Marine Star Sensor/Fiber Inertial Measurement Unit Research On Integrated Navigation Technology

Inertial navigation system,which is a completely autonomous navigation device,is the core navigation system of the surface ship.It has the advantages of strong concealment,high navigation accuracy in short-term,comprehensive and continuous output navigation parameters.However,the navigation errors accumulate over time and cannot work alone for a long time.The star sensor,observing the position of the star,can directly calculate the attitude information of the carrier relative to the inertial space in high precision.It has the advantages of strong autonomy,low power consumption,and high accuracy.But it also has the problem of low data update frequency and it cannot locate alone.In order to overcome the shortcomings of the above navigation systems and meet the requirements of the navigation system for all-weather and long time,a scheme of integrated navigation system composed of star sensor/ fiber inertial measurement unit(IMU)is proposed in this thesis.Focusing on the dynamic error correction of star sensor,high-precision optical fiber IMU technology and deep coupling technology of star sensor/ optical fiber IMU,a prototype of star sensor/ fiber IMU integrated navigation system is built to verify the effectiveness of the theoretical research results.The main work of the paper is summarized as follows:Aiming at the problem that the ship’s swaying will cause the image of the star spot on the image surface of the star sensor,affecting the accuracy of the attitude measurement of the star sensor,an dynamic error correction method of star sensor based on optical fiber gyroscope measurement is proposed after analyzing the mechanism of dynamic error of star sensor.This method introduces the angular velocity information from the optical fiber IMU into the star sensor,and uses the star sensor attitude data at the previous moment and the optical fiber IMU angular velocity information to predict the ship attitude at the next moment.Calculating the ideal coordinates of the known star at the next moment to track and predict the star point accurately,the dynamic measurement error of the star sensor caused by ship sway is effectively corrected.The accuracy of the optical fiber IMU not only affects the correction of the dynamic measurement error of the star sensor,but also restricts the system navigation accuracy.Since the fiber optic gyroscope is the core device of the IMU,an analysis of the fiber-optic gyro error generation mechanism caused by temperature changes is established.An improved temperature error model is established and a temperature error segment compensation scheme is proposed based on the temperature characteristics of the fiber optical gyroscope.The test results show that the scheme can effectively compensate the temperature drift to improve fiber optic gyroscope performance.In terms of system,using the idea of rotation modulation,based on the output error model of the device,the suppression mechanism of the dual-axis rotation for the optical fiber IMU is analyzed and designed,the corresponding optical fiber IMU dual-axis forward and reverse stop scheme is presented.Simulation results show that the proposed scheme can effectively suppress the inertial device error and provide guarantee for further improving the accuracy of the star sensor measurement and the accuracy of integrated navigation.Aiming at the problem that the positioning accuracy of the star sensor is affected by the accuracy of the external horizontal attitude,a high-precision method for determining the horizontal attitude based on the gravity of the inertial system is proposed.An adaptive digital filter to extract high precision gravity vector information from the output of the FIMU is proposed by combining the attitude information of the star sensor to obtain a high-precision horizontal reference.The horizontal reference information is used to assist the positioning of the star sensor,avoiding the coupling of the inertial guidance error to the star-sensitive position information,and improving the positioning accuracy of the star sensor.Aiming at the problem that the star sensor output attitude accuracy is unstable in the complex sea environment,the Kalman filter is not effective in the alignment of the star sensor /inertial integrated navigation system,a weighted recursive least square combination alignment method is proposed.Based on the recursive regression principle,the observation measurement analysis of the sensor uses weighted processing to quickly and accurately realize the precise alignment of the optical fiber IMU.The state change of the ship in a swaying environment has large randomness and amplitude disturbance.Therefore,based on the principle of star sensor/ optical fiber IMU integrated navigation system,the error equation of the inertial navigation system based on the star sensor is derived,a deep coupled inertial space nonlinear model of star sensor/ fiber IMU based on additive quaternion and multiplicative quaternion "attitude + position" matching is established.Attitude quaternion and position error are selected as the observation vector,RBACKF is used to estimate the system error state.Simulation results show that the scheme can effectively improve the accuracy of the integrated navigation system.Finally,the validity and feasibility of the above theoretical results were verified by using the existing test environment in the laboratory.The optical fiber IMU dual-axis rotary inertial navigation system was used to verify the rotation modulation error suppression scheme.Then a star sensor/ optical fiber IMU integrated navigation system is built to verify the effectiveness and feasibility of the star sensor/ optical fiber IMU deep-coupling navigation algorithm.