Heading stabilization for aided inertial navigation systems

• US 8,019,542 B2
• Filed: 03/31/2008
• Issued: 09/13/2011
• Est. Priority Date: 04/16/2007
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Rolfer, Tom, Hawkinson, Wesley J.
• Primary Examiner(s): Beaulieu; Yonel
• Application Number:
  US12/059,837
• Publication Number:
  US 20080319667A1
• Time in Patent Office: 1,261 Days
• Field of Search: 701/200, 701220-221, 342/357.3
• US Class Current: 701/220
• CPC Class Codes: G01C 21/1652 with ranging devices, e.g. LIDAR or RADAR
• CPC Class Codes: G01C 21/188 for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices

Abstract

A method of stabilizing heading in an inertial navigation system includes operating an inertial measurement unit comprising horizontal-sensing elements and off-horizontal-sensing elements while the inertial measurement unit is in a first orientation, calibrating the horizontal-sensing elements of the inertial measurement unit based on horizontal aiding measurements, forward-rotating the inertial measurement unit by a selected-rotation angle about a horizontal-rotation axis so that the inertial measurement unit is oriented in a second orientation, operating the forward-rotated inertial measurement unit while the inertial measurement unit is in the second orientation, and calibrating the rotated off-horizontal-sensing elements based on horizontal aiding measurements while the inertial measurement unit is in the second orientation. When the inertial measurement unit is in the first orientation, the horizontal-sensing elements are oriented in a horizontal reference plane. When the inertial measurement unit is in the second orientation, the off-horizontal-sensing elements are oriented in the horizontal reference plane.

Claims

1. A method of stabilizing heading in an inertial navigation system, the method comprising:

operating an inertial measurement unit comprising horizontal-sensing elements and off-horizontal-sensing elements, while the inertial measurement unit is in a first orientation, wherein the horizontal-sensing elements are oriented in a horizontal reference plane;

calibrating the horizontal-sensing elements of the inertial measurement unit based on horizontal aiding measurements;

forward-rotating the inertial measurement unit by a selected-rotation angle about a horizontal-rotation axis, wherein the inertial measurement unit is oriented in a second orientation, and wherein, while the inertial measurement unit is in the second orientation, the off-horizontal-sensing elements are oriented in the horizontal reference plane;

operating the forward-rotated inertial measurement unit while the inertial measurement unit is in the second orientation; and

calibrating the rotated off-horizontal-sensing elements based on horizontal aiding measurements while the inertial measurement unit is in the second orientation.

2. The method of claim 1, further comprising:

back-rotating the inertial measurement unit about the horizontal-rotation axis by the selected-rotation angle, wherein the inertial measurement unit is oriented in the first orientation;

operating the inertial measurement unit while the inertial measurement unit is in the first orientation; and

re-calibrating the horizontal-sensing elements of the inertial measurement unit based on horizontal aiding measurements while the inertial measurement unit is in the first orientation.

3. The method of claim 2, further comprising:

correcting a navigation solution for the inertial navigation system based on the calibrating of the horizontal-sensing elements; and

correcting the navigation solution for the inertial navigation system based on the calibrating of the off-horizontal-sensing elements.

4. The method of claim 1, wherein the off-horizontal-sensing elements are vertical-sensing elements, and wherein the selected-rotation angle is ninety degrees.

5. A method of stabilizing heading in an inertial navigation system, the method comprising:

operating an inertial measurement unit in an un-rotated orientation;

calibrating at least one horizontal-sensing gyroscope and at least one horizontal-sensing accelerometer based on horizontal aiding measurements received while operating the inertial measurement unit in the un-rotated orientation;

forward-rotating the inertial measurement unit about a horizontal-rotation axis, the horizontal-rotation axis being orthogonal to the direction sensed by at least one horizontal-sensing gyroscope;

operating the inertial measurement unit in a rotated orientation; and

calibrating a vertical gyroscope and a vertical-sensing accelerometer based on horizontal aiding measurements received while operating the inertial measurement unit in the rotated orientation.

6. The method of claim 5, further comprising:

back-rotating the inertial measurement unit about the horizontal-rotation axis, wherein the inertial measurement unit is oriented in the un-rotated orientation.

7. The method of claim 6, wherein a forward-rotation is a plus-ninety degree rotation, and wherein a back-rotation is a minus-ninety degree rotation.

8. The method of claim 6, further comprising:

periodically forward-rotating the inertial measurement unit through a plus-ninety degree rotation; and

back-rotating the inertial measurement unit through a minus-ninety degree rotation responsive to each forward rotation.

9. The method of claim 6, wherein operating an inertial measurement unit in the un-rotated orientation comprises:

generating information indicative of a horizontal axis tilt error at the horizontal-sensing gyroscope oriented to be sensitive to a first-horizontal axis, the first-horizontal axis being orthogonal to the horizontal-rotation axis;

generating information indicative of a horizontal velocity at the horizontal-sensing accelerometer oriented to be sensitive to the first-horizontal axis;

generating information indicative of a vertical axis heading error at the vertical-sensing gyroscope oriented to be sensitive to a vertical axis, the vertical axis being orthogonal to the horizontal-rotation axis and the first-horizontal axis; and

generating information indicative of a vertical velocity at the vertical-sensing accelerometer oriented to be sensitive to the vertical axis.

10. The method of claim 9, wherein operating the inertial measurement unit in the rotated orientation comprises:

generating information indicative of the horizontal axis tilt error at the vertical-sensing gyroscope oriented to be sensitive to the first-horizontal axis;

generating information indicative of the horizontal velocity at the vertical-sensing accelerometer oriented to be sensitive to the first-horizontal axis;

generating information indicative of the vertical axis heading error at the horizontal-sensing gyroscope oriented to be sensitive to the vertical axis; and

generating information indicative of the vertical velocity at the horizontal-sensing accelerometer oriented to be sensitive to the vertical axis.

11. The method of claim 10, wherein calibrating the at least one horizontal-sensing gyroscope and the at least one horizontal-sensing accelerometer based on horizontal aiding measurements comprises:

receiving information indicative of the horizontal axis tilt error, the information indicative of the horizontal velocity, the information indicative of the vertical axis heading error, and the information indicative of the vertical velocity from the inertial measurement unit in the un-rotated orientation;

estimating an un-rotated-horizontal-axis-position error based on the information received from the inertial measurement unit in the un-rotated orientation;

estimating an un-rotated-horizontal-axis-velocity error based on the information received from the inertial measurement unit in the un-rotated orientation; and

wherein calibrating the vertical-sensing gyroscope and the vertical-sensing accelerometer based on horizontal aiding measurements comprises;

receiving information indicative of the horizontal axis tilt error, the information indicative of the horizontal velocity, the information indicative of the vertical axis tilt error, and the information indicative of the vertical velocity from the inertial measurement unit in the rotated orientation;

estimating a rotated-horizontal-axis-position error based on the information received from the inertial measurement unit in the rotated orientation; and

estimating a rotated-horizontal-axis-velocity error based on the information received from the inertial measurement unit in the rotated orientation.

12. An inertial navigation system, comprising:

an inertial measurement unit;

rotational device on which the inertial measurement unit is positioned, the rotational device configured to rotate the inertial measurement unit about a horizontal axis from a first orientation to a second orientation;

a software module comprising;

a navigation module configured to receive input from the inertial measurement unit;

a Kalman filter communicatively coupled to the navigation module;

a software control component configured to control the rotation of the rotational device based on input received from the Kalman filter; and

at least one of a velocity sensor and a position sensor operable to measure a velocity and a position, respectively, and further operable to output the information indicative of a velocity and a position to the Kalman filter, respectively; and

a navigation processor for running the software module;

wherein the Kalman filter is configured to calibrate the inertial measurement unit in the first orientation and the second orientation and to correct output from the navigation module based on estimates of a bias in the inertial measurement unit.

13. The inertial navigation system of claim 12, wherein the inertial measurement unit comprises:

a horizontal-sensing gyroscope, wherein the Kalman filter estimates a horizontal axis tilt error of the horizontal-sensing gyroscope when the inertial measurement unit is in a first orientation;

a horizontal-sensing accelerometer communicatively coupled to the Kalman filter, wherein the Kalman filter estimates a horizontal velocity error of the horizontal-sensing accelerometer when the inertial measurement unit is in the first orientation;

a vertical-sensing gyroscope communicatively coupled to the Kalman filter, wherein the Kalman filter estimates a horizontal axis tilt error of the vertical-sensing gyroscope when the inertial measurement unit is in a second orientation; and

a vertical-sensing accelerometer communicatively coupled to the Kalman filter, wherein the Kalman filter estimates a horizontal velocity error of the vertical-sensing accelerometer when the inertial measurement unit is in the second orientation.

14. The inertial navigation system of claim 13, wherein the horizontal-sensing gyroscope is a first-horizontal-sensing gyroscope and the horizontal-sensing accelerometer is a first horizontal-sensing accelerometer, and wherein the inertial measurement unit further comprises:

a second-horizontal-sensing gyroscope, wherein the Kalman filter estimates a horizontal axis tilt error of the second-horizontal-sensing gyroscope when the inertial measurement unit is in the first orientation and the second orientation; and

a second-horizontal-sensing accelerometer communicatively coupled to the Kalman filter, wherein the Kalman filter estimates a horizontal velocity error of the second-horizontal-sensing accelerometer when the inertial measurement unit is in the first orientation and the second orientation.

15. The inertial navigation system of claim 12, wherein

the velocity sensor is a horizontal velocity sensor operable to measure a horizontal velocity and the position sensor is a horizontal position sensor operable to measure a horizontal position.

16. The inertial navigation system of claim 12, wherein the rotational device is configured to rotate the inertial measurement unit by ninety degrees from a first orientation to a second orientation.

17. The inertial navigation system of claim 12, wherein the navigation module is in a strapdown navigator.

18. The inertial navigation system of claim 12, wherein the software module further comprises a sensor compensator.

19. The inertial navigation system of claim 12, further comprising:

a servomotor mechanically coupled to the rotational device.

20. The inertial navigation system of claim 12, wherein the servomotor is mechanically coupled to the rotational device by a precision gear head.