Variable-Section Balance Spring for Reduced Watch Eccentricity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing balance springs in watch movements exhibit eccentricity due to unequal deformation of inner and outer coils under constant torque, disrupting the balance wheel's operation.
Innovation Solution
A spiral spring with a variable cross-section designed to satisfy the equation ∂s/∂l = C * ∂α/∂l, ensuring the inner and outer coils deform equally under constant torque, maintaining a consistent pitch and reducing eccentricity through features like variable thickness and localized adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a constant cross-section is used for the balance spring, then the manufacturing is simplified, but the inner and outer coils deform unequally causing eccentricity
Solution Approach 1:
The patent applies local quality by varying the cross-sectional dimensions of the blade along its length. Specifically, the thickness and/or height of the blade changes from the inner turn to the outer turn, creating different local stiffness characteristics. This allows the inner coils and outer coils to deform by similar amounts under constant torque, reducing eccentricity while maintaining manufacturing feasibility through controlled dimensional variation.
Solution Approach 2:
The patent implements parameter changes by modifying the cross-sectional parameters (thickness and/or height) of the blade as a function of its position along the length. This systematic variation of geometric parameters ensures that the product of cross-sectional area and radius (S×R) remains substantially constant, achieving uniform deformation distribution across all coils while allowing for practical manufacturing.
2Manufacturing precision
If the outer coils are modified to compensate for significant displacement, then the eccentricity is reduced, but the inner coils require less modification creating an asymmetrical design
Solution Approach 1:
The patent resolves the asymmetry issue by applying local quality variations throughout the entire blade length rather than concentrating modifications at specific locations. The cross-sectional dimensions are varied systematically from inner to outer turns, distributing the deformation compensation evenly across all coils. This creates a symmetrical deformation pattern where both inner and outer coils contribute equally to the overall spring behavior, eliminating the need for asymmetric corrections like Michel angles or Breguet curves.
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 spiral spring maintains consistent coil spacing and reduces eccentricity, improving the balance wheel's operation by evenly distributing deformation across the inner and outer coils.
Implementation Method 1
the blade has a variable cross-section chosen such that the equation ∂s/∂l = C * ∂α/∂l is satisfied at each point along the blade... the contraction and expansion of the spiral spring of the invention under constant torque are advantageously better distributed between the two ends of said spiral spring
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present invention relates to a spiral spring (1) intended to be associated with a balance wheel in a regulating organ of a watch movement and comprising a series of equidistant turns formed by a blade wound upon itself between a first inner turn (2) and a last outer turn (6). The blade has a variable cross-section chosen such that the equation ∂s∂l=C∂α∂l is satisfied at each point along the blade from at least the beginning of the third turn to at least the end of the antepenultimate turn, where ∂s∂l is the linear flexibility of the blade, C is a constant, ∂α∂l is the curvature of the blade at rest as a function of the length l of the blade, α is the winding angle at the length l of the blade. The present invention also relates to a regulating organ comprising a balance wheel and such a spiral spring (1), as well as a timepiece comprising such a spiral spring (1) or such a regulating organ.