Feed fluctuation of ball screw feed systems and its effects on part surface quality

• An electromechanical model is proposed to reveal the mechanism of feed fluctuation.
• The analytical expression of displacement fluctuation is deduced.
• Displacement fluctuation increases significantly in the situation of resonance.
• Feed fluctuation leads to bright and dark stripes of part.
• The mechanism of stripes is the periodic change of scallop height on part surface.

Feed fluctuation plays an important role on the part surface quality during the precision machining. In this paper, an analytical electromechanical model is developed to reveal the essential characteristics of the feed fluctuation for ball screw feed system, where the feedback control and driving circuit are equivalent to a “controlled current-source” and the mechanical transmission is modeled as a two-mass system. The analytical expression of displacement fluctuation is deduced and then the characteristics of feed fluctuation are investigated. Finally the influence of feed fluctuation on machining quality is analyzed. The results show that when the frequency of torque ripple is closer to the natural frequency of feed systems, the amplitude of displacement fluctuation increases significantly while that of the torque ripple has a sharp decrease. The displacement fluctuation along the feed direction contributes to the bright and dark stripes on the surface of workpiece in a precise cylindrical turning.