1. School of Electromechanical and Automotive EngineeringYantai University Yantai 264005 China
2. School of Mechanical EngineeringShenyang Jianzhu University Shenyang 110016 China
3. College of EngineeringShenyang Agricultural University Shenyang 110016 China
4. State Key Laboratory of RoboticsShenyang Institute of AutomationInstitutes for Robotics and Intelligent ManufacturingChinese Academy of Sciences Shenyang 110016 P. R. China