1. School of Mechanical Engineering Yanshan University Qinghuangdao 066004 China
2. Hebei Heavy Machinery Fluid Power Transmission and Control Lab Yanshan University Qinhuangdao 066004 China
3. Ningbo Research Institute Zhejiang University Ningbo 315100 China
4. State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang University Hangzhou 310027 China