1. School of Automation Science and Electrical Engineering, Beihang University (BUAA), Beijing 100191, China e-mail:
2. School of Automation Science and Electrical Engineering, Beihang University (BUAA), Beijing 100191, China
3. School of Mechano-Electronic Engineering, Xidian University, Xi'an 710071, China
4. Department of Production Engineering, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden
5. Deparment of Mechanical Engineering, University of Auckland, Auckland 1142, New Zealand