Design of a Soft Wrist Exoskeleton Based on SMA Actuator Module

A soft wrist exoskeleton based on shape memory alloy (SMA) actuator module is proposed to address the problems of exoskeleton robots in bionics, portability and human-robot interaction. Firstly, the maximum recoverable tensile length and phase transition temperature characteristics of SMA spring are studied, and a hybrid model of SMA spring and manganese steel for SMA actuator module is established. Then, the parameters of the hybrid model are optimized according to the motion range and the required tension of human wrist joint. Finally, a cooling method for SMA springs is proposed by mixing elastic element potential energy, air cooling and high and low current switching, and a control method is designed based on motion angle and phase transition temperature feedback. To verify the practical effect of the soft wrist exoskeleton, wear training and temperature measurement experiments are carried out. The experimental results show that the bionics and flexibility of the exoskeleton conforms to the movement characteristics of the human wrist, and its light weight and portability can improve the assistance effect in daily living activities.