1. National Key Laboratory for Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin, Heilongjiang 150001, P R China
2. School of Mechanic and Electrical Engineering, Henan University of Technology, Zhengzhou 450001, P R China
3. The State Key Laboratory of Robotics and Systems, Robotics Institute, Harbin Institute of Technology, Harbin, Heilongjiang 150080, P R China