Stiffness of a Ball Screw Including with Consideration to Deformation of the Screw, Nut and Screw Thread. 3rd Report, Effect of Contact Angle Change.

Abstract

The contact angle between the ball and thread groove in ball screws changes following the Hertzian contact deformation and elastic deformation of the thread. Hence, how the contact angle changes with the axial load is calculated, and the effect of it both on load distribution in the screw thread and on axial stiffness is examined for the single nut and the preloaded double nut. An increase in contact angle of some 2° is calculated under basic dynamic load rating. The nonuniformity of load distribution is not influenced by the contact angle change. However, the normal load of a ball at a contact point between the ball and thread groove decreases slightly. The axial stiffness of the ball screws, consequently, rises as the contact angle increases. The measured values of axial displacement are in approximate agreement with the calculated results.