Electronic flux gate compass calibration technique
First Claim
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1. A method for calibrating an electronic flux gate compass having at least a first output Xm representing magnetic field intensity in a first direction and a second output Ym representing magnetic field intensity in a second, orthogonal direction, comprising:
- (a) rotating said compass 360 degrees while said compass is maintained within a predetermined area defined by said first and said second orthogonal directions;
(b) during step (a), reading the maximum value of said first output Xmax, the minimum value of said first output Xmin, the maximum value of said second output Ymax, and the minimum value of said second output Ymin ;
(c) computing offset values Xoff and Yoff, as follows;
space="preserve" listing-type="equation">X.sub.off =(X.sub.max +X.sub.min)/2
space="preserve" listing-type="equation">Y.sub.off =(X.sub.max +Y.sub.min)/2;
(d) thereafter periodically reading said first output and said second output while said compass is moved;
(e) if;
abs(Xx -Xmax)-K1 and abs(Ym -Yoff)-K2, thenset Xmax =Xmax +C * (Xm -Xmax), orabs (Xm -Xmin)-K1 and abs(Ym -Yoff)-K2, thenset Xmin =Xmin +C * (Xm -Xmin), orabs(Ym -Ymax)-K2 and abs(Xm -Xoff)-K1, thenset Ymax =Ymax +C * (Ym -Ymax), orabs(Ym -Ymin)-K2 and abs(Xm -Xoff)-K1, thenset Ymin =Ymin +C * (Ym -Ymin),where K1, K2, and C are predetermined constants; and
(f) if and when the compass has been moved through a net 360 degrees, compute new Xoff and Yoff values in accordance with step (c).
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Abstract
An electronic flux gate compass calibration method and apparatus. An electronic flux gate compass mounted on a terrestrial vehicle is first rotated 360 degrees by driving the vehicle in a circle to determine four reference points where the locus of points representing the orthogonal outputs of the compass crosses over the X and Y axes of a reference Cartesian coordinate system. These four reference points are employed to calibrate the orthogonal outputs of the compass and compute a calibrated compass heading. Thereafter, as the vehicle moves from place to place, the output of the compass is monitored. If the output is within a predetermined region around one of the reference points, the reference point is modified to be closer to that output point. When the vehicle has moved through a closed loop, i.e., rotated a net 360 degrees, the compass is recalibrated.
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Citations
25 Claims
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1. A method for calibrating an electronic flux gate compass having at least a first output Xm representing magnetic field intensity in a first direction and a second output Ym representing magnetic field intensity in a second, orthogonal direction, comprising:
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(a) rotating said compass 360 degrees while said compass is maintained within a predetermined area defined by said first and said second orthogonal directions; (b) during step (a), reading the maximum value of said first output Xmax, the minimum value of said first output Xmin, the maximum value of said second output Ymax, and the minimum value of said second output Ymin ; (c) computing offset values Xoff and Yoff, as follows;
space="preserve" listing-type="equation">X.sub.off =(X.sub.max +X.sub.min)/2
space="preserve" listing-type="equation">Y.sub.off =(X.sub.max +Y.sub.min)/2;(d) thereafter periodically reading said first output and said second output while said compass is moved; (e) if; abs(Xx -Xmax)-K1 and abs(Ym -Yoff)-K2, then set Xmax =Xmax +C * (Xm -Xmax), or abs (Xm -Xmin)-K1 and abs(Ym -Yoff)-K2, then set Xmin =Xmin +C * (Xm -Xmin), or abs(Ym -Ymax)-K2 and abs(Xm -Xoff)-K1, then set Ymax =Ymax +C * (Ym -Ymax), or abs(Ym -Ymin)-K2 and abs(Xm -Xoff)-K1, then set Ymin =Ymin +C * (Ym -Ymin), where K1, K2, and C are predetermined constants; and (f) if and when the compass has been moved through a net 360 degrees, compute new Xoff and Yoff values in accordance with step (c). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. An apparatus for calibrating an electronic flux gate compass having at least a first output Xm representing magnetic field intensity in a first direction and a second output Ym representing magnetic field intensity in a second, orthogonal direction, said apparatus comprising:
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(a) rotating means for rotating said compass 260 degrees while said compass is maintained within a predetermined area defined by said first and said second orthogonal directions; (b) means for reading the maximum value of said first output Xmax, the minimum value of said first output Xmin, the maximum value of said second output Ymax, and the minimum value of said second output Ymin while said compass is being rotated by said rotating means; (c) offset computing means for computing offset values Xoff and Yoff, as follows;
space="preserve" listing-type="equation">X.sub.off =(X.sub.max +X.sub.min)/2
space="preserve" listing-type="equation">Y.sub.off =(Y.sub.max +Y.sub.min)/2;(d) means for periodically reading said first output and said second output while said compass is moved; (e) means for performing the computations;
ifabs(Xm -Xmax)<
K1 and abs(Ym -Yoff)<
K2, thenset Xmax =Xmax +C * (Xm -Xmax), or abs(Xm -Xmin)<
K1 and abs(Ym -Yoff)<
K2, thenset Xmin =Xmin +C * (Xm -Xmin), or abs(Ym -Ymax)<
K2 and abs(Xm -Xoff)<
K1, thenset Ymax =Ymax +C * (Ym -Ymax), or abs(Ym -Ymin)<
K2 and abs(Xm -Xoff)<
K1, thenset Ymin =Ymin +C * (Ym -Ymin), where K1, K2, and C are predetermined constants; and (f) means for causing said offset computing means to recompute Xoff and Yoff if and when the compass has been moved through a net 360 degrees. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25)
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Specification
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Current AssigneeGarmin AT, Inc. (Garmin Limited)
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Original AssigneeII Morrow, Inc.
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InventorsNguyen, Duc C.
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Primary Examiner(s)RAEVIS, ROBERT R
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Application NumberUS07/604,220Time in Patent Office757 DaysField of Search73/1 E, 33/356, 33/357, 364/571.01, 364/571.02, 364/571.04, 364/571.05, 364/571.06, 364/559US Class Current73/1.76CPC Class CodesG01C 17/38 Testing, calibrating, or co...
