Frictional Coupling With Complementary Rough Surfaces
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Solution Overview
Problem
Existing mechanical couplings face issues with security under shock or vibrational forces, often requiring additional components and limiting orientation flexibility, with insufficient retaining force and susceptibility to loosening.
Innovation Solution
A frictional coupling method involving surfaces with complementary shapes and surface roughness averaging less than 500 microinches, utilizing projections in a preselected pattern to create a friction fit that resists movement, with an elastic compressive range matching the surface roughness, ensuring secure engagement without additional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ball-and-dimple mechanical coupling is used, then the parts are retained securely, but it requires additional components (ball, spring, bore, dimple) and limits orientation flexibility
Solution Approach 1:
The patent removes the ball, spring, bore, and dimple components from the coupling mechanism, replacing them with a direct friction-based interface between complementary surfaces. This extraction of unnecessary components simplifies the device while maintaining retaining security through friction forces generated by the interference fit between the first and second surfaces.
Solution Approach 2:
The complementary surfaces design allows the coupling to function in multiple orientations without requiring additional components or adjustments. The friction-based mechanism provides universal retention capability across different orientations, eliminating the orientation limitations of ball-and-dimple couplings.
2Reliability
If a set screw coupling is used, then the first part is retained within the second part, but shock and vibration may gradually work the set screw loose
Solution Approach 1:
The patent replaces the set screw mechanical fastening system with a friction-based retention system. Instead of relying on a threaded screw that can gradually loosen under vibration, the invention uses friction forces generated by the interference fit between complementary surfaces, which do not suffer from gradual loosening and provide stable retention under shock and vibration.
3Reliability
If an interference-fit coupling is used, then the parts engage securely, but vibrational forces may cause directional elastic deformation and the tool may walk out of the recess
Solution Approach 1:
The patent applies local quality by creating specific surface characteristics on the complementary surfaces, including controlled roughness and geometric features. These localized surface properties enhance friction forces at the interface, preventing the tool from walking out under vibrational forces while maintaining secure engagement.
Solution Approach 2:
The invention employs composite surface structures combining smooth and rough regions, or different material properties at the interface, to optimize friction characteristics. This composite approach enhances resistance to vibrational forces while maintaining secure engagement between the tool and holder.
4Force
If traditional mechanical couplings are used, then retaining force is provided, but the amount of retaining force may be insufficient under shock and vibration
Solution Approach 1:
The patent changes the parameters of the coupling interface by optimizing surface roughness, contact area, and friction coefficients of the complementary surfaces. These parameter changes increase the friction-based retaining force, providing sufficient security under shock and vibration without requiring additional mechanical components.
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 solution provides a secure mechanical coupling that remains stable under shock and vibration, offering orientation flexibility and enhanced retaining force without additional components, effectively preventing unintended disassembly.
Implementation Method 1
The projections have an average elastic compressive range substantially equal to the surface roughness average of the first surface
Implementation Method 2
projections... are configured to produce a friction fit between the first surface and the second surface when the first and the second surfaces are biased against each other
Data Source
AI summary
A method of forming a coupling between a first part and a second part is disclosed. The method includes providing a first surface of the first part. The first surface has a first shape and a surface roughness average that is less than or equal to about 500 microinches (13 microns). The method also includes forming a second surface of the second part where the second surface has a second shape and the first shape and the second shape are substantially complementary shapes. Projections form at least a portion of the second surface in a preselected pattern, and are configured to produce a friction fit between the first surface and the second surface when the first surface and the second surface are biased against each other. The projections have an average elastic compressive range substantially equal to the surface roughness average.