Ball Rolling Surface Roughness for Low-Speed Linear Motion
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Solution Overview
Problem
Existing linear motion devices, such as ball screws, face issues with lubricant retention and wear under low-speed conditions due to insufficient evaluation of surface roughness, despite adhering to specified ranges for protruding peak and valley portions.
Innovation Solution
A new evaluation method is introduced, focusing on average surface roughness Sa excluding a predetermined ball rolling direction component, achieved through processes like shot peening, to form fine unevenness and improve lubricant retention and reduce friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the ball rolling surface is machined by grinding or turning finish with controlled surface roughness, then the manufacturing precision is improved, but the lubricant retention capability deteriorates under low-speed conditions
Solution Approach 1:
The invention changes the surface roughness parameter from the conventional range (Ra 0.03-0.3 μm) to a new range (Ra 0.06-0.5 μm), specifically optimizing it to balance lubricant retention with operational smoothness. This parameter change allows the surface to retain lubricant effectively even under low-speed conditions while maintaining manufacturing precision.
2Object-generated harmful factors
If the surface smoothness is increased to reduce wear, then the friction is reduced, but the lubricant retention capability deteriorates
Solution Approach 1:
The invention optimizes the surface roughness parameter to a specific range (Ra 0.06-0.5 μm) that balances two opposing requirements: smooth enough to reduce friction and wear, but rough enough to retain lubricant. This optimized parameter range resolves the contradiction between wear reduction and lubricant retention.
3Ease of operation
If the surface roughness is reduced to improve smoothness, then the friction decreases, but the lubricant supply and retention capability deteriorates particularly at low speeds
Solution Approach 1:
The invention establishes an optimized surface roughness range (Ra 0.06-0.5 μm) that ensures adequate lubricant retention capability while maintaining operation smoothness. This parameter optimization is particularly effective under low-speed conditions where lubricant retention is critical for preventing wear.
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 method enhances lubricant film formation and reduces friction, thereby preventing wear and maintaining operational efficiency even at low speeds.
Implementation Method 1
a fine unevenness is formed on the ball rolling surface of the screw shaft or the nut as processed traces, and the lubricant is accumulated in a concave portion (valley portion) of the unevenness to contribute to lubrication
Data Source
Figure 1~2B
Figure 3A~4B
Figure 5
AI summary
This linear motion device comprises: a guide shaft which is provided with a first ball rolling surface on the outer circumferential surface; a mobile body which is provided with a second ball rolling surface on the inner circumferential surface so as to face the first ball rolling surface and which moves relative to the guide shaft; and balls which roll in a space formed between the first ball rolling surface and the second ball rolling surface. In at least one of the first ball rolling surface and the second ball rolling surface, the average surface roughness Sa excluding a prescribed ball rolling-direction component is at least 0.1 µm.