Calibration method for a relative heading sensor
First Claim
1. A direction sensor for a vehicle navigation system, said direction sensor comprising:
- a relative heading sensor for producing a relative heading signal;
an absolute heading sensor for producing a first absolute heading signal;
means for determining a first maximum and a first minimum in said first absolute heading signal in a first direction as said vehicle is rotated through an angle of at least 360°
;
means for calculating a first difference between said relative heading signal at a first point corresponding to said first maximum and said relative heading signal at a second point corresponding to said first minimum;
means for dividing said first difference by 180°
to obtain a first relative heading conversion constant; and
means for calibrating said relative heading sensor by generating a calibrated relative heading using said first relative heading conversion constant and said relative heading signal at a third point.
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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.
133 Citations
8 Claims
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1. A direction sensor for a vehicle navigation system, said direction sensor comprising:
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a relative heading sensor for producing a relative heading signal; an absolute heading sensor for producing a first absolute heading signal; means for determining a first maximum and a first minimum in said first absolute heading signal in a first direction as said vehicle is rotated through an angle of at least 360°
;means for calculating a first difference between said relative heading signal at a first point corresponding to said first maximum and said relative heading signal at a second point corresponding to said first minimum; means for dividing said first difference by 180°
to obtain a first relative heading conversion constant; andmeans for calibrating said relative heading sensor by generating a calibrated relative heading using said first relative heading conversion constant and said relative heading signal at a third point. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification