EP3598241B1 - Clock mechanism having a constant-force device - Google Patents

Description

The present invention relates to a timepiece mechanism, in particular for a wristwatch or pocket watch, in which the escapement is powered by a so-called constant-force device.

Constant-force devices, also called remontoirs d'égalité, generally comprise, between the driving member (barrel spring) of the watch and the escapement wheel, an intermediate spiral spring which is periodically wound by the driving member and which drives the escape wheel. Examples of such devices are Gafner's remontoire or the constant-force device described in the document EP 2166419 . These devices make it possible to transmit to the escapement wheel a force which does not depend on the degree of winding of the driving member and thus to prevent the force received by the escapement and therefore by the oscillator from decreasing as the motor organ is disarmed.

Other types of intermediate spring than spiral springs have also been proposed. In the patent application CH 709914 , the intermediate spring is in the form of sinuous elastic arms which connect a pinion to a toothed serge, the pinion assembly - elastic arms - serge constituting a one-piece flexible escape wheel. In the patent application CH 704147 , there is proposed a one-piece energy transmission wheel set comprising rectilinear elastic arms which can be used as an intermediate spring for a constant-force device.

In all these so-called constant-force devices, the force delivered to the escapement is not in fact constant. It is the quantity of energy supplied to the escapement between two successive windings of the intermediate spring which is constant. The force decreases between two successive windings of the intermediate spring. The regularity of the oscillations of the oscillator is certainly much improved with such devices, but it remains disturbed.

The present invention aims to provide a watch mechanism with a constant-force device which mitigates this drawback.

To this end, a watch mechanism is provided comprising a motor member, an oscillator, an escapement to maintain the oscillations of the oscillator, an intermediate spring to supply the escapement with mechanical energy, one or more gears between the motor member and the intermediate spring and a blocking device allowing periodic winding of the intermediate spring by the motor member via the gear or gears, characterized in that the intermediate spring is a spring with non-linear behavior which produces, between a winding angle θ _a and a winding angle θ _b separated by at least 10°, an elastic restoring moment which does not vary by more than 10%, and in that the intermediate spring is pre-wound by a value θ _arm included in the range [θ _a , θ _b ], the timepiece mechanism being arranged so that, during its operation, the winding angle of the intermediate spring remains in the range [θ _a , θ _b ].

The present invention also proposes a timepiece, such as a wristwatch or a pocket watch, comprising this timepiece mechanism.

The intermediate springs of known constant-force devices, whether in the form of a spiral, sinuous elastic arms as described in CH 709914 or straight elastic arms as described in CH 704147 , all produce an elastic restoring moment which varies greatly, most often linearly, with the angle of lay. Unless you choose a very high winding frequency (very short duration between two windings), the variation in the elastic return moment will be significant and the effect will be perceptible at the level of the oscillator. In the present invention, an intermediate spring is used whose curve of the elastic return moment as a function of the winding angle is non-linear and has a plateau, the range of winding angles corresponding to this plateau being or including the operating range of the intermediate spring in the watch mechanism. Thus, the force delivered to the escapement is really substantially constant, unlike so-called constant-force devices of the state of the art.

• la figure 1 est une vue de dessus d'un mécanisme horloger à dispositif à force constante selon l'invention ;
• la figure 2 est une vue en coupe d'une partie du mécanisme horloger, prise suivant la ligne brisée C-C de la figure 1 ;
• la figure 3 est une vue de dessus d'un organe de liaison à ressort dit intermédiaire faisant partie du dispositif à force constante ;
• la figure 4 est une représentation graphique schématique illustrant l'allure de la courbe d'évolution du moment de rappel élastique exercé par le ressort intermédiaire dans l'organe de liaison ;
• la figure 5 représente les coordonnées de points définissant une forme particulière de bras élastique pour le ressort intermédiaire ;
• la figure 6 est une représentation graphique du moment de rappel élastique exercé par le ressort intermédiaire dans l'organe de liaison comprenant des bras élastiques de forme telle que représentée à la figure 5 ;
• la figure 7 est une vue de dessus d'un organe de liaison à ressort intermédiaire selon une variante de l'invention ;
• la figure 8 est une représentation graphique d'un moment de rappel élastique normalisé exercé par le ressort intermédiaire dans l'organe de liaison illustré à la figure 3 selon différentes variantes des bras élastiques du ressort intermédiaire, à savoir de tels bras à section constante (courbe A1) et de tels bras à section variable (courbes A2 à A4), la section variant selon un premier mode de variation ;
• la figure 9 est une représentation graphique d'un moment de rappel élastique normalisé exercé par le ressort intermédiaire dans l'organe de liaison illustré à la figure 3 selon deux variantes des bras élastiques du ressort intermédiaire, à savoir de tels bras à section constante (courbe B1) et de tels bras à section variable (courbe B2), la section variant selon un deuxième mode de variation ;
• la figure 10 est une représentation graphique du moment de rappel élastique exercé par le ressort intermédiaire utilisé dans l'invention et des moments de rappel élastiques exercés par cinq ressorts intermédiaires utilisés dans l'état de la technique.

Other characteristics and advantages of the present invention will appear on reading the following detailed description given with reference to the appended drawings in which:

• the figure 1 is a top view of a timepiece mechanism with a constant-force device according to the invention;
• the figure 2 is a sectional view of part of the watch mechanism, taken along the broken line CC of the figure 1 ;
• the picture 3 is a top view of a so-called intermediate spring connecting member forming part of the constant-force device;
• the figure 4 is a schematic graphic representation illustrating the shape of the evolution curve of the elastic return moment exerted by the intermediate spring in the connecting member;
• the figure 5 represents the coordinates of points defining a particular form of elastic arm for the intermediate spring;
• the figure 6 is a graphical representation of the elastic return moment exerted by the intermediate spring in the connecting member comprising elastic arms of the shape shown in figure 5 ;
• the figure 7 is a top view of an intermediate spring connecting member according to a variant of the invention;
• the figure 8 is a graphic representation of a normalized elastic restoring moment exerted by the intermediate spring in the connecting member illustrated in picture 3 according to different variants of the elastic arms of the intermediate spring, namely such arms with constant section (curve A1) and such arms with variable section (curves A2 to A4), the section varying according to a first mode of variation;
• the figure 9 is a graphic representation of a normalized elastic restoring moment exerted by the intermediate spring in the connecting member illustrated in picture 3 according to two variants of the elastic arms of the intermediate spring, namely such constant section arms (curve B1) and such variable section arm (curve B2), the section varying according to a second mode of variation;
• the figure 10 is a graphic representation of the elastic restoring moment exerted by the intermediate spring used in the invention and of the elastic restoring moments exerted by five intermediate springs used in the state of the art.

The figures 1 and 2 illustrate a watch mechanism 1, forming or forming part of a watch movement, with a constant-force device according to the invention. The watch mechanism 1 comprises a motor member 2, a mobile 3 driven by the motor member 2, an escapement 4 and an oscillator 5. The motor member 2 is typically in the form of one or more barrel springs (a single mainspring in the example shown) housed in one or more respective barrels 2a (a single barrel in the example shown). In the example illustrated, the escapement 4 is a lever escapement, more particularly a Swiss lever escapement, comprising a lever 6, an escapement wheel 7 cooperating with the lever 6 and an escapement pinion 8 coaxial and secured to the escape wheel 7, but it could be of another type. Oscillator 5 can be a balance-spring, as shown, or another type of oscillator such as an oscillator without pivots with flexible guidance.

Between the mobile 3 and the escapement wheel 7 is provided a constant force device 9. This constant force device 9 comprises a winding pinion 10, a second wheel 11 coaxial with the winding pinion 10 but free in rotation relative thereto and a connecting member 12 functionally interposed between the winding pinion 10 and the second wheel 11 with which it is coaxial. The winding pinion 10 meshes with the wheel of the mobile 3, designated by 14, while the pinion of the mobile 3, designated by 15, meshes with the barrel 2a. One could nevertheless make the winding pinion 10 mesh directly with the barrel 2a by adapting the gear ratio. The second wheel 11 meshes with the escapement pinion 8. The connecting member 12, shown alone in picture 3 , understand a hub 16 fixed in rotation to the winding pinion 10, a rim 17 fixed in rotation to the seconds wheel 11 and elastic arms or blades 18 uniformly distributed around the hub 16 and connecting the hub 16 to the rim 17. In the In the example shown the rim 17 is in the form of a closed circle but it could alternatively be interrupted and take the form of one or more circular arcs. The set of elastic arms 18 guides the serge 17 in rotation relative to the hub 16 and constitutes a so-called intermediate spring 19 capable of storing mechanical energy by stretching (by a relative rotation of the serge 17 and the hub 16 in one direction) and restore it by relaxing (by relative rotation of the rim 17 and the hub 16 in the other direction). The respective ends of the elastic arms 18 joined to the hub 16 together constitute a winding end of the intermediate spring 19. The respective ends of the elastic arms 18 joined to the rim 17 together constitute a torque delivery end of the intermediate spring 19.

The connecting member 12 is typically one-piece. It is for example made of metal, alloy, silicon, plastic, mineral glass or metallic glass. It can be produced by machining or by the LIGA technique, in particular in the case where it is made of a metal or alloy, by deep reactive ion etching called DRIE, in particular in the case where it is made of silicon, by molding, in particular in the case where it is made of plastic or metallic glass, or by laser cutting, in particular in the case where it is made of mineral glass.

As shown in figures 1 to 3 , rim 17 of connecting member 12 is secured in rotation to seconds wheel 11 by pins 11a carried by seconds wheel 11 and engaged in openings 17a made in rim 17. In the example shown , the openings 17a are oblong in order to compensate for any manufacturing defects, but they could have another shape, for example round. The rim 17 and the second wheel 11 could be made integral in rotation by any other suitable means. The connecting member 12 and the second wheel 11 could even constitute a single piece having the shape of the connecting member 12 with a toothing on the periphery of the serge 17. The hub 16 of the connecting member 12 and the winding pinion 10 are fixed on the same axis by driving, gluing Or other. The hub 16 and the winding pinion 10 could nevertheless be made integral in rotation in another way.

The constant force device 9 also comprises a blocking device 20 of the type described in the patent applications PCT/IB2018/052645 and PCT/IB2018/052646 of the applicant which are incorporated herein by reference. This blocking device 20 comprises a rotary drive member 21, preferably in the form of a finger as shown, coaxial and integral in rotation with the escapement wheel 7 and the escapement pinion 8, a rotary lock 22, preferably consisting of a star as shown, coaxial and integral in rotation with the winding pinion 10 and the hub 16, and a movable frame 23 having two closed contour openings 24, 25 which respectively receive the rotary members of drive 21 and locking 22. Two diametrically opposed drive elements 26 formed in the wall of the opening 24 cooperate with the rotary drive member 21. Two stop elements 27 formed in the wall of the opening 25 cooperate with the rotary locking member 22. The movable frame 23 is guided in translation along the double arrow F by a flexible guide device 28 with which it preferably forms a single piece. The mobile frame 23 could however be guided in rotation. The rotary drive member 21 could be kinematically connected to the escapement wheel 7 in a way other than being integral in rotation with the latter, for example by means of one or more gears. Similarly, the rotary blocking member 22 could be kinematically connected to the hub 16 and to the winding pinion 10 in a way other than by being integral in rotation with these, for example by means of a or more gears.

The operation of the clockwork mechanism 1 is as follows.

The intermediate spring 19, disarming, drives via the rim 17 the second wheel 11 which itself drives the escapement pinion 8 and therefore the escapement wheel 7. By the action of the oscillator 5 and the lever 6, escapement wheel 7, escapement pinion 8, rotary drive member 21, seconds wheel 11 and rim 17 of connecting member 12 rotate jerkily to the rhythm of the alternations of the oscillator 5, the escapement wheel 7, the escapement pinion 8 and the rotary drive member 21 rotating together in the clockwise direction of the figure 1 . Thus, the escapement 4 is powered only by energy coming from the intermediate spring 19 and therefore receives a force which does not depend on the degree of winding of the driving member 2.

Most of the time, the rotary blocking member 22, which is under tension by the torque exerted by the motor member 2 via the gear train formed by the barrel 2a, the mobile 3 and the winding pinion 10 , is blocked by one of the stop elements 27 against which bears one of its branches, which keeps the winding pinion 10 and therefore the hub 16 of the connecting member 12 stationary.

The intermediate spring 19 is periodically charged by the drive member 2 at times which are determined by the meeting between the rotary drive member 21 and each of the drive elements 26. As soon as the rotary drive member 21 comes into contact with one of the drive elements 26, it cooperates with the latter to move the mobile frame 23 in order to disengage the rotary blocking member 22 from the stop element 27 against which it was resting . The entire kinematic chain going from the motor member 2 to the hub 16 of the connecting member 12 is then released and begins to rotate abruptly until another branch of the rotary locking member 22 comes press the other stop element 27. During this sudden movement (considered as instantaneous with respect to the movement of the escapement wheel 7, of the escapement pinion 8 and of the rotary drive member 21), the intermediate spring 19 is armed. The intermediate spring 19 will be armed again, similarly, after the meeting between the rotary drive member 21 and the other drive element 26, then the cycle repeats.

The time interval separating two successive windings of the intermediate spring 19 (that is to say two successive jumps of the winding pinion 10 - hub 16 - rotary blocking member 22 assembly) is typically several seconds. The different gear ratios in the watch mechanism 1 and the number of branches of the rotary drive member 21 and of the rotary blocking member 22 are chosen so that the intermediate spring 19 accumulates the same quantity of energy than that delivered to the escapement 4 between two successive windings.

The locking device 20 is advantageous in particular for protecting the watch mechanism 1 against shocks and for reducing friction, as explained in the patent applications PCT/IB2018/052645 and PCT/IB2018/052646 . However, it is possible to use a more traditional anchor locking device, such as that used in Gafner's remontoire or described in the patent application EP 2166419 .

In the present invention, the elastic arms 18 which constitute the intermediate spring 19 are specially shaped to improve the constancy of the torque or elastic return moment exerted by this intermediate spring 19 and thus improve the regularity of the oscillations of the oscillator 5.

For the understanding of the invention, the behavior of the connecting member 12, considered in isolation, that is to say free of any interaction with the winding pinion 10 and with the second wheel 11, is described below. -below. The picture 3 represents this connecting member 12 isolated.

The isolated connecting member 12 shown in picture 3 has, due to the shape of its elastic arms 18, a privileged direction of rotation of its rim 17 with respect to its hub 16, this direction being defined as that which allows, from its state of rest, the greatest displacement relative angular of its serge 17 by relative to its hub 16. This preferred direction of rotation is clockwise at the picture 3 .

The insulated connecting member 12 can be reinforced by rotation of its rim 17 with respect to its hub 16 through an angle θ in its preferred direction of rotation, the angle θ=0° corresponding to the rest position of the connecting member 12 isolated, that is to say in the position in which the intermediate spring 19 is at rest (exerts no elastic return moment). During such winding, the intermediate spring 19 deforms to exert a restoring moment M(θ) depending on the position θ of the rim 17 relative to the hub 16, tending to cause the rim 17 to pivot relative to the hub 16 in the opposite direction to the winding direction, that is to say in the opposite direction to the privileged direction of rotation, thus tending to make it return to its state of rest.

When the rim 17 is in the angular position in which the angle θ is equal to x°, it is said that the connecting member 12 or the intermediate spring 19 is reinforced with x°.

The intermediate spring 19 is designed, in particular by its shape, to exert, in the connecting member 12, a substantially constant elastic return moment M(θ) over a range of angular positions [θ _a , θ _b ] of the serge 17 with respect to hub 16 by at least 10°, preferably by at least 15°, preferably by at least 20°, preferably by at least 25°.

“Substantially constant” moment is understood to mean a moment not varying by more than 10%, preferably 5%, more preferably 3%, typically 1.5%, it being understood that this percentage can be further reduced.

More specifically, let M _min and M _max respectively be the values of the minimum and maximum moments exerted by the intermediate spring 19 in the connecting member 12 isolated over a given range of angular positions of the rim 17 with respect to the hub 16, the moment exerted by the intermediate spring 19 is substantially constant when the inequality "(Mmax - Mmin)/((Mmax + M _min )/2) ≤ 0.1" is verified, more precisely, when the inequality "(Mmax - Mmin)/((Mmax + M _min )/2) ≤ y%", with y = 10, preferably 5, more preferably 3, for example 1.5, is verified.

• pour un angle θ compris entre 0° et une première valeur θ_a, le moment de rappel élastique augmente rapidement avec le déplacement angulaire θ ;
• au-delà de cette première valeur θ_a, le ressort intermédiaire 19 est dans une phase stable. En effet, entre cette première valeur θ_a et une seconde valeur θ_b, le moment de rappel élastique est sensiblement constant par rapport au déplacement angulaire θ, la courbe M(θ) prenant la forme d'un plateau ;
• au-delà de cette deuxième valeur θ_b le moment de rappel élastique augmente à nouveau jusqu'à atteindre une valeur limite M_limite, pour un déplacement angulaire θ=θ_limite. Cette valeur M_limite dépend des propriétés du matériau dans lequel le ressort intermédiaire 19 est réalisé et est atteinte lorsque le ressort intermédiaire 19 subit la contrainte maximale qu'il peut supporter.

The figure 4 schematically illustrates the shape of the evolution curve of the elastic return moment M(θ) as a function of the relative angular position θ of the rim 17 with respect to the hub 16. As can be seen, this curve is non-linear and the elastic restoring moment M(θ) globally follows an evolution in three phases:

• for an angle θ between 0° and a first value θ _a , the elastic restoring moment increases rapidly with the angular displacement θ;
• beyond this first value θ _a , the intermediate spring 19 is in a stable phase. Indeed, between this first value θ _a and a second value θ _b , the elastic restoring moment is substantially constant with respect to the angular displacement θ, the curve M(θ) taking the form of a plateau;
• beyond this second value θ _b the elastic restoring moment increases again until it reaches a limit value M _limit , for an angular displacement θ=θ _limit . This _limit value M depends on the properties of the material in which the intermediate spring 19 is made and is reached when the intermediate spring 19 undergoes the maximum stress that it can withstand.

It is possible to define limit values of angles θ _{a_y%} and θ _{b_y%} between which the elastic restoring moment is substantially constant, with a constancy of y%. For example, if one wants to obtain a constancy of the elastic restoring moment of 5%, one defines using the curve M(θ) the values of the angles θ _{a_5%} and θ _{b_5%} so that the inequality: "(Mmax-Mmin) / ((M _max +M _min )/2) <0.05" is verified; with M _max the maximum elastic restoring moment over the interval of angles [θ _{a_5%} , θ _{b_5%} ] and M _min the minimum elastic restoring moment over this same interval.

In the watch mechanism 1, the intermediate spring 19 is pre-armed with a value θ _arm included in the range [θ _a , θ _b ] and the gear ratios and the number of branches of the rotary drive member 21 and of the rotary blocking member 22 are chosen so that the winding angle θ remains in this range during the operation of said mechanism, so that the elastic return moment remains substantially constant. The pre-winding of the intermediate spring 19 can be carried out during the assembly of the watch mechanism 1 by simple angular positioning of the second wheel 11 with respect to the winding pinion 10 connected by the connecting member 12 to the second wheel 11. The closer the pre-winding value θ _arm chosen is to the value θ _b the greater the operating range of the intermediate spring 19 may be. Each winding of the intermediate spring 19 by the drive member 2 brings the winding angle θ of the intermediate spring 19 to the value θ _arm .

To obtain the nonlinear shape of the curve M(θ) shown in figure 4 , the elastic arms 18 can be shaped by topological optimization by applying the teaching of the publication “Design of adjustable constant-force forceps for robot-assisted surgical manipulation”, Chao-Chieh Lan et al., 2011 IEEE International Conference on Robotics and Automation, Shanghai International Conference Center, May 9-13, 2011, China .

The topological optimization discussed in the aforementioned article uses parametric polynomial curves such as Bézier curves to determine the geometric shape of the elastic arms.

Bézier curves are defined, together with a series of m=(n+1) control points (Qo, Q ₁ , ... Qn), by a set of points whose coordinates are given by sums of polynomials of Bernstein weighted by the coordinates of said control points.

The geometric shape of each of the elastic arms 18 of the intermediate spring 19 is a Bézier curve whose control points have been optimized to take into account, in particular, the dimensions of the connecting member 12 to be designed as well as the constraint "( M _max -M _min )/((M _max +M _min )/2) ≤ 0.05” sought. The inequality “(M _max -M _min )/((M _max +M _min )/2) ≤ 0.05” corresponds to a constancy of the elastic restoring moment of 5% over an angular range [θ _{a_5%} , θ _{b_5%} ].

où les $B_i^n$

sont les polynômes de Bernstein donnés par la fonction $$B_i\left(t\right)=\frac{\left(m-1\right)!}{i!\left(m-1-i\right)!}{t}^i{\left(1-t\right)}^{m-i-1}\mathrm{avec}\mathrm{t}\in \left[0,1\right],$$

et où les Q_i sont les points de contrôle Q₀ à Q_n. Elle correspond à la représentation graphique dans un repère orthonormé de l'ensemble des points définis par les couples de coordonnées (x ; y) définis respectivement par les fonctions x(t) et y(t), t ∈ [0, 1], ci-dessous : $$x\left(t\right)={\displaystyle {\sum }_{i=0}^{m-1}{Q}_{\mathit{ix}}{B}_i\left(t\right)}$$

$$y\left(t\right)={\displaystyle {\sum }_{i=0}^{m-1}{Q}_{\mathit{iy}}{B}_i\left(t\right)}$$

dans lesquelles Q_ix et Q_iy sont respectivement les coordonnées x et y des points de contrôle Q_i.More precisely, the geometric shape of each of the elastic arms is defined by the set of points $${\displaystyle {\sum }_{I=0}^{\mathrm{not}}{B}_I^{\mathrm{not}}\left(\mathrm{you}\right).Q_I,}\mathrm{with}\mathrm{you}\in \left[0,1\right],$$

where the $B_I^{\mathrm{not}}$

are the Bernstein polynomials given by the function $$B_I\left(\mathrm{you}\right)=\frac{\left(m-1\right)!}{I!\left(m-1-I\right)!}{\mathrm{you}}^I{\left(1-\mathrm{you}\right)}^{m-I-1}\mathrm{with}\mathrm{you}\in \left[0,1\right],$$

and where the Q _i are the control points Q ₀ to Q _n . It corresponds to the graphic representation in an orthonormal frame of reference of the set of points defined by the pairs of coordinates (x; y) defined respectively by the functions x(t) and y(t), t ∈ [0, 1], below : $$x\left(\mathrm{you}\right)={\displaystyle {\sum }_{I=0}^{m-1}{Q}_{\mathit{ix}}{B}_I\left(\mathrm{you}\right)}$$

$$\mathrm{there}\left(\mathrm{you}\right)={\displaystyle {\sum }_{I=0}^{m-1}{Q}_{\mathit{there}}{B}_I\left(\mathrm{you}\right)}$$

in which Q _ix and Q _iy are respectively the x and y coordinates of the control points Q _i .

The formulas given above give the coordinates of a Bézier curve of order m, that is, a Bézier curve based on m control points. For practical reasons, such a Bézier curve can be broken down into a succession of Bézier curves of order less than m, in which case the geometric shape of each of the elastic arms is a succession of Bézier curves.

Using this principle, the applicant has designed a particular connecting member 12 comprising three elastic arms 18 distributed uniformly around the hub 16. This connecting member 12 corresponds to that shown in the figures. The dimensions of this connecting device are as follows: External diameter of the serge: 12mm Outside diameter of the hub: 2mm Inner diameter of the serge: 10mm Height: 0.12mm Thickness of the elastic arms: 80µm Curvilinear length of each arm: 4.91mm

As part of this design, seven control points Q ₀ , Q ₁ , Q ₂ , Q ₃ , Q ₄ , Q ₅ , Q ₆ were used. The coordinates of these control points are shown in Table 1 below. <i><u>Table 1: Coordinates of control points Q</u>_<u>0</u></i><u>to</u><i><u>Q</u>_<u>6</u></i><u>.</u> Variables x-coordinates [mm] y-coordinates [mm] Q ₀ 0.756625 0.653875 _Q1 1.87325 1,619 _Q2 2.8125 -0.59125 _Q3 3.4375 0.4535 _Q4 3.75 1.032875 _Q5 4,375 0 _Q6 5 0

With these seven control points it would have been possible to produce a Bézier curve of order seven. However, according to the principle indicated above, the Bézier curve was broken down into two segments, a first segment corresponding to a curve of Bézier of order 4 based on control points Q ₀ to Q ₃ and a second segment corresponding to a Bézier curve of order 4 based on control points Q ₃ to Q ₆ .

By using the coordinates of the control points Q ₀ to Q ₆ above in the aforementioned functions x(t) and y(t), the applicant has obtained the coordinates of the points defining the geometric shape of an elastic arm. A certain number of these pairs of coordinates are given in table 2 below. <i><u>Table 2: Coordinates of passage points of the optimized elastic arm</u></i> x [mm] y [mm] 0.756625 0.653875 1.086132 0.854582 1.404044 0.903348 1.709407 0.838756 2.001267 0.699389 2.278672 0.523828 2.540668 0.350656 2.786302 0.218455 3.014621 0.165807 3.224671 0.231295 3.4155 0.4535 3.524275 0.58159 3.648736 0.628816 3.787142 0.611048 3.937748 0.544158 4.098813 0.444016 4.268592 0.326492 4.445344 0.207458 4.627324 0.102784 4.812791 0.028341 5 0

The graph of the figure 5 reveals the geometry of the outer diameter of the hub 16, of the inner diameter of the rim 17 and of one of the elastic arms 18 of the connecting member 12 that the applicant has designed, the geometry of said arm being defined by a curve passing through the set of point coordinates defined in table 2 above. This graph is produced in an orthonormal frame.

The figure 6 represents the results of a simulation of the evolution of the elastic return moment of the isolated connecting member 12 thus produced as a function of the angular position θ of its rim 17 with respect to its hub 16.

The simulation carried out considers the insulated connecting member 12 made of metallic glass, more precisely of Vitreloy 1b, but any suitable material can be used. For example materials such as silicon typically coated with oxide silicon, Nivaflex ^® 45/18 (alloy based on cobalt, nickel and chromium), plastic or CK101 (unalloyed structural steel) are also suitable and allow the production of connecting elements whose moment of elastic return is substantially constant over the same angular ranges [θ _a , θ _b ].

The angular operating range allowing the delivery of a substantially constant moment being a constant linked to the shape of the elastic arms 18, the operating angle θ _b must be less than the angle θ _lim corresponding to the limit before yielding or rupture of the intermediate spring 19. This makes it possible to define the maximum thickness that it is possible to achieve on the arms.

It emerges from the analysis of the results presented to the figure 6 that a constant of 2.4% of the elastic return moment is obtained for an angular displacement of the rim 17 of the connecting member 12 studied with respect to its hub 16 comprised between θ _{a_2.4%} , i.e. 13°, and θ _{b_2.4%} , ie 31°, ie over an operating range of 18°. The connecting member 12 thus produced therefore has a constant moment operating range (for a constant of 2.4%) of 18°. If we accept a constant of 9.1% of the elastic return moment then the connecting member thus produced has an operating range at constant moment of approximately 23°, with θ _{a_9.1%} ≈ 10.5° and θ _{b_9.1%} ≈ 33.5°.

Table 3 below gives, by way of indication, the values θ _{a_y%} , θ _{b_y%} and Δθ (range of angular positions at substantially constant moment) associated with the connecting member 12 made by the applicant as a function of the percentage of constancy considered there as well as the associated torque values M _min and M _max . <i><u>Table 3:</u></i> θ _{a_y%} θ _{b_y%} Angle range Δθ (°) _{Mmin Mmax} Percent constancy y (%) 13.5 30.5 17 1,310 1,331 1.6 13 31 18 1,303 1,335 2.4 12.5 31.5 19 1,294 1,339 3.4 12 32 20 1,284 1,343 4.5 10.5 33.5 23 1,242 1,360 9.1

By increasing the number of control points when designing the elastic arms 18, it should be possible to increase the precision of the shape of these elastic arms 18 and thus improve the constancy of the restoring moment.

It is also possible to improve the constancy of the restoring moment by designing the elastic arms 18 with a variable section. The figure 8 shows different curves representative of a normalized moment of force M(θ) exerted by the insulated connecting member 12 as a function of the angular position θ of its rim 17 with respect to its hub 16 (winding angle) for different variations section of the elastic arms 18. The highest curve, designated by A1, corresponds to elastic arms 18 of constant section and thickness of 30 μm. The curves located below curve A1 correspond to elastic arms 18 whose thickness decreases linearly from hub 16 to rim 17, the thickness at the junction point with hub 16 being 30 μm for each curve, the the thickness at the point of junction with the serge 17 being 29 μm for the curve A2, 28 μm for the curve A3 and 27 μm for the curve A4. An improvement in consistency is observed for curves A2, A3 and A4 compared to curve A1 over a range of angles of reinforcement of length greater than 15°.

Other modes of variation of the section of the elastic arms 18 can be envisaged. The figure 9 shows two curves B1 and B2 representative of a normalized moment of force M(θ) exerted by the isolated connecting member 12 as a function of the angular position θ of its rim 17 with respect to its hub 16 (winding angle) for different section shapes of the elastic arms 18. The curve la higher, B1, corresponds to elastic arms 18 of constant section and thickness of 30 μm. Curve B2 corresponds to elastic arms 18 whose thickness decreases linearly from the hub 16 to the middle of the arm then increases linearly from the middle of the arm to the rim 17, the thickness at the junction points with the hub 16 and with the rim 17 being 30 µm, the thickness in the middle of the arm being 29 µm. An improvement in consistency is observed for curve B2 compared to curve B1 over a range of angles of reinforcement of length greater than 15°.

In general, in cases where the elastic arms 18 have a variable section, this typically varies in a strictly monotonous manner (it increases or decreases without interruption but not necessarily linearly) over at least one continuous portion of the elastic arm representing 10% , preferably 20%, preferably 30%, preferably 40%, of the (curvilinear) length of the elastic arm. The variation of the section is also chosen to improve the constancy of the elastic restoring moment over the range [θ _a , θ _b ] compared to elastic arms of the same shape as the arms 18 but of constant section.

• C1 : le ressort intermédiaire 19 selon l'invention (conçu dans une taille réduite par rapport au ressort dont le comportement est représenté à la figure 6, afin de faciliter la comparaison avec l'état de la technique),
• C2 : un ressort en spirale classique,
• C3 : le ressort intermédiaire tel qu'utilisé dans le mécanisme selon la demande de brevet CH 709914 et constitué des bras flexibles désignés par le repère 11 à la figure 1 de ladite demande de brevet,
• C4 : le ressort intermédiaire formé par les bras flexibles de l'organe de liaison illustré à la figure 1 de la demande de brevet CH 704147 ,
• C5 : le ressort intermédiaire formé par les bras ou cols flexibles de l'organe de liaison illustré à la figure 2 de la demande de brevet CH 704147 ,
• C6 : le ressort intermédiaire formé par les bras flexibles de l'organe de liaison illustré à la figure 3 de la demande de brevet CH 704147 .

To illustrate the differences between the intermediate spring 19 used in the present invention and those of the state of the art, it is shown at figure 10 six curves C1 to C6 representing the relationship between the elastic restoring moment and the winding angle for six springs, namely:

• C1: the intermediate spring 19 according to the invention (designed in a reduced size compared to the spring whose behavior is shown in figure 6 , in order to facilitate comparison with the state of the art),
• C2: a classic spiral spring,
• C3: the intermediate spring as used in the mechanism according to the patent application CH 709914 and made up of flexible arms designated by the reference 11 at the figure 1 of said patent application,
• C4: the intermediate spring formed by the flexible arms of the connecting device illustrated in figure 1 of the patent application CH 704147 ,
• C5: the intermediate spring formed by the flexible arms or necks of the connecting member illustrated in figure 2 of the patent application CH 704147 ,
• C6: the intermediate spring formed by the flexible arms of the connecting device illustrated in picture 3 of the patent application CH 704147 .

As can be seen, the shape of the curve C1 of the intermediate spring 19 according to the invention is very different from that of the other curves C2 to C6. None of the curves C2 to C6 presents a plateau where the moment of force is substantially constant. For each of these intermediate springs, the simulation was performed over its normal deformation range, before the elastic arms touched, plastically deformed or failed. As soon as the elastic arms touch, the elastic return moment suddenly increases in absolute value, which further distances the shape of the curves C2 to C6 from that of the curve C1 of the intermediate spring 19 according to the invention.

It will clearly appear to those skilled in the art that the present invention is in no way limited to the embodiment presented in the figures.

It is for example very well conceivable to produce a connecting member 12 with elastic arms 18 of different shapes from those shown in the figures and/or the number of elastic arms 18 of which is different from that shown in the figures. The elastic arms 18 can in particular take a form as shown in figure 7 , based on the teaching of the article “Functional joint mechanisms with constant torque outputs”, Mechanism and machine theory 62 (2013) 166-181, Chia-Wen Hou et al. The height, length, thickness and/or material of the elastic arms 18, or even the inclination of the elastic arms 18 relative to the hub 16 (in the plane of the connecting member 12), can also be modified to adjust the value of the substantially constant elastic restoring moment.

It would also be possible to modify the watch mechanism 1 so that the intermediate spring 19 is armed via the rim 17 and delivers its torque via the hub 16.

Furthermore, the present invention can be applied to a constant-force escapement mechanism of the type described in the patent application CH 709914 , by replacing the flexible escape wheel of this mechanism by the connecting member 12 provided with a toothing to cooperate with the anchor 6.

Claims (13)

1. Timepiece mechanism (1) comprising a drive member (2), an oscillator (5), an escapement (4) to maintain the oscillations of the oscillator (5), an intermediate spring (19) to supply the escapement (4) with mechanical energy, one or more gears (2a, 3, 10) between the drive member (2) and the intermediate spring (19) and a blocking device (20) permitting periodic winding of the intermediate spring (19) by the drive member (2) via the gear(s) (2a, 3, 10), the intermediate spring (19) comprising at least one elastic arm (18), the or each elastic arm (18) being of a sinuous shape, characterised in that the intermediate spring (19) is a spring which behaves in a non-linear manner and which produces, between a winding angle θ_a and a winding angle θ_b, which are separated by at least 10°, an elastic return moment which does not vary by more than 10%, and in that the intermediate spring (19) is pre-wound by a value θ_arm within the range [θ_a, θ_b], the timepiece mechanism (1) being arranged so that, during operation thereof, the winding angle of the intermediate spring (19) remains in the range [θ_a, θ_b].
2. Timepiece mechanism (1) as claimed in claim 1, characterised in that the elastic return moment produced by the intermediate spring (19) does not vary by more than 5%, preferably does not vary by more than 3%, preferably does not vary by more than 1.5%, over the range [θ_a, θ_b].
3. Timepiece mechanism (1) as claimed in claim 1 or 2, characterised in that the winding angles θ_a and θ_b are separated by at least 15°, preferably by at least 20°, preferably by at least 25°.
4. Timepiece mechanism (1) as claimed in any one of claims 1 to 3, characterised in that the intermediate spring (19) comprises a plurality of said elastic arms (18) at a regular angular spacing.
5. Timepiece mechanism (1) as claimed in any one of claims 1 to 4, characterised in that the geometric shape of the or each elastic arm (18) is a Bezier curve or a succession of Bezier curves.
6. Timepiece mechanism (1) as claimed in any one of claims 1 to 5, characterised in that the or each elastic arm (18) has a variable cross-section, the variation in which is selected to improve the constancy of said elastic return moment in the range [θ_a, θ_b] with respect to an elastic arm of the same shape but a constant cross-section.
7. Timepiece mechanism (1) as claimed in any one of claims 1 to 6, characterised in that the intermediate spring (19) forms part of a piece (12) further comprising a hub (16) and a felloe (17), the intermediate spring (19) connecting the hub (16) and the felloe (17).
8. Timepiece mechanism (1) as claimed in claim 7, characterised in that said piece (12) is of one piece.
9. Timepiece mechanism (1) as claimed in any one of claims 1 to 8, characterised in that the blocking device (20) comprises a mobile member (23), a rotary driving member (21) kinematically connected to an escapement wheel (7) and to a torque-delivery end of the intermediate spring (19) and arranged to displace the mobile member (23), a rotary blocking member (22) kinematically connected to a winding end of the intermediate spring (19) and to the drive member (2), the rotary blocking member (22) being blocked by the mobile member (23) and periodically unblocked by the displacements of the mobile member (23) which are caused by the rotary driving member (21).
10. Timepiece mechanism (1) as claimed in claim 9, characterised in that the rotary driving member (21) is connected to the escapement wheel (7) for conjoint rotation therewith.
11. Timepiece mechanism (1) as claimed in claim 9 or 10, characterised in that the mobile member (23) is mobile in translation.
12. Timepiece mechanism (1) as claimed in any one of claims 9 to 11, characterised in that the mobile member (23) comprises first and second openings with a closed contour (24, 25), with the wall of which the rotary driving member (21) and the rotary blocking member (22) cooperate respectively.
13. Timepiece comprising a timepiece mechanism (1) as claimed in any one of claims 1 to 12.

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