Research On The Mechanism Of Coil Magnetic-thermal Induced Error In Small Fiber Optic Gyroscope

With the rapid development of my country’s commercial aerospace industry,the exploration field of new spacecraft is complex,and a stable and accurate inertial navigation system is required to provide the spacecraft with information such as position and attitude during work.Among many inertial systems,the Interferometric Fiber Optic Gyroscope(IFOG)has attracted the attention of researchers due to its advantages of no moving parts,high stability,and miniaturization.However,the space-use IFOG is limited by volume and weight at this stage,resulting in a significant reduction in the inner diameter of the fiber coil.In addition,the IFOG will be affected by the magnetic field and temperature field when it works,and the resulting magnetic and thermal errors will reduce the accuracy of the IFOG.However,the currently studied magnetic and thermal error models are not suitable for IFOG.Therefore,it is necessary to carry out research work on the magnetothermal error mechanism of IFOG in space environment to make up for the shortage of miniaturized IFOG in the space field.In this paper,aiming at the problem of non-reciprocal phase shift caused by the change of environmental state when IFOG is applied in space,the mechanism of each influencing factor on the fiber optic gyroscope is deeply analyzed.Theoretical research and experimental verification are carried out in three aspects: the research on the magnetic error of the fiber optic gyroscope and the research on the thermal error of the fiber optic gyroscope.The main research contents of this paper are as follows:Firstly,for a fiber coil with a small curved inner diameter for space,the refractive index and birefringence have obvious changes with the level,and this change is a nonnegligible factor in the analysis of the adaptability of IFOG physics.Aiming at the lack of the refractive index and birefringence distribution model of the IFOG fiber coil in the current research,this paper proposes a non-step quadrupole symmetrical winding method suitable for the spatially small fiber coil by analyzing the disadvantages of the standard quadrupole symmetrical coil method.Taking the fiber coil wound by the nonstep quadrupole symmetrical coil method as the research object,theoretical analysis of the stress of a single-layer fiber based on the theory of elasticity and the elastic-optic effect,the distribution model of the refractive index and birefringence of the fiber coil is established.Secondly,the IFOG for space is limited by weight and cannot use magnetic shielding materials as a structure,which causes the IFOG to be affected by the magnetic field during operation.Aiming at the inaccuracy of the existing IFOG magnetic induced error model,this paper proposes a three-dimensional IFOG magnetic induced error model.By analyzing the action mechanism of magnetic fields in different directions on the transmission characteristics of light waves in the fiber coil,the radial magnetic induced error model and the axial magnetic induced error model are deduced respectively by using the Jones matrix.Introduces the normally neglected axial magnetic field error into the magnetically induced error model.On this basis,the temperature dependence of Verdet constant and fiber birefringence is deeply analyzed,combined with the deduced fiber coil birefringence distribution model,the IFOG three-dimensional magnetically induced error model is established.The experimental results show that the accuracy of the IFOG three-dimensional magnetically induced error model is greatly improved compared with the existing theoretical error model.Thirdly,for the inaccuracy of the thermally induced error model of the small fiber coil used in space,an IFOG thermal induced error model based on the small fiber coil is proposed.Using the Shupe effect and thermal stress effect,the mechanism of the timevarying temperature field on the light wave phase in the fiber coil is studied.Combined with the deduced fiber coil refractive index distribution model,a three-dimensional thermal error model suitable for IFOG with small inner diameter is established.According to the design requirements for the fiber inertial group proposed by the spacecraft,a set of microfiber inertial group suitable for small space satellites was modeled by Creo software.The finite element analysis method is used to simulate the temperature distribution of the fiber coil in the thermal vacuum environment during the full temperature change process.In order to verify the generality of the theory,simulation experiments are also carried out under non-vacuum conditions.The experimental results show that the accuracy of the IFOG three-dimensional thermal-induced error model based on the small fiber coil is higher than the existing theoretical model,and the model is not only suitable for vacuum environment,but also suitable for non-vacuum environment.Finally,the experimental verification work is carried out on the small IFOG for space use.Firstly,the distribution model of the refractive index and birefringence of the fiber coil is experimentally verified.However,since the existing equipment cannot directly measure the refractive index and birefringence of the fiber coil in a distributed manner,this paper uses the optical coherence domain polarization measurement technology to perform distributed measurement of the polarization crosstalk of the fiber coil through a white light interferometer.The data are compared,and the correctness of the fiber coil distributed model is verified.Secondly,the experimental verification is carried out for the magnetically induced error model of the small fiber coil.In the process of the experimental verification of the magneto-induced error,by building a Helmholtz coil uniform magnetic field test platform,and testing the magnetic induction intensity of the designed and assembled Helmholtz coil,the test results are uniform at room temperature and high and low temperature.The results meet the experimental requirements.The magnetic field test platform is used to test the magnetic errors of the radial magnetic field and the axial magnetic field at room temperature.The experimental results verify the correctness of the three-dimensional magnetic error model.The three-dimensional radial magnetic error model is consistent with the existing theoretical model.Compared with the root mean square of the model error,it is reduced by 56.9%,and the three-dimensional axial magnetically induced error model is reduced by 35.7% compared with the model without considering the birefringence distribution.Finally,the experimental verification work is carried out the thermally induced error model of the small fiber coil.In the thermal vacuum experimental test system and high-precision thermostat,the thermal-induced error experimental verification in thermal vacuum environment and non-vacuum environment is carried out respectively.Compared with the equivalent radius model,the root mean square of the model error of the X-axis,Y-axis,and Z-axis fiber optic gyroscopes in the vacuum environment is reduced by 33.6%,33.5%,and 33.8%,respectively.Similarly,in the non-vacuum environment,the root mean square of the three-dimensional error model and the equivalent radius model of the three fiber optic gyroscopes are reduced by 34.1%,35.1%,and 33.8%,respectively.Correctness of the 3D thermally induce error model for fiber loops.