Underwater detector attitude solving method based on rotating coil induced electromotive force

Abstract

The application discloses a method for solving the attitude of an underwater detector based on the induced electromotive force of a rotating coil, and relates to the technical field of solving the attitude of an underwater detector, so as to solve the problem of large attitude measurement error, insufficient precision and stability of an existing underwater vehicle. The method comprises the following steps: a rotating coil module is fixedly connected to the inside of a detector sealing cabin and is bound to a body coordinate system, the coil rotates at a constant speed to cut a geomagnetic field to generate an induced electromotive force; the amplitude and phase are extracted through signal conditioning and waveform fitting, a coupling coefficient expression is constructed by relying on an IGRF geomagnetic model and a Rodrigues rotation formula, and the tilt angle and the azimuth angle are inversely solved by combining the measured and theoretical coefficients. The application realizes attitude measurement by relying on geomagnetic induction, avoids the defect of gyro drift, has strong anti-magnetic interference capability and high solving precision, and is suitable for autonomous attitude measurement and control of an underwater detector.

Description

Technical Field

[0001] This invention relates to the field of underwater detector attitude calculation technology, and discloses an underwater detector attitude calculation method based on the induced electromotive force of a rotating coil. Background Technology

[0002] When autonomous underwater vehicles (AUVs), underwater robots, and various underwater detection devices perform underwater navigation, detection, and measurement tasks, their attitude state directly affects the accuracy of navigation control and the reliability of measurement results. When the equipment is affected by ocean currents, hydrodynamic disturbances, or changes in its own motion state, the equipment body is prone to tilting and directional deflection, thereby affecting the stability of the equipment and the accuracy of measurement.

[0003] Currently, underwater equipment mainly uses inertial navigation systems, IMUs, electronic compasses, and multi-sensor fusion algorithms to achieve attitude measurement. Among these, inertial navigation systems are prone to accumulating drift errors during long-term operation; electronic compasses are susceptible to interference from complex marine magnetic environments and the magnetic fields of the equipment itself; and multi-sensor fusion algorithms suffer from computational complexity and high power consumption.

[0004] In existing technologies, most methods for measuring the attitude of underwater equipment rely on additional attitude sensors, resulting in complex system structures that struggle to simultaneously meet the requirements of low power consumption, miniaturization, and long-term stable operation. Therefore, a novel attitude detection method is needed that can utilize the principle of electromagnetic induction to calculate attitude. Summary of the Invention

[0005] This invention discloses an attitude calculation method for underwater detectors based on the induced electromotive force of a rotating coil, in order to solve the problems of large attitude measurement errors, insufficient accuracy and stability of underwater vehicles in the prior art.

[0006] The underwater detector attitude calculation method based on the induced electromotive force of a rotating coil includes the following steps: S1. The rotating coil attitude detection module is fixedly installed in the sealed chamber of the underwater detector and connected to the coordinate system of the underwater equipment body. It moves synchronously with the underwater equipment to map the attitude changes of the equipment in real time. S2. Drive the induction coil in the rotating coil attitude detection module to rotate at a constant speed around the module axis, continuously cutting the magnetic field lines of the Earth's magnetic field and generating a periodic induced electromotive force signal. S3. Real-time acquisition of the original induced electromotive force signal, and amplification, filtering, power frequency interference suppression and analog-to-digital conversion processing of the original signal to obtain an effective induced electromotive force signal with high signal-to-noise ratio; S4. Perform sine fitting, amplitude extraction and phase extraction on the effective induced electromotive force signal, and combine the preset geomagnetic field model, rotating coil model and Rodrigues rotation formula to calculate the tilt angle and azimuth angle of the underwater equipment in real time. S5. Output the calculated tilt angle and azimuth attitude parameters to the corresponding control system of the underwater equipment to complete the attitude self-correction, motion stability control and measurement error compensation of the underwater equipment.

[0007] Furthermore, the rotating coil attitude detection module includes an induction coil, a coil support structure, a rotation drive mechanism, a non-magnetic transmission shaft, a signal acquisition circuit, a signal conditioning circuit, a data processing unit, a power management unit, and a magnetic shielding and isolation structure; The induction coil can be any one of the following: single-turn coil, multi-turn coil, PCB planar coil, hollow coil, or iron-core reinforced coil.

[0008] Furthermore, the rotary drive mechanism is one or more combinations of a hollow cup brushless motor, an ultrasonic motor, a low magnetic leakage brushless DC motor, and a long-distance isolated drive structure; A magnetic isolation area is provided between the rotary drive mechanism and the induction coil, and the drive motor is positioned away from the induction coil.

[0009] Furthermore, the non-magnetic drive shaft is made of any one of the following materials: titanium alloy, ceramic, engineering plastic, or carbon fiber composite material; The rotation frequency of the induction coil is set to 10-50Hz.

[0010] Furthermore, the signal conditioning circuit includes a low-noise amplifier, a bandpass filter, a power frequency notch filter module, and an analog-to-digital converter module.

[0011] Furthermore, the data processing unit employs any one of a digital signal processor, a field-programmable gate array, an ARM processor, or an embedded microcontroller; The data processing unit's processing functions include sine fitting, amplitude extraction, phase extraction, attitude parameter inversion, and attitude compensation calculation.

[0012] Furthermore, a magnetic shielding and isolation structure is provided on the outside of the rotating coil attitude detection module. The magnetic shielding and isolation structure uses a high magnetic permeability shielding material to provide local magnetic isolation for the rotating drive mechanism area and the signal processing layout area inside the rotating coil attitude detection module.

[0013] Furthermore, the rotation coil attitude detection module is described using standard ZYX Euler angles, with rotation about the z-axis defined as the spin angle. Rotation around the y-axis is the pitch angle. Rotation about the x-axis is the roll angle. The core attitude parameter tilt angle is synthesized. and azimuth ; The tilt angle satisfy ; The tilt angle The angle between the axis of the rotating coil attitude detection module and the vertical direction; The azimuth angle The angle between the projection of the device's tilt direction onto the horizontal plane and the x-axis.

[0014] Furthermore, the geomagnetic field model is constructed by treating the geomagnetic field of the survey area as a stable field and setting the geomagnetic field vector. : ; In the formula, This refers to the horizontal component of the geomagnetic field. This represents the vertical component of the Earth's magnetic field. and Obtained using the IGRF geomagnetic reference model.

[0015] Furthermore, S4 specifically includes the following process: Let the radius of the coil be... The coil area is The coil rotates around the axis of the coil attitude detection module at an angular velocity Uniform rotation, initial moment coil normal vector ; The induced electromotive force is obtained based on Faraday's law of electromagnetic induction. : ; In the formula, The magnetic flux passing through the coil; Magnetic flux of the coil Determined by the dot product of the Earth's magnetic field and the effective area of ​​the coil: ; In the formula, The magnetic field strength vector of the Earth's magnetic field. The effective area vector of the induction coil. , These are the horizontal and vertical components of the Earth's magnetic field, respectively. , These are the real-time x and z axial components of the unit normal vector of the coil, respectively; The real-time x, y, and z axial components of the unit normal vector of the coil , , They are respectively: ; ; ; Simplify by differentiating the magnetic flux with respect to time: ; In the formula, , The dimensionless geomagnetic attitude coupling coefficient that integrates geomagnetic field and attitude information; Unit vector of the rotation axis ; The unit vector of the rotation axis is angular velocity of rotation is Then after time Then, the coil normal vector Considered Rotation angle around axis a ,and ,Will , Substituting into Rodrigues' rotation formula, we obtain the rotated vector. : ; In the formula, This is the real-time vertical orientation vector after the coil rotates. This is the initial vertical orientation vector before the coil rotates. The unit vector is the axis of rotation; Combined with tilt angle Azimuth By solving for the real-time component of the coil's unit normal vector and substituting it into the formulas for magnetic flux and electromotive force, and simplifying the equations, we obtain the theoretical coupling coefficient related to the geomagnetic field component and the equipment's attitude angle. and : ; ; By performing a sine fit on the collected effective electromotive force signal, the time-domain expression of the measured electromotive force is obtained: ; In the formula, For amplitude, For phase; and Obtained through measurement; By comparing the theoretical orthogonal expansion of the electromotive force with the measured sinusoidal fitting expression, the measured coupling coefficient can be obtained: ; ; By substituting the measured coupling coefficients into the theoretical coupling coefficient expression and solving the system of equations, the tilt angle of the underwater probe can be obtained through inversion. and azimuth .

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention sets up a rotating coil attitude detection module inside an underwater detection device, which causes the induction coil to cut magnetic field lines in the geomagnetic field and generate a periodic induced electromotive force. By analyzing the amplitude and phase parameters of the induced electromotive force, the device's tilt angle and azimuth angle can be calculated in real time and its attitude can be self-corrected.

[0017] This invention eliminates the need for complex inertial navigation systems and multi-sensor fusion structures, offering advantages such as simple structure, low power consumption, and no cumulative drift during long-term operation. It also effectively reduces the impact of complex underwater environments on attitude measurement stability, improving the stability and reliability of navigation control and measurement systems for underwater detection equipment. It is applicable to underwater autonomous vehicles, underwater robots, and other underwater detection equipment. Attached Figure Description

[0018] Figure 1 This is a flowchart of the technology of the present invention; Figure 2 This is a schematic diagram of the tilted breakdown of an underwater detector. Figure 3 The curves showing the change of amplitude and phase of the induced electromotive force over time; Figure 4 Geomagnetic coupling coefficient , Curve of measured value changing over time; Figure 5 Inclination angle Comparison curves of estimated and actual values ​​over time; Figure 6 Azimuth Comparison curves of estimated and actual values ​​over time; Figure 7 Inclination angle With azimuth The curve showing how the angle estimation error changes over time. Detailed Implementation

[0019] The present invention will be further illustrated below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the invention in any way. It should be understood that the described embodiments are merely some, not all, of the embodiments described in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0020] Figure 1The present invention provides a method for calculating the attitude of an underwater detector based on the induced electromotive force of a rotating coil, as shown in the technical flowchart below. The steps are as follows: establishing a probe attitude coordinate system, establishing a geomagnetic field model, establishing a dynamic model of the rotating coil, and then acquiring the induced electromotive force. The signal is subjected to a sliding window sine fit to extract the amplitude and phase, and attitude inversion coupling parameters are constructed. Finally, the tilt angle is calculated. With azimuth .

[0021] To verify the relationship between the underwater detector's attitude and the induced electromotive force in the coil. Figure 2 This is a schematic diagram of the tilted breakdown of the underwater detector, as shown below. Figure 2 As shown, a background magnetic field that recreates the real geomagnetic environment is constructed in MATLAB, and the settings are... = ,in =31.6μT, =41.9μT. Then, the coil radius was set. ,area The detection coil is made to rotate around the axis at a constant frequency of 16Hz.

[0022] Three continuous tilt attitude changes for the underwater probe were designed, with each stage completed sequentially within six coil rotation cycles. Stage I (first 6 cycles): =0°, =0° (i.e., rotation along the z-axis); Phase II (cycles 7-12). The angle increases linearly from 0° to 5°. Increase from 0° to 30°; Phase III (cycles 13-18). Increase from 5° to 10° The angle was increased from 30° to 60°.

[0023] To closely approximate the actual physical process, random perturbations were superimposed on the angle changes in the simulation to simulate non-ideal linear motion, and random noise was added to the measurement signal.

[0024] Furthermore, to avoid the occurrence of singularities in the coordinate system (when... =0° Numerical calculation divergence caused by undefined angles occurs when the algorithm detects... , When the time is right, it is determined to be in a state without tilt, and a value is directly assigned. =0°, =0°. To visually represent the spatial motion patterns of the underwater probe.

[0025] Figure 3 In the middle, stage I: Stabilizes at the maximum value, Approaching 0° corresponds to the initial state of the underwater probe with no tilt. Phase II: Monotonic decline, The synchronous monotonically increases, and the two are negatively correlated. This phenomenon quantitatively reflects the change in the effective cut magnetic flux of the coil with attitude angle during the tilting process of the underwater probe. Increase and press The physical nature of regular decay. Stage III: and All values ​​tend to stabilize, indicating that the attitude of the underwater probe no longer changes. Figure 3 This not only verified the sliding window method's effective ability to track the characteristics of non-stationary signals, but also directly confirmed the core relationships in the theoretical model. .

[0026] Figure 4 In the middle, stage I: Keep constant, Approximately zero, corresponding to the vertical state of the underwater detector ( =0°, =0°). Stage II: Slow descent, The two trends continue to rise, and their changes are related to the tilt angle of the underwater detector. and azimuth Their dynamic evolution is highly synchronized. Stage III: , The results tend to stabilize, reflecting the fixed characteristics of the final attitude. This result verifies the mapping relationship between the coefficients and attitude angles in the attitude calculation model, paving the way for subsequent calculations of the measured coupling coefficients and inversion. and It provides a reliable parameter basis.

[0027] The attitude angle of the underwater probe has been derived from the measured coupling coefficient. The theoretical expression for the coupling coefficient has been completed. By solving the simultaneous equations, the tilt angle of the underwater probe can be obtained. and azimuth The calculated tilt angle and azimuth The attitude parameters are output to the corresponding control system of the underwater equipment to complete the attitude self-correction, motion stability control and measurement error compensation of the underwater equipment.

[0028] To evaluate the accuracy of the solution method, the tilt angle is... and azimuth The measured value is compared with the preset true value, such as... Figure 5 , Figure 6 As shown, tilt angle With azimuth The angle estimation error versus time curve is shown below. Figure 7 As shown. By Figure 5 , Figure 6 , Figure 7 It can be seen that the tilt angle The average error is controlled between 0.2° and 0.5°, azimuth angle The average error is between 1° and 3°, and the overall fitting quality is better than 0.8. The error curve shows a significant peak around 0.4s, indicating a substantial increase in angle estimation error. The physical nature of this phenomenon is closely related to the algorithm's characteristics: 0.4s precisely corresponds to the critical point where the attitude angle transitions from a static, constant state to a slowly continuously changing state. therefore ,then It cannot be solved stably.

[0029] At this time, the tilt angle With azimuth The change in magnitude is extremely small, and the amplitude of the modulation signal of the induced electromotive force in the coil is weak, making it highly susceptible to interference from superimposed random noise, which leads to a decrease in the accuracy of the sliding window sine fitting. and The solution stability deteriorates; at the same time, the angle inversion equation under the near-zero angle condition exhibits numerical singularity, and small parameter solution deviations are amplified in the reverse direction. In addition, the step change in attitude constraints before and after the stage switch ultimately causes the tilt angle at the transition moment to deteriorate. With azimuth The inversion error exhibits a sharp, abrupt peak. Except for short-term errors at transition points, the algorithm of this invention maintains high estimation accuracy throughout the entire time period, demonstrating the effectiveness of the method.

[0030] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for calculating the attitude of an underwater detector based on the induced electromotive force of a rotating coil, characterized in that, Includes the following steps: S1. The rotating coil attitude detection module is fixedly installed in the sealed chamber of the underwater detector and connected to the coordinate system of the underwater equipment body. It moves synchronously with the underwater equipment to map the attitude changes of the equipment in real time. S2. Drive the induction coil in the rotating coil attitude detection module to rotate at a constant speed around the module axis, continuously cutting the magnetic field lines of the Earth's magnetic field and generating a periodic induced electromotive force signal. S3. Real-time acquisition of the original induced electromotive force signal, and amplification, filtering, power frequency interference suppression and analog-to-digital conversion processing of the original signal to obtain an effective induced electromotive force signal with high signal-to-noise ratio; S4. Perform sine fitting, amplitude extraction and phase extraction on the effective induced electromotive force signal, and combine the preset geomagnetic field model, rotating coil model and Rodrigues rotation formula to calculate the tilt angle and azimuth angle of the underwater equipment in real time. S4 specifically includes the following process: Let the radius of the coil be... The coil area is The coil rotates around the axis of the coil attitude detection module at an angular velocity Uniform rotation, initial moment coil normal vector ; The induced electromotive force is obtained based on Faraday's law of electromagnetic induction. : ； In the formula, The magnetic flux passing through the coil; Magnetic flux of the coil Determined by the dot product of the Earth's magnetic field and the effective area of ​​the coil: ； In the formula, The magnetic field strength vector of the Earth's magnetic field. The effective area vector of the induction coil. , These are the horizontal and vertical components of the Earth's magnetic field, respectively. , These are the real-time x and z axial components of the unit normal vector of the coil, respectively; The real-time x, y, and z axial components of the unit normal vector of the coil , , They are respectively: ； ； ； Simplify by differentiating the magnetic flux with respect to time: ； In the formula, , The dimensionless geomagnetic attitude coupling coefficient that integrates geomagnetic field and attitude information; Unit vector of the rotation axis ; The unit vector of the rotation axis is angular velocity of rotation is Then after time Then, the coil normal vector Considered Rotation angle around axis a ,and ,Will , Substituting into Rodrigues' rotation formula, we obtain the rotated vector. : ； In the formula, This is the real-time vertical orientation vector after the coil rotates. This is the initial vertical orientation vector before the coil rotates. The unit vector is the axis of rotation; Combined with tilt angle Azimuth By solving for the real-time component of the coil's unit normal vector and substituting it into the formulas for magnetic flux and electromotive force, and simplifying the equations, we obtain the theoretical coupling coefficient related to the geomagnetic field component and the equipment's attitude angle. and : ； ； By performing a sine fit on the collected effective electromotive force signal, the time-domain expression of the measured electromotive force is obtained: ； In the formula, For amplitude, For phase; and Obtained through measurement; By comparing the theoretical orthogonal expansion of the electromotive force with the measured sinusoidal fitting expression, the measured coupling coefficient can be obtained: ； ； By substituting the measured coupling coefficients into the theoretical coupling coefficient expression and solving the system of equations, the tilt angle of the underwater probe can be obtained through inversion. and azimuth ; S5. Output the calculated tilt angle and azimuth attitude parameters to the corresponding control system of the underwater equipment to complete the attitude self-correction, motion stability control and measurement error compensation of the underwater equipment.

2. The underwater detector attitude calculation method based on the induced electromotive force of a rotating coil according to claim 1, characterized in that, The rotating coil attitude detection module includes an induction coil, a coil support structure, a rotation drive mechanism, a non-magnetic transmission shaft, a signal acquisition circuit, a signal conditioning circuit, a data processing unit, a power management unit, and a magnetic shielding and isolation structure. The induction coil can be any one of the following: single-turn coil, multi-turn coil, PCB planar coil, hollow coil, or iron-core reinforced coil.

3. The underwater detector attitude calculation method based on the induced electromotive force of a rotating coil according to claim 2, characterized in that, The rotary drive mechanism is one or more combinations of hollow cup brushless motor, ultrasonic motor, low magnetic leakage brushless DC motor, and long-distance isolation drive structure. A magnetic isolation area is provided between the rotary drive mechanism and the induction coil, and the drive motor is positioned away from the induction coil.

4. The underwater detector attitude calculation method based on the induced electromotive force of a rotating coil according to claim 2, characterized in that, The non-magnetic drive shaft is made of any one of the following materials: titanium alloy, ceramic, engineering plastic, or carbon fiber composite material. The rotation frequency of the induction coil is set to 10-50Hz.

5. The underwater detector attitude calculation method based on the induced electromotive force of a rotating coil according to claim 2, characterized in that, The signal conditioning circuit includes a low-noise amplifier, a bandpass filter, a power frequency notch filter module, and an analog-to-digital converter module.

6. The underwater detector attitude calculation method based on the induced electromotive force of a rotating coil according to claim 2, characterized in that, The data processing unit can be any one of a digital signal processor, a field-programmable gate array, an ARM processor, or an embedded microcontroller. The data processing unit's processing functions include sine fitting, amplitude extraction, phase extraction, attitude parameter inversion, and attitude compensation calculation.

7. The underwater detector attitude calculation method based on the induced electromotive force of a rotating coil according to claim 2, characterized in that, The rotating coil attitude detection module is provided with a magnetic shielding and isolation structure on its outside. The magnetic shielding and isolation structure uses a high magnetic permeability shielding material to provide local magnetic isolation for the rotating drive mechanism area and the signal processing layout area inside the rotating coil attitude detection module.

8. The underwater detector attitude calculation method based on the induced electromotive force of a rotating coil according to claim 1, characterized in that, The rotating coil attitude detection module is described using standard ZYX Euler angles, with rotation about the z-axis defined as the spin angle. Rotation around the y-axis is the pitch angle. Rotation about the x-axis is the roll angle. The core attitude parameter tilt angle is synthesized. and azimuth ; The tilt angle satisfy ; The tilt angle The angle between the axis of the rotating coil attitude detection module and the vertical direction; The azimuth angle The angle between the projection of the device's tilt direction onto the horizontal plane and the x-axis.

9. The underwater detector attitude calculation method based on the induced electromotive force of a rotating coil according to claim 1, characterized in that, The geomagnetic field model is constructed by treating the geomagnetic field of the survey area as a stable field and setting the geomagnetic field vector. : ； In the formula, This refers to the horizontal component of the geomagnetic field. This represents the vertical component of the Earth's magnetic field. and Obtained using the IGRF geomagnetic reference model.

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