1. Department of Mechanical Engineering, Kagoshima University, 1-21-40 Korimoto, Kagoshima 890-0065, Japan
2. PRESTO, JST, 4-1-8 Honcho, Kawaguchi 332-0012, Japan
3. Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai 980-8579, Japan
4. Department of Intelligent Information Systems, Faculty of Science and Technology, Tohoku Bunka Gakuen University, 6-45-1 Kunimi, Sendai 981-8551, Japan