Research On The Error Mitigation For FOG Modulated Strapdown Inertial Navigation System

The effect of divergent position error on Strapdown Inertial Navigation System(SINS)is one of main factors resulted in the poor navigation ability.As an Inertial Measurement Unit(IMU)error auto-compensate technology,rotating modulation is a process by driving IMU tumbling motion and stopping at preset place for settled period,and then,the effect of IMU error on navigation calculating is avoided.The prototype based on Fiber Optical Gyro(FOG)SINS are studied in theoretical and engineering,including rotating scheme,error analyzed and restrained,IMU error estimated by dual-process.The main works are as follows:1.The influence of the angle between the vehicle's angular motion and the modulation axis on the rotating modulation results is analyzed based on the principle of modulated SINS.And,furthermore,according to the application environment of introducing rotating mechanism,the detailed analysis of the effect of rotary accuracy,angle measurement accuracy on rotating modulation results are presented.The angle variable motion and tilt angle of the rotation machine are included in rotary accuracy,and angle measurement delay and angle measurement accuracy of the rotation machine are included in angle measurement accuracy.On this basis,the method of estimation and measurement at the different positions id proposed.2.Firstly,the error model of FOG and accelerometer are established.Secondly,take the gyro as an example,the effect of the gyro's drift,scale factor error,installation error on navigation error in the rotating and stopping process are studied.Thirdly,the rotating scheme designed principle relative to the geographic coordinates is proposed,and then,the single-axis/double-axis/three-axis rotating scheme is designed by the principle.The feasibility of the schemes is verified by simulation.3.In the process of rotation modulation,the earth rotation,the angle velocity of rotation modulation and the vehicle's rotating motion are sensed by gyro.Because of the earth rotation is a kind of objective existence constant value,the coupling items between gyro errors and angular velocity of earth rotation cannot be eliminated by rotation modulation.In order to compensate the coupling items,which are caused by rotation relative to geography frame in modulated SINS,the rotation methodology relative to inertial frame is presented.Based on the propagation law,the three-axis rotation methodology for modulated SINS is put forward.According to the methodology,the four position three-axis rotation scheme is designed.4.Although the divergent position error can be decreased by rotating technology,a new kind of concussion error is incented to navigation error,which is related with rotational period.The navigation error equations for modulated SINS are derived detailed,the error mitigation methods based on the error characteristics are proposed.·The method to attitude error mitigation based on adjusting navigation parameters is proposed,which can reject the concussion error related with rotational angular velocity,so the attitude precision is improved.·The method to velocity error mitigation based on Butterworth filter is proposed.The concussion error with the modulated period is eliminated from the velocity error,which is obtained by the difference between Doppler Velocity Log(DVL)and SINS,by Butterworth filter.The velocity information without the concussion error with the modulated period is obtained.5.It will be extremely difficult or impractical to satisfy the attitude error mitigation method based on adjusting navigation parameters and the velocity error mitigation method based on Butterworth filter.Therefore,the double navigation calcualating program for modulated SINS is proposed.There are two group calculating program,one is calculating velocity and position information,the other is calculating attitude information.6.The effect of DVL constant error on misalignment angles steady-state error based on compass principle is derived,and the steady-state error is only influenced by DVL constant error.According to the result,the method for DVL constant error is proposed based on the double program:the DVL velocity error is calculated by attitude information,which is resolved respectively from compass solution method and inertial navigation solution method.7.A new approach is presented to calibrate the FOG drift and scale factor error based on a double calculating program.Based on the application environment of introducing rotating mechanism and the analysis of the relationship between the FOG error and misalignment,a FOG calibration error model is derived,and a three-step-six-position calibration path is analyzed.In this method,the FOG drift and scale factor error are calculated by from two groups of attitude information,which is are resolved,respectively,from calculating programsA and B in the navigation computer.The input signal of these two calculating programs is measured from one FOG.