DEFROSTING SYSTEM FOR A MECHANICAL PART, WITH AT LEAST ONE PIEZOELECTRIC ACTUATOR

Description

Technical field.

[0001] The present invention relates to a de-icing system for a mechanical part, comprising at least one piezoelectric actuator. Such a de-icing system is particularly—but not exclusively—suitable for a wind turbine blade, an aircraft leading edge, or a turbomachine blade. The invention also relates to a method for de-icing a mechanical part using the aforementioned de-icing system.

[0002] In general, the invention relates to the technical field of de-icing, and more particularly to de-icing systems using piezoelectric actuators. These de-icing systems are particularly advantageous in the field of renewable energies, such as wind power, and in aeronautics. These technical fields are not, however, limiting; the de-icing systems according to the invention can be easily adapted to other technical fields not mentioned. State of the art.

[0003] Certain mechanical parts, particularly in the aeronautics industry, can be subjected to extreme temperatures. Indeed, changes in altitude can lead to a significant drop in temperature. Frost can then form on certain aircraft engine components, such as blades or vanes, or on the wings or tail assembly. The accumulation of frost can drastically alter the physical characteristics of the part and lead to a decrease in engine performance, or a change in the aerodynamic behavior of the wings and tail assembly. The same is true for wind turbines, where the presence of frost on the blades can also reduce performance, particularly in terms of efficiency.

[0004] This is why numerous defrosting systems have been developed for various mechanical parts. The most common defrosting systems are thermal systems, where the heat produced defrosts the part. However, these systems have very high energy consumption.

[0005] Other systems use chemicals, but these pose a problem due to their bulk, as they require large volumes of product for defrosting. Furthermore, these products are generally not environmentally friendly.

[0006] In addition, "mechanical" defrosting systems using piezoelectric actuators have increasingly been developed to vibrate the part to be defrosted. These systems are compact and lightweight, have low energy consumption, and are environmentally friendly.

[0007] The published patent document EP 2 433 868 B1 discloses a system for de-icing mechanical parts for the aerospace industry. This system includes ultrasonic emitting devices, such as piezoelectric actuators, positioned against an internal surface of the part. These piezoelectric actuators are inserted into housings and are controlled by a control unit that enables their activation. However, these piezoelectric actuators are difficult to mass-produce and are integrated into a relatively complex and therefore expensive mounting structure. Furthermore, they are not well-suited to curved surfaces.

[0008] The published patent document EP3390228A1 discloses a defrosting device comprising an actuator having a fixed part and a moving part designed to alternately move away from and towards the fixed part, an intermediate element comprising a thrusting part arranged to be pushed by the moving part of the actuator when the moving part of the actuator moves away from the fixed part, and a motion transmission part designed to move in proportion to the movement of the thrusting part and intended to push a part to be defrosted in order to deform the part to be defrosted. Other defrosting systems are disclosed in patent documents US2021078711A1, CN113148181A, CA2770812A1, GB2472053A, and CN109436338A.

[0009] US patent document 9,155,430 B2 discloses a windshield defrosting system for motor vehicles comprising piezoelectric actuators. A method for defrosting the windshield is also described. This method includes a first step of transmitting ultrasonic waves to the surface of the mechanical part, followed by a second step of propagating these waves through the part. The propagation of the waves increases the temperature of the part, thus defrosting it. However, in practice, this type of system does not provide very effective defrosting because the duration of such defrosting is particularly long and highly dependent on the thickness of the frost on the windshield. Furthermore, the piezoelectric actuators are bonded to the part to be defrosted, making them vulnerable to mechanical stress, impacts, and humidity. Their maintenance is also relatively complex, if not impossible.

[0010] The invention aims to overcome all or part of the drawbacks of the aforementioned prior art. More specifically, the invention aims to provide a piezoelectric actuator defrosting system with improved defrosting efficiency compared to prior art systems. The invention also aims to provide a defrosting system with improved robustness compared to prior art systems. Furthermore, the invention aims to provide a defrosting system with simpler and less expensive design and maintenance compared to prior art systems. Presentation of the invention.

[0011] The solution proposed by the invention is a defrosting system according to claim 1 configured to be mounted on a surface of a mechanical part to be defrosted, said system comprising at least: - a piezoelectric actuator; a fixing device configured to fix the actuator on the surface; - at least one control unit configured to activate the actuator so as to excite the part to defrost it.

[0012] This system is remarkable in that the actuator comprises a stacked structure of prestressed piezoelectric elements acting along a longitudinal axis of the actuator. Furthermore, the mounting device is configured to rigidly fix the actuator so that the longitudinal axis is parallel to the surface. In addition, the mounting device includes a fixing element positioned at each of the two ends of the actuator (9), which fixing elements are configured so that activation of the actuator causes the workpiece to be excited in both extension and bending modes.

[0013] The piezoelectric actuator according to the invention features a stacked structure of prestressed piezoelectric elements (hereinafter referred to as the "prestressed piezoelectric pillar") offering excellent resistance to shock, humidity, cycling over time, and stress, as well as simplified repair and maintenance. Furthermore, after numerous tests, the applicant observed that the orientation of the prestressed piezoelectric pillar parallel to the surface and its method of attachment at both ends allows the part to be vibrated and excited in both its extension and bending modes. The ability to excite these two types of modes results in a de-icing system with a wide range of adaptability, as it is operational under a variety of operating conditions.

[0014] The parallel positioning of the actuator relative to the surface of the part also prevents the part from being subjected to significant damaging forces when it undergoes significant accelerations, which can be the case in the field of aeronautics.

[0015] Other advantageous features of the apparatus of the invention are listed below. Each of these features may be considered alone or in combination with the notable features defined above, insofar as they fall within the scope of the appended claims. Each of these features contributes, where applicable, to the resolution of specific technical problems defined further in the description and in which the notable features defined above do not necessarily participate. The latter may, where appropriate, be the subject of one or more divisional patent applications.In one embodiment, the actuator is fixed by means of the fastening elements such that the distance between the actuator and the surface is between 0 and 10 mm, preferably between 3 mm and 8 mm. In one embodiment, the distance is adjustable. In one embodiment, the control unit is configured to activate the actuator at a frequency between 1 kHz and 200 kHz and at a voltage between 100 V and 400 V. In one embodiment, the control unit is configured to activate the actuator at a frequency less than or equal to its resonant frequency. In one embodiment, a counterweight is positioned at each of the two ends of the actuator, said counterweights being identical and arranged symmetrically with respect to the center of the actuator.In one embodiment, the mass of the counterweights is such that the resonant frequency of the actuator corresponds to the resonant frequency of a vibration mode of the part to be defrosted. In another embodiment, the actuator is connected to a second circuit configured to operate the actuator in a frost detection mode. In another embodiment, the second circuit includes a voltage generator used to activate the actuator with a voltage between 1 mV and 10 V and a means for impedance analysis of the actuator. In another embodiment, the impedance analysis data of the actuator is used by the control unit to measure and / or evaluate the frost thickness on the part.In one embodiment, the control unit is coupled to a switch having at least two positions: a first position in which the actuator is connected to a first circuit configured to operate said actuator in a defrosting mode, and a second position in which said actuator is connected to the second circuit configured to operate said actuator in a frost detection mode. In one embodiment, the switch is only switched to the first position if the measured and / or evaluated frost thickness is equal to or greater than a predetermined threshold value.

[0016] The invention also relates to a method for defrosting a mechanical part, according to claim 14, comprising the following steps: - transmission of an excitation to the mechanical part by one or more piezoelectric actuators of a defrosting system; - propagation of the excitation in the mechanical part, so as to allow the defrosting of said part.

[0017] This process is remarkable in that the system conforms to one of the aforementioned characteristics. In addition, the process includes a step of activating the piezoelectric actuator(s) by the control unit, provided that the frost thickness on the part is equal to or greater than a threshold value, the activation step being prior to the excitation transmission step.

[0018] According to one embodiment, the process further includes a frost detection step on the part prior to the activation step.

[0019] According to one embodiment, the process includes a step of measuring and / or evaluating the thickness of the frost, located between the detection step and the activation step.

[0020] The invention further relates to a mechanical part comprising at least one defrosting system conforming to one of the aforementioned characteristics, which system is positioned on an internal or external surface of the part.

[0021] According to one embodiment, the part is a wind turbine or aircraft blade, or an aircraft turbomachine blade. Brief description of the figures.

[0022] Other advantages and features of the invention will become clearer upon reading the description of a preferred embodiment which follows, with reference to the attached drawings, which are provided as illustrative and non-limiting examples and on which: [ Fig. 1 ] is a cross-section of a part equipped with a defrosting system according to the invention; [ Fig. 2 ] illustrates a first embodiment of a defrosting system according to the invention; [ Fig. 3 ] illustrates a second embodiment of a defrosting system according to the invention; [ Fig. 4 ] Sketch a curve showing the impedance variation (Z) of a piezoelectric actuator as a function of the activation frequency (f); [ Fig. 5 ] illustrates an example of the architecture of a system conforming to the invention and combining a defrosting function and a frost detection function; [ Fig. 6 ] is a diagram representing the different stages of a process according to the invention. Description of the implementation methods,

[0023] The invention may implement one or more computer programs executed by equipment. For the sake of clarity, it should be understood in the context of the invention that " one step consists has to do something " "a piece of equipment does something" or that "The computer program does something." mean " "The computer program executed by a processing unit does something."

[0024] Where applicable, and to potentially supplement their current definition, the following clarifications are provided for certain terms used in the claims and description: The adjectives "internal" and "external" define the positioning of a surface of the mechanical part; an internal surface refers to a surface inside the part, and an external surface refers to a surface outside the part. A step prior to another step refers to a step that occurs before that other step. Similarly, a step subsequent to another step refers to a step that occurs after that other step. As used here, unless otherwise indicated, the possible use of the ordinal adjectives "first," "second," etc., to describe an object or step simply indicates that different occurrences of similar objects or steps are being mentioned and does not imply that the objects or steps so described must be in any particular sequence, whether in time, space, order, or any other way. "X and / or Y" means: X alone or Y alone or X+Y.In general, it is appreciated that on the various attached drawings, the objects are drawn arbitrarily to facilitate their reading.

[0025] There figure 1 Figure 1 represents a cross-section of a mechanical part 1, more specifically a wind turbine or aircraft blade. The mechanical part 1 here comprises a hollow structure 3 having an internal surface 3B and an external surface 3A. This structure 3 is generally made of lightweight materials known to those skilled in the art, for example, aluminum sheets. For illustrative purposes only, the following description refers to the de-icing of the blade 1 on whose surface 3A ice has accumulated. However, the de-icing system of the invention is applicable to any type of mechanical part that needs to be de-iced, such as aircraft wings and / or control surfaces, windows, ventilation inlets, cold storage walls, etc.

[0026] On the figure 1 The defrosting system comprises one or more piezoelectric actuators 9, each fixed to the surface of the part 1 by means of a fastening device. The piezoelectric actuators 9 are preferably fixed to the inner surface 3B but could be fixed to the outer surface 3A depending on the application.

[0027] At least one control unit 7 is configured to activate the actuator(s) 9 so as to excite the part 1 to defrost it. In practice, when the actuators 9 are activated by the unit 7, they vibrate the part 1, and these vibrations remove all or part of the frost G.

[0028] The control unit 7 can be in the form of a processor, microprocessor, or CPU (Central Processing Unit) and associated with memory in which one or more computer programs are stored. The code instructions of these programs, when executed by said processor, microprocessor, or CPU, enable the execution of the steps and / or functionalities described later in this description. A single unit 7 can activate one or more actuators 9 simultaneously or sequentially. It is also possible to have several control units 7, each activating one or more piezoelectric actuators in a specific area of ​​the room 1, for specific and / or localized defrosting in that area. The unit(s) 7 can be installed within the structure 3 or remotely from it.

[0029] The actuator(s) 9 can also be used to detect frost G and, if necessary, measure / evaluate its thickness e, between two defrosting phases. A single actuator 9 therefore has a dual function: defrosting and frost detection. Unit 7 can then adjust the activation frequency of the actuator(s) 9 accordingly. The operation of an actuator in "frost detection" mode is detailed further in the description with reference to Figures 4 and 5 .

[0030] The piezoelectric actuators 9, the control unit 7 and, where applicable, the frost detection devices, can be connected by wire (e.g. by cable) or wirelessly, in particular by a short-range wireless link of the type Bluetooth ®< , ANT ®< , ZigBee ®< , etc.

[0031] There figure 2Figure 9 illustrates a first embodiment of a piezoelectric actuator. The actuator 9 is configured to produce mechanical energy when an electric field is applied to it. It comprises a stacked structure of piezoelectric elements 91 (also referred to hereafter as the "piezoelectric pillar"). The piezoelectric elements 91 are advantageously in the form of piezoceramic or piezocomposite washers or discs with diameters ranging, for example, from 3 mm to 50 mm. The number of washers or discs can vary from 2 to 400 depending on the length of the pillar (which can range from 2 mm to 300 mm) and / or the mechanical force to be generated. As an example, hard PZT (Lead Zirconate Titanium) ceramic washers are used.Pillar 9 can be resin-coated at the time of assembly, outside the room to be defrosted, increasing its durability by further protecting it from moisture, dust, and other environmental conditions.

[0032] When the actuator 9 is energized, its piezoelectric elements 91 deform elastically to generate a mechanical stress. The elastic deformation consists of an elongation of the piezoelectric pillar along the longitudinal axis XX of the actuator 9. In other words, the actuator 9 elongates (extends) when energized. And when it is de-energized, the actuator 9 retracts (contracts) and returns to its original position. As an example, the piezoelectric pillar is configured so that its travel between the extension and contraction phases is between 1 µm and 150 µm.

[0033] The actuator 9 is preferably pre-stressed to improve the robustness and mechanical strength of the piezoelectric pillar. In one embodiment, screw elements engage with a rod 92 passing through elements 91, so as to apply a pre-stress to the piezoelectric pillar by compressing said pillar. On the figure 2 , the axis of the rod 92 coincides with the longitudinal axis XX.

[0034] The longitudinal axis XX of the actuator 9 is parallel to the surface 3B (disregarding geometric and / or assembly tolerances). "Parallel" means parallel to the plane containing the area of ​​surface 3B opposite the actuator 9 when said surface is flat in that area. If surface 3B is curved in that area, "parallel" means that the longitudinal axis XX is perpendicular to the normal N to said surface passing through the midpoint of the actuator 9, or more simply, that the actuator 9 is tangent to said surface 3B.

[0035] A fastening device 11 is configured to fix the actuator 9 so that the longitudinal axis XX is parallel to the surface 3B. The fastening device 11 comprises a first fastening element 11A positioned at a first end 9A of the pillar 9, and a second fastening element 11B positioned at the second end 9B of said pillar. According to an advantageous feature of the invention, the fastening elements 11A and 11B are each in the form of a right angle or an L-shaped piece, in order to simply ensure good parallelism between the longitudinal axis XX of the actuator 9 and the surface 3B. The fastening elements 11A and 11B can be made of metal or any other material suitable to those skilled in the art and providing sufficient rigidity to transmit the mechanical stresses of the actuator 9 to the part 1.

[0036] The fasteners 11A, 11B can be rigidly attached to the ends 9A, 9B by welding or by means of screws, which may be the same as those used to pre-tension the pillar 9 with the rod 92, or separate screws. Similarly, the fasteners 11A, 11B can be rigidly attached to the surface 3B by means of screws or by welding. The installation and securing of the defrosting system to the surface 3B is therefore very simple and quick.

[0037] In this particular configuration, where the actuator 9 is installed parallel to the surface 3B and fixed to each of its ends 9A, 9B, part 1 can be excited according to bending and extension modes. The extension and contraction of the pillar 9 along the longitudinal axis XX induce extensional forces F parallel to said longitudinal axis, which are mainly transmitted into part 1 by elements 11A, 11B. These extensional forces F tend to generate the formation of cracks on the surface of the frost G and its fracturing, potentially leading to delamination. These extensional forces F also induce bending moments Mf (along the y-axis on the figure 2) at the attachment points of elements 11A and 11B, which act as lever arms. These bending moments Mf cause bending excitation of part 1 (or at least of surface 3B), allowing fracturing and delamination of the frost G. Part 1 can thus be excited in two types of modes to optimize the vibrations of the structure in order to quickly and efficiently eliminate the frost G.

[0038] Since the fixing elements 11A and 11B act as lever arms, the distance d separating the pillar 9 from the surface 3B plays an important role in the bending excitation. Indeed, the greater the distance d, the greater the intensity of this bending excitation. Conversely, if the distance d is close to 0, the intensity of the bending excitation will be minimal, or even zero. Therefore, according to an advantageous embodiment, the distance d is between 0 mm and 10 mm, preferably between 3 mm and 8 mm. This distance d can be predetermined or adjustable, for example, by using a system of oblong holes formed in the elements 11A and 11B, into which the ends 9A and 9B are positioned. The optimal distance d can be defined empirically based on the characteristics of the frost G (e.g., its composition, its microstructure) and / or of part 1 and / or according to the preferred excitation modes in extension and bending to eliminate the frost G.

[0039] The activation of actuator 9 is achieved by energizing its piezoelectric elements 91. This energizing is managed by the control unit 7. For example, the control signal generated by the control unit 7 and applied to actuator 9 can have a voltage between 20 V and 400 V, with a current from 1 mA to 10 A. In one embodiment, the activation frequency band of actuator 9 (the frequency of the pillar's extension and contraction phases) is between 1 kHz and 150 kHz and can reach 200 kHz. The control unit 7 can adapt the control signal, in terms of voltage and / or current (e.g., sinusoidal or square wave control signal), to optimize performance in terms of generated mechanical stresses and / or vibration frequencies, etc.

[0040] Actuator 9 of the figure 2It does not need to be activated at its own resonant frequency to be effective. The best results in terms of defrosting efficiency are obtained when the vibration frequency generated by actuator 2 corresponds to one or more resonant frequencies of the part 1 to be defrosted. These resonant frequencies depend primarily on the geometry, material, and thickness of part 1 and the thickness e of the frost G on said part.

[0041] By design, actuator 9 of the figure 2 It can be excited over a wide frequency band (for example, between 1 kHz and 150 kHz), which offers a wide range of adjustment depending on the thickness of the frost. Its activation frequency can therefore be easily adjusted to match at least one of the resonant frequencies of the room to be defrosted.

[0042] Furthermore, the fact that actuator 9 can be excited over a wide frequency band simplifies the design of the de-icing system. Indeed, in some installations, the de-icing system may include several actuators mounted on different parts. For example, an aircraft wing is generally made up of several plates whose size and / or shape may vary. For a de-icing system installed on this aircraft wing, actuators 9 are fixed to all or part of these plates (i.e., the mechanical parts as defined in the invention). It is then unnecessary to specifically size each actuator according to the size and / or shape of the plate to which it is fixed. Instead, the actuators can all be identical and, for example, sized to operate in the same range between 30 kHz and 60 kHz.It is then sufficient to adjust the activation frequency of each of the actuators in a unique way to tune it specifically to at least one of the resonance frequencies of the corresponding plate.

[0043] When a part 1 to be defrosted needs to be excited with a higher power density in the actuator (due to its size and / or shape and / or material and / or the thickness of the frost G), the actuator 9 may include counterweights. This is the second embodiment illustrated in the figure 3A first counterweight 93A is positioned at the first end 9A of the pillar 9, and a second counterweight 93B is positioned at the second end 9B of said pillar. Each end of the pillar 9 is thus equipped with a counterweight. These counterweights 93A and 93B are identical and arranged symmetrically with respect to the center of the pillar 9 so that the assembly is balanced. The counterweights 93A and 93B can be rigidly fixed to the rod 92 or to the mounting elements 11A and 11B, for example, by means of screws or welds. The mass of the counterweights 93A and 93B depends on the desired resonant frequency of the actuator and can, for example, vary from 10 g to 500 g. In particular, the mass of the counterweights 93A, 93B is chosen so as to match the resonance frequency of the actuator 9 with the resonance frequency of a vibration mode of the part to be defrosted.

[0044] An actuator 9 according to the figure 3It operates optimally when activated at its own resonant frequency, but provides good defrosting results at activation frequencies lower than its resonant frequency. Therefore, this type of actuator 9 is preferentially used when one or more resonant frequencies of the part to be defrosted do not vary significantly with the frost thickness G. The actuator 9 is then configured (notably by selecting the counterweight masses 93A, 93B) so that its own resonant frequency is tuned to at least one of these resonant frequencies of the part to be defrosted.

[0045] Regardless of its specific embodiment, the actuator 9 can also be used to detect and measure, or at least assess, the frost thickness e G. In one embodiment, this information on the presence and / or thickness of the frost G is used as input data for the defrosting system activation process: if the measured / assessed thickness is less than a threshold value, then the defrosting mode is not activated. Conversely, if the measured / assessed thickness is greater than or equal to a threshold value, then the defrosting mode is activated. The activation frequency of the actuator 9 can then be adjusted according to this measured / assessed thickness.

[0046] According to one embodiment, the detection and measurement of frost thickness are based on an analysis of the impedance data of the actuator 9, in order to carry out an identification of one or more resonance frequencies of the part 1. This analysis is preferably carried out by the unit 7.

[0047] The resonant frequency Fe of part 1, without frost, in a resonant mode is of the type: Fe = C × k m Where: C is a coefficient, K the modal stiffness of the part and m the modal mass of said part.

[0048] With reference to the figure 4The impedance curve (solid line) Z of actuator 9 in the vicinity of this resonant frequency Fe exhibits a characteristic dip (Fm) and peak (Fn). The impedance Z corresponds to the ratio between the voltage U and the current I applied to the piezoelectric pillar 9 (Z=U / I). The values ​​of this reference impedance curve are stored in a system memory area, which may be the memory area of ​​unit 7 or another dedicated memory area.

[0049] In case of frost, the resonant frequency Fe' of part 1 becomes: Fe ′ = C × k ′ m ′ Where: k'>k (as frost becomes embedded on surface 3B, piece 1 becomes stiffer) and m'>m (m'=m+m G , with m G the mass of frost).

[0050] According to a particularly advantageous embodiment, frost detection is achieved by activating the piezoelectric pillar 9 with a low voltage value, i.e., between 1 mV and 10 V. The pillar 9 is activated over a frequency range around the resonant frequency Fe, for example over the range [X.Fe ; Y.Fe], with 0.1≤X≤0.9 and 1.1≤Y≤2. The impedance of the pillar 9 is then measured at each swept frequency of the frequency range.

[0051] The measured values ​​are then compared by unit 7 with those of the reference impedance curve. If the measured impedance curve coincides with the reference impedance curve, then there is no frost on part 1. Conversely, a deviation ΔF of the measured impedance curve (shown as a dotted line on the graph) indicates a deflection. figure 4 ) of the reference impedance curve (frequency shift), indicates the presence of frost on part 1.

[0052] The value of this deviation ΔF allows the frost thickness to be measured / evaluated. Indeed, series of impedance measurements can be taken beforehand with different frost thicknesses and stored in a memory area of ​​the system. Furthermore, a comparison of the measured values ​​with these known values ​​allows unit 7 to deduce the frost thickness, as well as the resonant frequency of the part 1 to be defrosted.

[0053] There figure 5This shows an example of a system architecture combining a defrosting function with a frost detection function. Actuator 9 is connected to control unit 7. A switch 17 toggles the system between "defrost mode" and "frost detection mode." Switch 17 can be activated manually or automatically by unit 7. In its first position, switch 17 connects actuator 9 to a first circuit 19 comprising a high-voltage generator 21 (e.g., 20 V to 400 V) used to activate the actuator in defrost mode. In its second position, switch 17 is connected to a second circuit 23 comprising a low-voltage generator 24 (e.g., 1 mV to 10 V) used to activate actuator 9 in frost detection mode. The second circuit 23 also includes an impedance analysis means 25 which may, for example, simply consist of an ammeter adapted to measure the current flowing through the actuator 9.The impedance analysis data is used by unit 7 to trigger the switching of switch 17. Circuits 19 and 23 can be in the form of electronic boards connected to unit 7.

[0054] There figure 6 This section details the various stages of the defrosting process according to the invention. Stages 201 and 203 are optional.

[0055] This process includes a first step 201 for detecting frost G on part 1. Switch 17 selects the second circuit 23. Pillar 9 is activated at low voltage over a predefined frequency range to perform impedance measurements as explained previously. The impedance analysis allows the presence of frost to be detected.

[0056] A second step 203 measures / evaluates the frost thickness e of the G, based on impedance measurements. If the measured / evaluated frost thickness value e is less than a predetermined threshold value Vthreshold (for example, 0.3 mm), switch 17 is not switched and defrosting of room 1 is not activated. Conversely, if the measured / evaluated frost thickness value e is equal to or greater than the threshold value Vthreshold, then switch 17 is switched and defrosting is activated. In this case, switch 17 is toggled to select the first circuit 19.

[0057] A third step 205 consists of activating the actuator(s) 9. The actuators 9 can be activated locally, if the analysis of the frost thickness is localized, or over the whole of the part 1. The activation frequency can be pre-parameterized or preferably set according to the measured / evaluated frost thickness so that the activation frequency coincides with the resonance frequency of the part 1 having frost.

[0058] A fourth step 207 corresponds to the transmission of the excitation, produced by the piezoelectric actuator(s) 9 to the part 1 via the fixing elements 11A, 11B.

[0059] A fifth step 209 corresponds to the propagation of the excitation in part 1. Within the framework of the invention, the excitation transmitted by the actuator(s) 9 is in flexure and extension. This propagation can be localized in a precise area of ​​part 1 or be transmitted throughout the entire part 1.

[0060] Step 209 leads to the sixth and final defrosting step 211. Excitation of part 1 allows fracturing and delamination of the frost by vibration according to one or more of its vibration modes.

[0061] The arrangement of the various elements and / or means and / or steps of the invention, in the embodiments described above, should not be interpreted as requiring such an arrangement in all implementations. In any event, it will be understood that various modifications may be made to these elements and / or means and / or steps without departing from the subject matter of the invention as defined in the attached claims.

[0062] Furthermore, one or more features described only in one embodiment may be combined with one or more other features described only in another embodiment, provided they fall within the scope of the appended claims. Similarly, one or more features described only in one embodiment may be generalized to other embodiments, even if these features are described only in combination with other features, provided they fall within the scope of the appended claims.

[0063] The use of the verb "comporter", "comprendre" or "include" and its conjugated forms does not exclude the presence of other elements or steps than those stated in a claim.

Claims

1. De-icing system configured to be mounted on a surface (3A, 3B) of a mechanical part (1) to be de-iced, said system comprising at least: - a piezoelectric actuator (9), - a fastening device (11) configured to fasten the actuator (9) to the surface (3A, 3B), - at least one control unit (7) configured to activate the actuator (9) according to extension phases when it is energised and according to contraction phases when it is not energised and returns to its original position, such that it energises the part (1) to de-ice it, wherein: - the actuator (9) comprises a stack structure of prestressed piezoelectric elements (91) acting along a longitudinal axis (X-X) of said actuator, - the fastening device (11) is configured to rigidly fasten the actuator (9) so that the longitudinal axis (X-X) is parallel to the surface (3A, 3B), characterised in that: the fastening device (11) comprises a first fastening element (11A) positioned at a first end (9A) of the actuator (9), and a second fastening element (11B) positioned at a second end (9B) of said actuator, which fastening elements are, in use, fastened to the surface (3A, 3B) of the part (1) to be de-iced, the fastening elements are configured such that activation of said actuator causes the part (1) to be de-iced to be excited according to extension and bending modes, the extension and contraction of the actuator (9) along the longitudinal axis (X- X) induce extension forces (F) parallel to said longitudinal axis, said extension forces also induce bending moments (Mf) at the fastening region of the first fastening element (11A) and at the fastening region of the second fastening element (11B), which fastening elements act as lever arms and cause flexural excitation of the part (1) to be de-iced.

2. De-icing system according to Claim 1, characterised in that the first fastening element (11A) and the second fastening element (11B) are each in the form of a bracket or an L-piece.

3. De-icing system according to Claim 2, characterised in that the actuator (9) is fastened by means of the fastening elements (11A, 11B) such that the distance (d) between said actuator and the surface (3A, 3B) is between 0 and 10 mm, preferably between 3 mm and 8 mm.

4. De-icing system according to Claim 3, characterised in that the distance (d) is adjustable.

5. De-icing system according to one of the preceding claims, characterised in that the control unit (7) is configured to activate the actuator (9) according to a frequency between 1 KHz and 200 KHz and according to a voltage between 100 V and 400 V.

6. De-icing system according to one of the preceding claims, characterised in that the control unit (7) is configured to activate the actuator (9) at a frequency less than or equal to its resonance frequency.

7. De-icing system according to one of the preceding claims, characterised in that a counterweight (93A, 93B) is positioned at each of the two ends (9A, 9B) of the actuator (9), said counterweights being identical and arranged symmetrically with respect to the middle of said actuator.

8. De-icing system according to Claim 7, characterised in that the mass of the counterweights (93A, 93B) is such that the resonance frequency of the actuator (9) corresponds to the resonance frequency of a vibration mode of the part (1) to be de-iced.

9. De-icing system according to one of the preceding claims, characterised in that the actuator (9) is connected to: - a first circuit (19) configured to activate said actuator in de-icing mode, and - a second circuit (23) configured to operate said actuator in an ice detection mode (G).

10. De-icing system according to Claim 9, characterised in that the second circuit (23) comprises a voltage generator (24) used to activate the actuator (9) according to a voltage between 1mV and 10V and a means (25) for analysing impedance of said actuator.

11. De-icing system according to Claim 10, characterised in that the impedance analysis data for the actuator (9) is used by the control unit (7) to measure and / or assess the thickness (e) of the ice (G) on the part (1).

12. De-icing system according to one of Claims 9 to 11, characterised in that the control unit (7) is coupled to a switch (17) having at least two positions: a first position in which the actuator (9) is connected to the first circuit (19) configured to operate said actuator according to a de-icing mode, and a second position in which said actuator is connected to the second circuit (23) configured to operate said actuator according to an ice detection mode (G).

13. De-icing system according to Claims 11 and 12, characterised in that the switch (17) is switched into the first position only on the condition that the measured and / or assessed thickness (e) of the ice (G) is greater than or equal to a predetermined threshold value.

14. Method for de-icing a mechanical part (1), comprising the following steps: - transmission of an excitation (207) to the mechanical part (1) by one or more piezoelectric actuator(s) (9) of a de-icing system, - propagation of the excitation (209) in the mechanical part (1), so as to enable the de-icing of the part (1), characterised in that: - the de-icing system is according to one of the preceding claims, - the method comprises a step (205) of activating the piezoelectric actuator(s) (9) by the control unit (7), on the condition that the thickness (e) of the ice (G) on the part (1) is greater than or equal to a threshold value, the activation step (205) being prior to the step of transmitting the excitation (207).

15. De-icing method according to Claim 14, characterised in that the method further comprises a step (201) of detecting ice (G) on the part (1) prior to the activation step (205).

16. De-icing method according to Claim 15, characterised in that the method comprises a step (203) of measuring and / or assessing the thickness (e) of the ice (G), carried out between the detection step (201) and the activation step (205).

17. Mechanical part (1) comprising at least one de-icing system, characterised in that the de-icing system is positioned on an inner (3B) or outer (3A) surface of the part (1), said system being according to one of Claims 1 to 13.

18. Mechanical part according to Claim 17, characterised in that said part is a wind turbine or aircraft blade, or a vane of an aircraft turbomachine.