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Compensation of large motion sensor displacements during long recordings of limb movements |
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| Authors: | Dominik Karch Keun-Sun Kim Katarzyna Wochner Heike Philippi Joachim Pietz Hartmut Dickhaus |
| Affiliation: | 1. Institute of Medical Biometry and Informatics, University of Heidelberg, Im Neuenheimer Feld 305, 69120 Heidelberg, Germany;2. Center for Child and Adolescent Medicine, University Hospital Heidelberg;3. Center of Developmental Medicine, Frankfurt;1. The State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China;2. State Key Laboratory for Mechanical Behavior of Materials, Xi''an Jiaotong University, Xi''an 710049, China;3. Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical and Materials Engineering, University of Texas at El Paso, El Paso, TX 79968-0521, USA;1. Materials Science and Metallurgy, University of Cambridge, UK;2. Materials Engineering and Industrial Technologies, University of Trento, Italy;3. Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany;1. Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, 40237 Düsseldorf, Germany;2. Department of Materials Physics, Montanuniversität Leoben, Franz Josef-Straße 18, 8700 Leoben, Austria;3. University Grenoble Alps, CEA-Grenoble, Institut Nanosciences et Cryogénie, rue des Martyrs 17, 38054 Grenoble, France;1. State Key Laboratory of Rolling and Automation, Northeastern University, No.3 Wenhua Road, Shenyang 110819, China;2. Department of Metallurgical, Materials, and Biomedical Engineering, University of Texas at El Paso, TX 79968, USA |
| 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. This 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 define a so called fixed technical frame is proposed as a robust reference frame which can adapt to a new sensor orientation on the skin. The 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. The reliability of the fixed technical frame is quantified 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 fixed technical frame. |
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