Vehicle compass system with continuous automatic calibration

• US 6,643,941 B2
• Filed: 07/24/2001
• Issued: 11/11/2003
• Est. Priority Date: 05/27/1999
• Status: Expired due to Term

• Current Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Original Assignee: Johnson Controls Technology Company (Johnson Controls International plc)
• Inventors: Olson, Thomas R., Slater, David J., Parks, Jeffrey N.
• Primary Examiner(s): Fulton, Christopher W.
• Assistant Examiner(s): DEJESUS, LYDIA M
• Application Number:
  US09/912,273
• Publication Number:
  US 20020035791A1
• Time in Patent Office: 840 Days
• Field of Search: 333/55.R, 333/56, 333/57, 333/58, 333/59, 333/61, 702/85, 702/92, 702/93, 702/94, 702/95
• US Class Current: 33/356
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

The compass system of the present invention utilizes an improved calibration routine in which a processing circuit of the compass recalibrates the compass each time three data points are obtained from a magnetic field sensor that meet predetermined criteria. One such criterion is that the three data points define corners of a triangle that is substantially non-obtuse. When three data points have been obtained that define a triangle meeting this criterion, the processing circuit calculates a center point for a circle upon which all three data points lie by solving the equation ²+y²+Ax+By+C=0 for A, B, and C, using the coordinate values (x,y) for the three data points and defining the center point as (−A/2, −B/2).

Claims

1. A vehicle compass system, comprising:

a magnetic field sensor mounted in the vehicle for sensing directional components of the earth'"'"'s magnetic field around the vehicle, the magnetic field sensor generating electrical signals representative of the earth'"'"'s magnetic field; and

a processing circuit coupled to the sensor configured to process the electrical signals generated by the sensor to provide data points representative of the vehicle'"'"'s current heading, wherein the processing circuit is configured to average a predetermined number of data points, to identify three averaged data points as candidate data points if the averaged data points meet predetermined spacing criteria, and to calibrate the system using the three candidate data points.

2. The vehicle compass system of claim 1, wherein the processing circuit is configured to calibrate the system each time three candidate data points are identified.

3. The vehicle compass system of claim 1, wherein the processing circuit is configured to determine whether the vehicle is moving and to only identify the three averaged data points if the vehicle is moving.

4. The vehicle compass system of claim 1, wherein the processing circuit is configured to compare a data point to a prior received data point and to only average the data point if the data point is within a threshold distance from the prior received data point.

5. The vehicle compass system of claim 1, wherein the magnetic field sensor includes first and second magnetic field sensors mounted in the vehicle for sensing directional components of the earth'"'"'s magnetic field relative to the vehicle'"'"'s heading, the first and second sensors generating electrical signals representative of the sensed directional components of the earth'"'"'s magnetic field.

6. The vehicle compass system of claim 1, wherein the first and second magnetic field sensors include magneto-inductive sensors.

7. The vehicle compass system of claim 1, wherein the processing circuit is configured to calibrate the system when the three candidate data points define corners of a triangle meeting predetermined criteria.

8. The vehicle compass system of claim 7, wherein the processing circuit is configured to determine that a triangle defined by the three candidate data points meets the predetermined criteria when the triangle is substantially non-obtuse.

9. The vehicle compass system of claim 8, wherein the processing circuit is configured to determine that the three candidate data points define corners of a substantially non-obtuse triangle with sides of lengths a, b, and c when the lengths of the sides satisfy the relationship {square root over (a²+b²)}/c≧

0.92, where c is the longest side.

10. A vehicle compass system, comprising:

a magnetic field sensor configured to detect the earth'"'"'s magnetic field and to generate electrical signals representing a direction of the vehicle'"'"'s travel in relation to the earth'"'"'s magnetic field; and

a processing circuit coupled to the sensor configured to process the electrical signals generated by the sensor to provide data points representative of the vehicle'"'"'s heading, wherein the processing circuit is configured to calibrate the system based on data points that define corners of a triangle meeting predetermined criteria, wherein the processing circuit is further configured to calibrate the system by detecting crossings of the data points.

11. The vehicle compass system of claim 10, wherein the processing circuit is configured to calibrate the system when three data points are detected that define corners of the triangle meeting the predetermined criteria.

12. The vehicle compass system of claim 10, wherein the processing circuit is configured to calibrate the system by calculating coordinates of a center point of a circle defined by a plot of the data points, wherein the processing circuit is configured to determine the vehicle'"'"'s current heading based upon the relation of coordinates of a data point and the calculated coordinates of the center point.

13. The vehicle compass system of claim 12, wherein the processing circuit is configured to determine whether the circle is an ellipse based on the crossings.

14. The vehicle compass system of claim 10, wherein the magnetic field sensor is a magneto-inductive sensor.

15. The vehicle compass system of claim 10, wherein the processing circuit is configured, if the three data points obtained from the sensor do not define a triangle that meets the predetermined criteria, to obtain a fourth data point from the sensor and to determine whether any combination of three of the four data points defines a triangle that meets the predetermined criteria.

16. A vehicle compass system, comprising:

a magnetic field sensor configured to detect the earth'"'"'s magnetic field and to generate electrical signals representing a direction of the vehicle'"'"'s travel in relation to the earth'"'"'s magnetic field; and

a processing circuit coupled to the sensor configured to process the electrical signals generated by the sensor to provide data points representative of the vehicle'"'"'s heading, wherein the processing circuit is configured to calibrate the system based on data points that define three sides of a triangle meeting predetermined criteria, the processing circuit configured to determine that a triangle defined by the three sides meets the predetermined criteria when the triangle is substantially non-obtuse.

17. A vehicle compass system, comprising:

a magnetic field sensor configured to detect the earth'"'"'s magnetic field and to generate electrical signals representing a direction of the vehicle'"'"'s travel in relation to the earth'"'"'s magnetic field; and

a processing circuit coupled to the sensor configured to process the electrical signals generated by the sensor to provide data points representative of the vehicle'"'"'s heading, wherein the processing circuit is configured to calibrate the system based on data points that define three sides of a triangle meeting predetermined criteria, the processing circuit configured to determine that the three sides define a substantially non-obtuse triangle with sides of lengths a, b, and c when the lengths of the sides satisfy the relationship {square root over (a²+b²)}/c≧

0.92 where c is the longest side.

18. A vehicle compass system, comprising:

a magnetic field sensor configured to detect the earth'"'"'s magnetic field and to generate electrical signals representing a direction of the vehicle'"'"'s travel in relation to the earth'"'"'s magnetic field; and

a processing circuit coupled to the sensor configured to process the electrical signals generated by the sensor to provide data points representative of the vehicle'"'"'s heading, wherein the processing circuit is configured to calibrate the system based on data points that define three sides of a triangle meeting predetermined criteria,

wherein, if the three sides do not define a triangle that meets the predetermined criteria, the processing circuit is configured to obtain a fourth data point from the sensor and to determine whether any combination of three out of four of the data points defines a triangle that meets the predetermined criteria.

19. A vehicle compass system, comprising:

a magnetic field sensor configured to detect the earth'"'"'s magnetic field and to generate electrical signals representing a direction of the vehicle'"'"'s travel in relation to the earth'"'"'s magnetic field; and

a processing circuit coupled to the sensor configured to process the electrical signals generated by the sensor to provide data points representative of the vehicle'"'"'s heading, wherein the processing circuit is configured to calibrate the system based on three data points that define corners of a triangle meeting predetermined criteria, wherein the processing circuit is configured to determine that a triangle defined by the three data points meets the predetermined criteria when the triangle is substantially non-obtuse.

20. The vehicle compass system of claim 19, wherein the processing circuit is further configured to determine that the triangle defined by the three data points meets the predetermined criteria when an angle of the triangle meets a predetermined minimum size criteria.

21. A vehicle compass system, comprising:

a magnetic field sensor configured to detect the earth'"'"'s magnetic field and to generate electrical signals representing a direction of the vehicle'"'"'s travel in relation to the earth'"'"'s magnetic field; and

a processing circuit coupled to the sensor configured to process the electrical signals generated by the sensor to provide data points representative of the vehicle'"'"'s hearing, wherein the processing circuit is configured to calibrate the system based on three data points that define corners of a triangle meeting predetermined criteria, wherein, the processing circuit is configured if the three data points obtained from the sensor do not define a triangle that meets the predetermined criteria, to obtain a fourth data point from the sensor and to determine whether any combination of three of the four data points defines a triangle that meets the predetermined criteria.

22. The vehicle compass system of claim 21, wherein the processing circuit is configured to determine that a triangle defined by the three data points meets the predetermined criteria when the triangle is substantially non-obtuse.