Towards Variable Assistance for Lower Body Exoskeletons

TL;DR

This paper introduces a novel safety-critical control framework for lower body exoskeletons that allows adjustable deviation from a gait, improving robustness and facilitating spinal learning in users.

Contribution

It proposes a control barrier function-based method to regulate joint deviations in exoskeletons, enhancing safety and adaptability during assisted walking.

Findings

Method effectively controls joint deviations in experiments.

Demonstrated robustness to patient perturbations.

Improves gait flexibility and safety.

Abstract

This paper presents and experimentally demonstrates a novel framework for variable assistance on lower body exoskeletons, based upon safety-critical control methods. Existing work has shown that providing some freedom of movement around a nominal gait, instead of rigidly following it, accelerates the spinal learning process of people with a walking impediment when using a lower body exoskeleton. With this as motivation, we present a method to accurately control how much a subject is allowed to deviate from a given gait while ensuring robustness to patient perturbation. This method leverages control barrier functions to force certain joints to remain inside predefined trajectory tubes in a minimally invasive way. The effectiveness of the method is demonstrated experimentally with able-bodied subjects and the Atalante lower body exoskeleton.