1. School of Electronics and Control EngineeringSchool of HighwayChang'an University Xi'an Shaanxi P. R. China
2. State Key Laboratory of Robotics and SystemHarbin Institute of Technology Harbin Heilongjiang P. R. China
3. The State Key Laboratory of Nonlinear Mechanics (LNM)Chinese Academy of SciencesInstitute of Mechanics Beijing P. R. China