Method and apparatus for automatic calibration of magnetic compass
First Claim
1. Apparatus for calibrating the distortions in the readings of a magnetic compass having a plurality of windings in a two dimensional plane and mounted in a vehicle comprising:
- first means coupled to the compass windings for obtaining the outputs from each of the windings as a function of time by weighting and combining the outputs from each of the windings at a first time and for a predetermined number of the next previous times to said first time to obtain a time filtered output for each of the windings;
second means coupled to said first means for receiving the time filtered outputs and for obtaining maximum and minimum filtered outputs for each of the windings as the vehicle is turned through a circle of 360°
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third means coupled to said second means for computing biases from the maximum and minimum filtered outputs equal to the average of the maximum and minimum filtered outputs from each winding;
fourth means coupled to said third means for applying said biases to said maximum and minimum outputs to obtain a series of calibration parameters;
fifth means coupled to said first means and said fourth means for applying said parameters to said time filtered outputs to convert said time filtered outputs from said first means to two winding outputs, said two windings being orthogonally related to one another;
sixth means for obtaining the calibrated compass heading from said two winding outputs.
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Accused Products
Abstract
A three winding induction compass mounted in a host vehicle has each winding output coupled to an analog to digital converter. Each winding output is weighted and accumulated by a push down stack circuit to obtain a time filtered output and the maximum and minimum values of each filtered output are determined and stored as the vehicle is turned in a 360° circle. The distortions due to the permanent and induced magnetism of the host vehicle and due to winding imbalance between the three windings and misorientation of the three windings are obtained from the maximum and minimum values to obtain calibration parameters. The calibration parameters for the windings are applied to the outputs of the three windings to obtain an equivalent two winding output which is normalized for determining the corrected compass heading.
103 Citations
24 Claims
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1. Apparatus for calibrating the distortions in the readings of a magnetic compass having a plurality of windings in a two dimensional plane and mounted in a vehicle comprising:
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first means coupled to the compass windings for obtaining the outputs from each of the windings as a function of time by weighting and combining the outputs from each of the windings at a first time and for a predetermined number of the next previous times to said first time to obtain a time filtered output for each of the windings; second means coupled to said first means for receiving the time filtered outputs and for obtaining maximum and minimum filtered outputs for each of the windings as the vehicle is turned through a circle of 360°
;third means coupled to said second means for computing biases from the maximum and minimum filtered outputs equal to the average of the maximum and minimum filtered outputs from each winding; fourth means coupled to said third means for applying said biases to said maximum and minimum outputs to obtain a series of calibration parameters; fifth means coupled to said first means and said fourth means for applying said parameters to said time filtered outputs to convert said time filtered outputs from said first means to two winding outputs, said two windings being orthogonally related to one another; sixth means for obtaining the calibrated compass heading from said two winding outputs. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. Apparatus for calibrating the distortions in the readings of a magnetic compass having a plurality of separated vector outputs having a common origin and mounted in a vehicle comprising:
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first means coupled to the compass for providing output terminals corresponding to each of said vector outputs; second means coupled to said first means terminals for calibrating the compass vector outputs for distortions due to the permanent and induced magnetism of the vehicle and providing first distortion correction signals; third means coupled to said first means terminals for calibrating the gain imbalance and separation misorientation between the vector outputs and providing second distortion correction signals; fourth means coupled to said second and third means for receiving said first and second distortion correction signals and for providing a calibrated compass heading. - View Dependent Claims (15, 16)
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17. A method for calibrating the distortions in the readings of a magnetic compass having a plurality of windings in a two dimensional plane and mounted in a vehicle comprising the steps of:
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first step of obtaining the outputs from each of the windings as a function of time by weighting and combining the outputs from each of the windings at a first time and for a predetermined number of the next previous times to said first time to obtain a time filtered output for each of the windings; second step of receiving the time filtered outputs and for obtaining maximum and minimum filtered outputs for each of the windings as the vehicle is turned through a circle of 360°
;third step of determining biases from the maximum and minimum filtered outputs equal to the average of the maximum and minimum filtered outputs from each winding; fourth step of applying said biases to said maximum and minimum outputs to obtain a series of calibration parameters; fifth step of applying said parameters to said time filtered outputs to convert said time filtered outputs from said first means to two winding outputs, said two windings being orthogonally related to one another; sixth step of obtaining the calibrated compass heading from said two winding outputs. - View Dependent Claims (18, 19, 20, 21)
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22. A method for calibrating the distortions in the readings of a magnetic compass having a plurality of separated vector outputs having a common origin and mounted in a vehicle comprising the steps of:
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first step of calibrating the compass vector outputs for distortions due to the permanent and induced magnetism of the vehicle and providing first distortion correction signals; second step of calibrating the gain imbalance and separation misorientation between the vector outputs and providing second distortion correction signals; third step of receiving said first and second distortion correction signals and for providing a calibrated compass heading. - View Dependent Claims (23, 24)
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Specification