Classifications

• • G—PHYSICS
  • G04—HOROLOGY
  • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
  • G04B17/00—Mechanisms for stabilising frequency
  • G04B17/04—Oscillators acting by spring tension
  • G04B17/045—Oscillators acting by spring tension with oscillating blade springs

Definitions

• the present invention relates to a watch component with a flexible pivot.
• the flexible pivot watch components are designed to rotate without a physical axis of rotation, thus without friction, around a virtual axis of rotation, thanks to an arrangement of elastic parts.
• the present invention relates to the first type of flexible pivots, namely the separate cross-leaf pivots. These pivots are known for their low stiffness, which allows their use in parts of a watch movement where little energy is available.
• a separate crossed-blade pivot comprises two resilient blades which connect a fastening portion of the component to a movable portion of the component and which extend in two respective parallel planes to cross each other without contact. Examples of such pivots are described in US Patents 3,520,127 and DE 201,823 and patent applications EP 2 91 1 012, EP 2 998 800 and WO 2016/096677.
• the patent application EP 2 91 1 012 describes a timepiece oscillator with separate crossed blades whose blades intersect at 7/8 th of their length in accordance with the theory developed by WH Wittrick. This intersection of the blades to 7/8 th of their length has the effect of minimizing the movements of the virtual axis of rotation and thus to make the frequency of the oscillator independent of the orientation of the watch relative to gravity.
• the patent application WO 2016/096677 teaches that with an angle between the elastic blades between 68 ° and 76 °, and preferably equal to 71.2 °, the moment resulting from the action of the blades can be linear as a function of the rotation angle of the moving part, thus making the frequency of the oscillator independent of the amplitude of oscillation.
• the present invention aims to meet this need and proposes for this purpose a flexible pivoting watch component, in particular an oscillator, comprising a fixing part, a movable part and first and second elastic strips connecting the fixing part and the moving part. , the first and second resilient blades extending in respective parallel planes and intersecting without contact to define a virtual axis of rotation of the movable portion relative to the attachment portion, characterized in that at least one of the first and second elastic blades has a stiffness that varies along the blade.
• the present invention provides a timepiece component according to claim 1, 5 or 13, particular embodiments being defined in the dependent claims.
• FIGS. 1 and 2 are respectively a top view and a perspective view of a pivot oscillator oscillator with split blades separated according to a particular embodiment of the invention
• FIG. 3 is a graph, obtained by numerical simulation, showing the optimal position t of the point of intersection of the blades of the flexible pivot. (ie the position that makes the oscillator insensitive to gravity) as a function of the ratio r between the thicknesses at the ends of each blade, in the case of blades having a thickness that varies linearly;
• FIG. 4 is a graph, obtained by numerical simulation, showing the equivalent stress exerted on the blades during a rotation of
• FIG. 5 is a graph, obtained by numerical simulation, containing four curves representing, each for a respective angle between the blades, the pairs (r, t) for which the frequency of the oscillator is independent of the amplitude of oscillation. , and further containing the gravity-insensitivity curve already illustrated in FIG.
• a watch oscillator with a flexible pivot 1 for a timepiece such as a wristwatch, comprises a fixing part 2 and a movable part 3 which surrounds the part of fixation 2.
• the fixing part 2 serves to mount the oscillator 1 on a fixed or mobile support of a clock mechanism, and comprises for this purpose two fixing lugs 2a, 2b intended to be attached to this support, this support being able to for example be a plate or an exhaust member.
• the movable portion 3 oscillates relative to the attachment portion 2 and thus plays the role of a pendulum.
• the fixing portion 2 and the movable portion 3 are connected by first and second elastic strips 4, 5 of the same length which extend in two respective planes parallel to the plane of the oscillator 1 and which intersect without contact to define a virtual axis of rotation A of the mobile part 3 relative to the fixed part 2.
• This virtual axis of rotation A is constituted by the line forming the intersection of the surfaces passing through the neutral fibers of the elastic strips 4, 5 and perpendicular to the plane of the oscillator 1 when the movable part 3 is in its equilibrium position. It corresponds, in top view, to the point of intersection of the elastic blades 4, 5.
• Oscillator 1 is associated with an escapement (not shown) which may be of conventional type such as a Swiss lever escapement or any other type.
• the resilient blades 4, 5 are typically straight in the idle state, as shown. They could nevertheless be curved.
• the center of mass of the mobile part 3 is on the virtual axis of rotation A.
• the fixing portion 2 comprises rigid parts
• the attachment portion 2 could be completely rigid.
• the two fixing lugs 2a, 2b could also be completely separated.
• Each elastic blade 4, 5 is joined at its ends to the fixing portion 2 and to the movable part 3 either directly or, as shown, by means of connectors 6 which soften the edges between the lateral faces of the elastic strips 4, 5 and parts 2, 3. In the present invention, such connectors 6 are not considered to be part of the resilient blades 4, 5.
• the section of each resilient blade 4, 5 varies along the blade.
• variation of the section is meant a variation of the size and / or shape of the section.
• Such a section variation causes a variation in stiffness along the blade and therefore changes the distribution of stresses in the blade when it works. This makes it possible to adjust certain characteristics of the oscillator.
• the shape of the section of each elastic blade 4, 5 remains constant, typically rectangular, but its thickness e varies along the blade.
• the thickness is the dimension of the blade in a plane parallel to the plane of the oscillator and perpendicular to the neutral fiber of the blade.
• the height that is to say the dimension of the blade perpendicular to the plane of the oscillator (parallel to the virtual axis of rotation A), is typically constant but it can also vary.
• the thickness e is the same for each elastic blade 4, 5 and varies linearly from one end to the other being greater at its end attached to the fixing portion 2 at its end. attached to the moving part 3.
• the ratio between the thickness e at the end attached to the movable part 3 and the thickness e at the end attached to the fixing part 2 is called r.
• the movable portion 3 may have a smaller diameter and the size of the oscillator 1 can be reduced.
• the position t of the point of intersection of the elastic blades 4, 5 is at least 14%, preferably at least 15%, preferably at least 16%, preferably at least 17%, preferably at least 18%, preferably at least 19%. It may advantageously be between 17 and 21%, more particularly between 18 and 20%.
• the graph of FIG. 4 shows the equivalent Von Mises stress (in MPa) experienced by the flexible pivot, that is to say by the combination of the two elastic strips 4, 5, for a 20 ° rotation of the movable part 3 with respect to the fixing part 2, as a function of the torques (r, t) situated on the curve of FIG. 3, the overall stiffness of the elastic blades 4, 5 being the same for each couple (r, t).
• the elastic return moment exerted by the flexible pivot 4, 5 on the movable portion 3 must be linear depending on the angle of rotation of the movable portion 3 relative to the fixing portion 2.
• the magnitude k be substantially constant, for example its variation in absolute value over a range of angles ⁇ ranging from 0 ° (equilibrium position of the moving part 3) to ⁇ 20 °, said variation being express by (k ( ⁇ 20 °) - k (0 °)) / k (0 °), ie less than 0.05% or even less than 0.02%.
• the graph of Figure 5 shows the influence on the isochronism of the angle ⁇ between the elastic blades 4, 5 (this angle is measured between the neutral fibers of the blades).
• the curve of FIG. 3 represents the pairs (r, t) for which the oscillator is insensitive to gravity, and curves J2 to J5 representing the pairs (r , t) for which the frequency of the oscillator is independent of the oscillation amplitude, more precisely for which the difference between the frequency of the oscillator at an oscillation amplitude of 20 ° and the frequency of the oscillator at an oscillation amplitude of 2 ° is minimal or zero.
• Each of the curves J2 to J5 corresponds to a respective angle a between the elastic blades, namely, for the curve J2 an angle of 70 °, for the curve J3 an angle of 80 °, for the curve J4 an angle of 90 °, and for curve J5 an angle of 100 °.
• the points of intersection between the curve J1 and the curves J2 to J5 define triplets (r, t, a) for which the oscillator is isochronous both with respect to gravity and with respect to oscillation amplitude.
• the oscillator can therefore have various configurations, each having its advantages and disadvantages with respect to others, in particular in terms of size, sensitivity to manufacturing tolerances, amplitude of oscillation or impact resistance.
• the angle ⁇ is at least 77 °, preferably at least 78 °, preferably at least 79 °.
• the angle a is for example between 77 ° and 83 °.
• the thickness of each resilient blade 4, 5 varies non-linearly. Preferably, however, the thickness of each resilient blade 4, 5 varies monotonically (increasing or decreasing) from one end to the other of the blade. More preferably, the thickness of each elastic blade 4, 5 varies strictly monotonically (without interruption of variation) from one end to the other or at least on a continuous portion of the blade representing 25%, preferably 30%, preferably 35%, preferably 40%, preferably 45%, preferably 50%, preferably 55%, preferably 60%, preferably 65%, preferably 70%, preferably 75%, preferably 80%, preferably 85%, preferably 90%, preferably 95%, of the length of the blade, this length being rectilinear or curvilinear according to the shape, straight or curved, resilient blades 4, 5 at rest.
• the thickness may also vary so that it is smaller at one end than the other, but non-monotonically between the two ends.
• the resilient blades 4, 5 may be identical or different, have the same stiffness being different, or have different stiffness.
• the oscillator according to the invention can be manufactured in a monolithic manner, for example in silicon or in any other suitable material according to the technique of deep reactive ion etching (DRIE), nickel, nickel alloy or any other suitable material according to the LIGA technique (lithography, electroplating, molding), steel, copper-beryllium, nickel silver or other metal alloy by milling or electro-erosion, or metal glass by molding.
• DRIE deep reactive ion etching
• the oscillator, or only the elastic blades 4, 5 may be covered with a layer of silicon oxide (SiO 2) to increase its mechanical strength and / or to exert a function of thermal compensation.
• SiO 2 silicon oxide
• Such monolithic fabrication is particularly suitable for oscillators intended to operate at high frequencies.
• the oscillator formed monolithically inertial parts, such as a serge and / or weights, made of a denser material than that of the oscillator, as described in the application EP 2 91 1 012.
• the oscillator according to the invention may comprise more than two elastic blades.
• it may comprise a second pair of elastic blades superimposed on the first pair of resilient blades 4, 5 and whose two blades intersect on the virtual axis of rotation A, to increase the stiffness of the flexible pivot out of the plane of rotation. the oscillator.
• the present invention can be applied to other watch components that an oscillator, for example to an escapement anchor, a lever or a rocker, to facilitate the optimization of their characteristics.

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• 2017
  • 2017-11-17 WO PCT/IB2017/057209 patent/WO2018109584A1/fr unknown
  • 2017-11-17 EP EP17809039.5A patent/EP3555708B1/de active Active

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