EP3030938B1 - Regulator system for mechanical watch - Google Patents

Description

The present invention relates to the regulating system of a mechanical timepiece. By regulating system or regulating organ is meant two separate devices: the resonator and the escapement.

The resonator is the organ producing a periodic movement which constitutes the time base of the timepiece. Well-known resonators are pendulums oscillating under the effect of gravitation, balance wheels forming with the associated hairspring a mechanical resonator oscillating around the shaft of the balance wheel and tuning forks oscillating by elastic deformation of their structure. The best known realization of tuning forks is the tuning fork used in music, the one produced in greatest number however is the resonator made of crystalline quartz used as a time base for electronic watches.

The escapement is the connecting element between the gear train of the timepiece and the resonator. The escapement has two functions. First, it must transmit to the resonator the energy necessary to maintain its oscillation. This function is normally performed by a mechanism transmitting to the resonator energy from the last wheel of the gear (hereafter called the escapement wheel). In addition to transmitting the energy supplying the resonator, the escapement must control the speed of progress of the gear train and synchronize it with the oscillation of the resonator. This second function is normally carried out by a part of the escapement mechanism which engages in the teeth of the escape wheel and only allows the active tooth to pass when the resonator has oscillated. Many escapement principles are known in watchmaking, the most widely used escapement in the field of wristwatches is the lever escapement, more particularly the Swiss lever escapement which is cited here by way of example only. A description of the Swiss lever escapement can be found, for example, in the document EP 2 336 832 A2 .

Mechanical escapements can only perform their functions by means of direct mechanical contact with the teeth of the escape wheel as well as with the resonator. In the example of the Swiss lever escapement, the lever is in contact with the resonator while the latter is close to the point of balance and it is almost permanently in contact with one of the teeth of the wheel. exhaust. The situation is aggravated by the fact that, in a mechanical escapement, the contacts both with the teeth of the escape wheel and with the resonator are at least partially accompanied by a sliding movement between the two elements in contact. A sliding movement necessarily involves losses of friction, which has several harmful consequences.

A major disadvantage of contact with the resonator involving friction is the fact of disturbing the movement of the resonator with forces which are not of the so-called "elastic" type of forces. This means that the resonator is disturbed with forces influencing its natural frequency. This disturbance influences the horological performances of the piece. It is easily understood that the disturbance of the movement of the resonator depends on the magnitude of the interaction of the escapement with the resonator. As the escapement wheel is driven by the gear train and the latter by the mainspring, the chronometric error created by the contact between the escapement mechanism and the resonator depends on the state of the mainspring. : the chronometric error is different if the barrel spring is very tight compared to the situation of a watch where the barrel spring is almost completely relaxed. This chronometric error is well known to specialists under the name of isochronism error.

In addition to this, sliding motion involves friction and hence energy losses. In order to reduce energy losses by friction, the elements in contact are greased or oiled with great care and very advanced lubricating products are used. This makes it possible to reduce losses by friction, but nevertheless implies that the chronometric performance becomes dependent on the performance of the lubricants. These vary over time, the lubricants degrade or no longer remain on the surface to be lubricated. Following this phenomenon, the performance of the watch deteriorates and it must be cleaned and lubricated again.

Many developments have been made to reduce the sliding contact between the escapement mechanism and the resonator. For exemple EP 1 967 919 B1 describes a coaxial escapement improving the conditions for transmitting energy between the escapement wheel and the resonator. Although this type of escapement is an improvement over the Swiss lever escapement, it cannot avoid sliding contacts and therefore cannot avoid the friction losses mentioned above.

Friction losses can, however, be avoided if the transmission of energy by mechanical contact is replaced by a transmission without contact, for example by magnetic or electrostatic forces. These obviously have no friction losses. An escapement where the mechanical contacts are replaced by magnets is called a magnetic escapement. Magnetic escapements have been known for a very long time. HS Baker was the first to file a patent (US) for a magnetic escapement in 1927, followed by CF Clifford (1938) and R. Straumann in 1941. These developments led to an industrial achievement: the German company Junghans produced a alarm clock fitted with a magnetic escapement in the early `60s. A description of this escapement can be found in the article by CF Clifford in the “Horological Journal” April 1962 edition . This exhaust, however, only fulfilled half of the classic functions of an escapement: it synchronized the escapement wheel to the movement of the oscillator, but the tuning fork-shaped oscillator was electrically driven. It was therefore not a mechanical movement, but rather an electromechanical or electronic watch (alarm clock). The superior performance of electronic quartz movements as well as their lower cost caused the magnetic escapement to lose all interest in the 1970s. The growing interest in mechanical watches is behind recent developments in this field; the document EP 2 466 401 A1 describes an embodiment which can be considered as the current state of the art. This document describes all the regulating organs of a mechanical watch, the resonator and the escapement. The resonator is a tuning fork shaped resonator in its shape similar to the tuning forks known from music. The tuning fork resonator has indeed a large number of advantages compared to the spiral balance wheel resonator. Firstly, it does not need bearings and therefore its quality factor is not degraded by friction in the bearings (its losses by oscillation are lower) and the tuning fork resonator does not need lubrication likely to request regular watch services. It is also well known that the tuning fork resonator provides much better chronometric performance than a balance-spring resonator. Max Hetzel and the Bulova company are at the origin of wristwatches equipped with tuning fork-shaped resonators, his patent was filed in 1953, and the technology used is described for example in the document US 2,971,323 . Three producers have marketed more than six million watches according to the principles described in this document; the company Bulova with the product called “Accutron”, the company Citizen with the product called “HiSonic” and the company Ebauches SA with a product called “Swissonic 100” or “Mosaba”. The three products, however, were not mechanical watches. The tuning fork resonator was in fact driven and maintained in oscillation by an electronic circuit supplying electrical impulses to two coils located opposite of magnets attached to the ends of the arms of the tuning fork similar to the product of the aforementioned Junghans company. The cog was driven by the tuning fork by means of a ratchet mechanism attached to one of the branches. The energy for the operation of the watch came from the power supply of the transistor driver circuit of the tuning fork. They were indeed electric or electronic watches. These products demonstrated the superior chronometric performance of a resonator in the form of a tuning fork compared to a balance-spring resonator: their rate accuracy was better than that of a watch fitted with a balance-spring resonator. It is also well known that the rate precision of an electronic quartz watch is much higher than that of a mechanical watch. This is also due to the stability of the quartz tuning fork resonator regulating the operation of these products.

The choice of a tuning fork resonator is therefore judicious and the document EP 2 466 401 A1 shows the tuning fork with two magnets (one magnet on each arm) similar to the aforementioned tuning fork watches. The escapement function is performed according to this document by an escapement wheel carrying a multitude of magnets located between the arms of the tuning fork and in such a way that the magnets of the tuning fork are opposite a pair of wheel magnets exhaust as shown in the figure 1 of this request. The operation of the magnetic escapement according to EP 2 466 401 A1 is described in this document and is here only briefly summarized for the description of the invention which is the subject of the present application. It is understood that, if the magnets of the escape wheel are opposite the magnets of the tuning fork and this with the correct polarity (an N pole is opposite an S pole), the branches of the tuning fork are pulled towards the wheel d escapement, if the magnets are opposite each other with identical polarity, the branches of the tuning fork are pushed outwards. In rotation, the escape wheel will alternately transmit a force to the arms of the tuning fork pushing the arms outwards then pulling them inwards. It is understood that the rotation of the escape wheel goes excite the vibration of the tuning fork. A resonator is characterized by the fact that its vibration amplitude becomes very large when it is excited at its own resonant frequency and this is also the case with the tuning fork resonator described in the document EP 2 466 401 A1 . As the escape wheel approaches the speed of rotation exciting the tuning fork into its resonant frequency, its amplitude becomes substantially greater. As will be shown later in the detailed description of the invention, the magnets of the tuning fork also exert a tangential force on the magnets of the escape wheel. This tangential force acts in the direction of braking the escapement wheel when it begins to anticipate the speed given by the oscillations of the tuning fork. It is this tangential force which synchronizes the speed of the escapement wheel with the frequency of the tuning fork and thereby controls the rate of the watch.

The device according to the document EP 2 466 401 A1 has however several disadvantages which are the consequence of the fact that the tuning fork interacts with the escapement wheel so as to produce tangential forces which vary greatly when the wheel advances by one tooth. It is easily understood that the tangential forces acting on the escapement wheel produce a torque which pulls the wheel into the position where the magnets on the wheel and on the tuning fork are opposite and of opposite polarity. This is the position of stable equilibrium. Starting from the position of stable equilibrium and turning the escape wheel p. ex. Clockwise interaction between the magnets on the wheel and on the tuning fork will first create a torque pulling the wheel back into the equilibrium position. This is the case until the magnets of identical polarity are opposite each other. In this situation, the arrangement of the magnets is again symmetrical and there are no longer any tangential forces and therefore no torque on the escape wheel. This position is the unstable equilibrium position of the wheel. If the escape wheel continues to rotate in the same direction a torque pulling the wheel to the next stable equilibrium position develops. It can be seen that the tangential forces exerted on the escape wheel by the system described in EP 2 466 401 A1 vary greatly as the wheel advances from one stable equilibrium position to the next. This situation has several significant disadvantages.

The first consequence is the fact that the escape wheel is blocked by the forces of the magnets when it is stationary. It is easy to understand that, if the magnets of the escape wheel are opposite the magnets of the tuning fork and of opposite polarity, the two pairs of magnets attract each other and the escape wheel remains blocked in this position. This situation occurs each time the train of the watch is stopped, which occurs if the watch is not worn and stops at the end of its power reserve, but also when setting the time when the gear train is stopped for start-up at the precise second. This phenomenon is well known and typical for timepieces provided with a magnetic escapement of the prior art. Timepieces fitted with magnetic escapements of the C.F. Clifford type had sophisticated mechanisms for spinning the escape wheel when the movement was started.

The second disadvantage of the system described in EP 2 466 401 A1 is its sensitivity to desynchronization in the event of a shock. Placing magnets on the escape wheel and on the arms of the tuning fork leads to significant forces between the two regulating organs. The mechanical power needed to synchronize a mechanical watch, however, is very small. The mechanical power being given by the product between the tangential force and the speed, it is found that large forces necessarily lead to low speeds. In the case of a rotary motion, they lead to a low escape wheel rotational speed. Wristwatches in particular are subjected to quite violent shocks. If the watch falls on the ground, shocks of several thousand times the terrestrial acceleration are reached. Even in normal use, shocks producing accelerations much higher than Earth's acceleration are common. A shock is not usually not just linear acceleration, the watch normally touches or falls on a corner of the room so the acceleration is a combination of linear acceleration and angular acceleration. If the angular component of the acceleration due to the shock accelerates the escapement wheel to an angular velocity exceeding the speed of synchronization with the tuning fork, the aforementioned synchronization mechanism will no longer work and the escapement wheel continues to accelerate, driven by the gear train and the barrel spring of the watch. In such a case, the watch loses all its chronometric qualities, the hands turn at a much too high speed. The risk of desynchronization in a system according to the document EP 2 466 401 A1 is also high because the synchronization between the escapement wheel and the movement of the tuning fork resonator takes place at the relative positions of the two organs where the forces of attraction are great and this is the case only once per oscillation of the resonator in the position drawn in figure 1 .

Another disadvantage of the realization according to the document EP 2 466401 A1 is related to the shape of the tuning fork described in this document. The tuning fork resonator is indeed a tuning fork in the shape of an oscillating bar, bent in a U. This type of tuning fork is well known in music and is used to tune instruments. It is known from its application in music that this type of tuning fork transmits its vibration through its rod attached to the middle of the U of the tuning fork. The musician knows well that the sound of the tuning fork is much more audible if the tuning fork is placed on a surface capable of vibrating at its frequency, for example on the lid of the piano. This is due to the fact that the tuning fork transmits its vibrational energy through its rod to the lid of the piano which - considering its large surface area - transmits it to the air like a loudspeaker. A horological resonator should however keep its energy in the resonant structure and not lose it in the fixing, losses in the fixing degrade its quality factor and therefore its chronometric properties. Attaching a U-shaped tuning fork to the foot is therefore very disadvantageous. The document EP 2 466 401 A1 mentions the fact that the U-shaped tuning fork has two points that remain stationary, the nodal points (or axes). The U-shaped tuning fork could theoretically be attached to its support at its two points. Under the conditions of a wristwatch in particular and considering the great accelerations which it must resist, this solution is however not feasible: either the attachment of the tuning fork is actually small enough not to disturb the vibration of the resonator, in which case the device does not resist shocks, or the device resists shocks in which case the attachment is physically too great and this results in significant energy losses. It is clear that the U-shaped tuning fork does not allow mounting in the watch movement satisfying the conditions required for this application.

Other horological resonators provided with magnetic escapements comprising tuning forks are disclosed in the documents DE1177077B , GB1128394A And US3208287A .

The object of the present invention is to remedy the drawbacks of the magnetic escapements of the prior art by providing a regulating system for a mechanical timepiece based on the magnetic interaction between a resonator and an escapement wheel, such as defined by patent claim 1.
This is achieved with a magnetic escapement interacting with the resonator with negligible tangential forces when the resonator is stopped and generally lower so as to allow a sufficiently high rotational speed of the escape wheel to render the timepiece insensitive. to shocks. One of the preferred embodiments of the invention makes it possible to synchronize the escape wheel with the tuning fork resonator at each half-oscillation of the tuning fork resonator, which further increases the resistance to shocks. The tuning fork resonator according to one of the embodiments of the invention has a structure allowing solid embedding ensuring the resistance to shocks of the resonator and of its assembly.

• la figure 1 montre l'art antérieur, notamment le système selon le document EP 2 466 401 A1 ,
• la figure 1a représente le dispositif selon la figure 1 en rotation et les forces tangentielles agissant sur la roue d'échappement quand le résonateur est à l'arrêt,
• la figure 1b montre graphiquement les forces tangentielles selon la figure 1a pendant la rotation de la roue d'échappement d'une position d'équilibre à la prochaine,
• la figure 2 montre le dispositif selon une réalisation préférée de l'invention,
• la figure 3 montre une coupe à travers le dispositif montré en figure 2 dans le plan B-B',
• la figure 4 montre une coupe à travers le dispositif de la figure 2 dans le plan A-A',
• la figure 5 montre les forces tangentielles agissant sur la roue d'échappement dans le dispositif selon la figure 2 quand le résonateur est à l'arrêt,
• la figure 6 montre graphiquement les forces tangentielles selon la figure 5 agissant sur la roue d'échappement pendant la rotation de la roue par une dent,
• la figure 7 montre les forces tangentielles sur la roue d'échappement du dispositif selon l'invention quand le diapason vibre à sa fréquence de résonance et synchronise la vitesse de la roue d'échappement,
• la figure 8 montre le couple produit par les forces tangentielles sur la roue d'échappement du dispositif selon l'invention quand la roue d'échappement est synchronisée sur l'oscillation du résonateur et ceci en fonction du déphasage entre le mouvement d'oscillation du diapason et la rotation de la roue d'échappement,
• la figure 9 montre le dispositif selon l'invention avec un résonateur double - diapason en forme de H.

The invention is explained in more detail with reference to the appended figures in which:

• there figure 1 shows the prior art, in particular the system according to the document EP 2 466 401 A1 ,
• there picture 1a represents the device according to the figure 1 in rotation and the tangential forces acting on the escape wheel when the resonator is stationary,
• there figure 1b graphically shows the tangential forces according to the picture 1a during the rotation of the escape wheel from one equilibrium position to the next,
• there figure 2 shows the device according to a preferred embodiment of the invention,
• there picture 3 shows a cut through the device shown in figure 2 in plane B-B',
• there figure 4 shows a section through the device of the figure 2 in plane A-A',
• there figure 5 shows the tangential forces acting on the escape wheel in the device according to the figure 2 when the resonator is stopped,
• there figure 6 graphically shows the tangential forces according to the figure 5 acting on the escape wheel during wheel rotation by a tooth,
• there figure 7 shows the tangential forces on the escape wheel of the device according to the invention when the tuning fork vibrates at its resonant frequency and synchronizes the speed of the escape wheel,
• there figure 8 shows the torque produced by the tangential forces on the escapement wheel of the device according to the invention when the escapement wheel is synchronized with the oscillation of the resonator and this as a function of the phase difference between the oscillation movement of the tuning fork and the rotation of the escape wheel,
• there figure 9 shows the device according to the invention with a double H-shaped tuning fork resonator.

With reference to the figures the invention will be explained in detail. There figure 1 shows the prior art according to the document EP 2 466 401 A1 . The U-shaped tuning fork resonator 1 carries at the end of each branch a permanent magnet 2 oriented so that the magnetic fields created by the magnets are in the same direction. The escape wheel 3 is arranged between the branches of the tuning fork and carries in the example drawn six permanent magnets 4 alternately oriented so as to show the magnets of the tuning fork opposite or identical magnetic poles. The escape wheel also carries the pinion 5 meshing in the gear train of the timepiece.

There picture 1a shows the tangential forces that develop when the escape wheel turns slowly and the resonator is stationary. This is the starting situation of the watch movement. The geometry in figure 1 being symmetrical with respect to a plane through the axis of the wheel and passing through the magnets of the tuning fork, there can be no tangential force. By turning the escape wheel for example clockwise as indicated by the arrow 6, the magnets of opposite polarity attract each other which will produce the forces 7 and 8. It can be seen that the two tangential forces produce a torque on the wheel exhaust which acts in the same direction and against rotation in the direction of arrow 6.

There figure 1b shows the resulting tangential force (the sum of the two forces 7 and 8 shown in picture 1a ) of the prior art according to the figure 1 as a function of the angle of rotation of the escape wheel 3. The angle of rotation represented corresponds to the advancement of the escape wheel from one position of stable equilibrium to the next. The movement begins with the angle of rotation 0 in the situation drawn in figure 1 . This situation corresponds to the stable equilibrium of the escape wheel and it is indicated by the arrow designated by A. By turning as drawn in picture 1a towards the position where the magnets of the escape wheel are opposite the magnets of the tuning fork but in identical polarity, the escape wheel will have made the half of the rotation (denoted by 0.5) and it arrives in the position of unstable equilibrium. This position is designated in figure 1b with arrow B. In this first half of the rotational movement the tangential force is positive, it acts against the rotation of the escape wheel. As soon as the point of unstable equilibrium B is exceeded, the tangential force pulls the escape wheel in the direction of rotation, in the diagram in figure 1b this shows through negative forces. At the end of the rotation, at the angle of rotation denoted by 1, the escape wheel will again be in position A, but it will have advanced one step. In the situation drawn in figure 1 , this step corresponds to a 120° rotation of the escape wheel.

There figure 2 shows one of the preferred embodiments of the present invention. The escapement wheel 9 carries a crown of ferromagnetic material 10 provided with internal 11 and external 12 toothing. The escapement wheel meshes with the wheel train of the timepiece by means of the pinion 13. clockwork and its mainspring (barrel spring) are well known and are not shown in the figures. Above the ferromagnetic crown 10 is the tuning fork resonator 14. The tuning fork resonator comprises two branches 16 and 17 attached to a solid base 15. The embodiment drawn schematically in figure 2 is explained in more detail with reference to figures 3 and 4 which show the sections through the structure in the planes AA' and B-B', the view in these sections is in the direction of the arrows in fig.2 .

There picture 3 is a central section through the escape wheel in plane BB' showing the interaction between the ferromagnetic structure and the tuning fork resonator. The hatched surfaces correspond to cut parts of the structure, while the white surfaces are visible surfaces outside the plane of the cut. The two branches of the tuning fork 16 and 17 which can be seen here cut close to their free end carry magnets 18 and 19. The indication “N/S” in the magnets indicates their polarity. The bottom side of the magnets carries pole pieces 20 and 21 which direct the flux magnetic to the ferromagnetic structure 10 of the escape wheel. In the position drawn in the figure 2 And 3 , the right pole piece 21 is opposite a tooth of the ferromagnetic structure while the left pole piece 20 is between two teeth.

There figure 4 shows the central section according to the plane A - A'. The figure shows the mounting of the tuning fork in the cage of the movement 22, this part is normally called "plate" by the person skilled in the art and, in a highly schematic way, the bearing of the escapement wheel. The central section is seen through the escapement wheel, the shaft of the wheel 23 being interrupted in the region of the magnets and the tuning fork to allow the representation of those elements which are outside the plane of the section. The foot of the tuning fork 15 is cut and we see the rigid mounting that the structure of the tuning fork according to the invention allows to achieve.

Referring to the figures, the operation of the regulating members according to the invention will now be described in detail. THE figure 2 And 3 show that the embodiment according to the invention causes the tuning fork to interact with the crown made of ferromagnetic material with its external toothing on one arm of the tuning fork (the arm 16) and with the internal toothing on the other arm (the arm 17). It is also noted that the interaction with the ring gear is alternating, when the pole piece of the right arm 17 is opposite a tooth of the ferromagnetic ring gear 10, the pole piece of the other arm 16 is between two teeth. It is well known that a piece of ferromagnetic material is attracted by a magnet and it is found that the rotation of the escape wheel will produce forces acting in the radial direction and varying according to the relative angular position between the teeth of the crown ferromagnetic and the pole pieces of the tuning fork. The tuning fork being a structure capable of vibrating and entering into resonance will be excited by the rotation of the escapement wheel even if the escapement wheel does not carry magnets as is the case in the prior art .

There figure 5 shows the tangential forces 25 and 26 which develop in the structure according to the invention when the escape wheel rotates in the direction of the arrow 24. It can be seen that by turning the escape wheel clockwise by relative to its position of equilibrium, a pole piece of the tuning fork moves away from one tooth of the ferromagnetic structure while the other approaches. This will produce tangential forces as drawn by arrows 25 and 26 and it will be seen that the two tangential forces produce torques at the escape wheel in opposite directions. As a result, the torques created by the tangential forces cancel each other out.

There figure 6 is a graphical representation of the tangential forces 25 and 26 as a function of the angle of rotation of the escape wheel. It can be seen that the two forces 25 and 26 oppose each other, giving the very weak resultant force, designated 27. If the two magnets have the correct magnetization, the resultant force 27 is zero, the inevitable manufacturing tolerances mean, however, that the two forces 25 and 26 do not compensate each other exactly and this results in the weak force 27 represented in figure 6 . By way of example, if one of the magnets has a magnetization which deviates from the design value by 1%, the force 27 will also have a value corresponding to 1% of the forces 25 or 26 respectively. It can be seen that the system according to the invention makes it possible to reduce the resulting tangential force very significantly compared to the prior art. The wheel rotation scale covers the advancement of the wheel by one tooth, in the situation corresponding to the picture 2 there are 36 teeth, the wheel will have traveled 10° in the designated range of 0 to 1 on the axis of rotation of the wheel.

The situation drawn in figure 6 is valid for a speed of rotation of the escape wheel far from resonance, typically when the wheel starts, and it is seen that the resulting tangential force 27 is very low, theoretically even zero. This allows the timepiece to start without an auxiliary starting device, which makes the mechanism of the regulating organs of the room considerably simpler and more reliable.

If the speed of rotation of the escape wheel approaches the value producing in tune an excitation at its resonant frequency, the amplitude of vibration of its arms becomes high and can reach several hundredths of a millimeter. The higher the vibration amplitude of the tuning fork, the more the interaction between the oscillating tuning fork and the rotating escape wheel will create high tangential forces, forcing the wheel to rotate synchronously with the movement of the tuning fork resonator. It has indeed been found that the tangential forces increase more than linearly with the vibration amplitude of the tuning fork. In comparison with the forces illustrated in figure 6 , the tangential forces become more than twenty times greater if the tuning fork is in resonance.

There figure 7 shows the tangential forces acting on the escape wheel when the escape wheel is synchronized to the frequency of the tuning fork resonator. The result shown in figure 7 shows the magnetic forces of the device drawn in picture 2 . The horizontal axis indicates the rotation of the escape wheel by one complete tooth. At the zero position, the tooth is opposite the pole piece as drawn in picture 2 . At positions 5 and -5 the wheel is rotated by half a tooth, the range of rotation shown in the figure 7 corresponds to the rotation of the wheel by one complete tooth. The vertical axis is that of the tangential forces. Curve 28 shows the force exerted by the pole piece on arm 17, curve 29 the negative value of that exerted by the pole piece on arm 16 and curve 30 gives the sum of the two curves. The figure shows the situation when the escape wheel is synchronized with the oscillation of the tuning fork. This condition is met when the escape wheel rotates one tooth in time as the resonator completes one oscillation. It can be seen that the tangential force shown in curve 30, which indicates the sum of the forces of the two arms, is substantially weaker than either of the forces 28 and 29. One could deduce from the figure 7 that the tuning fork, even when oscillating at high amplitude, is not able to synchronize the escape wheel on its own frequency. The resultant tangential force is in fact weak and it can be seen that it also has positive and negative components which are of close magnitude so that the overall result covering the resultant force during the advancement of a complete tooth will be very weak. This comes from the fact that the figure 7 shows the situation where the tuning fork resonator vibrates exactly in phase with the rotation of the escape wheel. By this is meant that the tooth of the toothing 11 is exactly opposite the pole piece of the arm 17, when the tuning fork is at its end, separated. In this situation, there is effectively no transfer of energy between the resonator and the escape wheel. However, this case is only of interest for the explanation of the synchronization mechanism, in reality it does not exist. The escape wheel, which is driven by the mainspring of the timepiece through the gear train, normally tends to spin faster than the tuning fork resonator oscillates. Its movement of the teeth precedes the vibration of the tuning fork. A person skilled in the art calls the advance of the wheel its phase shift with respect to the movement of the tuning fork. Phase shift is measured in °, 0° means no phase shift; at 180° the phase shift corresponds to an advance of half a tooth and at minus 180° the escape wheel would be behind by half a tooth.

There figure 8 shows the torque resulting from the interaction between the vibrating tuning fork and the escape wheel as a function of the phase difference between the rotation of the escape wheel and the vibration of the resonator. The tangential forces of the two arms of the tuning fork are multiplied with their corresponding radius to obtain the torque acting on the escape wheel and the vertical axis indicates the sum of the two torques, therefore the resulting torque on the escape wheel. Negative torque values in the figure 8 correspond to a torque which brakes the escapement wheel, positive torque values accelerate the escapement wheel. There figure 8 shows that in the range from 0 to 100° approximately the braking torque acting on the escape wheel increases continuously with the phase shift. This means that the greater the driving torque of the escape wheel, the more the escape wheel will be out of phase with respect to the movement of the tuning fork. On the contrary, if there is no more torque driving the escapement wheel, the phase shift drops to zero. This case happens when the mainspring is at the end of its power reserve and the timepiece stops. There figure 8 clearly shows that the speed of rotation of the escape wheel is synchronized with the frequency of the tuning fork insofar as the barrel spring succeeds in driving the timepiece. The phase shift of the two synchronized movements determines the torque braking the escapement wheel and synchronizes it to the frequency of the tuning fork resonator.

There figure 8 corresponds to the situation of a vibrating resonator with a fixed amplitude. This is however not the case. If the resonator brakes the escapement wheel, there is necessarily a transfer of energy from the wheel to the resonator. The energy transferred to the tuning fork resonator will increase its amplitude of vibration until the energy losses of the resonator, due for example to the friction in the air of its branches, are again equal to the contribution of energy coming from of the escape wheel. The resonator being able to neither create nor lose energy must in fact always vibrate at an amplitude leading to the equality of the energy supplied by the escape wheel and the energy lost in friction and other losses. As the losses increase with the vibration amplitude, we see that the vibration amplitude must increase if the energy (the torque) transmitted to the resonator increases.

The greater the vibration amplitude becomes, the greater the braking at the same phase shift becomes. Although the operating range of the escapement according to the invention as shown in figure 8 is already large enough and quite sufficient for a practical application, the physics of the system shows that the operating domain is indeed much larger.

The tuning fork resonator according to the invention has a very different shape from a U-shaped tuning fork according to the prior art described in the document EP 2 466 401 A1 . As depicted in figure 2 , the tuning fork consists of two branches attached to a foot 15 in the form of a solid plate. This geometry has several advantages over the prior art resonator shown in figure 1 . The advantages are the consequence of the movements and deformations in this tuning fork structure. The tuning fork according to figure 2 deforms as if the two arms 16 and 17 were embedded and immobile at their base and oscillate at their free end in a left-right movement in counter phase. It can be seen that this movement of the arms is in a first approximation devoid of movements in the direction of the length of the tuning fork. The foot 15 of the tuning fork therefore does not move, it undergoes the stresses coming from the oscillating arms. These stresses deform the foot 15 close to the bases of the arms of the tuning fork, they are however attenuated very quickly and strongly towards the base of the foot. This offers the possibility of a simple and solid assembly in the lower zone of the foot 15, for example by screws as drawn in picture 2 . This results in a tuning fork resonator with little loss of vibration energy in the recess and simultaneously a solid assembly satisfying the shock resistance requirements of a watch movement.

The structure drawn in figure 2 is not the only possibility of a resonator satisfying the requirements of a magnetic escapement according to the invention. There figure 9 shows as an example a double tuning fork structure. The double tuning fork structure offers the possibility of attaching masses 31 and 32 to the end of the two additional branches. These masses 31 and 32 can be mounted at an adjustable position and make it possible to adjust the resonance frequency of the double tuning fork. Other methods of adjusting a tuning fork to the chronometric frequency are known from skilled in the art, such as the removal of small amounts of mass at the end of the temples by laser material ablation.

It goes without saying that the invention is not limited to the embodiments which have just been described and that various modifications and simple variants can be envisaged by those skilled in the art without departing from the scope of the invention as defined. by the appended claims.

It goes without saying in particular that it is possible to provide shielding of the regulator system of the invention and in particular of the escape wheel to limit or even eliminate the influence of external magnetic fields on the operation of the system. Typically one can consider two flanges made of a ferromagnetic material arranged on either side of the escape wheel.

According to another variant, provision may also be made to replace the discrete permanent magnets with one or more magnetic layers, typically in a platinum and cobalt alloy (50-50 at.%) or in samarium cobalt.

Furthermore, although the regulator system of the invention has been described above in connection with the use of magnets and therefore of magnetostatic forces, it is also envisaged according to the invention to replace the discrete magnets or the layer or layers magnetic by electrets and electrostatic forces. The construction of the regulator system is entirely similar and is dimensioned according to the permanent electrostatic fields established between the branches of the resonator and the escapement wheel. In short, in this mode using electrostatic forces and torques, it is possible to use a conductive material either for the branches of the resonator if the escapement wheel is electrified and charged with sufficient energy, or for the escapement wheel. exhaust if it is the branches of the resonator which are electrified and charged, this conductive material is locally polarized. Typically the tuning fork resonator can carry electrets at the end of each arm and the wheel escapement is conductive or electrified locally, on the teeth of the wheel coming opposite the electrets of the resonator, with opposite charges to the electrets of the resonator.

Claims (9)

1. A regulator system for a mechanical timepiece based on the magnetic interaction between a resonator (14) and an escapement wheel (9), said interaction creating radial and tangential forces (25, 26) acting on the escapement wheel (9) and generating torques therein, the regulator system comprising:

   a tuning fork resonator (14) provided with two arms each carrying a permanent magnet (18, 19) and wherein the magnetic flux of said magnets (18, 19) is directed towards the outside of the tuning fork at one arm and at the other towards the inside of the tuning fork, and

   an escapement wheel carrying a ferromagnetic structure (10) in the shape of a crown gear, provided with an internal toothing (11) and an external toothing (12) each cooperating magnetically with an arm of said resonator,

   the regulator system is arranged with said internal (11) and external (12) toothing disposed so that if a tooth of said internal toothing is opposite the magnet of one arm of the tuning fork, the magnet located on the other arm of the tuning fork is located between two teeth of said external toothing and vice versa, so that the torques due to said tangential forces act in opposite directions and cancel each other out when the system is started when a torque is applied to the escapement wheel by a driving member while the regulator system is still stationary in its starting position.
2. The regulator system according to claim 1 characterised in that the escapement wheel (9) interacts with the resonator (14) at each half oscillation of the resonator with substantially equal and opposite tangential forces.
3. The regulator system according to claim 1 characterised in that the tuning fork (14) is composed of two arms (16, 17) attached to a foot (15) having a section larger than that of the arms.
4. The regulator system according to claim 1 characterised in that the resonator has the shape of a double H-shaped tuning fork, the central part of which serves as a base for the four arms.
5. The regulator system according to any one of the preceding claims, characterised in that the resonator carries means for adjustment at the chronometric frequency in the form of adjustable weights (31, 32) disposed on the structure of the resonator or of pads provided to be removed by ablation.
6. The regulator system according to claim 1 characterised in that the permanent magnet is made in the form of one or more magnetic layers.
7. The regulator system according to claim 6 characterised in that the magnetic layer(s) are made of a platinum and cobalt alloy.
8. The regulator system according to one of claims 1 to 2 characterised in that the tuning fork resonator carries electrets on each arm and in that the escapement wheel is conductive or locally electrified with charges opposite to the electrets of the resonator.
9. A horological movement including a regulator system according to one of the preceding claims.

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