Torque control by EMG feedback in normal and stroke subjects performing ankle angle tracking with a rehabilitation robot

The goal of this study was to investigate the eligibility of using surface electromyography (EMG) as a feedback signal for ankle torque control in both normal and stroke subjects performing ankle joint angle tracking with a rehabilitation robot. The potential advantage of using EMG as an estimator of active torque is direct facilitation of torque control of individual muscle. A fuzzy PD+I controller was implemented to control the robot. A static EMG-torque map was constructed at 5 ankle positions experimentally for each subject. The map was interpolated to estimate the active dorsiflexion torque exerted on the ankle from the EMG of tibialis anterior muscle. Both EMG and the output of the torque sensor were acquired and a weighting factor was used to adjust the relative contribution from these two signals for controlling the robot. Six normal subjects and seven stroke patients were recruited. The angle trajectory to be tracked was alternating ramps (37s) of dorsiflexion and plantarfiexion. The results showed that all the tested combinations of EMG and the torque sensor signal could be used as the feedback signal for torque control during angle tracking with the robot. The normal subjects had a better performance than the stroke patients and the tracking performance was better when only the signal from the torque sensor was used.