The rotational inertial navigation system (INS) has received wide attention in recent years because it can achieve high precision without using costly inertial sensors. However, the introduction of the turntable causes additional errors, including mounting errors between the inertial measurement unit (IMU) axes and the turntable axes. Analysis, calibration and compensation of the mounting errors are necessary in rotational INS. In this paper, the mounting errors are introduced into the sensor model of a dual-axis rotational INS. Analysing the improved model indicated that the mounting errors’ effect on the IMU errors is inconspicuous, but the effect on the output attitude is significant. If the output attitude is not required, the mounting errors can be ignored; conversely, it is important to calibrate and compensate for such errors. A calibration method for the mounting errors is designed using the thin-shell (TS) algorithm, and the method's precision has the same order of magnitude as the residuals of gyro misalignment in the simulation test. Laboratory experimental results validate the theory and proved that the calibration and compensation method for mounting errors proposed in this paper helps improve the output attitude's precision without a precise installation.

http://iopscience.iop.org/article/10.1088/0957-0233/24/11/115002/pdf

Analysis and calibration of the mounting errors between inertial measurement unit and turntable in dual-axis rotational inertial navigation system

A novel algorithm for marine strapdown gyrocompass based on digital filter

Rotation modulation (RM) technology can effectively improve the navigation accuracy of strapdown inertial navigation system (SINS) by the periodic rotation of the rotation mechanism. But the original error characteristics of SINS will be changed after introducing the rotation modulation technology. Aiming at the practical micro-electro-mechanical system RMSINS, the error characteristics are comprehensively analyzed, and then a complete error model is established. At the same time, a reasonable parameter calibration scheme and the compensation method are designed to compensate the error in this paper. On this basis, static and dynamic experiments are carried out. The position accuracies of the rotation modulation state in the static and dynamic experiments are about ten times and about three times than that of the non-rotation state. The experimental results show that the proposed error analysis and compensation method are feasible which have been applied to the practical engineering.

Error Analysis and Compensation of MEMS Rotation Modulation Inertial Navigation System

The errors of an inertial navigation system (INS) in response to gyros' errors can be effectively reduced by the rotation technique, which is a commonly used method to improve an INS's accuracy. A gyro's error consists of a deterministic contribution and a stochastic contribution. The compensation effects of gyros' deterministic errors are clear now, but the compensation effects of gyros' stochastic errors are as yet unknown. However, the compensation effects are always needed in a rotational inertial navigation system's (RINS) error analysis and optimization study. In this paper, the compensation effects of gyros' stochastic errors, which are modelled as a Gaussian white (GW) noise plus a first-order Markov process, are analysed and the specific formulae are derived. During the research, the responses of an INS's and a RINS's position error equations to gyros' stochastic errors are first analysed. Then the compensation effects of gyros' stochastic errors brought by the rotation technique are discussed by comparing the error propagation characteristics in an INS and a RINS. In order to verify the theory, a large number of simulations are carried out. The simulation results show a good consistency with the derived formulae, which can indicate the correctness of the theory.

The Compensation Effects of Gyros' Stochastic Errors in a Rotational Inertial Navigation System

An initial alignment method for strapdown gyrocompass based on gravitational apparent motion in inertial frame

Litton Marine Systems has developed a marine gyrocompass/navigator for the U.S. Navy which has been designated the AN/WSN-7B. It is a more reliable state-of-the-art strapdown, ring-laser gyro, based replacement for the WSN-2 gyrocompass, with the added requirement of being an inertial navigator with an accuracy of 1 nm in 24 hours. This paper provides a detailed description of the AN/WSN-7B, delineates the key features, and presents the latest laboratory and at-sea test results. These results show that the 1 nm in 24 hours navigation requirement as well as the velocity and attitude specifications are satisfied.

Terry Tucker

Papers

The AN/WSN-7B Marine Gyrocompass/Navigator