| The fiber optical gyroscopes (FOGs) have been widely used in many situations such as land, sea, air and space because of its numerous advantages. Just for the FOGs strap-down inertial navigation system (SINS), the navigation accuracy largely depends on the precise of FOGs, so the accuracy of FOGs in SINS is expected to be that the higher the better. The zero-bias stability of inertial grade FOGs need to be below 0.1(°) / h, but the zero-bias error, as for a FOG under geomagnetic field without any suppression measures, will be as high as the level of 1(°)/h with worse zero-bias stability. As a result, it's meaningful to study the magnetic errors mechanism in the FOGs, from which some restrain measures are expected to be found to improve the precision of FOGs and the systems made of FOGs.Firstly, the mechanism and mathematic model of radial magnetic error in the fiber coil were studied and established based on the magneto-optical Faraday effects and Jones matrix theory. It can be found in the theory analysis that the faraday nonreciprocal phase shift between the clockwise and counterclockwise light in the fast axis of polarization maintaining optical fiber (PMF) is opposite to the shift in the slow axis. Based on this result, a dual-45°weld-plan in PMF FOGs is proposed in the thesis. In this scheme, the radial magnetic sensitivity magnitude was suppressed to 0.08(°)/h·Ga-1 and the zero-bias stability was not worse than that in the dual-0°weld-plan.Secondly, the thesis has a theory analysis of the axial magnetic error in the fiber coils.There are two reasons for the axial error. The first one still is the Faraday effects because of the small axial magnetic field projection component along the light propagation direction. The other one is that the asymmetry distribution of refractive index in the optical fiber will lead to the shift of quasi-TM mode light electric field in the fiber. Simulation results show that the axial error is at least three orders of magnitude less than the radial error,but the experiment results show the two errors are basically same, which comes to a conclusion that the second reason is the main factor for the axial magnetic error. In the thesis, we have tried using the software compensation project to improve the FOGs' magnetic performance. The project based on HMC58831 magnetic sensor can compensate the bias error just as the effect of a magnetic shield, but the FOG's zero-bias stability in the compensation project is not as good as the one with a magnetic shield.Thirdly, the thesis describes the magnetic shielding theory and the finite element analysis theory of static magnetic field. The modeling of static magnetic field boundary problem and corresponding variational problem was accomplished based on electromagnetic field theory.The process of finite element solution to variational problem was executed surrounding the solving of parallel plane magnetic field boundary problem, which will be a good theoretical basis for the finite element analysis of magnetic shielding. In addition, after introducing the finite element simulation software ANSYS,some basic configurations of the software in the research were declared.Finally, ANSYS simulations and corresponding experiments were performed to the analysis and design of a magnetic shielding. The researches show that the factors of magnetic permeability, thickness, gap, holes and shielding shape of the shielding all have an influence on the shielding effect (SE), with the gap determining the continuity of magnetic circuit and shielding shape elements more significant than the others. Based on this result,a shielding structure with a SE of 40dB was designed by the simulation. The shield is enough to weaken the influence of earth magnetic field on FOGs below 0.002(°)/ h combining with the dual- 45° weld-plan. |
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