Title of Invention:

DE-ICING OF STRUCTURES USING UNMANNED AERIAE VEHICEES AND HOT AIR AND/OR IR/MICROWAVE RADIATION

Technical Field

[0001] The present invention relates generally to unmanned aerial vehicles (UAVs) equipped with one or more heat sources, to be applied for de-icing of structures such as airfoils, wind turbine blades, airplane wings, helicopter wings, marine structures, power lines and the like and associated method.

Background Art

[0002] De-icing of large structures subjected to cold weather, e.g. wind turbines, is well known and carried out commercially, e.g. using hot air being circulated in the blades or using electrical heating foils on the blades, in particular on the leading edges. These methods have considerable weaknesses as evidenced by the literature.

[0003] De-icing using hot water and helicopters has been suggested, see e.g.

https://www.youtube.com/watch?v=-90g8SrOtgQ. alternatively using drones/UAVs and cold or hot water, see e.g. https://www.theverge.com/tldr/20l 8/3/26/l7l63464/drone-de- ice-clean-wind-turbine-aerones. Recently, improved unmanned aerial vehicle (UAV) technology has become available: UAVs are able to carry more heavy loads. However, supply of hot water to remote locations like wind parks is a cost issue, and a drone would need to carry the weight of a water hose up to nacelle height, e.g. 100 m. Typically, more than 50% of the load carrying capacity of the drone would be used for carrying water. Alternatively, in the case of supplying water from the ground, overcoming the considerable water column at this height would require heavy duty pumping equipment.

[0004] WO2013172762 describes de-icing of e.g. wind power turbine blades whereby electromagnetic induction or IR/microwave radiation is used to heat up a layer or a coating on said surface of the structure heatable by microwave or infrared radiation or electromagnetic induction. Radiation can be supplied both from the inside of the structure as well as from the outside, for instance by means of magnetrons placed inside or on the structure. However, the method is not suitable for retrofitting as it requires application of the layer or coating on the structure and is therefore difficult to implement in already existing structures.

[0005] In summary, the known methods and devices are either cumbersome and/or suboptimal for de-icing structures in remote and inaccessible locations. Thus, there is a need for an improved apparatus and method for de-icing structures.

Summary of Invention

[0006] An object of the present invention is to provide a solution which achieves these advantages. This object is achieved in a first aspect of the invention, in which there is provided an unmanned aerial vehicle (UAV) suitable for de-icing a structure, the UAV comprising at least one heat source mounted thereon and arranged to deliver heat to a surface of said structure in order to melt ice accreted on the surface of said structure.

[0007] By mounting a heat source directly on the UAV, it is possible to deliver heat to the surface of the structure in a more energy-efficient way whilst reducing the weight of the payload compared to other known methods. In comparison to prior art, the invention succeeds in providing a simple, economic, repair-friendly and stable solution for de-icing and anti-icing.

[0008] In an advantageous embodiment, the at least one heat source comprises a hot air blower, an infrared (IR) heater and/or a microwave generator. The UAV may carry hot air generation equipment, or it may carry IR and/or microwave radiation sources, or both, as the case may be. These heat sources have the advantage over the prior art that the heat is generated in real time locally on the UAV, and that they are substantially unlimited as long as sufficient electrical power supply is provided and relatively light-weight compared to water.

[0009] Comparing hot air and IR radiation with microwave radiation, it should be noted that microwave-assisted de-icing also requires modification of the turbine blades or the control system of the wind turbine generator (WTG) with microwave absorbing coating. The common denominator of the technologies is, however, the feature that drones or UAVs are used to deliver heat in the form of hot air and/or radiation to the structures which shall be de-iced. [0010] In a preferred embodiment, the at least one heat source is arranged to deliver said heat from a distance of 0.1-3 m, preferably from 0.15-2 m. The heat source is sufficiently powerful to direct the heat to the desired areas from a distance which facilitates maneuvering in relation to the structure and minimizes heat loss to the surroundings.

[0011] In a further preferred embodiment, the at least one heat source is arranged to deliver a power density to the surface of said structure in the range 0.1-20 kW/m ² , preferably 0.2-5 kW/m ² . The power density is chosen to be sufficient for melting accreted ice as fast as possible but without damaging the underlying structure.

[0012] In an advantageous embodiment, the UAV further comprises an electrical cable arranged to be connected to an electrical power supply separate from the UAV. The electrical cable allows for unlimited supply of electrical energy which not only allows for continuous flight of the UAV, but also continuous delivery of heat for melting the ice, such that the UAV does not need to land in order to restock (hot) water or charge batteries.

[0013] In an alternative embodiment, the UAV is arranged to carry payloads in the range 2-150 kg. The payload capacity of the UAV is adapted to the specific components required for the de-icing or anti-icing procedure.

[0014] In a preferred embodiment, the UAV further comprises means for monitoring the progress of the de-icing, said monitoring means being arranged to detect presence and/or magnitude of ice and/or temperature of the surface of said structure. Monitoring the progress of de-icing is advantageous as it enables the operator to quickly proceed to the next section of the structure as soon as the ice has been removed, avoiding superfluous or excessive heating of the structure.

[0015] In a second aspect of the present invention, there is provided a method for de- icing of a structure, comprising the steps:

— providing an unmanned aerial vehicle (UAV), the UAV comprising at least one heat source arranged to deliver heat to a surface of said structure;

— maneuvering the UAV in close proximity to a surface of said structure to be de-iced; and

— operating the at least one heat source of the UAV to deliver heat to the surface of said structure sufficiently long to melt and remove ice. [0016] As an alternative, the method according to the present invention may be used for anti-icing, i.e. preventive heating of certain sections, especially the leading edge of an airfoil or wind turbine blade

[0017] In a preferred embodiment, the at least one heat source comprises a hot air blower, an infrared (IR) heater and/or a microwave generator.

[0018] In an advantageous embodiment, the surface of said structure is heated to above 0 °C to facilitate removal of ice and/or prevent accretion of ice.

[0019] In an further preferred embodiment, said structure is selected from airfoils, wind turbine blades, aircraft wings, helicopter wings, marine structures, off-shore platforms, ships, and power lines.

[0020] In an alternative embodiment, maneuvering the UAV further comprises positioning the UAV at a distance in the range 0.1-3 m, preferably 0.2-2 m from the surface of said structure.

[0021] In a preferred embodiment, the method further comprises maneuvering the UAV in a predetermined sequence along the surface of said structure. By means of the predetermined sequence, a more efficient de-icing procedure is achieved in that accreted ice is removed from one section of the structure at a time.

[0022] In an advantageous embodiment, the method further comprises monitoring the progress of the de-icing by detecting presence and/or magnitude of ice and/or temperature of the surface of said structure.

[0023] In other aspects, the invention describes useful embodiments for de-icing and anti-icing of wind turbines, aircrafts, civil engineering objects and off-shore constructions.

Brief Description of Drawings

[0024] The invention is now described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 shows a schematic view of an unmanned aerial vehicle in perspective according to one embodiment of the present disclosure; Fig. 2 shows a schematic view of an unmanned aerial vehicle from the side according to one embodiment of the present disclosure;

Fig. 3 shows a schematic view of an unmanned aerial vehicle used in a method according to one embodiment of the present disclosure for de-icing the blades a wind turbine;

Description of Embodiments

[0025] In the following, a detailed description of an unmanned aerial vehicle and de- icing method according to the present invention is presented. In the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures. It will be appreciated that these figures are for illustration only and are not in any way restricting the scope of the invention.

[0026] Referring to Fig.1 , an unmanned aerial vehicle (UAV) or drone 8 is shown in a schematic view. The UAV comprises a construction or body 1 supporting four rotating propellers 2, each mounted on an axis 3. The number of propellers may be varied according to the desired flight characteristics, payload etc. of the UAV 8. The body 1 may carry electronics, batteries for independent flight mode etc., and is strong enough to carry payloads of e.g. 2-150 kg.

[0027] Referring now to Fig. 2, there is shown a drone suitable for executing the de- icing tasks according to the invention, viewed from the side. Propellers 2 are connected through axis 3 to the main body 1 which in turn carries heat source equipment such as infrared heaters/lamps, hot air blowers/generators or microwave equipment, and visible/IR cameras as known in the art. The equipment box 4 is connected to the body 1 with connectors 5.

[0028] In one general embodiment, a drone 8 is equipped with one or more heat sources 4 in the form of electrical hot air generators and blowing devices. Many

constructions of such devices are known and commercially available.

[0029] Alternatively, or simultaneously, the drone 8 is equipped with infrared lamps. Such lamps emit radiation e.g. between the red edge of the visible spectrum at 700 nanometers (nm) to 1 millimeter (mm). This range of wavelengths corresponds to a frequency range of circa 430 THz to 300 GHz. Such lamps are also known and used industrially for e.g. paint curing. [0030] Alternatively, the drone is equipped with microwave-generating radiation sources. In this case, the structure to be de-iced has previously been equipped with a layer or a coating which absorbs microwaves efficiently, such as disclosed in WO2013172762.

[0031] For removal or melting of ice and snow, a minimum energy input of 332 kJ/kg ice is required, corresponding to 0.092 kWh electricity per kg ice without any losses. Naturally, in the operation of the drone 8, substantial losses will occur by hot air not hitting the surface of e.g. the turbine blade, by additional heating requirement for heating up ice from below 0 °C, by overheating, by heating the composite structure rather than the adhered ice, and many other loss processes. Still, especially in comparison with heating a wind turbine blade from the inside, requiring heating up the whole composite construction, the technology promises to be highly energy-efficient.

[0032] The typical power input can be 1 kW to 100 kW or more but guaranteeing a limitation of heating of the object to be de-iced to max. 70 °C, preferably max. 50 °C.

[0033] The progress of de-icing can be monitored in various ways. Ice detectors are available, e.g. based on spectroscopy techniques, which can detect presence as well as magnitude of ice on the surface to be de-iced.. The temperature of the surface can be monitored using IR cameras or pyrometers. Optical cameras can provide visual information. Lamps can be installed for night-time de-icing. These optical techniques can be used for guiding and steering the UAV which ideally should“fly” alongside the structure to be de-iced in a distance between e.g. 0,1 m and 0,5 m.

[0034] A control software can be employed in order to perform the de-icing process using an UAV and hot air/IR/microwaves automatically and according to prevailing conditions, in any sequence. It is highly practical to heat smaller sections, e.g. 1-10 m ² at a time, quickly, and heat the next sections once the first section is de-iced, and so forth. Blades may be turned downwards for individual de-icing and avoiding of ice throw.

[0035] In one embodiment, the independent methods of hot air blown to a surface carrying ice and the radiation with infrared lamps are combined, and the two methods cooperate in synergy. Hot air is helping with the removal of liquid water or molten ice, such that IR radiation is primarily used for melting of still solid ice. [0036] To stabilize the drone, an airflow in the opposite direction, compared with the hot air flow, may be generated.

[0037] Referring now to Fig. 3, there is shown a drone 8 carrying out a de-icing mission on a wind turbine 7. In this example, the drone 8 receives e.g. electricity or air from a support truck 10 on the ground through electrical cable 9. The electrical energy may be supplied from an electrical generator on the support truck 10, or from a stationary electricity source. The drone 8 can land on the support truck 10 and may be transported to the next de-icing task.

[0038] In one embodiment, electricity to the UAV 8 is supplied by a stationary electrical power supply on the ground, e.g. from the wind turbine base. The electrical cable 9 may transport any voltage, with higher voltages such as 400 V or 690 V being preferred as a lighter cable can be used. Equipment for converting high voltage to the voltage required by the hot air and/or IR generating equipment 4 can be placed on the UAV 8.

[0039] Alternatively, the drone 8 may be powered by on-board batteries. IR radiators may be powered by an on-board fuel cylinder containing natural gas, propane or hydrocarbon fuel. IR radiators may also be powered by electricity instead of fuel.

Alternatively, gas and electricity can be supplied from the ground via cables and pressure hoses.

[0040] In one general embodiment relating to microwaves, the microwave technology preferred in this invention is described in PCT/EP/2015/078990. More particular, the microwaves generated by solid state radio frequency (RF) power transistors is in the range of 500 MHz to 100 GHz, preferably 900 MHz to 6 GHz, most preferably at 915 MHz or 2,45 GHz. The choice of wavelength or frequency is made depending on various parameters, including cost of equipment, choice of equipment (magnetrons or solid-state radio frequency equipment), distance of UAV to the structure (as high frequency radiation is easier to direct, i.e. can be directed less divergent), regulations relating to RF emissions and others.

[0041] The microwaves are transmitted by required components, such as waveguides or antennas, to a microwave absorbing layer so as to heat up said microwave absorbing layer by the same being absorbing microwaves to above 0 °C and thereby facilitating removal of ice or preventing accretion of ice on said structure. The UAV is used to carry the microwave and electrical equipment, and the UAV is directed towards the parts of the structure which require de-icing. Video control onboard the UAV, including infrared cameras, may be used to control the de-icing process.

[0042] For enabling said heating, a plurality of said solid state radio frequency power transistors, alternatively magnetrons or klystrons, including suitable antennas are placed suitably close to an area of a structure which requires heating in case a de-icing or anti-icing operation.

[0043] Power densities of 1-5 kW/m2, calculated as energy absorbed by the microwave-absorbing layer or more are preferred in order to achieve fast de-icing, but guaranteeing a limitation of heating of the absorbing layer to max. 50 or 60 or 70 or 80 °C.

[0044] The method disclosed regarding hot air and IR radiation is particularly useful for retrofitting of existing wind turbine blades or other structures operating in cold climates. The method is advantageous compared to UAV-assisted de-icing with water jets as the UAV does not have to carry the considerable weight of a water supply hose including the water column. The method is further useful for de-icing and anti-icing in aircrafts. A particular advantage is that no chemicals such as anti-freeze solvents have to be employed. Those would be lost during the process, and they would enter the

environment. Further, no modification of wind turbines is necessary by coating or changes in the control system.

[0045] One specific embodiment relates to keeping overhead power lines, especially earth lines, free from ice. The UAV is optionally controlled from a ground-based vehicle.

[0046] Preferred embodiments of a device and method for de-icing and anti-icing have been disclosed above. However, the person skilled in the art realises that this can be varied within the scope of the appended claims without departing from the inventive idea.

[0047] All the described alternative embodiments above or parts of an embodiment can be freely combined or employed separately from each other without departing from the inventive idea as long as the combination is not contradictory.