Ball Screw Bridge Window Asymmetry Reducing Edge Loads
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Solution Overview
Problem
Bridge-type ball screws experience excessive edge loads near the ball circulation parts due to the circular bridge window design, leading to premature flaking of the screw groove caused by excessive surface pressure.
Innovation Solution
The design incorporates bridge members with linking grooves that cross the lead angle of the screw groove at a right angle, forming an oval or rectangular bridge window with linear parts, and ball circulation grooves with an S-shape, which redirect the balls to a non-load area, reducing edge loads and surface pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a circular bridge window is used in the bridge-type ball screw, then the structure is simple and compact, but excessive edge loads are generated near the ball circulation parts causing premature flaking
Solution Approach 1:
The bridge window is changed from a circular shape to an asymmetric shape with a non-circular contour. This asymmetric design allows the linking groove to approach the screw groove at an optimized angle, reducing edge loads on the screw groove edge while maintaining structural simplicity. The asymmetric shape redistributes the load more evenly across the bridge member-screw groove interface.
2Device complexity
If the linking groove edge meets the screw groove edge directly, then the structure is compact, but excessive surface pressure causes premature flaking of the screw groove
Solution Approach 1:
An intermediate region is introduced between the linking groove edge and the screw groove edge. This intermediate region acts as a mediator that distributes the contact load over a larger area, preventing excessive surface pressure concentration at the direct edge interface. The intermediate region may include a rounded transition zone or a specifically designed contact surface that reduces stress concentration.
3Productivity
If balls roll directly from the screw groove to the linking groove, then the circulation is efficient, but edge loads are generated on the screw groove near the ball circulation part
Solution Approach 1:
The ball circulation path is optimized by changing the geometric relationship between the screw groove and linking groove in multiple dimensions. The asymmetric bridge window shape and the angled approach of the linking groove create a three-dimensional circulation path that reduces edge loads while maintaining circulation efficiency. The balls approach the linking groove at an optimized angle rather than directly, distributing loads more favorably.
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
This configuration extends the life of the ball screw by alleviating edge loads and preventing premature flaking of the screw groove, ensuring reliable operation under axial loads.
Implementation Method 1
A large number of balls 54 are accommodated within a rolling track formed by the opposite screw grooves. The balls 54, rolling along the screw groove 53a, are guided to the linking groove 55a of the bridge member 55.
Data Source
AI summary
A ball screw (1, 10) has a bridge member (5) formed with a linking groove (5a) on its inner surface that makes the rolling track a circulating track. The bridge member (5) is fit into a bridge window (6, 9) formed on a barrel of a nut (3, 8). The bridge window (6) has a pair of opposite linear parts or walls (6a, 6a). These linear parts or walls have openings, formed by the helical screw groove, leading to the linking groove of the bridge member. The linear parts or walls are arranged so that they cross the lead angle (θ) of the nut screw groove at a right angle.