Research On The Initial Alignment Of SINS Employed In Land Moving Vehicle

Initial alignment plays an important role in the aiming of the guns in the land-used inertial navigation system.Initial alignment provides the initial attitude for the strapdown inertial navigation.The precision of the following inertial navigation is directly influenced by the initial alignment precision.To improve the rapid reaction capability,it is required to shorten the alignment time and realize the in-motion alignment.Based on the background of the initial alignment for a land-used strapdown inertial navigation system(SINS),the initial alignment for a SINS in the static base,rocking base and moving base have been researched,respectively,aiming to increase the alignment precision or shorten the alignment time.When the base remains static or the shaking is not obvious,the normal initial alignment method used is the analytic coarse alignment.The analytic coarse alignment is based on the algorithm about obtaining the attitude given two vectors.The six outputs of the inertial measurement unit(IMU),namely,the angular velocities and the linear velocities in three directions of the space are needed for the analytic coarse alignment.A new analytic alignment method called the simplified analytic alignment method is proposed in this dissertation,which uses three outputs(with both the gyroscope output and the accelerometer output included)and the signs or rough values of the leaving three outputs.The simplified analytic alignment method reveals that the six outputs are reluctant for solving the attitude.With different groups of the outputs selected,the attitude could be obtained using the simplified analytic alignment method,respectively.In the vehicular environment,the vibration could be severe in certain direction due to the factors from the engine's working and so on.The interference on the alignment from the output in the severely affected direction could be reduced using the simplified analytic alignment method.In addition,the method could be used for the fault detection of the IMU,fast field self-calibration of the IMU,fast two-position alignment and so on.Simulations and vehicular experimental results demonstrate the validity of the proposed method.The IMU error is one of the main factors that affect the alignment precision.Multi-position alignment methods are used to compensate the IMU errors and improve the alignment precision.Inspired by the simplified alignment method,a conclusion is given that any two positions,as the minimum condition of the multi-position alignment,could be theoretically enough to obtain the constant bias of the IMU.Besides,a multi-position analytic alignment method with two given accurate angles rotated(for the convenience of computation,90° and 180° are selected)about any axis is proposed.The rotation axis could be not along the head axis of the IMU for the method which could be used to reduce the manufacturing cost and compensate the installation error of the existing single-axis rotation SINS.The analytic alignment might have large error and even not work in the base with obvious vibration.Inertial frame alignment becomes the research focus in resent years owing to its robustness to vibration disturbances and effectiveness with any initial attitude error.In the rocking base,the angular vibration could be wholly eliminated but the linear vibration for the inertial frame alignment.Two types of methods including the low-pass filtering in frequency domain and the fitting in time domain are used to eliminate the linear vibration.It is proposed that the initial velocity owing to the linear vibration could affect the precision of the inertial frame alignment remarkably,and improved algorithms have been used to eliminate the linear vibration with the initial velocity owing to the linear vibration included.Simulations and the vehicular experimental results show that the highest precision and fastest convergence could be obtained using the improved method.The in-motion alignment cannot be performed based solely on the SINS.The devices like GPS and odometer are required to supply velocity or position observations for in-motion alignment of SINS.However,GPS is easily influenced and not reliable in wartime.The odometer is easily disturbed by the factors such as the beat,slipping and deformation of the wheel.The autonomous in-motion alignment for SINS aided by Laser Doppler velocimeter(LDV)which supplies velocity observation is studied in this dissertation.The inertial frame alignment method has been extended to the use in in-motion alignment.Based on the predecessor's research,it is concluded that three key aspects,namely,the equation model used,the update of the initial attitude,and the update of the position-related matrix,basically form the in-motion alignment and together determine the alignment performance.Improvements have been made on both the update of the initial attitude and the update of the position-related matrix.In addition,a backtracking navigation method has been used to shorten the alignment time and improve the alignment precision.Simulations and vehicular experimental results demonstrate the validity of the proposed method.Finally,the in-motion fine alignment based on the SINS/LDV integrated navigation system is studied to eliminate the inertial sensor errors and the disturbances from the motion.A field calibration is required to eliminate the installation error for the SINS/LDV integrated navigation before they work.A field calibration method based on the scale factor model of the LDV is proposed and the method improves the field calibration efficiency.Based on the scale factor model,the system equations and observation equations for the fine alignment of SINS/LDV have been established.Simulations and vehicular experimental results demonstrate the validity of the proposed method.