1. School of Electromechanical and Automotive Engineering Yantai University Yantai 264005 China
2. School of Mechanical Engineering Shenyang Jianzhu University Shenyang 110016 China
3. State Key Laboratory of Robotics Shenyang Institute of Automation, Institutes for Robotics and Intelligent Manufacturing Chinese Academy of Sciences Shenyang 110016 P. R. China