Robust Plug-and-Play Joint Axis Estimation Using Inertial Sensors

Robust Plug-and-Play Joint Axis Estimation Using Inertial Sensors

Olsson, Fredrik (Uppsala University)
Kok, M. (TU Delft Team Jan-Willem van Wingerden)
Seel, Thomas (Technical University of Berlin)
Halvorsen, Kjartan (Uppsala University; Tecnologico de Monterrey)

2020

Inertial motion capture relies on accurate sensor-to-segment calibration. When two segments are connected by a hinge joint, for example in human knee or finger joints as well as in many robotic limbs, then the joint axis vector must be identified in the intrinsic sensor coordinate systems. Methods for estimating the joint axis using accelerations and angular rates of arbitrary motion have been proposed, but the user must perform sufficiently informative motion in a predefined initial time window to accomplish complete identifiability. Another drawback of state of the art methods is that the user has no way of knowing if the calibration was successful or not. To achieve plug-and-play calibration, it is therefore important that 1) sufficiently informative data can be extracted even if large portions of the data set consist of non-informative motions, and 2) the user knows when the calibration has reached a sufficient level of accuracy. In the current paper, we propose a novel method that achieves both of these goals. The method combines acceleration- and angular rate information and finds a globally optimal estimate of the joint axis. Methods for sample selection, that overcome the limitation of a dedicated initial calibration time window, are proposed. The sample selection allows estimation to be performed using only a small subset of samples from a larger data set as it deselects non-informative and redundant measurements. Finally, an uncertainty quantification method that assures validity of the estimated joint axis parameters, is proposed. Experimental validation of the method is provided using a mechanical joint performing a large range of motions. Angular errors in the order of 2 ∘ were achieved using 125-1000 selected samples. The proposed method is the first truly plug-and-play method that overcome the need for a specific calibration phase and, regardless of the user's motions, it provides an accurate estimate of the joint axis as soon as possible.

gyroscopes and accelerometers
inertial measurement units
joint axis identification
kinematic constraints
sensor-to-segment calibration
validation on mechanical joint

http://resolver.tudelft.nl/uuid:c16dfdc0-4b56-4d9a-9c64-93e2d8986c43

https://doi.org/10.3390/s20123534

1424-8220

Sensors, 20 (12)

Institutional Repository

journal article

© 2020 Fredrik Olsson, M. Kok, Thomas Seel, Kjartan Halvorsen