Magnetic positioning system

Abstract

The invention discloses a magnetic positioning system, which relates to the technical field of magnetic field measurement and positioning and is used for realizing six-degree-of-freedom real-time tracking of a tracking target in a space range. A magnet is carried on a rotating bearing, a controller is adopted to drive a motor, a low-frequency magnetic field signal is generated, a magnetic sensor measures the generated magnetic signal, real-time rotating information output by an angle encoder for fixing a rotating shaft of the motor is combined, and space pose information of the sensor is solved through a calculation program. The system can realize instantaneous positioning of low-frequency periodic magnetic signals, solves the problems that a low-frequency magnetic field positioning technology is slow in speed and a high-frequency magnetic field positioning technology is easily interfered by metal, improves the convenience and stability of a magnetic positioning method, and reduces the cost of the magnetic positioning method.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic field measurement and positioning, 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 at key parts of moving objects, 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 space.

[0003] The positioning result is very important for the entire process of motion capture. Common spatial positioning methods can be divided into optical, inertial, magnetic positioning, etc. Among them, optical positioning is the most widely used and most accurate positioning method. However, the optical positioning system is costly, easily affected by occlusion, and the positioning markers are large in size, which requires a high applicable environment; the inertial positioning system has a high capture rate and is not affected by the environment, but the positioning accuracy is relatively low; magnetic positioning has the characteristics of no line of sight interference, high response sensitivity, and small size, and 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 according to the frequency of the magnetic field they rely on. The existing high-frequency electromagnetic positioning system uses coils and peripheral frequency matching circuits to build signal transmission and receiving modules, and solves the module posture information through nonlinear fitting of periodic signals. Low-frequency magnetic positioning systems usually 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 posture of the target magnet.

[0005] The traditional high-frequency magnetic positioning system has high positioning accuracy and refresh rate, but it is easily disturbed by external environment such as metal equipment, which affects the positioning use during tracking. Although the traditional low-frequency magnetic positioning system is not easily disturbed by metal eddy currents, it has the problems of slow positioning speed and less posture information, which will affect the actual use of motion capture. Summary of the invention

[0006] In view of the above problems, the present invention provides a magnetic positioning system for overcoming the above problems or at least partially solving the above problems. The system can realize instantaneous positioning of low-frequency periodic magnetic signals, solve the problems that low-frequency magnetic field positioning technology is slow and high-frequency magnetic field positioning technology is susceptible to metal interference, improve the convenience and stability of the magnetic positioning method, and reduce the cost of the magnetic positioning method.

[0007] The present invention provides the following scheme:

[0008] A magnetic positioning system, comprising:

[0009] A magnetic field generating unit, the magnetic field generating unit comprising a magnet, a rotation drive component and an angle encoder; the rotation drive component 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;

[0010] A measuring unit, the measuring unit comprising a magnetic field measuring sensor, the magnetic field measuring sensor being used to obtain magnetic signal information;

[0011] A computing unit, the computing unit is communicatively connected to the measuring unit and the angle encoder, and the computing unit is used to perform the following operations:

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

[0013] Using the magnetic signal information and the rotation angle information to construct a physical model of the magnet's spatial motion;

[0014] Using the physical model in combination with an analytical algorithm to obtain initial spatial coordinate information of the magnetic field measurement sensor;

[0015] 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.

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

[0017]

[0018] 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.

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

[0020]

[0021] 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 according to the physical model.

[0022] Preferably: the value of coordinate z is obtained through the module value relationship and the constraint condition of z>0, and the values ​​of coordinate x and coordinate y are obtained by solving the following two equations:

[0023]

[0024]

[0025] Where: d represents the distance modulus, K represents the inductance coefficient between the sensor and the permanent magnet, B x , B y , B z Represents the three-axis components.

[0026] Preferably: 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.

[0027] Preferably, the rotary drive assembly includes a stepper motor and a stepper motor encoder.

[0028] Preferably: the stepper motor encoder is used to control the stepper motor to rotate at a target frequency period.

[0029] Preferably, the angle encoder includes any one of a capacitive angle encoder and a photoelectric angle encoder.

[0030] Preferably, the magnetic field measurement sensor comprises an anisotropic magnetoresistive AMR sensor.

[0031] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0032] A magnetic positioning system provided in an embodiment of the present application is used to achieve real-time tracking of a target with six degrees of freedom in a spatial range. By mounting 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, and the calculation program is used to solve the spatial posture information of the sensor in combination with the real-time rotation information output by the angle encoder of the fixed motor shaft. The system can achieve instantaneous positioning of low-frequency periodic magnetic signals, solve the problem that low-frequency magnetic field positioning technology is slow and high-frequency magnetic field positioning technology is susceptible to metal interference, improve the convenience and stability of the magnetic positioning method, and reduce the cost of the magnetic positioning method.

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

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 It 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 is a structural schematic diagram of a magnetic field generating unit provided in an embodiment of the present invention;

[0038] Figure 4 It 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 technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field belong to 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, the magnetic field generating unit includes a magnet 9, a rotation drive component and an angle encoder 2; the rotation drive component is used to drive the magnet 9 to rotate so as to form a low-frequency magnetic field signal radiated to the surroundings; the angle encoder 2 is used to obtain the 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 component 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 comprises a magnetic field measuring sensor 7, wherein the magnetic field measuring sensor 7 is used to obtain magnetic signal information, and the magnetic field measuring sensor 7 comprises an anisotropic magnetoresistive AMR sensor.

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

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

[0046] The physical model of the magnet's spatial motion is constructed using the magnetic signal information and the rotation angle information; further, the physical model is used to represent the geometric relationship between the magnetic field measurement sensor and the magnet, which is represented 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 by the following formula:

[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 according to the physical model.

[0054] The value of coordinate z is obtained through the modulus relationship and the constraint condition of 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] By using the relationship between the magnetic moment angles, the angle cosθ between the coordinate P (x, y, z) and the plane XOY is obtained, 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, thereby 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 embodiment of the present application uses magnets and motors to construct low-frequency magnetic field signals, and the rotating structure is simple and stable, low-cost and easy to implement. At the same time, the system uses angle encoders and sensors to realize numerical measurement of magnetic fields, realizes non-periodic signal positioning prediction through analytical algorithms, and can achieve real-time tracking, solving the problems that traditional high-frequency electromagnetic signal-based positioning systems are susceptible to interference, low-frequency magnetic positioning has no analytical solution, and has a slow response speed.

[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 a low-frequency magnetic field, including a magnet, a motor and a driver, and a single-axis rotation system.

[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 an 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 is composed of a small motor (such as a 36 stepper motor, 0.9° resolution), a driver, and a structural tooling, which 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 a single-chip microcomputer STM32F103), which is responsible for system control, motor drive signal generation, data acquisition of measurement sensors and transmission to a PC; the magnetic field measurement sensor is composed of anisotropic magnetoresistive AMR sensors (such as MMC5603NJ, which can realize spatial three-axis orthogonal magnetic field measurement) and capacitive or photoelectric angle encoders (such as EMT-233BV), which are responsible for realizing magnetic signal measurement and angle information measurement of rotating magnets; 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 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 the operation of the system; 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: After the system is in operation, the controller sends a control signal to drive the motor to drive the magnet to rotate and generate a low-frequency magnetic field. The three-dimensional vector information of the magnetic field is measured by the magnetic sensor. At the same time, the physical model of the magnet's spatial motion is constructed in combination with the magnet rotation angle information measured by the angle encoder. The initial spatial coordinate information of the target sensor is obtained through the proposed analytical algorithm, and this information is used as a reference to assist the subsequent system to achieve dynamic tracking of the target. At the same time, the system outputs the six-degree-of-freedom posture prediction results 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 with a specific frequency ω1 around the rotation axis 8 on the plane 10, generating a low-frequency magnetic signal, and constructs a rectangular coordinate system XYZ 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 its angle with 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, so the geometric relationship formula between the sensor and the magnet can be constructed:

[0072]

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

[0074]

[0075] According to the modulus form of the magnetic dipole formula Then 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 Construct 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 function expansion formula, we can get the symmetric solution value about the parameter α. Since this algorithm only performs target positioning and tracking in the space range of Z>0, combined with the identity constraint of the above formula, we can get a unique solution value. On this basis, according to the relationship between the magnetic moment angle in the previous article, we can get the angle cosθ between the coordinate P(x, y, z) and the plane XOY, and solve the distance d by using the modulus form of the magnetic dipole formula.

[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 the coordinate z can be obtained through the modulus relationship and the constraint condition of Z>0, and the analytical initial value of the coordinate P(x, y, z) can be obtained through formulas (7)-(8). Since the sensor rotates R(α, β, γ) during measurement and there is interference from the earth's magnetic field in the surrounding space environment, B 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, the collected raw data is digitally filtered at the corresponding frequency to eliminate interference from DC and other frequency magnetic signals. In order to reduce the interference caused by noise such as rotation and device fluctuations, and to ensure the accuracy of the solution, nonlinear optimization algorithms such as levenberg-Marquardt and particle swarm are used to optimize the six-degree-of-freedom information (x, y, z, α, β, γ) based on the analytical initial value and magnetic dipole model, and the result is output as the positioning prediction value at the current moment. The optimization objective function can be set as follows according to 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 target in six degrees of freedom within a spatial range. By mounting the magnet on the rotating bearing, the motor is driven by a controller to generate a low-frequency magnetic field signal, and then the magnetic sensor measures the generated magnetic signal, and the real-time rotation information output by the angle encoder of the fixed motor shaft is combined to solve the spatial posture information of the sensor using a calculation program. The system can achieve instantaneous positioning of low-frequency periodic magnetic signals, solve the problem that low-frequency magnetic field positioning technology is slow and high-frequency magnetic field positioning technology is susceptible to metal interference, improve the convenience and stability of the magnetic positioning method, and reduce the cost of the magnetic positioning method.

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

[0094] It can be known from the description of the above implementation methods 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 such an understanding, the technical solution of the present application can be essentially or partly embodied in the form of a software product that contributes to the prior art. The computer software product can be stored in a storage medium such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes several 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 the various embodiments of the present application or certain parts of the embodiments.

[0095] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can 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 may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without creative work.

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

Claims

1. A magnetic positioning system, characterized in that: include: A magnetic field generating unit, the magnetic field generating unit comprising a magnet, a rotation 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 is communicatively connected to the measuring unit and the angle encoder, and the computing unit is used to perform the following operations: Receiving the magnetic signal information and the rotation angle information; Using the magnetic signal information and the rotation angle information to construct a physical model of the magnet's spatial motion; Using the physical model in combination with an analytical algorithm to obtain initial spatial coordinate information of the magnetic field measurement sensor; 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.

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, which is expressed by the following formula: 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.

3. The magnetic positioning system according to claim 1, characterized in that: The objective function optimized by the nonlinear optimization algorithm is expressed as follows: 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 according to the physical model.

4. The magnetic positioning system according to claim 3, characterized in that: The value of coordinate z is obtained through the modulus relationship and the constraint condition of z>0, and the values ​​of coordinate x and coordinate y are obtained by solving the following two equations: Where: d represents the distance modulus, K represents the inductance coefficient between the sensor and the permanent magnet, B x , B y , B z Represents the three-axis components.

5. The magnetic positioning system according to claim 4, characterized in that: By using the relationship between the magnetic moment angles, the angle cosθ between the coordinate P (x, y, z) and the plane XOY is obtained, and the distance modulus d is obtained by solving the modulus form of the magnetic dipole formula.

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

7. The magnetic positioning system according to claim 6, characterized in that: The stepper motor encoder is used to control the stepper motor to rotate at a target frequency period.

8. 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.

9. 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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