Research On Key Technologies Of Positioning And Orientation Measurement Of Fiber Optic Gyro Strapdown Inertial Navigation System In Confined Space

With the continuous development of the economy and the urbanization,the demands of surveying and mapping users for high-precision navigation and positioning in the open environment have gradually turned to river-sea tunnels,urban subways,underground shopping malls and other closed or semi-enclosed confined spaces.These confined spaces are often accompanied by a variety of complex environments,such as large burial depth,high temperature,high pressure,and magnetic field interference,which can cause certain interference to our positioning and orientation measurement accuracy,and put forward new challenges to the operation mode and safety hidden dangers.Moreover,the fact that satellite signals cannot be received normally in confined space leads to the failure of traditional space geodesy technology.In this case,it is a scientific research of great significance to carry out accurate and effective position and orientation surveying in the complex environment of the confined space and ensure the reliability and environmental adaptability.As a passive navigation system,the Inertial Navigation System(INS)has the advantages of strong autonomy,high short-term accuracy,real-time continuity,comprehensive information and so on.It has shown its great application potential in many military and civil fields.And the Strapdown Inertial Navigation System(SINS),as the mainstream of the development trend of INS,is developing rapidly.The inertial measurement unit of collection motion parameters directly with solid carrier phase,using the sensitive load system relative to the inertial space observations can be calculated and then we want to pose sensory information.The accuracy of gyroscope in SINS plays a decisive role in the final positioning and orientation measurement results,and the gyroscope equipped with SINS mostly adopts optical gyroscope(laser gyroscope and fiber optic gyroscope),among which the Fiber Optic Gyro(FOG)has attracted the attention of many research institutions at home and abroad because of its price advantage and high reliability.Therefore,we chose the Fiber Optic Gyro Strapdown Inertial Navigation System(FOG-SINS)as the research object for positioning and directional measurement in a confined space.Although the FOG-SINS system has many advantages,its errors will gradually accumulate over time,which will lead to a serious consequence that the accuracy of orientation parameters will gradually decline or even become unusable.In order to limit the error drift of FOG-SINS,we conducted research on the key technology of high-precision positioning and orientation around complex environment interference in confined space,mainly from four aspects of technical research,the original signal de-noising(signal level),improving the precision of initial alignment(initial conditions),magnetic levitation gyro assisted orientation(directional transfer)and odometer enhances combined positioning(positioning correction),to achieve positioning and directional measurement accuracy improvement and quality control in the confined spaces,and provide some reference for practical engineering application solutions.Therefore,the main research contents are as follows:1.Signal Lever: By analyzing the time-varying,non-linear and non-stationary random noise in the original FOG signal,an adaptive denoising algorithm based on empirical mode decomposition considering the colored noise was designed.According to the theoretical noise energy and the improved Hausdorff distance method,the IMF were divided into three categories:noise modes,mixed modes and information modes,and we processed them separately.Through the turntable experiment,multiple sets of static and dynamic data were denoised,and the processing effect was verified from various levels,such as intuitive line type,spectrum analysis,Allan variance analysis,and measurement index statistics,and all of which show that the adaptive processing algorithm is superior to the traditional method.2.Initial Conditions: The initial alignment conditions for surveying and mapping users in the confined space are divided into three categories: a stable and ideal static base,a shaking base that interferes with mechanical vibration,and a nonlinear environment with a large misalignment angle.We analyzed different models in various alignment environments,including traditional analytical coarse alignment,carrier inertial system coarse alignment,fine alignment based on Kalman optimal estimation,nonlinear error equation based on Euler platform error angle and unscented Kalman non-linear filtering and other method models.Through simulation and actual vehicle-mounted experiments,the initial alignment models under the conditions of static base,swaying base and large misalignment angles were classified and discussed,which verified the applicability of the models under different environmental conditions and provided a good initial value guarantee for the navigation integration algorithm.3.Directional Transfer: Aiming at the problem that the initial heading angle is more difficult to align,the magnetic levitation gyro total station(GAT)is introduced as an external aid to provide stable and accurate absolute heading information,and we pointed out the research idea of treating the complex disturbance in the confined space as the optimization problem of the observed data.In order to better ensure the accuracy of GAT directional transmission,through the analysis of the north-seeking and directional principle and dynamic model,aiming at the uneven characteristics of the GAT signal in the interference environment,a filtering optimization strategy combining permutation entropy and variational mode decomposition(VMD)was proposed.The interference data collected in the directional surveying of the No.5and No.6 branches of Qinling Ultra-long Tunnel of Hanjiang to Weihe River Project was analyzed by the proposed method,and four typical fluctuating signals had achieved ideal smoothing processing effects.4.Positioning Correction: In view of the problem that the positioning error of the SINS system will gradually increase with the passage of time,the odometer's dead reckoning technology that does not require radio signals and a feature database was introduced to correct it.Through the analysis of the odometer measurement principle and the position calculation method,the error equation of the odometer dead reckoning was derived from the standard SINS system,and the specific function models of the odometer-assisted combined positioning were constructed.With reference to the existing lines of Xi'an Metro,two sets of simulation experiments of typical line types are designed,and the single system and combined system models are used to implement positioning calculations.The comparison results show that the combined positioning model enhanced by the odometer can meet the requirements of highprecision vehicle positioning and realize the correction of the positioning error of the SINS system.