1. School of Electrical and Information Engineering, Zhengzhou University, Zhengzhou, China
2. School of Automation Science and Engineering, South China University of Technology, Guangzhou, China
3. School of Mechanical Science & Engineering, Huazhong University of Science and Technology, Wuhan, China
4. Department of Mechanical Engineering, School of Engineering, University of California, Merced, Merced, CA, USA