Vehicle compass compensation

• US 20030115764A1
• Filed: 01/28/2003
• Published: 06/26/2003
• Est. Priority Date: 04/08/1999
• Status: Active Grant

• Current Assignee: Donnelly Corporation (Magna International Incorporated)
• Original Assignee: Donnelly Corporation (Magna International Incorporated)
• Inventors: Schofield, Kenneth, Blank, Rodney K., Schierbeek, Kenneth L., DeVette, Gregory H., Hoekstra, Eric J., Veiseh, Merdad
• Granted Patent: US 6,922,902 B2
• Time in Patent Office: Days
• 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 and 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;

an electronic circuit responsive to said sensor assembly for determining the Earth magnetic field, said sensor detecting at least one data point and said electronic circuit adjusting said sensor according to an approximation of a center of the Earth magnetic field calculated from said at least one data point and an estimated value of Earth magnetic field magnitude; and

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

2. The vehicular electronic compass system in claim 1, wherein said at least one data point is one of a substantially minimum value and maximum value along one coordinate axis and wherein said approximation of a center of the Earth magnetic field is determined by adjusting said data point along said one coordinate axis by the estimated value of Earth magnetic field magnitude.

3. The vehicular electronic compass system in claim 2, wherein said sensor detecting another data point of the other of the substantially minimum value and maximum value along said one coordinate axis, said electronic circuit using said data points to determine an actual value of Earth magnetic field magnitude.

4. The vehicular electronic compass system in claim 2, wherein said electronic circuit establishes an approximation of a center of the Earth magnetic field along another coordinate axis from a value of said at least one data point with respect to said another coordinate axis.

5. The vehicular electronic compass system in claim 4, wherein said electronic circuit updates said approximation of a center of the Earth magnetic field along the other coordinate axis by determining another data point of one of a substantially minimum value and a maximum value along said other coordinate axis and adjusting said another data point along said coordinate axis by said estimate of Earth magnetic field magnitude.

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

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

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

9. The vehicular electronic compass system of claim 1, wherein said sensor assembly senses Earth magnetic field and a deviating magnetic field and said electronic circuit adjusts said sensor to substantially nullify the deviating magnetic field.

10. A vehicular electronic compass system comprising:

a magneto-responsive sensor assembly for sensing a 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 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, 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.

11. The vehicular compass system of claim 10, 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.

12. The vehicular compass system of claim 10, 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.

13. The vehicular compass system of claim 12, wherein said value is approximately one-half of the Earth magnetic field magnitude.

14. The vehicular compass system of claim 12, 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.

15. The vehicular compass system in claim 14, wherein said substantially equal coordinates are approximately one-half of the Earth magnetic field magnitude.

16. The vehicular compass system of claim 12, 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.

17. The vehicular compass system of claim 10, 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.

18. The vehicular compass system in claim 10, wherein said sensor assembly comprises one of a magneto-inductive sensor, a magneto-resistive sensor and a flux gate sensor.

19. The vehicular compass system in claim 10, wherein said sensor assembly comprises a magneto-resistive sensor.

20. The vehicular compass system in claim 10, 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.

21. The vehicular compass system in claim 20, wherein said electronic circuit collects additional data points and calculates a new estimated offset if said estimated offset is not valid.

22. The vehicular compass system of claim 10, 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.

23. The vehicular compass system of claim 22, 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.

24. The vehicular compass system in claim 23, wherein said portion is approximately one-half.

25. The vehicular compass system of claim 22, 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.

26. The vehicular compass system of claim 25, 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.

27. The vehicular compass system of claim 22, 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.

28. The vehicular compass system in claim 27, 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.

29. A vehicular electronic compass system, comprising:

a magneto-responsive sensor assembly for sensing a magnetic field;

an electronic circuit responsive to said sensor assembly for determining at least one of magnitude and direction of the Earth magnetic field, said electronic circuit collecting data points, determining from the collected data points an offset value of the Earth magnetic field, and adjusting a directional heading output of said sensor assembly to account for said offset value;

said electronic circuit including an extended range calibration function identifying a change in magnetic signature from at least one of said sensor assembly and said offset value and adjusting said sensor assembly in response to a change in magnetic signature; and

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

30. The vehicular electronic compass system in claim 29, wherein said calibration function identifies a change in magnetic signature from said sensor reaching a limit of operation of said electronic circuit.

31. The vehicular electronic compass system in claim 30, wherein said electronic circuit calculates a new offset after adjusting said sensor assembly.

32. The vehicular electronic compass system in claim 29, wherein said calibration function identifies a change in magnetic signature from an abnormal relation between collected data points and said offset.

33. The vehicular electronic compass system in claim 32, wherein said abnormal relation comprises said offset falling outside of opposite peak values of data points.

34. The vehicular electronic compass system in claim 33, wherein said electronic circuit calculates a new offset value after adjusting said sensor assembly.

35. The vehicular electronic compass system in claim 29, wherein said electronic circuit occasionally calculates new values of said offset value and wherein said calibration function identifies a change in magnetic signature from a chance in said offset value which exceeds a predetermined amount.

36. The vehicular electronic compass system in claim 35, wherein said predetermined amount comprises a predetermined portion of an operating range of said electronic circuit.

37. The vehicular electronic compass system in claim 36, wherein said electronic circuit calculates a new offset value after adjusting said sensor assembly.

38. The vehicular electronic compass system in claim 29, wherein said electronic circuit includes a microcomputer system having a digital-to-analog converter converting digital values to analog signals supplied to said sensor for adjusting said sensor assembly.

39. The vehicular electronic compass system in claim 38, wherein said microcomputer system further includes an analog-to-digital converter converting outputs of said sensor assembly to digital signals, said analog-to-digital converter having a range of operation defining a limit of operation of said electronic circuit.

40. The vehicular electronic compass system in claim 29, wherein said magneto-responsive sensor comprises one of a magneto-inductive sensor, a magneto-resistive sensor, a magneto-capacitive sensor, and a flux gate sensor.

41. The vehicular electronic compass system in claim 29, wherein said magneto-responsive sensor comprises a magneto-resistive sensor.

42. The vehicular electronic compass system of claim 29, wherein said sensor assembly comprises first and second magneto-responsive sensors oriented in a predetermined angular relationship with each other and in a predetermined orientation with respect to the vehicle.

43. A vehicular electronic compass system, comprising:

a magneto-responsive sensor assembly for sensing a magnetic field;

a microcomputer system responsive to said sensor assembly for determining at least one of magnitude and direction of the Earth magnetic field, said microcomputer system collecting data points, determining from the collected data points an offset value of the Earth magnetic field and adjusting a directional heading output of said sensor assembly to account for said offset, wherein said microcomputer system occasionally calculates a new value of said offset, wherein said microcomputer system having a digital-to-analog converter converting digital values to analog signals for adjusting said sensor assembly and an analog-to-digital converter converting outputs of said sensor assembly to digital values, said analog-to-digital converter having a range of operation;

said microcomputer system adjusting said sensor assembly and calculating a new value of said offset in response to at least one of (i) an output of said sensor assembly exceeding said range of operation of said analog-to-digital converter, (ii) an abnormal relation between collected data points and the value of said offset, and (iii) a change in value of said offset which exceeds a predetermined amount; and

an electronic display coupled with said microcomputer system for displaying a direction of the Earth magnetic field.

44. The vehicular electronic compass system in claim 43, wherein said magneto-responsive sensor comprises one of a magneto-inductive sensor, a magneto-resistive sensor, a magneto-capacitive sensor, and a flux gate sensor.

45. The vehicular electronic compass system in claim 43, wherein said magneto-responsive sensor comprises a magneto-resistive sensor.

46. The vehicular electronic compass system of claim 43, wherein said sensor assembly comprises first and second magneto-responsive sensors oriented in a predetermined angular relationship with each other and in a predetermined orientation with respect to the vehicle.

47. The vehicular electronic compass system in claim 43 wherein said abnormal relation comprises said offset value falling outside of opposite peak values of data points.

48. The vehicular electronic compass system in claim 43 wherein said predetermined amount comprises a predetermined portion of said range of operation.

49. A calibration method for calibrating a compass for use on a vehicle, said method comprising:

sampling at least one data point of a magnetic field with a magnetic sensor;

determining coordinates for said at least one data point relative to an origin of a coordinate system associated with the vehicle;

estimating an origin of an Earth magnetic field from an estimated value of the Earth magnetic field magnitude and at least one data point; and

adjusting the sensor to offset the estimated origin to the coordinate system associated with the vehicles.

50. The calibration method of claim 49 further comprising:

sampling pair of data points that are substantially oppositely positioned relative to one axis of said coordinate system;

averaging the substantially opposite values of said pair of data points to determine deviation from a zero value of the coordinate system; and

adjusting an output of the system as a function of said deviation.

51. The calibration method of claim 50 further comprising validating said deviation by comparing said deviation with another value determined by a different technique.

52. The calibration method of claim 51 including sampling additional data points if said deviation is not valid.

53. A calibration method for calibrating a compass system for use on a vehicle, said method comprising:

sampling at least one pair of data points that are substantially oppositely positioned relative to an axis of a coordinate system;

averaging the substantially opposite values of said pair of data points to determine deviation from a zero value of the coordinate system; and

adjusting an output of the compass system as a function of said deviation.

54. The calibration method of claim 53 further comprising validating said deviation by comparing said deviation with another value determined by a different technique.

55. The calibration method of claim 54 including sampling additional data points if said deviation is not valid.

56. A calibration method for calibrating a compass for use on a vehicle, comprising:

collecting data points with a sensor assembly, determining from the collected data points an offset value of the Earth magnetic field, and adjusting a directional heading output of said sensor assembly to account for said offset; and

identifying a change in magnetic signature from at least one of said sensor assembly and said offset value and adjusting said sensor assembly in response to a change in magnetic signature.

57. The calibration method of claim 56 wherein a change in magnetic signature is identified from said sensor reaching a limit of operation of said electronic circuit.

58. The calibration method of claim 56 wherein a change in magnetic signature is identified from an abnormal relation between collected data points and said offset.

59. The calibration method of claim 56 wherein a change in magnetic signature is identified from an abnormal relation between collected data points and said offset.

60. The calibration method of claim 59 wherein said abnormal relation comprises said offset falling outside of opposite peak values of data points.