1. Department of Computer Engineering, Sungkyunkwan University (SKKU), 2066 Seobu-ro, Suwon 440-746, Republic of Korea
2. Robot Research Division, Daegu Gyeongbuk Institute of Science and Technology (DGIST), 50-1 Sang-ri, Hyeonpung-meyeon, Daegu 711-873, Republic of Korea