1. School of Mechanical Engineering; Taiyuan University of Technology; Taiyuan 030024 China
2. Shanxi Key Laboratory of Fully Mechanized Coal Mining Equipment; Taiyuan 030024 China
3. School of Mechanical Science & Engineering; Huazhong University of Science & Technology; Wuhan 430074 China
4. School of Mechanical Engineering; Hebei University of Technology; Tianjin 300130 China