Hairspring Stiffness Tuning by Localized Material Removal
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Solution Overview
Problem
The manufacturing of hairsprings with precise dimensions and stiffness is challenging due to geometric dispersion and variable stiffness, leading to high scrap rates and manufacturing complexities, especially when etching multiple hairsprings in silicon wafers.
Innovation Solution
A method involving deep reactive ion etching or chemical etching to form hairsprings with dimensions 1% to 20% larger than necessary, followed by precise removal of material using laser machining, oxidation, or chemical etching to achieve predetermined stiffness, with optional surface modifications for thermal compensation and reduced thermal sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple balance springs are etched into a silicon wafer, then productivity is improved, but manufacturing precision deteriorates due to significant geometric variation between springs
Solution Approach 1:
The patent applies preliminary action by intentionally over-dimensioning the etched springs (1% to 20% larger than final dimensions) and then performing selective material removal. This preliminary over-etching allows subsequent precision adjustment through localized material removal, resolving the contradiction between批量生产 and precision by separating the roughing and finishing operations.
Solution Approach 2:
The patent applies local quality by removing material non-uniformly from different parts of the spring. Specifically, material is removed more from certain zones (e.g., outer turns or specific angular sectors) than others, creating localized adjustments that correct geometric variations while maintaining overall spring functionality. This localized material removal addresses the precision issue without requiring complete re-etching of all springs.
2Manufacturing precision
If laser machining is used to adjust oscillation frequency, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts the frequency adjustment function from the main manufacturing process by performing selective material removal after the primary etching. Instead of using complex real-time control during etching, the invention separates the bulk material removal (etching) from the precision adjustment (material removal), simplifying the primary manufacturing device while achieving precise frequency control through a secondary, simpler operation.
3Manufacturing precision
If dimensional accuracy is increased to eliminate adjustments, then manufacturing precision is improved, but loss of substance increases due to material removal
Solution Approach 1:
The patent minimizes material loss by applying local quality - removing material only where and where needed rather than uniformly across the entire spring. By targeting specific zones for material removal, the invention achieves the required dimensional accuracy with minimal waste, resolving the contradiction between precision and material conservation.
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 method ensures high dimensional precision and stiffness consistency, significantly reducing scrap rates and simplifying the manufacturing process while maintaining or improving isochronism and mechanical strength.
Implementation Method 1
the balance spring is machined using a laser beam to reduce its elastic torque
Implementation Method 2
oxidizing the spiral formed in step a) to transform said thickness of silicon-based material to be removed into silicon dioxide
Data Source
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Figure 7
AI summary
Method of manufacturing a hairspring (5, 5a-5c) of a predetermined stiffness (C) comprising the steps of manufacturing a) a hairspring (5, 5a-5c) according to thickened dimensions, determining the stiffness (C) of the hairspring (5, 5a-5c) formed during step a) in order to remove, in a localized manner, the volume of material to obtain the hairspring (5, 5a-5c) with the dimensions necessary for said predetermined stiffness (VS).