Abstract
In this study, we investigated the possibility of extending our equilibrium point control model by functional electrical stimulation (FES). While FES has been studied extensively in an isometric environment, the goal of the present work is to extend it to an unconstrained environment. Our model uses the electrical agonist-antagonist muscle (EAA) ratio, which is closely related to the joint angle corresponding to the equilibrium point. In addition, EAA activity has a close relationship with joint stiffness. We represented FES control by a model that has a neuromuscular system and a musculoskeletal system. We verified whether our model is reasonable through analysis of the frequency characteristics. We modeled the musculoskeletal system for human elbow joint movement, and verified our model by studying the frequency characteristics between input and output. We assumed that the EAA ratio is an input while the elbow joint angle is an output. We showed that by coupling the model of neuromuscular system and the model of musculoskeletal system, we were able to explain the frequency characteristic of the total model. From these results, we showed the validity of our model and indicated the possibility of achieving FES control under an unconstrained environment.
