Research On Initial Alignment Of SINS Under The Condition Of Latitude Information Constraints

Initial alignment technology is one of the most important technologies of strapdown inertial navigation system.The alignment time and alignment precision of initial alignment are the two major indexes to measure the performance of strapdown inertial navigation system.Therefore,initial alignment is a very important work in the SINS system,and many domestic research achievements on this work are relatively mature.However,how to locate the initial alignment of SINS under the condition of latitude information constraints,especially in the dynamic environment,is still a key problem to be solved.This work is also of great significance.In some special circumstances,such as forest,underground,deep sea and other complex conditions,GPS and other equipment can not be used to obtain latitude information.In some cases,only the accuracy of attitude information is required,but the accuracy of position information is not required.In these cases,the initial alignment of SINS must be completed by measuring information of inertial sensors themselves.In this paper,the initial alignment of inertial navigation system under the condition of latitude information constraints is studied.The latitude estimation and initial alignment are performed independently by using the real-time output of accelerometers and gyroscopes.The research work of this paper is mainly divided into the following aspects:Firstly,the influence of latitude unknown on the initial alignment of SINS is analyzed.Analysis shows that initial alignment is inseparable from latitude information,and the influence of latitude error on attitude error is quantified.For the dual vector attitude determination under dynamic condition,the pitch angle error is proportional to the latitude error.Therefore,under the condition of unknown latitudes,the precondition of initial alignment with dual vector attitude determination is to estimate the latitude value with high accuracy.On this basis,the method of latitude self-alignment under the condition of static base and sloshing base is discussed respectively,and the error analysis of the two methods is carried out.Through analysis and simulation,we can see that the latitude error based on the latitudinal latitude selfalignment method is mainly affected by the output error of accelerometer.Based on this,this paper proposes an improved latitude self-alignment method,including accelerometer output processing method based on velocity integral and wavelet filtering.Through theoretical deduction and experimental analysis,these two methods can effectively suppress the output interference of accelerometers,but in contrast,the curve of the output results of the latitude self-alignment method based on wavelet filtering is more smooth,so this method is used to estimate the latitude.The experimental data verify that under the mooring condition,the latitude estimation error within 5 minutes can converge to less than 0.5 degrees.Secondly,based on the latitudinal estimation,the alignment method based on dual vector attitude determination is proposed.This method defines a new coordinate system,the carrier's inertial coordinate system.Through the chain decomposition,the pose matrix is decomposed into four matrix multiplication forms,and the solution of the pose matrix is transformed into the solution of the key sub matrix.The experimental results show that after 5 minutes of latitude estimation and 2 minute alignment,the horizontal error angle based on latitude estimation and dual vector determination under mooring state can be within 0.02 degrees,and the direction error angle is less than 0.2 degrees.Moreover,this method can not be applied to the alignment of the online moving carrier.Under the condition of moving base,the basic inertial navigation equation is deformed.With the aid of external velocity information,the solution of initial attitude is transformed into Wahba attitude determination problem by using the mutual substitution relationship between four elements and attitude matrix.The simulation proves the applicability of the algorithm under the condition of moving base.Finally,a direct alignment method based on the construction of orthogonal bases is proposed to solve the problem that it will take a long time to estimate the latitude and the accuracy of the alignment error depends on the latitude.The method does not require latitude information,and solves the problem of attitude matrix transformation into the projection value of orthogonal basis in the coordinate system.The direct alignment method of the accelerometer and the gyroscope is only applicable to the condition of the base seat.Based on this paper,an orthogonal basis construction method based on the gravitational apparent motion is proposed.The carrier solidification inertial coordinate system is still used,the attitude matrix is decomposed into two forms of matrix multiplication,and the solution of the attitude matrix is transformed into the construction of the orthogonal basis of the key matrix,that is,the projection value of the orthogonal base in the inertial coordinate system of the carrier is solved by the projection value of the navigation system.Simulation results show that the algorithm is suitable for initial alignment of rocking base under unknown latitudes.