[1] Peking Univ, Coll Engn, Robot Res Grp, Beijing 100871, Peoples R China
[2] Scuola Super Sant Anna, BioRobot Inst, Pisa, Italy
[3] UPEC, Lab Images Signals & Intelligent Syst LISSI, F-94400 Vitry Sur Seine, France
[4] Columbia Univ, Dept Mech Engn, Robot & Rehabil Lab, ROAR Lab, New York, NY 10027 USA