Calibration method for a relative heading sensor
First Claim
1. A method of calibrating a relative heading sensor in a system also having an absolute heading sensor, the method comprising the steps of:
- rotating said sensors through an angle of at least 360°
;
reading said absolute heading sensor at each of a plurality of points during said rotating step;
reading said relative heading sensor at each of said points;
finding a maximum absolute heading and a minimum absolute heading in at least a first direction;
calculating a difference between a first relative heading reading at a point corresponding to said maximum absolute heading and a second relative heading reading at a point corresponding to said minimum absolute heading;
dividing said differences by 180°
to obtain a first relative heading conversion constant; and
calibrating said relative heading sensor, using said first relative heading conversion constant with a third relative heading reading from said relative heading sensor to generate a calibrated relative heading.
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Abstract
The invention provides a direction sensor and a method of calibrating a direction sensor having a relative heading sensor and an absolute heading sensor. The method allows calibration of both the relative heading sensor and the absolute heading sensor at the same time, by taking advantage of the known angular relationship between maxima and minima on the measurement curve of the absolute heading sensor. Such maxima and minima are found by rotating the sensors through an angle of at least 360°, reading the absolute and relative heading sensor outputs at numerous points and comparing each successive output. The relative heading sensor output at the minimum is subtracted from that at the maximum, and the difference divided by the known angle to arrive at a conversion constant for the relative heading sensor. The center and radii of the measurement curve of the absolute heading sensor may be found by determining the maxima and minima of the curve in two perpendicular directions.
117 Citations
14 Claims
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1. A method of calibrating a relative heading sensor in a system also having an absolute heading sensor, the method comprising the steps of:
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rotating said sensors through an angle of at least 360°
;reading said absolute heading sensor at each of a plurality of points during said rotating step; reading said relative heading sensor at each of said points; finding a maximum absolute heading and a minimum absolute heading in at least a first direction; calculating a difference between a first relative heading reading at a point corresponding to said maximum absolute heading and a second relative heading reading at a point corresponding to said minimum absolute heading; dividing said differences by 180°
to obtain a first relative heading conversion constant; andcalibrating said relative heading sensor, using said first relative heading conversion constant with a third relative heading reading from said relative heading sensor to generate a calibrated relative heading. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of calibrating a direction sensor, said direction sensor having a relative heading sensor and a geomagnetic sensor, said geomagnetic sensor producing a first output signal proportional to the geomagnetic field in an X-direction and a second output signal proportional to the geomagnetic field in a Y-direction, said X and Y directions being perpendicular, the method comprising the steps of:
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rotating said sensors through an angle of at least 360°
;reading said geomagnetic sensor at each of a plurality of points about said angle; reading said relative heading sensor at each of said points; finding a first maximum and a first minimum heading in said first output signal; finding a second maximum and a second minimum heading in said second output signal; calculating a first difference between a first relative heading reading at a point corresponding to said first maximum and a second relative heading reading at a point corresponding to said first minimum; dividing said first difference by 180°
to obtain a first relative heading conversion constant;locating the center of a measurement curve of said geomagnetic sensor relative to a predetermined origin, said measurement curve being defined by said second output signal as a function of said first output signal when the geomagnetic sensor is rotated about 360°
, said center being at the point (X0, Y0) wherein
space="preserve" listing-type="equation">X.sub.0 =(X.sub.max +Y.sub.min)/2
space="preserve" listing-type="equation">Y.sub.0 =(Y.sub.max +Y.sub.min)/2and wherein X0 is the first output signal at the center, Y0 is the second output signal at the center, Xmax is the first maximum, Xmin is the first minimum, Ymax is second maximum and Ymin the second minimum; determining a first and a second radius of said measurement curve, said first and second radii being defined as
space="preserve" listing-type="equation">a=(X.sub.max -Y.sub.min)/2
space="preserve" listing-type="equation">b=(Y.sub.max -Y.sub.min)/2wherein a is the first radius and b is the second radius; calibrating said relative heading sensor, using said first relative heading conversion constant with a third relative heading reading from said relative heading sensor to generate a calibrated relative heading; and employing said center of said measurement curve and said first and second radii with said first and second output signals to generate a calibrated absolute heading. - View Dependent Claims (13, 14)
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Specification