Patent Publication Number: US-11036185-B2

Title: Timepiece mechanism for displaying the lunar day and moon phase, with a correction system using a double kinematic chain

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of European Patent Application No. 17201110.8 filed on Nov. 10, 2017 the entire disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention concerns the field of horology. It concerns, more specifically, a mechanism, commonly called an astronomical complication, which allows the display of both:
         the lunar day, whose duration separates two successive crossings of a given meridian (which may be represented, in the clock or watch provided with the mechanism, by two successive midday crossings);   and the moon phase, i.e. the (variable) portion of the moon illuminated by the sun.       

     BACKGROUND OF THE INVENTION 
     The astronomical features of the moon have been known for a long time and are notably described by James Ferguson in “Astronomy explained upon Sir Isaac Newton&#39;s principles”, the fifth edition of which was published in 1772. 
     The mean value of the lunar day (separating two crossings of the meridian) is 24 hours, 50 minutes and 28.328 seconds. 
     The solar day to lunar day ratio is thus: 
     
       
         
           
             
               
                 86400 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 s 
               
               
                 89428.328 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 s 
               
             
             = 
             0.96613682 
           
         
       
     
     As for the mean value of the lunation (the duration separating two full moons), this is 29 days, 12 hours, 44 minutes and 2.8 seconds. 
     Claiming to be inspired by Ferguson, E. Cloux, in his Horology course given at the Technical College of the Vallee de Joux (Switzerland) in 1949, drew a lunar day and moon phase display mechanism, in superposition on the solar day (with a mean value of 24 hours). 
     The mechanism drawn by E-Cloux, represented in  FIG. 1 , included the following elements:
         a moon bearing  101  provided with a meridian wheel  102  (with 59 teeth) and rotatably mounted about a main axis X 1 ;   a sphere  103  representing the moon, rotatably mounted relative to moon bearing  101  about a radial axis X 2  perpendicular to main axis X 1 ; radial axis Y 1  carries a moon pinion  104  (with 20 teeth);   a first rotating element  105  (with 57 teeth) rotatably mounted about main axis X 1  and which, it is understood, must mesh with a drive mechanism (not represented) also employed for displaying the minutes and/or hours of the solar day;   a moon wheel set  106  (with two integral wheels each with 57 teeth) rotationally coupling, with gear reduction, first rotating element  105  to meridian wheel  102 ;   a central wheel  107  (with 20 teeth), integral with first rotating element  105  and meshing with moon pinion  104 .       

     This ingenious mechanism makes it possible to display the moon crossing the meridian in 24 hours, 50 minutes, 31.58 seconds, and a lunation in 29.5 days. 
     It is seen that these are approximations of the mean lunar day and the mean lunation, imposed by the choice of gear ratio:
 
24  h&gt; 59/57=24  h  50 min 31.58  s  
 
     However, the mechanism drawn by E. Cloux has no member for making corrections to the display that are made necessary either by deviations resulting from the aforecited approximations, or, quite simply, by the mechanism stopping once the power source is depleted (usually a mainspring in mechanical watches, which, if not rewound will unwind completely). 
     Consequently, it is an object of the invention to propose a solution which makes it possible to correct, in a simple and reliable manner, the lunar day and lunation in the mechanism presented above. 
     SUMMARY OF THE INVENTION 
     To achieve the aforecited object, there is proposed a timepiece mechanism for displaying the lunar day and the moon phase, which includes:
         a first rotating element rotatably mounted about a main axis and meshing with a drive mechanism,   a moon bearing provided with a meridian wheel and rotatably mounted about a main axis,   a sphere representing the moon, rotatably mounted relative to the moon bearing about a radial axis perpendicular to the main axis, the radial axis carrying a moon pinion,   a moon wheel set rotationally coupling, with gear reduction, the first rotating element to the meridian wheel,   a central wheel, rotatably mounted about a main axis on the first rotating element and meshing with the moon pinion,   a second rotating element, meshing with the moon wheel set and friction mounted, at an interface, on the first rotating element to rotate integrally therewith about the main axis while the torque resulting from various circumferential forces respectively exerted on the first rotating element and on the second rotating element is lower, than a friction torque determining the maximum adhesion force at the interface, the second rotating element together with the moon wheel set and the moon bearing forming a first kinematic chain downstream of the first rotating element,   a transmission wheel, integral in rotation with the central wheel and provided externally with a toothing and internally with at least one jumper spring engaging and meshing with the toothing of a star wheel integral in rotation with the second rotating element, to rotationally couple said second rotating element to the central wheel while the torque resulting from the various circumferential forces exerted respectively on the star wheel and on the transmission wheel is lower than a jump torque, beyond which the jumper spring is radially shifted by sliding over the star wheel until it is disengaged therefrom, said at least one jumper spring and the star wheel being configured such that the jump torque is lower than said friction torque, the transmission wheel together with the central wheel and the moon pinion forming a second kinematic chain downstream of the star wheel,   a system for correcting the lunar day display, which includes a first drive element capable of having, at least momentarily, a meshing relationship with the first kinematic chain in order to force rotation of the moon bearing about the main axis, via a first correction train partially formed by at least one portion of the first kinematic chain, when a first correction torque, greater than said friction torque, is applied to said first correction train by a user, and   a system for correcting the moon phase, which includes a second drive element capable of having, at least momentarily, a meshing relationship with the second kinematic chain in order to force rotation of the sphere about said radial axis, via a second correction train partially formed by at least one portion of the second kinematic chain and independent of the first kinematic chain, when a second correction torque, greater than said jump torque, is applied to said second correction train by a user.       

     As a result of this double correction system, which acts by using two distinct kinematic chains, it is possible to correct, in a simple and reliable manner, the lunar day display and the moon phase display. 
     According to a main embodiment, the lunar day display correction system and the moon phase correction system include a joint correction device for activating the lunar day display and, without activating the lunar day display, the moon phase. This joint correction device includes a sliding pinion which alone forms the first and second drive elements, said sliding pinion being able to adopt two adjustment positions, namely:
         a lunar day adjustment position, in which the sliding pinion meshes with the moon wheel set to force rotation of the moon bearing about said main axis via said at least one portion of the first kinematic chain;   a moon phase adjustment position, in which the sliding pinion meshes with the transmission wheel to force rotation of the sphere about said radial axis via said at least one portion of the second kinematic chain.       

     The correction device advantageously includes a carrier pinion which meshes with the sliding pinion and at least one small connecting rod which joins the axes of rotation of the sliding pinion and of the carrier pinion. 
     The first rotating element includes, for example, a toothed wheel which extends perpendicularly to the main axis, integral with a pipe which extends along the main axis. The second rotating element then includes an auxiliary wheel which extends perpendicularly to the main axis, integral with a sleeve which is friction fitted onto the pipe of the first rotating element. 
     The friction connection between the second rotating element and the first rotating element is advantageously achieved by indenting, which for example takes the form of a one-off deformation of the internal diameter of the tube of the second rotating element, in order to ensure friction on the conical slot made in the pipe of the first element. 
     According to a preferred embodiment, the moon wheel set includes two superposed integral wheels, namely:
         a lower wheel, which meshes with the auxiliary wheel of the second rotating element, and   an upper wheel, which meshes with the meridian wheel of the moon bearing.       

     According to a particular embodiment:
         the auxiliary wheel of the second rotating element has 64 teeth,   the lower wheel of the moon wheel set has 43 teeth,   the upper wheel of the moon wheel set has 37 teeth, and   the meridian wheel of the moon bearing has 57 teeth.       

     The central wheel preferably carries a crown toothing meshed with the moon pinion; further, the central wheel is advantageously fitted onto the pipe of the first rotating element. 
     The moon bearing is preferably mounted on the central wheel, for example, fitted onto the latter with the insertion of a smooth bearing. 
     The transmission wheel advantageously includes a pair of diametrically opposite jumper springs. 
     Finally, the star wheel typically has 29 or 30 teeth, or, in a preferred variant, 59 teeth. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the invention will appear in light of the following description of one embodiment, made with reference to the annexed drawings, in which: 
         FIG. 1  is a cross-sectional view of a known mechanism for displaying the lunar day and moon phase, as proposed by E. Cloux. 
         FIG. 2  is an exploded perspective view illustrating a watch provided with a mechanism for displaying the lunar day and moon phase according to the invention. 
         FIG. 3  is a perspective, larger scale view of the display mechanism of  FIG. 2 . 
         FIG. 4  is a partial cross-sectional view of the mechanism of  FIG. 3 , along the cross-sectional plane IV-IV; an inset shows a larger scale detail. 
         FIG. 5  is a plan view of the mechanism of  FIG. 4  (to show the underlying components, the moon bearing has been removed). 
         FIG. 6  is a larger scale view of a detail of the mechanism, taken at the same time in inset VI at the top left of  FIG. 5 . 
         FIG. 7  is a top view of the mechanism, illustrating the lunar day correction. 
         FIG. 8  is a similar view to that of  FIG. 5  illustrating the moon phase correction. 
         FIG. 9  is a larger scale view of a detail of the mechanism, taken in inset IX at the top left of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  represents a timepiece. This could be a clock or a pendulum clock, but, in the illustrated example, it is a watch  1 —and more precisely a wristwatch, able to be worn on the wrist. In a conventional manner, this watch  1  includes a case  2  which includes a case middle  3 , a back cover and a crystal (not represented), and, fixed to the horns  4  of the case middle, a bracelet  5  for wear on the wrist. 
     Watch  1  includes, housed inside case  2 , a timepiece movement which includes a bottom plate  7  and, mounted on the plate, at least one timepiece mechanism  8  designed to ensure display of the lunar day and moon phase. 
     As we will see, mechanism  8  is also designed to ensure display of the minutes and hour of the mean solar day but such a display is optional and could be provided by a separate mechanism. 
     Mechanism  8  belongs to the family of ‘astronomical’ complications; it is organised around a main axis A 1  perpendicular to the general plane of plate  7 . 
     The moon is displayed as a body, in the form of a sphere  9  driven in a double movement:
         revolution about main axis A 1  to provide the lunar day indication;   rotation about a specific (radial) axis A 3  to provide the moon phase indication.       

     According to an embodiment illustrated in  FIG. 4 , main axis A 1  is materialized by an arbor  10  which, in this example, is formed on a centre wheel set  11 , which is itself mounted on plate  7 . This central wheel set is provided here with a wheel  12  whose function is not relevant to the present context. 
     As seen in  FIG. 4 , display mechanism  8  is engaged by a drive mechanism  13 , hereafter referred to as the motion-work, which includes several superposed rotationally integral wheels with a common axis A 2  which is offset relative to main axis A 1  and parallel thereto. In the illustrated example, motion-work  13  includes three superposed wheels, namely:
         a large wheel  14 , provided with a peripheral toothing typically having a number of teeth Z 1 =72;   a medium wheel  15 , provided with a peripheral toothing typically having a number of teeth Z 2 =24;   a small wheel  16 , provided with a peripheral toothing typically having a number of teeth Z 3 =12.       

     Motion-work  13  is driven in rotation by a drive device (not represented) including an energy source and a transmission. As astronomical complications are usually associated with mechanical watches, it is preferable for the energy source to be a mainspring associated with a balance/balance spring regulator. Nevertheless, if the energy source were a battery associated with a quartz resonator it would not be outside the scope of the invention. 
     As already mentioned, mechanism  8  is designed to display the minutes and the hour of the mean solar day. 
     For the minute display, mechanism  8  includes a cannon pinion  17 , rotatably mounted about main axis A 1  and provided with a centre pinion  18  meshing with large wheel  14 , and with a tube  19  fitted (with the possibility of rotation) onto arbor  10  of centre wheel set  11 . Cannon pinion  17  carries a minute hand  20  which, as illustrated in  FIG. 4 , is pressed onto tube  19 , at an upper end of the latter. Centre pinion  18  is provided with a peripheral toothing typically including a number of teeth Z 4 =16. Cannon pinion  17  makes one revolution about main axis A 1  in one hour. 
     For the hour display, mechanism  8  includes an hour wheel set  21 , rotatably mounted about main axis A 1  and provided with an hour wheel  22  meshing with medium wheel  15 , and a hollow shaft  23  fitted (with the possibility of rotation) onto tube  19  of cannon pinion  17 . Hour wheel set  21  carries an hour hand  24  which, as illustrated in  FIG. 4 , is driven onto hollow shaft  23 , at an upper end of the latter. 
     Hour wheel  22  is provided with a peripheral toothing typically having a number of teeth Z 5 =64, such that the gear reduction ratio (i.e. the ratio of rotational speeds) between hour wheel  22  and centre pinion  18  is: 
     
       
         
           
             
               
                 
                   Z 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
                 
                   Z 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
               × 
               
                 
                   Z 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
                 
                   Z 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   5 
                 
               
             
             = 
             
               
                 
                   16 
                   72 
                 
                 × 
                 
                   24 
                   64 
                 
               
               = 
               
                 1 
                 12 
               
             
           
         
       
     
     Consequently, hour wheel set  21  makes one revolution about main axis A 1  in 12 hours. 
     For the lunar day and moon phase display, mechanism  8  includes, firstly, a first rotating element  25  rotatably mounted about main axis A 1  and meshing with motion-work  13 . 
     More specifically, in the example illustrated, in particular, in  FIG. 4 , first rotating element  25  includes a toothed wheel, called solar wheel  26  (or 24-hour wheel), which extends perpendicularly to main axis A 1 , and a pipe  27 , integral with the solar wheel and which extends along main axis A 1 . 
     According to one embodiment illustrated in  FIG. 4 , pipe  27  is fitted (with the possibility of rotation) onto hollow shaft  23  of hour wheel set  21 . 
     In the illustrated example, pipe  27  is tiered, and includes a lower tier  28 , integral with solar wheel  26 , and an upper tier  29 , of smaller diameter than that of tier  28 . The lower tier and the upper tier are separated by a shoulder  30 . 
     Solar wheel  26  meshes with small wheel  16  of motion-work  13 . This solar wheel is provided with a peripheral toothing typically having a number of teeth Z 6 =64, such that the gear reduction ratio between first rotating element  25  and hour wheel set  21  is: 
     
       
         
           
             
               
                 
                   Z 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   5 
                 
                 
                   Z 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
               × 
               
                 
                   Z 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   3 
                 
                 
                   Z 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   6 
                 
               
             
             = 
             
               
                 
                   64 
                   24 
                 
                 × 
                 
                   12 
                   64 
                 
               
               = 
               
                 1 
                 2 
               
             
           
         
       
     
     Consequently, first rotating element  25  makes one revolution about main axis A 1  in 24 hours. In other words, the first rotating element can be used to measure the mean solar day. It can also be employed to display the mean solar day. Thus, in the illustrated embodiment (cf.  FIG. 3 ), the first rotating element carries, at an upper end of upper tier  29  of pipe  27 , a solar hand  31  (also called a 24-hour hand), which may be round in shape and/or have a circular opening to represent the sun. 
     Mechanism  8  includes, secondly, a moon bearing  32  rotatably mounted about main axis A 1 . The moon bearing is provided with a meridian wheel  33 . The moon bearing is also provided with a moon cover  34 , fixed to the meridian wheel to rotate integrally therewith. In a variant, the meridian wheel and the moon cover form a one-piece part. 
     Meridian wheel  33  is provided with a peripheral toothing typically having a number of teeth Z 7 =57. 
     As seen in  FIG. 4 , moon bearing  32  is hollow, and has an internal cavity  35  arranged inside moon cover  34 . 
     Mechanism  8  includes, thirdly, a sphere  9  representing the moon, rotatably mounted relative to moon bearing  32  about a radial axis A 3  perpendicular to main axis A 1 . Sphere  9  advantageously has two hemispheres of contrasting colours, namely:
         a dark hemisphere  36  (grey in the drawings), representing the portion of the side of the moon not illuminated by the sun;   a light coloured hemisphere  37  (white in the drawings), representing the portion of the moon illuminated by the sun.       

     Hemispheres  36 ,  37  can be made distinct by applying paint. However, in a preferred embodiment, the hemispheres are half-spherical calottes made from different materials and assembled to form sphere  9 . Thus, dark hemisphere  36  can be made from biotite mica, obsidian or any other dark mineral, while light hemisphere  37  can be made of metal (for example silver or grey gold), or from a light-coloured mineral (for example moonstone). 
     Further, in the illustrated example, radial axis A 3  is formed by a runner  38  that passes through sphere  9  and rotates integrally therewith. At an inner end, the runner is mounted in a sleeve  39  fitted into a hole  40  made in moon bearing  32 . 
     As seen in  FIG. 4 , radial axis A 3  (i.e. runner  38 ) carries, at an inner end, a moon pinion  41 , which is rotates integrally therewith. The moon pinion is housed inside inner cavity  35  of moon bearing  32 . 
     Moon pinion  41  is provided with a peripheral toothing typically having a number of teeth Z 8 =14. 
     Mechanism  8  includes, fourthly, a second rotating element  42 , rotatably mounted about main axis A 1 . According to an embodiment illustrated in  FIG. 4 , the second rotating element includes an auxiliary wheel  43 , which extends perpendicularly to main axis A 1 , and a sleeve  44  integral with the auxiliary wheel and which extends along main axis A 1 . Auxiliary wheel  43  is provided with a peripheral toothing typically having a number of teeth Z 9 =64 teeth. 
     Second rotating element  42  is mounted on first rotating element  25  with friction at their interface, referenced  45  (the interface is the surface where the first rotating element and the second rotating element make contact). 
     More precisely, sleeve  44  is friction fitted onto pipe  27  of the first rotating element. Even more precisely, the sleeve is friction fitted onto the lower tier  28  of the pipe. This friction fit is intended to make second rotating element  42  integral (in rotation about main axis A 1 ) with first rotating element  25 , while the torque, referenced C 1 , resulting from various circumferential forces respectively exerted on the first rotating element and on the second rotating element is lower than a friction torque, referenced CF, which determines the maximum adhesion force at interface  45 . 
     In other words:
         while C 1 &lt;CF, first rotating element  25  and second rotating element  42  rotate integrally, with no sliding at their interface  45 , and behave like a one-piece part;   as soon as C 1 ≥CF, the maximum adhesion force at interface  45  between first rotating element  25  and second rotating element  42  is reached, and they become rotationally separate, such that the second rotating element can pivot independently of the first rotating element about main axis A 1 , with sliding at interface  45 .       

     The friction connection at interface  45  between the second rotating element and the first rotating element can, in practice, be achieved by an indent  46 , which takes the form, for example, as illustrated in the detailed inset of  FIG. 4 , of a conical groove made in pipe  27  of the first rotating element. 
     Second rotating element  42  is provided with a star wheel  47 . This peripherally formed star wheel  47 , is, for example, cut externally in sleeve  44 . It includes a series of triangular teeth  48 , which are 30 in number here, but could be 29 in number, or even 59 in number (which is the approximate number of half-days in one lunation). 
     Mechanism  8  includes, fifthly, a central wheel  49 , mounted on first rotating element  25  and geared with moon pinion  41 . This central wheel advantageously carries a crown toothing  50  (i.e. whose teeth extend parallel to main axis A 1 ) meshed with moon pinion  41 . This toothing is, for example, cycloidal and has a number of teeth Z 10  equal to the number of teeth Z 8  of the moon pinion (namely Z 10 =14 here). 
     In the example illustrated in  FIG. 4 , central wheel  49  is fitted onto pipe  27  of first rotating element  25 . More precisely, the central wheel is fitted onto shoulder  30 . The interface between the central wheel and the first rotating element is a sliding interface, so that the central wheel can rotate independently of the first rotating element. 
     According to a preferred embodiment illustrated in  FIG. 4 , moon bearing  32  is mounted on central wheel  49 . To allow rotation of moon bearing  32  relative to the central wheel, a smooth bearing  51  is inserted therebetween. 
     Mechanism  8  includes, sixthly, a moon wheel set  52  which rotationally couples, with gear reduction, first rotating element  25  to meridian wheel  33  (and thus to moon bearing  32 ) to allow the moon bearing to be rotated by first rotating element  25 . More precisely, moon wheel set  52  rotationally couples second rotating element  42  (integral in rotation with first rotating element  25  while C 1 &lt;CF) to the meridian wheel. 
     Moon wheel set  52  is offset, rotatably mounted about an axis A 4  parallel to main axis A 1 . According to an embodiment illustrated in  FIG. 4 , the moon wheel set includes two superposed integral wheels, namely:
         a lower wheel  53 , which meshes with auxiliary wheel  43  of second rotating element  42 ;   an upper wheel  54 , which meshes with meridian wheel  33  of moon bearing  32 .       

     Lower wheel  53  is provided with a peripheral toothing typically having a number of teeth Z 11 =43. Upper wheel  54  is provided with a peripheral toothing typically having a number of teeth Z 12 =37 teeth. Consequently, the gear reduction ratio, referenced R, of solar wheel  26  to meridian wheel  33  (equal to the rotational speed ratio of moon bearing  32  to first rotating element  25 ) is: 
     
       
         
           
             R 
             = 
             
               
                 
                   
                     Z 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     9 
                   
                   
                     Z 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     11 
                   
                 
                 × 
                 
                   
                     Z 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     12 
                   
                   
                     Z 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                 
               
               = 
               
                 
                   
                     64 
                     43 
                   
                   × 
                   
                     37 
                     57 
                   
                 
                 = 
                 0.96613627 
               
             
           
         
       
     
     This gear reduction ratio provides the displayed mean lunar day value, referenced J: 
     
       
         
           
             J 
             = 
             
               
                 
                   24 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   h 
                 
                 R 
               
               = 
               
                 24 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 h 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 50 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 min 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 28.378 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 s 
               
             
           
         
       
     
     This is an excellent approximation of the real mean lunar day. Indeed, the lunar day displayed shows a loss of only 5/100ths of a second per solar day relative to the real lunar day (i.e. one day of loss every eight years). 
     The lunar day display is ensured by the circular path (i.e. the revolution) of sphere  9  about main axis A 1 . The moon crossing the zenith is represented by sphere  9  crossing twelve o&#39;clock. 
     According to a preferred embodiment, illustrated in dotted lines in  FIG. 3 , the watch is advantageously provided with a bar  55 , visible to the wearer, and which represents the earth&#39;s horizon line. 
     The path of approximately 180° of sphere  9  above bar  55  (from the point of view of the wearer) represents the moon&#39;s path in the visible sky (lunar day), while the path of approximately 180° of sphere  9  below the bar represents the moon&#39;s path in the non-visible sky (lunar night). 
     Moon wheel set  52  is advantageously mounted on a bridge  56  which is itself fixed to plate  7 . Its axis of rotation A 4  is, for example, materialized by a screw in helical engagement with bridge  56 . 
     Mechanism  8  includes, seventhly, a transmission wheel  57  integral with central wheel  49 , designed to make the latter rotate integrally with second rotating element  42  during normal operation of mechanism  8 , and conversely, to allow rotation of one relative to the other when the display is corrected, in conditions which will be set out below. 
     Transmission wheel  57  is provided externally with a toothing  58  and internally with at least one jumper spring  59 . 
     According to an embodiment illustrated in  FIG. 8 , transmission wheel  57  is provided with a pair of diametrically opposite jumper springs  59 . This number is not limiting. Thus, three jumper springs arranged at 120° could be provided. 
     As illustrated in  FIG. 6  and  FIG. 9 , the (or each) jumper spring  59  includes a strip spring  60  (curved in the illustrated example), which extends into a hollow  61  made in transmission wheel  57 . Seen from above, strip spring  60  extends from a fixed end  61  to a free end  63  in the anticlockwise direction (cf.  FIG. 6 ). Jumper spring  59  is also provided, at the free end of the strip spring, with a triangular head  64  of complementary size and shape to the space separating two adjacent teeth  48  of star wheel  47 . 
     The (or each) jumper spring  59  is engaged and mesh (via its head  64 ) with the toothing of star wheel  47 . In its position of equilibrium (in the absence of any stress), jumper spring  59  would occupy a position in which head  64  is separated from main axis A 1  by a distance smaller than the radius of the star wheel. 
     In normal operation, the (or each) jumper spring  59  is retained by its head  64  between two adjacent teeth  48  of star wheel  47 . Jumper spring  59  is held in this position by its own elastic return force which tends to draw head  64  in the direction of main axis A 1 . 
     During normal operation, second rotating element  42 , which is integral with first rotating element  25  (and thus driven therewith in rotation) rotates about main axis A 1  in the clockwise direction (seen from above). Star wheel  47  consequently exerts on head  64  of the (or of each) jumper spring  59  a stress that causes the latter to butt, which tends to keep head  64  between two adjacent teeth  48  of the star wheel. In these conditions, the second rotating element (with the first rotating element) and transmission wheel  57  (with central wheel  49 ) are integral in rotation about main axis A 1  and rotate together in the clockwise direction about the latter ( FIG. 6 ). 
     Central wheel  49  is made integral with transmission wheel  57 , for example by means of feet  65 , protruding onto the central wheel, driven into holes made in transmission wheel  57 . In a variant, this attachment can be achieved using screws. 
     During a correction of the moon phase display, a drive torque is applied to transmission wheel  57  to drive it in rotation about main axis A 1  (in the anticlockwise direction when seen from above, cf.  FIG. 8  and  FIG. 9 ) without, however, this rotation being transmitted by star wheel  47  to second rotating element  42 . 
     Second rotating element  42 , friction mounted on first rotating element  25 , resists the rotation of transmission wheel  57 , and the torque resulting from the various circumferential forces exerted respectively on first rotating element and on transmission wheel  57  is referenced C 2 . 
     It is at this point that the elasticity of jumper spring(s)  56  plays a part. Each jumper spring  59  is set—i.e. dimensioned—to:
         remain locked meshed with star wheel  47  while torque C 2  is lower than a jump torque CS;   be radially shifted by sliding over star wheel  47  (and more precisely by head  64  sliding over teeth  48 ) until it is disengaged, as illustrated in dotted lines in  FIG. 9 , as soon as torque C 2  becomes greater than jump torque CS. It will be noted that this radial shift is permitted by the flexibility of strip spring  60 .       

     Jump torque CS is lower than friction torque CF, i.e.:
 
 CS&lt;CF  
 
     Consequently, the application of torque C 2  alone can never cause second rotating element  42  to slide relative to first rotating element  25 . The first and second rotating elements therefore remain integral in rotation (and thus immobile) during a moon phase correction. 
     During normal operation, central wheel  49  (with crown toothing  50 ) rotates integrally with the second rotating element (and thus with the first rotating element) at a rate of one complete revolution about main axis A 1  in 24 hours. 
     Given gear reduction ratio R presented above, moon bearing  32  (with sphere  9 ) makes its own complete revolution more slowly (in 24 hours, 50 minutes and 28.378 seconds), And, given the fact that moon pinion  41  and crown toothing  50  include the same number of teeth (Z 8 =Z 10 ), sphere  9  is driven slowly in rotation about radial axis A 3  (in the clockwise direction when mechanism  8  is observed from the side, in the direction of radial axis A 3 ). 
     Sphere  9  makes one complete rotation about its axis A 3  in a number L of days corresponding to the displayed lunation value, i.e.: 
     
       
         
           
             L 
             = 
             
               
                 1 
                 
                   1 
                   - 
                   R 
                 
               
               = 
               
                 29.53012048 
                 = 
                 
                   29 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   j 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   12 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   h 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   43 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   min 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   22.4 
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     This is an excellent approximation of the real lunation, with a loss of around 7 minutes per month compared to said real lunation (i.e. one day of loss every 17 years). 
     We have seen that the differences between the displayed lunar day and the real lunar day, on the one hand, and the displayed moon phase and the real moon phase on the other hand, are small. One lunar day correction and one lunation correction would be required after several years of uninterrupted operation of watch  1 . 
     However, users who are diligent enough not to let the power reserve of a mechanical watch become depleted are rare. Thus, corrections required to reset the displays after watch  1  has stopped due to absent-mindedness of the user are more frequent than corrections required to make up losses accumulated by mechanism  8  during uninterrupted operation. 
     To correct the lunar day display, mechanism  8  is provided with a correction device  66  including a pinion  67  able to mesh with moon wheel set  52  to force rotation of moon bearing  32  about main axis A 1  via a first correction train which bypasses transmission wheel  57  and which includes moon wheel set  52  and meridian wheel  33 . 
     To correct the moon phase display, mechanism  8  is provided with a correction device  66  which includes a pinion  67  able to mesh with transmission wheel  57  to force rotation of sphere  9  about radial axis A 3  via a second train which includes the transmission wheel, central wheel  49  and moon pinion  41 . 
     Mechanism  8  could have two distinct correction devices to correct the lunar day display and the moon phase display separately. To activate them separately, watch  1  could be provided with two distinct winding mechanisms that could be operated independently of one another by the user (or a watchmaker). 
     However, in a preferred embodiment illustrated in the drawings, and more particularly in  FIG. 5 ,  FIG. 7  and  FIG. 8 , mechanism  8  includes a single device  66  for correcting the lunar day and moon phase display. 
     This correction device  66  includes a sliding pinion  67  able to adopt two adjustment positions, namely:
         a lunar day adjustment position, in which sliding pinion  67  meshes with moon wheel set  52  to force rotation of moon bearing  32  about main axis A 1  via the first kinematic chain ( FIG. 7 );   a moon phase adjustment position, in which sliding pinion  67  meshes with transmission wheel  57  to force rotation of sphere  9  about radial axis A 3  via the second kinematic chain ( FIG. 8 ).       

     In the example illustrated in  FIG. 7  and  FIG. 8 , correction device  66  includes a carrier pinion  68  which meshes with sliding pinion  67  and at least one connecting rod  69  which joins the axes of rotation of the sliding pinion and of the carrier pinion. In practice, correction device  66  includes a pair of superposed connecting rods  69 , arranged on either side of the carrier pinion and the sliding pinion. 
     Carrier pinion  68  is rotatably mounted on bridge  56  about an axis A 5  parallel to main axis A 1  and advantageously materialized by a screw helically engaged with bridge  56 . 
     Correction device  66  includes a winding mechanism  70  provided with a stem  71  mounted in a sliding pivot arrangement about and along a winding axis A 6  perpendicular to main axis A 1 , and with a crown  72  integral in rotation with stem  71 . The stem passes through case middle  3  and the crown is accessible to the user. 
     According to a particular embodiment illustrated in  FIG. 8 , correction device  66  includes a toothed, intermediate, phase wheel (hereinafter more simply referred to as intermediate phase wheel  73 ) which meshes with transmission wheel  57  and via which, in the moon phase adjustment position, sliding pinion  67  meshes with the transmission wheel. The intermediate phase wheel is rotatably mounted on the bridge about an axis A 7  materialized by a screw helically engaged with bridge  56 . 
     Correction device  66  also includes a sliding member  74  provided with a winding pinion  75  (for example with a Breguet toothing) and a sliding pinion  76 , mounted in a sliding pivot arrangement about and along winding axis A 6 , and coupled to winding mechanism  70 , for example by a traditional pull out piece and lever mechanism (not represented), between:
         a correction position ( FIG. 7  and  FIG. 8 ) in which sliding pinion  76  is coupled to carrier pinion  68 , and   a position of release in which sliding pinion  76  is uncoupled from carrier pinion  68  (and in which winding pinion  75  is coupled to a winding pinion that is not represented, via which the mainspring of watch  1  is wound by rotating winding crown  72 ).       

     Transmission of the rotation of winding mechanism  70  to carrier pinion  68  is advantageously achieved via an intermediate train, which typically includes a first intermediate wheel  77 , meshed with sliding pinion  76 , and a second intermediate wheel  78 , inserted between the first intermediate wheel and the carrier pinion. 
     Finally, in an embodiment illustrated in particular in  FIG. 2  and  FIG. 4 , mechanism  8  includes a covering  79  in the form of a disc integral with moon bearing  32  (and for example sandwiched between meridian wheel  33  and moon cover  34 ). Covering  79  has an opening  80  of circular shape inside which is housed sphere  9 . This covering, which rotates with moon bearing  32 , is intended to symbolise the celestial vault. To this end, in the illustrated example, cover  79  carries symbols  81  (etched, painted, or in relief) representing a constellation of stars. 
     Correction of the lunar day display causes a rotation of sphere  9  about its axis A 3  and consequently a change in the moon phase display. This is why correction of the lunar day display must precede correction of the moon phase display. 
     Prior to any correction, cam  74  must be placed in the correction position, by pulling (in a conventional manner for the user or watchmaker) winding crown  72 , which pushes sliding pinion  76  towards first intermediate wheel  77  to place them in mesh. 
     To correct the lunar day display, winding crown  72  must be rotated in a determined direction which depends on the number of pinions in intermediate train  77 ,  78 . In the embodiment illustrated in  FIG. 7 , the winding crown must be rotated in the clockwise direction seen along winding axis A 6 . 
     Rotation of winding crown  72  then drives, via intermediate train  77 ,  78 , carrier pinion  68  in the clockwise direction (seen from above), which also tends to pivot connecting rods  69  in the clockwise direction and causes (or maintains) the meshing of sliding pinion  67  with moon wheel set  52 . 
     The clockwise rotation of carrier pinion  68  then successively drives in rotation:
         sliding pinion  67 , meshed with carrier pinion  68 , in the anticlockwise direction;   moon wheel set  52 , meshed with sliding pinion  67 , in the clockwise direction,   moon bearing  32 , whose meridian wheel  33  is meshed with upper wheel  54  of the moon wheel set, in the anticlockwise direction.
 
As a result, sphere  9  is driven in a movement of revolution about main axis A 1  in the anticlockwise direction. All these movements are illustrated by the arrows in  FIG. 7 .
       

     It will be noted that, during the lunar day correction, the resulting torque C 2  which is exerted on auxiliary wheel  43  exceeds friction torque CF, such that, while first rotating element  25  remains rotationally immobile about axis A 1  (since it is blocked by motion work  13 ), indent  46  yields and allows the auxiliary wheel to slide relative to pipe  27  at their interface  45 . 
     The rotation of the winding crown  72  is stopped when the angular position of radial axis A 3  of sphere  9  about main axis A 1  is deemed to be correct, which ends the lunar day display correction. 
     The moon phase display must then be corrected. To do so, winding crown  72  must be rotated in the opposite direction to the direction followed during correction of the lunar day display. In the example illustrated in  FIG. 8 , winding crown  72  must be rotated in the anticlockwise direction seen from along winding axis A 6 . 
     The rotation of winding crown  72  drives, via intermediate train  77 ,  78 , carrier pinion  68  in the anticlockwise direction (seen from above), which also tips connecting rods  69  in the anticlockwise direction until sliding pinion  67  meshes with intermediate phase wheel  73 . 
     As the rotation of winding crown  72  continues, the anticlockwise rotation of carrier pinion  68  successively drives in rotation:
         sliding pinion  67 , meshed with carrier pinion  68 , in the anticlockwise direction;   intermediate phase wheel  73 , meshed with the sliding pinion, in the clockwise direction.       

     As soon as torque C 2  attains jump torque CS (which the user or watchmaker&#39;s fingers are quite capable of causing to happen), transmission wheel  57 , whose toothing  58  is meshed with intermediate phase wheel  73 , is itself driven in rotation in the clockwise direction. All these movements are illustrated by the arrows in  FIG. 8 . 
     However, jump torque CS is lower than the friction torque CF of second rotating element  42  on first rotating element  25 . Consequently, despite the rotation of transmission wheel  57 , the second rotating element remains immobile, since it is integral in rotation with the first rotating element, which is locked by motion-work  13 . 
     Consequently, the jumper or jumpers  59  is/are shifted radially and jump from one tooth to the next as transmission wheel  57  rotates, as illustrated in dotted lines in  FIG. 9 . 
     Central wheel  49 , integral in rotation with transmission wheel  57 , is driven, with its toothing  50 , in rotation about axis A 1  in the clockwise direction. As moon bearing  32  remains immobile, this rotation of the central wheel causes, via moon pinion  41  with which it meshes, rotation of sphere  9  about its radial axis A 3 , in the clockwise direction (seen from along axis A 3 ). 
     In a first variant, by adding, for example, an additional wheel set to the moon phase correction train between the transmission wheel and the sliding pinion, the sphere then rotates in the anticlockwise direction, which corresponds to its direction of rotation in normal operation. In a second variant, assuming that, during a lunar day correction, sphere  9  is driven in a movement of revolution about main axis A 1  in the clockwise direction, then the additional wheel set can be inserted in the kinematic chain of correction device  66 . By way of alternative, in a third variant, one wheel set is removed from the kinematic chain of correction device  66 . Finally, it is also possible to obtain a moon phase correction by reversing the relative position of the moon wheel set and the transmission wheel, the moon phase correction would then be made by rotating the crown in the clockwise direction, whereas the lunar day correction would be made by rotating the crown in the anticlockwise direction. 
     When star wheel  47  has 29 or 30 teeth, each jump of jumper spring(s)  59  from one tooth to the other corresponds to a correction of one day. When the star wheel has 59 teeth, each jump of the jumper spring(s) from one tooth to the other corresponds to a half-day correction. The wearer or watchmaker is informed of this correction (of one day or respectively a half-day) by the click sound that accompanies the jump of the jumper spring(s). 
     Once corrections to the lunar day display and the moon phase display are completed, the wearer pushes winding crown  72  back in, which moves cam  74  in translation, uncoupling sliding pinion  76  from first intermediate wheel  77 . 
     During normal operation of watch  1 , it is not inconvenient for sliding pinion  67  to remain meshed with moon wheel set  52  (as illustrated in  FIG. 5 ) or with intermediate phase wheel  73 , since winding mechanism  70  is uncoupled from carrier pinion  68 . 
     It is seen that the correction device  66  presented above makes it possible, in a simple, efficient, precise and reliable manner, to correct the lunar day and moon phase in mechanism  8 . For the wearer or the watchmaker, the direction of rotation alone determines the correction applied.