1. School of Physics and Electronics Central South University Changsha 410083 P. R. China
2. Division Microrobotics and Control Engineering Department of Computing Science University of Oldenburg D-26129 Oldenburg German
3. School of Mechanical and Mining Engineering Hunan Normal University Changsha 410083 P. R. China
4. School of Mechanical and Mining Engineering The University of Queensland QLD 4072 Australia