Research On Initial Alignment Technologies Of GFSINS

Gyroscope-free strapdown inertial navigation system (GFSINS) as an autonomous navigation system has the characteristics with a long life, low cost, low energy consumption, fast response. Traditional strapdown inertial navigation system does not apply in fields of large overload, large angular velocity. GFSINS fixes accelerometer on the carrier, uses the accelerometer output signal to solve linear acceleration and angular velocity vector. This method is especially suitable for difficult situations used in routine application SINS as large acceleration and large angular velocity. This paper discusses aspects of GFSINS, which includes accelerometer configuration, angular velocity calculation, initial alignment approach on stationary base, initial alignment approach on dynamic base.Firstly, the feasibility of GFSINS configuration is given:configuration matrix J is full rank. If accelerometer is failed, when isolates failure of the accelerometer, use the remaining accelerometer to constitute GFSINS, and then proposes using the extended configuration matrix to analyze this case, judge navigation information can be completely calculated or not. This paper analyzes accelerometer configuration conditions rely on outside information form, independent GFSINS. Considering engineering realization, a twelve-accelerometer configuration is used in GFSINS, when one accelerometer is failed, it can be ensure to work properly with the different presentation for the system.Secondly, angular velocity calculation methods are studied for promoting navigation precision. The advantages and disadvantages are analyzed to methods of integral algorithm, extraction algorithm and logarithmic algorithm for solving angular velocity, and simulation verification. In order to eliminate the influence of random noises of accelerometer, a kind of adaptive filter is designed. Simulation is complete under the different magnitude of noise, variety of noise and initial estimated valve of state variable, and results show adaptive filter has better precision than Kalman filter.Then, initial alignment approach on stationary base of GFSINS is studied. To calculate the initial angular velocity of GFSINS, a method is present to determine the symbol of initial angular velocity and uses absolute value of extraction algorithm for angular velocity calculating to determine the initial angular velocity, and then completes the initial coarse alignment. In the case of small misalignment angle, the error equations of the GFSINS are established, Kalman filter is used for error estimates. Since the error covariance in the Kalman filtering method needs to be operational before the estimated effect of each state, and based on Piece Wise Constant System,(referred to PWCS) singular value analysis method does not require a substantial measure prior Kalman filter operation, system state variables can be considerable measure, for the system design time savings. Presents a constant angular velocity calculating method for determining the error, this method can analyze the error calculating constant angular velocity can be estimated using Kalman filter. When the initial azimuth misalignment angle is big, the nonlinear alignment error equations are derived, and the nonlinear filtering methods of EKF and UKF are studied. Because of the possible problem of the state covariance matrix in UKF, The singular value decomposition method of UT transformation is used to calculate Sigma point, and then solves the state covariance matrix. Compared with two nonlinear filtering methods, the results show that the performance of improved UKF algorithm is superior to EKF.Finally, initial alignment approach on dynamic base of GFSINS is studied. The impacts on transfer alignment are lever arm effect and flexural movement. Error equations of transfer alignment model are derived, in which the error state equations are the equation of the system, while the measurement equations of transfer alignment model are related to the methods of matching transfer alignment. The measurement equation of the form is different from matching methods. This article discusses several transfer alignment methods, analyzes the advantages and disadvantages of several methods of matching transfer alignment through simulation. Attitude matrix matching method for the transfer alignment is improved, studies the practical of improved attitude matrix matching method, and receives conclusions.