Optimization-based gravity-assisted calibration and axis alignment of 9-degrees of freedom inertial measurement unit without external equipment

Abstract

Applicable in numerous fields, low-cost micro-electromechanical system inertial measurement units often require on-sight calibration by the end user due to the existence of systematic errors. A 9-degrees of freedom inertial measurement unit comprises a tri-axis accelerometer, a tri-axis gyroscope, and a tri-axis magnetometer. Various proposed multi-position calibration methods can calibrate tri-axis accelerometers and magnetometers to a degree. Yet the full calibration of a tri-axis gyroscope and axis alignment of all the sensors still often requires equipment such as a rate table to generate a priori known angular velocities and attitudes or relies on the disturbance-prone magnetometer output as a reference. This study proposes an augmentation to the popular multi-position calibration scheme, capable of fully calibrating and aligning the sensor axes of the 9-degrees of freedom inertial measurement unit while eliminating the reliance on external equipment or magnetometer. The algorithm does not rely on the inertial measurement unit attitude during various stages of the multi-position data acquisition. Instead, it uses the gravity vector measured by the accelerometer to calibrate the gyroscope and align the magnetometer axes with the sensor body frame. Experimental results using a navigation module with factory calibration and extensive simulation results indicate the current method's ability in estimating large calibration parameters with relative errors below 0.5%.