Sensorless Impedance Control for the TWIN Lower Limb Exoskeleton: A Preliminary Study

Abstract

The need of compliant control strategies, such as force interaction controllers, to improve the quality of lower limb robotic rehabilitation in terms of active patient participation has shown a growing interest in the past decades. On the other hand, the importance of more compact, lighter and, therefore, wearable exoskeleton devices appears still to be an unresolved issue limiting the adoption and utilization of robotic exoskeletons. In this work, the authors propose the design, implementation and preliminary validation of an impedance controller for the TWIN lower limb exoskeleton based on a model and without the support of any torque/force sensors (sensorless). The model was built as a result of experimental tests on the hip and knee joints of the exoskeleton and it provides a friction losses estimation, giving an overview of the TWIN joints' torque. The developed solution demonstrates satisfactory performances in terms of disturbance compensation and mechanical impedance representation, highlighting the possibility to combine advanced control strategies with compact, lightweight and undersensorized actuators, thus possibly favoring the adoption and utilization of robotic rehabilitation.