1. School of Automation, Beijing University of Posts and Telecommunications, No. 10 Xitucheng Road, Beijing 100876, China; School of Mechanical and Electrical Engineering, Guilin University of Electronic Technology, No. 1 Jinji Road, Guilin, Guangxi 541004, China
2. School of Mechanical and Electrical Engineering, Guilin University of Electronic Technology, No. 1 Jinji Road, Guilin, Guangxi 541004, China