Balance Spring Oscillator Rate Deviation Compensation
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Solution Overview
Problem
Current balance-spring oscillators for timepieces face challenges in achieving isochronism, particularly in minimizing rate variations due to the balance wheel and hairspring, with existing methods struggling to reduce deviations below 1 second/day between vertical positions.
Innovation Solution
The design of a balance-spring oscillator where the balance wheel and hairspring are optimized such that the rate variations due to the balance wheel and hairspring compensate each other, with specific geometric and stiffness adjustments to ensure that the curves representing these rates intersect at zero amplitude and have opposite slopes, allowing for partial or complete cancellation of rate deviations across different vertical positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the lack of balance of the balance wheel and the geometry of the hairspring are optimized to compensate each other's rate variations, then the rate deviations between vertical positions are significantly reduced, but the design complexity and manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by systematically varying the geometric parameters of the hairspring (blade thickness, width, curvature radius) and the balance wheel parameters (mass distribution, moment of inertia) to achieve optimal compensation. The hairspring geometry is modified with specific thickness variations (e.g., 0.02mm to 0.04mm) and curvature adjustments to tune the rate variations and achieve cancellation with the balance wheel's lack of balance effects.
Solution Approach 2:
The patent implements local quality by creating non-uniform properties in specific locations of the hairspring and balance wheel. The hairspring blade thickness is varied locally along its length, with different sections having different thicknesses to create specific stiffness distributions. The balance wheel also has localized mass adjustments through counterweights or cutouts at specific positions to achieve the desired lack of balance characteristics for compensation.
2Measurement precision
If the hairspring geometry is modified to reduce rate variations, then the isochronism improves, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent modifies hairspring parameters including blade thickness (varying from 0.02mm to 0.04mm), width, and curvature radius to optimize isochronism. These parameter changes create a hairspring geometry that compensates for rate variations without requiring overly complex structures, maintaining manufacturability while achieving improved timekeeping accuracy across different positions.
3Measurement precision
If the balance wheel lack of balance is increased to compensate for hairspring rate variations, then the rate deviations are reduced, but the balance wheel manufacturing precision requirements increase
Solution Approach 1:
The patent applies local quality to the balance wheel by creating specific mass distributions through counterweights, cutouts, or material removal at localized positions. This allows precise control of the lack of balance parameter to achieve compensation, with the mass adjustments concentrated in specific areas rather than requiring uniform precision across the entire balance wheel structure.
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
This approach significantly reduces rate deviations between vertical positions, enhancing the precision of timepieces by ensuring that the rate variations are minimized, achieving deviations of less than 1 second/day in the normal operating range.
Implementation Method 1
the rate due to the weight of the hairspring
Implementation Method 2
the restoring forces between the pivots of the oscillator shaft and the bearings
Implementation Method 3
The weight of the hairspring generates another disturbing torque, depending on the inclination of the timepiece with respect to the horizontal position
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to an oscillator for a timepiece, comprising a balance (1) and a spiral hairspring (3; 3'), the balance having a balance defect. The balance defect of the balance and the geometry of the spiral hairspring are such that: (a) the curves (S1-S4; S1'-S4') representing the rate of the oscillator as a result of the weight of the spring according to the amplitude of oscillation of the balance in at least four vertical positions of the oscillator interspaced by 90° each pass though zero at an amplitude of oscillation of the balance of between 200° and 240°; (b) between the amplitude of oscillation of 150° and the amplitude of oscillation of 280°, the curves (B1 - B4; B1'-B4') representing the rate of the oscillator as a result of the balance defect of the balance according to the amplitude of oscillation of the balance in said vertical positions of the oscillator each have an average slope of an opposite sign to the average slope of the corresponding curve among said curves (S1-S4; S1'-S4') representing the rate of the oscillator as a result of the weight of the spiral hairspring. The rate deviations between the vertical positions can thereby be reduced.