多チャンネル型機能的電気刺激によるヒト肘関節運動の平衡点制御

Abstract

Functional electrical stimulation (FES) has been considered to be an effective technique for aiding quadriplegic persons. However, the musculoskeletal system is highly nonlinear and varies with time; moreover, it is subjected to fatigue and has variable reflex characteristics. It is also difficult to stably and accurately control the limbs using FES. In this paper, we propose a simple FES method that is consistent with the motion control mechanism observed in humans. We focus on joint motion by a pair of agonist-antagonist muscles of the musculoskeletal system, and define the “electrical agonist-antagonist muscle ratio (EAA ratio)” and “electrical agonist-antagonist muscle activity (EAA activity)” in the light of the agonist-antagonist muscle ratio and agonist-antagonist muscle activity, respectively, proposed to extract the equilibrium point and stiffness from Electromyography (EMG) signals. The agonist-antagonist muscle ratio and agonist-antagonist muscle activity are based on the theory that the equilibrium point and stiffness of the agonist-antagonist motion system controlled by the central nerve system. We derived the transfer function between the input EAA ratio and force output of the end-point; this transfer function model is expressed as a cascade-coupled dead time system and secondary delay system. Through the agonist-antagonist muscle stimulation pattern determined by this transfer function model, high-speed, high-precision, and smooth control of the hand force were achieved.