Abstract
The generation of precise hand movements with functional electrical stimulation (FES) via surface electrodes on the forearm faces several challenges. Besides the biomechanical complexity and the required selectivity, the rotation of the forearm during reach-and-grasp tasks leads to a relative change between the skin and underlying tissue, resulting in a varying FES response. We present a new method for automatic adaptation of virtual electrodes (size, position) and stimulation intensity in an electrode array to guarantee a secure grasp during forearm movements. The method involves motion tracking of arm and hand with inertial sensors. This enables the estimation of grasping strength when using elastic objects. Experiments in healthy volunteers revealed that our method allows generating a strong, stable grasp force regardless of the rotational state of the forearm.
Zusammenfassung
Die Erzeugung präziser Handbewegungen mit funktioneller Elektrostimulation über Elektroden am Unterarm ist eine Herausforderung. Neben der biomechanischen Komplexität und der erforderlichen Selektivität führt die Drehung des Unterarms zu einer relativen Verschiebung von Haut und darunter liegendem Gewebe, was zu einer veränderten Reaktion auf die FES führt. Wir stellen eine neue Methode zur automatischen Anpassung einer virtuellen Elektrode (Größe, Position) und der Stimulationsintensität in einem Elektrodenarray vor, mit der ein sicherer Griff während Unterarmbewegungen gewährleistet wird. Über Inertialsensoren werden Arm- und Handbewegungen erfasst. Zusätzlich kann die Griffstärke bei komprimierbaren Objekten geschätzt werden. In Experimenten an gesunden Probanden konnte eine starke, stabile Greifkraft unabhängig vom Rotationszustand des Unterarms erzeugt werden.
Funding source: Bundesministerium für Bildung und Forschung
Award Identifier / Grant number: FKZ16SV7069K
Funding statement: The presented work was partly conducted within the research project BeMobil, supported by the German Federal Ministry of Education and Research (FKZ16SV7069K).
About the authors
Christina Salchow-Hömmen received her Bachelor’s (2012) and Master’s degree (2014) in Biomedical Engineering from the Technische Universität Ilmenau, Germany. During her studies, she stayed at the Washington University in St. Louis, USA, for a seven-month research internship. Since 2014, she is a Ph.D. candidate at the Control Systems Group at the Technische Universität Berlin, Germany. Her research focuses on rehabilitation engineering and neuroscience.
Till Thomas received his Bachelor’s degree (2015) in Biomedical Engineering from the Ernst-Abbe-Hochschule Jena – University of Applied Sciences, Germany. During his studies towards his Master’s degree at the Technische Universität Berlin (Germany), he worked as a student assistant at the Control Systems Group. In 2018, he spoke at the AUTOMED workshop in Villingen-Schwenningen.
Markus Valtin received his Diploma (2012) in Electrical Engineering at the Technische Universität Berlin, Germany. Since 2012, he is a Ph.D. candidate at the Control Systems Group. His research focuses on Rehabilitation Engineering with the main topics functional electrical stimulation via electrode arrays and inertial sensor applications.
Thomas Schauer studied Electrical Engineering at the University Magdeburg in Germany from 1992 to 1997. He received his Ph.D. degree in Mechanical Engineering from the University of Glasgow in Scotland. From December 2001 until April 2006 he has been working as research assistant and project leader at the Max Planck Institute for Dynamics of Complex Technical Systems (Magdeburg, Germany) in the Systems and Control Theory Group. Since 2006 he holds a position as senior researcher in the Control Systems Group at the Technische Universität Berlin and manages the research topic “Rehabilitation Engineering and Assistive Technology”.
Acknowledgment
We thank all volunteers, Würth Elektronik (Germany) for manufacturing the electrode arrays, and Axelgaard Manufacturing Co. (Ltd., USA) for contributing the hydro-gel layers.
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