Study On The Dither Coupled Errors And The Error Restrain Methods For The DRIG SINS

Dither ring laser gyroscope(DRLG) has been applied broadly in the inertial navigation field with the technique improvement. Dither coupled errors are unavoidable in the inertial measurement unit(IMU) composed of DRLG. The analysis of the dither coupled error characteristics and the study of the restrain methods are very important to improve the accuracy of the inertial navigation system(INS). The author analyses dither coupled errors of the rigid-strapdown INS and the flexible-strapdown INS by their kinematics characteristics. Specially, the author investigates the coupling response characteristics of the IMU stimulated by the dither, and then, proposes the rule of “four centers superposition” for the IMU design to restrain the dither coupled errors. The following investigations are made in this thesis:a) The author derives the propagation equations of the dither coupled errors of IMU and strapdown INS, and builds the kinematics models of IMU and strapdown INS, then verifies the results by means of the finite element simulations. The simulation platform of coupled response is built up to simulate the coupled responses to the complicated structures and multiple stimulators, especially the responses to different structure parameters.b) The dither coupled errors and the restraining methods for the rigid-strapdown INS are investigated. For the rigid-strapdown INS, the inertial sensors are attached to the vehicle rigidly. The transfer of the dither energy is suffered from the problem of large scale and high ratio variations. Anthoer problem is that the transfer of the dither energy is largely affected by the external environments. These problems break the rule of the dither-bias lock-in removment and result in obvious increase of the constant and random bias of the DRLG. The dither coupled errors are effectively restrained by the following two methods: the first method is to optimize the kinematic parameters of the IMU and the INS. The second one is to mitigate the external vibrations so as to reduce the constant bias of the inertial sensors.c) The dither coupled errors and the restraining methods for the flexible-strapdown INS are investigated as well. For the flexible-strapdown INS, the dither coupled energy transfer between the IMU and the base is mitigated by the shock absorber. As a result, the coupled dither of the DRLG is limited within the IMU, and the relatively stable kinematic modes are formed. The main source of the dither coupled errors is the pesudo-coning motion of the IMU caused by the dither of the DRLG. The response amplitude is affected by both the frequency ratio of the DRLG dither to that of the absorber and the inertia ratio of DRLG to the IMU. By studying the influences of the layout of the absorber on the pesudo-coning motion, an optimized design of the layout is proposed. Considering the problem of the sensing axis errors caused by the low ratio of the high order resonance frequency to the dither frequency, a new structure of the rotor is proposed to enlarge the frequency ratio. In an experimental system, the design rule of “four centers superposition” is applied to restrain the dither coupled errors of the IMU. The error restraining method is verified together with the optimization design of the mass and cubage.In order to improve the sensor accuracy of the inertial navigation system, the author investigates the system kinematics and the inner structure of DRLG, and analyses the theory of the production of the dither coupled errors by means of theoretical analysis and finite element simulation, then propose the error restraining method. The experiments show that the achievements of this thesis are valuable to enhance the structure kinematics of the DRLG SINS, especially the high-end ones.