Split Ferrule Non-Circular Opening Watch Balance Shaft Fixation
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Solution Overview
Problem
Existing ferrule designs for high-precision watch movements, particularly those made from materials like silicon, quartz, or diamond, face challenges in securely fixing balance springs without exceeding the elastic limit, leading to fragility and unbalance due to lack of plastic deformation and insufficient elasticity.
Innovation Solution
A split ferrule with a non-circular central opening that features symmetrical support parts and arms, optimized through digital simulations to distribute stress evenly and maintain balance, allowing for secure fixation of balance shafts without plastic deformation, suitable for materials without a plastic deformation domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the opening diameter is made smaller than the shaft diameter to ensure good holding, then the holding torque is improved, but the ferrule becomes fragile and prone to breakage due to excessive stress in brittle materials
Solution Approach 1:
The ferrule is divided into two symmetrical halves separated by a longitudinal elasticity slot, allowing each half to deform independently and accommodate the shaft while distributing stress evenly, preventing localized stress concentration that would cause breakage in brittle materials
Solution Approach 2:
The opening contour is designed as non-circular with symmetrical support parts that have different geometries relative to the elasticity slot, optimizing the distribution of elastic deformation and stress across the two halves to accommodate shaft diameter variations without exceeding material elastic limits
2Strength
If the ferrule is made massive and rigid to ensure structural strength, then the strength is improved, but the amplitude of elastic deformation is limited making the ferrule more fragile
Solution Approach 1:
The longitudinal elasticity slot divides the ferrule into two flexible halves that can deform independently, providing the necessary elastic deformation capacity to accommodate shafts within the tolerance interval while maintaining overall structural integrity through the symmetrical design
Solution Approach 2:
The ferrule halves are designed as thin-walled flexible structures that can elastically deform to accommodate the shaft, replacing the need for massive rigid construction and enabling brittle materials like silicon to achieve both strength and flexibility
3Ease of manufacture
If a circular opening is used for the balance staff, then the manufacturing is simplified, but the ferrule causes unbalance and has limited adaptability to different shaft diameters
Solution Approach 1:
The non-circular opening contour with symmetrical support parts provides optimized contact geometry for balancing the balance staff, while the elasticity slot allows the opening to effectively adapt to different shaft diameters within the tolerance interval through elastic deformation of the two halves
Solution Approach 2:
The opening geometry dynamically adapts to different shaft diameters through elastic deformation of the ferrule halves, allowing the same ferrule design to accommodate a range of shaft sizes while maintaining proper balance and contact
4Force
If the opening diameter is made smaller to improve holding torque, then the rotational torque is improved, but the tolerance range for shaft diameters is reduced
Solution Approach 1:
The elasticity slot enables the opening parameters to dynamically change through elastic deformation of the ferrule halves, allowing the effective opening diameter to adapt to shaft diameter variations while maintaining adequate holding torque across the tolerance interval
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
The ferrule design ensures adequate rotational torque and prevents unbalance, maintaining structural integrity and functionality across a range of axis diameters within a desired tolerance interval, reducing the risk of breakage and enhancing robustness.
Implementation Method 1
the diameter of the opening intended to receive the balance staff is smaller than the diameter of the balance staff, so as to ensure good holding of the staff after driving. This difference in diameter is generally absorbed at least in part by plastic deformation of the collet material.
Implementation Method 2
optimized through digital simulations to distribute stress evenly and maintain balance, allowing for secure fixation of balance shafts without plastic deformation
Implementation Method 3
ensures adequate rotational torque and prevents unbalance
Implementation Method 4
adequate rotational holding torque
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a slotted ferrule having a non-circular central opening (2) for receiving a balance staff. The slotted ferrule comprises a slot (1). The contour (3) of the central opening (2) has more than two but limited number of bearing portions (4, 5, 12, 14, 15) for cooperating with said balance staff. At least two bearing portions (4, 5 or 14, 15) are located on arms (6, 7 or 27, 28), and the ferrule includes recesses (23, 24, 25, 26) between the arms and the adjacent portion of the arms.