Planetary Roller Screw Mechanism Lead Multiplication
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Solution Overview
Problem
Current planetary roller screw mechanisms are limited to a lead of 50 mm due to machining challenges, high friction, and robustness issues, making it difficult to increase the lead without making the mechanism bulky or reducing its capacity.
Innovation Solution
A planetary roller screw mechanism with a screw shaft having multiple external threads, a nut with internal threads, and rollers with external threads, where the number of external threads of the screw shaft is a multiple of the rollers' threads, and the nut's threads are a multiple of the rollers', allowing for a longer lead without increasing bulkiness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the lead of the planetary roller screw mechanism is increased beyond 50 mm, then the mechanism can achieve higher axial displacement per rotation, but the machining precision deteriorates due to increased helix angle and thread depth requirements
Solution Approach 1:
The invention divides the single-threaded screw shaft into multiple independent threads (at least two threads). Each thread can be machined separately with standard grinding wheels at acceptable helix angles, avoiding the need for deep single-thread machining. This segmentation allows the lead to be increased by having multiple threads work simultaneously while maintaining manufacturability and precision.
2Length of moving object
If the helix angle is increased to achieve longer lead, then the axial displacement per rotation increases, but the friction forces between screw shaft and rollers increase
Solution Approach 1:
By dividing the lead into multiple threads (segmentation), each thread operates at a lower helix angle for the same overall lead. This reduces the friction forces at each thread-roller interface while achieving the desired long lead through the combined action of multiple threads.
3Length of moving object
If the thread depth is increased to achieve longer lead, then the lead increases, but the manufacturing time for grinding screw shaft, nut and rollers increases
Solution Approach 1:
Segmenting the lead into multiple shallower threads reduces the depth each thread requires, allowing faster grinding operations. Multiple threads can be machined in parallel or sequence more quickly than one deep thread, reducing total manufacturing time while achieving the same lead.
4Length of moving object
If the number of threads on screw shaft is increased to achieve longer lead, then the lead increases, but the roller diameter must be reduced making the nut inner diameter smaller and reducing mechanism capacity
Solution Approach 1:
The invention segments the lead into multiple threads with optimized spacing and geometry. This allows maintaining larger roller diameters and nut inner diameters compared to using a single thread with equivalent lead, thereby preserving mechanism capacity and strength while achieving long lead.
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 solution enables a lead multiplication by a coefficient equal to the number of external threads of the rollers, achieving leads greater than 50 mm with improved robustness and ease of assembly, while maintaining a compact design.
Implementation Method 1
Each roller is provided with at least two external threads, whereas the number of external threads of the screw shaft is a multiple of the number of external threads of a roller and the number of internal threads of the nut is a multiple of the number of external threads of a roller
Data Source
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AI summary
This planetary roller screw mechanism (2) comprises a screw shaft (4) provided with at least one external thread (T4), a nut (6) provided with at least three internal threads (T6) and at least three rollers (8) arranged, radially with respect to a central axis (X4) of the screw shaft, between the screw shaft and the nut. Each roller (8) is provided with at least two external threads (T81, T82). The number of external threads (T4) of the screw shaft (4) is a multiple of the number of external threads (T8) of a roller (8). The number of internal threads (T6) of the nut (6) is a multiple of the number of external threads (T8) of a roller (8).