CH715392A2 - Timepiece comprising a mechanical movement, the progress of which 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 regulation device is arranged to be able to apply a plurality of regulation 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 march of mechanical movement.

In particular, the electronic regulation 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, patent application US 2013/0 051 191 relates to a timepiece comprising a balance spring and an electronic circuit for regulating the oscillation frequency of this balance spring. The hairspring is made of a piezoelectric material or has two side layers of piezoelectric material on a silicon core, two external side electrodes being arranged on the side 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 FIGS. 1 to 4, a timepiece of the type described in the above-mentioned American patent application will be described. In order not to load the drawing, we have shown in FIG. 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 piton 12 secured to 'a balance bridge (not shown) of the mechanical movement. Fig. 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 (AIN), 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.

[0005] FIG. 3 (which reproduces FIG. 1 of the prior document considered with some additional information coming from FIGS. 2 and 7) shows the general arrangement of the regulating device 32 which is incorporated in the timepiece in question and in particular the circuit regulation electronics 24. This circuit 24 comprises a first capacitor 34 connected to the two electrodes of the piezoelectric hairspring and a plurality of switchable capacitors 36a to 36d which are arranged in parallel with the first capacitor, so as to form a variable capacitor Cv in order to be able to vary the value of the capacity connected to the electrodes of the balance spring and thus vary, according to the teaching of the document, the rigidity of the balance spring. 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 of a bridge with four diodes, which supplies a direct voltage VDCet 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-supplied 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 mechanical resonator oscillates, forms an electromechanical transducer (an electric current generator).

As indicated in document US 2015/0 051 191 in paragraph 0052, the electronic control 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 in fig. 4 which shows the curve 50 giving the walking distance as a function of the value of the variable capacity Cv. It is observed in fact that the deviation 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 running 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 regulation system only makes sense for mechanical movements of average quality, even of 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 at best possibilities. 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 invention relates to 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 march of the timepiece, 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 regulation device is arranged so as to be able to vary momentarily the electrical resistance generated by this regulation device 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 TP, 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 distinct 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 temporal distance DT equal to a number N multiplied by half of a regulation period Treg determined for each of said moments, ie a mathematical relation DT = 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 DT 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 DT = (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 regulating 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 DT with the regulation period Treg equal to a period of setpoint 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 regulating device is arranged to apply, during the continuous time period, periodically the regulating pulses with a trigger frequency FD (N) = 2 · F0c / N in the context of the general variant exposed previously, respectively FD (M) = 2 · F0c / (2M - 1) within the framework of the advantageous variant also mentioned previously. 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, according to whether at least a certain positive or negative time drift is detected, respectively a first correction period 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 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 some positive time drift is detected before the time considered, that is to say on a second correction frequency Fcor2 = 1 / Tcor2 when said at least one negative time drift is detected before the time considered.

According to a preferred variant, when said at least some positive or negative time drift is detected, the regulating device is arranged to periodically apply, during the next moment among said moments, the plurality of corresponding regulating pulses with respectively a first frequency FINF, according to the previously mentioned variant FINF = 2 · Fcor1 / N or FINF = 2 · Fcor1 / (2M - 1), or with a second frequency FSUP, according to the previously mentioned variant FSUP = 2 · Fcor2 / N or FSUP = 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 time 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 be able to detect a time drift in the running 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, to correct the time drift.

Brief description of the figures

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: <tb> fig. 1, <SEP> 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 hairspring piezoelectric; <tb> fig. 2 <SEP> is an enlargement of a portion of the piezoelectric hairspring of fig. 1; <tb> fig. 3 <SEP> partially shows the electrical diagram of the device for regulating the timepiece of FIG. 1; <tb> fig. 4 <SEP> gives the running distance for the timepiece of the previous figures as a function of a variable capacity applied between the two electrodes of the piezoelectric hairspring; <tb> fig. 5 <SEP> shows the evolution of the oscillation frequency 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 frequency setpoint for the mechanical oscillator of the timepiece; <tb> fig. 6 <SEP> shows the electrical diagram of a regulation device incorporated in a variant of a first main embodiment of a timepiece according to the invention; <tb> fig. 7 <SEP> shows the electrical diagram of a regulation device incorporated in a preferred variant of the first main embodiment; <tb> fig. 8 <SEP> shows the electrical diagram of a regulating device incorporated in a variant of a second main embodiment of a timepiece according to the invention; <tb> fig. 9 <SEP> 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 provided by a hysteresis comparator to be able to count the periods of oscillation of the mechanical resonator ; and <tb> fig. 10 <SEP> 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 balance and a piezoelectric hairspring, for example as shown in fig. 1 and 2, and arranged to clock the movement 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 regulating 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 supplying 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 regulating device is arranged so as to be able to vary momentarily the electrical resistance generated by this regulating device between the two electrodes of the hairspring, in order to be able to generate at least at times regulating pulses which are distinct and each have a certain duration TP, each regulation pulse consisting of a momentary decrease in the electrical resistance of the regulation system, namely the aforementioned electrical resistance relative to a nominal electrical resistance which is generated by the regulation device between the two electrodes apart from the separate control 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 DT equal to a number N multiplied by half of a regulation period Treg determined for each of said moments, ie a mathematical relation DT = 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 relationship between the time distance DT and the regulation period Treg, and thus to determine the regulation frequency.

In an advantageous variant, the time distance DT 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 DT = (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 trigger frequency FD (N) = 2 · Freg / N for the general variant, and FD (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 described 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 explain this physical phenomenon, fig. 5 shows the behavior of a mechanical oscillator equipped with a piezoelectric hairspring, of the type described above, to which short-term short-circuit pulses are applied periodically, for example less than a tenth of a period setpoint 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 incorporating it being designed to operate naturally substantially at a setpoint frequency F0c equal by definition to the reverse of the setpoint period.

In the example shown in fig. 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 FD close double the setpoint frequency but different, ie FD≈ 2 · F0c, in addition to the specific case of a triggering frequency Fd exactly equal to twice the natural frequency and therefore twice the setpoint 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 FD (N), respectively FD (M) mentioned previously) during moments during which a plurality of periodic short-circuit pulses are applied. The following results are obtained: The curve CF0 corresponds to a frequency for triggering short-circuit pulses FD0 = 10.00 Hz, and it is observed that the oscillation frequency stabilizes at the set frequency FS0 = F0c = 5.00 Hz; The curves CF1 and CF2 correspond to tripping frequencies of the short-circuit pulses which are greater than FD0, ie respectively FD1 = 10.03 Hz and FD2 = 10.08 Hz, and it is observed that the oscillation frequency is synchronized respectively on the synchronization frequencies FS1 = 5.015 Hz and FS2 = 5.04 Hz after a transient phase occurring at the start of each moment of application of short-circuit pulses; and The curves CF3, CF4 and CF5 correspond to tripping frequencies of the short-circuit pulses which are lower than FD0, that is to say FD3 = 9.96 Hz, FD4 = 9.94 Hz and FD5 = 9.88 Hz, and it is observed that the oscillation frequency is synchronized respectively with the synchronization frequencies FS3 = 4.98 Hz, FS4 = 4.97 Hz and FS5 = 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 FDX, 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 trigger frequency selected appropriately. This application is the subject of the first main embodiment. By using the induced voltage signal between the electrodes of the balance spring when the mechanical resonator oscillates, one can easily count the periods of oscillation and determine a time drift, in particular detect when a certain positive or negative time 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 a semi-open or semi-closed loop, is the subject of the second main embodiment.

In fig. 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 energized by a clock circuit 42, the latter supplying a reference signal SRefsoit at the frequency of the quartz FQ, preferably at a frequency adjusted to 32,768 Hz, or at a fraction of this frequency FQ, for example FQ / 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 SRefest supplied to a frequency divider 64 which outputs a control signal Scom to a timer 58 which, in response to the control signal, supplies a short-circuit signal Sec to a switch 60 arranged between the two electrodes 20, 22 of the piezoelectric hairspring 8 (shown diagrammatically in FIG. 6) at the frequency imposed by the control signal. This process takes place without interruption in a continuous time period which lasts as long as the regulator 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 fig. 2 and 10) which are arranged so as to be able to present between them an induced voltage U (t) by the piezoelectric material when the latter is put under mechanical stress during an oscillation of the mechanical oscillator (see fig. 9).

The Scomest control signal is a frequency signal having, in a general variant, a trigger frequency FD (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 setpoint frequency F0c between (K - 1) / K and (K + 1) / K, this number N is less than K / 40, or N <K / 40. In an advantageous variant, the control signal Scom is a frequency signal which has a trigger frequency FD (M) = 2 · F0c / (2M - 1), the number M. being an integer greater than zero which is selected from 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, i.e. 2M - 1 <K / 40. Preferably, the numbers N and M are constant and predefined for the continuous time range during which the short-circuit pulses are applied which define the regulation pulses.

The timer 58, at each pulse of the control signal, closes the switch 60 (passing switch and therefore conductive) during a time interval TR, so that the short-circuit pulses each have a duration TR, which is preferably provided for less than a quarter of the setpoint 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 range, after a possible transient phase when the regulation device is activated, a continuous synchronization of the frequency of the mechanical oscillator with the set frequency F0c.

In fig. 7 shows the electronic diagram of a regulation device, identical to that described above, which is associated with a supply circuit 66, formed by a rectifier 68 of an induced voltage U (t) between the two electrodes 20, 22 of the hairspring 8 when the mechanical resonator oscillates and arranged to supply the regulating device 62, the rectified voltage being stored in a storage capacity CAL, 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 fig. 1) to which it is fixed.

In fig. 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 includes an auxiliary oscillator and which provides a reference signal SRef 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 SRef, 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 control 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 regulating device. The hysteresis comparator provides a digital “Comp” signal (see fig. 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 zero crossing 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 the other of its two extreme positions (defining the amplitude of the mechanical oscillator respectively on the two sides of the neutral position), as shown in fig. 9.

The “Comp” signal is supplied to a first “Up” input of a bidirectional counter CB forming the measuring device. The bidirectional counter is thus incremented by one unit for each period of oscillation of the mechanical oscillator (in particular on 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 'Down' input a clock signal Shorfourni by the frequency divider DIV1 & DIV2, this clock signal corresponding to a set frequency F0c for the mechanical oscillator which is determined by the oscillator auxiliary of the auxiliary time base. Thus, the bidirectional counter supplies the logic control circuit 56 with an SDT signal corresponding to a cumulative error over time between the oscillation frequency of the mechanical oscillator and the setpoint 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 Scom to the timer 58 which, in response to this control signal, controls the temporary closing of the transistor 60 by applying a signal Sec to it. 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 on / conductor the transistor 60 (closed switch), the timer determining the duration TR 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 regulating device, which has already been described previously.

The control method according to the second main embodiment, implemented by the control device 62 and implemented in the control logic 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 whether at least some positive or negative time drift is detected, respectively a first correction period Tcorl 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 to establish d '' 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 some der 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 DT between two short-circuit pulses, in each separate correction moment, is equal to an odd number 2 M - 1 multiplied by the half of the Treg regulation period determined for each of the correction moments, ie a mathematical relation DT = (2M - 1) · Treg / 2, M being a positive integer greater than zero, the Treg regulation period 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 control logic circuit 56, the regulating device 62 is arranged to periodically apply, during the next correction moment, a plurality of '' corresponding regulation pulses with respectively a first trigger frequency FINF = 2 · Fcor1 / N or a second trigger frequency FSUP = 2 · Fcor2 / N. The number N is preferably provided 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 FINF trigger frequency occurs, the latter is expected to be greater than a first limit frequency FL1 (N, K) = [(K - 1) / K] · 2 · F0c / N with K> 40 · N, and, for each of the correction moments where the second FSUP trigger frequency occurs, the latter is provided less than a second limiting frequency FL2 (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 control logic circuit 56, the regulating device 62 is arranged to periodically apply, during the next correction moment, a plurality of '' corresponding regulation pulses with respectively a first FINF tripping frequency = 2 · Fcor1 / (2M - 1) or a second FSUP tripping frequency = 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 FINF trigger frequency occurs, the latter is expected to be greater than a first limit frequency FL1 (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 occurs FSUP release, the latter is expected to be lower than a second limiting frequency FL2 (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 to determine the start of a first regulation pulse, from among the plurality of regulation pulses provided for the correction time 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 FIG. 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 FIG. 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 median plane 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. There is therefore 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 an aluminum nitride crystal formed by a growth of this crystal from the conductive layer 76 (internal electrode) and perpendicular thereto.

Claims (20)

1. 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 clock the running of the timepiece, this timepiece further comprising a regulating 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 (SRet), 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 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 elect rods being electrically connected to the regulating device which is arranged to be able to vary the impedance of the regulating system, which is formed by said piezoelectric material, said at least two electrodes and the regulating 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 (TP), each regulating pulse consisting of a momentary decrease 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 regulating device 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 DT equal to one number N multiplied by half of a Treg regulation period determined for each of said moments, ie a mathematical relation DT = N · Treg / 2, N being a positive integer greater than zero, the Treg regulation period 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. 2. 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 correction period 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 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 moment considered, that is to say on a second correction frequency Fcor2 = 1 / Tcor2 when said at least a certain negative time drift is detected before the moment considered. 3. Timepiece according to claim 2, characterized in that the time distance DT 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 DT = ( 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. 4. Timepiece according to claim 2, characterized in that, when said at least some positive or negative time drift is detected, the regulating device (62) is arranged to apply periodically, during the next moment among said moments , the corresponding plurality of regulation pulses with respectively a first trigger frequency FINF = 2 · Fcor1 / N or a second trigger frequency FSUP = 2 · Fcor2 / 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. 5. Timepiece according to claim 3, characterized in that, when said at least some positive or negative time drift is detected, the regulating device (62) is arranged to apply periodically, during the next moment among said moments , the corresponding plurality of regulation pulses with respectively a first FINF tripping frequency = 2 · Fcor1 / (2M - 1) or a second FSUP tripping frequency = 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. 6. Timepiece according to claim 4, characterized in that, for each of said moments when the first FINF trigger frequency occurs, the latter is provided greater than a first limit frequency FL1 (N, K) = [(K– 1) / K] · 2 · F0c / N with K> 40 · N, and, for each of said moments when the second trip frequency FSUP occurs, the latter is expected to be less than a second limit frequency FL2 (N, K) = [(K + 1) / K] · 2 · F0c / N with K> 40 · N. 7. Timepiece according to claim 5, characterized in that, for each of said moments when the first trigger frequency Finf occurs, the latter is provided greater than a first limit frequency FL1 (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 FSUP occurs, the latter is expected to be lower than a second frequency limit FL2 (M, K) = [(K + 1) / K] · 2 · F0c / (2M - 1) with K> 40 · (2M - 1). 8. Timepiece according to claim 1, characterized in that said moments are contiguous and together form a continuous time range; and in that the regulating 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 DT with said period of Treg regulation 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 time range continues. 9. Timepiece according to claim 8, characterized in that the time distance DT is equal to an odd number 2M - 1 multiplied by half of the setpoint period T0c, ie a mathematical relation DT = (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 an initial transient phase possible. 10. Timepiece according to claim 8, characterized in that the regulation device (52) is arranged to apply, during the continuous time period, periodically the regulation pulses with a triggering frequency FD (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. 11. Timepiece according to claim 9, characterized in that the regulation device (52) is arranged to apply, during the continuous time period, periodically the regulation pulses with a triggering frequency FD (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. 12. Timepiece according to claim 10, characterized in that the number N is constant and predefined for the continuous time range. 13. Timepiece according to claim 11, characterized in that the number M is constant and predefined for the continuous time range. 14. Timepiece according to any one of claims 2 to 13, characterized in that the regulation pulses each have a duration (TR) less than a quarter of the setpoint period T0c. 15. Timepiece according to any one of claims 2 to 13, characterized in that the duration (TR) of said regulation pulses is less than or equal to one tenth of the setpoint period T0c. 16. 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 momentarily close this switch during said regulation pulses so as to make it conducting / conducting, these regulation pulses then defining short-circuit pulses. 17. 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 thermally compensating 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. 18. 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. 19. Timepiece according to claim 18, characterized in that said piezoelectric layer (78) consists of an aluminum nitride crystal formed by a growth of this crystal perpendicular to said conductive layer (76) and from this conductive layer. 20. 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 of 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 regulating device, 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.