1. College of Mechanical and Equipment Engineering, Hebei University of Engineering, Handan 056038, P. R. China
2. School of Mechatronic Engineering, China University of Mining and Technology, Xuzhou 221116, P. R. China
3. Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, USA
4. Jiangsu Key Laboratory of Mine Mechanical and Electrical Equipment, China University of Mining and Technology, Xuzhou 221116, P. R. China