Load Distribution of Ball Screw With Consideration of Contact Angle Variation and Geometry Errors

Abstract

Hundreds of mirror segments are needed to realize the laser fusion system and the next generation ground based extra-large telescopes. In order to manufacture the mirror segments, the ultra-precise optics grinding machine is essential equipment. As the most widely used motion transfer device in these machines, the ball screw mechanism need predetermine its positional accuracy. And the positional accuracy is based on load distribution of ball screw. This will be discussed in the article. Based on existing analytical models, an improved model is developed to accurately predict load distribution of ball screw. In this model, variation of contact angle is considered. And a simple approach considering of the influence of the geometry errors on the load distribution is developed. The results of this model demonstrate the load distribution of ball screw is not average and load of every ball falls from the position near the load to further. Downward trend is more marked when introducing the variation of contact angle into the model. Besides, the effect of geometry errors on the load distribution is not as remarkable as existing models. Based on the model, the larger ratio of helical pitch to screw diameter is, the worse the nonuniformity of load distribution is. This will impair the stiffness of ball screw and its positional accuracy. The calculated results are significant to ball screw design.