Stimulation Interval Evaluation for Lower-Limb Cycling Movement Based on Torque Observer

A functional electrical stimulation (FES) assisted cycling ergometer incorporating passive or active movement has been proven to be effective in rehabilitation for stroke patients. Although a conventional five-bar linkage model of lower-limb cycling movement was proposed earlier to evaluate the stimulation interval, the accuracy of the obtained anthropometric data of patients still remains uncertain. To properly deliver FES during cycling for restoring the physical strength of patients, this study proposes a method of stimulation interval evaluation by integrating a torque observer into a motor driven cycle ergometer. The torque observer design, which is based on the measured motor current and position information, is employed to evaluate the stimulation interval without measuring the anthropometric data of patients. Simulated and experimental results were compared to verify the effectiveness of the proposed torque observer approach; meanwhile, the results of the study showed that the torque observer indeed provides a proper stimulation interval for FES in comparison to that of the conventional five-bar linkage model.