Single-axis rotation inertial navigation system and method for monitoring on-line compensation azimuth drift of gyroscope

Abstract

The invention discloses a single-axis rotation inertial navigation system and method for monitoring gyroscope on-line compensation azimuth drift, and belongs to the technical field of inertial navigation, the system comprises a main IMU, a single-axis rotation mechanism, a monitoring assembly and a data signal processing module; rotating shafts at the upper end and the lower end of a main IMU are installed in rolling bearings at the top and the bottom of an outer shell, an orientation torque motor shaft in a single-shaft rotating mechanism and the rotating shafts at the two ends of the main IMU are coaxially installed, and rotating shafts at the left end and the right end of a rotating table body in a monitoring assembly are installed in rolling bearings in the main IMU in the horizontal direction. The data signal processing module is distributed on the side surface of the main IMU and in a top electronic cabin of the outer shell; the monitoring assembly comprises a monitoring gyroscope, and the main IMU comprises an orientation gyroscope. According to the method, the azimuth gyroscopic drift is equivalent to a mean value in a monitoring period by using a segmented mean value algorithm, so that the on-line estimation compensation of the azimuth gyroscopic drift can be realized, and the autonomy and the concealment of the inertial navigation system during the working period are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of inertial navigation, and in particular relates to a single-axis rotating inertial navigation system and method for monitoring gyroscope online compensation of azimuth drift. Background Art

[0002] With the development of inertial navigation technology, underwater and surface vehicles have put forward higher requirements for the long flight time, high precision and high concealment of inertial navigation systems. With the development and application of small and medium-sized unmanned submarines, inertial navigation systems are also facing the comprehensive challenge of how to achieve smaller size, lower cost and higher precision. Single-axis rotating inertial navigation systems have been widely used due to their own advantages, but the azimuth gyro drift that cannot be modulated has become one of the important factors restricting its navigation accuracy. In order to suppress the negative impact of this drift on navigation accuracy, the following two suppression methods are commonly used: (1) Increasing the number of rotating frame axes, that is, dual-axis or three-axis rotating inertial navigation systems. This technology can simultaneously modulate the gyro drift in three directions, but it will increase the system volume, the complexity of the rotation strategy and the difficulty of rotation control. (2) Filter estimation algorithm. This technology relies on external measurement information such as GPS and geomagnetic topographic maps to estimate the gyro drift online. However, the introduction of external measurement information will inevitably destroy the autonomy and concealment of the inertial navigation system. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0004] A single-axis rotating inertial navigation system for monitoring gyro online compensation of azimuth drift, comprising: a main IMU, a single-axis rotating mechanism, a monitoring component, and a data signal processing module;

[0005] Among them, the rotation axes of the upper and lower ends of the main IMU are installed in the rolling bearings at the top and bottom of the outer shell. The azimuth torque motor shaft in the single-axis rotation mechanism is coaxially installed with the rotation axes at both ends of the main IMU. The rotation axes of the left and right ends of the rotating table in the monitoring component are installed in the rolling bearings in the horizontal direction inside the main IMU. The data signal processing modules are distributed on the side of the main IMU and in the electronic cabin on the top of the outer shell. The monitoring component includes a monitoring gyroscope, and the main IMU includes an azimuth gyroscope. The rotating table is set Rotate between.

[0006] A single-axis rotating inertial navigation method for monitoring gyro online compensation for azimuth drift, used in the single-axis rotating inertial navigation system for monitoring gyro online compensation for azimuth drift, comprising:

[0007] Step 1: The single-axis rotating inertial navigation system is powered on and initialized. The single-axis rotating inertial navigation system enters the coarse alignment stage, fine alignment stage and navigation stage in sequence;

[0008] Step 2: The navigation phase begins. The first monitoring cycle begins at the beginning of the navigation phase. A monitoring cycle is divided into the sky-pointing phase and the ground-pointing phase.

[0009] Step 3: During the pointing stage, the rotating platform stops at Position, monitor the gyro and the azimuth gyro's sensitive axis in the same direction and point to the sky at the same time, collect the outputs of the two gyros and calculate the difference between the two gyro outputs ;

[0010] Step 4: At the end of the pointing phase, calculate the average difference between the two gyro outputs during this phase. ;

[0011] Step 5: Rotate the stage from Rotate to Position and dock, the single-axis rotation inertial navigation system enters the ground pointing stage of the first monitoring cycle;

[0012] Step 6: During the ground pointing phase, the rotating platform stops at Position, monitor the gyro and the azimuth gyro sensitive axis pointing in opposite directions, collect the outputs of the two gyros and calculate the sum of the two gyro outputs ;

[0013] Step 7: At the end of the ground pointing phase, calculate the mean of the sum of the two gyro outputs during this phase. ;

[0014] Step 8: Calculate the drift estimate of the azimuth gyro and monitoring gyro during this monitoring period 、 ;

[0015] Step 9: Verify the validity of the drift estimate calculated by S8 and compare and azimuth gyro drift threshold 、 and monitor gyro drift thresholds If the drift estimation values ​​of both gyros do not exceed the threshold, the drift compensation values ​​of the azimuth gyro and the monitoring gyro are updated. 、 ;

[0016] Step 10: This monitoring cycle ends and the rotating table rotates to and docked;

[0017] Step 11: Repeat steps 3 to 10 until the system is operational.

[0018] The present invention has the following beneficial effects:

[0019] The present invention addresses the problem that azimuth gyro drift in a single-axis rotating inertial navigation system cannot be observed and modulated online. By combining an additional monitoring gyro with a piecewise average algorithm, online compensation of azimuth gyro drift is achieved. The specific technical advantages are as follows:

[0020] The present invention solves the problem of large volume and complex rotation control in dual-axis or three-axis inertial navigation systems by adding a horizontally flippable monitoring gyroscope to the internal space of the IMU (Inertial Measurement Unit, hereinafter referred to as IMU) of the single-axis rotation inertial navigation system through a simple mechanical structure design and rotation control method.

[0021] The present invention uses a segmented mean algorithm to convert the azimuth gyro drift into an average value within a monitoring period. Based on the simplicity of the algorithm and the absence of external measurement, the present invention realizes online estimation and compensation of the azimuth gyro drift, thus ensuring the autonomy and concealment of the inertial navigation system during operation.

[0022] The present invention has conducted specific navigation experiments, and the results show that the navigation accuracy after the online compensation of azimuth drift of the present invention is improved by more than 40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the overall structure of the single-axis rotation inertial navigation system of the present invention, wherein 1-main IMU, 2-single-axis rotation mechanism, 3-monitoring component, 4-data signal processing module;

[0024] Figure 2 Flowchart of the online compensation azimuth gyro drift algorithm of the present invention;

[0025] Figure 3 This is a comparison curve diagram of radial position errors before and after azimuth drift compensation of the present invention. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0027] To address the problem that azimuth gyro drift in traditional single-axis rotating inertial navigation systems cannot be observed and modulated online, the present invention proposes a single-axis rotating inertial navigation system and method for online compensation of azimuth drift by a monitoring gyro. A monitoring gyro that can rotate around a horizontal axis is attached to the inside of the IMU (inertial measurement unit), thereby achieving online periodic compensation of azimuth gyro drift.

[0028] The overall structure of the single-axis rotating inertial navigation system for monitoring gyro online compensation of azimuth drift of the present invention is as follows: Figure 1 As shown, it includes: a main IMU1, a single-axis rotation mechanism 2, a monitoring component 3 (including a monitoring gyroscope), and a data signal processing module 4; wherein, the rotation axes at the upper and lower ends of the main IMU1 are installed on rolling bearings at the top and bottom of the outer shell, the single-axis rotation mechanism 2 is coaxially installed with the main IMU1 on the top of the outer shell, the rotation axes at the left and right ends of the monitoring component 3 are installed on rolling bearings in the horizontal direction inside the main IMU1, and the data signal processing module 4 is distributed on the side of the main IMU1 and in the electronic compartment at the top of the outer shell.

[0029] The main IMU1 consists of three gyroscopes and three accelerometers. The angular velocity and acceleration information they output are used for navigation calculation to obtain the real-time attitude, velocity, and position information of the carrier. Among them, the gyroscope with the sensitive axis pointing to the sky is the azimuth gyroscope, which is fixed to the top of the main IMU1 with bolts; the east and north gyroscopes with the sensitive axis pointing to the horizontal are fixed to the outer side of the main IMU1 with bolts respectively. The three gyroscopes are installed orthogonally.

[0030] The single-axis rotation mechanism 2 includes an azimuth torque motor and an azimuth grating, which drives the main IMU 1 to continuously rotate forward and reverse around the azimuth axis to eliminate the constant drift of the gyroscope and accelerometer and the scale coefficient error in the horizontal direction.

[0031] The monitoring component 3 includes a monitoring gyroscope, a rotating platform, a monitoring grating, a monitoring torque motor, a worm gear mechanism and a reference mechanical block; the reference mechanical block includes an upper mechanical block and a lower mechanical block.

[0032] The monitoring gyro is fixedly installed on the rotating platform. The rotating shaft of the monitoring torque motor is connected to the worm of the worm gear mechanism through a key. The worm gear of the worm gear mechanism drives the rotating platform to rotate. The rotating platform rotates between When docking, fit the mechanical stopper. When docking, the lower mechanical stop is engaged, and the worm gear mechanism realizes reverse self-locking during docking; the monitoring grating and the worm gear of the worm gear mechanism are coaxially installed on the side of the main IMU1.

[0033] The data signal processing module 4 includes an FPGA clock module, a data acquisition board, and a data solution board; the FPGA clock module provides a unified clock for the system, and the data acquisition board is electrically connected to each gyroscope, each accelerometer, monitoring grating, monitoring torque motor, and data solution board. The data solution board receives data from the data acquisition board and completes the navigation algorithm and online compensation algorithm.

[0034] Further, such as Figure 2 As shown, the single-axis rotation inertial navigation method for monitoring gyro online compensation of azimuth drift of the present invention includes:

[0035] Step 1: Power on and initialize the single-axis rotation inertial navigation system: Return the azimuth torque motor to zero, and the monitoring torque motor drives the rotation platform to zero (at When docked, the mechanical stopper is engaged (the monitoring gyro's sensitive axis points to the sky). The azimuth torque motor drives the main IMU1 to continuously rotate forward and reverse around the azimuth axis. The single-axis rotation inertial navigation system enters the coarse alignment stage, fine alignment stage, and navigation stage in sequence.

[0036] Step 2: The navigation phase begins. The first monitoring cycle begins at the beginning of the navigation phase. A monitoring cycle is divided into Stages and ground stage.

[0037] Step 3: During the pointing stage, the rotating platform stops at Position, monitor the gyro and the azimuth gyro's sensitive axis in the same direction and point to the sky at the same time, collect the outputs of the two gyros and calculate the difference between the two gyro outputs :

[0038] ;

[0039] ;

[0040] in, is the azimuth gyro output, is the Earth's rotation angular velocity, is the latitude of the system location, is the angular velocity of the azimuth motor, is the azimuth gyro drift value, To monitor the gyro output, To monitor the gyro drift value.

[0041] Step 4: At the end of the pointing phase, calculate the average difference between the two gyro outputs during this phase. :

[0042] ;

[0043] in, is the navigation time, They are the starting and ending times of the pointing-to-the-sky stage respectively.

[0044] Step 5: Rotate the stage from Rotate to Position and dock, the single-axis rotation inertial navigation system enters the ground pointing stage of the first monitoring cycle.

[0045] Step 6: During the ground pointing phase, the rotating platform stops at Position, monitor the gyro and the azimuth gyro sensitive axis pointing in opposite directions, collect the outputs of the two gyros and calculate the sum of the two gyro outputs :

[0046] ;

[0047] .

[0048] Step 7: At the end of the ground pointing phase, calculate the mean of the sum of the two gyro outputs during this phase. :

[0049] ;

[0050] in, are the start and end times of the ground-pointing phase respectively.

[0051] Step 8: Calculate the drift estimate of the azimuth gyro and monitoring gyro during this monitoring period 、 :

[0052] .

[0053] Step 9: Verify the validity of the drift estimate calculated by S8 and compare and 、 and If the drift estimation values ​​of both gyros do not exceed the threshold, the drift compensation values ​​of the azimuth gyro and the monitoring gyro are updated:

[0054] ;

[0055] like Greater than or Greater than , it is considered that the monitoring of this cycle is invalid, and the drift compensation values ​​of the azimuth gyro and the monitoring gyro are not updated; is the azimuth gyro drift threshold, To monitor the gyro drift threshold.

[0056] Step 10: This monitoring cycle ends and the rotating table rotates to and dock.

[0057] Step 11: Repeat steps 3 to 10 until the system is operational.

[0058] The following will describe the technical solution provided by the present invention in detail with reference to specific implementation examples. It should be understood that the following specific implementation examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. for , the angular velocity of the azimuth torque motor is , monitor the torque motor rotation angular velocity is The monitoring cycle is 8 hours.

[0059] Among them, the online compensation algorithm in the data solution board includes:

[0060] Step 1: Power on the single-axis rotation inertial navigation system DC voltage, complete initialization. Azimuth torque motor returns to zero, monitoring torque motor drives the rotating platform back to zero (fits the mechanical block when it stops at 0°), that is, monitoring the gyro sensitive axis pointing to the sky, and the azimuth torque motor is The angular velocity drives the main IMU1 to rotate continuously forward and reverse around the azimuth axis, and the single-axis rotation inertial navigation system enters the coarse alignment state for 4 minutes, the fine alignment state for 20 minutes, and the navigation state in sequence.

[0061] Step 2: When navigation starts, the first monitoring period begins, which is divided into two time periods: sky-pointing (0-4 hours) and ground-pointing (4-8 hours).

[0062] Step 3: When the monitoring gyro is pointing to the sky and is stopped, the rotating platform is in contact with the upper mechanical stopper. At this position, the sensitive axes of the monitoring gyro and the azimuth gyro point to the sky in the same direction. The output of the two gyroscopes is collected at a sampling frequency and the difference between the two gyroscope outputs is calculated. :

[0063] ;

[0064] .

[0065] Step 4: When the navigation reaches 3 hours and 58 minutes, the pointing phase ends. At the same time, the average of the difference between the two gyro outputs from 0 to 3 hours and 58 minutes is calculated. :

[0066] ;

[0067] in, For time.

[0068] Step 5: At the same time, the monitoring torque motor receives the motor commutation signal sent by the data solver board and drives the rotating table from Rotate to Position, and docked with the lower mechanical stop. This is the transition stage. The navigation time continues to 4 hours, and the single-axis rotation inertial navigation system enters the ground pointing stage of the first monitoring cycle.

[0069] Step 6: When the monitoring gyro is pointing to the ground, its sensitive axis points in the opposite direction to the sensitive axis of the azimuth gyro. The outputs of the two gyros are collected at a sampling frequency of 200 Hz and the sum of the two gyro outputs is calculated. :

[0070] ;

[0071] .

[0072] Step 7: When the navigation reaches 7 hours and 58 minutes, the ground pointing phase ends. At the same time, the average of the sum of the two gyro outputs from 4 hours to 7 hours and 58 minutes is calculated:

[0073] ;

[0074] in, is the navigation time, is the mean azimuth gyro drift, To monitor the mean gyro drift.

[0075] Step 8: According to S4 and S7 and , calculate the estimated drift of the two gyroscopes in the first monitoring period:

[0076] .

[0077] Step 9: Determine the validity of the drift estimate calculated by S8 and compare and 、 and If the average values ​​of both gyros do not exceed the threshold, the drift compensation values ​​of the azimuth gyro and the monitoring gyro are updated at the same time:

[0078] ;

[0079] like Greater than or Greater than , it is considered that the monitoring of this cycle has failed, and the drift compensation values ​​of the azimuth gyro and the monitoring gyro are not updated.

[0080] Step 10: After the first monitoring cycle ends, the monitoring torque motor receives the motor commutation signal sent by the data solver board and drives the rotating table from Rotate to Position, fit and dock with the upper mechanical stop. This is the transition stage, until the navigation enters the second monitoring cycle of pointing to the sky stage after 8 hours.

[0081] Step 11: The second monitoring period is 8-16 hours, and steps S3-S10 are repeated.

[0082] Step 12: The third monitoring period is 16-24 hours, and steps S3-S10 are repeated.

[0083] Step 13: The system continues to navigate to the 25-hour power-off time.

[0084] Table 1 shows the comparison of navigation results before and after azimuth drift compensation, where CEP (Circular Error Probable) represents the maximum radial position error and circular error probability.

[0085] Figure 3 This graph compares radial position error before and after azimuth drift compensation. The horizontal axis represents time, and the vertical axis represents position error. The solid line shows the radial position error curve before azimuth drift compensation, while the dashed line shows the radial position error curve after azimuth drift compensation. By implementing an additional monitoring gyro and a piecewise averaging algorithm, three online estimations and compensations for azimuth gyro drift were performed during the 25-hour navigation experiment, significantly improving navigation accuracy.

[0086] Table 1

[0087]

[0088] The above descriptions are merely embodiments of the present invention and are not intended to limit the scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied to other related system fields, are also included in the scope of protection of the present invention.

[0089] The contents not described in detail in the specification of the present invention belong to the prior art known to those skilled in the art.

Claims

1. A single-axis rotating inertial navigation system for monitoring gyro online compensation of azimuth drift, characterized in that: include: Main IMU, single-axis rotation mechanism, monitoring components, data signal processing module; Among them, the rotation axes of the upper and lower ends of the main IMU are installed in the rolling bearings at the top and bottom of the outer shell. The azimuth torque motor shaft in the single-axis rotation mechanism is coaxially installed with the rotation axes at both ends of the main IMU. The rotation axes of the left and right ends of the rotating table in the monitoring component are installed in the rolling bearings in the horizontal direction inside the main IMU. The data signal processing modules are distributed on the side of the main IMU and in the electronic cabin on the top of the outer shell. The monitoring component includes a monitoring gyroscope, and the main IMU includes an azimuth gyroscope. The rotating table is set Rotate between.

2. The single-axis rotating inertial navigation system for monitoring gyro online compensation of azimuth drift according to claim 1, characterized in that: The main IMU consists of three gyroscopes and three accelerometers. The angular velocity and acceleration information they output are used to obtain the real-time attitude, velocity and position information of the carrier through navigation calculation. Among them, the gyroscope with the sensitive axis pointing to the sky is the azimuth gyroscope, which is fixed to the top of the main IMU by bolts; the east and north gyroscopes with the sensitive axis pointing to the horizontal are fixed to the outer side of the main IMU by bolts respectively. The three gyroscopes are installed orthogonally, and the three accelerometers are installed on the three-way orthogonal bracket on the side of the main IMU.

3. The single-axis rotating inertial navigation system for monitoring gyro online compensation of azimuth drift according to claim 2, characterized in that: The single-axis rotation mechanism includes an azimuth torque motor and an azimuth grating. Both the azimuth torque motor and the azimuth grating are installed on the top of the single-axis rotation inertial navigation system and are coaxially installed. The azimuth torque motor drives the main IMU to continuously rotate forward and reverse around the azimuth axis, eliminating the constant drift of the gyroscope in the horizontal direction, the constant zero bias of the accelerometer, and the constant error of the scale factor of the two.

4. The single-axis rotating inertial navigation system for monitoring gyro online compensation of azimuth drift according to claim 3, characterized in that: The monitoring component includes a monitoring gyroscope, a rotating platform, a monitoring grating, a monitoring torque motor, a worm gear mechanism and a reference mechanical stop; the reference mechanical stop includes an upper mechanical stop and a lower mechanical stop; The monitoring gyro is fixedly installed on the rotating platform. The rotating shaft of the monitoring torque motor is connected to the worm of the worm gear mechanism through a key. The worm gear of the worm gear mechanism drives the rotating platform to rotate. The rotating platform rotates between When docking, fit the mechanical stopper. When docking, the lower mechanical stop is engaged, and the worm gear mechanism realizes reverse self-locking during docking; the monitoring grating and the worm gear of the worm gear mechanism are coaxially installed on the side of the main IMU.

5. The single-axis rotating inertial navigation system for monitoring gyro online compensation of azimuth drift according to claim 4, characterized in that: The data signal processing module includes an FPGA clock module, a data acquisition board, and a data solver board. The FPGA clock module provides a unified clock for the system. The data acquisition board is electrically connected to the main IMU, including three gyroscopes and three accelerometers, a monitoring grating, a monitoring torque motor, and a data solver board. The data solver board receives data from the data acquisition board and completes the navigation algorithm and online compensation algorithm.

6. A single-axis rotating inertial navigation method for monitoring gyro online compensation of azimuth drift, used in a single-axis rotating inertial navigation system for monitoring gyro online compensation of azimuth drift as claimed in any one of claims 1 to 5, characterized in that: include: Step 1: The single-axis rotating inertial navigation system is powered on and initialized. The single-axis rotating inertial navigation system enters the coarse alignment stage, fine alignment stage and navigation stage in sequence; Step 2: The navigation phase begins. The first monitoring cycle begins at the beginning of the navigation phase. A monitoring cycle is divided into the sky-pointing phase and the ground-pointing phase. Step 3: During the pointing stage, the rotating platform stops at Position, monitor the gyro and the azimuth gyro's sensitive axis in the same direction and point to the sky at the same time, collect the outputs of the two gyros and calculate the difference between the two gyro outputs ; Step 4: At the end of the pointing phase, calculate the average difference between the two gyro outputs during this phase. ; Step 5: Rotate the stage from Rotate to Position and dock, the single-axis rotation inertial navigation system enters the ground pointing stage of the first monitoring cycle; Step 6: During the ground pointing phase, the rotating platform stops at Position, monitor the gyro and the azimuth gyro sensitive axis pointing in opposite directions, collect the outputs of the two gyros and calculate the sum of the two gyro outputs ; Step 7: At the end of the ground pointing phase, calculate the mean of the sum of the two gyro outputs during this phase. ; Step 8: Calculate the drift estimate of the azimuth gyro and monitoring gyro during this monitoring period 、 ; Step 9: Verify the validity of the drift estimate calculated by S8 and compare and azimuth gyro drift threshold 、 and monitor gyro drift thresholds If the drift estimation values ​​of both gyros do not exceed the threshold, the drift compensation values ​​of the azimuth gyro and the monitoring gyro are updated. 、 ; Step 10: This monitoring cycle ends and the rotating table rotates to and docked; Step 11: Repeat steps 3 to 10 until the system is operational.

7. The single-axis rotation inertial navigation method for monitoring gyro online compensation of azimuth drift according to claim 6, characterized in that: Step 1 includes: the azimuth torque motor returns to zero, the monitoring torque motor drives the rotating platform to return to zero, the azimuth torque motor drives the main IMU to continuously rotate forward and reverse around the azimuth axis, and the single-axis rotation inertial navigation system enters the coarse alignment, fine alignment and navigation states in sequence.

8. The single-axis rotation inertial navigation method for monitoring gyro online compensation of azimuth drift according to claim 6, characterized in that: In step 3, the difference between the two gyro outputs : ； ； in, is the azimuth gyro output, is the Earth's rotation angular velocity, is the latitude of the system location, is the angular velocity of the azimuth motor, is the azimuth gyro drift value, To monitor the gyro output, To monitor gyro drift value; In step 4, the average difference between the two gyro outputs in this stage is : ； in, is the navigation time, They are the starting and ending times of the pointing-to-the-sky stage respectively.

9. The single-axis rotation inertial navigation method for monitoring gyro online compensation of azimuth drift according to claim 8, characterized in that: In step 6, the sum of the two gyro outputs : ； ； In step 7, the sum of the two gyro outputs is averaged : ； in, are the start and end times of the ground-pointing phase respectively.

10. The single-axis rotating inertial navigation method for monitoring gyro online compensation of azimuth drift according to claim 6, characterized in that: In step 8, the drift estimation values ​​of the azimuth gyro and the monitoring gyro in this monitoring period are 、 : ； In step 9, update the drift compensation values ​​of the azimuth gyro and the monitoring gyro 、 : ； like Greater than or Greater than , it is considered that the monitoring of this cycle is invalid, and the drift compensation values ​​of the azimuth gyro and the monitoring gyro are not updated; is the azimuth gyro drift threshold, To monitor the gyro drift threshold; 、 are the initial drift compensation values ​​of the azimuth gyro and the monitoring gyro respectively; For the Monitoring cycle, It is the total number of monitoring cycles during a single navigation of the system.

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