3D Dynamic Biped Walker with Flat Feet and Ankle Springs: Passive Gait Analysis and Extension to Active Walking. - Tetsuya Kinugasa; Takashi Ito; Hiroaki Kitamura; Kazuhiro Ando; Shinsaku Fujimoto; Koji Yoshida; Masatsugu Iribe (J. Robotics Mechatronics, 2015)