Patent Publication Number: US-11640142-B2

Title: Striking or musical watch provided with at least one acoustic radiating membrane and method for manufacturing the membrane

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to European Patent Application No. 18202869.6 filed on Oct. 26, 2018, the entire disclosure of which is hereby incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention concerns a striking or musical watch provided with an acoustic radiating membrane. The watch comprises, in particular, a watch case with a back cover and a case middle, closed by a crystal to display time information on a dial underneath the crystal. The watch also contains, inside the watch case, a striking mechanism for generating a sound or piece of music at predefined moments or on demand. 
     The invention also concerns a method for making an acoustic radiating membrane for a striking or musical watch. 
     STATE OF THE ART 
     It is known to provide a watch with a striking mechanism to generate a sound or piece of music. To this end, a gong of the striking watch or a vibration plate of the musical watch are arranged inside the watch case. Thus, the vibrations of the gong or the vibration plate strips are transmitted to the various external parts. These external parts are, in particular, the case middle, the bezel, the crystal and the back cover of the watch case. These large external parts start to radiate sound into the air under the effect of the transmitted vibrations. When a sound is produced either by a gong struck by a hammer, or by one or more vibrating strips of the vibration plate, these external parts are capable of radiating the produced sound into the air. 
     However, in a conventional musical or striking watch, the acoustic performance, based on the complex vibro-acoustic transduction of the external parts, is poor. In order to improve and increase the acoustic level of a sound or a note, the geometry and boundary conditions of the external parts must be considered. The configuration of the external parts is also dependent on the aesthetics of the watch and operating constraints, which may limit possibilities of adaptation. 
     Thus, in order to further improve the vibro-acoustic performance of the striking mechanism, one or more membranes are arranged to be placed inside the watch case. The membranes are designed and configured such that the note or notes produced in the watch case are radiated effectively. The frequencies of the notes generated must be close to the natural vibration modes of the membrane or membranes so that they come into resonance. 
     European Patent Application No. EP 0 028 429 A1 discloses a watch with an electroacoustic alarm device. This device is intended to improve acoustic performance and sound quality. The watch crystal is retained on the case middle by a support ring. This support ring is an annular vibrating membrane. Between two edges of the membrane, there is a curved central area. A central arbor is secured to the crystal and activated by an excitation electromagnet for vibration. The membrane can be obtained by electroforming. A sound is generated by the action of an electronic device excited by an alternating current, which does not provide the same quality as a sound generated by a striking mechanism using mechanical action, which constitutes a drawback. 
     European Patent Nos. EP 2 409 200 B1 and EP 2 738 625 B1 disclose a watch case with a case middle closed, on one side, by a bezel and a crystal, and on another side by a case back. The bezel and crystal are connected by a resilient annular metal member shaped like bellows with at least one annular fold with a curvature of between 90° and 180° to give the bezel and the crystal connected to the bellows a freedom of movement perpendicularly or parallel to a dial. However, these Patents emphasise the particular shape of the membrane while using it to provide a freedom of movement to the bezel and not as a radiating element for a striking mechanism. The natural oscillation frequency of the assembly formed of the crystal and the metal member is higher than the frequency band of the transmitted signal to avoid any degradation or distortion of the sound, which does not effectively radiate the sound produced. This thus constitutes a drawback. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to overcome the drawbacks of the prior art by providing a striking or musical watch provided with at least one acoustic radiating membrane arranged to produce a rich sound with better acoustic radiation of low frequency vibrations via the membrane connected to a crystal or a bezel connected to a crystal of the watch case. 
     The invention therefore concerns the aforecited striking or musical watch, which includes the features defined in the independent claim  1 . 
     Specific embodiments of the striking or musical watch are defined in the dependent claims  2  to  13 . 
     One advantage of the striking or musical watch lies in the fact that the membrane is configured such that, when excited by the generation of a sound from at least one gong or one strip of a vibration plate, there is a transverse wave transmission. The thin membrane connects, on one hand, a bezel secured to a crystal or directly a watch crystal, and on the other hand, a watch case middle. Thus, the bezel and crystal together, or simply the crystal, become mobile and vibrate at the same vibration modes as the membrane to obtain vibration modes of less than 4 kHz, or 1 kHz or less, depending on the thickness of the membrane and/or also its curvature. The membrane acts as a spring in relation to the bezel/crystal or to the crystal which forms the mass. The frequency of the first vibration mode depends on the square root of stiffness over mass. This first vibration mode is of the piston type. Thus, the lower the stiffness of the membrane, the lower the frequency of the first vibration mode, which is desired. 
     Advantageously, the membrane can be made by an electroforming process. It can be made with a thickness of less than 80 μm, for example, as low as 37 μm, which makes it possible to reduce the radiation frequency to 500 Hz while still offering good acoustic radiation up to frequencies of around 8 to 10 kHz. By working at such low frequencies, it is possible to obtain a warmer, louder sound, since the more radiated modes there are, the more the human ear interprets this as a loud sound, and a more distinct sound when music is produced. 
     The membrane can be made from a metal material, such as 5N gold. 
     To this end, the invention also concerns a method for manufacturing at least one acoustic radiating membrane for a striking or musical watch, which includes the features defined in the independent claims  14  and  15 . 
     One particular manufacturing step is defined in the dependent claim  16 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, advantages and features of a striking or musical watch provided with at least one acoustic radiating membrane and the method for manufacturing the membrane will appear more clearly in the following description, particularly with reference to the drawings, in which: 
         FIG.  1    represents a partial cross-sectional view of a striking or musical watch having a membrane in the vicinity of the crystal and middle part of a watch case according to a first embodiment of the invention, 
         FIGS.  2   a  to  2   c    represent several embodiments of the annular membrane, of which a cross-section of one side is shown, according to the invention, 
         FIG.  3    represents a partial cross-sectional view of a striking or musical watch having a membrane in the vicinity of the crystal and the middle part of the watch case according to a second embodiment of the invention, and 
         FIGS.  4   a  to  4   e    schematically represent different steps for making the membrane, shown in cross-section, of the second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, all the parts of a watch striking mechanism provided with an acoustic radiating membrane that are well known in this technical field will be described only briefly. The focus is mainly on the arrangement of the membrane inside the watch case and on its configuration to allow adequate acoustic radiation following the generation of a sound inside the watch case. 
       FIG.  1    thus represents a first embodiment of a mechanical striking or musical watch  1 , which includes at least one acoustic radiating membrane  2 . This acoustic radiating membrane  2  is made of metallic material or amorphous metal and is a connecting piece in the form of a loop with walls of a certain thickness. It can be considered to be a membrane spring. This membrane  2  is arranged to be connected by a first edge portion  23  to a middle part  4  of a watch case, particularly on the upper part of case middle  4 , and by a second edge portion  20  to a bezel  3  fixed to watch crystal  5  via a gasket  12 . According to a variant, second edge portion  20  of membrane  2  can also be directly connected to a watch crystal  5 . 
     It is to be noted that the first edge portion  23  of membrane  2  can be secured to the upper part of case middle  4 , particularly inside an annular groove via a complementary bezel  13 . This complementary bezel can be screwed onto the upper part of case middle  4  or secured by adhesive bonding or welding or brazing or pressed thereon so that the lower portion of complementary bezel  13  secures the first edge portion inside the annular groove of case middle  4 . Complementary bezel  13  can also serve as protection for the assembly comprising bezel  3  connected to crystal  5  and to membrane  2 . 
     In  FIG.  1   , striking or musical watch  1  also includes a striking mechanism represented simply by a certain number of gongs  9  disposed, in this configuration, underneath watch dial  6 . The striking mechanism is connected to a timepiece movement  14  disposed between dial  6  and a back cover  7 , which is secured to a lower part of case middle  4  by a sealing gasket  8 . These gongs  9 , which are spaced apart from one another, can each be struck by a particular hammer (not represented) normally at determined times in order to each generate a different sound and which can also generate a tune. It is also possible to provide a vibration plate with strips of different lengths (not represented) to be activated by a disc or cylinder with members for actuating the strips in order to generate music according to the arrangement of the actuation members. 
     Membrane  2 , as represented in  FIGS.  1  to  4   , is of annular shape with an arcuate or curved part, which points towards watch crystal  5  in an active region  11  of membrane  2  in a direction Z perpendicular to the plane of the watch. The arcuate part is a portion of a circle in cross-section as shown, which is extended by a straight part, defining a frustoconical portion up to first edge portion  23 . According to this first embodiment, the second edge portion  20  of membrane  2  is secured by a retaining ring  10 , which is pressed, for example, onto a cylindrical external wall of the bottom of bezel  3 . An internal annular groove can be provided in the retaining ring, used to guide an internal fold of second edge portion  20  of membrane  2 . Further, this securing ring  10  can be welded or soldered to the bottom part of bezel  3  to ensure a good seal of the assembly of membrane  2  and bezel  3 . 
     Bezel  3  also includes an upper edge, where watch crystal  5  lies, secured by gasket  12  to an upper internal wall of bezel  3 . A lower internal edge of bezel  3  lies above dial  6  without touching it to allow mobility of bezel  3  and crystal  5  which are retained by membrane  2 . A space of between 70 and 100 μm is provided between bezel  3  and dial  6 , or between bezel  3  and complementary bezel  13 , to allow mobility of the membrane  2 /bezel  3  assembly. As desired, bezel  3  connected to crystal  5 , or crystal  5 , is movable with respect to case middle  4  by means of membrane  2  during the vibration of membrane  2  after a sound is generated by the watch striking mechanism in the watch case. Bezel  3  connected to membrane  2  vibrates at the same vibration modes as membrane  2 , which are considerably lower than the vibration modes of conventional external watch parts. 
     It is to be noted that, once the annular membrane is secured to bezel  3  connected to crystal  5  or simply to crystal  5 , and to case middle  4 , the inside of the striking or musical watch case is sealed while allowing freedom of movement to bezel  3  connected to membrane  2  or to crystal  5  connected to membrane  2 . 
     The membrane is configured with a wall of a specific thickness, dependent on the mass of bezel  3  connected to crystal  5 , or only of crystal  5 , to obtain a low frequency f 0  of the first vibration mode. It is desired to have a low frequency of less than or equal to 4 kHz and preferably less than or equal to 1 kHz. To this end, account is taken of the equation f 0 =(½π)·(k/m) 1/2  where k is the stiffness of membrane  2 , which depends on the thickness thereof, and m is the mass of bezel  3  connected to crystal  5 , or simply of crystal  5 . It is thus possible to lower the resonance frequency of membrane  2  connected to bezel  3  by increasing the mass m of bezel  3  connected to crystal  5 . However, it is preferable to reduce the thickness of membrane spring  2  to decrease first vibration mode frequency f 0  by reducing the stiffness k of membrane  2 . Excitation of membrane  2  thus occurs by transmitting transverse waves generated by the vibration of one or more gongs  9  disposed underneath the dial in this first embodiment. 
     This membrane  2  connected to bezel  3  with crystal  5 , or connected only to crystal  5 , can cover an acoustic radiation band from 1 kHz to 10 kHz with the external watch parts. If the thickness of membrane  2  is reduced to decrease its stiffness following an electroforming manufacturing process explained below, the acoustic radiation band may even lie between 500 Hz and 10 kHz. 
     By way of non-limiting example, it is possible to have a sapphire crystal  5  with a thickness of 2 mm and a diameter on the order of 37.8 mm with a bezel  3  made of metal, such as gold, in order to have a mass on the order of 13 grams. Bezel  3  is annular in shape with an inner diameter on the order of 36 mm and an external diameter on the order of 41.9 mm, and a thickness on the order of 3.55 mm. Membrane  2 , which can be electroformed, as explained below with reference to  FIGS.  4   a  to  4   e   , can preferably be made of 5N gold to match the desired resonance frequency, since most of the external parts are also made of gold. Active region  11  of the membrane can be a space between bezel  3  and complementary bezel  13  which is 1.2 mm wide by 2 mm high in direction Z. 
       FIGS.  2   a  to  2   c    represent several embodiments of the annular membrane, of which a cross-section of one side is shown, according to the invention. In  FIG.  2   a   , membrane  2  has an arcuate part  21 , wherein the angle of the portion of a circle is greater than 180° from second edge portion  20  to a straight part  22  that connects to first edge portion  23 . In  FIG.  2   b   , membrane  2  has an arcuate part  21 , wherein the angle of the portion of a circle is substantially equal to 180° from second edge portion  20  to a straight part  22  that connects to first edge portion  23 . In  FIG.  2   c   , membrane  2  has an arcuate part  21 , wherein the angle of the portion of a circle is substantially smaller than 180° from second edge portion  20  to a straight part  22  that connects to first edge portion  23 . 
     The curvature of membrane  2  in its active region can also affect its stiffness and thus impact the reduction of the first vibration mode frequency under the effect of a force in direction Z, given the reduced dimensions, where membrane  2  is located. 
     Preferably the thickness of the membrane is substantially the same throughout membrane  2 , for example a specific thickness which may be on the order of 80 μm and can be reduced to a thickness on the order of 37 μm to lower the first vibration mode frequency to 500 Hz for a 5N gold membrane with a bezel connected to the crystal as indicated above. This has the advantage of working at a low frequency and obtaining a warmer, louder sound, since there are several radiated modes interpreted by the human ear as a loud sound, and a more distinct sound in the case of a set of notes produced to play a tune. 
       FIG.  3    represents a partial cross-sectional view of a striking or musical watch having a membrane in the vicinity of the crystal and the middle part of the watch case according to a second embodiment of the invention. The only difference in this second embodiment concerns the second edge portion  20  of membrane  2 . This second edge portion includes a heel  20  used to start manufacture of the membrane by electroforming. Once membrane  2  is made with its second edge portion heel  20 , this heel, which is an annular gold ring for example, can be directly pressed onto an external cylindrical wall of the bottom of bezel  3 . This therefore makes it possible to obtain a one-piece membrane  2  and securing heel  20 . 
     A method for manufacturing the membrane which, once finished, is mounted inside the striking watch, will be explained below. To this end, reference will be made to  FIGS.  4   a    to  4   e.    
     In  FIG.  4   a   , a metal ring of annular shape  20  is provided. Preferably, this annular ring  20  can be made of 5N gold although other metal materials may be envisaged. 
     In  FIG.  4   b   , a profile-turned substrate  30  is made as a base for making the membrane by electroforming. This substrate has a complementary profile to the shape of the membrane to be made. The substrate must be capable of dissolving at the end of the membrane manufacturing process without damaging the membrane. The substrate has an annular cavity  31  having the dimensions of the annular ring. 
     In  FIG.  4   c   , annular ring  20  is pressed into annular cavity  31  of substrate  30 . This annular ring is at the mouth of the cavity and will act as the starting point for forming the membrane. 
     In  FIG.  4   d   , the membrane is made starting from heel  20  and on complementary-shaped substrate  30  by electroforming with a metal material such as 5N gold. Depending on the shape of the substrate, the membrane is formed with its annular arcuate part  21 , its straight part  22  and first edge portion  23 . The second edge portion is directly connected to heel  20 . 
     Finally, in  FIG.  4   e   , the substrate is dissolved so that only the membrane with its portions  20  to  23  remain. Refining can also be provided by dipping the membrane into an electroforming bath to finish the part, particularly to refine its thickness. Subsequently, the membrane can be secured in the striking watch, particularly between the movable bezel and the case middle. 
     From the description that has just been given, several variants of the musical or striking watch provided with the acoustic radiating membrane can be devised by those skilled in the art without departing from the scope of the invention defined by the claims. The membrane could be made by an electroforming process with a metal other than gold.