field distribution of the magnetic beacon, derives the relationship between the minimum value of the total alternating magnetic field intensity at the target point and the relative distance between the magnetic beacon and the target point, constructs a positioning model using the relationship between the minimum value of the total magnetic field intensity and the relative distance, and realizes the determination of the target position in an analytical manner by linearizing the non - linear equation. The positioning accuracy is not affected by the postures of the magnetic beacon and the sensor.

[0070] The method of the present invention significantly improves the calculation efficiency. Not only the real - time performance of the system is significantly improved, but also the accurate estimation of the target position can be realized. It effectively solves the multi - solution problem that occurs when using the analytical positioning model to solve, greatly expands the application scenarios of the ultra - low - frequency magnetic field positioning system, enables it to stably cover complex environments such as underground, is not affected by the terrain of the environment, and gets rid of the dependence on the road surface conditions. Brief Description of the Drawings

[0071] Figure 1 is a schematic diagram of the position of the rotating permanent - magnet - type magnetic beacon;

[0072] Figure 2 is x i y i z i is a diagram of the relative azimuth relationship between the magnetic beacon and the target point in the x - y - z coordinate system;

[0073] Figure 3 is a flow chart of an underground target positioning method based on a rotating permanent - magnet - type magnetic beacon of the present invention. Detailed Embodiments

[0074] Detailed Embodiment 1: Combined with Figure 3 This embodiment is described. An underground target positioning method based on a rotating permanent - magnet - type magnetic beacon according to this embodiment specifically includes the following steps:

[0075] Step 1: As Figure 1 shown, four identical rotating permanent - magnet - type magnetic beacons are respectively placed at four points with known spatial positions. The position coordinates of the four magnetic beacons in the reference coordinate system (the reference coordinate system is determined by RTK, and the reference coordinate system is the northeast - sky inertial coordinate system) are respectively denoted as (x1, y1, z1), (x2, y2, z2), (x3, y3, z3) and (x4, y4, z4);

[0076] Four different magnetic beacon body coordinate systems x i y i z i (i = 1, 2, 3, 4) are determined by the rotating planes and rotating axes of each permanent magnet. The four magnetic beacons rotate around fixed axes at rotational speeds n1, n2, n3 and n4 respectively (that is, each magnetic beacon rotates around the z - axis of its own body coordinate system), generating ultra - low - frequency magnetic fields;

[0077] Step 2: Denote the position coordinates of the underground target point in the reference coordinate system as (x, y, z). Place the magnetic sensor at the underground target point, and use the magnetic sensor to collect the hybrid alternating magnetic field data in the x b y b z b of the sensor coordinate system;

[0078] The sensor coordinate system is a coordinate system with the centroid of the sensor as the origin and having certain heading angle, pitch angle, and roll angle with respect to the reference coordinate system;

[0079] Step 3: Design band-pass filters according to the rotation frequencies of the four magnetic beacons (the rotation frequencies can be converted from the rotational speeds), and then use each designed band-pass filter to filter the hybrid alternating magnetic field data collected in Step 2 to obtain the alternating magnetic field vectors of each rotating permanent magnet type magnetic beacon at the underground target point and

[0080] wherein, represents the components of the alternating magnetic field vector of the first magnetic beacon at the underground target point in the directions of each axis of the sensor coordinate system, and the same applies to others;

[0081] Then, according to and construct a positioning model;

[0082] Step 4: Obtain the estimated position of the target point according to the positioning model constructed in Step 3.

[0083] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the rotational speeds n1 = 420 rpm, n2 = 660 rpm, n3 = 1020 rpm, n4 = 1380 rpm.

[0084] Other steps and parameters are the same as those in Specific Embodiment 1.

[0085] In the present invention, the rotational speeds of each magnetic beacon can be the above specific values, but are not limited to the above values, as long as the rotation frequencies f1, f2, f3, and f4 of each magnetic beacon are relatively prime to each other.

[0086] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that the construction of the positioning model according to and is specifically as follows:

[0087] Step 3-1: According to the magnetic dipole model, obtain the alternating magnetic field vectors of each rotating permanent magnet type magnetic beacon at the position of the target point in its own body coordinate system

[0088] x of the body coordinate system of the rotating permanent magnet type magnetic beacon i y i z i (i = 1, 2, 3, 4) With the centroid of the magnetic beacon as the origin, and there are certain heading angle, pitch angle and roll angle between the body coordinate system and the reference coordinate system;

[0089]

[0090] Among them, t represents time;

[0091] M represents the magnitude of the magnetic moment of the permanent magnet;

[0092] μ represents the magnetic permeability of the medium;

[0093] f i represents the rotation frequency of the i-th magnetic beacon;

[0094] φ i represents the initial phase of the i-th magnetic beacon;

[0095] Such as Figure 2 shown, r i represents the relative distance between the i-th magnetic beacon and the target point in the x i y i z i of the body coordinate system of the i-th magnetic beacon;

[0096] represents the pitch angle between the i-th magnetic beacon and the target point in the x i y i z i of the body coordinate system of the i-th magnetic beacon;

[0097] θ i represents the azimuth angle between the i-th magnetic beacon and the target point in the x i y i z i of the body coordinate system of the i-th magnetic beacon;

[0098] Step Three Two. Since the body coordinate system of the magnetic beacon is not aligned with the sensor coordinate system and the reference coordinate system, the alternating magnetic field vector The expressions in the sensor coordinate system and the reference coordinate system are respectively:

[0099]

[0100] Among them, represents the expression of the alternating magnetic field vector in the sensor coordinate system;

[0101] Expression of the alternating magnetic field vector in the reference coordinate system;

[0102] Denote the rotation matrix from the body coordinate system of the i-th magnetic beacon to the sensor coordinate system;

[0103] Denote the rotation matrix from the body coordinate system of the i-th magnetic beacon to the reference coordinate system;

[0104] Step 3: The total magnetic field intensities of the i-th magnetic beacon in the body coordinate system, the sensor coordinate system, and the reference coordinate system are respectively:

[0105]

[0106] Where: Denote the total magnetic field intensity of the i-th magnetic beacon in the body coordinate system;

[0107] Denote the total magnetic field intensity of the i-th magnetic beacon in the sensor coordinate system;

[0108] Denote the total magnetic field intensity of the i-th magnetic beacon in the reference coordinate system;

[0109] From Equation (3), the total magnetic field intensities of the i-th magnetic beacon in different coordinate systems are the same, so the minimum values of the total magnetic field intensities of the i-th magnetic beacon in different coordinate systems are also the same;

[0110]

[0111] Where, Denote the minimum value of the total magnetic field intensity of the i-th magnetic beacon in the body coordinate system;

[0112] Then according to and Construct a non-linear equation system (i.e., positioning model) for estimating the target position:

[0113]

[0114] Other steps and parameters are the same as those in the first or second specific implementation manners.

[0115] Specific implementation manner 4: The difference between this implementation manner and one of the first to third specific implementation manners is that the rotation matrices and are respectively:

[0116]

[0117] Where, α iDenote the heading angle of the body coordinate system (x i y i z i ) of the i-th magnetic beacon relative to the reference coordinate system (x g y g z g );

[0118] α b Denote the heading angle of the sensor coordinate system (x b y b z b ) relative to the reference coordinate system (x g y g z g );

[0119] β i Denote the pitch angle of the body coordinate system (x i y i z i ) of the i-th magnetic beacon relative to the reference coordinate system (x g y g z g );

[0120] β b Denote the pitch angle of the sensor coordinate system (x b y b z b ) relative to the reference coordinate system (x g y g z g );

[0121] γ i Denote the roll angle of the body coordinate system (x i y i z i ) of the i-th magnetic beacon relative to the reference coordinate system (x g y g z g );

[0122] γ b Denote the roll angle of the sensor coordinate system (x b y b z b ) relative to the reference coordinate system (x g y g z g ).

[0123] Other steps and parameters are the same as those in any one of the specific embodiments one to three.

[0124] Specific embodiment five: The difference between this embodiment and any one of the specific embodiments one to four is that the specific process of step four is as follows:

[0125] Step Four One: Let

[0126]

[0127] where \(i = 1, 2, 3, 4\);

[0128] Then, Equation (5) is simplified and expressed as:

[0129]

[0130] Subtract Equation ② to Equation ④ in Equation (10) from Equation ① respectively, and linearize the non - linear equation system of Equation (10) into:

[0131]

[0132] Step Four Two: Represent Equation (11) equivalently as \(AX = B\), where \(A\), \(X\), and \(B\) are respectively:

[0133]

[0134] Step Four Three: Through matrix inversion, obtain the estimated result \(X\) of the target point position:

[0135] \(X = A^{-1}B\) (13) -1 B (13)

[0136] Other steps and parameters are the same as those in any one of the specific embodiments one to four.

[0137] Through this embodiment, rapid, stable, and accurate positioning of the target point can be achieved.

[0138] Specific Embodiment Six: The difference between this embodiment and any one of the specific embodiments one to five is that the positions of the four magnetic beacons in the reference coordinate system satisfy that the matrix \(A\) is non - singular.

[0139] Other steps and parameters are the same as those in any one of the specific embodiments one to five.

[0140] When placing the four magnetic beacons, try to avoid the coefficient matrix \(A\) being singular to ensure the positioning accuracy.

[0141] Specific Embodiment Seven: The difference between this embodiment and any one of the specific embodiments one to six is that in the non - linear equation system As prior information, it is determined by pre - calibration.

[0142] Other steps and parameters are the same as those in any one of the specific embodiments one to six.

[0143] Specific Embodiment Eight: The difference between this embodiment and any one of the specific embodiments one to seven is that the calibration method of the prior information is:

[0144] Construct the expression of the construction error e(K0):

[0145]

[0146] Wherein, represents the minimum value of the total magnetic field strength measured at the l-th known point (i.e., obtained from the right end of formula (5)), represents the expression of the minimum value function of the theoretical total magnetic field strength at the l-th known point (i.e., obtained from the left end of formula (5)), and K0 represents the estimation of the prior information;

[0147] Identify K0 in formula (14) based on the magnetic field data collected at each known point, and use the identified K0 as the prior information

[0148] Other steps and parameters are the same as those in any one of the specific embodiments one to seven.

[0149] Specific embodiment nine: The difference between this embodiment and any one of the specific embodiments one to eight is that the least squares method is used to identify K0 in formula (14) according to the magnetic field data collected at each known point.

[0150] Other steps and parameters are the same as those in any one of the specific embodiments one to eight.

[0151] In the identification process of the present invention, for each known point, only the data of one magnetic target collected at this known point needs to be used to participate in the identification. Finally, the data collected at multiple known points are used together for identification.

[0152] Simulation verification:

[0153] Two groups of simulation experiments are carried out to verify the underground multi-magnetic beacon positioning system. Among them, Experiment 1 is that there is no attitude error between the magnetic beacon and the magnetic sensor relative to the reference coordinate system; Experiment 2 is that there are attitude errors between the magnetic beacon and the magnetic sensor relative to the reference coordinate system, and at the same time, the method in the present invention is compared with the feature vector method for positioning based on the optimization algorithm.

[0154] The simulation conditions of Experiment 1 are as follows: The permanent magnets rotate at a constant speed around their respective z axes at known positions, where the magnetic moment magnitude is 524 A·m 2 , there is an interference magnetic field with a mean value of 45000 nT and white noise with an amplitude of 10 nT in the environment, the magnetic permeability of the medium is 4π×10 -7 H / m, the positions and rotation speeds of the magnetic beacons are shown in Table 1, 6 test points are selected, and the comparison results of the estimated position errors and running times of the method of the present invention and the feature vector method are shown in Table 2:

[0155] Table 1 Information on the positions and rotation speeds of the magnetic beacons in Experiment 1

[0156] Magnetic beacon Position in the reference coordinate system / m Rotational speed / rpm 1 (0,0,0) 420 2 (1,0,0) 660 3 (0,1,0) 1020 4 (0,0,1) 1380

[0157] Table 2 Experimental 1 Positioning Comparison

[0158]

[0159] As can be seen from Table 2, the method of the present invention and the feature vector method have almost the same positioning accuracy under the condition of no attitude error. However, the present invention realizes positioning in an analytical manner, showing a high operation efficiency.

[0160] In Experiment 2, on the basis of the simulation conditions of Experiment 1, there is a fixed attitude error of the magnetic sensor relative to the reference coordinate system at the test point: α b =-81.06°, β b =140.31°, γ b =-52.86°, and each magnetic beacon has the attitude error shown in Table 3. Among them, the position estimation results of the two positioning methods are shown in Table 4.

[0161] Table 3 Magnetic Beacon Position and Attitude Information in Experiment 2

[0162] Magnetic beacon Position in the reference coordinate system / m Attitude error / ° 1 (0,0,0) <![CDATA[α1 = 72.01°, β1 = 344.21°, γ1 = 83.42°]]> 2 (1,0,0) <![CDATA[α2 = -23.54°, β2 = 207.08°, γ2 = 53.19°]]> 3 (0,1,0) <![CDATA[α3 = -69.98°, β3 = 21.52°, γ3 = -17.67°]]> 4 (0,0,1) <![CDATA[α4 = 50.45°, β4 = 84.52°, γ4 = 16.92°]]>

[0163] Table 4 Experimental 2 Positioning Comparison

[0164] Position Error of the present invention / m Solution time / ms Error of the eigenvector method / m Solution time / ms 1 0.010 8.2 4.6 124.6 2 0.015 7.0 6.6 120.2 3 0.004 6.8 4.2 113.9 4 0.003 6.6 3.3 118.0 5 0.006 6.7 5.3 125.1 6 0.007 6.5 3.5 116.6

[0165] As can be seen from Table 4, when there are attitude errors for both the magnetic beacon and the magnetic sensor relative to the reference coordinate system, the method of the present invention can still maintain a high positioning accuracy and operation efficiency, while the positioning effect of the feature vector method is not good. Compared with the traditional feature vector positioning method based on the optimization algorithm, the method of the present invention significantly enhances the robustness to the attitude errors of the magnetic beacon and the sensor, effectively improves the positioning accuracy under complex conditions such as uneven road surfaces, improves the algorithm operation efficiency, and greatly expands the application scenarios of the system.

[0166] The above numerical examples of the present invention are only to illustrate in detail the calculation model and calculation process of the present invention, rather than to limit the implementation manner of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to enumerate all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. An underground target positioning method based on a rotating permanent magnet type magnetic beacon, characterized in that, The method specifically includes the following steps: Step 1: Place four identical rotating permanent magnet type magnetic beacons at four points with known spatial positions respectively, and record the position coordinates of the four magnetic beacons in the reference coordinate system as (x1, y1, z1), (x2, y2, z2), (x3, y3, z3) and (x4, y4, z4); the four magnetic beacons rotate around a fixed axis at rotational speeds n1, n2, n3 and n4 respectively; Step 2: Denote the position coordinates of the underground target point in the reference coordinate system as (x, y, z). Place the magnetic sensor at the underground target point, and use the magnetic sensor to collect the hybrid alternating magnetic field data in the x b y b z b of the sensor coordinate system; Step 3: Design band-pass filters according to the rotation frequencies of the four magnetic beacons, and then use each designed band-pass filter to filter the mixed alternating magnetic field data collected in Step 2 to obtain the alternating magnetic field vectors of each rotating permanent magnet type magnetic beacon at the underground target point and Among them, represents the components of the alternating magnetic field vector of the first magnetic beacon at the underground target point in the directions of the axes of the sensor coordinate system; Then, according to and construct a positioning model; Step 4: Obtain the estimated position of the target point according to the positioning model constructed in Step 3.

2. The underground target positioning method based on a rotating permanent magnet type magnetic beacon according to claim 1, wherein The rotational speeds n1 = 420 rpm, n2 = 660 rpm, n3 = 1020 rpm, n4 = 1380 rpm.

3. The underground target positioning method based on a rotating permanent magnet type magnetic beacon according to claim 2, characterized in that, The said according to and to construct a positioning model, specifically as follows: Step 3.1: According to the magnetic dipole model, obtain the alternating magnetic field vectors at the target point positions of each rotating permanent magnet type magnetic beacon in its own body coordinate system Wherein, t represents time; M represents the magnitude of the magnetic moment of the permanent magnet; μ represents the magnetic permeability of the medium; f i represents the rotation frequency of the i-th magnetic beacon; φ i represents the initial phase of the i-th magnetic beacon; r i represents the relative distance between the i-th magnetic beacon and the target point in the body coordinate system x i y i z i of the i-th magnetic beacon denotes the pitch angle between the i-th magnetic beacon and the target point in the body coordinate system x of the i-th magnetic beacon i y i z i of the i-th magnetic beacon; θ i represents the azimuth angle between the i-th magnetic beacon and the target point in the body coordinate system x i y i z i of the i-th magnetic beacon Step 32, Alternating magnetic field vector The expressions in the sensor coordinate system and the reference coordinate system are respectively as follows: Among them, represents the expression of the alternating magnetic field vector in the sensor coordinate system; Expression of the alternating magnetic field vector in the reference coordinate system; Denote the rotation matrix from the body coordinate system of the i-th magnetic beacon to the sensor coordinate system; Denote the rotation matrix from the body coordinate system of the i-th magnetic beacon to the reference coordinate system; Step 3: The total magnetic field intensities of the i-th magnetic beacon in the body coordinate system, the sensor coordinate system and the reference coordinate system are respectively: Wherein: represents the total magnetic field intensity of the i-th magnetic beacon in the body coordinate system; represents the total magnetic field intensity of the i-th magnetic beacon in the sensor coordinate system; Denote the total magnetic field intensity of the i-th magnetic beacon in the reference coordinate system; From Equation (3), it can be obtained that the total magnetic field intensities of the i-th magnetic beacon in different coordinate systems are the same, so the minimum values of the total magnetic field intensities of the i-th magnetic beacon in different coordinate systems are also the same; Among them, represents the minimum value of the total magnetic field intensity of the i-th magnetic beacon in the body coordinate system; Then, according to and a non-linear equation set for estimating the target position is constructed:

4. The underground target positioning method based on a rotating permanent magnet type magnetic beacon according to claim 3, characterized in that The rotation matrix and are respectively: where α i represents the heading angle of the body coordinate system of the i-th magnetic beacon relative to the reference coordinate system; α b represents the heading angle of the sensor coordinate system relative to the reference coordinate system; β i represents the pitch angle of the body coordinate system of the i-th magnetic beacon relative to the reference coordinate system; β b represents the pitch angle of the sensor coordinate system relative to the reference coordinate system; γ i represents the roll angle of the body coordinate system of the i-th magnetic beacon relative to the reference coordinate system; γ b represents the roll angle of the sensor coordinate system relative to the reference coordinate system.

5. The underground target positioning method based on a rotating permanent magnet type magnetic beacon according to claim 4, characterized in that, The specific process of Step 4 is as follows: Step 4-1: Let Wherein, i = 1, 2, 3, 4; Then Equation (5) is simplified and expressed as: Subtract Equation ② to Equation ④ in Equation (10) from Equation ① respectively, and linearize the non-linear equation system of Equation (10) into: Step 4-2: Represent Equation (11) equivalently as AX = B, where A, X and B are respectively: Step 4-3: Through matrix inversion, obtain the target point position estimation result X: X = A -1 B(13).

6. The underground target positioning method based on a rotating permanent magnet type magnetic beacon according to claim 5, characterized in that, The positions of the four magnetic beacons in the reference coordinate system satisfy that the matrix A is non-singular.

7. A method for underground target positioning based on a rotating permanent magnet type magnetic beacon according to claim 6, characterized in that, In the non-linear equations As prior information, it is determined by pre-calibration in advance.

8. A method for underground target positioning based on a rotating permanent magnet type magnetic beacon according to claim 7, characterized in that The prior information is calibrated as follows: Construct an expression for the error e(K0): Among them, represents the minimum value of the total magnetic field strength measured at the l-th known point, represents the functional expression of the minimum value of the theoretical total magnetic field strength at the l-th known point, and K0 represents the estimate of the prior information; Identify \(K_0\) in Equation (14) based on the magnetic field data collected at each known point, and use the identified \(K_0\) as prior information 9. A method for underground target positioning based on a rotating permanent magnet type magnetic beacon according to claim 8, characterized in that, The least squares method is used to identify K0 in Equation (14) according to the collected magnetic field data at each known point.

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