Asymmetrical Ball Screw Threads for High Axial Load Efficiency
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Solution Overview
Problem
Existing ball screw mechanisms experience excessive friction and are unsuitable for applications with high-amplitude axial forces in a constant direction, irrespective of the direction of rotation.
Innovation Solution
The ball screw mechanism features asymmetrical threads with specific geometrical configurations, including varying flanks and pitch distances, ensuring minimal contact area and optimal lubrication in one direction while maintaining sufficient contact for high loads, and reduced friction in the opposite direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the ball screw mechanism uses symmetrical threads with equal radii of curvature on both flanks, then the mechanism can handle bidirectional loads with balanced friction, but it cannot optimize for unidirectional high-amplitude forces
Solution Approach 1:
The patent applies asymmetry by designing threads with different radii of curvature on the two flanks. The first flank has a larger radius of curvature optimized for rolling contact during normal operation to minimize friction, while the second flank has a smaller radius of curvature that can withstand high-amplitude static forces when the mechanism is at rest. This asymmetric configuration allows the mechanism to handle unidirectional high-amplitude forces efficiently.
Solution Approach 2:
The patent implements local quality by assigning different functional properties to different parts of the thread structure. Each flank of the thread is given a specific radius of curvature tailored to its functional requirement: one flank for dynamic rolling contact with low friction, and the other for static load bearing. This localized optimization of thread geometry resolves the contradiction between friction reduction and force handling capacity.
2Productivity
If the ball screw mechanism is designed for high-amplitude forces in one direction, then it achieves optimal performance in that direction, but it experiences excessive friction when rotating in the opposite direction
Solution Approach 1:
The asymmetric thread design with different radii of curvature on each flank enables the mechanism to maintain efficiency in the primary direction of operation while reducing excessive friction during reverse rotation. The larger radius flank handles the high-amplitude forces during normal operation, and the smaller radius flank provides adequate support during reverse rotation without generating excessive friction.
3Force
If the radius of curvature of thread flanks is reduced to take up large static forces, then the force capacity increases, but friction increases significantly
Solution Approach 1:
The patent resolves this contradiction by applying local quality through asymmetric thread design. The first flank is designed with a larger radius of curvature specifically for dynamic operation where low friction is critical, while the second flank uses a smaller radius of curvature optimized for static load bearing. This localized differentiation allows each flank to excel at its specific function without compromising the other.
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 improved lubrication, maintaining high capacity and efficiency under high-amplitude axial forces in a consistent direction, while minimizing friction in the opposite direction.
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 between the screw thread and the nut thread ensures good lubrication of the mechanism
Data Source
AI summary
A ball screw mechanism, including a screw defining a reference axis, a nut and at least two balls positioned to roll on a screw thread formed on the screw and a nut thread formed on the nut, the screw thread and nut thread having a helical pitch P. In a sectional plane containing the reference axis and passing through a center of a ball, any segment perpendicular to the reference axis, located at a distance x from the center of the first ball and having a first end which belongs to the screw thread and a second end which belongs to the nut thread, has a center which, in an orthonormal reference frame having an abscissa axis coincident with the reference axis and an ordinate axis passing through the center of the first ball.