Silicon Balance Spring with DLC Coating for Timepiece
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Solution Overview
Problem
The silicon balance spring in timepiece governors faces challenges with durability and temperature characteristics, leading to accuracy issues, particularly due to the use of thick and expensive silicon dioxide coatings required to enhance strength and temperature stability.
Innovation Solution
A silicon balance spring with a DLC coating of about 1 µm thickness is used, combined with a balance wheel design featuring weight members with a higher coefficient of thermal expansion than the support members, which adjusts the moment of inertia to counteract changes in the spring constant due to temperature, thereby maintaining oscillation period stability without the need for thick coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon dioxide coating is applied to the balance spring to improve strength and temperature characteristics, then the strength and temperature stability are improved, but the manufacturing cost increases and the coating thickness must be 5 μm or more requiring several tens of hours to form
Solution Approach 1:
The patent changes the coating thickness parameter from the conventional 5 μm or more to 1 μm or less, achieving the same protective effect with a much thinner coating. This parameter change reduces both manufacturing time and cost while maintaining the strength and temperature characteristics improvement.
Solution Approach 2:
The patent uses a thinner coating that can be applied more quickly and at lower cost, effectively replacing the expensive and time-consuming thick silicon dioxide coating process while achieving the same functional outcome.
2Strength
If a diamond-like carbon (DLC) coating is applied to the balance spring to enhance strength, then the strength is improved, but the temperature characteristics deteriorate with increased change rate of spring constant
Solution Approach 1:
The patent uses a composite structure combining a silicon base material with a DLC coating. The silicon base provides good temperature characteristics while the thin DLC coating enhances strength. This composite approach allows the balance spring to benefit from both materials' advantages without suffering from the temperature instability that occurs with thicker coatings.
Solution Approach 2:
The patent applies the DLC coating only as a thin surface layer (1 μm or less) rather than a thick coating, providing local strength enhancement at the surface while maintaining the bulk silicon material's superior temperature characteristics. This localized application of different material properties resolves the contradiction between strength and temperature stability.
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 solution enhances the strength of the balance spring, reduces manufacturing costs, and prevents accuracy deterioration due to temperature changes, while minimizing the thickness and cost of the coating required.
Implementation Method 1
a coating film that is applied to a surface of the base member to improve strength of the balance spring
Implementation Method 2
The coefficient of thermal expansion of the weight member in accordance with the temperature change is larger than a coefficient of thermal expansion of the support member
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
To reduce manufacturing cost, improve the strength of a balance spring, and prevent or suppress deterioration in the accuracy of the rate of a timepiece caused by a temperature change in a governor for the timepiece. A governor (10) includes a balance spring (1) including a base member made of silicon, for example, and a balance wheel (2). The balance spring (1) includes a coating film of DLC that is applied to a surface of the silicon base member to improve the strength of the balance spring. A spring constant of the balance spring (1) changes in accordance with the temperature change. A moment of inertia of the balance wheel (2) changes in accordance with the temperature change. A change in an oscillation period due to the temperature change is suppressed by the change in the spring constant of the balance spring (1) and by the change in the moment of inertia of the balance wheel (2).