The initial alignment technology is one of the key technologies of inertial navigation, and its precision will directly affect the navigation results. Based on certain scheme, the Rotation-Modulation Strap-down Inertial Navigation System (RMSINS) can modulate the errors of inertial sensors; therefore, the precision of navigation system can be improved. But the errors of initial alignment of the system cannot be modulated. So it is essential to study on the initial alignment technology of rotation-modulation system and to find a proper alignment scheme for such systems. In this paper, especially aimed at single-axis RMSINS, the error models of the sensors are deduced and established. The open loop gyrocompass method is introduced and improved. The results of semi-physical simulation based on recursive least square algorithm prove that the alignment scheme provides high precision, rapid speed and valid effect. The research will have important value for the theoretical research of RMSINS and its engineering implementation.

Initial alignment of rotation modulation SINS based on improved open loop gyrocompass method

Zero velocity update technology (ZUPT) has frequently been used as a tool to reduce divergence when the inertial navigation system (INS) is working in pure inertial mode In general, the normal gravity model is adopted to calculate the gravity vector, and the effect of gravity disturbance is neglected We present a new point of view to explain the influence of gravity disturbance on INS and point out that gravity disturbance is one of the most significant error sources of the high-precision INS Two real-time gravity disturbance compensation methods are proposed An about 110-km-long vehicle test has been conducted in mountainous terrain with a drastic change of gravity disturbance The test results proved the correctness of the new explanation and the feasibility of the two on-line compensation algorithms for land vehicles With gravity disturbance compensation in conjunction with ZUPTs, the total horizontal error at the end of the test was reduced from 893 to 375 m, and the elevation error was reduced from 163 to 080 m

Analysis and on-line compensation of gravity disturbance in a high-precision inertial navigation system

Rotation modulation can significantly improve the navigation accuracies of an inertial navigation system (INS) and a strap-down configuration dominating in this type of INS. However, this style of construction is not a good scheme since it has no servo loop to counteract a vehicle manoeuvre. This paper proposes a rotary upgrading method for a rotational INS based on an inertially stabilized platform. The servo control loop is reconstructed on a four-gimbal platform, and it has the functions of providing both a level stability relative to the navigation frame and an azimuth rotation at a speed of 1.2◦/s. With the platform’s rotation, the observability and the convergence speed of the estimation for the initial alignment can be improved, as well as the biases of the gyroscopes and accelerometers be modulated into zero-mean periodic values. An open-loop initial alignment method is designed, and its detailed algorithms are delivered. The experiment result shows that the newly designed rotational INS has reached an accuracy of 0.38 n mile/h (CEP, circular error probable). The feasibility and engineering applicability of the designed scheme have been validated.

Rotary upgrading method and its experimental study of an inertially stabilized platform

Theme T Delco Carousel IMU in the Titan IIIC vehicle is similar to the conventional inertial platform except that two sets of the inertial instruments are mounted on a platform which rotates at 1 rpm about an inertially fixed axis. Derivations of navigation equations for acceleration resolution and drift compensation for the IMU are presented. The equations have been checked out and implemented in the flight computer.

A. C. Liang

Papers

Drift Compensation and Acceleration Resolution for a Rotating Platform IMU