Electronic compass system

• US 6,968,273 B2
• Filed: 08/02/2002
• Issued: 11/22/2005
• Est. Priority Date: 03/01/2002
• Status: Active Grant

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Bechtel, Jon H., Ockerse, Harold C., Bugno, Mark D.
• Primary Examiner(s): Beaulieu, Yonel
• Application Number:
  US10/210,910
• Publication Number:
  US 20030167121A1
• Time in Patent Office: 1,208 Days
• Field of Search: 701/36, 701/205, 701/224, 33/270.2, 73/17.6, 73/10.1
• US Class Current: 701/224
• CPC Class Codes: G01C 17/30 Earth-inductor compasses
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

An electronic compass system includes a magnetic sensor circuit having at least two sensing elements for sensing perpendicular components of the Earth'"'"'s magnetic field vector. A processing circuit is coupled to the sensor circuit to filter, process, and compute a heading. The processing circuit further selects an approximating geometric pattern, such as a sphere, ellipsoid, ellipse, or circle, determines an error metric of the data points relative to the approximating pattern, adjusts the pattern to minimize the error, thereby obtaining a best fit pattern. The best fit pattern is then used to calculate the heading for each successive sensor reading provided that the noise level is not noisy and until a new best fit pattern is identified. The electronic compass system is particularly well suited for implementation in a vehicle rearview mirror assembly.

Claims

1. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing three perpendicular components of the Earth'"'"'s magnetic field vector, and for generating output signals representing the three sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, approximating a three-dimensional geometric pattern derived from the three sensed components, computing a heading of the vehicle as a function of at least two of the sensed components while referencing the three-dimensional geometric pattern, and generating a heading signal representing the computed heading, wherein said processing circuit approximates the three-dimensional geometric pattern based on at least five reference data points derived from the sensed components.

67. The electronic compass of claim 1 and further comprising a heading indicator coupled to said processing circuit for receiving the heading signal and for providing an indication of the vehicle heading to a vehicle occupant.

68. The electronic compass of claim 67, wherein said heading indicator is a display.

69. The electronic compass of claim 1, wherein the three-dimensional geometric pattern is an approximating pattern representing the best fit to the data points derived from the sensed components.

2. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing at least two perpendicular components of the Earth'"'"'s magnetic field vector and for generating output signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, selecting an approximating geometric pattern that constitutes a best fit to select data points corresponding to the sensed components taken over time, computing a heading of the vehicle as a function of at least two of the sensed components while referencing the selected approximating geometric pattern, and generating a heading signal representing the computed heading, wherein the best fit approximating geometric pattern is determined by initially assuming an approximating geometric pattern and computing an error metric based on the initial assumption, changing the assumed approximating geometric pattern until the error metric is minimized, and then utilizing the changed approximating geometric pattern with the minimum error metric for determining vehicle heading.

3. The electronic compass of claim 2, wherein the best fit approximating geometric pattern is determined by iterative processing by which an approximating geometric pattern is repeatedly compared and changed based on the sensed components.

4. The electronic compass of claim 2, wherein said magnetic sensor circuit senses three perpendicular components of the Earth'"'"'s magnetic field vector, and wherein said processing circuit selects a three-dimensional approximating geometric pattern derived from the three sensed components and computes a heading of the vehicle as a function of at least two of the sensed components while referencing the three-dimensional geometric pattern.

70. The electronic compass of claim 2 and further comprising a heading indicator coupled to said processing circuit for receiving the heading signal and for providing an indication of the vehicle heading to a vehicle occupant.

71. The electronic compass of claim 2, wherein the approximating geographic pattern is a circle.

72. The electronic compass of claim 2, wherein the approximating geographic pattern is an ellipse.

73. The electronic compass of claim 2, wherein the approximating geographic pattern is a three-dimensional geometric pattern.

74. The electronic compass of claim 2, wherein the approximating geographic pattern is a sphere.

75. The electronic compass of claim 2, wherein the approximating geographic pattern is an ellipsoid.

5. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing at least two perpendicular components of the Earth'"'"'s magnetic field vector and for generating output signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, selecting an approximating geometric pattern that constitutes a best fit to select data points corresponding to the sensed components taken over time, computing a heading of the vehicle as a function of at least two of the sensed components while referencing the selected approximating geometric pattern, and generating a heading signal representing the computed heading, wherein said processing circuit selects the approximating geometric pattern based on at least five reference data points derived from the sensed components.

6. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing three perpendicular components of the Earth'"'"'s magnetic field vector, and for generating output signals representing the three sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, determining a geometric pattern, computing a heading of the vehicle as a function of the at least two of the sensed components while referencing the geometric pattern, determining the magnitude of an error vector extending from the perimeter of the geometric pattern to the most recent sensed components from the three sensed perpendicular components, and generating a heading signal representing the computed heading when the magnitude of the error vector does not exceed a predetermined threshold.

7. The electronic compass of claim 6 and further comprising a heading indicator coupled to said processing circuit for receiving the heading signal and for providing an indication of the heading of the vehicle to a vehicle occupant.

8. The electronic compass of claim 7, wherein said heading indicator is a display.

9. The electronic compass of claim 6, wherein said processing circuit determines the geometric pattern based on at least five reference data points derived from the sensed components.

10. The electronic compass of claim 6, wherein said processing circuit determines a three-dimensional geometric pattern derived from the three sensed components and computes a heading of the vehicle as a function of at least two of the sensed components while referencing the three-dimensional geometric pattern.

11. The electronic compass of claim 6, wherein said processing circuit selects a geometric pattern that constitutes a best fit to select data points corresponding to the sensed components taken over time.

12. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing at least two perpendicular components of the Earth'"'"'s magnetic field vector and for generating output signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, iteratively selecting an approximating geometric pattern by repeatedly comparing and changing the geometric pattern based on the sensed components taken over time, computing a heading of the vehicle as a function of at least two of the sensed components while referencing the geometric pattern, and generating a heading signal representing the computed heading, wherein said processing circuit selects the approximating geometric pattern based on at least five reference data points derived from the sensed components.

13. The electronic compass of claim 12, wherein said magnetic sensor circuit senses three perpendicular components of the Earth'"'"'s magnetic field vector, and wherein said processing circuit iteratively selects a three-dimensional approximating geometric pattern derived from the three sensed components and computes a heading of the vehicle as a function of at least two of the sensed components while referencing the three-dimensional geometric pattern.

14. The electronic compass of claim 12, wherein said processing circuit iteratively selects an approximating geometric pattern that constitutes a best fit to select data points corresponding to the sensed components taken over time.

76. The electronic compass of claim 12, wherein the approximating geographic pattern is a circle.

77. The electronic compass of claim 12, wherein the approximating geographic pattern is an ellipse.

78. The electronic compass of claim 12, wherein the approximating geographic pattern is a three-dimensional geometric pattern.

79. The electronic compass of claim 78, wherein the approximating geographic pattern is a sphere.

80. The electronic compass of claim 78, wherein the approximating geographic pattern is an ellipsoid.

15. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing at least two perpendicular components of the Earth'"'"'s magnetic field vector and for generating output signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, iteratively selecting an approximating geometric pattern by repeatedly comparing and changing the geometric pattern based on the sensed components taken over time, computing a heading of the vehicle as a function of at least two of the sensed components while referencing the geometric pattern, and generating a heading signal representing the computed heading, wherein said processing circuit determines the magnitude of an error vector extending from the perimeter of the selected approximating geometric pattern to the most recent sensed components, and generates a heading signal representing the computed heading when the magnitude of the error vector does not exceed a predetermined threshold.

16. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing at least two perpendicular components of the Earth'"'"'s magnetic field vector and for generating output signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, computing a heading of the vehicle as a function of at least two of the sensed components, and generating a heading signal representing the computed heading, said processing circuit further configured to;

(a) establish a plurality of angle buckets each corresponding to mutually exclusive angular ranges about an approximating geometric pattern,

(b) accumulate a point set including a plurality of data points each corresponding to the sensed components read at a different vehicle heading than the other data points,

(c) calculate a heading angle for a data point in the point set,

(d) select an angle bucket having an angular range in which the heading angle falls for the data point,

(e) assign the data point to the angle bucket selected in step (d),

(f) repeat steps (c)-(e) until all data points have been assigned to an angle bucket, and

(g) adjust the approximating geometric pattern based on the data points in the point set.

17. The electronic compass of claim 16, wherein said processing circuit is further configured to (h) replace a data point in the point set with a new data point if the data point to be replaced corresponds to an angle bucket that has already been assigned a different data point.

18. The electronic compass of claim 16, wherein said processing circuit selects the approximating geometric pattern based on at least five data points each stored in separate angle buckets.

19. The electronic compass of claim 16, wherein said magnetic sensor circuit senses three perpendicular components of the Earth'"'"'s magnetic field vector, and wherein said processing circuit selects a three-dimensional approximating geometric pattern derived from the three sensed components and computes a heading of the vehicle as a function of at least two of the sensed components while referencing the three-dimensional geometric pattern.

20. The electronic compass of claim 16, wherein said processing circuit selects an approximating geometric pattern that constitutes a best fit to select data points corresponding to the sensed components taken over time.

21. The electronic compass of claim 16, wherein said processing circuit determines the magnitude of an error vector extending from the perimeter of the approximating geometric pattern to the most recent sensed components, and generates a heading signal representing the computed heading when the magnitude of the error vector does not exceed a predetermined threshold.

22. The electronic compass of claim 16, wherein said processing circuit iteratively selects an approximating geometric pattern by repeatedly comparing and changing the geometric pattern based on the sensed components taken over time.

23. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit including at least two sensing elements, each for sensing a component of the Earth'"'"'s magnetic field vector that is perpendicular to the component sensed by the other sensor and for generating output data signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output data signals, associating the output data signals from each of said sensing elements to establish a data point, applying a smoothing filter to smooth the data point by utilizing a weighted average with the most recent data point given a greater weight than prior data points, computing a heading of the vehicle as a function of the most recent data point, and generating a heading signal representing the computed heading, wherein said processing circuit determines the magnitude of an error vector extending from the perimeter of the approximating geometric pattern to the most recent sensed components, and generates a heading signal representing the computed heading when the magnitude of the error vector does not exceed a predetermined threshold.

24. The electronic compass of claim 23, wherein said processing circuit iteratively selects an approximating geometric pattern by repeatedly comparing and changing the geometric pattern based on the sensed components taken over time.

25. The electronic compass of claim 23, wherein said magnetic sensor circuit senses three perpendicular components of the Earth'"'"'s magnetic field vector, and wherein said processing circuit selects a three-dimensional approximating geometric pattern derived from the three sensed components and computes a heading of the vehicle as a function of at least two of the sensed components while referencing the three-dimensional geometric pattern.

81. The electronic compass of claim 23, wherein the smoothing filter applied by said processing circuit is an exponential smoothing filter.

82. The electronic compass of claim 23, wherein said processing circuit selects an approximating geometric pattern and computes the heading of the vehicle as a function of at least two of the sensed components while referencing the approximating geometric pattern.

83. The electronic compass of claim 82, wherein the approximating geometric pattern is selected based on at least five reference data points derived from the sensed components.

84. The electronic compass of claim 82, wherein said processing circuit selects an approximating geometric pattern that constitutes a best fit to select data points corresponding to the sensed components taken over time.

26. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit including at least two sensing elements, each for sensing a component of the Earth'"'"'s magnetic field vector that is perpendicular to the component sensed by the other sensor and for generating output data signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output data signals, associating the output data signals from each of said sensing elements to establish a data point, determining a second derivative of the position of the data point relative to at least one prior data point, comparing the magnitude of the second derivative to a first threshold to determine whether the output data signals of the sensing elements are noisy, computing a heading of the vehicle as a function of the most recent data point, and generating a heading signal representing the computed heading.

27. The electronic compass of claim 26, wherein, when the magnitude of the second derivative exceeds the first threshold, said processing circuit sets a delay counter as a function of the extent to which the second derivative exceeds the first threshold and prevents use of the output data signals for approximation until the delay counter has expired.

28. The electronic compass of claim 26, wherein said processing circuit applies a smoothing filter to smooth a received data point by utilizing a weighted average with the received data point given a greater weight than prior data points.

29. The electronic compass of claim 26, wherein said processing circuit selects an approximating geometric pattern and computes the heading of the vehicle as a function of at least two of the sensed components while referencing the approximating geometric pattern.

30. The electronic compass of claim 29, wherein the approximating geometric pattern is selected based on at least five reference data points derived from the sensed components.

31. The electronic compass of claim 29, wherein said processing circuit selects an approximating geometric pattern that constitutes a best fit to select data points corresponding to the sensed components taken over time.

32. The electronic compass of claim 29, wherein said processing circuit determines the magnitude of an error vector extending from the perimeter of the approximating geometric pattern to the most recent sensed components, and generates a heading signal representing the computed heading when the magnitude of the error vector does not exceed a predetermined threshold.

33. The electronic compass of claim 29, wherein said processing circuit iteratively selects an approximating geometric pattern by repeatedly comparing and changing the geometric pattern based on the sensed components taken over time.

34. The electronic compass of claim 26, wherein said magnetic sensor circuit senses three perpendicular components of the Earth'"'"'s magnetic field vector, and wherein said processing circuit selects a three-dimensional approximating geometric pattern derived from the three sensed components and computes a heading of the vehicle as a function of at least two of the sensed components while referencing the three-dimensional geometric pattern.

35. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit including at least two sensing elements, each for sensing a component of the Earth'"'"'s magnetic field vector that is perpendicular to the component sensed by the other sensor and for generating output data signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output data signals, associating the output data signals from each of said sensing elements to establish a data point, determining a noise level of the output data signals of the sensing elements by monitoring variations in the sensed levels, setting a delay counter as a function of the noise level, preventing use of the output data signals for geometric approximation until the delay counter has expired, computing a heading of the vehicle as a function of the most recent data point, and generating a heading signal representing the computed heading.

36. The electronic compass of claim 35, wherein said processing circuit does not update the heading using the most recent data point when the noise level exceeds a noise threshold.

37. The electronic compass of claim 35, wherein said processing circuit increases the delay counter each time a data point is received that results in a determination that the noise level exceeds a noise threshold.

38. The electronic compass of claim 35, wherein said processing circuit decrements the delay counter each time a data point is received that results in a determination that the noise level does not exceed a noise threshold.

39. The electronic compass of claim 35, wherein said processing circuit selects an approximating geometric pattern and computes the heading of the vehicle as a function of at least two of the sensed components while referencing the approximating geometric pattern.

40. The electronic compass of claim 39, wherein the approximating geometric pattern is selected based on at least five reference data points derived from the sensed components.

41. The electronic compass of claim 39, wherein said processing circuit selects an approximating geometric pattern that constitutes a best fit to select data points corresponding to the sensed components taken over time.

42. The electronic compass of claim 39, wherein said processing circuit determines the magnitude of an error vector extending from the perimeter of the approximating geometric pattern to the most recent sensed components, and generates a heading signal representing the computed heading when the magnitude of the error vector does not exceed a predetermined threshold.

43. The electronic compass of claim 39, wherein said processing circuit iteratively selects an approximating geometric pattern by repeatedly comparing and changing the geometric pattern based on the sensed components taken over time.

44. The electronic compass of claim 35, wherein said magnetic sensor circuit senses three perpendicular components of the Earth'"'"'s magnetic field vector, and wherein said processing circuit selects a three-dimensional approximating geometric pattern derived from the three sensed components and computes a heading of the vehicle as a function of at least two of the sensed components while referencing the three-dimensional geometric pattern.

45. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing at least two perpendicular components of the Earth'"'"'s magnetic field vector and for generating output signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, determining a calibration point based on a number of reference data points derived from the sensed components, determining a noise threshold that varies as a function of the number of reference points used to compute the current calibration point, determining whether the sensed components exceed the noise threshold, computing a heading of the vehicle as a function of the at least two of the sensed components while referencing the calibration point when the sensed components do not exceed the noise threshold, and generating a heading signal representing the computed heading.

46. The electronic compass of claim 45, wherein said processing circuit determines the calibration point by selecting an approximating geometric pattern that defines the relative location of the calibration point.

47. The electronic compass of claim 46, wherein said processing circuit selects the approximating geometric pattern based on at least five reference data points.

48. The electronic compass of claim 46, wherein said magnetic sensor circuit senses three perpendicular components of the Earth'"'"'s magnetic field vector, and wherein said processing circuit selects a three-dimensional approximating geometric pattern derived from the three sensed components and computes a heading of the vehicle as a function of at least two of the sensed components while referencing the three-dimensional geometric pattern.

49. The electronic compass of claim 46, wherein said processing circuit selects an approximating geometric pattern that constitutes a best fit to the reference data points.

50. The electronic compass of claim 46, wherein said processing circuit determines the magnitude of an error vector extending from the perimeter of the approximating geometric pattern to the most recent sensed components, and generates a heading signal representing the computed heading when the magnitude of the error vector does not exceed a predetermined threshold.

51. The electronic compass of claim 46, wherein said processing circuit iteratively selects an approximating geometric pattern by repeatedly comparing and changing the geometric pattern based on the sensed components taken over time.

52. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing at least two perpendicular components of the Earth'"'"'s magnetic field vector and for generating output signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, determining an approximating geometric pattern based on a plurality of reference data points derived from the sensed components, determining a noise threshold that varies as a function of the extent to which the approximating geometric pattern fits the reference data points used to define the approximating geometric pattern, computing a heading of the vehicle as a function of the at least two of the sensed components while referencing the approximating geometric pattern when the sensed components do not exceed the noise threshold, and generating a heading signal representing the computed heading.

53. The electronic compass of claim 52, wherein said processing circuit selects the approximating geometric pattern based on at least five reference data points.

54. The electronic compass of claim 52, wherein said magnetic sensor circuit senses three perpendicular components of the Earth'"'"'s magnetic field vector, and wherein said processing circuit selects a three-dimensional approximating geometric pattern derived from the three sensed components and computes a heading of the vehicle as a function of at least two of the sensed components while referencing the three-dimensional geometric pattern.

55. The electronic compass of claim 52, wherein said processing circuit selects an approximating geometric pattern that constitutes a best fit to select data points corresponding to the sensed components taken over time.

56. The electronic compass of claim 52, wherein said processing circuit determines the magnitude of an error vector extending from the perimeter of the approximating geometric pattern to the most recent sensed components, and generates a heading signal representing the computed heading when the magnitude of the error vector does not exceed a predetermined threshold.

57. The electronic compass of claim 52, wherein said processing circuit iteratively selects the approximating geometric pattern by repeatedly comparing and changing the geometric pattern based on the sensed components taken over time.

58. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing at least two perpendicular components of the Earth'"'"'s magnetic field vector and for generating output signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, selecting a first approximating geometric pattern based on a first set of reference data points derived from the sensed components, computing a heading of the vehicle as a function of at least two of the sensed components while referencing the first approximating geometric pattern, generating a heading signal representing the computed heading, selecting a second approximating geometric pattern based on reference data points received after the first approximating geometric pattern is selected, utilizing the second approximating geometric pattern if the second approximating geometric pattern is significantly different from the first approximating geometric pattern, and reselecting the first approximating geometric pattern if the subsequently obtained reference data points better fit the first approximating geometric pattern.

59. The electronic compass of claim 58, wherein said processing circuit selects one of the first and second approximating geometric patterns based on at least five reference data points derived from the sensed components.

60. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing at least two perpendicular components of the Earth'"'"'s magnetic field vector and for generating output signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, deriving a first set of reference data points from the sensed components using at least one first threshold, selecting a first approximating geometric pattern based on the first set of reference data points, computing a heading of the vehicle as a function of at least two of the sensed components while referencing the first approximating geometric pattern, generating a heading signal representing the computed heading, deriving a second set of reference data points from the sensed components using at least one second threshold that is more stringent than the first threshold, selecting a second approximating geometric pattern based on the second set of reference data points, utilizing the second approximating geometric pattern if the second approximating geometric pattern is significantly different from the first approximating geometric pattern, and reselecting the first approximating geometric pattern if subsequently obtained reference data points better fit the first approximating geometric pattern.

61. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing at least two perpendicular components of the Earth'"'"'s magnetic field vector and for generating output signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, determining an approximating geometric pattern based on at least five reference data points derived from the sensed components, computing a heading of the vehicle as a function of the at least two of the sensed components while referencing the approximating geometric pattern, and generating a heading signal representing the computed heading.

62. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing at least two perpendicular components of the Earth'"'"'s magnetic field vector and for generating output signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, determining that the vehicle is moving when the sensed components exhibit a noise level exceeding a minimum noise threshold, computing a heading of the vehicle as a function of the at least two of the sensed components, and generating a heading signal representing the computed heading, wherein said processing circuit does not change the displayed heading when the vehicle is not moving.

63. The electronic compass of claim 62, wherein said processing circuit determines that the vehicle is moving when the noise level exceeds the minimum noise threshold for a predetermined time.

64. An electronic compass for a vehicle, comprising:

a magnetic sensor circuit for sensing at least two perpendicular components of the Earth'"'"'s magnetic field vector and for generating output signals representative of the sensed components; and

a processing circuit coupled to said magnetic sensor circuit for receiving the output signals, determining an approximating geometric pattern based on reference data points derived from the sensed components, computing an error metric representing the degree to which the approximating geometric pattern fits the reference data points, computing a heading of the vehicle as a function of the at least two of the sensed components while referencing the approximating geometric pattern, and generating a heading signal representing the computed heading.

65. The electronic compass of claim 64, wherein the approximating geometric pattern is determined by initially assuming an approximating geometric pattern and computing an error metric based on the initial assumption, changing the assumed approximating geometric pattern until the error metric is minimized, and then utilizing the changed approximating geometric pattern with the minimum error metric for determining vehicle heading.

66. The electronic compass of claim 64, wherein the computed error metric is used to establish a confidence level that is used to establish thresholds to which a raw data point is compared for determining whether the raw data point may be considered reference data point.