Asymmetric Ball Screw Threads for High Axial Load and Low Friction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing ball screw mechanisms experience excessive friction and are unsuitable for applications with large magnitude axial forces in a constant direction, regardless of the mechanism's direction of rotation.
Innovation Solution
A ball screw mechanism design with asymmetrical thread profiles, where the screw and nut threads have varying radii of curvature and pitch, ensuring a larger contact area in one direction while maintaining sufficient space for lubrication and minimizing contact in the opposite direction, thereby reducing friction and enhancing load-bearing capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If symmetric thread profiles with equal radii of curvature are used, then the mechanism can withstand loads in both directions, but friction increases excessively when subjected to large magnitude axial forces in a constant direction
Solution Approach 1:
The patent applies asymmetry by designing the screw thread and nut thread with different radii of curvature on their respective flanks. Specifically, the screw thread has a first flank with a first radius of curvature and a second flank with a second radius of curvature, where the radii differ. The nut thread similarly has asymmetric flanks with different radii of curvature. This asymmetric configuration allows the mechanism to optimize contact conditions for unidirectional loading, reducing friction when subjected to large axial forces in a constant direction while maintaining adequate load-bearing capacity.
2Force
If large contact area is provided between balls and threads, then load-bearing capacity increases, but space for lubrication decreases
Solution Approach 1:
The patent applies local quality by creating different geometric characteristics in different regions of the thread profile. The thread flanks have varying radii of curvature at different locations, allowing larger contact areas in regions where load-bearing is critical while maintaining sufficient clearance and space in other regions for effective lubrication. This localized optimization of geometric properties enables simultaneous achievement of high load capacity and reliable lubrication.
3Loss of energy
If smaller radii of curvature are used on thread flanks, then contact area decreases reducing friction, but load-bearing capacity decreases
Solution Approach 1:
The asymmetric thread design allows different radii of curvature to be applied to different flanks of the screw and nut threads. This enables the mechanism to have smaller radii of curvature on flanks where reduced friction is critical for unidirectional operation, while maintaining larger radii on other flanks to preserve load-bearing capacity. The asymmetric configuration optimizes the trade-off between friction reduction and load support for the specific application of unidirectional axial forces.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The mechanism achieves reduced friction and increased load-bearing capacity in one direction, while maintaining effective lubrication and preventing contact under high loads, thus optimizing performance under unidirectional axial forces.
Implementation Method 1
at least two balls of radius R positioned so as to roll on a screw thread formed on the screw and a nut thread formed on the nut
Implementation Method 2
The minimum distance L maintained between screw thread and nut thread ensures good lubrication of the mechanism
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A ball screw mechanism (1) comprises a screw (10) defining a reference axis (200), a nut (12) and at least two balls (2) positioned to roll on a screw thread (34) formed on the screw (10) and a nut thread (134) formed on the nut (12), the screw thread (34) and the nut thread (134) having a helix pitch P.In a section plane containing the reference axis (200) and passing through a center (C1) of a ball (2a), any segment (240) perpendicular to the reference axis (200), located at a distance x from the center (C1) of the first ball (2a), and having a first end which belongs to the screw thread (34) and a second end which belongs to the nut thread (134), has a center (C2) which, in an orthonormal reference frame (R) having an abscissa axis coincident with the reference axis (200) and an ordinate axis which passes through the center (C1) of the first ball (2a), has an abscissa equal to x and an ordinate y, defining a function x → y = f(x) which, when x varies between 0 and P, passes through a minimum Y0 reached for an abscissa X0 and through a maximum Y1 reached for an abscissa X1, Y1-Y0 being greater than 0.1mm. The length L of the segment (240) is always greater than 0.25mm.