Bidirectional Roller Screw Preloading for Stable Rolling Contact
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Solution Overview
Problem
Conventional planetary roller screw transmission devices suffer from skidding and idling of rollers due to manufacturing tolerances, leading to reduced frictional force, poor rolling contact, and decreased structural life, with retainer units unable to provide preload compensation or guide rollers effectively.
Innovation Solution
A roller screw bidirectional axial preloading structure with two groups of rollers arranged in a circumferentially interleaved manner, utilizing two elastic elements to apply opposite axial preloads, ensuring stable rolling contact and compensating for manufacturing gaps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional retainer units are used to hold rollers, then the rollers are mechanically located, but the rollers experience skidding and idling due to manufacturing gaps
Solution Approach 1:
The elastic elements apply preliminary axial preload forces to the rollers in both directions before operation begins. This pre-compression eliminates the manufacturing gaps between rollers, screw, and nut, preventing skidding and idling from occurring during operation. The preload acts as a preventive measure against the harmful effects of tolerance accumulation.
Solution Approach 2:
The retainer units are designed with asymmetric gap structures that create different clearance conditions on either side of the rollers. This preliminary structural arrangement prepares the system to accommodate thermal expansion and load variations by having pre-defined compensation paths, ensuring stable rolling contact under varying operating conditions.
2Stability of the object's composition
If bidirectional axial preloads are applied to rollers, then rolling stability is enhanced, but device complexity increases
Solution Approach 1:
The bidirectional preload mechanism merges the functions of two separate unidirectional preloading systems into a single integrated structure. The retainer units with asymmetric gaps and the elastic elements work together as a unified system that simultaneously applies preload in both axial directions, eliminating the need for separate adjustment mechanisms and reducing overall structural complexity.
Solution Approach 2:
The elastic elements automatically adjust the preload forces based on the actual operating conditions, thermal expansion, and load variations. The system self-regulates the contact pressure between rollers, screw, and nut without requiring external control mechanisms, maintaining optimal rolling stability while minimizing the need for complex control systems.
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
Enhances rolling stability, reduces frictional loss, and extends service life by maintaining pure rolling contact and improving transmission efficiency and accuracy.
Implementation Method 1
two elastic elements to be separately located at two axially outer sides of the first and the second retainer to respectively apply an axially force on the first and the second rollers
Data Source
AI summary
A roller screw bidirectional axial preloading structure includes a screw, a nut, and a plurality of first and second rollers arranged around the screw in an interleaved manner and respectively having two ends connected to a first and a second retainer. A first gap is formed between the first retainer and one end of each first roller, and a second gap is formed between the second retainer and the other end of each second roller, such that the first and the second gaps are axially spaced while circumferentially interleaved around the screw. Two elastic elements are located outside the first and second retainers to apply two forces, which are transmitted via the first and second retainers to the first and the second rollers to create two directionally opposite axial preloads on the first and second rollers, giving the roller screw good mechanical power transmission accuracy and stability in motion.