Roller Screw Thread Geometry for Higher Load and Longer Life
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Solution Overview
Problem
Roller screw mechanisms with point contact geometries have limited load capacities and lifetimes due to small surface areas supporting mechanical stresses, restricting their performance and reliability.
Innovation Solution
Implementing a roller screw mechanism with curvilinear contact geometries, where threads of rollers with straight or curved profiles interact with screw and nut threads, distributing forces over larger surfaces, allowing for higher load capacities and longer lifespans, and enabling higher feeds per revolution and optimizations in weight, volume, efficiency, and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If point contact geometry is used in roller screw mechanisms, then the device complexity is reduced and manufacturing is easier, but the load capacity and lifetime are limited due to small surface areas supporting mechanical stresses
Solution Approach 1:
The patent applies curvilinear contact geometry where the contact zones between screw-roller and roller-nut are defined by curved surfaces rather than point contacts. The screw thread profile and roller thread profile are designed with specific curvature radii (Rs for screw, Rr for roller) that create an osculating contact geometry, transforming the contact from a point to a curved surface area, thereby increasing load capacity while maintaining manufacturability through defined geometric parameters
2Duration of action of stationary object
If point contact geometry is used in roller screw mechanisms, then the manufacturing process is simpler, but the lifetime is reduced due to small surface areas supporting mechanical stresses
Solution Approach 1:
The patent defines curvilinear contact geometry with specific curvature radii (Rs for screw thread, Rr for roller thread) that create osculating contact zones. This curved surface contact distributes mechanical stresses over larger areas compared to point contacts, significantly reducing contact stress and extending component lifetime while maintaining reasonable manufacturing complexity through parametric geometric definitions
3Strength
If curvilinear contact geometry is implemented, then load capacities and lifespans are enhanced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent specifies precise geometric parameters for the curvilinear contact geometry, including curvature radii (Rs for screw, Rr for roller), osculation conditions, and thread profiles. These parameter definitions provide a systematic approach to achieving the desired contact geometry, allowing for controlled manufacturing precision requirements while maximizing load capacity through optimized curvature relationships
Data Source
Figure 1A~1C
Figure 2A~2C
Figure 3A~3C
AI summary
The invention relates to a roller screw mechanism comprising a screw (110) provided with an external screw thread; a nut (130) coaxially surrounding the screw (110) and provided with an internal screw thread; and rollers (120) each one provided with an external screw thread, each roller (120) being interposed between the screw (110) and the nut (130) so that the screw threads of the rollers mesh in the screw threads of the screw and of the nut, the mechanism being characterized in that the screw threads of the rollers are the conjugate of the screw threads of the screw and of the nut so that, at the rollover, the screw threads of the rollers engage on their two flanks with the screw threads of the screw and of the nut with a contact geometry that includes a curvilinear segment.