A system and method for takeoff and landing of an unmanned aerial vehicle (UAV)
PT 20240336
Key information
Title
A system and method for takeoff and landing of an unmanned aerial vehicle (UAV)
Application number
20240336
Case type
National
Status
08.04.2024 Godkjent til meddelelse
Filed
08.04.2024
Effective date
08.04.2024
Publicly available
09.10.2025
Next annual fee due
30.04.2027
Applicant
BIRDVIEW AS (NO)
Inventor
Pouyan Shariffiasl (NO)
Agent
Aera A/S (DK)
Abstract and drawing
Disclaimer: This text has been machine-scanned and may contain errors – please refer to "Publications" for legally binding content.
The invention relates to a system and method for safe take-off and landing of an unmanned aerial vehicle (UAV) for example, a drone on a platform during harsh environment conditions. The system employs one or more transceivers on the platform that are in continuous communication with the transceivers on the UAV and to guide and monitor the UVA to allow autonomous landing or take-off of the UAV. The method comprises instructing the UAV to fly to a predetermined altitude above the landing pad on the platform and hold the position for a predefined time period. When the process is successful, the UAV is instructed to take-off or land in a controlled manner, thus ensuring safe operations and prevention of accidents.
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P29011NO00_Application specification 1163505
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Description, claims and drawings
Disclaimer: This text has been machine-scanned and may contain errors – please refer to "Publications" for legally binding content.Description
TITLE: A system and method for takeoff and landing of an unmanned aerial vehicle (UAV)FIELD OF THE INVENTIONThe present invention relates to an unmanned aerial vehicle (UAV such as drones) and more particularly to a system and a method for safe takeoff and landing of such an unmanned aerial vehicle during harsh environments.BACKGROUND AND PRIOR ARTThe advances in technology of unmanned aerial vehicles (UAVs) for example: UAVs has resulted in their increased use in onshore, offshore applications such as platforms, ships, boats and the like.The employment of UAVs in offshore applications is prone to several challenges particularly, during landing of the UAVs. During landing operations, the UAV may face technical and operational problems. This is also due to the harsh environmental conditions at the sea and this may be a demanding task. Various factors have to be considered during UAV operations in offshore environments such as environmental conditions, path optimization and robot control, sufficient accuracy to land on moving platforms or ships, predication of the future movements of the platform or the ship etc.The environmental conditions may be harsh on ships or platforms, as they are influenced by winds, heavy fog, precipitation, snow or sleet, sways due to ocean waves. Much of the current UAVs rely on vision based systems such as machine vision in which visual fiducial markers like QR is positioned on a landing pad on the ship or platform. The UAVs employ these markers to navigate their way and land on the landing pad. However, under harsh conditions as described above, the landing can be a problem as the UAV may not be able to accurately locate the visual marker on the landing pad. This may also lead to UAV accidents such as crash landing.The second factor of path optimization plays an important role in accurate positioning and robot control operations. As the ship may be moving or the platform may be a moving platform, the UAV must continuously change and optimize its trajectory in order to perform an accurate landing. This would require advanced controllers that compute the UAV’s trajectory once and continuously predicts and updates the UAV’s trajectory as the platform or ship moves. Thus, the system must be robust.The third factor to consider is accuracy of the landing platform. Satellite-based global positioning systems are employed in present UAVs; however, they do not provide sufficient accuracy for landing on a moving platform or ship. There are challenges with position estimates and algorithms employed by the positioning systems. When
the UAV approaches the ship or platform the external noise and other disturbances effect the compass measurements and can cause significant disruptions making accurate landing difficult.The fourth factor is prediction of the movements of the ship or the platform. To accurately determine the trajectory of the ship or the platform it is necessary to compute the movements of the ship continuously, so that the future movements may be predicted. When the UAV tries to generate an optimal trajectory to hit the landing pad, the trajectory must consider the movements of the target as well.CN108829139A describes landing and control methods for unmanned aerial vehicles on sea. The method employs control systems on the ship with image capturing devices, distance measurement devices mounted on a beam, whose one end is mounted on the ship and can be moved in horizontal and vertical planes.KR101960174B1 describes an electro-magnetic based landing and takeoff device for rough environments. A bracket is installed on the floor of the ship and supports the electromagnetic device and the power supply. The electromagnetic device is provided with a detachable coil and a core at the bottom of the leg stand. The ship is provided with means for holding magnetic iron means attachable to the leg stand of the UAV with an electromagnet.CN108234950A describes a monitoring system on a ship that employs high definition image transmitters mounted on the UAV for collection of images and a control terminal disposed on the ship to control the mooring UAV.The aforementioned systems employ image based monitoring techniques. These techniques fail in harsh conditions such as snow, fog, sleet, heavy rain etc. As the UAV is unable to locate the visual markers or capture accurate imagining of the landing pad. During such harsh environments, the communication systems may also be impacted. Thus, leading to failure in safe landing of the UAVs and causing UAV accidents.SUMMARY OF THE INVENTIONThe present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention.A first embodiment of the present invention regards a system for takeoff and landing of an unmanned aerial vehicle (UAV) on a platform, the system comprising at least one unmanned aerial vehicle capable of landing and taking off from a platform autonomously, comprising transceivers for at least communicating with transceivers in the platform; the platform arranged on a structure and providing a surface for takeoff and landing of the unmanned aerial vehicle (UAV),wherein the platform can
be comprised of one or more transceivers configured to communicate with the unmanned aerial vehicle (UAV) and provide information allowing the unmanned aerial vehicle (UAV) to allow it to guide itself during takeoff and landing .Further, the transceivers of the landing pad and transceivers on the unmanned aerial vehicle communicate through radio communication signals, and the system can comprise additional sensors, positioning and monitoring devices configured to guide the unmanned aerial vehicle during takeoff and landing, the system can comprise a controller arranged on the structure for controlling the communications between the unmanned aerial vehicle and the structure and issuing signals to the said transceivers . A second aspect of this invention is a method for takeoff and landing of an unmanned aerial vehicle (UAV), wherein during takeoff the method comprises steps of: sending instruction signals via the transceivers on the landing pad to the one or more transceivers on the unmanned aerial vehicle to cause the vehicle to fly to a defined altitude (X) above the landing pad; and hold a position at the defined altitude (X) for a time period (T1). The X can be defined as altitude (X) in the range of 5 to 10 meters and the time period (T1) can be in the range of 2 to 10 seconds, and wherein the controller can send instruction signals to the unmanned aerial vehicle to takeoff from the landing pad.A third aspect of this invention is a method for takeoff and landing of an unmanned aerial vehicle, wherein during landing the method comprises steps of :a. sending instruction signals to the unmanned aerial vehicle to fly at a defined altitude from a center of the landing pad; andb. sending instruction signals to the unmanned aerial vehicle to hold a position at the defined altitude for a defined time period; andc. landing the unmanned aerial vehicle by sending instruction signals to the vehicle to continue to fly downwards to the landing pad.Further the method performs step b only if step a is successful, and the method performs step c, if step b is successful and the position is held for the defined time period (T2). The defined altitude (Y) is in the range of 10 to 15 meters from the landing pad, and the time period (T2) is in the range of 5 to 10 seconds.The defined distances in altitudes such as X and Y are for take-off and landing operations respectively and the defined time periods T1 and T2 correspond to the time for which the positions are held during the defined take-off and landing operations. This solution allows the unmanned aerial vehicle to land and take off from a platform during harsh weather conditions and when the platform is moving since the platform can be mounted to e.g. a ship. A preferred technical advantage of the invention is
accurate prediction and monitoring systems on ships or platforms that are continuously in motion. Another preferred advantage would be to provide systems that do not rely on visual imagining data for accurate landing on UAVs.Another objective is to provide a simple and cost effective solutions for landing UAVs in harsh conditions in the sea.BRIEF DESCRIPTION OF THE DRAWINGSFollowing drawings are appended to facilitate the understanding of the invention. The drawings show embodiments of the invention, which will now be described by way of example only, where:Fig. 1a and 1b illustrates prior art system showing a top view of the platform and the UAV.Fig. 2 illustrates prior art system employing real time locating system.Fig. 3 is a system illustrating transceivers employed on the platform and the UAV, according to the present invention.Fig. 4 is a perspective view, of UAV takeoff according to the present invention. Fig. 5a-5c is a perspective view, seen from above, of UAV landing sequence.Fig. 6 depicts a flowchart of method steps for landing a UAV safely on the platform according to the present invention.DETAILED DESCRIPTION OF THE INVENTIONIn the following, embodiments of the invention will be discussed in more detail with reference to the appended drawings. It should be understood, however, that the drawings are not intended to limit the invention to the subject-matter depicted in the drawings.Positioning using only satellite-based global positioning systems does not provide sufficient accuracy to land on a moving platform. It is therefore necessary to develop the sensor fusion algorithms necessary to integrate a local positioning system. This will ensure that the position estimates have sufficient accuracy to land on the moving platform.The platform movements themselves must be modeled accurately so that a rough prediction of future movements can be calculated. This is necessary since the future
trajectory of the platform is crucial for the trajectory optimization process of the UAV.The UAV tries to generate an optimal trajectory to hit the target, and when the target moves, this trajectory must account for the target movement.Fig. 1a illustrates a prior art system showing a top view of a platform used by a UAV e.g. when landing and taking off. In its simplest embodiment it can be a flat surface for the UAV to use for landing and taking off. However, there can be added further technical solutions to the platform in order to aid the unmanned aerial vehicle (UAV) 30 to assess the right (required correct) angle and height to perform a landing. In its simplest solution the aids can be lights that makes it easier for the unmanned aerial vehicle (UAV) 30 to spot the platform 10 from an onboard camera. The camera can be used for both recording images in real life that can be transferred to a pilot that is positioned at another location, or it can be for a recording images that an onboard computer that evaluates and analyses images and data in order to control the unmanned aerial vehicle (UAV) 30.The lights may also be positioned such that it is possible for the unmanned aerial vehicle (UAV) 30 to evaluate the angle of the unmanned aerial vehicle (UAV) 30 in relation to the platform 10. It is also known to use visual aids that makes it possible for the unmanned aerial vehicle (UAV) 30 to assess the angle and height of the UAV in relation to the platform 10. These visual aids are usually colored lines and/or symbols that can be detected in an image and the onboard computer can assess the length of the lines and/or symbols, the distance between the lines and/or symbols and the angles of the lines and/or symbols, and maybe even the thickness for the lines and/or symbols may be employed for detection and analysis.All these solutions are visual aids that help guiding an unmanned aerial vehicle (UAV) 30 when the weather is clear, during daylight and the platform is in at least relative calm state. However, a problem arises when the weather is bad, and the platform 10 is located on a vessel like e.g. a fishing vessel. If the conditions are bad or harsh for e.g. rain or snow and windy, making the platform 10 move and/or the visibility poor, the images captured by the camera on the unmanned aerial vehicle (UAV) 30 are not of sufficient quality to give the UAV information enough to land safely on the platform 10.If the gathered information required for landing the UAV is not good enough the UAV risks landing either as a crash or too hard on the platform. This is can result in the UAV getting destroyed or destruction to electronics of the UAV.
Fig. 1b is an image of a prior art UAV, although the image is depicting an UAV with 4 propellers, this is just an illustration of one possibility and the UAV in question can have a set of propellers 80 that is different to what is depicted here. In this image the UAV has a body and a set of propellers 80 that is mounted on arms 40 extending out from the body. Both the UAV and the platform 10 can be marked with an identification tag like an RTLS 20.Due to a low accuracy in position estimates from the global satellite navigation system, a local Real Time Localization System (RTLS) must be integrated into the platform 10 and UAV for centimeter-level precision, improving the accuracy of local position estimates of the UAV by several orders of magnitude.RTLS are generally used in indoor and/or in confined areas, such as buildings, and do not provide global coverage. RTLS tags are affixed to mobile items to be tracked or managed. RTLS reference points, which can be either transmitters or receivers, are spaced throughout a building (or similar area of interest) to provide the desired tag coverage. In most cases, the more RTLS reference points that are installed, the better the location accuracy, until the technology limitations are reached.In this example, the RTLS system keeps track of the position of the UAV in relation to the platform 10, however the limitation of the RTLS system makes it impossible to handle the conditions on a vessel such as a fishing vessel in the middle of the ocean. For an autonomous takeoff and landing, the system uses an algorithm that tries to land and takeoff from a platform 10 using the relative position between the platform 10 to land on and the UAV 30.This technology was validated in simulation, which appeared to be effective, but it was not validated on a real scenario. However, the RTLS technology was not precise enough to land on the platform 10 when it was used on a real UAV. Hence, the RTLS technology was deprecated.The RTLS tags 20 were used to know the position from one tag to another tag. The idea on the automatic landing algorithm based on RTLS was to use four RTLS tags 20 on the platform 10 (Figure 1a) and four tags 20 on the UAV (Figure 1b). Hence, it was possible to know the position from the platform to the UAV and vice versa. In this prior art solution, the UAV had an RTLS tag 20 on each arm 40 while the platform 10 also has an RTLS tag in each corner. This enables the UAV to know the roll and pitch with respect to the platform. The roll and pitch are used by the landing
algorithm to know the position of the platform 10 with respect to the UAV, which is necessary for the landing algorithm.Fig. 2 illustrates a system employing real time locating system.Much of the current research on autonomous landing and takeoff from boats centers around the idea of machine vision, where a visual identification marker (like QR) is placed on the landing pad 50 and the UAV 30 uses it to navigate. However, with heavy fog and precipitation such as snow or sleet, visual methods such as these cannot be relied upon.There is no marine UAV system today that is robust and powerful enough to handle takeoff and landing from a moving platform in darkness/night, fog and sea state 6 -7 on the Beaufort scale and since the platform is not fixed, the UAV 30 must continuously change and optimize its trajectory in order to land on the platform 10. This is a much more difficult task than landing on a fixed platform 10, as this only requires calculating a trajectory once, and executing it using a simple controlle r. Therefore, we need a controller that continuously predicts and optimizes the UAV's trajectory as the platform 10 moves.Real-time kinematic positioning (RTK) is a solution to eliminate the disturbances affecting the compass so that the UAV can recognize its positioning.In this solution, the landing algorithm is based on RTK GPS. The RTK landing algorithm uses three RTK GPS and one IMU (Inertial measurement unit). The idea behind the RTK landing algorithm is to get the position from the center of the platform 10 to the UAV 30 as well as the velocity of the platform 10. By using the center of the platform 10 to the UAV and the velocity of the platform, the control algorithm the UAV rapidly matches the velocity of the platform with the feedforward term. Moreover, with the proportional term for position the UAV can reach the position of the platform 10.This setup for the RTK landing algorithm comprises having two RTK GPS on the platform 10 as well as an IMU while the remaining RTK is on the UAV.The RTK system composed of three RTK GPS that returns the position from the base RTK GPS to the rover RTK GPS with respect to the NED (North East Down) frame. However, it is desired to land on the center of the platform. Hence, the black vector (Figure 2) has to be translated. Moreover, it has to be rotated because the moving platform 10 will rotate among time. Hence, to perform the rotation the compass RTK
and the IMU are added into the system, the IMU outputs roll and pitch while the compass among with the base RTK outputs yaw with respect to the NED frame. By using the roll, pitch and yaw on a direct cosine matrix (DCM) (Equation 1) it is possible to rotate the offset I b-frame to n-frame (Equation 2 as shown below).( )Fig. 3 is a system illustrating transceivers 60, 70 employed on the platform 10 and the UAV, according to the present invention.For explanatory purposes, the altitude (X) may be defined for take-off operations and the altitude (Y) may be defined for landing operations. Similarly, the time period (Tl) may correspond to take-off operations and time period (T2) may correspond to landing operations as described throughout the description.The image displays the system 1 comprised of a platform 10 with a landing pad 50 and a UAV 30. The UAV 30 is equipped with a transceiver 70. This transceiver is capable of communicating with a transceiver 60 on the platform 10. Further, the transceiver 60 is placed on the landing pad 50 in order to guide the UAV to the correct place to land on the landing pad 50.The term platform and landing platform may be used interchangeably throughout the description. However, it must be understood to mean the same. Alternatively, the term landing pad 50 may be construed to mean an area within the platform 10.In the present invention the RTLS system is mounted on both the UAV, and the platform 10. The idea is to mount the anchors on each comer of the landing platform, as illustrated in fig. la. Anchors may also be placed in other places on the ship to improve the tracking performance. The landing platform 10 will be at least 2x2m in size and will be placed at least lm above the deck of the ship; the idea is that the RTLS system should pick up the UAV as it approaches the ship and guide it during landing. The UAV will converge on the x,y-position of the platform 10 first, tracking it from a height of about 30m. Then it will descend down to the platform. We assume that the air column directly above the landing platform is free of obstacles. The UAV will be clearing masts, about 20 meters at the highest, before starting its descent.
What is needed is position estimates of the UAV in 3D space. Orientation estimates are also desirable, but not strictly necessary.These estimates will be fed to a ROS (Robotic operating System) system where the sensor fusion with the rest of the sensor suite will be done. As the ship rolls and heaves, a transformation will be performed such that the position estimates remain consistent independently of the motion of the ship. Therefore, there is no need for a graphical user interface, as this is integrated into the system.Fig. 4 is a perspective view, of UAV takeoff according to the present invention. In this figure the UAV 30 takes off from the platform 10 and rises a predetermined fixed altitude X, in order to ensure that the UAV 30 is clear of the moving platform 10 when taking off to go on a mission. The fixed altitude is controlled via QGC (Quasi-Complex gradients). This altitude is held for a few seconds (e.g.3 seconds).Fig. 5a-5c is a perspective view of a UAVs landing sequence according to the present invention.5a. is a view from above of the initial step of a UAVs 30 landing sequence. The UAV 30 flies at a predetermined altitude to the center of the platform 10. The predetermined altitude is e.g. 10 m above the center of the altitude. The RTLS tags 20 on the platform 10 and the UAV ensures that the UAV finds the platform and is able to position itself over the landing pad 50 on the platform 10.5b. is a view from the side of the second step of the landing sequence. The UAV 30 holds a fixed position above the platform at the predetermined altitude from figure 5a. The UAV holds this position for a predetermined amount of time. If the UAV moves to far away from the platform in a horizontal direction within this predetermined amount of time, the UAV reverts to the previous step in the landing sequence. The limit of the space that the UAV can move is indicated as the space between the grey boxes and is in real life monitored by the RTLS tags.5c. is a view from the side showing that the UAV flies at a constant speed downwards the platform 10 until it hits the platform 10 if it is able to stay within the space indicated in the previous step. Further there is no reverting past this point.Fig. 6 depicts a flowchart of method steps for landing a UAV safely on the platform according to the present invention.601 UAV flies horizontally at predefined altitude from the center of the platform 10.
602 It is determined if, the altitude X is within the predefined limit? If yes, proceedto step 603, if the answer is no, go back to step 601.603 Hold the position X at the defined position above the platform 10 for x-seconds.604 It is determined if the position is held stable and within the threshold? If theanswer is yes, proceed to step 605, If the answer is no, go back to step 603.605 Fly at a constant speed until the UAV lands on the platform.In the preceding description, various aspects of the UAV (Unmanned Aerial Vehicle),Landing platform according to the invention have been described with reference tothe illustrative embodiment. For purposes of explanation, specific numbers, systems,equations and configurations were set forth in order to provide a thoroughunderstanding of the system and its workings. However, this description is notintended to be construed in a limiting sense. Various modifications and variations ofthe illustrative embodiment, as well as other embodiments of the system, which areapparent to persons skilled in the art to which the disclosed subject matter pertains,are deemed to lie within the scope of the present invention.LIST OF REFERENCE NUMBERSPrior art (figs 1-4):10 RTLS platform20 RTLS tags on platform and UAV30 UAV or unmanned aerial vehicle40 Arms of the UAV50 Landing pad on the platform60 Transceivers on platform70 Transceivers on UAV80 Propellers on UAV90 Additional devices such as sensors, GPS systems, monitoring systems.
Claims
CLAIMS1. A system (1) for takeoff and landing of an unmanned aerial vehicle (UAV) (30) on a platform (10), the system (1) comprising:- at least one unmanned aerial vehicle (30) capable of landing and taking off from a landing pad (50) on a platform (10) autonomously, comprising transceivers (70) for at least communicating with transceivers (60) in the platform (10);- the landing pad (50) arranged on the platform (10) and providing a surface for takeoff and landing of the unmanned aerial vehicle (UAV, 30),c h a r a c t e r i z e d i n that: the platform (10) is comprised of one or more transceivers (60) configured to communicate with the unmanned aerial vehicle (UAV) and provide information allowing the unmanned aerial vehicle (UAV) to allow it to guide itself during takeoff and landing.2. The system in accordance with claim 1, wherein the transceivers (60) of the platform (10) and transceivers (70) on the unmanned aerial vehicle (30) communicate through radio communication signals.3. The system in accordance with any one of claim 1-2, wherein the system comprises additional sensors, positioning and monitoring devices (90) configured to guide the unmanned aerial vehicle during takeoff and landing.4. The system in accordance with any of the claims 1-3, wherein the system comprises a controller (100) arranged on the platform (10) for controlling the communications between the unmanned aerial vehicle (30) and the platform (10) and issuing signals to the said transceivers (60, 70).5. A method for takeoff and landing of an unmanned aerial vehicle (UAV) (30), employing the system in accordance with claims 1 to 4, wherein during takeoff the method comprises steps of:- sending instruction signals via the transceivers (60) on the landing pad (50) to the one or more transceivers (70) on the unmanned aerial vehicle (30) to cause the vehicle (30) to fly to a defined altitude (X) above the landing pad (50); and - hold a position at the defined altitude (X) for a time period (T1).6. The method in accordance with claim 5, wherein the defined altitude (X) is in the range of 5 to 10 meters.7. The method in accordance with claim 6, wherein the time period (T1) is in the range of 2 to 10 seconds, and wherein the controller (100) sends instructions signals to the unmanned aerial vehicle (30) to takeoff from the landing pad (50).8. A method for takeoff and landing of an unmanned aerial vehicle (30), employing the system in accordance with claims 1 to 4, wherein during landing the method comprises steps of:-a. sending instruction signals to the unmanned aerial vehicle (30) to fly at a defined altitude (Y) from a center of the landing pad (50);-b. sending instruction signals to the unmanned aerial vehicle (30) to hold a position at the defined altitude (Y) for a defined time period (T2); and- c. landing the unmanned aerial vehicle (30) by sending instruction signals to the vehicle (30) to continue to fly downwards to the landing pad (50).9. The method in accordance with claim 9, wherein the method performs step b. only if step a. is successful.10. The method in accordance with claim 9, wherein the method performs step c., if step b. is successful and the position is held for the defined time period (T2).11. The method in accordance with claims 9 to 11, wherein the defined altitude (Y) is in the range of 10 to 15 meters from the landing pad (50).12. The method in accordance with claims 9 to 12, wherein the time period (T2) is in the range of 5 to 10 seconds.