Patent Grant
9971309
This application claims priority from European Patent Application No. 15180503.3 filed Aug. 11, 2015, the entire disclosure of which is hereby incorporated herein by reference.
The present invention concerns a mechanical timepiece movement provided with a feedback system for the movement.
For many years, mechanical watch movements have undergone multiple improvements, particularly in order to adjust or regulate the oscillation frequency of the sprung balance used as the resonator for the local oscillator. The conventional mechanical watch movement and, in particular, its Swiss lever escapement, is characterized by its robustness to shocks experienced by the watch. This means that the state of the watch is, in general, unaffected by a one-time shock. However, the efficiency of such an escapement is not very good, for example around 30%. Further, the Swiss lever escapement does not permit the use of resonators with a high frequency or low amplitude.
WO Patent Application No. 2006/045824 A2 discloses a regulating member for returning the oscillating sprung balance to a position of equilibrium. An escapement is also provided for maintaining the oscillation of the balance wheel about its position of equilibrium. To achieve this, the balance wheel is connected to at least one movable permanent magnet, whereas the regulating member has a fixed permanent magnet so as to generate a magnetic field returning the balance to its position of equilibrium. There is no description regarding a feedback system capable of adjusting the oscillation frequency of the sprung balance, which constitutes a drawback.
In order to maintain a local oscillator resonator at a high frequency, the principle of the Swiss lever escapement has to be adjusted. To achieve this, an increase in the frequency of the regulating member requires more energy to maintain the oscillator. To reduce energy, it is possible to reduce the oscillator mass or inertia, to reduce the oscillation amplitude, to increase the quality factor of the oscillator, or to improve the energy transmission efficiency between the drive member and the regulating member. Thus, with a conventional Swiss lever escapement, too much energy is consumed by accelerating and stopping multiple times per second. Even if the Swiss lever and its wheel are made as light as possible, this does not make it easy to achieve a high frequency oscillator.
In a mechanical movement proposed by De Bethune, there is proposed a magnetic escapement with a continuous sinusoidal transmission of energy. A mechanical drive member transmits a torque force to a reduction gear train. At the end of said gear train, a magnetic rotor transmits energy to the resonator of the local oscillator, on which permanent magnets are fixed. The gear train speed is synchronized with the natural resonator frequency. The resonator, as the regulating member, controls the measurement of time. The speed of motion of the time indicator hands is controlled by a precise and regular division of time.
Such a resonator can replace the conventional sprung balance to better satisfy the requirements and constraints of high frequency oscillation in order to improve precision. There are no longer any specific points of attachment. The resonator is stiffer and permits the use of a first natural vibration mode. The quality factor is also higher than a conventional oscillator even at low amplitude.
However, according to the embodiment described above for the De Bethune movement, there is no shock resistance. In such conditions, the hands are likely to advance rapidly after any shocks. Further, there is no description of a feedback system for simply and precisely adjusting the oscillation frequency of a sprung balance, as in the present invention, which constitutes a drawback.
The invention seeks a means for using a local oscillator resonator, which has a high quality factor, a high frequency and/or low amplitude. This is achieved without relinquishing the robustness to shocks of a Swiss lever escapement.
It is therefore a main object of the invention to overcome the aforementioned drawbacks by proposing a mechanical timepiece movement provided with a feedback system capable of precisely adjusting the oscillation frequency of a local oscillator resonator of the mechanical movement.
To this end, the present invention concerns a mechanical timepiece movement which includes at least one barrel, a set of gear wheels driven at one end by the barrel, and an escapement mechanism of a local oscillator with a resonator in the form of a sprung balance, the escapement mechanism being driven at another end of the set of gear wheels, and a feedback system for the timepiece movement,
wherein the feedback system includes at least one precise reference oscillator combined with a frequency comparator for comparing the frequency of the two oscillators and a mechanism for regulating the resonator of the local oscillator to slow down or accelerate the resonator based on the result of a comparison in the frequency comparator.
Particular embodiments of the mechanical timepiece movement are defined in the dependent claims 2 to 22.
One advantage of the mechanical timepiece movement according to the invention lies in the fact that it is possible to optimise the precision of the reference oscillator with no concerns as to its shock resistance and therefore to optimise the shock resistance of the local oscillator with no concerns as to its precision.
Another advantage is that it is possible to offer a product, which respects the aesthetic codes of watchmaking, as a result of the presence of a sprung balance as the local oscillator, while increasing precision through the use of a reference oscillator, which may be at a high frequency.
wherein the mechanical timepiece movement includes at least one barrel, a set of gear wheels driven at one end by the barrel, and an escapement mechanism of a local oscillator with a resonator in the form of a sprung balance, the escapement mechanism being driven at another end of the set of gear wheels, and a feedback system for the timepiece movement,
wherein the feedback system includes at least one precise reference oscillator combined with a frequency comparator for comparing the frequency of the two oscillators and a mechanism for regulating the resonator of the local oscillator to slow down or accelerate the resonator based on the result of a comparison in the frequency comparator.
The objects, advantages and features of the mechanical timepiece movement provided with a feedback system for the mechanical movement will appear more clearly in the following non-limiting description made with reference to the drawings, in which:
In the following description, all those components of the mechanical timepiece movement that are well known to those skilled in the art in this technical field will be described only in a simplified manner.
As seen schematically in
Transmission assembly 12 includes a set of gear wheels 12 driven at a first end wheel by barrel 11. The wheels of the set of gear wheels 12 are preferably toothed wheels. A last drive wheel of the set of gear wheels 12 drives an escapement mechanism of a local oscillator 13. This local oscillator 13 also includes a resonator, which takes the form of a sprung balance.
Feedback system 2 may be connected to the input of local oscillator 13 in order to control, in particular, the oscillation frequency of the local oscillator resonator. The connection between conventional mechanical movement 1′ and feedback system 2 may be achieved via the last wheel of the set of gear wheels 12.
Feedback system 2 includes, firstly, a reference oscillator 21, which is precise, i.e. at least more precise than the resonator of local oscillator 13. Feedback system 2 further includes a frequency comparator 22, which is connected or combined with the reference oscillator or resonator 21 in order to compare the rate of the two oscillators 21, 13, and a regulating mechanism 23. This regulating mechanism 23 can adjust the oscillation frequency of the resonator of local oscillator 13 based on the result of the comparison in frequency comparator 22. The frequency of the resonator, such as the sprung balance of local oscillator 13, can thus be adjusted by the regulating mechanism, which will be explained hereinafter, to slow down or accelerate the local oscillator resonator.
It is to be noted that the “rate” or frequency of the local oscillator or of the reference oscillator, means the oscillation frequency or the rotational speed of a wheel in connection with the local oscillator and/or the reference oscillator.
The set of gear wheels 12 may also include a second wheel 122, whose central pinion 122′ is driven by the external toothing of first wheel 121. There is also a multiplication of rotational speed with second wheel 122 rotating faster than first wheel 121. A third wheel 123 may also be provided and be driven, via a central pinion 123′, by the external toothing of second wheel 122. There is also a multiplication of rotational speed with third wheel 123 rotating faster than second wheel 122. This third wheel 123 may be the last wheel of the set of gear wheels 12 for driving one or more time indicator hands of the mechanical watch.
The last wheel 123 of the set of gear wheels 12 drives an escapement mechanism of local oscillator 13. This escapement mechanism may include an escape wheel 16, whose central pinion 16′ is driven by last wheel 123, and a Swiss lever 15 meshing with the escape wheel and cooperating in a conventional manner with a sprung balance 14. The sprung balance 14 has a balance spring 14′ attached, on the one hand, at one end to the balance rotation staff and, on the other hand, at the other end to a balance spring stud which is generally attached to the watch plate. The oscillation frequency of the sprung balance is controlled and adjusted by feedback system 2.
A first embodiment of feedback system 2 is shown in
It is to be noted that the reference resonator is combined with the frequency comparator. There is a magnetic interaction with a rotating wheel connected to the conventional mechanical movement to excite the reference resonator and to compare the rate or frequency of the oscillators.
An exciter wheel 31 can be directly connected to one of the wheels of the set of gear wheels of the conventional mechanical movement. This exciter wheel may also be one of the wheels of said set of gear wheels or there may be a multiplier or division arrangement between one of the wheels of the set and exciter wheel 31. Exciter wheel 31 thus rotates at a certain rotational speed Vext, which is proportional to the angular excitation frequency or pulsation of the local oscillator. This exciter wheel 31 has a certain number N of peripheral teeth. The number of teeth N may be an odd number, for example the exciter wheel may have 9 teeth.
The reference oscillator or resonator of the feedback system has at least one permanent magnet 33 disposed at a free end of an arm 32 of the resonator, which is attached via a base 34 to a movable frame 35 mounted on a plate of the watch movement. This permanent magnet 33 is disposed in proximity to exciter wheel 31 and preferably the magnetic polarization of the magnet is oriented towards the centre of exciter wheel 31.
Permanent magnet 33 is attracted to exciter wheel 31 when a tooth is presented close to the magnet, and is much less attracted to the exciter wheel when the magnet faces an empty space between two of the exciter wheel teeth. Since the exciter wheel rotates at a certain rotational speed Vext, magnet 33 will thus oscillate at a second frequency ω0 through magnetic interaction with said exciter wheel 31.
During the rotation of exciter wheel 31 and as a function of its number N of peripheral teeth, an excitation frequency ωext is determined on the basis of the natural rotational speed of the wheel Vext. The excitation frequency ωext is therefore equal to N·Vext, where N is the number of teeth of the exciter wheel. The number of teeth N may be an odd number, for example the exciter wheel may have 9 teeth. It is therefore this excitation frequency ωext, which can be compared to the oscillation frequency ω0 of the reference oscillator to compare the rate of the two oscillators.
Preferably, two arms 32, 32′ may be provided, each with a permanent magnet 33, 33′ mounted at their first end to define a tuning fork. The second ends of the two arms 32, 32′ are joined and attached via base 34 to frame 35. The two permanent magnets 33, 33′ are disposed in proximity to exciter wheel 31 and in diametrically opposite positions with exciter wheel 31 between the two permanent magnets 33, 33′.
Moving frame 35 is preferably a hollow wheel disposed coaxially to exciter wheel 31. This hollow wheel 35 is maintained in free rotation on the plate by means of rollers or pins or ball bearings 38 in contact with an inner surface of hollow wheel 35. The number of rollers or pins or ball bearings 38 must be at least three in order for the frame or hollow wheel to be able to rotate on the same axis of rotation as the exciter wheel. Frame or hollow wheel 35 is, however, maintained in a defined position by at least one return spring 36, or two return springs 36, 36′ attached on one side to the plate. Preferably, the return springs 36, 36′ are connected to the hollow wheel in diametrically opposite positions.
When exciter wheel 31 rotates at a certain rotational speed Vext, the tuning fork reference oscillator will be excited at an oscillation frequency ω0. The excitation of the reference oscillator is obtained as a result of the rotation of exciter wheel 31, which is made of a ferromagnetic material for magnetic interaction with the permanent magnet or magnets 33, 33′ carried at a first end of arms 32, 32′. Said exciter wheel 31 may also simply have ferromagnetic portions on or in the teeth for magnetic interaction with permanent magnets 33, 33′. There may also be a continuous deposit of ferromagnetic material over the peripheral teeth of exciter wheel 31. A magnetic interaction torque or lock torque thus also occurs. Since the rotation of the exciter wheel is in the counterclockwise direction, frame 35 will also tend to move in the counterclockwise direction, while being retained by return springs 36, 36′.
The rotational speed of exciter wheel 31 may increase gradually and then stabilise in principle close to the reference rotation frequency ω0. As indicated above, in such case there is a lock torque. However, if the interaction torque is further increased, the system unlocks and the speed of exciter wheel 31 is then limited only by friction. It is therefore sought to synchronize the rate of the two oscillators via the feedback system.
As also shown in
It is also to be noted that frame 35 and return springs 36, 36′ can be incorporated in a one-piece component. Further, the reference oscillator may take a different form from a tuning fork. The permanent magnets may also be disposed on the exciter wheel with the ferromagnetic arms 32, 32′ of the tuning fork. An end portion of each arm faces the exciter wheel to be excited by the rotation of said exciter wheel 31.
The regulating mechanism is represented by output wheel 37 of the feedback system, which meshes with a toothed base portion, for example, in the form of an arc of a circle, of a moving regulating member 137. The regulating member is mounted to rotate on the watch plate about an axis parallel to the axis of rotation of the balance, but outside of sprung balance 14. The regulating member thus includes a beak at the end of an arm opposite the toothed portion. The regulating beak is capable of moving closer to or further from a last coil of balance spring 14′ as a function of an angle of rotation θ of the beak which depends on the frequency comparison in the feedback system.
The moving beak of regulating member 137 acts on the active length L0 of the balance spring from a given elongation. The period of oscillation of the sprung balance depends on the active length of balance spring 14′. During oscillation, the balance spring alternately retracts and extends. If an obstacle, such as the stiff beak, is placed on the trajectory of extension of the last wheel of the spring, the active length of the spring is momentarily changed during the oscillation. This results in a decrease in the mean active length and thus a decrease in the oscillation period.
It is clear that it is also possible to envisage not using output wheel 37, but allowing the toothed portion of the frame to mesh directly with the toothed portion of regulating member 137.
For this second embodiment of the regulating mechanism, regulating member 137 includes a toothed base portion, for example, in the form of the arc of a circle, which can mesh directly with the toothed portion of the frequency comparator frame. The regulating member is mounted to rotate on the watch plate about an axis parallel to the axis of rotation of the balance, but outside of sprung balance 14. The regulating member also includes an arched portion of complementary shape to an outer surface of balance 14 to vary the friction caused by air on the balance. This arched portion is disposed on a side opposite to the toothed portion with respect to the axis of rotation of the regulating member. As a function of the difference between rotation frequencies ωext−ω0, the arched portion can move closer to or further from the outer surface of the balance to adjust the rate or frequency of the local oscillator. Thus, with careful selection of the isochronism curve of the sprung balance used, the sprung balance frequency decreases with the increase in friction caused by the arched portion of regulating member 137 approaching the balance, and vice versa.
It is to be noted that for the two embodiments described with reference to
Adjustment of the oscillation frequency of balance 14 can also be achieved by a magnetic coupling between regulating member 137 and said balance in addition to friction caused by air.
As regards the feedback system and according to another embodiment, a different arrangement of the reference oscillator may be provided for magnetic interaction with the exciter wheel to determine the rate or frequency of the two oscillators. The exciter wheel may include magnetic tracks annularly arranged on one surface and regularly spaced from each other. These annularly distributed magnetic tracks are centred on the axis of rotation of the exciter wheel. When the exciter wheel rotates, at least one magnetic coupling element, which is a permanent magnet of the reference oscillator, is excited by each rotating magnetic track of the exciter wheel. This permanent magnet is elastically maintained on a moving frame, which can move angularly or linearly to compare the frequency of the two oscillators and to enable a regulating mechanism to adjust the oscillation frequency of the sprung balance.
As explained in detail with reference to
The reference oscillator or resonator is a resonator with crossed strips 44, 45, 48, 49. It includes, on an arched sector 42, at least one permanent magnet 43 close to toothed exciter wheel 41. The stiff arched sector, which may be made of metallic material, is connected via two first crossed flexible strips 44, 45 to a first base plate 46. These first crossed elastic strips 44, 45 extend at a distance from each other in two parallel planes. These two parallel planes are also parallel to the plane of exciter wheel 41, and to the watch plate, on which are mounted the various elements of the mechanical movement and of the feedback system.
The first base plate 46 is also fixed on a second plate 47 of a complementary part of the crossed strip resonator. This second plate 47 is connected via two second crossed flexible strips 48, 49 to a securing plate 50, which is fixedly mounted on the watch plate. These second crossed elastic strips 48, 49 extend at a distance from each other in two parallel planes, which are also parallel to the two planes of the first elastic strips 44, 45. These second crossed flexible strips 48, 49 are situated between first elastic strips 44, 45 and the watch plate.
The first and second base plates 46, 47 are movable and move angularly as a function of the lock torque between the resonator and the wheel. The first and second base plates 46, 47 are illustrated in arched form, but may take another general shape, such as a rectangular parallelepiped, and form only one piece. During the rotation of exciter wheel 41, which is preferably made of ferromagnetic material, arched sector 42 with its permanent magnet 43 oscillates at a frequency ω0 in the plane of the exciter wheel. A magnetic interaction occurs and, as a function of the rotational speed of the exciter wheel, there is an angular displacement of plates 46, 47 caused by a defined lock torque.
In this second embodiment, the regulating mechanism is formed here by a regulating beak 53, which is attached, for example, to second base plate 47. A second permanent magnet 52 is disposed on regulating beak 53 cooperating, for example, with an aluminium plate 51 disposed underneath the beak and on the watch plate. This aluminium plate 51 can attenuate the vibrations of beak 53 following the oscillation of arched sector 42 acting like a Foucault brake.
As a function of the comparison of rotation frequencies ωext−ω0, plates 46 and 47 are displaced with respect to their position of equilibrium. The angular displacement of plates 46, 47 moves beak 53 in the direction of balance spring 14′ of balance 14 to regulate the oscillation frequency of the local oscillator, as explained with reference to
According to a different variant embodiment, arched sector 42 could be replaced by a flywheel carrying at least one permanent magnet 43 or having a magnetized portion made in the metallic material of the flywheel to be excited by exciter wheel 41 as it rotates. The flywheel may be connected to first base plate 46 by the two first crossed flexible strips 44, 45 remote from each other and intersecting on a virtual pivot axis parallel to the axis of rotation of the exciter wheel. The crossed strips may be disposed at an angle α relative to the pivot axis, which may be comprised between 60° and 80°.
The two second crossed flexible strips 48, 49 are also remote from each other, but disposed between the first crossed strips 44, 45 and the watch plate, on which is fixed securing plate 50 of the combined reference oscillator and frequency comparator.
From the description that has just been given, several variant embodiments of the mechanical timepiece movement provided with a feedback system for the movement can be devised by those skilled in the art without departing from the scope of the invention defined by the claims. It is possible to envisage providing the exciter wheel with at least one permanent magnet to interact with a ferromagnetic metallic portion of the reference resonator in order to make it oscillate at a determined frequency. The exciter wheel may be a circular wheel with no teeth, but with ferromagnetic portions regularly spaced from each other and disposed over the entire periphery of the exciter wheel to interact magnetically with the permanent magnets of the reference oscillator. The frequency comparator frame can be linearly displaced when an arm or a magnetized element of the reference oscillator is magnetically coupled with the exciter wheel to control the adjustment of the regulating mechanism.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15180503 | Aug 2015 | EP | regional |
| Number | Name | Date | Kind |
|---|---|---|---|
| 2248165 | Dicke | Jul 1941 | A |
| 3134220 | Meisner | May 1964 | A |
| 3183426 | Haydon | May 1965 | A |
| 3512351 | Heeks | May 1970 | A |
| 3648453 | Aizawa | Mar 1972 | A |
| 3756014 | Zatsky | Sep 1973 | A |
| 3937001 | Berney | Feb 1976 | A |
| 3952497 | Schulz | Apr 1976 | A |
| 4106280 | Schulz | Aug 1978 | A |
| 20100214879 | Lechot | Aug 2010 | A1 |
| 20130070572 | Helfer | Mar 2013 | A1 |
| 20130170330 | Hessler | Jul 2013 | A1 |
| 20160357149 | Stranczl | Dec 2016 | A1 |
| Number | Date | Country |
|---|---|---|
| 2 207 303 | Jun 1974 | FR |
| 2 305 768 | Oct 1976 | FR |
| 378511 | Aug 1932 | GB |
| Entry |
|---|
| European Search Report dated Feb. 19, 2016 in European Application 15180503, filed on Aug. 11, 2015 ( with English Translation). |
| Number | Date | Country | |
|---|---|---|---|
| 20170045861 A1 | Feb 2017 | US |
