Three-axis rotation inertial navigation system modulation method

Abstract

The invention relates to a three-axis rotation inertial navigation system modulation method, which adopts a three-axis rotation modulation system scheme of outer heading, middle roll and inner heading, and mainly comprises the following steps: firstly, carrying out inertial navigation self-alignment, including nineteen-position self-calibration and subsequent alignment, and carrying out pure inertial navigation after alignment is completed; during continuous alignment and pure inertial navigation, sixteen-position double-shaft rotation is executed through the inner shaft and the middle shaft, in the process, the navigation attitude of the IMU is subjected to two times of coordinate transformation through an inner shaft coordinate system and a middle shaft coordinate system, the navigation attitude at the moment is extracted, the difference between the navigation attitude at the moment and the set reference target navigation attitude is obtained, PID calculation is conducted through the difference value, the outer shaft is driven to rotate, and the navigation attitude of the IMU is obtained. And the influence of the course of the carrier system on the rotation modulation effect is isolated.

Description

Technical Field

[0001] The invention relates to the technical field of inertial navigation, and in particular to a modulation method for a three-axis rotating inertial navigation system. Background Art

[0002] The strapdown inertial navigation system collects data from gyroscopes and accelerometers, and uses a navigation computer to calculate the carrier's real-time speed, position, attitude, heading and other information. The errors of inertial sensitive elements including gyroscopes and accelerometers are the main determinants of inertial navigation system errors. Improving the accuracy of inertial sensitive elements from a process perspective is technically difficult and time-consuming, and it cannot exceed the current possibilities. Therefore, after the accuracy of inertial sensitive elements reaches certain requirements, using methods to compensate for inertial sensitive element errors to further improve the performance of the inertial navigation system is a realistic way to achieve higher navigation accuracy. By adding a rotation and control mechanism to the outside of the inertial element or IMU, flipping or rotation is used to average out the impact of inertial element drift on navigation. With a small increase in system cost, the potential of the optical gyroscope is fully tapped to obtain higher navigation accuracy.

[0003] At present, the mature 16-position dual-axis modulation system solution adopts the form of external roll and internal heading, which can modulate all errors except the gyro scale factor error and the coupling term of the earth's rotation angular velocity, but it cannot isolate the heading motion of the actual carrier, and there is a heading effect in the actual navigation process due to the influence of geomagnetism, etc. If the form of external heading and internal roll is adopted, although the problems encountered in the above form in practice can be solved, it is affected by observability and cannot perform self-calibration of zero bias, scale factor and installation error, and cannot meet the needs of long-term maintenance-free.

[0004] In response to the problems of dual-axis modulation, relevant literature proposes a three-axis modulation scheme around the Earth's center inertial system. Although this series of schemes can theoretically modulate all inertial device errors, it is difficult to control the motor to rotate at a specified angular velocity in practice, considering that the angular velocity of the Earth's rotation is very small. In summary, it is necessary to compile a three-axis rotation inertial navigation system modulation scheme that can achieve system-level self-calibration, isolate the carrier motion, and be applied to actual systems. Summary of the invention

[0005] The present invention discloses a modulation scheme design for a three-axis rotating inertial navigation system, which can isolate the heading motion of a carrier on the basis of traditional two-axis modulation and improve the long-term navigation accuracy of the inertial navigation system.

[0006] The present disclosure provides a three-axis rotation inertial navigation system modulation method, comprising the following steps:

[0007] Considering that the laser gyro scale factor has high stability and the coupling error term with the earth's rotation angular velocity is small, and the mid-roll and inner heading schemes can realize the system-level self-calibration process and further correct the scale factor and installation error of the inertial navigation, a three-axis rotation modulation system scheme of outer heading, mid-roll and inner heading is proposed on the basis of dual-axis rotation modulation.

[0008] The inertial navigation system first performs self-alignment: during the self-alignment process, a 19-position self-calibration is first performed through the inner axis and the middle axis of the indexing mechanism. After the self-calibration is completed, the zero bias, scale factor and installation error of the gyroscope and accelerometer are corrected to further reduce the error term coupled with the scale factor and the angular velocity of the earth's rotation; after the self-calibration is completed, a subsequent alignment is performed, and after the alignment is completed, pure inertial navigation is performed.

[0009] During subsequent alignment and pure inertial navigation, a sixteen-position two-axis rotation is performed via the inner and middle axes of the indexing mechanism.

[0010] During the sixteen-position dual-axis rotation, the IMU and the geographic system cannot remain relatively fixed due to the movement of the carrier. When the carrier is stationary, the attitude of the IMU itself will keep changing during the dual-axis rotation. When the outer axis does not rotate, the attitude of the carrier remains unchanged, so the IMU's heading is extracted through two coordinate transformations in the inner axis coordinate system and the middle axis coordinate system; in order to keep the IMU and the geographic system relatively fixed, the current heading is subtracted from the set reference heading for PID calculation to drive the outer axis to rotate, and the heading of the isolated carrier system is isolated, thereby effectively suppressing the influence of the heading motion of the carrier on the rotation modulation effect, making the effect of the rotation modulation close to the level of no heading motion of the carrier, and further ensuring the actual inertial navigation autonomous long-flight high-precision navigation.

[0011] Compared with the prior art, the beneficial effects of the present invention are: (1) a modulation scheme design for a three-axis rotating inertial navigation system is proposed, which can take into account dual-axis modulation, isolated carrier heading motion and system-level self-calibration; (2) the method is easy to implement in an actual system; (3) it can improve the long-term navigation accuracy of the inertial navigation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above and other objects, features and advantages of the present disclosure will become more apparent through a more detailed description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present disclosure.

[0013] Figure 1 This is a schematic diagram of IMU dual-axis rotation modulation;

[0014] Figure 2 A flow chart is designed for a three-axis rotation modulation scheme according to the present disclosure. DETAILED DESCRIPTION

[0015] The preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0016] The present invention proposes a three-axis rotation inertial navigation system modulation scheme design, which is implemented in the following specific manner:

[0017] Considering that the laser gyro scale factor has high stability and the coupling error term with the earth's rotation angular velocity is small, and the mid-roll and inner heading schemes can realize the system-level self-calibration process and further correct the scale factor and installation error of the inertial navigation, a three-axis rotation modulation system scheme of outer heading, mid-roll and inner heading is proposed on the basis of dual-axis rotation modulation.

[0018] The inertial navigation system is first self-aligned. After the coarse alignment is completed, the inner axis and the middle axis are first self-calibrated at nineteen positions. After the self-calibration is completed, the zero bias, scale factor and installation error of the gyroscope and accelerometer are corrected to further reduce the coupling error term of the scale factor and the angular velocity of the earth's rotation.

[0019] The rotation order of the two axes during the calibration process is shown in the following table:

[0020] Table 1 Biaxial rotation order in calibration

[0021]

[0022]

[0023] A system-level calibration method is used to solve the attitude and velocity position of the device output data, and the difference between the solved velocity position and the actual velocity position is used as the observation quantity to design a reasonable calibration path, and the rotation is realized through the dual-axis indexing mechanism. The Kalman filter is used to estimate the gyro and accelerometer errors, and the zero bias, scale factor and installation error of the gyro and accelerometer are obtained, and a one-time feedback correction is performed.

[0024] After the self-calibration is completed, the subsequent alignment is performed, and the pure inertial navigation is performed after the alignment is completed. During the subsequent alignment and pure inertial navigation, a sixteen-position two-axis rotation is performed through the inner axis and the middle axis of the indexing mechanism. In addition, the sixteen-position two-axis rotation is performed during the alignment, which can improve the observability of the inertial navigation system and improve the alignment accuracy.

[0025] During the sixteen-position dual-axis rotation, the IMU and the geographic system cannot remain relatively fixed due to the movement of the carrier. When the carrier is stationary, the attitude of the IMU itself will keep changing during the dual-axis rotation. When the outer axis does not rotate, the attitude of the carrier remains unchanged. Therefore, the IMU's heading attitude is extracted by performing two coordinate transformations in the inner axis coordinate system and the middle axis coordinate system. The specific coordinate transformation formula is shown below.

[0026]

[0027] Among them, u is the IMU coordinate system, n is the geographic coordinate system, u1 is the coordinate system converted by the IMU through the internal axis angle encoder, and u2 is the coordinate system converted by the central axis angle encoder based on the u1 coordinate system. is the attitude quaternion of IMU and geographic system, It is the attitude quaternion of the coordinate system and geographic system after the IMU is converted by the internal axis encoder. is the attitude quaternion of the coordinate system and the geographic system after the IMU is converted twice by the internal and middle axis angle encoders, ψ is the angle output by the internal axis angle encoder, θ is the angle output by the middle axis angle encoder, and u x 、u y are the angles between the IMU and the inner axis of the indexing mechanism in the X and Y directions, v x 、v y are the angles between the IMU and the center axis of the transfer mechanism in the X and Z directions, respectively.

[0028] First, the heading of the IMU itself is obtained Through the above two formulas, we can get pass The heading in this coordinate system can be obtained. In order to keep the IMU and the geographic system relatively fixed, the heading at this time is subtracted from the set reference target heading, and PID calculation is performed through the difference. The obtained PWM value is used to send instructions to the motor driver to drive the external axis to rotate, thereby isolating the heading of the carrier system, thereby effectively suppressing the influence of the carrier's heading motion on the rotation modulation effect, and making the effect of rotation modulation close to the level when the carrier has no heading motion, further ensuring the actual inertial navigation autonomous long-flight high-precision navigation.

[0029] The above technical scheme is only an exemplary embodiment of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the application methods and principles disclosed in the present invention, and it is not limited to the method described in the above specific embodiment of the present invention. Therefore, the method described above is only preferred and does not have a restrictive meaning.

Claims

1. A three-axis rotation inertial navigation system modulation method, comprising the following steps: S1, set the outer axis of the three-axis inertial navigation system to point toward the sky, the middle axis to point toward the north, and the inner axis to point toward the sky; S2, the inertial navigation system performs self-alignment, including: firstly performing 19-position self-calibration through the inner axis and the middle axis of the indexing mechanism to correct the initial error; then performing subsequent alignment to correct the heading and attitude errors; after the alignment is completed, performing pure inertial navigation; S3, during subsequent alignment and pure inertial navigation, a sixteen-position two-axis rotation is performed by the inner and middle axes of the indexing mechanism; S4, during the execution of the sixteen-position dual-axis rotation, the IMU's heading attitude is converted twice through the inner axis coordinate system and the middle axis coordinate system to extract the current heading attitude; the current heading is subtracted from the set reference heading to perform PID calculation to drive the outer axis rotation, isolate the influence of the heading motion of the carrier system on the rotation modulation effect, and make the rotation modulation effect close to the level when the carrier has no heading motion.

2. The method according to claim 1, characterized in that In step S2, the specific method of the self-calibration includes: By solving the attitude and speed position of the device output data, taking the difference between the solved speed position and the real speed position as the observation quantity, a reasonable calibration path is designed, and the rotation is realized through the dual-axis indexing mechanism; The Kalman filter is used to estimate the errors of the gyro and accelerometer, obtain the zero bias, scale factor and installation error of the gyro and accelerometer, and perform a one-time feedback correction; The rotation order of the two axes during the calibration process is shown in the following table:

3. The method according to claim 1 or 2, characterized in that: The initial error in step S2 includes one or more of the zero bias, scale factor and installation error of the gyroscope and the accelerometer.

4. The method according to claim 1 or 2, characterized in that: In step S4, the method for performing the coordinate transformation includes: Among them, u is the IMU coordinate system, n is the geographic coordinate system; u1 is the coordinate system of the IMU converted by the internal axis angle encoder, and u2 is the coordinate system converted by the central axis angle encoder based on the u1 coordinate system; is the attitude quaternion of IMU and geographic system, It is the attitude quaternion of the coordinate system and geographic system after the IMU is converted by the internal axis encoder. is the attitude quaternion of the coordinate system and the geographic system after the IMU is converted twice by the internal and middle axis angle encoders, ψ is the angle output by the internal axis angle encoder, θ is the angle output by the middle axis angle encoder, and u x 、u y are the angles between the IMU and the inner axis of the indexing mechanism in the X and Y directions, v x 、v y are the angles between the IMU and the center axis of the transfer mechanism in the X and Z directions, respectively.

5. The method according to claim 4, characterized in that The step S4 specifically comprises the following steps: Obtained through the IMU's own heading Through the above two formulas, we can get pass Get the heading in the coordinate system; In order to keep the IMU and the geographic system relatively fixed, the current heading is subtracted from the set reference target heading, and PID calculation is performed based on the difference. The obtained PWM value is used to send instructions to the motor driver to drive the external axis to rotate, thereby isolating the heading of the carrier system, suppressing the influence of the carrier heading motion on the rotation modulation effect, and making the rotation modulation effect close to the level when the carrier has no heading motion.

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