Directional Self-Locking Screw Actuator for Manual Aircraft Hoisting
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Solution Overview
Problem
Self-locking ACME screw actuators used for lifting heavy loads, such as aircraft engine cowl, cannot be manually hoisted without disconnection, while non-self-locking actuators require a 'no-back' device to hold the load in place, presenting a challenge in manual lifting scenarios.
Innovation Solution
A hybrid screw actuator design that is self-locking in compression and non-self-locking in extension, utilizing a combination of lead screw and ball screw with specific helical contact and raceway surfaces and ball bearings to achieve the desired directional locking and unlocking properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a self-locking ACME screw actuator is used, then safety is improved because there is no need for a mechanical lock, but manual hoisting becomes impossible without disconnection
Solution Approach 1:
The screw actuator dynamically switches between self-locking and non-self-locking states based on the direction of axial load. When compressed (load in first direction), the threads engage to provide self-locking. When tensioned (load in second direction), the threads disengage to allow manual hoisting. This dynamic behavior resolves the contradiction by adapting the locking property to the operational phase.
Solution Approach 2:
The friction coefficient between screw and nut changes based on axial load direction. In compression, high friction enables self-locking; in tension, low friction allows free movement for manual hoisting. This parameter change resolves the contradiction by transforming the friction characteristic according to the operational requirement.
2Ease of operation
If a non-self-locking screw actuator is used, then manual hoisting becomes possible, but a no-back device is required to hold the load in place
Solution Approach 1:
The screw actuator performs multiple functions: it provides self-locking to hold the load during normal operation, and allows manual hoisting when needed. The single device replaces the need for separate no-back devices by integrating the holding function into the screw-nut interface through directional friction control.
Solution Approach 2:
The screw actuator self-regulates its locking behavior based on load direction without requiring external control mechanisms. The frictional properties automatically engage or disengage based on whether the load is compressing or tensing the threads, eliminating the need for additional control devices.
3Device complexity
If a self-locking ACME screw actuator is used, then mechanical locks are eliminated, but the screw cannot be decoupled from the nut for hoisting
Solution Approach 1:
The patent replaces the traditional mechanical lock system with a friction-based directional locking mechanism. Instead of using physical locks to hold the load, the system uses controlled friction between screw and nut that engages in compression and disengages in tension, allowing decoupling without mechanical locks.
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
Enables safe self-locking during compression, allowing for manual lifting without mechanical locks and easy disengagement for hoisting, while maintaining non-self-locking in tension to facilitate manual operation with minimal frictional resistance.
Implementation Method 1
When the screw is loaded relative to the nut in a second axial direction, the plurality of ball bearings are compressed between the first helical raceway surface and the second helical raceway surface
Implementation Method 2
When the screw is loaded relative to the nut in a first axial direction, the first helical contact surface is compressed against the second helical contact surface
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3C
AI summary
A screw actuator (100, 110, 200, 210, 320), includes: a screw (110, 112, 210) comprising a first helical contact surface (112A, 113B, 122A, 123B, 212A, 222A) and a first helical raceway surface (113A, 123A, 213, 223); a nut (120, 220) comprising a second helical contact surface (112A, 113B, 122A, 123B, 212A, 222A) and a second helical raceway surface (113A, 123A, 213, 223); and a plurality of ball bearings (130, 230) in a helical raceway formed by the first helical raceway surface (113A, 123A, 213, 223) and the second helical raceway surface (113A, 123A, 213, 223). When the screw (110, 112, 210) is loaded relative to the nut (120, 220) in a first axial direction (F1, F2), the first helical contact surface (112A, 113B, 122A, 123B, 212A, 222A) is compressed against the second helical contact surface (112A, 113B, 122A, 123B, 212A, 222A). When the screw (110, 112, 210) is loaded relative to the nut (120, 220) in a second axial direction (F1, F2), the plurality of ball bearings (130, 230) are compressed between the first helical raceway surface (113A, 123A, 213, 223) and the second helical raceway surface (113A, 123A, 213, 223).