Reduction of Vibrations in Ball Screw Driven Machine Tools by the Optimal Selection of Nut Parameters

Due to the growing need for sustainable manufacturing processes, machine tool designers are constantly looking for ways to reduce unwanted structural vibrations without having to increase the mass/inertia of moving components, which in turn increases the energy consumption and cost of the machines. Recent research has shown that, due to the coupling introduced by the nut, the torque applied to ball screw drives by the motor causes undesirable lateral (bending) vibrations of the screw, which adversely affects the fatigue life and positioning accuracy of ball screw drives. By analyzing the stiffness matrix connecting the screw to the nut, this paper shows that the helix angle of the screw and the entry/exit angles of the balls have the most influence on the degree of coupling between motor torque and lateral vibrations of the screw. Consequently, by carefully selecting the helix angle of the screw together with the entry/exit angles of the balls, the undesirable lateral vibrations of the screw can be minimized, without having to increase the diameter (i.e. stiffness/inertia) of the ball screw. The merits and limitations of the proposed method are demonstrated using simulations on a single-axis ball screw driven machine.