| Strapdown inertial navigation system(SINS)is a core navigation system of ships,aircrafts,guided weapons and other carriers.The reliability and long-term accuracy are the key technical indicators related to the efficiency of mission execution.However,traditional SINS is limited by its own three-axis orthogonal configuration structure and navigation mechanism.The system is out of order directly due to the failure of a single inertial device and the navigation error accumulates rapidly over time.It is difficult to improve the reliability and precision of inertial devices.Therefore,more attention has been paid to system reliability and navigation accuracy through redundancy technology and rotation modulation technology in the system level.The device-level redundancy has cost and volume advantages obviously.And rotation modulation technology can ensure the autonomy of the system while improving the accuracy.The research and implementation of the combination of two methods is of great significance for improving the SINS performance comprehensively.Firstly,the relationship between reliability,reliability increase,reliability ratio and redundancy number is calculated and analyzed.And different influences of orthogonal configuration structure and oblique configuration structure on system reliability are analyzed.The basic principle of SINS and rotation modulation method for modulating the error of inertial devices are summarized.The overall design of the rotation modulation method for SINS is established.The redundancy scheme optimization criterion of multiple-index constraints is built.The performance of redundancy scheme is analyzed from the aspects of system reliability,navigation characteristics and fault-condition measurement accuracy.The overall scheme and algorithm implementation of rotation modulation based on redundant configuration are designed.The optimization of rotation modulation and modulation effect analysis are completed from the aspects of rotation-axis selection,rotation scheme improvement and rotation angular rate determination.Aimed at the redundant system with four and six gyroscopes,the rotation modulation schemes of redundant SINS are designed.For four-gyro redundant system,a tetrahedron configuration scheme is optimized.The system reliability and single-fault condition accuracy are compared with the oblique configuration and the rectangular pyramid configuration.The inertial measurement unit(IMU)platform installation structure based on the tetrahedron configuration is designed and processed by Pro/E software.A single-axis reciprocating rotation modulation scheme and an eight-sequence dual-axis rotation modulation scheme based on tetrahedron configuration are respectively designed to suppress the error of redundant inertial devices.The simulation results show that the system reliability is 1.75times that of the non-redundant system,and the speed accuracy and positioning accuracy are obviously improved.For the six-gyro redundant system,a hexagonal pyramid configuration scheme is designed.Compared with the six-oblique configuration scheme and the dodecahedron configuration scheme,the performance of the scheme in system reliability,single-fault and multi-fault condition measurement accuracy and engineering realization has significant advantages.The optimized hexagonal pyramid configuration scheme is equipped with SINS,and the single-axis 180~?-360~?rotation modulation scheme and the sixteen-sequence dual-axis rotation modulation scheme are designed.The hexagonal pyramid configuration scheme and the rotation modulation method are combined organically.The simulation results validate the effectiveness of the schemes for improving system reliability and navigation accuracy. |
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