High-precision Initial Alignment Of FOG Strapdown Inertial Navigation System

With the extensive application of fiber optic gyroscope,high-precision fiber optic strapdown inertial navigation systems are widely used in military and civilian fields.The precision of navigation system will be directly affected by the precision of initial alignment which is the key technology of SINS.To development of high precision FOG SINS,increasing the precision of initial alignment is the key way which must be passed.The reasonable state error estimation and compensation method and the accurate system error model is the key technology to improve the precision of initial alignment.The domestic research on initial alignment technology mainly focus on the state error estimation and compensation method,ignores the analysis of temperature,less vibration,environmental disturbance error factors during the initial alignment process.This paper mainly studies the error model during the initial alignment process,like temperature compensation model,FOG random drift model,gravity disturbance model,which is compensated to improve the precision of the initial alignment.In view of the temperature error of inertial devices during the initial alignment,temperature characteristic of test was carried out,which indicated that FOG is little affected by temperature and quartz-flex accelerometer requires temperature compensation.According to the different temperature characteristics of accelerometer,designing different temperature compensation algorithms to improve the initial alignment scheme,verifying the impact of temperature compensation to the initial alignment,which obtained temperature compensation during the initial alignment can significantly inhibit the accumulation of errors of inertial navigation solution,can improve the heading angle precision of initial alignment heading.In view of the FOG random drift error during initial alignment,ARMA model is used in modeling and compensating of random drift error.ARMA modeling process is described,which modeling with the fiber optic gyro data during the coarse alignment and compensating random drift error during the fine alignment.FOG random drift is analyzed by Allan variance method,bias stability of that compensated by ARMA model can be increased by one order of magnitude.At the same time,it is verified that compensating the gyro random drift during initial alignment can improve the alignment precision,reduce fluctuation of the attitude Angle curve.In view of gravity disturbance error during initial alignment,the effect that gravity disturbance on navigation errors is verified by the two method of based-on the single channel and based-on the navigation algorithm.The normal gravity formula,the gravity field spherical harmonic model,the generalized Markov model are presented,then gravity disturbance vector in a certain regional was built by the gravity field spherical harmonic model.In the normal gravity formula as a benchmark,using the gravity field spherical harmonic model and the generalized Markov model to compensate gravity disturbance during initial alignment,which obtained that two compensation methods play an important role in the field of ultra-precision initial alignment.When gravity disturbance was compensated by the generalized Markov model,because only gravity disturbance of the horizontal direction was considered,compensation of gravity disturbance was too large;the heading angle precision had declined.Improving the heading angle precision by making accelerometer bias model more precise or adjusting the accelerometer bias parameters is future research direction.At the same time,research on error sources during the initial alignment not only can improve the precision of the alignment system,but also is beneficial to researching the high precision navigation algorithm.