1. Mechanical Systems Safety Research Division, Korea Institute of Machinery and Materials, 104 Sinseong-ro, Yuseong-gu, Daejeon 305-343, Republic of Korea
2. Department of Precision Mechanical Engineering, Kyungpook National University, 2559, Gyeongsang-daero, Sangju, Gyeongsangbuk-do, 742-711, Republic of Korea