1. a Department of Robotics, Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu-shi 525-8577, Japan, School of Mechatronics, Harbin Institute of Technology, Harbin, P. R. China
2. b Department of Robotics, Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu-shi 525-8577, Japan;, Email: shugen@se.ritsumei.ac.jp