1. State Key Laboratory of Mechanical Transmission, Chongqing University, 174 Shazhengjie, Shapingba District, Chongqing 40044, China
2. Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208
3. Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208;
4. State Key Laboratory of Mechanical Transmission, Chongqing University, 174 Shazhengjie, Shapingba District, Chongqing 40044, China e-mail: