Patent Description:
The invention relates to a tethered automatic unmanned aerial vehicle system.

<CIT> discloses a multi-copter that is attached to a tether, wherein an evaluation unit determines a tension in the tether and an acceleration of the multi-copter to derive an elevation angle. Further, an angle of incidence of the tether and gravity may be determined at the multi-copter, such as to determine from the detected angle an angular position of the multi-copter with respect to an operator.

<CIT> discloses an unmanned aerial vehicle tethered to a substrate, wherein a tether sensor is mounted on the substrate. The tether sensor determines an orientation of the tether relative to the substrate. A micro controller, receiving the measured orientation from the tether sensor, determines an orientation of the tether relative to the substrate, and as a function of the orientation, determines a corrective value and outputs the corrective value to the unmanned aerial vehicle as at least one of a roll output and a pitch output control signal.

Unmanned aerial vehicles (UAV) for civil and military use are known in the art. For example, remote controlled multi-copters can be equipped with a variety of functional payloads such as cameras, heat sensors, communication sensors, lasers and the like for aerial monitoring, situational awareness, target acquisition and inspection.

These multi-copters have the advantage that they are easy to use, less expensive than manned aerial vehicles and require comparably little storage space.

Navigation typically relies on satellite-based positioning systems such as the global positioning system (GPS).

The UAV also comprises electronic components that are sensitive to the magnetic field such as a compass. The compass is of key importance for safe and controlled flight.

A drawback on such UAVs is that electromagnetic noise, e.g. due to signal jamming or spoofing, or bad signal transmission due to physical obstructions can cause the electric components for navigation to fail or can impair communication with the remote control for the UAV.

Under such circumstances the UAV becomes uncontrollable. Moreover, strong winds might be prohibitive for safe flight of the UAV.

In emergency applications however, it is crucial that a UAV can lift off independent of GPS signal reception, winds or electromagnetic noise.

An object of the present invention is to provide an aerial system that is capable to perform flight missions independent of environmental conditions. The object is achieved by the system having the features of claim <NUM> and a method with the features of claim <NUM>.

Advantageous embodiments are provided by the dependent claims.

According to claim <NUM>, a tethered automatic unmanned aerial vehicle system comprises at least the components:.

The system is characterized in that the ground station comprises a preload assembly with a movable member that is arranged in contact with the tether and that is configured to alter a tether path length of an adjustable tether path in the ground station, particularly wherein the movable member is rotatably mounted such that the member can rotate around an axis of the member, wherein the movable member is arranged translationally movable on a guide of the preload assembly that allows the tether path length in the ground station to be adjusted in length by moving the movable member along the guide, such that a load on the tether can be adjusted by moving the movable member.

The system according to the invention is capable for flight missions independent of an electromagnetic noise environment and/or an availability of a satellite-based positioning signal, such as a GPS signal. Moreover, even in strong wind conditions, the danger of a loss of the UAV is greatly reduced, as the tether connection secures the UAV against being blown away.

The term "unmanned aerial vehicle", short UAV, such as the term "multi-copter" particularly refer to a powered, aerial vehicle that does not carry a human operator and has rotary wings to provide vehicle lift. Particularly, the UAV is configured to be piloted remotely and to carry a payload, such as a camera, a heat sensor, a communication sensor, a laser and the like for aerial monitoring, situational awareness, target acquisition and inspection.

As the angle-sensor is arranged on the UAV - and not at the ground station - a solid angle providing information about a three-dimensional angle of incidence of the tether, particularly with respect to a horizontal plane, and thus a direction towards the ground station can be determined by the UAV.

According to another embodiment of the invention, the angle-sensor is further arranged and configured to determine a yaw angle with respect to a yaw axis of the UAV relative to the tether and thus relative to the direction of the ground station. The yaw axis particularly points vertically away with respect to the UAV, particularly opposite the gravitational pull. This embodiment particularly allows for compensating a flight attitude of the UAV relative to the horizontal plane and thus to determine the angle of incidence relative to the horizontal plane by adjusting for the determined yaw angle.

The term "ground station" particularly refers to a system comprising a landing platform and/or a remote control system for the UAV. Also, the ground station can comprise an evaluation module, such as a computer, for evaluating sensor data and/or signals of the components of the aerial system.

According to another embodiment of the invention, the UAV comprises a data storage configured to store and/or update a position of the ground station.

According to another embodiment of the invention, the tether is longer than <NUM>, particularly longer than <NUM>, particularly longer than <NUM>, wherein a free tether length can be automatically adjusted by the system.

The tether has essentially no stiffness such that it is very flexible. Particularly, the tether is so flexible that it generates or has essentially no restoring forces when bent.

By preloading the tether, it is possible to increase the accuracy of the determined angle of incidence and thus the angular position determination.

According to another embodiment of the invention, the UAV and/or the ground station is configured to determine a relative altitude of the particularly flying UAV with respect to the ground station.

This is particularly possible by accounting for a free length of the tether between the UAV and the ground station and the angle of incidence.

Spherical coordinates can be used for determining the altitude of the UAV.

According to another embodiment, a height sensor and /or an ambient pressure sensor can be used for determining the flight altitude of the UAV.

According to another embodiment, the system, particularly the UAV and/or the ground station is configured to autonomously determine a three-dimensional position of the UAV with respect to the ground station, with the information about the free tether length and the angle of incidence.

According to this embodiment, no global or external positioning signals are needed to determine the relative position if the UAV.

According to another embodiment of the invention, the tether is connected to the unmanned aerial vehicle by an angle-adjustable mount assembly, such as a pivot assembly or a swivel assembly, wherein the angle-adjustable mount assembly comprises an inertial measurement unit, short IMU, wherein the angle-adjustable mount assembly is configured to map, particularly by means of a rigid mechanical connection or relation of the IMU and the mount assembly, the angle of incidence to the IMU such that the IMU assumes a corresponding angle with the angle-adjustable mount assembly, particularly wherein the IMU is connected to the tether.

This embodiment allows for precise determination of the angle of incidence. It is noted that the IMU is particularly not configured and arranged in the UAV to determine an orientation of the UAV in space, for which IMUs are used typically in UAVs.

The IMU is configured to determine the angle of incidence. The IMU is particularly configured to provide IMU data comprising the information about the angle of incidence to an evaluation on the UAV for further processing of IMU data.

According to another embodiment of the invention, the mount assembly and particularly the IMU is arranged rotatably on a ball-bearing and/or a gimbal that is configured to rotate at least around a roll and a pitch axis of the UAV. This allows compensating for a pitch and roll angle the UAV might assume, leaving the mount assembly unaltered and non-sensitive to the pitch and roll angle of the UAV. The UAV can for example adopt roll and pitch angles due to wind or its own flying motion.

The roll and pitch angle of the UAV are well-defined axis of the UAV and known the person skilled in the art. The roll axis particularly extends along a forward direction of the UAV, wherein the pitch axis particularly extends orthogonally to the roll and aw axis.

According to another embodiment of the invention, the angle-sensor comprises aa gyroscope and/or an optical sensor, particularly wherein the sensor is not an image sensor.

This embodiment allows for a quick, economic and reliable determination of the angle of incidence.

According to another embodiment of the invention, the optical sensor comprises an illumination module, such as an LED and a detection module, such as a quadrant diode.

According to another embodiment of the invention, the tether comprises a data cable for transmitting an angle-sensor signal, IMU data and/or angle-sensor data to the ground station.

According to another embodiment of the invention, the tether comprises a communication cable for transmitting control signals from a remote control that is particularly operated by an operator to the UAV.

This embodiment allows for secure and interference-free transmission of control signals to the UAV. Thus, even in high-electromagnetic noise environments the UAV is capable to receive and detect the control signals from the remote control.

The communication and/or the data cable might comprise a coating for shielding the communication and/or data cable from electromagnetic noise.

According to another embodiment of the invention, the tether comprises an electricity supply cable that is configured to provide electricity to the UAV for flying and operation.

This allows for an extended and temporal almost unlimited use of the UAV, as compared to battery-driven UAVs.

According to another embodiment of the invention, the evaluation module arranged on the UAV is configured to evaluate the angle-sensor data and/or the IMU data. The evaluated data are then transmitted via the appropriate cable or by a RF-transmission module to the ground station and/or to the remote control to adjust a position and/or orientation of the UAV.

According to another embodiment of the invention, the tether is configured to transmit sensor data from an additional sensor such as a camera or a telemetry-system to the ground station.

According to another embodiment of the invention, the ground station comprises a rotatably mounted tether drum configured to roll up and to roll off the tether from the tether drum such as to adjust the free tether length of the tether between the unmanned aerial vehicle and the ground station.

This embodiment allows for a variable use of the system and also for compact storage of the tether.

According to another embodiment of the invention, the preload assembly with the movable member is arranged in contact with the tether.

The preload assembly may serve for an ordered winding and unwinding from a tether drum, which allows for a faultless functioning for the system during operation.

According to a further embodiment of the invention, the movable member is rotatably mounted such that the member can rotate around an axis of the member, particularly wherein the movable member is arranged between an opening of the ground station through which the tether exits the ground station towards the unmanned aerial vehicle and the tether drum.

According to another embodiment of the invention, the guide extends vertically and the movable member moves vertically along the guide of the preload assembly that allows the tether path length in the ground station, particularly the tether path length between tether the drum and the opening in the ground station to be adjusted in length by moving the movable member along the guide, such that a load on the tether can be adjusted by moving the movable member.

This embodiment allows for facile, robust and efficient realization of the movable member.

According to another embodiment of the invention, the movable member, particularly a shaft or a wheel, is rotatably mounted such that the member can rotate around an axis of the member, particularly wherein the movable member is arranged between an opening of the ground station through which the tether exits the ground station towards the unmanned aerial vehicle and the tether drum, wherein the movable member is arranged translationally movable on the guide, particularly wherein the guide extends vertically and the movable member moves vertically along the guide of the preload assembly that allows the tether path length in the ground station, particularly the tether path length between tether the drum and the opening in the ground station to be adjusted in length by moving the movable member along the guide, such that a load on the tether can be adjusted by moving the movable member.

Particularly, the movable member is in constant contact with the tether independent of the position of the tether.

This embodiment provides a robust and easy way to precisely control a preload of the tether with a short reaction time.

Moreover, this embodiment allows for adjusting the preload of the tether without the need to engage in a tether drum activation (roll up or roll down), which renders the system more energy efficient.

According to another embodiment of the invention, the movable member is formed as an elongated shaft.

According to another embodiment of the invention, the movable member is a wheel that is in contact with the tether at a rim portion of the wheel, particularly wherein the wheel comprises a circumferential recess that serves as a guide for the tether.

According to another embodiment of the invention, the tether is arranged such in the ground station that it extends from the tether drum downward, then extends around a lower portion, i.e. a ground facing portion of the movable member, particularly wherein the tether extends between ground and the axis of the movable member, and then upwards through the receiving opening of the ground station.

According to another embodiment of the invention, the movable member is spring loaded, such that a spring force from a spring of the preload assembly pushes the movable member onto the tether. The preload assembly is particularly a spring assembly.

According to another embodiment of the invention, the preload assembly comprises at least one position sensor for example in form of a distance sensor or an infrared sensor configured to determine a position of the movable member in the guide.

According to another embodiment of the invention, the preload assembly comprises a load sensor configured to determine a tether load of the tether between the ground station and the UAV, wherein the system is configured to adjust the tether load for example by moving the movable member the along the guide, or by rolling up or rolling down the tether from the tether drum, particularly in response to the determined tether load, such that the tether load remains higher than a predefined minimum tether load.

According to another embodiment of the invention, the preload of the tether is adjusted by a weight of the movable member weight in connection with gravity.

According to another embodiment of the invention, the preload assembly comprises a load sensor, wherein the load sensor is configured such that the tether load is determined with the load sensor arranged at the ground station.

According to another embodiment of the invention, the preload assembly comprises a spring damping assembly, wherein the spring damping assembly is configured such that the tether load is determined with the load sensor arranged at the ground station.

According to another embodiment of the invention, the tether path inside the ground station exhibits a local minimum located such in the tether path that a fluid, such as water, on the tether accumulates at the minimum for dripping off at the minimum, particularly wherein said minimum is located between the tether drum and the receiving opening of the ground station, particularly wherein the local minimum is adopted at the movable member.

This embodiment combines the preload control with a fluid drop-off arrangement.

According to another embodiment of the invention, the ground station is arranged or comprised by a vehicle, such as a car or a ship.

This embodiment provides a versatile aerial system that can be transported to an operation site by the vehicle.

The system is particularly further configured to be operatable with the ground station on the vehicle.

According to another embodiment of the invention, the system is configured to be operated during motion of the vehicle comprising the ground station.

The term "operated" in the context of this embodiment particularly includes a state of the system during which the unmanned aerial vehicle is flying. An operator for the UAV can in the vehicle.

According to another embodiment of the invention, the system is configured to drag the unmanned aerial vehicle in the air behind the vehicle comprising the ground station.

According to another embodiment of the invention, the ground station comprises a receiving opening for the tether through which the tether exits (and enters) the ground station towards the unmanned aerial vehicle, wherein at the receiving opening the ground station comprises a centering channel extending essentially vertically from the receiving opening, wherein the centering channel is configured to receive an elongated member attached to the unmanned aerial vehicle such that a lateral position of the unmanned aerial vehicle is stabilized during landing, particularly wherein the centering channel is a funnel.

The elongated member of the UAV extends essentially downwards form the UAV, i.e. towards the ground, particularly when no force is applied to the elongated member.

The assembly formed by the centering channel and the elongated member of the UAV allows for a landing aid for the UAV on the ground station even during adverse, i.e. gusty weather conditions.

According to another embodiment of the invention, the elongated member is rigidly coupled to the angle-sensor, particularly the IMU such that the angle-sensor adopts the same or a corresponding orientation as the elongated member.

According to another embodiment of the invention, the elongated member is attached to a bearing, particularly a ball-bearing or a gimbal such that it can assume any angle of incidence.

According to another embodiment of the invention, the tether is attached, particularly with a first end to the elongated member, particularly to a first end of the elongated member, such that the landing procedure can be performed by shortening the free tether path length. Centering of the UAV with respect to the ground station is facilitated by design of said assembly.

According to another embodiment of the invention, the elongated member has a length between <NUM> and <NUM>.

According to another embodiment of the invention, the centering channel comprises a ball bearing at the channel walls for holding the elongated member at reduced friction.

According to another aspect of the invention, a method for operating a tethered unmanned aerial vehicle, particularly a multi-copter, with a system according the invention is provided, wherein the method comprises at least the steps of:.

According to another embodiment of the invention, the method further comprises the step of adjusting a determined tether load such that the determined tether load is larger than a minimum tether load.

According to another embodiment of the invention, the tether load is adjusted with the preload assembly of the ground station.

Terms and definitions provided for the system are particularly applicable to the method in the same fashion and vice versa.

The system and method according to the invention solves several problems in the art. For example, there is no limitation of operation environments due to weather or electromagnetic noise or due to the absence of a global positioning system signal e.g. due to buildings or other physical obstructions.

The system according to the invention is particularly well-suited for applications in the civil and military sector. Moreover, in the field of physical security, the system can be used to protect critical infrastructure, such as chemical plants, power stations and wastewater treatment plants, as well as pipelines, railway lines and borders, with a minimum of personnel. Inspection and monitoring tasks for wind farms or railway lines are also conceivable.

For the vehicle-associated field of application, i.e. the ground station being arranged on or attached to a vehicle, the application areas cover for example situation overview, e.g. major events, driving patrol, as well as communication intelligence or electronic intelligence, target detection, as well as monitoring and inspection. The system according to the invention is configured to operate independently of GPS positioning or image positioning and is not disturbed by signal jamming or spoofing.

Furthermore, during flight the UAV can be automatically pulled behind a vehicle while keeping a predefined position relative to the vehicle / ground station on the vehicle.

Particularly, exemplary embodiments are described below in conjunction with the Figures. The Figures are appended to the claims and are accompanied by text explaining individual features of the shown embodiments and aspects of the present invention. Each individual feature shown in the Figures and/or mentioned in said text of the Figures may be incorporated (also in an isolated fashion) into a claim relating to the device according to the present invention.

In <FIG> several embodiments of the system <NUM> according to the invention is shown. The system <NUM> comprises an unmanned aerial vehicle (UAV) <NUM> in form of a multi-copter <NUM>. The multi-copter <NUM> is configured to hover (<FIG>) as well as to fly directionally. The multi-copter <NUM> can be a quadro-, hexa-, octa-, or a multi-copter with even more rotors <NUM> or rotor bearing arms <NUM>. The UAV can also be a VTOL (Vertical Take-Off and Landing vehicle), i.e. a multi-copter having non-rotatory wings for directional flight. The multi-copter <NUM> can have a landing gear <NUM> (cf. <FIG>), wherein said landing gear <NUM> is particularly automatically raised or stowed once the multi-copter <NUM> is in the air.

The multi-copter <NUM> is tethered to a ground station <NUM> be means of a tether <NUM> that extends between the multi-copter <NUM> and the ground station <NUM>.

The tether <NUM> is connected with a first end <NUM> to a body <NUM> of the multi-copter <NUM> and with a second end <NUM> to the ground station <NUM>. The connection of the tether <NUM> to the multi-copter <NUM> is such that the multi-copter <NUM> can determine an angle of incidence <NUM> of the tether <NUM> relative to a horizontal plane P or gravity G, which is equivalent. For this purpose, the tether <NUM> is mechanically connected with the first end <NUM> to an angle-sensor <NUM> that is configured to determine the angle of incidence <NUM> (cf. <FIG>, panel B). From the determined angle of incidence <NUM> a position of the multi-copter <NUM> with respect to the ground station <NUM> is determined. The angle of incidence is determined for example by an inertial measurement unit <NUM> (IMU), i.e. the angle-sensor can be an IMU. The IMU <NUM> comprises a three axes gyroscope and a three axes accelerometer and might also comprise a compass. The three axes gyroscope is used for determining the angle of incidence <NUM> of the tether <NUM> (cf. The compass is configured to determine the yaw axis <NUM> of the UAV <NUM>.

In order for the angle-sensor <NUM> to detect and determine the angle of incidence <NUM>, the tether <NUM> is connected to the angle-sensor <NUM> for example by means of an angle-adjustable mount assembly <NUM> that is configured to swivel or pivot for adopting the angle of incidence <NUM> without contributing or causing resistance or friction that could influence the angle of incidence <NUM>. The angle-adjustable mount assembly <NUM> automatically, particularly by design, decouples the flight attitude of the UAV <NUM> from the angle-sensor <NUM>. For example, during strong side winds the multi-copter might assume an angle <NUM> relative to the horizon, i.e. the multi-copter is tilted around the roll and/or the pitch axis such that the yaw axis <NUM> is not pointing along gravity G anymore. Nonetheless, due to the mount assembly <NUM>, the angle of incidence can be still determined correctly as the tilt around the roll and/or pitch axis is compensated at the mount assembly <NUM> such that the angle-sensor <NUM> remains unaffected.

The angle of incidence <NUM> is for example defined by an angle of the tether <NUM> with respect to a horizontal plane P that extends orthogonal to the gravitational pull G.

The angle of incidence <NUM> can also be measured with respect to the body <NUM> of the multi-copter <NUM>. However, this might require an additional instrument for taking into account an angle <NUM> of the body <NUM> of the multi-copter <NUM> with respect to the horizontal plane P, as the body <NUM> of the multi-copter <NUM> might not extend parallel to the horizontal plane P at all times during flight. From both angles the angles the angle of incidence <NUM> relative to the horizontal plane P can be determined.

The mount assembly <NUM> comprises a rigid elongated member <NUM> that points essentially downwards from the multi-copter <NUM> towards the ground <NUM>. The tether <NUM> is attached with its first end <NUM> to the first (lower) end <NUM> of the elongated member <NUM>. The elongated member <NUM> is pivotally and rotatably connected to the body <NUM> of the multi-copter <NUM> at a pivot portion or pivot point <NUM>. The elongated member <NUM> has an upper end <NUM> that is located at the multi-copter body <NUM>, wherein the pivot point <NUM> is arranged between the first, i.e. lower end <NUM> and the second, i.e. upper end <NUM> of the elongated member <NUM>. Therefore, any change of the angle of incidence <NUM> of the tether <NUM> causes the elongated member <NUM> to pivot or rotate around the pivot point <NUM>. As a consequence, the second end <NUM> of the elongated member <NUM> will adopt a different position and can thus be used as an indicator of the angle of incidence <NUM>. In the example, the inertial measurement unit <NUM> (IMU) is rigidly connected to the second end <NUM> of the elongated member <NUM> such that the IMU <NUM> is sensitive to the position, particularly the angle of the second end <NUM> of the elongated member <NUM> with respect to the pivot point <NUM> and therefore to the angle of incidence <NUM>. The angle-sensor in this embodiment is the IMU <NUM>. Moreover, the IMU <NUM> is sensitive, particularly only sensitive to the angle of incidence <NUM> relative to the horizontal plane P. This is particularly advantageous as the body <NUM> of the UAV <NUM> might adopt an angle <NUM> with respect to the horizontal plane P during flight, e.g. due to wind conditions or active flight (cf. <FIG>, panel B).

The pivot portion <NUM> for example comprises a ball-bearing <NUM> that allows for an adoption of any solid angle of the elongated member <NUM> and the body <NUM> of the UAV <NUM>.

Alternatively, the pivot portion <NUM> comprises a two axes gimbal <NUM> that pivotally holds the elongated member <NUM>.

Therefore, the mount assembly <NUM> maps the angle of incidence <NUM> to the IMU <NUM> by means of the elongated member <NUM> and its relative arrangement with respect to the pivot portion <NUM>.

The elongated member <NUM> is particularly a stiff straight rod that extends between <NUM> to <NUM> downwards from the multi-copter <NUM>.

The data of the IMU <NUM> might be processed and/or evaluated by an evaluation module (not shown) on the multi-copter <NUM>, particularly by a processor or a computer arranged on the multi-copter <NUM>.

The multi-copter <NUM> has a further IMU (not shown) that can be used for gathering flight and pose information, i.e. flight attitude and velocity of the multi-copter <NUM>. This second IMU is mandatorily rigidly connected to the body of the multi-copter <NUM> (and not a movable portion of the UAV).

The flexible tether <NUM> can be a simple rope, a nylon thread and/or comprises various different functionalities that might be comprised in dedicated cables (not shown) that are comprised by said tether <NUM>.

For example, the tether <NUM> can comprise a communication cable that is configured to transmit control commands from the ground station <NUM> to the multi-copter <NUM>.

This communication cable can be additionally shielded or configured such that electromagnetic interference from the environment is reduced.

Additionally, the tether <NUM> can comprise a data cable that is configured to transmit the IMU data and other data generated by the multi-copter <NUM> to the ground station <NUM> or a remote control.

The data cable can be the communication cable, particularly a glass-fiber cable.

Also, the tether <NUM> can comprise an electric cable configured to provide electricity to the multi-copter <NUM>. In this embodiment, the ground station <NUM> comprises or is connected to an electric energy source (not shown) that is connected to said electric cable. The electric cable in turn connects to the multi-copter <NUM> and provides electricity to the electric components of the multi-copter <NUM>, such as the motors for the rotors <NUM> and the electronic and electric components on the multi-copter <NUM>.

This allows for a dramatically reduced weight of the multi-copter <NUM> while gaining an essentially unlimited operational flight time allowing long-term missions.

The ground station <NUM> comprises a tether drum <NUM> for rolling up and down the tether <NUM> such that a free length <NUM> of the tether <NUM> is adjustable. The tether drum <NUM> can be motorized.

The tether drum <NUM> comprises a wheel or a drum <NUM> for storing the rolled-up tether <NUM>. From the tether drum <NUM> the tether <NUM> is guided to a receiving opening <NUM> of the ground station <NUM> through which the tether <NUM> exits and enters the ground station <NUM> for connecting with the multi-copter <NUM>.

Along the path of the tether <NUM> inside the ground station <NUM> there is a preload assembly <NUM> (cf. <FIG>) arranged that is configured to automatically adjust a load on the tether <NUM> extending between the multi-copter <NUM> and the ground station <NUM>.

The preload assembly <NUM> comprises a movable member <NUM> that is in constant contact with the tether <NUM> and that can move such that the free path length between the tether drum <NUM> and the multi-copter <NUM> can be adjusted, i.e. elongated or shortened, by particularly translationally moving the movable member <NUM>.

The movable member <NUM> is particularly a wheel that folds the tether path inside the ground station <NUM>. The movable member <NUM> is particularly arranged on a guide (indicated by two arrows at the movable member <NUM>) that allows for translational movement.

In one embodiment the movable member <NUM> is vertically movable wherein in another embodiment the movable member <NUM> is horizontally movable.

The ground station <NUM> can comprise additional components <NUM> for guiding a defining a path of the tether <NUM> inside the ground station <NUM>.

The preload assembly <NUM> allows for adjusting the free tether length <NUM> without activating the tether drum <NUM>. As the tether drum <NUM> is usually a comparably heavy device which needs a strong motor to turn the drum <NUM>, any actuation involving the tether drum <NUM> is usually only suitable for a coarse actuation of the tether length <NUM>. The preload assembly <NUM> therefor allows for a more precise actuation as it comprises light weight components and does not carry any unrolled tether portions. The preload assembly <NUM> allows the system to quickly adjust rapidly changing loads on the tether <NUM>, for example due to wind gusts or uneven terrain, in case the ground station is mounted on a vehicle.

The control of the preload assembly <NUM>, and thus the load that is put on the tether <NUM>, can be implemented in at least two ways according to the invention.

According to a first embodiment of the control of the preload assembly <NUM>, the movable member <NUM> is guided vertically and the tether <NUM> extends between the ground <NUM> and a ground-facing portion of the movable member <NUM>. Then, the tether <NUM> extends upwards towards the receiving opening <NUM> of the ground station <NUM>.

The movable member <NUM> is pulled by means of gravity G and thus puts a load on the tether <NUM> that is determined by the weight of the movable member <NUM>. This is a passive load control of the tether <NUM>. Additionally, the movable member <NUM> can be attached to a spring damping assembly <NUM> that can compensate for sudden load changes on the tether <NUM>. The spring damping assembly <NUM> can also be configured to for provide a preload on the tether <NUM>.

Alternatively, the control of the preload can be achieved with a motorized movable member <NUM> that adopts a position along the guide by means of a motor control.

For this purpose, the preload assembly <NUM> might comprise a force sensor for determining a load on the tether <NUM>.

The force sensor can be implemented or comprised by the spring damping assembly <NUM>.

Additionally, the preload assembly can comprise a position sensor <NUM> that is configured to determine a position of the movable member <NUM> along the guide. Any adjustment of the position of the movable member <NUM> can be determined based on the position sensor's signals. For increased redundancy and precision two position sensors <NUM> can be used for determining the position of the movable member <NUM>. The position sensor <NUM> is particularly an optical sensor.

A delicate phase during operation of aerial systems is the landing of the multi-copter.

In order to provide an automated and facile landing mechanism the invention offers an elegant solution that makes use of the elongated member <NUM> in a second way which is shown in detail in <FIG> and <FIG>.

For this purpose, the ground station <NUM> has a centering structure <NUM> arranged at the receiving opening <NUM> for the tether <NUM>.

In a first embodiment, the centering structure <NUM> comprises a centering channel <NUM> that extends along a vertical direction, i.e. parallel to gravity G (cf. <FIG>, panel B).

The centering channel <NUM> may protrude upwards, while its upper opening corresponds to the receiving opening <NUM>, or form a recess starting at the receiving opening <NUM> and extending inward the ground station <NUM>.

The centering channel <NUM> is for example a rigid pipe structure having an essentially cylindrical cross-section through which the tether <NUM> extends (<FIG> panel B).

Preferably, the centering channel <NUM> is a funnel with a wider opening (i.e. the receiving opening) pointing upwards and the smaller opening being closer to ground <NUM>.

During landing the elongated member <NUM> has to be brought to the receiving opening <NUM> of the centering channel <NUM> and then the tether <NUM> can be rolled-up such that the multi-copter <NUM> is pulled towards the centering channel <NUM>, while the elongated member <NUM> limits lateral motion of the multi-copter <NUM> due to the engagement in the centering channel <NUM>, which provides secure guidance during landing.

It is noted that the elongated member <NUM> is automatically pulled in the centering channel <NUM>, particularly when the free length <NUM> of the tether <NUM> is shorter than the centering channel <NUM>.

Alternatively, or additionally to the centering channel <NUM>, the centering structure <NUM> can comprise a ball bearing <NUM> arranged at receiving opening <NUM> (cf. <FIG>, panel A). Said ball bearing <NUM> reduces friction of the tether <NUM> when an angle <NUM> between ground station <NUM> and tether <NUM> becomes too small. The angle <NUM> between ground station <NUM> is particularly measured with respect to the horizontal plane P.

The angle <NUM> between the tether <NUM> and the ground station <NUM> can also be measured with a sensor (not shown) arranged at the receiving opening <NUM>.

From the free length <NUM> of the tether <NUM> and the angle of incidence <NUM> measured at the multi-copter <NUM>, a position of the multi-copter <NUM> relative to the ground station <NUM> can be determined.

Moreover, from the angle of incidence <NUM> also a yaw angle of the multi-copter <NUM> can be determined at least relative to the ground station <NUM>.

The multi-copter <NUM> is configured to carry a payload such as a camera or other sensors during flight and acquired data that is sent to the ground station <NUM>.

The system <NUM> can comprise a remote control (not shown) for control the multi-copter <NUM> and its components as well as the free tether length <NUM>, such that with the remote control the position and orientation of the multi-copter <NUM> can be controlled. Additionally, the remote control can comprise a real-time data transmission from the payload sensors.

The remote control can be comprised by the ground station <NUM> or form a separate component of the system <NUM>.

Claim 1:
A tethered automatic unmanned aerial vehicle system (<NUM>) comprising at least the components:
- an unmanned aerial vehicle (<NUM>), wherein the unmanned aerial vehicle (<NUM>) is a multi-copter with a body (<NUM>),
- a ground station (<NUM>),
- a flexible tether (<NUM>) that is connectable or that is connected to the unmanned aerial vehicle (<NUM>) and to the ground station (<NUM>), such that the unmanned aerial vehicle (<NUM>) is tethered to the ground station (<NUM>),
wherein the unmanned aerial vehicle (<NUM>) comprises an angle-sensor (<NUM>) configured and arranged to determine an angle of incidence (<NUM>) between the tether (<NUM>) and gravity (G) or a horizontal plane (P) or the body (<NUM>) of the multi-copter, such as to determine from the detected angle of incidence (<NUM>) at least an angular position of the unmanned aerial vehicle (<NUM>) with respect to the ground station (<NUM>), wherein the ground station (<NUM>) is configured to preload the tether (<NUM>), when the system (<NUM>) is in operation, such that the detected angle of incidence (<NUM>) is indicative of the angular position of the unmanned aerial vehicle (<NUM>) with respect to the ground station (<NUM>) or gravity (G),
characterized in that
the ground station (<NUM>) comprises a preload assembly (<NUM>) with a movable member (<NUM>) that is arranged in contact with the tether (<NUM>) and that is configured to alter a tether path length of an adjustable tether path in the ground station (<NUM>), wherein the movable member (<NUM>) is arranged translationally movable on a guide of the preload assembly (<NUM>) that allows the tether path length in the ground station (<NUM>) to be adjusted in length by moving the movable member (<NUM>) along the guide, such that a load on the tether (<NUM>) can be adjusted by moving the movable member (<NUM>).