1. Center for Advanced Intelligence Project, RIKEN, Tokyo 103-0027, Japan hiroyuki.hanada@riken.jp
2. Center for Advanced Intelligence Project, RIKEN, Tokyo 103-0027, Japan noriaki.hashimoto.jv@riken.jp
3. Department of Mechanical Systems Engineering, Nagoya University, Nagoya 464-8603, Japan taji@nagoya-u.jp
4. Department of Mechanical Systems Engineering, Nagoya University, Nagoya 464-8603, Japan
5. Center for Advanced Intelligence Project, RIKEN, Tokyo 103-0027, Japan ichiro.takeuchi@mae.nagoya-u.ac.jp