Research On Initial Alignment Method Of GNSS/IMU Integrated Navigation For Spin-stabilized Projectile

Attacking precision requirement of weapon system has been increasing in modern warfare, and it is necessary to improve attacking accuracy of weapon system. Smart transformation is an effective way to improve the attacking precison of the conventional munition, so the smart transformation technology such as course correction munition and terminal activated munition become research hotspots. However, the ballistic measurement is important to spin-stabilized projectile trajectory correction. To measure the spin-stabilized projectile trajectory by using GNSS/MIMU integrated navigation system, not only has the advantages of high measurement accuracy of GNSS and strong anti-interference ability of MIMU, but also can avoid the problems that, the GNSS cannot continuously detect the ballistic because of GNSS signal loss or being interferenced, and the trajectory parameters exist error accumulation when MIMU detecting ballistic separately. For the course correction of spin-stabilized projectile, the problem of MIMU initial alignment when the integrated system dectecting the ballistic is studied in this paper, aiming to solve the problem that MIMU initial alignment cannot be accomplished by the conventional method, because MIMU cannot test the projectile rolling-rate under the condition of high spin. The research is structured as follow:On the basis of the rigid body trajectory model of the spin-stabilized projectile and its ballistic data, the projectile motion characteristics are analyzed, and the effects of projectile motion characteristic to initial alignment is studied. Based on the strapdown calculation model and the MIMU error model, a data simulation model of MIMU is established, and the initial alignment data resources are obtained. Results show that, projectile significant mutation is existent at the early ballistic, a large MIMU measurement data variation is caused, so it is necessary to avoid this trajectory stage during initial alignment; because the projectile attack angle is less than 2deg, the trajectory angle and azimuth angle can be equivalent as pitch angle and yaw angle; because the MIMU installation error is existent, the tested angle rate of the gyro installed along the perpendicular axis is coupled with a signal which proportional to rotation angular velocity, and the MIMU installation error cannot be ignored during initial alignment.Concerning the problem of the spin-stabilized projectile rolling rate cannot being measured by MIMU, the roll attitude detection method of the spin-stabilized projectile, based on the phase-locked tracking algorithm is studied, to obtain the roll attitude from the gyro data which installed along the perpendicular axis. The detected rolling attitude is then used to replace the gyro data which installed along the projectile axis for the ballistic parameters calculation and MIMU initial alignment. On the basis of MIMU testing signal model, the influence on phase-locked tracking algorithm is analyzed, and three order phase-locked loop characteristics and its parameters selection method are studied, to choose phase-locked tracking loop parameters which is suitble for spin-stabilized projectile. Based on phase-locked tracking algorithm and the appropriate parameters chosen by analysis and simulation, a spin-stabilized projectile roll attitude detection model is established. The roll attitude detection model is validated by numerical simulations using the simulated MIMU data. Results show that, the roll attitude detection method based on phase-locked tracking algorithm can effectively track the rotation signal of the spin-stabilized projectile, and the rapid detection of spin-stabilized projectile roll attitude is realized.The spin-stabilized projectile launch overload may lead to MIMU’s zero drift, and the large error of strapdown matrix could cause alignment filtering divergence. Above all, it is necessary to carry out the GNSS/MIMU integrated navigation system coarse initial alignment research of spin-stabilized projectile, aiming to obtain the strapdown matrix rapidly in projectile flight process. The GNSS position and velocity error characteristics of spin-stabilized projectile are analyzed and the error model is established, and simulated by the position and velocity data. The method of using satellite position and velocity data to calculate the pitch angle and roll angle of the projectile and the gyro install error and its bias error is studied, to obtain strapdown matrix rapidly and realize coarse alignment. The proposed fast coarse alignment method is verified by simulation test using MIMU simulated data and GNSS data. Results show that, the coarse alignment method can obtain the strapdown matrix and MIMU error rapidly, meet the speed and precision need of the coarse alignment.The coarse initial alignment error is large and unsuitable for the strapdown solution, so it is necessary to study the precision alignment method of integrated navigation system, aiming to obtain the precision initial parameters. The gyro mearsured data installed along projectile axis is replaced with rolling attitude results detected by phase-lcoked tracking algorithm, to establish the initial alignment state space equation, which considering the MIMU install error and under the condition of position and velocity matching. The precise alignment method based on the standard kalman filter, adaptive kalman filter and robust adaptive kalman filter separately is proposed respectively, and the precise alignment method is verificated by simulation using MIMU and GNSS simulated data. The results show that, considering the MIMU installation error and roll attitude detection results to replace the gyroscope measurement data is feasible for initial alignment, the standard kalman filter alignment time is long and the precision is low, the adaptive kalman filter can significantly shorten the alignment time and improve the alignment accuracy, but it is easily influenced by the gross error, however, the robust kalman filter can avoid the course error influence, is more suitable for the high dynamic initial alignment, can easier to solve the problem of spin-stabilized projectile integrated navigation system precision alignment problem.