A Fast Calibration and Compensation Method for Magnetometers in Strap-Down Spinning Projectiles

Abstract

Attitude measurement is an essential technology in projectile trajectory correction. Magnetometers have been used for projectile attitude measurement systems as they are small in size, lightweight, and low cost. However, magnetometers are seriously disturbed by the artillery magnetic field during launch. Moreover, the error parameters of the magnetometers, which are calibrated in advance, usually change after extended storage. The changed parameters have negative effects on attitude estimation of the projectile. To improve the accuracy of attitude estimation, the magnetometers should be calibrated again before launch or during flight. This paper presents a fast calibration method specific for a spinning projectile. At the launch site, the tri-axial magnetometer is calibrated, the parameters of magnetometer are quickly obtained by optimal ellipsoid fitting based on a least squares criterion. Then, the calibration parameters are used to compensate for magnetometer outputs during flight. The numerical simulation results show that the proposed calibration method can effectively determine zero bias, scale factors, and alignment angle errors. Finally, a semi-physical experimental system was designed to further verify the performance of the calibration method. The results show that pitch angle error reduces from 3.52° to 0.58° after calibration. The roll angle error is reduced from 2.59° to 0.65°. Simulations and experimental results indicate that the accuracy of magnetometer in strap-down spinning projectile has been greatly enhanced, and the attitude estimation errors are reduced after calibration.

Correction Strategy of Mortars with Trajectory Correction Fuze Based on Image Sensor

“…It should be noted that our investigated object is mortar, which can be regarded as a non-spinning projectile. When a projectile with rotation is considered, a magnetic sensor [28,29,30] may be necessary for the transformation. [DAxDAyDAz]=[cosθcosψcosθsinψ−sinθ−sinψcosψ0sinθcosψsinθsinψcosθ][DNxDNyDNz]…”

Optimization of a New High Rotary Missile-Borne Stabilization Platform

“…In addition, due to the limitation of the GFSINS navigation principle and accelerometer manufacturing process, it is very difficult to continue to improve the navigation accuracy of the GFSINS [17,18]. Small caliber conventional rockets use servo motors to reverse rotation on the roll axis to keep the inertial measurement unit stationary or micro-rotation relative to the inertial space [19,20,21,22]. However, these single-axis stabilized inertial navigation platforms that utilize the motor to achieve the stability of the rolling shaft have complicated system structures and poor anti-overload performance due to the introduction of the servo motor, and are difficult to apply in conventional projectiles with high launch overloads.…”

Online Correction Method for Ratio Methods by Using Geomagnetic Sensors Based on Kalman Filter

“…The device corrects the magnetometer by the generated magnetic field. In [34], an offline calibration method is proposed to eliminate the errors of the sensors. The errors, which are caused by the difference in the sensor output ratio, the nonorthogonal of the sensors or constant disturbing magnetic field, are greatly suppressed.…”

“…The core work of this paper is to eliminate the data offset caused by a disturbing magnetic field during the flying condition of a spinning projectile. An offline calibration to eliminate the sensor errors, such as those introduced in [34], is the premise of this study. For the application of geomagnetic measurement on spin stabilized projectile, compared with other filters mentioned in this paper, the filter proposed in the paper can correctly estimate the real signal at the sampling frequency of 1 kHz and signal disturbance ratio of 1.…”