METHOD OF HARMONIC TUNING OF AT LEAST ONE GONG OF A WATCH STRIKING MECHANISM

Abstract

A method for tuning a gong of a striking watch. The gong is fastened at one end to a gong holder, which can be mounted in a watch case. The gong is struck by a hammer to be vibrated on a support of the measuring instrument to determine by a fast Fourier transform frequency peaks in a band of audible frequencies. A comparison in a first natural mode of a vibration frequency in the plane XY with a vibration frequency outside the plane Z is performed and a ratio calculation r=|f1p−f1h|/f1p, where f1p is the vibration frequency in the plane XY, and f1h is the vibration frequency outside the plane Z. If the ratio r is less than or equal to a desired value of 0.006, the gong is tuned. If it is greater, the method is repeated until the ratio value is achieved.

Claims

1. A method of harmonic tuning of a gong (1) of a striking watch, the gong (1) being fastened to at least one gong holder (2) by at least one of its ends or by an intermediate portion located between the first end and the second end of the gong (1), and for which a ratio of vibration frequencies generated on the one hand in a watch plane XY, and on the other hand outside the watch plane according to the axis Z following a strike of a hammer against the gong (1), the method comprising: placing the gong (1) by means of its gong holder (2) on an adapted support of a measuring instrument or placing a watch case comprising a striking mechanism with the gong (1) on an adapted support of the measuring instrument, striking the gong (1) in a direction defined by a hammer which is external or forming part of the striking mechanism of the watch, picking up the dynamic response of the gong activated and vibrated by the strike of the hammer, by the measuring instrument, processing the dynamic response signal of the gong by performing a fast Fourier transform in a processor unit or in a microcontroller of the measuring instrument, determining at least two frequency peaks which correspond, in a selected natural mode, to the vibration frequencies in the plane XY and outside the plane Z of the vibrating gong in an audible frequency band from 20 Hz to 5 kHz, calculating at least one ratio r=|fip−fih|/fip≤0.006 or r′=|fih−fip|/fih≤0.006, where fip is the vibration frequency in the plane XY of the i.sub.th selected natural mode, and fih is the vibration frequency outside the plane Z of the i.sub.th natural mode, the calculation of the ratio r or r′ depending on the direction of striking of the hammer against the gong, and comparing the ratio r or r′ to a desired value equal to 0.006 in such a way that if r or r′ is equal to or less than the desired value of 0.006 the gong is considered tuned, on the other hand, if r or r′ is greater than the desired value, a gong adjustment operation is carried out before repeating the steps of the method from the striking of the gong by the hammer.

2. The method of harmonic tuning of a gong (1) according to claim 1, wherein the dynamic response of the activated and vibrating gong is a sound or audible signal picked up by a microphone unit of the measuring instrument.

3. The method of harmonic tuning of a gong (1) according to claim 1, wherein the dynamic response of the activated and vibrating gong is a vibratory signal picked up by a laser vibrometer.

4. The method of harmonic tuning of a gong (1) according to claim 1, wherein all the natural frequencies of the gong in the audible frequency band from 20 Hz to 5 kHz are tuned.

5. The method of harmonic tuning of a gong (1) according to claim 1, for which the gong (1) is configured to be disposed in a gong plane which corresponds to the watch plane, wherein the gong is struck by the hammer in one direction of the gong plane and wherein the ratio r=|fip−fih|/fip≤0.006 is calculated to determine whether gong adjustment operations must be carried out.

6. The method of harmonic tuning of a gong (1) according to claim 1, for which the gong (1) is configured to be disposed in a gong plane which corresponds to the watch plane, wherein the gong is struck by the hammer in a direction outside the gong plane Z, perpendicular to the watch plane or in a direction of an oblique strike, and wherein the ratio r′=|fih−fip|/fih≤0.006 is calculated to determine whether gong adjustment operations must be carried out.

7. The method of harmonic tuning of a gong (1) according to claim 1, wherein several simulations depending on the frequency difference of the vibration frequencies in the plane XY and outside the plane Z allow to precisely establish the type of machining and adjustment to be carried out to have the ratio r and/or r′ equal to or less than the desired value of 0.006 after one or two successive adjustment steps.

8. The method of harmonic tuning of a gong (1) according to claim 1, wherein a database in the measuring instrument is designed in such a way that it automatically knows, according to the frequency peaks determined in the measuring instrument following the FFT analysis, what adjustment to be carried out precisely on the gong to correct and tune said gong at once.

9. The method of harmonic tuning of a gong (1) according to claim 1, wherein each adjustment of the gong is carried out by milling or grinding or by local crushing of the gong material.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0016] The purposes, advantages and features of the method of harmonic tuning of at least one gong of a striking watch will appear better in the following description, in particular with regard to the drawings wherein:

[0017] FIGS. 1a and 1b show a top view showing a plan view of a gong fastened to a gong holder and a side view showing an out-of-plan view of the gong before the strike of a hammer,

[0018] FIGS. 2a and 2b show a top view showing a plan view of a gong which is vibrating and fastened to a gong holder and a side view showing an out-of-plane view of the vibrating gong, and

[0019] FIGS. 3a and 3b show a graph of an FFT analysis of a signal picked up for example by a microphone of the measuring instrument to represent frequency peaks at two partial frequencies on the one hand before adjusting the gong in FIG. 3a, and on the other hand after adjusting the gong in FIG. 3b with the two vibration frequencies close to each other at two frequency levels.

DETAILED DESCRIPTION OF THE INVENTION

[0020] In the following description, all the well-known parts of a striking mechanism of a striking watch, provided with at least one gong, will be described only briefly. Reference will be made exclusively to the method of harmonic tuning of at least one gong of a striking watch in such a way that the gong, once tuned, no longer generates dissonance or beat following the strike of a hammer in any direction, for example in the direction of the plane of the gong XY or in the out-of-plane direction of the gong Z or in an oblique direction.

[0021] FIGS. 1a and 1b show only a gong 1 of a conventional arrangement mainly in the shape of a circular arc, which can be disposed around a watch movement when mounted in the watch case. The cross section of the gong 1 over part of its length or over its entire length may be circular, oval, hexagonal, octagonal, bean-shaped or other shapes. In this case, the gong is in a plane, which is the watch plane. It can also be considered that the cross section of the gong varies from one end to the other end.

[0022] As shown in FIG. 1a, this gong 1 in the shape of an arc of a circle is configured in a watch plane XY, which is here the gong plane XY with one end fastened to a gong holder 2, while another end is left free to move. It can also be considered to fasten the gong to the gong holder 2 in an intermediate part between the first end and the second end or also to fasten each end of the gong to a respective gong holder 2 without end that is free to move. FIG. 1b shows only the gong 1 in side view. The gong holder 2 is generally designed to be fastened by a fastening means 3, such as screws, on a support such as a watch movement plate, or optionally fastened to an inner surface of the middle part of the watch case or on another external element or even on a membrane. The gong 1 can be struck by a hammer not shown in a defined direction, for example in the direction of the gong plane XY or the direction outside the plane Z, or even also in an oblique direction. This generates a sound with one or more vibration frequencies depending on the number of partials generated in connection with the material constituting the gong and the conditions of shock between the hammer and the gong. Said hammer is generally intended to strike the gong 1 near the gong holder 2 on an inner side of the arrangement of the gong depending on the space available.

[0023] By striking the gong 1 with the hammer in a direction of the gong plane XY, it would be expected to generate at least one vibration frequency in the plane XY. That means that normally only the natural modes whose deformations are located in the plane XY must be activated. But in practice, depending on the machining tolerances of the gong 1, and again the clearances of the hammer in its pivoting, the striking of the hammer on the gong 1 activates at least two basic natural modes with, on the one hand, a vibration frequency in the plane XY and also an out-of-plane vibration frequency in the parasitic direction Z.

[0024] As a non-limiting example shown in FIGS. 2a and 2b of the vibrating gong 1, the frequency spectrum of the generated sound then contains the two frequencies 1′788 Hz and 1′731 Hz, which are on the one hand the vibration frequency in the plane XY, and on the other hand the out-of-plane vibration frequency in the direction Z. The two frequencies generated in the first natural mode of vibration are very close to each other and to a frequency difference likely to be perceived by the human ear in the predominantly defined audible frequency range of at least 20 Hz up to 5 kHz. In this range of audible frequencies, the perception of these two vibration frequencies by the human ear causes a dissonance or beat, which very clearly deteriorates the quality of the perceived sound.

[0025] So that the human ear is not able to perceive the two vibration frequencies, it is necessary to tune them in such a way as to respect the formula or ratio in absolute values r=|fip−fih|/fip≤0.006, where fip is the vibration frequency in the plane XY of the i.sub.th natural mode, and fih is the vibration frequency outside the parasitic plane Z of the i.sub.th natural mode. If these tuned vibration frequencies lead to a ratio of the order of 0.006, which is a target value or a defined threshold, then the sound generated by the striking of the gong is clear and harmonious and of course without perception of dissonance by the human ear, which is wanted. But as can be calculated with this example of vibration frequencies above, a ratio r=0.032 is reached, which is roughly 5 times greater than the expected value. The frequency difference between these two vibration frequencies must therefore be corrected. This is what the method of the present invention seeks to achieve.

[0026] The method also allows to tune the vibration frequencies in the plane XY and outside the plane Z in such a way as to respect the formula or ratio r=|fip−fih|/fip≤0.006 or r′=|fih−fip|/fih≤0.006, where fip is the vibration frequency in the plane XY of the i.sub.th natural mode selected, and fih is the vibration frequency outside the plane Z of the i.sub.th natural mode. The ratio r is selected in the case of a strike substantially in the plane of the gong XY, while the ratio r is selected in the case of a strike substantially outside the plane Z, that is to say perpendicular to the plane of the gong XY.

[0027] Of course as shown in FIGS. 1a, 1b, 2a, 2b, 3a, 3b, once the gong 1 is struck by the hammer, it generates a first base frequency f1p, f1h and several partials of higher frequency at least in the range of audible frequencies from 20 Hz to 5 kHz. For frequencies above 5 kHz, the proximity of two vibration frequencies in the plane and outside the plane is no longer of much importance, because they are no longer dissociated by the human ear. Tuning the vibration frequencies should be done primarily for frequencies in the audible frequency range of 20 Hz to 5 kHz. However, it can also be considered to perform the tuning of the gong 1 in a range of audible frequencies from at least 20 Hz to 10 kHz or 20 kHz.

[0028] To tune the gong 1 of the striking mechanism of the watch (not shown), it can be placed in particular by means of the gong holder on a suitable support of a measuring instrument to be struck by a hammer on the outside of the watch case. The gong 1 can also be directly part of the striking mechanism of the watch, in order to place the watch case comprising the striking mechanism with the gong 1 on a suitable support of the measuring instrument and control the striking of the gong 1 by the hammer of the mechanism at predetermined or programmed times.

[0029] Once the gong 1 is struck by the hammer, a microphone unit or a vibrometer of the measuring instrument can pick up the sound or vibration signal from the vibrating gong. A filtering of the sound or vibration signal can still be carried out, then a fast Fourier transform FFT operation of the filtered or non-filtered signal from the microphone unit or the laser vibrometer is carried out in a processor unit or in a microcontroller of the measuring instrument. A storage of the output signals after the FFT can still be carried out in the measuring instrument. A graphic representation of the different frequency peaks of several vibration frequencies in the plane XY and outside the plane Z as a function of the different audible modes of the vibrating gong, can be made after the FFT as shown for example in FIGS. 3a and 3b described below.

[0030] It should be noted that in general, the measuring instrument is adapted to measure the dynamic response of the gong once struck by the hammer. This means that the dynamic response comprises both a sound or audible signal, as well as a vibratory signal.

[0031] FIGS. 3a and 3b show graphs of an FFT analysis of a signal from the microphone unit or vibrometer. The output signals are recorded in the measuring instrument. The frequency peaks observed in FIGS. 3a and 3b relate to vibration frequencies in the plane XY and outside the plane Z of the vibrating gong. The vibration frequencies in the plane XY and outside the plane Z are observed on the one hand before modification of the gong, that is to say before carrying out an adjustment of said gong in FIG. 3a, and on the other hand after modification of the gong in FIG. 3b. This vibration is composed of several natural or partial frequencies, two of which are shown in FIGS. 3a and 3b in the range of audible frequencies. This is a first natural frequency close to 1.7 kHz and a second natural frequency close to 3 kHz.

[0032] At the first natural frequency in FIG. 3a, two frequency peaks are generated, which are a first vibration frequency f1p in the plane XY and a first vibration frequency outside the plane f1h along the axis Z. At the second natural frequency, two frequency peaks are generated which are a second vibration frequency f2p in the plane XY and a second vibration frequency outside the plane f2h along the axis Z.

[0033] In FIG. 3b for the first natural frequency, after all the steps of final adjustment of the gong, two frequency peaks are generated which are a first vibration frequency of the gong tuned in the plane XY f1pf, and a first vibration frequency of the gong tuned outside the plane Z f1hf. At the second natural frequency, two frequency peaks are generated which are a second vibration frequency of the gong tuned f2pf in the plane XY and a second vibration frequency of the gong tuned outside the plane f2hf along the axis Z.

[0034] Once the control is carried out automatically by the measuring instrument or by vision on the graphs of FIGS. 3a and 3b, the ratio r1=|f1p−f1h|/f1p and the ratio r2=|f2p−f2h|/f2p must be calculated. It must then be determined whether each ratio r1 and r2 is less than or equal to the desired value of 0.006. If so, the gong is considered to be tuned, but if not, the gong should be tuned and at least one adjustment should be done, that is to say a localised machining on part of the gong and preferably near the gong holder. This machining, which is generally carried out by mechanical means, allows to carry out this adjustment in particular following knowledge of the frequency difference between the vibration frequency in the plane XY and the vibration frequency outside the plane Z of the first natural frequency and/or the second natural frequency.

[0035] Depending on prior knowledge of various previous stored adjustments and the result obtained, one or more successive adjustments on the gong can be performed until the ratio r1 and/or r2 is equal to or less than the desired value of 0.006. This means that after the first adjustment, the measuring instrument again picks up the sound generated by the vibrating gong. An FFT processing of the signal coming from the microphone is then carried out in order to control at the output the frequency peaks of the vibration frequencies in the plane XY and outside the plane Z of the first natural frequency and of the second natural frequency. A calculation of the ratios r1 and r2 is again performed to determine if each ratio is less than or equal to the desired value of 0.006. If so, no further corrections are made to the gong, while if not, a new adjustment operation must be carried out, and so on until the expected ratio is obtained.

[0036] This adjustment operation can be carried out manually or automatically. Under these conditions and depending on the various adjustments carried out previously and stored, each adjustment can preferably be carried out automatically by a machining tool of an automatic machining machine. It can be milling or grinding or crushing (plastic deformation). Several simulations depending on the frequency difference of the vibration frequencies in the plane XY and outside the plane Z allow to precisely establish the type of machining and the adjustment to be carried out in order to have the ratio r1 and/or r2 equal to or less than the desired value of 0.006 after very few successive adjustment steps.

[0037] As previously indicated, the purpose of this procedure is to bring the two frequency peaks closer together, that is to say the vibration frequency in plane XY mode and the vibration frequency in the out-of-plane Z mode so that the ratio described is less than or equal to 0.006. For this purpose, adjustments on the gong are carried out and each acoustic or vibratory recording is analysed after these adjustments to study the frequency content of the measured signal.

[0038] From experience, it is possible to know exactly where to perform the adjustment and the necessary size of the adjustment to be able to correct the two vibration frequencies in the plane XY and outside the plane Z in one operation at best. A database in the measuring instrument is designed in such a way that it automatically knows, according to the frequency peaks determined in the measuring instrument following the FFT analysis, what adjustment to be carried out precisely on the gong to correct and tune said gong at once.

[0039] It should also be noted that for all natural mode frequencies in the audible frequency range (0 to 5 kHz), a control is performed with the same ratio, which must be less than or equal to 0.006 so that the human ear no longer dissociates these two vibration frequencies close to each other. In addition, any shape of the gong can be considered, in particular or mainly with a shape lying in a plane so as to be able to control vibration frequencies in the plane XY and outside the plane Z. However, it can also be considered to have a gong describing a three-dimensional shape and not only in a plane, for example the gong could be in the shape of a corkscrew or the like. Regardless of the actual shape of the gong, a vibration in the plane XY, a vibration outside the plane Z of at least one natural mode or all natural modes are measured in the range of audible frequencies.

[0040] From the description which has just been given, several variants of the method of harmonic tuning of a gong can be designed by the person skilled in the art without departing from the scope of the invention defined by the claims. Each adjustment of the gong can be carried out mainly near the gong holder manually by a watchmaker, or automatically by a machining machine controlled by the measuring instrument, for example.