Silicon Watch Hand Elastic Clamping Structure
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Solution Overview
Problem
Existing solutions for fixing assembly elements in timepieces made of brittle materials like silicon, such as watch hands and toothed wheels, face challenges due to the lack of plastic deformation capabilities and high stiffness issues, leading to inadequate clamping force and potential slippage, especially when dealing with conventional metal shafts with tight diameter tolerances.
Innovation Solution
The use of elastic structures with parabolic and rectilinear branches etched into the assembly element's inner wall, which radially deflect to clamp the shaft, providing improved clamping force distribution and compensating for manufacturing tolerances, while also offering a self-locking effect to prevent relative rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flexible blades are arranged on the periphery of the opening to allow fixing on a shaft, then the assembly element can be retained on the shaft, but the high stiffness of these blades poses problems during assembly and can lead to relative slippage
Solution Approach 1:
The elastic structure is divided into multiple independent branches (typically 3-6 branches) distributed around the opening periphery. Each branch independently deforms during assembly and provides clamping force, allowing the shaft to be inserted while the branches flex outward and then snap back to provide retention. This segmentation reduces the stiffness problem while maintaining retention reliability.
Solution Approach 2:
The elastic branches are designed to dynamically adapt their shape during assembly - they flex outward when the shaft is inserted and then return to their original position to provide clamping force. This dynamic behavior allows easy assembly while ensuring reliable retention, resolving the contradiction between assembly ease and retention reliability.
2Reliability
If a hollow cylinder is forced onto a conventional rotation shaft, then the assembly element is fixed on the shaft, but the elastic and plastic properties of metal materials are required which are not available in brittle materials like silicon
Solution Approach 1:
The invention changes the material parameter from plastic (metal) to elastic (brittle material like silicon). Instead of relying on plastic deformation to achieve fixation, the solution uses elastic deformation of the branches. The branches are designed with specific geometry and thickness to provide sufficient elastic compliance during assembly while maintaining strength for reliable fixation, enabling silicon and other brittle materials to be used effectively.
Solution Approach 2:
The elastic branches act as flexible thin-walled structures that can deform elastically during assembly. These branches are designed with appropriate thickness and geometry to provide the necessary compliance for insertion while maintaining sufficient strength for retention, enabling brittle materials to achieve fixation without plastic deformation.
3Force
If the elastic structures have high stiffness to provide sufficient clamping force, then the retention force is adequate, but the radial deflection is insufficient to compensate for manufacturing tolerances
Solution Approach 1:
The elastic branches are designed with optimized geometry to provide both sufficient clamping force and adequate radial deflection. The branches flex radially outward during assembly to accommodate shaft diameter variations within tolerance ranges, then return to provide the necessary clamping force for reliable retention, simultaneously addressing both force and tolerance compensation requirements.
Solution Approach 2:
The invention optimizes the geometric parameters of the elastic branches (thickness, length, curvature) to achieve the right balance between stiffness and compliance. The branches are designed to be compliant enough to deflect radially and compensate for manufacturing tolerances, while maintaining sufficient stiffness to provide adequate clamping force for reliable retention.
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 clamping force and control on the shaft, prevents material breakage, and effectively secures rotating elements like clock hands, ensuring reliable attachment and rotation without slippage, even under high angular accelerations and varying shaft diameters.
Implementation Method 1
The elastic structures which are etched in the plate and which each comprise at least one bearing surface for radially clamping the shaft in order to ensure the fixing of the assembly element with respect to the shaft
Implementation Method 2
The force required for a conventional watch hand is for example of the order of one Newton
Data Source
Figure 1~4
Figure 5
Figure 6~8
AI summary
The component e.g. hour hand (18), has an opening (32) for insertion of a cylindrical rotational arbor (26). An internal wall (33) of the opening has elastic structures (34) that are engraved in silicon on insulator (SOI) type plate. Each structure has a fork which is connected to the wall by a material bridge (40). The fork has two arms (42, 44) that are extended from both sides of the bridge and globally towards the arbor, where each arm has parabolic curve shape. Each arm has a support surface (36) at vicinity of free ends (46, 48) of the surface.