1. Faculty of Advanced Engineering, Tokyo University of Science, Tokyo, Japan
2. Department of Mechanical Engineering, Tokyo University of Science, Chiba, Japan
3. Department of Biomedical Engineering, Faculty of Engineering, The Hong Kong Polytechnic University, Hong Kong, China
4. Northwestern University Prosthetics-Orthotics Center, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
5. Department of Systems and Control Engineering, Tokyo Institute of Technology, Tokyo, Japan