Composite Ball Screw Shaft With Fiber-Wound Threads for Axial Load
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Solution Overview
Problem
Ball screws used in high precision applications, especially in aircraft, face challenges with weight due to metal components and limited axial load transfer with plastic components, necessitating a balance between weight and load-carrying capacity.
Innovation Solution
A composite threaded ball screw shaft made of fibre-reinforced polymer material with a helical ridge formed by wound fibres, providing high axial load carrying capability and reduced weight, and a protective outer layer with a 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 low friction and wear resistance. This composite approach allows the shaft to achieve both high strength for load bearing and low weight compared to solid metal construction, while the ball bearings roll on the polymer surface reducing friction.
2Weight of moving object
If plastic is used for the ball screw shaft, then weight is reduced, but axial load transfer capability deteriorates
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 maintains the weight reduction benefit. The composite structure allows each material to contribute its superior properties: metal for strength and polymer for weight savings and low friction.
Solution Approach 2:
Different materials are applied to different regions of the shaft: the metal core handles axial loads internally, while the polymer outer layer interacts with the ball bearings to provide low friction. This local optimization allows each material to perform its best function in the appropriate location.
3Strength
If metal is used for the ball screw shaft, then axial load transfer capability is improved, but manufacturing complexity increases due to close tolerances
Solution Approach 1:
The polymer outer layer is applied to the surface that requires precision (the ball raceway), while the metal core provides structural strength. This allows the polymer to be precision-formed or machined to close tolerances for the ball interface, while the metal core can be manufactured with more standard tolerances, overall reducing manufacturing complexity.
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 shaft achieves strength comparable to metal while being lighter, with improved resistance to bending and buckling, and a low friction surface for efficient operation.
Implementation Method 1
a helical ridge formed on an outer surface of the shaft, the helical ridge being formed from a fibre-reinforced polymer material comprising a plurality of helical fibres wound around the shaft in the same sense and grouped together to form the ridge
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. The ball bearings ensure low friction.
Data Source
AI summary
A threaded shaft for a ball screw comprising: a shaft of fibre-reinforced polymer material; and a helical ridge 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 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.