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Research On Calibration And Initial Alignment Technology Of Strapdown Inertial Navigation System

Posted on:2021-03-11Degree:MasterType:Thesis
Country:ChinaCandidate:G C CaoFull Text:PDF
GTID:2428330605976534Subject:Electronic and communication engineering
Abstract/Summary:PDF Full Text Request
With the gradual improvement of the accuracy of inertial devices,strapdown inertial navigation system(SIINS)has been widely used in military and civil fields.The initial alignment technology is the key to realize the precise navigation and guidance of this kind of system,so it has become a research hotspot at home and abroad in recent years.In order to improve the alignment accuracy and stability,this paper studies the initial alignment technology of SINS with different accuracy.Firstly,for MEMS inertial navigation system,considering that the MEMS inertial device has no north seeking ability,the magnetometer can be used to assist to improve the heading observation.In the MEMS inertial navigation system,the heading information obtained by magnetometer is easily interfered by external magnetic field,so the calibration of magnetometer is the key to achieve accurate initial alignment.Magnetometer interference can be categorized into two types:hard or soft iron distortion.Hard iron distortions are created by ferromagnetic materials with permanent magnetic fields while soft iron distortions are considered deflections or alterations in the existing magnetic fields.Generally,the calibration methods of magnetometer include batch least square(LS)?two-step batch-processing?approximate maximum likelihood estimation and so on.In this paper,a real-time calibration method combining recursive least square(RLS)and maximum likelihood estimation(ML)methods is proposed.Compared with the common calibration methods,this method has the advantages of high precision and strong anti-interference ability.Furthermore,through the adaptive judgment of iterative convergence,the calibration time is greatly shortened and the operation efficiency is improved.Based on this,the axis misalignment error and gyroscope bias can be estimated by gyroscope assisting magnetometer,and the calibration of magnetometer and gyroscope can be implemented at the same time.Simulation results verify the effectiveness of the algorithm.Secondly,for the high-precision inertial navigation system,the initial alignment in the in-flight base assisted by GPS is mainly studied in this paper.The principles of alignment based on absolute velocity integration algorithm and position loci algorithm are analyzed in detail,and the two methods are compared.Compared with the alignment method based on absolute velocity integration algorithm,the alignment method based on position loci can effectively solve the problem that the GPS output velocity information is easy to be interfered by the outliers,but its alignment accuracy is still affected by the accumulation error of the inertial instrument.Therefore,based on the position loci algorithm,this paper proposes a sliding window algorithm to eliminate the accumulated error.A sliding window with a window length of 20s is designed in the time domain.Due to the reduction of the integration interval,it effectively eliminates the cumulative error of the traditional full window integration.Simulation results show that the proposed algorithm reduces the average heading alignment error from-0.3520° to-0.1635° and alignment accuracy increases 53.6%during 300s alignment.Simulation results verify the effectiveness of the proposed algorithm.Finally,based on the above methods,the experimental demonstration of initial alignment is carried out by using MEMS inertial sensor.The experimental results show that the magnetometer can be calibrated well in different test environments and the heading observation error after calibration all can be within 1°,further verifying the effectiveness of the algorithm.The above results can be widely used in strapdown inertial navigation system.
Keywords/Search Tags:Strapdown inertial navigation, Initial alignment, The calibration of magnetometer, Sliding window
PDF Full Text Request
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