Identification of human limb stiffness in 5 DoF and estimation via EMG

Abstract

To approach robustness and optimal performance, biological musculo-skeletal 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.