Bi-material Oscillating Weight for Self-winding Watches

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Solution Overview

Problem

Existing oscillating weights for self-winding watches made from composite materials face issues with fragility due to the addition of heavy metal particles, which can make the material brittle, and the challenge of achieving a strong and clean joint between different composite materials, particularly in small dimensions.

Innovation Solution

A bi-material oscillating weight is created by molding a central part from a composite material without heavy metal particles and overmolding a heavy sector made from a composite material with heavy metal particles, using a lateral rib with alternating sections to ensure interlocking and rigidity, preventing deformation and contamination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Weight of moving object

If heavy metal particles are added to composite material to increase density, then the oscillating weight achieves sufficient mass for self-winding mechanism, but the material becomes brittle and fragile

Engineering Contradiction:

Improveoscillating weight massVSAvoidmaterial toughness

Core Design Contradiction:

Weight of moving objectVSStrength

Solution Approach 1:

The oscillating weight is divided into two distinct parts: a heavy sector made from composite material with heavy metal particles (for mass) and a central part made from composite material without heavy metal particles (for flexibility and impact absorption). This segmentation allows each part to have optimized properties for its specific function.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the oscillating weight have different material compositions tailored to local requirements. The heavy sector uses high-density composite material to provide mass, while the central part uses flexible composite material to absorb impacts and prevent breakage.

Inventive Principle:

Principle #3Local quality

2Adaptability or versatility

If heavy sector and central part are made from different composite materials by overmolding, then the oscillating weight can have both heavy sector and flexible central part, but heavy metal particles diffuse from heavy sector to central part causing color alteration and unsightly spots

Engineering Contradiction:

Improvebi-material constructionVSAvoidjoint appearance quality

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

A lateral rib structure acts as an intermediary element between the heavy sector and central part. This rib provides a physical barrier and transition zone that prevents direct contact and diffusion between the two composite materials, thereby preventing heavy metal particle migration and maintaining appearance quality.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If heavy sector and central part are made from different composite materials by overmolding, then the oscillating weight can have both heavy sector and flexible central part, but adhesion between the two materials is poor and the joint is weak

Engineering Contradiction:

Improvebi-material constructionVSAvoidjoint adhesion

Core Design Contradiction:

Adaptability or versatilityVSStrength

Solution Approach 1:

The lateral rib is divided into alternating sections with and without undercuts, creating a segmented structure that provides multiple mechanical interlocking points. This segmentation increases the effective bonding area and distributes stress across multiple locations, strengthening the joint between heavy sector and central part.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The lateral rib incorporates asymmetric undercut features that create mechanical interlocking in specific directions. These undercuts are strategically placed to provide enhanced adhesion where needed while maintaining the overall structural integrity of the joint.

Inventive Principle:

Principle #4Asymmetry

4Length of stationary object

If the lateral rib is made thin to reduce thickness at the joint location, then the oscillating weight meets dimensional requirements, but the lateral rib becomes prone to deformation

Engineering Contradiction:

Improvejoint thicknessVSAvoidlateral rib rigidity

Core Design Contradiction:

Length of stationary objectVSStrength

Solution Approach 1:

The lateral rib is segmented into alternating sections with and without undercuts. This segmentation allows the rib to maintain thin overall thickness while creating localized reinforcement zones where undercuts provide mechanical interlocking, preventing deformation without increasing overall dimension.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The lateral rib is formed from composite material that combines the properties of both the heavy sector material and central part material, creating a transition zone with optimized mechanical properties that balances thinness with sufficient rigidity and resistance to deformation.

Inventive Principle:

Principle #40Composite materials

Data Source

PatentUS9862129B2Method for making an oscillating weight made from composite materials

Publication Date: 2018.01.09 ETA SA MFG HORLOGERE SUISSE

AI summary

A method for making an oscillating weight for an automatic winding mechanism of a self-winding watch including a central part made from a first composite material and a heavy sector made from a second composite material charged with heavy metal particles, the method including: forming the central part with a lateral rib and a rebate by injecting the first composite material into a mold; overmolding the heavy sector onto the central part by injecting the second composite material into a mold containing the central part, so that the second composite material fills the rebate and a gap underneath the lateral rib, so that the lateral rib is embedded in the second composite material and the central part and the heavy sector are interlocked.