MOBILE TURNING SYSTEM OF A CLOCK MOVEMENT

Description

Scope of the invention

[0001] The present invention relates to a rotating moving system of a clockwork movement, in particular a resonator mechanism. The invention also relates to a clockwork movement equipped with such a rotating system. Background of the invention

[0002] In watch movements, the shafts of rotating parts generally have pivots at their ends, which rotate in bearings mounted in the mainplate or in the bridges of a watch movement. For certain parts, particularly the balance wheel, it is common practice to equip the bearings with a shock-absorbing mechanism. Indeed, since the pivots of a balance wheel shaft are generally thin and the mass of the balance wheel is relatively high, the pivots can break under the effect of an impact without a shock-absorbing mechanism.

[0003] The configuration of a conventional shock-absorbing bearing 1 is represented by the figure 1An olive-shaped domed stone 2 is driven into a bearing support 3 commonly called a chaton, on which a counter-pivot stone 4 is mounted. The chaton 3 is held against the bottom of a bearing block 5 by a damping spring 6 arranged to exert an axial force on the upper part of the counter-pivot stone 4. The chaton 3 also has a conical outer wall arranged to correspond with a conical inner wall located at the periphery of the bottom of the bearing block 5. There are also variants in which the chaton has an outer wall with a convex, i.e., domed, surface.

[0004] However, the frictional torque on the axis due to the weight of the object varies depending on the object's orientation relative to gravity. These variations in frictional torque can lead to a variation in the amplitude of oscillation for the pendulum. Indeed, when the object's axis is perpendicular to gravity, its weight rests on the hollow stones, and the frictional force generated by the weight has a lever arm with respect to the axis equal to the radius of the pivot. When the object's axis is parallel to gravity, the weight rests on the end of the pivot. In this case, if the end of the pivot is rounded, the frictional force generated by the weight is applied to the axis of rotation and therefore has a zero lever arm with respect to the axis.These differences in lever arm generate differences in friction torque, which can also generate differences in speed if isochronism is not perfect.

[0005] To control this problem, another damping bearing configuration was devised, partly shown on the figure 2The bearing has a thrust bearing 7, comprising a cavity 8 to receive a pivot 12 of the axis 9 of the rotating part. Such a cavity may be pyramidal in shape, with the base of the cavity formed by the apex 11 of the pyramid. The pivot 12 is conical to fit into the cavity 8, but the solid angle of the pivot 12 is smaller than that of the cavity 8. This configuration makes the lever arm of the friction force almost zero in all directions relative to gravity, assuming that the pivot 12 remains perfectly centered in the cavity 8. To achieve this, it is generally necessary to pre-constrain the system, for example with a spring-mounted bearing that constantly presses on the pivot. However, this spring adds to the weight of the rotating part and increases friction. Furthermore, it is difficult to guarantee a good surface finish on the base of the cavity, as it is difficult to access by polishing. Summary of the invention

[0006] One aim of the invention is, therefore, to propose a mobile system for a clockwork movement that avoids the aforementioned problem.

[0007] For this purpose, the invention relates to a mobile system comprising a rotating mobile according to the terms of the attached claim 1.

[0008] Thanks to the invention, the variation in friction between horizontal and vertical positions relative to gravity is reduced. By choosing a contact angle less than or equal to arctan 1 2 The frictional torque due to weight at the contact between the pivots and the bearing cavities is essentially the same regardless of the direction of gravity. Indeed, such an angle compensates for variations in contact force due to changes in orientation relative to gravity by providing different lever arms of the frictional force on the two bearings.

[0009] Thus, this counter-pivot configuration allows for minimal variation in the friction torque of the pivots within the counter-pivots, regardless of the axis's position relative to gravity. This is important, for example, for a balance staff in a watch movement. The pyramidal shape of the cavity, as well as that of the pivot, minimizes the difference in friction torque between the various positions of the axis relative to gravity.

[0010] According to the invention, the second bearing cooperates with the second pivot to allow the rotating mobile to rotate about its axis, the second bearing comprising a second pyramidal cavity having at least three faces, the second pivot being able to cooperate with the second cavity of the counter-pivot in order to be able to rotate in the second cavity, at least a second contact zone between the second pivot and a face of the second cavity being generated, the normal to the second contact zone forming a second contact angle with respect to the plane perpendicular to the axis of the second pivot, characterized in that the minimum contact angles of the two pivots and the two bearings are defined by the following equation, cotα h + cotα b = 4 cos π N ≥ 2 preferably, cotα h + cotα b = 4 cos π N ≥ 2 preferably cotα h + cotα b = 4 cos π N ≥ 2 , 5 or even cotα h + cotα b = 4 cos π N ≥ 3 , or even cotα h + cotα b = 4 cos π N ≥ 4 , Or N is the number of faces of the two pyramids.

[0011] According to an advantageous embodiment, the minimum contact angles ( α b , α h ) are defined by the following equations: Or N is the number of faces of the two pyramids, BH is the distance between the ends of the two pivots, GH is the distance between the end of the first pivot in contact with the first bearing and the center of mass of the balance wheel, and GB is the distance between the end of the second pivot in contact with the second bearing and the center of mass of the balance wheel.

[0012] According to the invention, the first contact angle ( α h ) is less than or equal to arctan 1 2 and the second contact angle ( α b ) is greater than or equal to arctan 1 2 .

[0013] According to an advantageous embodiment, it comprises as many contact zones as there are faces of the pyramidal cavity, with one contact zone per face.

[0014] According to an advantageous embodiment, the cavity comprises three or four faces.

[0015] According to an advantageous embodiment, the faces are at least partly concave or convex.

[0016] According to an advantageous embodiment, the first pivot has a conical shape.

[0017] According to an advantageous embodiment, the two minimum contact angles are equal.

[0018] According to an advantageous embodiment, the end of the pivot is defined by the intersection between the normal to the contact and the axis of the pivot.

[0019] According to an advantageous embodiment, the pivots have rounded ends.

[0020] According to an advantageous embodiment, the rounded ends of the two pivots have identical radii.

[0021] The invention also relates to a watch movement comprising a mainplate and at least one bridge, said mainplate and / or bridge comprising such a moving system. Brief description of the drawings

[0022] Other features and advantages of the present invention will become apparent from the reading of several embodiments given solely by way of non-limiting examples, with reference to the accompanying drawings in which: there figure 1 represents a cross-section of a shock-absorbing support bearing for the shaft of a rotating object according to a first embodiment of the prior art; the figure 2 schematically represents a counter-pivot of a bearing and a pivot of an axis of a rotating object according to a second embodiment of the prior art; the figure 3represents a perspective view of a rotating mobile system, here a resonating mechanism comprising a rotating moving part, such as a pendulum, according to a first embodiment of the invention; the figure 4 represents a cross-sectional view of the rotating mobile system of the figure 3 ; there figure 5 represents a pivot and a bearing according to the first embodiment of the invention; the figure 6 schematically represents a model of the bearings and pivots of a rotating mobile system according to the first embodiment of the invention; the figure 7 schematically represents a first embodiment of a bearing model comprising a four-sided pyramidal cavity, the figure 8 represents a graph showing the optimal contact angles for the two bearings and pivots for each position of the center of mass on the axis of the rocker arm of the first embodiment, the figure 9is a graph showing the difference in the optimal radii of the ends of the two pivots as a function of the position of the center of mass of the first embodiment, the Figure 10 represents a graph showing the optimal contact angles for the two bearings and pivots for each position of the center of mass on the balance wheel axis in a second embodiment in which the cavity has three faces, the figure 11 is a graph showing the difference in the optimal radii of the ends of the two pivots as a function of the position of the center of mass for the second embodiment, the figure 12 is a graph showing how the optimal angles vary as a function of the relative position of the center of mass, in a configuration of the first embodiment where the ends of the pivots are identical, the figure 13 is a graph showing the variation of εdepending on the relative position of the center of mass for the second configuration of the first embodiment, the figure 14 is a graph showing how the optimal angles vary as a function of the relative position of the center of mass, in a configuration of the second embodiment where the ends of the pivots are identical, the figure 15 is a graph showing the variation of ε depending on the relative position of the center of mass for the second configuration of the second embodiment. Detailed description of preferred embodiments

[0023] In the description, the same numbers are used to designate identical objects. In a watch movement, a bearing serves to support the axis of a rotating component, for example, a balance staff, allowing it to rotate around its axis. The watch movement generally comprises a mainplate and at least one bridge, not shown in the figures, said mainplate and / or bridge having an opening, the movement further comprising a rotating component and a bearing inserted into the opening.

[0024] THE figures 3 And 4They show a rotating mobile system equipped with a balance wheel 13 and a balance spring 14, the balance wheel 13 having a shaft 16. The shaft 16 includes a pivot 15, 17 at each end. Each bearing 18, 20 has a cylindrical bearing block 83 having a housing 14, a counter-pivot 22 arranged in the housing 14, and an opening 19 in one face of the bearing 18, 20, the opening 19 allowing passage for inserting the pivot 15, 17 into the bearing up to the counter-pivot 22. The counter-pivot 22 is mounted on a bearing support 23 and includes a cylindrical main body having a cavity configured to receive the pivot 15, 17 of the shaft 16 of the rotating mobile. The pivots 15, 17 of the axis 16 are inserted into the housing 14, the axis 16 being held while being able to rotate to allow the movement of the rotating mobile.

[0025] The two bearings 18 and 20 are shock-absorbing and also include an elastic support 21 for the counter-pivot 22 to dampen shocks and prevent the shaft 16 from breaking. An elastic support 21 is, for example, a flat spring with axial deformation onto which the counter-pivot 22 is mounted. The elastic support 21 is fitted into the housing 14 of the bearing block 13 and it holds the counter-pivot 22 in the housing 14. Thus, when the timepiece is subjected to a violent shock, the elastic support 21 absorbs the shock and protects the shaft 16 of the rotating mechanism.

[0026] In the implementation of figures 5 and 6 , the pivot 15, 17 has a first cone shape 26 substantially circular presenting a first opening angle 31. The opening angle 31 is the half-angle formed inside the cone by its external wall.

[0027] The cavity 28 of the counter-pivot 22 has a pyramidal shape with several faces 24. In the first embodiment of the figures 5 to 7The pyramidal cavity 28 has four faces 24. In a second embodiment, not shown in the figures, the pyramidal cavity has three faces. In other embodiments, the number of faces of the pyramid may be greater (5, 6, etc.).

[0028] The bottom of cavity 28 is truncated flat, but it can be pointed or truncated rounded, according to other embodiments. Cavity 28 has a second opening angle 32 at its apex. For the pivot 15, 17 to rotate within cavity 28, the second opening angle 32 is greater than the first opening angle 31 of the first cone 26. Preferably, the faces 24 of cavity 28 have the same orientation with respect to the axis of the pivot. In other words, the half-opening angle of cavity 28 is identical for all faces.

[0029] The pivot 15, 17 and the faces of the cavity 28 cooperate to form at least one contact zone 29. Preferably, the pivot is in contact with all the faces 24 of the cavity 28, thus creating a contact zone with each face 24, i.e., four for the first embodiment or three for the second embodiment. A contact zone 29 is defined by the portion of the face 24 of the conical pyramid in contact with the pivot 15, 17. The normals to each contact zone 29 are straight lines perpendicular to each contact zone 29. The normals form an angle, called the contact angle, with the plane perpendicular to the axis of the pivot. The normal corresponds to the straight line perpendicular to the face of the cavity 28. Thus, the contact angle is equivalent to half the opening angle of the cavity pyramid 28.

[0030] According to the invention, the contact angle is less than or equal to arctan 1 2 For this to work, the second angle must be less than or equal to 90°, preferably less than or equal to 60°, or even less than or equal to 2 ∗ arctan 1 2 = 53.13 ° .

[0031] These angle values ​​are calculated from equations modeling the friction of the pivots and bearings. To describe the formulas that give the optimal angles, the following geometric quantities are defined, sketched on the figure 6 : α b And α h are the angles between the faces of the cavity and the axis of symmetry of the cavities, for the lower and upper bearings; R b And Rh are the radii of the spherical caps at the ends of the pivots at the top and bottom of the balance wheel axis; B and H are the centers of the spherical caps at the ends of the pivots at the bottom and top of the balance wheel axis; G is the position of the center of mass, assumed to be on the right BH (balanced pendulum); µ b And µ h are the coefficients of friction at the bottom and at the top.

[0032] To evaluate the difference in friction as a function of gravity, the angle θ between the axis of the pendulum and gravity travels the entire interval [0°, 180°].

[0033] Two types of constraints are applied to the geometry of the moving system: C 1: no constraints on the radii R b And Rh and the angles α b And α h C2: For ease of manufacturing, it is required R b = R h , and we assume µ b = µ h .

[0034] We denote by Mfr,max, respectively Mfr,min, the maximum, respectively minimum, friction torque at all angles θ considered (i.e., the entire range [0°, 180°]). We seek to minimize the maximum relative variation of torque, defined by ε = M fr , max − M fr , min M fr , min

[0035] In case C1, for a rotating mobile axis equipped with two pivots, as schematically shown on the figure 6 , the contact angle ( α The optimal relationship between the pivot-bearing pairs is defined by the following equations: Or N is the number of faces of the two pyramids, BH is the distance between the ends of the two pivots, GH is the distance between the end of the first pivot (17) in contact with the first bearing (18) and the center of mass (G) of the balance wheel, and GB is the distance between the end of the second pivot (15) in contact with the second bearing (20) and the center of mass (G) of the balance wheel 2.

[0036] These equations are derived from a three-dimensional model of the contact between the pivot and the counter-pivot, in which the pivot end is modeled as a sphere. In the general case, B and H are defined by the intersection of the normal to the contact and the pivot axis. Preferably, the pivot ends are rounded, with B and H defined by the center of the sphere. Thus, the radius of the rounded end corresponds to the segment between the contact and the intersection of the normal to the contact and the pivot axis.15, 17

[0037] This relationship applies to pivots of different shapes. The radii R b And Rh rounded ends can be different from each other.

[0038] Thus, depending on the position of the center of mass G, the first cones of the two pivots 15, 17 can have different opening angles. But if they conform to this relationship, the variation in friction between the vertical and horizontal positions is reduced compared to other pivot and cavity geometries.

[0039] For the first four-sided embodiment, the graph of the figure 8 shows the optimal contact angles for both bearings and pivots for each position of the center of mass on the balance wheel axis.

[0040] The special case where the center of mass G is in the middle of B and H, and if the coefficients of friction are equal between the bottom and the top, then we have symmetrical bearings ( R b = R h ) , with α b And α h = approx. 35°. Thus, the desirable opening angle for pyramids is approximately 70°. In other cases, the contact angles of the two bearing-pivot pairs are different. We observe that one of the two contact angles always has a value less than or equal to 35°, and the other angle has a value greater than or equal to 35°. Another case where the center of mass is located one-third of the way along the axis of a first pivot: the optimal contact angle of this first pivot is 45°, while the second pivot has an optimal contact angle of 30°. Thus, the cavities have an opening angle of 90°, and the other pyramid has an opening angle of 60°.

[0041] Each optimal contact angle falls within a range from 20° to 90°. The smallest contact angle is that of the pivot closest to the center of mass.

[0042] The graph of the figure 9This shows the difference in the optimal radii of the ends of the two pivots as a function of the position of the center of mass. Thus, we observe that for a center of mass in the middle of the balance shaft axis, the radii are preferably equal for both ends.

[0043] For the second three-sided embodiment, the graph of the Figure 10 shows the optimal contact angles for the two bearings and pivots for each position of the center of mass on the balance shaft axis. The special case where the center of mass G is midway between B and H, and if the friction coefficients are equal between the bottom and the top, then we have symmetrical bearings ( R b = R h ) , with α b And α h =Approximately 45°. Thus, the desirable opening angle for cones is approximately 90°. In other cases, the contact angles of the two bearing-pivot pairs are different. We observe that one of the two contact angles always has a value less than or approximately equal to 45°, and the other angle has a value greater than or approximately equal to 45°. Another case where the center of mass is located at one-quarter of the length of the axis of a first pivot: the optimal contact angle of this first pivot is approximately 65°, while the second pivot has an optimal contact angle approximately equal to 35°. Thus, for conical cavities, we have one cone with an opening angle of 130°, and the other cone with an opening angle of 70°.

[0044] Each optimal contact angle falls within a range from 27° to 90°. The smallest contact angle is that of the pivot closest to the center of mass.

[0045] The graph of the figure 11 This shows the difference in the optimal radii of the ends of the two pivots as a function of the position of the center of mass. Thus, we observe that for a center of mass in the middle of the balance shaft axis, the radii are preferably equal for both ends.

[0046] In a second configuration of the mobile system, the two pivots have identical shapes to those of the first model ( R b = R h ) , such as the examples of figures 4 and 6 .

[0047] The graphs of Figures 12 and 13 show how the optimal angles and variation vary ε depending on the relative position of the center of mass for the first four-sided embodiment. In this case, one of the two angles always has a value less than or equal to arctan 1 2 = 26 , 6 approximately, and the other angle with a value greater than or equal to arctan 1 2 The special case where the center of mass G is midway between B and H, and if the coefficients of friction are equal between the bottom and the top, then we have bearings with α b And α h = arctan 1 2 = 26.6 ° approximately.

[0048] The graphs of Figures 14 and 15 show how the optimal angles and variation vary ε depending on the relative position of the center of mass for the second three-sided embodiment. In this case, one of the two angles always has a value less than or equal to arctan 1 2 = 26 , 6 approximately, and the other angle with a value greater than or equal to arctan 1 2 The special case where the center of mass G is midway between B and H, and if the coefficients of friction are equal between the bottom and the top, then we have bearings with α b And α h = arctan 1 2 = 26.6 ° approximately.

[0049] Examples of variation in friction torque as a function of orientation θare shown in Figure 16 for the first embodiment, and in Figure 17 for the second embodiment. The curves are symmetrical for an angle greater than 90°. Thus, for pivots of the same shape and radius, the point of symmetry of the curve is offset from 90°.

[0050] Regardless of the embodiment, the minimum contact angles of the two pivots and the two bearings, the minimum contact angles ( α h , α b The two pivots (15, 17) and the two bearings (18, 20) are defined by the following equation, cotα h + cotα b = 4 cos π N ≥ 2 preferably cotα h + cotα b = 4 cos π N ≥ 2 preferably cotα h + cotα b = 4 cos π N ≥ 2 , 5 or even cotα h + cotα b = 4 cos π N ≥ 3 , or even cotα h + cotα b = 4 cos π N ≥ 4 , Or N is the number of faces of the two pyramids. Indeed, to obtain the best results regarding the friction torque with the two bearings, the minimum contact angles ( α h , α b ) must answer these equations.

Claims

1. A rotary mobile system (10) for a horology movement, the system (10) comprising a rotary mobile, for example a balance (13), a first and a second bearing (18, 20), in particular shock absorbers, for a first and a second pivot (15, 17) of the axis (16) of the rotary mobile, the mobile component comprising a centre of mass (G) at one position on its axis (16), the first bearing (18, 20) comprising an endstone (22) comprising a main body with a pyramidal cavity (19) configured to receive the first pivot (17) of the axis (16) of the rotary mobile component, the cavity having at least three faces giving it its pyramidal shape, the first pivot (17) being capable of engaging with the cavity (19) of the endstone (22) so as to be able to rotate in the cavity (19), at least one contact zone (29) between the first pivot (17) and a face (24) being generated, the normal to the contact zone or zones (29) forming a contact angle (α) relative to the plane perpendicular to the axis (16) of the pivot (17), characterised in that the second bearing (20) engages with the second pivot (15) to allow the rotary mobile to rotate around its axis (16), the second bearing (20) comprising a second pyramidal cavity (89) comprising at least three faces (24), the second pivot (15) being capable of engaging with the second cavity (89) of the endstone (22) so as to be able to rotate in the second cavity (89), at least one second contact zone (90) being generated between the second pivot (17, 30) and a face on the second cavity (89), the normal to the second contact zone (90) forming a second contact angle (αb) relative to the plane perpendicular to the axis of the second pivot (15), characterised in that the minimum contact angles (αh, αb) of the two pivots (15, 17) and of the two bearings (18, 20) are defined by the following equation, cotα h + cota b = 4 cos π N ≥ 2 , preferably cotα h + cotα b , = 4 cos π N ≥ 2 , 5, or cotα h + cotα b = 4 cos π N ≥ 3 , or even cotα h + cotα b = 4 cos π N ≥ 4, wherein N is the number of faces on the two pyramids, the first contact angle (αh) is less than or equal to arctan 1 2 and the second contact angle (αb) is greater than arctan 1 2 .

2. The rotary mobile system according to claim 1, characterised in that the minimum contact angles (αh, αb) are defined by the following equations: wherein N is the number of faces on the two pyramids, BH is the distance between the ends of the two pivots, GH is the distance between the end of the first pivot (17) in contact with the first bearing (18) and the centre of mass (G) of the balance, and GB is the distance between the end of the second pivot (15) in contact with the second bearing (20) and the centre of mass (G) of the balance 2.

3. The rotary mobile system according to any of the preceding claims, characterised in that it comprises as many contact zones (29, 90) as there are faces (24) on the pyramidal cavity with one contact zone (29, 90) per face (24).

4. The rotary mobile system according to any of the preceding claims, characterised in that the cavity (28) comprises three or four faces (24).

5. The rotary mobile system according to any of the preceding claims, characterised in that the first pivot (17) has a conical shape.

6. The rotary mobile system according to any of the preceding claims, characterised in that the faces (24) are at least partially concave or convex.

7. The rotary mobile system according to any of the preceding claims, characterised in that the two contact angles (αb, ah) are equal.

8. The rotary mobile system according to any of the preceding claims, characterised in that the end of the pivot (15, 17) is defined by the intersection between the normal at the contact and the arbor of the pivot (15, 17).

9. The rotary mobile system according to any of the preceding claims, characterised in that the pivots (15, 17) have a rounded tip, the rounded tips of the two pivots (15, 17) having identical radii (Rb, Rh).

10. A horology movement comprising a plate and at least one bar, said plate and / or the bar comprising an orifice, characterised in that it comprises a rotary mobile system (10) according to any of the preceding claims.