1. Robotics Research Center, School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University , Beijing 100044 , PR China
2. Research Center of Robotics Technology and Equipment, Tangshan Research Institute, Beijing Jiaotong University , Tangshan 063000 , China
3. Key Laboratory of Vehicle Advanced Manufacturing, Measuring and Control Technology, Ministry of Education, Beijing Jiaotong University , Beijing , China