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Knee exoskeleton enhanced with artificial intelligence to provide assistance-as-needed.

Robotic therapy is a useful method applied during rehabilitation of stroke patients (to regain motor functions). To ensure active participation of the patient, assistance-as-needed is provided during robotic training. However, most existing studies are based on a predetermined desired trajectory, which significantly limits the use of this method for more complex scenarios. In this paper, artificial intelligence (AI) agents are introduced to enhance the robot so that a knee exoskeleton can be autonomously controlled. A new assist-as-needed (AAN) method is proposed, where the subjects and agents cooperatively control movements. An electromyographic (EMG)-controlled knee exoskeleton with an interesting screen game is developed. Two different AI agents, modular pipeline and deep Q-network, are introduced; both can control the exoskeleton to play the screen game independently. The human-robot cooperative control is studied with two different assistant strategies, i.e., fixed assistant ratio and AAN. Eight healthy subjects participated in the initial experiment, and four assistant modes were studied. The game scores obtained by the two agents were significantly higher than those obtained by healthy subjects (EMG control), indicating that using the agents to assist stroke rehabilitation is possible. The AAN method demonstrated a better performance than the fixed assistant ratio method, indicated by the higher integral muscle activation level and participant score. Compared to a fully active control (EMG control) and fully fixed guidance (AI control), human-robot cooperative control had significantly higher integral muscle activation levels, i.e., the subjects were more involved and motivated during training. Using AI agents to power rehabilitation robots is a promising way to realize AAN rehabilitation.