Vehicle compass system with continuous automatic calibration

• US 6,301,794 B1
• Filed: 05/27/1999
• Issued: 10/16/2001
• Est. Priority Date: 05/27/1999
• Status: Expired due to Fees

• Current Assignee: Johnson Controls Technology Company (Johnson Controls International plc)
• Original Assignee: Johnson Controls, Inc. (Johnson Controls International plc)
• Inventors: Olson, Thomas R., Slater, David J., Parks, Jeffrey N.
• Primary Examiner(s): Gutierrez, Diego F. F.
• Assistant Examiner(s): DEJESUS, LYDIA M
• Application Number:
  US09/320,924
• Time in Patent Office: 873 Days
• Field of Search: 333/55.R, 333/56, 333/57, 333/58, 333/59, 333/61
• 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 x²+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. An electronic compass system for a vehicle comprising:

a magnetic field sensor for detecting the earth'"'"'s magnetic field and for generating electrical signals representing a direction of the vehicle'"'"'s travel in relation to the earth'"'"'s magnetic field; and

a processing circuit coupled to said sensor for processing the electrical signals generated by said sensor to provide a vehicle direction output signal representative of the vehicle'"'"'s current heading, said processing circuit processes the electrical signals generated by said sensor by translating the electrical signals into data points represented by their coordinates with respect to an origin, said processing circuit calibrates the system by recalculating coordinates of a center point of a circle defined by a plot of the data points that would be derived as the vehicle travels through a non-linear path and determining offset compensation corresponding to the offset of the center of the circle with respect to the origin, said processing circuit calibrates the system when three data points are detected that define corners of a triangle meeting predetermined criteria.

2. The compass system as defined in claim 1, wherein said processing circuit determines that a triangle defined by the three data points meets the predetermined criteria when the triangle is substantially non-obtuse.

3. The compass system as defined in claim 2, wherein said processing circuit determines that the three 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+L +b²+L )}/c≧

0.92, where c is the longest side.

4. The compass system as defined in claim 1, wherein said processing circuit recalibrates each time three new data points are obtained that define corner points of a triangle meeting the predetermined criteria.

5. The compass system as defined in claim 1, wherein said processing circuit recalculates the center point coordinates by averaging the newly calculated center point with the previously calculated center point.

6. The compass system as defined in claim 5, wherein said processing circuit averages the newly calculated center point with the previously calculated center point if the newly calculated center point is within a distance of the previously calculated center point equal to 0.5 times the radius of the circle having the previously calculated center point.

7. The compass system as defined in claim 1, wherein said processing circuit calculates the center point coordinates by solving the equation x²+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).

8. The compass system as defined in claim 7, wherein said processing circuit calculates the radius r of the circle with the newly calculated center point as r={square root over ((A²+L +B²+L −

4+L C)/4+L )}.

9. The compass system as defined in claim 8, wherein said processing circuit discards the three data points prior to recalculating the center of the circle if a distance between the most recently calculated circle center point and any of the three data points is greater than 1.5 times the most recently calculated radius or is less than 0.5 times the most recently calculated radius.

10. The compass system as defined in claim 1, wherein said processing circuit determines the vehicle'"'"'s current heading based upon the relation of the coordinates of the most recently obtained data point and the most recently calculated center point of the circle.

11. The compass system as defined in claim 1, wherein said processing circuit recalculates the center point of the circle using the three data points that define the triangle meeting the predetermined criteria.

12. The compass system as defined in claim 11, wherein the three data points used to recalculate the center point of the circle are each averages of raw data points obtained from the electrical signals output from said sensor.

13. The compass system as defined in claim 1, wherein said sensor includes a magnetic sensor mounted in the vehicle to sense components of the earth'"'"'s magnetic field in a direction parallel to a longitudinal axis of the vehicle, and a second sensor mounted to the vehicle to sense components of the earth'"'"'s magnetic field in a direction perpendicular to the longitudinal axis of the vehicle, and wherein said processing circuit translates the electrical signals output from said first sensor as the Y coordinates of a data point and translates the electrical signals output from said second sensor as the X coordinates of the data point.

14. The compass system as defined in claim 13, wherein said first and second sensors are magneto-inductive sensors.

15. The compass system as defined in claim 1, wherein, if any three data points obtained from said sensor do not define a triangle that meets the predetermined criteria, said processing circuit obtains a fourth data point from said sensor and determines whether any combination of three of the four data points defines a triangle that meets the predetermined criteria.

16. The compass system as defined in claim 15, wherein, if said processing circuit determines that no combination of the four data points defines a triangle that meets the predetermined criteria, said processing circuit discards at least one of the four data points and obtains a new data point to evaluate in combination with the remaining data points whether any such combination defines a triangle that meets the predetermined criteria.

17. An electronic compass for a vehicle comprising:

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, said first and second sensors generating electrical signals representative of the sensed directional components of the earth'"'"'s magnetic field; and

a processing circuit coupled to said sensors for processing the electrical signals generated by said sensors to provide a vehicle direction output signal representative of the vehicle'"'"'s current heading, said processing circuit processes the electrical signals generated by said sensors by translating the electrical signals into raw data points relative to reference levels defining an origin of a reference coordinate plane, said processing circuit obtains averaged data points by collecting and averaging successive sets of a predetermined number of raw data points, identifies three such averaged data points as candidate data points if the averaged data points meet predetermined spacing criteria, and calibrates the compass using the three candidate data points each time three such candidate data points are identified.

18. The compass system as defined in claim 17, wherein, prior to calibrating the compass, said processing circuit determines whether three candidate data points define a triangle that meets predetermined triangle criteria and, if the three candidate data points do not define a triangle that meets the predetermined triangle criteria, said processing circuit repeatedly discards and replaces candidate data points with newly obtained candidate data points until three candidate data points are identified that define a triangle meeting the predetermined triangle criteria.

19. The compass system as defined in claim 18, wherein the predetermined triangle criterion that the triangle must meet is to be substantially non-obtuse.

20. The compass system as defined in claim 19, wherein a triangle is considered to be substantially non-obtuse and thereby meet the predetermined criteria if the sides of the triangle a, b, and c satisfy the relation {square root over (a²+L +b²+L )}/c≧

0.92, where c is a longest side.

21. The compass system as defined in claim 18, wherein a triangle meets the predetermined criteria if the sides of the triangle a, b, and c satisfy the relation {square root over (b²+L +c²+L )}/a<

3, where a is the shortest side.

22. The compass system as defined in claim 18, wherein a triangle meets the predetermined criteria if the sides of the triangle a, b, and c satisfy the relations {square root over (a²+L +b²+L )}/c≧

0.92 and {square root over (b²+L +c²+L )}/a<

3, where a is the shortest side.

23. The compass system as defined in claim 17, wherein said processing circuit calibrates the compass by calculating center point coordinates of a circle upon which the three candidate data points lie and by calculating offset compensation values to offset all raw data points obtained from said sensors by comparing the calculated center point to the origin of the reference coordinate plane.

24. The compass system as defined in claim 23, wherein said processing circuit calculates the coordinates of the circle center point by solving the equation x²+y²+Ax+By+C=0 for A, B, and C, using the coordinate values (x, y) for the three candidate data points, and defining the center point as (−

A/2, −

B/2).

25. A method of calibrating an electronic compass used in a vehicle, the method comprising the steps of:

(a) collecting raw data points from two magnetic sensors that sense perpendicular components of the earth'"'"'s magnetic field, the raw data points representing the vehicle'"'"'s current heading;

(b) averaging each collected raw data point with a predetermined number of previously collected raw data points to obtain an averaged data point;

(c) identifying the averaged data point as a first candidate data point;

(d) repeating steps (a) and (b) to obtain a second and a third averaged data point;

(e) identifying the second and third averaged data points as second and third candidate data points, respectively; and

(f) calibrating the compass using the first, second, and third candidate data points each time three such candidate data points are obtained.

26. The method as defined in claim 25 and further including the steps of:

(g) determining whether the first, second, and third candidate data points define a triangle meeting predetermined criteria;

(h) discarding at least one of the first, second, and third candidate data points if the first, second, and third candidate data points do not define a triangle meeting the predetermined criteria;

(i) repeating steps (a) and (b) to obtain and identify replacement candidate data points for any candidate data points that are discarded in step (h); and

(j) repeating steps (g) through (i) until three candidate data points are identified that define a triangle meeting the predetermined criteria prior to performing step (f).

27. The method as defined in claim 26, wherein the predetermined criterion that the triangle must meet is to be substantially non-obtuse.

28. The method as defined in claim 27, wherein a triangle is considered to be substantially non-obtuse and thereby meet the predetermined criteria if the sides of the triangle a, b, and c satisfy the relation {square root over (a²+L +b²+L )}/c≧

0.92, where c is the longest side.

29. The method as defined in claim 26, wherein a triangle meets the predetermined criteria if the sides of the triangle a, b, and c satisfy the relation {square root over (b²+L +c²+L )}/a<

3, where a is the shortest side.

30. The method as defined in claim 26, wherein a triangle meets the predetermined criteria if the sides of the triangle a, b, and c satisfy the relations {square root over (a²+L +b²+L )}/c≧

0.92 and {square root over (b²+L +c²+L )}/a<

3, where a is the shortest side.

31. The method as defined in claim 25, wherein the step (f) of calibrating the compass includes the substeps of:

(i) calculating center point coordinates for a circle upon which all three candidate data points lie by solving the equation x²+y²+Ax+By+C=0 for A, B, and C using the coordinate values (x, y) for the three candidate data points, and defining the center point as (−

A/2, −

B/2); and

(ii) determining offset compensation values to offset all raw data points obtained from the magnetic sensors by comparing the center point calculated in step (i) to an origin reference point.

32. An electronic compass system for a vehicle comprising:

a magnetic field sensor for detecting the earth'"'"'s magnetic field and for generating electrical signals representing the direction of the vehicle'"'"'s travel in relation to the earth'"'"'s magnetic field; and

a processing circuit coupled to said sensor for processing the electrical signals generated by said sensor to provide a vehicle direction output signal representative of the vehicle'"'"'s current heading, said processing circuit processes the electrical signals generated by said sensor by translating the electrical signals into data points represented by their coordinates with respect to an origin, said processing circuit calibrates the system by recalculating coordinates of a center point of a circle defined by a plot of the data points that would be derived as the vehicle travels through a non-linear path and determining offset compensation corresponding to the offset of the center of the circle with respect to the origin, said processing circuit calibrates the system when three data points are detected that meet predetermined criteria, whereby the three data points define corners of a substantially non-obtuse triangle.

33. The compass system as defined in claim 32, wherein said processing circuit determines that the three 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 relation {square root over (a²+L +b²+L )}/c≧

0.92, where c is the longest side.

34. A compass system for a vehicle comprising:

a magnetic field sensor for detecting the earth'"'"'s magnetic field and for generating electrical signals representing the direction of the vehicle'"'"'s travel in relation to the earth'"'"'s magnetic field; and

a processing circuit coupled to said sensor for processing the electrical signals generated by said sensor to provide a vehicle direction output signal representative of the vehicle'"'"'s current heading, said processing circuit processes the electrical signals generated by said sensor by translating the electrical signals into data points represented by their coordinates with respect to an origin of a reference coordinate plane, said processing circuit calibrates the system by recalculating coordinates of a center point of a circle defined by a plot of the data points that would be derived as the vehicle travels through a non-linear path and determining offset compensation corresponding to the offset of the center of the circle with respect to the origin, said processing circuit calculates the coordinates of the center point of a circle using three data points derived from the electrical signals output from said sensor by solving the equation x²+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).

35. The compass system as defined in claim 34, wherein the three data points used to calculate the center point are averaged data points that represent an average of a predetermined number of raw data points directly translated from the electrical signals received from said sensor.

36. The compass system as defined in claim 35, wherein the averaged data points that are used by said processing circuit to calculate the center point define a triangle meeting predetermined criteria.

37. The compass system as defined in claim 36, wherein the predetermined triangle criterion that the triangle must meet is to be substantially non-obtuse.

38. The compass system as defined in claim 36, wherein a triangle meets the predetermined triangle criteria if the sides of the triangle a, b, and c satisfy the relations {square root over (a²+L +b²+L )}/c≧

0.92 and {square root over (b²+L +c²+L )}/a<

3, where a is the shortest side.

39. The compass system as defined in claim 35, wherein said processing circuit averages the newly calculated center point with the previously calculated center point if the newly calculated center point is within a distance of the previously calculated center point equal to 0.5 times the radius of the circle having the previously calculated center point.

40. The compass system as defined in claim 39, wherein said processing circuit calculates the radius r of the circle with the newly calculated center point as r={square root over ((A²+L +B²+L −

4+L C)/4+L )}.

41. The compass system as defined in claim 35 and further including a display coupled to said processing circuit for receiving the vehicle direction output signal and displaying the vehicle'"'"'s heading.

42. A method of calibrating an electronic compass used in a vehicle, the method comprising the steps of:

(a) collecting raw data points by translating electrical signals received from a magnetic sensor that senses perpendicular components of the earth'"'"'s magnetic field, the raw data points representing the vehicle'"'"'s current heading;

(b) averaging sets of a predetermined number of collected raw data points to obtain a plurality of averaged data points;

(c) identifying the averaged data points as candidate data points if the averaged data points meet predetermined spacing criteria;

(d) calculating center point coordinates for a circle upon which three candidate data points lie by solving the equation x²+y²+Ax+By+C=0 for A, B, and C, using the coordinate values (x,y) for the three candidate data points, and defining the center point coordinates as (−

A/2, −

B/2); and

(e) determining offset compensation values to offset all raw data points obtained from the magnetic sensors by comparing the center point calculated in step (i) to an origin reference point.

43. The method as defined in claim 42 and further including the steps of:

(f) prior to performing steps (d) and (e), determining whether three candidate data points define a triangle meeting predetermined triangle criteria; and

(g) if the three candidate data points do not define a triangle that meets the predetermined triangle criteria, repeatedly discarding and replacing candidate data points with newly obtained candidate data points until three candidate data points are identified that define a triangle meeting the predetermined triangle criteria.

44. The method as defined in claim 43, wherein the predetermined triangle criterion that the triangle must meet is to be substantially non-obtuse.

45. The method as defined in claim 44, wherein a triangle is considered to be substantially non-obtuse and thereby meet the predetermined criteria if the sides of the triangle a, b, and c satisfy the relation {square root over (a²+L +b²+L )}/c≧

0.92, where c is the longest side.

46. The method as defined in claim 43, wherein a triangle meets the predetermined triangle criteria if the sides of the triangle a, b, and c satisfy the relation {square root over (b²+L +c²+L )}/a<

3, where a is the shortest side.

47. The method as defined in claim 43, wherein a triangle meets the predetermined triangle criteria if the sides of the triangle a, b, and c satisfy the relations {square root over (a²+L +b²+L )}/c≧

0.92 and {square root over (b²+L +c²+L )}/a<

3, where a is the shortest side.