Continuous locomotion mode classification using a robotic hip exoskeleton

Abstract

Human augmentation through robotic exoskeleton technology can enhance the user’s mobility for a wide range of ambulation tasks. This is done by providing assistance that is in line with the user’s movement during different locomotion modes (e.g., ramps and stairs). Several machine learning techniques have been applied to classify such tasks on lower limb prostheses, but these strategies have not been applied extensively to exoskeleton systems which often rely on similar control inputs. Additionally, conventional methods often identify modes at a discrete time during the gait cycle which can delay the corresponding assistance to the user and potentially reduce overall exoskeleton benefit. We developed a gait phase-based Bayesian classifier that can classify five ambulation modes continuously throughout the gait cycle using only mechanical sensors on the device. From our five ablebodied subject experiment with a robotic hip exoskeleton, we found that implementing multiple models within the gait cycle can reduce the classification error rate by 35% compared to using a single model $(p \lt 0.05)$. Furthermore, we found that utilizing bilateral sensor information can reduce the error by 43% compared to using a unilateral information $(p \lt 0.05)$. Our study findings provide valuable information for future exoskeleton developers to utilize different on-board mechanical sensors to enhance mode classification for a faster update rate in the controller and provide more natural and seamless exoskeleton assistance between locomotion modes.