Design of high-precision ball screw based on small-ball concept

- Position deviations were found to be related to torque fluctuations, which depended on the position (rotation).
- The cascade control system could not suppress the torque fluctuations due to the ball circulation under high gain conditions.
- Using smaller balls, ball screws were designed to have smaller torque fluctuations.
- Experiment results show that both the torque fluctuations and the position deviations associated with the ball circulation were significantly reduced.

This paper addresses a design method of ball screws for high-precision feed drives of machine tools. The torque fluctuation of a ball screw influences position deviation, which deteriorates the contorting accuracy. The torque fluctuation comes from the load change of the contacting balls between the nut and the screw shaft during ball circulation. In order to decrease the load change, a ball screw that employs smaller balls was designed and evaluated in the measurement tests. The experimental results showed that the designed ball screw could decrease both the torque fluctuation and position deviation.