Non-linear adaptive impedance controller for rehabilitation purposes

Rehabilitation robotics is a field of research in continuous growth and evolution. Its main purpose is to develop suitable robotics devices and control strategies to assist patient's movements during training. To do that, advanced control strategies and implementation of suitable force feedback for these robotic devices have been developed for rehabilitation purposes. This paper describes a novel control strategy, focused in a nonlinear adaptive impedance controller based on position errors, whose aims are: to adapt the exercise to the type and level of injury of patients, to avoid the phenomenon of slack and to help to evaluate performance indices of training sections. Moreover, thanks to the simplicity of the control algorithm and the no additional sensors it can be easily applied in low-cost devices. Several tests are presented using a five-bar linkage robotic device used for upper limbs rehabilitation therapies. The related results help to evaluate performances of this adaptive controller and show its 'assist-as-needed' feature.