CH714143A2 - Piezoelectric element for a frequency self-regulating circuit, and oscillating mechanical system and device comprising same. - Google Patents

Abstract

The present invention relates to a piezoelectric element (3) for a frequency self-regulating circuit (10). The element comprises a spiral spring (7) formed of a piezoelectric crystal band, a first electrode connected to the self-regulating circuit, and disposed on at least a first face of the band, and a second electrode connected to the circuit of the band. self-regulation, and arranged on at least one second face of the strip. The first and second electrodes are disposed on a portion or the entire length of the spiral spring in a predetermined angular distribution. The invention relates for example to the field of watchmaking and in particular that of mechanical or electromechanical watches.

Description

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a piezoelectric element for a frequency self-regulation circuit.

The invention also relates to an oscillating mechanical system comprising the piezoelectric element and a pendulum.

The invention further relates to a device comprising the oscillating mechanical system and a self-regulating circuit of the oscillation frequency of the oscillating mechanical system.

STATE OF THE ART

Piezoelectric elements are commonly used in the field of electromechanical systems, for example for the manufacture of oscillators used as a time base, or for applications of mass sensors, force, gyroscope and many others.

In the field of watchmaking, including mechanical or electromechanical watches, it is known to provide an oscillating mechanical system of a piezoelectric element. The oscillating mechanical system may typically comprise a rocker on which is mounted a spiral spring, one end of which is fixed to the axis of rotation of the rocker arm and the other end is fixed to a fixed element of a plate. The mechanical system is kept in oscillation by means of a generally mechanical energy source. This energy source can be for example a cylinder driving a gear train with an escape wheel cooperating with an anchor. This rotary anchor actuates for example an anchor fixed near the axis of rotation of the balance. The balance with the spiral spring can thus form a regulating member of a clockwork movement. This oscillating regulating organ determines the driving speed of the gear train with the escape wheel leading to the time indicating hands. The piezoelectric element may comprise the spiral spring, on which it is known to deposit films of a piezoelectric material (PZT type), for example on the inner and outer faces of the spring. In this respect, patent applications JP 2002-228774 or EP 2 590 035 A1 can be cited. However, the deposition of such films of piezoelectric material over the entire length of the spiral spring introduces an expensive additional step in the manufacture of the spring, which is a disadvantage.

In these two patent applications, the adjustment of the oscillation frequency of the balance combined with the piezoelectric spiral spring is performed by means of a frequency self-regulating electronic circuit. The electronic circuit can be powered directly by the alternating voltage generated by the piezoelectric element, which has been rectified and stored on a capacitor. For the adjustment of the oscillation frequency, a comparison is made between a reference frequency signal supplied by an oscillator stage, and the alternating signal of the generator. On the basis of this comparison, a frequency matching signal is generated, which, when applied to the piezoelectric element, allows to induce a compressive or extending force on this element to slow or accelerate the oscillation. oscillating mechanical system.

Another example of a device comprising an oscillating mechanical system provided with a piezoelectric element, and a self-regulating circuit of the oscillation frequency of the oscillating mechanical system, is provided by the patent application WO 2011/131. 784 A1. According to a particular embodiment of this device, the piezoelectric element comprises a spiral spring formed of a strip of piezoelectric material, a first electrode disposed on an inner face of the spring, and a second electrode disposed on an outer face of the spring. The electrodes are connected to the frequency self-regulating circuit. However, a disadvantage of the proposed piezoelectric element is that it does not make it possible to use the piezoelectric effect of the element in a precise and optimal manner, without having to considerably complicate the design of the system.

SUMMARY OF THE INVENTION

The invention therefore aims to provide a piezoelectric element for a self-regulating frequency circuit, simple to perform and to use the piezoelectric effect accurately and optimally, to be able to precisely regulate the frequency of oscillation of an oscillating mechanical system and to overcome the aforementioned drawbacks of the state of the art.

For this purpose, the invention relates to a piezoelectric element for a frequency self-regulation circuit, which comprises the characteristics mentioned in the independent claim 1.

Particular shapes of the piezoelectric element are defined in the dependent claims 2 to 13.

The use of a piezoelectric crystal for the spiral spring allows a simple and economical realization of the piezoelectric element, while maintaining good piezoelectric performance. In addition, the particular arrangement of the first and second electrodes in a predetermined angular distribution on the spring allows the electrodes to collect all or part of the electrical charges induced by a mechanical stress, overcoming the problem of changing the polarity of the charges due to the change of crystalline orientation of the piezoelectric crystal. This change in polarity of the charges occurs according to a periodic angular distribution within the spiral spring. Indeed, the crystalline structure of the piezoelectric material induces a dependence of the piezoelectric coefficient on the orientation of the mechanical stress in a horizontal plane XY. In other words, in the direction of the stress in the XY plane, the electric charges created can be positive or negative, and their value between a zero value and a maximum value, as illustrated for example in FIG. 2 in the case of quartz. Thanks to the piezoelectric element according to the invention, the problem of the cancellation of the positive and negative electrical charges in each of the electrodes is overcome. Without this being limiting in the context of the present invention, the piezoelectric crystal is, for example, a quartz monocrystal.

According to a first embodiment of the invention, the first and second electrodes are disposed on a portion of an outer coil of the spiral spring, said portion comprising an end of the spiral spring and defining a predetermined angular sector. An advantage of this first embodiment is the simplicity of manufacture of the piezoelectric element, and in particular of its electrodes.

According to a second embodiment of the invention, the first electrode comprises first portions disposed on the first face of the strip of piezoelectric material and second portions disposed on at least one face of the strip of piezoelectric material distinct from the first side; and the second electrode comprises first portions disposed on the second face of the web of piezoelectric material and second portions disposed on at least one face of the web of piezoelectric material distinct from the second face. The first and second portions of the first electrode, respectively the second electrode, are alternately interconnected at junction areas. The junction zones are distributed over the spiral spring at a predetermined angular periodicity. An advantage of this second embodiment is to maximize the collection of electrical charges created, and thus maximize the amount of electrical energy collected.

Advantageously, the piezoelectric element comprises a first groove dug in the first face of the piezoelectric material strip, and a second groove dug in the second face of the piezoelectric material strip. The first electrode is disposed, at least partially, in the first groove, and the second electrode is disposed, at least partially, in the second groove. This makes it possible to increase the capacitive coupling between the electrodes, and thus to increase the piezoelectric performances of the element.

To this end, the invention also relates to an oscillating mechanical system comprising the piezoelectric element for a frequency self-regulation circuit, which comprises the characteristics mentioned in claim 14.

For this purpose, the invention also relates to a device comprising the oscillating mechanical system and the self-regulating circuit of the oscillation frequency of the oscillating mechanical system, which comprises the characteristics mentioned in claim 15.

Particular forms of the device are defined in claims 16 and 17.

BRIEF DESCRIPTION OF THE FIGURES

The aims, advantages and characteristics of the piezoelectric element for a frequency self-regulating circuit, and the oscillating mechanical system and the device comprising it, will appear better in the following description on the basis of at least one form of FIG. non-limiting embodiment illustrated by the drawings in which: FIG. 1 schematically shows a device, which comprises an oscillating mechanical system provided with a piezoelectric element according to the invention, and a self-regulating circuit of the oscillation frequency of the oscillating mechanical system; fig. 2 is an amplitude diagram of the piezoelectric effect of the piezoelectric element according to an exemplary embodiment of the invention, according to the orientation of a constraint in an XY plane; fig. 3 represents the piezoelectric element according to a first embodiment of the invention; fig. 4 shows a portion of an outer turn of a spiral spring of the piezoelectric element of FIG. 3; fig. 5 shows a portion of a spiral spring of the piezoelectric element according to a second embodiment of the invention, in a first embodiment of electrodes disposed on the spiral spring; fig. 6 shows a portion of a spiral spring of the piezoelectric element according to the second embodiment of the invention, in a second embodiment of electrodes disposed on the spiral spring; fig. 7 is a sectional view of the piezoelectric element of FIG. 6, taken along a section plane VI I-VII; fig. 8 is a sectional view of the piezoelectric element of FIG. 6, taken along a section plane VI II-VI II; and FIG. 9 shows a simplified block diagram of the electronic components of the self-regulating circuit of FIG. 1 according to an exemplary embodiment, the circuit being connected to the piezoelectric element of the oscillating mechanical system.

DETAILED DEORTION OF THE INVENTION

In the following description, reference is made to a piezoelectric element for a frequency self-regulation circuit, in particular a self-regulating circuit of the oscillation frequency of an oscillating mechanical system. All electronic components of the frequency self-regulation circuit, which are well known to those skilled in the art, are only described in a simplified manner. As described below, the self-regulating circuit is mainly used to regulate the oscillation frequency of a rocker on which is mounted the spiral spring of the piezoelectric element. However, other oscillating mechanical systems can also be envisaged, but in the rest of the description only reference will be made to an oscillating mechanical system in the form of a rocker on which is mounted the spiral spring of the piezoelectric element. .

FIG. 1 shows a device 1, which comprises an oscillating mechanical system 2, 3 and a self-regulating circuit 10 of the oscillation frequency fosc of the oscillating mechanical system. In a mechanical watch, the oscillating mechanical system may comprise a rocker 2, which is formed of a metal ring connected for example by three arms 5 to an axis of rotation 6, and a piezoelectric element 3, which comprises a spiral spring 7. As shown in FIGS. 3 to 8, the piezoelectric element 3 further comprises at least two electrodes 8a-8d electrically connected to the frequency self-regulating circuit 10. Referring back to FIG. 1, a first end 7a of the spiral spring 7 is held fixed by a stud 4 of a balance bridge (not shown). This pendulum bridge is fixed to the plate (not shown) of the movement of the watch. A second end 7b of the spiral spring 7 is fixed directly on the axis of rotation 6 of the balance 2.

The rocker 2 with its spiral spring 7 is held in oscillation by means of a power source (not shown), which may be electrical, but preferably mechanical. This source of mechanical energy may be a cylinder, which traditionally drives a gear train with an escape wheel cooperating with an anchor. This rotary anchor actuates for example an anchor fixed near the axis of rotation of the balance. The balance with the spiral spring can thus form a regulating member of a clockwork movement.

The spiral spring 7 is formed by means of a strip of piezoelectric material of thickness generally less than 0.25 mm, for example of the order of 0.1 to 0.2 mm. The piezoelectric material may be a piezoelectric crystal or a PZT piezoelectric ceramic. Preferably, the piezoelectric crystal is a single crystal, typically monocrystalline quartz in the embodiments of FIGS. 2 to 8. The spiral spring 7 is for example machined in single-crystal quartz Z-section, in other words section perpendicular to the Z axis or optical axis of a monocrystalline quartz bar. A hairspring with mutually spaced turns from a piezoelectric crystal strip is obtained by micromachining in a hydrofluoric acid bath as described in US patent application 2015/0 061 467 A1, which is incorporated herein by reference. At least two metal electrodes are deposited on at least two faces of the piezoelectric crystal strip in an arrangement which will be described in more detail later. More specifically, the electrodes are arranged on a part or the entire length of the spiral spring 7 in a predetermined angular distribution. Each electrode is for example an Au / Cr type electrode (Gold / Chrome).

FIG. 2 represents the amplitude of the piezoelectric effect of the element 3 when it comprises a spiral spring 7 made of quartz, according to the orientation of a stress in a horizontal plane XY. As shown in this figure, the quartz crystal structure induces a dependence of the piezoelectric coefficient on the orientation of the mechanical stress in the XY plane. In other words, in the direction of the stress in the XY plane, the electric charges created by the spiral spring 7 can be positive or negative, and their value between a zero value and a maximum value. The crystalline structure of the quartz being trigonal, the maximum of the electric charges is repeated every 60 °, with a change of polarity of the charges every 60 ° also.

[0024] A first embodiment of the invention will now be described with reference to FIGS. 3 and 4. According to this first embodiment, the piezoelectric element 3 comprises two electrodes 8a, 8b. The two electrodes 8a, 8b are arranged on a portion 12 of an outer turn 14 of the spiral spring 7. The portion 12 comprises the first end 7a of the spiral spring 7 and defines a predetermined angular sector. In the preferred embodiment in which the spiral spring 7 is formed of a quartz band, the predetermined angular sector is substantially equal to 60 °. Thus, and with reference to FIG. 2, this first embodiment of the invention makes it possible to avoid the mutual cancellation of the electric charges, due to the change in polarity induced by the change in crystalline orientation of the spiral spring 7 made of quartz. The electrodes 8a, 8b collect a part of the electrical charges induced by a mechanical stress, avoiding the mutual cancellation of the charges.

[0025] Preferably, as illustrated in FIG. 4, the piezoelectric element 3 may comprise at least one groove 16a dug in an upper face of the piezoelectric crystal band designated upper face. During the winding of the piezoelectric crystal band with the electrodes 8a, 8b, the upper face carrying the electrode 8a is the perpendicular to the axis of rotation of the balance parallel to the plane of the spiral, while the inner face for the 8b electrode is opposite the axis of rotation of the balance. The first electrode 8a among the two electrodes is disposed in the groove 16a of the upper face, and the second electrode 8b is disposed on the inner face.

Figs. 5 to 8 illustrate a second embodiment of the invention for which elements similar to the first embodiment, described above, are identified by identical references, and are therefore not described again.

According to a first embodiment shown in FIG. 5, a first electrode 8a among the two electrodes comprises first portions 18a disposed on the outer face of the piezoelectric crystal strip, and second portions 18b disposed on a face of the upper face band. A second electrode 8b includes first portions 20a disposed on the inner face of the piezoelectric crystal strip, and second portions 20b disposed on the upper face. Preferably, the two electrodes 8a, 8b extend over the entire length of the spiral spring 7, although only a portion of the latter, and therefore only a first portion 18a, 20a and a second portion 18b, 20b of each electrode 8a , 8b, are shown in FIG. 5.

The first portions 18a and the second portions 18b of the first electrode 8a are alternately interconnected at first junction regions 22. The first portions 20a and the second portions 20b of the second electrode 8b are alternately connected to each other. second junction zones 24, adjacent to the first junction zones 22. The first and second junction zones 22, 24 are distributed over the spiral spring 7 at a predetermined angular frequency. The second portions 18b, 20b of the first and second electrodes 8a, 8b extend successively and alternately from each other on the upper face of the piezoelectric crystal strip, according to the same predetermined angular periodicity. In a variant that is not shown, the second portions 18b, 20b of the first and second electrodes 8a, 8b could extend in the same manner on one face of the piezoelectric crystal band designated lower face. In the preferred embodiment in which the spiral spring 7 is formed of a quartz band, the predetermined angular periodicity is substantially equal to 60 °.

According to a second embodiment shown in FIGS. 6 to 8, in addition to the first and second electrodes 8a, 8b, the piezoelectric element 3 also comprises third and fourth electrodes 8c, 8d. As illustrated in FIG. 6, the third electrode 8c, which is of the same polarity as the first electrode 8a, is connected thereto at a first connection terminal 26. The fourth electrode 8d, which is of the same polarity as the second electrode 8b, is connected to it in a second connection terminal 28. The first and second connection terminals 26, 28 are each connected to the frequency self-regulating circuit 10. In a particular embodiment, not shown in the figures, the first and second connection terminals 26, 28 are arranged on the pin 4 now fixing the first end 7a of the spiral spring 7.

The first electrode 8a comprises first portions 30a disposed on the outer face of the piezoelectric crystal strip, and second portions 30b disposed on each side of the strip of the outer face. The second electrode 8b comprises first portions 32a disposed on the upper face of the piezoelectric crystal strip, and second portions 32b disposed on each side of the strip separate from the upper face. The third electrode 8c comprises first portions 34a disposed on the inner face of the piezoelectric crystal strip, and second portions disposed on each face of the strip separate from the inner face. The fourth electrode 8d includes first portions 36a disposed on the underside of the piezoelectric crystal strip, and second portions disposed on each face of the separate strip of the bottom face. Preferably, the four electrodes 8a, 8b, 8c, 8d extend over the entire length of the spiral spring 7, although only a portion of the spiral spring 7 is shown in FIG. 6. The second parts of the third and fourth electrodes 8c, 8d are thus not visible in FIGS. 6-8.

The first portions 30a and the second portions 30b of the first electrode 8a are alternately interconnected at first junction areas 38. The first portions 32a and the second portions 32b of the second electrode 8b are alternately connected to one another. second portions 34a and second portions of the third electrode 8c are alternately interconnected at third junction regions 42. The first portions 36a and the second portions of the fourth electrode 8d are alternately connected between each other. they are in fourth junction zones 44.

The different junction areas 38-44 are distributed over the spiral spring 7 according to a predetermined angular periodicity.

As illustrated in FIG. 7, each junction area 38-44 straddles two adjacent faces of the piezoelectric crystal band. Thus, the first, second, third and fourth electrodes 8a, 8b, 8c, 8d extend successively and alternately from each other on each side of the piezoelectric crystal band, according to a predetermined angular sub-periodicity. In the preferred embodiment in which the spiral spring 7 is formed of a quartz band, the predetermined angular sub-periodicity is substantially equal to 60 °.

[0034] Referring to FIG. 2, this second embodiment of the invention makes it possible to avoid the mutual cancellation of the electrical charges, due to the change in polarity induced by the change in crystalline orientation of the spiral spring 7 made of quartz. Via a periodic change of faces of the electrodes, they collect all the electrical charges induced by a mechanical stress, avoiding the mutual cancellation of the charges. Within the framework of the device 1 comprising the oscillating mechanical system 2, 3, all the electrical charges created by the oscillating system 2, 3 are collected, thus making it possible to maximize the amount of electrical energy collected and supplied to the circuit 10.

Although not shown in FIGS. 5 to 8, the piezoelectric element 3 according to this second embodiment may advantageously comprise electrode support grooves, hollowed in opposite faces of the piezoelectric crystal strip, which are the upper and lower faces.

During the oscillation of the balance 2 with the spiral spring 7, a compressive force or an extension force is applied alternately to the piezoelectric crystal band, which together generate an alternating voltage. The oscillation frequency of the balance 2 with the spiral spring 7 may be typically between 3 and 10 Hz. The self-regulating circuit 10 thus receives this AC voltage, via the electrodes to which it is connected. The self-regulating circuit can be connected directly or via two metal wires to the electrodes.

FIG. 9 shows the various electronic elements of an exemplary embodiment of the self-regulating circuit 10 for regulating the oscillation frequency of the oscillating mechanical system. Other examples of self-regulating frequency circuits can be considered without departing from the scope of the invention.

The self-regulating circuit 10 is connected to two electrodes or groups of electrodes of the piezoelectric element 3. The self-regulating circuit 10 is able to rectify the alternating voltage VP received from the piezoelectric element 3 by the intermediate of a traditional rectifier 51. The rectified voltage of the alternating voltage VP is stored on a capacitor Ce. This voltage rectified between the terminals VDD and VSS of the capacitor Ce can be sufficient to supply all the electronic elements of the self-regulation circuit without the aid of a source of additional voltage such as a battery or an energy conversion element, such as a solar cell, a thermoelectric generator or the like.

The self-regulation circuit 10 comprises an oscillator stage 55, connected for example to a resonator of the MEMS type 56. The oscillating circuit of the oscillator stage with the MEMS resonator provides an oscillating signal, which may be of a frequency less than 500 kHz, for example of the order of 200 kHz. Thus, the oscillator stage 55 can preferably provide a reference signal VR whose frequency can be equal to the frequency of the oscillating signal of the oscillator circuit.

In order to regulate the oscillation frequency of the oscillating mechanical system, a comparison must be made in the self-regulation circuit 10 between the alternating voltage VP and the reference signal VR. To do this, the self-regulating circuit 10 comprises comparison means 52, 53, 54, 57 for comparing the frequency of the alternating voltage VP with the frequency of the reference signal VR. In the case where the frequency of the reference signal corresponds to the frequency of the oscillating circuit of the oscillator stage 55, that is to say at a frequency of the order of 200 kHz, the comparison means must be designed to in such a way as to take account of the large difference in frequency between the alternating voltage VP and the reference signal VR.

The comparison means consist firstly of a first half-wave counter 52, which receives as input the alternating voltage VP of the piezoelectric element, and which supplies a first NP count signal to a unity of processor 57. The comparison means further comprises a second alternating counter 54, which receives the reference signal VR as input, and which supplies a second count signal NR to the processor processing unit 57.

To take account of the frequency difference between the alternating voltage VP and the reference signal VR, a measurement window 53 is furthermore provided between the first alternation counter 52 and the second alternation counter 54. This measurement window 53 determines the counting time of the second half-wave counter 54. The processor-processing unit 57 provides configuration parameters to the measuring window 53 for determining the counting time for the second counter. alternations. These configuration parameters are stored in a memory that is not represented in the processor processing unit. These configuration settings may be different depending on whether it is a lady's watch or a men's watch. The various operations processed in the processor processing unit 57 may be controlled by a clock signal supplied for example by the oscillating circuit of the oscillator stage 55.

The counting time of the second alternating counter 54 is adapted proportionally to the counting time of a certain number of alternations counted by the first half-wave counter 52 in the first counting signal NR. The unit of Processor processor 57 may optionally also control the first alternation counter 52 to define the start and end of a count period. However, it can also be envisaged that the first half-wave counter 52 provides information on the beginning and the end of a given number of half-waves counted to the processor unit 57. If it is intended to count by For example, 200 half cycles in the first half-wave counter, the measurement window 53 is configured so that the second half-wave counter 54 counts a number of half cycles of the reference signal VR for a period of about 5000 times less. This duration may also be dependent on the counting time, for example, of the 200 alternations of the first half-wave counter 52. This makes it possible to reduce the electrical consumption of the self-regulation circuit.

The start of counting controlled by the measuring window 53 can be determined by the first alternation counter 52, but can also preferably be controlled directly by the processor processing unit 57. The processing unit is processor 57 may first receive the first count signal HP relative to a first

Claims (17)

claims A piezoelectric element (3) for a frequency autoregulation circuit (10), the piezoelectric element (3) comprising: - a spiral spring (7) formed of a strip of piezoelectric material; a first electrode (8a), intended to be connected to the frequency self-regulation circuit (10), and disposed on at least a first face of the band made of piezoelectric material; a second electrode (8b), intended to be connected to the frequency self-regulating circuit (10), and disposed on at least one second face of the band made of piezoelectric material; characterized in that the piezoelectric material is a piezoelectric crystal or a piezoelectric ceramic; and in that the first and second electrodes (8a, 8b) are arranged on a portion or the entire length of the spiral spring (7) in a predetermined angular distribution. 2. Piezoelectric element (3) according to claim 1, characterized in that the first and second electrodes (8a, 8b) are arranged on a portion (12) of an outer turn (14) of the spiral spring (7), said portion (12) comprising an end (7a) of the spiral spring (7) and defining a predetermined angular sector. 3. Piezoelectric element (3) according to claim 1, characterized in that the first electrode (8a) comprises first portions (18a; 30a) disposed on the first face of the strip of piezoelectric material and second portions (18b; 30b). ) disposed on at least one side of the strip of piezoelectric material distinct from the first face; in that the second electrode (8b) comprises first portions (20a; 32a) disposed on the second face of the piezoelectric material web and second portions (20b; 32b) disposed on at least one face of the piezoelectric material web distinct from the second face; the first and second portions of the first electrode (8a), respectively of the second electrode (8b), being alternately interconnected at junction areas (22, 24; 38, 40); and in that said junction regions (22, 24; 38, 40) are distributed over the spiral spring (7) at a predetermined angular periodicity. 4. Piezoelectric element (3) according to claim 3, characterized in that the second portions (18b) of the first electrode (8a) and the second portions (20b) of the second electrode (8b) are arranged on a third face of the band made of piezoelectric material; and in that said second portions (18b, 20b) of the first and second electrodes (8a, 8b) extend successively and alternately from each other on the third face of the piezoelectric material strip according to said predetermined angular periodicity . 5. Piezoelectric element according to claim 3, characterized in that it comprises a third electrode (8c) and a fourth electrode (8d); the third electrode (8c) being connected to the first electrode (8a) at a first connection terminal (26) to be connected to the frequency self-regulating circuit (10), the third electrode (8c) comprising first parts ( 34a) disposed on a third face of the strip of piezoelectric material and second portions disposed on at least one face of the strip of piezoelectric material separate from the third face; the fourth electrode (8d) being connected to the second electrode (8b) at a second connection terminal (28) to be connected to the frequency self-regulating circuit (10), the fourth electrode (8d) comprising first portions ( 36a) disposed on a fourth face of the web of piezoelectric material and second portions disposed on at least one face of the web of piezoelectric material distinct from the fourth face; the first and second portions of the third electrode (8c), respectively of the fourth electrode (8d), being alternately interconnected at junction regions (42, 44); and in that said junction zones (42, 44) are distributed over the spiral spring (7) according to said predetermined angular periodicity. 6. Piezoelectric element (3) according to claim 5, characterized in that each second portion of the first, second, third, respectively fourth electrode extends on each side of the strip of piezoelectric material distinct from the first, second, third respectively fourth face; and in that the first, second, third and fourth electrodes (8a-8d) extend successively and alternately from each other on each face of the piezoelectric material strip, according to a predetermined angular sub-periodicity. 7. Piezoelectric element (3) according to one of claims 4 to 6, characterized in that the electrodes are arranged over the entire length of the spiral spring. 8. piezoelectric element (3) according to any one of the preceding claims, characterized in that the piezoelectric crystal is a single crystal. 9. Piezoelectric element (3) according to claim 8, characterized in that the piezoelectric crystal is a monocrystal selected from the group consisting of topaz, berlinite, lithium niobate, lithium tantalate, gallium phosphate gallium arsenate, aluminum silicate, germanium dioxide, a monocrystal of the tourmaline group, a monocrystal of the III-V semiconductor group of zinc-blende structure and a single crystal of the semiconductor group II- VI of wurtzite structure. 10. Piezoelectric element (3) according to claim 8, characterized in that the piezoelectric crystal is monocrystalline quartz. 11. Piezoelectric element (3) according to claim 10, characterized in that the spiral spring (7) is machined in Z-cut monocrystalline quartz. A piezoelectric element (3) according to claim 10 or 11 when dependent on claim 2 or 3, characterized in that the predetermined angular sector, the predetermined angular periodicity or the predetermined angular sub-periodicity is substantially equal. at 60 °. 13. Piezoelectric element (3) according to any one of the preceding claims, characterized in that it further comprises at least one groove (16a) hollowed in the first upper or lower face of the strip of piezoelectric material, said first electrode (8a) being disposed, at least partially, in said groove (16a), said second electrode (8b) being arranged, at least partially, on a second outer or inner face. 14. Oscillating mechanical system for a frequency self-regulating circuit (10), comprising a rocker (2) and a piezoelectric element (3) provided with a spiral spring (7), the spiral spring (7) being mounted on said balance (2), characterized in that the piezoelectric element (3) is according to any one of the preceding claims. Device (1) comprising the oscillating mechanical system according to claim 14 and a self-regulating circuit (10) of the oscillation frequency of the oscillating mechanical system, said self-regulating circuit (10) comprising an oscillator stage (55) capable of supplying a reference signal (VR), frequency comparison means (52, 53, 54, 57) between two signals, and a frequency matching unit (58) connected to the piezoelectric element (3) of the oscillating mechanical system capable of supplying a frequency matching signal (VA), characterized in that the piezoelectric element (3) of the oscillating mechanical system is capable of generating an alternating voltage (VP) at a frequency corresponding to the mechanical system oscillating, the first and second electrodes (8a, 8b) of the piezoelectric element being connected to the self-regulating circuit (10) so as to receive the frequency matching unit (58) the frequency matching signal (VA), based on the result of a frequency comparison, in the frequency comparison means, between the alternating voltage (VP) and the reference signal (VR). Device (1) according to claim 15, characterized in that the self-regulating circuit (10) of the oscillation frequency of the oscillating mechanical system further comprises a rectifier (51) for rectifying the generated alternating voltage (VP). by the piezoelectric element (3) and for storing the rectified voltage on at least one capacitor (Cc) in order to supply electricity to the self-regulation circuit. Device (1) according to claim 15 or 16, characterized in that the oscillator stage (55) of the self-regulating circuit (10) comprises an oscillating circuit connected to a MEMS resonator (56) for providing an oscillating signal, so that the oscillator stage (55) provides the reference signal (VR), all the electronic components of the self-regulating circuit being grouped together to form a single electronic module.