Adjustable Bracelet Clasp With Indexed Setting Retention

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Solution Overview

Problem

Existing bracelet clasps that allow for adjustable length lose their setting when opened, requiring manual reinsertion for the desired length each time, and do not provide fine-tuning for variations in wrist circumference throughout the day or season.

Innovation Solution

A watch strap clasp with a cap connected to strap strands via a sliding end link and a pressure-operated control member, featuring a toothed element and return springs, allowing the length to be adjusted without losing the setting, with indexed positions and quick handling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a folding buckle clasp with a sliding adjustment mechanism is used, then the bracelet length can be adjusted, but the setting is lost when the clasp is opened

Engineering Contradiction:
Improvebracelet length adjustmentVSAvoidsetting retention
Core Design Contradiction:
Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies preliminary action by automatically re-engaging the toothed element with the rack teeth upon closing the clasp. The spring-loaded toothed element is pre-positioned to automatically engage with the rack teeth at the correct position, ensuring the bracelet length setting is restored without manual intervention each time the clasp is closed.

Inventive Principle:
Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback through the automatic engagement mechanism where the toothed element responds to the closing action by automatically engaging with the rack teeth at the appropriate position. This feedback loop ensures that the setting is retained and restored without requiring the wearer to manually reposition components.

Inventive Principle:
Principle #23Feedback

2Reliability

If a locking mechanism is added to retain the bracelet length setting, then setting retention is improved, but the device complexity increases

Engineering Contradiction:
Improvesetting retentionVSAvoidclasp mechanism complexity
Core Design Contradiction:
ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the locking function into the existing sliding adjustment mechanism by integrating the toothed element with the rack teeth. The toothed element is part of the same assembly as the sliding components, and its engagement with the rack teeth provides automatic locking without requiring a separate, independent locking mechanism.

Inventive Principle:
Principle #5Merging (Combining)

Solution Approach 2:

The patent applies self-service through the automatic engagement of the toothed element with the rack teeth upon closing the clasp. The spring-loaded toothed element automatically engages at the correct position without requiring manual intervention or a separate locking action, simplifying the overall mechanism while maintaining setting retention.

Inventive Principle:
Principle #25Self-service

3Reliability

If the toothed element is always engaged with rack teeth, then the bracelet length is fixed, but adjustability is lost

Engineering Contradiction:
Improvesetting retentionVSAvoidbracelet length adjustability
Core Design Contradiction:
ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent applies dynamics by making the engagement between the toothed element and rack teeth reversible. The toothed element can be disengaged from the rack teeth to allow adjustment of the bracelet length, and automatically re-engaged when the clasp is closed. This dynamic engagement provides both adjustability and setting retention at different states.

Inventive Principle:
Principle #15Dynamics

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

Enables maintaining the strap length setting without inadvertent loss and provides simple, quick adjustment, accommodating variations in wrist circumference.

Implementation Method 1

at least one spring arranged in a housing of the cap to push the terminal link into the second position where it is totally disengaged from the cap when the control member is actuated

Methodology Applied
Scientific EffectElasticity: Elasticity

Implementation Method 2

a pressure-operated control member for moving a toothed element fixed to the control member from a first position in which the toothed element is engaged with a rack tooth fixed to the end link of the clasp, towards a second position in which the toothed element is freed from its engagement with the rack teeth

Methodology Applied
Scientific EffectMechanical Force: Mechanical Force

Data Source

PatentEP4646959A1Adjustable bracelet clasp
Publication Date: 2025.11.12 CO DES MONTRES LONGINES FRANCILLON SA
  • EP4646959A1 patent drawingFigure 1
  • EP4646959A1 patent drawingFigure 2
  • EP4646959A1 patent drawingFigure 3

AI summary

The invention relates to a clasp (100) for a watch strap comprising a cap (3) connected on one side to a first strap strand and on the other side to a second strap strand, connecting means being interposed between the second strap strand and the cap (3) of the clasp (1), these connecting means comprising an end link (10) sliding along a longitudinal direction of the clasp (1) between a frame (8) integral with the cap and the cap (3), from a first position in which the end link (10) is at least partially engaged in the cap (3) of the clasp (1), to a second position in which the end link (10) is disengaged from the cap (3) of the clasp (1), the clasp comprising a pressure-operated control member (6) for moving a toothed element (7) integral with the control member (6) from a first position in which the toothed element (7) is engaged with a rack tooth (11,11') integral with the terminal link (10) of the clasp, towards a second position in which the toothed element (7) is released from its engagement with the rack teeth (11, 11'), the clasp being characterized in that the control member (6) is accessible from the cap (3) through an opening (34) formed in the cap, the control member comprising at least one housing (62) in which a return spring (14) is disposed, this spring (14) bearing against the frame and in that it comprises at least one other spring (15) arranged in a housing of the cap to push the terminal link (10) into the second position where it is totally disengaged from the cap (3) when the control member is actuated.