Watch movement equipped with an oscillator including a piezoelectric hairspring

Abstract

A timepiece movement comprising, on the one hand, an analog time display, a gear train, a barrel and an electromechanical oscillator (10), the electromechanical oscillator being formed by a resonator (12) comprising a balance wheel and a piezoelectric hairspring and a mechanical escapement (18), and, on the other hand, an electronic control circuit (20) connected to an electrical energy source (30) and arranged to control the application of a voltage to at least one electrode of the piezoelectric hairspring in order to generate driving electric pulses for the oscillator. The timepiece movement is configured such that, in a first main state, the barrel alone can maintain the oscillator in functional oscillation at a first amplitude, while in a second main state, the electronic control circuit supplies power to the piezoelectric hairspring in order to partially or completely maintain the resonator in oscillation at a second amplitude greater than the first amplitude, the second amplitude being preferably constant, for any spatial orientation.

Description

Technical Field

[0001] The present invention relates to a watch movement comprising a mainspring barrel and an analog time display, the analog time display being driven by the mainspring barrel via a gear train, and a hairspring-balance mechanism for controlling the operation of the watch movement. The hairspring is of the piezoelectric type with electrodes arranged on both side surfaces. The present invention also relates to a watch incorporating such a watch movement and an electrical energy source. Background Art

[0002] From patent US 9,721,169 a timepiece movement is known comprising an oscillator of the balance-spring type with a piezoelectric balance spring provided with electrodes connected to a variable capacitor in order to be able to vary the stiffness of the balance spring and thus adjust its natural frequency in order to improve the precision of the time display.

[0003] Patent applications EP 3 540 528 and EP 3 629 103 describe respectively a method for regulating the average frequency of a balance-spring and a method for synchronizing the frequency of a balance-spring using a piezoelectric balance connected to an electronic control unit provided with a quartz oscillator. Summary of the Invention

[0004] The object of the present invention is to improve a mechanical watch movement by integrating an electronic system, thereby increasing its operating precision without completely eliminating the balance-spring mechanism used to time the movement's operation, in particular the driving of its analog display. Furthermore, the invention proposes improving the watch movement in such a way that it can continue to operate even when the electronic system is idle, in particular due to a lack of available electrical energy.

[0005] The present invention relates to a timepiece movement comprising an analog time display, a gear train, a barrel kinematically connected to the analog time display via the gear train, and an oscillator formed by a resonator including a balance wheel and a piezoelectric hairspring, and a mechanical escapement coupling the balance wheel to the gear train, the piezoelectric hairspring being formed in part from a piezoelectric material and comprising at least two electrodes, at least one of which being connected to an electronic control circuit, the piezoelectric material and the at least one electrode being arranged so as to exert an electrical stress on the piezoelectric hairspring under the control of the electronic control circuit. Furthermore, the timepiece movement is configured such that the barrel alone is capable of driving the analog time display and of maintaining the functional oscillation of the oscillator at a first amplitude that is dependent, in particular, on the spatial orientation of the timepiece movement. Furthermore, the electronic control circuit is arranged to be connectable to a source of electrical energy and to control the application of a voltage to the at least one electrode in order to generate drive electrical pulses for the oscillator, which drive electrical pulses provide the oscillator with sufficient energy so that, for each spatial orientation of the timepiece movement, the oscillator is capable of functionally oscillating with a second amplitude that is greater than a maximum nominal value of the first amplitude for that spatial orientation.

[0006] According to a preferred embodiment, the electronic control circuit is arranged to control the application of the voltage in such a way as to keep the second amplitude substantially constant for any spatial orientation of the timepiece movement and any level of winding of the barrel. To this end, in a particular alternative embodiment, the electronic control circuit comprises a circuit for detecting the amplitude of the voltage induced in the piezoelectric balance spring and a feedback loop for maintaining this amplitude at a given set value, thereby making it possible to regulate the oscillation amplitude of the resonator.

[0007] In an advantageous alternative embodiment, said maximum nominal value is less than or equal to 300° for any spatial orientation of the timepiece movement, and said second amplitude is greater than 300° for any spatial orientation of the timepiece movement and any winding level of the barrel.

[0008] The invention also relates to a watch integrating an energy source formed by a generator arranged so as to collect external energy and convert it into electrical energy, thereby making it possible to power the electronic control circuit and the piezoelectric balance spring.

[0009] Due to the features of the present invention, the accuracy of a watch incorporating a movement according to the present invention can be improved, particularly due to the large amplitude of the balance wheel oscillations, which can be maintained by the driving electrical pulses provided to the electromechanical oscillator via the piezoelectric balance spring. Thus, this preferred embodiment can first compensate for the reduction in torque provided by the barrel, thereby maintaining a substantially constant oscillation-maintaining power for each spatial orientation of the watch movement or watch incorporating a watch movement. Consequently, in this preferred embodiment, the frequency variations of the oscillator typically associated with time-varying torque provided by the barrel in conventional mechanical movements are eliminated. Furthermore, this preferred embodiment can eliminate amplitude variations for different spatial positions of the watch movement or watch incorporating a watch movement. Finally, this preferred embodiment can prevent operational variations in the watch movement that are prone to occur in conventional mechanical movements due to other reasons, such as oil aging, hard spots in the gear train, or instantaneous increases in torque requirements, such as when switching from one day to the next. Thus, the present invention can effectively address various issues that can occur in mechanical watch movements and lead to loss of isochronism, which can cause time drift in the current time display. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The invention will be described in more detail hereinafter using the accompanying drawings given as non-limiting examples, in which:

[0011] - Figure 1 is a perspective view of an embodiment of a timepiece movement according to the invention (without an oscillating mass for winding the barrel);

[0012] - Figure 2 yes Figure 1 Bottom view of the watch movement in Figure 1, with the balance bridge and index-assembly removed;

[0013] - Figure 3 yes Figure 1 An enlarged schematic diagram of a resonator forming an electromechanical oscillator in an embodiment of a timepiece movement;

[0014] - Figure 4 is formed Figure 3 A cross-sectional view of a piezoelectric balance spring in a resonator;

[0015] - Figure 5 Schematically illustrates a watch according to the invention comprising a timepiece movement according to the invention, the watch being represented here in a first main operating state;

[0016] - Figure 6 Indicates the second main operating state Figure 5 watches in; and

[0017] - Figure 7is a schematic representation of the electronic control circuitry of the electromechanical oscillator incorporated in the preferred embodiment of the invention. DETAILED DESCRIPTION

[0018] With reference to the accompanying drawings, various embodiments of a timepiece movement according to the invention will be described, as well as the general arrangement of a watch according to the invention.

[0019] The timepiece movement 2 comprises an analog time display 4, a gear train 6, a barrel 8 driving the analog display via this gear train, and an electromechanical oscillator 10 formed by a resonator 12 comprising a balance wheel 14 and a piezoelectric hairspring 16, and a mechanical escapement 18 coupling the balance wheel to the gear train. The timepiece movement is equipped with an oscillating mass 24 ( Figure 1 and 2 Not shown, but in Figure 5 and 6 ). The balance wheel pivots in a balance bridge 26 carrying an indexing assembly 28 for setting the oscillation frequency of resonator 12 , as is standard for mechanical watch movements.

[0020] Generally speaking, the piezoelectric balance spring is formed at least partially from a piezoelectric material and comprises at least two electrodes, at least one of which is connected to the electronic control circuit 20. Figure 3 The resonator 12 and the electronic control circuit 20 are shown in FIG. 1 , to which the two outer electrodes 68 and 69 of the piezoelectric balance spring 16 are connected via electrical connections 21A and 21B. A cross-sectional view of the piezoelectric balance spring 16 is shown in FIG. Figure 4 , illustrated in a non-limiting manner. This balance spring comprises a central body 60 made of silicon, a silicon oxide coating 62 deposited on the surface of the central body to provide thermal compensation for the balance spring, a first conductive coating 64 deposited on the silicon oxide coating, and a piezoelectric material in the form of a piezoelectric coating 66 deposited on the first conductive coating 64. In a particular alternative embodiment, the piezoelectric coating consists of aluminum nitride crystals formed by growing the crystals perpendicularly from and on the first conductive coating. Two external electrodes 68 and 69, formed by a second portion of the conductive coating on the piezoelectric coating, are arranged on the two sides of the balance spring and connected to two corresponding terminals 70 and 71 of the electronic control circuit 20. Thus, the piezoelectric layer 66 comprises a first portion 74A and a second portion 74B, extending on the two sides of the central body 60 and having respective crystal structures symmetrical with respect to a midplane 76 parallel to the two sides, as a result of their growth from the first conductive coating 64. Thus, in the two lateral portions 74A and 74B, the piezoelectric coating 66 has two respective piezoelectric axes 78A and 78B that are perpendicular to the piezoelectric coating and in opposite directions.

[0021] For the same total mechanical stress applied to the piezoelectric balance spring 16 (contraction or extension of the balance spring relative to its rest position), a reversal of the sign of the induced voltage occurs between the internal electrode 64 formed by the first conductive coating and each of the two external lateral electrodes 68 and 69, since the mechanical stresses in the first and second lateral portions 74A and 74B are opposite when the balance spring contracts or extends from its rest position, that is, one of these two portions is compressed while the other of these portions is extended / stretched, or vice versa.

[0022] As can be seen from the above considerations, the local induced voltages in the first and second portions 74A, 74B of the piezoelectric coating have the same polarity along a geometric axis perpendicular to the two sides, so a single common internal electrode 64 is sufficient, extending on both sides of the central body 60. It is thus possible to obtain an induced voltage between the two external electrodes 68 and 69, corresponding to the sum of the two local induced voltages (in absolute value) generated in the first and second portions 74A and 74B of the piezoelectric coating 66, respectively. Based on these considerations, it is also possible to apply a certain voltage between the two electrodes 68 and 69 in order to actively constrain the balance spring during the excitation of the resonator 12, in particular to provide it with a drive pulse. It should be noted that the internal electrode formed by the first conductive coating 64 does not require its own electrical connection to the electronic control circuit 20 or to the mass of the timepiece movement, although this is not excluded.

[0023] Within the scope of the present invention, the piezoelectric material 66 and the two electrodes 68 and 69 are arranged so as to be able to exert an electrical stress on the piezoelectric balance spring under the control of the electronic control circuit 20, thereby providing a drive pulse for the resonator 12, which drive pulse at least partially contributes to maintaining the functional oscillation of the resonator, preferably with a substantially constant amplitude. To this end, the electronic control circuit 20 is arranged to be connected to a source of electrical energy 30 and to control the application of a voltage between the external electrodes 68 and 69, thereby generating the drive pulse for the resonator 12. In general, according to the present invention, the electronic control circuit is arranged to manage the application of a voltage to at least one of the two external electrodes 68 and 69, so as to generate a drive pulse for the electromechanical oscillator 10 via the piezoelectric balance spring constrained by the applied voltage, thereby providing the oscillator with sufficient electrical energy so that, in the absence of a drive pulse from an electrical source, the resonator 12 can exhibit a functional oscillation with an amplitude greater than the maximum nominal value of the amplitude of the functional oscillation of the resonator for each spatial orientation of the timepiece movement.

[0024] In particular, provision is made for supplying the electromechanical oscillator 10 with drive electrical pulses, i.e., energy pulses, which make it possible to maintain, or contribute to maintaining, the functional oscillation of the resonator 12. The frequency of these drive pulses depends, inter alia, on their duration and their voltage. In particular, such drive pulses can be designed so that they occur once during each half-cycle (alternation) of the resonator or once per oscillation cycle of the resonator.

[0025] Figure 5 and 6 A watch 22 according to the present invention is schematically illustrated, comprising a timepiece movement according to the present invention. The components of the timepiece movement already described will not be described in detail here. Watch 22 includes an electrical energy source 30, formed by a generator configured to generate electricity, thereby powering the electronic control circuit 20 and the piezoelectric balance spring. In the illustrated alternative embodiment, the generator is connected to a storage unit, in particular a rechargeable battery or supercapacitor, via a circuit for managing the power supplied to the electronic control circuit 20 and the electromechanical oscillator 10. It should be noted that the voltage required to power the piezoelectric balance spring lies within a voltage range between 10V and 40V. This voltage is significantly higher than the voltage of batteries typically included in watches, as well as significantly higher than the voltage provided by a horological solar cell. Therefore, the power management circuit is configured to boost the voltage accumulated in the storage unit or directly supplied by the generator. To this end, it includes a voltage booster, such as a boost pump.

[0026] Various types of generators can be provided, particularly at least one solar cell positioned on the dial or bezel of the watch. In another embodiment, a thermopile is provided that receives heat from the user's arm as external energy for the watch. The thermopile is thus configured to convert the user's body heat into electrical energy. This alternative embodiment is particularly advantageous because, when the watch is worn and thus undergoes changes in its spatial orientation, it allows the electrical energy supply to the electromechanical oscillator to be activated, thereby increasing its oscillation amplitude and improving its accuracy, as described in more detail below. When the watch is not worn and the power supply is inactive, the watch can be maintained in a stable position, so that the oscillation amplitude, and therefore the frequency, of the electromechanical oscillator are no longer affected by changes in the watch's orientation. On the other hand, when the watch is worn, that is, when the amplitude and therefore the frequency of a conventional mechanical movement vary depending on the spatial orientation of the watch, the power supply is activated and the electronic control circuit is operated. In this case, the present invention generally improves the operation of the watch and, in a preferred embodiment, described in more detail below, maintains a constant oscillation amplitude of the electromechanical oscillator, sufficient to drive the analog display, regardless of spatial orientation and the level of winding of the mainspring barrel. Finally, it should be noted that, in another embodiment, the watch according to the invention does not comprise a generator to make it autonomous, but rather comprises a battery in the form of a single cell.

[0027] exist Figure 5 , illustrates a first main state present during operation of watch 22, and in particular, of the timepiece movement 2 incorporated therein. In this first main operating state, the electrical energy source 30 does not contain sufficient stored electrical energy or does not receive sufficient electrical energy from the generator to properly power the piezoelectric balance spring, resulting in the electronic control circuit 20 generating no driving electrical pulses. In this first state, the timepiece movement 2 thus behaves like a conventional mechanical movement. The escapement 18 is a standard escapement that not only performs counting but is also arranged so that the mainspring barrel can provide a mechanical sustaining pulse to the resonator 12 via the gear train to achieve its functional oscillation. This timepiece movement is thus configured so that the mainspring barrel can drive the analog display 4 of watch 22 and independently sustain the oscillator in functional oscillation at a first amplitude that depends, inter alia, on the spatial orientation of the timepiece movement.

[0028] In the first main operating state, the resonator's oscillation frequency will therefore vary depending on the spatial orientation of the watch movement and, more generally, the level of barrel winding. It is known that when the torque provided by the barrel decreases, the resonator's oscillation amplitude also decreases significantly in the last third of the power reserve. This reduction in amplitude generally leads to a decrease in oscillation frequency, thereby affecting operating accuracy. Furthermore, the amplitude varies depending on the orientation of the watch movement (and more specifically the resonator), making this first state not ideal, but useful within the scope of the present invention, which aims, in particular, to keep the watch movement operating in the absence of an adequate power supply. This first state is particularly intended for situations in which the watch in question is not being worn and is advantageously retained in a convenient, given position. Frequency variations of the resonator are thus limited, as variations in amplitude due to changes in the resonator's orientation do not occur.

[0029] exist Figure 6 , a second main state is shown which is provided during the operation of the watch 22, in particular of the timepiece movement 2. In this second main operating state, the electrical energy source 30 comprises sufficient stored electrical energy or receives sufficient electrical energy from a generator to properly power the piezoelectric balance spring, so that the electronic control circuit 20 thereby generates the driving electrical pulses. The electronic control circuit thus generates the driving electrical pulses by supplying the corresponding terminals 70, 71 (see Figure 4 and 7 ) to manage the application of a voltage to at least one of the two electrodes 68, 69 of the piezoelectric balance spring so as to generate a drive pulse for oscillator 10, which drive pulse provides oscillator 10 with sufficient energy to enable it to oscillate functionally with a second amplitude for each spatial orientation of the timepiece movement, this second amplitude being greater than the maximum nominal value of the first amplitude mentioned above and occurring in the first main state for this spatial orientation.

[0030] In a first alternative embodiment, the maximum nominal value of the first amplitude is less than or equal to 300° for any spatial orientation of the timepiece movement, and in particular of its resonator 12, and the second amplitude is greater than 300° for any spatial orientation of the timepiece movement and any level of winding of the barrel.

[0031] In a second alternative embodiment, the maximum nominal value of the first amplitude is between 240° and 300° for any spatial orientation of the timepiece movement, and in particular of resonator 12, and the second amplitude is between 305° and 300° for any spatial orientation of the timepiece movement and any level of barrel winding.

[0032] In particular, as described above, by electrically increasing the amplitude of resonator 10 when the watch is worn by the user, its total energy is increased, and thus its ability to withstand accelerations, particularly those caused by sudden movements, is increased without increasing mechanical energy consumption. This improves the precision of the time display. In particular, if the second main operating state is ensured when the watch in question is worn, the present invention can provide a transmission ratio between the barrel and the escape wheel that is greater than that of a conventional mechanical movement, thereby increasing the power reserve, while preferably ensuring functional oscillation of oscillator 10 in any spatial orientation of the watch, and therefore of the watch movement, but at least in a given orientation, at least during stable conditions and in particular in the absence of acceleration, such as when the watch is not being worn.

[0033] Depending on the configuration of the mechanical escapement, the level of barrel winding, and the power supplied to electromechanical oscillator 10, two alternative operations can occur in the aforementioned second main state of watch 22. In the first alternative, the maintenance of resonator 12 and the alternating movement of the pallet assembly of the mechanical escapement are performed substantially or entirely by supplying power to the piezoelectric balance spring, in particular by driving electrical pulses, particularly due to the inertia of the gear train (including the escape wheel). In this case, the speed at which the balance wheel of resonator 12 drives the pallet assembly is too high to allow the escape wheel to provide a significant torque to the pallet assembly during each step of the escape wheel after it is unlocked. In the second alternative, the maintenance of the resonator and the alternating movement of the pallet assembly are jointly performed by barrel 8 and electrical energy source 30. It is conceivable that, when the second main state is activated, the watch according to the invention operates in only one or the other of these two alternatives. However, in another watch according to the invention, the first optional operation and the second optional operation occur at different times, in particular according to the winding level of the barrel and optionally the spatial orientation of the other watch, in particular its resonator.

[0034] refer to Figure 7 A preferred embodiment of the invention will now be described in which electronic control circuit 20 is arranged so as to control the application of voltage to the piezoelectric balance spring in order to keep the amplitude of resonator 12 / oscillator 14 substantially constant in the second main operating state of the timepiece movement and, in particular, for any spatial orientation of the timepiece movement and any level of winding of the barrel.

[0035] In this preferred embodiment, the electronic control circuit 20 includes a peak voltage detector 46 arranged to substantially detect the amplitude of the voltage induced in the piezoelectric balance spring 16 when the resonator 12 oscillates, and a regulating circuit 20A receiving a signal S from the peak voltage detector that is related to the amplitude of the induced voltage. A , and is arranged to be responsive to a signal S provided by a peak voltage detectorA The set point value S C To manage the supply voltage V supplied to the piezoelectric hairspring through the phase-locked loop 20B A , in order to obtain an oscillation of the resonator with a substantially constant amplitude. Setpoint value S C corresponds to the setpoint amplitude provided for the oscillation of the resonator 12. The regulating circuit 20A comprises processing parts P, I, D arranged in parallel and known to those skilled in the art, which respectively adjust the amplitude according to the setpoint value S C With the amplitude signal S A The difference between the values of is processed by the integral and derivative over time through a proportional response. The regulation circuit also receives a reference voltage V R , the reference voltage V R Finally, in order to isolate the piezoelectric balance spring from the peak voltage detector and the regulating circuit and avoid disturbing their power supply, a buffer element 44 (high input impedance transistor) is provided upstream of the peak voltage detector.

[0036] In one principal alternative embodiment, the phase-locked loop 20B servo-controls the phase of the periodic supply signal as a function of the phase of the induced voltage signal supplied, in particular, to terminal 71, so that the supply voltage constrains the piezoelectric balance spring in the direction of its movement, which is either contraction or extension, depending on the current half-cycle. For example, the circuit 20B detects the zero crossing of the induced voltage, in particular at terminal 71. Thus, for a pulse to become a drive pulse, the polarity of the supply voltage is selected so as to constrain the piezoelectric balance spring in the direction of its movement, which is alternately extension and contraction, during each half-cycle of the resonator's oscillation.

[0037] In a particular embodiment, a quartz oscillator is associated with the electronic control circuit 20. The quartz oscillator can be used for various needs. In particular, the supply voltage V A The management may include the following steps: A and set point value S C , in particular their difference, to modulate the drive pulses with a variable cycle ratio / duty cycle. In an advantageous alternative to this particular embodiment, the drive electrical pulses are triggered at a set point frequency Fc of the oscillator 10 / resonator 12, which is determined very accurately by a quartz oscillator. If the frequency F of the supply signal S The resonant frequency of the resonator (i.e., its natural frequency F N) are not too far apart, such powering of the piezoelectric balance spring makes it possible to impose the set point frequency on the resonator 12 which is partially or completely maintained by the drive electric pulses, so that the electromechanical oscillator 10 will be able to oscillate at the set point frequency with the precision of quartz and with an amplitude greater than the corresponding amplitude in the first main operating state, in particular greater than a given limit value, regardless of the spatial orientation of the watch movement. The quartz oscillator - more generally the electronic oscillator - is the master oscillator in this system, while the electromechanical oscillator is the slave oscillator. The electromechanical oscillator is indirectly slaved to the electronic oscillator by generating the drive electric pulses which are supplied to the electromechanical oscillator, the triggering of which is controlled / determined by the electronic oscillator. In general, in order to be able to impose the set point frequency on the electromechanical oscillator via the drive electric pulses, the set point frequency Fc, at a harmonic of this set point frequency (e.g. twice the set point frequency (Fc)) is preferably set to zero. S =2·Fc)) or at a lower frequency F S =2·Fc / N (where N is an integer greater than 2 (N>2)) to provide a driving electric pulse. This number N must be small enough, especially according to the natural frequency F of the electromechanical oscillator. N and according to an amount of electrical energy to be supplied to the electromechanical oscillator in order to obtain an increased amplitude advantageously maintained above a predetermined limit value.

[0038] The advantageous alternative embodiment described above can be easily implemented to achieve a gain in the operating accuracy of the timepiece movement, and therefore of the watch incorporating it, in the second main operating state, without substantially increasing the power consumption associated with partially or completely maintaining a relatively wide-amplitude oscillation. It should be noted that, in this advantageous alternative embodiment, the power supply circuit does not necessarily include a phase-locked loop for controlling the drive pulses; this simplifies its design. However, in the case where the electromechanical oscillator is maintained both by the barrel (via the mechanical escapement) and by the electronic control circuit via the electrical pulses applied to the piezoelectric balance spring, it may prove useful to periodically detect the phase of the electromechanical oscillator, and in particular the periodic detection of the zero crossings of the induced voltage in the piezoelectric balance spring (implemented by a circuit for detecting such zero crossings), in order to effectively manage at least one initial operating cycle, in particular by reducing the duration of this initial operating cycle before the synchronization phase in which the frequency and phase of the periodic electrical pulses are applied to the electromechanical oscillator, so that the drive pulses occur substantially when the resonator passes through its idle position. In general, in this advantageous alternative embodiment, the electronic control circuit is therefore associated with the quartz oscillator and is arranged to generate drive electrical pulses having a specific supply frequency determined by the quartz oscillator and depending on the set-point frequency of the electromechanical oscillator, the electromechanical oscillator being configured so that, for any spatial orientation of the timepiece movement and any level of winding of the barrel, its natural oscillation frequency remains within a range of values sufficiently close to the set-point frequency so that, at least after an initial operating cycle and without excessive disturbances, the drive electrical pulses are able to impose the set-point frequency Fc on the electromechanical oscillator 10, which has functional oscillations with the aforementioned second amplitude, which is preferably constant.

[0039] By combining the advantageous alternative embodiment described above with the preferred embodiment of the electronic control circuit 20 described above, a double regulation of the oscillation frequency of the electromechanical oscillator is obtained in the second main operating state, namely a first amplitude regulation which tends to keep the amplitude constant regardless of the spatial orientation of the watch movement, thereby reducing the variations in the natural frequency of the resonator associated with the spatial orientation of the watch movement, so that, for any possible spatial orientation, this natural frequency remains close to the setpoint frequency Fc, as long as the initial setting is correctly performed, and by the supply frequency F defined above. S ——Preferably F S =2·Fc / N, where N is equal to a non-zero integer - or more generally, the second adjustment is obtained by generating the driving electric pulses with a time interval between the driving electric pulses, the value of the time interval D T Equal to the integer N multiplied by half the set point period Tc (Tc = 1 / Fc), or the mathematical relationship D T= N·Tc / 2, where N is greater than zero. The number N can be variable and is selected within a range of values that can impose the setpoint frequency Fc on the electromechanical oscillator, this range of values depending on the range of possible natural frequencies of the oscillator that remains sufficiently close to the setpoint frequency due to the first regulation mentioned above.

[0040] Therefore, the first amplitude adjustment makes it possible to adjust the natural frequency F of the electromechanical oscillator regardless of the orientation of the watch movement. N The maximum deviation from the setpoint frequency Fc is minimized, ensuring a second regulation with a relatively large functional amplitude by means of the periodic supply signal determined by the quartz oscillator, in particular the electric drive pulses at the setpoint frequency Fc, provided that the number N is not too large. Thus, in the second main operating state, the operating accuracy of the watch movement is equal to that of the quartz oscillator, for any spatial orientation of the watch movement and any level of winding of the barrel.

[0041] In another embodiment, an advantageous alternative embodiment of this particular embodiment may not be combined with the preferred embodiment of the electronic control circuit, so that no amplitude regulation is provided, and at least after an initial operating phase the power supply frequency F defined above is used. S Drive electrical pulses are generated to apply the frequency of the electromechanical oscillator. In this case, in order for the frequency of the drive electrical pulses to be such that the setpoint frequency Fc is applied to the electromechanical oscillator, these drive electrical pulses are preferably designed so that their frequency corresponds to a small number N, such as N=1 or N=2. Note that an even number N is preferred because this allows the supply voltage to maintain the same polarity. In a simplified alternative embodiment, the supply circuit does not include a circuit for detecting zero crossings of the induced voltage.

Claims

1. A timepiece movement (2) comprising an analog time display (4), a gear train (6), a barrel (8) kinematically connected to the analog time display via the gear train, and an electromechanical oscillator (10), the electromechanical oscillator (10) being formed by a resonator (12) comprising a balance wheel (14) and a piezoelectric hairspring (16), and a mechanical escapement (18) coupling the balance wheel to the gear train, the piezoelectric hairspring being formed at least partially of a piezoelectric material (66) and comprising at least two electrodes (68, 69), at least one of which is connected to an electronic control circuit (20), the piezoelectric material and the at least one electrode being arranged so as to enable an electrical stress to be applied to the piezoelectric hairspring under the control of the electronic control circuit. force, the watch movement being configured so that the barrel can drive the analog time display and independently maintain the functional oscillation of the electromechanical oscillator at a first amplitude, the first amplitude being dependent on the spatial orientation of the watch movement; the watch movement being characterized in that the electronic control circuit (20) is arranged to be connectable to a source of electrical energy (30) and to be able to control the application of a voltage to the at least one electrode to generate a drive electrical pulse for the electromechanical oscillator, the drive electrical pulse providing the electromechanical oscillator with sufficient energy so that, for any spatial orientation of the watch movement, the electromechanical oscillator can functionally oscillate at a second amplitude, the second amplitude being greater than the maximum nominal value of the first amplitude for that spatial orientation.

2. The watch movement according to claim 1, characterized in that The electronic control circuit (20) is arranged to control the application of the voltage in such a way that the second amplitude is kept substantially constant for any spatial orientation of the timepiece movement and any winding level of the barrel.

3. The watch movement according to claim 2, characterized in that The electronic control circuit (20) includes a peak voltage detector (46) arranged to substantially detect the magnitude of a voltage induced in the piezoelectric balance spring (16) when the resonator (12) oscillates, and a regulating circuit (20A) receiving a signal (S) from the peak voltage detector related to the magnitude of the induced voltage. A ) and is arranged to be able to determine the set point value (S) of the signal provided for the peak voltage detector according to the set point value (S C ) to manage the supply voltage (V A ) to achieve oscillation of the resonator with a substantially constant amplitude.

4. The watch movement according to claim 1, characterized in that The electronic control circuit is associated with a quartz oscillator contained in the watch movement, the electronic control circuit being arranged to generate the drive electrical pulses at a specific supply frequency, the specific supply frequency being determined by the quartz oscillator and depending on a set-point frequency of the electromechanical oscillator (10), the electromechanical oscillator being configured so that, for any spatial orientation of the watch movement and any level of winding of the barrel, its natural oscillation frequency remains within a range of values sufficiently close to the set-point frequency so that the drive electrical pulses can impose the set-point frequency on the electromechanical oscillator while the electromechanical oscillator functionally oscillates at the second amplitude.

5. The watch movement according to claim 2 or 3, characterized in that: The electronic control circuit is associated with a quartz oscillator contained in the watch movement, the electronic control circuit being arranged to generate the drive electrical pulses at a specific supply frequency, the specific supply frequency being determined by the quartz oscillator and depending on a set-point frequency of the electromechanical oscillator (10), the electromechanical oscillator being configured so that, for any spatial orientation of the watch movement and any level of winding of the barrel, its natural oscillation frequency remains within a range of values sufficiently close to the set-point frequency so that the drive electrical pulses can impose the set-point frequency on the electromechanical oscillator while the electromechanical oscillator functionally oscillates at the second, substantially constant amplitude.

6. The watch movement according to any one of claims 1 to 4, characterized in that: For any spatial orientation of the timepiece movement, the maximum nominal value is less than or equal to 300°, and for any spatial orientation of the timepiece movement and any winding level of the barrel, the second amplitude is greater than 300°.

7. The watch movement according to claim 6, characterized in that For any spatial orientation of the timepiece movement, the maximum nominal value is between 240° and 300°, and for any spatial orientation of the timepiece movement and any winding level of the barrel, the second amplitude is set between 305° and 300°.

8. A watch (22) comprising a timepiece movement (2) according to any one of the preceding claims, characterised in that The electrical energy source is incorporated in the watch and comprises a generator arranged to collect external energy and convert it into electricity, thereby being able to power the electronic control circuit (20) and the piezoelectric balance spring (16).

9. The watch according to claim 8, characterized in that The generator includes a light sensor.

10. The watch according to claim 8, characterized in that The generator comprises a thermopile arranged to convert a user's body heat into electricity.

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