US-12625467-B2 - Method for manufacturing a sprung balance oscillator for high torque variation balance springs

US12625467B2US 12625467 B2US12625467 B2US 12625467B2US-12625467-B2

Abstract

A method for manufacturing an oscillator for a timepiece made from a balance and a balance spring, the method including measuring the average moment of inertia of a batch of balances; providing pinned up balance springs, the balance springs having an excess number of coils forming up to three more turns than the final number of coils; making a first predetermined external cut of the balance springs over a length of one to two coils, then measuring the torque of the balance springs and sorting them according to the value of the measured torque; assembling the balance springs, whose measured torque corresponds to the balances, are assembled to form an oscillator with an intermediate frequency and to determine the length to be cut to achieve the desired oscillation frequency; making a second external cut of the balance springs selected to achieve both the desired oscillation frequency and a target value.

Inventors

Marco Verardo
Laurent JEANNERET

Assignees

NIVAROX-FAR S.A.

Dates

Publication Date: 20260512
Application Date: 20240918
Priority Date: 20231120

Claims (6)

1 . A method for manufacturing an oscillator for a timepiece made from a balance and a balance spring, wherein the method comprises the following steps of: measuring an average moment of inertia of a batch of balances; providing pinned up balance springs, the balance springs having an excess number of coils forming up to three more turns than a final number of coils; making a first predetermined external cut of the balance springs with a defined excess of a length of one to two coils, then measuring a torque of the balance springs and sorting them according to a value of the measured torque; assembling the balance springs whose measured torque corresponds to the balances to form an oscillator with an intermediate frequency; making a second external cut of the balance springs selected to achieve both a desired oscillation frequency and a target value to obtain an attachment point angle (α) within +/−50° of a theoretical value.
2 . The manufacturing method according to claim 1 , wherein the balance springs are made from a blank made of a metal or metal alloy.
3 . The manufacturing method according to claim 2 , wherein the blank is covered with a surface layer of a ductile material.
4 . The manufacturing method according to claim 2 , wherein the metal or metal alloy is selected from titanium, niobium, zirconium or a combination of these metals.
5 . The manufacturing method according to claim 2 , wherein the balance springs are shaped by a step of wire drawing and/or rolling the blank, alternating with at least one heat treatment step, with a step of winding in form the balance spring being carried out before the final heat treatment step.
6 . The manufacturing method according to claim 3 , wherein the ductile surface layer is removed after rolling, and before winding in.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to European Patent Application No. 23210963.7 filed on Nov. 20, 2023, the entire disclosure of which is hereby incorporated herein by reference. TECHNICAL FIELD OF THE INVENTION The invention relates to the general technical field of mechanical oscillators used in particular in the watchmaking industry. More particularly, the invention relates to a method for manufacturing oscillators including a balance spring and a balance. TECHNOLOGICAL BACKGROUND Despite the extreme precision and reproducibility of machining operations, adjustments almost always have to be made, either during an assembly operation or, more frequently, during an adjustment or fine-tuning operation, in particular for an unbalance adjustment and inertia adjustment in the case of moving parts, and for a frequency adjustment in the case of an oscillator. The pairing of certain components must be perfected in particular at the assembled stage which components, when taken independently, are within the machining or production tolerances, but which cannot be assembled purely and simply because of the operating restrictions specific to the sub-assembly or to the assembly once installed. This is particularly true of the regulating members of timepieces, and especially of sprung balance assemblies. It would appear that unbalance and inertia adjustments, both static and dynamic, are already very delicate at the stage of individual components, and that these adjustment operations become extremely complex when the components are assembled. Dynamic adjustments in particular are tricky to implement. Various techniques are known for adjusting a sprung balance sub-assembly, two of which are most commonly used. The “Omegametric” system consists of: classifying the balance springs already cut at the right point of attachment according to their torque;classifying balances according to their inertia;pairing a balance chosen from a particular class, with a balance spring also chosen from a particular class, these classes being compatible with each other to achieve the chosen precision of frequency. This method requires large stocks of components and imposes numerous logistical constraints. An alternative is the “Spiromatic” system: a pinned balance spring on a balance;this balance spring is cut to the length that gives a torque adapted to the inertia of the balance. With good control of balance inertia and balance spring torque dispersions, this cutting point lies within a maximum tolerance of +/−50° of the theoretical target value. This method does not guarantee a high degree of precision of the point of attachment of the balance spring in relation to the outlet of the collet, which can result in a loss of chronometric performance. This is particularly true when the balance springs have a wide nominal torque distribution. The first technique is very expensive, and the second is mediocre in terms of chronometric performance. Moreover, they are unsuitable, or poorly suited, when there is a very large variation in the torque of the balance springs at the end of the manufacturing process. This makes the combination with a balance and the adjustments difficult, and has an impact on the chronometric performance of the oscillator, which is typically mediocre. SUMMARY OF THE INVENTION One of the aims of the invention is to provide a cost-effective method for assembling an oscillator. More specifically, one of the aims of the invention is to propose a method for manufacturing an oscillator including a balance spring and a balance, which method is cost-effective despite the large torque dispersion of the balance springs. To this end, the invention relates to a method for manufacturing an oscillator for a timepiece made from a balance and a balance spring, the method comprising the following steps of: measuring the average moment of inertia of a batch of balances;providing pinned up balance springs, the balance springs having an excess number of coils forming up to three more turns than the final number of coils;making a first predetermined external cut of the balance springs with a defined excess of a length of one to two coils, then measuring the torque of the balance springs and sorting them according to the value of the measured torque;assembling the balance springs whose measured torque corresponds to the balances to form an oscillator with an intermediate frequency;making a second external cut of the balance springs selected to achieve both the desired oscillation frequency and a target value to obtain an attachment point angle within +/−50° of the theoretical value. According to other advantageous alternative embodiments of the invention: the balance springs are made from a blank made of a metal or metal alloy;the blank is covered with a surface layer of a ductile material;the metal or metal alloy is selected from titanium, niobium, zirconium or a combination of these metals;the balance sprin