Motion Tracking with Coupled Magnetometers and Dynamic IMU Measurement Fusion in Nonuniform Magnetic Fields

This paper presents a method of motion tracking of highly dynamic multi-link systems with Inertial Measurement Units (IMU) embedded with magnetometers in spaces with nonuniform magnetic fields. As IMUs may accumulate error due to drift, magnetometers are used to correct orientation estimation. While magnetic distortion is typically compensated for at a point with magnetic field uniformity and assumed constant through spaces, this method introduces real-time calibration using two oppositely facing triaxial magnetometers and a triaxial accelerometer and gyroscope. Using the described array of magnetometers, local hard iron distortion can be measured at any position. Along with the inconsistent distortion throughout a nonuniform space, the measured direction of magnetic north may also change. To compensate for the inconsistency, a sensor model using the last measured magnetic north direction as the heading is used, rather than assuming a constant magnetic north direction like conventional methods. The proposed sensor suite and model reduces the error by half an order of magnitude less than conventional magnetometer usage. With the proposed method, drift is corrected for, even in nonuniform magnetic fields.