Synergetic control strategy for a hybrid FES-exoskeleton system: A simulation study

Abstract

This paper proposes a novel control strategy for a hybrid assistive system that combines functional electrical stimulation (FES) with a powered lower extremity exoskeleton to provide adaptive torque assistance for paraplegic patients. The control architecture is based on central pattern generator (CPG) that acts as a feature extractor, and a proportional-derivative (PD) controller that adaptively regulates the exoskeleton's assistive torque. Currently our work focuses on controlling the swing of shank, so two muscle groups (Vasti and Hamstrings) are stimulated to produce active torque for knee joint. However some drawbacks such as rapid muscle fatigue and uneven muscle response severely limit FES-aided systems. We use a powered extremity exoskeleton to adaptively compensate the torque loss. The CPG model keeps its output in phase with the measured angle trajectory to predict total torque with a torque estimator. The PD controller regulates the gain that determines how much of estimated total torque should feed back to the musculoskeletal system. The control system is implemented in MATLAB/SIMULINK. © 2013 Springer-Verlag Berlin Heidelberg.