Internal Ball Screw Return Path to Reduce Entering-Exiting Fluctuation
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Solution Overview
Problem
Internal deflector type ball screws experience entering-exiting fluctuation due to the complex three-dimensional curve shape of the circulation path, leading to reduced smooth circulation of steel balls, load balance issues, and decreased service life, while existing solutions either deform during heat treatment or compromise load capacity and strength at high-speed rotation.
Innovation Solution
A ball screw design with a ball return path length set between scoop-up points to be between -0.1 to +0.3 times the diameter of the balls, and a maximum inclination angle of the ball return path adjusted based on the lead angle of the screw grooves to minimize entering-exiting fluctuation, ensuring smooth operation and improved low-speed characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a complex three-dimensional curve shape circulation path is used in internal deflector type ball screw, then the ball screw becomes more compact, but entering-exiting fluctuation occurs and smooth circulation of steel balls is reduced
Solution Approach 1:
The circulation path is divided into multiple linear sections rather than using a complex three-dimensional curve. The ball return path is segmented into: (1) a first ball return path extending in a radial direction from the rolling path, (2) a second ball return path extending in an axial direction, and (3) a third ball return path extending in a radial direction to return to the rolling path. This segmentation eliminates curve-induced entering-exiting fluctuation while maintaining compact internal circulation.
2Reliability
If circulation internal deflectors are provided in the nut, then ball circulation is improved, but the deflectors deform during heat treatment of the nut
Solution Approach 1:
The circulation function is extracted from the nut structure by providing the ball return paths directly on the screw shaft outer peripheral surface. The screw shaft itself serves as the circulation path carrier, eliminating the need for separate circulation internal deflectors in the nut that would deform during heat treatment.
Solution Approach 2:
The screw shaft is given multiple functions: it not only transmits rotational motion and supports the rolling paths but also directly provides the ball return paths on its outer peripheral surface. This multi-functionality eliminates the need for separate circulation components that would compromise dimensional stability.
3Reliability
If elastic bodies are interposed between balls to absorb fluctuation, then entering-exiting fluctuation is reduced, but load capacity is reduced and high-speed rotation performance deteriorates
Solution Approach 1:
Instead of using elastic bodies to absorb fluctuation, the invention converts the potential harm of entering-exiting fluctuation into benefit by designing a linear ball return path geometry that prevents the fluctuation from occurring in the first place. The straight-line ball return paths eliminate curve-induced length changes, so no elastic compensation is needed, preserving full load capacity and high-speed performance.
Data Source
AI summary
A ball screw includes a screw, a nut, a plurality of balls and a ball return path. A spiral screw groove is formed on an outer peripheral surface of the screw shaft. The nut is disposed around the screw shaft. A spiral screw groove is formed on an inner peripheral surface of the nut. The balls are housed in rolling paths formed by the two screw grooves facing each other. The ball return path circulates the balls in no more than one turn of the rolling paths. A length of the ball return path between scoop-up points where the balls are scooped up from the screw groove of the screw shaft is set to a value which is from −0.1 to +0.3 times of a diameter of the balls with respect to an integer value of a number of the balls filled between the scoop-up points.