1. School of Mechanical Engineering Southwest Jiaotong University Chengdu, Sichuan 610031 China
2. Institute of Optics and Electronics Chinese Academy of Sciences Chengdu, Sichuan 610209 China
3. School of Electronics, Electrical and Communication Engineering University of Chinese Academy of Sciences Beijing 100049 China
4. Technology and Equipment of Rail Transit Operation and Maintenance Key Laboratory of Sichuan Province Chengdu, Sichuan 610031 China
5. Chair of Materials Handling, Material Flow, Logistics, Technical University of Munich Garching 85748 Bavaria Germany