Human-inspired balancing assistance: Application to a knee exoskeleton

As the impedance profiles of the human joints vary substantially during motion, the employment of variable impedance systems into exoskeletons, orthoses and prostheses that will be able to produce human-like mechanics could have significant benefits. In this direction, this manuscript presents a generic technique to estimate active joint stiffness based on an EMG-driven musculoskeletal model whose parameters are adjusted using experimental data obtained from common perturbation methods. In addition, a human balancing experiment was carried out to investigate correlations between the anteroposterior excursions of the center of pressure (CoP) with kinematic, kinetic, electromyographic measurements as well as the model stiffness of the knee joint. Motivated by the results of the cross-correlation analysis we present a human-inspired balancing assistance control for lower limb exoskeletons that permits for volitional stiffness regulation. Preliminary experimental evaluation is conducted using an assistive knee exoskeleton. The results indicate that the proposed control technique can be generalized to command a whole lower limb exoskeleton in order to provide effective balancing assistance to the user.