A lightweight semi-active ankle exoskeleton utilized NiTiCu-based shape memory alloys for energy storage

Nowadays, exoskeletons have a place in many fields, such as industrial production, medical rehabilitation, and military. However, there are still many shortcomings in the existing exoskeleton, such as heavyweight and complex structures for active exoskeleton. The driving ability of passive exoskeletons is limited. To reduce the energy consumption of wearers, based on the characteristics of the semi-active ankle exoskeleton, this paper proposes to use NiTiCu-based shape memory alloys (SMA) as the energy storage source to improve the power density. Compared to NiTi-based SMA, the phase transformation process of NiTiCu-based SMA is more rapid, which can solve the response delay problem to a certain extent. The ankle exoskeleton uses SMA deformation to compress the bias spring. When the human ankle joint needs auxiliary torque, the SMA releases the energy stored by the bias spring and transfers the energy to the ankle exoskeleton to achieve the effect of assisting the human ankle joint. During the assistance process, a control system based on the SMA mathematical model is constructed. The above-mentioned ideas provide a new approach for further expanding power density and can be widely applied in the field of robotics. During characterization, this semi-active ankle exoskeleton can effectively complete the movement state of upstairs and walking, achieve an effective power of 180 N, and store maximum energy up to 5 J for the human ankle.