Assist-as-needed Hip Exoskeleton Control for Gait Asymmetry Correction via Human-in-the-loop Optimization

Gait asymmetry is a significant clinical characteristic of hemiplegic gait that most stroke survivors suffer, leading to limited mobility and long-term negative impacts on their quality of life. Although a variety of exoskeleton controls have been developed for robot-aided gait rehabilitation, little attention has been paid to correcting the gait asymmetry of stroke patients, and it remains challenging to properly share control between the exoskeleton and patients with partial motor control. In view of this, an assist-as-needed (AAN) hip exoskeleton control with human-in-the-loop optimization is proposed to correct gait asymmetry in hemiplegic gait. To realize the AAN concept, an objective function was designed for real-time evaluation of the subject's gait performance and active participation, which considers the variability of natural human movement and guides the online tuning of control parameters on a subject-specific basis. In this way, subjects were stimulated to contribute as much as possible to movement, thus maximizing the efficiency and outcomes of gait rehabilitation. Finally, an experimental study was conducted to verify the feasibility of the proposed control with simulated hemiplegic gait, and the common hypothesis that AAN controls can improve active human participation was clearly validated from a biomechanics perspective.