Watch Movement Manufacturing: Balance Spring Sorting and Torque Adjustment
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Solution Overview
Problem
The existing manufacturing processes for watch movements face challenges in achieving a stable oscillation frequency due to the variation in torque and moment of inertia of balance springs and balance wheels, leading to inefficiencies and increased rework, especially when trying to accommodate a wider range of hairspring stiffness without compromising chronometric properties.
Innovation Solution
The method involves sorting spiral springs and balance wheels into sequential classes with varying stiffness and inertia, pairing them accordingly, and adjusting the torque available to the escapement wheel to maintain an acceptable oscillation amplitude, allowing for a greater range of hairspring stiffness without rework by reducing torque during operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of balance spring classes is increased to encompass a larger portion of production, then more balance springs can be used without rework, but the amplitude variation becomes unmanageable (rising to 50°)
Solution Approach 1:
The patent divides the balance spring classes into two distinct groups: a first group with lower stiffness balance springs and a second group with higher stiffness balance springs. Each group is paired with balance wheels having specific moment of inertia ranges. This segmentation allows the system to accommodate a wider overall range of balance spring stiffness values while maintaining controlled amplitude variation within each group, thereby resolving the contradiction between using more balance springs without rework and maintaining acceptable amplitude precision.
2Manufacturing precision
If conventional classification into 20 classes is used, then amplitude variation is controlled (20° to 25°), but manufacturing losses occur when spirals fall outside the classes
Solution Approach 1:
The patent changes the parameter distribution strategy by creating two groups with different stiffness characteristics rather than using a single uniform classification system. The first group handles lower stiffness balance springs with corresponding balance wheels, while the second group handles higher stiffness balance springs. This parameter change allows the system to accept balance springs with a wider overall stiffness range without increasing amplitude variation beyond acceptable limits, thereby reducing manufacturing losses from rejected spirals while maintaining precision.
3Ease of manufacture
If balance springs of wider stiffness range are used, then rework is reduced, but oscillation amplitude becomes too large increasing galloping risk
Solution Approach 1:
By segmenting balance spring classes into two groups with different stiffness characteristics, the patent enables the use of a wider overall range of balance springs without rework while preventing excessive oscillation amplitude. Each group is designed with specific moment of inertia ranges for balance wheels that correspond to the stiffness characteristics of the balance springs in that group, ensuring that amplitude remains within safe limits and galloping is avoided even though the overall range of usable springs is expanded.
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 approach reduces manufacturing losses and rework, enabling the use of a wider range of hairsprings while maintaining acceptable oscillation amplitude and chronometric properties, effectively doubling the number of usable classes without increasing amplitude variation beyond acceptable limits.
Implementation Method 1
the restoring torque provided by its associated hairspring
Implementation Method 2
the moment of inertia of the balance wheel
Implementation Method 3
the torque available to the escape wheel
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A method for manufacturing a series of watch movements (1), comprising the steps of: - manufacturing a plurality of balance springs (13); - measuring the stiffness of each of said balance springs (13) and sorting them according to a plurality of stiffness classes; - manufacturing a plurality of balance wheels (11) according to a distribution of moments of inertia determined as a function of said stiffness classes of said balance springs (13); - measuring the moment of inertia of each of said balance wheels (11) and sorting them according to a plurality of classes by moment of inertia; - define a first group of spiral spring classes (13) and a second group of spiral spring classes (13), the classes of each individual group being sequential, the average stiffness of the spiral springs (13) of the second group of spiral spring classes (13) being greater than the average stiffness of the spiral springs (13) of the first group of spiral spring classes (13);- to match each class of spiral springs (13) with a corresponding class of balance wheels (11); - to assemble a plurality of balance-spiral oscillators (9) (11, 13) each comprising a spiral spring (13) and a balance wheel (11) matched by classes; - to assemble a series of watch movements (1) each comprising one of said oscillators (9) balance-spring (11, 13) arranged to be maintained by an escapement (7, 15) comprising an escape wheel (7) driven by a finishing gear (5), in which, for oscillators (9) comprising a spiral spring (13) of the second group of classes, said corresponding movements (1) are arranged in such a way that the torque available to said escape wheel (7) is less than the torque available to the escape wheel (7) for movements incorporating oscillators (9) comprising a spiral spring (13) of the first group of classes.;