Research On Rotating Inertial Navigation System With Four-frequency Differential Laser Gyroscope

The auto-compensation techniques of rotation is widely used in high accuracy inertial navigation systems based on ring laser gyros, in order to increase navigation performance with limited cost increase. The auto-compensation techniques and some other crucial techniques in optical gyro inertial navigation system developing are studied in theoretical and engineering aspects. An experimental two-axis rotating inertial navigation system based on four-mode differential laser gyros is developed and tested. The work of this thesis includes following five parts.(1) Theoretical research on the auto-compensation principle of rotating INS. On the analysis of the essence of drift auto-compensation by rotation, discussions and conclusions are made on the genuine problems in rotating inertial navigation systems, such as compensating pattern, axis direction, rotation period, and etc. Using the method proposed of analyzing the error effect of inertial elements, the compensation of scale factor error, misalignment error, accelerometer second-order non-linearity error is studied.(2) Research on the indexing scheme of rotating INS. Based on the analysis of single axis rotating system, several indexing schemes are put forward, including single axis indexing scheme with vehicle azimuth isolation and two position single axis indexing scheme without vehicle azimuth isolation. Emphasis is made on the analysis of four position indexing scheme which keeps rotating angle within 360 degrees. A modified four position scheme is put forward, which can be used as reference in the design of single axis indexing scheme. An eight-sequence and a sixteen-sequence two-axis indexing scheme are put forward referring to the platform rotating scheme of electrostatic gyroscope system. Analysis and simulating show that the sixteen-sequence scheme is very practical, which can compensate all the drift error, misalignment, non-symmetric scale factor error of inertial elements, as well as the partial error of four-mode differential laser gyro induced by constant magnetic field.(3) Software and hardware design of the experimental dual axis rotating navigation system based on four mode differential laser gyro. A lot of works on hardware among many fields are done, including: selection of the main elements used in the system, mechanical design and implementation of the dual axis navigation system (such as IMU, axis system, frame, base, and etc.), design and implementation of driving and control circuit of dc moment motor. Software works include navigation software (such as motor control, initial alignment, navigation algorithm, etc), integrated testing software of the navigation system, SCM program of motor driver, mode scanning and frequency stabilizing program of differential gyro.(4) Study on the calibration and initial alignment techniques of inertial navigation. An calibration method of laser gyro IMU is put forward on the analysis and conclusion of calibration model and calibration accuracy. The experimental navigation system is calibrated with this method, using tilting rate and position turning table. Second order nonlinear error of accelerometer and magnetic induced error of differential laser gyro are compensated. An initial alignment scheme is put forward which can be used under arbitrary azimuth misalignment angle. And a multi-stage cyclic alignment and calibration method is put forward, which ensures the valid estimation and correction of error parameter in the Kalman filter. The methods put forward are successfully used in the experimental navigation system.(5) Navigation test of the experimental dual axis rotating system. Navigation tests of 24 hour period are made on the experimental system, in the mode of dual axis rotating, single axis rotating and non-rotating. Accuracy analysis is made on the navigation result and error analysis is made on the experimental system. The navigation results prove the validity of the research and implementation. The rotating scheme can average out the drift of laser gyros and accelerometers in the navigation system, and is a valid way of navigation accuracy enhancement.The theoretically innovations of the thesis include: analysis on many kinds of error effect and error factor in rotating navigation system, with some formulas deduced; many practical single axis and dual axis rotating schemes, with error analysis; new calibration and initial alignment methods. These innovations can be used as reference in the design of rotating navigation system.