1. Department of Medical Engineering Kawasaki University of Medical Welfare 288, Matsushima Kurashiki Okayama 701‐0193 Japan
2. Department of Electrical & Electronic Engineering Okayama University of Science 1‐1, Ridai‐cho, Kita‐ku Okayama 700‐0005 Japan
3. Head Office Scale Corporation 4‐41, Akibadai, Wadayama‐cho Asago City Hyogo Japan
4. Department of Systems Engineering Okayama University 3‐1‐1, Tsushima‐naka, Kita‐ku Okayama 700‐8530 Japan