Vehicle compass system with continuous automatic calibration

• US 7,127,823 B2
• Filed: 11/10/2005
• Issued: 10/31/2006
• Est. Priority Date: 05/27/1999
• Status: Expired due to Fees

• 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): BENNETT, GEORGE B
• Application Number:
  US11/271,358
• Publication Number:
  US 20060075646A1
• Time in Patent Office: 355 Days
• Field of Search: 333/55.R, 33356-359, 333/61, 335/02, 702/85, 702 92- 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 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. A method for calibrating an electronic vehicular compass, comprising:

receiving electronic data from a sensor circuit in the vehicle, the sensor circuit configured to measure an effect of the earth'"'"'s magnetic field;

calculating a first smoothed data point based on data received from the sensor;

calculating a second smoothed data point based on data received from the sensor;

calculating a third smoothed data point based on data received from the sensor; and

calculating deviation compensation data based on the first smoothed data point, the second smoothed data point, and the third smoothed data point.

2. The method for calibrating an electronic compass of claim 1, wherein

calculating the first smoothed data point comprises calculating an average of a plurality of raw data points;

and

calculating the second smoothed data point comprises calculating an average of a plurality of raw data points.

3. The method for calibrating an electronic compass of claim 2, wherein calculating an average of a plurality of raw data points comprises equally weighting each of the raw data points used to calculate the first smoothed data point.

4. The method for calibrating an electronic compass of claim 1, further comprising

calculating a fourth smoothed data point;

and

calculating deviation compensation data based on the fourth smoothed data point.

5. The method for calibrating an electronic compass of claim 1, wherein calculating deviation compensation data comprises calculating new deviation compensation data and calculating the new deviation compensation data comprises calculating the new deviation compensation data based on old deviation compensation data.

6. The method for calibrating an electronic compass of claim 1, further comprising determining to use the second smoothed data point to calculate deviation compensation data based on a criteria related to a distance the second smoothed data point is from the first smoothed data point, the criteria comprising that the second smoothed data point is a minimum distance from the first smoothed data point.

7. The method for calibrating an electronic compass of claim 6, wherein the minimum distance is variable.

8. The method for calibrating an electronic compass of claim 6, wherein the third smoothed data point is obtained before the first smoothed data point.

9. The method for calibrating an electronic compass of claim 6, further comprising determining to use the third smoothed data point to calculate deviation compensation data based on a criteria related to a distance the third smoothed data point is from another smoothed data point, the criteria comprising that the third smoothed data point is a minimum distance from another smoothed data point.

10. The method for calibrating an electronic compass of claim 9, further comprising determining to use a fourth smoothed data point to calculate deviation compensation data based on a criteria related to a distance the fourth smoothed data point is from other smoothed data points, the criteria comprising that the fourth smoothed data point is a minimum distance from other smoothed data points.

11. The method for calibrating an electronic compass of claim 1, further comprising determining to use data to calculate deviation compensation data based on a determination that suggests that a noise level that interferes with data received from the sensor is low.

12. The method for calibrating an electronic compass of claim 1, further comprising displaying a heading based on a smoothed data point.

13. The method for calibrating an electronic compass of claim 1, further comprising displaying a heading based on at least one of the first smoothed data point, the second smoothed data point, and the third smoothed data point.

14. The method for calibrating an electronic compass of claim 1, further comprising displaying a heading based on each of the first smoothed data point, the second smoothed data point, and the third smoothed data point.

15. The method for calibrating an electronic compass of claim 1, further comprising determining a criteria related to movement of the vehicle, wherein data is excluded from being used to calculate deviation compensation data based on the determination of the criteria related to movement of the vehicle.

16. The method for calibrating an electronic compass of claim 1, wherein the deviation compensation data comprises a center point, the method further comprising

calculating a radius based on the first smoothed data point, the second smoothed data point, and the third smoothed data point;

calculating a first value based on a distance of a fourth smoothed data point to the center point;

calculating a threshold value based on the radius; and

comparing the first value to the threshold value.

17. The method for calibrating an electronic compass of claim 16, wherein the threshold value is a first threshold value and is less than the radius, the method further comprising

calculating a second threshold value based on the radius, the second threshold value being greater than the radius;

and

comparing the first value to the second threshold value.

18. The method for calibrating an electronic compass of claim 16, further comprising

storing a plurality of smoothed data points to be used in calculating new deviation compensation data;

and

not using the stored plurality of smoothed data points to calculate new deviation compensation data based on the comparison of the first value to the threshold value.

19. The method for calibrating an electronic compass of claim 18, wherein comparing the first value to the threshold value comprises at least one of

(1) determining whether the first value is greater than a threshold that is greater than the radius;

and

(2) determining whether the first value is less than a threshold that is less than the radius.

20. The method for calibrating an electronic compass of claim 16, wherein comparing the first value to the threshold value comprises at least (1) determining whether the first value is greater than a first threshold that is greater than the radius, the first threshold calculated based on the radius;

and (2) determining whether the first value is less than a second threshold that is less than the radius, the second threshold calculated based on the radius.

21. The method for calibrating an electronic compass of claim 16, further comprising determining not to use the fourth smoothed data point to calculate new deviation compensation data based on the comparison of the first value to the threshold value.

22. The method for calibrating an electronic compass of claim 1, wherein calculating the third smoothed data point comprises calculating the third smoothed data point based on data that is received from the sensor substantially sequentially.

23. The method for calibrating an electronic compass of claim 22, wherein calculating the third smoothed data point comprises calculating the third smoothed data point based on data that is received from the sensor sequentially.

24. The method for calibrating an electronic compass of claim 22, wherein data received from the sensor when noise is present is excluded from use in calculating the third smoothed data point.

25. A method for calibrating an electronic vehicular compass, comprising:

receiving electronic data from a sensor circuit, in the vehicle, that is configured to measure an effect of the earth'"'"'s magnetic field;

excluding data received from the sensor for use in calculating new deviation compensation data based on a criteria related to a presence of noise;

calculating a first smoothed data point;

determining to use the first smoothed data point to calculate new deviation compensation data;

calculating a second smoothed data point;

determining to use the second smoothed data point to calculate new deviation compensation data, determining to use the second smoothed datapoint to calculate new deviation compensation data comprising determining that the second smoothed data point is a minimum distance from another smoothed data point to be used to calculate new deviation compensation data;

calculating a third smoothed data point;

determining to use the third smoothed data point to calculate new deviation compensation data, determining to use the third smoothed data point to calculate new deviation compensation data comprising determining that the third smoothed data point is a minimum distance from another smoothed data point to be used to calculate new deviation compensation data; and

calculating new deviation compensation data based on old deviation compensation data, the first smoothed data point, the second smoothed data point, and the third smoothed data point.

26. The method for calibrating an electronic compass of claim 25, further comprising displaying a heading based on a smoothed data point.

27. The method for calibrating an electronic compass of claim 25, further comprising determining a criteria related to movement of the vehicle, wherein data is excluded from being used to calculate deviation compensation data based on the determination of the criteria related to movement of the vehicle.

28. 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 and configured to process the electrical signals generated by the sensor to provide data points representative of the vehicle'"'"'s current heading, the processing circuit being configured to calculate smoothed data points, to identify three smoothed data points as candidate data points if the smoothed data points meet predetermined spacing criteria, and to calibrate the system using the three candidate data points.

29. The vehicle compass system of claim 28, wherein the predetermined spacing criteria comprises a minimum distance criteria.

30. The vehicle compass system of claim 29, wherein the processing circuit is further configured to identify a fourth smoothed data point, and to determine whether the fourth smoothed data point is a minimum distance from at least two of the first smoothed data point, the second smoothed data point, and the third smoothed data point.

31. The vehicle compass system of claim 28, wherein the processing circuit is further configured to calculate vehicle heading information based on a smoothed data point.

32. The vehicle compass system of claim 28, wherein the processing circuit is further configured to collect data for calibrating the system based on whether the vehicle is moving.

33. The vehicle compass system of claim 28, wherein a strictness of a criteria used to select smoothed data points to use to calibrate the system is variable.

34. The vehicle compass system of claim 28, further comprising a power supply circuit configured to receive a vehicle electrical voltage and to provide an operating voltage to the sensor and the processing circuit of the vehicle compass system.

35. A method for calibrating an electronic compass for a vehicle, comprising:

storing old deviation compensation data;

receiving data from a magnetic field sensor that is located in the vehicle;

calculating a first smoothed data point based on the data received from the magnetic field sensor;

calculating a second smoothed data point based on the data received from the magnetic field sensor;

calculating a third smoothed data point based on the data received from the magnetic field sensor;

determining new deviation compensation data based on the first smoothed data point, the second smoothed data point, the third smoothed data point, and the old deviation compensation data; and

displaying a heading on a display located in the vehicle based on the new deviation compensation data.

36. The method of claim 35, wherein determining new deviation compensation data based on the first smoothed data point, the second smoothed data point, the third smoothed data point, and the old deviation compensation data comprises,

calculating intermediate deviation compensation data based on the first smoothed data point, the second smoothed data point, and the third smoothed data point;

and

calculating new deviation compensation data based on the intermediate deviation compensation data and a plurality of old deviation compensation data, the intermediate deviation compensation data being more heavily weighted than any of the plurality of old deviation compensation data.

37. The method of claim 35, wherein displaying a heading on a display located in the vehicle based on the new deviation compensation data comprises displaying a heading on the display based on the new deviation compensation and a fourth smoothed data point.

38. The method of claim 36, further comprising displaying a heading on the display based on the first smoothed data point and the old deviation compensation data.