Research On Rotary North Finder Based On Ring Laser Gyro

North finder plays an important role in military applications. Aiming to high accuracy north finder based on ring laser gyro (RLG), this dissertation has discussed four north finding schemes as follows: continuous rotary scheme based on differential RLG, rotary multi-position sampling scheme based on differential RLG, continuous rotary scheme based on constant rate biased RLG, and rotary multi-position sampling scheme based on constant rate biased RLG. Theoretical models and error models of the four schemes have been established, and the corresponding experimental systems have been developed, then comprehensive experiments have been carried out. After detailed theoretical analysis and experimental investigation this dissertation comes to an important conclusion that the main approach to realize high accuracy RLG north finder is rotary two-position sampling scheme based on constant rate biased RLG. This dissertation has done the following work:1. Multiple north finding schemes have been studied. By detailed theoretical analysis and simulation with RLG data, this dissertation gets the following conclusions: the rotary scheme is better than the strapdown scheme, and rotary two-position sampling scheme achieves the highest accuracy.2. Rotary two-position sampling scheme based on constant rate biased RLG has been proposed. This scheme can take full advantage of both the small random walk feature of RLG and high accuracy of two-position north finding algorithm. Meanwhile, it can overcome the mechanical disturbance in mechanically dithered RLG. The north finding accuracy of the prototype based on this scheme is better than 0.5' within 300s, with potentialities to be improved.3. Four different north finder prototypes have been designed and developed. Through a series of experiments, we find the following phenomena: the RLG output noise turns larger due to the swash of spin axis in continuous rotary scheme, and the RLG output varies due to the thermal deformation of the RLG support in constant rate biased RLG.4. The conclusion that rotary multi-position sampling scheme is better than continuous rotary scheme is proved by experiments, and the main error sources of each scheme have been found. For rotary multi-position sampling scheme based on differential RLG, random walk of RLG is the main error. For continuous rotary scheme based on differential RLG, the swash of spin axis is the main error, and the north finding accuracy becomes lower when the platform rotates faster. For rotary multi-position sampling scheme based on constant rate biased RLG, the following two errors are most important: bias residual deviation of RLG caused by mechanical factor and sampling noise of RLG caused by positioning error. For continuous rotary scheme based on constant rate biased RLG, the angular measurement error and the swash of spin axis are the main errors, and the north finding accuracy becomes lower when the platform rotates faster.5. Effective measures have been taken to reduce the north finding error. The sliding two-position north finding algorithm can reduce the effect of RLG drift. The pulse subdivision technique can reduce the sampling noise of RLG. Mounting the differential RLG with its discharge tube perpendicular to the rotary platform can reduce the earth's magnetic effect. Calibration by RLG can reduce the error of optical angular encoder.6. The calibration method of scale factor of RLG in rotary north finder has been studied, and scale factor of RLG has been calibrated using a marble platform and a hexahedron. The calibration method of system offset of north finder based on RLG has been proposed, and the system offset of the prototype has been calibrated.7. The data processing method of north finder on disturbing base has been studied. Grouping weighting method following wavelet filtering efficiently reduces the effect of base disturbance.