EP3570119B1 - Mechanism for displaying a periodic event and timepiece comprising such a mechanism - Google Patents

Description

Technical area

The present invention relates to the field of watchmaking. It relates more particularly to a mechanism for displaying a periodic event such as the phases of the moon or a date indication.

The invention also relates to a timepiece comprising such a mechanism for displaying a periodic event.

State of the art

Astronomical clocks and date watches have been well known since the 16th and 17th centuries, respectively, and numerous mechanisms intended for displaying periodic calendar events have been proposed in the state of the art. The most common in wristwatches are the simple or perpetual calendar, as well as the phases of the moon. In a general and simplified manner, these different mechanisms include a date or moon gear train comprising a star wheel with the number of teeth (7 for the weekly calendar, 12 for the months, 31 for the days, 59 for the moons, etc. ) is arranged in a kinematic connection on the one hand with the hours mobile of the finishing gear of a watch movement, a date or moon phase indicator with a disc or star being integral in rotation with the star wheel. The cog is designed to take the star wheel one step per day to follow the normal calendar evolution and display the corresponding information on or in the face of the watch.

We also know certain mechanisms of this type designed to provide a retrograde display, as for example described in the patents. CH 703 546 B1 or CH 701 836 B1 . However, to operate the return jumps of the retrograde needle, these mechanisms require the use of cams of complex shapes associated with rakes in kinematic connection with the retrograde needle, all in a small footprint, so as not to affect the other functions. the watch movement, which makes their realization and their implementation difficult, often with fairly summary display details. We also know the document EP 3 070 538 A1 , which discloses a display mechanism, provided with a retrograde-driven movable indicator and an annular cam at the periphery of the movement.

The object of the present invention is to provide a mechanism for retrograde display of a periodic event which is simpler to produce, more reliable in its operation and more precise than the mechanisms known from the prior art.

Disclosure of the invention

• Un cadran muni d'un index représentatif d'un évènement périodique à afficher, tel que notamment un quantième ou les phases de la lune ;
• Un organe indicateur agencé mobile en rotation par rapport audit index sur le cadran pour afficher un dit évènement périodique ;
• Un rouage d'affichage dudit évènement périodique adapté pour être agencé en liaison cinématique avec la roue des heures d'un mouvement horloger,
• une came agencée en liaison cinématique avec le rouage d'affichage et l'organe indicateur et comportant un chemin de came de longueur déterminée en fonction de l'événement périodique à afficher par l'organe indicateur sur l'index du cadran ;

caractérisé en ce que :

• le cadran comporte une première et une deuxième parties circulaires et concentriques, la première partie portant ledit index et la deuxième partie étant agencée mobile en rotation autour de la première par l'intermédiaire du rouage d'affichage, le chemin de came étant formé sur ladite deuxième partie du cadran
• le rouage d'affichage comportant une couronne dentée solidaire de la deuxième partie du cadran et adaptée pour réaliser l'accouplement du rouage d'affichage au mobile des heures d'un mouvement horloger, et
• un organe suiveur de came étant monté mobile par rapport au première et seconde partie du cadran et en liaison cinématique avec l'organe indicateur pour déplacer ce dernier relativement à l'index lors de la rotation de la seconde partie de cadran.

More precisely, and according to a first aspect, the invention relates to a mechanism for displaying a periodic event comprising:

• A dial provided with an index representative of a periodic event to be displayed, such as in particular a date or the phases of the moon;
• An indicator member arranged to be movable in rotation with respect to said index on the dial to display a said periodic event;
• A gear for displaying said periodic event adapted to be arranged in kinematic connection with the hour wheel of a watch movement,
• a cam arranged in kinematic connection with the display gear and the indicator member and comprising a cam path of length determined as a function of the periodic event to be displayed by the indicator member on the index of the dial;

characterized in that:

• the dial comprises a first and a second circular and concentric parts, the first part carrying said index and the second part being arranged movable in rotation around the first by means of the display gear, the cam track being formed on said second part of the dial
• the display train comprising a toothed crown integral with the second part of the dial and adapted to achieve the coupling of the display train to the mobile of the hours of a watch movement, and
• a cam follower member being mounted movable relative to the first and second part of the dial and in kinematic connection with the indicator member to move the latter relative to the index during the rotation of the second part of the dial.

Such a display mechanism has the advantage of being of an extremely simple structure, not necessarily compact, and applicable both for the display of a date and of phases of the moon, while offering an additional playful character. for the user by functional mobility of the second part of the dial relative to the first part while providing a facility of greater display precision by an increased diameter of the toothed crown compared to conventional date gear wheels, and therefore to work on finer gear ratios.

Various particular features of the mechanism of the invention are the subject of claims 2 to 18.

In particular, in one embodiment, the first and the second part of the dial are coplanar, each having an upper face called the display and a lower face called the gear train, the cam path and the index representative of a periodic event. to be displayed being arranged on said display faces of the second and first parts respectively.

Preferably, said toothed crown is formed or fixed on the gear face of the second part of the dial.

According to one embodiment, the cam track comprises n identical and consecutive sections on the display face of the second part of the dial; preferably n is equal to 12.

According to various embodiments determined by aesthetic considerations of the display, the cam track consists of a projecting wall or a slide hollowed out in the display face of the second part of the dial.

In these different embodiments of the cam track, said wall or slide is formed by plastic deformation, molding, deposition, removal of material, assembly or machining of the second part of the dial.

According to one embodiment, the follower member is a linear feeler movable in translation in a direction radial to the second part of the dial, said feeler comprising a rack arranged in engagement with a pinion integral with the indicator member.

According to another embodiment, the follower member is a movable finger rotatably secured to the indicator member about an axis of rotation perpendicular to the plane of the dial.

Whatever the case, however, the follower is held in permanent support in the cam track by a spring.

According to one embodiment, the first part of the dial is circular and concentric with the second part of the dial.

According to one embodiment, the periodic event is a phase of the moon, said index representing the different phases of the moon over a lunation of 29.53 days and the cam path being configured such that the indicator member indicates continuously follows the representations of the consecutive phases of a lunation and returns to a so-called “new moon” position at the end of a lunation.

According to one embodiment, said index representing the different phases of the moon over a half-moon, the cam track being configured such that the indicator member runs through said index in a direction of rotation over a half-moon from a so-called “new moon” position up to a so-called full moon position, then traverses said index in the opposite direction over the following half-moon.

According to one embodiment of a moon phase display mechanism, the latter comprises a second index indicating the increasing or decreasing nature of a moon phase positioned on one of the first and second parts of the dial. and a cursor positioned on the other of the first and second parts of the dial, said index being configured so that the cursor is positioned opposite the appropriate index indication during the entire period of growth, respectively decrease of the moon on a lunation.

As a variant, the periodic event can also be a date. In this case, the index will include indices of the days of the month and the toothed crown could for example be a date crown.

The subject of the invention is also a timepiece comprising a mechanical or quartz watch movement and a display mechanism as defined above, the display gear of which is coupled to the mobile of the hours of the watch movement by said toothed crown.

Brief description of the drawings

• La figure 1 représente une vue d'ensemble d'un mécanisme d'affichage d'un évènement périodique selon l'invention dans une forme de réalisation préférée relative à l'affichage de phases de la lune ;
• La figure 2 représente une vue partielle sans la première partie de cadran du mécanisme de la figure 1 représentant plus particulièrement le rouage d'affichage du mécanisme d'affichage ;
• Les figures 3A à 3C représentent des vue partielles analogues à la figure 1 de différentes positions d'affichage de phases de lune à l'aide du mécanisme de l'invention ;
• Les figures 4A à 4C représentent des vue partielles analogues à la figure 1 de différentes positions d'affichage d'une second index d'indication de la croissance de phases de lune pour chacune des positions représentées aux figures 3A à 3C.

Other details of the invention will emerge more clearly on reading the following description, given with reference to the appended drawings in which:

• The figure 1 represents an overall view of a mechanism for displaying a periodic event according to the invention in a preferred embodiment relating to the display of phases of the moon;
• The figure 2 shows a partial view without the first part of the dial of the mechanism of the figure 1 more particularly showing the display gear of the display mechanism;
• The figures 3A to 3C represent partial views similar to the figure 1 different positions of moon phase display using the mechanism of the invention;
• The figures 4A to 4C represent partial views similar to the figure 1 different display positions of a second index indicating the growth of moon phases for each of the positions shown in figures 3A to 3C .

Embodiment of the invention

We have represented on the figures 1 and 2 , an embodiment of a mechanism for displaying a periodic event, and more particularly in the precise example of phases of the moon, according to the invention. Such a display mechanism is in particular intended to be mounted in a timepiece such as a watch, in kinematic connection with a watch movement, in particular a mechanical movement, of the timepiece, both not shown on the figures.

This mechanism comprises in the first place, as shown in the figure 1 , a display dial C of a timepiece such as a watch in top view, on which the visible elements of the display mechanism of the invention are visible. These elements include in particular in the example shown a first part of dial C1, of substantially circular shape, and a second part of dial C2, in the form of a ring arranged concentrically and coplanar with the first part C1. Each of the parts C1, C2 of the dial C has an upper face called the display and a lower face called the gear train. The dial ring C2 is advantageously arranged to be movable in rotation around the first part C1 by means of a display gear R, shown in FIG. figure 2 , providing a kinematic connection of the ring C2, provided with an internal toothed ring 1, formed or fixed on the gear face of the ring C2 of the dial. with the hour wheel 3 of the finishing gear of a watch movement via a pinion 2 driven on the axis of rotation of the hour wheel 3.

The first part C1 of the dial C comprises on its display face a main moon index 14 representative of a periodic event to be displayed, in this case the phases of the moon over a complete lunation. In the embodiment shown, said main moon index 14 comprises a circular track 14a indicating the days on an increasing phase of a lunation from a position "0", called "new moon" to a position called full. moon, indicated by a number 14, associated with a graduated scale 14b representative of the evolution of the moon's luminosity on this increasing phase, said graduated scale 14b being composed of segments of increasing and progressive lengths, the largest of which is arranged opposite the runway sector 14a corresponding to the fourteenth day of lunation. An indicator member, consisting of a so-called moon hand 8, is associated with the main moon index 14 in order to progressively indicate, in the manner of a conventional hourly date indication, on which day of the lunation we are. This moon hand 8 is mounted to be movable in rotation with respect to the fixed part of the dial C1 so as to be able to pivot on its axis above the dial C or, where appropriate below the latter, in particular if the fixed part C1 of said dial C is transparent. Said moon hand 8 is furthermore arranged in a kinematic connection ( fig. 2 ) with the display gear R via a pinion 9 on which the needle is fixed (in this case screwed) and a cam follower member 7 provided with a rack meshing the pinion 9 and arranged mobile in translation in a radial slot 17 formed in part C1 of dial C.

The cam follower member 7 advantageously bears in abutment at the level of a contact end 71 on a cam track 13 formed on the display face of the movable ring C2 of the dial C. Said cam track 13 is advantageously made up of n identical and consecutive sections 13s, in this case of twelve sections 13s each composed of two successive and consecutive cam segments 13a, 13b such that the contact end 71 of the cam follower 7 slides through the entire d 'a section 13s over a complete lunation, and therefore traverses a said cam segment 13a, 13b over a period equal to half a lunation during the rotation of the ring C2 of the dial C under the effect of the display gear R via its toothed ring 1 as will be described below. Of course, the number of sections 13s of the cam path 13 is determined by the periodic event to be displayed by the display mechanism of the invention. In this case, 12 sections 13s are used to display the 12 complete lunations of a 12-month calendar year.

The cam track 13 is preferably made of a projecting wall or of a slide hollowed out in the display face of the second part C2 of the dial, in particular for example by plastic deformation, molding, deposition, removal of material, assembly or machining of the second part C2 of the dial C.

The moon hand 8 is advantageously rotated vis-à-vis the main moon index 14 in a retrograde rotational movement, traversing on a first half-moon the entire track 14a of the index of main moon 14 in one direction while the contact end 71 of the cam follower 7 slides on a first cam segment 13a, 13b, then on the next half-moon doing the reverse traversing in the other direction while the follower cam 7 slides on the other cam sector 13b, 13a respectively.

In order to impart its retrograde movement to the needle 8 opposite the index 14, the cam track 13 is advantageously configured in the embodiment shown so that the sliding of the contact end 71 of the cam follower 7 on a segment 13b of the cam track 13 induces a sinister translational movement of the cam follower 7 in the slot 17 and a sliding on a segment 13a a dextral translational movement, respectively a clockwise rotation movement and a counterclockwise rotation movement of the needle 8 vis-à-vis the index 14. Also the segments 13a, 13b are oriented relative to each other successively to form the cam path 13 over the entire upper surface of the ring C2 at an obtuse angle α open towards the center of the dial C of between 110 ° and 135 °, thus giving the cam track 13 a serrated shape.

In order to assist the sinister translational movement of the cam follower 7 and of the needle 8 in the counterclockwise direction, a leaf spring 10 is advantageously arranged integral with a first end of the pinion 9 carrying the needle 8 and fixed to a second end on the fixed part C1 of the dial C, or as a variant on a plate of the watch movement associated with the display device of the invention.

In addition to the main moon index 14 of the days and light intensity of a lunation, the display mechanism of the invention also comprises a secondary index 15 indicating the increasing or decreasing character of the moon. This secondary index 15 simply comprises two contiguous sectors 15a, 15b respectively bearing a "+" sign and a "-" sign and of equal length arranged on a edge of the fixed part C1 of the dial C such that the middle 15m of the two sectors 15a, 15b is aligned radially with a moon cursor 18 on the mobile ring C2 of the dial C when, as shown in figure 1 , the contact end 71 of the cam follower 7 is located in the angle α between two segments 13a, 13b of the cam track 13, the needle 8 then being facing the graduation "14", that is to say - say mid-month and full moon. IN practice, the C2 ring carries 12 moon sliders 18 distributed regularly on the periphery

The dial C of the display mechanism of the invention finally comprises, in the example shown, but in an accessory manner and not essential to the display mechanism of the invention, a secondary dial 16 for displaying the time located at 12 o'clock. and above the main dial C, this secondary display dial 16 being associated with hour and minute hands respectively driven on a barrel integral with the hour wheel 3 ( fig.2 ) and on the roadway coaxial with the barrel of the hour hand in a conventional manner.

The figure 2 shows in detail the constitution of the display gear R of the display mechanism of the invention making it possible to achieve the kinematic connection between the hours wheel 2 of a watch movement and the ring C2 of the display dial C of the mechanism display, which carries the cam path 13 actuating via the cam follower the movement of the needle 8 with respect to the index 14 and moving the cursor 18 opposite the secondary index 15 to indicate the increasing or decreasing nature of the moon over a half-lunation indicated by index 14 and hand 8.

• un pignon des heures 2, coaxial à la roue des heures 3, et comportant une denture z1 de 24 dents,
• une première roue de lune 4, dite à friction, comportant une denture périphérique z2 de 62 dents,
• un premier pignon de lune 5 coaxial à la première roue de lune à friction, ledit premier pignon comportant une denture z3 de 16 dents,
• une première roue de renvoi 6 ,
• une deuxième roue de lune 12 comportant une denture périphérique z4 de 93 dents,
• un second pignon de lune 11 porté par la deuxième roue de lune 12 et comportant une denture z5 de 10 dents et engrenant avec,
• un anneau de lune C2, formant comme précédemment indiqué une partie périphérique du cadran C, et comportant une couronne dentée intérieure 1 comportant une denture z6 de 236 dents.

This display gear R, or moon gear, thus comprises, from the hour wheel 3:

• a gear of hours 2, coaxial with the wheel of hours 3, and comprising a toothing z1 of 24 teeth,
• a first so-called friction moon wheel 4 comprising a peripheral toothing z2 with 62 teeth,
• a first moon pinion 5 coaxial with the first friction moon wheel, said first pinion comprising a toothing z3 of 16 teeth,
• a first return wheel 6,
• a second moon wheel 12 comprising a peripheral toothing z4 with 93 teeth,
• a second moon pinion 11 carried by the second moon wheel 12 and comprising a toothing z5 of 10 teeth and meshing with,
• a moon ring C2, forming as previously indicated a peripheral part of the dial C, and comprising an internal toothed crown 1 comprising a toothing z6 of 236 teeth.

The moon display gear R is thus arranged such that the first moon wheel 4 meshes through its toothing z2 the toothing z1 of the hours pinion 2 on the one hand and the first moon pinion 5 meshes via its toothing z3 with the first intermediate wheel 6, which itself meshes with the ^2nd wheel groups 12 arranged in kinematic connection with the moon pinion 11 with the ring C2 moon via the ring gear 1. This kinematic chain thus makes it possible to drive with a suitable reduction the ring C2 in rotation in a counterclockwise direction from the hour wheel 3, this rotation allowing through the cam track 13 on which the cam follower 7 is supported to move the moon hand 8 , coupled by its pinion 9 to the rack of the cam follower 7, vis-à-vis the main moon index 14.

The display mechanism of the present invention thus advantageously provides an original moon phase display with a hand moving in a retrograde movement, without a schematic visual representation of the moon, as provided by an overwhelming majority of displays of the moon. moon phases of the prior art. It also does not require any moon disc, and uses a mobile part of the dial C2 as an actuating cam of the moon hand 8, which provides a simplification of the display mechanism, as well as a double animation. in the dial by displacement of the ring C2 around the fixed central part C1 which causes the displacement of the moon hand 8 vis-à-vis the main moon index 14 and the moon cursors 18 vis-à-vis -vis of the secondary index 15.

Another major advantage of the display mechanism of the invention is its increased precision compared to known moon phase display mechanisms, conferred in particular by the large toothing z6 of the ring gear 1 of the ring C2. Indeed, the lunation ratio RL obtained for a lunation by the mechanism of the invention is calculated such that: $$\mathit{RL}=\frac{\mathrm{<figure-callout\; id="6"\; label="z"\; filenames="imgf0002.png"\; state="\{\{state\}\}">z</figure-callout>}6\mathrm{xz}4\mathrm{<figure-callout\; id="2"\; label="xz"\; filenames="imgf0002.png"\; state="\{\{state\}\}">xz</figure-callout>}2}{12\mathrm{<figure-callout\; id="5"\; label="xz"\; filenames="imgf0002.png"\; state="\{\{state\}\}">xz</figure-callout>}5\mathrm{<figure-callout\; id="3"\; label="xz"\; filenames="imgf0002.png"\; state="\{\{state\}\}">xz</figure-callout>}3\mathrm{<figure-callout\; id="1"\; label="xz"\; filenames="imgf0002.png"\; state="\{\{state\}\}">xz</figure-callout>}1}=29.530729$$

That is to say a precision of 29 days, 12h, 44 minutes and 15 seconds. Also, considering the values of revolution of the Earth and the Sun agreed in 1961, a defect of 1 day on the lunation display will be noted only after 577 years. The need for adjustment correction of the mechanism of the invention over the life of the timepiece comprising it can therefore be considered as almost improbable.

The operation and the mode of display and reading of the phases of the moon according to the display mechanism of the invention are shown in figures 3A-3C , the figures 4A-4D showing enlargements of figures 3A-3C on the secondary index 15.

The figure 3A represents the display of a waxing moon on the 8th day of the lunar month. The contact end 71 of the cam follower 7 and resting on an increasing segment 13b of the cam track 13 on the ring C2 of the dial, the moon hand being pointed at the number 8 of the track 14a of the The main moon index 14. The crescent character of the moon is then indicated by the radial alignment of a cursor 18 on the ring C2 with the sector 15a bearing the indication “+” on the secondary index 15.

From the 8th day of growth until the 15th day, the C2 ring continues to rotate counterclockwise so that the cam follower 7 slides on the segment 13b of the cam track until it reaches a position of equilibrium. between said segment 13b and the consecutive sector 13a, in the angle α, as shown in figure 3B . The moon hand 8 is then in a substantially horizontal position pointing towards the upper end of the track 14a of the main moon index 14, facing the graduation 14 and the largest luminosity segment. So it's the full moon, and the middle marker 15m of the secondary index 15 is then aligned with a cursor 18 on the ring C2, as shown figure 4B .

The figure 3C finally represents the display of a waning moon on the 22nd day of the lunation. The moon hand 8 is then in its retrograde movement back to "0" of track 14a of the main moon index 14. The contact end 71 of the cam follower 7 and resting on a decreasing segment 13a of the cam track 13 on the ring C2 of the dial, the moon hand being pointed at the number 8 of the track 14a of the main moon index 14. The decreasing character of the moon is then indicated by l radial alignment of a cursor 18 on the ring C2 with the sector 15b bearing the indication "-" on the secondary index 15, as shown in Fig. 4C .

The display mechanism of the invention thus allows by its configuration a simplified and animated representation of a new kind of a periodic event such as the phases of the moon as previously described or even according to a similar mechanism for the display of dates. For this, it suffices in particular to choose a configuration of the cam track 13, of its sections 13s and / or segments 13a, 13b of length and shapes adapted to cooperate with one or more appropriate indicator members to inform the desired periodic event, of same as adjusting the display cog if necessary.

In particular, in an example not shown in the figures, an annual calendar can be displayed simultaneously with the moon phases, for example, by means of a month disc carried on a date star with 12 teeth rotatably mounted on the fixed part. of the dial C, a sensor movable in translation in a manner analogous to the cam follower 7 of the moon hand 8 being arranged and biased by a spring between the cam path 13 and the date star so as to make said star pivot by one step each time the probe passes from a section 13s of the cam track 13 to a consecutive section 13s. The date of the date can then be displayed where appropriate by a hand actuated in a manner substantially identical to the moon hand 8, or a date disc in accordance with the conventional date mechanisms of the prior art.

Of course, variations of the display mechanism of the invention can be envisaged for a person skilled in the art, in particular as regards the nature and shape of the indicator members and of the associated indexes to give the desired periodic event information. .

Claims (18)

1. Periodic event display mechanism comprising:

   - a dial (C) provided with an index (14) representative of a periodic event to be displayed, such as in particular a date or the phases of the moon;

   - an indicator member (8) arranged rotatably with respect to said index (14) on the dial (C) to display a said periodic event;

   - a display train (R) of said periodic event adapted to be arranged in kinematic connection with the hour wheel (3) of a watch movement,

   - a cam arranged in kinematic connection with the display train (R) and the indicator member (8) and comprising a cam track (13) of a length determined as a function of the periodic event to be displayed by the indicator member on the index (14) of the dial;

   characterised in that:

   - the dial (C) comprises a first part (C1) carrying said index (14) arranged in a second annular part (C2) rotatable about the first part by means of the display train (R), the cam track (13) being formed on said second part (C2) of the dial;

   - the display train (R) comprising a toothed crown (1) integral with the second part (C2) of the dial (C) and adapted to couple the display train (R) to the hour wheel (3) of a watch movement, and

   - a cam follower member (7) being mounted so as to be movable relative to the first (C1) and second (C2) parts of the dial (C) and in kinematic connection with the indicator member (8) in order to move the latter relative to the index (14) along a retrograde trajectory during the rotation of the second part (C2) of the dial.
2. Mechanism for displaying a periodic event according to claim 1, characterised in that the first and second parts (C1, C2) of the dial are coplanar, each having an upper so-called display face and a lower so-called gear face, the cam track (13) and the index (14) representative of a periodic event to be displayed being arranged on said display faces of the second and first parts (C2, C1), respectively.
3. Mechanism for displaying a periodic event according to claim 1 or 2, characterised in that said toothed crown (1) is formed or fixed on the gear face of the second part (C2) of the dial.
4. Mechanism for displaying a periodic event according to one of claims 1 to 3, characterised in that the cam track (13) comprises n sections and consecutive on the display face of the second part (C2) of the dial.
5. Mechanism for displaying a periodic event according to one of claims 1 to 3, characterised in that the cam track (13) comprises n sections identical and consecutive on the display face of the second part (C2) of the dial.
6. Mechanism for displaying a periodic event according to claim 4 or 5, characterised in that n is equal to 12.
7. Mechanism for displaying a periodic event according to one of claims 1 to 6, characterised in that the cam track (13) is made of a protruding wall or a slide-way recessed in the display face of the second part (C2) of the dial.
8. Mechanism for displaying a periodic event according to claim 7, characterised in that said wall or slide-way is formed by plastic deformation, moulding, deposition, removal of material, assembly or machining of the second part of the dial.
9. Mechanism for displaying a periodic event according to one of claims 1 to 8, characterised in that the follower member (7) is a linear feeler movable in translation in a radial direction at the second part (C2) of the dial, said feeler comprising a rack arranged in mesh with a pinion (9) integral with the indicator member (8).
10. Mechanism for displaying a periodic event according to one of claims 1 to 8, characterised in that the follower member (7) is a mobile finger integral in rotation with the indicator member about an axis of rotation perpendicular to the plane of the dial (C).
11. Mechanism for displaying a periodic event according to one of claims 1 to 10, characterised in that the follower member (7) is kept in permanent rest in the cam track (13) by a spring (10).
12. Mechanism for displaying a periodic event according to one of claims 1 to 11, characterised in that the first part (C1) of the dial is circular and concentric to the second part (C2) of the dial.
13. Mechanism for displaying a periodic event according to one of claims 1 to 12, characterised in that the periodic event is a phase of the moon, said main moon index (14) representing the various phases of the moon and the cam track (13) being configured so that the indicator member (8) follows said consecutive phases of a lunation and returns to a position called "new moon" at the end of a lunation.
14. Mechanism for displaying a periodic event according to claim 13, characterised in that said main moon index (14) represents the various phases of the moon over a half-lunation, the cam track being configured such that the indicator member traverses said main moon index (14) in one direction of rotation over a half-lunation from a position called "new moon" to a position called "full moon" and then traverses said main moon index (14) in the opposite direction over the next half-lunation.
15. Mechanism for displaying a periodic event according to claim 13 or 14, characterised in that said main moon index (14) comprises a track (14a) representing the different days of a half-lunation, and a scale (14b) representing the brightness of the moon on each of the lunation days represented on the track (14a).
16. Mechanism for displaying a periodic event according to claims 11 and 15, characterised in that it comprises a second index (15) for indicating the increasing or decreasing nature of a moon phase positioned on one of the first and second parts (C1, C2) of the dial and a cursor (18) positioned on the other of the first and second parts (C1, C2) of the dial, said second index (15) being configured such that the cursor (18) is positioned opposite the indication of increase or decrease during the entire corresponding period.
17. Mechanism for displaying a periodic event according to claims 1 to 11, characterised in that the periodic event is a date.
18. Timepiece comprising a mechanical or quartz watch movement and a display mechanism according to one of the preceding claims, the display train of which is coupled to the hour wheel of the watch movement by said toothed crown.

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