Resonance Impedance Shaping Control of Hip Robotic Exoskeleton

The hip assistance robotic exoskeleton has been demonstrated as an effective device to assist elderly and disabled people with gait disorders. The assistance efficiency of these devices, however, is less optimized because the parameters in the active impedance control are manually designated. This paper presented a novel assistance control scheme to address the sub-optimal issue. This study poses that the assistance efficiency can be maximized by modifying the mechanical impedance to resonate with the muscle driving force, in which the human-exoskeleton coupling system is approximated with a second-order dynamical system. Based on this, the exoskeleton virtual stiffness is adaptively tuned to make the system intrinsic frequency align with the intended swing frequency. The proposed assistance control scheme demonstrated an increased assistance efficiency than the conventional active impedance control in a simulated study. Experiments that were managed on a newly custom-made hip assistance robotic exoskeleton also demonstrated strong evidence of improved gait kinematics with decreased muscle-skeleton efforts.