Composite Ball Screw Shaft for High Axial Load at Low Weight
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Solution Overview
Problem
Conventional ball screws face challenges in high precision applications due to the weight of metal components and limited axial load transfer capabilities of plastic components, particularly in long-length applications.
Innovation Solution
A composite threaded ball screw shaft made from fibre-reinforced polymer materials, such as Carbon Fibre Reinforced Polymer (CFRP), with a helical ridge and groove structure that provides high axial load carrying capability while being lightweight, combined with a protective outer layer and optional hard top coat for wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metal is used for the ball screw shaft, then axial load transfer capability is improved, but weight increases
Solution Approach 1:
The ball screw shaft is constructed as a composite structure with a metal core providing axial load transfer capability and a polymer outer layer providing corrosion resistance and surface properties. This composite approach allows the shaft to achieve both high strength for load bearing and reduced weight compared to solid metal shafts, while the hollow further reduces weight without significantly compromising structural integrity
2Weight of moving object
If plastic is used for the ball screw shaft, then weight is reduced, but axial load transfer capability decreases
Solution Approach 1:
The shaft uses a metal core to provide the necessary axial load transfer capability that pure plastic cannot achieve, while the polymer outer layer and hollow structure reduce the overall weight. The composite design allows plastic to contribute weight reduction without sacrificing the load-bearing capacity provided by the metal core
3Weight of moving object
If the shaft is made hollow to reduce weight, then weight and bending resistance are improved, but manufacturing complexity increases
Solution Approach 1:
The shaft is manufactured as a hollow structure with internal support ribs that segment the hollow space. This segmentation provides structural reinforcement to prevent buckling while maintaining weight reduction benefits, and the ribbed structure can be formed using standard extrusion or injection molding techniques, managing manufacturing complexity
4Strength
If fibre reinforcement is added to polymer, then strength is improved, but manufacturing complexity increases
Solution Approach 1:
The shaft uses a metal core instead of fibre-reinforced polymer for the load-bearing core, which simplifies manufacturing compared to fibre winding or AFP processes. The polymer outer layer can be injection molded around the metal core, creating a composite structure without the complexity of fibre reinforcement processing
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 fibre-reinforced polymer ball screw shaft achieves strength comparable to metal while being significantly lighter, offering improved resistance to bending and buckling, and maintaining low friction for precise linear motion conversion.
Implementation Method 1
The grooves formed by these threads receive ball bearings that can roll within the grooves and transmit forces between the shaft and the nut. The ball bearings ensure low friction.
Implementation Method 2
The grooves formed by these threads receive ball bearings that can roll within the grooves and transmit forces between the shaft and the nut.
Data Source
Figure 1~2
Figure 3~4
Figure 5a~5b
AI summary
A threaded shaft (1) for a ball screw comprising: a shaft of fibre-reinforced polymer material; and a helical ridge (3) formed on an outer surface of said shaft, said helical ridge being formed from a fibre-reinforced polymer material comprising a plurality of helical fibres (5) wound around the shaft in the same sense and grouped together to form the ridge. The helical ridge formed from grouped helical fibres all wound with the same sense provides excellent axial load carrying capability as the fibres run continuously from end to end of the shaft and can thus transmit load from end to end. This adds much greater strength than a shaft formed from plastics only. The load carrying capability of the fibre wound helical ridge can indeed approach that of existing metal threads while still being much lighter in weight. The fibre shaft will also exhibit better characteristics in terms of resistance to bending and buckling, particularly in long length applications. As the helical ridge forms a raised spiral around the shaft it also forms a groove running parallel to the ridge, the groove being between adjacent raised parts of the ridge formed by successive turns of the helical ridge around the shaft.