Beijing Key Laboratory of Advanced Manufacturing Technology;
College of Mechanical Engineering and Applied Electronics Technology;
Beijing University of Technology;
Beijing 100124;
P. R. China;
Institute of Standavd Metrology;
Chinese Acadmy of Railway Sciences;
Beijing 100081;
P. R. China;
Beijing Key Laboratory of Electrical Discharge Machining Technology;
Beiiing 100191;
P. R. China;
fractal; theory; axial; contact; stiffness; ball; screw; contact; stress; minimum; excess;