Shaft Locking Mechanism for Fast Armrest Positioning Without Back-Drive
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Solution Overview
Problem
Existing adjustable aircraft armrests lack a fast and stable locking mechanism that prevents back-drive, leading to undesirable orientations and user fatigue, as current mechanisms for infinite adjustability are either cumbersome or unstable.
Innovation Solution
A locking mechanism featuring a locking shaft with guide grooves, a nut with corresponding grooves, and a button-activated system that includes biasing elements and ball stops to prevent lateral and linear motion, ensuring secure engagement and disengagement of the locking shaft and nut, thereby preventing back-drive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a threaded rod mechanism is used for infinite adjustability, then the armrest can be adjusted to any position, but the adjustment process becomes cumbersome and time-consuming
Solution Approach 1:
The continuous threaded rod adjustment is segmented into discrete positioning steps using a rack and pinion system. The rack is divided into multiple engagement positions that correspond to different armrest orientations, allowing rapid selection of predetermined positions without continuous manual threading.
Solution Approach 2:
The manual threading operation is replaced with a cam-actuated release mechanism. A cam lever, when actuated, automatically disengages the locking elements from the rack teeth, enabling rapid position changes without the time-consuming manual threading motion.
2Device complexity
If a simple retaining mechanism is used, then the structure remains simple, but the armrest becomes unstable with significant back-drive
Solution Approach 1:
The locking elements are preliminarily positioned on the rack teeth before final engagement. The cam mechanism pre-aligns the locking elements with the rack teeth, ensuring positive engagement and preventing back-drive without requiring complex multi-stage locking systems.
Solution Approach 2:
The rack and pinion system acts as an intermediary between the simple cam actuator and the armrest positioning. The rack teeth provide multiple engagement points that translate the simple cam rotation into reliable multi-position locking, bridging the gap between simplicity and stability.
3Productivity
If a fast locking mechanism is implemented, then adjustment time is reduced, but the locking mechanism may become more complex
Solution Approach 1:
The locking and positioning functions are merged into a single cam-actuated operation. Rotating the cam lever simultaneously releases the locking elements from the rack teeth and allows the armrest to move to the desired position, combining multiple functions into one simple motion.
Solution Approach 2:
The locking mechanism transitions from a static threaded rod system to a dynamic cam-actuated system. The cam provides rotational motion that automatically cycles the locking elements through engagement and disengagement phases, enabling rapid position changes without complex control systems.
Data Source
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Figure 1C
AI summary
A locking mechanism to prevent back-drive includes a locking shaft (100) with guide grooves. Locking shaft guides engage the guide grooves to constrain lateral motion of the locking shaft. A nut (110) includes corresponding grooves to the locking shaft, and engages the locking shaft to prevent linear translation. The locking mechanism may be incorporated into a aircraft seat armrest to create a positive lock in the armrest position.