Method for frequency tuning of an assembly of plates of a watch, and watch comprising the assembly of tuned plates

Abstract

The present invention relates to a method for frequency tuning a set of plates (4, 5) of a watch (1). The plates are arranged one above the other, forming a watch dial, with a defined space between them. A mechanical shock is applied to the set of plates, and the vibration frequency of each plate is checked. If the vibration frequency differs from that of the other plates, a frequency adjustment is made to obtain an identical vibration frequency for each plate, thus tuning the plates at least according to the first natural mode of vibration and preventing any contact between the plates following a mechanical shock.

Description

[0001] The invention relates to a method for frequency tuning a set of plates of a watch. The plates are preferably watch dial plates. The plates can also be used as acoustic radiation membranes of a striking or musical watch.

[0002] The invention also relates to a watch comprising the set of plates tuned according to the tuning method. Prior art

[0003] In the case of a watch with overlapping plates as a watch face, great care must be taken to avoid any mechanical shock to the watch that may cause contact between the overlapping plates, which may lead to breakage or cracking of one of the plates made of a fragile material. Generally, the plates are spaced far enough apart to avoid contact with each other due to mechanical shock. However, spacing the plates far enough apart is not suitable for mounting in a traditional watch case, as a lot of space is lost for mounting the various components.

[0004] A watch may also have a striking mechanism to generate a sound (note) or music. To do this, the gong of the striking watch or the keyboard of the musical watch are generally located in the watch case. Thus, the vibrations of the gong or the keyboard blades are transmitted to the various parts of the watch case. These parts include, for example, the case middle, the bezel, the crystal and the back of the watch case, or even a dial with superimposed plates decorated to give the watch an aesthetic appearance.

[0005] In the case of a musical or striking watch, the acoustic efficiency, based on the complex vibro-acoustic transduction of the external parts, is low. To improve and increase the acoustic level perceived by the user of the striking or musical watch, the material, geometry and boundary conditions of the external parts must be taken into account. The configurations of these external parts are also dependent on the aesthetics of the watch and operating constraints, which can limit the possibilities of adaptation.

[0006] The frequency content of the sound of a striking or musical watch must be rich in a frequency range between 0.5 kHz and 5 kHz or even 10 kHz. Traditional exterior parts do not allow efficient radiation in this frequency band. Thus, to further improve the vibro-acoustic efficiency of the striking mechanism, it is planned to place one or more membranes in the watch case, for example, one on top of the other with a space separating them. The membranes are sized and configured so that the note(s) generated in the watch case are radiated efficiently. The frequencies of the notes generated must be close to the natural vibration modes of the membranes for them to enter into resonance.On the other hand, nothing is generally provided for the frequency tuning of these membranes, in particular so that they do not come into contact with each other, mainly during a mechanical shock of the watch or also during the generation of a note or music.

[0007] The constraints relating to the arrangement of acoustic membranes are generally in contrast with the rules of mechanical construction allowing to guarantee the water resistance, as well as the mechanical resistance of the watch to shocks and significant external pressures.

[0008] Patent application EP 1 795 978 A2 describes a watch, which includes a striking device. This striking device comprises two bell-shaped membranes, which are held coaxially in the watch case on top of each other by central support rods. There is also provided between the two bells and the back of the watch case, another thin membrane stretched and fixed between the caseband and the pierced back of the watch case. Depending on an adjustment of the radial tension of the other membrane, it is possible to adjust the acoustic radiation frequency of this membrane. On the other hand, the two other bell-shaped membranes are not arranged to improve the acoustic level of the sound generated by the striking device, which is a disadvantage. In addition, no frequency tuning is sought by a frequency tuning method to improve the resistance to mechanical shocks that the watch may undergo.

[0009] Patent application GB 2 234 369 A describes a watch with a rotating glass, which comprises, in particular, a base element and a mechanism bridge fixed together with a train wheel mechanism located therebetween, a dial located on the mechanism bridge, a rotatable reference plate located above the dial, a rotatable index ring for rotating with the reference plate, a rotatable reference ring and a watch glass mounted on the reference ring. No frequency tuning is sought by a frequency tuning method to improve the resistance to mechanical shocks that the watch may undergo.

[0010] Patent application EP 3 009 894 A1 describes an arrangement with acoustic radiation membranes for a striking or musical watch. The arrangement comprises a first membrane arranged superimposed on a second membrane. Peripheral edges of the two membranes are intended for holding the membranes in a watch case. The first acoustic radiation membrane is configured to efficiently radiate frequencies in a first frequency band, while the second acoustic radiation membrane is configured to efficiently radiate frequencies in a second frequency band different from the first frequency band. An interposed ring is further arranged between the peripheral edges of the first and second membranes to define an acoustic cavity.There is no provision for frequency tuning of the membranes so that they do not come into contact with each other following activation of the gong or the blades, or mainly following a mechanical shock. Summary of the invention

[0011] The invention therefore aims to overcome the drawbacks of the aforementioned state of the art by proposing a method for frequency tuning a set of plates forming the dial of a watch so as to resist mechanical shocks of the watch, which may be a striking or musical watch.

[0012] To this end, the invention relates to a method for frequency tuning of a set of plates of a watch, which comprises the characteristics of independent claim 1.

[0013] Particular steps of the method of frequency tuning a set of plates of a watch are defined in dependent claims 2 to 10.

[0014] An advantage of the method of frequency tuning a set of plates of a watch lies in the fact that at least two plates forming the dial can be tuned to improve their resistance to mechanical shocks. Preferably, each plate forming the dial can also act as an acoustic radiation membrane for a striking or musical watch. Each plate is tuned in frequency, in particular by controlling for example the first natural mode of vibration. The two plates, spaced from each other by a relatively small defined distance, are therefore tuned in such a way as not to come into contact with each other following a mechanical shock of the watch. Following the frequency tuning of the plates, one of the plates being made of a fragile material, such as sapphire, the two plates are likely to vibrate in phase so as not to come into contact with each other during a mechanical shock.It can also be used to enhance the acoustic radiation of a note or music generated by the striking or musical watch.

[0015] Advantageously, a first dial plate is made of metallic material, while a second dial plate is made of sapphire, which is a hard, fragile and brittle material. In the watch case, the sapphire plate may be 0.4 mm thick or even less.

[0016] Advantageously, the sapphire plate can act as a second dial, allowing new aesthetic codes to be introduced, or it can also play the role of a vibrating and radiating membrane in cooperation with the first dial plate in the case of a striking or musical watch.

[0017] For this purpose, the invention also relates to a watch comprising the set of plates tuned according to the tuning method, which comprises the characteristics of independent claim 11. Brief description of the figures

[0018] The aims, advantages and characteristics of the method of frequency tuning of a set of plates forming the dial of a watch will appear better in the following description, in particular with regard to the drawings in which: there figure 1 represents a cross-section of a watch, for example a striking or musical watch, with a set of plates forming a dial and spaced apart from each other and tuned in frequency to improve resistance to mechanical shocks according to the invention, the figure 2 represents a cross-section of the deformation of the first natural mode of at least one plate of the set of plates forming a dial according to the invention, the Figures 3a and 3b represent two graphs of the set of plates forming a dial vibrating following a mechanical shock or during a ringing or music before and after the frequency tuning of the set of plates according to the invention, and the figure 4represents a numerical model for determining vibration frequencies and frequency tuning of the set of plates of a watch according to the invention. Detailed description of the invention

[0019] In the following description, all well-known parts of a watch, for example a striking or musical watch, will be described only briefly. Reference will be made exclusively to the method of frequency tuning a set of plates of a watch to improve the resistance to mechanical shocks that the watch and the set of plates can withstand.

[0020] There figure 1schematically represents a cross-section of a watch 1 provided with a set of plates 4, 5 forming a dial in this embodiment. The watch 1 also comprises a case composed of a caseband 2 closed on an upper side by a glass 3 and on a lower side by a back 8. The watch movement 7 is located between the back 8 and the dial assembly 4, 5. Time-indicating hands 6 are connected to the watch movement 7 and emerge from the set of plates 4, 5 to indicate the time on a dial 5 of the set of dial plates.

[0021] Of course, it must be understood that the set of plates may be located elsewhere in the watch case and necessarily used as a set of plates forming a dial. It may be two plates spaced apart from each other forming part of the middle 2 of the watch case, or part of the bottom 8 of the watch case for example, or another place in the watch case.

[0022] The set of plates 4, 5 forming a dial comprises a first dial plate 4, for example made of a metallic material, and above this first dial plate 4, a second plate 5 made of a fragile hard material, for example made of sapphire or other fragile material. Preferably, the second plate 5 is substantially transparent so that the aesthetic inlays or indexes can be seen on the lower surface of the second plate 5, or even also on the upper surface of the first plate 4.

[0023] The two plates 4, 5 are mounted spaced apart from each other by a defined distance. For example, a distance equal to or less than 1 mm may be provided between the two plates 4, 5. Preferably, the distance separating the plates 4, 5 may be much less than 1 mm, for example 0.1 mm in order not to lose too much space in the watch case 1. However, the plates 4, 5 spaced apart from each other must be configured so as not to come into contact with each other during mechanical shocks. A frequency tuning process is therefore carried out to be able to adapt the vibration frequency to at least the first natural mode of vibration of one and the other of the plates 4, 5 as discussed in the remainder of the description.

[0024] It should be noted that during a mechanical shock, the elements that constitute the casing and the movement of the watch 1 undergo strong accelerations. The set of plates 4, 5 forming the dial, under this acceleration, deforms and can potentially come into contact with neighboring parts such as for example the hands 6. In the particular case of the construction of the present invention, a sapphire plate 5 can be added spaced apart from a dial plate 4 for aesthetic codes and can come into contact with the dial plate 4 during a mechanical shock. Depending on the height of the fall of the casing, the first dial plate 4 of the set can come into contact with the second sapphire plate 5, which can cause a breakage of this second sapphire plate 5 as it is a fragile material.To ensure that watches, which include the set of plates 4, 5, are resistant to mechanical shocks, it is necessary to correctly size all the elements that make up the watch. However, the aesthetics of the watch generate constraints, which are sometimes incompatible with a construction guaranteeing good mechanical resistance during a mechanical shock.

[0025] Since sapphire is a fragile material, it is best to avoid any direct impact on this type of material. In watch 1 with a set of plates 4, 5, and to avoid any contact between the two plates 4, 5, there are several possibilities, which are: Increase the stiffness of the first dial plate 4 to prevent it from deforming. The first dial plate 4 is an aesthetic element, decorated and often made with noble and very dense materials. It is therefore necessary for the first dial plate 4 to have a significant thickness to prevent it from deforming. However, this would increase the total thickness of the casing, which is not desired. Increase the clearance between the first dial plate 4 and the second sapphire plate 5. The first dial plate 4 could deform during the mechanical shock without coming into contact with the other second plate 5, which would also vibrate. Increasing the distance between the first dial plate 4 and the second sapphire plate 5 directly affects the thickness of the casing and the aesthetics of the watch. The readability of the dial could also be worsened.Match the natural frequencies of the first dial plate 4 and those of the second sapphire plate 5 so that the first dial plate 4 and the second sapphire plate 5 vibrate in phase and do not collide without increasing the play between the two elements fixed by the design.

[0026] It should be noted that the present invention is mainly based on the last point of the list cited above. A numerical model has therefore been developed to predict the dynamics of the first dial plate 4 and the second sapphire plate 5 during an impact suffered by the casing. The first dial plate 4 and the second sapphire plate 5 are represented by mass-spring-damper systems as shown in figure 4 described below (modeling the deformation of the first natural mode of the first dial plate 4 and that of the second sapphire plate 5). The two masses are separated from each other by a clearance imposed by the construction ( figure 4 ).

[0027] THE Figures 3a and 3b represent the graphs relating to the frequency tuning process of the plates of the set before and after the frequency tuning operations. The Figure 3a represents the state before frequency tuning, while the Figure 3b represents the state after frequency tuning. The vibration of the first plate is shown in solid lines, while the vibration of the second plate is shown in broken lines.

[0028] For the frequency tuning method, the vibration of each plate 4, 5 is controlled following a mechanical shock generated by a test apparatus on which the plate(s) 4, 5 are placed superimposed one above the other with a determined space between the two plates. Depending on the vibration of each plate, it can be seen whether one plate comes into contact with the other plate, which is the case shown in Figure 3a. The mechanical shock occurs at time T = 0. Since the mechanical shock, each plate 4, 5 vibrates or oscillates at a frequency depending on the dimensions of the plate, the shape of the plate, the material composing it. We note that the first metal plate oscillates at a frequency slightly higher than 1 kHz, while the second sapphire plate oscillates at a frequency higher than the vibration frequency of the first plate and slightly higher, for example above 2 kHz with an attenuation of the vibration for one or the other of the plates in time. We can see that with these differences in vibration the second plate comes directly into contact with the first plate (darker parts on the Figure 3a) and subsequently by point contacts shown by points which is likely to cause breaking points of the second plate made of fragile material. After a frequency analysis of the vibration of each plate by the test apparatus, it is possible to determine the means of correction of each plate or of at least one of the plates so as to arrive at an in-phase vibration of the two vibrating plates. In this case, once the plates vibrate at a substantially equivalent frequency, they are therefore in phase according to at least the first natural mode of vibration without contact against each other as shown in Figure 3b .

[0029] As a reminder following this step of the process shown in Figure 3awhere the plates come into contact with each other, a configuration of at least one of the plates is necessary. At least one of the plates must be configured or adapted, in order to make it vibrate at the vibration frequency of at least a first natural mode of vibration of the other plate. Thus, following a mechanical shock imposed on the plates 4, 5, the two plates adapted in vibration frequency in particular according to at least the first natural mode of vibration no longer come into contact with each other, which makes it possible to protect the second plate 5 made of fragile material as shown in Figure 3b .

[0030] To adapt the vibration frequency of the plates, it may be possible to act on at least one of the plates by adding a mass at a specific position, for example in its center, to have the same phase deformation as the other vibrating plate. The added mass can be driven to the center of the second plate. It may also be possible to add several small weights at different locations on the plate.

[0031] It is also conceivable to modify the stiffness or boundary conditions of the set of plates or at least one of the plates to avoid any contact of each plate against the other following a mechanical shock. Of course, instead of adding a mass or modifying the stiffness, it can also be planned to act on one of the plates by means of a laser to carry out a local engraving or removal of material to modify the vibration frequency until having a vibration frequency at least of the first vibration modes equal for the two plates. Thanks to this, it is possible to space the two plates by a small defined distance, for example 0.1 mm from each other, while ensuring that they do not come into contact with each other following a mechanical shock.

[0032] It should be noted that for the configuration of one or other of the plates 4, 5, a developed numerical model can be used ( figure 4) implemented in the test apparatus and capable of determining the adaptation means for tuning the frequency of one of the plates. Of course, several successive stages of controlling the vibration frequency of each plate can be imagined to arrive step by step at configuring at least one of the plates to obtain at the end of the process an in-phase vibration of the two plates.

[0033] It is necessary to characterize the natural frequencies of the dial and those of the sapphire plate (because they depend on the manufacturing tolerances of these components) to adjust the mass added to the center of the sapphire plate on a case-by-case basis.

[0034] The frequency testing device for frequency tuning of the process will not be described in further detail, since the elements composing the device are already known for other fields.

[0035] As previously stated, the set of plates forming the dial can also serve as acoustic radiation membranes of a striking or musical watch and for which it is sought to tune said plates or membranes so that they vibrate in phase without coming into contact with each other.

[0036] For illustration purposes, the figure 2 represents just a section of the deformation of at least the first eigenmode of the first dial plate 4. Of course, it could also have illustrated the deformation of the first eigenmode of the set of plates 4, 5 or of the higher eigenmodes.

[0037] From the description which has just been given, several variants of the method of frequency tuning of a set of plates of a watch can be designed by those skilled in the art without departing from the scope of the invention defined by the claims.

Claims

1. Method for frequency tuning a set of plates (4, 5) of a watch (1), the plates being disposed on top of one another with a space defined between the plates, and wherein a mechanical shock to the set of plates is generated, the vibration frequency of each plate being checked, wherein the set of plates forms a dial of the watch (1), with at least a first dial plate (4) and a second plate (5) on top of and spaced apart from the first plate (4), and characterised in that a vibration frequency matching operation is carried out for at least one of the plates if different from the other plate so as to obtain an identical vibration frequency for each plate in order to tune the plates at least according to the first vibration eigenmode to avoid any contact between the plates as a result of any mechanical shock.

2. Method for frequency tuning a set of plates (4, 5) according to claim 1, wherein the second plate is made of a fragile, brittle material, such as sapphire, characterised in that the set of dial-forming plates (4, 5) is tested in a test apparatus, which generates a mechanical shock to the set of plates (4, 5), in that the vibration frequency of each plate is determined, in that a vibration frequency matching operation is carried out for one of the plates in order to tune the two plates to the same vibration frequency so as to be in phase to avoid any contact between the plates as a result of any future mechanical shock.

3. Method for frequency tuning a set of plates (4, 5) according to one of the preceding claims, wherein the first plate (4) is spaced apart from the second plate (5) by 0.1 mm or less, characterised in that the vibration frequency of the second plate (5) is matched at least to the first vibration eigenmode of the first plate (4) which is made of a metal material.

4. Method for frequency tuning a set of plates (4, 5) according to claim 3, characterised in that a plurality of frequency determination and matching operations are carried out until obtaining the same vibration frequency relative to at least one first vibration eigenmode resulting from a mechanical shock to the plates.

5. Method for frequency tuning a set of plates (4, 5) according to one of the preceding claims, characterised in that in order to match the vibration frequency of one of the plates so that it is in phase with the vibration frequency of the other plate, a weight is added to one of the plates, the vibration frequency whereof is greater than that of the other plate.

6. Method for frequency tuning a set of plates (4, 5) according to claim 5, characterised in that a weight is driven into the centre of the second plate.

7. Method for frequency tuning a set of plates (4, 5) according to one of claims 1 to 4, characterised in that in order to match the vibration frequency of one of the plates so that it is in phase with the vibration frequency of the other plate, the stiffness or limit conditions of the set of plates or of at least one of the plates is modified.

8. Method for frequency tuning a set of plates (4, 5) according to one of claims 1 to 4, characterised in that in order to match the vibration frequency of one of the plates so that it is in phase with the vibration frequency of the other plate, a laser is used to locally etch or remove material in order to obtain the same vibration frequency on at least the first vibration eigenmode of the two plates.

9. Method for frequency tuning a set of plates (4, 5) according to one of claims 1 to 4, characterised in that a digital model developed in the test apparatus is used for the frequency tuning of the set of plates (4, 5) with frequency matching for each test.

10. Method for frequency tuning a set of plates (4, 5) according to one of the preceding claims, characterised in that the two plates (4, 5) forming a dial of a watch are frequency matched as sound-radiating membranes of a striking or musical watch.

11. Watch (1) comprising the set of plates (4, 5) forming a dial of a watch and tuned according to the frequency tuning method according to one of the preceding claims.

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