1. Research Institute of Robotics, Shanghai Jiao Tong University, Shanghai 200240, China
2. Department of Automation, Shanghai Jiao Tong University and Key Laboratory of System Control and Information Processing, Ministry of Education of China, Shanghai 200240, China
3. College of Mechatronic Engineering and Automation, National University of Defense Technology, Changsha 410073, China
4. Toyota Central R&D Labs., Inc., Nagakute 4801192, Japan