DE102021102659B3 - Method for detecting the formation of ice on a rotating rotor blade and rotor blade device - Google Patents

Abstract

The invention relates to a method for detecting the formation of ice (13) on a rotating rotor blade (1). According to the invention, the rotor blade (1) rotates in the area of a light barrier device with a measuring axis (4). If, as a result of the peripheral speed (3) of the rotor blade (1), the measuring axis (4) passes a measuring area (8) of the rotor blade (1), the time span of the shading of the light receiver of the light barrier device depends on the extent of the ice (13) forming on the rotor blade (1). The extent of the ice (13) on the rotor blade 1 can then be determined from the measured period of time (taking into account the radius (9) and the peripheral speed (3)). The method according to the invention can be used for a helicopter, an air taxi, a drone , an aircraft engine, a wind turbine, a power plant, a turbine, a compressor or a ventilation system.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method for detecting the formation of ice on a rotating rotor blade. In this case, the rotor blade can be, for example, a rotor blade of a helicopter, an air taxi, a drone, an aircraft engine, a wind turbine, a power plant or a ventilation system, where the formation of ice on the rotor blade can lead to functional impairments. Furthermore, the invention relates to a rotor blade device in the form of a helicopter, air taxi, drone, engine, wind turbine, power plant or ventilation system.

STATE OF THE ART

In helicopters, sensors for ice detection are used, which are attached to the helicopter cell, for example. Ice builds up on the sensors under icing conditions. Icing conditions for the helicopter are derived from the icing condition of the sensors. The sensors are cyclically de-iced by heating, with which successive new measurements can be made.

In wind turbines, sensors record flow noise or a natural frequency of vibrations in the rotor blade. From a change in the flow noise or the natural frequency of the vibrations of the rotor blade, conclusions can then be drawn about the formation of ice on the rotor blade. It is also possible for the control personnel to carry out a visual check of the formation of ice on the rotor blade. It is also known that a video camera is attached to a nacelle of the wind energy installation, with which the extent of the deposit of ice on the rotor blade can then be determined by means of image evaluation. Furthermore, it is known to draw conclusions about icing of the rotor blade in wind power plants from a comparison of the setpoint power curve and the actual power curve.

DE 10 2018 116 941 A1 discloses the cumulative consideration, on the one hand, of the natural frequency of vibrations of the rotor blade and, on the other hand, of a comparison of the desired power curve with the actual power curve for determining the ice that is deposited on the rotor blade.

According to EP 2 549 454 B1 the ice on a rotor blade of a wind turbine is estimated by evaluating the torque that is required to change the angle of attack of the rotor blade.

Further prior art relating to a wind turbine is out EP 2 984 339 B1 , EP 3 203 066 B1 and EP 3 397 861 B1 famous.

WO 2013/149811 A1 discloses a method for detecting the accumulation of ice or snow on a rotor blade of a wind turbine, in which two parallel light beams from lasers are directed onto the surface of the rotor blade to be inspected. The light beams have different wavelengths, which are selected in such a way that the light of the light beams is reflected to different extents by the ice or snow. By comparing the intensities of the reflected light of the two light beams, a conclusion can then be drawn about the amount of ice or snow that has accumulated on the rotor blade.

Further state of the art is out US 10,429,511 B2 famous.

OBJECT OF THE INVENTION

• - eine Erfassung des Eises ermöglicht und alternativ oder kumulativ zu den herkömmlichen Verfahren Einsatz finden kann und/oder
• - hinsichtlich des apparativen Aufwands verbessert ist,
• - einer Integration in die Rotorblatteinrichtung und/oder
• - der Auswerteverfahren und/oder
• - der Wechselwirkung hinsichtlich des Betriebs der Rotorblatteinrichtung

verbessert ist.The present invention is based on the object of proposing a new method for detecting the formation of ice on a rotating rotor blade, which in particular

• - enables the ice to be recorded and can be used as an alternative or in addition to the conventional methods and/or
• - is improved in terms of equipment,
• - an integration into the rotor blade device and/or
• - the evaluation method and/or
• - the interaction regarding the operation of the rotor blade assembly

is improved.

Furthermore, the invention is dedicated to the task of proposing a rotor blade device, in particular a helicopter, an air taxi, a drone, an aircraft engine, a wind turbine, a power plant (here a turbine or a compressor) or a ventilation system, in which such an improved procedure can be used.

SOLUTION

The object of the invention is achieved according to the invention with the features of the independent patent claims. Other preferred inventions appropriate configurations can be found in the dependent patent claims.

DESCRIPTION OF THE INVENTION

The method according to the invention is used for a rotor blade device in which a rotor blade rotates about an axis of rotation. The formation of ice on the rotor blade is determined using a light barrier device. The light barrier device has a light transmitter and a light receiver. For example, the light transmitter can be a laser, while the light receiver is suitable for receiving laser light sent by the laser and for generating a measurement signal that correlates with the intensity of the received laser light. The light emitter and the light receiver are arranged relative to one another in such a way that the light emitter emits light along a measurement axis in the direction of the light receiver. For one embodiment of the invention, the measuring axis is oriented parallel to the axis of rotation of the rotor blade. Within the scope of the invention, however, there can also be an inclination with respect to this alignment of the measuring axis. In this case, the measurement axis has a directional component that is oriented parallel to the rotation axis. The measuring axis is arranged in such a way that it is located in the movement area of the rotor blade, so that the light sent by the light transmitter along the measuring axis is temporarily moved along a measuring section of the rotor blade. The light thus sweeps over the rotor blade in the area of the measurement section. During the scanning of the measurement section, the light receiver is shadowed by the measurement section from the light transmitter. The measuring section is provided on the rotor blade at a predetermined radius spaced from the axis of rotation.

In the method according to the invention, the period of time required by the measuring section of the rotor blade to pass the measuring axis is determined. This period of time correlates with the duration of the shadowing of the light receiver in relation to the light transmitter by the measuring section of the rotor blade. Furthermore, the extension of the measurement section of the rotor blade (with the ice) is determined in the method according to the invention. This determination is made taking into account on the one hand the period of time that the measurement section of the rotor blade with the ice needs to pass the measurement axis and on the other hand taking into account the speed of the measurement section of the rotor blade.

This can be explained using a simple example that does not limit the invention:

oder $$\text{t = B/}\left(\text{n}2\mathrm{\pi }\text{R}\right).$$

If the rotor blade has a width B in the measuring section, the measuring section of the rotor blade is at a distance R from the axis of rotation and the period of time is t, which the measuring section moves through the measuring axis without ice, and the speed of the rotor blade is n, so the following dependency results from the circular movement of the measuring section around the axis of rotation: $$\text{B}=\text{n}\mathrm{\pi }\text{R}$$

or $$\text{t = B/}\left(\text{<figure-callout id="2" label="n" filenames="DE102021102659B3\_0006.png,DE102021102659B3\_0007.png" state="{{state}}">n</figure-callout>}2\mathrm{\pi }\text{R}\right).$$

If, on the other hand, the width of the measuring section of the rotor blade has increased to (B + E) as a result of ice accumulation, where E describes the sum of a displacement of the effective leading edge and the effective trailing edge of the rotor blade as a result of ice accumulation, the same applies to the itself time span t _E changed as a result of the deposition $${\text{t}}_{\text{E}}=\left(\text{B}+\text{E}\right)/\left(\text{<figure-callout id="2" label="n" filenames="DE102021102659B3\_0006.png,DE102021102659B3\_0007.png" state="{{state}}">n</figure-callout>}2\mathrm{\pi }\text{R}\right).$$

The extension E as a result of the deposition of the ice can be determined from the above equations from the time period t _E determined in the method according to the invention.

This simplified example applies to an ideal theoretical rotational movement of the rotor blade for a planar configuration of the rotor blade without pitching it, without elastic, dynamic oscillations of the rotor blade and for an alignment of the measuring axis vertical to the plane of rotation of the rotor blade. If these ideal conditions are not present, the above equations can be adjusted accordingly to take the different effects into account. For example, the trigonometric functions must be taken into account if the measurement axis is not oriented vertically to the plane of rotation of the rotor blade and/or the rotor blade is curved and/or tilted in the measurement section.

It is possible, for example, for the speed of the measuring area to be determined from a drive speed of a motor that causes the rotor blade to rotate. It is also possible that the speed of the rotor blade and thus also the measuring range is known in a control unit of the rotor blade device and is used within the scope of the method according to the invention.

A multifunctional use of the light barrier unit is used for one proposal of the invention. For this proposal of the invention, the light barrier unit is initially used, as explained above tert, the determination of the period of time that the measuring section of the rotor blade with the ice needs to pass the measuring axis, from which the extent of the ice can then be determined. In addition, the light barrier unit is used to determine the frequency at which the measurement section (possibly with the ice) passes the measurement axis. In the simplest case, this frequency results from the frequency of the shading of the light receiver by the rotor blade. The speed of the measuring area can then be determined directly from this frequency.

A particular aspect of the method according to the invention is dedicated to possible error effects in that light may also be scattered or absorbed and thus not reach the light receiver if there is water on the rotor blade and/or water in the air in the area of the measuring axis (in the form of of drops) is arranged. A reduction in the intensity of the received light could then be incorrectly identified as shadowing of the light receiver by the rotor blade and/or the ice. The invention proposes that a special wavelength of the light transmitter and the reception area of the light receiver is used: It is proposed that the wavelength of the light be selected in such a way that the light from ice that forms on the rotor blade is scattered at least to a greater extent and/or is absorbed than is the case for unfrozen water on the rotor blade and/or in the air in the area of the measuring axis. Here, the scattering and/or absorption can be smaller by a factor of at least 5, at least 10, at least 15, at least 20, at least 50 or even at least 100 for the non-frozen water than for the ice.

Within the scope of the invention, there are many possibilities for the type of processing of the determined extent of the measuring section of the rotor blade with the ice and thus also of the extent E of the ice.

For a proposal of the invention, an indicator for ice forming is determined. For one variant of the invention, this takes place taking into account a change signal of the determined extent of the measurement section with the ice. If the extent of the measurement section increases continuously or even exponentially, it can be concluded that increasing ice deposition is taking place. If, on the other hand, the determined extent of the measurement section decreases with the ice, this can be taken as an indicator that ice on the rotor blade is decreasing, which can be done by thawing the same, which then results in a continuous reduction in the extent. However, it is also possible that there is a sudden reduction in the determined extent of the measurement section with the ice. This may indicate that ice has been detached from the rotor blade in one piece.

For a further variant of the invention, the indicator is determined taking into account an amount of the determined extent of the measurement section with the ice.

Finally, for a further variant of the invention, it is possible for the indicator to be determined from an amount of the difference between the determined extent of the measurement section with the ice and a reference value of the extent of the measurement section without ice.

The extent taken into account for the different variants or the difference can be evaluated with an absolute value with regard to a course, an amount of change, a development of change or the speed of change. It is also possible for an extent or difference in extents to be evaluated by comparison with at least one threshold value.

It is possible that the evaluation is dependent on other operating parameters. An operating parameter can be, for example, that an angle of attack of the rotor blade is taken into account. As a result of the adjustment of the rotor blade, there is anyway a changed time span t, which the measuring section of the rotor blade needs without ice in order to pass the measuring axis. In this case, the determined changed extent E must also be converted on the basis of the angle of attack. To name just another non-limiting example of the invention, an operating parameter of the rotor blade to be taken into account can be an elastic deflection of the rotor blade, which is quasi-static or can also be dynamic.

• Für eine Variante wird in Abhängigkeit des Indikators eine Warneinrichtung aktiviert. Bei der Warneinrichtung kann es sich um ein optisches oder akustisches Warnsignal handeln. So kann beispielsweise dem Piloten eines Hubschraubers bei sich an dem Rotorblatt ausbildendem Eis über eine Warnleuchte oder einen Warnton die Ausbildung des Eises zur Kenntnis gebracht werden. Der Fahrer kann dann eine Eisschutzeinrichtung wie beispielsweise eine Heizeinrichtung zum Abtauen des Eises betätigen, eine Veränderung der Höhe zur Verringerung der Temperatur ansteuern, ein Gebiet mit wärmerem Wetter ansteuern oder die Betriebsbedingungen des Rotorblatts verändern, um Eis abzuwerfen oder die Ablagerung des Eises zu verringern. Möglich ist auch, dass der Pilot des Hubschraubers eine Landung des Hubschraubers vornimmt.

Once such an indicator has been determined, it can be further processed and used as follows within the scope of the method according to the invention:

• Depending on the indicator, a warning device is activated for one variant. The warning device can be an optical or acoustic warning signal. For example, when ice is forming on the rotor blade, the pilot of a helicopter can be informed of the formation of the ice via a warning light or a warning tone. The driver can then operate an ice protection device such as a heater to thaw the ice, command a change in altitude to reduce the temperature, an area with would be change weather or alter blade operating conditions to shed ice or reduce ice deposition. It is also possible for the pilot of the helicopter to land the helicopter.

For another variant of the invention, the operating conditions can be changed automatically depending on the indicator. For example, an ice protection device such as a heating device of the rotor blade can be activated automatically.

Within the scope of the invention, the extent of the measurement section with the ice and thus the extent E of the ice on the rotor blade can certainly be determined during normal operation. However, it is also quite possible that the operating conditions are changed to determine the extent of the measurement section with the ice. For example, when the rotor blade device is designed as a turbine, compressor, ventilation system or wind turbine, the speed of the rotor blade can be reduced, which means that the time span can be measured and the extent of the measurement section of the rotor blade can be determined with a higher resolution. Such a reduction in the rotational speed of the rotor blade can also be used advantageously to reduce any deformations or vibrations as a result of the rotation of the rotor blade at high speeds or in a resonance range, so that the measurement accuracy is not impaired as a result.

For a further proposal of the invention, special precautions are taken to ensure that the operation of the light barrier device is not impaired by ice that could build up on the light transmitter and/or the light receiver. It is possible here for ice to be avoided by the fact that the light is emitted by the light transmitter or received by the light receiver in a direction that is opposite to the flow on the rotor blade device. It is also possible for the light transmitter and/or the light receiver to be encapsulated. It is also possible to influence the flow conditions in such a way that water or ice does not reach the light transmitter and/or the light receiver as a result of the oncoming flow. For example, the light emitter or the light receiver can be arranged in a flow-calmed area, or the inflowing fluid is even blown out in the area of the light emitter or light receiver in order to keep moisture away from it. The energy for the outflow of the fluid can also be taken from the inflow. For a special proposal of the invention, however, a de-icing device for the light transmitter and/or the light receiver is operated, which is preferably a heating device for the light transmitter or the light receiver. It is possible that the de-icing device is operated cyclically. The operation of the de-icing device can be dependent on a measured outside temperature. For a special proposal of the invention, when the previously explained indicator indicates that ice has been deposited on the rotor blade, the de-icing device is automatically actuated once or cyclically.

The invention includes embodiments in which the measuring axis remains unchanged while the method according to the invention is being carried out. However, it is also possible for the measuring axis of the light barrier device to be changed relative to the axis of rotation in such a way that the distance between the measuring area and the axis of rotation can be changed. In this case, the distance can be changed in steps or steplessly. It is thus possible for the _extents E ₁ , _{E 2} , _{E 3} , . This allows even more precise detection of the ice deposited on the rotor blade, which can also be used to detect, for example, when ice is not deposited evenly over the longitudinal extent of the rotor blade, but only in partial areas or in the different partial areas with different intensity.

Two light barrier devices are provided for a further embodiment. Each light barrier device can have a transmitter and a receiver. However, it is also possible for the light barrier devices to have a common receiver but two transmitters which then (alternately or permanently) emit light along the measurement axis at different angles to the same receiver. For this proposal of the invention, the rotor blade is moved through the respective measuring axis as a result of the rotation about the axis of rotation with different measuring sections each assigned to a light barrier device and spaced apart from one another along the longitudinal axis of the rotor blade. In this way, the extent of the accumulating ice can be determined at two points along the longitudinal extent of the rotor blade.

A further solution to the problem on which the invention is based is a rotor blade device. The rotor blade device can be used, for example, as a helicopter, air taxi, drone, engine of an aircraft, wind turbine, Be trained power plant, turbine, compressor or ventilation system. The rotor blade device then has the rotor blade rotating about the axis of rotation. When the rotor blade device is configured as a helicopter, the rotor blade can be the at least one main rotor rotating about the axis of rotation oriented in the direction of the vertical axis and/or a tail rotor rotating about a transverse axis of the helicopter. For the configuration of the rotor blade device as an aircraft engine, as a turbine or as a compressor, the rotor blade can be a guide vane. When the rotor blade device is designed as a wind energy installation, the rotor blade is the rotor blade that rotates about the approximately horizontal axis of rotation, which can be changed according to the wind direction.

As explained above, the rotor blade device has a light barrier device with a light transmitter and a light receiver.

According to the invention, the rotor blade device has a control unit. The control unit is equipped with control logic, by means of which a method as explained above can be carried out. Here, a "control" also includes a "regulation".

In a further embodiment of the rotor blade device (particularly when it is configured as a helicopter or as a wind power plant), the rotor blade is rotatably mounted on a stator that projects from a base body and passes through the rotor blade. In this case, the light emitter (or the light receiver) is preferably held on the stator, and the stator may also have a rotor assembly unit on which the light emitter (or the light receiver) can then be held. On the other hand, the light receiver (or in the other case the light transmitter) is held on the base body. The light transmitter and the light receiver are arranged on different sides of the plane of rotation of the rotor blade. In some circumstances, this results in a particularly compact configuration with good integration of the light barrier device into the rotor blade device.

The invention also proposes (particularly when the rotor blade device is designed as a wind turbine) that the light transmitter (or in another case the light receiver) is arranged in the area of a mast carrying the rotor blade, while the other component of the light receiver and the light transmitter is then in the Area of another mast or in the area of a floor platform is arranged. In this case, the mast carrying the rotor blade and the further mast or the ground station are arranged on different sides of the plane of rotation of the rotor blade.

For an embodiment according to the invention, the light transmitter is designed as a laser. A point laser is preferably used in this case. For another embodiment, the light transmitter can also be a line laser. The line cross-section of the emitted light can then impinge on a larger section of the rotor blade and interact with any ice there. In this case, the light receiver can evaluate the line laser beam over the entire cross-section with a single measurement signal, which can result in a kind of averaging and thus, under certain circumstances, an increase in the measurement accuracy. However, it is also possible for several light receivers to be arranged above the line cross-section of the laser light from the line laser, so that any ice along the extent of the rotor blade in the area in which the line laser beam strikes the rotor blade can be detected with different measurement signals.

In principle, the light transmitter and in particular the laser can emit light with any desired wavelength or with at least one wavelength spectrum. For one proposal of the invention, a laser emits light (exclusively with one wavelength or with at least one wavelength range) with a wavelength in the range from 500 nm to 800 nm (e.g. in the range from 550 nm to 750 nm or 600 nm to 700 nm or 620 nm up to 680 nm). Light in this wavelength range is advantageous because it is visible, which can be advantageous when installing or aligning the measuring axis, ie the light transmitter or light receiver. Furthermore, using light in this wavelength range can reduce the risk of injury if the light accidentally hits an eye. In addition, under certain circumstances the extinction coefficient of ice at this wavelength is sufficiently high to shield the laser light from any photodiode used as a light receiver. Since the extinction coefficient of ice and liquid water is very similar over the wavelength, a wavelength with a very high extinction coefficient is not selected so that the laser light can still penetrate any cloud of drops.

It is also possible for a wavelength to be determined by testing under existing icing conditions (in particular LWC or Liquid Water Content and MVD or Medium Volumetric Droplet Diameter) and/or as a function of the distance between the light transmitter and the light receiver.

According to one proposal of the invention, the light receiver is designed as a photodiode.

Within the scope of the invention, there are many possibilities for the evaluation when using the photodiode. For one embodiment, the photodiode is evaluated using a circuit. In the circuit, the photodiode is connected in series with a (ohmic) resistor. In this case, the voltage drop across the resistor can be evaluated as a measurement signal (exclusively or also).

Optionally, for the configuration of the circuit explained above, a capacitance can also be connected in parallel to the line branch with the resistor and the photodiode in the circuit.

For a further proposal, in the rotor blade device the light is sent from the light transmitter in the direction of the light receiver with at least one directional component which is oriented in the direction of the main flow direction.

Advantageous developments of the invention result from the patent claims, the description and the drawings.

The advantages of features and combinations of several features mentioned in the description are merely exemplary and can have an effect alternatively or cumulatively without the advantages necessarily having to be achieved by embodiments according to the invention.

The following applies to the disclosure content - not the scope of protection - of the original application documents and the patent: Further features can be found in the drawings - in particular the illustrated geometries and the relative dimensions of several components to one another as well as their relative arrangement and operative connection. The combination of features of different embodiments of the invention or of features of different patent claims is also possible, deviating from the selected dependencies of the patent claims and is hereby suggested. This also applies to those features that are shown in separate drawings or are mentioned in their description. These features can also be combined with features of different patent claims. Likewise, features listed in the patent claims can be omitted for further embodiments of the invention, but this does not apply to the independent patent claims of the granted patent.

The features mentioned in the patent claims and the description are to be understood with regard to their number in such a way that exactly this number or a larger number than the number mentioned is present without the need for an explicit use of the adverb “at least”. So if, for example, an element is mentioned, this is to be understood in such a way that exactly one element, two elements or more elements are present. These characteristics may be complemented by other characteristics or they may be the only characteristics that make up the product in question.

The reference signs contained in the claims do not limit the scope of the subject-matter protected by the claims. They only serve the purpose of making the claims easier to understand.

character list

• 1 zeigt stark schematisiert ein Rotorblatt einer Rotorblatteinrichtung im Bereich eines Messabschnitts ohne Ablagerung von Eis.
• 2 zeigt eine 1 entsprechende Darstellung, wobei sich hier allerdings in dem Messabschnitt des Rotorblatts Eis gebildet hat.
• 3 zeigt eine als Hubschrauber ausgebildete Rotorblatteinrichtung in einer stark schematisierten Darstellung.
• 4 zeigt eine als Windenergieanlage ausgebildete Rotorblatteinrichtung in einer stark schematisierten Darstellung.
• 5 zeigt den Verfahrensablauf eines erfindungsgemäßen Verfahrens.
• 6 zeigt einen Schaltkreis zur Auswertung des Signals eines Lichtempfängers, der als Photodiode ausgebildet ist.

The invention is further explained and described below with reference to preferred exemplary embodiments illustrated in the figures.

• 1 shows a highly schematic representation of a rotor blade of a rotor blade device in the area of a measurement section without deposits of ice.
• 2 shows one 1 Corresponding representation, although here ice has formed in the measuring section of the rotor blade.
• 3 shows a rotor blade device designed as a helicopter in a highly schematic representation.
• 4 shows a rotor blade device designed as a wind turbine in a highly schematic representation.
• 5 shows the process sequence of a method according to the invention.
• 6 shows a circuit for evaluating the signal of a light receiver, which is designed as a photodiode.

FIGURE DESCRIPTION

1 1 shows a rotor blade 1 in a highly schematic manner. The rotor blade 1 rotates about an axis of rotation 2 at a speed n, which results in a peripheral speed 3 of the rotor blade 1 . The axis of rotation 2 extends vertically to the plane of the drawing 1 . For a simplified view, the rotor blade 1 is flat and also extends with its transverse extent in the plane of the drawing.

Also vertical to the drawing plane according to 1 a measuring axis 4 extends along the measuring axis 4. Light emitted by a light transmitter 5 extends to a light receiver 6. The light transmitter 5 and the light receiver 6 form a light barrier device 7.

As a result of the rotation of the rotor blade 1, the measuring axis 4 passes a measuring section 8 of the rotor blade 1, which in 1 is indicated by dashed lines and extends in the circumferential direction around the axis of rotation 2 . The measuring section 8 is curved in the shape of a circular arc as a result of the rotation about the axis of rotation 2, with this for a sufficient radius R, which is 1 denoted by the reference number 9, can be regarded as straight without this leading to a significant error influence.

1 shows the rotor blade 1 without the formation of ice on the same. In this case, the base body of the rotor blade 1 forms a leading edge 10 and a trailing edge 11. In the area of the measuring section 8, these have a spacing 12 which corresponds to the width B without ice.

kann darauf geschlossen werden, dass sich kein Eis an dem Rotorblatt 1 abgelagert hat.With the rotational movement of the rotor blade 1 , the light is first transmitted from the light transmitter 5 along the measuring axis 4 to the light receiver 6 . If the front edge 10 reaches the area of the measuring axis 4 , the light receiver 6 is shadowed. This shadowing lasts for a period of time t until the measuring axis 4 passes the rear edge 11 . If the time span of the shading of the light receiver 6 is measured and is this time span $$\text{t}=\text{B}/\left(\text{<figure-callout id="2" label="n" filenames="DE102021102659B3\_0006.png,DE102021102659B3\_0007.png" state="{{state}}">n</figure-callout>}2\mathrm{\pi }\text{R}\right)$$

it can be concluded that no ice has been deposited on the rotor blade 1.

2 shows the situation for ice 13 deposited on the rotor blade 1, which in 2 is shown hatched. The deposition of the ice 13 on the rotor blade 1 results in the leading edge 10 and the trailing edge 11 being displaced, with the result that the distance 12 increases. The distance 12 results here from the sum of the width B of the base body of the rotor blade 1 in the area of the measuring section 8 and the extent of the ice E, which leads to the displacement of the leading edge 10 and the trailing edge 11 . The extension E results from the sum of the displacement as a result of the ice 13 in the area of the front edge 10 and the displacement by the ice 13 in the area of the rear edge 11. The increase in the distance 12 has the consequence that the period of shading of the light receiver 6 to a period of time t _E which is determined in the method according to the invention. The extent of the ice E can then be determined from the determined time span t _E as follows: $$\text{E}={\text{<figure-callout id="2" label="n E" filenames="DE102021102659B3\_0006.png,DE102021102659B3\_0007.png" state="{{state}}">n</figure-callout>}}_{\text{E}}\text{2}\mathrm{\pi }\text{R - B}\text{.}$$

3 shows a rotor blade device 14 schematically, here in the form of a helicopter 15 . In contrast, the light receiver 6 is held on a stator 18 which does not rotate with the rotor blade 1, or on a non-rotating structure of the stator 18. The light transmitter 5 and the light receiver 6 are arranged on different sides of the plane of rotation 19 of the rotor blade 1 . However, it is also possible to swap the positions of the light transmitter 5 and the light receiver 6.

As in 3 As can be seen, the measuring axis 4 can also not be oriented parallel to the axis of rotation 2 of the rotor blade, but can be inclined at an angle 20 with respect to the axis of rotation 2 . The angle 20 can be between 0° and 90°, for example 10° to 80° or 20° to 70° or 30° to 60°. In this case, the determined extension E must be converted, taking the angle 20 into account.

4 shows a rotor blade device 14 which is designed as a wind energy installation 21 . There are two light barrier devices 7 here, which and their associated components and sections are distinguished from one another with the added letters a, b. The light transmitters 5a, 5b are held on a mast 22, it also being possible for another embodiment that the light transmitters 5a, 5b are held on a ground station. The light receivers 6a, 6b are held at different heights on a mast 23 on which the rotor blade 1 is rotatably mounted. In this case, the light receivers 6a, 6b are at different heights. The measuring axes _4a , _4b are inclined at different angles and hit the rotor blade 1 at different measuring sections _8a , _8b Measurement sections 8a, 8b are detected. It is also possible for the light transmitters 5a, 5b to be held on the mast 23, while one light receiver 6 or two light receivers 6a, 6b are then held on the mast 22.

5 shows a highly schematic block diagram of a method according to the invention. In a method step 24, the rotational speed n or the peripheral speed 3 of the measuring area 8 is determined. Preferably, in the method step 24 the frequency of the shading of the light receiver 6 is determined and the speed is determined from this frequency.

In a method step 25, a period of time t _E is then determined, which is required for the measuring axis 4 to be able to move from the front edge 10 (without ice or with ice) along the measuring section 8 to the rear edge 11 (without ice or with ice). In a method step 26, an extent of the ice E is then determined from the determined time span t _E . Here (in contrast to the above simplifying formulas) further geometric conditions and operating parameters can be taken into account. For example, it can be taken into account if the rotor blade 1 is not straight in the measuring region 8 but is curved, the measuring section 8 of the rotor blade 1 is pitched, in which case the pitch angle can change during operation of the rotor blade device 14 and/or it can an angle 20 can be taken into account, by which the measuring axis 4 is inclined relative to the axis of rotation 2 .

In a method step 27, an indicator for the ice that is forming is then determined. This can be done on the basis of a change signal of the extent E determined or on the basis of an amount of the extent E determined.

A measure is then initiated in a method step 28 on the basis of the indicator. This can occur, for example, when the indicator exceeds a threshold value, there is a major change in the indicator, or another change in the indicator indicates a need for action. Within the scope of the invention, there are many possibilities for the measure introduced in method step 28 . Thus, by activating a warning device, the operator or pilot can be informed that ice has formed on the rotor blade 1 . It is possible that the operating conditions will change depending on the indicator. For example, a change in the speed of the rotor blade, a change in the angle of attack and the like can take place. It is also possible that a protective device is activated and in particular a heating device of the rotor blade is activated in order to at least partially remove the ice that has formed. It is also possible that the operator is given a signal to deactivate the rotor blade assembly, to land the helicopter or to fly to another area with higher temperatures. For example, if a pilot of a helicopter can be made aware of the icing condition, the pilot can avoid a safety-critical condition of the helicopter sooner than if the pilot would only notice the icing of the rotor blade with a severe degradation in performance of the helicopter without the method according to the invention. On the other hand, the configuration of the method according to the invention makes it possible to avoid a protective device or other measures being taken only when this is really necessary. For example, the operation of a heating device can be avoided if no ice has yet been deposited on the rotor blade. Excessive operation of the heater could reduce a remaining range for the helicopter and degrade energy efficiency. In the event that the method according to the invention is used for a wind turbine, it is not necessary to wait until the ice is detected on the rotor blade, until such a large imbalance or detuning of the natural angular frequency occurs that this can be detected by a corresponding measuring system according to the status of Technology can be recognized and/or until ice has formed on the rotor blade in a quantity that poses a risk to persons and property if it falls or is thrown away.

If the rotor blade 1 is one with a rotated profile, the width B or the distance 12 is determined according to the chord of the profile.

By means of a suitable structure, sampling rates, receiver currents and light sensitivities can be adjusted in such a way that the useful signal is separated from interference signals and the speed of the rotor blade 1 and the layer thickness of the ice that has formed in the area of the leading edge 10 and in the area of the trailing edge 11 can be determined.

It will be clear to a person skilled in the art that the method must be adapted accordingly, in particular with the determination of the rotational speed, if a plurality of rotor blades are distributed over the circumference.

Furthermore, for the person skilled in the art, if the invention is used for a wind turbine, several light transmitters 5 and light receivers 6 should be distributed over the circumference of the mast 23 so that the formation of the ice can also be detected if there is a change in the The axis of rotation 2 of the rotor blade 1 is aligned depending on the wind direction. In this case, too, it can be advantageous if a light transmitter 5 or a light receiver 6 is held on a stator or a structure for the rotatable mounting of the rotor blade 1, since this is then automatically pivoted with the change in the alignment of the axis of rotation 2.

The wavelength of the light, in particular of a laser beam, is preferably selected in such a way that it is scattered or absorbed by the ice, while water droplets in the area of the measuring axis 4 or water on the rotor blade 1 do not have a significant influence on the received light signal.

The extent of the ice is preferably determined with a measurement uncertainty of ±0.1 mm.

When using the ice detection system according to the invention, pilots may be able to fly without an ice protection system even if they are aware of light and short-term icing conditions, for example in order to transport ambulances, rescue the injured or carry out a search mission as a police helicopter. Since the rate of ice growth is comparatively slow under these icing conditions, when ice starts to grow on the rotor blades, which can be detected according to the invention, there is sufficient time to leave the icing conditions. In addition, the weather data is not available in such detail that local and temporal icing conditions can be accurately predicted. For safety reasons, according to the state of the art, an aircraft unprotected against icing conditions usually remains on the ground.

If an ice protection system, in particular a heating device of the rotor blade 1, is present, the ice protection system can be switched on automatically depending on the indicator determined according to the invention. The source of human error is thus avoided. The pilot can then be notified of ice detection and activation of the ice protection system. The pilot may be able to change or deactivate the activation of the ice protection system with an input, since he has a higher priority in the hierarchy than the aircraft and can therefore intervene in the event of a malfunction of the ice detection or ice protection system. Crashes due to a lack of awareness of an icing state of the rotor blade no longer occur for the embodiment according to the invention.

The activation of the ice protection system requires energy input, which leads to increased fuel consumption or reduced performance in the ice protection systems currently in use. An automated shutdown of the ice protection system is also possible when using the method according to the invention.

The advantages described here also apply accordingly to the use of propellers on air taxis.

In the case of a wind turbine, the formation of ice is detected according to the invention. Here, too, an automatic, immediate activation of an ice protection system is made possible. As a result, a reduction in the efficiency of the wind energy plant due to the accumulation of ice is avoided and the wind energy plant can continue to generate the highest possible yield. Since the wind turbines at many locations have to be switched off when ice forms to prevent the ice from being shed, they do not generate any income during the ice-related downtime. A visual inspection is then required, which personnel must carry out on site. The staff then has to look at the system and confirm that it is free of ice, with which the wind turbine can then start up. The method according to the invention can, for example, when the rotor blades rotate slowly at a speed at which ice cannot be shed into critical areas, check whether ice has built up (too large an extent) on the rotor blades and, if necessary, carry out an automatic restart enable. An on-site inspection is therefore not necessary. The wind energy installation can also be started up again as quickly as possible and automatically recognized. In contrast to a so-called characteristic curve method, the system can reliably detect the formation of ice even at low wind speeds. It is also possible that the method according to the invention is used when the rotor blades are not moved by the wind through the laser beam, in which case the rotor blades can then be twisted by motor. In contrast to detectors mounted on the nacelle of the wind turbine, there are no false alarms based on icing reports.

Fans in building ventilation and turbines in the power plant area can be checked for possible icing using the method according to the invention. Here too, to protect the system, de-icing can be switched on or the system can be stopped.

It is possible for the light receiver 6 to be arranged in a cylindrical housing in order to shield the entry of ambient light. It is also possible that the emitted light can contain a carrier frequency in order to provide protection against interference.

However, it is also possible for the rotational axis 2 to be rotated cyclically in the direction of a predetermined measurement axis, in which the light receivers 6 are then aligned with the measurement axis 4 of the light transmitter 5, to monitor whether ice has formed on the rotor blade 1 of the wind turbine . Preferably, the measurement is then carried out for a low speed of the rotor blade 1. If the measurement shows that no ice or ice has deposited to an acceptable extent on the rotor blade 1, then a provision of the Axis of rotation 2 take place in the direction of the flow.

6 shows an example of a circuit 29 with a light receiver 6 designed as a photodiode. A voltage source 31 acts on the photodiode 30 and a resistor 32 in an electrical series circuit. Optionally, the voltage source 31 on the one hand and the electrical branch with the photodiode 30 and the resistor 32 (as in 6 shown) a capacity 33 may be connected in parallel. The voltage drop across the resistor 32 is evaluated using a voltmeter 34 .

The photodiode 30 generates a photocurrent. Using the voltmeter 34, a voltage is measured across the resistor 32, which is proportional to the photocurrent of the photodiode 30, which simplifies the metrological detection.

The photodiode 30 is not only used in no-load operation, so that the voltage is not measured directly at the photodiode 30 . The reason for this is that the measuring devices generally have a high input resistance, so that the charge generated by the photodiode 30 flows away too slowly via the measuring device. An interruption of the light barrier device 7 could not be detected with a direct measurement of the voltage across the photodiode 30 at high peripheral speeds of the rotor blade 1, since the charge then under certain circumstances cannot flow away quickly enough. Instead, the current from the photodiode 30 flows for the switching circuit 29 via a series-connected (preferably ohmic) resistor 32. The resistance of the resistor 32 can be chosen so small that the charge flows off quickly enough and the rotor blade 1 can be passed through the Light barrier device 7 can be detected. However, the resistance of the resistor 32 should not be chosen so small that the voltage drop across the resistor 32 is so small that the voltage to be measured can no longer be sufficiently distinguished from the measurement noise.

It is possible for this purpose to apply a blocking voltage to the photodiode 30, which reduces the capacitance of the photodiode 30 and further reduces the fall time of the signal. This form of operation of the photodiode 30 is also referred to as “photoresistive operation”. If the capacitance 33 is also used for an option, as shown, the capacitance can be used to filter interference voltages induced in the lines.

For one embodiment of the invention, the light transmitter 5, in particular the laser, sends the light against the direction of movement of the helicopter 15 or in the direction of flow when the helicopter 15 is moving, which preferably applies to the main direction of movement in the direction of the longitudinal axis of the helicopter 15. It is also sufficient if at least one component of the direction in which the light is emitted is oriented counter to the direction of movement or in the direction of flow. Such an arrangement of the light transmitter 5 relative to the light receiver 6, such an orientation of the measuring axis 4 and such a transmission direction of the light can ensure that the exit opening or exit optics of the light transmitter 5 does not ice up (so quickly). Icing of the light transmitter 5 would be disadvantageous, since the light would then be scattered by the ice as it exited the light transmitter 5 and would no longer reach the light receiver 6 with sufficient intensity along the measurement axis 4 . On the other hand, the light receiver 6 (in particular the photodiode 30) can still work and be used as a detector even when iced up, since a sufficiently large proportion of the laser light continues to reach the light receiver 6.

However, it is entirely possible for the light transmitter 5 and/or the light receiver 6 to be protected against icing by additional measures.

In principle, a point laser can be used as the light transmitter 5 , in which case the light receiver 6 determines a measurement signal and is arranged on the measurement axis 4 . It is also possible for a line laser to be used, the light of which can then impinge on a plurality of light receivers 6, in particular photodiodes, arranged in a row corresponding to the line of the line laser. In this way, an increase in the measurement accuracy and/or a detection of the ice at several points and/or a measurement of the thickness of the ice layer can be made possible.

Reference List

1

rotor blade

2

axis of rotation

3

peripheral speed

4

measuring axis

5

light transmitter

6

light receiver

7

light barrier device

8th

measurement section

9

radius

10

leading edge

11

trailing edge

12

distance

13

ice cream

14

rotor blade setup

15

helicopter

16

body

17

tail rotor

18

stator

19

plane of rotation

20

angle

21

wind turbine

22

mast

23

mast

24

process step

25

process step

26

process step

27

process step

28

process step

29

circuit

30

photodiode

31

voltage source

32

resistance

33

capacity

34

tension meter

Claims (21)

Method for detecting the formation of ice (13) on a rotating rotor blade (1) with - a rotor blade (1) which rotates about an axis of rotation (2) - a light barrier device (7) which has a light transmitter (5) and a light receiver ( 6), wherein the light transmitter (5) transmits light along a measuring axis (4) in the direction of the light receiver (6), - wherein the measuring axis (4) has at least one directional component which is oriented parallel to the axis of rotation (2), and - the rotor blade (1) is moved with a measuring section (8) through the measuring axis (4) as a result of the rotation about the axis of rotation (2), the method having the following method steps: a) determining the period of time (t _E ) which the Measurement section (8) of the rotor blade (1) with the ice (13) required to pass the measurement axis (4), and b) determining the extent (B+E) of the measurement section (8) of the rotor blade (1) taking into account ba ) the period of time (t _E ) and bb) the speed it of the measuring section (8) of the rotor blade (1). procedure after claim 1 , characterized in that the speed of the measuring area (8) is determined by means of the light barrier device (7) from the frequency with which the measuring section (8) passes the measuring axis (4). Method according to one of the preceding claims, characterized in that the wavelength of the transmitted light is selected such that the light from ice (13) forming on the rotor blade (1) is scattered and/or absorbed to a greater extent than from ice that is not frozen Water on the rotor blade (1) and/or in the air in the area of the measuring axis (4). Method according to one of the preceding claims, characterized in that an indicator for ice (13) forming taking into account a) a change signal of the determined extent (B+E) of the measuring section (8) with the ice (13) and/or b) an amount of the determined extent (B+E) of the measurement section (8) with the ice (13) and/or c) an amount (E) of the difference between the determined extent (B+E) of the measurement section (8) with the ice ( 13) and a reference value of the extension (B) of the measurement section (8) without ice is determined. procedure after claim 4 , characterized in that an indicator for forming ice (13) is determined taking into account an operating parameter of the rotor blade (1). procedure after claim 4 or 5 , characterized in that depending on the indicator a) a warning device is activated and/or b) there is a change in the operating conditions and/or c) a protective device is activated. Method according to one of the preceding claims, characterized in that the operating conditions are changed during a determination of the extension of the measuring section (8) with the ice (13). procedure after claim 7 , characterized in that the speed (n) of the rotor blade (1) is reduced during a determination of the extension of the measuring section (8). Method according to one of the preceding claims, characterized in that a de-icing device of the light transmitter (5) and/or the light receiver (6) is operated. Method according to one of the preceding claims, characterized in that the measuring axis (4) of the light barrier device (7) is changed relative to the axis of rotation (2) in such a way that the distance (9) of the measuring area (8) from the axis of rotation (2) can be changed . Method according to one of the preceding claims, characterized in that two light barrier devices (7a, 7b) are present and the rotor blade (1) as a result of the rotation about the axis of rotation (2) with different ones, each assigned to a light barrier device (7a; 7b) and along the Measuring sections (8a; 8b) arranged spaced apart along the longitudinal axis of the rotor blade (1) are moved through the respective measuring axis (4a; 4b). Rotor blade device (14) in the form of a helicopter (15), air taxi, drone, aircraft engine, wind turbine (21), power plant, turbine, compressor or ventilation system a) a rotor blade (1) which rotates about an axis of rotation (2), b) a light barrier device (7) which has a light transmitter (5) and a light receiver (6), the light transmitter (5) sending light along a measuring axis (4) in the direction of the light receiver (6), c) the measuring axis (4) having at least one directional component which is oriented parallel to the axis of rotation (2), d) the rotor blade (1) is moved with a measuring section (8) through the measuring axis (4) as a result of the rotation about the axis of rotation (2) and e) a control unit with control logic for carrying out the method according to one of the preceding claims. Rotor blade device (14) after claim 12 , in particular in the configuration as a helicopter (15) or as a wind turbine (21), characterized in that a) the rotor blade (1) is mounted on a stator (18) which projects from a base body (16) and passes through the rotor blade (1), b) the light transmitter (5) or the light receiver (6) is held on the stator (18), c) the light receiver (6) or the light transmitter (5) is held on the base body (16), d) the base body ( 16) and the light transmitter (5) or the light receiver (6) are arranged on different sides of a plane of rotation (19) of the rotor blade (1). Rotor blade device (14) after claim 12 in the form of a wind energy installation (21), characterized in that the light transmitter (5) or the light receiver (6) is arranged in the region of a mast (23) carrying the rotor blade (1) and the other component is separated from the light receiver (6) and the Light transmitter (5) is arranged in the area of a further mast (22) or a ground platform, the mast (23) carrying the rotor blade (1) and the further mast (22) or the ground station being on different sides of the plane of rotation (19) of the rotor blade (1) are arranged. Rotor blade device (14) according to one of Claims 12 until 14 , characterized in that the light transmitter (5) is designed as a laser. Rotor blade device (14) after claim 15 , characterized in that the laser is designed as a point laser or line laser. Rotor blade device (14) after claim 15 or 16 , characterized in that the laser emits light with a wavelength in the range from 500 nm to 800 nm. Rotor blade device (14) according to one of Claims 12 until 17 , characterized in that the light receiver (6) is designed as a photodiode (30). Rotor blade device (14) according to one of Claims 12 until 18 , characterized in that the photodiode (30) is evaluated by means of a circuit (29) in which the photodiode (30) is connected in series with a resistor (32), the voltage drop across the resistor (32) being evaluated as the measurement signal . Rotor blade device (14) after claims 19 , characterized in that the resistor (32) and the photodiode (30) has a capacitance (33) connected in parallel. Rotor blade device (14) according to one of Claims 12 until 20 , characterized in that the light is sent from the light transmitter (5) in the direction of the light receiver (6) at least with a directional component which is oriented in the direction of the main flow direction.

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