Rotary Inertial Navigation System with a Low-cost MEMS IMU and Its Integration with GNSS

Abstract

Micro-electro-mechanical-systems (MEMS) inertial measurement unit (IMU) outputs are corrupted by significant sensor errors, such as noises, biases, scale factors, and installation errors. Consequently, the navigation errors of a low-cost inertial system with the MEMS IMU will accumulate quickly over time in stand-alone mode. Methods that can effectively mitigate the navigation errors without a need for external aiding, will be of great value for many applications. This research proposed a rotary inertial navigation system (INS) to mitigate navigation errors caused by MEMS inertial sensor errors when external aiding information is not available. A rotary INS is an inertial navigator in which the IMU is installed on a rotation platform. Application of proper rotation schemes can effectively cancel and reduce sensor errors. For example, the rotation of an IMU with a constant angular rate can modulate the constant inertial bias into periodic signals, and an integration of the modulated inertial data over a complete rotation cycle can eliminate the effect of the bias on the navigation solutions.

Improvement of current inertial system’s observability in the absence of system maneuvers is also highly desired in applications. It is well known that the position and velocity from external aiding are extensively used to estimate the INS errors, and the weak maneuvers result in poor system observability and eventually degrade the navigation performance due to inaccurate estimation of INS errors. As the rotation changes the position of the IMU, the system observability is significantly improved in a rotary inertial system.

Although the rotary INS has been applied to inertial system with high-end IMUs, it has not been investigated for low-cost MEMS IMUs. Given the fact that the MEMS IMU features significant sensor errors, as well as large and fast error variations, there are many issues and challenges that need to be addressed for effective navigation error mitigation and applications by rotary INS with MEMS IMUs. The conducted turntable tests and kinematic field tests indicate that with proper data processing, the horizontal position errors can be reduced by about 2~5 times in an inertial system with a rotating low-cost MEMS IMU, compared to those errors in a non-rotating system. Moreover, the observability of the roll and pitch errors, the accelerometer biases in the horizontal axes, and the gyro bias in the vertical direction can be significantly improved by IMU rotations.