Spring-Button Shaft Coupler for Debris-Tolerant Secure Engagement
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Solution Overview
Problem
Existing shaft couplers face issues with sticking, inadequate resistance to disengagement, and durability in dirty environments, particularly during chimney maintenance where they are subjected to torsional and longitudinal forces, and are challenging to engage and disengage, especially when worn or coated with debris.
Innovation Solution
A coupler design featuring two opposing side buttons captured within a cavity of the male fitting, with a compression spring urging the buttons outwardly into a cavity of the female fitting, providing resistance to torsional and longitudinal forces, and featuring anti-rotation flats for secure engagement and easy disengagement, even in adverse conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single snap-like plunger lock is used in the coupler, then the device complexity is reduced, but the reliability of engagement and resistance to disengagement deteriorates
Solution Approach 1:
The single plunger lock is segmented into two opposing plungers that work independently. Each plunger engages with its own cavity in the mating fitting, providing redundant locking action. This segmentation increases reliability without significantly increasing overall device complexity, as both plungers share a common spring mechanism.
Solution Approach 2:
Each plunger is given specialized local features including a beveled leading edge for easy engagement, a flat top surface for user actuation, and a specific cavity geometry for spring retention. These local quality enhancements ensure reliable engagement and disengagement while maintaining overall structural efficiency.
2Ease of operation
If the coupler is made small in diameter for easy transport and storage, then the ease of operation is improved, but the strength to resist torsional and longitudinal forces deteriorates
Solution Approach 1:
The coupler employs asymmetric features including non-circular cross-sections (square or rectangular) and strategically positioned flats on opposing sides. These asymmetric elements provide anti-rotation capability and torsional strength while maintaining a compact diameter. The flats serve dual purposes: structural reinforcement and user grip points for easy handling.
Solution Approach 2:
Strength is achieved by transitioning from purely radial loading to multi-dimensional load distribution. The opposing flats and non-circular geometry distribute torsional and longitudinal forces across multiple contact points and structural elements, maximizing strength-to-diameter ratio.
3Manufacturing precision
If the plunger is made with tight tolerances for precise engagement, then the manufacturing precision is improved, but the ease of operation in dirty environments deteriorates
Solution Approach 1:
Instead of relying on tight tolerances to prevent debris interference, the design inverts the approach by using generous clearance fits with beveled leading edges. The bevel acts as a debris-deflecting feature that guides the plunger into the cavity regardless of contamination, making the system more tolerant of dirty environments while maintaining reliable engagement.
Solution Approach 2:
The plunger-cavity interface uses dynamic clearance rather than static tight fit. The spring-loaded plunger maintains continuous contact pressure against the cavity wall, creating a self-adjusting connection that compensates for wear and debris accumulation while maintaining engagement reliability.
4Device complexity
If the plunger uses a simple spring mechanism for engagement, then the device complexity is reduced, but the durability when subjected to wear and debris deteriorates
Solution Approach 1:
The spring mechanism incorporates cushioning features including a pre-compressed spring design and recessed spring seating. The spring is positioned to absorb shock loads and debris impacts before they can damage critical engagement surfaces. This beforehand cushioning protects the simple spring mechanism from wear while maintaining durability.
Solution Approach 2:
The spring acts as an intermediary element between the user's disengagement force and the plunger's locking action. This intermediary mechanism distributes forces evenly, reduces stress concentrations, and provides a buffer against sudden shocks and debris interference, enhancing overall durability without increasing 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 coupler effectively resists inadvertent disengagement and maintains functionality even when worn or coated with debris, offering strong resistance to torsional and longitudinal forces while ensuring easy engagement and disengagement, making it suitable for small diameter applications.
Implementation Method 1
a spring, at least partially within the cavity, urging the button outwardly
Data Source
Figure 1~3
Figure 4~7
Figure 8~11
AI summary
A coupler for connecting two segments of a shaft comprises a first fitting (22) and a second fitting (24), each of what is attachable to the end of a shaft segment. The first fitting (22) has at least one spring loaded button (30). The first fitting is received within the cavity of the second fitting. A coupler button has recess in the base for receiving a spring (50) and there are planar button-guiding surfaces (62, 68) within the first fitting. The second fitting preferably has one or more exterior surface flats (42) which align with the direction of button movement and which mate with one or more flats within the second fitting cavity.