Improved Calibration Procedure for Wireless Inertial Measurement Units without Precision Equipment

TL;DR

This paper enhances a wireless IMU calibration method to be faster and more robust, reducing calibration time from 5 to under 2 minutes without losing accuracy, making it more practical for end-users.

Contribution

The authors improve Tedaldi's calibration method by introducing algorithmic and procedural enhancements, including fewer required orientations and handling wireless packet loss.

Findings

Calibration with 12 orientations is sufficient for high accuracy.

Calibration time reduced from 5 minutes to under 2 minutes.

Method maintains accuracy despite fewer calibration orientations.

Abstract

Inertial measurement units (IMUs) are used in medical applications for many different purposes. However, an IMU's measurement accuracy can degrade over time, entailing re-calibration. In their 2014 paper, Tedaldi et al. presented an IMU calibration method that does not require external precision equipment or complex procedures. This allows end-users or personnel without expert knowledge of inertial measurement to re-calibrate the sensors by placing them in several suitable but not precisely defined orientations. In this work, we present several improvements to Tedaldi's method, both on the algorithmic level and the calibration procedure: adaptions for low noise accelerometers, a calibration helper object, and packet loss compensation for wireless calibration. We applied the modified calibration procedure to our custom-built IMU platform and verified the consistency of results across multiple calibration runs. In order to minimize the time needed for re-calibration, we analyzed how the calibration result accuracy degrades when fewer calibration orientations are used. We found that N=12 different orientations are sufficient to achieve a very good calibration, and more orientations yielded only marginal improvements. This is a significant improvement compared to the 37 to 50 orientations recommended by Tedaldi. Thus, we were reduced the time required to calibrate a single IMU from ca. 5 minutes to less than 2 minutes without sacrificing any meaningful calibration accuracy.