Dynamic magnetic anomaly compensation

• US 20050099177A1
• Filed: 11/05/2004
• Published: 05/12/2005
• Est. Priority Date: 11/06/2003
• Status: Active Grant

• Current Assignee: Sonicworks, Inc.
• Original Assignee: Stephen John Greelish
• Inventors: Greelish, Stephen John
• Granted Patent: US 7,400,142 B2
• Time in Patent Office: Days
• US Class Current: 324/252
• CPC Class Codes: G01R 33/025 Compensating stray fields G01R33/0017 takes precedence

Abstract

An array of three-axis magnetometers used for dynamic magnetic anomaly compensation are located at the corners of a parallelopiped, with pairs of magnetometer outputs used to derive a magnetic anomaly gradient vector used to compensate a compass and/or the output of a gyroscope in an inertial management unit. The system may be used in a neutrally buoyant remotely operated vehicle to permit ascertaining of course and position in the absence of surface control signals.

Claims

1. A system for dynamically compensating for magnetic anomalies due to the proximity of ferromagnetic objects or electric motors, comprising:

a parallelopiped;

three-axis magnetometers located at selected corners of said parallelopiped, said magnetometers having their three orthogonal axes aligned with the three orthogonal axes of the other magnetometers; and

,

a processor coupled to the outputs of said magnetometers to derive the magnetic anomaly gradient vector, whereby said magnetic anomaly gradient vector may be used to compensate for heading errors from instruments for which heading is an output.

2. The system of claim 1, wherein the number of said magnetometers is four.

3. The system of claim 1, wherein the number of said magnetometers is eight.

4. The system of claim 1, wherein said processor includes means for deriving the difference along a given axis between the outputs of pairs of said magnetometers.

5. The system of claim 1, wherein said magnetometers include GMR sensors.

6. The system of claim 1, wherein said instrument for which heading is an output includes a compass and wherein said magnetic anomaly gradient is used to compensate said compass for said magnetic anomaly.

7. The system of claim 6, wherein said instrument for which heading is an output includes a gyroscope, and wherein said heading output is corrected in accordance with the output of said compensated compass.

8. The system of claim 1, wherein said instrument for which heading is an output includes a gyroscope and wherein said magnetic anomaly gradient vector is used to compensate said gyroscope.

9. The system of claim 8, wherein said magnetic anomaly gradient vector is used to re-cage said gyroscope.

10. A method for assuring positional control of a remotely operated vehicle adapted to be maneuvered around the hull of a vessel when acoustic network positioning signals are unavailable, comprising the steps of:

providing the remotely operated vehicle with an inertial management unit having a compass and a gyroscope for ascertaining the position of the remotely operated vehicle and for controlling the position thereof;

establishing the position of the remotely operated vehicle utilizing the acoustic network;

establishing the position of the remotely operated vehicle utilizing the inertial management unit when the position associated with the acoustic network is unreliable;

detecting any magnetic anomaly gradient vector at the remotely operated vehicle; and

,

compensating the positional output of the inertial management unit utilizing the detected magnetic anomaly gradient vector.

11. The method of claim 10, wherein the magnetic anomaly gradient vector is utilized to compensate the output of the compass in the inertial management unit.

12. The method of claim 10, wherein the magnetic anomaly gradient vector is used to compensate the gyroscope.

13. The method of claim 11, wherein the output of the compensated compass is used to compensate the gyroscope.

14. The method of claim 10, wherein the detecting step includes the steps of locating a number of three-axis magnetometers at selected corners of a parallelopiped such that the three axes of the magnetometers are aligned with respective axes of the other magnetometers;

differencing the outputs of selected pairs of the magnetometers so as to generate a magnetic gradient along a predetermined one of the axes; and

,

combining the results of the differences to generate the magnetic anomaly gradient vector.

15. For use in a neutrally buoyant remotely operated vehicle to permit ascertaining position of said vehicle in the absence of surface control signals, apparatus for compensating the compass used by the inertial management system for said vehicle for magnetic anomalies in the vicinity of said compass, comprising:

an array of three-axis magnetometers disposed at selected corners of a parallelopiped, said magnetometers having their axes co-aligned; and

,

a processor for deriving from pairs of outputs of said magnetometers the magnetic anomaly gradient at said compass and for generating a deviation correction for said compass responsive to said magnetic anomaly gradient, thus to cancel out the effect of said gradient on said compass, whereby said compass may be used by said inertial management unit in the absence of surface control signals regardless of local magnetic anomalies.

16. The apparatus of claim 15, wherein said inertial management unit includes a gyroscope and wherein the heading output of said gyroscope is corrected in accordance with the corrected output of said compass.

17. The apparatus of claim 15, wherein said inertial management unit includes a gyroscope and wherein said magnetic anomaly gradient is used to re-cage said gyroscope.

18. The apparatus of claim 15, wherein said magnetometers include GMR sensors.