1. State Key Laboratory of Fluid Power and Mechatronic Systems, Zhejiang University, No. 38 Zheda Road, Xihu District, Hangzhou 310027, China e-mail:
2. School of Mechanical Engineering, Zhejiang University, No. 38 Zheda Road, Xihu District, Hangzhou 310027, China e-mail:
3. Department of Mechanical Engineering, University of Bath, Bath BA2 7AY, Avon, UK e-mail: