EP0694824B1 - Timepiece with electro acoustic transducer - Google Patents

Description

The present invention relates to a part timepieces comprising an electro-acoustic transducer, and more precisely a timepiece the glass of which forms the movable element of this transducer.

Such a timepiece is described, by example, in patent US-A-4 271 498. It includes in in this case a ring made of a piezoelectric material including one side is fixed to the movement and the other side is fixed at the heel of the ice.

When an AC electrical signal is applied to electrodes placed on the ring of piezoelectric material, the thickness of the latter varies, resulting ice displacement and wave production acoustic in the air surrounding the timepiece. The electro-acoustic transducer formed by the movement of the timepiece, this ring and this crystal then works as a speaker.

When, on the contrary, an acoustic wave subjects the ice at alternating pressure, the displacements of this ice causes variations in the thickness of the ring made of piezoelectric material which cause the appearance between the electrodes mentioned above an electrical signal. In this case, the transducer electro-acoustic works like a microphone.

In such a transducer, the amplitude of the ice displacement is obviously always the same to variations in the thickness of the material ring piezoelectric.

It follows that, when this transducer operates as speaker, the amplitude of the displacements of the ice is weak, so the sound produced by these displacement is also low.

Likewise, when this transducer operates as microphone, the amplitude of the electrical signal produced in response to ice movement is also weak.

An object of the present invention is to provide a timepiece comprising an electro-acoustic transducer which does not have the disadvantages mentioned above, i.e. a transducer which, when used as a speaker, produces sound significantly stronger than the known transducer described above in response to an electrical signal of the same amplitude and which, when used as a microphone, provides a electric signal of amplitude clearly greater than this known transducer in response to displacement identical to ice.

This goal is achieved by the timepiece whose features are listed in claim 1 attached.

• la figure 1 représente, à titre d'exemple non limitatif, une première forme d'exécution de la pièce d'horlogerie selon la présente invention vue en coupe transversale, partielle et schématique;
• les figures 2 à 4 représentent, également à titre d'exemples non limitatifs, des dispositifs piézo-électriques utilisables dans la pièce d'horlogerie selon la présente invention, vus en plan;
• les figures 5 et 6 sont des coupes partielles et schématiques illustrant, toujours à titre d'exemples non limitatifs, des manières de réaliser des dispositifs piézo-électriques tels que ceux des figures 2 à 4, et
• la figure 7 représente, également à titre d'exemple non-limitatif, une deuxième forme d'exécution de la pièce d'horlogerie selon la présente invention vue en coupe transversale, partielle et schématique.

Other objects and advantages of the present invention will be made evident by the description which will be given below with the aid of the appended drawings in which:

• Figure 1 shows, by way of non-limiting example, a first embodiment of the timepiece according to the present invention seen in cross section, partial and schematic;
• Figures 2 to 4 show, also by way of nonlimiting examples, piezoelectric devices usable in the timepiece according to the present invention, seen in plan;
• FIGS. 5 and 6 are partial and schematic sections illustrating, still by way of nonlimiting examples, ways of producing piezoelectric devices such as those of FIGS. 2 to 4, and
• Figure 7 shows, also by way of non-limiting example, a second embodiment of the timepiece according to the present invention seen in cross section, partial and schematic.

In its embodiment shown in section schematic and partial in Figure 1, the part of watchmaking according to the present invention is designated by the general reference 1.

The timepiece 1 comprises a box 2 of which only the middle part has been represented.

A movement 3 is fixed to the box 2 by means which have not been shown because they can be similar to any of the many ways well known that can be used for this purpose.

For a reason that will be made clear later, we will call mechanical assembly 4 the one formed by box 2 and movement 3.

The timepiece 1 also includes means display of time information and possibly non-hourly, which may be of any kind.

In the present example, these display means are simply consisting of a 5 hour hand and by a 6 minute hand which are both driven by movement 3 in front of a dial 7 fixed to the latter.

The timepiece 1 also has a crystal 8 arranged above the hands 5 and 6 and the dial 7 and intended, in a conventional manner, to protect the latter.

It will be admitted that, in this embodiment of the timepiece according to the present invention, the crystal 8 is of the kind generally called round ice, that is to say that, in a plan view of the timepiece, the glass 8 has the general shape of a circle centered on an axis of symmetry of this ice 8. We will see later that the ice 8 may have a different shape.

Glass 8 is fixed to movement 3, and therefore to the mechanical assembly 4, via a piezoelectric device 9 including some examples will be described later.

We will simply mention here that the faces main devices 9, that is to say those which are respectively located on the side of the glass 8 and on the side of the upper part of movement 3, are flat and perpendicular to the axis of rotation, not visible in the Figure 1, needles 5 and 6. In addition, the device 9 has a peripheral zone 9a fixed to the glass 8 and an internal zone 9b fixed to movement 3. It should be noted that when timepiece 1 is seen in a direction perpendicular to the main faces of the piezoelectric device 9, the fixing zones 9a and 9b from the latter to ice 8 and movement 3 are separate from each other.

For a reason that will be made clear later, movement 3 is shaped so that there are still free spaces 10 and 11 between the piezoelectric device 9 and the upper face of movement 3 and, respectively, the underside of the dial 7.

The means of fixing the glass 8 to the zone device 9a of device 9 and internal area 9b from the latter to movement 3, which were not represented, may consist, for example, of layers of adhesive material such as glue, resin thermoplastic synthetic or other.

The timepiece 1 also preferably comprises a seal, such as that shown in Figure 1 with the reference 12, attached to the periphery of the glass 8 and the middle of the box 2, for example by collage. For a reason which will also be returned evident below, this seal is shaped, when present, so that the glass 8 can be move easily relative to the box 2.

As will be described in detail later, the device 9 comprises an element made of a piezoelectric material which can be any of the various piezoelectric materials well known to specialists such as, for example, one of the lead-based ceramics, zirconium and titanium commonly called PZT. The device 9 further comprises electrodes, and it is arranged to way that when these electrodes are subjected to a excitation signal constituted by an alternating voltage produced by a suitable circuit located for example in the movement 3, it undergoes a bending deformation such that its peripheral zone 9a moves relative to its zone internal 9b in a substantially perpendicular direction to the planes of its main faces, alternately in one way and the other. This direction and these senses of displacement are symbolized in figure 1 by the arrow double F.

The displacement of the peripheral zone 9a of the device 9 obviously causes identical displacement ice 8 with respect to the mechanical assembly 4.

This displacement of the glass 8 creates an acoustic wave in the air surrounding timepiece 1, and the fundamental frequency of this acoustic wave is obviously equal to that of the applied excitation signal to the electrodes of the device 9. It follows that if this frequency is in the frequency range audible, i.e. between about 15Hz and 15kHz, the wave acoustic created by the displacement of the ice 8 produced sound perceptible by anyone nearby of timepiece 1 and, in particular, when the timepiece watchmaking 1 is a wristwatch, by the wearer of the latter.

It is obvious that if the frequency and / or the amplitude of the piezoelectric device excitation signal 9 are variable, so is the frequency fundamental and, respectively, of the amplitude of the wave acoustics created by the displacement of the glass 8 and the its produced by this acoustic wave.

We see that the glass 8, the piezoelectric device 9 and the mechanical assembly 4 form a electro-acoustic transducer that works like a loudspeaker when an excitation signal is applied to the electrodes of the device 9.

A person skilled in the art will readily see that if the glass 8 moves relative to mechanical assembly 4 in response to an acoustic wave propagating in the air surrounding the timepiece 1, this movement causes a bending deformation of the piezoelectric device 9 such that its peripheral zone 9a moves relative to its internal zone 9b, also in the direction substantially perpendicular to the planes of its faces which is symbolized by the double F arrow in Figure 1.

This bending deformation of the piezoelectric device 9 causes the appearance between its electrodes a detection signal, consisting of a voltage alternative having the same frequency as the acoustic wave which causes the ice to move 8.

We see that when an acoustic wave acts on the glass 8, the electro-acoustic transducer formed by the latter, the piezoelectric device 9 and the mechanical assembly 4 functions as a microphone.

Figure 2 shows schematically, on a scale different from that of figure 1, an example of realization of the piezoelectric device 9 of the figure 1 seen in a direction perpendicular to the planes of its main faces.

In this example, the device 9 comprises an element made of a piezoelectric material 13 which has the general shape of a thin circular disc having a center C located on the axis of symmetry of the glass 8 and comprising a central opening 13a also circular and centered on point C.

The peripheral zone of element 13 constitutes the zone 9a for fixing the piezoelectric device 9 to the glass 8, and the area surrounding the opening 13a constitutes the zone 9b for fixing the device 9 to the movement 3.

The electrodes of the piezoelectric device 9, which have not been represented in FIG. 2 but of which examples will be described later, are arranged to way to create an alternating electric field in the piezoelectric material of element 13 when the excitation signal mentioned above is applied to them.

In addition, the element 13 and these electrodes are arranged so that this electric field causes a bending deformation of device 9 such as this one takes an alternately concave and convex shape or, in in other words, an open flared cup shape alternately on the side of the glass 8 and on the side of the movement 3.

A piezoelectric device 9 such as that which just described using figure 2 is fine heard usable in a timepiece whose ice is circular.

It should however be noted that such a piezoelectric device can also be used in a timepiece whose crystal has the shape of a polygon regular, this glass then not being attached to this device that in some points of its periphery, these points being located for example at the vertices or in the middle of the sides of this polygon.

Figure 3 shows schematically, on a scale different from that in Figure 1, another example of realization of the piezoelectric device 9 of the figure 1, seen in a direction perpendicular to the planes of its main faces.

In this example, the device 9 comprises an element in a piezoelectric material 14 which also has the general shape of a thin circular disc whose center, also designated by C, is also located on the axis of symmetry of the glass 8, and which also comprises a circular central opening 14a.

The element 14 also has radial slots 14b having a constant width in this example, which define between them tongues 14c all identical and connected to each other by their base, that is to say by their end located on the side of the central opening 14a. The peripheral area of tabs 14c constitutes the area 9a for fixing the device 9 to ice 8, and the bottom part of these tabs 14c which is located around the opening central 14a constitutes the fixing zone 9b from device 9 to movement 3.

The electrodes of the piezoelectric device 9, which were also not shown in Figure 3, are arranged so that when subjected to a excitation signal, the tabs 14c all undergo a bending deformation which gives the device 9 this figure 3 a shape similar to that which was described in connection with the disc 13 in FIG. 2.

Figure 4 shows schematically, on a scale different from that in Figure 1, another example of realization of the piezoelectric device 9 of this figure 1, seen in a direction perpendicular to the planes of its main faces.

In this example, the device 9 comprises an element in a piezoelectric material which consists of a plurality of thin tabs 15.

The tongues 15, which are shown schematically in Figure 4 in the position they occupy in timepiece 1, each has the general shape of a rectangular parallelepiped, and their large faces, i.e. those that are parallel to the plan of figure 4, together constitute the faces main features of the device 9.

The tongues 15 are arranged in this example of so that their longitudinal axes all go through a central point, also located on the axis of symmetry of the ice 8 and designated by C.

The tongues 15 are all fixed to the glass 8 in their external areas, i.e. those that are furthest from central point C, all of which therefore constitutes the area 9a for fixing the piezoelectric device 9 with ice 8. These tabs 15 are further fixed to movement 3 by their internal zones, i.e. those which are closest to the central point C, all of which therefore constitutes the area 9b for fixing the piezoelectric device 9 with movement 3.

The electrodes of the piezoelectric device 9, which were also not shown in Figure 4, are arranged on the tongues 15 so that, when subjected to the excitation signal, these tongues 15 all undergo bending deformation in the direction perpendicular to their large faces, alternately in one direction and in the other.

The piezoelectric device 9 in one piece of watchmaking according to the present invention can obviously be achieved in many different ways than those which have been described above with the aid of FIGS. 2 to 4.

So in realizations similar to that which is illustrated in Figure 3, the material element piezoelectric device 9 may have a number tabs, such as tabs 14c, different from that of the latter, that is to say eight.

In addition, and whatever the number of these tongues, their shape may be different from that they have in Figure 3.

So, for example, these tabs can have a shape such that the slots between them, such as the slots 14b have a width which increases or which decreases towards their open end.

Likewise, again for example, the outer end of these tabs can be straight, not arched of circle as in figure 3. In such a case, the piezoelectric material element of the device 9a the general shape of a regular polygon whose number of sides equals the number of tabs for this item, and this device 9 is intended to be used, preferably, in a timepiece whose glass has a shape corresponding polygonal.

Still in achievements similar to that which is illustrated in Figure 3, the tabs of the element made of piezoelectric material of device 9 can be joined to each other by their external ends, that is to say those who oppose the opening central such as the opening 14a, the slots separating these tabs being in such a case open on the side of this central opening.

In achievements similar to that which is illustrated by FIG. 4, the element made of piezoelectric material of device 9 may also include a number of tabs, similar to tabs 15, different from the number of the latter, that is to say eight, and the shape of these tabs may be different from the parallelepiped shape of these tongues 15.

It should be noted that an element made of piezoelectric material formed of independent tabs such as the tongues 15 of the element shown in Figure 4 can be used in a timepiece according to the present invention whatever the shape, round, oval, polygonal or other, ice 8. All that is needed these tabs are arranged so that one of their ends is fixed to this glass 8 and that the other of their ends is fixed to movement 3. We will see easily that the axes don't even have to be longitudinal of these plates all pass through the same point.

Likewise, the only condition that these tabs is that their ends attached to the ice 8 will all move approximately the same amount and in the same direction in response to the applied excitation signal to the electrodes of the piezoelectric device 9. We will see as easily as this condition can be fulfilled even if these tabs do not all have the same dimensions, for example for reasons of space available in the timepiece case according to the invention.

Whatever its general form, the device piezoelectric 9 of a timepiece according to the present invention can be realized in various ways two of which will be described below using Figures 5 and, respectively 6, taking arbitrarily as an example of this device 9 one that has been shown in figure 2.

In the case of Figure 5, which is a section partial and schematic according to any radius of this device 9 of FIG. 2, the element made of piezoelectric material 13 of the latter has two plates designated by 13a and 13b, both of which have a form general identical to that of element 13 and which are fixed to each other, for example by a layer of adhesive material, not shown, such as glue, epoxy resin, or the like.

The plates 13a and 13b are both in one piezoelectric material which can be any various piezoelectric materials well known to piezoelectric specialists, such as the mentioned PZT above. Whatever its nature, this piezoelectric material is polarized in a perpendicular direction on the faces of the plates 13a and 13b and therefore on the faces main features of the device 9.

In this example, the direction of polarization of the material of the plate 13a, which is symbolized by the arrow Pa, is opposite to the direction of polarization of the material of the plate 13b, which is symbolized by the arrow Pb.

The electrodes of the device 9, designated by the references 16a and 16b, have been deposited on the faces elements 13 by any of the various well-known methods in the matter. When these electrodes 16a and 16b are subjected to voltage alternative which constitutes the mentioned excitation signal above, the electric field created by this voltage has so also a direction perpendicular to the faces elements 13.

This electric field has been symbolized in Figure 5 by arrow E in a situation where its direction is opposite to that of the polarization Pa of the wafer 13a and identical to that of the Pb polarization of the wafer 13b.

Those skilled in the art will readily see that, in this situation, the wafer 13a expands in one direction radial parallel to the planes of its faces, as is symbolized by the arrow with two diverging points Ga, and that the wafer 13b contracts, also in a radial direction parallel to the planes of its faces, which is symbolized by the arrow with two converging points Gb. The element 13 therefore deforms in bending in a direction substantially perpendicular to the planes of its faces, its face carrying the electrode 16a becoming convex and its face carrying the electrode 16b becoming concave.

A person skilled in the art will see as easily that, in the reverse situation, i.e. in the situation where the direction of the electric field E is identical to that of the polarization Pa of the wafer 13a and opposite to that of the polarization Pb of the wafer 13b, the element 13 is also deforms in bending, in the same direction but in the opposite direction to the previous one, its face bearing the electrode 16a then becoming concave and its bearing face the electrode 16b becoming convex.

The internal zone 9b of the piezoelectric device 9 being attached to movement 3 as described above using FIG. 1, its peripheral zone 9a is therefore moves well in direction substantially perpendicular to the planes of its faces symbolized by the arrow F in this figure 1.

In the case of Figure 6, which is also a section partial and schematic according to any radius of the device 9 of FIG. 2, the element made of piezoelectric material 13 of the latter also includes two plates, which are also designated by the references 13a and 13b and which will not be described here because they are identical to the plates designated by the same references in figure 5.

Note, however, that in the case of this figure 6, the plates 13a and 13b are arranged so that the senses of their respective polarizations, also designated by Pa and Pb, are the same.

The device 9 in this case comprises two electrodes 17a and 17b arranged on the outer faces of the plates 13a and 13b and a third electrode 17c disposed between these plates 13a and 13b, which are fixed to each other through it.

This electrode 17c may for example have been deposited on the face of the plate 13a intended to be find next to the plate 13b and have been fixed to the latter by a layer of adhesive material which was not represented. This electrode 17c can also consist of a thin metal sheet on the faces of which the plates 13a and 13b have were respectively deposited by the well known technique thin layer deposition.

The electrodes 17a and 17b are electrically connected to each other in a way that has not been shown, so that they functionally form only one single electrode which will be called electrode 17ab. It follows that when the alternating voltage which constitutes the above mentioned excitation signal is applied between this electrode 17ab and the electrode 17c, the field electric created by this voltage has two components Ea and Eb acting respectively on the plate 13a and on plate 13b, these two components Ea and Eb both being perpendicular on the faces of these plates 13a and 13b but having meanings opposites.

Those skilled in the art will readily see that, as the piezoelectric device 9 of FIG. 5, that of the Figure 6 deforms in alternative bending in the direction perpendicular to the planes of its faces main when an excitation signal is applied between its electrodes 17ab and 17c.

In the case of FIG. 7, which represents a second embodiment of the timepiece according to the present invention seen in partial cross section and schematic, the third electrode 17c shown in the Figure 6 has been replaced by a metal plate 17d disposed between the piezoelectric plates 13a and 13b and thus forming the piezoelectric device 9. The references in this figure 7 correspond to references of figure 1.

Advantageously, the metal plate 17d is thrust in the continuity of its plan towards the outside of so that this 17d plate protrudes from the outside relating to timepiece 1 the ends of the plates 13a, 13b. So this is the 9a end of the 17d plate which serves as support and as point of fixing the crystal 8 of the timepiece 1.

Thanks to this metal plate 17d, the frequency response of the piezoelectric device 9 can be modified by choosing a certain thickness, length and rigidity of the metal plate 17d. Thus, the bandwidth of the piezoelectric device 9 can be adapted to requirements. The plate 17d can be produced for example from Copper-Beryllium (CuBe). In this example, the metal plate 17d has a thickness of around 100 μm (100 · 10 ^-6 m), and a diameter of around 41 mm (41 · 10 ^-3 m). In addition, the earthing of the piezoelectric device 9 comprising a metal plate 17d is facilitated compared to the device 9 described in FIGS. 1 and 6, because the entire length of the plate 17d is available for this purpose. In addition, the piezoelectric device is thus made less fragile.

Note that the electrodes, examples of which just described can cover all of the faces of the plates on which they are arranged, or only part of these faces, in particular the part located between the fixing zones of the piezoelectric device ice and defined mechanical assembly above.

Many changes can be made to the timepiece which has just been described without as well depart from the scope of the present invention.

Among these modifications, which cannot be all described, we will mention the one which consists in have at least the piezoelectric device 9 substantially in the same plane as the dial 7, around this one.

We will also mention the modification which consists to fix the piezoelectric device 9 on the dial 7, making sure to leave between this device 9 and this dial 7 a free space similar to the space 10 in FIG. 1. In such a case, it will be assumed that the mechanical assembly 4 defined above also includes the dial 7.

We will also mention the modification which consists in arrange the piezoelectric device 9 so that it either located around the glass 8 and fixed either to the periphery of movement 3 either at the inner wall of the case middle 2.

In such a case, the attachment zones of the device 9 with ice 8 and mechanical assembly 4 are obviously the inner area and, respectively, the outer area of this device 9.

In summary, we see that in a timepiece according to the present invention, the piezoelectric device which connects the ice to the mechanical assembly formed by the case, the movement and, if necessary, the dial is arranged to deform in flexion in a direction perpendicular to the planes of its faces in response to an excitation signal applied to its electrodes, its areas of attachment to this glass and to this mechanical assembly being distinct from each other when the timepiece is seen in this same direction.

Those skilled in the art will readily understand that, thanks to this arrangement, the amplitude of the displacement of the ice in response to a given excitation signal, and therefore the intensity of the sound produced is much greater, all other things being equal, in a room of watchmaking according to the present invention that in a known timepiece such as that which was briefly described above.

Likewise, again thanks to this arrangement, the amplitude displacement of ice in response to a wave given acoustics, and therefore the amplitude of the signal detection appearing between the electrodes of the device piezoelectric, is much more important, all other things being equal, in a timepiece according to the present invention that in a room of known watchmaking.

Claims (10)

1. Timepiece (1) comprising a casing (2), a movement arranged in said casing (2) and forming with the latter a mechanical set (4), a glass (8), and means for joining said glass (8) to said mechanical set (4) comprising a piezo-electric device (9) having a first attachment zone (9a) fixed to said glass (8) and a second attachment zone (9b) fixed to said mechanical set (4), said piezo-electric device (9) having a first face situated in a plane and being arranged such that it undergoes, in response to an exciting signal, a deformation producing a displacement of said glass (8) relative to said mechanical set (4) in a direction at least substantially perpendicular to said plane, characterized in that said first attachment zone (9a) and said second attachment zone (9b) are distinct one from the other when said timepiece (1) is looked at in a direction perpendicular to said plane, and in that said deformation of said piezo-electric device (9) is a flexion deformation in a direction perpendicular to said plane.
2. Timepiece according to claim 1, characterized in that said piezo-electric device (9) comprises, on the one hand, two plates (13a,13b) of a polarised piezo-electric material, the two polarisations (Pa,Pb) of the piezo-electric material of said plates (13a,13b) both being perpendicular to said plane, and said plates (13a,13b) each being delimited by two flat faces parallel to said plane and being attached one to the other so that a first face of each of said plates (13a,13b) is arranged facing a first face of the other of said plates (13a,13b), and, on the other hand, electrodes (16a,16b,17a,17b,17c) arranged such that they create in said plates (13a,13b) and in response to an exciting signal, an electric field (E;Ea,Eb) perpendicular to said plane and being in the same direction as the direction of one of said polarisations (Pa,Pb) and being in the opposite direction of that of the other of said polarisations (Pa,Pb).
3. Timepiece according to claim 2, characterized in that said polorisations (Pa,Pb) have opposite directions, and in that said electrodes (16a,16b) are arranged such that said electric field (E) has the same direction in both of the two plates (13a,13b).
4. Timepiece according to claim 2, characterized in that said polarisations (Pa,Pb) have the same direction, and in that said electrodes are arranged such that said electric field has a first component (Ea) in one of said plates (13a,13b) and a second component in the other of said plates (13a,13b), the directions in which these components (Ea,Eb) are facing being opposed to one another.
5. Timepiece according to claim 1, characterized in that said device (9) comprises an element (13) of a piezo-electric material having the general form of a circular disk having a central zone in which is situated one of said attachment zones (9a,9b) and a peripheral zone in which is situated the other of said attachment zones (9a,9b).
6. Timepiece according to claim 5, characterized in that said element (13) comprises a central circular opening (13a), the zone of said element (13) which is situated around said opening (13a) constituting said central zone.
7. Timepiece according to claim 1, characterized in that said piezo-electric device (9) comprises an element (14) of a piezo-electric material comprising a plurality of strips (14c) connected one to the other by one of their extremities, the central zone of said element constituting one of said attachment zones (9a,9b) and the peripheral zone of said element constituting the other of said attachment zones (9a,9b).
8. Timepiece according to claim 7, characterized in that said element (14) comprises a central opening (14a), the zone of said element (14) which is situated around said opening (14a) constituting said central zone.
9. Timepiece according to claim 1, characterized in that said device (9) comprises a plurality of strips (15) of a piezo-electric material each having a first and a second extremity, said first extremities constituting together one of said attachment zones (9a,9b) and said second extremities constituting together the other of said attachment zones (9a,9b).
10. Timepiece according to claim 4, characterized in that said piezo-electric device (9) further comprises a metal sheet (17d) arranged between said piezo-electric plates (13a,13b) in such a way that the exterior extremity of said metal sheet (17d) surpasses the exterior extremities of said piezo-electric plates (13a,13b) thus forming said first attachment zone (9a).

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