Extending kalibr: Calibrating the extrinsics of multiple IMUs and of individual axes

TLDR

Robotic systems increasingly employ multiple IMUs, often mounted far from the center of gravity or to avoid obstruction, causing each unit to sense different accelerations during rotational motions. This work derives a method to spatially calibrate multiple IMUs within a single estimator using the open‑source kalibr toolbox. We extend kalibr to estimate IMU intrinsics, enabling accurate calibration of low‑cost IMUs. The extended estimator precisely determines intrinsics and can localize individual accelerometer axes inside a commercial IMU to millimeter precision.

Abstract

An increasing number of robotic systems feature multiple inertial measurement units (IMUs). Due to competing objectives-either desired vicinity to the center of gravity when used in controls, or an unobstructed field of view when integrated in a sensor setup with an exteroceptive sensor for ego-motion estimation-individual IMUs are often mounted at considerable distance. As a result, they sense different accelerations when the platform is subjected to rotational motions. In this work, we derive a method for spatially calibrating multiple IMUs in a single estimator based on the open-source camera/IMU calibration toolbox kalibr. We further extend the toolbox to determine IMU intrinsics, enabling accurate calibration of low-cost IMUs. The results suggest that the extended estimator is capable of precisely determining these intrinsics and even of localizing individual accelerometer axes inside a commercial grade IMU to millimeter precision.