Patent Grant
9128464
This application claims priority from European Patent Application No. 11181512.2 filed Sep. 15, 2011, the entire disclosure of which is incorporated herein by reference.
The invention relates to a timepiece comprising oscillators intermittently synchronised by an escapement.
Generally, the regulating member of a watch is formed by a harmonic, damped, almost isochronous resonator, whose oscillation is maintained by an escapement system, which transfers the energy to the resonator at each oscillation vibration (lever escapement) or each oscillation period (detent escapement).
There are several problems concerning maintenance of the oscillation of the regulating member, also called the resonator. Thus, the transfer of energy to the resonator disturbs its frequency (and therefore the rate of the watch) in every case where the transfer is not symmetrical relative to the point of rest of the resonator. Further, the energy spent by the escapement per vibration (or per period) and the resonator frequency determine the power reserve of the watch, which is thus limited.
Moreover, since the amplitude of the oscillator is limited by geometrical reasons, in order to increase the energy of the oscillator (and therefore its stability against external disturbances) its elastic constant must be increased, which may mean that it is impossible to start up high frequency oscillators.
Finally, the mean efficiency of the escapement and fluctuations in efficiency are affected, amongst other things, by the acceleration of the escapement components. Thus, the more quickly the resonator recovers, the higher the efficiency and time constant will be. Hence, for very high frequency resonators, losses must necessarily be increased (and the power reserve decreased) and/or fluctuations in efficiency must be increased.
It is an object of the present invention to overcome all or part of the aforecited drawbacks by proposing a timepiece whose frequency (improved display resolution) and mechanical energy (improved stability and precision) are increased, and wherein the oscillation maintenance and power reserve are also improved.
The invention therefore relates to a timepiece comprising a first resonator oscillating at a first frequency and connected by a main gear train to a main energy source via a main escapement, a second resonator oscillating at a second frequency, which is a product of the first frequency according to a factor which is a rational number, characterized in that the second resonator also cooperates with the main escapement in order to release the main escapement to maintain the first resonator only when said second resonator oscillates.
It is clear that the invention enables the maintenance frequency of a resonator to be reduced below its frequency. The invention also ensures that a high frequency movement can auto-start while preserving its power reserve, particularly by improving the efficiency of the escapement functions. Finally, the invention substantially reduces rate errors generated by disturbances outside the watch.
In accordance with other advantageous features of the invention:
Other features and advantages will appear clearly from the following description, given by way of non-limiting illustration, with reference to the annexed drawings, in which:
As explained above, it is an object of the invention to integrate, in a mechanical wristwatch, a high frequency resonator (e.g. 10 Hz or 50 Hz or more) whose oscillation maintenance is synchronised by a low frequency resonator (e.g. 1 Hz or 2 Hz) in order to maintain the resonator over a period higher than its frequency.
In an example embodiment illustrated in
Preferably, according to the invention, the second frequency f2 is a fraction of the first frequency (f2=f1/N or f2=f1/2N where N is an integer number greater than 1). It is thus clear that main resonator R1 is maintained solely with the period of the secondary resonator.
However, the factor may also be a rational number N′ if the gear ratio Ri is different between each oscillator. Indeed, in this variant, the frequencies on the wheel which secures the two escapements must be linked by a multiple integer number. However, the gear ratio can arbitrarily and independently subdivide the frequency of the oscillators. The oscillator frequencies may then not be linked by an integer number, but by a rational number (f2=f1/N′ where N′ is equal to N*R1/R2 where N is an integer number greater than 1).
This configuration advantageously means that a basic movement (or chronograph movement) can be made with a high resolution (for example 1/20th of a second or 1/100th of a second). It also increases the precision and shock resistance of the main resonator and increases the power reserve while guaranteeing that even a very high frequency movement, for example 50 Hz, can auto-start. Finally, this configuration allows low amplitude resonators to be maintained and the display train and/or maintenance train to be partially or totally omitted.
According to a first embodiment illustrated in
By way of example, it can be assumed that wheel 3 is free if the two resonators R1 and R2 are situated around the point of rest in the angular interval (−20°, +20°). To ensure that the main resonator R1 is maintained, if the two resonators have a considerably different phase, i.e. they pass the point of rest at two different moments, detent 7 of secondary resonator R2 may be devised to increase the angular interval in which main escapement D2 is released by secondary resonator R2. It is thus clear that detent 7 of secondary resonator R2 preferably includes release over a larger angular interval than the angle of detent 5 at which main resonator R1 releases wheel 3.
Consequently, as soon as the detent is released, since the braking force acting on the oscillator is applied very close to the centre of rotation of the oscillator, the resulting perturbation torque is very low, i.e. the angle of release for secondary resonator R2 may thus be considerably increased without affecting the rate.
If, after a shock, the phase difference of the resonators is too great and oscillation cannot be maintained, it is clear that the increasing or decreasing isochronism curve of main resonator R1 allows the phase to be made up between the two resonators after a few oscillations. In fact, main resonator R1 will lose amplitude until phasing is re-established between the oscillation of secondary resonator R2 and one of the N oscillations of main resonator R1. It is thus clear that the additional rate error on the display will be less than or equal to one period of main resonator R1, which means that it will become smaller the higher the frequency f1 becomes.
According to a second embodiment illustrated in
However, compared to the first embodiment, it is noted that resonators R1 and R2 release, by detent, two different wheels 11 and 15, which mesh (in parallel or in series) with the main gear train T2. Once released, wheel 15 is not locked again until wheel 11, and therefore escapement D2, is released. In this case, escapement D2 is released at each oscillation period (or vibration) of main resonator R1 and at each oscillation of secondary resonator R2, maintenance is guaranteed independently of the phase difference of resonators R1 and R2.
The example illustrated in
When main resonator R1 passes, wheel 11 is released by detent 13 at top toothing 12 and allows main resonator R1 to be maintained, before being locked again by detent spring 13 on top toothing 12 and/or by wheel 15 which then plays a part comparable to a stopping device. Of course, wheel 11 remains locked when main resonator R1 passes if secondary resonator R2 has not previously released wheel 15.
It is thus clear that the two embodiments of main escapement D2 provide substantially the same advantages and use a single main escapement D2 for the two resonators R1 and R2, i.e. the resonators are maintained using the same main energy source B2 by main escapement D2.
According to a variant of the above two embodiments, the second resonator R2 is also connected to a secondary gear train T3 to a secondary energy source B3 via a second escapement D3. Indeed, if it becomes necessary to maintain secondary resonator R2 outside main escapement D2, a second escapement D3 preferably a Swiss lever escapement, maintains secondary resonator R2. Thus, at each vibration of secondary resonator R2, the latter is powered by secondary energy source B3 (or, alternatively, by the main energy source B2 by means of a gear) via the secondary gear train T3.
A particular alternative of this variant which requires maintaining secondary resonator R2 outside main escapement D2 is shown in
The advantages of the invention have been quantified from the variant of the first embodiment of main escapement D2. If the elastic constant of the resonator is kj and its inertia mj its oscillation frequency is:
fj=√{square root over (kj)}/mj/2π (1)
For a stationary amplitude Aj, the mechanical energy of the resonator j is:
Ej=½kjAj2 (2)
The resonator energy loss j at each oscillation is:
and depends on the resonator quality factor Qj (which, for viscous friction, increases with frequency).
The escapement must supply the same quantity of energy. If the torque applied to the resonator is constant over a given angle θj, the maintenance energy is:
Increasing the resonator frequency increases the quality factor Qj, which promotes improved timing. If the resonator energy is constant, losses decrease and the maintenance energy also decreases. Since the angle of energy transmission cannot be decreased indefinitely, the maintenance torque must be decreased.
Moreover, the condition necessary for starting is that the maintenance torque exceeds the elastic return torque of the resonator at the exit angle thereof.
Cech>kjθj/2 (5)
This means that the maintenance torque cannot be decreased indefinitely while maintaining the auto-start property of the resonator, and, at the same time, without decreasing the mechanical energy of the resonator which decreases its stability against external disturbance.
It must also be realised that the increase in frequency and decrease in maintenance torque results in a higher resonator speed (v=2π f A, (6)) at the point of rest, i.e. at the moment when maintenance does not cause rate errors, while the acceleration of the escape wheel sets is lower. It is thus observed that the escapement efficiency drops because the escapement is unable to catch up with the resonator. It is thus clear that the escape wheel sets must catch up with the resonator speed during the time available for maintenance:
Cech/mech>v/dtech=v2/θj (7)
where mech is the equivalent inertia of the escapement.
Finally, if the frequency and energy of the resonator are increased, the power reserve will necessarily decrease, since the escapement must maintain the resonator more often and with more energy each time.
Thus, quantitatively, for an ordinary resonator with a frequency f equal to 10 Hz, an inertia m equal to 2 mg·cm2, an elastic coefficient k equal to 0.79 μNm·rad−1 and a quality factor Q equal to 600, the maintenance energy Eech is substantially equal to 25 nJ. According to relation (4), therefore, maintenance torque Cech is substantially equal to 28 nNm, for a maintenance angle θj of 50°. The system does not auto-start because the term k·θj/2 is greater than the maintenance torque Eech according to relation (5).
On the other hand, the time available for maintenance, which corresponds to the resonator passing from the point of rest, is reduced to dtech equal to 40°, i.e., according to relation (6), a time of 2.3 milliseconds for an amplitude A equal to 280°. To achieve sufficient acceleration of the escape wheel sets with such a low maintenance torque, according to relation (7), the inertia of the maintenance wheel sets has to be considerably reduced to an equivalent inertia of substantially 2.10−3 mg·cm2.
If a resonator of the same type is maintained by an escapement D2 according to the invention, at a frequency f2 equal to 1 Hz, the lost energy to be compensated for at each maintenance function is 20 times higher. At parity, with a maintenance angle θj equal to 50°, the maintenance torque Cech is 20 times higher, i.e. approximately 0.7 μNm, and the self-start system accords with relation (5).
Likewise, the acceleration of the maintenance wheel sets is increased 20 fold and efficiency can be freely optimised, the only constraint being geometrical and tribological and no longer dynamic and related to the energy balance. Consequently, since efficiency is improved, the power reserve is necessarily improved.
To demonstrate the advantages of the timepiece of the invention, the coupled movement equations were resolved numerically. A secondary resonator R2 with an inertia m2 equal to 10 mg·cm2, a frequency f2 equal à 1 Hz and a quality factor Q2 equal to 150 was considered. Moreover, the main resonator R1 has a mechanical energy equal to 9.6 μJ, whereas secondary resonator R2 has an energy equal to 0.5 μJ.
Moreover,
Consequently, the response of a timepiece according to the invention to a given disturbance P is similar, or even better than the response of an equivalent single resonator Rx, i.e. with the same energy Ex, same frequency fx et same amplitude Ax. Further, secondary resonator R2 advantageously forms an anti-tripping system for the maintenance function, particularly by preventing rate errors linked to dual maintenance.
Depending upon the embodiment, variant and/or alternative selected above, timepiece 1 according to the invention proposes three types of display device A1, A2 and/or A3.
A first display type includes a display device A1 comprising a display energy source B1 connected to a gear train for the display T1 secured to a distribution mechanism D1 controlled by main resonator R1. Preferably according to the invention, the distribution mechanism D1 is formed by a detent 9 controlled by main resonator R1 so as to release, at each period or vibration of main resonator R1, wheel 10 connected to gear train T1 without providing any additional maintenance torque to first resonator R1.
It is thus clear that display device A1 takes advantage of the high frequency of main resonator R1 by displaying the movement, for example of wheel 10, i.e. with improved resolution such as, for example, up to 1/20th of a second or up to 1/100th of a second. Consequently, in the case of the two embodiments and/or the variant explained above, display device A1 can display the time with improved resolution. Further, in the case of the alternative explained above, display device A1 can display the measured time with improved resolution.
A second display type includes a time display device A2 connected to secondary gear train T2. It is therefore clear that the display occurs at the same time that main resonator R1 is being maintained. In this case, the high frequency is not used to improve resolution but to improve stability. It is also clear that this configuration forms a very efficient anti-tripping system for detent escapement D2, regardless of the embodiment used.
Finally, a third display type includes a time display device A3 connected to secondary gear train T3. This third type is entirely dedicated to the above alternative in which main resonator R1 is used solely for measuring a time. Indeed, since secondary resonator R2 is the only one permanently operating, the time display can only be performed using secondary gear train T3.
In light of the above explanations, it is clear that the invention reduces the maintenance frequency of a resonator to below its frequency. The invention also ensures that a high frequency movement can auto-start while preserving its power reserve, particularly by improving the efficiency of the escapement functions. Finally, the invention substantially reduces rate errors generated by disturbances outside the watch.
Of course, this invention is not limited to the illustrated example but is capable of various variants and alterations that will appear to those skilled in the art. In particular, other types of resonators and/or escapements can be envisaged without departing from the scope of the invention. By way of example, some mechanical components could advantageously be replaced and/or assisted by magnetic components.
Finally, the timepiece may comprise a single energy source, i.e. a single energy source fitted with gears may respectively form the energy sources B1 and/or B2 and/or B3 described above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 11181512 | Sep 2011 | EP | regional |
| Number | Name | Date | Kind |
|---|---|---|---|
| 1232285 | Greeley | Jul 1917 | A |
| 7815363 | Buttet et al. | Oct 2010 | B2 |
| 7950846 | Hessler et al. | May 2011 | B2 |
| 20020088295 | Oechslin | Jul 2002 | A1 |
| 20050007888 | Jolidon | Jan 2005 | A1 |
| 20060221775 | Zaugg | Oct 2006 | A1 |
| 20100002548 | Hessler et al. | Jan 2010 | A1 |
| 20100214879 | Lechot et al. | Aug 2010 | A1 |
| Number | Date | Country |
|---|---|---|
| 156801 | Aug 1932 | CH |
| 697523 | Nov 2008 | CH |
| 2 141 555 | Jan 2010 | EP |
| 2 221 676 | Aug 2010 | EP |
| Entry |
|---|
| U.S. Appl. No. 13/609,786, filed Sep. 11, 2012, Helfer, et al. |
| U.S. Appl. No. 13/609,943, filed Sep. 11, 2012, Helfer, et al. |
| European Search Report issued Apr. 26, 2012 in corresponding European Application No. 11 18 1512 filed on Sep. 15, 2011 (with an English Translation). |
| Number | Date | Country | |
|---|---|---|---|
| 20130070569 A1 | Mar 2013 | US |
