Design of a Series Elastic Actuator with Doublelayer Parallel Spring for Lower Limb Exoskeletons This paper presents a novel Series Elastic Actuator (SEA) with doublelayer parallel spring for lower limb exoskeletons (LLE). The SEA can improve the humanrobot 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 doublelayer parallel spring arrangement is adopted. The stiffness of SEA is 312Nmrad, 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.

Design and Validation of an Asymmetric BowdenCableDriven Series Elastic Actuator Weight, size and torque control for hand exoskeleton robots are challenging due to lack of small and compact bidirectional torque actuators. In this paper, an asymmetric Bowdencabledriven series elastic actuator (ABLESEA) for hand exoskeleton robots was proposed based on the fact that the required torques for finger movements are asymmetric. Compared to series elastic actuator and transmission system that were designed separately, the elastic elements of ABLESEA were placed in transmission parts to connect series elastic actuator with transmission system, which makes system compact. ABLESEA is 71 mm xc3x97 19.5mm xc3x97 20mm in dimension and weighs 30g except motor which is placed remotely. The dynamic model of ABLESEA was established, and feedback proportionalderivative (PD) control plus a feedforward term was used to track the reference torque for the ABLESEA. The reference torque tracking test at different frequencies was performed at the developed prototype. Meanwhile, the peak torque of ABLESEA was tested. The experimental results verified that the torque bandwidth of the proposed series elastic actuator could reach 4Hz, and the peak torque of ABLESEA could reach 0.3Nm, which meet the design requirement.