Accurancy Of Optic Gyro Strapdown Inertial Navigation System Calibration

As a key technology in modern weapon system, the testing technology of the inertial navigation system includes three aspects: testing equipments, testing methods and procedure, data processing method. The testing equipments (such as a turntable) are tools of evaluating the inertial instrument performance, so the accuracy of the inertial instrument's testing results rely on the accuracy of the equipments used. This paper concerns how the calibration accuracy is affected by turntable errors. Some analytic conclusions are derived, and simulations and experiments are performed to verify the analysis.This paper firstly describes a traditional calibration method–the schism calibration method which is widely applied in engineering projects. After describing the principle of this method, the input-output models of the accelerometers and gyros are established. Demonstrated by the accelerometers'typical multi-position calibrations, i.e., 6-position, 12-position and 24-position and the gyro's angular rate tests, the calibration procedures are designed in detail, and the mathematical formulation of calibration parameters is derived.The performance of a turntable is analyzed, and the model of the turntable's error is established. Using the transformation from the quaternion to the direction cosine matrix, this paper derives the turntable's error propagation in calibration, and gets the direction cosine matrix from the turntable's initial frame to the the calibration coordinate reference frame. According to the error propagation, we analyze the errors of accelerometers multi-position calibration (mainly the typical 6-position, 12-position and 24-position calibration methods) and gyros'angular rate calibration caused by the turntable error. Based on the analysis, relationship between accuracy of traditional schism calibration and the turntable errors is given.Different from the schism calibration method which establishes the reference coordinate frame refered to a turntable, the calibration method based on equations establishes a reference coordinate frame according to the gyro triad. After analyzing the method, the paper states that the gyro parameters thus calibrated are little affected by the turntable's error, although the calibration method needs more complex computation. The calibration accuracy of the accelerometors is equivalent to the traditional schism calibration method.The analytic conclusions are verified by simulations with Matlab. Experiments are designed to evaluate the influence of the angular errors of the turntable's middle frame and inner frame. Both simulation and experiment results agree well with the analysis.