Convex Thread Flank Self-Locking for Miniature Screws
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Solution Overview
Problem
Current self-locking screw/nut assemblies in watchmaking are not effective for adjusting tightening over a few turns without damaging threads or requiring additional operations, especially for screws/nuts with diameters less than 2.75 mm, as they either deform irreparably or require glue for security.
Innovation Solution
A threaded rod or tapped element with a convex flank design that creates negative thread flank clearance in the middle part, allowing for adjustable self-locking by distributing stress across the sidewall, enabling secure tightening in a minimal number of turns without deformation or glue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional screw is forcefully engaged in a nut to achieve self-locking, then tightening security is improved, but the thread and tapping are irreparably deformed
Solution Approach 1:
The patent applies local quality by creating a convex flank on the screw thread with a specific geometry that concentrates the locking action on a localized central portion of the thread flank. This localized engagement area has different properties (convex shape with controlled clearance) compared to the rest of the thread, allowing self-locking without uniform deformation across the entire thread structure.
Solution Approach 2:
The patent changes the geometric parameters of the thread flank by introducing a convex profile with specific clearance characteristics. The convex flank creates a negative clearance zone in the middle portion that controls the engagement behavior, while the rest of the flank maintains positive clearance to prevent damage. This parameter change transforms the engagement mechanism from forceful deformation-based locking to controlled geometric locking.
2Reliability
If glue is applied to the screw to prevent loosening, then self-locking is improved, but additional operations are required and dismantling becomes difficult
Solution Approach 1:
The patent implements self-service by designing the screw thread with a convex flank that automatically provides self-locking functionality through its geometric configuration. The negative clearance zone in the middle of the convex flank creates inherent friction and mechanical interlocking that prevents loosening without requiring external substances like glue or additional locking mechanisms.
Solution Approach 2:
The patent extracts the locking function from external substances (glue) and integrates it directly into the screw thread geometry itself. The convex flank with negative clearance zone embodies the locking mechanism within the thread structure, eliminating the need for separate locking agents or additional operations.
3Reliability
If the screw thread is compressed radially into the nut thread to secure tightening, then self-locking is improved, but material displacement accumulates and damages threads
Solution Approach 1:
The patent applies local quality by concentrating the compression and material displacement control in the specific region of the convex flank's middle portion where the negative clearance exists. This localized control prevents material from being displaced along the entire thread length, thereby avoiding damage to other thread portions while still achieving secure locking.
Solution Approach 2:
The patent converts the potentially harmful effect of material displacement into a beneficial locking mechanism. The controlled negative clearance in the convex flank's middle portion causes localized material compression that generates friction and mechanical interlocking, transforming what would be damaging displacement into a self-locking force.
Data Source
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AI summary
The present invention relates to an assembly system comprising an externally threaded rod (2) or a threaded element (3) having a nominal diameter less than or equal to 2.75 mm, said thread having a front flank (5) and a rear flank (6), a root (7), and a crest (8) between the front and rear flanks. The rod or threaded element has a convex front and/or rear flank, and the thread flank clearance between said flank(s) and the rod or threaded element is alternately positive near the crest (8), negative in a mid-portion (9), and positive near the root (7), with respect to the threaded element. The present invention also relates to an assembly system comprising a threaded rod or a threaded element according to the invention.