Vehicle compass compensation

• US 6,513,252 B1
• Filed: 03/31/2000
• Issued: 02/04/2003
• Est. Priority Date: 04/08/1999
• Status: Expired due to Fees

• Current Assignee: Donnelly Corporation (Magna International Incorporated)
• Original Assignee: Donnelly Corporation (Magna International Incorporated)
• Inventors: Blank, Rodney K., DeVette, Gregory H., Veiseh, Merdad, Schofield, Kenneth, Schierbeek, Kenneth L., Hoekstra, Eric J.
• Primary Examiner(s): Gutierrez, Diego
• Assistant Examiner(s): REIS, TRAVIS M
• Application Number:
  US09/540,702
• Time in Patent Office: 1,040 Days
• Field of Search: 333/56, 333/55.R, 333/57, 333/33, 702/92, 702/295, 702/115, 324/202, 324/225, 324/244, 324/247, 324/260
• US Class Current: 33/356
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

A compass compensation system is provided for automatically continuously calibrating an electronic compass for a vehicle, without requiring an initial manual calibration or preset of the vehicle magnetic signature. The system initially adjusts a two axis sensor of the compass in response to a sampling of at least one initial data point. The system further calibrates the compass by sampling data points that are substantially opposite to one another on a plot of a magnetic field and averaging an ordinate of the data points to determine a respective zero value for the Earth magnetic field. The system also identifies a change in magnetic signature and adjusts the sensor assembly.

Claims

1. A vehicular electronic compass system comprising:

a magneto-responsive sensor assembly for sensing a magnetic field including an earth magnetic field and a deviating magnetic field;

an electronic circuit responsive to said sensor assembly for determining at least one of a magnitude and direction of the Earth magnetic field, said electronic circuit collecting a plurality of data points along the earth magnetic field relative to a coordinate system associated with the vehicle, each of said data points having at least two components relative to said coordinate system, said electronic circuit averaging at least one component of at least two of said data points to determine an estimated value of the Earth magnetic field along at least one axis of said coordinate system, thereby calculating an estimated offset of the Earth magnetic field due to the deviating magnetic field, said electronic circuit adjusting a directional heading output to account for the offset; and

an electronic display coupled with said electronic circuit for displaying a direction of the Earth magnetic field;

wherein said at least two data points are located at intersect points where said line segments intersect at said coordinate system at a value equal to a portion of the Earth magnetic field magnitude.

2. The vehicular compass system of claim 1, wherein said at least two data points have substantially equal values for one ordinate on the coordinate system, the other ordinate values are averaged to determine said estimated offset for one of the x and y ordinates for the Earth magnetic field.

3. The vehicular compass system of claim 1, wherein said value is approximately one-half of the Earth magnetic field magnitude.

4. The vehicular compass system of claim 1, wherein said at least two data points are located at an intersect point of two line segments which intersect one another at substantially equal coordinates of said coordinate system.

5. The vehicular compass system in claim 4, wherein said substantially equal coordinates are approximately one-half of the Earth magnetic field magnitude.

6. The vehicular compass system of claim 1, wherein said at least two data points are located at a plurality of octant switch points, where the compass switches from one directional reading to another.

7. The vehicular compass system of claim 1, wherein said sensor assembly comprises first and second sensors oriented in a predetermined angular relationship with each other and in a predetermined orientation with respect to the vehicle.

8. The vehicular compass system in claim 1, wherein said sensor assembly comprises one of a magneto-inductive sensor, a magneto-resistive sensor and a flux gate sensor.

9. The vehicular compass system in claim 1, wherein said sensor assembly comprises a magneto-resistive sensor.

10. The vehicular compass system in claim 1, wherein said electronic circuit calculates another estimated offset of the Earth magnetic field due to the deviating magnetic field and compares said estimated offset with said another estimated offset in order to confirm validity of said estimated offset.

11. The vehicular compass system in claim 10, wherein said electronic circuit collects additional data points and calculates a new estimated offset if said estimated offset is not valid.

12. A vehicular electronic compass system comprising:

a magneto-responsive sensor assembly for sensing a magnetic field including an earth magnetic field and a deviating magnetic field;

an electronic circuit responsive to said sensor assembly for determining at least one of a magnitude and direction of the Earth magnetic field, said electronic circuit collecting a plurality of data points along the earth magnetic field relative to a coordinate system associated with the vehicle, each of said data points having at least two components relative to said coordinate system, said electronic circuit averaging at least one component of at least two of said data points to determine an estimated value of the Earth magnetic field along at least one axis of said coordinate system, thereby calculating an estimated offset of the Earth magnetic field due to the deviating magnetic field, said electronic circuit adjusting a directional heading output to account for the offset; and

an electronic display coupled with said electronic circuit for displaying a direction of the Earth magnetic field;

wherein each of said plurality of data points are at an intersection of at least two line segments and a plot of the Earth magnetic field on said coordinate system, each of said at least two line segments being substantially parallel to one axis of said coordinate system;

wherein said plurality of data points include at least four data points, said at least two line segments pass through a point on one axis of said coordinate system, said point being positioned at a value substantially equal to a portion of the Earth magnetic field magnitude.

13. The vehicular compass system in claim 12, wherein said portion is approximately one-half.

14. The vehicular compass system of claim 12, wherein said plurality of data points are at eight locations along four line segments, each line segment being substantially parallel to one axis of said coordinate system and passing through one axis at a point substantially equal to a portion of Earth magnetic field magnitude.

15. The vehicular compass system of claim 14, wherein said system collects additional data at each of said eight locations and continuously adjusts said output of said sensor as additional pairs of points are collected.

16. The vehicular compass system of claim 12, wherein said a plurality of data points are at four locations along four line segments, each line segment being one of substantially parallel to one axis of said coordinate system and passing through one of said axis at a point where a coordinate value of a vertical line segment is substantially equal to a coordinate value of a horizontal line segment, an intersecting point of said line segments being equal to a portion of the Earth magnetic field magnitude from an origin of said coordinate system.

17. The vehicular compass system in claim 16, wherein said system collects data points until a pair of points along one of said four line segments is collected and averages one coordinate value to determine an estimated zero value along one axis of the coordinate system.