Patent Grant
11480925
This application is a United States national stage application of International Application No. PCT/EP2018/056649, filed Mar. 16, 2018, which designates the United States, and claims priority to European Patent Application No. 17163250.8, filed Mar. 28, 2017, and European Patent Application No. 17172491.7, filed May 23, 2017, and the entire contents of each of the above applications are hereby incorporated herein by reference in entirety.
The present invention relates to a mechanical timepiece comprising a movement wherein the running is enhanced by a device for correcting a potential time drift in the operation of the mechanical oscillator which paces the running of the movement. Such a time drift occurs particularly when the average natural oscillation period of said mechanical oscillator is not equal to a set-point period. This set-point period is determined by an auxiliary oscillator which is incorporated into the correction device.
In particular, the mechanical timepiece is formed, on one hand, by a movement comprising:
Timepieces as defined in the field of the invention have been proposed in some prior documents. The patent CH 597 636, published in 1977, proposes such a timepiece with reference to
The electronic circuit comprises a time base comprising a quartz generator and serving to generate a reference frequency signal FR, this reference frequency being compared with the frequency FG of the mechanical oscillator. The frequency FG of the oscillator is detected via the electrical signals generated in the coil by the pair of magnets. The regulation circuit is suitable for momentarily inducing a braking torque via a magnetic magnet-coil coupling and a switchable load connected to the coil.
The use of a magnet-coil type electromagnetic system for coupling the balance-hairspring with the electronic regulation device gives rise to various problems. Firstly, the arrangement of permanent magnets on the balance results in a magnetic flux being constantly present in the timepiece movement and in this magnetic flux varying spatially periodically. Such a magnetic flux may have a harmful action on various members or elements of the timepiece movement, particularly on elements made of magnetic material such as parts made of ferromagnetic material. This may have repercussions on the proper operation of the timepiece movement and also increase the wear of pivoted elements. It may indeed be envisaged to screen to a certain degree the magnetic system in question, but screening requires particular elements which are borne by the balance. Such screening tends to increase the size of the mechanical resonator and the weight thereof. Furthermore, it limits the aesthetic configuration possibilities for the balance-hairspring.
Those skilled in the art are also aware of mechanical timepiece movements with which a device for regulating the frequency of the balance-hairspring thereof which is of the electromechanical type is associated. More specifically, the regulation occurs via a mechanical interaction between the balance-hairspring and the regulation device, the latter being arranged to act upon the oscillating balance by a system formed by a stop arranged on the balance and an actuator equipped with a movable finger which is actuated at a braking frequency in the direction of the stop, without however touching the felloe of the balance. Such a timepiece is described in the document FR 2.162.404. According to the concept proposed in this document, it is sought to synchronise the frequency of the mechanical oscillator on that of a quartz oscillator by an interaction between the finger and the stop when the mechanical oscillator exhibits a time drift relative to a set-point frequency, the finger being envisaged to be able to either lock momentarily the balance which is then stopped in the movement thereof during a certain time interval (the stop bearing against the finger moved in the direction thereof upon the return of the balance towards the neutral position thereof), or limit the oscillation amplitude when the finger arrives against the stop while the balance rotates in the direction of one of the end angular positions thereof (defining the amplitude thereof), the finger then stopping the oscillation and the balance starting to move straight away in the opposite direction.
Such a regulation system has numerous drawbacks and it could seriously be doubted that it could form an operational system. The periodic actuation of the finger relative to the oscillation movement of the stop and also a potentially large initial phase shift, for the oscillation of the stop with respect to the periodic movement of the finger towards this stop, pose a number of problems. It should be noted that the interaction between the finger and the stop is limited to a single angular position of the balance, this angular position being defined by the angular position of the actuator relative to the axis of the balance-hairspring and the angular position of the stop on the balance when idle (defining the neutral position thereof). Indeed, the movement of the finger is envisaged to make it possible to stop the balance by a contact with the stop, but the finger is arranged not to come into contact with the felloe of the balance. Furthermore, it should be noted that the time of an interaction between the finger and the stop is also dependent on the amplitude of the oscillation of the balance-hairspring.
It should be noted that the synchronisation sought appears to be unlikely. Indeed, in particular for a balance-hairspring wherein the frequency is greater than the set-point frequency timing the to-and-fro movements of the finger and with a first interaction between the finger and the stop which retains momentarily the balance returning from one of the two end angular positions thereof (correction reducing the error), the second interaction, after numerous oscillations without the stop touching the finger during the alternating movement thereof, will certainly be a stopping of the balance by the finger with immediate inversion of the direction of oscillation thereof, in that the stop abuts against the finger while the balance rotates towards said end angular position (correction increasing the error). Thus, not only is there an uncorrected time drift for a time interval that may be long, for example several hundred oscillation periods, but some interactions between the finger and the stop increase the time drift instead of reducing it! It should further be noted that the phase shift of the oscillation of the stop, and therefore of the balance-hairspring, during the second interaction mentioned above may be significant according to the relative angular position between the finger and the stop (balance in the neutral position thereof).
It may thus be doubted that the desired synchronisation is obtained. Furthermore, in particular if the natural frequency of the balance-hairspring is close but not equal to the set-point frequency, scenarios where the finger is locked in the movement thereof towards the balance by the stop which is situated at this time opposite the finger are foreseeable. Such parasitic interactions may damage the mechanical oscillator and/or the actuator. Furthermore, this limits practically the tangential range of the finger. Finally, the holding duration of the finger in the interaction position with the stop must be relatively short, therefore limiting a correction inducing a delay. In conclusion, the operation of the timepiece proposed in the document FR 2.162.404 appears to be highly unlikely to a person skilled in the art, and such a person is deterred from such a teaching.
An aim of the present invention is that of finding a solution to the technical problems and drawbacks mentioned above in the technological background.
Within the scope of the present invention, it is sought generally to enhance the precision of the running of a mechanical timepiece movement, i.e. reduce the daily time drift of this mechanical movement. In particular, the present invention seeks to achieve such an aim for a mechanical timepiece movement wherein the running is initially optimally adjusted. Indeed, a general aim of the invention is that of finding a device for preventing a potential time drift of a mechanical movement, namely a device for regulating the running of such a mechanical movement to increase the precision thereof, without for all that renouncing on being able to function autonomously with the best possible precision that this mechanical movement can have by means of the specific features thereof, i.e. in the absence of the regulation device or when the latter is inactive.
Another aim of the present invention is to achieve the aforementioned aims without having to incorporate electrical and/or electronic devices into the timepiece according to the invention, i.e. by using members and systems specific to so-called mechanical watches, which watches can integrate, according to various developments in the mechanical horology field, magnetic elements such as magnets and ferromagnetic elements, but not devices requiring an electrical power supply and thus an electrical power source.
For this purpose, the present invention relates to a timepiece as defined hereinabove in the technical field, wherein the mechanical oscillator mentioned is a slave oscillator and the regulation device is of the mechanical type, this mechanical regulation device being formed by a mechanical auxiliary oscillator, which defines a master oscillator, and by a mechanical braking device of the mechanical resonator of the slave oscillator. The mechanical braking device is arranged to be able to apply to the mechanical resonator of the slave oscillator a mechanical braking torque during periodic braking pulses which are generated at a braking frequency selected solely as a function of a set-point frequency for the slave oscillator and determined by the master oscillator. Then, the mechanical system formed by the mechanical resonator of the slave oscillator and the mechanical braking device is configured so as to enable the mechanical braking device to be able to start the periodic braking pulses at any position of said mechanical resonator in a range of positions, along the general oscillation axis of this mechanical resonator, which extends at least on a first of the two sides from the neutral position of said mechanical resonator over at least one first range of amplitudes that the slave oscillator is liable to have on this first side for a usable operating range of this slave oscillator.
In a general alternative embodiment, the mechanical system mentioned is configured such that said range of positions of the mechanical resonator of the slave oscillator, wherein the periodic braking pulses may start, also extends on the second of the two sides from the neutral position of said mechanical resonator over at least one second range of amplitudes that the slave oscillator is liable to have on this second side, along the general oscillation axis, for the usable operating range of this mechanical oscillator.
In a preferred alternative embodiment, each of the two parts of the range of positions of the mechanical resonator identified hereinabove, incorporating respectively the first and second ranges of the amplitudes that the slave oscillator is liable to have respectively on the two sides from the neutral position of the mechanical resonator thereof, exhibits a certain range whereon it is continuous or quasi-continuous.
In a general alternative embodiment, the mechanical braking device is arranged such that the periodic braking pulses each have essentially a duration of less than one quarter of the set-point period corresponding to the reciprocal of the set-point frequency. In a particular alternative embodiment, the periodic braking pulses have a duration of less than 1/10 of the set-point period. In a preferred alternative embodiment, the duration of the periodic braking pulses is essentially envisaged to be less than 1/40 of the set-point period.
By means of the features of the invention, surprisingly, the slave mechanical oscillator is synchronised on the master mechanical oscillator effectively and rapidly, as will become apparent hereinafter from the detailed description of the invention. The mechanical regulation device forms a device for synchronising the slave mechanical oscillator on the master mechanical oscillator, without closed-loop servo-control and without a measurement sensor of the movement of the mechanical oscillator. The mechanical regulation device therefore functions with an open loop and makes it possible to correct both an advance and a delay in the natural running of the mechanical movement, as will be explained hereinafter. This result is absolutely remarkable. The term ‘synchronisation on a master oscillator’ denotes herein a servo-control (open-loop, therefore with no feedback) of the slave mechanical oscillator to the master mechanical oscillator. The operation of the regulation device is such that the braking frequency derived from the reference frequency of the master oscillator is forced on the slave oscillator, which paces the running of the time data item indicator mechanism. This does not consist of the scenario of coupled mechanical oscillators, or even of the standard case of a forced oscillator. In the present invention, the braking frequency of the mechanical braking pulses determines the medium frequency of the slave oscillator.
The term ‘time the running of a mechanism’ denotes setting the pace of the movement of the moving parts of this mechanism when operating, in particular determining the rotational speeds of the wheels thereof and thus of at least one indicator of a time data item.
In a preferred embodiment, the mechanical system formed by the mechanical resonator and the mechanical braking device is configured so as to enable the mechanical braking device to start, in the usable operating range of the slave mechanical oscillator, a mechanical braking pulse substantially at any time of the natural oscillation period of this slave mechanical oscillator. In other words, one of the periodic braking pulses may start substantially at any position of the mechanical resonator of the slave mechanical oscillator along the general oscillation axis of this mechanical resonator.
As a general rule, the braking pulses have a dissipative nature as a portion of the energy of the oscillator is dissipated by these braking pulses. In a main embodiment, the mechanical braking torque is applied substantially by friction, in particular by means of a mechanical braking member applying a certain pressure on a braking surface of the mechanical resonator, which exhibits a certain range (not isolated) along the oscillation axis.
In a particular embodiment, the braking pulses apply a braking torque on the slave resonator, the value whereof is envisaged so as not to momentarily lock this slave resonator during the periodic braking pulses. In this case, preferably, the abovementioned mechanical system is arranged to enable the mechanical braking torque generated by each of the braking pulses to be applied to the slave resonator during a continuous or quasi-continuous time interval (not zero or isolated, but having a certain significant duration).
The invention will be described in more detail hereinafter using the appended drawings, given by way of examples that are in no way limiting, wherein:
The timepiece 2 further comprises a mechanical correction device 20 for correcting a possible time drift in the operation of the mechanical oscillator 18, this mechanical correction device comprising, for this purpose, a mechanical braking device 24 and a master mechanical oscillator 22 (hereafter also referred to as the ‘master oscillator’). The master oscillator is associated/coupled with the mechanical braking device in order to provide it with a reference frequency that sets the pace of the operation thereof and determines the braking frequency of the mechanical braking pulses provided by the mechanical braking device. It should be noted that the master oscillator 22 is an auxiliary mechanical oscillator insofar as the main mechanical oscillator, which paces the running of the timepiece movement directly, is the mechanical oscillator 18, the latter thus being a slave oscillator. Generally, the auxiliary mechanical oscillator is by nature or by design more precise than the main mechanical oscillator. In an advantageous alternative embodiment, the master oscillator 22 is associated with a mechanism for equalising the force applied thereon in order to maintain the oscillation thereof.
The master oscillator 22 comprises an auxiliary mechanical resonator 28, in this case conventionally formed by a balance 30 and a hairspring, and an auxiliary maintenance device formed by an auxiliary escapement 32, which comprises, for example, a pallet assembly 33 and an escapement wheel 34 which rotates in steps, one step being carried out at each alternation of the master oscillator. Thus, the average rotational speed of the wheel 34 is determined by the reference frequency of the master oscillator 22. The braking device 24 comprises a control mechanism 48 and a braking pulse generator mechanism 50 (also referred to as a ‘pulse generator’ hereafter) arranged such that it generates mechanical braking pulses at a braking frequency determined by the control mechanism. This control mechanism comprises a control wheel 37, which is rigidly connected to a wheel set 36 or forming same. The braking pulse generator mechanism comprises a braking member, formed by a pivoting member 40 and a spring 44 associated with the pivoting member.
The wheel set 36 is kinematically connected to an auxiliary mechanical power source 26. This wheel set 36 is a wheel set for transmitting mechanical power from the auxiliary source 26, firstly to the master oscillator 22 and secondly to the braking pulse generator 50. This is an advantageous alternative embodiment insofar as the mechanical correction device requires a single mechanical power source. Since the escapement 32 maintains the resonator 28 via the wheel set 36 which meshes with a pinion of the escapement wheel 34, the latter communicates a pace to the wheel set 36 and thus determines the average angular velocity (since it advances in steps), which is a function of the reference frequency of the master oscillator.
The pivoting member 40 is mounted on a rotational axis 43 and thus forms a two-armed lever. The first end 41 of the lever engages with the control wheel 37, which bears pins 38 arranged such that they successively come into contact with said first end in order to actuate the lever so as to firstly arm the pulse generator by laterally pressing against this first end to then make the lever pivot by compressing the spring 44. The pulse generator is thus armed as the control wheel advances in steps until a step at which a braking pulse is triggered when the pin in contact with the first end passes beyond this first end, which is thus released. The braking device will be adjusted such that this release occurs at once at a determined step of the control wheel. The lever 40 in this case forms a sort of hammer. In order to apply mechanical braking pulses to the balance 8, the lever 40 has, at the second end thereof, a relatively rigid strip spring 42 which forms a braking pad. Following the step at which a braking pulse is triggered, the lever is driven in rotation, thanks to the pressure applied by the spring 44 thus compressed, towards the felloe 9 of the balance and the strip spring undergoes a substantially radial movement relative to the rotational axis of the balance when approaching the felloe. The pulse generator is configured such that the braking pad comes into contact with the lateral surface 46 of the felloe 9 during the first oscillation of the lever subsequent to the release thereof and such that it thus applies a certain force couple on the balance in order to momentarily brake the latter. The braking pulse generator is preferably configured such that the movement of the lever is sufficiently damped to prevent rebounds that would create a series of braking pulses instead of a single braking pulse at the braking frequency. However, this damping is adjusted such that the braking pad comes into contact with the balance during the first oscillation of the lever after the triggering thereof.
The braking pulse generator is arranged such that the periodic braking pulses can have a certain duration, mainly by dynamic dry friction. In this respect, the rigidity and the mass of the strip spring 42 can be selected in a suitable manner. The strip spring 42 allows the shock during the impact thereof on the balance to be damped while extending the duration of contact and while inducing braking by friction between this strip spring and the braking surface envisaged on the balance. Adequate rigidity will also be chosen for the spring 44 and the position of the lever relative to the braking surface will be determined when this spring is idle (in the ‘non deformed’ position). Finally, it should be noted that other parameters of the pulse generator will be advantageously adjusted, in particular the length of each of the two arms thereof and the position of the anchoring of the spring on one of the two arms thereof.
In an advantageous alternative embodiment, the balance of the master resonator is mounted on flexible strips. Similarly, the pallet assembly of the escapement can be formed by flexible strips defining a bistable system and can include no pivoted shaft. In another specific alternative embodiment, the coupling between the pallet assembly and the escapement wheel is magnetic. In such a case, a magnetic escapement with a stop pin is obtained. Any high-precision mechanical oscillator can thus be incorporated into a timepiece according to the invention. For the purposes of illustration, the master oscillator 22 oscillates at a natural frequency of 10 Hz and has an intrinsic precision that is greater than the slave oscillator 18, the set-point frequency whereof is equal to 3 Hz. The escapement wheel 34 includes twenty teeth and thus performs half a revolution per second (½ rps). In the alternative embodiment shown, the control wheel bears five pins 38 evenly spaced apart on the felloe thereof. Since the reduction ratio between the pinion of the escapement wheel and the control wheel is in this case envisaged to be 7.5 (6-tooth pinion and 45-tooth wheel), the control wheel 37 performs 1/15 revolutions per second ( 1/15 rps) and the pulse generator is thus armed and released every third of a second, thus generating braking pulses at a frequency of ⅓ Hz (referred to as the ‘braking frequency’). Since the set-point frequency for the main oscillator 18 is 3 Hz, the mechanical correction device 20 induces a mechanical braking pulse every nine set-point periods, which substantially corresponds to one pulse every nine oscillation periods of the main oscillator, the natural frequency whereof is adjusted as well as possible on the set-point frequency. The synchronisation obtained by the mechanical correction device according to the invention will be described in detail hereafter.
In an alternative embodiment, the control wheel is envisaged such that it only bears a single pin so as to induce a single braking pulse per revolution. In such a case, the braking frequency is equal to 1/15 Hz and one braking pulse occurs every forty-five set-point periods. In another alternative embodiment which is also functional, as will be shown by the description of the synchronisation phenomenon obtained by the invention, the control wheel has two diametrically opposed pins. In such a case, the braking frequency is equal to 2/15 Hz and one braking pulse occurs every twenty-two and a half periods, i.e. only every forty-five alternations (uneven number) of the slave main oscillator 18.
As a general rule, the mechanical braking device 24 is arranged to be able to apply periodically to the mechanical resonator 6 braking pulses at a braking frequency selected only according to the set-point frequency for the slave main oscillator and determined by the master auxiliary oscillator 22. The mechanical braking device comprises a braking member capable of momentarily coming into contact with a braking surface of the slave mechanical resonator 6. For this purpose, the braking member is movable and has a to-and-fro movement that is controlled by a mechanical control device which periodically actuates same at a braking frequency, such that the braking member periodically comes into contact with the braking surface of the slave mechanical resonator in order to apply braking pulses thereto.
Then, the mechanical system, formed by the slave mechanical resonator 6 and the mechanical braking device 24, is configured so as to enable the mechanical braking device to be able to start the periodic braking pulses at any position of the slave mechanical resonator at least in a certain continuous or quasi-continuous range of positions whereby this slave mechanical resonator is suitable for passing along the general oscillation axis thereof. The alternative embodiment represented in
It should be noted that the braking surface may be other than the outer lateral surface of the felloe of the balance. In an alternative embodiment not shown, it is the central shaft of the balance that defines a circular braking surface. In this case, a pad of the braking member is arranged so as to apply a pressure against this surface of the central shaft upon the application of the mechanical braking pulses.
In a general operating mode, the mechanical braking device 24 is arranged such that the periodic braking pulses each have essentially a duration of less than one quarter of the set-point period for the oscillation of the slave mechanical oscillator 18.
By way of non-limiting examples, for a main timepiece resonator formed by a balance-hairspring, wherein the constant of the hairspring k=5.75 E-7 Nm/rad and the inertia I=9.1 E-10 kg·m2, and a set-point frequency F0c equal to 4 Hz, it is possible to consider a first alternative embodiment for a timepiece movement, the non-synchronised running whereof is somewhat imprecise, with a daily error of about five minutes, and a second alternative embodiment for a further timepiece movement, the non-synchronised running whereof is more precise with a daily error of about thirty seconds. In the first alternative embodiment, the range of values for the average braking torque is between 0.2 μNm and 10 μNm, the range of values for the duration of the braking pulses is between 5 ms and 20 ms and the range of values relative to the braking period for the application of the periodic braking pulses is between 0.5 s and 3 s. In the second alternative embodiment, the range of values for the average braking torque is between 0.1 μNm and 5 μNm, the range of values for the duration of the periodic braking pulses is between 1 ms and 10 ms and the range of values for the braking period is between 3 s and 60 s, i.e. at least once per minute.
It should be noted that the slave main oscillator is not limited to a version comprising a balance-hairspring and an escapement with a stop pin, in particular of the Swiss lever type. Other mechanical oscillators can be envisaged, in particular with a flexible strip balance. The escapement can include a stop pin or be of the continuous rotating type. This is also true for the auxiliary mechanical oscillator forming the master oscillator. Since the master oscillator is the oscillator that ultimately gives the high precision sought for the running of the mechanical movement, an oscillator of the mechanical type is thus ideally selected therefor that is as precise as possible, bearing in mind that this oscillator does not need to drive the one or more mechanisms of the horological movement, in particular a time indicator mechanism. This is shown by the second embodiment of the invention described hereafter.
The master oscillator 54 is of the magnetic escapement type. It comprises a resonator 60 formed by a balance 62 and a hairspring 66 (shown schematically). In an alternative embodiment, the balance is mounted on flexible strips. This balance comprises two arms, which are situated on two sides of the pivot axis thereof and which bear two magnets 63 and 64 at the respective ends thereof. These two magnets are used to couple the resonator 60 to an escapement wheel 68. This escapement wheel and the magnets 63 and 64 form the magnetic escapement of the master oscillator 54. The escapement wheel comprises a magnetic structure formed by two annular tracks 70 and 72. Each of the two annular tracks has an alternation of annular sectors 74 and 76, one sector 74 and one adjacent sector 76 jointly defining an angular period of the magnetic structure. The two tracks are angularly out of phase by half a period. As a whole, a sector 74 has at least one physical feature or defines at least one physical parameter, relative to the magnets borne by the balance, which is different from an analogous physical feature of a sector 76 or from an analogous physical parameter defined by a sector 76. In other words, the magnetic potential for any of the two magnets passing over a sector 74 is different from the magnetic potential that it has when passing over a sector 76. In particular, it is envisaged that a minimum magnetic potential appears in one of the two sectors, whereas a maximum magnetic potential appears in the other of these two sectors. Thus, if the escapement wheel rotates, it induces an oscillation of the resonator 60 at the natural oscillation frequency thereof, which thus imposes a continuous rotational speed on the escapement wheel as a function of the value of this oscillation frequency, hereafter referred to as the ‘reference frequency’. The escapement wheel advances by one angular period of the magnetic structure per oscillation period of the balance 62. It should be noted that if it is the resonator that is directly excited and oscillates at the resonant frequency (natural frequency) thereof, then the escapement wheel is driven in rotation at the aforementioned continuous rotational speed. The term ‘continuous rotational speed’ is understood herein to mean that the wheel rotates without stopping; however, there can be a periodic variation in speed.
A plurality of alternative embodiments can be considered for the magnetic structure of the escapement wheel 68. In a first alternative embodiment, the sectors 74 are made of a ferromagnetic material, whereas the sectors 76 are made of a non-magnetic material. In a second alternative embodiment, the sectors 74 are made of a magnetised material, whereas the sectors 76 are made of a non-magnetic material. In a third alternative embodiment, the sectors 74 are made of a material that is magnetised in a first direction whereas the sectors 76 are made of a material that is magnetised in a second direction opposite to the first direction (opposite polarities). In the latter case, each of the two magnets 63 and 64 is subjected to a magnetic repulsion force above one of the two sectors and to a magnetic attraction force above the other sector Other perfected alternative embodiments are described in the patent application EP 2 891 930. Reference can be made to this document in order to better understand the functioning of the master oscillator 54.
The escapement wheel bears, at the periphery thereof, a finger 58 arranged such that it can actuate the pulse generator 50 at each revolution performed by the escapement wheel. This finger belongs to the braking device 56 and the role thereof is similar to that of a pin 38 of the first embodiment. Thus, the escapement wheel and the actuating finger 58 jointly form a control mechanism of the pulse generator 50. A sequence of the operation of the correction device of the second embodiment is given in
In
For the purposes of illustration, the reference frequency of the master oscillator 54 is equal to 12 Hz and the magnetic structure of the escapement wheel has magnetic periods of 30°, i.e. a total of 12 periods. The braking pulse generator mechanism is thus actuated at a braking frequency of 1 Hz since the escapement wheel performs one revolution per second. In another alternative embodiment, the number of magnetic periods is equal to 24 such that the braking frequency is thus equal to 2 Hz.
Before presenting further particular embodiments, the noteworthy operation of a timepiece according to the invention will be described in detail, in addition to how the synchronisation of the slave main oscillator on the master auxiliary oscillator is obtained.
The text hereinafter will describe, with reference to
In
It should be noted that the pulses P1 and P2 are represented in
It should further be noted that the braking pulses may be applied with a constant force couple or a non-constant force couple (for example substantially in a Gaussian or sinusoidal curve). The term ‘braking pulse’ denotes the momentary application of a force couple to the mechanical resonator which brakes the oscillating member thereof (balance), i.e. which opposes the oscillation movement of this oscillating member. In the case of a couple different to zero which is variable, the duration of the pulse is defined generally as the part of this pulse which has a significant force couple to brake the mechanical resonator. It should be noted that a braking pulse may exhibit a significant variation. It may even be choppy and form a succession of shorter pulses. In the case of a constant couple, the duration of each pulse is envisaged to be less than a half of a set-point period and preferably less than a quarter of a set-point period. It should be noted that each braking pulse may either brake the mechanical resonator without however stopping same, as in
Each free oscillation period T0 of the mechanical oscillator defines a first alternation A01 followed by a second alternation A02 each occurring between two end positions defining the oscillation amplitude of this mechanical oscillator, each alternation having an identical duration T0/2 and exhibiting a passage of the mechanical resonator via the zero position thereof at a median time. The two successive alternations of an oscillation define two half-periods during which the balance respectively sustains an oscillation movement in one direction and subsequently an oscillation movement in the other direction. In other words, an alternation corresponds to an oscillation of the balance in one direction or the other between the two end positions thereof defining the oscillation amplitude. As a general rule, a variation in the oscillation period during which a braking pulse occurs and therefore an isolated variation of the frequency of the mechanical oscillator are observed. In fact, the time variation relates to the sole alternation during which the braking pulse occurs. The term ‘median time’ denotes a time occurring substantially at the midpoint of the alternations. This is specifically the case when the mechanical oscillator oscillates freely. On the other hand, for the alternations during which regulation pulses occur, this median time no longer corresponds exactly to the midpoint of the duration of each of these alternations due to the disturbance of the mechanical oscillator induced by the regulation device.
The behaviour of the mechanical oscillator in a first correction scenario of the oscillation frequency thereof, which corresponds to that shown in
In this first case, the braking pulse is therefore generated between the start of an alternation and the passage of the resonator via the neutral position thereof in this alternation. The angular velocity in absolute values decreases during the braking pulse P1. Such a braking pulse induces a negative time phase shift TC1 in the oscillation of the resonator, as shown in
With reference to
In the second scenario in question, the braking pulse is therefore generated, in an alternation, between the median time at which the resonator passes via the neutral position thereof (zero position) and the end time at which this alternation ends. The angular velocity in absolute values decreases during the braking pulse P2. Remarkably, the braking pulse induces in this case a positive time phase shift TC2 in the oscillation of the resonator, as shown in
The physical phenomenon mentioned above for mechanical oscillators is involved in the synchronisation method implemented in a timepiece according to the invention. Unlike the general teaching in the field of timepieces, it is possible not only to reduce the frequency of a mechanical oscillator with braking pulses, but it is also possible to increase the frequency of such a mechanical oscillator also with braking pulses. Those skilled in the art would expect to be able to practically only reduce the frequency of a mechanical oscillator with braking pulses and, by way of corollary, to be able to only increase the frequency of such a mechanical oscillator by applying drive pulses when supplying power to said oscillator. Such an intuitive idea, which has become established in the field of timepieces and therefore comes first to the mind of those skilled in the art, proves to be incorrect for a mechanical oscillator. Thus, as described in detail hereinafter, it is possible to synchronise, via an auxiliary oscillator defining a master oscillator, a mechanical oscillator that is very precise moreover, whether it momentarily has a frequency that is slightly too high or too low. It is therefore possible to correct a frequency that is too high or a frequency that is too low merely by means of braking pulses. In sum, applying a braking couple during an alternation of the oscillation of a balance-hairspring induces a negative or positive phase shift in the oscillation of this balance-hairspring according to whether said braking torque is applied respectively before or after the passage of the balance-hairspring via the neutral position thereof.
The resulting synchronisation method of the correction device incorporated in a timepiece according to the invention is described hereinafter.
The error induced in
The teaching given above makes it possible to understand the remarkable phenomenon of the synchronisation of a main mechanical oscillator (slave oscillator) on an auxiliary mechanical oscillator, forming a master oscillator, by the mere periodic application of braking pulses on the slave mechanical resonator at a braking frequency FFR corresponding advantageously to double the set-point frequency F0c divided by a positive whole number N, i.e. FFR=2F0c/N. The braking frequency is thus proportional to the set-point frequency for the master oscillator and merely dependent on this set-point frequency once the positive whole number N is given. As the set-point frequency is envisaged to be equal to a fractional number multiplied by the reference frequency, the braking frequency is therefore proportional to the reference frequency and determined by this reference frequency, which is supplied by the auxiliary mechanical oscillator which is by nature or by design more precise than the main mechanical oscillator.
The synchronisation mentioned above obtained by the correction device incorporated in the timepiece according to the invention will now be described in more detail with the aid of
The braking is characterised in that it opposes the movement of the resonator regardless of the direction of the movement thereof. Thus, when the resonator passes via an inversion of the direction of the oscillation thereof during a braking pulse, the braking torque automatically changes sign at the time of this inversion. This gives braking pulses 104a which have, for the braking torque, a first part with a first sign and a second part with a second sign opposite the first sign. In this scenario, the first part of the signal therefore occurs before the end position and opposes the effect of the second part which occurs after this end position. While the second part reduces the instantaneous frequency of the mechanical oscillator, the first part increases same. The correction then decreases to stabilise eventually and relatively quickly at a value for which the instantaneous frequency of the oscillator is equal to the set-point frequency (corresponding in this case to the braking frequency). Thus, the transitory phase is succeeded by a stable phase, also referred to as synchronous phase, where the oscillation frequency is substantially equal to the set-point frequency and where the first and second parts of the braking pulses have a substantially constant and defined ratio.
The graphs in
The graphs in
With the aid of
If a first pulse occurs at the time t1 or t2, there will therefore be theoretically a repetition of this scenario during the next oscillation periods and an oscillation frequency equal to the set-point frequency. Two things should be noted for such a scenario. Firstly, the probability of a first pulse occurring exactly at the time t1 or t2 is relatively low though possible. Secondly, should such a particular scenario arise, it would not be able to last for a long time. Indeed, the instantaneous frequency of a balance-hairspring in a timepiece varies slightly over time for various reasons (oscillation amplitude, temperature, change of spatial orientation, etc.). Although these reasons represent disturbances that it is generally sought to minimise in fine watchmaking, the fact remains that, in practice, such an unstable equilibrium will not last very long. It should be noted that the higher the braking torque, the closer the times t1 and t2 are to the two passage times of the mechanical resonator via the neutral position thereof following same respectively. It should also be noted that the greater the difference between the natural oscillation frequency F0 and the set-point frequency F0c, the closer the times t1 and t2 are also to the two passage times of the mechanical resonator via the neutral position thereof following same respectively.
Let us now consider what happens when deviating slightly from the time positions t1 or t2 during the application of the pulses. According to the teaching given with reference to
It should be noted that the pulses Imp1a, respectively Imp1b, Imp2a and Imp2b occupy relatively stable time positions. Indeed, a slight deviation to the left or to the right of one of these pulses, due to an external disturbance, will have the effect of returning a subsequent pulse to the initial relative time position. Then, if the time drift of the mechanical oscillator varies during the synchronous phase, the oscillation will automatically sustain a slight phase shift such that the ratio between the first part and the second part of the pulses Imp1a, respectively Imp1b, Imp2a and Imp2b varies to a degree which adapts the correction induced by the braking pulses to the new difference in frequency. Such behaviour of the timepiece according to the present invention is truly remarkable.
In the synchronous phase (
The teaching given above and the synchronisation obtained by means of the features of the timepiece according to the invention also apply to the scenario where the braking frequency for the application of the braking pulses is not equal to the set-point frequency. In the case of the application of one pulse per oscillation period, the pulses taking place at the unstable positions (t1, Imp1; t2, Imp2; t3, Imp3; t4, Imp4) correspond to corrections to compensate for the time drift during a single oscillation period. On the other hand, if the braking pulses envisaged have a sufficient effect to correct a time drift during a plurality of oscillation periods, it is then possible to apply a single pulse per time interval equal to this plurality of oscillation periods. The same behaviour as for the scenario where one pulse is generated per oscillation period will then be observed. Taking the oscillation periods where the pulses occur into consideration, there are the same transitory phases and the same synchronous phases as in the scenario described above. Furthermore, these considerations are also correct if there is a whole number of alternations between each braking pulse. In the case of an odd number of alternations, a transition is made alternatively, depending on the case, from the alternation A1 or A3 to the alternation A2 or A4 in
Though of little interest, it should be noted that the synchronisation is also obtained for a braking frequency FFR greater than double the set-point frequency (2F0), namely for a value equal to N times F0 where N>2. In an alternative embodiment where FFR=4F0, there is merely a loss of energy in the system with no effect in the synchronous phase, as one out of every two pulses occurs at the neutral point of the mechanical resonator. For a braking frequency FFR higher than 2F0, the pulses in the synchronous phase which do not occur at the end positions cancel the effects thereof pairwise. It is therefore understood that these are theoretical scenarios with no major practical sense.
To minimise the disturbances generated by the braking pulses and particularly the energy losses for the timepiece movement, short pulse durations, or even very short pulse durations, will preferably be selected. Thus, in a particular alternative embodiment, each of the braking pulses has a duration of less than 1/10 of the set-point period. In a preferred alternative embodiment, the braking pulses each have a duration between 1/250 and 1/40 of said set-point period. In the latter case, for a set-point frequency equal to 4 Hz, the duration of the pulses is between 1 ms and 5 ms.
With reference to
However, stable synchronisation may already be obtained, after a certain period of time, with a mechanical system, formed by the slave mechanical resonator and the mechanical braking device, which is configured so as to enable the mechanical braking device to be able to start the periodic braking pulses at any position of the slave mechanical resonator solely in a continuous or quasi-continuous range of positions of this defined resonator, on a first of the two sides from the neutral position of the slave mechanical resonator, by the range of amplitudes of the slave oscillator for the usable operating range thereof. Advantageously, this range of positions is increased, on the side of minimal amplitude, at least by an angular distance corresponding to the duration of a braking pulse, so as to enable for a minimal amplitude a braking pulse by dynamic dry friction. So that the mechanical system can act in all the alternations and not merely in all the oscillation periods, it is then necessary for this mechanical system to be configured so as to enable the mechanical braking device to also be able to start the periodic braking pulses at any position of the mechanical resonator on the second of the two sides from said neutral position, within the range of amplitudes of the slave mechanical oscillator for the usable operating range thereof. Advantageously, the range of positions is also increased, on the side of minimal amplitude, at least by an angular distance corresponding substantially to the duration of a braking pulse.
Thus, in a first general alternative embodiment, the continuous or quasi-continuous range mentioned above of positions of the slave mechanical resonator extends, on a first of the two sides from the neutral position thereof, at least over the range of amplitudes that the slave oscillator is liable to have on this first side for a usable operating range of this slave oscillator and moreover advantageously, on the side of minimal amplitude of the range of amplitudes, at least over an angular distance corresponding substantially to the duration of the braking pulses. In a second general alternative embodiment, in addition to the continuous or quasi-continuous range defined hereinabove in the first general alternative embodiment, which is a first continuous or quasi-continuous range, the mechanical system mentioned above is configured so as to enable the mechanical braking device to also be able to start the periodic braking pulses at any position of the slave mechanical resonator, on the second of the two sides from the neutral position thereof, at least in a second continuous or quasi-continuous range of positions of this slave mechanical resonator extending over the range of amplitudes that the slave oscillator is liable to have on this second side for said usable operating range and moreover advantageously, on the side of minimal amplitude of the latter range of amplitudes, at least over said first angular distance.
Finally, within the scope of the present invention, two periodic braking pulse categories may be distinguished relative to the intensity of the mechanical force couple applied to the slave mechanical resonator and the duration of the periodic braking pulses. As regards the first category, the braking torque and the duration of the braking pulses are envisaged, for the usable operating range of the slave oscillator, so as not to momentarily lock the slave mechanical resonator during the periodic braking pulses at least in the majority of the transitory phase described above. In this case, the system is arranged such that the mechanical braking torque can be applied to the slave mechanical resonator, at least in said majority of a possible transitory phase, during each braking pulse.
In an advantageous alternative embodiment, the oscillating member and the braking member are arranged such that the periodic braking pulses can be applied, at least in said majority of a possible transitory phase, essentially by dynamic dry friction between the braking member and a braking surface of the oscillating member. As regards the second category, for the usable operating range of the slave oscillator and in the synchronous phase described above, the mechanical braking torque and the duration of the periodic braking pulses are envisaged so as to lock the mechanical resonator during the periodic braking pulses at least in the end part thereof.
In a particular alternative embodiment, in the synchronous phase, a momentary locking of the slave mechanical resonator by the periodic braking pulses is envisaged while, in an initial part of a possible transitory phase where the periodic braking pulses occur outside the end positions of the slave mechanical resonator, the latter is not locked by these periodic braking pulses.
The operation of the correction device differs from that of the previous embodiments in that the control mechanism formed by the escapement wheel 68 and the actuating finger 58 acts in reverse on the braking pulse generator mechanism 50A. As in
The force of the spring 44A can be very low in this case, however sufficient damping is preferably envisaged in order to prevent an oscillation of the lever, after the release thereof, causing a second parasitic braking pulse during the braking period following the first pulse. The duration of the braking pulses is determined by the angular distance over which the actuating finger remains in contact with the end of the lever after the time at which the strip spring touches the braking surface. This angular distance can be set to a given value, in particular by adjusting the length of the actuating finger. It should be noted that the braking torque increases in this case during the braking pulse, then decreases almost instantaneously as soon as the lever is released. This force couple can be set to a given value, in particular as a function of the rigidity of the strip spring and the length ratio between the two arms of the lever.
As opposed to the previous embodiment, the control mechanism advances in steps. The generation of a braking pulse is envisaged during a step of the escapement wheel (
| Number | Date | Country | Kind |
|---|---|---|---|
| 17163250 | Mar 2017 | EP | regional |
| 17172491 | May 2017 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/056649 | 3/16/2018 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2018/177774 | 10/4/2018 | WO | A |
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| Number | Date | Country | |
|---|---|---|---|
| 20200026240 A1 | Jan 2020 | US |
