1. Department of Adaptive Machine Systems Graduate School of Engineering Osaka University Yamadaoka 2‐1 Suita Osaka 567‐0047 Japan
2. The Institute of Scientific and Industrial Research (ISIR) Osaka University Mihogaoka 8‐1 Ibaraki Osaka 567‐0047 Japan
3. Pacific Northwest National Laboratory P.O. Box 999 Richland WA 99352 USA
4. Senju Metal Industry Co., Ltd. Senju Hashido‐cho 23 Adachi‐ku Tokyo 120‐8555 Japan