Recirculation Crossover Insert with Smooth Transition Region
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In ball screw assemblies, the wear and tear over time lead to axial and radial lash between the screw and nut, causing the crossover insert's legs to contact the helical land, resulting in stress fractures and potential breakage due to increased stress concentrations at the joint.
Innovation Solution
The crossover insert features a smooth transition region with a radii portion and a tapered portion that minimizes stress concentrations by merging the legs into the central body, reducing the likelihood of fatigue cracks, and maintains a clearance fit with the screw and nut.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the legs are provided as a clearance fit within the ball raceway during normal use, then the legs remain in free floating relation and do not contact the screw or nut, but over extended periods wear and lash increase causing the legs to contact the helical land of the screw thread
Solution Approach 1:
The patent modifies the geometric parameters of the leg-body junction by introducing a smooth transition region with specific curvature radius (R1) and taper angle (α). This changes the stress distribution parameters at the junction, transforming the stress concentration factor from a high value that causes fatigue failure to a minimized value that resists fatigue crack formation, thereby extending the service life before leg contact occurs.
Solution Approach 2:
The patent applies curvature by designing the transition region with a rounded fillet (curvature radius R1) at the junction between the leg and central body, replacing the sharp corner geometry. This curved transition distributes stress more evenly across the junction area, preventing stress concentration and fatigue crack initiation, thus improving the durability of the crossover insert under prolonged operational conditions.
2Reliability
If the legs are designed to serve as backup sliding surface during failure scenarios, then they prevent freewheeling of the screw relative to the nut, but the union region between the leg and body becomes susceptible to stress fractures under increased stress concentrations
Solution Approach 1:
The patent optimizes the geometric parameters of the transition region, specifically the curvature radius (R1 = 0.02-0.05 times the leg width) and taper angle (α = 5-15 degrees), to minimize stress concentration factors. This parameter optimization ensures that when the legs engage the helical land during failure scenarios, the stress is distributed more uniformly across the leg-body junction, preventing stress fracture while maintaining the backup sliding function.
Solution Approach 2:
The rounded fillet geometry at the leg-body junction creates a smooth stress flow path, eliminating sharp corners that would act as stress concentrators. This curved transition region allows the legs to withstand the increased stress loads during failure scenarios without developing stress fractures at the union region, thereby maintaining structural integrity while providing the backup function.
3Productivity
If the legs extend from the central body in opposite directions to recirculate balls between adjacent turns, then they enable ball recirculation over remaining 60-50 degrees, but create stress concentrations at the joint of legs and central body
Solution Approach 1:
The patent introduces a curved transition region with fillet radius R1 at the junction where the legs meet the central body. This curvature eliminates sharp corners and creates a smooth geometric transition that distributes stress evenly across the joint area. The legs maintain their functionality for ball recirculation while the rounded junction prevents stress concentration, thereby resisting fatigue crack formation and improving the overall strength of the crossover insert.
Data Source
AI summary
A linear motion assembly and recirculation insert therefor is provided. The assembly includes a ball nut having a through bore with an internal helical groove and a screw having an external helical groove. The external helical groove is radially aligned with the internal helical groove to define a plurality of ball raceways. A plurality of inserts is fixed within the bore of the ball nut. The inserts each have a central body fixed within a recessed pocket of the ball nut, with the body having a radially inwardly facing, generally s-shaped groove to route the balls between adjacent turns. A pair of legs extends in opposite directions from the central body, wherein the legs are sized for a clearance fit with the external helical groove. The legs merge with the central body over a smooth transition region that minimizes stress concentrations at the joint between the legs and central body.