Sensorless admittance control of cycle ergometer for rehabilitation

This paper proposes a new control scheme for the cycle ergometer, sensorlsss admittance control. The Proposed control algorithm consists of admittance controller, exercise intensity and speed adjustment controller, and interaction torque estimator which can decrease the cost of the cycle ergometer while providing the advantages of impedance control. With impedance control, the device can provide various dynamic responses by tuning impedance to various rehabilitation exercise scenarios. The admittance controller is adopted instead of the impedance controller for stability. The disturbance observer is established with a friction model and dynamic model of the device to estimate the interaction torque without torque sensor. Some experiments are conducted to verify the performance of the interaction torque estimator and to verify the performance of the sensorless admittance controller. The results show that the torque was well estimated for the different ratio of impedance with the passive operation mode and the auto operation mode.