Identification of Human Limb Stiffness in 5 DoF and Estimation via EMG

To approach robustness and optimal performance, biological musculoskeletal systems can adapt their impedance while interacting with their environment. This property has motivated modern robotic designs including variable-impedance actuators and control methods, based on the capability to vary visco-elastic properties actively or passively. Even though variable-impedance actuation and impedance control in robotics is resolved to a great part, a general set of rules by which impedance is adjusted related to the task at hand is still lacking. This paper aims to fill this gap by providing a method to estimate the stiffness of the human arm in more than two degrees of freedom by perturbation. To overcome ill-conditionedness of the impedance and inertial matrices, we propose and validate methods to separately identify inertial and stiffness parameters. Finally, a model is proposed to estimate the joint stiffness from EMG-measurements of muscle activities. 1 Motivation, Problem Statement, Related Work Dynamic interaction with the environment means handling impacts and unknown contact forces. Therefore compliant systems are active topics of research in the field of robotics. Surpassing traditional rigid robots, the control loops of modern robotic systems are extended with additional impedance parameters, viz. stiffness and damping. Dominic Lakatos, Daniel Rüschen, Jörn Vogel and Patrick van der Smagt Institute of Robotics and Mechatronics, German Aerospace Center (DLR), D-82234 Oberpfaffenhofen, Germany e-mail: {dominic.lakatos,daniel.rueschen,joern.vogel,smagt}@ dlr.de Justin Bayer Chair for Robotics and Embedded Systems of the Department of Informatics of the Technische Universität München, D-80333 München e-mail: [email protected].