Motion platform magnetic compensation method based on time-varying magnetic interference model

Abstract

The invention provides a motion platform magnetic compensation method based on a time-varying magnetic interference model, and the method comprises the steps: decomposing a magnetic interference compensation task into a development stage and a task stage, and obtaining an initial value of a magnetic compensation coefficient of a magnetic interference model through a conventional calibration mode in the development stage; in the task stage, the magnetic compensation coefficient of the magnetic interference model is decomposed into a time-varying coefficient and a time-invariant coefficient, high-altitude maneuvering does not need to be carried out through a traditional calibration mode, and rapid optimization of the magnetic compensation coefficient of the magnetic interference model is achieved on an air route flying to a task area through simple maneuvering flight in combination with a recursive algorithm. According to the method, the complexity of traditional calibration flight is reduced, the optimization speed of magnetic compensation coefficients of magnetic interference compensation in different task areas is improved, and the method has better adaptability to diversified scenes with limited cruising ability and high task instantaneity requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic interference compensation, and in particular to a motion platform magnetic compensation method based on a time-varying magnetic interference model. Background Art

[0002] Magnetic anomaly detection technology mainly obtains target information by installing a magnetometer on a moving platform to measure the changes in the geomagnetic field caused by magnetic targets. It has the advantages of good concealment and high positioning accuracy, and is widely used in many fields such as military, geological exploration, humanitarian rescue, and geomagnetic navigation. Affected by the magnetic material of the moving platform, magnetic interference from the moving platform is inevitable in magnetic field measurement. Therefore, high-precision magnetic compensation technology is the key to improving the ability to detect magnetic anomalies.

[0003] Most of the current motion platform magnetic compensation technologies are based on the TL model proposed by Tolles and Lawson. The TL model divides the platform magnetic interference into three categories: residual magnetic field, induced magnetic field and eddy current magnetic field, and gives the mathematical expressions of the three types of magnetic fields. The magnetic compensation process can be divided into calibration mode and compensation mode according to different working modes. In the calibration mode, the motion platform obtains collected data by completing the specified maneuvers and solves the compensation coefficient through the magnetic interference model solution method; in the compensation mode, the interference magnetic field compensation is performed according to the solved compensation coefficient.

[0004] When solving the traditional TL model, it is assumed that the geomagnetic field in the calibration area is a constant magnetic field, and the compensation coefficient solved is a time-invariant coefficient. Therefore, the compensation coefficient solved by the traditional calibration method is only valid in a certain range of areas. When changing the mission area, it is necessary to complete the specified maneuvers again to obtain a new compensation coefficient. In addition, in order to meet the requirements of constant geomagnetic field, aeromagnetic survey generally requires the calibration flight altitude to be above 2000 meters. Limited by the diverse scenarios such as the endurance of the motion platform and the immediacy of the mission, the traditional calibration method is difficult to meet the needs of rapid adjustment of compensation coefficients in different areas. Summary of the invention

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the present invention proposes a magnetic compensation method for a motion platform based on a time-varying magnetic interference model, which can meet the needs of rapid adjustment of compensation coefficients in different regions.

[0006] The present invention provides a motion platform magnetic compensation method based on a time-varying magnetic interference model, comprising:

[0007] Step 1: The motion platform performs motorized motion in the calibration area according to the prescribed route and action to collect magnetic field data, and the motion platform is equipped with an optical pump magnetometer and a vector magnetometer;

[0008] Step 2: Establish the coordinate system of the motion platform, assume that the geomagnetic field in the calibration area is a constant value, and establish the classic magnetic compensation TL model:

[0009]

[0010] Among them, B d is the magnetic interference of the moving platform, which is obtained by subtracting the earth's magnetic field from the magnetic field measured by the optically pumped magnetometer. i 、a ij , b ij are the magnetic compensation coefficients of residual magnetic field, induced magnetic field and eddy current magnetic field, respectively, U i and U j are the components of the direction cosine U of the three coordinate axes of the geomagnetic field in the motion platform coordinate system, i=1,2,3, j=1,2,3, which are the x, y and z axes in the motion platform coordinate system respectively. Expand them and write them as U1=cosX, U2=cosY, U3=cosZ, where X, Y and Z are the angles between the x, y and z axes of the motion platform coordinate system and the geomagnetic field respectively. The expressions of cosX, cosY and cosZ are as follows:

[0011]

[0012] Among them, B x , B y and B z are the measured values ​​of the geomagnetic field along the x, y and z axes of the motion platform coordinate system measured by the vector magnetometer;

[0013] Step 3: Calculate the magnetic compensation coefficient p using least squares, recursive least squares or adaptive methods i 、a ij , b ij The initial value of the magnetic field is calculated and the average magnetic field value of the calibration area after compensation is calculated.

[0014] Step 4: The motion platform performs maneuvering motion according to the set route and action on the way to the mission area to collect magnetic field data;

[0015] Step 5: Decompose the time-varying part and the time-invariant part in the classic magnetic compensation TL model to obtain the time-varying magnetic interference model:

[0016]

[0017] in, is the magnetic interference of the moving platform at the mth sampling moment, p i , is the time-invariant coefficient, is the geomagnetic field that changes with the time of movement, and is the time-varying coefficient;

[0018] Step 6: Magnetic compensation coefficient p obtained in step 2 i 、a ij , b ij Initial value and average magnetic field value of the calibration area after compensation Calculate the initial value p of the coefficient of the time-varying magnetic interference model i , The calculation formula is as follows:

[0019]

[0020] in, The optically pumped magnetometer observations at the starting point for solving the magnetic disturbance model coefficients in the mission area;

[0021] Step 7: Since the distances between adjacent sampling points in the collected data are mostly in the order of meters or sub-meters, it is assumed that the geomagnetic field of adjacent sampling points remains unchanged. The time-varying magnetic interference model can be expressed as:

[0022]

[0023] Step 8: Calculate the magnetic compensation coefficient of the time-varying magnetic interference model using the recursive least squares method or other derivative algorithms of the recursive least squares method. p i , Optimization;

[0024] Step 9: Perform magnetic interference compensation for the motion platform according to the calculated results of the magnetic compensation coefficient, and use the initial coefficient or the coefficient optimized in the previous task as the initial value for adaptive optimization when the task area is switched next time.

[0025] After adopting the above technical solution, the present invention has at least the following beneficial effects:

[0026] The present invention decomposes the magnetic interference compensation task into a development stage and a task stage. In the development stage, the initial value of the magnetic compensation coefficient of the magnetic interference model is obtained by a traditional calibration method. In the task stage, the magnetic compensation coefficient of the magnetic interference model is decomposed into two parts: a time-varying coefficient and a time-invariant coefficient. There is no need to perform high-altitude maneuvers through traditional calibration methods. On the route to the mission area, a simple maneuvering flight combined with a recursive algorithm is used to achieve rapid optimization of the magnetic compensation coefficient of the magnetic interference model. This method reduces the complexity of traditional calibration flights, improves the optimization speed of the magnetic compensation coefficient of magnetic interference compensation in different mission areas, and has better adaptability to diversified scenarios with limited endurance and high mission immediacy requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0028] Figure 1 Flowchart of a motion platform magnetic compensation method based on a time-varying magnetic interference model provided by an embodiment of the present disclosure;

[0029] Figure 2 Schematic diagram of a "square" - shaped maneuvering movement route;

[0030] Figure 3 Schematic diagram of a "cross" - shaped maneuvering movement route. Detailed implementation manners

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0032] Taking the unmanned aerial vehicle (UAV) platform as an example, a magnetic compensation method for a motion platform based on a time - varying magnetic interference model will be described. As Figure 1 shown, steps 1 - 3 are the development stage, and steps 4 - 9 are the mission stage, which specifically include the following steps:

[0033] Development stage

[0034] Step 1: The UAV conducts magnetic field data collection by using a "square" - shaped or "cross" - shaped maneuvering flight. The "square" - shaped maneuvering movement route is as Figure 1 shown, and the "cross" - shaped maneuvering movement route is as Figure 2 shown. During the flight, three periodic maneuvering actions of pitch, roll, and yaw are simultaneously performed, and after completing the last flight path, it returns to the initial position to end the flight.

[0035] Step 2: Establish a motion platform coordinate system. Assuming that the geomagnetic field in the calibration area is a constant value, establish a classical magnetic compensation T - L model:

[0036]

[0037] Among them, B d is the magnetic interference of the motion platform, which is obtained by subtracting the geomagnetic field value from the magnetic field value measured by an optically pumped magnetometer. p i and a ij, b ij are the magnetic compensation coefficients of residual magnetic field, induced magnetic field and eddy current magnetic field, respectively, U i and U j are the components of the direction cosine U of the three coordinate axes of the geomagnetic field in the motion platform coordinate system, i=1,2,3, j=1,2,3, which are the x, y and z axes in the motion platform coordinate system respectively. Expand them and write them as U1=cosX, U2=cosY, U3=cosZ, where X, Y and Z are the angles between the x, y and z axes of the motion platform coordinate system and the geomagnetic field respectively. The expressions of cosX, cosY and cosZ are as follows:

[0038]

[0039] Among them, B x , B y and B z are the measured values ​​of the geomagnetic field along the x, y and z axes of the motion platform coordinate system measured by the vector magnetometer;

[0040] Step 3: Calculate the magnetic compensation coefficient p using least squares, recursive least squares or adaptive methods i 、a ij , b ij The initial value of the magnetic field is calculated and the average magnetic field value of the calibration area after compensation is calculated.

[0041] Mission Phase

[0042] Step 4: The drone performs a unidirectional maneuvering flight, and simultaneously performs three maneuvers, namely pitching, swinging, and yaw, to collect magnetic field data during the flight;

[0043] Step 5: Decompose the time-varying part and the time-invariant part in the classic magnetic compensation TL model to obtain the time-varying magnetic interference model:

[0044]

[0045] in, is the magnetic interference of the moving platform at the mth sampling moment, p i , is the time-invariant coefficient, is the geomagnetic field that changes with the time of movement, and is the time-varying coefficient;

[0046] Step 6: Magnetic compensation coefficient p obtained in step 2 i 、a ij , b ij Initial value and average magnetic field value of the calibration area after compensation Calculate the initial value p of the coefficient of the time-varying magnetic interference model i , The calculation formula is as follows:

[0047]

[0048] in, The optically pumped magnetometer observations at the starting point for solving the magnetic disturbance model coefficients in the mission area;

[0049] Step 7: Since the flight speed of the drone generally does not exceed 60m / s, when the magnetic field data sampling rate is 20Hz, the distance between adjacent sampling points is 3m. Here, it is assumed that the geomagnetic field of adjacent sampling points remains unchanged. The time-varying magnetic interference model can be expressed as:

[0050]

[0051] Step 8: Calculate the magnetic compensation coefficient of the time-varying magnetic interference model using the recursive least squares method or other derivative algorithms of the recursive least squares method. p i , The optimization ends the recursive calculation according to the evaluation indicators such as compensation accuracy and improvement ratio;

[0052] Step 9: Perform magnetic interference compensation for the motion platform according to the calculated results of the magnetic compensation coefficient, and use the initial coefficient or the coefficient optimized in the previous task as the initial value for adaptive optimization when the task area is switched next time.

[0053] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Any person skilled in the art may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the claims.

Claims

1. A magnetic compensation method for a motion platform based on a time-varying magnetic interference model, characterized in that: include: Step 1: The motion platform performs motorized motion in the calibration area according to the prescribed route and action to collect magnetic field data, and the motion platform is equipped with an optical pump magnetometer and a vector magnetometer; Step 2: Establish the coordinate system of the motion platform, assume that the geomagnetic field in the calibration area is a constant value, and establish the classic magnetic compensation TL model: Among them, B d is the magnetic interference of the moving platform, which is obtained by subtracting the earth's magnetic field from the magnetic field measured by the optically pumped magnetometer. i 、a ij 、b ij are the magnetic compensation coefficients of residual magnetic field, induced magnetic field and eddy current magnetic field, respectively, U i and U j are the components of the direction cosine U of the three coordinate axes of the geomagnetic field in the motion platform coordinate system, i=1,2,3, j=1,2,3, which are the x, y and z axes in the motion platform coordinate system respectively. Expand them and write them as U1=cosX, U2=cosY, U3=cosZ, where X, Y and Z are the angles between the x, y and z axes of the motion platform coordinate system and the geomagnetic field respectively. The expressions of cosX, cosY and cosZ are as follows: Among them, B x , B y and B z are the measured values ​​of the geomagnetic field along the x, y and z axes of the motion platform coordinate system measured by the vector magnetometer; Step 3: Calculate the magnetic compensation coefficient p using least squares, recursive least squares or adaptive methods i 、a ij 、b ij The initial value of the magnetic field is calculated and the average magnetic field value B of the calibration area after compensation is calculated. e0 ; Step 4: The motion platform performs maneuvering motion according to the set route and action on the way to the mission area to collect magnetic field data; Step 5: Decompose the time-varying part and the time-invariant part in the classic magnetic compensation TL model to obtain the time-varying magnetic interference model: in, is the magnetic interference of the moving platform at the mth sampling moment, p i 、a ij 0 、b ij 0 is the time-invariant coefficient, is the geomagnetic field that changes with the time of movement, and is the time-varying coefficient; Step 6: Magnetic compensation coefficient p obtained in step 2 i 、a ij 、b ij The initial value and the average magnetic field value B of the calibration area after compensation e0 Calculate the initial value p of the coefficient of the time-varying magnetic interference model i 、a ij 0 、b ij 0 , B e 0 , the calculation formula is as follows: Among them, B t 0 The optically pumped magnetometer observations at the starting point for solving the magnetic disturbance model coefficients in the mission area; Step 7: Since the distances between adjacent sampling points in the collected data are mostly in the order of meters or sub-meters, it is assumed that the geomagnetic field of adjacent sampling points remains unchanged. The time-varying magnetic interference model can be expressed as: Step 8: Calculate the magnetic compensation coefficient of the time-varying magnetic interference model using the recursive least squares method or other derivative algorithms of the recursive least squares method. p i , Optimization; Step 9: Perform magnetic interference compensation for the motion platform according to the calculated results of the magnetic compensation coefficient, and use the initial coefficient or the coefficient optimized in the previous task as the initial value for adaptive optimization when the task area is switched next time.

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