Model-based Control for Gait Assistance in the Frontal Plane

There is a growing interest in developing devices for human gait assistance. Most research focuses on the sagittal plane's assistance, assuming that walking is predominantly a sagittal plane motion. However, movements in the frontal plane have particular importance for balance control as well as load carrying. This paper studies hip abduction assistance and proposes using a simple human locomotion model as a guideline for designing and controlling assistive devices. We introduce the force modulated compliant hip (FMCH) model in the frontal plane, which applies the ground reaction force to tune the hip abductor/adductor stiffness. The effects of this model-based control approach on walking gait are investigated through leg muscles' activation, metabolic costs, and adaptability to a new condition (carrying 38 kg extra load) for seven healthy young subjects using an experiment-based simulation in OpenSim. Our results show 6.72 ± 0.6% and 11 ± 0.3% reduction in metabolic cost for walking at a freely selected speed and while load carrying, respectively. Also, compensating for increased muscle activation while carrying extra load due to the hip compliance adjustment by leg force feedback approves the adaptability of the proposed control approach.