1. Department of Mechanical Engineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata, Japan
2. LG Technology Department, NSK Precision Co., Ltd., 1-1 Ohnuma, Hanyu, Saitama, Japan
3. LG Technology Department, NSK Precision Co., Ltd., 78 Toriba, Maebashi, Gunma, Japan
4. Research Department, NSK Precision Co., Ltd., 78 Toriba, Maebashi, Gunma, Japan