Over-Molded Ball-Screw Nut for Anti-Rotation and Position Control
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Solution Overview
Problem
Existing ball-screw actuators face challenges in preventing relative rotation between components and effectively controlling the axial and lateral positions of the nut, which can lead to inefficiencies and increased manufacturing complexity.
Innovation Solution
A ball-screw actuator is manufactured with a hollow metal screw nut core and a plastic over-molded outer shell, featuring anti-rotation, axial position control, and lateral position control elements, along with knurling on the exterior surface and recirculation units within the internal threads to manage the movement of rolling elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metal screw nut core is used with internal threads, then the structural strength is improved, but the manufacturing complexity increases due to the need for separate anti-rotation and position control features
Solution Approach 1:
The patent combines multiple functional features (anti-rotation, axial position control, lateral position control) into a single integrated plastic outer shell that is over-molded onto the metal core. This merging of functions into one component reduces the total number of parts and simplifies manufacturing while maintaining all necessary control capabilities.
Solution Approach 2:
The patent uses a composite structure consisting of a metal core for strength and a plastic outer shell for functional features. This composite material approach allows each material to contribute its superior properties - metal provides structural integrity while plastic provides ease of manufacturing for complex geometric features like anti-rotation and position control elements.
2Reliability
If multiple separate components are used for anti-rotation and position control, then the functional reliability is improved, but the device complexity increases
Solution Approach 1:
The patent merges anti-rotation features, axial position control features, and lateral position control features into a single integrated plastic outer shell. This integration maintains functional reliability by ensuring all control features work together as a unified system while reducing device complexity by eliminating the need for multiple separate components.
Solution Approach 2:
The plastic outer shell serves multiple functions simultaneously: it provides anti-rotation engagement, axial position control, and lateral position control. This multi-functionality approach maintains comprehensive control capabilities while reducing the overall number of components in the system.
3Ease of manufacture
If a solid metal nut is used, then the manufacturing simplicity is improved, but the weight increases and manufacturing precision decreases for position control features
Solution Approach 1:
The patent uses a composite structure with a hollow metal core and a plastic outer shell. The hollow metal core reduces weight compared to a solid metal nut, while the plastic outer shell enables precise position control features. This composite approach simultaneously achieves weight reduction and improved manufacturing precision for control features.
Solution Approach 2:
The patent applies different material properties to different parts of the nut: the metal core provides structural strength and can be hollow for weight reduction, while the plastic outer shell provides the precise geometric features needed for anti-rotation and position control. Each material is used where its properties are most beneficial.
4Reliability
If recirculation paths are added to the internal threads, then the operational reliability is improved, but the manufacturing complexity increases
Solution Approach 1:
The recirculation paths are pre-formed as integral features of the internal threading during the manufacturing process. By incorporating the recirculation paths into the thread design itself rather than adding them as separate components, the patent maintains operational reliability for ball recirculation while avoiding the manufacturing complexity of separate recirculation mechanisms.
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 solution enhances the actuator's stability and manufacturing simplicity by preventing relative rotation and accurately controlling the nut's position, improving performance and reducing costs through the use of a plastic over-molded shell with integrated features.
Implementation Method 1
The plastic over-molded outer shell has an anti-rotation feature configured to engage a mating feature of a housing to prevent relative rotation therebetween
Implementation Method 2
The method may also include knurling at least a portion of an exterior surface of the screw nut core prior to adding the plastic outer shell
Implementation Method 3
A set of balls radially separate the spindle from the nut and permit relative rotation with minimal resistance
Data Source
AI summary
A ball-screw actuator includes a screw nut having a metal core and an over-molded plastic outer shell. The plastic outer shell includes features which would be expensive to manufacture in a single piece metal screw nut, such as an anti-rotation feature, an axial position control feature, and a lateral position control feature. The anti-rotation feature may take the form of an axial groove or of an axial ridge.