Abstract: A ball nut and screw assembly has a backdrive control member that travels with the ball nut and has an internal thread complementary to and engaging the helical ball receiving groove on the screw. The backdrive control member is indexable on the screw relative to the ball nut to adjust the load of a spring that is interposed between the control member and ball nut. The spring acts to urge these components apart and thereby determine the frictional drag of the threaded engagement between the control member and the ball screw. The preload of the spring is set by indexing the control member to effect sufficient drag to prevent axial loads on the nut and screw from causing backdrive translation of the nut. The backdrive control member also removes lash from the ball nut and screw assembly under reversing loads at load magnitudes equal to or less than that produced by the load spring.

Abstract: A ball nut and screw assembly has a conventional helical raceway and balls received therein that react load through the centerline of the assembly and an added helical raceway and balls received therein that react radial load on the ball nut to the relief of the first mentioned raceway and balls.