Hybrid FES-Exoskeleton Controller to Assist Sit-To-Stand movement

Sit To Stand (STS) movement is an important daily living activity and usually a difficult task to achieve, particularly, by post stroke patients. In this study a hybrid control approach that combines the use of an impedance-based exoskeleton controller and an event-based Functional Electrical Stimulation (FES) of the knee extensor muscle to assist the STS transfer movement within an assistance as needed strategy. Actuation of the active lower limb exoskeleton is done using a Serial Elastic Actuator (SEA) that uses a torsion spring to guarantee the measurement of the human exoskeleton interaction torque. The measured torque is fed to a linear desired impedance model to generate a desired trajectory, which will be tracked by the exoskeleton's actuators. Experiments were conducted with one healthy subject to evaluate the feasibility and effectiveness of the proposed approach. The obtained performances show the synergy between the assistance provided through FES of the quadriceps muscle during the extension sub-phase of the STS movement and the one delivered by the knee joint actuator of the lower limb exoskeleton. (C) 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.