1. Faculty of EngineeringShinshu University 4‐17‐1, Wakasato, Nagano‐City Nagano 380‐8553 Japan
2. Nagano Prefectural Institute of Technology 813‐8, Shimonogo, Ueda‐City Nagano 386‐1211 Japan
3. College of Engineering, Kanazawa Institute of Technology 7‐1, Ogigaoka, Nonoichi‐City Ishikawa 921‐8501 Japan
4. National Institute of Technology, Nagano College 716, Tokuma, Nagano‐City Nagano 381‐8550 Japan