Optical sensor

Abstract

Optical sensor (100), in particular for a wind turbine, comprising: a light source (110) emitting light (130) into a predetermined monitoring area (150), and a receiving and evaluation unit (120) designed to detect at least one object (140) within the surveillance area (150) based on received light (142) emitted by the light source (110) and remitted by the object (140), wherein the light source (110) is further configured to emit light at at least two different wavelengths, and wherein the receiving and evaluation unit (120) is further configured to determine a respective intensity of the light (142) remitted by the object (140) for a respective one of the at least two wavelengths and to detect at least one predetermined material (160) on the object (140) based on a ratio of at least two intensities at different wavelengths.

Description

[0001] The invention relates to an optical sensor, which is particularly intended for a wind turbine, and to a wind turbine with such an optical sensor.

[0002] Wind turbines in wind power plants are generally exposed to environmental influences and weather conditions. During operation, water, and at low temperatures, ice, can adhere to the rotor blades. This affects and potentially reduces the performance of the wind turbine. In extreme cases, damage can occur.

[0003] If a layer of ice forms on the rotor blades of a wind turbine, this layer of ice can break away from the rotor blades when temperatures rise, for example, and impact the ground in a certain area below the wind turbine. This is known as ice breakage. Such ice breakage poses a significant danger to people and objects located within the area below the wind turbine. Therefore, it is common practice to shut down wind turbines in good time when there is a risk of ice formation.

[0004] Systems are known that use two sensors to protect wind turbines. One of the sensors detects whether there is ice on the rotor blades of a wind turbine, while another sensor monitors the fall zone or danger zone below the wind turbine for people and / or objects. A control system shuts down the wind turbine if both ice is present and a person or object is present in the monitored danger zone. Optical systems that use multiple wavelengths in the infrared range to detect ice are also known.

[0005] A disadvantage of existing systems is that multiple sensors are required to monitor a wind turbine both for ice on the rotor blades and for people or objects below the turbine. Furthermore, it can be difficult for existing systems to reliably assess a detected layer of ice on a wind turbine's rotor blade, for example, with regard to the thickness of the ice layer.

[0006] An object of the invention is to provide an optical sensor and a wind turbine with such a sensor that is capable of simultaneously monitoring rotor blades of a wind turbine with respect to a predetermined foreign material such as ice and a predefined area below the wind turbine with respect to objects and persons.

[0007] This object is achieved by an optical sensor and a wind turbine having the features of the respective independent claims. Advantageous developments of the invention are specified in the subclaims, the description, and the drawings.

[0008] The optical sensor, which is particularly intended for a wind turbine, comprises a light source that emits light into a predetermined monitoring area, and a receiving and evaluation unit that is designed to detect at least one object within the monitoring area based on received light that is emitted by the light source and remitted (in particular reflected) by the object. The light source is further designed to emit light at at least two different wavelengths, while the receiving and evaluation unit is additionally designed to determine a respective intensity of the light remitted by the object for a respective one of the at least two wavelengths and to detect at least one predetermined material on the object based on the ratio of at least two intensities at different wavelengths.

[0009] If the optical sensor is installed on a wind turbine, the at least one object can include both people and objects such as vehicles in a predetermined protective field below the wind turbine, as well as a rotor blade of the wind turbine. The optical sensor is thus preferably mounted on such a wind turbine in such a way that the monitoring area at least temporarily covers both the predetermined protective field below the wind turbine and at least one area on a rotor blade of the wind turbine. The monitoring area can, for example, permanently cover a predefined protective field below the wind turbine, and a rotor blade of the wind turbine can also move through the monitoring area of ​​the sensor during its operation.

[0010] The optical sensor thus has a dual function: on the one hand, it detects the presence of objects in the monitoring area, and on the other hand, it can detect one or more materials on such an object, which could, for example, be foreign materials or foreign bodies on such an object. Such foreign materials include, in particular, water or ice, which could, for example, be present on a wind turbine rotor blade as an object in the monitoring area.

[0011] Since the light source emits at least two different wavelengths and the reflection or remission of the emitted light at these different wavelengths is evaluated accordingly, only a single optical sensor is required for the detection of objects in the monitored area and for the detection of at least one predetermined material, especially foreign material, on such objects. This reduces the costs of the required sensor technology, especially during wind turbine operation.

[0012] Since the at least one material is predetermined, which is in particular water and / or ice, the at least two wavelengths can be determined based on the properties of the material. This is done in such a way that the ratio of the at least two light intensities detected due to the reflection or remission of light at these wavelengths allows the detection of the at least one predetermined material.

[0013] The sensor can be configured for a time-of-flight measurement in a predetermined spatial area surrounding the optical sensor. For example, the sensor can comprise a laser scanner that allows three-dimensional scanning of the monitored area and can be configured, in particular, for distance measurement. For each point in three-dimensional space where an object is detectable, the optical sensor can further detect the presence of the predetermined material.

[0014] The optical sensor can also be a frequency-modulated continuous wave (FMCW) system. For example, an FMCW LIDAR system can enable distance measurement between the object and the sensor with high spatial resolution. Furthermore, such systems enable long ranges with low interference. Furthermore, FMCW optical systems can operate in a near-infrared wavelength range, for example, between 1300 nm and 1800 nm, where the ratio of light remission for water and ice, for example, changes depending on the wavelength, enabling the detection of these materials based on the intensity ratios.

[0015] According to one embodiment, the light source emits the light at at least two discrete, predetermined wavelengths, while the receiving and evaluation unit is further configured to detect light in a wavelength range that includes the at least two discrete wavelengths of the light source. In other words, the receiving and evaluation unit can be configured to receive and evaluate light in a broadband wavelength range that includes the at least two discrete wavelengths at which the light source emits the light. The receiving and evaluation unit can thus comprise an optically broadband detector for which no special technical requirements exist and which can therefore be designed cost-effectively.

[0016] Alternatively, the light source can emit light in a predetermined broad wavelength range, while the receiving and evaluation unit can further be configured to detect light at at least two discrete, predetermined wavelengths that lie within the wavelength range of the light source. In this embodiment, the receiving and evaluation unit comprises a narrowband and, for example, tunable detector that has, for example, filters that are only transmissive in a narrow range around the at least two predetermined wavelengths, while broadband illumination with respect to the wavelength is provided by the light source. As a result, in this embodiment, the demands on the light source are low, while the determination of the at least two discrete, predetermined wavelengths for detecting the predetermined material on an object takes place within the receiving and evaluation unit.

[0017] Furthermore, the at least two discrete, predetermined wavelengths can be selected such that the receiving and evaluation unit is capable of detecting at least two types of the predetermined material or two predetermined materials on the object based on the ratio of the at least two intensities at the at least two wavelengths. For example, the remission of light at the at least two discrete, predetermined wavelengths can be different for the different types of material or different materials, for example, for water and ice.

[0018] The sensor can therefore be designed to detect the light remission of water and ice, which are different types of material. As mentioned above, the ratio of light remission for water and ice changes in the near infrared, for example, between 1300 and 1800 nm, so the ratio of two light intensities within this wavelength range allows the detection of water and ice on an object.

[0019] According to a further embodiment, the receiving and evaluation unit can be further configured to classify an object if the object is detectable in the sensor's monitoring area. In other words, a detected object can be assigned to one of several object classes.

[0020] Such object classes can, for example, include an object class for people, an object class for vehicles, and further object classes for other objects. If the optical sensor is designed for time-of-flight measurement in a predetermined spatial area, e.g., as an appropriately configured laser scanner, as a TOF camera (TOF for English: Time Of Flight), or as an FMCW LIDAR system, the three-dimensional detection of object points enables, for example, an assignment to known object patterns in the sense of object recognition, which can be carried out using the receiving and evaluation unit. Based on the recognition of a predetermined contour and / or dimensions of an object in a predetermined area, an object can be assigned to a specific object class.

[0021] For example, if the object is 5 m long, it is very likely that the object is a vehicle and not a person.

[0022] According to a further embodiment, the optical sensor comprises an optical scanner, in particular a laser scanner.

[0023] The invention further relates to a wind turbine comprising a rotor with multiple rotor blades and an optical sensor, as described above. The optical sensor is mounted on the wind turbine such that the monitoring area of ​​the sensor at least temporarily covers a predetermined area below the rotor. During operation of the wind turbine, at least one of the multiple rotor blades is also located at least temporarily within the monitoring area of ​​the sensor. This enables the sensor to detect at least one predetermined material on at least one of the multiple rotor blades.

[0024] Since the wind turbine includes the optical sensor described above, the statements regarding the optical sensor apply accordingly, particularly with regard to advantages and preferred embodiments. Furthermore, it is understood that all features mentioned herein can be combined with one another, unless explicitly stated otherwise.

[0025] The optical sensor of the wind turbine thus has the dual function described above, which is adapted to the requirements of a wind turbine. On the one hand, the sensor monitors the predetermined area below the rotor of the wind turbine, which can also be referred to as the protective field or protective zone, for the presence of objects such as people and vehicles. On the other hand, the optical sensor is attached to the wind turbine in such a way that at least part of the surface of one of the rotor blades of the wind turbine is at least temporarily visible to the optical sensor, so that the latter can detect a predetermined material such as water and / or ice on this rotor blade. The rotor blade is therefore one of the objects that is visible to the optical sensor within the monitoring zone. The wind turbine therefore only requires a single optical sensor to simultaneously monitor the predetermined area or zone.to monitor the protective field beneath the rotor and to be able to detect a predetermined material such as water and / or ice on at least one of the rotor blades. This reduces the complexity of the sensor technology required for safe operation of the wind turbine.

[0026] According to one embodiment of the wind turbine, the optical sensor is attached to a static element of the wind turbine. The sensor can be mounted, for example, in the region of a rotational axis of the rotor, for example, on a bracket near its bearings. The sensor can be aligned such that the monitoring area of ​​the sensor below the rotor of the wind turbine covers a predetermined area on the ground below the wind turbine.

[0027] Additionally, this embodiment requires that the optical sensor at least partially "sees" at least one rotor blade of the wind turbine, i.e., that the rotor blade is located within the monitoring range of the optical sensor for a predetermined period of time and, for example, roams through it. If the time required for a rotor blade to roam through the monitoring range is recorded, and the dimensions of the monitoring range are known, a so-called "roaming speed" of the rotor blade through the monitoring range can be determined based on the time period, which in turn can allow the rotational speed of the wind turbine's rotor to be determined.

[0028] Alternatively, the optical sensor can be attached to one of the multiple rotor blades. In one embodiment, the optical sensor can be attached to an inner end of one of the multiple rotor blades. The inner end can be located near the axis of rotation of the rotor, so that the monitoring area of ​​the sensor permanently covers, for example, almost one side of a rotor blade. Since the optical sensor in this embodiment rotates with the rotor blade to which it is attached, the optical sensor or its monitoring area sweeps over a predetermined protective field on the ground below the wind turbine within a certain period of time during the rotation of the rotor. This protective field can be defined by the range of the optical sensor, which defines the boundary or maximum distance of an object for the monitoring area.

[0029] The predetermined protective field beneath the rotor of the wind turbine can thus be defined by superimposing the monitoring area of ​​the sensor as it rotates together with the rotor blade and a plane in the area of ​​the ground below the wind turbine. In other words, the protective field can be defined by the field of view of the optical sensor, which determines its monitoring area, sweeping over a specific area on the ground as the sensor rotates together with the rotor.

[0030] In an alternative embodiment, the optical sensor is attached to an outer end of one of the plurality of rotor blades. The outer end of the rotor blade is located at its tip, which is at the greatest distance from the rotor's axis of rotation. However, this embodiment requires that at least a portion of the rotor blade is visible to the sensor, even when attached to the outer end of this rotor blade, and that the sensor is oriented such that it can monitor a predetermined protective field below the rotor for a predetermined period of time. Attaching the optical sensor to an outer end of the rotor blade has the advantage that a short range of the optical sensor is required due to a relatively short distance to the ground when the rotor blade is at its lowest position above the ground.The range of the optical sensor can therefore be shorter in this embodiment than in the embodiment in which the optical sensor is attached to an inner end of one of the plurality of rotor blades.

[0031] The sensor can further be configured to detect the remission of light for water and ice. The at least two wavelengths at which the optical sensor can emit or detect light are thus selected in this embodiment such that the remission of light for water and ice differs at these predetermined wavelengths. This allows water and ice to be detected based on the intensity ratio at these selected wavelengths.

[0032] The optical sensor can further be designed to determine the thickness of an ice layer on one of the multiple rotor blades, taking into account a reference measurement. The reference measurement can, for example, be carried out under conditions which ensure that no ice is present on any of the rotor blades of the wind turbine. Depending on the thickness of the ice layer, the optical sensor can further emit a warning signal which can be taken into account during operation of the wind turbine. Alternatively, monitoring of the area beneath the wind turbine for the presence of objects can only be activated when the thickness of the ice layer on one of the rotor blades exceeds a predetermined value. During a reference measurement without ice, the sensor measures the distances to the rotor blade, for example, and then has a reference value on the basis of which it can measure the current layer thickness.

[0033] A respective optical sensor, as described above, can furthermore be provided on several, preferably on all, rotor blades of the wind turbine. Using several optical sensors on respective rotor blades, the reliability with which the at least one predetermined material, in particular ice, can be detected on the rotor blades can be improved. Furthermore, the predetermined area beneath the wind turbine can be monitored more reliably than when using an optical sensor on only one rotor blade, since the predetermined area is scanned more frequently or at a higher frequency by the optical sensors. Conversely, the time interval in which no sensor covers or scans the predetermined area is shorter when using several sensors on respective rotor blades than when using a sensor on only one rotor blade.

[0034] The invention is described below by way of example using an advantageous embodiment with reference to the accompanying figures. They show, schematically: Fig. 1 an optical sensor according to the invention, Fig. 2 a wind turbine according to the invention with the sensor of Fig. 1 and Fig. 3A and Fig. 3B two further embodiments in which the optical sensor of Fig. 1 is attached to a rotor blade of a wind turbine in a different way.

[0035] Fig. 1 shows a schematic representation of an optical sensor 100, which comprises a light source 110 and a receiving and evaluation unit 120. The receiving and evaluation unit 120 in turn comprises a receiving section 122, which is designed to detect incident light and convert it into a corresponding electrical signal, and an evaluation section 124. The evaluation section 124 is provided to output a control signal 126 for controlling the light source 110. Furthermore, the evaluation section 124 outputs an output signal 128 of the optical sensor 100.

[0036] The light source 110 emits light in the form of a laser beam 130 into the environment of the optical sensor 100. The emitted light can be remitted or reflected by an object 140, so that a remitted or reflected portion of the laser beam 130 emitted by the light source 110 strikes the receiving part 122 of the receiving and evaluation unit 120 as received light 142.

[0037] The optical sensor 100 is also assigned a predetermined monitoring area 150, the boundaries 152 of which are schematically indicated by dashed lines. The light source 110 emits light into the predetermined monitoring area 150 by changing the direction of the laser beam 130, as indicated by the arrow 154. Due to the deflection of the laser beam 130, it sweeps over the predetermined monitoring area 150, from which the receiving unit 122 receives the remitted or reflected light 142. The monitoring area 150 is thus defined by the spatial region into which the light source 110 emits the laser beam 130 and from which the receiving part 122 of the receiving and evaluation unit 120 can simultaneously receive the remitted or reflected light 142.The predetermined monitoring area 150 is limited in the viewing direction of the optical sensor 100 by the range of the light source 110, as indicated schematically by the arrow 156.

[0038] The optical sensor 100 is provided, by means of the receiving and evaluation unit 120, to detect objects, such as the object 140, within the monitored area 150 based on the received light 142 emitted by the light source 110 and remitted or reflected by the object 140. Furthermore, the light source 110 is provided to emit the light or the laser beam 130 at at least two different wavelengths. The receiving and evaluation unit 120 is correspondingly provided to determine the intensity of the remitted or reflected light 142 for each of the at least two wavelengths. Based on the ratio of at least two intensities of the remitted or reflected light at the at least two different wavelengths, the receiving and evaluation unit 120 can detect at least one predetermined material or foreign material 160 on the object 140.

[0039] To detect the at least one material or foreign material 160 on the object 140, the at least two wavelengths at which the light source 110 emits light in the form of the laser beam 130 are selected such that the remission or reflection of light at the foreign material 160 whose detection is desired is different. The material 160 then has a known remission ratio at the at least two wavelengths.

[0040] If the foreign material 160 that is to be detected by the sensor is, for example, ice, i.e., if a layer of ice on the object 140 is to be detected, wavelengths in the near infrared between 1300 nm and 1800 nm are suitable for detecting ice, since in this wavelength range the remission ratio, for example between water and ice, changes depending on the wavelength. Based on the evaluation of the intensity differences, which are determined by the receiving and evaluation unit 120 at the at least two wavelengths, the optical sensor 100 can not only detect the presence of an object 140 within the monitored area 150 and determine its spatial position, but can also detect the foreign material 160, for example, ice, on the object 140.

[0041] The optical sensor 100 operates according to the principle of a laser scanner. Furthermore, the optical sensor 100 can be configured, for example, either as a TOF camera (Time of Flight), which performs time-of-flight measurements, or as a frequency-modulated continuous wave (FMCW) LIDAR system. Such variants of the optical sensor 100 allow distance measurement in a predetermined three-dimensional spatial area, i.e., in the monitoring area 150 of the optical sensor 100.

[0042] By comparing with a reference measurement, it is further possible to determine the thickness of the foreign material 160 on the object 140, for example, the thickness of a layer of ice. The reference measurement is performed under conditions that ensure that no foreign material 160 is present on the object 140. If it is also known that the object 140 is in the same position when the foreign material 160 is present as it was during the reference measurement, the thickness of the foreign material 160 can be determined from a measurement using a TOF camera or an FMCW LIDAR system in that such a measurement determines the spatial position or three-dimensional position of the surface of the foreign material 160 facing the optical sensor 100.Since the reference measurement provides the spatial position of the corresponding surface of the object 140 without the foreign material 160, the thickness of the foreign material 160 on the object 140 can be determined by comparing the two measurements.

[0043] In Fig. Figure 2 schematically illustrates a wind turbine 200 to which an optical sensor 100 is attached, as described above. The wind turbine 200 includes a rotor 210 with rotor blades 212 mounted for rotation on a rotor shaft 214.

[0044] The optical sensor 100 operates according to the principle of a laser scanner. It periodically scans the monitoring area 150, for example, by deflecting the laser beam 130 emitted by the light source 110. The monitoring area 150 of the optical sensor 100 is thus defined by controlling the deflection of the laser beam 130 such that it covers the desired monitoring area 150.

[0045] The optical sensor 100 is attached to a holder 216 as part of the wind turbine 200, which is constructed in such a way that the optical sensor 100 or the monitoring area 150 associated with the optical sensor 100 is always oriented in the same downward direction towards the ground below the wind turbine 200 or the rotor 210. During operation of the wind turbine 200 with the rotating rotor 210, the optical sensor 100 therefore rotates in the embodiment of Fig. 2 does not move with the rotor 210, so that the monitoring area 150 of the sensor 100 is to be regarded as stationary and defines a protective field 220 below the rotor 210 of the wind turbine 200.

[0046] As in connection with Fig. 1, the sensor 100 is designed to detect objects 140 within the monitoring area 150 or the protective field 220 below the rotor 210. In Fig. 2, a person 230 and a vehicle 232 are shown as examples of objects 140 located on the ground below the wind turbine 200 within the protective field 220. Furthermore, the rotor blades 212 also represent objects 140 that are visible or detectable by the sensor 100 as soon as a respective one of the rotor blades 212 is located within the monitoring area 150 during a rotation of the rotor 210. During the rotation of the rotor 210, the respective rotor blade 212 thus traverses the monitoring area 150 of the sensor 100 for a specific period of time determined by the rotational speed of the rotor 210. During this period, an area or section 240 of the respective rotor blade 212 is located within the monitoring area 150 of the sensor 100.

[0047] Since the sensor 100 emits at least two wavelengths in the range between 1300 nm and 1800 nm, the sensor 100 is able to detect not only the presence of the rotor blade 212 within the monitoring area 150, but also the presence and thickness of a layer of foreign material 160 (cf. Fig. 1) such as ice on the rotor blade 212. The optical sensor 100 can therefore detect a layer of ice on the rotor blade 212 in addition to the presence of objects 140 within the monitoring area.

[0048] As explained above, the optical sensor 100 can also determine the thickness of such an ice layer on the rotor blade 212 based on a reference measurement. For this purpose, a reference measurement is performed under conditions that ensure that no ice layer is present on the rotor blades 212. Such conditions can be determined, for example, based on the air humidity, the air temperature, and the air pressure if these variables are detected by an additional sensor.

[0049] Monitoring of the protective field 220 below the rotor 210 of the wind turbine 200 with respect to the presence of at least one object 140 can, for example, also be activated only when the foreign material 160, which is in particular ice, is detected on at least one of the rotor blades 212. Furthermore, even if ice is detected on one of the rotor blades 212, monitoring of the protective field 220 can, for example, only be activated when the thickness of the ice layer exceeds a predetermined value.

[0050] In addition, the time period during which one of the rotor blades 212 passes through the monitoring area 150 of the sensor 100 and is thus visible to the optical sensor 100 can be measured. If the dimensions of the monitoring area 150 of the optical sensor 100 are known, a so-called "sweeping speed" of the rotor blade 212 through the monitoring area 150 and, consequently, the rotational speed of the rotor 210 can be determined.

[0051] Based on the determined rotational speed of the rotor 210 and the thickness of the foreign material 160 or the ice layer on the rotor blades 212, the size of the protective field 220 can also be adjusted. For example, at a high rotational speed of the rotor 210, a larger protective field 220 can be set than at low rotational speeds of the rotor 210. Likewise, the protective field 220 can be enlarged if a certain thickness of the ice layer on one of the rotor blades 212 is exceeded. The size of the protective field 220 is adjusted by changing the spatial area covered by the laser beam 130 (see Fig. 1) scans.

[0052] If the optical sensor 100 is configured as a TOF camera or as an FMCW LIDAR system, a three-dimensional scanning of objects 140 within the monitoring area 150 is possible using the optical sensor 100. Based on the three-dimensional measurement points of the optical sensor 100, which can be assigned to respective objects 140, the optical sensor 100 is further capable of classifying the objects 140. The detected objects 140 can thus be assigned to specific object classes, for example, based on predefined contours or predefined ranges for their dimensions, such as a "person" object class or a "vehicle" object class. In other words, the optical sensor 100 is configured to distinguish, for example, between the person 230 and the vehicle 232 in the detected objects 140 and to assign them to corresponding object classes.

[0053] The operation of the wind turbine 200 is further controlled depending on the presence or thickness of the ice layer on the rotor blades 212. If icing of the rotor blades 212 is detected and the thickness of the ice layer exceeds a predetermined value, the wind turbine 200 can be shut down to prevent endangering persons 230 and other objects 140 within the protective field 220 due to a so-called ice break. During such an ice break, the ice layer or ice mass detaches from the rotor blades 212, causing pieces of ice within the protective field 220 to fall to the ground, thereby posing a danger to persons 230 and other objects 140 within the protective field 220.

[0054] However, if only a small amount of ice or a thin layer of ice is detected on the rotor blades 212 and no persons 230 are within the protective field 220, the wind turbine 200 can continue to operate, even if, for example, a vehicle 232 is within the protective field 220. In such a case, no or only minor damage can be expected from falling pieces of ice. However, if a person 230 is detected within the protective field 220, the wind turbine 220 will be shut down even with a thin layer of ice, since even small pieces of ice pose a danger to the person 230 when they fall. The decision to continue operating the wind turbine 200 therefore depends, if necessary, on the thickness of the detected layer of ice or the detected mass of ice and on the classification of the objects 140 within the protective field 220.

[0055] In Fig. 3, alternative embodiments for attaching the optical sensor 100 to the wind turbine 200 are schematically shown. In the two embodiments of Fig. 3A and Fig. 3B, the optical sensor 100 is attached to one of the rotor blades 212, so that the optical sensor 100 rotates together with the rotor 210 about its axis of rotation 215 during operation of the wind turbine 200.

[0056] The Fig. 3A and Fig. 3B are to be understood as perspective views of the rotor blade area. In each illustration, the rotational axis 215 points diagonally from the right behind the plane of the figure to the left in front of the plane of the figure. The optical sensor 100 is designed as a scanner, with its scanning plane extending diagonally to the left in the same direction as the rotational axis 215. The scanning direction is indicated by the double arrow 222. The dashed lines 223 in the Fig. 3A and Fig. 3B are therefore directed diagonally forwards from the plane of the figure, while the dashed line 224 in the Fig. 3B is directed obliquely backward. The dashed lines 223 and 224 lie in the respective scanning plane of the optical sensor 100, which is designed as a scanner and rotates together with the rotor blade 212 about the rotation axis 215 when the rotor 210 rotates.

[0057] Due to the arrangement of the optical sensor 100 designed as a scanner on the rotating rotor blade 212, the scanning plane rotates in the arrangements of the Fig. 3A and B with the rotor 210. The rotor rotation therefore automatically causes the protective field to be swept below the rotor blade 212, in contrast to the arrangement of the Fig. 2 with fixed sensor 100. There, an additional pivoting of the scanning plane must be realized to cover the monitoring area 150 and thus the protective field 220.

[0058] In the embodiment of Fig. 3A, the optical sensor 100 is mounted on an inner end of the rotor blade 212 near the rotor shaft 214 or near the rotational axis 215 of the rotor 210. The monitoring area 150 of the optical sensor 150 therefore comprises an outer surface of the rotor blade 212, to which the optical sensor 100 is mounted. The rear surface of the rotor cannot be detected here, unless, for example, another sensor is provided there. When the rotor 210 rotates, the monitoring area 150 of the optical sensor 100 periodically scans the ground below the wind turbine 200 for a respective predetermined period of time. The protective field 220 (cf. Fig. 2) below the rotor 210 is thus determined in this embodiment by the range of the optical sensor 100 during the periodic sweep of the ground by the monitoring area 150.

[0059] In the embodiment of Fig. 3B, the optical sensor 100 is mounted on an outer end of the rotor blade 212. This outer end of the rotor blade 212 is located at a tip of the rotor blade 212, which is the greatest distance from the rotor shaft 214 or the rotation axis 215. Also in the embodiment of Fig. 3B, at least a portion of the rotor blade 212 is visible to the optical sensor 100 to enable the above-described monitoring of the rotor blade 212 for ice, as illustrated by the dashed lines.

[0060] In the embodiment of Fig. 3B, the optical sensor 100 or its monitoring area 150 is additionally directed towards the ground, ie away from the rotor blade 212, so that the monitoring area 150 of the optical sensor 100 is aligned in the same way as in the embodiment of Fig. 3A periodically sweeps over the ground below the rotor 210 and thereby defines the protective field 220. The embodiment of Fig. 3B has the advantage that a shorter range of the optical sensor 100 than in the embodiment of Fig. 3A is necessary because the optical sensor 100 is located closer to the ground during operation of the wind turbine 200 when the monitoring area 150 of the optical sensor 100 sweeps over the ground. Furthermore, with a corresponding arrangement or a correspondingly extended scanning plane (for example, up to the back of the rotor blade), objects on the back of the rotor blade 212 can also be detected in the embodiment of Fig. 3B due to the attachment of the optical sensor 100 at the tip of the rotor blade 212, while such objects are not visible for the embodiment of Fig. 3A (if only one sensor is present) are not visible. List of reference symbols 100 optical sensor 110 Light source 120 reception and evaluation unit 122 Receiver 124 Evaluation section 126 control signal 128 output signal 130 emitted light or laser beam 140 objects 142 remitted or reflected light 150 surveillance area 152 Boundary of the surveillance area 154 Shift of the laser beam 156 Range of the optical sensor 200 wind turbines 210 Rotor 212 rotor blade 214 Rotor shaft 215 axis of rotation 216 Bracket for the optical sensor 220 protective field 222 Scan direction 223, 224 dashed lines to clarify the orientation of the scan plane 230 people 232 vehicles 240 area visible to the optical sensor on the rotor blade

Claims

[1] Optical sensor (100), in particular for a wind turbine, comprising: a light source (110) emitting light (130) into a predetermined monitoring area (150), and a receiving and evaluation unit (120) designed to detect at least one object (140) within the surveillance area (150) based on received light (142) emitted by the light source (110) and remitted by the object (140), wherein the light source (110) is further configured to emit light at at least two different wavelengths, and wherein the receiving and evaluation unit (120) is further configured to determine a respective intensity of the light (142) remitted by the object (140) for a respective one of the at least two wavelengths and to detect at least one predetermined material (160) on the object (140) based on a ratio of at least two intensities at different wavelengths. [2] Optical sensor (100) according to claim 1, wherein the light source (110) emits the light (130) at at least two discrete, predetermined wavelengths, and the receiving and evaluation unit (120) is further configured to detect light (142) in a wavelength range comprising the at least two discrete wavelengths of the light source (110). [3] Optical sensor (100) according to claim 1, wherein the light source (110) emits the light (130) in a wavelength range, and the receiving and evaluation unit (120) is further configured to detect light (142) at at least two discrete, predetermined wavelengths that lie within the wavelength range of the light source (110). [4] Optical sensor (100) according to claim 2 or 3, wherein the at least two discrete, predetermined wavelengths are selected such that the receiving and evaluation unit (120) is capable of detecting at least two types of the predetermined material (160) on the object (140) based on the ratio of the at least two intensities at the at least two wavelengths. [5] The optical sensor (100) of claim 4, wherein the sensor (100) is configured to be capable of detecting the remission of light with water and ice as the different types of the material (160). [6] Optical sensor (100) according to one of claims 1 to 5, wherein the receiving and evaluation unit (120) is further configured to classify an object (140) if the object (140) is detectable in the monitoring area (150) of the sensor (100). [7] Optical sensor (100) according to one of claims 1 to 6, wherein the optical sensor (100) comprises an optical scanner, preferably a laser scanner, which is designed in particular for distance measurement. [8] Wind turbine (200), comprising: a rotor (210) with a plurality of rotor blades (212), an optical sensor (100) according to one of claims 1 to 7, which is mounted on the wind turbine (200) in such a way that the monitoring area (150) of the sensor (100) at least temporarily covers a predetermined area below the rotor (210), wherein during operation of the wind turbine (200) at least one of the plurality of rotor blades (212) is at least temporarily located in the monitoring area (150) of the sensor (100) and the sensor (100) is thereby able to detect at least one predetermined material (160) on the at least one of the plurality of rotor blades (212). [9] Wind turbine (200) according to claim 8, wherein the optical sensor (100) is attached to a static element (214) of the wind turbine (200). [10] Wind turbine (200) according to claim 8, wherein the optical sensor (100) is mounted on one of the plurality of rotor blades (212). [11] Wind turbine (200) according to claim 10, wherein the optical sensor (100) is mounted on an inner end of one of the plurality of rotor blades (212). [12] Wind turbine (200) according to claim 10, wherein the optical sensor (100) is mounted on an outer end of one of the plurality of rotor blades (212). [13] Wind turbine (200) according to one of claims 8 to 12, wherein the sensor (100) is designed to be able to detect the remission of light for water and ice. [14] Wind turbine (200) according to claim 13, wherein the optical sensor (100) is further configured to determine a thickness of an ice layer on one of the plurality of rotor blades (212) taking into account a reference measurement. [15] Wind turbine (200) according to one of claims 8 to 14, wherein an optical sensor (100) according to one of claims 1 to 7 is provided on several, preferably all, rotor blades (212).

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