Gyro-compensated real-timeEKF magnetic field calibration method

Magnetic field information plays an important role in determining the heading angle and attitude information, but it is highly susceptible to interference from surrounding ferromagnetic materials. The traditional ellipsoid fitting algorithm for magnetic field calibration requires high quality magnetometer data, which is not customer-friendly. This paper implemented a more convenient and accurate real-time magnetic field calibration using a smartphone-based platform. Firstly, according to the physical relationship between angular velocity and magnetic field, the state transition equation of magnetometer data was derived by using the gyro data recursively. The magnetometer measurements were used in the measurement equation, and the extended Kalman filter algorithm was used to complete the real-time EKF magnetic field compensated by the gyroscope. Then, the data from the magnetometer and the gyroscope were retrieved in real time on the mobile phone, and a real-time EKF magnetic field calibration operation was performed on the two, producing the calibration result as the output.It was then compared with the uncalibrated data and the calibration data obtained via the ellipsoid fitting algorithm.During the comparison experiment, the gyroscope compensation algorithm can not only achieve real-time calibration with any change to the external magnetic field environment, but can also complete the calibration of the magnetometer data within 2 s. In terms of calibration accuracy, when the mobile phone is stationary, the EKF algorithm can reduce the magnetic field interference in real time, with the value of the quality parameter Q of the calibration being 0.72.When the mobile phone is wound around "8", the quality parameter Q of the calibration is observed to be 0.53, which is better than 0.03 - its value for the ellipsoid fitting algorithm. When four scenarios of daily activities on the mobile phone are simulated, the quality parameters Q obtained are 0.73, 0.54, 0.52, and 0.48, respectively, and in these cases, the ellipsoid fitting algorithm is observed to be incapableof calibration. Thus, real-time, high-precision, easy-to-use magnetic field calibration is achieved. Experimental testsdemonstrate that the magnetic field calibration method based on extended Kalman filter can dynamically calibrate magnetic field interference in real time. Its calibration speed is fast, its precision is high, and its anti-interference ability is adequate. Therefore, it has a wide range of applications in consumer electronics, vehicle inertial navigation systems, and the military. © 2019, Science Press. All right reserved.