Electronic compass and compensation of large magnetic errors for operation over all orientations
First Claim
1. A method of compensating an electronic compass to obtain accurate azimuth data for any orientation of the electronic compass despite the presence of perturbing magnetic effects, the method comprising:
- obtaining a measured magnetic field vector HMEAS representing magnetic field strength along three axes and a measured gravity vector GMEAS representing gravitational field strength along the same three axes;
using a matrix compensation coefficient LE and a vector compensation coefficient HPE to correct measured magnetic field data by applying a formula of the form Ĥ
EARTH≡
LE·
HMEAS−
HPE, where Ĥ
EARTH is the compensated value for the Earth'"'"'s true magnetic field; and
calculating the azimuth data as a function of the corrected magnetic field data.
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Accused Products
Abstract
A three-axis algebraic model is used to numerically compensate for magnetic errors in measured magnetic field values in an electronic compass for any orientation of the compass. This model is based on physical principles and uses a linear algebra approach that facilitates computation of the parameters needed for compensation. During a calibration procedure of the electronic compass, magnetic and gravity fields are measured in three axes at each of a variety of combinations of orientations and azimuths. This set of measured magnetic and gravity fields is used to calculate a matrix compensation coefficient and a vector compensation coefficient using a system of equations. These compensation coefficients are stored and then used during normal operations of the electronic compass to correct all subsequently measured magnetometer data to obtain corrected values for the Earth'"'"'s magnetic field, from which the correct azimuth can be calculated.
43 Citations
27 Claims
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1. A method of compensating an electronic compass to obtain accurate azimuth data for any orientation of the electronic compass despite the presence of perturbing magnetic effects, the method comprising:
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obtaining a measured magnetic field vector HMEAS representing magnetic field strength along three axes and a measured gravity vector GMEAS representing gravitational field strength along the same three axes;
using a matrix compensation coefficient LE and a vector compensation coefficient HPE to correct measured magnetic field data by applying a formula of the form Ĥ
EARTH≡
LE·
HMEAS−
HPE, where Ĥ
EARTH is the compensated value for the Earth'"'"'s true magnetic field; and
calculating the azimuth data as a function of the corrected magnetic field data. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of compensating an electronic compass to obtain accurate azimuth data for any orientation of the electronic compass despite the presence of perturbing magnetic effects, the method comprising:
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obtaining, for each of a plurality of combinations of orientations and azimuths, a measured magnetic field vector HMEAS representing magnetic field strength along three axes and a measured gravity vector GMEAS representing gravitational field strength along three axes;
calculating, as a function of the plurality of measured magnetic field vectors HMEAS and the plurality of measured gravity vectors GMEAS, a matrix compensation coefficient LE and a vector compensation coefficient HPE by solving a system of equations;
storing a plurality of component values of the matrix compensation coefficient LE and of the vector compensation coefficient HPE in a memory associated with the electronic compass;
subsequently retrieving the plurality of component values of the matrix compensation coefficient LE and of the vector compensation coefficient HPE from the memory;
obtaining a measured magnetic field vector HMEAS representing magnetic field strength along three axes and a measured gravity vector GMEAS representing gravitational field strength along three axes;
using the matrix compensation coefficient LE and the vector compensation coefficient HPE to correct measured magnetic field data by applying a formula of the form Ĥ
EARTH≡
LE·
HMEAS−
HPE, where Ĥ
EARTH is the compensated value for the Earth'"'"'s true magnetic field; and
calculating the azimuth data as a function of the corrected magnetic field data. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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12. An electronic compass arrangement, comprising:
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a three-axis magnetometer, configured to obtain a measured magnetic field vector HMEAS representing magnetic field strength along three axes;
a three-axis gravity sensor arrangement, configured to obtain a measured gravity vector GMEAS representing gravitational field strength along three axes;
a microprocessor arrangement, communicatively coupled to the three-axis magnetometer and to the three-axis gravity sensor arrangement and configured to use a matrix compensation coefficient LE and a vector compensation coefficient HPE to correct measured magnetic field data by applying a formula of the form Ĥ
EARTH·
LE·
HMEAS−
HPE, where Ĥ
EARTH is the compensated value for the Earth'"'"'s true magnetic field, andcalculate the azimuth data as a function of the corrected magnetic field data.;
and a memory, communicatively coupled to the microprocessor arrangement and configured to store the matrix compensation coefficient LE and the vector compensation coefficient HPE.
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20. A microprocessor-readable medium having microprocessor-executable instructions stored thereon, the microprocessor-executable instructions causing a microprocessor to, upon execution of the microprocessor-executable instructions:
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obtain a measured magnetic field vector HMEAS representing magnetic field strength along three axes and a measured gravity vector GMEAS representing gravitational field strength along three axes;
use a matrix compensation coefficient LE and a vector compensation coefficient HPE to correct measured magnetic field data by applying a formula of the form Ĥ
EARTH≡
LE·
HMEAS−
HPE, where Ĥ
EARTH is the compensated value for the Earth'"'"'s true magnetic field; and
calculate the azimuth data as a function of the corrected magnetic field data. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27)
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Specification