While existing literature encompasses exoskeleton-assisted sit-stand tasks, the integration of energy recovery mechanisms remains unexplored. To push these boundaries further, this study introduces a portable pneumatic knee exoskeleton that operates in both quasi-passive and active modes, where active mode is utilized for aiding in standing up (power generation), thus the energy flows from the exoskeleton to the user, and quasi-passive mode for aiding in sitting down (power absorption), where the device absorbs and can store energy in the form of compressed air, leading to energy savings in active mode. The absorbed energy can be stored and later reused without compromising exoskeleton transparency in the meantime. In active mode, a small air pump inflates the pneumatic artificial muscle (PAM), which stores the compressed air, that can then be released into a pneumatic cylinder to generate torque. All electronic and pneumatic components are integrated into the system, and the exoskeleton weighs 3.9 kg with a maximum torque of 20 Nm at the knee joint. The paper describes the mechatronic design, mathematical model and includes a pilot study with an able-bodied subject performing sit-to-stand tasks. The results show that the exoskeleton can recover energy while assisting the subject and reducing muscle activity. Furthermore, results underscore air regeneration's impact on energy-saving in portable pneumatic exoskeletons.

翻译：尽管现有文献涵盖了外骨骼辅助的坐站任务，但能量回收机制与这些任务的集成仍属未探索领域。为突破这一边界，本研究提出一种便携式气动膝关节外骨骼，可同时运行于准被动模式与主动模式：主动模式用于辅助站立（能量输出），使能量由外骨骼流向使用者；准被动模式用于辅助坐下（能量吸收），此时装置以压缩空气形式吸收并储存能量，从而在主动模式下实现节能。吸收的能量可被存储并在后续重复利用，且在此过程中不损害外骨骼的透明性。主动模式下，小型气泵为储存压缩空气的气动人工肌肉（PAM）充气，随后压缩空气释放至气动缸体产生扭矩。所有电子与气动组件集成于系统内，外骨骼重3.9 kg，可在膝关节处产生20 Nm最大扭矩。本文阐述了该外骨骼的机电设计、数学模型，并包含一项针对健康受试者执行坐-站任务的预实验研究。结果表明，该外骨骼可在辅助受试者并降低肌肉活动度的同时实现能量回收。此外，结果凸显了空气再生对便携式气动外骨骼节能效果的促进作用。