Sensor installation monitoring

• US 10,551,196 B2
• Filed: 04/30/2015
• Issued: 02/04/2020
• Est. Priority Date: 04/30/2015
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Wu, Shuwu, Li, Ji, Thomas, Tyler, Wan, Howard E.
• Primary Examiner(s): Chang, Jay C
• Application Number:
  US14/701,254
• Publication Number:
  US 20160320190A1
• Time in Patent Office: 1,741 Days
• Field of Search: None
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01C 23/005 Flight directors indicating arrangements specially adapted for rotary gyroscopes G01C19/32
• CPC Class Codes: G01S 19/40 Correcting position, velocity or attitude
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]
• CPC Class Codes: G01S 19/49 whereby the further system is an inertial position system, e.g. loosely-coupled
• CPC Class Codes: G01S 19/53 Determining attitude

Abstract

Technology for correcting a misalignment between an inertial measurement unit (IMU) and a moving platform is described. A first attitude of the moving platform can be identified based on a truth source. A second attitude of the moving platform can be calculated using IMU measurements. A delta attitude can be calculated from a difference between the first attitude and the second attitude. Natural error can be removed from the delta attitude to produce an angular misalignment value between axes of the IMU and axes of the moving platform. A total misalignment value can be determined by adding the angular misalignment value to a baseline misalignment value. The IMU can incorporate the total misalignment value for subsequent attitude measurements of the moving platform in order to produce substantially accurate attitude measurements of the moving platform when the axes of the IMU are misaligned with the axes of the moving platform.

Claims

1. A method for correcting a misalignment between an inertial measurement unit (IMU) and a moving platform utilizing one or more processors and memory, the method comprising:

identifying a first attitude of the moving platform based on an attitude truth source;

calculating a second attitude of the moving platform using IMU measurements from the IMU and global positioning system (GPS) measurements from a GPS receiver on the moving platform, the IMU being installed on the moving platform, and the GPS receiver comprising an antenna operable to receive GPS signals from one or more GPS satellites;

calculating a delta attitude from a difference between the first attitude and the second attitude;

removing natural error from the delta attitude using a first low pass filter to produce an angular misalignment value between axes of the IMU and axes of the moving platform; and

determining a total misalignment value by adding the angular misalignment value to a baseline misalignment value,

updating the baseline misalignment value, the IMU incorporating the total misalignment value for subsequent attitude measurements of the moving platform in order to produce attitude measurements of the moving platform when the axes of the IMU are physically misaligned with the axes of the moving platform, therefore negating the physical misalignment between the IMU and the moving platform.

2. The method of claim 1, further comprising:

providing a mean of the natural error from the delta attitude to a second low pass filter;

determining that the mean of the natural error is less than a defined threshold; and

using the angular misalignment value to determine the total misalignment value.

3. The method of claim 2, further comprising:

determining that the mean of the natural error is greater than a defined threshold; and

recalculating the angular misalignment value using an updated first attitude and the second attitude.

4. The method of claim 2, wherein the first low pass filter has a first time constant (τ

₁) and the second low pass filter has a second time constant (τ

₂), wherein τ

₂ is substantially less than τ

₁.

5. The method of claim 1, wherein incorporating the total misalignment value at the IMU for the subsequent attitude measurements is the same in result to physically realigning the axes of the IMU with the axes of the moving platform in order to correct the misalignment.

6. The method of claim 1, further comprising monitoring an accuracy level for the subsequent attitude measurements of the moving platform from the IMU for a defined period of time, wherein the accuracy level is monitored by comparing the subsequent attitude measurements with the attitude truth source.

7. The method of claim 1, wherein the step of determining the second attitude of the moving platform is performed using the GPS measurements in combination with the IMU measurements.

8. The method of claim 1, wherein the moving platform includes a ship or an aircraft or a ballistic missile or a land vehicle.

9. The method of claim 1, wherein the attitude truth source is a real time attitude determination (RTAD) system or an equivalent high integrity attitude determination system.

10. The method of claim 1, wherein the attitude truth source provides rotational angles of roll, pitch and yaw in real-time of the moving platform.

11. A method for correcting a misalignment between an inertial measurement unit (IMU) and a moving platform utilizing one or more processors and memory, the method comprising:

calculating a current attitude of the platform using IMU measurements from the IMU and global positioning system (GPS) measurements from a GPS receiver on the moving platform, wherein the IMU and the GPS receiver are installed on the moving platform;

comparing the current attitude to a known attitude of the moving platform from an attitude truth source of the moving platform in order to determine a delta attitude;

removing natural error from the delta attitude to produce an angular misalignment value between axes of the IMU and axes of the moving platform;

determining a total misalignment value by adding the angular misalignment value to a baseline misalignment value; and

updating the baseline misalignment value, and performing attitude measurements of the moving platform using the total misalignment value, wherein the physical misalignment between the IMU and the moving platform is effectively corrected when using the total misalignment value, therefore negating the physical misalignment between the IMU and the moving platform.

12. The method of claim 11, wherein the known attitude of the moving platform is determined using the attitude truth source, the attitude truth source including a real time attitude determination (RTAD) system or an equivalent high integrity attitude determination system.

13. The method of claim 11, wherein the step of calculating the current attitude of the moving platform is performed using the GPS measurements in combination with the IMU measurements.

14. The method of claim 11, wherein the step of removing the natural error from the delta attitude is performed using a first low pass filter.

15. The method of claim 11, further comprising:

providing a mean of the natural error from the delta attitude to a second low pass filter;

determining that the mean of the natural error is less than a defined threshold; and

using the angular misalignment value to determine the total misalignment value.

16. The method of claim 15, further comprising:

determining that the mean of the natural error is greater than a defined threshold; and

recalculating the angular misalignment value using an updated current attitude and the known attitude.

17. A system for correcting a misalignment between an inertial measurement unit (IMU) and a moving platform, the system comprising:

the inertial measurement unit (IMU) installed on the moving platform, wherein the IMU is operable to perform IMU measurements;

a global positioning system (GPS) receiver installed on the moving platform, the GPS receiver comprising an antenna operable to receive GPS signals from one or more GPS satellites, and operable to determine GPS measurements using the GPS signals;

an attitude truth source comprising a known attitude of the moving platform, and operable to provide the known attitude of the moving platform; and

one or more processors and memory to;

identify the known attitude of the moving platform using the attitude truth source;

calculate a current attitude of the moving platform using the IMU measurements from the IMU and the GPS measurements from the GPS receiver;

calculate a delta attitude from a difference between the known attitude and the current attitude;

determine an angular misalignment value between axes of the IMU and axes of the moving platform using the delta attitude;

identify natural error from the angular misalignment value;

determine that a mean of the natural error is less than a defined threshold;

determine a total misalignment value by adding the angular misalignment value to a baseline misalignment value; and

updating the baseline misalignment value, the IMU incorporating the total misalignment value for subsequent attitude measurements of the moving platform in order to produce attitude measurements of the moving platform when the axes of the IMU are physically misaligned with the axes of the moving platform, therefore negating the physical misalignment between the IMU and the moving platform.

18. The system of claim 17, wherein the one or more processors and memory are further configured to monitor an accuracy level of the subsequent attitude measurements of the moving platform from the IMU for a defined period of time, wherein the accuracy level is monitored by comparing the subsequent attitude measurements with the attitude truth source.

19. The system of claim 17, wherein the moving platform is a ship or an aircraft or a ballistic missile or a land vehicle.

20. The system of claim 17, wherein the attitude truth source is a real time attitude determination (RTAD) system.