EP4689392A1

EP4689392A1 - Method and system for inspecting a plank for a wind turbine blade

Info

Publication number: EP4689392A1
Application number: EP23716806.7A
Authority: EP
Inventors: Aparna Chakrapani Sheila-Vadde; Biswajit MEDHI
Original assignee: LM Wind Power AS
Current assignee: LM Wind Power AS
Priority date: 2023-03-30
Filing date: 2023-03-30
Publication date: 2026-02-11
Also published as: WO2024199661A1; CN120882972A

Abstract

An inspection system (200) for inspecting a pultrusion plank (300) for a wind turbine (10) is described. The inspection system includes an array device (210) of at least two microwave probes (211; 212) including a first microwave probe (211) and a second microwave probe (212) being offset from each other. The first microwave probe (211) and the second microwave probe (212) define a first and a second probing area (301, 302), forming an overlap area (303) between the first probing area (301) and the second probing area (302). The first microwave probe and the second microwave probe are adapted to provide different frequencies and/or modes of microwaves for inspecting the plank. The inspection system further includes a control unit (400) adapted to vary the frequencies and/or modes of the microwaves from first microwave probe and the second microwave probe during inspection of the plank.

Description

METHOD AND SYSTEM FOR INSPECTING A PLANK FOR A WIND TURBINE

BLADE

FIELD

[0001] The present disclosure generally relates to an inspection system for a part of a wind turbine blade, and more particularly to an inspection system for a plank of a wind turbine blade. The present disclosure further relates to a method for inspecting a plank of a wind turbine blade.

BACKGROUND

[0002] Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modem wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known foil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.

[0003] The size of rotor blades contributes to the energy efficiency of wind turbines. In particular, an increase in rotor blade size can increase the energy production of a wind turbine. The economic benefits of increased wind turbine sizes or rotor blade sizes are weighed against respective costs of manufacturing, transporting, assembly or repair of the wind turbines. For instance, the repair of the blades can be very time-consuming and labor intensive. Often, cranes are used to grip the blades and lower the blades from a rotor hub of a wind turbine to the ground such that the rotor blades can be replaced, or such that maintenance or repair of the blades can be performed on the ground or at a maintenance station. [0004] However, avoiding repair itself as well as costs and efforts associated with the repair is still the most sustainable and most cost-efficient way. Having less defects from the beginning, by inspecting parts or components before assembly, helps avoiding the repair and maintenance efforts.

[0005] Accordingly, the present disclosure is directed to an inspection system and an inspection method for a plank of a wind turbine blade that can reduce repair efforts and costs for a wind turbine blade, or even avoid the replacement of a wind turbine blade.

BRIEF DESCRIPTION

[0006] Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

[0007] In one aspect, the present disclosure is directed to an inspection system for inspecting a pultrusion plank for a wind turbine. The inspection system includes an array device of at least two microwave probes, wherein the array of at least two microwave probes includes a first microwave probe and a second microwave probe. According to embodiments described herein, the first microwave probe and the second microwave probe are offset from each other. The first microwave probe defines a first probing area, and the second microwave probe defines a second probing area, and wherein the offset between the first microwave probe and the second microwave probe is chosen to form an overlap area between (or including parts of) the first probing area and the second probing area. Further, the first microwave probe and the second microwave probe are adapted to provide different frequencies and/or modes of microwaves for inspecting the plank. The inspection system further includes a control unit for controlling the first microwave probe and the second microwave probe of the array of at least two microwave probes, wherein the control unit is adapted to vary the frequencies and/or modes of the microwaves generated by at least one of the first microwave probe and the second microwave probe during inspection of the plank.

[0008] With the inspection system according to embodiments described herein, it is possible to inspect (especially individual) pultrusion planks. The pultrusion planks can be inspected by the inspection system according to embodiments described herein before the planks are assembled to a wind turbine blade, or even before the planks form stacks in horizontal and vertical direction to form the spar beam, a pin joint, or any other component of a wind turbine blade or a wind turbine blade shell. With the system according to embodiments described herein, the planks can be inspected as they move along at a certain speed.

[0009] The inspection system according to embodiments described herein allows for inspecting the area of a pultrusion plank, especially by inspecting the (entire) width of a pultrusion plank, when the pultrusion plank passes by. Particularly, the inspection system according to embodiments described herein allows for inspecting long sections of the pultrusion plank as it passes by the inspection system by inspecting at any instant, the width (especially the full width) of a pultrusion plank in one shot. Specifically, an array device (or simple, an array) of microwave probes enables the inspection over the (especially full) width of the pultrusion plank. An array device (or array) of microwave probes or sensors as described in embodiments herein ensures that the entire width of the pultrusion plank can be inspected and, thus, increases the overall quality of the inspection, especially compared to the inspection with only one single sensor. With a single sensor, the coverage can be incomplete or non-uniform across the width leading to poorer sensitivity to defects at the edges for example. Alternately, a single sensor can be scanned along the width, however this can lead to increased inspection time. For instance, the microwave probes of the array of microwave probes according to embodiments described herein may each be operated in a core area of a probing area of the probe, where the most reliable inspection results are achieved. The edge regions of the probing area of the microwave probes, where the inspection reliability may decrease, get additionally covered by adjacent probes of the array of microwave probes.

[0010] On the other hand, the array of microwave probes according to embodiments described herein offers a great flexibility to use all, some, or even just one microwave probe of the array of microwave probes, particularly depending on the plank to be inspected, and more particularly dependent on the width of the plank to be inspected.

[0011] According to embodiments described herein, the microwave probes of the array device of microwave probes have overlapping probing areas or inspection areas. This may lead to a secure and reliable measurements with low or no risk to miss a defect, especially since some areas of the pultrusion plank may be inspected by two (adjacently located) microwave probes at a time. Overlapping probing areas reduce the risk or even avoid any blind spots being not detected on the pultrusion plank.

[0012] In another aspect, the present disclosure is directed to an inspection method for inspecting a pultrusion plank for a wind turbine. The inspection method includes inspecting the pultrusion plank by an array device of at least two microwave probes including a first microwave probe and a second microwave probe. According to embodiments described herein, inspecting includes probing a first probing area defined by the first microwave probe with microwaves provided by the first microwave probe and probing a second probing area defined by the second microwave probe with microwaves provided by the second microwave probe, wherein an overlap area of the first probing area and the second probing area is probed by the first microwave probe and the second microwave probe. The inspection method further includes varying the frequencies and/or modes of the microwaves provided by at least one of the first microwave probe and the second microwave probe by a control unit during inspecting of the pultrusion plank and using multiple frequencies and modes for inspecting the pultrusion plank across the length and/or width of the pultrusion plank.

[0013] The inspection method according to embodiments described herein may offer a high sensitivity for the pultrusion plank inspection in that the sensitivity of detecting defects is high, especially compared to known systems. Typically, the high sensitivity for detecting defects may be sufficiently above a level of noise including disturbing signals (e.g. signals coming from the manufacturing environment without relation to any defects in the plank to be inspected) in embodiments described herein. Also, the inspection method as described in embodiment herein may yield a fairly uniform response. Typically, the uniform response may be obtained by selecting appropriate frequencies and modes for the respective microwave probes of the array of microwave probes according to embodiments described herein.

[0014] According to embodiments described herein, the inspection method uses microwave radiation for inspecting a pultrusion plank for a wind turbine blade, especially a wind turbine blade shell. According to some embodiments, microwave radiation may be reflected from the pultrusion plank (allowing using the reflected radiation for detection of defects), refracted from the surface of the pultrusion plank (allowing using the refracted radiation for detection of defects), and/or may interfere with the pultrusion plank to be inspected (allowing using the kind and quantity of interference for detection of defects). Typically, the inspection method according to embodiments described herein may mainly use reflection effects of the microwave radiation.

[0015] These and other features, aspects and advantages of the present invention will be further supported and described with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

[0017] FIG. 1 illustrates a perspective view of a wind turbine;

[0018] FIG. 2 illustrates a simplified, internal view of a nacelle of a wind turbine, particularly illustrating the nacelle during normal operation;

[0019] FIGs. 3 to 5 illustrate schematic top views of inspection systems and planks for a wind turbine blade according to embodiments described herein;

[0020] FIGs. 6 and 7 illustrate schematic side views of inspection systems and planks for a wind turbine blade according to embodiments described herein; and,

[0021] FIG. 8 illustrates a schematic flow chart of an inspection method for a wind turbine blade according to embodiments described herein.

DETAILED DESCRIPTION

[0022] Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. It is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0023] Referring now to the drawings, FIG. 1 illustrates a perspective view of a wind turbine 10 according to the present disclosure. As shown, the wind turbine 10 generally includes a tower 108 extending from a support surface 14 (herein also referred to as ground), a nacelle 16 mounted on the tower 108, and a rotor 18 coupled to the nacelle 16.

[0024] As shown in FIG. 1, the rotor 18 includes a rotatable rotor hub 20 and at least one rotor blade 22 coupled to and extending outwardly from the rotor hub 20. For example, in the illustrated embodiment, the rotor 18 includes three rotor blades 22. However, in an alternative embodiment, the rotor 18 may include more or less than three rotor blades 22. Each rotor blade 22 may be spaced about the rotor hub 20 to facilitate rotating the rotor 18 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the rotor hub 20 may be rotatably coupled to an electric generator 24 (FIG. 2) positioned within the nacelle 16 to permit electrical energy to be produced.

[0025] The wind turbine 10 may also include a wind turbine controller 26 centralized within the nacelle 16. However, in other embodiments, the controller 26 may be located within any other component of the wind turbine 10 or at a location outside the wind turbine 10. Further, the controller 26 may be communicatively coupled to any number of the components of the wind turbine 10 in order to control the components. As such, the controller 26 may include a computer or other suitable processing unit. In several embodiments, the controller 26 may include suitable computer-readable instructions that, when implemented, configure the controller 26 to perform various different functions, such as receiving, transmitting and/or executing wind turbine control signals.

[0026] Referring now to FIG. 2, a simplified, internal view of the nacelle 16 of the wind turbine 10 shown in FIG. 1, particularly illustrating the drivetrain components thereof, is illustrated. More specifically, as shown, the generator 24 may be coupled to the rotor 18 for producing electrical power from the rotational energy generated by the rotor 18. The rotor 18 may be coupled to the main shaft, which is rotatable via a main bearing (not shown). The main shaft may, in turn, be rotatably coupled to a gearbox output shaft of the generator 24 through a gearbox 30. As is generally understood, the main shaft provides a low speed, high torque input to the gearbox 30 in response to rotation of the rotor blades 22 and the rotor hub 20. The gearbox 30 converts the low speed, high torque input to a high speed, low torque output to drive the gearbox output shaft and, thus, the generator 24.

[0027] Each rotor blade 22 may also include a pitch adjustment mechanism configured to rotate each rotor blade 22 about its pitch axis 28 via a pitch bearing. Similarly, the wind turbine 10 may include one or more yaw drive mechanisms communicatively coupled to the controller 26, with each yaw drive mechanism(s) being configured to change the angle of the nacelle 16 relative to the wind (e.g., by engaging a yaw bearing of the wind turbine 10).

[0028] Typically, wind turbine blades are composed of several components, such as a shell including core elements and spar elements, reinforcing elements, resin, and the like. For obtaining a reliable result of the production of a wind turbine blade, in particular with a repeatable quality meeting the defined standards, the individual components of a wind turbine blades may be monitored before assembly according to some embodiments described herein. In particular, parts of the wind turbine blade, such as pultrusion planks for forming the wind turbine blade may be inspected before assembly. As will be appreciated, several planks are assembled to form stacks in horizontal and vertical direction to form the spar beam of a wind turbine blade, in particular a wind turbine blade shell.

[0029] The term “wind turbine blade shell” as used herein may be understood as the shell of a wind turbine blade. In particular, the shell of the wind turbine blade may be described as the outer covering of a wind turbine blade. According to some embodiments, the outer surface of shell of a wind turbine blade is exposed to wind and other environmental factors, such as the atmospheric/weather conditions. In some embodiments, the shell of the wind turbine blade may be described as a kind of skin of the wind turbine blade. Especially, the shell of the wind turbine blade may have an aerodynamical shape, such that the blade shell enables an efficient energy yield. In some embodiments, the shell of a wind turbine blade may be adapted for withstanding load/forces acting on the wind turbine blade. According to some embodiments, the shell of the wind turbine blade may surround other elements of the wind turbine blade, such as reinforcing elements, shaping elements, load carrying elements, and the like.

[0030] The term “plank” as used herein may be understood as a part of a wind turbine, specifically a part of a wind turbine blade, or even more specifically a part of a wind turbine blade shell. According to some embodiments, a plank as used herein may be a part of the wind turbine during production of the wind turbine and may, typically, form the wind turbine blade (especially the wind turbine blade shell) together with other parts. According to some embodiments, a plank may be a part of a material, such as an elongated part of a material, a shelf, a continuous material, or a board. In some embodiments, a pultrusion plank as referred to herein may be a plank which is produced by pultrusion. Typically, planks may be used to be stacked for forming the spar cap or main spar or other components of a wind turbine blade shell.

[0031] In some embodiments, the planks may include or may be made from carbon. For instance, the planks to be inspected may be carbon pultrusion planks containing a defined amount of carbon. In another embodiment, the planks to be inspected may be pultrusion planks containing or being made with glass fibers. According to some embodiments, the planks may be pulled along at a certain speed, especially through the manufacturing plant, e.g. from one manufacturing station to another manufacturing station. According to some embodiments described herein, the inspection of the planks may take place during motion of the planks. In particular, the inspection may be performed by an array of micro wave probes.

[0032] The term “inspection” or “inspecting” as used herein may be understood in that an object, which is inspected, or which is subjected to inspection is tested, screened, checked, or scanned. In particular, the object to be inspected may be checked or tested against defined standards during inspection, and especially for deviations from defined standards. A standard against which the inspected object is checked or tested may for instance be a production guideline, a reference value, a reference image, a reference pattern, a defined threshold of values, images, or patterns, a quality standard defining a minimum of quality, and the like. According to some embodiments described herein, the inspection or inspecting may be performed by an inspection system, typically a probe device or probing device, or the like.

[0033] Fig. 3 shows an inspection system 200 for inspecting a plank 300 used for a wind turbine blade. According to embodiments described herein, the inspection system 200 includes a first microwave probe 211 and a second microwave probe 212. Typically, the first microwave probe 211 and the second microwave probe 212 are arranged in an array device 210 or as an array device 210.

[0034] The term “microwave probe” as used herein may be understood as a probing device using microwave radiation for probing. Typically, the microwave probe may be adapted for probing objects, such as parts of a wind turbine, especially parts of a wind turbine blade, more especially the wind turbine blade shell, such as pultrusion planks, bondlines, or the like. A microwave probe may be attached to a source for microwaves. According to some embodiments, which may be combined with other embodiments described herein, a microwave probe as described herein may include one or more sensors, and/or detection devices, such as sensors and/or detection devices for sensing and detecting radiation, such as microwave radiation (especially reflected microwave radiation), but also sensors and/or detection devices for sensing and detecting position information of the object to be inspected, attribute information of the object to be inspected (such as material information, size information, information about the intended use of the object and the like). Typically, the microwave probes may be operating in near field mode. In some embodiments, the microwave probe may be waveguides (adapter), horn antennas, patch antennas or the like. A probe can act as both the transmitter and the receiver when inspection is done in the reflection mode. In the transmission mode, there would be two probes, one acting as the transmitter and the other as the receiver with the microwaves passing through the medium being inspected.

[0035] Typically, the microwave probe as described herein may be adapted to provide different frequencies and/or modes of microwaves for inspecting the plank. According to some embodiments, the different frequencies and/or modes of microwaves may be generated and altered during operation of the microwave probes. In some embodiments, the frequencies and/or modes of microwaves may be altered based on a command of a control unit being connected to the micro wave probes. According to some embodiments, the frequencies and/or modes of microwaves may be altered for inspecting a defined section of a plank with different frequencies and/or modes of microwaves. Typically, the frequencies and/or modes of microwaves may be altered within a time interval of about microseconds to milliseconds. It is typically difficult to get uniform sensitivity to defects in the probing area for a given mode shape. A combination of modes can enable detection of defects with approximately equal sensitivity within the probing area according to embodiments described herein.

[0036] According to some embodiments, a microwave probe as described herein may be adapted for operating at frequencies specifically between about 300 MHz to about 300GHz, and more specifically between about 1 GHz to about 100 GHz. According to some embodiments, which may be combined with other embodiments described herein, a microwave probe as described herein may be adapted for operating at wavelengths particularly between about 0,3 mm to about Im, and more particularly between about 1 mm to about 30 cm.

[0037] According to some embodiments described herein, an array device of at least two microwave probes (also denoted as array of microwaves probes herein) may be understood as an arrangement of two or more microwave probes. The array of microwave probes may be arranged in any arbitrary shape, such as a row, a line, a set, arranged in a quadrangular shape, a triangular shape, a round shape, a polygonal shape, arranged in an irregular manner or the like. According to some embodiments, the arrangement of an array of at least two microwave probes as referred to herein will depend on the width of the plank to be inspected and may specifically include between 2 and 20, more specifically between 2 and 10, and even more specifically between 3 and 10 microwave probes. In one embodiment, the number of microwave probes in an array is 4.

[0038] In particular, each of the microwave probes in the array of microwave probes may have a defined place for operation. In some embodiments, the microwave probes may be movable in that the microwave probes may be mounted in a different configuration, or in an array having a different shape during assembly or when operation is stopped or paused. According to some embodiments, the array itself may be movable for placing it (e.g. in a manufacturing plant) for operation. In some embodiments, the microwave probes in the array of microwave probes may individually be movable, as described in detail below. In other embodiments, the array of microwave probes may be a static array of micro wave probes. In particular, a static array of microwave probes is an array, whose elements do not move during operation

[0039] According to some embodiments, a microwave probe as described herein may define a respective probing area. The probing area as referred to in embodiments described herein may be understood as an area, which the microwave probe is able to probe or inspect. Specifically, each of the microwave probes in the array of microwave probes may be sensitive to the area substantially beneath it, e.g. the area of the plank beneath it. According to some embodiments, a probing area may be the area of an inspection range of a microwave probe, more specifically a probing area may be the area covered by the microwave radiation of the microwave probe projected on an object to be inspected.

[0040] Referring back to Fig. 3, the array 210 of microwave probes includes two microwave probes 211, 212 as an example. In particular, each of the microwave probes covers a probing area 301, 302. For instance, the first microwave probe 211 covers a first probing area 301 and the second microwave probe 212 covers a second probing area 302. Particularly, the probing area of a microwave probe may have an extension in the width direction 311 and the length direction 310 of the plank 300. According to some embodiments described herein, the probing areas of the microwave probes of the array of microwave probes cover the (particularly entire) width 304 of the plank.

[0041] Specifically, the width 304 of the plank may be measured in a width direction 311, running substantially perpendicular to the length direction 310 of the plank. In Fig. 3, the length of a plank may be measured in the moving direction 305, as can be seen in the coordinate system of Fig. 3. [0042] According to some embodiments described herein, the first probing area 301 and the second probing area 302 overlap with each other in the width direction 311. Additionally, or alternatively, the first probing area 301 and the second probing area 302 may overlap with each other in the length direction 310. Particularly, an overlap area 303 is covered by the probing areas of at least two microwave probes of the array of microwave probes. More particularly, two (particularly adjacently arranged) microwave probes of the array of microwave probes probe the overlap area 303. According to some embodiments, which may be combined with other embodiments described herein, the overlap area 303 may have a smaller extension in the width direction 311 than the probing area(s) of the microwave probes.

[0043] In particular, an overlap area may be used for ensuring a complete probing of the plank, especially probing of the whole width of the probe. With the array of microwaves according to embodiments described herein, the moving plank and the overlap area including overlapping parts of the probing areas, a reliable and secure probing of the plank can be realized. According to some embodiments, the overlap area allows a safe operation of the microwave probes and prevents defects to be overseen.

[0044] According to some embodiments, the overlap of the first probing area and the second probing area may be realized by an offset of the microwave probes in the array of microwave probes. Typically, the probing areas of the microwave probes may be offset to each other in the length direction 310. In some embodiments, the probing areas of the microwave probes may be offset to each other in the width direction 311. According to some embodiment, the probing areas of the microwave probes may be offset to each other in the width direction 311 and in the length direction 310.

[0045] Typically, the microwave probes of the array of microwave probes may be offset to each other in the length direction 310. In some embodiments, the microwave probes of the array of microwave probes may be offset to each other in the width direction 311. According to some embodiment, the microwave probes of the array of microwave probes may be offset to each other in the width direction 311 and in the length direction

310. Typically, a probing area or a microwave probe being offset to another probing area or another microwave probe, respectively, may be understood in that the location of the probing area or the microwave probe is shifted in one or more direction(s) with respect to the other probing area or the other microwave probe (such as shifted in length direction 310, in width direction

311, or both). In some embodiments, the offset may be calculated from the midpoint of a microwave probe.

[0046] According to some embodiments described herein, the array 210 of microwave probes 211, 212 may be adapted for inspecting a pultrusion plank 300 having a width 304 of particularly between about 50 mm and about 200 mm, more particularly between about 70 mm and about 150 mm, and more particularly between about 80 mm and about 120 mm. In one example, the inspection system may be adapted to a width of the pultrusion plank of typically about 100 mm. In some embodiments, the inspection system may be adapted for a pultrusion plank having a thickness of between about 1 mm and about 20 mm, specifically between about 2 mm and about 15 mm, and more specifically between about 3 mm and about 10 mm. In one example, the inspection system as described herein may be adapted to a thickness of the pultrusion plank of typically about 5 mm. For instance, the number of microwave probes, the offset of the microwave probes with respect to each other, the size of the overlap area, the size of the single microwave probes, the kind of the microwave probes, and the like may be adapted to the width of the pultrusion plank.

[0047] According to some embodiments, which may be combined with other embodiments described herein, the array of microwave probes may be adapted for inspecting a pultrusion plank 300 including a material being electrically conductive or partly electrically conductive. In particular, the microwave probes may be adapted for inspecting surface and near-surface defects in a pultrusion plank, including carbon, using reflected radiation. In the case of glass fiber pultrusion planks, part of the incident microwave power will get reflected from air-glass and glass-air interfaces. Part of the microwaves will penetrate through the glass since glass is not electrically conducting and is a low loss material for microwaves to pass through. In this case both reflection mode as well as transmission mode will give information about defects in the region of the plank being inspected. According to some embodiments, the detection device(s) may be adapted to using one or both modes, namely the reflection mode and the transmission mode (e.g. by adapting the position of the detection devices, and/or the sensitivity of the detection devices).

[0048] According to some embodiments described herein, a control unit 400 is provided in the inspection system 200. In particular, the control unit 400 is able to control the first microwave probe 211 and the second microwave probe 212 of the array 210 of microwave probes. In some embodiments, which may be combined with other embodiments described herein, the first microwave probe 211 and the second microwave probe 212 may separately be connected to the control unit 400, as exemplarily shown in Fig. 3. Specifically, the control unit 400 is adapted to vary the frequencies and/or modes of the microwaves generated by the first microwave probe 211 and/or the second microwave probe 212 during inspection of the plank. For instance, during inspection of a probing area, the frequency of the microwave radiation sent out by the microwave probe may be varied. According to some embodiments, which may be combined with other embodiments described herein, the mode of the microwave radiation sent out by the microwave probe may be varied during inspection of a probing area. In that way, one probing area may be inspected with different frequencies and/or modes, and, typically, the risk of missing a defect, is still reduced. Typically, different defects (such as defect having a different size, a different position of the defect, a different kind of defect, a different material, and the like) may be seen and identified by the inspection system, when different frequencies and/or modes are applied.

[0049] According to some embodiments, which may be combined with other embodiments described herein, the sensitivity of a microwave probe for a defect can be varying along the dimension of the microwave probe for a given mode distribution. The respective sensitivity (sufficiently above the noise level) and fairly uniform response may be obtained by selecting and combining appropriate frequencies and modes according to some embodiments.

[0050] Especially, noise as used herein refers to variations in the signal coming from various sources like inherent inhomogeneities in the material (given that it is a composite material and not, e.g. a homogenous material), surface undulations and the like. According to some embodiments described herein, the part is inspected for a defect. Especially, the defect has to be larger than any inherent non-uniformities in the sample (noise sources mentioned above), so that the signal from the defect is significantly larger than the noise level. In some embodiments, a fairly uniform response may be a substantially uniform response where the field strength is substantially uniform across the entire inspection area. A particular mode has a distribution of electric field along the dimension of the probe, in one example case, it can have a maximum field strength at the middle and minimum on either end. In this case, if a defect is towards either end, it may not get picked up well due to the low field strength at the ends. However, embodiments described herein can interrogate with a different mode (at a different frequency) which provides higher field strength and therefore better detectability of defects in those regions.

[0051] In some embodiments, the array of microwave probes 210 (as a whole) may be connected to the control unit 400. For instance, the control unit 400 may be connected to a center data point (such as a data exchange point) of the array of microwave probes. According to some embodiments, the control unit 400 may deliver data and control signals to the array of microwave probes. In particular, in the case that the control unit 400 is connected to the array of microwave probes by a central connection, the array of microwave probes may include several data lines communicating the signals from the control unit via the center data point to the single microwave probes of the array of microwave probes.

[0052] Fig. 4 shows an embodiment of an inspection system having an array of microwave probes including four microwave probes 211, 212, 213, and 214. Each of the microwave probes 211, 212, 213, and 214 is connected to the control unit 400 in the example of Fig. 4. As can be seen in Fig. 4, each of the microwave probes of the array of microwave probes are offset to each other. In the example of Fig. 4, the microwave probes are offset to each other in the length direction 310 as well as the width direction 311. Typically, each of the microwave probes of the array of microwave probes provides a respective probing area. Especially, two adjacently located microwave probes of the array of microwave probes have an overlapping probing area and form an overlap area, respectively. In the example of Fig. 4, three overlap areas are formed by the four microwave probes 211, 212, 213, and 214.

[0053] In Fig. 5, the array of microwave probes is connected to other elements of the inspection system according to some embodiments described herein. Typically, the array or array device 210 of microwave probes may be connected to the control unit 400 as well as further elements 420, 430, which may be for instance a data processing element, an image processing element, a signal-producing element, a clock element, a data storing element, a network analyzer, a multiplexer, further control elements for dynamically positioning the microwave probes (being e.g. additionally connected to the production line of the wind turbine blade), and the like.

[0054] In some embodiments, which may be combined with other embodiments, another set of microwave probes, or another array of microwave probes may be mounted on the back side of the plank for inspection of the back side of the plank. Typically, the set or array of microwave probes arranged on the back side of the plank may be denoted as backside array of microwave probes or bottom array of microwave probes (especially compared to the array of microwave probes, which may be denoted as frontside array of microwave probes or top array of microwave probes in this context). According to some embodiments, the backside array of microwave probes may be similar to, or even the same as the array of microwave probes at the frontside of the pultrusion plank. The backside array of microwave probes being similar to the array of microwave probes may refer to the number of the microwave probes, the arrangement of the microwave probes in the array, the location of the microwave probes, the location of the array of the microwave probes, the kind of microwave probes used, and the like. In the case of glass fiber pultrusions, for through transmission mode, the frontside array of microwave probes can be used as transmitters and the backside array can be used as receivers. The front side and back side array can be used in reflection mode as well.

[0055] According to some embodiments, which may be combined with other embodiments described herein, the top and bottom array of microwave probes may be multiplexed, to collect data across the width of the pultrusion plank simultaneously. For instance, the array 210 of microwave probes shown in Fig. 5 may be connected to a multiplexer 420. Typically, the multiplexer 420 may be used for selecting between several input signals and for forwarding the selected input to a single output line. According to some embodiments, one sided inspection may suffice for materials used for wind turbine planks, or materials that are substantially transparent (or almost transparent) to microwaves.

[0056] According to some embodiments, the inspection system as shown in Fig. 5 may further include a network analyzer 430 or equivalent electronics. Typically, the network analyzer 430 may be an instrument that measures network parameters of the electrical network. Although Fig. 5 exemplarily shows the multiplexer 420 and the network analyzer 430 connected in series, the further elements for data transfer of the inspection system may also be differently arranged, e.g. in a parallel arrangement, side- by-side, each one separately connected to the control unit, each one separately connected to the array of microwave probes, or in any useful configuration and arrangement with respect to each other.

[0057] The term “substantially” as used herein may be understood in that there may be a deviation from the attribute denoted with “substantially.” For instance, the term “substantially perpendicular” may include a deviation up to 15° from the perpendicular direction, more particularly up to 10° from the perpendicular direction, and even more particularly up to 5° from the perpendicular direction.

[0058] Fig. 6 shows an embodiment of an inspection system including two rollers 501, 502 according to embodiments described herein. In some embodiments, the inspection system may include more than two rollers, especially more than one pair of rollers on top and bottom of the plank. For instance, rollers of the inspection system may be foreseen in regular or irregular distances, per length unit, or in a fixed number, or the like. In particular, a moving device 500 for the plank to be inspected may be part of the manufacturing plant, in which the inspection system is used. In particular, the moving device 500 is adapted for conveying the plank 300 past the array 210 of microwave probes 211, 212. For instance, the moving device may include a conveyor, a conveyor belt, one or more rollers, one or more motors, especially for driving the conveying mechanism, and the like.

[0059] Especially, as the planks are pulled along, there can be vibrations to the plank which can cause changes in the probing signal. Changes in the probing signal may lead to an unreliable result in the defect detection of the probing. According to some embodiments, changes in the signal due to vibrations can be avoided by locally conveying the planks between the rollers of the inspection system. According to some embodiments, the inspection system may include a spring-loaded roller mechanism, or another mechanism providing a defined load to the rollers, typically to keep the lift-off of the pultrusion plank reasonably flat, or to keep a substantially constant lift-off of the probes with respect to the sample. In some embodiments, the inspection system having rollers is described as including a constant-standoff mechanism for maintaining a substantial constant distance between the microwave probes and the plank. Keeping the lift-off of the pultrusion plank flat, or maintaining a substantial constant distance between the microwave probes and the sample may lead to a reliable probing and reliable probing results, which may be used for a secure error detection according to some embodiments.

[0060] In some embodiments, the term “substantially constant distance” may include a constant distance over a defined length, or between two elements, and may typically include a deviation up to about 15% of the distance, more typically up to about 10% of the distance, and even more typically up to about 5% of the distance.

[0061] According to some embodiments, which may be combined with other embodiments described herein, the microwave probes may be coupled to the rollers 501, 502 for maintaining the substantial constant distance between the microwave probes and the plank.

[0062] Fig. 7 shows an embodiment of an inspection system. A pultrusion plank 300 is shown, which is supported by rollers 501, 502, as explained in detail above. Fig. 7 exemplarily shows two microwave probes 211 and 215. Additional microwave probes may be placed behind the microwave probes 211, 215 without being visible in the schematic side view of Fig. 7. In the embodiment of Fig. 7, one of the microwave probes (i.e. microwave probe 211) is arranged at a top side of the pultrusion plank 300, the other one of the microwave probes (i.e. microwave probe 215) is arranged at a bottom side of the pultrusion plank 300. The microwave probes 211 and 215 of the embodiment of Fig. 7 are coupled to the rollers 501 and 502. Especially, microwave probe 211 is coupled to one roller 501 (e.g. via a coupling device 701). Further, microwave probe 215 may be coupled to one roller 502 (e.g. via a coupling device 702).

[0063] According to some embodiments, the microwave probes of the array of microwave probes may be attached to the roller devices by coupling devices. The coupling devices as described herein may allow to compensate the effects of vibrations of the plank on the measurement by moving the microwave probes along with the vibrational motion of the plank that means that the probe substantially mimics the vibration of the plank. Specifically, the microwave probes may be mounted so as to be movable, preferably individually movable. In some embodiments, the microwave probes may be movable in a direction substantially perpendicular to the plank surface, e.g. for moving together with a movement of the plank in the direction substantially perpendicular to the plank surface. The direction substantially perpendicular to the plank surface may also be described as a direction substantially perpendicular to the moving directions 305 of the plank 300.

[0064] In some embodiments, the coupling devices as described herein may be some kind of rod or bar, which may be rigidly mounted to a roller device as well as to a microwave probe. In particular, the coupling device is designed so as to be able to transmit the movements from the roller device to the microwave probe. According to some embodiments, the rollers being physically coupled to the microwave probes may be denoted as a constantstandoff mechanism in some embodiments. According to some embodiments, the microwave probes being coupled or linked to a roller device may be placed near to the coupled roller device. The microwave probe being near to the roller device, to which it is coupled, ensures an immediate compensation of vibrations and a reliable measurement result due to immediate correction of the distance between plank and microwave probe.

[0065] In some embodiments, which may be combined with other embodiments described herein the constant-standoff mechanism may measure vibrations of the pultrusion plank, e.g. by a sensor, and may transmit the measuring results to the microwave probes via data lines, or to a center data point of the array of microwave probes. The array of microwave probes, or the single microwave probes may consider the measured vibrations of the pultrusion plank. In some embodiments, the microwave probes may move along with the vibrations of the pultrusion plank. According to some embodiments, which may be combined with other embodiments described herein, the vibration measurement may be considered when processing the probing results. In some embodiments, the measured vibrations of the pultrusion plank may be added to the probing results obtained by the microwave probes. For instance, the control unit may calculate the deviation of the probing results due to vibrations of the pultrusion plank and may correct the probing results accordingly.

[0066] According to some embodiments, which may be combined with other embodiments described herein, the inspection system 200 may be adapted to be coupled to a pultrusion plank production system. The inspection system may be used for an in-process inspection of the pultrusion plank 300 in some embodiments. Typically, the in-process inspection may for instance mean that the inspection system may be placed between two production stations or manufacturing stations at the manufacturing plant of a wind turbine blade. According to some embodiments, the inspection system as described herein may be movable for having flexibility of placing the inspection system within a manufacturing plant of a wind turbine blade. Typically, the inspection system, or at least the array of microwave probes may be coupled to the production system of the wind turbine blade in the manufacturing plant, e.g. by being connected to the plant network or the like.

[0067] Fig. 8 shows a schematic flow chart of an inspection method 600 for inspecting a pultrusion plank 300 for a wind turbine 10. According to embodiments described herein, the inspection method 600 includes in block 601 inspecting the plank 300 by an array 210 of microwave probes 211, 212. Particularly, the array of microwave probes used in the inspection method 600 may be an array of microwave probes as described in detail above. According to some embodiments, the inspection method 600 may be performed with an inspection system according to embodiments described herein.

[0068] In block 602, the inspecting of the pultrusion plank includes probing a first probing area 301 defined by the first microwave probe 211 with microwaves provided by a first microwave probe 211 and a second probing area 302 defined by the second microwave probe 212 with microwaves provided by a second microwave probe 212. According to some embodiments, a probing area may be described as being the area on the object to the inspected (such as the pultrusion plank), which is substantially beneath the microwave probe. Especially, the probing area may be an area, in which the radiation of the microwave probe hits the pultrusion plank.

[0069] The first probing area 301 and the second probing area 302 have an overlap, which is denoted as an overlap area 303. In particular, the overlap area 303 may be probed by two adjacently arranged microwave probes, such as by the first microwave probe 211 and the second microwave probe 212, especially at the same time. In some embodiments, the overlap area is enabled by a respectively chosen offset of adjacently arranged microwave probes in the array of microwave probes. According to some embodiments described herein, the overlap area may lead to a reliable inspection of the (especially full) width of the pultrusion plank. Especially, the overlap area may avoid a defect to be missed, e.g. if the plank is not sufficiently covered by probing areas, or if edges and gaps appear between two probing areas of adjacently arranged microwave probes.

[0070] In block 603, the inspection method 600 further includes varying the frequencies and/or modes of the microwaves provided by at least one of the first microwave probe 211 and the second microwave probe 212 during inspecting of the plank. According to some embodiments, a mode of a microwave may be described by a modal frequency and a mode shape, which may vary. For instance, a control unit 400 may be used for varying the frequencies and/or modes of the microwave probes appropriately and suitably for the respective inspection task. With varying frequencies and/or modes of the microwave probes, multiple frequencies and modes can be used for inspecting the pultrusion plank. According to some embodiments, the variation of the frequencies and/or modes of the microwave probes during inspection may yield a secure, exact, and reliable result of the probing.

[0071] According to some embodiments, which may be combined with other embodiments described herein, the inspection method may include using the results of the inspection with varying frequencies and/or modes of each of the microwave probes for separating the noise of the measurement from the signal. In some embodiments, the control unit may be provided with the probing results from the microwave probes and may separate the noise from the signal, especially by calculations based on the probing results obtained with different frequencies and/or modes. As explained above, a defect that is in the noise level (not detected) when using one mode could get picked up when using another mode. Looking at the response from different modes will help in defect detection according to embodiments described herein.

[0072] According to some embodiments described herein, the variation of the frequencies and/or modes of the microwave probes may be performed by the control unit, especially based on defined parameters. In some embodiments, the parameters may for instance be the defect to be found (especially surface defects, or near surface defects, visual and non-visual defects, and the like), the reduction of false calls (i.e. the erroneous detection of a defect), finding the best signal-to-noise ratio, and the like. According to embodiments described herein, the control unit may be equipped with respective computer programs to determine the operational parameter of the microwave probes with varying frequencies and/or modes.

[0073] According to some embodiments, which may be combined with other embodiments described herein, the inspection method may include moving the pultrusion plank 300 past the array 210 of microwave probes 211, 212. For instance, the array of microwave may be placed in a manufacturing plant for wind turbine blades and may especially be integrated into the production line. Typically, the inspection system may be statically placed for operation at a location, where the pultrusion plank passes (anyway) during the production process of the wind turbine blade.

[0074] In some embodiments, the inspection system may include one or more rollers (such as rollers 501, 502 exemplarily shown in Fig. 6). According to some embodiments, the inspection method may include coupling the one or more rollers to the microwave probes, or the array of microwave probes. For instance, coupling the one or more rollers to the microwave probes (or the array of microwave probes) may include a physical coupling (such as by a coupling device, as described with respect to Fig. 7 in detail above), and/or measuring the vibrations of the pultrusion plank and transmitting the measurement to the microwave probe or the array of microwave probes. In this way, the microwave probes, the array of microwave probes, or the control unit may be able to reduce spacing variations due to the vibrations of the pultrusion plank, especially balancing the spacing variations (e.g. by a respective movement of the probes). In some embodiments, the measurement may be used to calculate a correction of the probing results, e.g. by the control unit.

[0075] The inspection system and the inspection method according to embodiments described herein allows for a better, faster, and more robust inspection system and inspection method that may reduce costs and improve detectability of defects at the same time. Defects as described herein may for instance be fiber misalignment, foreign object, cracks, wrinkles and the like. The inspection method and the inspection system as described in embodiments herein is typically contactless, so that there is no liquid coupling or the like used compared to known techniques, which makes the inspection system and inspection method according to embodiments described herein even more robust and reliable. [0076] Exemplary embodiments of an inspection system and an inspection method are described above in detail. The systems and methods are not limited to the specific embodiments described herein, but rather, elements of the systems and/or steps of the methods may be utilized independently and separately from other elements and/or steps described herein.

[0077] Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.

[0078] Embodiments of the present invention have been described above with reference to block diagrams and flowchart illustrations of system and methods. It will be understood that each block of the block diagrams and flowchart illustrations, and combinations of blocks in the block diagrams and flowchart illustrations, respectively, can be implemented by various means including computer program instructions. These computer program instructions may be loaded onto a general-purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions which execute on the computer or other programmable data processing apparatus create a means for implementing the functions specified in the flowchart block or blocks.

[0079] These computer program instructions may also be stored in a non- transitory computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including computer-readable instructions for implementing the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer- implemented process such that the instructions that execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks.

[0080] Accordingly, blocks of the block diagrams and flowchart illustrations support combinations of means for performing the specified functions, combinations of steps for performing the specified functions and program instruction means for performing the specified functions. It will also be understood that each block of the block diagrams and flowchart illustrations, and combinations of blocks in the block diagrams and flowchart illustrations, can be implemented by special purpose hardware-based computer systems that perform the specified functions or steps, or combinations of special purpose hardware and computer instructions.

[0081] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; the number or type of embodiments described in the specification.

[0082] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. While various specific embodiments have been disclosed in the foregoing, those skilled in the art will recognize that the spirit and scope of the claims allows for equally effective modifications. Especially, mutually non-exclusive features of the embodiments described above may be combined with each other. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art.

List of reference signs

10 wind turbine

14 support surface

16 nacelle

18 rotor

20 rotor hub

22 rotor blade

24 electrical generator

26 controller of wind turbine

28 pitch axis

30 gearbox

200 inspection system

210 array of microwave probes

211-214 microwave probes

300 plank

301 first probing area

302 second probing area

303 overlap area

304 width of plank

305 moving direction of plank

310 length direction

311 width direction

400 control unit

420;430 further elements of inspection system

500 moving device

501, 502 rollers

600 method 601-603 blocks

701, 702 coupling devices

Claims

CLAIMS:

1. An inspection system (200) for inspecting a pultrusion plank (300) for a wind turbine (10), the inspection system (200) comprising: an array device (210) of at least two microwave probes (211; 212), wherein the array (210) of at least two microwave probes includes a first microwave probe (211) and a second micro wave probe (212), wherein the first microwave probe (211) and the second microwave probe (212) are offset from each other; wherein the first microwave probe (211) defines a first probing area

(301), and the second microwave probe (212) defines a second probing area

(302), and wherein the offset (213) between the first microwave probe (211) and the second microwave probe (212) is chosen to form an overlap area (303) between the first probing area (301) and the second probing area (302); and, wherein the first microwave probe (211) and the second microwave probe (212) are adapted to provide different frequencies and/or modes of microwaves for inspecting the plank (300); the inspection system further comprising: a control unit (400) for controlling the first micro wave probe (211) and the second microwave probe (212) of the array device (210) of the at least two microwave probes, wherein the control unit (400) is adapted to vary the frequencies and/or modes of the microwaves generated by at least one of the first microwave probe (211) and the second microwave probe (212) during inspection of the plank (300).

2. The inspection system of claim 1, wherein the inspection system comprises a constant-standoff mechanism for maintaining a substantial constant distance between the microwave probes (211; 212) and the pultrusion plank (300).

3. The inspection system according to claim 1 or 2, wherein the inspection system comprises one or more rollers (501; 502) and wherein the first and second microwave probes (211; 212) are coupled to the one or more rollers (501; 502) for maintaining a substantial constant distance between the microwave probes (211; 212) and the pultrusion plank (300).

4. The inspection system according to any of the preceding claims, wherein the first and second microwave probes (211; 212) are individually movable dynamically, particularly in a direction substantially perpendicular to the surface of the pultrusion plank (300) to be inspected.

5. The inspection system according to any of the preceding claims, wherein the inspection system (200) is adapted to be coupled to a pultrusion plank production system for an in-process inspection of the pultrusion planks (300).

6. The inspection system according to any of the preceding claims, wherein the inspection system (200) is adapted for the inspection of a pultrusion plank (300) for a wind turbine blade (22).

7. The inspection system according to any of the preceding claims, wherein the first microwave probe (211) and the second microwave probe (212) are offset to each other in the width direction (311) of the pultrusion plank (300) to be inspected, or wherein the first micro wave probe (211) and the second microwave probe (212) are offset to each other in the width direction (311) of the pultrusion plank (300) and in the length direction (310) of the plank (300) to be inspected.

8. The inspection system according to any of the preceding claims, wherein the first microwave probe (211) and the second microwave probe (212) are adapted for generating microwaves having a frequency of 300 MHz to 300GHz, in particular of 1 GHz to 100GHz, and a wavelength of Im to 0,3 mm, in particular 30 cm to

1 mm.

9. An inspection method (600) for inspecting a pultrusion plank (300) for a wind turbine (10), the inspection method (600) comprising: inspecting (601) the pultrusion plank (300) by an array device (210) of at least two microwave probes (211; 212) comprising a first microwave probe (211) and a second microwave probe (212), wherein inspecting comprises: probing (602) a first probing area (301) defined by the first microwave probe (211) with microwaves provided by the first microwave probe (211) and probing (602) a second probing area (302) defined by the second microwave probe (212) with microwaves provided by the second microwave probe (212); wherein an overlap area (303) of the first probing area (301) and the second probing area (302) is probed by the first microwave probe (211) and the second microwave probe (212); the inspection method (600) further comprising: varying (603) the frequencies and/or modes of the microwaves provided by at least one of the first microwave probe (211) and the second micro wave probe (212) by a control unit (400) during inspecting of the pultrusion plank (300) and using multiple frequencies and modes for inspecting the pultrusion plank across the length and/or width of the pultrusion plank (300).

10. The inspection method according to claim 9, wherein the inspection method further comprises maintaining a substantial constant distance between at least one of the first and second microwave probes (211; 212) and the pultrusion plank (300) by a constant- standoff mechanism.

11. The inspection method according to any of claims 9 to 10, wherein the inspection system further comprises one or more rollers (501; 502) and wherein the method further comprises: coupling at least one of the first and second microwave probes (211; 212) to the one or more rollers (501; 502) for maintaining a substantially constant distance between at least one of the first and second microwave probes (211; 212) and the pultrusion plank (300).

12. The inspection method according to any of claims 9 to 11, further comprising using the results of the inspection with varying frequencies and/or modes of the first and/or second microwave probes (211; 212) for separating noise from signal.

13. The inspection method according to any of claims 9 to 12, further comprising coupling the array device (210) of microwave probes (211; 212) to a production system producing the plank (300) for the wind turbine (10).

14. The inspection method according to any of claims 9 to 13, wherein the inspected pultrusion plank (300) is a pultrusion plank for a wind turbine blade (22).

15. The inspection method according to any of claims 9 to 14, further comprising measuring vibrations of the pultrusion plank (300) and adding the information about the vibrations of the pultrusion plank (300) to results obtained by the first and/or second microwave probes (211; 212).