Design of a Series Elastic Actuator with Double-layer Parallel Spring for Lower Limb Exoskeletons

This paper presents a novel Series Elastic Actuator (SEA) with double-layer parallel spring for lower limb exoskeletons (LLE). The SEA can improve the human-robot interaction comfort and have the ability to absorb shock and vibration. In order to make the assembly process simple and convenient, the series elastic unit adopt split structure, which includes an inner ring structure, an outer ring structure and rectangular springs as elastic element. At the same time, in order to meet the requirements of the stiffness and dimensions of the SEA, a double-layer parallel spring arrangement is adopted. The stiffness of SEA is 312Nm/rad, which is obtained by the stiffness calibration experiment. In the experiments, the SEA is used in the knee joint of LLE and an impedance controller is designed to achieve knee joint tracking motion. Finally, the experiments results show the position tracking performance of the LLE, which illustrates the effectiveness of the SEA.