A method for calibrating an optical fiber inertial measurement unit

Abstract

This invention discloses a calibration method for fiber optic inertial measurement units (IMUs), belonging to the field of inertial navigation technology. Addressing the challenge of traditional calibration methods relying on turntables and being unsuitable for field applications, this invention achieves rapid on-site calibration in three steps: first, the gyroscope scaling factor error is calibrated using an external rotation speed excitation method; then, the gyroscope zero-bias error is solved using a ground speed multi-position method; finally, the calibrated gyroscope is used to determine the geostationary orientation, completing the calibration of the accelerometer scaling factor and zero-bias error. This method eliminates the need for disassembly or turntable equipment, significantly reducing the difficulty of field calibration. It offers advantages such as ease of operation and high efficiency, making it suitable for periodic on-site calibration and compensation of IMUs.

Description

Technical Field

[0001] This invention relates to the field of inertial navigation technology, and more specifically to a calibration method for a fiber optic inertial measurement unit. Background Technology

[0002] An inertial measurement unit (IMU) is an integrated inertial sensor unit capable of simultaneously measuring angular velocity and linear acceleration. It combines a three-axis gyroscope and a three-axis accelerometer to form a sensor suite. It is a core component of inertial navigation, attitude control, and guidance technologies. As the core component of inertial navigation, the IMU's error is a major source of error affecting the inertial navigation system. In engineering applications, it is necessary to compensate for the IMU's errors.

[0003] The errors of an inertial measurement unit (IMU) include 24 error coefficients, such as gyroscope zero-bias error, gyroscope scale factor, gyroscope installation error, accelerometer zero-bias error, accelerometer scale factor, and accelerometer installation error. Currently, the conventional error compensation scheme involves calibrating each error coefficient. Traditional calibration methods use a multi-axis turntable, rotating the IMU at multiple positions and angular velocities. This method is typically performed before the IMU leaves the factory. However, from an engineering perspective, the error coefficients of the IMU are not fixed; constant errors and scale factors change over time. Therefore, periodic calibration of the IMU is necessary. Because traditional calibration schemes rely on multi-axis turntables, secondary calibration is cumbersome and complex. In some cases, field calibration cannot even be performed without disassembling the entire system.

[0004] To address the above issues, this paper proposes a novel calibration method for inertial measurement units (IMUs), which enables secondary calibration and compensation on-site without disassembly or the use of precision equipment such as turntables, allowing for rapid field calibration. Summary of the Invention

[0005] To address the aforementioned shortcomings in the prior art, this invention provides a method for calibrating an optical fiber inertial measurement unit.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for calibrating an optical fiber inertial measurement unit includes the following steps: S1. Calibrate the scaling factor error of the gyroscope using the external rotation speed excitation method; S2. Calibrate the zero bias error value of the gyroscope using the ground speed multi-position method; S3. Based on the calibrated gyroscope, calibrate and compensate for the scaling factor error and zero bias error of the accelerometer.

[0007] Furthermore, step S1 specifically includes the following steps: S11. Apply angular velocities of ω to the three axes of the gyroscope respectively. The excitation signal; S12. Collect the output data of each axis at the forward and reverse speeds, and record it as follows: , , where i is one of the three axes x, y, z, and + and - represent the forward and reverse directions of the rotational speed of Ω, respectively; S13. Calculate the scaling factor error for each axis based on the collected forward and reverse rotational speeds. The calculation method is as follows:

[0008] In the formula, The scaling factor error is for each axis.

[0009] Furthermore, step S2 specifically includes the following steps: S21. In a static environment, the inertial measurement unit can be placed in multiple arbitrary positions; S22, collects the three axes of the gyroscope at each position. Output data ; S23. Establish a combined equation based on the fact that the sum of the squares of the ground velocity components at the three axial positions equals the square of the ground velocity. S24. Solve the established combined equations to obtain the zero bias error values ​​in the three directions.

[0010] Furthermore, the combined equation in S23 is expressed as:

[0011] In the formula, These are the zero-bias error values ​​for the x, y, and z axes, respectively. This is the ground speed value.

[0012] Furthermore, step S3 specifically includes the following steps: S31. After the gyroscope is calibrated, rotate each axis of the gyroscope to the up and down positions respectively; S32. When the axis points upwards, collect the output of the accelerometer on that axis. When the axis points to the ground, the data acquisition output is... , where i is one of the three axes x, y, and z; S33. Calculate the scale factor error of the accelerometer according to the formula. and zero bias error ; S34. Correction is performed when there is an angular error between the gyroscope axis and the upward direction.

[0013] Furthermore, the scaling factor error in S33 and zero bias error The specific calculation method is as follows: ; .

[0014] Furthermore, the correction in S34 when there is an angular error between the gyroscope axis and the celestial direction specifically includes: Calculate the angle between the corresponding axis and the placement plane. :

[0015] In the formula, This represents the component of Earth's rotational angular rate that rises dramatically. This is the output value when the gyroscope axis points upwards; Correction for scaling factor error: In the formula, This is the corrected scale factor error; Correcting zero bias error: In the formula, This is the corrected zero bias error.

[0016] The present invention has the following beneficial effects: This application implements a novel calibration method for inertial measurement units (IMUs). During calibration, no turntable or other equipment is required, significantly reducing the difficulty of calibrating IMUs in the field. Furthermore, the implementation method and operation process of this application are quick, simple, and efficient. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the fiber optic inertial measurement unit calibration method of the present invention. Detailed Implementation

[0018] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0019] A calibration method for fiber optic inertial measurement units, such as Figure 1 As shown, it includes the following steps: S1. Calibrate the scaling factor error of the gyroscope using the external rotation speed excitation method; In this embodiment, an external rotational speed excitation method is used to apply excitation signals with specific angular velocities to the three axes of the gyroscope. The excitation signals are set as follows: The outputs for the three axes are obtained respectively, denoted as... , Where i represents x, y, and z, and + and - represent the forward and reverse directions of the Ω rotational speed, respectively. The scale factor error for each axis is calculated using the following formula: ; Where i is one of the x, y, or z axes.

[0020] In practical implementation, an excitation signal, i.e., a stepped wave signal corresponding to a fixed angular rate, is added to the modulation program of the gyroscope and superimposed on the modulator. Based on the working principle of a closed-loop fiber optic gyroscope, when an external feedback phase is superimposed: ; in: For the Segnek phase shift, after simplification, we get: ; According to the above formula, by adding an additional angular velocity feedback phase to the gyroscope, a corresponding angular velocity information can be obtained. The scale factor refers to the ratio of the output to the input. When the scale factor of the inertial measurement unit gyroscope is accurate, the input and output are equal, and the ratio is 1. When there is an error, the scale factor error can be obtained by the ratio of the current output to the fixed input. In actual operation, the difference between the positive and negative directions of the fixed rotational speed is taken to eliminate the influence of zero bias and other rotational speed errors.

[0021] S2. Calibrate the zero bias error value of the gyroscope using the ground speed multi-position method; Even in a stationary environment, a gyroscope is not absolutely stationary; each axis is sensitive to the ground velocity component of its current position. In a stationary environment, the angular velocity output of each axis of the gyroscope can be expressed by the following formula: ; in, To output angular velocity, For scaling factor error, The component of ground speed at the current position. It is an intrinsic zero bias value. This refers to the errors caused by the non-orthogonal deviation of the other two axes.

[0022] It is evident that, in addition to the ground velocity component at the current position, there are also scaling factor errors, zero bias values, and non-orthogonal deviations caused by installation errors. During factory testing, the non-orthogonal deviations caused by installation errors have already been corrected. Since the scaling factor error has already been corrected, the effects of the above two errors are no longer considered here. Now, only the inherent zero bias error value remains. If we know the accurate ground velocity component for each axis at the current position, we can obtain the inherent zero bias error value for each axis.

[0023] In the field, without standard calibration equipment, accurate ground velocity position information cannot be provided. However, by taking advantage of the known condition that the sum of the squares of the ground velocity components at the three axial positions equals the square of the ground velocity, sufficient data can be obtained from multiple positions, and the zero-bias unknown can be solved by combining equations.

[0024] Find a flat surface and, in a static environment, place the product arbitrarily at three locations, collecting the output data from the three-axis gyroscope at each location. Record the gyroscope output at these three locations as follows: The zero bias of a gyroscope is denoted as , where i represents the three axes x, y, z, and j represents different positions, represented by 1, 2, 3, ...

[0025] available:

[0026]

[0027]

[0028] By expanding the above formula, subtracting each pair of values, and representing the results of the known quantities with the letters M and N, the formula is simplified, and the calculation results are as follows:

[0029]

[0030]

[0031] in, ~ , Given quantities, we can obtain the solution by combining formulas. Three zero-bias error values.

[0032] S3. Based on the calibrated gyroscope, calibrate and compensate for the scaling factor error and zero bias error of the accelerometer.

[0033] After the gyroscope calibration is completed, the accurate accelerator positions in the sky, earth, and horizontal directions can be found based on the gyroscope's sensitivity to ground speed, thereby obtaining the accelerator's scaling factor and zero bias error value.

[0034] After the gyroscope calibration is complete, point the X, Y, and Z axes of the gyroscope upwards. When the gyroscope output for the current axis is the angular velocity component of the ground velocity at the local position, collect the output of the current axis accelerator and record it as follows. ; Flip the current axis to make it align with the ground. When the current axis gyroscope output is the negative of the ground velocity component at the local position, collect the output of the current axis accelerator, and record it as . Based on the obtained output, the scaling factor error and zero bias error of the accelerator are calculated: Add scale factor error: ; Add zero bias error: ; The above method, when a certain axis points upwards, if there is an angular error between the platform and the horizontal plane of the ground velocity component, preventing the gyroscope output from being the ground velocity component at the current position, can be solved by multiplying the obtained output error by the angular error of the ground velocity component's position. The output of a certain axis gyroscope when pointing upwards is collected. (where n is x, y, z), then the angle between this axis and the plane in which it is placed. for: ; in, The component value of the Earth's rotational angular rate soaring to the sky.

[0035] Therefore, the scaling factor error becomes: ; The zero bias error becomes: .

[0036] The technical implementation of this application is illustrated by the following specific embodiments: Step 1: First, by providing excitation signals, calibrate the scaling factor error of each axis of the gyroscope.

[0037] In a static environment, excitation signals of ±Ω angular velocities along the X, Y, and Z axes of the gyroscope were input via peripheral interfaces. Output data for both positive and negative rotational speeds along the three axes were collected and recorded for at least 1 minute. The average value of each 1-minute data set was calculated, resulting in six test values ​​for each axis (positive and negative rotational speeds). The scaling factor error for each axis was calculated using a formula, and the scaling factor for each axis was corrected based on the scaling factor error.

[0038] Step 2: Solve for the zero-bias error values ​​of each axis of the gyroscope using the ground speed multi-position method.

[0039] In a static horizontal environment, the IMU is placed at 3-4 arbitrary positions, and the output of the gyroscope along the three axes at each position is collected and recorded. The acquisition time is no less than 1 minute, and the average value of the 1-minute data is calculated to obtain a total of 9 test values ​​along the three axes. The zero bias of the gyroscope along the three axes is calculated and compensated for.

[0040] Step 3: Use the calibrated gyroscope to find the vertical position of each axis of the accelerator, and then measure the scale factor error of the accelerator.

[0041] In a static horizontal environment, data was collected from the gyroscope and accelerator at each position along the X, Y, and Z axes (pointing upwards and downwards) for at least 1 minute. The average value of each 1-minute data collection was calculated, resulting in a total of 12 test values ​​for the gyroscope and accelerator across the three axes. The scaling factor error and zero bias error of the accelerator along the three axes were then calculated.

[0042] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0043] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0044] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0045] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

[0046] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A calibration method for an optical fiber inertial measurement unit, characterized in that, Includes the following steps: S1. Calibrate the scaling factor error of the gyroscope using the external rotation speed excitation method; S2. Calibrate the zero bias error value of the gyroscope using the ground speed multi-position method; S3. Based on the calibrated gyroscope, calibrate and compensate for the scale factor error and zero bias error of the accelerometer, specifically including the following steps: S31. After the gyroscope is calibrated, rotate each axis of the gyroscope to the up and down positions respectively; S32. When the axis points upwards, collect the output of the accelerometer on that axis pointing upwards. When the axis points to the ground, the output in that direction is collected. , where i is one of the three axes x, y, and z; S33. Calculate the scale factor error of the accelerometer according to the formula. and zero bias error Among them, the scaling factor error and zero bias error The specific calculation method is as follows: ； ； S34. When there is an angular error between the gyroscope axis and the upward direction, corrections are made, specifically including: Calculate the angle between the corresponding axis and the placement plane. : In the formula, This represents the component of Earth's rotational angular rate that rises dramatically. This is the output value when the gyroscope axis points upwards; Correction for scaling factor error: In the formula, This is the corrected scale factor error; Correcting zero bias error: In the formula, This is the corrected zero bias error.

2. The fiber optic inertial measurement unit calibration method according to claim 1, characterized in that, S1 specifically includes the following steps: S11. Apply angular velocities of ω to the three axes of the gyroscope respectively. The excitation signal; S12. Collect the output data of each axis at the forward and reverse speeds, and record it as follows: , , where i is one of the three axes x, y, z, and + and - represent the forward and reverse directions of the rotational speed of Ω, respectively; S13. Calculate the scaling factor error for each axis based on the collected forward and reverse rotational speeds. The calculation method is as follows: In the formula, The scaling factor error is for each axis.

3. The fiber optic inertial measurement unit calibration method according to claim 1, characterized in that, S2 specifically includes the following steps: S21. In a static environment, the inertial measurement unit can be placed in multiple arbitrary positions; S22, collects the three axes of the gyroscope at each position. Output data ; S23. Establish a combined equation based on the fact that the sum of the squares of the ground velocity components at the three axial positions equals the square of the ground velocity. S24. Solve the established combined equations to obtain the zero bias error values ​​in the three directions.

4. The fiber optic inertial measurement unit calibration method according to claim 3, characterized in that, The combined equation in S23 is expressed as follows: In the formula, These are the zero-bias error values ​​for the x, y, and z axes, respectively. This is the ground speed value.

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