Planetary Roller Screw Structure for Precise High-Load Motion
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Solution Overview
Problem
Conventional planetary roller screws struggle to achieve both precise displacement control and high load withstanding capacity simultaneously, which is necessary for applications in electric vehicles and humanoid robots.
Innovation Solution
The planetary roller screw design includes a main screw, nut, and planetary assembly with identical pitches for the external and internal threads, opposite helix directions, and an annular frame portion to stabilize rollers, allowing for decelerated displacement and precise motion control without reducing load pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the pitch of the main screw, nut, and rollers is increased, then the linear moving speed and load withstanding capacity are improved, but the displacement control precision deteriorates
Solution Approach 1:
The system is segmented into a main screw, nut, and multiple planetary rollers that work together. The load is distributed across multiple rollers simultaneously, allowing each roller to bear a portion of the total load. This segmentation enables the system to maintain high load withstanding capacity while using a larger pitch for faster motion, as the precision control is achieved through the coordinated action of multiple rollers rather than relying on a single high-precision interface.
Solution Approach 2:
The invention transitions from a single-degree-of-freedom screw mechanism to a planetary mechanism with rotational and orbital motions. The rollers rotate on their own axes while simultaneously orbiting around the main screw axis, creating a two-dimensional motion pattern. This dimensional change allows the system to achieve precise displacement control through the geometric relationship of the planetary motion, independent of the pitch size, thereby resolving the contradiction between large pitch (high speed/load) and precision control.
2Manufacturing precision
If the pitch of the main screw, nut, and rollers is decreased, then the displacement control precision is improved, but the load withstanding capacity and linear moving speed deteriorate
Solution Approach 1:
The invention merges the functions of multiple rollers working in parallel within a planetary configuration. Instead of relying on a single screw-nut interface, the system combines multiple roller-nut interfaces that share the load simultaneously. This merging of multiple load-bearing paths allows the system to maintain high load withstanding capacity even when using a smaller pitch for precision control, as the total load capacity is the sum of individual roller capacities.
3Device complexity
If a conventional planetary roller screw is used, then the structure is simple, but it cannot achieve both precise displacement control and high load withstanding capacity simultaneously
Solution Approach 1:
The invention introduces dynamic elements to the planetary roller screw system, specifically allowing the rollers to rotate on their own axes in addition to their orbital motion around the main screw. This dynamic capability enables the rollers to adapt to varying load conditions and maintain optimal contact with the nut, improving both displacement control precision and load withstanding capacity without significantly increasing structural complexity. The dynamic rotation of rollers ensures smooth operation and reduces friction compared to fixed-orientation rollers.
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 design achieves precise motion control with maintained load withstanding capacity, reducing manufacturing costs and improving smoothness by minimizing friction and noise through pure rolling motion.
Implementation Method 1
The external thread of each roller meshes with the external thread of the main screw and the internal thread of the nut
Implementation Method 2
minimizing friction and noise through pure rolling motion
Data Source
AI summary
A planetary roller screw adapted for solving insufficient structural strength of the conventional planetary roller screw while proceeding with precise motion control is disclosed. The planetary roller screw includes a main screw having an external thread, a nut having an internal thread, and a planetary assembly having rollers. Each roller includes an outer periphery having an external thread. The pitches of the external thread of the main screw, the internal thread of the nut, and the external thread of each roller are identical. The helix direction of the external thread of the main screw is opposite to that of the internal thread of the nut. When one of the main screw, the nut, and the planetary assembly acting as a driving member rotates, a linear displacement direction of the planetary assembly relative to the nut is opposite to that of the main screw relative to the planetary assembly.