A system and method for takeoff and landing of an unmanned aerial vehicle (UAV)

Abstract

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 UAV 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.

Description

[0001] A SYSTEM AND METHOD FOR TAKEOFF AND LANDING OF AN UNMANNED AERIAL VEHICLE (UAV)

[0002] FIELD

[0003] The present invention relates to an unmanned aerial vehicle (UAV), such as a drones, and more particularly to a system and a method for safe take off and landing of such an unmanned aerial vehicle, for example in and / or during harsh environments.

[0004] BACKGROUND

[0005] The advances in technology of unmanned aerial vehicles (UAVs) have resulted in their increased use in onshore and offshore applications such as platforms, ships, boats and the like.

[0006] 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 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, prediction of the future movements of the platform and / or the ship etc.

[0007] The first factor to be considered is environmental conditions, which may be harsh on ships or platforms, for example, 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, such as QR codes, are 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 environmental 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.

[0008] 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.

[0009] 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 (i.e. land on) the landing pad, the trajectory must consider the movements of the target as well.

[0010] 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.

[0011] KR101960174B1 describes an electro-magnetic based landing and take off 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.

[0012] 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.

[0013] The aforementioned systems employ vision and / or image-based monitoring techniques. These techniques fail in harsh conditions such as snow, fog, sleet, heavy rain etc. since 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, leading to failure in safe landing of the UAVs and causing UAV accidents.

[0014] SUMMARY OF THE INVENTION

[0015] The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention. 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 one or more transceivers on the UAV and to guide and monitor the UAV 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.

[0016] First aspect

[0017] A first aspect provides a system for take off and landing of an unmanned aerial vehicle (UAV) on a platform, the system comprising at least one UAV capable of landing and taking off from a platform autonomously, comprising one or more transceivers for at least communicating with transceivers in the platform; the platform arranged on a structure and providing a surface for take off and landing of the UAV, wherein the platform comprises one or more transceivers configured to communicate with the UAV and provide information allowing the UAV to allow it to guide itself during takeoff and landing.

[0018] Additionally and / or alternatively, the first aspect provides a system comprising a platform, a UAV and a controller; wherein the platform comprises a first transceiver and a device configured to measure rotation of the platform about 1 , 2 and / or 3 mutually orthogonal axes; wherein the UAV comprises a second transceiver; wherein the controller is configured to control the first transceiver to transmit signals to the second receiver to control take off and / or landing of the UAV, based on the measured rotation of the platform about 1 , 2 and / or 3 mutually orthogonal axes, for example using RTK.

[0019] In one example, the one or more transceivers of the landing pad and one or more transceivers on the UAV communicate through radio communication signals. In one example, the system, for example the platform and / or the UAV, comprises one or more additional sensors, positioning and / or monitoring devices (for example, one or more GPS and / or GNSS devices, IMUs, compasses and / or altimeters) configured to guide the UAV during takeoff and landing. In one example, the system comprises a controller arranged on the structure for controlling the communications between the UAV and the structure and issuing signals to the said transceivers.

[0020] In one example, the system comprises a device, such as an IMU and / or a compass, configured to measure rotation of the platform about 1 , 2 and / or 3 mutually orthogonal axes, for example pitch, yaw and / or roll. In this way, rotation (angular position, angular speed and / or velocity and / or angular acceleration) of the platform about 1 , 2 and / or 3 mutually orthogonal axes may be measured, for example during take off and / or landing. In one example, controller is configured to control the UAV and / or the UAV is configured to take off and / or land conditionally, for example only when the measured rotation of the platform about 1 , 2 and / or 3 mutually orthogonal axes are within predetermined ranges and / or when respective rates of change and / or speeds, velocities and / or accelerations of the measured rotation of the platform about 1 , 2 and / or 3 mutually orthogonal axes are within predetermined ranges. In this way, rotation, change of rotation and rate of change of rotation of the platform may be estimated and / or predicted, for example during take off and / or landing. In this way, the UAV may take off and / or land when the platform is sufficiently stable, thereby reducing risk and / or improving safety.

[0021] In one example, the controller comprises and / or is a computer, comprising a processor and a memory.

[0022] In one example, the platform is provided on a watercraft, such as a boat, ship, hovercraft, submersible or submarine. In one example, the system comprises the watercraft.

[0023] IMU

[0024] In one example, the system comprises an Inertial Measurement Unit (IMU), configured to measure pitch, yaw and / or roll (for example, respective angles thereof) of the platform. In this way, the pitch, yaw and / or roll (for example, respective angles thereof), preferably roll and / or pitch (for example, respective angles thereof), of the platform may be measured, for example in real time and / or during landing and / or takeoff of the UAV from the platform. In one example, the platform comprises the IMU. In one example, the information allowing the UAV to allow it to guide itself during takeoff and landing comprises the measured pitch, yaw and / or roll (for example, respective angles thereof) of the platform. In one example, the controller is configured to control the one or more transceivers of the landing pad to communicate the measured pitch, yaw and / or roll (for example, respective angles thereof) of the platform to the UAV. In this way, the UAV is provided with the measured pitch, yaw and / or roll (for example, respective angles thereof) of the platform. In this way, the UAV may take off and / or land conditionally, for example only when the pitch, yaw and / or roll (for example, respective angles thereof) of the platform are within predetermined ranges and / or when respective rates of change and / or speeds, velocities and / or accelerations of the pitch, yaw and / or roll (for example, respective angles thereof) of the platform are within predetermined ranges. In this way, the UAV may take off and / or land when the platform is sufficiently stable, thereby reducing risk and / or improving safety. In one example, the respective transceivers of the platform and / or the UAV are configured to respectively transmit and / or receive respective rotations (for example, pitch, yaw and / or roll) thereof. Suitable IMUs are known.

[0025] Compass

[0026] In one example, the system comprises a compass, configured to measure yaw (for example, angle thereof) of the platform. In this way, the yaw (for example, angle thereof) of the platform may be measured, for example in real time and / or during landing and / or takeoff of the UAV from the platform. In one example, the platform comprises the compass. In one example, the information allowing the UAV to allow it to guide itself during takeoff and landing comprises the measured yaw (for example, angle thereof) of the platform. In one example, the controller is configured to control the one or more transceivers of the landing pad to communicate the measured yaw (for example, angle thereof) of the platform to the UAV. In this way, the UAV is provided with the measured yaw (for example, angle thereof) of the platform. In this way, the UAV may take off and / or land conditionally, for example only when the yaw (for example, angle thereof) of the platform is within a predetermined range and / or when a rate of change and / or a velocity of the yaw (for example, angle thereof) of the platform are / is within (a) predetermined range(s). In this way, the UAV may take off and / or land when the platform is sufficiently stable, thereby reducing risk and / or improving safety. In one example, the respective transceivers of the platform and / or the UAV are configured to respectively transmit and / or receive respective orientations (for example, yaw) thereof. Suitable compasses are known.

[0027] Pitch, yaw and / or roll

[0028] In one example, the measured pitch, yaw and / or roll (for example, respective angles thereof) (i.e. rotation about 1 , 2 and / or 3 mutually orthogonal axes) of the platform are with respect (i.e. relative) to local tangent plane coordinates (LTP), which are part of a spatial reference system based on the tangent plane defined by the local vertical direction and the Earth's axis of rotation. LTP coordinates are also known as local ellipsoidal system, local geodetic coordinate system, local vertical, local horizontal coordinates (LVLH), or topocentric coordinates. LTP coordinates consist of three coordinates: one represents the position along the northern axis, one along the local eastern axis, and one represents the vertical position. Two right-handed variants exist: east, north, up (ENU) coordinates and north, east, down (NED) coordinates. LTP coordinates serve for representing state vectors that are commonly used in aviation and marine cybernetics.

[0029] In one example, the measured pitch, yaw and / or roll (for example, respective angles thereof) (i.e. rotation about 1 , 2 and / or 3 mutually orthogonal axes) are used to rotate positional information, for example provided by GPS, GNSS and / or RTLS, of the platform and / or the UAV, such as described below in more detail.

[0030] GPS and / or GNSS

[0031] In one example, the platform comprises a GPS and / or a GNSS, for example a first GPS and / or a GNSS. In one example, the UAV comprises a GPS and / or a GNSS, for example a second GPS and / or a GNSS. In one example, the respective transceivers of the platform and / or the UAV are configured to respectively transmit and / or receive respective positions thereof. Suitable GPS and GNSS are known.

[0032] RTK

[0033] In one example, the system is configured to use real-time kinematic (RTK) positioning for take off and / or landing of the UAV. In this way, the UAV may take off and / or land precisely and / or accurately landing, such as in and / or during harsh environments such as a dim / dark / foggy / rainy environment, versus using conventional machine-vision or infrared to detect a tagged marking on the point of landing on ground / platforms, thereby reducing risk and / or improving safety. In one example, the UAV is configured to guide itself during takeoff and / or landing using RTK positioning, for example wherein the RTK positioning uses information received from the platform. In one example, the information allowing the UAV to allow it to guide itself during takeoff and landing comprises the measured pitch, yaw and / or roll (for example, respective angles thereof) of the platform. In one example, the UAV includes a computer, comprising a processor and a memory, configured to implement the RTK positioning, for example using a RTK positioning algorithm, such as described below in more detail. In one example, the platform comprises an RTK device (such as a first RTK device), for example a computer, comprising a processor and a memory, configured to implement RTK positioning, for example using a RTK positioning algorithm, such as described below in more detail. In one example, the UAV comprises an RTK device (such as a second RTK device), for example a computer, comprising a processor and a memory, configured to implement RTK positioning, for example using a RTK positioning algorithm, such as described below in more detail. In one example, the platform and the UAV comprise respective RTK devices (such as a first RTK device and a second RTK device, respectively). In one example, the system, for example the platform, comprises another RTK device (such as a third RTK device), configured as a compass to provide orientation-heading angle of the platform (i.e. yaw). In this way, this orientation-heading angle is complementary to the IMU and / or compass yaw, thereby improving precision and / or accuracy.

[0034] In one example, the system, for example the controller, is configured to repeatedly and / or continuously estimate respective positions and / or rotations of the platform and / or the UAV for guiding the UAV during takeoff and / or landing, for example using information received respectively thereby and / or respectively measured thereby. In one example, the controller is configured to permit or deny takeoff and / or landing of the UAV based on the estimated respective positions and / or rotations of the platform and / or the UAV. In one example, the system, for example the controller, is configured to repeatedly and / or continuously estimate respective positional trajectories and / or rotational trajectories of the platform and / or the UAV for guiding the UAV during takeoff and / or landing, for example using information received respectively thereby and / or respectively measured thereby. In one example, the controller is configured to permit or deny takeoff and / or landing of the UAV based on the estimated respective positional trajectories and / or rotational trajectories of the platform and / or the UAV. In one example, the controller is configured to implement a remedial action if the takeoff and / or landing is denied. In one example, the controller is configured to maintain the UAV within a volume projected vertically above the platform during takeoff and / or landing.

[0035] Altimeter

[0036] In one example, the system comprises one or more altimeters. In one example, the UAV comprises an altimeter and / or the platform comprises an altimeter. In this way, altitude precision and / or accuracy is improved during take off and / or landing in harsh environments, thereby reducing risk and / or improving safety. While a UAV altimeter may be redundant in view of a barometer included in the UAV, the UAV altimeter will improve the safety level since if there are wind gusts or changes in air temperature and pressure, which is common in sea environment, the altimeter provides extra altitude information to assist the RTK signals to perform the taking off, flying and landing tasks, thereby avoiding colliding with ships / platforms or the water, thereby reducing risk and / or improving safety.

[0037] Altitude

[0038] In one example, the controller is configured to send instruction signals via the transceivers on the platform to the one or more transceivers on the UAV to cause the UAV to fly to a defined altitude (Z) above the landing pad; and hold a position at the defined altitude (Z) for a time period (T1 ). In one example, the altitude (Z) is in a range from 5 to 10 meters. In one example, the time period (T1 ) is in a range from 2 to 10 seconds. In one example, the controller is configured to send instruction signals via the transceivers on the platform to the one or more transceivers on the UAV to cause the UAV to take off from the landing pad.

[0039] In one example, the controller is configured to send instruction signals via the transceivers on the platform to the one or more transceivers on the UAV to cause the UAV to:

[0040] (a) fly at a defined altitude from a center of the platform or landing pad;

[0041] (b) hold a position at the defined altitude for a defined time period; and (c) land by sending instruction signals to the UAV to continue to fly downwards to the platform or landing pad.

[0042] In one example, the controller is configured to cause the UAV to perform step (b) only if step (a) is successful. In one example, the controller is configured to cause the UAV to perform (c), only if step (b) is successful and the position is held for the defined time period (T2). In one example, the defined altitude (Z) is in a range from 10 to 15 meters from the platform or landing pad. In one example, the time period (T2) is in a range from 5 to 10 seconds.

[0043] In one example, the controller is configured to cause the UAV to fly at the defined altitude and / or hold the position at the defined altitude via and / or using QGC (Quasi-Complex gradients).

[0044] Manual take over (override)

[0045] In one example, the system comprises a remote controller, configured for fully and / or partially controlling the UAV, for example by a human or a non-human pilot, such as switching between normal operations and RTK missions, to start the RTK mission, to stop the mission if needed. For enhancing safety, the pilot may manually take over the flight, for example take off and / or landing, by applying manual mode in the GCS (Ground Control System) or by switching the buttons in a Remote Controller, and transit the mission into Hold / Altitude mode so the pilot can safely bring the UAV back to its home position.

[0046] Integrated System

[0047] In one example, the system comprises a QGC (also known as QGroundControl) in Ground Control System, having an interface for the signals and a GUI to visualize the information of the RTK system, such as relative position, carrier solution, GNSS valid, locked satellites as LED flags, etc., to ensure the readiness and safety for performing the RTK.

[0048] In one example, the system also includes a Companion Computer in and / or for the UAV, to set all configurations automatically, compute the sensor fusing algorithm, handle and monitor tasks, and / or to perform real time monitoring and logging.

[0049] RTLS

[0050] In one example, the system comprises a RTLS (Real-Time Locating System) for tracking a position of the UAV relative to the platform. Suitable RTLS are known.

[0051] Vision In one example, the system comprises a vision-based system for guiding the UAV relative to the platform, for example wherein the platform comprises markers and wherein the UAV comprises an imaging device, such as a camera. When the UAV is taking off and landing, this system provides vision information for the UAV to check its current position relative to the markers and hence the platform. With a sensor fusing technology, the vision-based system works harmoniously with an RTK system to ensure safe landing. In some extreme condition, where the RTK system is somehow interference with its GPS signals and communication stability, the controller may instead rely on the vision-based system for safe landing. This will reduce the risk of aborting the precise landing, or the chance for a pilot to take over.

[0052] Steps

[0053] The system according to the first aspect may be configured to perform any of the steps described with respect to the second aspect and / or the third aspect.

[0054] Second aspect

[0055] A second aspect provides a method for take off 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 UAV to cause the UAV to fly to a defined altitude (Z) above the landing pad; and hold a position at the defined altitude (Z) for a time period (T 1 ). In one example, the altitude (Z) is in a range from 5 to 10 meters. In one example, the time period (T1 ) is in a range from 2 to 10 seconds. In one example, the method comprises sending instruction signals, for example by a controller, via the transceivers on the landing pad to the one or more transceivers on the UAV to cause the UAV to take off from the landing pad. In one example, wherein during takeoff, the landing pad rotates about 1 , 2 and / or 3 mutually orthogonal axes, for example pitching, yawing and / or rolling.

[0056] In one example, the method comprises and / or is a method of take off of the UAV.

[0057] The method according to the second aspect may include any of the steps described with respect to the first aspect and / or be performed using a system according to the first aspect.

[0058] Third aspect

[0059] A third aspect provides a method for take off and landing of an unmanned aerial vehicle (UAV), wherein during landing the method comprises steps of: (a) sending instruction signals to the UAV to fly at a defined altitude from a center of the landing pad; and

[0060] (b) sending instruction signals to the UAV to hold a position at the defined altitude for a defined time period; and

[0061] (c) landing the UAV by sending instruction signals to the UAV to continue to fly downwards to the landing pad.

[0062] In one example, the method performs step (b) only if step (a) is successful. In one example, the method performs step (c), only if step (b) is successful and the position is held for the defined time period (T2). In one example, the defined altitude (Z) is in a range from 10 to 15 meters from the landing pad. In one example, the time period (T2) is in a range from 5 to 10 seconds. In one example, wherein during landing, the landing pad rotates about 1 , 2 and / or 3 mutually orthogonal axes, for example pitching, yawing and / or rolling.

[0063] The defined distances in altitudes such as Z are for takeoff and landing operations and the defined time periods T 1 and T2 correspond to the time for which the positions are held during the defined takeoff and landing operations, respectively.

[0064] In one example, the method comprises and / or is a method of landing the UAV.

[0065] The method according to the third aspect may include any of the steps described with respect to the first aspect and / or any steps of the second aspect and / or be performed using a system according to the first aspect.

[0066] This solution allows the unmanned aerial vehicle to land and takeoff 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.

[0067] Another objective is to provide a simple and cost effective solutions for landing UAVs in harsh conditions in the sea.

[0068] BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Following 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: Figures 1 a and 1 b schematically depict a prior art system, showing a top view of the platform and the UAV;

[0070] Figure 2 schematically depicts a system, employing a real time locating system, according to the present invention;

[0071] Figure 3 schematically depicts a system including transceivers employed on the platform and the UAV, according to the present invention;

[0072] Figure 4 schematically depicts a side elevation view of a UAV takeoff, according to the present invention;

[0073] Figures 5a to 5c schematically depict a views (Figure 5a: plan view; Figure 5b: side elevation view; Figure 5c: side elevation view) of a UAV landing sequence, according to the present invention; and

[0074] Figure 6 is a flowchart of method steps for landing a UAV safely on the platform, according to the present invention.

[0075] DETAILED DESCRIPTION OF THE DRAWINGS

[0076] In 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] Figure 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 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 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 recording images that an onboard computer that evaluates and analyses images and data in order to control the UAV 30.

[0081] The lights may also be positioned such that it is possible for the UAV 30 to evaluate the angle of the UAV 30 in relation to the platform 10. It is also known to use visual aids that makes it possible for the 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.

[0082] All these solutions are visual aids that help guiding an 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 UAV 30 are not of sufficient quality to give the UAV information enough to land safely on the platform 10.

[0083] 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 can result in the UAV getting destroyed or destruction to electronics of the UAV.

[0084] Figure 1 b 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.

[0085] 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.

[0086] 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.

[0087] For an autonomous take off and landing, the system uses an algorithm that tries to land and take off from a platform 10 using the relative position between the platform 10 to land on and the UAV 30.

[0088] 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.

[0089] 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 1 a) and four tags 20 on the UAV (Figure 1 b). Hence, it was possible to know the position from the platform to the UAV and vice versa.

[0090] 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.

[0091] Figure 2 illustrates a system employing a real time locating system (RTLS), according to the present invention.

[0092] Much of the current research on autonomous landing and take off from boats centers around the idea of machine vision, where a visual identification marker (such as a QR code) 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.

[0093] There is no marine UAV system today that is robust and powerful enough to handle take off 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 controller. Therefore, we need a controller that continuously predicts and optimizes the UAV's trajectory as the platform 10 moves.

[0094] Real-time kinematic (RTK) positioning is a solution to eliminate the disturbances affecting the compass so that the UAV can recognize its positioning.

[0095] 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 10, the control algorithm the UAV rapidly matches the velocity of the platform with the feed-forward term. Moreover, with the proportional term for position the UAV 30 can reach the position of the platform 10.

[0096] 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.

[0097] The RTK system composed of three RTK GPS that returns the position from the platform 10 RTK GPS to the UAV 30 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 (DOM) (Equation 1 ) it is possible to rotate the offset I b-frame to n-frame (Equation 2 as shown below).

[0098] Figure 3 is a system illustrating transceivers 60, 70 employed on the platform 10 and the UAV 30, according to the present invention.

[0099] For explanatory purposes, the altitude (Z) may be defined for takeoff operations and the altitude (Z) may be defined for landing operations. Similarly, the time period (T1 ) may correspond to takeoff 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.

[0100] 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.

[0101] In the present invention the RTLS system is optionally mounted on both the UAV 30, and the platform 10. The idea is to mount the anchors on each corner of the landing platform, as illustrated in Figure 1a. 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 1 m above the deck of the ship; the idea is that the RTLS system should pick up the UAV 30 as it approaches the ship and guide it during landing. The UAV 30 will converge on the x,y-position of the platform 10 first, tracking it from a height of about 30m. Then, the UAV 30 will descend down to the platform 10. We assume that the air column directly above the landing platform is free of obstacles. The UAV 30 will be clearing masts, about 20 meters at the highest, before starting its descent.

[0102] What is needed is position, for example RTK position, estimates of the UAV in 3D space, for example pitch and / or roll, such as provided by the RTK positioning described with respect to Figure 2. Orientation (for example, yaw) estimates are also desirable, but not strictly necessary. In this example, the system 1 comprises an RTK positioning system, as described with respect to Figure 2.

[0103] 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 (i.e. pitches), a transformation will be performed, as described with respect to Equations 1 and 2, 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.

[0104] In more detail, the landing pad may include an IMU, 1 or 2 uBlox, a power source and optionally a remote communication device.

[0105] The system may include a QR code RTLS as redundant system to provide more robust information for landing.

[0106] Figure 4 is a perspective view, of UAV 30 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 (QGroundControl). This altitude is held for a few seconds (e.g. 3 seconds).

[0107] Figure 5a to 5c is a perspective view of a UAV landing sequence according to the present invention.

[0108] Figure 5a is a view from above of the initial step of a UAV 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 30 ensures that the UAV 30 finds the platform 10 and is able to position itself over the landing pad 50 on the platform 10.

[0109] Figure 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 30 holds this position for a predetermined amount of time. If the UAV 30 moves too far away from the platform in a horizontal direction within this predetermined amount of time, the UAV 30 reverts to the previous step in the landing sequence. The limit of the space that the UAV 30 can move is indicated as the space between the grey boxes and is in real life monitored by the RTLS tags 20.

[0110] Figure 5c is a view from the side showing that the UAV 30 flies at a constant speed downwards towards the platform 10 until it hits (i.e. lands on) 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.

[0111] Figure 6 depicts a flowchart of method steps for landing a UAV safely on the platform according to the present invention.

[0112] Step 601 : The UAV flies horizontally at predefined altitude from the center of the platform 10.

[0113] Step 602: It is determined if, the altitude X is within the predefined limit? If yes, proceed to step 603, if the answer is no, go back to step 601 .

[0114] Step 603: Hold the position X at the defined position above the platform 10 for x-seconds.

[0115] Step 604: It is determined if the position is held stable and within the threshold? If the answer is yes, proceed to step 605, If the answer is no, go back to step 603.

[0116] Step 605: Fly at a constant speed until the UAV lands on the platform. In the preceding description, various aspects of the system, the UAV and the platform according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems, equations and configurations were set forth in order to provide a thorough understanding of the system and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the system, which are apparent 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 numbers

[0117] 10 RTLS platform

[0118] 20 RTLS tags on platform and UAV

[0119] 30 UAV or unmanned aerial vehicle

[0120] 40 Arms of the UAV

[0121] 50 Landing pad on the platform

[0122] 60 Transceivers on platform

[0123] 70 Transceivers on UAV

[0124] 80 Propellers on UAV

[0125] 90 Additional devices such as sensors, GPS systems, monitoring systems.

Claims

AMENDED CLAIMS received by the International Bureau on 05 August 2025 (05.08.2025)CLAIMS1. A system (1) for take off and landing of an unmanned aerial vehicle, UAV, (30) on a platform (10), the system (1) comprising: at least one UAV (30) capable of landing and taking off from a landing pad (50) on a platform (10) autonomously, comprising one or more 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 take off and landing of the UAV (30); wherein the platform (10) comprises one or more transceivers (60) configured to communicate with the UAV (30) and provide information allowing the UAV (30) to guide itself during takeoff and landing; wherein the system (1) comprises a device, such as an IMU and / or a compass, configured to measure rotation of the platform (10) about 1 , 2 and / or 3 mutually orthogonal axes, for example pitch, yaw and / or roll; wherein the information allowing the UAV (30) to guide itself during takeoff and landing comprises the measured rotation of the platform (10) about 1 , 2 and / or 3 mutually orthogonal axes; wherein the system (1) is configured to use real-time kinematic, RTK, positioning for take off and / or landing of the UAV (30); and wherein the system (1) is configured to repeatedly and / or continuously estimate respective positional trajectories and / or rotational trajectories of the platform (10) and / or the UAV (30) for guiding the UAV (30) during takeoff and / or landing.

2. The system in accordance with claim 1 , wherein the one or more transceivers (60) of the platform (10) and the one or more transceivers (70) on the UAV (30) communicate through radio communication signals.

3. The system in accordance with any one of claims 1 to 2, wherein the system (1) comprises additional sensors, positioning and monitoring devices (90) configured to guide the UAV (30) during takeoff and landing.

4. The system (1) in accordance with any of claims 1 to 3, wherein the system (1) comprises a controller (100) arranged on the platform (10) for controlling the communications between the UAV (30) and the platform (10) and issuing signals to the said one or more transceivers (60, 70).

5. The system (1) in accordance with any of claims 1 to 4, wherein the platform (10) comprises a GPS and / or a GNSS and / or wherein the UAV (30) comprises a GPS and / or a GNSS.

6. The system (1) in accordance with any of claims 1 to 5, wherein the UAV (30) is configured to take off and / or land conditionally, for example only when the measured rotation of the platform (10) about 1 , 2 and / or 3 mutually orthogonal axes are within predetermined ranges and / or when respective rates of change and / or speeds, velocities and / or accelerations of the measured rotation of the platform (10) about 1 , 2 and / or 3 mutually orthogonal axes are within predetermined ranges.

7. The system (1) in accordance with any of claims 1 to 6, wherein the system (1) comprises a compass, configured to measure yaw of the platform (10).

8. The system (1) in accordance with any of claims 1 to 7, wherein the system (1) is configured to repeatedly and / or continuously estimate respective positional trajectories and / or rotational trajectories of the platform (10) and / or the UAV (30) for guiding the UAV (30) during takeoff and / or landing.

9. The system (1) in accordance with claim 8, wherein the system (1) is configured to permit or deny takeoff and / or landing of the UAV (30) based on the estimated respective positional trajectories and / or rotational trajectories of the platform (10) and / or the UAV (30).

10. The system (1) in accordance with any of claims 1 to 9, wherein the system (1) comprises a Real-Time Locating System, RTLS, for tracking a position of the UAV (30) relative to the platform (1).11 . The system (1) in accordance with any of claims 1 to 9, wherein the system (1) comprises a vision-based system for guiding the UAV (30) relative to the platform (10).

12. A method for take off and landing of an unmanned aerial vehicle, UAV, employing the system in accordance with any one of claims 1 to 11 , 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 UAV to cause the UAV to fly to a defined altitude above the landing pad; and hold a position at the defined altitude for a time period.

13. The method in accordance with claim 12, wherein the defined altitude is in the range of 5 to 10 meters.

14. The method in accordance with claim 13, wherein the time period is in the range of 2 to 10 seconds, and wherein the controller sends instructions signals to the UAV to takeoff from the landing pad.

15. A method for takeoff and landing of an unmanned aerial vehicle, UAV, employing the system in accordance with any one of claims 1 to 11 , wherein during landing the method comprises steps of:(a) sending instruction signals to the UAV to fly at a defined altitude from a center of the landing pad;(b) sending instruction signals to the UAV to hold a position at the defined altitude for a defined time period; and(c) landing the UAV by sending instruction signals to the UAV to continue to fly downwards to the landing pad.

16. The method in accordance with claim 15, wherein the method performs step (b) only if step (a) is successful.

17. The method in accordance with claim 15, wherein the method performs step (c), if step (b) is successful and the position is held for the defined time period.

18. The method in accordance with any one of claims 15 to 17, wherein the defined altitude is in the range of 10 to 15 meters from the landing pad.

19. The method in accordance with any one of claims 15 to 18, wherein the time period is in the range of 5 to 10 seconds.[0001][0002]STATEMENT UNDER ARTICLE 19(1) PCT[0003]The cited prior art does not disclose the subject matter of amended claim 1 at least.

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