Research On Modulation Method And Alignment Of Inertial Navigation System Of Fiber Optic Gyro With Uniaxial Rotation

With the continuous improvement of precision and technical maturity of the fiber optic gyroscope(FOG), FOG occupy an increasingly important position in the high-precision navigation system. At present, the rotating modulation technology is one of important technologies to improve the precision of inertial navigation system. Using the rotating modulation technique in fiber optic gyro inertial navigation system, can reach a higher navigation accuracy. In this paper, against the subject background of a long-endurance underwater device, single-axis rotation of the fiber optic gyroscope modulation system is conducted in-depth research. The research mainly can be divided into four parts:(1) Automatic compensation principle and analysis in the error characteristic of single-axis rotation modulation system. In this paper, first of all, Laplace transform is conducted on Φ angle error model, in the frequency domain rotation modulation technology is analyzed on the error compensation nature of the inertial navigation. Through the analysis of inherent sources of error in the inertia component, such as constant drift, random walk error, scale factor error, installation error, in-depth and detailed exposition of the gyro drift and horizontal gyro nonlinearity scale factor error will be installed modulated away. In addition, the corresponding analysis on the resulting from t he modulation process is conducted, draw a conclusion that gyro error, accelerometer error is the root causes of generating sawtooth speed curve. In addition to the error source of inertial components itself, this article also analyzes the error caused by the process of rotating mechanism, and the navigation calculation formula is given to compensate, reduce the influence of the rotational error of the system and improve the navigation accuracy. The changes of the carrier’s heading during the motion can produce certain influence to the rotate modulation effect, this article through the analysis of ship movement, analyzes modulation effect of rotating modulation system caused by the heading angle changes of ships.(2) Rotating modulation system solutions. In this paper, through the Laplace transform of inertial navigation system error model,analyzes the error oscillation characteristics of single-axis rotation of inertial navigation system. Through the analysis of oscillation amplitude of the speed and positi on caused by the rate of rotation angle error, obtain the relationship between the navigation error caused by the rate of rotating angular and the various error sources. The paper launched rotation period selection formulas, providing a theoretical basis for different systems to select the angle of rotation rate. At the same time, the Fourier series transformation is conducted on the scheme of switching to stop, further elaborated the choice of switching to stop the program cycle. Through the analysis of the influence of the error in the rotation modulation system, pointing out the insufficient of order in the classic program of turn rotary to stop, by improving the classic program of turn rotary to stop, makes navigation accuracy is improved by an order of magnitude. Moreover, by analyzing the angular acceleration of the indexing mechanism in the size of the process of starting and stopping, draw the conclusion that the larger the angular acceleration obtained will reduce the impact on the progress of the navigation. Finally, on the basis of the scheme in the rotation, and composition of single shaft rotation modulation of fiber optic gyroscope system is introduced.(3) Rotating modulation system alignment method research. The great virtue of the single shaft rotation modulation system is in the process of alignment can change the course of the inertial navigation system, improve the observability of the system error state variables, achieve the goal of quick estimate the state variables. Through the analysis on of the equation state, pointing out the horizontally gyro drift and the horizontally accelerometer bias in the inertial navigation system is not observable. By using a combination of the alignment methods to improve observability of the system, the heading, horizontally gyro drift and the horizontally accelerometer bias of the system can be estimated quickly, heading accuracy can reach 1’ or less, Gyro drift estimates can be achieved 0.006 °/h or less, the accelerometer bias estimates of RMS can be achieved 35 ug. Finally, through the use of new alignment means on estimating the heading gyro drift, the result is 0.012°/h gyro drift can be estimated in two hours, effectively reducing the estimated time, with great engineering significance.(4) single-axis fiber optic rotary modulated inertial navigation system verification test. In accordance with the need of use, this paper proposes two kinds of working mode: 3 hours navigation with 0.5 hour alignment and 6 hours navigation with 3 hour alignment respectively. By testing for the two modes of operation, the speed, position error statistics meet the project target, verify the correctness of alignment and rotating modulation scheme.