Design of a Series Elastic Actuator with Double-layer Parallel Spring for Lower Limb Exoskeletons. - Chao-feng Chen; Dongmei Wu; Wei Dong 004; Zhijiang Du; Long He 002; Linxiang Huang; Jia-Qi Wang; Yong-Jun Shi; Guoqiang Xu; Fang Si; Tiantian Xiao (ROBIO, 2019)