1. Intelligent Systems and Biomedical Robotics Group, School of Computing, University of Portsmouth, Portsmouth, PO1 3HE, United Kingdom
2. State Key Laboratory of Mechanical System and Vibration, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
3. College of Machinery and Automation, Wuhan University of Science and Technology, Wuhan 430081, P. R. China