Abstract
Micro-electro-mechanical-systems (MEMS) inertial measurement unit (IMU) outputs are corrupted by significant sensor errors. The navigation errors of a MEMS-based inertial navigation system will therefore accumulate very quickly over time. This requires aiding from other sensors such as Global Navigation Satellite Systems (GNSS). However, it will still remain a significant challenge in the presence of GNSS outages, which are typically in urban canopies. This paper 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. A rotary INS has the potential to significantly increase the time period that INS can bridge GNSS outages and make MEMS IMU possible to maintain longer autonomous navigation performance when there is no external aiding. In this research, several IMU rotation schemes (rotation about X-, Y- and Z-axes) are analyzed to mitigate the navigation errors caused by MEMS IMU sensor errors. As the IMU rotation induces additional sensor errors, a calibration process is proposed to remove the induced errors. Tests are further conducted with two MEMS IMUs installed on a tri-axial rotation table to verify the error mitigation by IMU rotations.
Highlights
Tens of years ago, to maintain long term autonomous navigation performance, the inertial navigation system (INS) was designed based on high end inertial sensors such as ring laser gyro (RLG)and fiber optical gyro (FOG)
The inertial measurement unit (IMU) rotation modulates the constant biases of inertial sensors that perpendicular to the rotation axis, and the attitude and velocity errors caused by such biases are self-eliminated after a complete rotation cycle; The constant biases of inertial sensors in the rotation axis cannot be modulated, and the attitude and velocity errors caused by such errors propagate in the same way as in conventional INS; The IMU rotation induces an extra error in the gyro of the rotation axis due to gyro scale factor, and this error results in accumulated attitude errors in the direction of the corresponding rotation axis; The IMU rotation induces extra errors in the gyros that are perpendicular to the rotation axis due to gyro installation errors, resulting in attitude and velocity errors
As the IMU rotation induces additional gyro biases, which eventually leads to navigation errors [17,26], a calibration process is proposed for rotary INS with IMU rotation about Z-axis
Summary
To maintain long term autonomous navigation performance, the inertial navigation system (INS) was designed based on high end inertial sensors such as ring laser gyro (RLG). Comparing to the low-cost MEMS IMU, FOG and RLG errors are orders of magnitude smaller, and the application of the rotation modulation technique to FOG and RLG based IMU can effectively mitigate the error accumulations. For MEMS IMU, due to their significant bias instability, scale factor, installation errors, as well as noise, how can the application of the rotation modulation technique help reduce the navigation errors is not clear so far which requires investigation. Real rotated tests must be conducted in order to fully investigate the feasibility of MEMS-based rotary systems for practical applications. This is the main objective of this contribution with the following specific research efforts:. IMUs on a MEMS tri-axial rotation calibration process is proposed and3.introduced
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