Method for selecting calibration data for an auto-calibrating compass

• US 5,297,063 A
• Filed: 12/27/1991
• Issued: 03/22/1994
• Est. Priority Date: 12/27/1991
• Status: Expired due to Fees

• Current Assignee: Chrysler Corporation (Stellantis NV)
• Original Assignee: Chrysler Corporation (Stellantis NV)
• Inventors: Cage, Russell E.
• Primary Examiner(s): Harvey, Jack B.
• Assistant Examiner(s): Choi, Jae H.
• Application Number:
  US07/815,264
• Time in Patent Office: 816 Days
• Field of Search: 364/559, 364/571.01, 364/571.02, 364/571.03, 364/571.04, 364/571.05, 364/571.06, 364/571.07, 364/571.08, 73/1 E, 33/356
• US Class Current: 702/92
• CPC Class Codes: G01C 17/38 Testing, calibrating, or compensating of compasses
• CPC Class Codes: G01D 18/004 Continuous recalibration
• CPC Class Codes: G01D 3/02 with provision for altering or correcting the law of variation

Abstract

A method for selecting calibration data which uses mean square error to minimize variations in the calculated origins of the earth'"'"'s magnetic field vector. A microcomputer having a memory calculates and stores the origin of the earth'"'"'s magnetic field vector from the last three headings or data points. The x and y coordinates of the origins are summed with all the previous x and y coordinates and the mean square errors of the x and y coordinates are calculated. A figure of merit for the mean square errors is calculated. An adjusted origin is determined and stored by weighing the newly calculated origin by a figure of merit and adding it to the previous origin. Provision is made for reinitializing all quantities to zero when the sum of the mean square errors exceeds a predetermined maximum.

Claims

1. A method for determining heading from an origin of the earth'"'"'s magnetic field vector in an auto-calibrating electronic compass comprising the steps of:

(a) orienting first and second sense coils of a flux-gate sensor perpendicular to each other in the earth'"'"'s magnetic field;

(b) saturating said sense coils with a drive signal;

(c) measuring an induced voltage in said sense coils induced by said magnetic field;

(d) measuring and storing, in a memory unit connected to a processing unit, at least three heading data points related to said induced voltage, each said heading data point having an x and a y coordinate, each said heading data point being measured and stored after the orientation of the flux-gate sensor with respect to the earth'"'"'s magnetic field vector, as measured at the flux-gate sensor, has changed;

(e) calculating and storing x and y coordinates for an earth'"'"'s magnetic field circle center;

(f) adding said center coordinates to a sum of previous center coordinates;

(g) calculating mean square errors of said center and said previous center coordinates;

(h) calculating a figure of merit associated with the accuracy of said center coordinates;

(i) calculating and storing x and y coordinates for a new center for said earth'"'"'s magnetic field circle by adding to one of said previous center coordinate, said center coordinates calculated in step (b) as weighted by said figure of merit;

(j) subtracting said new center coordinates from said stored heading data points to yield compensated heading data points having a compensated y coordinate and a compensated x coordinate;

(k) dividing the compensated y coordinate by the compensated x coordinate to obtain a quotient, and calculating the arctangent of said quotient; and

(l) using said calculated arctangent of said quotient to obtain a new vehicle heading for conveying information regarding true heading to a display unit.

2. The method of claim 1 further comprising:

(k) reinitializing said center coordinates and said sum of said previous center coordinates when a sum of previous mean square errors exceeds a predetermined maximum.

3. The method of claim 2 wherein said predetermined maximum is proportional to the square of the magnitude of the earth'"'"'s magnetic field as measured at said flux-gate sensor.

4. The method of claim 1, wherein said figure of merit is based on the number of times, N, that said center coordinates have been calculated.