HK1217368B - Resonator with reduced sensitivity to climatic variations - Google Patents

Description

Resonators with reduced sensitivity to climate change

Technical Field

The present invention relates to a thermally compensated sprung balance resonator, wherein the compensating spring has a reduced sensitivity to climate changes.

Background Art

During the intense condensation tests conducted on the watch movement, it became apparent that the operation of the movement was affected.

Summary of the Invention

One object of the present invention is to overcome all or part of the above-mentioned drawbacks by providing a balance spring having a non-metallic core having a reduced sensitivity to climate variations.

The present invention therefore relates to a compensating spring for a thermally compensated sprung-balance resonator, comprising a core formed from at least one non-metallic material, including quartz or doped (or undoped) silicon, on which a silicon dioxide coating is at least partially formed, characterised in that the core is partially coated with a layer that blocks and impermeable to moisture, so as to render the compensating spring less sensitive to climate changes.

It should therefore be clear that, even in the event of severe condensation, the operation of the compensating spring will be less disrupted, so that the overall operation of the resonator formed in cooperation with the balance wheel is not affected or is hardly affected.

Other advantageous features according to the invention are:

- said layer which is barrier and impermeable to moisture has a thickness of less than 50 nanometers;

The layer which is a barrier and impermeable to moisture comprises chromium, titanium or tantalum.

Furthermore, the invention relates to a thermally compensated resonator for a timepiece, comprising a balance wheel, characterized in that it cooperates with a compensating balance spring according to any of the variants described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention will appear more clearly from the following description given in a non-limiting manner with reference to the accompanying drawings, in which:

- FIG. 1 shows a compensating balance spring according to the invention;

- Figures 2 to 7 show variations of the cross-section of the compensation spring according to the invention.

DETAILED DESCRIPTION

A study was carried out to determine how a watch movement would perform under severe condensation. The study was performed by suddenly crossing the dew point, for example by maintaining a hygrometry rate greater than 80% and by reducing the temperature by at least 15°C.

The results show that the operation of the timepiece is affected, in particular, when the balance resonator's balance spring is formed at least partially of crystalline or amorphous silicon oxide. This type of balance spring can be formed, for example, of doped or undoped crystalline silicon (on which a silicon dioxide coating is formed at least partially) or of quartz.

Research has also shown that the effects of severe condensation can be minimized by forming a local barrier against moisture on the compensation spring consisting of crystal or amorphous silicon oxide.

The present invention thus relates to a compensating spring for a thermally compensated sprung-balance resonator, comprising a core made of at least one non-metallic material. Advantageously, according to the invention, this core is partially coated with a moisture barrier, i.e., a layer that blocks and impermeable to moisture, in order to render the compensating spring less sensitive to climate changes.

According to the invention, a “partially coated” core means not fully coated, i.e. only a portion of the core is coated, for example one or more faces or even only part of one face. However, it is preferred that the oxidized parts are coated to the greatest extent possible without coating the entire balance spring.

According to the invention, the moisture-proof layer has a thickness of less than 50 nm, preferably around 10 nm, in order to avoid mechanically affecting the functioning of the balance spring. However, the thickness of the moisture-proof layer may be up to several micrometers, but in this case thermal compensation of the balance-sprung resonator must be taken into account.

Furthermore, the moisture barrier is preferably electrically conductive and has low sensitivity to magnetic fields, such as being diamagnetic, antiferromagnetic, or paramagnetic.

By way of example, the moisture barrier may thus comprise chromium, titanium, tantalum, aluminium, zirconium, aluminium oxide, chromium oxide, chromium tungsten alloy, polytetrafluoroethylene (PTFE) or silicon _nitride ( _Si3N4 ). However, one of chromium, titanium, tantalum or alloys thereof is preferred since they show the best results.

Figures 1 to 7 show a variant of a balance spring 1 obtained according to the invention and intended for thermally compensating a resonator formed in conjunction with a balance wheel. Compensating spring 1 preferably comprises a collet 3 integral with a band 5 wound in several turns. According to the invention, at least one band 5 of compensating spring 1 is only partially coated with a layer 7 forming a barrier to moisture.

The strip 5 has a length l, a thickness e and a height h. It comprises a core 9a, 9b, 9c, 9c, 9e, 9f formed of at least one material 11, 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f.

According to the variants of Figures 2 to 7, the cores 9a, 9b, 9c, 9d, 9e, 9f can be formed from a single material 11a, for example quartz, or from several materials 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f.

When the core 9b, 9c, 9d, 9e, 9f is formed from several materials, it can be fully coated with 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f or partially coated with 11b, 13b, 15b, 11c, 17c, 19c of several materials before the band 5 of the balance spring 1 is partially coated with the layer 7 that is waterproof (that is, it blocks and does not penetrate moisture).

Each coating 13b, 15b, 17c, 19c, 13d, 15d, 17d, 19d, 13e, 15e, 17e, 19e can be of the same type and the same thickness or of different types and different thicknesses. By way of example, the cores 9b, 9c, 9d, 9e, 9f can include doped or undoped silicon 11b, 11c, 11d, 11e, 11f, on which the silicon dioxide coating 13b, 15b, 17c, 19c, 13d, 15d, 17d, 19d, 13e, 15e, 17e, 19e, 21f is at least partially formed.

As shown in Figures 2 to 7 , a partial coating 7 may be present over all or part of the thickness e and/or all or part of the height h and/or all or part of the length l, without the balance spring being entirely coated. However, it is preferred that the oxidized components are coated to the greatest extent possible, as is the case in Figures 3 and 4 , wherein the oxidized coatings 13b, 15b, 17c, 19c are preferably protected by a moisture-proof layer 7.

The invention also relates to a method for manufacturing a compensation spring 1 for a thermally compensated sprung balance resonator, comprising the following steps:

a) forming a balance spring comprising a thermally compensated core 9a, 9b, 9c, 9d, 9e, 9f formed from at least one material 11a, 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f;

b) Partially coating the cores 9a, 9b, 9c, 9d, 9e, 9f with at least one moisture-proof layer 7, in order to make the balance spring 1 less sensitive to climate changes.

According to the invention, step a) can be achieved by etching the desired pattern of the balance spring in the desired plate to form all or part 11a, 11b, 11c, 11d, 11e, 11f of the cores 9a, 9b, 9c, 9d, 9e, 9f. In the case of crystalline silicon and quartz, deep reactive ion etching (DRIE) can be envisaged to achieve step a).

Of course, step a) also comprises the partial or complete coating of at least one second stage 13b, 15b, 17c, 19c, 13d, 15d, 17d, 19d, 13e, 15e, 17e, 19e, 21f of the balance spring obtained by etching in the first stage, so as to complete the core 9b, 9c, 9d, 9e, 9f. When a doped or undoped crystalline silicon wafer has already been etched in the first stage of step a), this second stage may, for example, consist of a thermal oxidation process to form silicon dioxide.

Step b) allows the deposition of at least one moisture barrier layer 7 having a thickness of less than 50 nm and preferably of the order of 10 nm. Step b) can be carried out, for example, by any thin-layer deposition method, such as vapor deposition, to preferably deposit one of chromium, titanium or tantalum, or alloys thereof, which are also advantageously electrically conductive materials that are insensitive to magnetic fields.

Of course, the invention is not limited to the examples shown, but can be subjected to various modifications and alternatives that will occur to a person skilled in the art. In particular, any material capable of forming a moisture barrier can be envisaged, not limited to chromium, titanium or tantalum, or one of their alloys, or even to the other materials mentioned in the description.

In the case of a timepiece comprising a component making the balance spring visible, such as a “skeleton” timepiece or a timepiece with a transparent back, the moisture-proof material may also be chosen according to its particular colour so as to improve its aesthetic appearance.

Claims (10)

1. A compensating hairspring (1) for a thermally compensated balance wheel resonator, the compensating hairspring (1) comprising a core (9a, 9b, 9c, 9d, 9e, 9f) formed of at least one nonmetallic material (11a, 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f), the nonmetallic material comprising quartz, characterized in that the core (9a, 9b, 9c, 9d, 9e, 9f) is partially coated with at least one layer (7) that is moisture-proof and contains chromium, so as to reduce the sensitivity of the compensating hairspring (1) to climate change. 2. A compensating hairspring (1) for a thermally compensated balance wheel resonator, the compensating hairspring (1) comprising a core (9a, 9b, 9c, 9d, 9e, 9f) formed of at least one nonmetallic material (11a, 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f), the nonmetallic material comprising quartz, characterized in that the core (9a, 9b, 9c, 9d, 9e, 9f) is partially coated with at least one layer (7) made of titanium that is moisture-proof and impermeable, so as to reduce the sensitivity of the compensating hairspring (1) to climate change. 3. A compensating hairspring (1) for a thermally compensated balance wheel resonator, the compensating hairspring (1) comprising a core (9a, 9b, 9c, 9d, 9e, 9f) formed of at least one nonmetallic material (11a, 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f), the nonmetallic material comprising quartz, characterized in that the core (9a, 9b, 9c, 9d, 9e, 9f) is partially coated with at least one layer (7) that is moisture-proof and contains tantalum, so as to reduce the sensitivity of the compensating hairspring (1) to climate change. 4. A compensating hairspring (1) for a thermally compensated balance wheel resonator, the compensating hairspring (1) comprising a core (9a, 9b, 9c, 9e, 9f) formed of at least one nonmetallic material (11a, 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f), the nonmetallic material comprising silicon, wherein a silicon dioxide coating is at least partially formed on the core, characterized in that the core (9a, 9b, 9c, 9d, 9e, 9f) is partially coated with a chromium-containing layer (7) that is moisture-blocking and impermeable, thereby reducing the sensitivity of the compensating hairspring (1) to climate change. 5. A compensating hairspring (1) for a thermally compensated balance wheel resonator, the compensating hairspring (1) comprising a core (9a, 9b, 9c, 9e, 9f) formed of at least one nonmetallic material (11a, 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f), the nonmetallic material comprising silicon, wherein a silicon dioxide coating is at least partially formed on the core, characterized in that the core (9a, 9b, 9c, 9d, 9e, 9f) is partially coated with a layer (7) made of titanium that is moisture-blocking and impermeable, so as to reduce the sensitivity of the compensating hairspring (1) to climate change. 6. A compensating hairspring (1) for a thermally compensated balance wheel resonator, the compensating hairspring (1) comprising a core (9a, 9b, 9c, 9e, 9f) formed of at least one nonmetallic material (11a, 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f), the nonmetallic material comprising silicon, wherein a silicon dioxide coating is at least partially formed on the core, characterized in that the core (9a, 9b, 9c, 9d, 9e, 9f) is partially coated with a moisture-blocking and impermeable layer (7) comprising tantalum, so as to reduce the sensitivity of the compensating hairspring (1) to climate change. 7. A compensating hairspring (1) for a thermally compensated balance wheel resonator, the compensating hairspring (1) comprising a core (9a, 9b, 9c, 9e, 9f) formed of at least one nonmetallic material (11a, 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f), the nonmetallic material comprising doped silicon, wherein a silicon dioxide coating is at least partially formed on the core, characterized in that the core (9a, 9b, 9c, 9d, 9e, 9f) is partially coated with a chromium-containing layer (7) that is moisture-blocking and impermeable, thereby reducing the sensitivity of the compensating hairspring (1) to climate change. 8. A compensating hairspring (1) for a thermally compensated balance wheel resonator, the compensating hairspring (1) comprising a core (9a, 9b, 9c, 9e, 9f) formed of at least one nonmetallic material (11a, 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f), the nonmetallic material comprising doped silicon, wherein a silicon dioxide coating is at least partially formed on the core, characterized in that the core (9a, 9b, 9c, 9d, 9e, 9f) is partially coated with a layer (7) made of titanium that is moisture-blocking and impermeable, so as to reduce the sensitivity of the compensating hairspring (1) to climate change. 9. A compensating hairspring (1) for a thermally compensated balance wheel resonator, the compensating hairspring (1) comprising a core (9a, 9b, 9c, 9e, 9f) formed of at least one nonmetallic material (11a, 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f), the nonmetallic material comprising doped silicon, wherein a silicon dioxide coating is at least partially formed on the core, characterized in that the core (9a, 9b, 9c, 9d, 9e, 9f) is partially coated with a moisture-blocking and moisture-impermeable layer (7) comprising tantalum to reduce the sensitivity of the compensating hairspring (1) to climate change. 10. A resonator for thermal compensation of a clock, the resonator comprising a balance wheel, characterized in that the balance wheel cooperates with a compensating hairspring (1) according to any one of claims 1-9.