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Method and apparatus for data fusion of a three-axis magnetometer and three axis accelerometer

  • US 9,915,550 B2
  • Filed: 08/01/2013
  • Issued: 03/13/2018
  • Est. Priority Date: 08/02/2012
  • Status: Active Grant
First Claim
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1. A computer-implemented method of fusing data from a three-axis magnetometer and a three-axis accelerometer to provide a magnetic heading of a device, the method comprising:

  • receiving, as input, unprocessed magnetic field measurements from the magnetometer associated with the device and unprocessed acceleration measurements from the accelerometer associated with the device;

    filtering the unprocessed magnetic field measurements to remove outlying data points and noise and obtaining filtered magnetic field data;

    applying a first Kalman filter to the filtered magnetic field data to generate first soft iron and hard iron matrices, wherein the first Kalman filter is based on the principle that the magnitude of local Earth'"'"'s magnetic field vector is constant;

    applying a second Kalman filter to the filtered magnetic field data to generate a coupled soft iron/misalignment correction matrix, wherein the second Kalman filter is based on the principle that an angle between the local Earth'"'"'s magnetic field vector and the gravitational acceleration vector is constant;

    multiplying the coupled soft iron/misalignment correction matrix by the first soft iron matrix to generate a soft-iron correction matrix;

    filtering the unprocessed acceleration measurements to remove outlying data points and noise and obtaining filtered acceleration measurements;

    correcting the filtered acceleration measurements as a function of one or more error sources and obtaining corrected acceleration measurements;

    correcting the filtered magnetic field data for hard-iron and soft-iron distortions and obtaining corrected magnetic field measurements;

    computing quasi-static roll and pitch angles of the device as a function of the corrected acceleration measurements;

    forming a transformation matrix from a body frame to a level coordinate frame as a function of the computed quasi-static roll and pitch angles;

    transforming the corrected magnetic field measurements from the body frame to the level frame and generating a horizontal magnetic field vector;

    determining a magnetic heading of the device as a function of the generated horizontal magnetic field vector and the generated soft-iron correction matrix;

    providing, to an application operating on the device, the magnetic heading of the device;

    deriving, by the application, angular rates of the device; and

    performing auto-calibration of at least one of;

    the magnetometer and the accelerometer, based on the corrected acceleration measurements and the derived angular rates.

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