Vehicle compass compensation

• US 7,331,115 B2
• Filed: 07/08/2005
• Issued: 02/19/2008
• Est. Priority Date: 04/08/1999
• Status: Expired due to Fees

• Current Assignee: Donnelly Corporation (Magna International Incorporated)
• Original Assignee: Donnelly Corporation (Magna International Incorporated)
• Inventors: DeVette, Gregory H, Blank, Rodney K, Schierbeek, Kenneth L, Hoekstra, Eric J, Schofield, Kenneth, Veiseh, Merdad
• Primary Examiner(s): Bennett; G. Bradley
• Assistant Examiner(s): REIS, TRAVIS M
• Application Number:
  US11/177,552
• Publication Number:
  US 20050262714A1
• Time in Patent Office: 956 Days
• Field of Search: 335/02, 333/56, 333/57, 333/58, 333/59, 333/55.R
• 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 calibration method for calibrating a compass for use on a vehicle, said method comprising:

sampling data points of a magnetic field with a magnetic sensor;

determining coordinates for the sampled data points relative to an origin of a coordinate system associated with the vehicle and identifying coordinates of a peak of the Earth magnetic field from the coordinates of the sampled data points;

assuming an assumed value of the Earth magnetic field magnitude based on the surface of the Earth where said sampling of the data points is occurring;

estimating an origin of an Earth magnetic field from the assumed value of the Earth magnetic field magnitude and the coordinates of the peak of the Earth magnetic field;

adjusting the magnetic sensor by applying magnetic biasing to said magnetic sensor based on said estimating in order to offset the estimated origin of the Earth magnetic field to the coordinate system associated with the vehicles; and

after said adjusting, displaying an output of the compass and determining coordinates for additional data points wherein an output of the compass may be displayed after identifying one peak of the Earth magnetic field.

2. The calibration method of claim 1 wherein said determining coordinates for additional data points comprises:

sampling a pair of data points that are substantially oppositely positioned relative to one axis of said coordinate system associated with the vehicle;

averaging the substantially opposite values of said pair of data points to determine deviation from the one axis of the coordinate system associated with the vehicles; and

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

3. The calibration method of claim 2 further comprising validating said deviation by comparing said deviation with another value determined by a different technique.

4. The calibration method of claim 3 including determining coordinates for additional data points if said deviation is not valid.

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

adjusting a magnetic sensor by applying a magnetic biasing to said magnetic sensor in order to offset an estimated origin of the Earth magnetic field to a coordinate system associated with the vehicle;

sampling data points with said magnetic sensor and selecting from the sampled data points a pair of data points, said pair of data points selected as being positioned on a common side relative to a first axis of a coordinate system associated with the vehicle and substantially equally spaced from said first axis;

said pair of data points further selected as being positioned on opposite sides relative to a different second axis of the coordinate system and substantially equally spaced from said second axis;

determining the distances of said pair of data points from said second axis and averaging the distances of said pair of data points from said second axis to determine deviation from a zero value of the coordinate system associated with the vehicle; and

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

6. The calibration method of claim 5 further comprising validating said deviation by comparing said deviation with another value determined by a different technique.

7. The calibration method of claim 6 including sampling additional data points if said deviation is not valid.

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

adjusting a magnetic sensor by applying a magnetic biasing to said magnetic sensor in order to offset an origin of the Earth magnetic field to a coordinate system associated with the vehicle;

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

identifying a change in magnetic signature from at least one of said sensor and said offset value including determining a particular change in relationship between collected data points and said offset value and confirming the change in magnetic signature by determining the particular change in relationship for a certain number of collected data points including ensuring that the certain number of collected data points are collected over a plurality of vehicle ignition cycles, wherein said change in magnetic signature occurs from at least one chosen from (i) body work on the vehicle, (ii) a magnetic device mounted to the vehicle, (iii) a sunroof installed on the vehicle, and (iv) change in the vehicle'"'"'s surrounding; and

repeating said adjusting said magnetic sensor in response to identifying a change in magnetic signature.

9. The calibration method of claim 8 wherein a change in magnetic signature is also identified from said sensor reaching a limit of operation.

10. The calibration method of claim 9 wherein a change in magnetic signature is identified from an abnormal relation between collected data points and said offset.

11. The calibration method of claim 8 wherein a change in magnetic signature is identified from an abnormal relation between collected data points and said offset.

12. The calibration method of claim 11 wherein said abnormal relation comprises said offset falling outside of opposite peak values of data points.