| The errors of the missile-borne inertial measurement unit(IMU)need to be calibrated periodically,because they change with time.The conventional discreet calibration needs to disassemble IMU and prolong the time of combat readiness.In this paper,a disassembly-free systematic calibration method for flexible IMU is provided,which is based on high precision SINS/GPS integrated navigation system of Missile Launching Vehicle.The method,which uses the difference of attitude and velocity between the SINS/GPS integrated navigation system and the flexible SINS as measurements,can estimate the IMU error parameters by reasonable vehicle maneuver,so as to get rid of dependence on high precision turntable and improve the efficiency of calibration.The main contents include the error modeling,parameter estimation,observability analysis,optimal calibration path design and experimental verification:1.The error model of quartz accelerometer and flexible gyroscope is established,which includes biases,scale factor errors and specific force acceleration dependency errors,and the error model of the flexible gyroscope is further simplified by the characteristics of the flexible gyroscope.Installation errors between SINS/GPS integrated navigation system and flexible SINS are analyzed and the lever arm error equations and the lever arm velocity compensation method are deduced.2.A 40-dimensional state equation of the Kalman filter which uses velocity error,attitude error and IMU error as the state vector of the system is established,and system measurement equation is built based on the difference of attitude and velocity between the SINS/GPS integrated navigation system and the flexible SINS.The general principle of Kalman filter parameter selection is given.3.The observability analysis method based on PWCS and singular value theory is researched and the definition of observable degree is given to evaluate the estimable level of each system state.Aiming at the situation where the state quantity is not uniform,a method for the observability analysis of the unified state quantity dimension is proposed,which overcome the theoretical defect of the observability measure in some degree.4.According to the maneuverability of the missile carrier loader,four kinds of maneuvering modes,such as rolling,turning,multi angle pitching and continuous pitching maneuvering,are designed and the observable degree of system state under different maneuvering conditions is analyzed.Based on observable degree analysis,the calibration path composed of turning,rolling and multi angle pitching maneuvering is designed to actuate IMU errors.The simulation results show that the error estimation results are consistent with the results of the observability analysis.5.The experiment of discreet calibration and systematic calibration is carried out on the three-axis turntable.In systematic calibration experiment,different maneuvers of the missile launching vehicle are simulated by corresponding movements of the three-axis turntable.The test results show that the systematic calibration can estimate 32 error parameters of IMU,which are consistent with simulation results,and compared with the results of discreet calibration,the accelerometer and gyro bias residuals calibrated by the systematic calibration are within 0.03-0.07 mg and 0.03?0.08 °/h.According to the navigation results by compensating the error parameters,the accuracy of system level calibration is equivalent to that of the discreet calibration;which meets the requirements of tactical grade SINS. |
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