Patent Publication Number: US-6698918-B2

Title: Method for fixing jewels in a watch movement part and device for implementing the same

Description:
The present invention concerns a method for setting and fixing jewels in parts of a watch movement, allowing both the relative positioning accuracy of the wheels to be increased and the cost price of the finished product to be reduced. 
     In high quality watch movements, in order to reduce friction and increase the longevity of the product, jewels or rubies are used essentially for the shoulders of the staffs of certain wheels, designated bearings, end-stones or cup-bearings, and as regards the escapement, for the entry and exit pallets of the lever escapement and for the impulse-pin. There currently exist different techniques for fixing these jewels in the appropriate places, such as the plate, bridge, escapement lever and roller plate, but the most common, it may be said since the beginning of the horological industry, consists in driving the jewel either into a setting, or more often directly into a housing machined in the part intended to receive said jewel. Tolerances both as regards the jewel and the housing have to be very low, of the order of 5μ, in order to prevent the jewel deforming the housing or conversely having any play during use. For bearings, it is also imperative to have perfect vertical positioning of the drilled hole, which is not necessarily obtained by driving in the jewels given that they generally have rounded edges. Likewise, precise positioning along the vertical axis is also necessary so that two facing bearings, or two facing end-stones respect the distance-of-centres provided for the wheels which they support, which requires precise machining both of the thickness of the jewel and of the bottom of the housing. Moreover, this requirement for accuracy is also necessary for the relative positioning of the drilled holes for the bearings arranged in a same plane and intended to receive gear-wheel pivots. This spatial positioning is also of very high importance as regards the escapement jewels, impulse pin and pallets, which are currently driven in and/or bonded. Driving in jewels inevitably causes a deformation in the roller-table which then has to be rectified by diamond polishing and bonding also necessitates a machining operation in order to remove the surplus of the adhesive material used. 
     In order not to be tied to such a high level of accuracy and to avoid the drawbacks of driving in the jewels, Swiss Patent No. 384 473 proposes a cam device allowing an end-stone to be wedged in two hollows in the wall of the housing. The device disclosed in Swiss Patent No. 362 286 proposes a similar device formed by a bayonet assembly device. Other devices propose means for wedging a jewel via elastic rings locking into grooves in the wall of the recess. It is clear that such devices permit lower tolerance requirements as regards machining the jewel and the housing, but they are not entirely satisfactory as regards the spatial positioning of the jewels and securing them to their support. 
     As regards the machines or robots which set and secure the jewels, to the best of the Applicant&#39;s knowledge, these are driving techniques such as those disclosed for example in Swiss Patent Nos. 378 242 and 417 479. 
     The object of the present invention is to overcome the drawbacks of the aforecited prior art by transferring the requirement for accuracy to a setting device and relying on laser technology to secure the jewels in their housing. 
     The invention thus concerns a method allowing jewels to be secured in parts of a watch movement by laser beam by means of a setting device. “Parts” means the fixed parts of a watch movement, such as the plates and bridges, or the moving parts such as the escapement, the jewels then being designated bearings, end-stones, impulse pins or pallet-stones. These jewels are obtained synthetically, from a fine alumina powder and machined essentially by diamond polishing to make them at the dimensions of the housing in which they are currently secured by being driven therein. The method according to the invention consists however, in using a setting device very precisely, with respect to a reference surface of the part wedged onto the setting device, the spatial position of the jewel with respect to its housing whose machining tolerances will therefore be able to be much less strict. 
     The method consists in: 
     a) providing the setting device with spatial positioning means for one or several jewels with respect to one or several reference planes of said setting device and means for wedging a part, 
     b) wedging the part in which the jewel is to be set on the setting device, 
     c) putting one or several jewels in the respective housings securing their spatial position in the part with the positioning means of the setting device, 
     d) focusing and moving a laser beam tip on the points of abutment of the jewel against the wall of a housing, on the periphery of the opening of a housing or on a fusible material added around said opening so as to secure the jewel to the housing, and 
     e) releasing and removing the part from the setting device. 
     When the jewels are intended for pivoting wheels, and in particular when they are jewel holes, otherwise designated “bearings”, the positioning means are formed by studs anchored in the surface of the setting device and passing through a through passage provided at the bottom of the housing. The diameter of the distal part of the stud is substantially equal to the diameter of the hole of the bearing. The part anchored in the setting device may have the same diameter than the distal part, the jewel resting on the bottom of the housing which then will have to be machined to a very precise dimension. The part of the stud anchored can also have a larger diameter than the distal part allowing a shoulder to be provided for vertically positioning the jewel with respect to the reference surface of the part, independently of the accuracy of manufacture of the bottom. 
     For prismatic jewels, such as escapement pallets or escapement impulse-pins, the setting device includes positioning means which are reversed with respect to those previously cited, namely cavities arranged in the surface of the setting device and in which the jewels can be temporarily immobilised with great precision by locking means, such as locking screws or spring pins. 
     Depending on the shape of the parts in which the jewels are to be set, it may be necessary to provide a setting device with several levels. 
     Of course, the spatial positioning accuracy of the jewels also depends on the wedging accuracy of the jewel, such accuracy can be obtained for example by means of stops arranged on an edge of the part, or by means of studs passing through it, these wedging means being mounted with precision on the setting device. 
     As will be indicated in more detail in the following examples, once the jewel has been positioned, it is definitively secured in the housing by means of a laser beam allowing the jewel to be welded to the wall, or the small play existing between the outer edge of the jewel and the wall to be filled either by melting an edge above the opening, in a single piece with the part, or by melting an added fusible material. 
    
    
     Other features and advantages of the present invention will appear more clearly upon reading the following detailed description of implementation examples of the method, given purely by way of non-limiting illustration, with reference to the annexed drawings, in which: 
     FIG. 1 shows a schematic cross-section of the setting of a bearing according to a first embodiment; 
     FIG. 2 shows a variant of the setting shown in FIG. 1; 
     FIGS. 3A and 3B shows schematic cross-sections of the setting of a bearing according to a second embodiment; 
     FIGS. 4A and 4B show schematic cross-sections of the setting of a bearing according to third embodiment; 
     FIG. 5 is a top view of a setting for a part having three bearings; 
     FIG. 6 shows the cross-section along the line VI—VI of FIG. 5; 
     FIG. 7 shows a bottom view of an escapement roller-table; 
     FIG. 8 shows a top view of the setting device for the escapement roller-table shown in FIG. 7; and 
     FIG. 9 shows a cross-section along the line IX—IX of FIGS. 7 and 8 of a setting device according to the invention for the escapement impulse-pin. 
    
    
     FIGS. 1 to  4 B show a cross-section along the line I—I of FIG. 5 of several embodiments of the method according to the invention for fixing or setting a jewel hole  20 , more generally designated a “bearing” in a part  1  of a watch movement, such as a plate or a bridge. In all the Figures, dimensions have been greatly exaggerated, given that the diameter of a bearing is of the order of a millimeter and relative dimensions have not necessarily been respected in order to make the drawings clearer. 
     With reference first of all to FIGS. 1 and 2, it can be seen that part  1  includes in its upper face  1   a  a housing  3  delimited by a wall  4  and the bottom of which includes a through passage  5  joining lower face  1   b.  The diameter of this through passage is generally much greater than the drilled hole of bearing  20  to give access to an oil sink  21 . Part  1  is placed on a setting device including a base  11  whose perfectly polished upper surface forms a reference plane  13  for the horizontal x, y co-ordinates. Reference plane  13  includes at least a stud  15  the lower part  17  of which is anchored in base  11 , as shown, or it can be in one piece with said base  11 . Distal part  16  of stud  15  extends at least as far as upper face  1   a  of part  1  and its diameter is substantially equal to the drilled hole of bearing  20  which has to be placed in the housing, i.e. ideally with no play allowing a movement of translation of the stud in the drilled hole. Reference plane  13  also includes means for wedging part  1  in the x, y referential, these means being for example stops  19  or a stud  9 , as shown in FIG.  6 . Bearings  20  are then threaded onto studs  15  and placed in their respective housings  3 , with a slide fit, i.e. with a fit which would be insufficient in itself to guarantee sufficient hold for use. In the corresponding embodiments of FIGS. 1 and 2, studs  15  thus allow the relative position of bearings  20  to be fixed in reference plane  13  with respect to the wedging of part  1  on the setting device, and also with respect to each other, as shown in the schematic view of FIG.  5 . FIG. 5 shows, by way of example, a top view of a setting device  11  supporting a part  1  including three bearings  20   a,    20   b,    20   c,  positioned very precisely in the x, y plane by studs  15   a,    15   b,    15   c  while being able to have a certain lateral play  24  with respect to wall  4  of housing  3 , as shown for example in FIGS. 4A and 4B. 
     In the embodiment shown in FIG. 1, spatial positioning along the vertical axis z is obtained via the manufacturing accuracy of the flange  1   c  of the bottom of housing  3 , on which the outer shoulder of jewel  20  rests and via the manufacturing accuracy of the jewel thickness. 
     In the embodiment shown in FIG. 2, spatial positioning along vertical axis z is obtained via a shoulder  18  of stud  16  located between its part  17  anchored in base  11  and its distal part  16 . As can be seen, bearing  20  is positioned with sliding friction in housing  3  possibly leaving a free space  22  between flange  1   c  and the bottom of bearing  20 . Thus, in this embodiment, the spatial referential for bearings  20  is formed solely by the setting device. 
     Once bearings  20  have been set in place with sliding friction in part  1 , the contour of the opening is traced by a laser beam so as to create a melting zone  6  between the edge of bearing  20  and wall  4  of housing  3 . 
     In a known manner, the watch movement “part” plate or bridge, is generally of metal, such as brass, or steel and the jewel is a synthetic stone cut from a cylinder of corundum. According to a preferred embodiment, in order to increase the cohesion between these two categories of material, a deposition of titanium dioxide is made beforehand on wall  4  of housing  3 , for example by using chemical vapour deposition (CVD) technology. 
     Once the jewels are secured to the part, one need only remove the part from the setting device, all the accuracy requirements as regards the position of the bearings being in a way transferred from the setting device to the part. Of course, this method enables the same setting device to be used to set jewels in a large number of parts, which allows the unit cost of the parts to be reduced, given that it is no longer necessary to machine them individually with great accuracy. 
     In the embodiment of the method shown in FIGS. 3A and 3B, the setting device is the same as that shown in FIG.  1 . However, it can be seen in FIG. 3A that the periphery of housing  3  includes an edge  7   a  integral with part  1 , this edge  7   a  may be continuous as shown, or discontinuous. After laser beam  30  has been applied, edge  7   a  is bent down towards the centre of housing  3  to form a raised portion  7   b  which holds bearing  20  at the bottom of housing  3 . FIGS. 4A and 4B show an embodiment wherein the setting device is the same as that shown in FIG. 2, but differs from it in that bearing  20  is positioned solely by stud  15  by arranging a small space  22  between the bottom of housing  3  and another space  24  between the wall. In other words, these spaces  22 ,  24  allow very wide tolerances to be obtained for the manufacture of housing  3  and for the manufacture of bearing  20 . Bearing  20  is immobilised in housing  3  by adding a cord  8  of fusible material onto the periphery, such as silver or a silver and lead, tin or indium based composition. When laser beam  30  is applied, fusible material  8  forms a mass  8   b  which infiltrates spaces  22 ,  24  and locks bearing  20  in the spatial position determined by stud  15 . 
     The top view of FIG.  5  and the cross-section of FIG. 6 show by way of example a portion of part  1  including three bearings  20   a,    20   b,    20   c,  the relative positioning of whose pivoting holes is determined by three studs  15   a,    15   b,    15   c  anchored in base  11  of the setting device. It can also be seen that part  1  is wedged on the setting device by means of a stud  9 , anchored in base  11 , and two steps  19 , these wedging means being given by way of example, since it is obviously possible to envisage other equivalent ones. 
     FIGS. 7 to  9  show an embodiment of the method wherein the setting device allows an impulse pin of an escapement roller-table to be fixed. 
     FIG. 7 shows a bottom view of such a roller-table  2  which includes in a known manner a large roller plate  26 , having close to its edge and perpendicular to its plane, a housing  23  which passes right through it to accommodate an impulse pin  10  (not shown), joined by a sleeve  27  to a small roller-table  28  provided with a notch  28   a.    
     FIG. 8 shows a top view of setting device  12  the structure of which will be better understood with reference also to FIG. 9 which shows a cross-section along the line IX—IX of FIGS. 7 and 8, escapement roller-table plate  2  set in place on setting device  12 . This device includes a first reference plane  13 , provided with a stud  9  which passes through sleeve  27 , reference plane  13  acting as a support for the base of small roller-table  28 . The setting device also includes a second reference plane  14 , parallel to plane  13 , at a level corresponding to the distance which separates the base from small roller-table  28  and the lower surface of large roller-table  26 . The wall which joins the two reference planes  13 ,  14  includes a raised portion  29  having the same shape as notch  28   a  and forming with stud  9  the means for wedging escapement roller-table  2 . Of course, other wedging means may be envisaged. The second reference plane  14  includes a cavity  25  intended to accommodate and position a jewel forming the impulse pin. In the example shown, half-moon shaped jewel  10 , temporarily immobilised by means of a locking screw  31  of parallel axis to reference planes  13 ,  14 . Once jewel  10  has been immobilised spatially on the setting device, one need only set escapement roller-table  2  in place and secure jewel  10  by laser beam according to one of the previously indicated embodiments. Since jewel  10  is mounted with play or sliding friction, no mechanical stress is imposed on the very thin external wall of housing  23 , so that no subsequent machining is necessary. The driving in technique would have produced a deformation of the edge of the large roller-table at the location of the housing so that it would have been necessary to perform a diamond polishing operation which eventually leads to at least 50% of the parts being discarded. The method according to the invention saves a machining operation and allows a greater percentage of conforming parts to be produced. 
     By adapting the method which has just been described for an escapement roller-table, those skilled in the art can design without any difficulty a device for setting and fixing pallet stones by means of a laser beam.