1. Department of Automation, Hohai University, Nanjing 210024, China
2. School of Electrical Engineering, Zhengzhou University, Zhengzhou 450001, China
3. Anhui Engineering Laboratory of Human Robot Integration System and Equipment, School of Electrical Engineering and Automation, Anhui University, Hefei 230601, China
4. School of Engineering, University of California, Merced, CA 95343, USA
5. Department of Automation, University of Science and Technology of China, Hefei 230026, China