1. Department of Control Engineering and Robotic, Mokpo National University, 1666 Youngsan-ro, Cheonggye-myeon, Muan-gun, Jeonnam 58554, South Korea
2. Department of Biomedical Engineering, Hokkai-Gakuen University, 4-1-40 Asahi-machi, Toyohira, Sapporo, Hokkaido 062-8605, Japan