Compensation of large motion sensor displacements during long recordings of limb movements

Abstract

In motion capture applications using electromagnetic tracking systems the process of anatomical calibration associates the technical frames of sensors attached to the skin with the human anatomy. Joint centers and axes are determined relative to these frames. A change of orientation of the sensor relative to the skin renders this calibration faulty. is sensitivity regarding sensor displacement can turn out to be a serious problem with movement recordings of several minutes duration. We propose the "dislocation distance" as a novel method to quantify sensor displacement and to detect gradual and sudden changes of sensor orientation. Furthermore a method to de ne a so called xed technical frame is proposed as a robust reference frame which can adapt to a new sensor orientation on the skin. e proposed methods are applied to quantify the effects of sensor displacement of 120 upper and lower limb movement recordings of newborns revealing the need for a method to compensate for sensor displacement. e reliability of the xed technical frame is quanti ed and it is shown that trend and dispersion of the dislocation distance can be significantly reduced. A working example illustrates the consequences of sensor displacement on derived angle time series and how they are avoided using the xed technical frame.

Design and validation of surface-marker clusters for the quantification of joint rotations in general movements in early infancy

“…2D), the largest range of difference was found in the lateral/medial component, the longitudinal axis being most susceptible to slippage of the inertial sensor as it is housed in a large rigid casing (38 Â 53 Â 21 mm 3 ). Finally, when rotations around all axes were considered, good agreement between methods was observed (see Table 1), with statistics consistent with those published by Saber-Sheikh et al (2010) who compared the XSens inertial sensor with an EMT system such as that used by Karch et al (2010).…”

“…The clusters were holed along the main axis to maximize flexibility across that axis, thus making it possible to bend the cluster and closely fit the profile of the limb. This approach limits slippages during movement or contact that may result in shifting of the cluster (a problem discussed in Karch et al, 2010 in the context of EMTs). A smooth fabric (in this case black felt) was placed between the skin and Velcro to avoid skin irritation.…”

Kinematic assessment of stereotypy in spontaneous movements in infants

“…ese angle time-series constitute the degrees of freedom of the model (according to [14,15,16]). At the age of 24 months the infants attended a follow-up examination in order to determine if they had developed .…”

Infant trunk posture and arm movement assessment using pressure mattress, inertial and magnetic measurement units (IMUs)

“…Electromagnetic (EM) tracking systems [ 24 ] have been used in cooperation with motion sensor displacement removal methods [ 25 ] to surpass the line-of-sight requirements of optical systems, but suffer from movement limitations due to wiring.…”