Ball Screw Return Tube Tongue Shape for High-Speed Durability
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Solution Overview
Problem
The challenge of increasing the allowable rotational speed of ball screws is limited by the stress applied to the tongue due to high-speed ball collisions, leading to potential fatigue and durability issues.
Innovation Solution
A ball screw design with a return tube tongue that gradually narrows from the root to the tip, reducing the rigidity and stress concentration, and optionally using flexible materials like SUS630 or SUS631 for the return tube.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the allowable rotational speed of the screw shaft is increased to achieve higher speed operation, then productivity is improved, but stress on the tongue increases due to high-speed ball collisions reducing reliability
Solution Approach 1:
The tongue shape is changed from a conventional uniform thickness to a gradually narrowing profile from root to tip. This parameter change in geometry reduces the stress concentration at the tongue root where balls collide, allowing higher rotational speeds without compromising fatigue strength
Solution Approach 2:
The tongue is designed with non-uniform thickness distribution, being thicker at the root for strength and gradually narrowing toward the tip. This local quality variation optimizes the balance between withstanding ball collision stresses and reducing overall stress concentration, enabling higher speed operation
2Strength
If a thick tongue is used to increase strength, then reliability is improved, but the impact of balls on the tongue increases at high speeds worsening the stress situation
Solution Approach 1:
The tongue thickness parameter is varied along its length, being maximum at the root and gradually decreasing toward the tip. This parameter gradient allows the tongue to have sufficient strength at the critical root region while reducing the impact area and stress concentration at the ball contact zone
Solution Approach 2:
The tongue profile features smooth curved transitions rather than sharp corners, with the narrowing shape creating gradual stress distribution. This curvature design eliminates stress concentration points that would occur with abrupt thickness changes, reducing ball impact effects
Data Source
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AI summary
A ball screw includes a screw shaft formed with an outer peripheral thread groove, a nut formed with an inner peripheral thread groove, a plurality of balls accommodated in a rolling path defined by the outer peripheral thread groove and the inner peripheral thread groove facing each other, and a return tube configured to return the balls from one end to the other end of the rolling path. The return tube includes a tongue that protrudes toward the rolling path and scoops up the balls from the rolling path. The tongue has a shape that gradually narrows from a root to a tip of the tongue.