METHOD FOR Strain MEASUREMENT ON A COMPONENT OF A WIND ENERGY PLANT, ARRANGEMENT FOR Strain MEASUREMENT, USE OF THE ARRANGEMENT AND METHOD FOR MOUNTING THE ARRANGEMENT

Description

[0001] The invention relates to a method for measuring strain on a component of a wind turbine, in particular a rotor blade, an arrangement for measuring strain on a component of a wind turbine, in particular a rotor blade, and the use of an arrangement for measuring strain on a component of a wind turbine, in particular a rotor blade. Furthermore, the invention relates to a method for mounting an arrangement for measuring strain on a component of a wind turbine, in particular a rotor blade.

[0002] The increasing power output of modern wind turbines is accompanied by ever larger rotor blades and taller towers. This also increases the mechanical stresses on these structures. High mechanical stresses, especially bending moments generated by wind loads, can lead to bulging, delamination, and cracking of the rotor blades. To ensure the reliability of the rotor blades, structural tests, particularly cyclic fatigue tests, are typically carried out on test rigs for model validation and certification.

[0003] In cyclic fatigue tests, rotor blades are often vibrated near their natural frequency, for example between 0.5 Hz and 1.5 Hz, by means of an electric motor mounted on the blade with an eccentrically attached weight on its shaft. The rotor blades are typically cyclically bent 1e6 to 5e6 or up to 1e7 times across one broad side of the airfoil. A distinction is made between uniaxial and biaxial fatigue tests. In uniaxial fatigue tests, the rotor blade is loaded separately in both the vertical and horizontal directions, i.e., in the flapping direction or the pivoting direction. In biaxial fatigue tests, the rotor blade is excited simultaneously in both the flapping and pivoting directions.

[0004] Strains occurring on the surface of the material, particularly in highly stressed areas of the rotor blades, such as the spar cap, trailing edge, leading edge, and outer area, must be recorded and monitored during fatigue tests. Strain gauges with strain gauges are known for this purpose in the prior art. The strains that occur are often very high, so the strain gauges can frequently fail after only a few cycles. Due to the increasingly elastic materials used in rotor blades, strain gauges can, for example, break under bending and thus fail. Strain gauge failure results in additional costs due to test interruptions, particularly the need to restart the fatigue test or repeat the test day, and a postponement of the certification date.Furthermore, strain gauges are generally designed to measure strain only over relatively small areas, such as a 10 mm long measuring grid. Due to the small dimensions of the strain gauges, the desired accuracy often cannot be achieved. In addition, measurement errors can occur, for example, by measuring a different strain, particularly from resin pockets, rather than the strain of the material itself.

[0005] Known methods and arrangements using an inductive distance sensor that enables non-contact measurement for the continuous monitoring of vibrations occurring on rotor blades during the operation of a wind turbine are generally not suitable for use on a test bench in the context of cyclic fatigue tests. Such methods and arrangements, as known, for example, from German patent application DE 198 47 982 C2, are specifically designed to be positioned on the inner side of the rotor blade in the root region and therefore to withstand significantly lower loads.

[0006] The German Patent and Trade Mark Office, or the European Patent Office, has searched the following prior art in the priority application for the present application: DE 198 47 982 C2, DE 10 2014 218 518 A1, DE 11 2018 004 704 T5, US 4 651 436 A, EP 2 037 212 A1, WO 2003 / 029 750 A1, US 2011 / 288447 A1, US 4 064 744 A, CN 203 274 631 U, DE 10 2011 083747 A1, FR 2 784 178 A1 and US 2020 / 226480 A1.

[0007] It is therefore an objective to provide a method for strain measurement on a component of a wind turbine, in particular a rotor blade, an arrangement for such strain measurement, a use of such an arrangement, and a method for mounting an arrangement for strain measurement on a component of a wind turbine, in particular a rotor blade, which reduce or eliminate one or more of the aforementioned disadvantages of existing solutions. In particular, it is an objective to provide a solution that ensures higher accuracy of strain measurement in a test rig during a cyclic fatigue test and simultaneously reliably withstands the strain changes and cycles occurring during a cyclic fatigue test.

[0008] According to a first aspect, the problem is solved by a method for measuring strain on a component of a wind turbine according to claim 1.

[0009] The solution described here employs a method for the cyclical detection of a component's strain. This involves a sensor holder with a sensor unit and a counter-holder, which can be aligned and fixed to a surface to enable the sensor unit to cyclically detect changes in the distance between the holder and the counter-holder. The sensor holder can detect this change in distance at the height of the measuring axis, which is positioned above the surface. Specifically, the height of the measuring axis corresponds to the height at which the sensor unit can be positioned above the component's surface. During the cyclical calculation of the component's strain, the cyclically detected change in distance is corrected for the height of the measuring axis. Alternatively or additionally, the cyclically detected change in distance is corrected for the component's neutral axis.This allows the elongation of the component to be calculated cyclically.

[0010] This method ensures higher accuracy in strain measurements during cyclic fatigue testing on a test rig. Furthermore, it guarantees that cyclic fatigue testing can be performed without interruption at very high strain cycles and over a large number of cycles. In particular, this allows for the reliable measurement of strains occurring on the material surface in highly stressed areas of rotor blades, such as in the spar flange, trailing edge, and outer sections.

[0011] In particular, the defined starting positions can be understood to mean that the sensor holder and the counter-holder can be fixedly attached to the surface of the component at a precisely defined distance from each other in the defined starting positions. Furthermore, the sensor holder and the counter-holder can be aligned with each other in the defined starting positions and, in particular, have a precise longitudinal alignment. This ensures that a change in the distance between the sensor holder and the counter-holder can be determined precisely.

[0012] The term "sensor holder" can preferably be understood to mean any type of retaining element designed to be positioned on the surface of the component and to securely hold a sensor unit at the level of the measuring axis, in particular to fix it in a fixed position. Preferably, the sensor holder can be a type of block with a through-opening at the level of the measuring axis for receiving the sensor unit. Preferably, the sensor unit can be passed through the through-opening and fixed in a defined position. For example, the sensor unit can be clamped in the through-opening. In particular, the sensor unit can be clamped in the through-opening by means of a screw, especially a plastic screw. Preferably, the sensor holder can have a blind hole that extends orthogonally to and from one side of the sensor holder to the through-opening.In particular, the sensor unit can be clamped in the through-hole by screwing a screw, especially a plastic screw, into the blind hole.

[0013] The counter-holder can preferably be designed essentially like the sensor holder, as a type of block. In particular, the counter-holder can preferably be any type of retaining element designed to be arranged on the surface of the component and to form or accommodate a counter-element of the sensor unit for detecting changes in distance. Preferably, the sensor holder and the counter-holder can be essentially identical in design.

[0014] The sensor unit can, in particular, comprise a sensor element configured to detect changes in the distance between the sensor holder on which the sensor unit is mounted and the counter-holder, and to provide a corresponding measured value. In particular, an inductive displacement sensor can be used to detect the change in distance. A contact-operated inductive displacement sensor is especially preferred. For example, an LVDT (Linear Variable Differential Transformer) sensor and a probe can be provided. An LVDT sensor and inductive probes operate, for example, with a probe element connected to the object being measured, such as a counter-holder, which has a ferromagnetic core that is immersed in a magnetic field and thereby alters it. The sensor unit can preferably comprise a primary coil and secondary coils. The primary coil can be supplied with an alternating voltage.A voltage can be induced in the secondary coils via the core, which is movably mounted inside the coil, particularly with axial displacement. This voltage preferably changes when this core, which is connected to the object being measured via the probe element, moves, thus providing a measure of its deflection. The probe element can have a probe tip and is connected to the counter element, i.e., the object being measured, via this probe tip. In particular, the probe element can also have a return spring. The return spring can, for example, be arranged in a sliding bearing. This allows the sensor element to be clamped in the sensor holder with the aid of the counter element. Particularly preferably, the sensor can be positioned approximately at the midpoint of an available stroke of the LVDT sensor.

[0015] Compared to non-contact sensors, this measuring principle offers significant advantages. With non-contact sensors, the induced voltage change is not linear, and linearization typically does not occur. Therefore, non-contact sensors are subject to greater measurement inaccuracies. Another disadvantage is a relatively high temperature dependence, caused by the temperature-dependent permeability of the ferrite core. For this reason, a non-contact measuring principle is not suitable for use on test benches.

[0016] Preferably, the sensor unit can be arranged directly on the sensor holder. Preferably, a probe head of a probe element of the sensor unit can be arranged directly on the sensor holder.

[0017] The measuring axis can, in particular, run substantially parallel to the surface of the component. Preferably, the height of the measuring axis can be between 5 mm and 50 mm, more preferably between 10 mm and 12 mm above the surface of the component. In particular, a minimum height of the measuring axis above the surface of the component can be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm. In particular, a maximum height of the measuring axis above the surface of the component can be 10 mm, 11 mm, 12 mm, 15 mm, 20 mm, 25 mm, 30 mm, 40 mm, or 50 mm. In particular, a small height above the measuring axis minimizes the necessary correction of the measured value for changes in the distance between the sensor holder and the counter-holder by calculating the component's strain.This height ensures that the change in distance at the surface can be measured relatively accurately compared to greater heights, in order to calculate the strain of the component taking the height into account.

[0018] A neutral axis of a component can be understood, in particular, as a zero line. In strength of materials, a neutral axis can be understood as a fiber or layer of a beam cross-section whose length does not change when twisted or bent. Accordingly, no tensile or compressive stress is preferably induced at the neutral axis by the applied load.

[0019] Particularly preferably, the step of cyclically detecting the change in the distance between the sensor holder and the counter-holder can include exciting the component to a natural frequency oscillation.

[0020] Particularly preferably, the movement of the sensor holder and the counter-holder at the level of the measuring axis can be detected by cyclically recording the change in the distance between the sensor holder and the counter-holder. Specifically, the movement of the center point of the counter-holder on the measuring axis and the center point of the sensor holder on the measuring axis is detected.

[0021] In particular, the method is suitable for use on a test bench during a cyclic fatigue test, especially with strain amplitudes of more than 3000 µm / m, especially between 3000 µm / m and 4000 µm / m or more than 4000 µm / m and / or more than 1e6 cycles, especially more than 1e7 cycles, for strain measurement on a component of a wind turbine, especially a rotor blade, especially in an outer area and / or an end edge and / or on a spar flange.

[0022] The figures 1e6 and 1e7 cycles are given in scientific notation. The "e" (engineering notation) stands for 10x, where x equals 6 or 7, respectively. Thus, a fatigue test can, in particular, comprise more than one million or more than 10 million cycles.

[0023] In particular, the method may further preferably include the step of zeroing the sensor unit before cyclically detecting the change in the distance between the sensor holder and the counter-holder.

[0024] In another preferred embodiment, the cyclic detection of the change in distance between the sensor holder and the counter-holder provides strain amplitudes of more than 3000 µm / m, in particular between 3000 µm / m and 4000 µm / m or more than 4000 µm / m.

[0025] It is particularly preferred if the cyclical detection of the change in distance between the sensor holder and the counter-holder provides for more than 1e6, in particular more than 1e7, cycles.

[0026] According to a further preferred embodiment, it is provided that the strain of the component is averaged over a material range between 11 mm and 1 m, in particular between 50 mm and 500 mm, particularly 200 mm, by cyclically detecting a change in the distance between the sensor holder and the counter-holder and by cyclically calculating the strain of the component.

[0027] Preferably, in a strain measurement on a rotor blade, it can be provided that the strain of the component is averaged over a material area of ​​at least 11 mm, in particular between 50 mm and 500 mm, particularly 200 mm, by cyclically detecting a change in the distance between the sensor holder and the counter-holder and by cyclically calculating the strain of the component.

[0028] Preferably, in a strain measurement on a tower of a wind turbine, it can be provided that the strain of the component is averaged over a material area of ​​at least between 50 mm and 1 m, in particular 1 m, by cyclically detecting a change in the distance between the sensor holder and the counter-holder and by cyclically calculating the strain of the component.

[0029] In particular, the sensor holder and the counter-holder in their defined starting position can be spaced apart from each other by between 11 mm and 1 m, especially between 50 mm and 500 mm, and especially 200 mm. This allows the strain to be measured locally and averaged over this material area.

[0030] Compared to measurements using strain gauges, the strain is therefore measured over a larger area. This increases the accuracy of the measurement, reduces or prevents measurement errors, and ensures better comparability of measurements.

[0031] The method comprises providing a connecting rod arranged on the counter-holder, which extends from the counter-holder towards an axially displaceable sensing element of the sensor unit and preferably remains in contact with the sensing element during the cyclic detection of changes in the distance between the sensor holder and the counter-holder, wherein the step of detecting the change in the distance between the sensor holder and the counter-holder includes detecting a change in the position of the sensing element. Preferably, the connecting rod can remain in contact with the sensor unit during the cyclic detection of changes in the distance between the sensor holder and the counter-holder. According to the invention, the step of detecting the change in the distance between the sensor holder and the counter-holder includes detecting a change in the position of a sensing element of the sensor unit.

[0032] The connecting rod can preferably serve as a counter element for the sensor unit. Providing the connecting rod can, in particular, include inserting one end of the connecting rod into a recess in the counter holder.

[0033] The connecting rod can preferably be designed as a rod. Accordingly, the connecting rod can be elongated, preferably cylindrical or polygonal. The connecting rod can, in particular, have a longitudinal extension that is greater than its vertical and / or horizontal extension.

[0034] In particular, the connecting rod can preferably be designed to be rigid in the longitudinal direction.

[0035] Preferably, the connecting rod can be made of a material that matches the material of the component. This allows, in particular, automatic compensation for thermal expansion. For example, the connecting rod can comprise or consist of composite material and / or aluminum and / or glass fiber reinforced plastic and / or carbon fibers and / or balsa wood and / or polyester resin and / or vinyl ester resin and / or epoxy resin.

[0036] Preferably, the connecting rod can be in contact with the axially displaceable sensing element of the sensor unit. In particular, the axially displaceable sensing element can have a probe head that is in contact with the connecting rod.

[0037] In particular, the connection between the sensor unit or touch element or...

[0038] The probe head remains in contact during the cyclical detection of the change in distance between the sensor holder and the counter-holder. This ensures a contact-based measuring principle.

[0039] The sensing element can preferably be designed as a spring-loaded sensing element and include a return spring. The return spring can, for example, be arranged in a sliding bearing. This allows the sensing element to be clamped in the sensor holder using the counter element. The presence of the return spring prevents, for example, damage to the assembly during strain measurement.

[0040] In particular, the connecting rod can also be arranged without any fixing, i.e., without a fixing, in the recess of the counter element and held in position by the tension provided by the sensor unit, especially the return spring of the sensing element. For example, the recess can be a depression in one side of the counter support facing the connecting rod, in which the connecting rod rests.

[0041] According to the invention, the change in the distance between the sensor holder and the counter-holder is detected by sensing a change in the position of the sensing element.

[0042] Particularly preferably, the sensor unit can comprise a spring-loaded sensing element, a coil arrangement and a ferromagnetic core connected to the sensing element and displaceable coaxially relative to the coil arrangement, wherein the step of detecting the change in the distance between the sensor holder and the counter-holder comprises detecting a change in the position of the core in a coil element of the sensor unit.

[0043] In particular, the difference between the length of the connecting rod and the distance between the sensor holder and the counter-holder can be approximately 50 mm. Preferably, the difference between the length of the connecting rod and the distance between the sensor holder and the counter-holder can be a maximum of 50 mm, 40 mm, 30 mm, 20 mm, or 10 mm. Particularly preferably, the connecting rod can have a length that corresponds approximately to the distance between the sensor holder and the counter-holder. This allows, in particular, ideal temperature compensation to be achieved.

[0044] Preferably, the sensor unit can extend from the sensor holder towards the counter-holder on the measuring axis. In particular, the sensor unit can extend from the sensor holder, especially from a center point of the sensor holder on the measuring axis, over a length of the measuring axis of approximately 50 mm, or a maximum of 50 mm, or a maximum of 40 mm, or a maximum of 30 mm, or a maximum of 20 mm, or a maximum of 10 mm.

[0045] According to a further embodiment, the method includes compensating for a tilting of the sensor holder and / or the counter-holder that occurs during the cyclic detection of the change in distance, so that preferably the connecting rod remains essentially on the measuring axis.

[0046] Tilting can be understood to mean, in particular, that the sensor holder and / or the counter-holder is moved from its defined starting position, especially due to applied loads. This can, for example, cause the sensor holder and / or the counter-holder to rotate or lift off the component surface at one point. Such tilting can result in the sensor holder and the counter-holder no longer being precisely aligned with each other. Without compensation for such tilting, measurement errors and inaccuracies could occur, or the strain measurement setup could be damaged.

[0047] Compensation for any tilting that occurs can be done automatically.

[0048] Preferably, compensation for any tilting that occurs can be ensured by mounting a convex end of the connecting rod in a concave recess of the counter-support. Compensation for any tilting that occurs is ensured by mounting one end of the sensor unit facing the connecting rod, in particular a probe head of the axially displaceable sensing element, in a concave curve of a concave end of the connecting rod.

[0049] According to a further aspect, the problem is solved by an arrangement for strain measurement on a component of a wind turbine, in particular a rotor blade, comprising a sensor holder and a counter-holder configured to be fixedly mounted in defined initial positions relative to each other, and a sensor unit held by the sensor holder, wherein the sensor unit is configured to detect a change in the distance between the sensor holder and the counter-holder at the level of a measuring axis spaced apart from the surface of the component. The strain measurement arrangement according to the invention is claimed in claim 7.

[0050] The solution described here provides an arrangement that enables strain measurement on a component of a wind turbine, in particular a rotor blade. For this purpose, a sensor holder with a sensor unit and a counter-holder are provided, which can be aligned relative to each other on a surface and fixed in place to detect changes in the distance between the sensor holder and the counter-holder using the sensor unit. The sensor holder can detect the change in distance at the height of the measuring axis, which is spaced from the surface. Specifically, the height of the measuring axis corresponds to the height at which the sensor unit can be positioned above the surface of the component.

[0051] Preferably, the sensor unit can be designed to cyclically detect the change in distance between the sensor holder and the counter-holder.

[0052] In particular, the sensor unit can transmit a signal from the sensor, preferably representing the change in distance between the sensor holder and the counter-holder, to a processing unit configured to cyclically calculate the strain of the component. In particular, a correction can be made taking into account the height of the measuring axis and / or the neutral axis.

[0053] Preferably, the arrangement can be configured to perform a procedure as described above.

[0054] Such an arrangement ensures higher accuracy in strain measurements during cyclic fatigue testing on a test rig. Furthermore, it guarantees that cyclic fatigue testing can be performed without interruption at very high strain cycles and over a large number of cycles. In particular, this allows for the reliable measurement of strains occurring on the material surface in highly stressed areas of rotor blades, such as in the spar area, at the trailing edge, and in an outer region.

[0055] A preferred embodiment of the arrangement is characterized in that the arrangement comprises an adhesive, in particular a double-sided adhesive tape, which is designed to fix the sensor holder and the counter-holder in a fixed position on the surface of the component, wherein the adhesive preferably comprises or consists of acrylate and / or has an adhesive force of at least 300 N / 100 mm and / or is designed to withstand a shear stress of at least 400 kPa.

[0056] Preferably, an adhesive tape, preferably double-sided, or an adhesive film can be provided for attaching the sensor holder and the counter-holder to the surface. Adhesive tapes or films are preferably less rigid compared to other adhesives. This reduces or prevents the risk of tearing. The bonding method proposed here using an adhesive tape or film is, in particular, a soft bond. Such a soft bond is characterized, in particular, by its higher elasticity compared to bonding with other adhesives, especially liquid adhesives, which exhibit higher stiffness and / or brittleness. Other adhesives could include, for example, LOCTITE 401 (ethyl cyanoacrylate), LOCTITE HY 4080 (methacrylates and cyanoacrylate), LOCTITE HY 4090 (epoxy resin and cyanoacrylate), and Henkel S25 (PU).

[0057] The adhesive tape or adhesive film can, in particular, have a foam backing which may preferably comprise a general-purpose adhesive, especially general-purpose acrylic, on one or both sides. In particular, a foam type with a tightly closed cell structure can be provided.

[0058] In particular, the adhesive can consist of acrylic. The acrylic adhesive has a viscosity sufficient to flow into a surface, especially that of the component and / or the sensor holder and / or the counter-holder.

[0059] Preferably, the adhesive tape or film can be designed so that it does not harden. This ensures flexibility during strain measurement.

[0060] Preferably, the adhesive tape can tolerate differential movements in a shear plane up to three times its thickness. In particular, a shear stress of a dynamic overlap shear test can be at least 400 kPa, and more specifically at least or approximately 415 kPa. Within the scope of the dynamic shear test, a maximum shear force of 6.45 cm² on stainless steel at room temperature can be measured at a jaw speed of 12.7 mm / min. Shearing preferably results from the action of an offset force couple, a shear force or a shear force, on a body and leads to shear distortion of the region between the forces. With the shear distortion, the force couple causes the shear stress, also called shear strain, where a shear modulus, also called shear modulus, sliding modulus (G-modulus), or torsional modulus, describes a magnitude of the distortion relative to the applied shear stress.

[0061] The shear modulus G can be related, in particular, to an elastic modulus E, a Poisson's ratio v, and a bulk modulus K. The adhesive tape or film can, in particular, comprise or consist of linearly elastic material. For the shear modulus, it can be found, in particular, that 1 / 3 E < G > 1 / 2 E.

[0062] In particular, the adhesive tape or adhesive film may have a thickness of approximately 1 mm to 2 mm, especially between 1.3 mm and 1.8 mm, and especially 1.55 mm.

[0063] Preferably, a static shear test can show that the adhesive film or tape (322.58 mm²) can withstand the following weights for seven days: 1500 g at 22 °C and / or 750 g between 66 °C and 177 °C. The static shear test can be performed particularly on stainless steel.

[0064] The adhesive tape or film is particularly preferably able to have a tensile strength of at least 500 kPa, and more preferably at least or approximately 550 kPa. The tensile strength may, in particular, refer to a normal tensile strength, preferably a maximum force on aluminum at room temperature and a baking speed of 50 mm / min in a test system.

[0065] Preferably, the adhesive force can be a 90° adhesive force. Preferably, the adhesive tape or film can have a 90° adhesive force of at least 300 N / 100 mm, in particular of approximately or at least 315 N / 100 mm. The 90° adhesive force can be determined on stainless steel at room temperature and a test system with a baking speed of 305 mm / min, preferably by measuring an average force.

[0066] This allows a moderate stretching and / or movement to be transferred across an adhesive surface.

[0067] By bonding the sensor holder and the counter-holder to the surface in this way, it can be ensured, in particular, that any movement of the sensor holder and the counter-holder at the level of the measuring axis, especially the center point of the counter-holder on the measuring axis and the center point of the sensor holder on the measuring axis, is detected. This ensures a very accurate measurement of the strain.

[0068] The use of adhesive tape, especially double-sided tape, ensures a consistently strong bond. This helps prevent cracks in the adhesive, particularly those running lengthwise along the beam. Furthermore, double-sided tape allows for a particularly simple bonding process, saving assembly time and reducing or eliminating the risk of faulty installation. Compared to traditional joining methods, adhesive tape offers further advantages. For example, it ensures even force distribution across the entire bonding surface, preventing stress concentrations. Additionally, surfaces remain unchanged, and the assembly can be removed without damage, especially after a fatigue test. Furthermore, it can compensate for component tolerances.For example, adhesive tape can also have a good sealing function as protection against the ingress of dirt and moisture, which could potentially affect the adhesive bond.

[0069] The adhesive provided is characterized in particular by the fact that the bond withstands strain vibrations of more than 3000 µm / m, especially between 3000 µm / m and 4000 µm / m or more than 4000 µm / m, especially at more than 1e6, especially 1e7, cycles.

[0070] Alternatively or additionally, adhesive can be applied to an underside and / or in a designated groove on the underside of the sensor holder and / or the counter-holder to attach them to the surface.

[0071] According to a preferred embodiment, the sensor holder and / or the counter-holder are angular, in particular square or cuboid in shape. This design allows the sensor holder and the counter-holder to be aligned with each other particularly easily and precisely. Furthermore, it simplifies, for example, the preparation and application of adhesive tape. In particular, it simplifies the precise cutting of the adhesive tape.

[0072] Alternatively, for example, the sensor holder and / or the counter-holder can be cylindrical, include a cylindrical section, or have an alternative geometry.

[0073] In particular, the sensor holder and the counter-holder are preferably designed to be fixedly mounted at defined starting positions between 11 mm and 1 m, in particular between 50 mm and 500 mm, in particular 200 mm, spaced apart from each other, wherein preferably the arrangement in a mounting state comprises a gauge which is detachably attached to the counter-holder and the sensor holder, wherein the gauge aligns the counter-holder and the sensor holder to each other and sets a defined distance between the counter-holder and the sensor holder.

[0074] This spacing enables local measurement over a larger measuring range compared to strain gauges. This allows for more accurate measurements and increases the comparability of measurements.

[0075] Using the jig during assembly makes it particularly easy to position the sensor holder and the counter-holder in their defined starting positions relative to each other. This ensures both the precise alignment and the exact distance between the sensor holder and the counter-holder.

[0076] Preferably, the teaching piece can be designed as a spacer. In particular, the teaching piece can be a beam that has receptacles at defined intervals for receiving the sensor holder and the counter-holder. The receptacles can, in particular, be designed as recesses and preferably have a geometry that ensures precise alignment of the sensor holder and the counter-holder with respect to each other.

[0077] Preferably, the jig can have bores in the area of ​​the receptacles, particularly around them. These bores serve, in particular, to allow mounting aids, especially plate-shaped ones, to be positioned on one side of the jig in the area of ​​the receptacles and screwed to the jig. Alternatively to bores, other openings, such as material recesses, can also be provided. Instead of being screwed, the mounting aids can also be attached to the jig in another way. For example, the mounting aids can also be glued to the jig.

[0078] The mounting aids can, in particular, cover the receptacles on one side of the gauge. The counter-holder and the sensor holder can preferably be inserted into the receptacles of the gauge and, in particular, detachably attached to the mounting aids that are attached to the gauge, especially by gluing or screwing.

[0079] For example, the sensor holder and the counter-holder can be detachably attached to the gauge, in particular by gluing or screwing.

[0080] Using this jig ensures particularly easy assembly. At the same time, it prevents measurement errors caused by incorrect alignment and / or spacing of the sensor holder and the counter-holder. Furthermore, it ensures lower measurement uncertainty.

[0081] The arrangement comprises a connecting rod mounted on the counter-support, extending from the counter-support towards the sensor unit. The connecting rod has a concave end. The sensor unit comprises an axially displaceable sensing element, which is connected to the connecting rod, and the connecting rod is clamped between the counter-support and the axially displaceable sensing element.

[0082] According to the invention, an end of the sensor unit facing the connecting rod, in particular a probe head of the axially displaceable probe element, is arranged in a concave curve of the concave end of the connecting rod.

[0083] By arranging the end of the sensor unit facing the connecting rod, in particular the probe head of the axially displaceable probe element, within the concave curve of the concave end of the connecting rod, any tilting of the sensor holder from its defined starting position can be compensated for. The probe element can, in particular, be spring-loaded, as described above. Preferably, the sensor unit can, as also described above, comprise a probe element, a coil assembly, and a ferromagnetic core connected to the probe element and displaceable coaxially relative to the coil assembly.

[0084] According to another aspect, the problem is solved by using an arrangement according to at least one of the preceding claims in a test rig during a cyclic fatigue test for strain measurement on a component of a wind turbine, in particular a rotor blade.

[0085] A cyclic fatigue test can preferably be characterized by the provision of strain amplitudes of more than 3000 µm / m, in particular between 3000 µm / m and 4000 µm / m or more than 4000 µm / m. Furthermore, more than 1e6, and in particular more than 1e7, cycles can be provided.

[0086] According to another aspect, the problem is solved by a method for mounting an arrangement for strain measurement on a component of a wind turbine according to claim 13.

[0087] The fixed attachment of the sensor holder and the counter-holder to the surface of the component can, in particular, include applying an adhesive to the underside of the sensor holder and the underside of the counter-holder, or arranging the sensor holder and the counter-holder on the top side of the component so that the underside of the sensor holder and the underside of the counter-holder face the surface of the component. In particular, the counter-holder and the sensor holder can then be pressed into place.

[0088] In particular, the adhesive can be double-sided tape. It is also intended that the double-sided tape be cut to fit the underside of the counter-holder and the underside of the sensor holder, a protective film be removed, and it be adhered to the underside of the sensor holder or the underside of the counter-holder. Subsequently, a protective film can be removed from a second adhesive side to adhere and thus secure the sensor holder or the counter-holder to the top side of the component.

[0089] According to a preferred further development, the step of setting the defined initial position of the sensor holder and the defined initial position of the counter-holder relative to each other by means of the gauge includes arranging the gauge on the sensor holder and the counter-holder, including removing the gauge from the sensor holder and the counter-holder, in particular after the sensor holder and the counter-holder have been permanently attached to the surface of the component in the defined initial positions relative to each other.

[0090] In a preferred embodiment of the method, it is provided that the method comprises arranging a connecting rod on the counter holder, in particular inserting an end of the connecting rod facing the counter holder into a recess of the counter holder, such that a longitudinal axis of the connecting rod lies essentially on the measuring axis, wherein preferably the sensor unit is in contact with an end of the connecting rod facing away from the counter holder, in particular a probe head of a probe element of the sensor unit is in contact with the end of the connecting rod facing away from the counter holder.

[0091] Preferably, the sensor unit, in particular the sensing element, can extend coaxially to the connecting rod.

[0092] It is particularly preferred that the sensor unit and the connecting rod be clamped together, so that the connecting rod is clamped between the sensor unit and the counter element. Preferably, the end of the connecting rod facing the counter support can first be inserted into the recess of the counter support. Subsequently, the sensor unit can be arranged on the sensor holder. Then, the sensor unit can be clamped, particularly by means of the connecting rod. In this way, a center point of an available stroke of the sensor unit can be set.

[0093] The assembly of the arrangement may, in particular, comprise the following steps, preferably in this order: attaching the sensor holder and the counter-holder to the jig, gluing the sensor holder and the counter-holder to the surface of the component, removing the jig from the sensor holder and the counter-holder, inserting one end of the connecting rod into the recess of the counter-holder, passing the sensor unit through a through-opening of the sensor holder, positioning the sensing element, in particular the probe head, and clamping the sensor unit, in particular by means of a plastic screw, in the sensor holder.

[0094] In particular, the stylus can be clamped in its end position. This ensures, in particular, that any tilting of the sensor holder and / or the counter-holder has little or no influence on the measurement result.

[0095] For further advantages, design variants and details of the other aspects and their possible further training, please also refer to the previously given description of the corresponding features and further training.

[0096] The solutions described here are not limited to the use of strain measurement on a rotor blade of a wind turbine, although the method can be used particularly advantageously and economically in this case.

[0097] Preferred embodiments are described by way of example with reference to the accompanying figures. These show: Figure 1: a schematic, three-dimensional view of an exemplary embodiment of a wind turbine; Figure 2: an exemplary embodiment of a strain measurement arrangement; Figure 3A: an exemplary representation of a jig in a top view; Figures 3B, 3C: exemplary representations of a jig with a counter-holder and a sensor holder in different perspectives; Figure 4A: exemplary representations of a sensor holder and a counter-holder in different perspectives; Figure 4B: an exemplary representation of an assembly aid in a top view; Figure 5: exemplary embodiments of the ends of a connecting rod; Figure 6: an exemplary representation of the process steps of a strain measurement method; and Figure 7: an exemplary representation of the process steps of a method for assembling a strain measurement arrangement.

[0098] In the figures, identical or essentially functionally equivalent elements are designated with the same reference numerals. General descriptions usually refer to all embodiments unless differences are explicitly stated.

[0099] The explanation of the invention by means of examples with reference to the figures is, in particular, essentially schematic, and the elements explained in the respective figure may be exaggerated for better illustration, while other elements may be simplified. For example, the following illustrates Figure 1 A wind turbine as such, schematically.

[0100] Figure 1Figure 1 shows a schematic, three-dimensional view of a wind turbine 100. The wind turbine 100 has a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 with three rotor blades 108 and a spinner 110 is mounted on the nacelle 104. During operation of the wind turbine 100, the aerodynamic rotor 106 is set into rotation by the wind and thus also rotates an electrodynamic rotor or generator rotor, which is directly or indirectly coupled to the aerodynamic rotor 106. The electric generator is located in the nacelle 104 and generates electrical energy.

[0101] Figure 2Figure 2 shows an exemplary representation of an arrangement for strain measurement 200. The arrangement 200 comprises a sensor holder 220 and a counter-holder 210. In the example shown here, the sensor holder 220 and the counter-holder 210 are aligned with each other and fixedly mounted at a defined distance from each other in their defined initial positions on the surface of a component. Preferably, the sensor holder 220 and the counter-holder 210 can each be attached by means of a double-sided adhesive tape (in Figure 2 (not shown) be permanently attached to the surface.

[0102] The counter-holder 210 and the sensor holder 220 are designed as essentially square blocks. This makes it particularly easy to align the counter-holder 210 and the sensor holder 220 precisely with each other.

[0103] The arrangement 200 also includes a connecting rod 240. An end 242 facing the counter-holder 210 is arranged in a recess 211. The connecting rod 240 extends from the counter-holder 210 along a measuring axis in the direction of the sensor unit.

[0104] The sensor holder 220 has a through-opening 221 through which the sensor unit is guided. The sensor unit is preferably coaxial with the connecting rod 240. In particular, both the sensor unit and the connecting rod 240 lie on the measuring axis. Preferably, the through-opening 221 of the sensor holder 220 and the recess 211 of the counter-holder 210 are at the level of the measuring axis.

[0105] In the example shown here, the sensor unit is clamped in the through-hole 221 by means of a plastic screw 260 and is thus fixed in place.

[0106] The sensor unit comprises a spring-loaded probe element with a return spring 251 and a probe head 252, a coil assembly arranged in a housing, and a ferromagnetic core connected to the probe element and displaceable coaxially relative to the coil assembly. A voltage can be induced in the coil assembly, particularly in secondary coils, via the core. This voltage changes preferably when the core, which is connected to the probe element via the connecting rod 240, moves, thus providing a measure of its deflection. Through the connection of the probe element to the connecting rod 240 via the probe head 252, the sensor unit, and therefore also the sensor holder 220, is in contact with the counter-holder 210.

[0107] The sensor element can be clamped in the sensor holder 220 using the return spring 251 and the connecting rod 240.

[0108] In Figure 3AAn exemplary representation of a gauge 270 is shown. The embodiment of the gauge 270 shown here is essentially designed as a beam with receptacles 271, 272 at a defined distance for receiving the sensor holder and the counter-holder (in Figure 3A (not shown). By using the jig during assembly, the sensor holder and the counter-holder can be positioned particularly easily in the defined starting positions relative to each other. This ensures both the exact alignment and the exact distance between the sensor holder and the counter-holder.

[0109] The receptacles 271 and 272 are designed specifically as feedthroughs and have an inner geometry and dimension that essentially correspond to the outer geometry and dimension of the sensor holder and the counter-holder. By inserting the sensor holder and the counter-holder into one of the receptacles 271 and 272, respectively, they can be precisely aligned with each other, ensuring a defined distance.

[0110] To simplify assembly, the gauge 270 has bores 273, 274 in the area of ​​the receptacles 271, 272. The bores 273, 274 serve in particular to allow a plate-shaped assembly aid 281, 282 to be positioned on one side of the gauge 270 in the area of ​​the receptacles 271, 272 and screwed to the gauge 270. The assembly aids 281, 282 can cover the receptacles 271, 272 on one side of the gauge. The counter-holder 210 and the sensor holder 220 can then be attached as shown in the Figures 3B and 3C shown, are inserted into the receptacles 271, 272 of the gauge 270 and are detachably attached, in particular by gluing or screwing, to the assembly aids 281, 282 which are attached to the gauge.

[0111] As in Figure 3BAs shown, the teaching 270 can ensure that the sensor holder 220 and the counter-holder 210 are arranged at a defined distance d from each other. This defined distance d, measured from a center point 222 of the sensor holder 220 at the level of the measuring axis and a center point 212 of the counter-holder 210 at the level of the measuring axis, can be, in particular, between 11 mm and 1 m, more specifically between 50 mm and 500 mm, and more specifically 200 mm.

[0112] Figure 4A This shows a design of a square block from all perspectives, which can be used both as a sensor holder and as a counter-holder. Alternatively, a sensor holder and / or a counter-holder could also be designed cylindrically, for example.

[0113] The sensor holder and the counter-holder can be of identical construction. The block has a bottom surface 301, which can be attached to the surface of a component using an adhesive. The top surface 330, opposite the bottom surface 301, has a blind hole 331. The top surface 330 of the block can be positioned in a receptacle of a jig in an assembly state and screwed to an assembly aid. For this purpose, an assembly aid 281, as shown in Figure 4B The mounting aid 281 is shown, used, and attached to one side of the gauge via the bores 283 of the mounting aid 281 and corresponding bores arranged in the gauge. The blind hole 331 is designed to correspond to the bore 284 of the mounting aid 281 in order to screw the mounting aid 281 to the block.

[0114] The block also has a first side 310 in which an opening of a through-opening 311 is arranged. The through-opening 311 extends from the first side 310 to an opposite side and is specifically designed to accommodate a sensor unit.

[0115] A second side 320 has a recess 321. The recess can, in particular, have a concave, especially semicircular, cross-section. In particular, the second side 320 can be a side facing the connecting rod, wherein the recess 321 is designed to receive an end of the connecting rod facing the block.

[0116] A blind hole 341 on another side extends from this side to the through opening 311, the blind hole 341 being orthogonal to the through opening 311. After the jig, in particular after mounting the sensor holder and the counter-holder on a surface of the component, has been removed from the block and a sensor unit has been passed through the through opening 311, a screw can be screwed into the blind hole 343 to fix the sensor unit in the through opening 311.

[0117] In the Figures 5A, 5B The ends 241, 242 of a connecting rod 240 are shown in detail. Figure 5A Figure 1 shows a convex end 242 of the connecting rod 240, which can be arranged in a concave recess of the counter-holder. Figure 5B shows a concave end 241 of the connecting rod 240, which is specifically designed to accommodate a probe 252 of the sensor unit in the concave curve.

[0118] By mounting the convex end 242 of the connecting rod 240 in a concave recess of the counter-holder and by mounting one end of the sensor unit facing the connecting rod 240, in particular a probe head 252 of the axially displaceable probe element, in the concave rounding of the concave end 241 of the connecting rod 240, tilting of the sensor holder and / or the counter-holder that occurs during the cyclic detection of the change in distance can be compensated for.

[0119] In Figure 6Exemplary process steps of a method for strain measurement on a component of a wind turbine, in particular a rotor blade, are shown. In step 1, a sensor holder and a counter-holder are provided. The sensor holder and the counter-holder are fixedly attached to a surface of the component in defined initial positions relative to each other. In step 2, a sensor unit is provided, held by the sensor holder. In step 3, a change in the distance between the sensor holder and the counter-holder is cyclically detected. This change in distance can be detected by the sensor unit at the height of a measuring axis spaced from the surface of the component. In step 4, the strain of the component is cyclically calculated, taking into account the height of the measuring axis spaced from the surface of the component and / or a neutral fiber of the component.

[0120] The method described here can achieve a standard deviation of approximately 0.3%. This results in a significantly reduced standard deviation compared to known strain measurement methods, especially those using strain gauges.

[0121] Figure 7This figure illustrates the process steps of a procedure for mounting a strain measurement device on a component of a wind turbine, specifically a rotor blade. In step 11, a sensor holder and a counter-holder are prepared. Subsequently, in step 12, a defined initial position of the sensor holder and a defined initial position of the counter-holder are set relative to each other. This can be done, in particular, using a gauge. In step 13, the sensor holder and the counter-holder can then be fixed in position relative to each other on a surface of the component in the defined initial positions. Step 14 involves arranging a sensor unit on the sensor holder. The sensor unit is mounted at the level of a measuring axis spaced apart from the surface of the component. Finally, in step 15, the sensor unit can be fixed in position on the sensor holder.

[0122] The solution described here offers several advantages. In particular, it enables cyclic fatigue tests with very high strain cycles and a large number of cycles. The high reliability of this solution significantly reduces costs by minimizing or preventing the risk of strain measurement system failure during a cyclic fatigue test. Furthermore, the absolute strain of a component can be measured with considerably higher accuracy compared to existing solutions.

[0123] The solutions described here ensure, in particular, the longevity of the arrangement. Furthermore, the arrangement can be reused multiple times. Reference symbol list

[0124] Step 1 - Provide a sensor holder and a counter-holder. Step 2 - Provide a sensor unit held by the sensor holder. Step 3 - Cyclically detect a change in the distance between the sensor holder and the counter-holder. Step 4 - Cyclically calculate the strain of the component, taking into account the height of the measuring axis spaced from the surface of the component and / or a neutral fiber of the component. Step 11 - Provide a sensor holder and a counter-holder. Step 12 - Set a defined initial position of the sensor holder and a defined initial position of the counter-holder relative to each other. Step 13 - Permanently attach the sensor holder and the counter-holder to a surface of the component in the defined initial positions relative to each other. Step 14 - Arrange a sensor unit on the sensor holder. Step 15 - Permanently fix the sensor unit to the sensor holder. 100 Wind turbine 102 Tower 104 Nacelle 106 Rotor108 Rotor blade 110 Spinner 200 Strain gauge assembly / assembly 210 Counter holder 211 Recess 212 Center point 220 Sensor holder 221 Through hole 222 Center point 240 Connecting rod 241 Concave end / end facing the sensor unit 242 Convex end / end facing the counter holder 251 Return spring 252 Probe head 260 Plastic screw 270 Gauge 271, 272 Mounts 273, 274 Holes 281, 282 Mounting aids 283 Holes 284 Hole 301 Bottom 310 First side 311 Through hole 320 Second side 321 Recess 330 Top 331 Blind hole 341 Blind hole d Distance

Claims

1. Method for strain measurement on a component of a wind turbine, in particular a rotor blade, comprising the steps: - providing a sensor holder and a counter holder (1), wherein the sensor holder and the counter holder are fixedly mounted on a surface of the component in defined initial positions relative to each other, - providing a sensor unit (2) held by the sensor holder, ∘ providing a coupling rod arranged on the counter holder, which extends from the counter holder towards an axially displaceable sensing element of the sensor unit, wherein the coupling rod (240) has a concave end (241), ∘ wherein an end of the sensor unit facing the coupling rod (240) is arranged in a concave curvature of the concave end (241) of the coupling rod (240), - cyclically detecting a change of a distance between the sensor holder and the counter holder (3) by means of the sensor unit at the level of a measuring axis spaced from the surface of the component, wherein the step of detecting the change of the distance between the sensor holder and the counter holder comprises detecting a change in a position of the sensing element, and - cyclically calculating an elongation of the component, taking into account the height of the measuring axis spaced from the surface of the component and / or a neutral fibre of the component (4).

2. Method according to the preceding claim, wherein the cyclic detection of the change of the distance between the sensor holder and the counter holder provides strain amplitudes of more than 3000 µm / m, in particular between 3000 µm / m and 4000 µm / m or more than 4000 µm / m.

3. Method according to at least one of the preceding claims, wherein the cyclic detection of the change of the distance between the sensor holder and the counter holder provides for more than 1e6, in particular more than 1e7, cycles.

4. Method according to at least one of the preceding claims, wherein the cyclic detection of a change in a distance between the sensor holder and the counter holder and by the cyclic calculation of the elongation of the component the elongation of the component is detected on average over a material range between 11 mm and 1 m, in particular between 50 mm and 500 mm, in particular 200 mm.

5. Method according to at least one of the preceding claims, wherein the coupling rod is in connection to the sensing element during the cyclic detecting of the change of the distance between the sensor holder and the counter holder.

6. Method according to the preceding claim 5, comprising compensating for a tilting of the sensor holder and / or the counter holder occurring during the cyclic detecting of the change of the distance, so that the coupling rod preferably remains substantially on the measuring axis.

7. Arrangement for strain measurement (200) on a component of a wind turbine (100), in particular a rotor blade (108), comprising - a sensor holder (220) and a counter holder (210), which are designed to be mounted in defined initial positions relative to each other, and - a sensor unit held by the sensor holder (220), wherein the sensor unit is designed to detect a change of a distance (d) between the sensor holder (220) and the counter holder (210) at the level of a measuring axis spaced from the surface of the component, - a coupling rod (240) arranged on the counter holder (210), which extends from the counter holder towards an axially displaceable sensing element of the sensor unit, wherein the coupling rod (240) has a concave end (241), wherein an end of the sensor unit facing the coupling rod (240) is arranged in a concave curvature of the concave end (241) of the coupling rod (240).

8. Arrangement (200) according to the preceding claim 7, comprising an adhesive, in particular a double-sided adhesive tape, which is designed to fix the sensor holder (220) and the counter holder (210) fixedly on the surface of the component, wherein the adhesive preferably comprises or consists of acrylate and / or has an adhesive force of at least 300 N / 100 mm and / or is designed to withstand a shear stress of at least 400 kPa.

9. Arrangement (200) according to at least one of the preceding claims 7 or 8, wherein the sensor holder (220) and / or the counter holder (210) is / are angular, in particular square or cuboid in shape.

10. Arrangement (200) according to at least one of the preceding claims 7 to 9, wherein the sensor holder (220) and the counter holder (210) are designed to be mounted fixedly at a distance of between 11 mm and 1 m, in particular between 50 mm and 500 mm, in particular 200 mm, from each other in the defined starting positions, wherein, preferably, the arrangement (200) in an assembled state comprises a gauge (270) which is detachably attached to the counter holder (210) and the sensor holder (220), wherein the gauge (270) aligns the counter holder (210) and the sensor holder (220) with respect to each other and sets a defined distance (d) between the counter holder (210) and the sensor holder (220).

11. Arrangement (200) according to at least one of the preceding claims 7 to 10, comprising a coupling rod (240) arranged on the counter holder (210), which extends from the counter holder (210) in the direction of the sensor unit, wherein the sensor unit comprises the axially displaceable sensing element, which is in connection with the coupling rod (240), and the coupling rod (240) is clamped between the counter holder (210) and the axially displaceable sensing element, wherein, preferably, a sensing head (252) of the axially displaceable sensing element is arranged in a concave curvature of the concave end (241) of the coupling rod (240).

12. Use of an arrangement (200) according to at least one of the preceding claims 7 to 11 in a test bench during a cyclic fatigue test for strain measurement on a component of a wind turbine (100), in particular a rotor blade (108).

13. Method for mounting an arrangement for strain measurement on a component of a wind turbine, in particular a rotor blade, comprising the steps: - providing a sensor holder and a counter holder (11), - providing a coupling rod arranged on the counter holder, wherein the coupling rod (240) has a concave end (241), - wherein an end of the sensor unit facing the coupling rod (240) is arranged in a concave curvature of the concave end (241) of the coupling rod (240), - setting a defined initial position of the sensor holder and a defined initial position of the counter holder relative to each other (12), in particular by means of a gauge, - fixedly attaching the sensor holder and the counter holder to a surface of the component in the defined initial positions relative to each other (13), - arranging a sensor unit on the sensor holder (14) at the height of a measuring axis spaced from the surface of the component, and - fisedly fixing the sensor unit in place on the sensor holder (15).

14. Method according to the preceding claim 13, wherein the step of setting the defined initial position of the sensor holder and the defined initial position of the counter holder relative to each other by means of the gauge comprises arranging the gauge on the sensor holder and the counter holder, comprising - removing the gauge from the sensor holder and the counter holder, in particular after the sensor holder and the counter holder have been fixedly attached to the surface of the component in the defined initial positions relative to each other (13).

15. Method according to at least one of the preceding claims 13 or 14, comprising arranging a coupling rod on the counter holder, in particular inserting an end of the coupling rod facing the counter holder into a recess in the counter holder so that a longitudinal axis of the coupling rod lies substantially on the measuring axis, Wherein, preferably, the sensor unit is in connection with an end of the coupling rod facing away from the counter holder, in particular a sensing head of a sensing element of the sensor unit is in connection with the end of the coupling rod facing away from the counter holder.