Amorphous Ferromagnetic Balance Wheel Magnetic Shielding

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Solution Overview

Problem

Mechanical timepieces are susceptible to magnetic interference, causing rate deviations due to remanent magnetization of balance springs, and existing shielding solutions are either cumbersome, costly, or fail to provide omnidirectional protection, affecting both functionality and aesthetics.

Innovation Solution

A magnetic shielding device using an amorphous ferromagnetic material for the balance wheel, with a casing circle and arms that deflect magnetic fields orthogonally to minimize remanent magnetization, reducing bulk and cost while maintaining aesthetic appeal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If traditional metallic alloy balance spring is used, then excellent mechanical qualities are achieved, but susceptibility to remanent magnetization occurs causing rate deviations

Engineering Contradiction:

Improvemechanical qualitiesVSAvoidmagnetic susceptibility

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

A ferromagnetic balance wheel is introduced as an intermediary component between the external magnetic field and the balance spring. This mediator attracts and concentrates magnetic field lines, preventing them from reaching the balance spring and causing remanent magnetization, while the balance spring itself remains made of traditional metallic alloy to maintain its excellent mechanical properties

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If complete magnetic shielding with multiple components is implemented, then protection against magnetic fields is achieved, but weight and size increase significantly

Engineering Contradiction:

Improvemagnetic protectionVSAvoidwatch weight

Core Design Contradiction:

Object-affected harmful factorsVSWeight of moving object

Solution Approach 1:

The magnetic shielding function is merged with the existing balance wheel component. The balance wheel is made of ferromagnetic material that serves dual purposes: maintaining the oscillating mass for timekeeping and providing magnetic shielding by attracting and concentrating magnetic field lines away from the balance spring, eliminating the need for separate shielding components

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The balance wheel is given multiple functions: it serves as the oscillating mass for timekeeping regulation and simultaneously acts as a magnetic shield. This multi-functionality eliminates the need for additional dedicated shielding components, reducing overall weight and complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Object-affected harmful factors

If complete magnetic shielding enclosure is added, then magnetic field protection is improved, but device complexity and cost increase

Engineering Contradiction:

Improvemagnetic shieldingVSAvoidnumber of components

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Object-affected harmful factors

If balance spring is made from non-magnetic material, then magnetic susceptibility is neutralized, but mechanical qualities deteriorate

Engineering Contradiction:

Improvemagnetic resistanceVSAvoidmechanical properties

Core Design Contradiction:

Object-affected harmful factorsVSStrength

Solution Approach 1:

Inventive Principle:

Principle #24Intermediary (Mediator)

5Object-affected harmful factors

If shielding components are positioned between movement and case back, then magnetic protection is achieved, but aesthetic visibility of movement is obscured

Engineering Contradiction:

Improvemagnetic protectionVSAvoidaesthetic visibility

Core Design Contradiction:

Object-affected harmful factorsVSIllumination intensity

Solution Approach 1:

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The magnetic shielding function is extracted from the static case back structure and integrated into the dynamic balance wheel. This allows shielding to occur within the movement itself rather than requiring opaque case back components, preserving aesthetic visibility while providing protection

Inventive Principle:

Principle #2Taking out (Extraction)

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

Achieves high-performance magnetic shielding with minimal bulk and cost, ensuring isochronism and improving the aesthetic visibility of the movement by deflecting magnetic fields effectively without additional parts, thus reducing rate deviations and maintaining performance.

Implementation Method 1

A magnetic shielding device using an amorphous ferromagnetic material for the balance wheel

Methodology Applied

Scientific EffectFerromagnetism: Ferromagnetism

Implementation Method 2

with a casing circle and arms that deflect magnetic fields orthogonally to minimize remanent magnetization

Methodology Applied

Scientific EffectMagnetic field deflection: Magnetic Field

Implementation Method 3

The rate deviation is also influenced, but to a lesser extent, by the phenomenon of magnetostriction, which tends to lengthen or shorten the ribbon of the balance spring when subjected to a magnetic field

Methodology Applied

Scientific EffectMagnetostriction: Magnetostriction

Data Source

PatentEP2652560B1Magnetic screening for timepiece hairspring

Publication Date: 2019.11.13 THE SWATCH GRP RES & DEVELONMENT LTD

Figure 1A~1B
Figure 2~3

AI summary

Device for protecting a hairspring (1) of a timepiece against disturbing magnetic fields comprising a balance (2) made of an amorphous ferromagnetic material.