Hybrid FES orthosis incorporating closed loop control and sensory feedback

Abstract

A hybrid functional electrical stimulation (FES) orthosis is described, comprising a rigid ankle-foot brace, a multi-channel FES stimulator with surface electrodes, body mounted sensors, a ‘rule-based’ controller and an electro-cutaneous display for supplementary sensory feedback. The mechanical brace provides stability, without FES activation of muscles, for standing postures normally adopted by patients. This avoids inducing muscle fatigue during prolonged upright activity. However, stability is conditional upon the position of the ground reaction vector (GRV) relative to the knee joint. The finite state FES controller reacts automatically to destabilizing shifts of the GRV by stimulating appropriate anti-gravity musculature to brace the leg. The FES system also features a control mode to initiate and terminate flexion of the leg during forward progression. A simple mode of supplementary sensory feedback was used during the laboratory standing tests to assist the patient in maintaining a set posture. Preliminary results of laboratory tests for two spinal cord injured subjects are presented.