A ball screw is a mechanism that converts the motion from linear to rotational and/or vice versa. It is usually composed by a screw shaft, one or two nuts, a set of spheres, seals and the recirculation inserts. It is characterised by low friction levels obtained by interposing rolling elements between the screw and nut grooves, as in bearings. However, in contrast to them, the rolling elements moves along a helical path. Therefore, to prevent them to come out from the nut, a recirculating channel is present, which picks up the spheres and lead back them to the beginning of the helical path contained inside the nut. Ball screws are characterised by high efficiency levels, high static and dynamic stiffness, low friction, high positioning precision and repeatability and the possibility to compensate for the backlash applying a preload. Thanks to these features, ball screw drive systems are employed in several applications, such as manufacturing machines, aircraft, space launchers, trains, helicopters, torpedoes, and so forth. The ball screw mechanism is the key component of ball screw drives and its comprehension is fundamental in preventing performance degradations and catastrophic failures, such as a jamming. Nevertheless, due to its intrinsic complexity of investigation, experimental analyses of what happens within this component are very difficult. For this reason, several models have been formulated in literature to understand the motion of the spheres or the static load distribution. Hitherto, most of the models used a quasi-static approach describing the motion of the element in steady state conditions, disregarding the actions of inertia. Unfortunately, these models are not suitable for health monitoring and prognostic, therefore this paper presents a detailed three-dimensional dynamic model of a double nut preloaded ball screw with the aim to support model-based health monitoring for this component. The model can accurately describe the kinematics and dynamics of each element within the mechanism and allows to understand the complex interaction between the gothic arch helical grooves and the spheres under time-variant speed and external loads. The configuration of the mechanism with a only rotating driving screw and only translating nuts is considered. Each sphere has all its six degrees of freedom and its motion is constrained between the grooves only by the 3D Hertzian contact with the grooves. A simplified grease lubrication model is applied to calculate the friction forces and rolling resistance moments in each sphere depending on the local load and speed and on the lubricant temperature. Each sphere can have up to two contact points with each gothic arch groove and therefore, variable contact angles are considered for each contact point. The backlash is automatically taken into consideration depending on the relative dimensions of the sphere and the grooves. The results of dynamic simulations are presented to demonstrate the dynamic capabilities of the present model, which poses the basis for a complete understanding of the internal dynamics of the mechanism. This model can thus be used as a virtual test bench on which to insert artificial defects to study their effects on the ball screw performance for health monitoring purposes.


Multibody Dynamic Model of a Double Nut Preloaded Ball Screw Mechanism With Lubrication

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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