EP3629103A1 - Timepiece comprising a mechanical movement of which the oscillation is regulated by an electronic device - Google Patents

Abstract

The timepiece comprises a mechanical oscillator, formed by a balance and a piezoelectric hairspring (8), and a regulating device for regulating the frequency of the mechanical oscillator. This regulation device is arranged to be able to generate regulation pulses (Scc) temporally separated and each consisting of a momentary decrease in an electrical resistance applied by the regulation device between two electrodes (20, 22) of the piezoelectric hairspring relative to a nominal electrical resistance. The regulating device is arranged to be able to apply a plurality of regulating pulses during each moment of a succession of distinct correction moments or without interruption over a continuous time range, so as to respectively synchronize the mechanical oscillator on a frequency of correction whose value depends on a positive or negative time drift detected or on a set frequency for the mechanical oscillator.

Description

Technical area

The present invention relates to a timepiece comprising a mechanical movement, provided with a mechanical oscillator which is formed by a balance and a hairspring, and an electronic regulating device for regulating the frequency of the mechanical oscillator which controls the running of the mechanical movement.

In particular, the electronic regulating device comprises an auxiliary oscillator of the electronic type generally more precise than the mechanical oscillator, in particular a quartz oscillator.

Technological background

Several documents relate to the electronic regulation of a mechanical oscillator in a timepiece. In particular, the patent application US 2013/0051191 relates to a timepiece comprising a balance spring and an electronic circuit for regulating the frequency of oscillation of this balance spring. The hairspring is made of a piezoelectric material or comprises two lateral layers of piezoelectric material on a silicon core, two external lateral electrodes being arranged on the lateral surfaces of the hairspring. These two electrodes are connected to the electronic regulation circuit which comprises a plurality of switchable capacitors arranged in parallel and connected to the two electrodes of the hairspring.

Using the Figures 1 to 4 , a timepiece of the type described in the above-mentioned American patent application will be described. To avoid loading the drawing, we have shown Figure 1 only the mechanical resonator 2 of the mechanical movement of the timepiece, this resonator comprising a balance 4 oscillating around a geometric axis 6 and a hairspring 8 whose terminal curve 10 conventionally passes through a stud 12 secured to a balance bridge (not shown) of the mechanical movement. The Figure 2 schematically shows a portion of the hairspring 8. This hairspring is formed by a central body 14 made of silicon, two lateral layers 16, 18 made of piezoelectric material, in particular aluminum nitride (AlN), and two external metal electrodes 20, 22. The two electrodes are connected by conductive wires 26, 28 (diagrammatic representation) to an electronic regulation circuit 24.

The Figure 3 (which reproduces the figure 1 of the previous document considered with some additional information from figures 2 and 7 ) shows the general arrangement of the regulating device 32 which is incorporated in the timepiece in question and in particular the electronic regulating circuit 24. This circuit 24 comprises a first capacitor 34 connected to the two electrodes of the piezoelectric hairspring and a plurality of switchable capacitances 36a to 36d which are arranged in parallel with the first capacitance, so as to form a variable capacitance Cv in order to be able to vary the value of the capacitance connected to the electrodes of the balance spring and thus vary, according to the teaching of the document, the rigidity hairspring. The circuit 24 further comprises a comparator 38, the two inputs of which are connected respectively to the two electrodes of the hairspring 8, this comparator being designed to supply a logic signal making it possible to determine, thanks to successive changes in the logic state of this logic signal, the passages by zero of the voltage induced between the two electrodes of the hairspring. The logic signal is supplied to a logic circuit 40 which also receives a reference signal from a clock circuit 42 associated with a quartz resonator 44. Based on a comparison between the reference signal and the logic signal supplied by the comparator 38, the logic circuit 40 controls the switches of the switchable capacitors 36a to 36d.

In addition, there is provided following the switchable capacitance circuit a full-wave rectifier circuit 46, conventionally formed by a bridge with four diodes, which supplies a _DC voltage V _DC and charges a storage capacity 48. This electrical energy supplied by the piezoelectric hairspring provides power to the device 32. There is therefore an autonomous electrical system because it is self-powered in the sense that the electrical energy comes from the mechanical energy supplied to the mechanical resonator 2 including the piezoelectric hairspring 8, when the resonator mechanical oscillates, forms an electromechanical transducer (an electric current generator).

As stated in the document US 2015/0051191 in its paragraph 0052, the electronic regulation circuit 24 can only reduce the oscillation frequency of the mechanical resonator 2 by increasing the value of the variable capacitance Cv. This finding is confirmed by the graph of the Figure 4 which shows the curve 50 giving the path difference as a function of the value of the variable capacity Cv. It is observed in fact that the path difference obtained is always less than zero and increases in absolute value when the value of the variable capacity increases. Thus, the regulation system requires that the natural frequency of the mechanical oscillator (frequency in the absence of regulation) is greater than the nominal frequency (setpoint frequency) of this mechanical oscillator. In other words, provision is made to adjust the mechanical oscillator so that its natural frequency corresponds to a frequency greater than the set frequency, the regulation circuit having the function of making this natural frequency decrease more or less so that the step corresponds to the set frequency. Thus, a great disadvantage of such a system lies in the fact that the progress of the mechanical movement is not optimal in the absence of electronic regulation. For a high-precision mechanical watch movement, one must in fact degrade its own mechanical characteristics by a non-optimal adjustment. We can conclude that such an electronic control system only makes sense for quality mechanical movements average or even poor quality, the precision of these mechanical movements depending on the electronic regulation system.

Summary of the invention

The present invention aims to provide a timepiece, provided with a mechanical resonator comprising a hairspring formed at least partially of a piezoelectric material and an electronic regulation system, associated with the piezoelectric hairspring, which does not have the drawbacks of the timepiece of the prior art described above, in particular which can be associated with a mechanical movement whose progress is initially adjusted optimally, that is to say to the best of its ability. Thus, the invention aims to provide an electronic regulation system which is, thanks to the use of a piezoelectric hairspring, discrete and autonomous and which is truly complementary to the mechanical movement by making it possible to increase its precision without degrading by elsewhere an optimal initial adjustment of this mechanical movement.

To this end, the subject of the invention is a timepiece comprising a regulating device arranged to be able to regulate the average frequency of a mechanical oscillator, formed by a balance and a hairspring, which cadences the running of the timepiece. horology, this regulating device comprising an auxiliary time base, formed by an auxiliary electronic oscillator, which provides a reference frequency signal for regulation. The hairspring is formed at least partially by a piezoelectric material and by at least two electrodes arranged so as to present between them a voltage induced by the piezoelectric material undergoing mechanical stress and electrically connected to the regulating device which is arranged to be able to vary the impedance of the regulation system formed by the piezoelectric material, the at least two electrodes and the regulation device. The regulating device is arranged so as to be able to temporarily vary the electrical resistance generated by this regulation between the at least two electrodes, in order to be able to generate at least at times regulation pulses which are distinct and each have a certain duration T _P , each regulation pulse consisting of a momentary decrease in said electrical resistance relative to a nominal electrical resistance which is generated by the regulation device between the two electrodes apart from the separate regulation pulses. The regulation device is arranged to be able to apply a plurality of regulation pulses during each of said moments, so that any two successive regulation pulses among each plurality of regulation pulses present between their beginnings a time distance D _T equal to one number N multiplied by half of a regulation period Treg determined for each of said moments, ie a mathematical relation D _T = N · Treg / 2, N being a positive integer greater than zero. The regulation period Treg and the number N are selected so as to allow synchronization of the mechanical oscillator on a regulation frequency Freg = 1 / Treg during each of said moments. The regulating device is arranged to determine by means of the reference time base the start of each of the regulating pulses, so as to satisfy the aforementioned mathematical relationship between the temporal distance and the regulating period, and thus to determine the frequency of regulation.

According to an advantageous variant, the time distance D _T is equal to an odd number 2M - 1 multiplied by half of a regulation period Treg determined for each of said moments, ie a mathematical relation D _T = (2M - 1) · Treg / 2, M being a positive integer greater than zero. The regulation period Treg and the number M are selected so as to allow synchronization of the mechanical oscillator on a regulation frequency Freg = 1 / Treg during each of said moments.

According to a first main embodiment, said moments are contiguous and together form a continuous time range. The regulation device is arranged to apply during the continuous time range the regulation pulses so that any two successive regulation pulses intervening in this continuous time range present between their beginnings the time distance D _T with the regulation period Treg equal to one setpoint period T0c, which is the inverse of the setpoint frequency F0c, so as to be able to synchronize continuously, after a possible initial transient phase, the frequency of the mechanical oscillator with a setpoint frequency F0c during the continuous time range.

In a particular variant, the regulation device is arranged to periodically apply, during the continuous time period, the regulation pulses with a triggering frequency F _D (N) = 2 · F0c / N within the framework of the general variant described above. , respectively F _D (M) = 2 · F0c / (2M- 1) in the context of the advantageous variant also mentioned above. In a preferred variant, the number N, respectively M is constant and predefined for the continuous time range.

According to a second main embodiment, the timepiece further comprises a device for measuring a time drift in the operation of the mechanical oscillator relative to its set frequency F0c, and the regulating device is arranged to select , before each of said moments, for the regulation period Treg, depending on whether at least some positive or negative time drift is detected, respectively a first correction period Tcor1 which is greater than a setpoint period T0c, equal to the reverse of the setpoint frequency, or a second correction period Tcor2 which is less than the setpoint period. Each of said moments is provided with a duration sufficient for the establishment of a synchronous phase in which the frequency of the mechanical oscillator is synchronized either on a first correction frequency Fcor1 = 1 / Tcor1 when said at least a certain positive time drift is detected before the considered moment, or on a second correction frequency Fcor2 = 1 / Tcor2 when said at least a certain negative temporal drift is detected before the considered moment.

According to a preferred variant, when said at least a certain positive or negative time drift is detected, the regulation device is arranged to periodically apply, during the next moment among said moments, the plurality of corresponding regulation pulses with respectively a first frequency F _INF , according to the previously mentioned variant FNF = 2 · Fcor1 / N or F _INF = 2-Fcor1 / (2M-1), or with a second frequency F _SUP , according to the previously mentioned variant F _SUP = 2 · Fcor2 / N or F _SUP = 2 · Fcor2 / (2M - 1). In particular, the number N, respectively M is constant during each of said moments and it is either predetermined or determined before the next moment considered.

Thanks to the characteristics of the timepiece according to the invention, it is possible to correct both an advance and a delay in the natural progress of a mechanical movement by acting by regulation pulses, each having a limited duration, which vary the resistance between the at least two electrodes of the hairspring which is formed at least partially of a piezoelectric material.

In the first main embodiment, the separate regulation pulses are applied without interruption and the instants of their triggering are determined so that the frequency of the mechanical oscillator is permanently synchronized to a set frequency, so that no temporal drift occurs after an initial phase allowing the desired synchronization to be obtained. This first embodiment is very advantageous by the simplicity of its electronic circuit.

In the second main embodiment, advantage is taken of the fact that the regulation system generates an induced voltage between the two electrodes of the hairspring, which makes it possible to easily count the alternations or the periods of the mechanical oscillator and thus to be able to detect a temporal drift in the progress of the timepiece. In this case, provision is made to apply regulation pulses only at separate times and only when a certain time drift is detected, in a differentiated manner depending on whether this time drift is positive or negative, in order to correct the time drift.

Brief description of the figures

• La Figure 1, déjà décrite, montre une pièce d'horlogerie de l'art antérieur comprenant un résonateur mécanique, formé d'un balancier et d'un spiral piézoélectrique, et un circuit électronique de régulation qui est relié aux deux électrodes du spiral piézoélectrique;
• La Figure 2 est un agrandissement d'une portion du spiral piézoélectrique de la Figure 1 ;
• La Figure 3 montre partiellement le schéma électrique du dispositif de régulation de la pièce d'horlogerie de la Figure 1 ;
• La Figure 4 donne l'écart de marche pour la pièce d'horlogerie des figures précédentes en fonction d'une capacité variable appliquée entre les deux électrodes du spiral piézoélectrique;
• La Figure 5 montre l'évolution de la fréquence d'oscillation du résonateur mécanique lors d'une application périodique d'impulsions de régulation pour diverses fréquences de déclenchement de ces impulsions de régulation autour d'une fréquence égale au double d'une fréquence de consigne pour l'oscillateur mécanique de la pièce d'horlogerie;
• La Figure 6 montre le schéma électrique d'un dispositif de régulation incorporé dans une variante d'un premier mode de réalisation principal d'une pièce d'horlogerie selon l'invention;
• La Figure 7 montre le schéma électrique d'un dispositif de régulation incorporé dans une variante préférée du premier mode de réalisation principal;
• La Figure 8 montre le schéma électrique d'un dispositif de régulation incorporé dans une variante d'un deuxième mode de réalisation principal d'une pièce d'horlogerie selon l'invention;
• La Figure 9 montre le graphe de la tension induite entre les deux électrodes du spiral piézoélectrique en fonction de la position angulaire du résonateur mécanique, ainsi qu'un signal fourni par un comparateur à hystérèse pour pouvoir compter les périodes d'oscillation du résonateur mécanique; et
• La Figure 10 est une coupe transversale d'un mode de réalisation préféré d'un spiral piézoélectrique formant le résonateur mécanique d'une pièce d'horlogerie selon l'invention.

The invention will be described below in more detail with the aid of the appended drawings, given by way of non-limiting examples, in which:

• The Figure 1 , already described, shows a timepiece of the prior art comprising a mechanical resonator, formed of a balance and a piezoelectric hairspring, and an electronic regulation circuit which is connected to the two electrodes of the piezoelectric hairspring;
• The Figure 2 is an enlargement of a portion of the piezoelectric hairspring of the Figure 1 ;
• The Figure 3 partially shows the electrical diagram of the device for regulating the timepiece of the Figure 1 ;
• The Figure 4 gives the step difference for the timepiece of the preceding figures as a function of a variable capacity applied between the two electrodes of the piezoelectric hairspring;
• The Figure 5 shows the evolution of the frequency of oscillation of the mechanical resonator during a periodic application of regulation pulses for various triggering frequencies of these regulation pulses around a frequency equal to twice a set frequency for l 'mechanical oscillator of the timepiece;
• The Figure 6 shows the electrical diagram of a regulating device incorporated in a variant of a first main embodiment of a timepiece according to the invention;
• The Figure 7 shows the electrical diagram of a regulating device incorporated in a preferred variant of the first main embodiment;
• The Figure 8 shows the electrical diagram of a regulating device incorporated in a variant of a second main embodiment of a timepiece according to the invention;
• The Figure 9 shows the graph of the voltage induced between the two electrodes of the piezoelectric hairspring as a function of the angular position of the mechanical resonator, as well as a signal supplied by a hysteresis comparator to be able to count the periods of oscillation of the mechanical resonator; and
• The Figure 10 is a cross section of a preferred embodiment of a piezoelectric hairspring forming the mechanical resonator of a timepiece according to the invention.

Detailed description of the invention

The timepiece according to the invention comprises, like the timepiece of the prior art described above, a mechanical timepiece movement provided with a mechanical oscillator, formed by a pendulum and a piezoelectric hairspring, for example as shown to the Figures 1 and 2 , and arranged to clock the progress of the watch movement, this mechanical oscillator having a preset frequency F0c. The hairspring is formed at least partially by a piezoelectric material and it comprises two electrodes 20, 22 arranged so as to be able to present therebetween a voltage induced by the piezoelectric material when the latter is put under mechanical stress during an oscillation of the mechanical oscillator. The timepiece further comprises a regulation device arranged to be able to regulate the average frequency of the mechanical oscillator and comprising an auxiliary time base, formed by an auxiliary electronic oscillator and providing a reference frequency signal. The two electrodes of the balance spring are electrically connected to the regulating device which is arranged to be able to vary the impedance of the regulating system which is formed by the piezoelectric material, the two electrodes and the regulating device.

According to the invention, the regulation device is arranged so as to be able to vary momentarily the electrical resistance generated by this regulation device between the two electrodes of the hairspring, in order to be able to generate at least at times regulation pulses which are distinct and each have a certain duration T _P , each regulation pulse consisting of a momentary decrease in the electric resistance of the regulation system, namely the aforementioned electric resistance relative to a nominal electric resistance which is generated by the regulation device between the two electrodes outside separate regulatory pulses. Generally, the regulation device is arranged to be able to apply at least at times a plurality of regulation pulses during each of these moments, so that any two successive regulation pulses among each plurality of regulation pulses have between their starts a time distance D _T equal to a number N multiplied by half of a regulation period Treg determined for each of said moments, that is to say a mathematical relation D _T = N · Treg / 2, N being a positive integer greater than zero . The regulation period Treg and the number N are selected so as to allow synchronization of the mechanical oscillator on a regulation frequency Freg = 1 / Treg during each of said moments, as will be explained in more detail below. The regulation device is arranged to determine by means of the reference time base the start of each of said regulation pulses, so as to satisfy the aforementioned mathematical relation between the time distance D _T and the regulation period Treg, and thus determine the regulation frequency.

In an advantageous variant, the time distance D _T is equal to an odd number 2M - 1 multiplied by half of a regulation period Treg determined for each of said moments, ie a mathematical relation D _T = (2M - 1) · Treg / 2, M being a positive integer greater than zero. This variant, which selects the odd numbers from the possible values for the number N mentioned in the general variant set out above, is advantageous because, according to the observations made by the inventors, the selection of an odd number results in a greater regulation efficiency relative to the case of an even number for the number N.

Preferably, during each moment when a plurality of regulation pulses occurs, the regulation device is arranged to periodically apply the regulation pulses with a triggering frequency F _D (N) = 2 · Freg / N for the variant general, and F _D (M) = 2 · Freg / (2M - 1) for the aforementioned advantageous variant.

In the context of the development which led to the present invention, the inventors have brought to light an entirely remarkable physical phenomenon in relation to a mechanical oscillator formed by a pendulum and a piezoelectric hairspring, this physical phenomenon making it possible to perform according to the invention a regulation of the average frequency of a mechanical oscillator incorporated in a mechanical movement by means of an electronic regulation device, as explained above. Next, the inventors have defined two types of regulation based on this physical phenomenon which are respectively implemented in two main embodiments which will be described in detail below. To expose this physical phenomenon, the Figure 5 shows the behavior of a mechanical oscillator equipped with a piezoelectric hairspring, of the type described above, to which short-circuit pulses of short duration, for example less than a tenth of a setpoint period T0c (in the case shown, the duration of the short-circuit pulses is 10 ms, i.e. one twentieth of the setpoint period T0c = 200 ms), the mechanical oscillator and the mechanical movement which incorporates it being designed to operate naturally substantially at a setpoint frequency F0c equal by definition to the reverse of the setpoint period.

• La courbe C_F0 correspond à une fréquence de déclenchement des impulsions de court-circuit F_D0 = 10.00 Hz, et on observe que la fréquence d'oscillation se stabilise à la fréquence de consigne Fso = F0c = 5.00 Hz ;
• Les courbes C_F1 et C_F2 correspondent à des fréquences de déclenchement des impulsions de court-circuit qui sont supérieures à F_D0, soit respectivement F_D1 = 10.03 Hz et F_D2 = 10.08 Hz, et on observe que la fréquence d'oscillation se synchronise respectivement sur les fréquences de synchronisation F_S1 = 5.015 Hz et F_S2 = 5.04 Hz après une phase transitoire intervenant au début de chaque moment d'application d'impulsions de court-circuit ; et
• Les courbes C_F3, C_F4 et C_F5 correspondent à des fréquences de déclenchement des impulsions de court-circuit qui sont inférieures à F_D0, soit respectivement F_D3 = 9.96 Hz, F_D4 = 9.94 Hz et F_D5 = 9.88 Hz, et on observe que la fréquence d'oscillation se synchronise respectivement sur les fréquences de synchronisation F_S3 = 4.98 Hz, F_S4 = 4.97 Hz et F_S5 = 4.94 Hz après une phase transitoire intervenant au début de chaque moment d'application d'impulsions de court-circuit.

In the example shown in Figure 5 , the natural frequency F0 of the mechanical oscillator is precisely equal to its set frequency F0c = 5 Hz and short-circuit pulses, forming regulation pulses according to the invention, are applied here with a trigger frequency F _D close to twice the set frequency but different, ie F _D ≈ 2 · F0c, in addition to the specific case of a trigger frequency F _D exactly equal to twice the natural frequency and therefore twice the set frequency. Various curves show the temporal evolution of the frequency of the mechanical oscillator for various triggering frequencies (for N = M = 1 in the formula of the triggering frequency F _D (N), respectively F _D (M) mentioned previously) during moments during which a plurality of periodic short-circuit pulses are applied. The following results are obtained:

• Curve C _F0 corresponds to a frequency for triggering short-circuit pulses F _D0 = 10.00 Hz, and it is observed that the oscillation frequency stabilizes at the set frequency Fso = F0c = 5.00 Hz;
• The curves C _F1 and C _F2 correspond to tripping frequencies of the short-circuit pulses which are greater than F _D0 , that is to say F _D1 = 10.03 Hz and F _D2 = 10.08 Hz, and it is observed that the oscillation frequency is synchronizes respectively on the synchronization frequencies F _S1 = 5.015 Hz and F _S2 = 5.04 Hz after a transient phase occurring at the start of each moment of application of short-circuit pulses; and
• The curves C _F3 , C _F4 and C _F5 correspond to tripping frequencies of the short-circuit pulses which are lower than F _D0 , _i.e. respectively F _D3 = 9.96 Hz, F _D4 = 9.94 Hz and F _D5 = 9.88 Hz, and it is observed that the oscillation frequency is synchronized respectively with the synchronization frequencies F _S3 = 4.98 Hz, F _S4 = 4.97 Hz and F _S5 = 4.94 Hz after a transient phase occurring at the start of each moment of application of pulses of short circuit.

Remarkably, the same synchronization frequencies were obtained for triggering frequencies of the short-circuit pulses respectively equal to the triggering frequencies F _DX , X = 1 to 5, mentioned above, divided by an odd number 2M- 1, M being a positive integer greater than zero, insofar as the ratio between the synchronization frequency and the natural frequency of the mechanical oscillator / the set frequency is between (K-1) / K and (K +1) / K with K> 40 · (2M-1). Similar results can be obtained with a division by an even number 2M and a similar condition between K and M, but a priori it seems that in the latter case synchronization is not established as effectively as for an odd number, the effect of the short-circuit pulses being less.

From the preceding observations and considerations, it is deduced that it is possible to synchronize a mechanical oscillator, having a piezoelectric hairspring as described above, by periodically applying short-circuit pulses between the two electrodes of this hairspring, on a frequency close to its natural frequency but different from the latter.

Thus, if the natural frequency deviates from the set frequency in the usual way, that is to say from one second to about fifteen seconds per day, it is easy to synchronize, by totally open-loop regulation, the frequency of the mechanical oscillator on the set frequency by continuously applying separate control pulses as described above with a frequency of trigger selected appropriately. This application is the subject of the first main embodiment. By using the signal of induced voltage between the electrodes of the balance spring when the mechanical resonator oscillates, one can easily count the periods of oscillation and determine a temporal drift, in particular to detect when a certain positive or negative temporal drift is reached, and then it is possible to apply, during a certain correction moment, a plurality of distinct regulation pulses as described above with a trigger frequency appropriately selected to synchronize the oscillation of the mechanical oscillator with a correction frequency different from the frequency of setpoint but selected close enough to this setpoint frequency to allow synchronization, and thereby correct the detected time drift. This application, which can be considered in semi-open or semi-closed loop, is the subject of the second main embodiment.

To the Figure 6 is shown the electronic diagram of a first variant of the first main embodiment. The electronic circuit, which forms the entire regulating device 52, is very simple. A quartz resonator 44 is excited by a clock circuit 42, the latter supplying a reference signal S _Ref either at the frequency of the quartz F _Q , preferably at a frequency adjusted to 32,768 Hz, or at a fraction of this frequency F _Q , for example F _Q / 4 and preferably at a fraction of the frequency adjusted in particular by means of an inhibition circuit known to the person skilled in the art. The reference signal S _Ref is supplied to a frequency divider 64 which outputs a control signal S _com to a timer 58 which, in response to the control signal, supplies a short-circuit signal Scc to a switch 60 arranged between the two electrodes 20, 22 of the piezoelectric hairspring 8 (shown schematically in the Figure 6 ) at the frequency imposed by the control signal. This process takes place without interruption in a continuous time range which lasts as long as the regulating device is active, that is to say as long as it is electrically powered.

The piezoelectric hairspring 8 is formed at least partially by a piezoelectric material and by at least two electrodes 20, 22 (see Figures 2 and 10 ) which are arranged so as to be able to present between them a voltage induced U (t) by the piezoelectric material when the latter is put under mechanical stress during an oscillation of the mechanical oscillator (see Figure 9 ).

The control signal S _com is a frequency signal having, in a general variant, a triggering frequency F _D (N) = 2 · F0c / N, the number N being an integer greater than zero which is selected so that , for a ratio between a maximum drift frequency in the operation of the mechanical oscillator and the set frequency F0c between (K-1) / K and (K + 1) / K, this number N is less than K / 40, ie N <K / 40. In an advantageous variant, the control signal S _com is a frequency signal which has a triggering frequency F _D (M) = 2 · F0c / (2M-1), the number M being an integer greater than zero which is selected so that, for a ratio between a maximum drift frequency in the operation of the mechanical oscillator and the set frequency between (K-1) / K and (K + 1 ) / K, we have 2M-1 less than K / 40, that is 2M-1 <K / 40. Preferably, the numbers N and M are constants and predefined for the continuous time range during which the short-circuit pulses are applied which define the regulation pulses.

The timer 58, on each pulse of the control signal, closes the switch 60 (passing switch and therefore conductive) during a time interval T _R , so that the short-circuit pulses each have a duration T _R , which is preferably less than a quarter of the set period T0c. In an advantageous variant, the duration of the regulation pulses is less than or substantially equal to one tenth of the setpoint period T0c. One thus obtains during the abovementioned continuous time period, after a possible transient phase during the activation of the regulating device, continuous synchronization of the frequency of the mechanical oscillator with the set frequency F0c.

To the Figure 7 is represented the electronic diagram of a regulation device, identical to that described above, which is associated with a supply circuit 66, formed of a rectifier 68 of an induced voltage U (t) between the two electrodes 20, 22 of hairspring 8 when the mechanical resonator oscillates and arranged to supply the regulating device 62, the rectified voltage being stored in a storage capacity C _AL , so that the regulating device with the supply circuit form a unit autonomous. In an advantageous variant, this autonomous unit is supported by the pendulum 4 (see Figure 1 ) to which it is attached.

To the Figure 8 is shown the electronic diagram of an advantageous variant of the second main embodiment. The timepiece comprises a regulating device 62 formed by an electronic regulating circuit 62a and an auxiliary time base which comprises an auxiliary oscillator and which supplies a reference signal S _Ref to the electronic regulating circuit. This time base comprises for example a quartz resonator 44 and a clock circuit 42 which supplies the reference signal S _Ref , already described in the context of the first main embodiment, to a divider having at least two stages DIV1 and DIV2, this divider being included in the circuit 62a. The piezoelectric hairspring 8 is similar to that described in the first main embodiment and its two electrodes 20, 22 are electrically connected to the electronic regulation circuit 62a.

The electronic regulation circuit includes a device for measuring a possible time drift in the progress of the watch movement relative to a set frequency for the mechanical oscillator which is determined by the auxiliary time base 42,44. The measuring device is formed by a hysteresis comparator 54, the two inputs of which are connected to the two electrodes 20, 22 of the piezoelectric hairspring 8. It will be noted that in the example given, the electrode 20 is electrically connected to an input of the comparator 54 via the ground of the regulation device. The hysteresis comparator provides a digital 'Comp' signal (see Figure 9 ) whose logic state changes just after each pass of the mechanical oscillator by its neutral position (angular position θ (t) equal to zero) and therefore after each pass through zero of the mechanical resonator forming this mechanical oscillator. The induced voltage U (t) generated by the piezoelectric hairspring is zero during the passage of the mechanical resonator through its neutral position (angular position 'zero'), while it is maximum, for a given charge applied between the two electrodes, when the mechanical resonator is in one or other of its two extreme positions (defining the amplitude of the mechanical oscillator respectively on both sides of the neutral position), as shown in Figure 9 .

The signal 'Comp' is supplied to a first input 'Up' of a bidirectional counter CB forming the measuring device. The bidirectional counter is thus incremented by one unit at each period of oscillation of the mechanical oscillator (in particular at each rising edge of the signal). It therefore continuously receives a measurement of the instantaneous oscillation frequency from the mechanical oscillator. The bidirectional counter receives at its second input 'Down' a clock signal S _hor supplied by the frequency divider DIV1 & DIV2, this clock signal corresponding to a set frequency F0c for the mechanical oscillator which is determined by l auxiliary time base auxiliary oscillator. Thus, the bidirectional counter supplies the control logic circuit 56 with a signal S _DT corresponding to a cumulative error over time between the oscillation frequency of the mechanical oscillator and the set frequency, this cumulative error defining the time drift of the mechanical oscillator relative to the auxiliary oscillator.

Next, the regulating device 62 comprises a switch 60 formed by a transistor and arranged between the two electrodes 20, 22 of the hairspring 8, this switch being controlled by the logic control circuit 56 which is arranged to be able to close, via a timer 58, momentarily this switch so as to make it conducting / conducting during the regulation pulses, which then define short-circuit pulses. The control circuit selectively supplies a control signal S _com to the timer 58 which, in response to this control signal, controls the momentary closing of the transistor 60 by applying to it a signal Scc. More specifically, the control circuit determines the instant of the start of each short-circuit pulse by triggering or resetting the timer ('Timer') which directly turns transistor 60 on / off (switch closed), the timer determining the duration T _R of each short circuit pulse. At the end of each short circuit pulse, the timer opens the switch again so that the transistor 60 is no longer on, that is to say that it becomes non-conductive again. In a general variant, the regulation pulses each have a duration of less than a quarter of the setpoint period T0c which is equal to the inverse of the setpoint frequency for the mechanical oscillator. In a preferred embodiment, the duration of the regulation pulses is less than or substantially equal to one tenth of a set period.

The electronic circuit 62a further comprises a supply circuit 66 of the regulation device, which has already been described previously.

The regulation method according to the second main embodiment, implemented by the regulation device 62 and implemented in the logic control circuit 56, is set out below. The control logic circuit is arranged to be able to determine whether a time drift measured by the measuring device corresponds to at least a certain advance (CB> N1) or to at least a certain delay (CB <- N2), N1 and N2 being positive integers. The regulation device, in particular its logic control circuit, is arranged to select, before each separate scheduled correction time, for the regulation period Treg as defined above, according to that at least a certain drift positive or negative time is detected, respectively a first correction period Tcor1 which is greater than the setpoint period T0c or a second correction period Tcor2 which is less than the setpoint period, each of the correction moments being provided with a sufficient duration the establishment of a synchronous phase in which the frequency of the mechanical oscillator is synchronized either on a first correction frequency Fcor1 = 1 / Tcor1 when said at least one certain positive time drift is detected before the considered moment, or on a second correction frequency Fcor2 = 1 / Tcor2 when said at least some negative temporal drift is detected before the considered moment, so as to correct the detected temporal drift.

In an advantageous variant, the control logic circuit 56 is arranged so that the time distance D _T between two short-circuit pulses, in each separate correction moment, is equal to an odd number 2M - 1 multiplied by half of the regulation period Treg determined for each of the correction moments, ie a mathematical relation D _T = (2M-1) · Treg / 2, M being a positive integer greater than zero, the regulation period Treg and the number M being selected so as to allow synchronization of the mechanical oscillator on a regulation frequency Freg = 1 / Treg during each of the correction moments.

In a particular variant, when said at least some positive or negative time drift is detected by the logic control circuit 56, the regulating device 62 is arranged to periodically apply, during the next correction moment, a plurality of pulses of corresponding regulation with respectively a first trigger frequency F _INF = 2 · Fcor1 / N or a second trigger frequency F _SUP = 2 · Fcor2 / N. The number N is preferably expected to be constant during each correction moment and it is either predetermined or determined before the next correction time considered.

In order to ensure the desired synchronization during each of the correction moments, it is advantageously provided that, for each of the correction moments where the first trigger frequency F _INF occurs, the latter is provided greater than a first limit frequency F _L1 (N, K) = [(K-1) / K] · 2 · F0c / N with K> 40 · N, and, for each of the correction moments where the second trip frequency F _SUP occurs, the latter is provided less than a second limiting frequency F _L2 (N, K) = [(K + 1) / K] · 2 · F0c / N with K> 40 · N.

In a specific variant, the integer N is expected to be smaller in an initial phase than in a final phase of each of the correction moments, so as to best reduce the initial transient phase.

In a preferred variant, when said at least some positive or negative time drift is detected by the logic control circuit 56, the regulating device 62 is arranged to periodically apply, during the next correction moment, a plurality of pulses of corresponding regulation with respectively a first trigger frequency F _INF = 2 · Fcor1 / (2M - 1) or a second trigger frequency F _SUP = 2 · Fcor2 / (2M-1). In particular, the number M is expected to be constant during each correction moment and it is either predetermined or determined before the next correction moment considered.

In order to ensure the desired synchronization during each of the correction moments, it is advantageously provided that, for each of the correction moments where the first trigger frequency F _INF occurs, the latter is provided greater than a first limit frequency F _L1 (M, K) = [(K-1) / K] · 2 · F0c / (2M -1) with K> 40 · (2M-1), and, for each of the correction moments where the second frequency of F _SUP trigger, the latter is expected to be less than one second limiting frequency F _L2 (M, K) = [(K + 1) / K] · 2 · F0c / (2M - 1) with K> 40 · (2M-1).

In a specific variant, so as to best reduce the initial transient phase in each correction moment, provision is made for determining the start of a first regulation pulse, from among the plurality of regulation pulses provided for the correction moment considered, relative to the angular position of the mechanical oscillator. For this purpose, the signal 'Comp' is also supplied to the logic control circuit 56. In this specific variant, the first regulation pulse is triggered by a rising edge or a falling edge of the signal 'Comp'.

Using the Figure 10 , a preferred embodiment of the piezoelectric hairspring 70 of the timepiece according to the invention will be described. This hairspring 70, shown in cross section, comprises a central body 72 of silicon, a layer of silicon oxide 74 deposited on the surface of the central body so as to thermally compensate the hairspring, a conductive layer 76 deposited on the oxide layer silicon, and a piezoelectric material deposited in the form of a piezoelectric layer 78 on the conductive layer 76. Two electrodes 20a and 22a are arranged on the piezoelectric layer 78 respectively on the two lateral sides of the hairspring (the two electrodes being able to partially cover the lower and upper sides of the hairspring without however joining).

In the particular variant shown in Figure 10 , the first part 80a and the second part 80b of the piezoelectric layer extending respectively on the two lateral sides of the central body 72 have, by their growth from the conductive layer 76, respective crystallographic structures which are symmetrical relative to a plane median 84 parallel to these two lateral sides. Thus, in the two lateral parts 80a and 80b, the piezoelectric layer has two same respective piezoelectric axes 82a, 82b which are perpendicular to the piezoelectric layer and in opposite directions. So we have an inversion of the sign of the induced voltage between the internal electrode and each of the two external lateral electrodes for the same mechanical stress. However, when the hairspring contracts or expands from its rest position, there is an inversion of the mechanical stress between the first and second parts 80a and 80b, that is to say that one of these parts undergoes compression while the other of these parts undergoes traction, and vice versa. In the end, it follows from these considerations that the voltages induced in the first and second parts have, along an axis perpendicular to the two lateral sides, the same polarity so that the conductive layer 76 can form a single internal electrode which extends on the two lateral sides of the central body 72, this internal electrode having no proper electrical connection with the regulation device. In a particular variant, the piezoelectric layer consists of a crystal of aluminum nitride formed by a growth of this crystal from the conductive layer 76 (internal electrode) and perpendicular thereto.

Claims (20)

Timepiece comprising a mechanical movement which is provided with a mechanical oscillator formed by a balance (4) and a hairspring (8; 70), this mechanical oscillator having a predefined set frequency F0c and being arranged to synchronize the running of the timepiece, this timepiece further comprising a regulation device (52, 62) arranged to be able to regulate the average frequency of the mechanical oscillator and comprising an auxiliary time base (42, 44), formed by an auxiliary electronic oscillator and providing a reference signal (S _Ref ), the hairspring being formed at least partially by a piezoelectric material and by at least two electrodes (20,22; 20a, 22a) arranged so as to be able to present between them a voltage induced U (t) by said piezoelectric material when the latter is placed under mechanical stress during an oscillation of the mechanical oscillator, the two electrodes being connected es electrically to the control device which is arranged to be able to vary the impedance of the control system which is formed by said piezoelectric material, said at least two electrodes and the control device; characterized in that the regulation device (62) is arranged so as to be able to vary momentarily the electrical resistance generated by this regulation device between said two electrodes, in order to be able to generate at least at times regulation pulses which are distinct and each have a certain duration (T _P ), each regulating pulse consisting of a momentary reduction in said electrical resistance relative to a nominal electrical resistance which is generated by the regulating device between said two electrodes outside said distinct regulating pulses, the regulation being arranged to be able to apply a plurality of said regulation pulses during each of said moments, so that any two successive regulation pulses among each plurality of regulation pulses present between their beginnings a time distance D _T equal to a number N multiplied by half of a regulation period Treg determined for each of said moments, ie a mathematical relation D _T = N · Treg / 2, N being a positive integer greater than zero, the regulation period Treg and the number N being selected so as to allow synchronization of the mechanical oscillator on a regulation frequency Freg = 1 / Treg during each of said moments, the regulation device being arranged to determine by means of the reference time base the start of each of said regulation pulses, so as to satisfy said mathematical relationship between said time distance and the regulation period, and thus to determine the regulation frequency . Timepiece according to claim 1, characterized in that it further comprises a device for measuring (54, CB) a time drift in the operation of the mechanical oscillator relative to its set frequency F0c, and in that the regulating device (62) is arranged to select, before each of said moments, for said regulating period Treg, according to whether at least some positive or negative time drift is detected by the regulating device, respectively a first period correction Tcor1 which is greater than a setpoint period T0c, equal to the inverse of the setpoint frequency, or a second correction period Tcor2 which is less than the setpoint period, each of said moments being provided with a duration sufficient to the establishment of a synchronous phase in which the frequency of the mechanical oscillator is synchronized either on a first frequency of correc tion Fcor1 = 1 / Tcor1 when said at least one certain positive temporal drift is detected before the moment considered, that is to say on a second correction frequency Fcor2 = 1 / Tcor2 when said at least one negative temporal drift is detected before the moment considered. Timepiece according to claim 2, characterized in that the time distance D _T is equal to an odd number 2M - 1 multiplied by half of the regulation period Treg determined for each of said moments, ie a mathematical relation D _T = (2M - 1) · Treg / 2, M being a positive integer greater than zero, the regulation period Treg and the number M being selected so as to allow synchronization of the mechanical oscillator on a regulation frequency Freg = 1 / Treg during each of said moments. Timepiece according to claim 2, characterized in that , when said at least a certain positive or negative time drift is detected, the regulating device (62) is arranged to periodically apply, during the next moment among said moments, the plurality of corresponding regulation pulses with respectively a first trigger frequency F _INF = 2 · Fcor1 / N or a second trigger frequency F _SUP = 2Fcor2 / N, the number N being expected to be constant during each of said moments and it is either predetermined or determined before the next moment considered. Timepiece according to claim 3, characterized in that , when said at least one positive or negative time drift is detected, the regulating device (62) is arranged to periodically apply, during the next moment among said moments, the plurality of corresponding regulation pulses with respectively a first trigger frequency F _INF = 2 · Fcor1 / (2M - 1) or a second trigger frequency F _SUP = 2 · Fcor2 / (2M - 1), the number M being provided constant during each of said moments and it is either predetermined or determined before the next moment considered. Timepiece according to claim 4, characterized in that , for each of said moments when the first trigger frequency F _INF occurs, the latter is provided greater than a first limit frequency F _L1 (N, K) = [(K- 1) / K] · 2 · F0c / N with K> 40 · N, and, for each of said moments when the second trip frequency F _SUP occurs, the latter is expected to be less than a second limit frequency F _L2 (N, K) = [(K + 1) / K] · 2 · F0c / N with K> 40 ·NOT. Timepiece according to claim 5, characterized in that , for each of said moments when the first trigger frequency F _INF occurs, the latter is provided greater than a first limit frequency F _L1 (M, K) = [(K- 1) / K] · 2 · F0c / (2M-1) with K> 40 · (2M-1), and, for each of said moments when the second trigger frequency F _SUP occurs, the latter is expected to be less than a second limit frequency F _L2 (M, K) = [(K + 1) / K] · 2 · F0c / (2M - 1) with K> 40 · (2M - 1). Timepiece according to claim 1, characterized in that said moments are contiguous and together form a continuous time range; and in that the regulation device (52) is arranged to apply during the continuous time range said regulation pulses so that any two successive regulation pulses intervening in this continuous time range present between their beginnings said time distance D _T with said regulation period Treg equal to a setpoint period T0c, which is the inverse of the setpoint frequency F0c, so as to be able to continuously synchronize, after a possible initial transient phase, the frequency of the mechanical oscillator with the setpoint frequency F0c during the continuous time range. Timepiece according to claim 8, characterized in that the time distance D _T is equal to an odd number 2M - 1 multiplied by half of the setpoint period T0c, i.e. a mathematical relation D _T = (2M - 1) · T0c / 2, M being a positive integer greater than zero, the number M being selected so as to allow synchronization of the mechanical oscillator on the set frequency F0c = 1 / T0c during the continuous time range after a transient phase possible initial. Timepiece according to claim 8, characterized in that the regulation device (52) is arranged to apply, during the continuous time period, the regulation pulses periodically with a triggering frequency F _D (N) = 2 · F0c / N, the number N being selected so that, for a ratio between a maximum drift frequency in the operation of the mechanical oscillator and the set frequency between (K-1) / K and (K + 1) / K, this number N <K / 40. Timepiece according to claim 9, characterized in that the regulation device (52) is arranged to apply, during the continuous time period, the regulation pulses periodically with a triggering frequency F _D (M) = 2 · F0c / (2M - 1), the number M being selected so that, for a ratio between a maximum drift frequency in the operation of the mechanical oscillator and the setpoint frequency between (K-1) / K and (K +1) / K, we have 2M-1 <K / 40. Timepiece according to claim 10, characterized in that the number N is constant and predefined for the continuous time range. Timepiece according to claim 11, characterized in that the number M is constant and predefined for the continuous time range. Timepiece according to any one of claims 2 to 13, characterized in that the regulation pulses each have a duration (T _R ) less than a quarter of the setpoint period T0c. Timepiece according to any one of claims 2 to 13, characterized in that the duration (T _R ) of said regulation pulses is less than or equal to one tenth of the setpoint period T0c. Timepiece according to any one of the preceding claims, characterized in that the regulation device (52, 62) comprises a switch (60) arranged between the two electrodes (20, 22) of the piezoelectric hairspring, this switch being controlled by a control circuit (56, 64) which is arranged to temporarily close this switch during said regulation pulses so as to make it conducting / conducting, these regulation pulses then defining short-circuit pulses. Timepiece according to any one of the preceding claims, characterized in that said hairspring (70) comprises a central body (72) of silicon, a layer of silicon oxide (74) deposited on the surface of said central body so as to compensate thermally the hairspring, a conductive layer (76) deposited on the silicon oxide layer, and said piezoelectric material deposited in the form of a piezoelectric layer (78) on said conductive layer, said two electrodes (20a, 20b) being arranged on the piezoelectric layer respectively on the two lateral sides of the hairspring. Timepiece according to claim 17, characterized in that first and second parts (80a, 80b) of the piezoelectric layer, which extend respectively on the two lateral sides of said central body (72), have structures respective crystallographic which are symmetrical relative to a median plane (84) parallel to these two lateral sides; and in that said conductive layer (76) forms a single internal electrode which extends on the two lateral sides of the central body, this internal electrode having no proper electrical connection with the regulating device. Timepiece according to claim 18, characterized in that said piezoelectric layer (78) consists of a crystal of aluminum nitride formed by a growth of this crystal perpendicular to said conductive layer (76) and from this conductive layer . Timepiece according to any one of the preceding claims, characterized in that the regulation device comprises or is associated with a supply circuit (66), formed by a rectifier (68) of an induced voltage U (t) between the two electrodes of the piezoelectric hairspring when the mechanical resonator oscillates and arranged to supply the device regulating, so that the regulating device with the supply circuit forms an autonomous unit; and in that said autonomous unit is supported by the pendulum to which it is fixed.

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