A magnetic positioning system

Abstract

The application discloses a magnetic positioning system, and relates to the technical field of magnetic field measurement and positioning, which is used for realizing six-degree-of-freedom real-time tracking of a target in a space range. The system is characterized in that a magnet is carried on a rotating bearing, a controller is used to drive a motor to generate a low-frequency magnetic signal, a magnetic sensor is used to measure the generated magnetic signal, real-time rotating information output by an angle encoder fixed on the motor rotating shaft is combined, and a calculation program is used to solve the space position information of the sensor. The system can realize instantaneous positioning of a low-frequency periodic magnetic signal, solves the problems of slow speed of a low-frequency magnetic field positioning technology and easy interference of a high-frequency magnetic field positioning technology, improves the convenience and stability of the magnetic positioning method, and reduces the cost of the magnetic positioning method.

Description

Technical Field

[0001] The present invention relates to the field of magnetic field measurement and positioning technology, and in particular to a magnetic positioning system based on a generated low-frequency magnetic field. Background Art

[0002] Motion capture is to set up trackers on the key parts of the moving object, and obtain the six-degree-of-freedom position data of the tracker in three-dimensional space after calculation and processing, to assist in reconstructing the movement process of the target object in the space range.

[0003] The positioning results are crucial to the entire motion capture process. Common spatial positioning methods can be categorized as optical, inertial, and magnetic. Optical positioning is the most widely used and most accurate method. However, optical positioning systems are costly, susceptible to occlusion, and require large positioning markers, requiring a high degree of environmental suitability. Inertial positioning systems offer a high capture rate and are unaffected by environmental interference, but their positioning accuracy is relatively low. Magnetic positioning, with its lack of line-of-sight interference, high response sensitivity, and compact size, is a commonly used positioning method for motion capture.

[0004] Magnetic positioning systems can be divided into high-frequency electromagnetic and low-frequency magnetic positioning systems based on the magnetic field frequency they rely on. Existing high-frequency electromagnetic positioning systems use coils and peripheral frequency matching circuits to construct signal transmission and reception modules, and calculate the module's position information through nonlinear fitting of periodic signals. Low-frequency magnetic positioning systems typically use the signal source radiated by the magnet itself to construct a low-frequency magnetic field signal and use array sensors to analyze the spatial position of the target magnet.

[0005] Traditional high-frequency magnetic positioning systems offer high positioning accuracy and refresh rates, but are susceptible to interference from external environments such as metal objects, which can affect positioning during tracking. While traditional low-frequency magnetic positioning systems are less susceptible to interference from metal eddy currents, they suffer from slower positioning speeds and less position information, hindering their practical use in motion capture. Summary of the Invention

[0006] In view of the above problems, the present invention provides a magnetic positioning system designed to overcome or at least partially resolve these issues. This system enables instantaneous positioning using low-frequency periodic magnetic signals, resolving the issues of slow low-frequency magnetic field positioning techniques and susceptibility to metal interference in high-frequency magnetic field positioning techniques. This system improves the convenience and stability of magnetic positioning methods and reduces their cost.

[0007] The present invention provides the following solutions:

[0008] A magnetic positioning system, comprising:

[0009] A magnetic field generating unit, comprising a magnet, a rotation driving assembly and an angle encoder; the rotation driving assembly is used to drive the magnet to rotate so as to form a low frequency magnetic field signal radiating to the surroundings; the angle encoder is used to acquire the rotation angle information of the magnet during rotation;

[0010] A measurement unit, comprising a magnetic field measurement sensor, which is used to acquire magnetic signal information;

[0011] A calculation unit, which is communicatively connected with the measurement unit and the angle encoder, and is used to perform the following operations:

[0012] Receiving the magnetic signal information and the rotation angle information;

[0013] Constructing a physical model of magnet space movement by using the magnetic signal information and the rotation angle information;

[0014] Obtaining initial space coordinate information of the magnetic field measurement sensor by using the physical model and combining an analytical algorithm;

[0015] Obtaining six-degree-of-freedom information of the magnetic field measurement sensor by using the initial space coordinate and combining a nonlinear optimization algorithm.

[0016] Preferably, the physical model is used to represent the geometric relationship between the magnetic field measurement sensor and the magnet, and is represented by the following formula:

[0017]

[0018] In the formula, K represents the induction coefficient of the sensor to perceive the magnetic field, d represents the distance module value, represents the geometric center distance of the magnetic field measurement sensor from the magnet, represents the magnetic moment deflection angle vector of the magnet.

[0019] Preferably, the objective function optimized by the nonlinear optimization algorithm is represented by the following formula:

[0020]

[0021] In the formula, x, y and z represent the initial space coordinate information of the magnetic field measurement sensor, α, β and γ represent the rotation of the magnetic field measurement sensor around the x, y and z axes, V i represents the magnetic induction intensity detected by the sensor at the i th moment, R represents the rotation matrix corresponding to the attitude angle of the sensor, B i represents the theoretical magnetic induction intensity at this moment constructed according to the physical model.

[0022] Preferably, the value of the coordinate z is obtained by modulus relation and constraint condition z>0, the values of the coordinates x and y are obtained by solving the following two equations:

[0023]

[0024]

[0025] In the formula, d represents a distance modulus, K represents a sensing coefficient of the sensor and the permanent magnet, B x , B y , B z represents three-axis components.

[0026] Preferably, the value of the distance modulus d is obtained by solving the modulus form of the magnetic dipole formula by using the relation between the magnetic moment included angles, and the value of the included angle cos θ between the coordinate P (x, y, z) and the plane XOY.

[0027] Preferably, the rotation driving assembly comprises a stepping motor and a stepping motor encoder.

[0028] Preferably, the stepping motor encoder is used to control the stepping motor to rotate periodically at a target frequency.

[0029] Preferably, the angle encoder comprises any one of a capacitive angle encoder or a photoelectric angle encoder.

[0030] Preferably, the magnetic field measurement sensor comprises an anisotropic magnetoresistance (AMR) sensor.

[0031] According to the specific embodiments of the present application, the following technical effects are disclosed:

[0032] The magnetic positioning system provided by the embodiments of the present application is used to realize six-degree-of-freedom real-time tracking of a target in a space range. The magnet is carried on a rotating bearing, a controller is used to drive a motor to generate a low-frequency magnetic field signal, a magnetic sensor is used to measure the generated magnetic signal, real-time rotation information output by an angle encoder fixed to the motor rotating shaft is combined, and a calculation program is used to realize solving of the spatial pose information of the sensor. The system can realize instantaneous positioning of a low-frequency periodic magnetic signal, solves the problems of slow speed of a low-frequency magnetic field positioning technology and easy interference of a high-frequency magnetic field positioning technology, improves the convenience and stability of the magnetic positioning method, and reduces the cost of the magnetic positioning method.

[0033] Of course, any product implementing the present application does not necessarily need to achieve all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0034] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0035] Figure 1 This is a connection block diagram of various modules of a magnetic positioning system provided by an embodiment of the present invention;

[0036] Figure 2 The embodiment of the present invention provides a flow chart of a magnetic positioning method;

[0037] Figure 3 1 is a structural diagram of a magnetic field generating unit provided by an embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of the analysis of the magnetic positioning system algorithm provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0040] See also Figure 1 , is a magnetic positioning system provided by an embodiment of the present invention, such as Figure 1 As shown, the system may include:

[0041] A magnetic field generating unit includes a magnet 9, a rotation drive assembly, and an angle encoder 2; the rotation drive assembly is used to drive the magnet 9 to rotate so as to generate a low-frequency magnetic field signal radiated to the surrounding area; the angle encoder 2 is used to obtain rotation angle information of the magnet 9 during the rotation process; in specific implementation, the embodiment of the present application can provide that the rotation drive assembly includes a stepper motor and a stepper motor encoder 4. Further, the stepper motor encoder 4 is used to control the stepper motor to rotate at a target frequency period.

[0042] The angle encoder 2 includes any one of a capacitive angle encoder and a photoelectric angle encoder.

[0043] The measuring unit includes a magnetic field measuring sensor 7 , which is used to obtain magnetic signal information. The magnetic field measuring sensor 7 includes an anisotropic magnetoresistive AMR sensor.

[0044] A computing unit, the computing unit being communicatively connected to the measuring unit and the angle encoder 2, and configured to perform the following operations:

[0045] receiving the magnetic signal information and the rotation angle information;

[0046] The magnetic signal information and the rotation angle information are used to construct a physical model of the magnet's spatial motion. Furthermore, the physical model is used to represent the geometric relationship between the magnetic field measurement sensor and the magnet, which is expressed by the following formula:

[0047]

[0048] Where: K represents the induction coefficient of the sensor sensing the magnetic field, d represents the distance modulus, Indicates the distance between the coordinates P(x,y,z) of the magnetic field measurement sensor and the geometric center of the magnet. The vector representing the magnetic moment deflection angle of the magnet.

[0049] Using the physical model in combination with an analytical algorithm to obtain initial spatial coordinate information of the magnetic field measurement sensor;

[0050] The six-degree-of-freedom information of the magnetic field measurement sensor is obtained by using the initial space coordinates in combination with a nonlinear optimization algorithm.

[0051] In a specific implementation, the embodiment of the present application can provide that the objective function optimized by the nonlinear optimization algorithm is expressed as follows:

[0052]

[0053] Where: x, y, z represent the initial spatial coordinate information of the magnetic field measurement sensor, α, β, γ represent the rotation of the magnetic field measurement sensor around the x, y, z axis, V i represents the magnetic induction intensity detected by the sensor at the i-th moment, R represents the rotation matrix corresponding to the sensor's own posture angle, and B i It represents the theoretical magnetic induction intensity at that moment constructed based on the physical model.

[0054] The value of coordinate z is obtained through the modulus relationship and the constraint condition z>0, and the values ​​of coordinate x and coordinate y are obtained by solving the following two equations:

[0055]

[0056]

[0057] Where: d represents the distance modulus, K represents the induction coefficient of the sensor sensing the magnetic field, B x , B y , Bz Represents the three-axis components.

[0058] The relationship between the magnetic moment angles is used to obtain the angle cosθ between the coordinate P(x, y, z) and the plane XOY, and the distance modulus d is obtained by solving the modulus form of the magnetic dipole formula.

[0059] The magnetic positioning system provided in the embodiment of the present application can drive the magnet to rotate periodically through a driver such as a motor, forming a low-frequency magnetic field signal radiating to the surrounding area, and combining the rotation angle information and the magnetic field signal measured by the magnetic sensor to realize the analysis of the six-degree-of-freedom posture of the magnetic sensor.

[0060] The system provided in the embodiments of this application uses magnets and motors to generate low-frequency magnetic field signals. Its rotational structure is simple and stable, with low cost and ease of implementation. Furthermore, the system uses angle encoders and sensors to measure the magnetic field numerically, and uses analytical algorithms to predict the location of non-periodic signals, enabling real-time tracking. This addresses the issues of traditional positioning systems based on high-frequency electromagnetic signals, such as susceptibility to interference, the lack of analytical solutions for low-frequency magnetic positioning, and slow response speeds.

[0061] The system provided in the embodiment of the present application mainly includes a magnetic field generating unit, a control unit, a measuring unit, a computing unit (including data processing and algorithm programs) and a matching power drive.

[0062] The magnetic field generating unit is mainly used to generate low-frequency magnetic field, including magnets, motors and drivers, and single-axis rotation systems.

[0063] The magnetic field measurement sensor of the measurement unit is mainly used to measure magnetic signals and magnet rotation information, including AMR magnetic signal sensors and angle encoders.

[0064] The control unit is mainly used to control the motor and data transmission, including the STM32 microcontroller and supporting data transmission equipment.

[0065] The computing unit is mainly used to calculate the six-degree-of-freedom information of the space target, including a PC computer and a data processing program.

[0066] The positioning algorithm is used to implement the analytical algorithm for target positioning, with the sensor's measurement value as input and the spatial six-degree-of-freedom posture information as output.

[0067] Among them, the magnetic field generator consists of a small motor (such as a 36-step motor with a resolution of 0.9°), a driver, and a structural tooling. It is responsible for loading the magnet and generating low-frequency magnetic field signals through rotation; the control unit is a common microcomputer data processing device (such as the single-chip microcomputer STM32F103), which is responsible for system control, motor drive signal generation, data acquisition of the measurement sensor, and transmission to the PC; the magnetic field measurement sensor is composed of an anisotropic magnetoresistive AMR sensor (such as MMC5603NJ, which can realize spatial three-axis orthogonal magnetic field measurement) and a capacitive or photoelectric angle encoder (such as EMT-233BV), which is responsible for realizing magnetic signal measurement and angular information measurement of the rotating magnet; the computing unit (such as a PC) is responsible for processing the collected data, realizing the position and posture solution of the target sensor, and outputting the prediction information; the supporting power supply is responsible for powering and driving the above modules to ensure the normal operation of the system.

[0068] The schematic diagram of the magnetic field generating unit structure provided in this application is as follows Figure 3 As shown, the magnet assembly 1 is responsible for loading and fixing the magnet 9 to ensure the stability of rotation; the angle encoder 2 is responsible for real-time measurement of the angle deflection information of the magnet during system operation; the stepper motor encoder 4 combines with the rotating bearing 3 to drive the magnet to generate a low-frequency magnetic signal of a specific frequency; the overall structural firmware 5 of the generating device is responsible for coupling various components to ensure the normal operation of the device.

[0069] The algorithm flow chart proposed in this application is as follows Figure 3 As shown in the figure, once the system is operational, a controller sends a control signal to the motor, which drives the magnet to generate a low-frequency magnetic field. The three-dimensional vector information of the magnetic field is measured by the magnetic sensor. This information, combined with the magnet's rotation angle measured by the angle encoder, is used to construct a physical model of the magnet's spatial motion. The proposed analytical algorithm then determines the initial spatial coordinates of the target sensor, which serves as a reference to assist subsequent systems in dynamically tracking the target. Simultaneously, the system outputs a predicted six-degree-of-freedom pose of the target sensor.

[0070] The following will be combined with reference Figure 2 and Figure 4 A detailed description of the system algorithm:

[0071] After the system is initialized, the magnet 9 rotates periodically around the rotation axis 8 on the plane 10 at a specific frequency ω1, generating a low-frequency magnetic signal. A rectangular coordinate system XYZ is constructed with the geometric center of the magnet as the coordinate origin. The sensor 7 is placed in the spatial coordinate system with coordinates P(x, y, z) and a distance from the geometric center of the magnet 9 of The distance modulus is d, and the angle between it and the plane XOY is θ. During the rotation process, the real-time measurement signal of the encoder is used to obtain the magnetic moment deflection angle vector of the magnet during the rotation process. According to the magnetic dipole model, a right-handed rectangular coordinate system with the geometric center of the magnet as the origin is established as the global coordinate system. Therefore, the geometric relationship formula between the sensor and the magnet can be constructed:

[0072]

[0073] Assume that at a certain moment t1, the magnet measurement value is The magnetic moment direction of the magnet obtained by the encoder is At this point, the angle between the magnetic moment and the distance vector is θ1, and the angle between the magnetic moment and the sensor's projection vector on the XOY plane is α. Based on the geometric relationship between spatial coordinates in a rectangular coordinate system, the following spatial geometric relationship exists: cosα·cosθ=cosθ1. At the next moment t2, if the angle between the magnetic moments is Δα, then cos(α+Δα)·cosθ=cosθ2. Therefore, combining the above two formulas yields the following relationship:

[0074]

[0075] According to the modular form of the magnetic dipole formula The relationship between the measurement data at connected moments can be constructed:

[0076]

[0077] There are unknown parameters α and θ. Therefore, another time t3 and its measured value are introduced Constructing the association formula:

[0078]

[0079] By relating the two formulas above, we can obtain the identity with only a single unknown parameter α:

[0080] (B' 2 -1)[B 2 cos(α+Δα) 2 -cosα 2 ]-(B 2 -1)[B' 2 cos(α+2·Δα) 2 -cosα 2 ]=0 (5)

[0081] By parameter transformation The above formula can be transformed into the following form:

[0082] tB 2 cos(α+Δα) 2 -B' 2 cos(α+2·Δα) 2 =(t-1)cosα2 (6)

[0083] Using the trigonometric expansion formula, we can obtain a symmetric solution about the parameter α. Since this algorithm only locates and tracks targets within the spatial range where Z > 0, combined with the identity constraint of the above formula, a unique solution can be obtained. Furthermore, based on the relationship between the magnetic moment angles mentioned above, we can obtain the angle cosθ between the coordinates P(x,y,z) and the plane XOY. Using the modular form of the magnetic dipole formula, we can solve for the distance d.

[0084] Expand the magnetic dipole formula by vector, then the three-axis component B x ,B y ,B z The following relationship exists:

[0085]

[0086]

[0087] Therefore, the value of coordinate z can be obtained by the modulus relationship and the constraint condition of Z>0, and the analytical initial value of coordinate P(x, y, z) can be obtained by formulas (7)-(8). Since the sensor has its own rotation R(α, β, γ) during measurement, and there is interference from the earth's magnetic field B in the surrounding space environment, g , so the actual measurement value obtained by the magnetic sensor can be expressed as follows:

[0088] V=R(B+B g )(9)

[0089] Since the magnetic field generating device rotates periodically at a frequency of ω1, digital filtering of the collected raw data at the corresponding frequency can eliminate interference from DC and other frequency magnetic signals. To reduce interference caused by noise such as rotation and device fluctuations and ensure the accuracy of the solution, nonlinear optimization algorithms such as Levenberg-Marquardt and particle swarm optimization are subsequently used to optimize the six-degree-of-freedom information (x, y, z, α, β, γ) based on analytical initial values ​​and a magnetic dipole model, and the results are output as the current positioning prediction value. The optimization objective function can be set as follows based on the sensor parameters to be determined:

[0090]

[0091] According to the above description, the positioning function of the algorithm program is completed by writing a program.

[0092] In summary, the magnetic positioning system provided by the present application is used to achieve real-time tracking of the six degrees of freedom of the tracking target within a spatial range. By placing a magnet on a rotating bearing, a controller is used to drive the motor to generate a low-frequency magnetic field signal, and then the magnetic sensor measures the generated magnetic signal. Combined with the real-time rotation information output by the angle encoder of the fixed motor shaft, the spatial posture information of the sensor is solved using a calculation program. The system can achieve instantaneous positioning of low-frequency periodic magnetic signals, solves the problems of slow speed of low-frequency magnetic field positioning technology and susceptibility to metal interference of high-frequency magnetic field positioning technology, improves the convenience and stability of the magnetic positioning method, and reduces the cost of the magnetic positioning method.

[0093] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0094] Through the description of the above embodiments, it can be seen that those skilled in the art can clearly understand that the present application can be implemented by means of software plus a necessary general hardware platform. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, can be embodied in the form of a software product, which can be stored in a storage medium such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in various embodiments or certain parts of the embodiments of the present application.

[0095] Each embodiment in this specification is described in a progressive manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple. For relevant parts, refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without expending creative work.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. A magnetic positioning system, characterized in that: include: A magnetic field generating unit, comprising a magnet, a rotary drive assembly, and an angle encoder; The rotation drive assembly is used to drive the magnet to rotate so as to form a low-frequency magnetic field signal radiated to the surroundings; the angle encoder is used to obtain the rotation angle information of the magnet during the rotation process; A measuring unit, the measuring unit comprising a magnetic field measuring sensor, the magnetic field measuring sensor being used to obtain magnetic signal information; A computing unit, the computing unit being communicatively connected to the measuring unit and the angle encoder, and configured to perform the following operations: receiving the magnetic signal information and the rotation angle information; Constructing a physical model of the magnet's spatial motion using the magnetic signal information and the rotation angle information; Using the physical model in combination with an analytical algorithm to obtain initial spatial coordinate information of the magnetic field measurement sensor; Using the initial spatial coordinates in combination with a nonlinear optimization algorithm to solve and obtain six-degree-of-freedom information of the magnetic field measurement sensor; The objective function optimized by the nonlinear optimization algorithm is expressed as follows: Where: Represents the initial spatial coordinate information of the magnetic field measurement sensor, Indicates the magnetic field measurement sensor around The rotation of the shaft, Indicates the The magnetic induction intensity detected by the sensor at each moment, Represents the rotation matrix corresponding to the sensor's own attitude angle, It represents the theoretical magnetic induction intensity at that moment constructed according to the physical model; Through the modulus relationship and The constraints on the coordinates are obtained The coordinates are obtained by solving the following two equations and coordinates Value: Where: Represents the distance modulus value, represents the inductance between the sensor and the magnet, ， ， Represents the three-axis components.

2. The magnetic positioning system according to claim 1, characterized in that The physical model is used to represent the geometric relationship between the magnetic field measurement sensor and the magnet, and is expressed by the following formula: Where: Indicates the inductance of the sensor sensing the magnetic field, Represents the distance modulus value, Indicates the coordinates of the magnetic field measurement sensor The distance from the geometric center of the magnet, The vector representing the magnetic moment deflection angle of the magnet.

3. The magnetic positioning system according to claim 1, characterized in that Using the relationship between the magnetic moment angles, we can get the coordinates With plane Angle The distance modulus is obtained by solving the modulus form of the magnetic dipole formula .

4. The magnetic positioning system according to claim 1, characterized in that The rotary drive assembly includes a stepper motor and a stepper motor encoder.

5. The magnetic positioning system according to claim 4, characterized in that: The stepper motor encoder is used to control the stepper motor to rotate at a target frequency period.

6. The magnetic positioning system according to claim 1, characterized in that The angle encoder includes any one of a capacitive angle encoder and a photoelectric angle encoder.

7. The magnetic positioning system according to claim 1, characterized in that The magnetic field measurement sensor includes an anisotropic magnetoresistive (AMR) sensor.

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