Design and Evaluation of the JSI-KneExo: Active, Passive, Pneumatic, Portable Knee Exoskeleton

This paper presents a portable stand-alone pneumatic knee exoskeleton that operates in both passive and active modes. The system can store and recover energy by means of compressed air in passive mode, leading to energy savings. In active mode, a small air pump inflates the pneumatic artificial muscle (PAM), which stores the compressed air, that can be then released into a pneumatic cylinder to generate torque. All electronic and pneumatic components are integrated into the system, and the exoskeleton weighs only 3.9 kg with a maximum torque of 20 Nm in the knee joint. Further, the system is modular, allowing wearability on one or both legs. The paper describes the mechatronic design, mathematical model and includes a validation study with an able-bodied subject performing sit-to-stand and squat-hold exercises. The results show that the exoskeleton can harvest energy while assisting the subject and reduce muscle activity, without compromising transparency. These results suggest that the presented exoskeleton could be a useful low-energy consumption device for individuals with low to moderate lower limb mobility impairments and improve endurance in both clinical and industrial settings.