1. School of Mechatronics Engineering, Harbin Institute of Technology, Harbin, Heilongjiang 150001, P. R. China
2. State Key Laboratory of Robotics and System, Harbin Institute of Technology, Harbin, Heilongjiang 150001, P. R. China
3. State Key Laboratory of Nonlinear Mechanics, Chinese Academy of Sciences, Beijing 100190, P. R. China
4. School of Electronics and Control Engineering, Chang’an University, Xi’an, Shanxi 710064, P. R. China