A Bioinspired Control Strategy for the CYBERLEGs Knee-Ankle-Foot Orthosis: Feasibility Study with Lower-Limb Amputees

Lower-limb loss is a dramatic event affecting quality of life and often reducing independence. An active Knee-Ankle-Foot Orthosis (KAFO) could represent an assistive tool for lower-limb amputees to reduce the additional metabolic effort resulting from compensatory strategies due to walking with a passive prosthesis. Within the CYBERLEGs project, a novel active KAFO was designed to assist the knee and the ankle joints during ground level walking. In this paper the mechatronic design of the device is presented for the first time. Moreover, the paper presents the control strategy developed to provide knee and ankle assistance and the experimental results with two volunteers with lower-limb amputation. The KAFO was shown to: (i) fulfill all the design functional requirements to comply with range of motion, torque, speed and power; and (ii) provide assistive torque in the most demanding phases of the gait cycle. Tests with end-users showed that the assistive action resulted in physiological profiles of the knee and ankle angles and torques, showing a first proof of feasibility for the presented system. Both subjects reported comfortable interaction with the exoskeleton, but results on the metabolic consumption were not conclusive. This feasibility study will be extended in the future with an optimized controller to further explore the effectiveness of the system.