1. State Key Laboratory of Fluid Power and Mechatronic Systems, School of Mechanical Engineering, Zhejiang University, Hangzhou 310027, China
2. Department of Mechanical Engineering, Wroclaw University of Science and Technology, Wroclaw 51-370, Poland
3. Department of Mechanical Engineering, NSF Engineering Research Center for Compact and Efficient Fluid Power, University of Minnesota, Minneapolis, MN 55455