Sacrificial Pin for Wristwatch Strap Attachment
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Solution Overview
Problem
The concentration of stresses on the assembly zone of a wristwatch, particularly when using fragile materials, leads to deterioration or breakage of components like the case or bracelet, resulting in high repair or replacement costs and damaging the manufacturer's image.
Innovation Solution
Incorporation of a sacrificial pin with a bearing surface of low mechanical strength, designed to break under predetermined forces, allowing disassembly of the wristwatch before the case or bracelet breaks, thus preserving the more expensive components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the attachment zone uses fragile materials or concentrated stress design, then the wristwatch achieves a compact and aesthetically pleasing structure, but the case or bracelet becomes susceptible to breakage under stress
Solution Approach 1:
The pin is divided into a head portion and a shank portion with distinct mechanical properties. The shank portion has reduced cross-sectional area creating a stress concentration zone that acts as a predetermined break point, separating the functional attachment role from the structural integrity role.
Solution Approach 2:
The pin acts as an intermediary sacrificial component between the case and bracelet. It is designed to fail first under excessive stress, protecting the more expensive case and bracelet from damage. The pin absorbs the harmful stress concentration that would otherwise damage the main components.
2Strength
If the attachment components are designed with high strength to prevent breakage, then the wristwatch achieves durability, but the cost of repair and replacement increases when damage does occur
Solution Approach 1:
The pin is designed as a low-cost sacrificial component that can be easily replaced. By making the pin inexpensive and simple in construction, the system allows for easy repair by replacing just the pin rather than the entire case or bracelet assembly when failure occurs.
Solution Approach 2:
The pin is pre-designed with a predetermined break point through its geometry (reduced cross-sectional area in the shank). This preliminary design ensures that the pin will fail in a controlled manner at a specific location, allowing for easy identification and replacement of the failed component.
3Reliability
If the pin is designed with high mechanical strength to prevent detachment, then the attachment becomes more secure, but the case or bracelet may break before the pin fails
Solution Approach 1:
Different portions of the pin have different mechanical properties. The head portion has sufficient strength to secure the attachment, while the shank portion has reduced strength with a predetermined break point. This local differentiation ensures the pin fails in a controlled manner before the case or bracelet break.
Solution Approach 2:
The mechanical parameters of the pin are specifically designed so that the shank portion has lower strength than the head portion and lower than the case or bracelet components. This parameter differentiation ensures the pin is the weakest link and will fail first, protecting the more valuable components.
Data Source
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AI summary
A device (100) for attaching a strap (3) to a watch case (2) (4). It includes at least one attachment (101) allowing the strap (3) to be detached from the case (2) when the attachment (1) is subjected to a predetermined force. A wristwatch (4) comprising a case (2) and at least one strap (3) pivotally articulated about a bearing surface (10) of a pin (1) constituting said device (100). This pin (1) is a sacrificial pin which has, at said bearing surface (10), at least one area (11) of mechanical resistance lower than the lowest mechanical resistance of said case (2) and the lowest mechanical resistance of said strap (3).