Research On Key Technology Of High-precision Attitude Measurement System With Ring Laser Gyroscope

With the development of ring laser gyroscope’s (RLG) producing technology andthe improvement of its precision in our country, research on the attitude measurementsystem using RLG as the core component has became attractive. Taking the marinestrapdown attitude measurement system as a research object, the key factors restrictingthe improvement of attitude measurement system’s precision and the relevant solutionmethods are studied in this thesis. The content of this thesis includes systematiccalibration algorithm of inertial measurement unit(IMU), analysis of the system errorscaused by gravity disturbances and the compensation for them, gravity-aided inertialattitude measurement system, alignment on moving base, the filtering delaycompensation, the realization of system software and hardware and so on. The maincontents and contributions are as follows:1. Systematic calibration algorithm. The equations of coning errors caused bycalibration errors of IMU in the condition of a typical coning motion in strapdownsystem are derived. We draw the conclusion that the main error factors of attitudeupdating coning errors among calibration errors are gyro non-orthogonal misalignmentangles and scale factor errors; Firstly a restriction on the reference frame of RLGs andaccelerometers is added in order to make the calibration result exclusive; The systematiccalibration algorithm based on a kalman filter which includs27dimensional stateparameters is proposed, and this filter only uses the velocity errors as the observationalvectors; A programming of calibration route is proposed and its observability isanalyzed, then a weighted feedback arithmetic based on observability analysis is putforward. The simulation and experimentation indicate that the results of the systematiccalibration method are more precise than the conventional method.The verification testshows that the estimation accuracy of the gyros’ misalignment angles exceeds2.2. Research on the effects of gravity disturbances on high-precision attitudemeasurement system and its compensation method. The single channel theoreticalanalysis is carried out and it is pointed out that the vertical deflection is the primaryfactor; The theoretical expression of solution errors caused by vertical deflection isderived, and then a simulation based on global gravity disturbances database is made,which proves the accuracy of the theoretical analysis;The effects of gravity disturbanceson initial alignment are researched and we draw a conclusion that the vertical deflectionwill lead to equal magnitude initial attitude errors;The experimentation carried out in anoceangoing survey ship indicates that the precision can be improved obviously thanbefore, after compensated using global vertical deflection database.3. In order to restrain the increase of errors of the pure inertial attitude measurementsystem, a method that uses gravity information assisted inertial measurement system isproposed. A direct information fusion algorithm for gravity-aided inertial measurement system is designed, whereas the gravity anomaly information has strong nonlinearility,so UKF is selected as the information fusion algorithm. A weighted and multicyclefeedback UKF arithmetic based on gravity anomaly grads is put forward, and thesimulation results indicate that the proposed algorithm can improve the precision inposition, velocity and attitude greatly, and this algorithm is not sensitive to initialposition errors and measurement noise. It does not need the analytical local gravity fieldmodeling and linearization compared with EKF(expanded kalman filter), and itsrobustness is strong in different gravity anomaly gradients. Furthermore, ahardware-in-the-loop simulation based on the data of oceangoing survey ship isaccomplished, and the results validate the algorithm’s feasibility and adaptability.4. Research on the initial alignment on moving base. The observability duringinitial alignment of strapdown single-axis rotating attitude measurement system onmoving base is studied by the PWCS method. The results demonstrate that theadditional motion is not necessary for rotating system to improve alignment precision.In order to improve the performance of initial alignment under large azimuthmisalignment and on moving base, a detailed derivation of nonlinear error models underthese conditions is proposed and a nonlinear alignment arithmetic based on UKF isdesigned. The results show that the UKF arithmetic is a appropriate method for initialalignment under large azimuth misalignment.5. Study on the FIR filtering delay compensation method. A filtering delaycompensator which is based on attitude movement tracking model and kalman filter isdesigned. The compensator can obtain the estimation of the real attitude angles bypredicting the current output attitude results for a certain time.The experiments showthat, this method can estimate and predict the carrier attitude effectively and cancompensate the adverse effect caused by FIR filter delay.6. Research on the realization of the hardware&software and experiments boardedon oceangoing survey ship.The realization of software&hardware is discussed, while adetailed design planning of all task modules of attitude measurement software based onVxworks real-time operating system is put forward; The5months’ system experimentsboarded on the ship were completed and the voyage reached up to20000nautical miles,the verification and analysis on the gravity compensation, gravity-aided inertialmeasurement, initial alignment on moving base, and systematic calibration algorithmwere carried out adequately during the voyage.