1. Department of Mechanical Engineering and Automation, School of Mechanical Engineering, Northwestern Polytechnical University, 127 West Youyi Road, Xi'an, Shaanxi 710072, China e-mail:
2. Key Laboratory of Contemporary Design and Integrated Manufacturing Technology, Ministry of Education, School of Mechanical Engineering, Northwestern Polytechnical University, 127 West Youyi Road, Xi'an, Shaanxi 710072, China e-mail: