Hairspring Attachment Using Low-Viscosity UV Curing

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Solution Overview

Problem

The existing methods for attaching hairsprings, particularly silicon ones, face challenges in inducing mechanical stresses and displacing the hairspring from its rest position, affecting the precision of mechanical timepieces due to the viscosity of hot-melt glue used in traditional fixing techniques.

Innovation Solution

A method involving the use of a fluid adhesive with viscosity between 200 and 400 mPa.s, which is polymerizable by ultraviolet radiation, is employed to glue the last turn of the hairspring to a stud, allowing the hairspring to return to its rest position before hardening, thus minimizing mechanical stresses and maintaining precision.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If hot-melt glue is used to attach the hairspring, then the hairspring is fixed securely, but the high viscosity of the glue induces mechanical stresses and displaces the hairspring from its rest position

Engineering Contradiction:

Improveattachment strengthVSAvoidhairspring position precision

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The patent changes the viscosity parameter of the adhesive from high (hot-melt glue) to low (200-400 mPa.s at application temperature). This parameter change allows the adhesive to flow freely during application, preventing mechanical stresses and displacement of the hairspring, while still providing sufficient attachment strength once cured.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies the adhesive in a liquid state with low viscosity before the hairspring is fully positioned. The low viscosity allows the hairspring to be placed in its rest position without resistance from the adhesive, and the adhesive then cures to provide secure attachment. This preliminary application in a fluid state prevents stress induction.

Inventive Principle:

Principle #10Preliminary action

2Ease of manufacture

If traditional manual insertion method is used to fix the hairspring ends, then assembly is simple, but the hairspring may rotate slightly which affects rate precision

Engineering Contradiction:

Improveassembly simplicityVSAvoidhairspring positioning precision

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent replaces the mechanical insertion and force-fitting method with a chemical bonding method using low-viscosity adhesive. This substitution eliminates the need for manual force application that causes rotation, while still achieving secure attachment. The adhesive provides a non-mechanical means of fixation that preserves positional precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Manufacturing precision

If silicon material is used for the hairspring, then the precision and magnetism resistance are improved, but the cost and assembly difficulty increase due to small dimensions

Engineering Contradiction:

Improvetimekeeping precisionVSAvoidassembly ease

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent uses a liquid adhesive with viscosity between 200-400 mPa.s that can be applied in a controlled manner to the tiny silicon hairspring. The fluid nature of the adhesive allows it to be deposited precisely on small components without requiring complex mechanical handling, thus facilitating assembly of delicate silicon parts while maintaining positioning accuracy.

Inventive Principle:

Principle #29Pneumatics and hydraulics

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

This approach ensures that the hairspring is fixed without inducing mechanical stresses, maintaining its regular operation and precision, as the fluid adhesive allows the hairspring to spontaneously return to its equilibrium position before hardening, thereby ensuring consistent oscillation frequency.

Implementation Method 1

A method involving the use of a fluid adhesive with viscosity between 200 and 400 mPa.s, which is polymerizable by ultraviolet radiation

Methodology Applied

Scientific EffectPhotopolymerization: Photopolymerisation

Implementation Method 2

A method involving the use of a fluid adhesive with viscosity between 200 and 400 mPa.s... allowing the hairspring to return to its rest position before hardening, thus minimizing mechanical stresses

Methodology Applied

Scientific EffectViscosity control:

Data Source

PatentEP3211486B1Method for attaching a hairspring for mechanical clock movement

Publication Date: 2018.09.26 ETA SA MFG HORLOGERE SUISSE

Figure 1A~1B
Figure 2A~3

AI summary

Method of fixing a last coil on the outside (12) of a watch spiral (4) in a groove (70) made in a stud (14), this method comprising the step of gluing the last coil on the outside (12) of the watch spiral (4) by means of a fluid glue having a viscosity between 200 and 400 mPa.s.