1. Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
2. Department of Computer Engineering, Takushoku University, Tokyo 112-8585, Japan
3. TACHI-S Co., Ltd., Tokyo 198-0025, Japan
4. Department of Mechanical Engineering, Tokyo Institute of Technology, Tokyo 152-8550, Japan