1. The State Key Laboratory of Mechanical System and Vibration, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
2. Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208
3. Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91105
4. Department of Advanced Manufacturing and Robotics, Peking University, Beijing 100871, China