1. a Department of Robotics and Mechatronics, Tokyo Denki University, 2-2 Kanda-nishiki-cho, Chiyoda-ku, Tokyo 101-8457, Japan;, Email: nkama@fr.dendai.ac.jp
2. b Department of Control and Systems Engineering, Tokyo Institute of Technology, 2-12-1 Oh-okayama, Meguro-ku, Tokyo 152-8552, Japan
3. c Department of Control and Systems Engineering, Tokyo Institute of Technology, 2-12-1 Oh-okayama, Meguro-ku, Tokyo 152-8552, Japan
4. d RIKEN-TRI Collaboration Center for Human-Interactive Robot Research, The Institute of Physical and Chemical Research (RIKEN), 2271-130 Anagahora, Shimoshidami, Moriyama-ku, Nagoya 463-0003, Japan