Study On Initialization Method Of Strap-down Inertial Navigation System

Strap-down inertial navigation system(SINS)is a kind of self-contained navigation system which provides velocity,position and time information.It has been used in mapping equipment and instruments widely.However,SINS initialization has the problems of long initialization time and low accuracy.Especially in the harsh working environment,SINS can not get the exact initial strapdown matrix.To solve the mentioned proplems,the thesis makes a deep research on calibration and initial alignment which are the the key technologies of initialization.In this thesis the main contents are as following.It analyzes the basic mechanical equations of SINS in detail,and deduces the navigation parameter update algorithm and navigation error equations.By combining the characteristic equation of navigation error equation and computer simulation,the paper analyzes the error propagation properties on stationary base and moving base separately.As the conclusions follow:the initial attitude misalignment has the greatest influence on the system error.Then it is the gyroscope constant drift.The zero error of the accelerometer has the least effect.There are three kinds of oscillations exisiting in the system,and there are Shuler,Foucault and earth periodical oscillations.In which Foucault periodical oscillation modulates Shuler periodical oscillation.Aiming at the engineering application problems such as accuracy,applicability and so on,it studys the Inertial Measurement Unit(IMU)calibration model.Taking the installation error angles of three-axis IMU as the starting point,the IMU calibration mathematical model is established based on spatial geometry.The paper transforms the IMU calibration mathematical modeling problem into calculating the coordinate system transformation matrix.Four kinds of gyroscope calibration linear mathematical models,four kinds of accelerometer calibration linear mathematical models and four kinds of accelerometer calibration nonlinear mathematical models are established.The mathematical models are simulated by designing discrete calibration.This provides a theoretical basis for SINS with different accuracy to select the IMU calibration mathematical model.According to long time and low accuracy of IMU calibration,it respectively designs the IMU fast and high-precision calibration programs.The thesis designs fast calibration method of gyroscope zero and accelerometer bias.The estimate errors of north misalignment and azimuth misalignment are related to the gyroscope zero and accelerometer bias.The fast calibration method utilizes this relationship.It designs three calibration positions and calculates six linearly independent equations to calibrate errors of gyroscope zero and accelerometer zero offset fast.When calibrating the scale factor and installation error,it takes the velocity error and attitude error as the observation and takes the last parameters as initial parameters.By combining IMU calibration parameter errors and taking the velocity error and attitude error as the observation values,a six-position systematic calibration method based on Kalman filter is designed.This method takes the velocity error and attitude error as the observation values,estimates twenty-four calibration parameter errors and compensates them.According to the estimation curve characteristic of gyroscope calibration parameter errors,the thesis two-level systematic calibration method to improve gyroscope calibration accuracy.In order to eliminate the effect of rocking motions interference on the initial alignment,a noval initial alignment with inertial frame is proposed.The coarse alignment integrates specific force in inertial coordinate system to eliminate periodic interference and designs infinite impulse response digital filter(IIR)to reduce high frequency interference.By analyzing the equation of initial alignment with inertial frame,it concluds that gyroscope drift has great influence on the alignment accuracy.So the gyroscope drift must be estimated and compensated.It utilizes a rotating mechanism to achieve.In the fine alignment,by establishing the state equations and observation equations of Kalman filter with inertial frame,it estimates the misalignment angle of earth centered inertial to revise the coarse alignment results.Simulation and experimental results show that the inertial-frame alignment can greatly greatly imrove the anti-interference ability and alignment accuracy of SINS on swaying base.The paper has 49 figures,7 tables and 171 references.