High-precision calibration method for real-time simulation of three-dimensional geomagnetic field

Abstract

The invention relates to the technical field of three-dimensional geomagnetic field real-time simulation, in particular to a high-precision calibration method for three-dimensional geomagnetic field real-time simulation. Comprising the following steps: S1, collecting input direct current, obtaining corresponding uniaxial magnetic field intensity under each current value, and forming a uniaxial fitting function of the current and the magnetic field under a uniaxial condition; s2, performing data error verification, and determining a current division section of a uniaxial fitting relational expression based on a data error verification result; s3, a fitting function of each current division section is determined, connection of the fitting function of each current division section is determined through iteration, and a single-axis optimization function of the current and the magnetic field is generated; s4, for a single dimension, acquiring magnetic field intensities of other two corresponding axes under each current value, and forming a single-axis influence fitting function under a single axis; s5, generating a uniaxial current fitting function; according to the calibration method, the influence of a hysteresis phenomenon and a coupling phenomenon on the generated magnetic field can be eliminated, and high-precision calibration of the simulated geomagnetic field is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of three-dimensional geomagnetic field real-time simulation, and in particular to a high-precision calibration method for three-dimensional geomagnetic field real-time simulation. Background Art

[0002] At present, in engineering practice, magnetic field is widely used in geomagnetic navigation, magnetic testing, magnetic device calibration and correction, etc., and the research on magnetic field simulation technology has important engineering value and practical significance. However, the magnetic field simulation system in the existing technology cannot meet the actual requirements in terms of magnetic field accuracy, distribution uniformity and range, and needs to be improved. In addition, how to simplify system operation and save construction costs is also an urgent problem to be solved.

[0003] Chinese patent application No. 201020687927.4 discloses a magnetic field simulation system and magnetic field simulation method, including a control subsystem, a DC regulated current power supply, a three-dimensional Helmholtz coil subsystem and a three-dimensional magnetic field measurement device, wherein: the control subsystem controls the DC regulated current power supply to input current into the three-dimensional Helmholtz coil subsystem to generate a magnetic field in the coil space of the three-dimensional Helmholtz coil subsystem; the three-dimensional magnetic field measurement device is located in the coil space for detecting magnetic intensity, and feeds back the measured magnetic intensity to the control subsystem, the control subsystem compares the actual measured magnetic intensity with the set value, and adjusts the current of the DC regulated current power supply into the coil space based on the comparison result, so that the difference between the actual measured magnetic intensity and the set value is controlled within a predetermined range, and a magnetic field with controllable intensity and direction, high uniformity and good stability can be generated. It can be seen that the magnetic field simulation system and magnetic field simulation method have the following problems: the generated magnetic field cannot be calibrated with high precision, and the patent does not specifically describe how to adjust the current of the DC regulated current power supply into the coil space by comparing the actual measured magnetic intensity with the set value. Summary of the invention

[0004] To this end, the present invention provides a high-precision calibration method for real-time simulation of the three-dimensional geomagnetic field, so as to overcome the problem in the prior art that high-precision calibration of the real-time simulation of the three-dimensional geomagnetic field cannot be performed.

[0005] To achieve the above object, the present invention provides a high-precision calibration method for real-time simulation of three-dimensional geomagnetic field, comprising:

[0006] Step S1, collecting the direct current passed through the three-dimensional Helmholtz coil, and obtaining the corresponding uniaxial magnetic field strength under each current value, to form a uniaxial fitting function of the current and the magnetic field under a single axis;

[0007] Step S2, performing data error verification based on the uniaxial fitting function, and determining the current division segments of the uniaxial fitting relationship based on the data error verification result;

[0008] Step S3, determining the fitting function of each current division segment according to the current division segment, and determining the connection of the fitting functions of each current division segment by iteration, so as to generate a single-axis optimization function of current and magnetic field;

[0009] Step S4, for a single dimension, obtaining the magnetic field strength of the other two axes corresponding to each current value, and forming a single-axis influence fitting function of the single-axis current and the other two-axis magnetic fields respectively under a single axis;

[0010] Step S5, generating a uniaxial current fitting function based on the uniaxial influence fitting function of the other two-axis magnetic fields and the uniaxial optimization function, so as to calculate the actual input current of the set three-dimensional magnetic field.

[0011] Furthermore, in step S2, the data error verification result is the data error between the single-axis set magnetic field strength and the single-axis actually generated magnetic field strength, and the current division segments are determined according to the range of the data error verification result.

[0012] Furthermore, in the step S3, the current sampling step length of the fitting function of each current division segment is set according to the data error of the current division segment, and the current sampling step length is inversely proportional to the data error.

[0013] Furthermore, in step S3, the fitting function of each current division segment is linearly fitted and nonlinearly fitted respectively using the least square method, and the optimized fitting function of each current division segment is determined according to the verification errors of the generated linear fitting function and nonlinear fitting function.

[0014] Furthermore, in step S3, the fitting functions of the corresponding current division sections are determined respectively according to the rising and falling trends of the real-time current simulation.

[0015] Furthermore, in the step S4, the uniaxial influence fitting function adopts linear fitting.

[0016] Furthermore, in step S4, according to each input current value of the other two axes and the corresponding magnetic field strength generated in the other two axes under each current value, the fitting coefficients of the single-axis current and the single-axis influence fitting functions of the other two-axis magnetic fields are calculated, and the single-axis influence fitting function is generated to calculate the actual required magnetic field strength of the single axis.

[0017] Furthermore, in the step S5, the actual input current of the set three-dimensional magnetic field is calculated by bringing the actual required magnetic field strength of the single axis and the single-axis influencing magnetic field strengths of the other two axes into the single-axis current fitting function.

[0018] Furthermore, in the step S5, it also includes:

[0019] Determine the initial current value corresponding to the actual required magnetic field of the single axis;

[0020] Determining the influence magnetic field strength in the uniaxial influence fitting function of the other two-axis magnetic fields based on the initial current value;

[0021] An initial current adjustment value is determined based on the ratio of the influencing magnetic field strength to the actual required magnetic field of the single axis.

[0022] Furthermore, in step S1, the precision control of the DC current includes:

[0023] The current to be output is divided into an integer part and a decimal part;

[0024] In the circuit, several resistors of different sizes are connected in parallel to shunt the current of several outputs to control the output, so as to improve the current control accuracy.

[0025] Compared with the prior art, the beneficial effect of the present invention lies in that the high-precision calibration method for real-time simulation of the three-dimensional geomagnetic field of the present invention divides the current segments by performing the data error verification on the single-axis fitting function, so that the single-axis fitting function is close to the logical relationship between the DC current and the actual generated single-axis magnetic field strength, thereby reducing the fitting error and improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field; and by iteratively determining the connection of the fitting functions of each current division segment to generate the single-axis optimization function, the fitting degree of the DC current value at the end point of the current division table and the single-axis magnetic field strength value is improved, thereby ensuring the accuracy and integrity of the single-axis optimization function; and by further optimizing the single-axis optimization function, the influence of the coupling phenomenon on the high-precision calibration of the real-time simulation of the three-dimensional geomagnetic field is eliminated, thereby improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0026] Furthermore, the present invention compares the error between the uniaxial set magnetic field intensity and the uniaxial actually generated magnetic field intensity with the error standard value, and adjusts the current division segment in which the data error is greater than the error standard value, so that the uniaxial fitting function in each current division segment is close to the logical relationship between the direct current and the actual uniaxial magnetic field intensity generated, thereby reducing the error between the simulated magnetic field intensity and the actual magnetic field intensity and increasing the fitting accuracy, so that the uniaxial fitting function can be further optimized subsequently, thereby improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0027] Furthermore, the present invention ensures the stability of current sampling and the accuracy of calibration by judging in real time whether to adjust the current sampling step, and adjusts the current sampling step in a current division segment where the data error is greater than the error standard value, thereby shortening the single lift value of the DC current in the current division segment, making the generated uniaxial fitting function close to the logical relationship between the DC current and the actual generated uniaxial magnetic field strength, making the uniaxial actual generated magnetic field strength fit the uniaxial optimization function, reducing the error between the simulated magnetic field strength and the actual magnetic field strength, and increasing the fitting accuracy, so that the uniaxial fitting function can be further optimized subsequently, thereby improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0028] Furthermore, the present invention judges the error between the uniaxial magnetic field intensity obtained by linear fitting and nonlinear fitting of the fitting function of each current segment and the corresponding actual uniaxial magnetic field intensity obtained under each current value, and selects a fitting method with a smaller error for fitting, so that the uniaxial actual generated magnetic field intensity fits the uniaxial optimization function, thereby improving the fitting accuracy of the optimization fitting function, and further improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field; and solves the segment judgment connection problem through iteration once, avoids missing the fitting situation of the current at the segment point, and ensures the integrity of the optimization fitting function and the accuracy of the fitting.

[0029] Furthermore, the present invention ensures the integrity and fitting accuracy of the single-axis optimization function by performing data fitting on the process of the single-axis input current rising and falling respectively and generating current expressions respectively, so as to combine them into the single-axis optimization function, thereby generating a more accurate simulated magnetic field that better fits the actual magnetic field, thereby improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0030] Furthermore, the present invention determines the fitting method of the uniaxial influence fitting function by adopting the linear fitting to the uniaxial influence fitting function, thereby reducing the workload for linear fitting or nonlinear fitting, which is a supplementary explanation of the method and improves the efficiency of magnetic field fitting.

[0031] Furthermore, the present invention eliminates the coupling effect brought by the other two axes by calculating the actual required magnetic field strength of the single axis, so as to perform the subsequent calculation of the single-axis current fitting function, thereby ensuring the fitting accuracy of the single-axis current fitting function, and then generating a more accurate simulated magnetic field that better fits the actual magnetic field, thereby improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0032] Furthermore, the present invention realizes that the actual current value input can be determined according to the magnetic field strength generated according to the actual need through calculation of the uniaxial current fitting function, and a simulated magnetic field can be generated whose data deviation from the actual magnetic field fitting is no greater than the standard deviation, thereby ensuring high-precision calibration of the three-dimensional geomagnetic field real-time simulation; and the input current is input according to different current segments and different step sizes, thereby ensuring the integrity and high efficiency of the simulation calibration method.

[0033] Furthermore, the present invention adjusts the DC current by determining an initial current adjustment value, thereby reducing the error between the magnetic field strength generated by the actual input current of the set three-dimensional magnetic field and the actual required magnetic field strength of the single axis, so as to generate a magnetic field with smaller data error and more consistent with the actual magnetic field, thereby reducing the coupling influence of the other two axes and improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0034] Furthermore, the present invention ensures the accuracy of the input current value and the generated magnetic field value by controlling the current accuracy, thereby avoiding further influence on the simulated glue due to inaccurate current accuracy, and makes the actual generated magnetic field strength of the single axis fit the single axis optimization function, thereby reducing the error between the simulated magnetic field strength and the actual magnetic field strength, increasing the fitting accuracy, and improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a flow chart of a high-precision calibration method for real-time simulation of three-dimensional geomagnetic field according to an embodiment of the present invention;

[0036] Figure 2 This is the relationship diagram of the X-axis voltage lifting magnetic field change;

[0037] Figure 3 This is the effect of the X-axis magnetic field lift on the Y-axis;

[0038] Figure 4 This is the effect of the X-axis magnetic field lift on the Z-axis;

[0039] Figure 5 To read the magnetic field offset map. DETAILED DESCRIPTION

[0040] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0042] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is merely for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0043] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0044] See also Figure 1 As shown, it is a flow chart of a high-precision calibration method for real-time simulation of three-dimensional geomagnetic field according to an embodiment of the present invention.

[0045] The embodiment of the present invention provides a high-precision calibration method for real-time simulation of a three-dimensional geomagnetic field, comprising:

[0046] Step S1, collecting the direct current passed through the three-dimensional Helmholtz coil, and obtaining the corresponding uniaxial magnetic field strength under each current value, to form a uniaxial fitting function of the current and the magnetic field under a single axis;

[0047] Step S2, performing data error verification based on the uniaxial fitting function, and determining the current division segments of the uniaxial fitting relationship based on the data error verification result;

[0048] Step S3, determining the fitting function of each current division segment according to the current division segment, and determining the connection of the fitting functions of each current division segment by iteration, so as to generate a single-axis optimization function of current and magnetic field;

[0049] Step S4, for a single dimension, obtaining the magnetic field strength of the other two axes corresponding to each current value, and forming a single-axis influence fitting function of the single-axis current and the other two-axis magnetic fields respectively under a single axis;

[0050] Step S5, generating a uniaxial current fitting function based on the uniaxial influence fitting function of the other two-axis magnetic fields and the uniaxial optimization function, so as to calculate the actual input current of the set three-dimensional magnetic field.

[0051] It can be understood that in step S1, the range of DC current values ​​needs to be set in advance before collecting DC current, and the range of DC current values ​​is determined according to the range of the single-axis set magnetic field strength and the magnetic field value corresponding to the input current value per milliampere; wherein, the range of the single-axis set magnetic field strength is the range of magnetic field strength required to be simulated in actual operation, and the magnetic field value corresponding to the input current value per milliampere is determined according to the actual current configuration, the measurement position of the magnetic field and other conditions.

[0052] In this embodiment, the range of the single-axis set magnetic field strength is -90000nT to 90000nT, and the magnetic field corresponding to the input current value per milliampere is 45nT. The range of the input current value is the quotient of the single-axis set magnetic field strength and the magnetic field corresponding to the input current value per milliampere, that is, the range of the input current value is -2A to 2A.

[0053] It is understandable that, in step S1, when collecting each current value, it is necessary to raise the current according to a certain step length, that is, a preset step length, and obtain the actual single-axis generated magnetic field strength at each current value.

[0054] The preset step length is determined according to the range of the input current value, and is 1 / 1000 to 1 / 100 of the length of the range of the input current value.

[0055] In this embodiment, the sampling step size is 0.01A, and the input current is continuously increased from -2A to 2A in steps of 0.01A. The fitting parameters of the input current value and the collected magnetic field value are obtained using the least squares function to form a uniaxial fitting function of the current and magnetic field under a single axis.

[0056] It can be understood that, for a single dimension, the single-axis input current is adjusted by adjusting the single-axis input voltage with the current sampling step, and the single-axis input voltage is positively correlated with the single-axis input current.

[0057] It can be understood that the data processing in the embodiments of the present invention includes but is not limited to the collection of DC current, the acquisition of uniaxial magnetic field strength, the calculation of current and the generation of functions, and also includes the integration, storage and transmission of calculation instructions of data. The data processing method used uses one or more of the existing technologies, which will not be repeated here.

[0058] The high-precision calibration method for real-time simulation of three-dimensional geomagnetic field of the present invention performs the data error verification on the single-axis fitting function to divide the current segment, so that the single-axis fitting function is close to the logical relationship between the direct current and the actual generated single-axis magnetic field strength, thereby reducing the fitting error and improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field; and iteratively determines the connection of the fitting functions of each current division segment to generate the single-axis optimization function, thereby improving the fitting degree of the direct current value at the end point of the current division table and the single-axis magnetic field strength value, and ensuring the accuracy and integrity of the single-axis optimization function; through further optimization of the single-axis optimization function, the influence of the coupling phenomenon on the high-precision calibration of the real-time simulation of the three-dimensional geomagnetic field is eliminated, and the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field is improved.

[0059] Specifically, in step S2, the data error verification result is the data error between the single-axis set magnetic field strength and the single-axis actually generated magnetic field strength, and the current division segments are determined according to the range of the data error verification result.

[0060] It is understandable that the hysteresis phenomenon between the current and the generated magnetic field causes data errors in the generated magnetic field relative to the set magnetic field, and the interference of the hysteresis phenomenon on the precise generation of the real-time magnetic field needs to be solved.

[0061] If the data errors corresponding to the input currents in a single current segment are all less than or equal to the standard error value, there is no need to adjust the length of the single current segment;

[0062] If the data error corresponding to a single input current in a single current segment is greater than the error standard value, it is necessary to reduce the length of the current division segment and perform data error verification again until the data error is less than or equal to the error standard value.

[0063] The current segments after the data error verification are completed are integrated into the current division segments of the uniaxial fitting relationship.

[0064] It can be understood that the length of the current division segment is inversely proportional to the data error.

[0065] It is understandable that the standard error value is determined according to the actual accuracy requirement for the simulated magnetic field; generally, if the actual accuracy requirement for the simulated magnetic field is higher, the standard error value needs to be reduced.

[0066] It can be understood that, from the foregoing, when collecting each current value, it is necessary to raise the current according to a certain step size, that is, a preset step size, and then obtain the corresponding uniaxial magnetic field strength under each current value, forming a uniaxial fitting function of the current and magnetic field under a single axis; therefore, the single current segment should contain at least two current values, and the difference between adjacent current values ​​is the preset step size.

[0067] In this embodiment, the preset step size is 0.01A, the difference between adjacent current values ​​is 0.01A, and the range of the input current value is -2A to 2A;

[0068] In a specific embodiment, the number of the current division segments is 40, the length of each current division segment is the same, which is 0.1A, and the error standard value is 20nT; in the current division segment of 0-0.1A, if the data error between the simulated magnetic field strength generated by increasing the current in steps of 0.01A and the actual magnetic field strength is 15nT, which is less than the error standard value 20nT, then there is no need to adjust the length of the current division segment; if the data error is 40nT, which is greater than the error standard value 20nT, then the length of the current division segment is reduced, and the 0-0.1A is divided into two current division segments of 0-0.05A and 0.05A-0.1A, and fitting functions are generated in these two current division segments respectively, and the size of the data error and the error standard value is judged again until the data error of each current division segment is less than or equal to the error standard value 20nT.

[0069] It is understandable that the actual average error of the magnetic field generated by a single axis must also meet the index requirement of being less than the standard error value.

[0070] Please refer to Table 1, which is an X-axis data error table in the three-dimensional geomagnetic field simulation according to an embodiment of the present invention.

[0071] In this embodiment, the average error of the actual magnetic field generated for X is greater than the standard error value, and the index requirement is not met; when the single-axis set magnetic field strength is 0-23000nT, the table lists several X-axis single-axis set magnetic field strengths corresponding to the actual generated X-axis magnetic field strengths, and the errors of each data are greater than the standard error value, and the errors of the unlisted data are also greater than the standard error value, so it is necessary to reduce the length of the current division segment corresponding to the single-axis set magnetic field strength of 0-23000nT.

[0072] Table 1

[0073]

[0074]

[0075] The present invention compares the error between the uniaxial set magnetic field intensity and the uniaxial actually generated magnetic field intensity with the error standard value, and adjusts the current division segment whose data error is greater than the error standard value, so that the uniaxial fitting function in each current division segment is close to the logical relationship between the direct current and the actual uniaxial magnetic field intensity generated, reduces the error between the simulated magnetic field intensity and the actual magnetic field intensity, increases the fitting accuracy, and enables the subsequent further optimization of the uniaxial fitting function, thereby improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0076] Specifically, in step S3, the current sampling step length of the fitting function of each current division segment is set according to the data error of the current division segment, and the current sampling step length is inversely proportional to the data error.

[0077] It can be understood that the original current sampling step length is the preset step length, and whether to adjust the preset step length is determined according to the data error.

[0078] For a single current segment:

[0079] If the data error is less than or equal to the error standard value, there is no need to adjust the preset step size of the corresponding current division segment;

[0080] If the data error is greater than the error standard value, the preset step size of the corresponding current division segment needs to be reduced until the data error is less than or equal to the error standard value, and the current sampling step sizes of other current division segments remain unchanged.

[0081] The current sampling step size needs to be reduced until the data error is greater than the error standard value.

[0082] In this embodiment, the preset step size is 0.01A.

[0083] In a specific embodiment, in the current division segment of 0 to 0.1A, if the data error between the magnetic field strength obtained by bringing a direct current of 0.01A or 0.05A into the fitting function and the corresponding actual magnetic field strength is 15nT, which is less than the error standard value of 20nT, then there is no need to adjust the current sampling step of the current division segment of 0 to 0.1A; if the data error is 45nT, which is greater than the error standard value of 20nT, then it is necessary to reduce the current sampling step in the current division segment of 0 to 0.1A. In this embodiment, the original 0.01A step is reduced to 0.005A, and the size relationship between the corresponding data error and the error standard value after reducing the current sampling step is determined again until the data error is less than or equal to the error standard value of 20nT.

[0084] The present invention ensures the stability of current sampling and the accuracy of calibration by judging in real time whether to adjust the current sampling step length, and adjusts the current sampling step length in a current division segment where the data error is greater than the error standard value, thereby shortening the single lift value of the DC current in the current division segment, making the generated uniaxial fitting function close to the logical relationship between the DC current and the actual generated uniaxial magnetic field strength, making the uniaxial actual generated magnetic field strength fit the uniaxial optimization function, reducing the error between the simulated magnetic field strength and the actual magnetic field strength, and increasing the fitting accuracy, so that the uniaxial fitting function can be further optimized subsequently, thereby improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0085] Please refer to Figure 2 As shown, it is a diagram showing the relationship between the X-axis voltage lifting magnetic field change in an embodiment of the present invention.

[0086] Specifically, in step S3, the fitting function of each current segment is linearly fitted and nonlinearly fitted respectively using the least square method, and the optimized fitting function of each current segment is determined according to the verification errors of the generated linear fitting function and nonlinear fitting function.

[0087] It can be understood that the verification error is the error between the fitted uniaxial magnetic field intensity and the corresponding actually obtained uniaxial magnetic field intensity at each current value, and a fitting function with a smaller error is selected as the optimized fitting function.

[0088] In this embodiment, the nonlinear single-axis optimization function calculation for the x-axis is as follows:

[0089]

[0090] It is understandable that when determining the actual magnetic field strength generated by the single axis, the magnetic field strength is first judged, the magnetic field range is determined, the corresponding fitting parameters are selected to obtain the corresponding input current value, and the segmented judgment connection problem is solved through iteration once.

[0091] In this embodiment, the fitting rule of the DC current and the magnetic field is repeatable, and the Y-axis and Z-axis coils also have this rule, which ensures that the magnetic field fitting is achieved through the least squares algorithm.

[0092] It can be understood that by dividing the current into segments and adjusting the current sampling step, the actual magnetic field strength generated by the single axis is fitted to the single axis optimization function, thereby improving the accuracy of the single axis optimization function and further improving the accuracy of the simulation algorithm calibration of the single axis magnetic field.

[0093] The present invention performs data fitting during the process of the uniaxial input current rising and falling respectively and generates current expressions respectively, so as to combine them into the uniaxial optimization function, thereby ensuring the integrity of the uniaxial optimization function and the accuracy of the fitting, and further generating a more accurate simulated magnetic field that better fits the actual magnetic field, thereby improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0094] Specifically, in step S3, the fitting functions of the corresponding current division sections are determined respectively according to the rising and falling trends of the real-time current simulation.

[0095] It can be understood that when the single-axis input current is raised and lowered respectively, the corresponding fitting parameters are different, and the corresponding current expressions are different. Therefore, it is necessary to perform data fitting respectively in the process of raising and lowering the single-axis input current, and generate the current expressions respectively, so as to combine them into the single-axis optimization function.

[0096] The present invention performs data fitting during the process of the uniaxial input current rising and falling respectively and generates current expressions respectively, so as to combine them into the uniaxial optimization function, thereby ensuring the integrity of the uniaxial optimization function and the accuracy of the fitting, and further generating a more accurate simulated magnetic field that better fits the actual magnetic field, thereby improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0097] Please refer to Figure 3 and Figure 4 As shown, Figure 3 The embodiment of the present invention is a diagram showing the influence of the X-axis magnetic field lifting on the Y-axis. Figure 4 The embodiment of the present invention is a diagram showing the influence of the X-axis magnetic field lifting on the Z-axis.

[0098] Specifically, in step S4, the uniaxial influence fitting function adopts linear fitting.

[0099] It can be understood that the wire current in the three-dimensional coil generates a magnetic field in the space around the wire. Due to the non-orthogonality of the three-axis Helmholtz coil system, there is mutual coupling between the coils, that is, the magnetic field generated by the single-axis coil in this direction is not only related to the input current, but the current coupling of the coils in the other two directions will also affect the accuracy of the generated single-axis magnetic field.

[0100] The regular relationship of the coupled magnetic fields of the other two axes corresponding to the single-axis current is fitted by using the least square method, that is, the single-axis influence fitting function, and the coupling influence of the other two axes is eliminated by using the single-axis influence fitting function.

[0101] In this embodiment, the induced magnetic field is generated by continuously raising the single-axis current for multiple times, and the changes in the induced magnetic fields of the other two axes are measured to observe the coupling influence law between the coils; as the induced magnetic field generated by the single-axis coil input current increases, the inductive influence on the other two axes increases, and the coupling influence has the characteristics of repeatability and a certain linear law.

[0102] In this embodiment, as the input current increases, the X-axis induced magnetic field increases from -90000nT to 90000nT. By recording the magnetic field offsets of the Y and Z axes, it is found that the zero bias magnetic field changes of the Y and Z axes are linearly superimposed. Therefore, the least squares method of linear fitting is used to fit the regular relationship of the coupled magnetic fields of the other two axes corresponding to the X-axis current. When simulating the magnetic field of the Y and Z axes, this regular relationship can be used to eliminate the coupling effect brought by the X-axis.

[0103] When current is passed through the Y and Z axes, the induced magnetic field changes. As can be seen from the figure, the induced magnetic field in the Y and Z axes increases, that is, when the current passed through the coil increases, the coupling effect on the X axis is different, but increases linearly.

[0104] As described above, the uniaxial influence fitting function for the three axes adopts linear fitting.

[0105] The present invention adopts the linear fitting to the uniaxial influence fitting function, determines the fitting mode of the uniaxial influence fitting function, reduces the workload for linear fitting or nonlinear fitting, is a supplementary explanation to the method, and improves the efficiency of magnetic field fitting.

[0106] Specifically, in step S4, according to the input current values ​​of the other two axes and the corresponding magnetic field strengths generated in the other two axes under each current value, the fitting coefficients corresponding to the single-axis current and the single-axis influence fitting functions of the other two-axis magnetic fields are calculated, and the single-axis influence fitting function is generated to calculate the actual required magnetic field strength of the single axis.

[0107] In this embodiment, for the X-axis, the actual required magnetic field strength of the single axis is:

[0108] B x_real =B xo -B y_x -B z_x .

[0109] Among them, B x_real is the actual required magnetic field strength of the single axis, B XO Set the magnetic field strength for the single axis, B y_x is the coupling magnetic field strength of the Y axis to the X axis, B z_x is the coupling magnetic field strength of the Z axis to the X axis.

[0110] It can be understood that the calculation of the uniaxial influence fitting function of the Y-axis and the Z-axis is the same as the above calculation, and the uniaxial actual required magnetic field strength of the corresponding axis is calculated respectively; the uniaxial actual required magnetic field strength of the Y-axis is B y_real =B yo -B x_y -B z_y , the actual required magnetic field strength of the single axis of the Z axis is B z_real =B zo -B y_z -B x_z ; said B y_x , B z_x , B x_y , B z_y , B y_z With B x_z Acquired through direct collection.

[0111] According to the current values ​​of each current division segment under the single axis, the actual required magnetic field strength of the corresponding single axis, and the coupling magnetic field strength of the other two axes to the single axis, the single axis influence fitting function of the coupling influence of the other two axes corresponding to each current division segment on the single axis is fitted, and the corresponding fitting coefficient is determined.

[0112] The present invention eliminates the coupling influence brought by the other two axes by calculating the actual required magnetic field strength of the single axis, so as to perform subsequent calculation of the single axis current fitting function, thereby ensuring the fitting accuracy of the single axis current fitting function, and further generating a more accurate simulated magnetic field that better fits the actual magnetic field, thereby improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0113] Specifically, in step S5, the actual input current of the set three-dimensional magnetic field is calculated according to the actual required magnetic field strength of the single axis and the single-axis influencing magnetic field strengths of the other two axes being brought into the single-axis current fitting function.

[0114] It can be understood that, in step S5, a uniaxial current fitting function is generated based on the uniaxial influence fitting function of the other two-axis magnetic fields and the uniaxial optimization function to calculate the actual input current of the set three-dimensional magnetic field.

[0115] In this embodiment, for the X-axis, when the uniaxial influence fitting function is obtained, the uniaxial current fitting function should be changed from the original I x =a*B x 2 +b*B x +c becomes:

[0116] I x =(a xx *B x 2 +bxx *B x +c xx )-(a yx *B y 2 +b yx *B y +c yx )-(a zx *B z 2 +b zx *B z +C zx );It is the uniaxial current fitting function of the X-axis.

[0117] Among them, a xx 、b xx 、c xx is the fitting coefficient of the uniaxial optimization function of the X-axis; a yx 、b yx 、c yx is the fitting coefficient corresponding to the uniaxial influence fitting function of the coupling effect of the Y axis on the X axis; a zx 、b zx 、c zx I is the fitting coefficient corresponding to the uniaxial influence fitting function of the coupling effect of the Z axis on the X axis; x The actual input X-axis DC current for setting the three-dimensional magnetic field.

[0118] It can be understood that the calculation of the uniaxial current fitting function of the Y-axis and the Z-axis is the same as the above calculation.

[0119] The uniaxial current fitting function of the Y-axis is:

[0120] I y =(a yy *B y 2 +b yy *B y +c yy )-(a xy *B x 2 +b xy *B x +c xy )-(a zy *B z 2 +b zy *B z +C zy ).

[0121] Among them, a yy 、b yy 、c yyis the fitting coefficient of the single-axis optimization function of the Y axis; a xy 、b xy 、c xy is the fitting coefficient corresponding to the uniaxial influence fitting function of the coupling effect of the X-axis on the Y-axis; a zy 、b zy , C zy I is the fitting coefficient corresponding to the uniaxial influence fitting function of the coupling effect of the Z axis on the Y axis; y The actual input Y-axis DC current for setting the three-dimensional magnetic field.

[0122] The uniaxial current fitting function of the Z axis is:

[0123] I z =(a zz *B z 2 +b zz *B z +c zz )-(a xz *B x 2 +b xz *B x +c xz )-(a yz *B y 2 +b yz *B y +C yz ).

[0124] Among them, a zz 、b zz 、c zz is the fitting coefficient of the single-axis optimization function of the Z axis; a xz 、b xz 、c xz is the fitting coefficient corresponding to the uniaxial influence fitting function of the coupling effect of the X-axis on the Z-axis; a yz 、b yz , C yz I is the fitting coefficient corresponding to the uniaxial influence fitting function of the Y-axis coupling effect on the Y-axis; z The actual input Z-axis DC current for setting the three-dimensional magnetic field.

[0125] It can be understood that the actual input current of the set three-dimensional magnetic field can be calculated by the uniaxial current fitting function, and the three-axis ideal input current value is input into the three-axis Helmholtz coil to generate a simulated magnetic field with an error within a certain range, thereby completing the calibration of the simulation algorithm of the three-axis magnetic field.

[0126] In this embodiment, after the calculation of the uniaxial current fitting function is completed, the uniaxial current fitting function is calibrated and the calibration result is verified. The verification result is as follows:

[0127] For the X-axis, the actual required magnetic field strength of the single axis set by the X-axis vector is recorded as B x0 The actual generated magnetic field strength of the single axis measured three times is recorded as B x1 , B x2 , B x3 The average error is recorded as ΔBarg. The actual required magnetic field strength of the single axis is randomly input, and it is repeated three times to observe the actual generated magnetic field strength of the single axis. The final results are shown in Table 2. The average errors of multiple tests are all around 10nT, and the maximum error is 17.48nT.

[0128] Please refer to Table 2, which is the calibration result of the uniaxial current fitting function of the X-axis.

[0129] Table 2

[0130]

[0131]

[0132] The calibration results in the table show that the average error is less than the standard error value, and the average error is less than the average error in Table 1, which meets the standard error value, and the simulation algorithm calibration of the three-axis magnetic field is completed.

[0133] The present invention realizes that the actual input current value can be determined according to the magnetic field strength generated according to the actual need by calculating the uniaxial current fitting function, and a simulated magnetic field can be generated whose data deviation from the actual magnetic field fitting is no greater than the standard deviation, thereby ensuring high-precision calibration of the three-dimensional geomagnetic field real-time simulation; and the input current is input according to different current division segments and different step sizes, thereby ensuring the integrity and high efficiency of the simulation calibration method.

[0134] Specifically, in the step S5, it also includes:

[0135] Determine the initial current value corresponding to the actual required magnetic field of the single axis;

[0136] Determining the influence magnetic field strength in the uniaxial influence fitting function of the other two-axis magnetic fields based on the initial current value;

[0137] An initial current adjustment value is determined based on the ratio of the influencing magnetic field strength to the actual required magnetic field of the single axis.

[0138] It can be understood that by determining the initial current adjustment value to adjust the DC current, the error between the magnetic field strength generated by the actual input current of the set three-dimensional magnetic field and the actual required magnetic field strength of the single axis is reduced.

[0139] The present invention adjusts the direct current by determining an initial current adjustment value, thereby reducing the error between the magnetic field intensity generated by the actual input current of the set three-dimensional magnetic field and the actual required magnetic field intensity of the single axis, so as to generate a magnetic field with smaller data error and more fitting to the actual magnetic field, reduce the coupling influence of the other two axes, and improve the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0140] Specifically, in step S1, the precision control of the DC current includes:

[0141] The current to be output is divided into an integer part and a decimal part;

[0142] In the circuit, several resistors of different sizes are connected in parallel to shunt the current of several outputs to control the output, so as to improve the current control accuracy.

[0143] It is understandable that in order to meet the requirement that the data error is less than the standard error value, the DC current needs to be accurately controlled. By utilizing the voltage divider effect of the resistors and configuring the appropriate resistor values, the DC current is distributed to two or more output channels, while keeping the DC current value on each channel within the required range, ensuring that the voltage or current value on each channel meets the current accuracy control requirements.

[0144] See also Figure 5 As described above, it is to read the magnetic field offset map.

[0145] In a specific embodiment, a short-term change in the current passing through the coil will cause a surge in current, resulting in jitter in the generated simulated magnetic field, and real-time reading of the collected magnetic field value will cause the read magnetic field value to shift; by using the least squares method to perform magnetic field simulation calibration and using a continuous step-size to increase the current, directly reading the collected magnetic field value will also cause the read magnetic field value to shift.

[0146] When the magnetic field is changed to pass DC current into the coil or the DC current is increased in steps, the magnetic field value is read with a delay. Through data analysis, the magnetic field overshoot caused by the surge in DC current will tend to stabilize within 100ns, so a delay of 100ns is added in the algorithm program, and the magnetic field value is read after it stabilizes.

[0147] In another specific embodiment, since the real-time performance of the magnetic field simulation system also requires that the maximum continuously adjustable frequency of the magnetic field is not less than 50 Hz, the collected magnetic field data is filtered to remove the noise affected by the circuit ripple, and 50 data are continuously collected within the collection dwell time for sliding filtering as the collection point data output, so as to obtain a better linear relationship.

[0148] The present invention ensures the accuracy of the input current value and the generated magnetic field value by controlling the current accuracy, thereby avoiding further influence on the simulated glue due to inaccurate current accuracy, and makes the actual generated magnetic field strength of the single axis fit the single axis optimization function, thereby reducing the error between the simulated magnetic field strength and the actual magnetic field strength, increasing the fitting accuracy, and improving the calibration accuracy of the real-time simulation of the three-dimensional geomagnetic field.

[0149] The parts not described in the present invention are applicable to the prior art. So far, the technical scheme of the present invention has been described in conjunction with the preferred embodiments shown in the drawings, but it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical schemes after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A high-precision calibration method for real-time simulation of three-dimensional geomagnetic field, characterized in that: include: Step S1, collecting the direct current passed through the three-dimensional Helmholtz coil, and obtaining the corresponding uniaxial magnetic field strength under each current value, to form a uniaxial fitting function of the current and the magnetic field under uniaxial conditions; Step S2, performing data error verification based on the uniaxial fitting function, and determining the current division segments of the uniaxial fitting relationship based on the data error verification result; Step S3, determining the fitting function of each current division segment according to the current division segment, and determining the connection of the fitting functions of each current division segment by iteration, so as to generate a single-axis optimization function of current and magnetic field; Step S4, for a single dimension, obtaining the magnetic field strength of the other two axes corresponding to each current value, and forming a single-axis influence fitting function of the single-axis current and the other two-axis magnetic fields respectively under a single axis; Step S5, generating a uniaxial current fitting function based on the uniaxial influence fitting function of the other two-axis magnetic fields and the uniaxial optimization function, so as to calculate the actual input current of the set three-dimensional magnetic field.

2. The high-precision calibration method for a three-dimensional geomagnetic field real-time simulation system according to claim 1, characterized in that: In the step S2, the data error verification result is the data error between the single-axis set magnetic field strength and the single-axis actually generated magnetic field strength, and the current division segments are determined according to the range of the data error verification result.

3. The high-precision calibration method for a three-dimensional geomagnetic field real-time simulation system according to claim 1, characterized in that: In step S3, the current sampling step length of the fitting function of each current division segment is set according to the data error of the current division segment, and the current sampling step length is inversely proportional to the data error.

4. The high-precision calibration method for a three-dimensional geomagnetic field real-time simulation system according to claim 2, characterized in that: In step S3, the fitting function of each current segment is linearly fitted and nonlinearly fitted respectively using the least square method, and the optimized fitting function of each current segment is determined according to the verification errors of the generated linear fitting function and nonlinear fitting function.

5. The high-precision calibration method for a three-dimensional geomagnetic field real-time simulation system according to claim 3, characterized in that: In step S3, the fitting functions of the corresponding current division sections are determined respectively according to the rising and falling trends of the real-time current simulation.

6. The high-precision calibration method for the three-dimensional geomagnetic field real-time simulation system according to claim 4, characterized in that: In the step S4, the uniaxial influence fitting function adopts linear fitting.

7. The high-precision calibration method for a three-dimensional geomagnetic field real-time simulation system according to claim 1, characterized in that: In step S4, according to the input current values ​​of the other two axes and the corresponding magnetic field strengths generated in the other two axes at each current value, the fitting coefficients corresponding to the single-axis current and the single-axis influence fitting functions of the other two-axis magnetic fields are calculated, and the single-axis influence fitting function is generated to calculate the actual required magnetic field strength of the single axis.

8. The high-precision calibration method for a three-dimensional geomagnetic field real-time simulation system according to claim 6, characterized in that: In the step S5, the actual input current of the set three-dimensional magnetic field is calculated by bringing the actual required magnetic field strength of the single axis and the single-axis influencing magnetic field strengths of the other two axes into the single-axis current fitting function.

9. The high-precision calibration method for a three-dimensional geomagnetic field real-time simulation system according to claim 1, characterized in that: In the step S5, it also includes: Determine the initial current value corresponding to the actual required magnetic field of the single axis; Determining the influence magnetic field strength in the uniaxial influence fitting function of the other two-axis magnetic fields based on the initial current value; An initial current adjustment value is determined based on the ratio of the influencing magnetic field strength to the actual required magnetic field of the single axis.

10. The high-precision calibration method for a three-dimensional geomagnetic field real-time simulation system according to claim 1, characterized in that: In step S1, the precision control of the DC current includes: The current to be output is divided into an integer part and a decimal part; In the circuit, several resistors of different sizes are connected in parallel to shunt the current of several outputs to control the output, so as to improve the current control accuracy.

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