Assistive Control of a Hip Exoskeleton Robot, using a DQN-Adjusted Delayed Output Feedback Method

Document Type : Research Article

Authors

1 Department of Mechanical Engineering, Sadjad University

2 Center of Advanced Rehabilitation and Robotic Research (FUM-CARE), Electrical Engineering Department Ferdowsi University of Mashhad, Mashhad, Iran

3 Center of Advanced Rehabilitation and Robotic Research (FUM-CARE), Mechanical Engineering Department, Ferdowsi University of Mashhad, Mashhad, Iran

Abstract

A major challenge in the development of an assistive exoskeleton robot is to design appropriate control algorithms. For these algorithms to work in any intended motion and to be easily implementable, they should be trajectory-independent and should require a minimum number of sensors. As a simple assistive strategy with all of these promising features, delayed output feedback control (DOFC) is shown to be effective in assisting the wearers in different types of motion. In this method, the assistive torques are defined in proportion to delayed feedback from the angle difference between the two legs. The authors have recently suggested an intelligent version of DOFC in which a Deep Q-Network (DQN) was used to adjust the feedback delay according to the speed of the motion. Simulation studies were used to investigate of the idea. By conducting some real-world experiments, the present paper extends the results to practical conditions. The provided results clearly verify that if the time delay is adjusted according to the walking speed, the DOFC method can effectively help the users in their motions of any speed. The results also indicated that a fixed or an inappropriate value of the delay may result in resistance against the user motion.

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