Linear Actuator Crossed-Thread Screw-Nut Segmentation
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Solution Overview
Problem
Existing linear electric actuators based on screw-nut systems face inefficiencies in motion transformation due to mechanical efficiency dependence on helix angle, leading to reduced output force and increased wear, particularly in 'fail-safe' applications requiring precise positioning.
Innovation Solution
The implementation of a screw-nut system with crossed threads, where the first and second threaded portions have opposite directions, allowing for a reduction factor in linear displacement and improved reversibility, coupled with a return spring for fail-safe operation and a polyphase electric motor for enhanced efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a strong reduction in motion transformation is used to increase output force, then the output force is improved, but the mechanical efficiency drops significantly
Solution Approach 1:
The screw is divided into two separate threaded portions with crossed threads, each engaging with its own nut. This segmentation allows the motion transformation to be split into two stages, effectively doubling the reduction ratio while maintaining better mechanical efficiency at each stage compared to a single high-ratio transformation.
2Force
If a low helix angle is chosen to increase output force, then the output force is improved, but the reverse efficiency deteriorates
Solution Approach 1:
By segmenting the motion transformation into two crossed-thread stages, each stage can use a moderate helix angle that balances forward and reverse efficiency. The cumulative effect of two stages achieves the desired force multiplication without sacrificing the ability of the elastic element to return the actuator to reference position during power failures.
3Measurement precision
If a strong motion reduction is used to improve positioning precision, then the axial resolution is improved, but the mechanical efficiency and reversibility worsen
Solution Approach 1:
The crossed-thread configuration with two nuts provides a doubled reduction ratio that enhances axial resolution for precise positioning.同时，each thread-nut interface operates at moderate angles that maintain acceptable mechanical efficiency and reversibility, unlike a single high-ratio interface.
4Ease of manufacture
If friction screws/nuts are used to simplify construction, then the ease of manufacture is improved, but wear increases leading to play and precision loss
Solution Approach 1:
By using two crossed-thread interfaces instead of one, the load and wear are distributed across two contact zones. This segmentation reduces the wear rate at each interface compared to a single high-load interface, extending the service life while maintaining the simple friction screw/nut construction.
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 enhances the actuator's efficiency, reliability, and precision by doubling the motion transformation reduction ratio, improving reversibility, and reducing the force required for elastic return, while maintaining a compact construction.
Implementation Method 1
an electric motor with a rotor and a stator
Implementation Method 2
a screw-nut system for moving a member to be moved at least in translation... the first and second threaded portions having cross threads relative to each other
Implementation Method 3
which has an elastic return element capable of bringing the actuator back to the reference position, during a power cut
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to an electric linear actuator comprising an electric motor (4) with a rotor (16) and a stator (18), a casing (8, 10) and a screw-nut system (16) for moving a member (15) that is to be moved. The screw-nut system (6) comprises a screw (20) with a first threaded portion (26) and a first nut (22) with a complementary screw thread engaging with the first threaded portion (26), the first nut (22) being rotationally coupled to the rotor. The screw (20) comprises a second threaded portion (28) and the screw-nut system comprises a second nut (24) engaging with the second threaded portion (28), the first and second threaded portions having screw threads of opposite hand.