<p>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 them back 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 or the time variability of operative conditions. Unfortunately, these models are not suitable for health monitoring and prognostic, therefore this paper presents a detailed three-dimensional multibody dynamic model of a ball screw with the aim to support model-based health monitoring for this component. The model, developed in the MSC ADAMS environment, 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 an only rotating driving screw and only translating nuts is considered, taking into account the joints’ compliance. 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, while the motion is transmitted by the friction, taken into account by means of a simplified continuous and differentiable friction model. 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. By analysing the axial vibration signal of the nut, the ball passing frequency is calculated and used to give a first validation of the model. The effects of the nut mass distribution and geometric errors on the load distribution are analysed. 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.</p>

Multibody Dynamic Adams Model of a Ball Screw Mechanism With Recirculation Channel

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.