Course effect error calibration and compensation method for inertial measurement combination

Abstract

The invention discloses a course effect error calibration and compensation method of an inertial measurement combination, which is based on a calibration system composed of a single-axis turntable, a switching tool, an optical component and aiming equipment, after related equipment of the system is installed in place, the aiming equipment performs light aiming on the optical component, and obtains a course angle of the optical component; and in combination with a space geometric transfer relationship of an optical assembly-switching tool-inertial measurement combination, a course angle light aiming value of the inertial measurement combination is indirectly obtained. Through high-precision angle position control of a single-axis turntable around a sky axis, self-alignment of an inertia measurement combination at any position in a full course range is realized, and a difference value between the self-alignment value and a course angle light aiming value is calculated for parameter estimation of a compensation model. And finally, embedding a compensation model in the inertial measurement combination to realize compensation of a self-alignment result. The method is simple in operation process, high in execution efficiency, low in cost and small in calculation amount.

Description

Technical Field

[0001] The present invention relates to the field of inertial navigation, and in particular to a method for calibrating and compensating a heading effect error of an inertial measurement unit. Background Art

[0002] Inertial navigation systems use built-in gyroscopes and accelerometers to sense the carrier's angular velocity and linear acceleration. Through multiple integrations, they determine the carrier's position, velocity, and attitude. This process requires no external input, radiates low energy, and is highly discreet and adaptable. Therefore, they are widely used in aerospace, precision mapping, and other fields. Inertial navigation systems that achieve navigation-grade accuracy often also perform self-alignment, using their own inertial sensor data to determine the carrier's angle relative to north. The accuracy of self-alignment directly impacts the accuracy of subsequent integral calculations, and errors cannot be eliminated through the inertial navigation system itself. Therefore, self-alignment technology has become a hot topic in inertial navigation research. The accuracy of self-alignment is affected by many factors, one of which is heading effect. Heading effect refers to the varying north-finding accuracy when self-aligning at different heading angles. Accuracy is affected by factors such as geomagnetic distribution, uneven temperature fields, servo interference torque, and mechanical vibration. It is a nonlinear model with high uncertainty and multiple factors. Although the causes of triggering the heading effect are complex and diverse, and it is impossible to completely eliminate the heading effect error through a certain model, multiple studies have shown that the heading effect at the same heading position has a high degree of repeatability. In addition, relevant studies have shown that the impact of the heading effect and the heading position show a trigonometric function relationship. Therefore, the self-alignment results of the product in the full heading range can be corrected by introducing an external high-precision north-seeking data source, and the obtained empirical value can be used to correct the product self-alignment output to reduce the impact of the heading effect error.

[0003] The paper "Calibration and Compensation of Heading Effects in Optical Inertial Navigation Platforms" discloses three methods for calibrating and compensating heading effects: calibration using a turntable's rotating housing, calibration using a heading sensor's rotating housing, and calibration using control-command heading precession. These methods essentially use the platform's three-axis command angular velocity to extract the drift of the three-axis gyroscope at the current heading position due to the heading effect when the heading effect reaches equilibrium. By stimulating multiple heading positions, the drift of multiple three-axis gyros can be calibrated. The calibrated drift is then used to compensate the gyro data, improving the system's self-alignment accuracy across the entire heading range. This method calibrates and compensates for heading effect errors without requiring an external heading reference, achieving an error reduction of almost an order of magnitude after calibration and compensation. However, this method relies on the platform's tracking characteristics, making it unsuitable for strapdown inertial measurement units (IMUs). Furthermore, the stabilization of the heading effect requires a long time, which means that calibration at multiple positions requires a significant amount of time for the heading effect to stabilize, which does not meet the efficiency requirements of streamlined production.

[0004] The paper "Strapdown Gyrocompass Calibration Method Based on Heading Error" discloses a method for calibrating and compensating for the heading effect of an inertial measurement unit (IMU). Through theoretical derivation, the relationship between the heading error of the strapdown compass alignment and gyro drift is derived. In its implementation, the IMU is fixed to a turntable, and gyro and accelerometer data are collected at different angles. The heading error is fitted to obtain a constant gyro drift error, and the gyro output is corrected to improve heading accuracy. This method does not fully disclose how the IMU is fixed to the turntable or how the heading reference is obtained. Furthermore, the method is based on an ideal gyrocompass alignment method, and the final compensation term for the error is the constant gyro drift. This makes it unsuitable for addressing errors caused by changing factors such as temperature fields and geomagnetic fields encountered during engineering implementation. Summary of the Invention

[0005] The technical problem solved by the present invention is to overcome the shortcomings of the existing technology and provide a method for calibrating and compensating the heading effect error of an inertial measurement unit, thereby improving the absolute accuracy of the inertial measurement unit over the entire heading range and meeting the requirements of assembly line production for compensation test efficiency.

[0006] The technical solution of the present invention is: a method for calibrating and compensating the heading effect error of an inertial measurement unit, comprising the following steps:

[0007] S1. Construct a calibration system, including a single-axis turntable, a transfer fixture, an optical assembly, and an aiming device; the single-axis turntable rotates about a celestial axis and has a plane C; the transfer fixture is fixed to the single-axis turntable and has a plane B perpendicular to plane C; the optical assembly is fixed to the transfer fixture and has a plane D parallel to plane B;

[0008] S2. Debug the calibration system to ensure that the perpendicularity between plane C and plane B, and the parallelism between plane B and plane D are within the required threshold range;

[0009] S3. Implement error calibration and compensation. Place the heading reference plane of the outer surface of the inertial measurement unit under test against and fix it to plane B. Use the aiming device to perform optical aiming on plane D of the optical component to obtain the heading angle of the optical component. According to the spatial geometric transfer relationship between the optical component, the adapter fixture, and the inertial measurement unit, the heading angle optical aiming value of the inertial measurement unit is indirectly obtained. By controlling the angular position of the single-axis turntable around the celestial axis, the inertial measurement unit is self-aligned within the full heading range, and the difference between the heading angle and the optical aiming value is calculated to estimate the parameters of the compensation model and obtain the compensation model. The compensation model is embedded in the inertial measurement unit to compensate for the self-alignment heading result of the inertial measurement unit.

[0010] Furthermore, the compensation model is obtained by controlling the angular position of the single-axis turntable around the celestial axis, performing position self-alignment of the inertial measurement unit within the full heading range, and calculating the difference between the heading angle and the optical aiming value to estimate the parameters of the compensation model. The specific steps include:

[0011] Set the total number of rotation tests to N, the rotation test count variable to k, and assign k to 0;

[0012] S31, calculate the single-axis turntable target position angle α k :

[0013]

[0014] Where, α is the current angle of the single-axis turntable;

[0015] S32, control the single-axis turntable to rotate to the target position angle α k ;

[0016] S33, the inertial measurement unit performs self-alignment, and the heading result is β k ;

[0017] S34, the value of variable k is increased by 1;

[0018] S35. If the value of variable k is equal to N, proceed to step S36, otherwise return to step S31;

[0019] S36. Fitting to obtain compensation model:

[0020] Calculate vector P1:

[0021]

[0022] Calculate vector P2:

[0023]

[0024] Calculate vector X:

[0025]

[0026] Where P1(n) represents the nth element in vector P1, and P2(n) represents the nth element in vector P2;

[0027] Calculate vector Y:

[0028]

[0029] Calculate vector A:

[0030]

[0031] Get the compensation model:

[0032] f(θ)=A1+A2·cos(θ)+A3·cos 2 (θ)+A4·cos 3 (θ)+·sin(θ)+A6·sin 3 (θ).

[0033] Furthermore, a compensation model is embedded in the inertial measurement unit to compensate the inertial measurement unit self-alignment heading result. The specific method is as follows:

[0034] The self-alignment heading result of the inertial measurement unit is β k ;

[0035] The inertial measurement unit output is the compensated result

[0036]

[0037] Furthermore, the calibration system is debugged. The specific steps include:

[0038] S21. Mechanically level the single-axis turntable so that plane C is parallel to the horizontal plane;

[0039] S22, fixing the transfer tooling on the plane C of the single-axis turntable;

[0040] S23. If the perpendicularity between plane B and plane C exceeds the set threshold, proceed to step S24; otherwise, proceed to step S25.

[0041] S24, fine-tune the plane on the transfer tooling that is fixed to the single-axis turntable, and return to step S22;

[0042] S25, fixing the optical component on the transfer fixture;

[0043] S26: If the parallelism between plane B and the aiming plane D of the optical assembly exceeds the set threshold, proceed to step S25; otherwise, proceed to step S28;

[0044] S27, adjusting the installation position of the optical component and the adapter tooling, and returning to step S25;

[0045] S28. Debugging is completed.

[0046] Furthermore, during the error calibration and compensation process in step S3, the calibration system is calibrated regularly. If the calibration is successful, the error calibration and compensation are continued. If the calibration fails, the calibration system is re-debugged.

[0047] Furthermore, the calibration system is calibrated regularly, specifically in the following ways:

[0048] In step S2, after the perpendicularity between planes C and B, and the parallelism between planes B and D, are adjusted to within the required threshold ranges, the single-axis turntable is operated to rotate to an angle α, and the aiming device is operated to optically aim at plane D of the optical component to obtain the optical aiming heading angle γ of plane B.

[0049] When the calibration system needs to be calibrated, operate the single-axis turntable to rotate it to angle α, operate the aiming device to aim at the optical component plane D, and obtain the optical aiming heading angle γ1 of plane B;

[0050] If |γ-γ1| is greater than the set threshold, the calibration is judged to have failed; otherwise, the calibration is judged to have succeeded.

[0051] The present invention also provides a calibration system for the aforementioned inertial measurement unit heading effect error calibration and compensation method, comprising:

[0052] Single-axis turntable, which rotates around the celestial axis and has a plane C;

[0053] The transfer fixture is fixed on the single-axis turntable and has a plane B perpendicular to the plane C;

[0054] The optical assembly is fixed to the adapter and has a plane D parallel to the plane B;

[0055] The aiming device is used to perform optical aiming on the plane D of the optical component to obtain the heading angle of the optical component. According to the spatial geometric transfer relationship between the optical component, the adapter fixture and the inertial measurement unit, the heading angle optical aiming value of the inertial measurement unit is indirectly obtained.

[0056] Furthermore, a mounting interface is left on the upper surface of plane C of the single-axis turntable for fixing the adapter tooling; the adapter tooling has an external interface that can be used to fix the inertial measurement combination and optical components, and can be fixed on plane C of the single-axis turntable.

[0057] Furthermore, the single-axis turntable includes but is not limited to an electrically controlled turntable or a graduated plate, the optical component includes but is not limited to a plane mirror or a prism, and the aiming device includes but is not limited to a gyrotheodolite or a combination of a north finder and a theodolite.

[0058] The advantages of this invention over existing technologies include: it only requires optical aiming at a single heading angle to determine the heading angle at any angle in the entire heading range. The compensation model requires minimal computational effort and can be embedded within an inertial measurement unit to improve self-alignment heading accuracy. Compared to other publicly available methods, this invention offers a simple operation process, high execution efficiency, and low cost, making it suitable for assembly line production. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is a schematic diagram of the calibration system principle of the present invention;

[0060] Figure 2 Flow chart of the method of the present invention;

[0061] Figure 3 This is a flow chart of the debugging phase of the method of the present invention;

[0062] Figure 4 This is a flow chart of the implementation phase of the method of the present invention;

[0063] Figure 5 This is a flow chart of the calibration stage of the method of the present invention. DETAILED DESCRIPTION

[0064] In order to better understand the technical solution of the present invention, the specific implementation methods of the present invention are described in detail below with reference to the accompanying drawings.

[0065] The method proposed in the present invention is implemented by the calibration system proposed in the present invention, and the system composition is shown as follows: Figure 1 As shown, it primarily consists of a single-axis turntable (e.g., an electronically controlled turntable, indexing plate, or other equipment capable of high-precision rotation about the celestial axis), a transfer fixture (the shape of which is determined by the mounting method of the measured object and the reserved mounting interface of the single-axis turntable), optical components (e.g., plane mirrors, prisms, etc.), and an aiming device (e.g., a gyro-theodolite or a combination of a north-finder and theodolite). Specific requirements include: the single-axis turntable rotates about the celestial axis and has a plane C; the transfer fixture is fixed to the single-axis turntable and has a plane B perpendicular to plane C, which serves as the high-precision machining surface of the transfer fixture; the optical component is fixed to the transfer fixture and has a plane D parallel to plane B, which serves as the aiming plane of the optical component. The upper surface of the single-axis turntable plane C has a mounting interface that can be used to fix the adapter tooling; the adapter tooling has sufficient rigidity, and the outer interface can be used to fix the inertial measurement unit and optical components, and can be fixed on the single-axis turntable plane C; the outer surface of the inertial measurement unit, which is the object to be measured, is machined with a high-precision plane A as a heading reference plane.

[0066] This method is implemented in three stages, such as Figure 2 As shown, the first use requires the debugging phase. After debugging is complete, the implementation phase begins. During implementation, the calibration phase is periodically entered. If the calibration is successful, the implementation phase continues; if the calibration fails, the system returns to the debugging phase. During the implementation phase, the aiming device performs optical aiming on the optical component to obtain the heading angle of the optical component. This is then combined with the spatial geometric transfer relationship between the optical component, the adapter, and the inertial measurement unit (IMU), to indirectly obtain the heading angle optical aiming value of the IMU. Through high-precision angular position control of the single-axis turntable around the celestial axis, the IMU can self-align at any position within the full heading range. The difference between the heading angle and the optical aiming value is then calculated and used to estimate the parameters of the compensation model. Finally, the compensation model is embedded within the IMU to compensate for the self-alignment results.

[0067] The specific implementation process is as follows:

[0068] (1) Enter the debugging stage, refer to Figure 3 ;

[0069] (2) Mechanically level the single-axis turntable so that plane C is parallel to the horizontal plane;

[0070] (3) Fix the transfer tooling on the plane C of the single-axis turntable;

[0071] (4) If the perpendicularity between plane B and plane C exceeds the threshold value A1 (A1 is an empirical value obtained based on the accuracy decomposition), proceed to step (5); otherwise, proceed to step (6);

[0072] (5) Fine-tune the plane on the transfer fixture that is fixed to the single-axis turntable and proceed to step (3);

[0073] (6) Fix the optical component on the adapter;

[0074] (7) If the parallelism between plane B and the aiming plane D of the optical component exceeds a threshold value A2 (A2 is an empirical value obtained based on the accuracy decomposition), proceed to step (8); otherwise, proceed to step (9);

[0075] (8) Adjust the installation position of the optical component and the adapter tooling, and proceed to step (6);

[0076] (9) Operate the single-axis turntable to rotate it to an angle α;

[0077] (10) operating the aiming device to aim at the optical component plane D;

[0078] (11) Obtain the optical aiming heading angle γ of plane B (plane D);

[0079] (12) Entering the implementation stage, please refer to Figure 4 ;

[0080] (13) After plane A of the inertial measurement unit and plane B of the transfer fixture are in place, the inertial measurement unit is fixed to the transfer fixture;

[0081] (14) Let the total number of rotation tests be N, the number of rotation tests be k and be assigned a value of 0;

[0082] (15) Calculate the target position angle α of the single-axis turntable k :

[0083]

[0084] (16) Control the single-axis turntable to rotate to the target position angle α k ;

[0085] (17) The inertial measurement unit performs self-alignment, and the heading result is β k ;

[0086] (18) The value of variable k is increased by 1;

[0087] (19) If the value of variable k is equal to N, go to step (20), otherwise go to step (15);

[0088] (20) The compensation model is obtained by least square fitting:

[0089] (20.1) Calculate the vector P1:

[0090]

[0091] (20.2) Calculate the vector P2:

[0092]

[0093] (20.3) Calculate the vector X:

[0094]

[0095] (20.4) Calculate the vector Y:

[0096]

[0097] (20.5) Calculate the vector A:

[0098]

[0099] (20.6) The compensation model function expression is obtained:

[0100] f(θ)=A1+A2·cos(θ)+A3·cos 2(θ)+A4·cos 3 (θ)++A5·sin(θ)+A6·sin 3 (θ)

[0101] (21) Embedding the compensation model into the inertial measurement unit;

[0102] (21.1) The self-alignment heading result of the inertial measurement unit is β k ;

[0103] (21.2) The inertial measurement unit output is the compensated result

[0104]

[0105] (22) If it is the calibration stage, go to step (23), otherwise go to step (1), refer to Figure 5 ;

[0106] (23) Operate the single-axis turntable to rotate it to an angle α;

[0107] (24) operating the aiming device to aim at the optical component plane D;

[0108] (25) Obtain the optical aiming heading angle γ1 of plane B (plane D);

[0109] (26) If |γ-γ1| is greater than the threshold A3 (A3 is an empirical value obtained based on the accuracy decomposition), go to step (27), otherwise go to step (28);

[0110] (27) If calibration fails, go to step (1);

[0111] (28) If the calibration is successful, proceed to step (12).

[0112] It will be understood that the present invention is described by way of example, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and any embodiment that falls within the scope of the claims of this application is intended to be within the scope of protection of the present invention.

[0113] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for calibrating and compensating a heading effect error of an inertial measurement unit, characterized in that: The steps include: S1. Construct a calibration system, including a single-axis turntable, a transfer fixture, an optical component, and a sighting device; the single-axis turntable rotates around a celestial axis and has a plane C; Transfer The tooling is fixed on a single-axis turntable and has a plane B perpendicular to the plane C; the optical component is fixed on the transfer tooling and has a plane D parallel to the plane B; S2. Debug the calibration system to ensure that the perpendicularity between plane C and plane B and the parallelism between plane B and plane D are within the required threshold range; S3. Implement error calibration and compensation. The heading reference plane of the outer surface of the inertial measurement unit to be measured is placed against and fixed to plane B. The plane D of the optical component is optically aimed at using the aiming device to obtain the heading angle of the optical component. The heading angle optical aiming value of the inertial measurement unit is indirectly obtained based on the spatial geometric transfer relationship of the optical component-adapter-inertial measurement unit. The position self-alignment of the inertial measurement unit is performed within the full heading range by controlling the angular position of the single-axis turntable around the celestial axis, and the difference is calculated from the heading angle optical aiming value. The parameters of the compensation model are estimated to obtain the compensation model. The compensation model is embedded in the inertial measurement unit to compensate for the self-alignment heading result of the inertial measurement unit.

2. The method for calibrating and compensating the heading effect error of an inertial measurement unit according to claim 1, characterized in that: The method controls the angular position of the single-axis turntable around the celestial axis, performs position self-alignment of the inertial measurement combination within the full heading range, calculates the difference with the heading angle optical aiming value, estimates the parameters of the compensation model, and obtains the compensation model. The specific steps include: Set the total number of rotation tests to N, the rotation test count variable to k, and assign k to 0; S31, calculate the single-axis turntable target position angle α k : Where, α is the current angle of the single-axis turntable; S32, control the single-axis turntable to rotate to the target position angle α k ; S33, the inertial measurement unit performs self-alignment, and the heading result is β k ; S34, the value of variable k is increased by 1; S35. If the value of variable k is equal to N, proceed to step S36, otherwise return to step S31; S36, fitting to obtain compensation model: Calculate vector P1: Calculate vector P2: Calculate the vector X: Where P1(n) represents the nth element in vector P1, and P2(n) represents the nth element in vector P2; Calculate the vector Y: Calculate vector A: Get the compensation model: f(θ)=A1+A2·cos(θ)+A3·cos 2 (θ)+A4·cos 3 (θ)+·sin(θ)+A6·sin 3 (θ).

3. The method for calibrating and compensating the heading effect error of an inertial measurement unit according to claim 2, characterized in that: The compensation model is embedded in the inertial measurement unit to compensate the self-alignment heading result of the inertial measurement unit. The specific method is as follows: The self-alignment heading result of the inertial measurement unit is β k ; The inertial measurement unit output is the compensated result 4. The method for calibrating and compensating the heading effect error of an inertial measurement unit according to claim 1, characterized in that: Debug the calibration system. The specific steps include: S21, mechanically leveling the single-axis turntable so that plane C is parallel to the horizontal plane; S22, fixing the transfer tooling on the plane C of the single-axis turntable; S23, if the perpendicularity between plane B and plane C exceeds the set threshold, proceed to step S24, otherwise proceed to step S25; S24, fine-tune the plane on the transfer tooling that is fixed to the single-axis turntable, and return to step S22; S25, fixing the optical component on the transfer tooling; S26, if the parallelism between plane B and the aiming plane D of the optical component exceeds the set threshold, proceed to step S25, otherwise proceed to step S28; S27, adjusting the installation positions of the optical assembly and the transfer tooling, and returning to step S25; S28. Debugging is completed.

5. The method for calibrating and compensating the heading effect error of an inertial measurement unit according to claim 1, characterized in that: In the process of implementing error calibration and compensation in step S3, the calibration system is calibrated regularly. If the calibration is successful, the error calibration and compensation are continued. If the calibration fails, the calibration system is re-debugged.

6. The method for calibrating and compensating the heading effect error of an inertial measurement unit according to claim 4, characterized in that: The calibration system should be calibrated regularly, as follows: In step S2, after the perpendicularity between plane C and plane B and the parallelism between plane B and plane D have been adjusted to within the required threshold range, the single-axis turntable is operated to rotate to an angle α, and the aiming device is operated to optically aim at the optical component plane D to obtain the optical aiming heading angle γ of plane B; When the calibration system needs to be calibrated, the single-axis turntable is operated to rotate to an angle α, and the aiming device is operated to optically aim at the optical component plane D to obtain the optical aiming heading angle γ1 of plane B; If |γ-γ1| is greater than the set threshold, the calibration is judged to have failed, otherwise, the calibration is judged to have succeeded.

7. A calibration system for the inertial measurement unit heading effect error calibration and compensation method according to claim 1, characterized in that: include: Single-axis turntable, the single-axis turntable rotates around the celestial axis and has a plane C; The transfer fixture is fixed on the single-axis turntable and has a plane B perpendicular to the plane C; The optical assembly is fixed to the transfer fixture and has a plane D parallel to the plane B; The aiming device is used to optically aim at the plane D of the optical component to obtain the heading angle of the optical component. According to the spatial geometric transfer relationship of the optical component-adapter-inertial measurement combination, the heading angle optical aiming value of the inertial measurement combination is indirectly obtained.

8. The method for calibrating and compensating the heading effect error of an inertial measurement unit according to claim 7, characterized in that: An installation interface is left on the upper surface of plane C of the single-axis turntable for fixing the adapter; the adapter has an external interface, which can be used to fix the inertial measurement combination and optical components, and can be fixed on plane C of the single-axis turntable.

9. The calibration system according to claim 7, characterized in that: The single-axis turntable includes but is not limited to an electrically controlled turntable or a dividing plate, the optical component includes but is not limited to a plane mirror or a prism, and the aiming device includes but is not limited to a gyrotheodolite or a combination of a north finder and a theodolite.

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