Patent ID: 7578214

Claim:
A preload structure for a ball screw comprising a screw, a nut, a plurality of rolling elements and a circulation system; wherein: the screw is formed with a helical groove in an outer surface thereof; the nut is formed with a helical groove in an inner surface thereof; the rolling elements are retained between the helical groove of the screw and the helical groove of the nut; and the circulation system is mounted on the nut and provided for circulation of rolling elements which have passed though the helical grooves; the preload structure for a ball screw characterized in that: the helical groove in the inner surface of the nut includes an interval helical track whose lead is different from a lead of the adjacent helical groove, so as to produce a lead deviation between the helical groove of nut and the helical groove of the screw; the lead of the interval helical track is different from a lead of the screw, the lead deviation between the interval helical track and the helical groove of the screw is gradually changed, when rolling from one side of the nut to the other side of the nut, a force applied on a rolling element is changed from large to smaller then back to larger.