Watch Balance Spring Stiffness Adjustment via Symmetrical Flexible Element
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Solution Overview
Problem
Existing balance springs in watch resonator mechanisms are sensitive to changes in the direction of the adjustment force, leading to potential creep in adhesives, manufacturing errors, and hysteresis in the adjustment mechanism, which affect the precision of rate adjustment.
Innovation Solution
A balance spring with a flexible element arranged in series, comprising two flexible parts connected symmetrically to the strip and a fixed mount, allowing for balanced variable force application and precise stiffness adjustment through pre-stressing means.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single flexible element is used for stiffness adjustment, then the adjustment mechanism is simple, but the system becomes sensitive to changes in the direction of the adjustment force, causing adhesive creep and hysteresis
Solution Approach 1:
The single flexible element is divided into two symmetrical flexible parts (first and second flexible parts) that connect the strip to the fixed mount. This segmentation allows the adjustment force to be distributed symmetrically, reducing sensitivity to directional changes and minimizing adhesive creep while maintaining structural simplicity
Solution Approach 2:
The patent employs symmetrical arrangement of the flexible parts relative to an axis, which is essentially applying asymmetry in reverse (using symmetry) to balance the forces. This symmetrical configuration ensures that adjustment forces are evenly distributed, eliminating hysteresis and improving adjustment precision without significantly increasing complexity
2Reliability
If the balance spring is tightened to eliminate play at the index pin, then the chronometric properties improve, but the rate adjustment becomes impossible after tightening and the balance spring may be stressed
Solution Approach 1:
The patent implements a dynamic adjustment mechanism where the flexible element can be continuously pre-stressed to vary the stiffness of the balance spring. This allows the system to maintain optimal chronometric properties while preserving the ability to adjust the rate by modifying the pre-stress level, rather than relying on static tightening that eliminates play
3Ease of manufacture
If adhesive is used to attach the fixed mount, then assembly is simplified, but the adhesive is sensitive to directional changes in adjustment force, causing creep and reducing adjustment precision
Solution Approach 1:
The symmetrical flexible parts act as counterbalancing elements that distribute adjustment forces evenly in opposite directions. This counterbalancing effect neutralizes the directional variations in force that would otherwise cause adhesive creep, allowing the use of simple adhesive bonding while maintaining high adjustment precision
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
The symmetrical arrangement of the flexible element minimizes sensitivity to changes in the adjustment force direction, reduces the risk of adhesive creep, and enhances the precision of rate adjustment by allowing continuous and precise variation of the stiffness of the balance spring.
Implementation Method 1
a flexible element arranged in series with the strip, the flexible element connecting one end of said strip to a fixed mount, so as to add additional stiffness to the continuation of the strip
Implementation Method 2
the flexible element includes two flexible parts, each connecting the strip to the fixed mount, the two parts being arranged relative to each other with axial symmetry along an axis
Data Source
AI summary
A balance spring for a watch resonator mechanism, the balance spring (100) including a flexible strip (2) wound on itself in a plurality of coils, the strip (2) having a predefined stiffness, the balance spring (100) including means for adjusting its stiffness, including a flexible element (5) arranged in series with the strip (2), the flexible element (5) connecting one end (4) of the strip (2) to a fixed mount (38), so as to add additional stiffness to the continuation of the strip (2), the flexible element (5) preferably having a stiffness greater than that of the strip (2), the flexible element (5) including two flexible parts (15, 16) each connecting the strip (2) to the fixed mount (38), the two flexible parts (15, 16) being arranged relative to each other with axial symmetry along an axis (A) preferably passing substantially through the centre (0) of the balance spring.