Calibrating a magnetic compass with an angular rate gyroscope and a global positioning system receiver

• US 6,408,251 B1
• Filed: 07/29/1999
• Issued: 06/18/2002
• Est. Priority Date: 07/29/1999
• Status: Expired due to Fees

• Current Assignee: HRL Laboratories LLC (The Boeing Co.)
• Original Assignee: HRL Laboratories LLC (The Boeing Co.)
• Inventors: Azuma, Ronald Tadao
• Primary Examiner(s): Hoff, Marc S.
• Assistant Examiner(s): PRETLOW, DEMETRIUS R
• Application Number:
  US09/363,178
• Time in Patent Office: 1,055 Days
• Field of Search: 702/92, 702/93, 702/104, 342/357.14, 342/357.06, 342/357.08, 342/457, 342/174, 701/224, 701/200, 701/214, 701/215, 701/221, 701/216, 701/300, 701/205, 701/206, 333/56, 332/72, 333/16--29, 73/11.6, 73/17.5, 73/17--
• US Class Current: 702/92
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

A method and apparatus for calibrating an electronic compass of the type having a compass sensor, a calibration table and a display. A computer operating under program control is used to update the calibration table of the electronic compass in response to physical movement of at least the electronic compass sensor and an angular rate gyroscope through a 360 degree movement. A pointing device associated with the electronic compass is initially directed to a known landmark position and is also directed to the known landmark position after completing the 360 degree movement. The computer utilizes global positioning system receiver, the known landmark position and a heading provided by the sensor to generate a correction value. The output of the sensor is compared with data generated based upon the gyroscope during the 360 degree movement to generate correction values for other compass headings. The correction values are transmitted to the electronic compass for updating its calibration table.

Claims

1. An apparatus for calibrating an electronic compass of a type having a compass sensor, a calibration table and a display, the calibration table calibrating data from the sensor before it is applied to the display, the calibration apparatus comprising:

a global positioning system receiver;

an angular rate gyroscope;

a computer operating under program control for updating the calibration table of the electronic compass in response to physical movement of at least the electronic compass sensor and the angular rate gyroscope through a 360 degree movement with a pointing device associated with the electronic compass being initially directed at the beginning of the movement to a known landmark position and also being directed to said known landmark position after completing the 360 degree movement, the computer utilizing the global positioning system receiver and the known landmark position to calculate a true heading of the electronic compass to the known landmark position, comparing that heading with the heading provided by the sensor to generate an associated correction and comparing an output of the sensor with data generated based upon the gyroscope during the 360 degree movement to generate corrections for other compass headings and transmitting the corrections to said electronic compass for updating its calibration table.

2. The apparatus of claim 1 wherein the global positioning system is a differential global position system.

3. The apparatus of claim 1 wherein the known landmark position is stored in a memory associated with said computer.

4. The apparatus of claim 3 wherein a plurality of known landmark positions are stored in said memory.

5. The apparatus of claim 1 wherein an analog to digital converter couples the gyroscope to said computer.

6. A method of calibrating an electronic compass of a type having a magnetic field sensor, a memory for a table of storing calibration data and a display for displaying a true heading of the compass as detected by the magnetic field sensor and corrected in accordance with data stored in the calibration table, said method comprising the steps of:

(a) aiming the electronic compass at a known landmark whose location is known;

(b) rotating the electronic compass together with at least an angular rate gyroscope through a full 360 degrees turn;

(c) collecting magnetic field sensor data and gyroscope data while the electronic compass and the angular rate gyroscope are being rotated;

(d) calculating the true heading of the electronic compass to the known landmark using (i) a known position of the electronic compass and (ii) the known position of the known landmark;

(e) calculating difference data based upon (i) a difference between the magnetic sensor data and a heading of the known landmark and (ii) for other compass headings using the magnetic sensor data, the heading of the known landmark and gyroscope data; and

(f) supplying the calculated difference data to said electronic compass for storage as said calibration table.

7. The method of claim 6 further including storing the location of the known landmark in memory.

8. The method of claim 7 further including storing the locations of a plurality of known landmarks in memory.

9. The method of claim 6 wherein the known position of the electronic compass is determined by a global positioning system receiver.

10. The method of claim 9 wherein global positioning system receiver is a differential global positioning system receiver.

11. An apparatus for calibrating an electronic compass of a type having a compass sensor, a calibration table and a display, the calibration table calibrating data from the sensor before it is applied to the display, the calibration apparatus comprising a computer operating under program control for updating the calibration table of the electronic compass, a pointing device associated with the electronic compass being directed a first known landmark position, the computer recording a bearing of a first known landmark at the first known landmark position and comparing that recorded bearing with a calculated bearing based upon the known position of the first known landmark and a known position of the electronic compass, the pointing device associated with the electronic compass being directed a second known landmark position, the computer recording a bearing of a second known landmark at the second known landmark position and comparing that recorded bearing with a calculated bearing using the known position of the second known landmark, and updating each entry in the calibration table when the results of the comparison for a pair of closest known landmarks shows that the bearings of the pair of closest known landmarks are different than the calculated bearings of the pair of closest known landmarks, the computer interpolating between the pair of closest known landmark positions to update the calibration table for bearings between the pair of closest known landmarks.

12. The apparatus of claim 11 wherein the computer interpolates between the pair of closest known landmark positions only when the pair of closest known landmark positions are both within a predetermined range of effect.

13. The apparatus of claim 12 wherein the computer interpolates between only one of said pair of closest known landmark positions and an original entry in the calibration table when the other of said pair of closest known landmark positions is outside said predetermined range of effect.

14. The apparatus of claim 11 further including a global positioning system receiver for determining the known position of the electronic compass.