Transfer Alignment And Error Compensation Technique For Strapdown Inertial Navigation System

Transfer alignment technology provides accurate initial reference for vehicles in motion.In rapidly changing modern war，transfer alignment technology has been applied to shipborneand airborne tactical guided weapons successfully. But in the transfer alignment ofcarrier-based aircrafts, the situation of carrier aircraft’s direction cannot be determined willlead to the large azimuth misalignment. Meanwhile, the shock of waves and maneuvering ofcarrier ship will cause flexural deformation, and high distance between shipborne inertialnavigation system(INS) and airborne INS give rise to the coupling of flexural deformationand lever arm effect, which make the error compensation problem more complicated. Aimingat above problems, the transfer alignment technology under large misalignments and errorcompensation methods will be studied in this paper through comparing and analysising ofdifferent error models, matching methods, filtering algorithms and error compensationmethods.The main error sources of transfer alignment like errors of inertial measurementunit(imu), errors of flexural deformation and lever arm errors are modeled firstly, then classictransfer alignment error models and rapid transfer alignment error models are deducedrespectively. According to the definition of velocity and attitude errors, the relations ofreference coordinate systems of two error models are analyzed. On the basis of above job, theconsistency and scope of the application of two error models are deeply studied, which laysthe foundations for the following matching methods and quaternion transfer alignmentalgorithm.Matching methods are important parts of transfer alignment technology, and the velocitymatching and attitude matching are mainly studied. Velocity matching is not subjected to theINS type, and have good comprehensive performance. Aiming at the observability problem ofvelocity matching, a more intuitive analytical method is proposed based on the analysis of therelation between measurements in velocity matching and states. The effectiveness is verifiedby deriving the relationship between states and measurement of multi-order differential underthe situation of uniform linear motion. When main INS and slave INS are both strapdowninertial navigation system(SDINS), attitude matching method becomes an important option.Because of the weak coupling relationship between measurements in attitude matching andvelocity errors, the attitude angle matching、 attitude matrix matching and measuredmisalignment matching are studied and compared according to the measurement obtainingand the complexity of the measurement equations, which resultes in the “velocity+attitude” matching, whose state and measurement equations are given finally. The velocity matchingand“velocity+attitude” matching are simulated under different maneuvering.Aiming at transfer alignment of large misalignment, the nonlinear filtering algorithm ismainly studied. To deal with the problem of high state dimension, the spherical sampling ischosen by comparing two simplex sampling strategy, so that the number of sigma point canbe reduced and real-time of algorithm can be achieved. Meanwhile, the square rootUKF(SRUKF) is used to improve the computational stability of nonlinear filtering algorithm.Finally the spherical sampling SRUKF(SSRUKF) is proposed. The effeteness of the methodis verified by the simulation experiment of transfer alignment of carrier-based aircraft underlarge azimuth misalignment.Aiming at the problems of singularity and high computational burden of euler anglemethod in transfer alignment under large misalignment, the nonsingular，precise and easyattitude quaternion is introduced. On the basis of defining error attitude quaternion, thequaternion classic transfer alignment error models and rapid transfer alignment error modelsare derived firstly. Corresponding to “velocity+attitude” matching, the quaternion measuredmisalignment matching method is studied deeply and the measurement equations are given,where the measurements are obtained by multiplying the immediate correction quaternion ofMINS and SINS. On the basis of above job, the quaternion UKF is studied. Thenon-redundant vectors of error quaternion are used to compute the covariance, so that thesingularity of quaternion covariance can be avoid. The covariance equation is adjustedappropriately by UT transformation. The method based on solving eigenvalue vector is usedto calculate the weighted mean of normal quaternion which is based on the construction of thecost function. Finally, the augmented UKF is given as a result of the multiplicative noise. Theeffeteness of proposed method is verified by the simulation experiment of transfer alignmentof carrier-based aircraft under large azimuth misalignment.The statistical properties of markov process which describe the flexural deformation arestudied and the equations are given to determine the noise variance for flexural deformation.On the basis of above job, the coupling of flexural deformation and lever arm effect isquantitatively analyzed, and equaled to the problem of noise compensation. In order to solvethe problem that the compensated noise cannot follow the external changes in real time,maximum likelihood method and strong tracking filtering are introduced. The idea ofadjusting covariance and gain matrix online is integrated to solve the problem that theSage-Husa adaptive filtering is unstable and sensitive to the initial value of filtering. To takefull advantage of current measurements, the weight of measurement noise covariance is increased, and the fading factors are redefined in strong tracking filtering. By combiningmaximum likelihood method, an improved Sage-Husa adaptive filtering is given finally. Theeffectiveness of Sage-Husa adaptive filtering is verified by the simulation experiment, wherethe variance of compensated noise is set smaller than the true value.