1. School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong Univ., Jiaoda East Rd., Haidian, Beijing 100044, P.R. China.
2. Professor, School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong Univ., Jiaoda East Rd., Haidian, Beijing 100044, P.R. China (corresponding author).
3. Master, School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong Univ., Jiaoda East Rd., Haidian, Beijing 100044, P.R. China.
4. Lecturer, School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong Univ., Jiaoda East Rd., Haidian, Beijing 100044, P.R. China.