1. Department of Mechanical Engineering and Intelligent SystemsThe University of Electro‐Communications1‐5‐1 Chofugaoka, ChofuTokyo182‐8585Japan
2. Department of Mechanical Information Science and TechnologyKyushu Institute of Technology680‐4 Kawazu Iizuka‐CityFukuoka820‐8502Japan
3. Department of Mechanical EngineeringBoston University110 Cummington StreetBostonMA02215USA