Abstract
Functional electrical stimulation (FES) and robotic exoskeletons are two important technologies widely used for physical rehabilitation of paraplegic patients. We developed a hybrid rehabilitation system (FEXO Knee) that combined FES and an exoskeleton for swinging movement control of human knee joints. This study proposed a novel cooperative control strategy, which could realize arbitrary distribution of torque generated by FES and exoskeleton, and guarantee harmonic movements. The cooperative control adopted feedfoward control for FES and feedback control for exoskeleton. A parameter regulator was designed to update key parameters in real time to coordinate FES controller and exoskeleton controller. Two muscle groups (quadriceps and hamstrings) were stimulated to generate active torque for knee joint in synchronization with torque compensation from exoskeleton. The knee joint angle and the interactive torque between exoskeleton and shank were used as feedback signals for the control system. Central pattern generator (CPG) was adopted that acted as a phase predictor to deal with phase confliction of motor patterns, and realized synchronization between the two different bodies (shank and exoskeleton). Experimental evaluation of the hybrid FES-exoskeleton system was conducted on five healthy subjects and four paraplegic patients. Experimental results and statistical analysis showed good control performance of the cooperative control on torque distribution, trajectory tracking, and phase synchronization.
Highlights
Neurologic injuries such as stroke and spinal cord injury may cause paresis in patients and give rise to movement disability
It demonstrates the efficiency of FEXO Knee, which can distribute the torque upon any requirements and keep Functional electrical stimulation (FES)-induced muscles and the exoskeleton work in a synchronized manner
The results reveal that the primary goal of FEXO Knee that aims to regulate the torque distribution between FES and the exoskeleton is accomplished to some extent
Summary
Neurologic injuries such as stroke and spinal cord injury may cause paresis in patients and give rise to movement disability. Physical rehabilitation is highly necessary for paralyzed individuals to restore mobility of extremities. Functional electrical stimulation (FES) and robotic exoskeletons are two important technologies used widely in extremity rehabilitation. Many FES systems have been developed by using either surface or implanted electrodes in the past decades (Popovic et al, 2001). As a neuro-rehabilitation approach that excites and activates muscles directly, FES can provide functional training and therapeutic benefits to paralyzed patients. Some advances in closed-loop control and multichannel selection
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