From Exoskeletons to Human-Machine Co-embodiment Systems: Research Progress, Key Challenges, and Future Directions

Exoskeletons are wearable robotic systems that directly interact with the human musculoskeletal system and have attracted significant attention for motion rehabilitation, physical augmentation, and task assistance. This paper provides a comprehensive review of recent advances in exoskeleton technologies from the perspectives of structural design, intention sensing, and control strategies. First, the development of rigid and soft exoskeleton architectures, along with representative systems and products, is summarized. Then, current approaches for human motion intention recognition are reviewed, including conventional physical sensing, bioelectrical signal-based methods, and multimodal sensing fusion. In addition, the progress of model-based, data-driven, and learning-based control strategies is discussed. Key challenges limiting the practical deployment of exoskeletons are identified, including human-robot compatibility, wearing convenience, cross-user generalization capability, adaptability to complex environments, and safe and reliable control. Finally, future research directions are discussed, highlighting the transition toward hybrid rigid-soft structures, intelligent sensing, closed-loop human-robot collaboration, and human-machine integrated systems. These developments are expected to extend exoskeleton applications beyond conventional scenarios to extreme environments such as ocean operations and deep-space exploration, providing new opportunities for rehabilitation, industrial assistance, elderly care, and special operations.