Method for controlling the flight path of an aircraft when flying over a mirror surface

Abstract

Method for controlling a flight path of a controllable aircraft (7) during a flyover of a mirror surface (5) of a reflector (3), preferably a reflector (3) of a heliostat (1) of a solar tower power plant, comprising the following steps: a) Providing the controllable aircraft (7) which has a camera (9) and a stationary marker (11) with a predetermined position which is reflected by the mirror surface (5) of the reflector (3), b) Taking an image of the mirror surface (5) of the reflector (3) using the camera (9) at a position of the controllable aircraft (7) above the reflector (3), c) Evaluating the image and determining a reflection (13) of the marker (11) on the mirror surface (5) in the image, d) Estimating the position of the reflection (13) of the marker (11) on the mirror surface (5), wherein a navigation vector (16) extending from the estimated position of the reflection (13) of the marker (11) on the mirror surface (5) and the position of the controllable aircraft (7) is estimated, and e) Steering the controllable aircraft (7) to a new position of the controllable aircraft (7) by specifying a velocity vector in the direction of the new position, wherein the velocity vector has velocity vector components (20) that are orthogonal to the navigation vector (16) and lie in a navigation plane (19) that is orthogonal to the navigation vector (16), or by specifying a waypoint at the new position, wherein the specified waypoint lies in a navigation plane (19) that is orthogonal to the navigation vector (16), or is specified with respect to the navigation plane (19).

Description

[0001] The present invention relates to a method for controlling the flight path of an aircraft during a flyover of a mirror surface, preferably via a heliostat.

[0002] Heliostats with one or more mirror surfaces can, for example, be part of a solar thermal tower power plant. For optimized operation of such a solar thermal tower power plant, heliostats must be calibrated to ensure precise tracking of the sun. Calibration refers to the adjustment of model parameters to several calibration points. A calibration point is defined as a measurement of the current actual orientation (azimuth, elevation) of the normal vector onto a mirror surface of a heliostat reflector, together with the target orientation. From this, correction values ​​for a specific heliostat position are determined and stored. These can be used, for example, in controlling the heliostat. To determine calibration points, it is known to fly over the heliostats using a controllable aircraft and capture and analyze images of the heliostats.

[0003] From DE 10 2021 133 719 A1 of the applicant, it is known to use a light source as a marker and that a flying device is moved along a predetermined flight pattern to take a large number of images of the heliostats. From the images, a virtual target is then determined by means of the reflections of the marker on the heliostat contained in the images, whereby a target vector is then determined for each heliostat to be measured based on the focal point on the virtual target.

[0004] Since a large number of images need to be evaluated to determine a virtual target, the images are usually evaluated afterwards, a process that is comparatively lengthy and complex.

[0005] A predetermined flight route or pattern has the disadvantage that a large number of images must be captured and analyzed, and no adjustments can be made in cases where the marker's reflection is not visible or insufficiently visible in an image. Furthermore, longer flight paths result, leading to a longer procedure duration.

[0006] Furthermore, determining an accurate slope deviation map or an averaged normal vector requires a sufficient information density of point measurements distributed as evenly as possible across the mirror surface. However, this is not readily achievable using a predetermined flight path, as adjusting the flight path to capture reflections from a marker at specific points on the mirror surface is not possible. MITSCHELL, Rebecca A.; ZHU, Guangdong: A non-intrusive optical (NIO) approach to characterize heliostats in utility-scale power tower plants: methodology and in-situ validation. In: Solar energy, Vol. 209, 2020, pp. 431–445. - ISSN 0038-092X; MITSCHELL, Rebecca A.; ZHU, Guangdong: A non-intrusive optical (NIO) approach to characterize heliostats in utility-scale power tower plants: sensitivity study. In: Solar energy, Vol. 207, 2020, pp. 450-457. - ISSN 0038-092X; and FARRELL, Tucker [et al.[A non-intrusive optical approach to characterize heliostats in utility-scale power tower plants: Flight path generation / optimization of unmanned aerial systems. In: Solar energy, Vol. 225, 2021, pp. 784-801. - ISSN 0038-092X] discloses a method for measuring individual heliostats of a CPS power plant (“Concentrating solar power”) or a field with a plurality of heliostats using a controllable aircraft equipped with a camera and a stationary marker with a predetermined position, which is reflected by the mirror surface of the reflector, wherein an image of the mirror surface of the reflector is captured by the camera at a position of the controllable aircraft above the reflector, and the image is evaluated and a reflection of the marker on the mirror surface in the image is determined. DE 10 2015 217 086 A1 of the applicant discloses a similar method.

[0007] It is therefore an object of the present invention to provide an improved method for controlling an aircraft during a flyover of a mirror surface, which in particular enables autonomous control of the flight route.

[0008] The problem underlying the invention is solved by methods according to claims 1, 2 or 3.

[0009] The inventive method for controlling a flight path of a controllable aircraft during a flyover of a mirror surface of a reflector, preferably a reflector of a heliostat of a solar tower power plant, provides the following steps: a) Providing a controllable aircraft equipped with a camera and a stationary marker with a predetermined position, which is reflected by the mirror surface of the reflector, b) Taking an image of the reflector's mirror surface using the camera at a position of the controllable aircraft above the reflector, c) Evaluating the image and determining a reflection of the marker on the mirror surface in the image, d) Estimating the position of the marker's reflection on the mirror surface, wherein, based on the estimated position of the marker's reflection on the mirror surface and the position of the controllable aircraft, a navigation vector extending from the estimated position of the marker's reflection on the mirror surface to the camera is estimated, and e) Steering the controllable aircraft to a new position of the controllable aircraft by specifying a velocity vector in the direction of the new position, wherein the velocity vector has velocity vector components orthogonal to the navigation vector which lie in a navigation plane which is orthogonal to the navigation vector, or by specifying a waypoint at the new position, wherein the specified waypoint lies in a navigation plane which is orthogonal to the navigation vector or is specified with respect to the navigation plane.

[0010] The position of the controllable aircraft can be determined, for example, via the aircraft's control system or via one or more sensors, such as a GPS sensor. The position of the controllable aircraft can, for example, correspond to the aircraft's center of gravity or the position of a sensor.

[0011] Since the camera's position on the controllable aircraft is known or can be determined, the position of the controllable aircraft can be used in step d) to calculate the camera's position. At large distances from a mirror surface, such as 10 m or more, the camera's distance from the determined position of the aircraft, which is in the centimeter range, is negligibly small, so the position of the controllable aircraft can also be used without conversion.

[0012] The velocity vector components in step e), which are orthogonal to the navigation vector, cause the marker's reflection on the mirror surface, as observed by the camera, to "move," allowing the reflection to be moved, for example, towards a desired point on the mirror surface. This also allows for a kind of scanning of the mirror surface, which, with further calculations or image analysis, enables the determination of a slope error map. When controlling the aircraft by specifying a velocity vector, the aircraft's new position does not necessarily have to be a predetermined position. The aircraft's new position can also result from a predetermined time, i.e., the new position is the position the aircraft reaches after the specified time following the velocity vector.

[0013] Using the velocity vector with velocity vector components orthogonal to the navigation vector and lying in the navigation plane, or the specified waypoint lying in the navigation plane, the aircraft can be controlled in a simple way, since the control specifications are in a form that is easy for the aircraft to implement.

[0014] The navigation plane can, in particular, pass through a point on the aircraft, for example, the point corresponding to the previously described position of the aircraft. If the waypoint does not involve a change in the aircraft's distance from the mirror surface, the waypoint lies within the navigation plane. For a flight route that involves a change in the aircraft's distance from the mirror surface, the waypoint is specified with respect to the navigation plane, for example, in a plane parallel to the navigation plane.

[0015] In a second variant, the inventive method for controlling a flight path of a controllable aircraft during a flyover of a mirror surface of a reflector, preferably a reflector of a heliostat of a solar tower power plant, provides the following steps: a) Providing a controllable aircraft having a marker and a stationary camera with a predetermined position directed at the mirror surface of the reflector, b) Taking an image of the mirror surface of the reflector using the camera, wherein the controllable aircraft is positioned above the reflector, c) Evaluating the image and determining a reflection of the marker on the mirror surface in the image, d) Estimating the position of the marker's reflection on the mirror surface, wherein, based on the estimated position of the marker's reflection on the mirror surface and the position of the controllable aircraft, a navigation vector extending from the estimated position of the marker's reflection on the mirror surface to the marker is estimated, and e) Steering the controllable aircraft to a new position of the controllable aircraft by specifying a velocity vector in the direction of the new position, wherein the velocity vector has velocity vector components orthogonal to the navigation vector which lie in a navigation plane which is orthogonal to the navigation vector, or by specifying a waypoint at the new position, wherein the specified waypoint lies in a navigation plane which is orthogonal to the navigation vector, or is specified with respect to the navigation plane.

[0016] The position of the controllable aircraft can be determined, for example, via the aircraft's control system or via one or more sensors, such as a GPS sensor. The position of the controllable aircraft can, for example, correspond to the aircraft's center of gravity or the position of a sensor.

[0017] Since the position of the markers on the controllable aircraft is known or can be determined, the position of the controllable aircraft can be used in step d) to calculate the position of the markers. At large distances from a mirror surface, such as 10 m or more, the distance of the markers from the determined position of the aircraft, which is in the centimeter range, is negligibly small, so the position of the controllable aircraft can also be used without conversion.

[0018] The velocity vector components in step e), which are orthogonal to the navigation vector, cause the marker's reflection on the mirror surface, as observed by the camera, to "move," allowing the reflection to be moved, for example, towards a desired point on the mirror surface. This also enables a kind of scanning of the mirror surface, which, with further calculations or image analysis, allows for the determination of a slope error map. When controlling the aircraft by specifying a velocity vector, the aircraft's new position does not necessarily have to be a predetermined position. The aircraft's new position can also result from a predetermined time, i.e., the new position is the position the aircraft reaches after the specified time following the velocity vector.

[0019] Using the velocity vector with velocity vector components orthogonal to the navigation vector and lying in the navigation plane, or the specified waypoint lying in the navigation plane, the aircraft can be controlled in a simple way, since the control specifications are in a form that is easy for the aircraft to implement.

[0020] The navigation plane can, in particular, pass through a point on the aircraft, for example, the point corresponding to the previously described position of the aircraft. If the waypoint does not involve a change in the aircraft's distance from the mirror surface, the waypoint lies within the navigation plane. For a flight route that involves a change in the aircraft's distance from the mirror surface, the waypoint is specified with respect to the navigation plane, for example, in a plane parallel to the navigation plane.

[0021] In a third variant, the inventive method for controlling a flight path of a controllable aircraft during a flyover of a mirror surface of a reflector, preferably a reflector of a heliostat of a solar tower power plant, provides the following steps: a) Providing a controllable aircraft comprising a camera and a marker, wherein the marker and the camera are each arranged at a predetermined position on the controllable aircraft, b) Taking an image of the reflector's mirror surface using the camera at a position of the controllable aircraft above the reflector, c) Evaluating the image and determining a reflection of the marker on the mirror surface in the image, d) Estimating the position of the marker's reflection on the mirror surface, wherein, based on the position of the marker's reflection on the mirror surface and the position of the controllable aircraft, a navigation vector is estimated which extends from the estimated position of the marker's reflection on the mirror surface to a predetermined point on the aircraft, and e) Steering the controllable aircraft to a new position of the controllable aircraft by specifying a velocity vector in the direction of the new position, wherein the velocity vector has velocity vector components orthogonal to the navigation vector which lie in a navigation plane which is orthogonal to the navigation vector, or by specifying a waypoint at the new position, wherein the specified waypoint lies in a navigation plane which is orthogonal to the navigation vector, or is specified with respect to the navigation plane.

[0022] The position of the controllable aircraft can be determined, for example, via the aircraft's control system or via one or more sensors, such as a GPS sensor. The position of the controllable aircraft can, for example, correspond to the aircraft's center of gravity or the position of a sensor.

[0023] Since the position of the marker and the position of the camera on the controllable aircraft are known or can be determined, the position of the controllable aircraft can be used in step d) to calculate the position of the marker or camera. At large distances from a mirror surface, such as 10 m or more, the distance of the camera or marker from the determined position of the aircraft, which is in the centimeter range, is negligibly small, so that the position of the controllable aircraft can also be used as a predetermined point without conversion.

[0024] The predetermined positions of the marker and the camera on the controllable aircraft do not necessarily have to be fixed. It is also possible, for example, that the camera's position can be changed by adjustment. For the procedure to work, it is only necessary that the positions of the marker and the camera are known or can be determined.

[0025] The navigation vector can, for example, run from the estimated position of the marker's reflection on the mirror surface to a point located midway between the camera and the marker. In this case, the navigation vector corresponds to the normal vector of the mirror surface.

[0026] The velocity vector components in step e), which are orthogonal to the navigation vector, cause the marker's reflection on the mirror surface, as observed by the camera, to "move," allowing the reflection to be moved, for example, towards a desired point on the mirror surface. This also allows for a kind of scanning of the mirror surface, which, with further calculations or image analysis, enables the determination of a slope error map. When controlling the aircraft by specifying a velocity vector, the aircraft's new position does not necessarily have to be a predetermined position. The aircraft's new position can also result from a predetermined time, i.e., the new position is the position the aircraft reaches after the specified time following the velocity vector.

[0027] The aircraft can be controlled in a simple manner using the velocity vector with velocity vector components orthogonal to the navigation vector and lying in the navigation plane, or the specified waypoint lying in the navigation plane, since the control specifications are provided in a form that is easy for the aircraft to implement.

[0028] The navigation plane can, in particular, pass through a point on the aircraft, for example, the point corresponding to the previously described position of the aircraft. If the waypoint does not involve a change in the aircraft's distance from the mirror surface, the waypoint lies within the navigation plane. For a flight route that involves a change in the aircraft's distance from the mirror surface, the waypoint is specified with respect to the navigation plane, for example, in a plane parallel to the navigation plane.

[0029] The different variants of the methods according to the invention differ in that, in the first variant, the camera is attached to the controllable aircraft and is therefore non-stationary, whereas the marker is stationary, for example on a tower of a solar power plant. In the second variant, the marker is non-stationary on the controllable aircraft, whereas the camera is stationary, for example on the tower of a solar power plant.

[0030] The third option involves both the marker and the camera being located on the controllable aircraft.

[0031] The reflector can be part of a heliostat and must have at least one mirror surface.

[0032] Preferably, the following steps are carried out in the methods according to the invention: f) Taking an image of the reflector's mirror surface using the camera at the new position of the controllable aircraft, g) Repeat steps c) to f) until a termination criterion is reached.

[0033] A termination in step g) upon reaching a termination criterion does not necessarily have to occur only when a repetition according to step g) has been fully carried out, but can also occur after carrying out step c), d) or e) in a repetition.

[0034] By capturing an image of the reflector's mirror surface with the camera at the new position of the controllable aircraft and repeating steps c) to f), the position of the marker's reflection can be determined when the controllable aircraft is in that new position. This provides feedback, enabling the controllable aircraft's flight path to be adjusted. In this way, the reflection can be autonomously guided to a desired point on the mirror surface. A desired point could, for example, be a point on the mirror surface for which a survey is to be performed to create a slope error map or a calibration point.

[0035] When controlling the controllable aircraft in step e) via the velocity vector, the new position of the aircraft can also result from the sampling rate of the camera, i.e., the new position is the one at which, during a flight with the given velocity vector, the camera takes the next picture.

[0036] The methods according to the invention are particularly suitable for measuring the mirror surface of a reflector. For example, in the first embodiment, where the camera is arranged on the aircraft, a normal vector of the mirror surface for the position of the reflection can be estimated from the position of the controllable aircraft, the position of the marker, and the estimated position of the reflection on the mirror surface. This normal vector can then be used, for example, to determine a calibration point for the reflector. In the second embodiment, where the marker is arranged on the aircraft, the normal vector can be estimated from the position of the controllable aircraft, the position of the camera, and the estimated position of the reflection on the mirror surface.In the third variant, where the camera and marker are arranged on the aircraft, the normal vector can be estimated from the position of the controllable aircraft, the predetermined point on the aircraft, and the estimated position of the reflection on the mirror surface or from the navigation vector. The methods according to the invention now advantageously allow the reflection on the mirror surface to be moved towards a desired position on the mirror surface, or to the desired position itself, by specifying the velocity vector or the waypoint accordingly.

[0037] In the inventive method according to the first variant, the controllable aircraft is first positioned above the reflector, and an image of the reflector's mirror surface is captured using the camera. The image is evaluated, and the marker's reflection on the mirror surface is determined. Subsequently, the position of the marker's reflection on the mirror surface is estimated, and the navigation vector is estimated based on this reflection's position and the position of the controllable aircraft.

[0038] The estimated navigation vector is then used to control the aircraft by specifying a velocity vector or a waypoint.

[0039] At a newly emerging position, another image can be taken, which can be used to check the position of the reflection on the mirror surface.

[0040] These steps are repeated until a predetermined termination criterion is reached, for example, a predetermined position of the reflection on the mirror surface.

[0041] Similarly, the second variant of the method according to the invention, in which the camera is stationary and the marker is moved with the controllable aircraft, also enables advantageous control of the aircraft.

[0042] In the third variant, the camera and marker are moved together with the controllable flying device. This variant has the particular advantage that no additional equipment needs to be installed in the vicinity of the reflector.

[0043] The data acquired during the methods according to the invention can, for example, be transferred to an external computing unit, which performs the image evaluation and determines the control data for controlling the controllable aircraft according to step e) and transmits it to the controllable aircraft. The external computing unit can, for example, be mobile and designed as a separate mobile device. Alternatively, the computing unit can also be arranged on the controllable aircraft.

[0044] Preferably, in the methods according to the invention, if the evaluation of the image in step c) shows that no reflection of the marker is visible in the image, the controllable aircraft is controlled along a predetermined flight pattern while simultaneously recording images with the camera and evaluating the images until a reflection of the marker is detected in an image, and preferably this image is then used in step d). In other words, if it is determined in step c) that no reflection of the marker is visible in the recorded image, a search function is performed, whereby the aircraft flies along a predetermined flight pattern and images are simultaneously recorded. The images are evaluated in a manner comparable to step c), and it is determined whether a reflection of the marker is visible in any of the images.As soon as a marker reflection is visible in an image, the search function is aborted and the procedure continues with step d), using the image in which the marker reflection was then visible. The flight pattern may include the aircraft approaching the reflector.

[0045] The advantage of this approach is that if, for example, the camera and / or the marker are very close to the mirror surface of the reflector of, for example, a heliostat, at a distance of about 5-10 m, the solid angle visible through the mirror surface is very large, so that the reflection of the marker can be easily found.

[0046] The specified flight pattern can be created based on a previous position, several previous positions, or a previous flight path of the controllable aircraft. In the simplest case, the aircraft flies to the last position from which an image was taken showing a reflection of the marker on the mirror surface. The specified flight pattern can also be created based on a previously estimated position of the marker's reflection on the mirror surface, or several previously estimated positions of the marker's reflection on the mirror surface.

[0047] If necessary, the velocity vector may be adjusted to prevent the marker's reflection from being lost again on the mirror surface.

[0048] Preferably, in the methods according to the invention, the controllable aircraft is positioned at a previously determined starting position as the position for step b) after step a) and before step b). Thus, a starting position of the controllable aircraft can be defined from which step b) begins. The starting position can, for example, be a position at which it is estimated that, upon subsequent image acquisition in step b) and evaluation of the image in step c), it will be highly likely that a reflection of the marker is detected in the image.

[0049] Preferably, a center point of the mirror surface is estimated, or another point on the mirror surface is specified. The position of the marker's reflection on the mirror surface relative to the estimated center point or the specified point is then determined and taken into account when specifying the velocity vector or the waypoint. For a reflector with multiple mirror surfaces, the center point of the reflector can also be estimated or specified and used. In other words, when determining the velocity vector, the velocity vector components or the waypoint can be positioned such that the marker's reflection on the mirror surface, as observed by the camera, "moves" towards, or remains in the vicinity of, the center point of the mirror surface or the reflector, or another point.

[0050] For example, to determine the velocity vector or to determine the waypoint to be specified, the relative position of the marker's reflection on the mirror surface to the center of the mirror surface or reflector, or to another point in the recorded image, can be determined in pixels as pixel spacing (distance in pixels in the image).

[0051] Since, for example, the distance of the marker's reflection on the mirror surface to a center point or other point varies in pixels depending on the size of the image area and thus on the distance of the aircraft, the pixel spacing can be normalized. To normalize the pixel spacing, a structure of known length can be identified in the image, the number of pixels corresponding to the length of the structure determined, and this determined number of pixels used to normalize the pixel spacing. This yields a distance that is independent of the image resolution.

[0052] Based on the position of the marker's reflection on the mirror surface relative to the estimated center point or the specified point, the components of the velocity vector or waypoint lying in the navigation plane are determined.

[0053] Depending on the desired task, the velocity vector or the waypoint can be determined or specified such that the reflection "travels" to the center point or another specified point. For scanning the mirror surface, various points on the mirror surface can be specified, with the reflection being directed to these points sequentially.

[0054] For example, the outer edge of the mirror surface or the reflector can be used as a structure of known length.

[0055] Preferably, it is provided that, if in step c) several reflections of the marker are determined in the image on the mirror surface of the reflector or on several mirror surfaces of the reflector, in step d) the positions of the several reflections of the marker are estimated and a summary of the estimated positions of the several reflections of the marker is carried out, preferably an averaging of the estimated positions, wherein the summarized position is then used as the position of the reflection of the marker for the estimation of the navigation vector of the mirror surface.

[0056] Since the navigation vector is estimated from the position of the reflection on the mirror surface, and this estimated navigation vector is taken into account when controlling the aircraft, averaging has the advantage that only one signal is used for subsequent steps. The averaging can, for example, be performed as an arithmetic mean of the estimated positions of the marker's multiple reflections.

[0057] For example, in reflectors with multiple mirror surfaces, such as heliostats, the mirror surfaces are often slightly angled relative to each other to concentrate the radiation. This allows a reflection to be visible on each of the different mirror surfaces simultaneously. By averaging the estimated positions of these reflections, a position relative to the entire reflector is estimated as the starting point for the navigation vector. If a specific point on the mirror surface or relative to the reflector is to be targeted, it can also be intended that the aggregated, e.g., averaged, position of the reflections should be moved to this point.

[0058] The marker can be, for example, an object with a pattern or a characteristic shape. Preferably, the marker has one or more light sources.

[0059] The methods according to the invention can be carried out at night or at times with low solar radiation, since the reflections of the marker are then advantageously visible on the mirror surface without being affected by reflections from the sun. To ensure that the position of the reflection on the mirror surface can be advantageously determined, in low light conditions or at night, the mirror surface can also be illuminated, or at least luminous markers can be arranged at the corners of the mirror surface to make the mirror surface visible in the image.

[0060] The methods according to the invention can, for example, also be carried out during the operation of a power plant of which the reflector is a part.

[0061] In variants where the camera is mounted on the aircraft, the camera can be swivelled. It can be designed so that the camera is aligned with the navigation vector, meaning that the camera's optical axis corresponds to the navigation vector. This ensures that the reflection and the captured mirror surface are located in the center of the image.

[0062] Accurate calculation of the navigation vector requires precise positioning of the marker's reflection on the mirror surface, i.e., precise positioning of the reflection in space. This necessitates not only the reflection's position in the image but also knowledge of the mirror surface's orientation: rotation of the mirror surface, due to leverage, translates the reflection's position. The problem is that the mirror surface's orientation is not always precisely known or determinable, thus also obscuring the reflection's exact position. Therefore, according to the methods of the invention, the reflection's position on the mirror surface or in space is estimated. This estimation can be performed in various ways: For example, a known point can be used to approximate the position of the reflection, such as the intersection of the rotation axes of a reflector, which is usually the center of the reflector, or another point that is close enough to the position of the reflection. In the image, for example, a pixel spacing or a normalized pixel spacing can be used to determine whether the position of the reflection is close enough to the known point to use it as an approximation of the reflection's position in the estimation.

[0063] It is also possible to estimate the orientation of the mirror surface, which can also be initial. For example, the orientation of the mirror surface can be determined using an initial normal vector, from which the position of the reflection in space can be estimated. Alternatively, the orientation of the mirror surface can be estimated from the image.

[0064] In the method according to the invention, it is not absolutely necessary that the orientation of the reflector is known beforehand, since, for example, the described search function can be used to fly until a reflection of the marker is recognizable in the recorded image and the further process steps can then be carried out.

[0065] The methods according to the invention advantageously enable the control of a flight path of an aircraft during a flyover of a mirror surface, with some variants also enabling autonomous control of the flight path.

[0066] If one of the methods according to the invention is used to control the flight path of a controllable aircraft during a survey of mirror surfaces, point measurements distributed across the mirror surface can be recorded by controlling the aircraft in such a way as to enable the recording of reflections of a marker at specific points on the mirror surface. In this way, a kind of scanning of the mirror surface can be carried out.

[0067] The invention will now be explained in more detail with reference to the following figures. These show: Fig. 1 a schematic representation of the controllable flying device with camera and marker for the first variant of the method according to the invention, Fig. 2 a schematic representation of the controllable flying device with marker and camera for the second variant of the method according to the invention and Fig. 3 A schematic representation of the controllable flying device with marker and camera arranged on it for the third variant of the method according to the invention.

[0068] According to a first embodiment of the method according to the invention, a heliostat 1 with a reflector 3 forming a mirror surface 5 is flown over by a controllable aircraft 7 on which a camera 9 is arranged. A stationary marker 11, which can be, for example, a light source, generates a reflection 13 on the mirror surface 5. The images recorded by the camera 9 are transmitted to an external processing unit 15 and evaluated. Based on the position of the reflection 13 of the marker 11 on the mirror surface 5, the position of the controllable aircraft 7, and the position of the marker 11, a navigation vector 16 is estimated, which extends from the estimated position of the reflection of the marker 11 on the mirror surface 5 to the camera 9.

[0069] The navigation vector 16 is now used to steer the controllable aircraft 7 to a new position. For example, the new position of the controllable aircraft 7 can be specified such that the reflection 13 of the marker 11 on the mirror surface 5 moves towards the center point 5a of the mirror surface, as indicated by the arrow 18. For this purpose, a velocity vector is specified for the controllable aircraft 7, where the velocity vector has velocity vector components 20 in a navigation plane 19 that is orthogonal to the navigation vector 16. Specifying the velocity vector allows for its simple implementation as a flight command for the aircraft 7. The position of the center point 5a can be estimated from the images, and the relative position of the reflection 13 to the center point 5a can be determined, for example, in pixels, for specifying the velocity vector.

[0070] Subsequently, another image of the mirror surface 5 of the heliostat 1 is captured and evaluated for a renewed estimation of the navigation vector 16. These steps are carried out until a termination criterion is reached. This allows autonomous control of the flight of the aircraft 7, since feedback is provided via the reflection 13 of the marker 11 on the mirror surface as to whether the reflection 13 is moving to the desired position.

[0071] To define the velocity vector, the distance between the reflection 13 of the marker 11 on the mirror surface 5 and the center point 5a of the mirror surface can be determined as the pixel distance in the recorded image. This distance is then normalized by the length in pixels of a known structure in the image, for example, an outer edge 21 of the mirror surface 5 of the reflector 3, in order to obtain a distance independent of the image resolution.

[0072] At the last position of the aircraft, for example, the normal vector 17 of the mirror surface 5 can be determined from the last position of the controllable aircraft 7, the position of the marker 11 and the last estimated position of the reflection 13 on the mirror surface 5.

[0073] In Fig. Figure 2 schematically illustrates the second variant of the method according to the invention. In the second variant of the method according to the invention, camera 9 and marker 11 are exchanged compared to the first variant, such that camera 9 is arranged in a stationary position, whereas marker 11 is attached to the controllable flying device 7. Otherwise, the Fig. 2 of the Fig. 1 and reference is made to the relevant description.

[0074] In Fig. Figure 3 shows the arrangement of camera 9 and marker 11 for a third variant of the method according to the invention.

[0075] In this embodiment, both the camera 9 and the marker 11 are arranged at a predetermined position on the controllable aircraft 7.

[0076] In controlling the controllable aircraft 7, it can generally be provided that the control is carried out in such a way that the reflection 13 of the marker 11 on the mirror surface 5 “moves” towards a center point 5a of the mirror surface 5. Reference symbol list 1 Heliostat 3 Reflector 5 Mirror surface 5a Center 7 controllable aircraft 9 Camera 11 markers 13 Reflex 15 external computing units 16 Navigation vector 17 Normal vector 18 Arrow 19 Navigation level 20 velocity vector components 21 outer edge

Claims

[1] Method for controlling a flight path of a controllable aircraft (7) during a flyover of a mirror surface (5) of a reflector (3), preferably a reflector (3) of a heliostat (1) of a solar tower power plant, comprising the following steps: a) Providing the controllable aircraft (7) which has a camera (9) and a stationary marker (11) with a predetermined position which is reflected by the mirror surface (5) of the reflector (3), b) Taking an image of the mirror surface (5) of the reflector (3) using the camera (9) at a position of the controllable aircraft (7) above the reflector (3), c) Evaluating the image and determining a reflection (13) of the marker (11) on the mirror surface (5) in the image, d) Estimating the position of the reflection (13) of the marker (11) on the mirror surface (5), wherein a navigation vector (16) extending from the estimated position of the reflection (13) of the marker (11) on the mirror surface (5) and the position of the controllable aircraft (7) is estimated, and e) Steering the controllable aircraft (7) to a new position of the controllable aircraft (7) by specifying a velocity vector in the direction of the new position, wherein the velocity vector has velocity vector components (20) that are orthogonal to the navigation vector (16) and lie in a navigation plane (19) that is orthogonal to the navigation vector (16), or by specifying a waypoint at the new position, wherein the specified waypoint lies in a navigation plane (19) that is orthogonal to the navigation vector (16), or is specified with respect to the navigation plane (19). [2] Method for controlling a flight path of a controllable aircraft (7) during a flyover of a mirror surface (5) of a reflector (3), preferably a reflector (3) of a heliostat (1) of a solar tower power plant, comprising the following steps: a) Providing a controllable flying device (7) having a marker and a stationary camera (9) with a predetermined position directed at the mirror surface (5) of the reflector (3), b) Taking an image of the mirror surface (5) of the reflector (3) using the camera (9), wherein the controllable flying device (7) is arranged at a position above the reflector (3), c) Evaluating the image and determining a reflection (13) of the marker (11) on the mirror surface (5) in the image, d) Estimating the position of the reflection (13) of the marker (11) on the mirror surface (5), wherein a navigation vector (16) extending from the estimated position of the reflection (13) of the marker (11) on the mirror surface (5) and the position of the controllable aircraft (7) is estimated, e) Steering the controllable aircraft (7) to a new position of the controllable aircraft (7) by specifying a velocity vector in the direction of the new position, wherein the velocity vector has velocity vector components (20) that are orthogonal to the navigation vector (16) and lie in a navigation plane (19) that is orthogonal to the navigation vector (16), or by specifying a waypoint at the new position, wherein the specified waypoint lies in a navigation plane (19) that is orthogonal to the navigation vector (16) or is specified with respect to the navigation plane (19). [3] Method for controlling a flight path of a controllable aircraft (7) during a flyover of a mirror surface (5) of a reflector (3), preferably a reflector (3) of a heliostat (1) of a solar tower power plant, comprising the following steps: a) Providing a controllable aircraft (7) comprising a camera (9) and a marker (11), wherein the marker and the camera (9) are each arranged at a predetermined position on the controllable aircraft, b) Taking an image of the mirror surface (5) of the reflector (3) using the camera (9) at a position of the controllable aircraft (7) above the reflector (3), c) Evaluating the image and determining a reflection (13) of the marker (11) on the mirror surface (5) in the image, d) Estimating the position of the reflection (13) of the marker (11) on the mirror surface (5), wherein a navigation vector (16) extending from the estimated position of the reflection (13) of the marker (11) on the mirror surface (5) to a predetermined point on the aircraft (7) is estimated based on the position of the reflection (13) of the marker (11) on the mirror surface (5) and the position of the controllable aircraft (7). e) Controlling the controllable aircraft (7) to a new position of the controllable aircraft (7) by specifying a velocity vector in the direction of the new position, wherein the velocity vector has velocity vector components (20) that are orthogonal to the navigation vector (16) and lie in a navigation plane (19) that is orthogonal to the navigation vector (16), or by specifying a waypoint at the new position, wherein the specified waypoint lies in a navigation plane (19) that is orthogonal to the navigation vector (16). [4] Method according to claim 1, 2 or 3, characterized by the steps: f) Taking an image of the mirror surface (5) of the reflector (3) using the camera at the new position of the controllable aircraft (7) and g) Repeat steps c) to f) until a termination criterion is reached. [5] Method according to any one of claims 1 to 4, characterized by, that if the evaluation of the image in step c) shows that no reflection (13) of the marker (11) is recognizable in the image, the controllable aircraft is controlled along a predetermined flight pattern with simultaneous recording of images with the camera and evaluation of the images until a reflection (13) of the marker (11) is determined in an image, preferably then using this image in step d). [6] Method according to claim 5, characterized by , that the specified flight pattern is created based on a previous position or several previous positions or a previous flight path of the controllable aircraft (7). [7] Method according to any of the preceding claims, characterized by, that a center point (5a) of the mirror surface (5) or of the reflector (3) is estimated or a point on the mirror surface (5) is specified, whereby the position of the reflection (13) of the marker (11) on the mirror surface (5) is determined relative to the estimated center point (5a) or to the point and is taken into account when specifying the velocity vector or the waypoint. [8] Method according to any of the preceding claims, characterized by , that for the purpose of determining the velocity vector or the waypoint to be specified, a relative position of the reflection (13) of the marker (3) on the mirror surface (5) to the center point (5a) of the mirror surface (5) or of the reflector (3) or to another point in the recorded image is determined in pixels as pixel distance. [9] Method according to claim 8, characterized by , that the pixel spacing is normalized. [10] Method according to claim 9, characterized by, that for the normalization of the pixel spacing a structure of known length is determined in the image, the pixel length of the structure is determined and the determined pixel number is used for the normalization of the pixel spacing. [11] Method according to claim 10, characterized by , that an outer edge of the mirror surface (5) or of the reflector (3) is used as the structure. [12] Method according to any of the preceding claims, characterized by , that after step a) and before step b) the controllable aircraft is positioned at a previously determined starting position as the position for step b). [13] Method according to any of the preceding claims, characterized by, that if in step c) several reflections of the marker (11) on the mirror surface (5) of the reflector (3) or several mirror surfaces (5) of the reflector (3) are determined in the image, in step d) the positions of the several reflections of the marker (11) are estimated and a summary of the estimated positions is carried out, wherein the summarized position is then used as the position of the reflection (13) of the marker (11) for the estimation of the navigation vector (16).

Images