1. Department of Precision Machinery and Precision Instrument, University of Science and Technology of China, Institute of Applied Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230026, P. R. China
2. Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei 230031, P. R. China
3. University of Science and Technology of China, Hefei 230026, P. R. China
4. Institute of Applied Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230088, P. R. China