Periodic variation of preloading in ball screws

The preloading is a main characteristic for the functionality of a ball screw. The path of preloading during operation with no thrust load is an indicator for the actual inner forces, the friction produced by the ball screw and finally for the quality of the unit. Due to manufacturing tolerances the preloading over the useful travel of the ball screw differs from its specified value. However, not only the overall loading of a ball screw varies, but also the local load distribution within the nut. This is expressed by a periodic variation of the internal forces which has an effect on the alignment of the nut and therefore on the uniformity and the motion characteristics of a ball screw feed drive. The following paper deals with the occurrence of these periodic force variations and offers an explanation for this particular phenomenon.