1. State Key Laboratory for Manufacturing Systems Engineering Xi'an Jiaotong University Xi'an 710049 China
2. School of Mechanical and Electrical Engineering Lanzhou University of Technology Lanzhou 730050 China
3. Advanced Technology Center Wuxi Little Swan Electric Co. Ltd. Wuxi 214101 Jiangsu Province China
4. School of Engineering Newcastle University Newcastle Upon Tyne NE1 7RU UK