1. Department of Mechanical Engineering and Intelligent Systems, Graduate School of Informatics and Engineering, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu-city, Tokyo, 182-8585, Japan
2. Department of Mechanical Engineering, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kouhoku-ku, Yokohama-city, Kanagawa 223-8522, Japan
3. Microtechnology R&D Division, Olympus Corporation, 2-3 Kuboyama-cho, Hachioji-city, 192-8512, Tokyo, Japan