Method of automatic continuous calibration for an electronic compass

• US 20030023380A1
• Filed: 07/30/2001
• Published: 01/30/2003
• Est. Priority Date: 07/30/2001
• Status: Active Grant

• Current Assignee: Innovative Design Solutions, Inc. (LCI Industries)
• Original Assignee: Innovative Design Solutions, Inc. (LCI Industries)
• Inventors: Manfreda, John, Haley, Shawn, Woloszyk, Mark, Ford, Rob
• Granted Patent: US 6,651,003 B2
• Time in Patent Office: Days
• US Class Current: 701/224
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses

Abstract

An autocalibration method for use within an electronic compass in a vehicle is disclosed. The method includes steps of initializing variables and then retrieving sensor readings from at least two axis. The method then compares the compass tilt to a predetermined threshold. Next the method will determine if the sensor reading is a minimum or maximum for the current calibration cycle. Next the method will determine if the maximum value of the sensor readings is greater than the predetermined minimum spread. Then the method will calculate an offset value for each axis and calculate a sensor value for each axis. Then the method will calculate an azimuth value with the new sensor values and determine the heading using the azimuth.

Claims

1. An autocalibration method for use with an electronic compass in a vehicle, said method including the steps of:

initializing variables;

retrieving sensor readings from at least two axis;

updating calibration based on said sensor readings;

calculating a first azimuth with said sensor readings;

updating a first heading from said first azimuth; and

determining if a display needs said updated first heading transferred thereto.

2. The method of claim 1 wherein the step of updating calibration further includes the steps of:

comparing compass tilt to a predetermined threshold;

determining if said sensor readings are valid;

determining if said sensor reading is a minimum or maximum for the current calibration cycle;

determining if a spread of each axis is greater than a predetermined minimum spread;

calculating an offset value for each axis;

calculating a sensor value for each axis;

calculating a second azimuth with said sensor values;

determining a second heading using said second azimuth; and

determining if eight consecutive cardinal headings have been sensed.

3. The method of claim 2 further including the step of comparing a cycle of axis data with a predetermined value and updating a calibration counter based on said comparison of a cycle of data with said predetermined value and on a number of said cycle data processed.

4. The method of claim 3 further including the step of updating calibration values for the compass.

5. The method of claim 1 wherein the step of calculating a first azimuth further includes the step of adjusting said sensor readings with calibration values.

6. The method of claim 5 wherein said step of calculating a first azimuth includes calculating a third azimuth and adjusting said third azimuth by a declination angle.

7. The method of claim 6 wherein said step of calculating a first azimuth further includes filtering said first azimuth with said third azimuth value.

8. The method of claim 6 wherein said step of calculating a third azimuth calculates the Arctan of the axis readings.

9. An autocalibration method for use in an electronic compass in a vehicle, said method including the steps of:

initializing variables used to calibrate a heading;

retrieving sensor readings from at least two axis;

updating calibration and azimuth values with said sensor readings;

determining if said heading needs updating; and

determining if display needs said updated heading transferred thereto.

10. The method of claim 9 further including the step of determining if one calibration cycle has been completed.

11. The autocalibration method of claim 10 wherein said updating calibration step includes the step of comparing a tilt value with a maximum threshold.

12. The autocalibration method of claim 10 wherein said updating calibration values includes the steps of:

testing said sensor readings to validate as true sensor readings;

determining if an X-axis reading is a maximum value for a current calibration cycle of the compass;

determining if said X-axis reading is a minimum value for a current calibration cycle of the compass;

determining if a Y-axis reading is a maximum value for a current calibration cycle of the compass;

determining if said Y-axis reading is a minimum value for a current calibration cycle of the compass;

determining if said X-axis maximum value minus said X-axis minimum is greater than a predetermined minimum spread; and

determining if said Y-axis maximum minus said Y-axis minimum is greater than a predetermined minimum spread.

13. The autocalibration method of claim 12 further including the steps of:

calculating an offset value for the X-axis and Y-axis; and

adjusting said X-axis and Y-axis values with said offset value.

14. The autocalibration method of claim 13 further including the steps of:

calculating a second azimuth value from said adjusted sensor readings; and

determining a second heading from said second azimuth value.

15. The autocalibration method of claim 14 further including the steps of:

determining if eight consecutive cardinal headings have been sensed;

comparing a filtered set of axis calibration values to said set of current calibration cycle'"'"'s axis values;

updating a calibration counter based on said comparing of said axis values; and

updating said calibration axis values with said calibration counter.

16. The autocalibration method of claim 13 wherein said offsets are calculated with every new valid sensor reading and without any influence of past readings other than said current cycle.

17. The autocalibration method of claim 13 wherein said second azimuth is calculated with every new said offset and without any influence of past readings other than the current cycle.

18. The autocalibration method of claim 13 wherein offset values have the form

19. The autocalibration method of claim 9 further including the steps of:

calculating current calibration values;

calculating a first azimuth value from said sensor values;

adjusting an X-axis sensor reading by current X-offset and X-scale values; and

adjusting a Y-axis sensor reading by current Y-offset and Y-scale values.

20. The auto calibration method of claim 19 wherein scale has the form max−

min.

21. The auto calibration method of claim 19 wherein offset has the form

22. The autocalibration method of claim 19 further including the steps of:

calculating a third azimuth value from said adjusted sensor readings;

adjusting said third azimuth value by a predetermined declination angle; and

calculating a filtered first azimuth value by filtering with said third azimuth value.

23. The autocalibration method of claim 22 wherein said filtered first azimuth value has the form filtered first azimuth+(third azimuth−

filtered first azimuth)/K.

24. A calibration method for use with a compass, said method including the steps of:

calculating a first azimuth without any past data; and

determining if a full circle is traversed by the compass with said first azimuth.

25. The method of claim 24 further including the steps of factoring data from a current cycle of said full circle determination into a filtered calibration data set with varying influence depending on a counter value.

26. A method to access the reliability of a calibration for a compass, said method including the steps of:

comparing a cycle of axis data with a filtered calibration axis data; and

updating a calibration counter value based on said comparison of cycle data with filtered calibration data and on a number of said cycle data processed to a present time.

27. The method of claim 26 further including the step of adjusting said calibration counter value to modify the reliability of the calibration.

28. The method of claim 26 further including the step of incrementing said counter value to modify the reliability of the calibration.

29. The method of claim 26 further including the step of factoring said current cycle data into said filtered calibration data based on said calibration counter value, to filter a new cycle of data.