Design of Active Disturbance Rejection Control for Rehabilitation-Assistant Device of Lower Limbs under Cross Coupling Effect

The robotic exoskeleton is a device which is designed to actuate the lower limbs of human leg for rehabilitation purposes. This device is used instead of physicians in rehabilitation clinics to recover the normal activities of dysfunctional parts. In this study, design of ADRC has been presented to control the motion of hip and knee joints for rehabilitated patients who wearing the exoskeleton device. The key of ADRC approach is to use extended state observer (ESO) for estimating the total uncertainties of the system and to compensate them in feedback-based control law. The proposed control scheme has been designed to reduce the coupling effect due to the cross coupling of upper and lower legs. The stability of ADRC-based system has been proven based on Lyapunov method. The effectiveness of proposed ADRC for hip and joint rehabilitated device has been verified via numerical simulations within MATLAB environment. The tests have been conducted including load and no-load exertion. As compared to proportional derivative controller, the numerical results revealed that the proposed ADRC gives better tracking performance and higher precision while maintaining appropriate control torque.