Method of manufacturing hairspring balance oscillator for high torque variation balance spring

Abstract

The invention relates to a method for manufacturing an oscillator (1) of a timepiece made of a balance (2) and a balance spring (3), the method comprising the following steps: measuring the mean moment of inertia of a batch of balance (2); -providing a fixed balance spring (3) having an excess number of coils forming at most three coils more than the final number of coils; -making a first predetermined external cut of the balance spring (3) over the length of the one to two coils, then measuring the torque of the balance spring (3) and classifying the balance spring according to the value of the measured torque; assembling a balance spring (3) whose measured torque corresponds to the balance (2) to form an oscillator having an intermediate frequency and to determine the length to be cut to achieve the desired oscillation frequency; -performing a second external cut on the balance spring (3), the second external cut being selected to achieve both the desired oscillation frequency and the target value to obtain an angle (alpha) of the attachment point (6) within + / -50 DEG of the theoretical value.

Description

Field of the Invention

[0001] The present invention relates to the general field of mechanical oscillators, which are used in particular in the watchmaking industry. More specifically, the present invention relates to a method for manufacturing an oscillator comprising a balance spring and a balance wheel. Background Art

[0002] Although machining operations have extremely high precision and repeatability, adjustments almost always have to be made during the assembly operation or more frequently during the adjustment or fine-tuning operation, particularly imbalance adjustment and inertia adjustment in the case of moving parts, and frequency adjustment in the case of oscillators.

[0003] The pairing of certain components must be perfect, especially during the assembly phase. When these components are taken independently, they are within the machining or production tolerances, but due to the operating limitations specific to the sub-assembly or the assembled components after installation, these components cannot be assembled purely and simply.

[0004] This is especially true for the regulating members of timepieces, and in particular for the balance spring assembly. It is obvious that the imbalance and inertia adjustments, both static and dynamic, are already very precise at the stage of the individual components, and these adjustment operations become extremely complex when assembling the components. Dynamic adjustment is particularly difficult to achieve. Various techniques are known for adjusting the balance spring sub-assembly, two of which are the most commonly used.

[0005] The "Omegasometric" system consists of:

[0006] - classifying the balance spring according to the torque of the balance spring that has been cut at the correct attachment points;

[0007] - classifying the balance wheel according to the inertia of the balance wheel;

[0008] - pairing a balance wheel selected from a specific category with a balance spring also selected from a specific category, these categories being compatible with each other to achieve the selected frequency accuracy.

[0009] This method requires a large inventory of components and imposes many logistics constraints.

[0010] An alternative is the "Spiromatic" system:

[0011] - a balance spring fixed on the balance wheel;

[0012] - the balance spring is cut to a length that provides a torque suitable for the inertia of the balance wheel. With good control of the balance wheel inertia and the balance spring torque spread, the cutting point is within a maximum tolerance of + / - 50° of the theoretical target value.

[0013] This method cannot guarantee a high precision of the attachment point of the balance spring relative to the outlet of the inner stud, which results in a loss of timekeeping performance. This is especially true when the balance spring has a wide rated torque distribution.

[0014] The first technique is very expensive, and the second technique is mediocre in terms of timekeeping performance. In addition, they are not suitable or less suitable when there are very large variations in the torque of the balance spring at the end of the manufacturing process. This makes it difficult to combine with balancing and regulation and has an impact on the timekeeping performance of the oscillator, which is usually mediocre. Summary of the Invention

[0015] One object of the present invention is to provide a cost-effective method for assembling an oscillator.

[0016] More specifically, one object of the present invention is to propose a method for manufacturing an oscillator including a balance spring and a balance wheel, which is cost-effective despite a large torque spread of the balance spring.

[0017] To this end, the present invention relates to a method for manufacturing an oscillator of a timepiece made of a balance wheel and a balance spring, the method comprising the following steps:

[0018] - Measuring the average moment of inertia of a batch of balance wheels;

[0019] - Providing a fixed balance spring having an excess number of coils forming at most three more turns than the final number of coils;

[0020] - Performing a first predetermined external cut on the balance spring with a defined excess of one to two coil lengths, then measuring the torque of the balance spring and classifying the balance spring according to the measured torque value;

[0021] - Assembling the balance spring whose measured torque corresponds to the balance wheel to form an oscillator with an intermediate frequency;

[0022] - Performing a second external cut on the spring, the second external cut being selected to achieve both the desired oscillation frequency and a target value to obtain an attachment point angle within + / - 50° of the theoretical value.

[0023] According to other advantageous alternative embodiments of the present invention:

[0024] - The balance spring is made of a blank made of a metal or a metal alloy;

[0025] - The blank is covered with a surface layer of a malleable material;

[0026] - The metal or metal alloy is selected from titanium, niobium, zirconium or a combination of these metals;

[0027] - The balance spring is formed by steps of stretching and / or rolling the blank, with at least one heat treatment step alternatingly performed, and the step of winding the balance spring in shape is carried out before the final heat treatment step;

[0028] - After rolling and before winding, the ductile surface layer is removed. Description of the Drawings

[0029] Referring to the accompanying drawings, other features and advantages of the present invention will become apparent from the following detailed description, which is given by way of example and is in no way limiting. In the drawings:

[0030] Figure 1 A fixed balance spring with an excessive number of coils is shown;

[0031] Figure 2 A fixed balance spring that has undergone a first external cut of one or two coils is shown;

[0032] Figure 3 An oscillator obtained using the manufacturing method according to the present invention is schematically shown. Detailed Description of the Invention

[0033] The present invention relates to a method for manufacturing an oscillator 1 intended to equip a watch movement.

[0034] "Manufacturing" is understood in the broadest sense to mean the steps involved in manufacturing the components of the oscillator 1 and the steps involved in assembling the components of the oscillator 1.

[0035] During a first step, a batch of balance wheels 2 is taken from the production run, and the batch of balance wheels 2 is obtained using a process that allows a given inertia of the balance wheels to be obtained. The average inertia of the batch of balance wheels 2 is measured to ensure that there is not too much scatter in the batch, and any balance wheel with an inertia too far from the average is removed from the batch.

[0036] In a second step, a fixed balance spring 3 is provided, which has an excessive number of coils forming up to three additional coils, as Figure 1 shown. This excessive number of coils allows the balance spring to be shortened later as part of the adjustment operation.

[0037] These balance springs are made from a blank made of metal or a metal alloy.

[0038] Then a surface layer of ductile material is deposited on the alloy blank to facilitate forming into wire form. This thickness of the ductile material means that the blank can be easily stretched, drawn, and rolled.

[0039] Finally, in order to form the balance spring 3, a blank covered with a malleable surface layer is deformed by wire drawing and then rolling, then undergoes at least one heat treatment step, and finally a winding step is performed to form the balance spring 3.

[0040] The deformation step generally represents one or more deformation processes, which may include wire drawing and / or rolling. If necessary, wire drawing may require the use of one or more drawing dies in the same deformation step or in different deformation steps. The wire drawing is carried out until a wire with a circular cross-section is obtained. The rolling can be carried out during the same deformation step as the wire drawing, or in another subsequent deformation step. Advantageously, the last deformation treatment applied to the alloy is a rolling operation, preferably having a rectangular profile compatible with the inlet cross-section of the winding machine spindle.

[0041] The addition of the malleable material can be electroplated or mechanical by PVD or CVD; in this case, a sleeve or pipe made of the malleable material is obtained, which is adjusted on the alloy blank and then thinned during one or more steps of deforming the blank.

[0042] Once all the deformation treatment operations have been carried out, that is, after the final rolling operation and before the winding operation, the malleable material is removed. For example, the malleable material layer of the wire is stripped from the wire by chemical etching (e.g., using an acid-based solution).

[0043] At the end of these steps, a balance spring 3 with an excess external length having at least three coils is obtained, which has an alloy core and a malleable housing.

[0044] The balance spring 3 thus obtained has a variable cross-section. This is because the wire forming the balance spring is not uniformly regular, since the alloy is not as easily deformable as copper, and thus, the cross-section of the wire changes after each deformation step. Therefore, there is a high torque variability between the produced balance springs 3, and in this case, the "Spiromatic" system cannot be envisaged or used.

[0045] The method according to the invention includes a third step, in which a first external cut 30 is formed to obtain a pre-cut balance spring 3, as Figure 2 shown. The length of the external cut 30 is formed on one or two coils such that an excess length remains on the balance spring 3 to form a subsequent second cut when adjusting the balance spring 3 on the balance 2.

[0046] Then, in a fourth step, the torque of the balance spring 3 is measured, and the balance springs 3 are classified according to the measured torque values to form multiple batches of balance springs having similar measured torques.

[0047] In the fifth step, a balance spring 3 whose measured torque corresponds to the inertia of the balance wheel 2 is assembled to form an oscillator having an intermediate frequency, and the length to be cut is determined to achieve a desired oscillation frequency.

[0048] Then, in the sixth step, a second external cut is performed on the selected balance spring 3 to not only achieve the desired oscillation frequency but also achieve a target value of the angle α formed by the attachment point 6 of the balance spring 3 to the stud and the exit 5 of the inner collet 4 after the second external cut, with a tolerance of ±50° of the theoretical value. The theoretical value is defined in such a way that once the curve is formed, the product requirements can be met.

[0049] Thus, this method allows a batch of balance springs to be paired in such a way that all the balance springs in the batch can be paired with the balance wheels in the batch within a tolerance of + / −50°.

[0050] Therefore, the method of the present invention provides a hairspring - balance wheel assembly tuned to a specific frequency with good reliability and accuracy.

Claims

1. A method for manufacturing an oscillator (1) for a timepiece made of a balance wheel (2) and a balance spring (3), characterized in that the method comprises the following steps: - measuring the average moment of inertia of a batch of balance wheels (2); - providing a fixed balance spring (3) having a number of excess coils forming at most three more than the final number of coils; - performing a first predetermined external cutting of the balance spring (3) with a defined excess of one to two coils in length, then measuring the torque of the balance spring (3) and classifying the balance spring according to the value of the measured torque; - Assembling a balance spring (3) whose measured torque corresponds to that of said balance wheel (2) so as to form an oscillator with an intermediate frequency; - A second external cut is made to the balance spring (3), the second external cut being chosen to achieve both the desired oscillation frequency and the target value to obtain an angle (α) of the attachment point (6) within + / - 50° of the theoretical value.

2. The manufacturing method according to claim 1, characterized in that: The balance spring (3) is made of a blank, and the blank is made of metal or a metal alloy.

3. The manufacturing method according to claim 2, characterized in that: The blank is covered with a surface layer of ductile material.

4. The manufacturing method according to claim 2, characterized in that: The metal or metal alloy is selected from titanium, niobium, zirconium or a combination of these metals.

5. The manufacturing method according to any one of claims 1 to 4, wherein: The balance spring (3) is formed by steps of wire drawing and / or rolling the blank, alternately with at least one heat treatment step, a step of winding the balance spring on the shape being carried out before the final heat treatment step.

6. The manufacturing method according to claim 3, characterized in that: After rolling and before coiling in, the ductile surface layer is removed.

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