| Summary: | Robot knee exoskeletons can not only help the rehabilitation training function of the elderly and disabled patients, but also enhance the performance of healthy people in normal walking and weigh-bearing walking by providing sufficient torques. In recent years, the exoskeletons of knee joints have been extensively explored. The review is to summarize the existing research results of mechanical structure design and actuation technologies, propose the future development trend, and promote the further development of the powered knee exoskeletons, related theories, and engineering applications. In this study, the mechanical structures of knee exoskeletons are first illustrated. Their mechanical structures are classified into two types: simple mechanical structures with one purely rotary DOF and biological geometry-based multi-DOF structures. Subsequently, the actuation design of wearable knee exoskeletons includes conventional driving actuators, pneumatic muscle actuators, variable stiffness actuators, and other actuators are compared and the driving compliance and the difficulty in the accurate control are analyzed. Furthermore, other crucial technologies such as motion intention recognition, control strategy and performance evaluation methods of most knee assistive devices are reviewed. Finally, the key technologies of structural design and actuation design in the research of knee exoskeletons are summarized and future research hotspots are proposed.
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