The present disclosure is related to a cleaning apparatus. More specifically, the disclosure is related to an apparatus for removing particles from a rotor blade, such as a rotor blade of a wind turbine. The particles may, for example, be contaminants in the form of dead insects, air pollution, and ice particles during the winter season.

In this document, the rotor blade to be cleaned is discussed in relation to rotor blades of a wind turbine, which is configured to convert wind power (kinetic energy) into rotational energy, which in turn drives a generator of electricity. However, it should be noted that the term wind turbine may also be a windmill provided with rotor blades having a cross section formed as an aerofoil. A windmill is configured to convert wind power into mechanical energy.

As a result of an increasing demand for alternative ways to produce electric energy from renewable sources (instead of fossil fuels), the number of wind turbines is increasing rapidly around the world.

Studies show that contaminants, for example dead insects sticking to the surface of the rotor blades of a wind turbine, may reduce the efficiency of the wind turbine considerably. Some studies indicate that contaminated rotor blades may reduce the efficiency of a wind turbine up to 5 - 10 %. Further, ice particles sticking to the rotor blades may dislodge during operation and be thrown at great speed from the rotor blades and thus become dangerous to the surroundings.

In an attempt to remedy the above challenges, an industry providing cleaning services for

P30295PC00 wind turbines has therefore emerged. One of the most common ways of cleaning rotor blades of a wind turbine is by means of a helicopter. In this context, the helicopter is provided with a tank carrying a cleaning liquid and a water jetting device for cleaning away foreign matters, such as insects or ice, sticking to the surface of the rotor blades. The jet water is normally heated and comprises cleaning chemicals. Use of a helicopter represents a significant risk, especially in so called wind parks comprising a plurality of wind turbines spaced apart rather narrowly. Besides having to navigate the helicopter close to and between the wind turbines, the helicopter must also return repeatedly to the ground to refill cleaning liquid. A further disadvantage of using a helicopter is related to its operative costs, which roughly amounts € 1700/hour in 2022, thereby resulting in a total cost of roughly € 25.000 for cleaning a wind turbine. A still further disadvantage of using a helicopter is related to the spill of cleaning liquid, which may comprise harmful chemicals. Substantially all cleaning liquids will fall to the base level, i.e., to the ground for a land- based wind turbine, or into the sea for an offshore wind turbine.

An alternative to using a helicopter is to use a mobile crane capable of bringing personnel up to the rotor blades in order to manually clean the rotor blades, for example by using a water jetting apparatus to do so. Although normally being less costly than using a helicopter, the use of a mobile crane requires access to the base of the wind turbine. For an offshore wind park, however, use of a mobile crane requires an acceptable weather window and a calm sea. This is often not the case and may therefore represent a challenge to the planning of a cleaning operation.

Still another method of cleaning the rotor blades of a wind turbine is the so-called rope access technique. This technique requires specially trained and certified personnel to descend, ascend, and traverse along various ropes to access and clean the perimeter of the rotor blades whilst being suspended from a harness. Although being far less risky than using a helicopter, this rope access technique is very time consuming.

Publication DE 32 26 629 Cl discloses an apparatus for cleaning the leading edges of an aerofoil of an aircraft. The apparatus includes a cleaning carriage arranged near the leading edge of the aerofoil. Guide rollers are arranged on the cleaning carriage near the top

P30295PC00 and bottom of the leading edge of the aerofoil. An endless cleaning element is passed over the guide rollers and rests on the leading edge. The guide rollers are secured to a bow-shaped frame surrounding the leading edge. A drive for the cleaning element is also provided, as well as a further drive provided for at least one of the guide rollers.

Publication US 10,640,236 discloses a cleaning assembly for cleaning the leading edges of aerofoils, in particular for aerofoil profiles on aircrafts or spacecrafts. The cleaning assembly comprises a cleaning device provided with at least one cleaning member. In operation, the cleaning device applies mechanical pressure to a planar region of an aerofoil and includes a drive having at least one drive element. The drive moves the cleaning device along the surface to be cleaned. The at least one cleaning member connects the cleaning device adhesively to the aerofoil. The at least one cleaning member may also have a sticky surface.

Publication KR 101246567 B discloses a device for cleaning a surface of a rotor blade of a wind turbine. The device comprises rotary brushes configured to move up and down along support members extending downwardly at each side of the rotor blade from a main body abutting against a leading edge of the rotor blade. The device further comprises a rotary brush configured to clean the leading edge of the rotor blade.

There is a need in the industry for an apparatus and a method capable of cleaning a perimeter of a rotor blade from a leading edge to a trailing edge thereof, i.e., between the suction surface and the pressure surface of the rotor blade, respectively. There is a further need in the industry for an apparatus capable of controlling the cleaning operation from a base level substantially without any risk to the personnel involved, wherein the rotor blade is thoroughly cleaned in a relatively short period of time, and wherein the environmental impact from the cleaning operation is non-existent or at least reduced.

The object of the invention is to remedy or to reduce at least one of the drawbacks of the prior art, or at least to provide a useful alternative to the prior art.

The object is achieved through features specified in the description below and in the subsequent claims.

P30295PC00 The invention solves the challenges of the prior art discussed above by using an apparatus that is deployed onto a rotor blade of a wind turbine, wherein the apparatus comprises a cleaning device that is moved in sliding contact with a perimeter portion of the rotor blade during operation.

The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

In a first aspect of the invention, there is provided an apparatus for removing particles from a rotor blade of a wind turbine. The apparatus comprises:

- a particle removing device configured for moving, during operation, in sliding contact with a perimeter portion of the rotor blade;

- a pressing means configured for urging, during operation, the particle removing device into contact with the perimeter portion of the rotor blade; and

- a driving device configured for effecting, during operation, sliding movement of the particle removing device relative to the perimeter portion of the rotor blade.

When in operation, the pressing means urges the particle removing device into contact with the rotor blade while moving the particle removing device in sliding contact with the perimeter portion of the rotor blade. By so doing, any particles sticking to the perimeter portion of the rotor blade are engaged by the particle removing device.

The particle removing device is elongated and has a length that exceeds (during operation of the apparatus) the largest perimeter portion of the rotor blade enclosed by the elongated particle removing device. Thus, the elongated particle removing device may extend below a portion of the rotor blade irrespective of the apparatus being at a tip or at the largest cross section of the rotor blade (close to the root of the rotor blade).

In one embodiment, the particle removing device may have a first end and a second end.

In an alternative embodiment, the particle removing device may be endless.

In a basic configuration of the apparatus, the particle removing device may have a length sufficient to allow (during operation of the apparatus) each of the ends of the particle

P30295PC00 removing device, or a portion of the endless particle removing device, to extend down towards the base supporting the wind turbine. Alternatively, each end of the particle removing device may be operatively connected to, for example, a rope or a line extending towards said base.

In such a basic configuration, and irrespective of being provided with a first end and a second end, or being endless, the pressing means and the driving device (for moving the particle removing device) may constitute the particle removing device or, alternatively, said rope or line when subjected to a tension force from, for example, operating personnel or a tension device located at the base. For a particle removing device provided with a first and a second end, and also for an endless particle removing device, reciprocating movement thereof may be provided. For an endless particle removing device, reciprocating or unidirectional movement of the particle removing device may be provided. For both embodiments, movement of the particle removing device along the longitudinal axis of the rotor blade may be provided by, for example, the operating personnel or said tension device.

The basic configuration of the apparatus according to the invention discussed above may be suitable for removing particles from rotor blades of wind turbines having an easily accessible base. An easily accessible base is typically a base or ground having an even elevation from which the apparatus can be operated for example by operators.

However, a nacelle of a wind turbine may typically be arranged 30-200 meters above the base supporting the wind turbine. The wind turbine base may be a ground surface for an onshore installation, or the base may be a water surface for a floating or bottom-fixed offshore installation. At least a portion of the ground beneath the operating area of the wind turbine may at some locations be rough or even impossible for personnel to access.

In what follows, embodiments of the apparatus according to the invention being i.a. operated substantially independent from the type of base or ground carrying the wind turbine, are disclosed.

When the particle removing device is in sliding contact with the surface of the rotor

P30295PC00 blade, particles on the surface may be removed. However, to enhance the cleaning effect, use of a liquid cleaning agent is preferred instead of a "dry" cleaning agent.

In one embodiment of the invention, the apparatus is provided with a device configured for adding a cleaning agent to the particle removing device.

The device for adding the cleaning agent may comprise at least one nozzle directed towards the particle removing device. Thus, the cleaning agent may be added directly to a portion of the particle removing device. Adding the cleaning agent directly to the particle removing device may reduce spill of the cleaning agent, which is important to reduce any negative impacts of the cleaning agent on the surrounding environment. . In one embodiment, the cleaning agent is supplied to the particle removing device using at least one nozzle in fluid communication with a source of the cleaning agent. In one embodiment, the source of the cleaning agent may be arranged at a base. The cleaning agent may, for example, be water or a chemical agent with or without water. The chemical agent may, for example, be a detergent, a degreaser, or similar. Preferably, the chemical agent is biodegradable.

In one embodiment, the apparatus further comprises a container configured for holding the cleaning agent. Thus, the source of the cleaning fluid may be the container.

In one embodiment, the container is arranged (during operation of the apparatus) underneath the rotor blade. Arranging the container underneath the rotor blade lowers the center of gravity of the apparatus. Thus, in operation, the apparatus may be more stable (with respect to the rotor blade) than in an embodiment wherein the container is secured to, for example, a top portion of the apparatus.

Preferably, the particle removing device is made from an absorbent material. In one embodiment, the particle removing device comprises microfibers secured to a core having suitable tensile strength and being chemically resistant to the chemical agent. For example, the core may be made from, but not limited to, polyamide.

As an addition or alternative to using at least one nozzle to supply the cleaning agent during operation, the particle removing device may be configured for passing within a por-

P30295PC00 tion of the container holding the cleaning agent. By so doing, the particle removing device may be soaked with cleaning agent while being submerged in the cleaning agent during its passage within the container.

In one embodiment, at least some of the container weight is carried by the particle removing device.

In an embodiment of the apparatus wherein the particle removing device has a first end and a second end, each of the ends may be secured to a first spooling device and a second spooling device, respectively.

In one embodiment, the first spooling device is operatively connected to a motor configured for rotating the spooling device and thus to wind a portion of the particle removing device onto the spooling device. The second spooling device is provided with a spring device configured for rotating the spooling device and thus to wind a portion of the particle removing device onto the spooling device when the motor of first spooling device is inactive. In such an embodiment, the spring device is tensioned by the motor of the first spooling device.

In another embodiment, each of the first spooling device and the second spooling device is provided with a motor. The motors are controlled so as to alternatingly wind a portion of the particle removing device onto the first spooling device and the second spooling device, respectively.

Irrespective of one or both spooling devices being provided with a motor, the particle removing device (having a first end and a second end) will provide reciprocating movement during operation.

In an alternative embodiment wherein the particle removing device is endless, the container may be provided with at least one axle or reversing roller operatively connected to a motor configured for rotating the axle. At least one axle thereof is configured for driving the particle removing device. At least in an embodiment wherein the container comprises a single axle, the particle removing device is preferably wound at least once around the axle to increase the friction between the axle and the particle removing device.

P30295PC00 Thus, in embodiments wherein the particle removing device extends into a container, as discussed above, the driving device (for effecting sliding movement of the particle removing device) may comprise at least one motor operatively connected to an axle arranged in connection with the container holding the cleaning agent.

In operation, the rotor blade to be cleaned is preferably arranged so that the longitudinal axis of the rotor blade is substantially horizontal, or somewhat inclined with respect to the direction of moving the apparatus along the rotor blade. For example, if the cleaning operation commences at a tip of the rotor blade, the tip may be arranged at a higher elevation than its root, which is connected to the hub of the nacelle. In this context, the term "somewhat inclined" means that the longitudinal axis of the rotor blade may be inclined up to for example 7° with respect to horizontal, but this inclination depends on the capacity of the movement device configured for moving the apparatus along a longitudinal axis of the rotor blade. As will be discussed below, the movement device may form a part of the apparatus, or the movement device may be an external force. Arranging the rotor blade horizontal or somewhat inclined, for example downwardly inclined from the tip of the rotor blade, will facilitate movement of the apparatus along the length of the rotor blade. A somewhat downwardly inclined rotor blade will thus represent an uphill gradient when moving the apparatus from the root to the tip of the blade. Therefore, and independent of the root of the rotor blade being located higher or lower than the tip of the rotor blade, the uphill gradient and the capacity of the movement device set limits for the inclination of the rotor blade.

As mentioned above, a nacelle of a wind turbine may typically be arranged 30-200 meters above the base supporting the wind turbine.

In a preferred embodiment, in order to reduce the length of the particle removing device and thus the weight of the apparatus, the container holding the cleaning agent is arranged closer to the rotor blade than to the base supporting the wind turbine. In one embodiment, the container is arranged up to 5 meters below the rotor blade.

In embodiments wherein the apparatus comprises a container, and wherein at least a portion of the particle removing device is moved/passed into the container, as discussed

P30295PC00 above, the cleaning agent within the container is spent gradually. To maintain a desired volume of cleaning agent within the container, the container may be operatively connected, via a liquid supply line, to a reservoir of the cleaning agent. The reservoir may be arranged at a distance from the container. In a preferred embodiment, the reservoir is arranged at a lower elevation than the container. Advantageously, the reservoir is supported directly or indirectly on the base. Supporting the reservoir on the base also has the effect that the weight of the reservoir is carried by the base, and not by the apparatus itself. A further benefit of connecting the container to the reservoir is that the volume of cleaning agent within the container can be relatively small. In a prototype of the apparatus, the volume of the container is 25 litres.

During operation of an apparatus provided with a container, as discussed above, the particles that are cleaned and removed from the surface of the rotor blade will gradually pollute the cleaning agent within the container. To reduce the content of polluting particles within the container, the container may be further provided with a drain line operatively connected to a receptacle for receiving the polluted cleaning agent. Preferably, the receptacle is arranged at the base. In one embodiment, the receptacle is provided with a cleaning device, for example in the form of a filter arrangement and/or a settling tank. Providing the receptacle with a cleaning device has the effect that at least some of the cleaning agent received from the container may be recirculated to the reservoir of the cleaning agent.

In a preferred embodiment, a pump configured for supplying the cleaning agent from the reservoir and into the container is arranged in connection with the reservoir. Thus, the weight of the pump does not add weight to the apparatus. Further, any pump configured for bringing the polluted cleaning agent from the container and into the receptacle is preferably arranged in connection with the receptacle to avoid adding weight to the apparatus.

In one embodiment, the apparatus may further comprise a motor-operated movement device configured for moving the apparatus along a longitudinal axis of the rotor blade. The movement device may comprise sets of wheels configured for abutting, during oper-

P30295PC00 ation of the apparatus, against a top portion, preferably a leading edge, of the rotor blade, wherein at least one wheel of the set of wheels is operatively connected to a motor configured for rotating the wheel. The motor may be an electrical motor or a fluid- operated motor. An electrical motor is preferred since an electrical motor will normally add less weight to the apparatus than, for example, a fluid-operated motor which, for example, may be a hydraulically operated motor or a motor operated by means of the liquid pressure of the cleaning agent. The electric source for supplying energy to any electric motor may be a battery or a generator. Irrespective of being a battery or a generator, the electric source is preferably arranged at a distance from the apparatus, for example at the base supporting the wind turbine. Thus, the motor may be connected to the energy source via a cable. The same applies for any fluid-operated motor.

In a preferred embodiment, the apparatus is configured for operation via remote control, either via a cable or wirelessly, in a way known perse. For an apparatus being remotely controlled via a cable, the apparatus is provided with a control line. Thus, the apparatus may comprise at least one power supply cable for supplying power to the apparatus.

The apparatus may further comprise a control line for controlling the apparatus.

In one embodiment of the apparatus, an umbilical line may be used to assemble at least some of the power cable, any control line, and fluid lines, all of which extend between the base and the apparatus. An umbilical line provides one "line" instead of a plurality of separate cables and lines.

As an alternative to moving the apparatus along a longitudinal axis of the rotor blade using a movement device forming a part of the apparatus, as discussed above, the apparatus may be moved along the longitudinal axis of the rotor blade using an external force. Such an external force may, for example, be provided by a drone, a hoisting crane, or personnel located on or near the base.

The pressing means of the apparatus may comprise a linkage comprising a plurality of links provided with tensioned joints configured for urging the linkage towards the perimeter portion of the rotor blade. Such links provided with tensioned joints will act as a bias-

P30295PC00 ing means in the apparatus.

The linkage may form a part of a path configured for guiding, during operation, the particle removing device along the perimeter portion of the rotor blade. The path may comprise at least two guiding elements operatively connected to the linkage. A linkage forming a part of a path provided with such guiding elements configured for guiding the particle removing device along a perimeter of the rotor blade, is of particular interest in embodiments wherein the particle removing device is operatively connected to said container, and particularly when operatively connected to at least one axle within the container. A path comprising a biased linkage and the guiding elements may also ensure sufficient contact between the particle removing device when positioned at a trailing edge portion of the rotor blade.

At least some of the links may be provided with rollers for guiding the particle removing device. Such rollers form a part of the path.

However, using a pressing means in the form of tensioned joints (i.e., a biasing means) during operation of the apparatus may cause undue squeezing of the particle removing device towards the perimeter of the rotor blade. Undue squeezing of the particle removing device may result in loss or spill of cleaning agent. To avoid such undue squeezing, the linkage may further comprise a plurality of spacers configured for keeping, during operation, the pressing means at a predetermined distance from the perimeter portion of the rotor blade. More particularly, the spacers may be configured for abutting against the perimeter portion of the rotor blade to keep a core of the particle removing device at a predetermined distance from the perimeter portion of the rotor blade. Preferably, such distance devices comprise rollers. Rollers provide gentle contact with the surface of the rotor blade, simultaneously providing substantially no friction against movement of the apparatus along the longitudinal axis of the rotor blade.

In a second aspect of the invention, there is provided a system for removing particles from a rotor blade of a wind turbine, wherein the system comprises:

- the apparatus according to the first aspect of the invention;

- a connector operatively secured to a portion of the apparatus; and

P30295PC00 - a hoisting device configured for engaging the connector to (at least) bring the apparatus onto the rotor blade.

Preferably, the hoisting device is also used to bring the apparatus away or down from the rotor blade.

In one embodiment of the system, the hoisting device is a drone. A drone can be operated from a remote location, for example from the base of any kind of onshore and offshore installation. Further, a drone can be used for connecting the apparatus to a rotor blade of a wind turbine of any hight.

It should be noted that in an embodiment wherein the apparatus is provided with a communication line (for liquid and/or electric power) extending to the base, the drone itself is secured indirectly to the base. A drone being indirectly secured to the base may be advantageous in that the operation of the drone therefore is not bound by public regulations on safe operation of drones.

In an alternative embodiment of the system, the hoisting device may (in some cases) be a crane or any other suitable device capable of bringing the apparatus to and from the rotor blade of the wind turbine. A crane, or any other suitable hoisting device, may be used to bring the apparatus to a rotor blade of a wind turbine of relatively low hight, typically up to 100 meters, and wherein an access path exists, such as a road for bringing the crane adjacent to an onshore wind turbine, or a water body (e.g. the sea) for bringing a vessel comprising a crane adjacent to an offshore wind turbine.

As an alternative or addition to the movement device discussed above, and irrespective of being a drone or a crane, the hoisting device may be used for moving the apparatus along the length of the rotor blade.

In a third aspect of the invention, there is provided a method for removing particles from a rotor blade of a wind turbine, wherein the method comprises:

- providing a system according to the second aspect of the invention;

- connecting the hoisting device to the connector of the apparatus and hoisting the apparatus onto a portion of the rotor blade; and

P30295PC00 - moving the particle removing device in sliding contact with a perimeter portion of the rotor blade;

- moving the apparatus along a longitudinal axis of the rotor blade; and

- removing the apparatus from the rotor blade.

The method may further comprise supplying a cleaning agent to the particle removing device.

The method may further comprise passing the particle removing device via a container holding a cleaning agent to repeatedly soak the particle removing device while in operation.

The method may further comprise providing fluid communication between the container and a fluid source at a base level.

The method may further comprise adding a cleaning agent to at least one portion of the particle removing device via a nozzle being in fluid communication with a fluid source at a base level.

In the following, examples of preferred embodiments are described and illustrated in the accompanying drawings, wherein:

Fig. 1 illustrates a prior art method of cleaning a rotor blade of a wind turbine by using a helicopter and a high-pressure washer;

Figs. 2a and 2b illustrate air flow past a clean and a dirty aerofoil, respectively;

Fig. 3 shows an apparatus according to an embodiment of the invention being hoisted by a drone towards a rotor blade;

Fig. 4 shows in larger scale the apparatus of fig. 3 being brought onto a tip of the rotor blade;

Fig. 5a shows an aerofoil of a rotor blade being enclosed by a portion of the apparatus, and wherein a particle removing device of the apparatus is in contact with a perimeter portion of the rotor blade;

P30295PC00 Fig. 5b illustrates, in smaller scale, the flexibility of the apparatus shown in fig. 5a when being moved along a longitudinal axis of the rotor blade, which has an increasing aerofoil from the tip towards the root of the rotor blade;

Figs. 6-8 show the apparatus in operation along the rotor blade;

Fig. 9 shows, in larger scale but viewed from a different angle, a detail of the apparatus shown in fig. 7;

Fig. 10 shows, in larger scale but viewed from a different angle, a detail of a top portion of the apparatus shown in fig. 9;

Fig. 11 shows an alternative embodiment of the apparatus; and

Fig. 12 shows a basic embodiment of the apparatus.

Any positional indications refer to the positions shown in the figures.

In the figures, same or corresponding elements are indicated by the same reference numerals. For clarity reasons, some elements may be without reference numerals in some of the figures.

A person skilled in the art will understand that the figures are just principal drawings. The relative proportions of individual elements shown in the figures may also be distorted.

Figure 1 shows one of the common prior art methods of removing particles from a rotor blade R, which is operatively connected to a hub H of a nacelle N of a wind turbine W.

A helicopter H is flying close to the rotor blade R. A person P is standing partly on the outside of the helicopter H while directing a cleaning liquid towards a surface of the rotor blade R. The person P is using a high-pressure washer receiving cleaning liquid from a tank within the helicopter H. Besides being a high-risk operation, the cleaning effect of this method is limited since the washing operation is based on jetting cleaning fluid onto the rotor blade R only. This is substantially different from the "contact cleaning" offered by the present particle removing device sliding against a perimeter of the rotor blade.

Figures 2a and 2b illustrate air flow passing a portion of a wing profile of, for example, a

P30295PC00 rotor blade of a wind turbine. Fig. 2a illustrates air flow passing a clean rotor blade, while fig. 2b illustrates air flow passing a rotor blade contaminated with particles thereon. The airflow passing the contaminated rotor blade is turbulent and reduces the blade's "lift coefficient" due to increased surface roughness caused by particles sticking to the surface. A reduced "lift coefficient" of a rotor blade reduces the efficiency of the rotor blade. Thus, to maintain the efficiency of the wind turbine, cleaning the surface of the rotor blade is required on a regular basis.

In figures 3-12, reference numeral 1 denotes an apparatus according to the present invention. The apparatus 1 comprises an elongated particle removing device 3 configured for moving in sliding contact with a perimeter portion of a rotor blade R, which is operatively connected to a hub H of a nacelle N of a wind turbine W. The apparatus 1 further comprises a pressing means 10 configured for urging, during operation, the particle removing device 3 against the perimeter portion of the rotor blade R. The apparatus further comprises a connector 68 connected to a hoisting device, such as a drone 70 (as shown in fig. 3), or a crane (not shown).

In several of the figures, the particle removing device is "hatched" to illustrate a preferred brush-like device.

In the embodiments shown, the particle removing device 3 has an elongated form with a length that exceeds the largest perimeter portion of the rotor blade R. Irrespective of the apparatus 1 being located at the tip or the largest cross section of the rotor blade R (close to the root of the rotor blade R), the elongated particle removing device 3 extends below a portion of the trailing edge RT of the rotor blade R.

The apparatus 1 further comprises a driving device configured for effecting, during operation, sliding movement of the particle removing device 3 relative to the perimeter portion of the rotor blade R. The driving device will be discussed in further details below.

In the embodiment of the apparatus shown in figures 3-10, the particle removing device 3 is endless.

Except for the basic embodiment of the apparatus shown in fig. 12, a lower portion of the

P30295PC00 particle removing device 3 is wound around a pair of spools or axles 21, 21', which are operatively connected to a container 20 configured for holding a cleaning agent. See figures 4, 6a-8, and 11.

The container 20 illustrated in figures 4, 6a, 7, and 8 is shown in larger scale in fig. 6b.

Fig. 6b shows the container 20 provided with a first rotatable axle 21 and a second rotatable axle 21' arranged below the first rotatable axle 21. The rotatable axles 21, 21' are arranged parallel to each other and are secured to an axle frame 22 located at either end thereof. A portion of these axle frames 22 protrudes above a top portion of the container 20 and is operatively connected to the first rotatable axle 21. Each axle frame 22 is provided with a bail 23 configured for guiding the particle removing device 3 towards each end portion of the rotatable axles 21, 21'.

The pair of rotatable axles 21, 21' are surrounded by the endless particle removing device 3, which is wound several times around the pair of rotatable axles 21, 21'.

In the embodiment wherein the particle removing device 3 is wound several times around the pair of axles 21, 21', at least one of the rotatable axles 21, 21' is operatively connected to a motor (not shown) configured to rotate the axle. When the motor rotates at least one of the axles, the endless particle removing device 3 is set in motion and will (when operating the apparatus 1) slide relative to the perimeter portion of the rotor blade R.

When the container 20 contains a cleaning agent and the second rotatable axle 21' is submerged in the cleaning agent, the particle removing device 3 will be submerged repeatedly while rotated on the pair of axles 21, 21'. Tests have shown that such repeated submerging of the particle removing device 3 within the container 20 provides effective cleaning and removal of contaminants from the particle removing device 3. Prior to this cleaning step, these contaminants have been removed from the rotor blade R and carried by the particle removing device 3 into the container 20.

In the alternative embodiment, which is shown fig. 11, the container 20 is provided with a spooling device comprising a first rotatable spool or axle 21 and a second rotatable spool or axle 21'. Both axles 21, 21'are arranged at the same elevation relative to the bottom of

P30295PC00 the container 20. Both axles 21, 21' are also arranged in parallel, and mutually distant to each other, and are secured to wall portions of the container 20.

The particle removing device 3 shown in fig. 11 comprises a first end 31 and a second end 32. The first end 31 is secured to the first rotatable axle 21, while the second end 32 is secured to the second rotatable axle 21'.

Each spool (or axle) 21, 2 l'is operatively connected to a motor (not shown) in order to rotate the spool. The motors may, for example, be arranged on the outside of the container 20. In one embodiment, the motors may be configured to rotate the spools simultaneously. When the particle removing device 3 is unwound from one of the spools (axles) 21, 21', it is therefore wound onto the other one of the spools 21', 21. In another embodiment, the motors are configured to allow one of the rotatable spools 21, 21' to wind the particle removing device 3 onto both spools, while the other spool rotates substantially freely.

As illustrated in fig. 11, the particle removing device 3 crosses itself somewhere between the trailing edge RT of the rotor blade R and the container 20. Due to this crossing, the particle removing device 3 is urged towards the perimeter portion of the rotor blade R.

A reciprocating and sliding movement of the particle removing device relative to the perimeter of the rotor blade R may thus be obtained simply by controlling the action of the spools 21', 21 and the crossing of the particle removing device 3. The links 11 provided with prestressed and tensioned joints, as discussed above, may therefore be superfluous in the embodiment shown in fig. 11.

During operation of an apparatus 1 provided with a container 20, as discussed above, the cleaning agent within the container will be spent gradually due to (at least) wetting of the perimeter of the rotor blade R. To maintain a desired volume of cleaning agent within the container 20, the container 20 is operatively connected, via a liquid supply line 24, to a reservoir 40 of the cleaning agent. The reservoir 40 is arranged at a distance from the container 20. In fig. 8, the reservoir 40 is in the form of a supply tank 40 carried by a vehicle V located adjacent to a mast M of the wind turbine W.

P30295PC00 The cleaning agent within the container 20 will also be contaminated with particles that have been removed from the perimeter of the rotor blade R. In the embodiments shown in figures 4, 6a-8, and 11, the container 20 is further provided with a drain line 26 operatively connected to a receptacle 42 for receiving a polluted cleaning agent. In fig. 8, the receptacle 42 is in the form of a tank 42 located on the vehicle V, which also carries the supply tank 40. The amount of cleaning agent drained from the container 20 is replaced with cleaning agent from the supply tank 40. As mentioned previously, the receptacle or tank 42 may be provided with a cleaning device, for example in the form of a filter arrangement and/or a settling tank. Thereby, at least some of the cleaning agent received from the container 20 may be recirculated to the supply tank 40. Recirculation of cleaning agent is of particular advantage when cleaning a wind turbine located far away from a supplier of cleaning agent, for example a wind park located in a coastal area, on a mountain, or offshore.

To achieve effective cleaning of the rotor blade R by means of the apparatus 1, the particle removing device 3 should abut against the perimeter portion of the rotor blade R.

In the embodiment shown in figures 3 - 11, the portion of the particle removing device 3 surrounding the perimeter portion of the rotor blade R is pressed against the rotor blade R using a pressing means to do so. The pressing means is in the form of a linkage 10 comprising a plurality of links 11 provided with prestressed and tensioned joints, which collectively constitute a biasing means. The biasing means is configured for urging the particle removing device against even the smallest cross-sectional portion along the axial length of the rotor blade. Prior to operating the apparatus 1, the biasing force to be exerted by the prestressed and tensioned joints may be adapted as required to properly clean the actual sizes of the rotor blades R of the wind turbine W.

The linkage 10 forms a part of a path 50 configured for guiding, during operation, the particle removing device 3 along the perimeter portion of the rotor blade R. In the embodiment shown, the path 50 comprises a plurality of guiding elements 52 operatively connected to the linkage 10. The guiding elements 52 comprise rollers 53, and arms provided with a ring-shaped end portion 54 through which the particle removing device 3 has been

P30295PC00 threaded. In the illustrations shown, for example in figures 5a, and 9-11, one guiding element 52 is connected to each link 11 of the linkage 10. However, the number of guiding elements 52 used may be less or more than the number of guiding elements 52 shown in the figures. Further the number of guiding elements 52 may be different from the number of links 11.

The path 50 is further provided with a plurality of spacers, here in the form of spacer wheels 56 configured to keep (in operation) the linkage 10, and thereby the guiding elements 52, at a predetermined distance from the perimeter portion of the rotor blade R. The spacer wheels 56 are configured to avoid undue squeezing of the particle removing device 3 when sliding along the perimeter of the rotor blade R. In fig. 5a, each link 11 is provided with a spacer 56.

As will be clear from figures 7 and 8, for example, only a limited portion between the tip and the root of the rotor blade R is surrounded by the particle removing device 3 during operation of the apparatus 1. To clean the rotor blade R, the apparatus 1 must therefore be moved along a longitudinal axis of the rotor blade R. Such a movement of the apparatus 1 may be achieved in many ways. One way is to move the apparatus 1 along the longitudinal axis of the rotor blade R by means of a hoisting device, which forms a part of a system according to the invention. The hoisting device may, for example, be a drone 70 (as shown in fig. 3) or a crane. Another way of moving the apparatus 1 along the rotor blade R may be to provide a connection to a base B, and then to apply a force from the base B to drag the apparatus 1 along the rotor blade R. Still another and possibly a preferred way of moving the apparatus 1 along the rotor blade R is to provide the apparatus 1 with a motor-operated movement device.

In the embodiment shown in figures 3-11, the apparatus 1 is provided with a motor- operated movement device comprising two pairs of wheels 60 configured for abutting (during operation) against a top portion, i.e., a leading edge RL, of the rotor blade R. Each wheel 60 is operatively connected to a body 62 via a wheel axle 64. At least one of the axles 64, but preferably at least two of the axles 64, houses a motor (not shown), preferably an electric motor, operatively connected to a respective wheel 60.

P30295PC00 It should be noted that an apparatus 1 configured with wheels 60, body 62 and axles 64 is also advantageous for an apparatus 1 configured to be moved along the longitudinal axis of the rotor blad R (as illustrated in fig. 5b) by means of a hoisting device, or by means of a drag force provided from the base B.

An apparatus 1 comprising one or more motors, as discussed above, must be supplied with power from a power source. A power source for an electric motor may be a chemical source, such a battery. However, a battery will add weight to the apparatus 1. An added weight to the apparatus 1 may be undesirable, especially if the apparatus 1 forms a part of a system according to the invention and comprises a hoisting device in the form of a drone 70.

To avoid added weight, the apparatus 1 of the embodiment shown in fig. 7 is provided with a power supply cable 66 for supplying power to the apparatus 1. The cable is operatively connected to a power source (not shown) at the base B. In the embodiment shown in fig. 8, the power source may be located in the vehicle V.

A further advantage of supplying power via a cable 66 from the base B, is that a motor configured for rotating at least one of the axles 21, 21' in said container 20, may also receive power via the power supply cable 66. Otherwise, said motor must be provided with power from a battery arranged in connection with the container 20. Such a battery will add weight to the apparatus 1 and will also result in a limited operating time of the apparatus 1.

As an alternative or addition to providing the apparatus with a container 20 for a cleaning agent, the path 50 may be provided with at least one nozzle 30 for adding a cleaning agent during operation of the apparatus 1. Preferably, the nozzle is directed towards a portion of the particle removing device 3. An example of such a nozzle arrangement is illustrated in fig. 9 and shows a nozzle 30 directing cleaning agent towards the particle removing device 3 and thus wetting the device 3 before reaching the trailing edge RT of the rotor blade R, and before sliding against the perimeter portion of the rotor blade R. The nozzle 30 is operatively connected, via

P30295PC00 a fluid line 30', to a source of cleaning agent at the base B. The source of cleaning agent may, for example, be the tank 40 shown in fig. 8.

Fig. 12 illustrates a basic configuration of the apparatus 1 according to the invention. Each of the first end 31 and the second end 32 of the particle removing device 3 is operatively connected to a respective line 31', 32' extending to a base B of the wind turbine W. The lines 31', 32' cross somewhere between the trailing edge RT of the rotor blade R and the base B. The crossing of the lines 31', 32' may, for example, be provided by two persons (not shown) standing some distance apart at the base B and grabbing each one of the lines 31', 32'. This crossing of the lines 31', 32' ensures that the particle removing device 3 is in close contact with the perimeter of the rotor blade R. Thus, the lines 31', 32' represent the pressing means of the apparatus 1. A reciprocating, sliding movement of the particle removing device 3 relative to the perimeter of the rotor blade is obtained by the persons alternating between applying a pulling force to each respective line 31', 32'. Thus, the lines 31', 32' also represent the driving device of the apparatus 1.

In the embodiment shown in fig. 12, the apparatus 1 is provided with a set of wheels 60 connected to a body 62, as discussed above. The body 62 is provided with a connector 68 allowing the body 62 (and the sets of wheels 60) to be connected to a hoisting device, such as the drone 70 shown in fig. 3, or a crane (not shown). Movement of the apparatus 1 along the longitudinal axis of the rotor blade R may, for example, be provided by applying a force via the lines 31', 32', or via the hoisting device, or by using a motor-operated movement device wherein at least one wheel 60 (of the set of wheels 60) is operatively connected to a motor for rotating the wheel 60, as discussed above. Thus, the lines 31', 32' may represent the pressing device (for urging the particle removing device into contact with the perimeter portion of the rotor blade R), the driving device (for effecting sliding movement of the particle removing device 3 relative to the perimeter portion of the rotor blade R), and even a moving device (for moving the apparatus 1 along the longitudinal axis of the rotor blade R).

The particle removing device 3 is operatively connected to the body 62 via arms provided with an annular or ring-shaped end portion 54 through which the particle removing de-

P30295PC00 vice 3 has been threaded. In the embodiment shown in fig. 12, the arms with the ringshaped end portion 54 are secured to the axles 64.

This basic configuration of the apparatus 1 provides "dry-cleaning" of the perimeter of the rotor blade R and may be suitable in some cleaning operations. However, the embodiments disclosed in figures 3-11 are preferred as they provide a more effective apparatus 1 and also requires less effort from personnel at the base B of the wind turbine (W).

From the above, it should be clear that the invention provides great advantages, in terms of lower costs, improved efficiency and safety, and less environmental impact, over prior art apparatuses and methods of cleaning rotor blades of a wind turbine. The apparatus 1 according to the invention may be operated continuously (24/7) when the apparatus 1 forms part of a system comprising a hoisting device 70 extending from, or being operatively connected to, the base B of the wind turbine W.

It should be noted that the above-mentioned embodiments illustrate the invention rather than limiting the invention. Those of skill in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. Any reference signs placed between parentheses in the claims shall not be construed to limit the claim. Use of the verb "comprise" and its conjugations do not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

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