Brittle Silicon Watch Escapement Assembly via Elastic Flexure
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Solution Overview
Problem
The assembly of silicon escapement wheels onto a shaft is challenging due to their brittleness, leading to alignment issues such as concentricity and tilt, as traditional press fitting is not possible, and requires a complex gluing process.
Innovation Solution
The use of cantilevered and resilient arms that define the opening for the shaft, allowing elastic deflection and clamping to achieve precise positioning and potentially eliminate the need for glue, with configurations such as equal or unequal bending stiffness, arc-shaped ends, and additional rigid structures for shock protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If press fitting is used to assemble metal escapement wheels onto shafts, then assembly is simple and strong, but this method cannot be applied to brittle silicon wheels without causing damage
Solution Approach 1:
The invention changes the mechanical parameters of the assembly system by replacing rigid press fitting with elastic flexures that have controlled stiffness. The flexures are designed with specific bending stiffness values that allow gentle insertion of brittle silicon wheels onto shafts without exceeding the material's fracture strength, while still providing secure retention.
Solution Approach 2:
The invention introduces an intermediary elastic element (the flexure) between the silicon wheel and the shaft. This intermediary component absorbs the mechanical mismatch between the brittle wheel and the rigid shaft, enabling assembly through elastic deformation rather than direct rigid contact.
2Ease of manufacture
If silicon wheels are glued onto shafts to avoid press fitting damage, then assembly is possible, but alignment precision deteriorates due to gluing complexity
Solution Approach 1:
The flexure design enables self-alignment during assembly. As the silicon wheel is inserted onto the shaft, the elastic flexures automatically adjust their deformation to center the wheel concentrically on the shaft, eliminating the need for complex gluing procedures and achieving high alignment precision through the mechanical design itself.
Solution Approach 2:
The invention transitions from a static rigid connection (press fitting) or chemical bond (gluing) to a dynamic elastic connection. The flexures can deform elastically during assembly to accommodate minor misalignments and then maintain a precise concentric relationship, providing both ease of assembly and high precision.
3Stability of the object's composition
If rigid support structures are used to position silicon wheels on shafts, then positioning appears stable, but the brittle material becomes susceptible to shock damage
Solution Approach 1:
The elastic flexures provide beforehand cushioning by being designed to deform elastically under shock loads. This pre-engineered compliance absorbs impact energy before it can transmit to the brittle silicon wheel, protecting it from shock damage while maintaining stable positioning during normal operation.
Solution Approach 2:
The invention replaces rigid support structures with flexible elastic elements (flexures) that provide both positioning stability and shock protection. These flexible components maintain the wheel's concentric positioning while their elastic nature allows them to absorb and dissipate shock energy, reducing the brittle material's susceptibility to impact damage.
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 enables almost perfect centring and tilt suppression of the escapement wheel on the shaft, simplifying assembly and reducing sensitivity to fabrication errors, potentially eliminating the need for adhesive, and providing robustness against shocks.
Implementation Method 1
the arms will resiliently deflect during insertion and, on the other hand, will clamp and hold in place an inserted shaft by elastic averaging
Data Source
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AI summary
The invention relates to a mechanical part (1) for a movement for a watch, which part (1) is made of a brittle material and has at least three cantilevered and resilient arms (3), and an opening (4) for receiving and holding a shaft. The distal ends (5) of the cantilevered and resilient arms (3) define the opening (4).