A fast online calibration method for IMU based on target information

Abstract

The present invention discloses an IMU online rapid calibration method based on target information. A target point with known latitude and longitude information at the take-off airport is selected. After the aircraft takes off, the latitude and longitude of the target point are sent to the pod, and the geographic positioning mode is entered. The installation deviation angle of the IMU is calculated based on the deviation between the calculated target latitude and longitude and the actual latitude and longitude of the target; the installation deviation angle of the IMU is written into the pod Flash to complete the calibration. Generally, the aircraft can complete the calibration by circling once near the airport, and the calibration time is less than 15 minutes. After the calibration is completed, the aircraft directly performs subsequent tasks. Compared with the traditional IMU calibration method, the IMU online rapid calibration method of the present invention has a faster calibration speed, does not occupy additional flight sorties, can be transplanted to other types of optoelectronic products, and has universality and applicability.

Description

Technical Field

[0001] The invention belongs to the technical field of inertial navigation, and in particular relates to an IMU online fast calibration method. Background Art

[0002] The key component of the airborne optoelectronic pod to achieve high-precision geographic tracking is the positioning attitude system (POS), which consists of an inertial measurement unit (IMU) and a navigation solver. The inertial measurement unit is installed on a stable platform and rigidly connected to the sight line, and can be sensitive to the geographic direction of the sight line. When performing geographic tracking tasks, the angle information of the target relative to the pod can be calculated based on the input target GPS coordinates, combined with the GPS coordinates of the optoelectronic pod and the attitude information of the stable platform. Control the pod's sight line to point to the target, and the target can be quickly found in the pod image. It is particularly suitable for rapid detection and attack tasks of target intelligence information, and can quickly lock the target and destroy it in time.

[0003] In the actual assembly process, there is an installation error between the axis of the inertial measurement unit and the pod's sight line, and they cannot be completely aligned. The existence of the installation error causes the angle information of the target relative to the pod calculated based on the target GPS coordinates to deviate from the actual angle. The field of view of the long-focal-length TV sensor or infrared thermal imager carried by the airborne optoelectronic pod is very small, and the existence of the deviation may cause the target to be unable to be found in the pod image. Therefore, it is necessary to calibrate and correct the installation error between the axis of the inertial measurement unit and the pod's sight line.

[0004] Traditional IMU calibration requires multiple IMU calibration and correction after the pod is installed and flies 1-2 sorties to improve the accuracy of target positioning, geographic tracking and linear displacement compensation. Currently, the IMU calibration of other optoelectronic pods in China cannot achieve rapid correction and requires multiple flight tests and post-calculations, and the calculation results often have errors compared to the actual results. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides an IMU online rapid calibration method based on target information, which selects a target point with known latitude and longitude information at the take-off airport. After the aircraft takes off, the latitude and longitude of the target point are sent to the pod, and the geolocation mode is entered. The installation deviation angle of the IMU is calculated based on the deviation between the calculated target latitude and longitude and the actual latitude and longitude of the target; the installation deviation angle of the IMU is written into the pod Flash to complete the calibration. Generally, the aircraft can complete the calibration by circling once near the airport, and the calibration time is less than 15 minutes. After the calibration is completed, the aircraft directly performs subsequent tasks. Compared with the traditional IMU calibration method, the IMU online rapid calibration method of the present invention has a faster calibration speed, does not occupy additional flight sorties, can be transplanted to other types of optoelectronic products, and has versatility and universality.

[0006] The technical solution adopted by the present invention to solve the technical problem includes the following steps:

[0007] Step 1: Select a building with known latitude and longitude at the airport as the calibration target point;

[0008] Step 2: Power on the pod on the ground, and point the pod’s aiming line directly in front of the aircraft nose;

[0009] Step 3: After the aircraft takes off, it circles over the airport, and the POS data of the positioning and attitude system gradually converges. When the heading error is less than 0.1 degrees, the data convergence is completed;

[0010] Step 4: When the POS data converges, use the laser photometer to measure the distance between the calibration target point and the pod, and calculate the latitude and longitude of the calibration target point by combining the latitude and longitude and attitude information of the pod itself;

[0011] Step 5: Use the latitude and longitude data of the calibration target point calculated in step 4 and the actual latitude and longitude data of the calibration target point to calculate the distance deviation;

[0012] Step 6: Use Φ, θ, and γ to represent the installation deviation angle between the IMU axis and the sighting line, where Φ is the installation deviation angle in the azimuth direction, θ is the installation deviation angle in the pitch direction, and γ is the installation deviation angle in the roll direction;

[0013] Step 7: Use the distance deviation obtained in step 5 to calculate the installation deviation angles Φ, θ, and γ:

[0014] Step 7-1: Set the installation deviation angle to a value range between -3 degrees and +3 degrees;

[0015] Step 7-2: Set three nested loops, with the outermost loop being the roll installation deviation angle γ, the middle loop being the azimuth installation deviation angle Φ, and the innermost loop being the pitch installation deviation angle θ; the step length of each loop is 0.1 degrees, and the positioning distance deviation corresponding to each group of Φ, θ, and γ between -3 degrees and +3 degrees is calculated in turn, and the interval of Φ, θ, and γ corresponding to the smallest distance deviation is taken;

[0016] Step 7-3: Reduce the step size of the three-layer nested loop to 0.01 degrees, and calculate the positioning distance deviation corresponding to each group of Φ, θ, and γ again in the value range of the previous step with a step size of 0.01, and take the Φ, θ, and γ values ​​corresponding to the minimum distance deviation;

[0017] Step 7-4: Verify the impact of this set of installation deviation angles Φ, θ, and γ on geographic tracking and positioning accuracy. If the target can enter the minimum field of view under the geographic tracking function and the positioning accuracy meets the requirements, this set of installation deviation angles Φ, θ, and γ is considered to be the optimal solution; otherwise, repeat steps 7-2 to 7-4 until the requirements are met;

[0018] Step 7-5: Write the optimal installation deviation angles Φ, θ, and γ into the pod FLASH for storage.

[0019] The beneficial effects of the present invention are as follows:

[0020] Compared with the traditional IMU calibration method, the IMU online rapid calibration method of the present invention has a faster calibration speed, fully utilizes the invalid mission time in the take-off phase, and does not occupy additional flight sorties; it can be transplanted to other types of optoelectronic products and has universality and applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a task flow chart of the IMU calibration method of the present invention.

[0022] Figure 2 This is a schematic diagram of the installation of the inertial measurement unit of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0024] The invention belongs to inertial navigation technology and is used for quickly calibrating the installation deviation of IMU during the hovering time after the aircraft takes off, thereby improving the geographic tracking accuracy and positioning accuracy of the pod.

[0025] like Figure 1 and Figure 2 As shown, an IMU online fast calibration method based on target information includes the following steps:

[0026] Step 1: Select a building with known latitude and longitude at the airport as the calibration target point;

[0027] Step 2: Power on the pod on the ground, and point the pod’s aiming line directly in front of the aircraft nose;

[0028] Step 3: After the aircraft takes off, it circles over the airport, and the POS data of the positioning and attitude system gradually converges. When the heading error is less than 0.1 degrees, the data convergence is completed;

[0029] Step 4: When the POS data converges, use the laser photometer to measure the distance between the calibration target point and the pod, and calculate the latitude and longitude of the calibration target point by combining the latitude and longitude and attitude information of the pod itself;

[0030] Step 5: Use the latitude and longitude data of the calibration target point calculated in step 4 and the actual latitude and longitude data of the calibration target point to calculate the distance deviation;

[0031] Step 6: Use Φ, θ, and γ to represent the installation deviation angle between the IMU axis and the sighting line, where Φ is the installation deviation angle in the azimuth direction, θ is the installation deviation angle in the pitch direction, and γ is the installation deviation angle in the roll direction;

[0032] Step 7: Use the distance deviation obtained in step 5 to calculate the installation deviation angles Φ, θ, and γ:

[0033] Step 7-1: Set the installation deviation angle to a value range between -3 degrees and +3 degrees;

[0034] Step 7-2: Set three nested loops, with the outermost loop being the roll installation deviation angle γ, the middle loop being the azimuth installation deviation angle Φ, and the innermost loop being the pitch installation deviation angle θ; the step length of each loop is 0.1 degrees, and the positioning distance deviation corresponding to each group of Φ, θ, and γ between -3 degrees and +3 degrees is calculated in turn, and the interval of Φ, θ, and γ corresponding to the smallest distance deviation is taken;

[0035] Step 7-3: Reduce the step size of the three-layer nested loop to 0.01 degrees, and calculate the positioning distance deviation corresponding to each group of Φ, θ, and γ again in the value range of the previous step with a step size of 0.01, and take the Φ, θ, and γ values ​​corresponding to the minimum distance deviation;

[0036] Step 7-4: Verify the impact of this set of installation deviation angles Φ, θ, and γ on geographic tracking and positioning accuracy. If the target can enter the minimum field of view under the geographic tracking function and the positioning accuracy meets the requirements, this set of installation deviation angles Φ, θ, and γ is considered to be the optimal solution; otherwise, repeat steps 7-2 to 7-4 until the requirements are met;

[0037] Step 7-5: Write the optimal installation deviation angles Φ, θ, and γ into the pod FLASH for storage.

Claims

1. A fast online calibration method of IMU based on target information, It is characterized in that The steps include: Step 1: Select a building with known latitude and longitude at the airport as the calibration target point; Step 2: Power on the pod on the ground, and point the pod’s aiming line directly in front of the aircraft nose; Step 3: After the aircraft takes off, it circles over the airport, and the positioning and attitude system data gradually converges. When the heading error is less than 0.1 degrees, the data convergence is complete. Step 4: When the POS data converges, use the laser photometer to measure the distance between the calibration target point and the pod, and calculate the latitude and longitude of the calibration target point by combining the latitude and longitude and attitude information of the pod itself; Step 5: Use the latitude and longitude data of the calibration target point calculated in step 4 and the actual latitude and longitude data of the calibration target point to calculate the distance deviation; Step 6: Use Φ, θ, and γ to represent the installation deviation angle between the IMU axis and the sighting line, where Φ is the installation deviation angle in the azimuth direction, θ is the installation deviation angle in the pitch direction, and γ is the installation deviation angle in the roll direction; Step 7: Use the distance deviation obtained in step 5 to calculate the installation deviation angles Φ, θ, and γ: Step 7-1: Set the installation deviation angle to a value range between -3 degrees and +3 degrees; Step 7-2: Set three nested loops, with the outermost loop being the roll installation deviation angle γ, the middle loop being the azimuth installation deviation angle Φ, and the innermost loop being the pitch installation deviation angle θ; the step length of each loop is 0.1 degrees, and the positioning distance deviation corresponding to each group of Φ, θ, and γ between -3 degrees and +3 degrees is calculated in turn, and the interval of Φ, θ, and γ corresponding to the smallest distance deviation is taken; Step 7-3: Reduce the step size of the three-layer nested loop to 0.01 degrees, and calculate the positioning distance deviation corresponding to each group of Φ, θ, and γ again in the value range of the previous step with a step size of 0.01, and take the Φ, θ, and γ values ​​corresponding to the minimum distance deviation; Step 7-4: Verify the impact of this set of installation deviation angles Φ, θ, and γ on geographic tracking and positioning accuracy. If the target can enter the minimum field of view under the geographic tracking function and the positioning accuracy meets the requirements, this set of installation deviation angles Φ, θ, and γ is considered to be the optimal solution; otherwise, repeat steps 7-2 to 7-4 until the requirements are met; Step 7-5: Write the optimal installation deviation angles Φ, θ, and γ into the pod FLASH for storage.

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