Reactive torque monitoring and cycling speed control of a belt-driven cycle ergometer

The lower limb cycle ergometer driven by a motor is a typical rehabilitation-assistive device for hemiparetic patients with abnormal muscle tone in their lower limbs. Since unusual muscle tone may cause excessive spasticity during rehabilitation, it is important to monitor reactive torques produced primarily by the abnormal muscle tone. Thus, this study investigated a state observer design applied to a belt-driven ergometer, where the motor current and position information were used to estimate reliable reactive torque. A dual feedback control loop was proposed to improve the resonance caused by the belt-driven structure and stabilize the cycling speed in the cycle rehabilitated device; meanwhile, the impedance model constructed by the feedback control loop is presented to generate the compliance characteristic for stably and gently controlling the speed response affected by reactive torque. Simulation and experiments of the belt-driven ergometer were conducted with results validating the effectiveness of the proposed control scheme in terms of stable cycle speed and observer performance.