Research On Integrated Alignment Technology For MEMS Based SINS

To improve the initial alignment accuracy and time of the MEMS Based SINS, aMEMS/GPS/electrical compass integrated alignment method is proposed in this thesis.First, this thesis present each constitute of this system in three aspect: principle,characteristics, and framework. And then discuss the advantage of SINS/GPS integration，choose SINS/GPS velocity integration mode, use indirect filtering and feedback emendation.These discussions are prepared for the study of MEMS/GPS/electrical compass integratedalignment method behind.Because of the low precision of MEMS gyros, traditional analytical coarse alignmentcan not be used. To solve this problem, MEMS accelerometers are used to measure the levelattitude angles and an electrical compass to measure the heading of the carrier in the coarsealignment step. In the coarse alignment step, azimuth angle is given by an electrical compassonly, and electrical compasses are easy to be disturbed by magnetic field, this lead to the largeazimuth error angle. To found a relatively precise error model, the third chapter put forwardthe inertial navigation system’s error equations based on the hypothesis of large azimuthangle. Extended Kalman Filtering (EKF) is used to estimate the errors of the non-linearsystem in fine alignment step.The effects of the integrated alignment method are inspected by Matlab simulation. Toobtain the simulation results of the in-motion alignment, we design a moving trace of thecarrier, simulate the different state of a plane, put the real time velocity, position and attitudeof a plane into the state equation of the system, use EKF to estimate the errors of the system.The simulation results show that after this integrated alignment, we may acquire small errorangles in a short time. To test the advantage of MEMS/GPS/electrical compass integratedalignment method in alignment accuracy and velocity, this thesis designs a comparativesimulation of MEMS/electrical compass integrated alignment method andMEMS/GPS/electrical compass integrated alignment method. The simulation result showsthat: MEMS/GPS/electrical compass integrated alignment method has a higher precision in ashort time. At the end of the thesis, test the practicability of this integrated system bysimulation, estimate the navigation parameter consist of three axes velocity, position, gyroexcursion and accelerometer error, forecast the navigation performance.At the end of the thesis, the observability of this system is discussed. The result of theanalysis shows that this integrated system is an unobservable system, and there are three unobservable states in this system. The observable degree of system states for in-motionalignment is discussed. The result of simulation shows that the north gyro excursion, east andup accelerometer error are unobservable. The observable degree of the up velocity error, eastand north position error, north and up attitude error is near1. Other states’ observable degreeis low. When the carrier changes its state, the system states’ observable degree changes aswell.