Vehicle compass system with continuous automatic calibration

• US 6,964,108 B2
• Filed: 12/01/2004
• Issued: 11/15/2005
• Est. Priority Date: 05/27/1999
• Status: Expired due to Term

• 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, G. Bradley
• Application Number:
  US11/001,532
• Publication Number:
  US 20050091861A1
• Time in Patent Office: 349 Days
• Field of Search: 333/55.R, 333/56, 33357-359, 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 compass, comprising:

calculating a first averaged data point using a first predetermined number of data points;

calculating a second averaged data point using a second predetermined number of data points;

calculating a third averaged data point;

calculating deviation compensation data based on a combination of the first averaged data point, the second averaged data point, and the third averaged data point;

determining if a vehicle is moving a predetermined speed; and

obtaining data for at least one of the first averaged data point, the second averaged data point, and the third averaged data point based on the determination of vehicle speed.

2. The method of claim 1, further comprising displaying a heading based on data that has been received from the electronic compass and that has been compensated based on the deviation compensation data.

3. The method of claim 1, wherein calculating the first averaged data point comprises calculating the first averaged data point based on a predetermined number of consecutive points that meet a predetermined criteria.

4. The method of claim 1, further comprising using the combination of the averaged data points to calculate an x-axis offset and a y-axis offset.

5. The method of claim 1, wherein the first predetermined number of data points and the second predetermined number of data points are a same number.

6. The method of claim 1, wherein calculating deviation compensation based on a combination of the first averaged data point, the second averaged data point, the third averaged data point comprises;

determining that the first averaged data point, the second averaged data point, and the third averaged data point do not meet a predetermined criteria;

determining a combination of any two of the first, second, and third averaged data points and a fourth averaged data point that meet the predetermined criteria; and

calculating the offset using the combination of three averaged data points that meet the predetermined criteria.

7. The method of claim 6, wherein the predetermined criteria includes at least one of;

a. the data points are a minimum distance apart from each other;

b. three of the data points do not form a substantially obtuse triangle; and

c. three of the data points do not form a triangle that is too acute.