In the fiber optic gyroscope (FOG) single-axis rotation inertial navigation system (SRINS), the Z-axis gyro drift (ϵz) dramatically limits its navigation precision and the Z-axis gyro scale factor error (δKGz) can cause greater navigation error because of the rotation process compared with the strap-down inertial navigation system. Hence, identification and compensation for the ϵz and δKGz are important in SRINS. An approach based on the azimuth error model of open-loop algorithm is proposed. This approach considers azimuth angle as a measurement and uses a least recursive square algorithm for identifying the ϵz and δKGz. Compared with the traditional method, which takes velocity and position errors as measurements, the time required for identifying ϵz with the proposed method is only approximately 10 min, while the traditional method requires 6 h to 12 h. Experimental results from an SRINS with FOGs demonstrate that the accuracy of identifying the ϵz reaches 0.002°/h and that of the δKGz reaches 8 ppm in 10 min. The positioning accuracy of the SRINS improves greatly after the identification and compensation.
Fiber optic gyros (FOGs) are sensitive to the environment fields where they are mounted, and their drifts are easily affected when surrounding temperature field or magnetic field changes. In FOG strapdown inertial navigation system (INS), gyro drifts caused by environmental fields are stable mostly, thus they could be calibrated and compensated beforehand and would not cause obvious alignment and navigation errors. However, in rotation INS (RINS), although navigation errors caused by the constant components of FOG drifts could be well attenuated, the gyro sensing axes are changing relative to the environmental fields in the RINS, which would lead to periodically changing gyro drift components when inertial measurement unit is pointing to different headings, thus producing serious alignment and navigation errors in FOG RINS. To solve this problem, a four-position heading effect calibration algorithm was proposed, and its effectiveness and validity were verified through a dual-axis FOG RINS by turntable experiments. The experimental results show that the azimuth alignment accuracy of the FOG RINS improves from 0.2 deg to about 0.04 deg, increasing five times approximately, which illustrates that the proposed heading effect calibration algorithm could further improve the navigation performance of FOG RINS significantly.
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