1. State Key Laboratory of Tribology Department of Mechanical Engineering Tsinghua University Beijing 100084 China
2. Department of Biomedical Engineering The Hong Kong Polytechnic University Hung Hom Kowloon Hong Kong China
3. The Hong Kong Polytechnic University Shenzhen Research Institute Shenzhen 518000 China
4. Beijing Research Institute of Automation for Machinery Industry Co., Ltd Beijing 100120 China