Errors of an inertial navigation unit caused by ring laser gyros errors

Abstract

A ring laser gyro (RLG) has proven its efficiency for the strapdown inertial navigation unit (INU) but RLG errors result in the vehicle's attitude errors and determine the accuracy of the entire INU. Therefore it is necessary to know the relationship between RLGs and INU errors that would give the opportunity to improve the attitude accuracy by calculating the compensation values. A strapdown INU consisting of three mutually orthogonal RLGs each measuring the angular rate along its sensitive axis is considered. Each RLG has some inherent errors and consequently the measurements are incorrect; so the problem is to conceive the 'error equation' that could relate attitude and RLG errors. Using quaternions as orientations parameters and introducing particular error quaternion, the author formed the 'errors equation' that gives the relationship between vehicle attitude errors and the incorrect value of angular velocity caused by RLGs errors. The next step is to reveal the connection between specific kind of RLG errors such as null-shift and variations and measured value. After performing this step, he designed the general 'errors equation' that allows him to compute vehicle attitude errors as a function of particular RLG errors. The 'errors equation' was designed for general case and was modified for a specific INU: RLG-azimuth that is called laser direction keeper (LDK). LDK uses the hardware mentioned above and differs from other INUs with the operation algorithm. This paper presents examples of the orientation accuracy evaluation for such technological problems as non-orthogonality of RLG axes and initial setting errors. The formulas for numerical integration of the 'error equation' along with the results of such calculations are displayed. >