WO2017021956A1

WO2017021956A1 - Sensing-device driven autonomous aircraft control

Info

Publication number: WO2017021956A1
Application number: PCT/IL2016/050836
Authority: WO
Inventors: Ohad ROZENBERG
Original assignee: Israel Aerospace Industries Ltd.
Priority date: 2015-08-05
Filing date: 2016-07-31
Publication date: 2017-02-09
Also published as: IL240374B

Abstract

The presently disclosed subject matter is related to the tracking of an object by a UAV. During tracking of an object, executed by a sensing device, a velocity of the object of interest is determined and based on at least the velocity of the object of interest and data indicative of a desired field of regard, UAV tracking velocity adapted for maintaining a distance between the UAV and the object of interest within a certain range is determined to allow retaining the object of interest within the desired field of regard while tracking.

Description

SENSING DEVICE DRIVEN AUTONOMOUS AIRCRAFT CONTROL

FIELD OF THE PRESENTLY DISCLOSED SUBJECT MATTER

The presently disclosed subject matter relates to the field of autonomously controlled aircrafts.

BACKGROUND

Unmanned aerial vehicles (also known as UAVs or drones) are sometimes utilized as an airborne system for surveillance and remote observation and tracking of objects. To this end UAVs are equipped with some type of data sensing unit (comprising a sensing device such as a camera, radar, sonar, etc.). The data sensing unit is used for surveying a scene and generating sensing-data, which includes data that was acquired by the sensing device or data generated by the sensing unit in relation to the acquired data (e.g. images of a scene, object-data characterizing identified objects within the images, etc.). The generated data can be transmitted, over a communication link, to a control unit where the sensing-data can be displayed on a display device to be viewed by an operator. The sensing unit can be further operable to lock on and track an object located in the surveyed scene.

The control unit enables to provide to the sensing unit control-data, including for example, different types of commands, such as lock and track command, zoom-in command, centering command, etc. Once the sensing unit has locked on an object in the scene, it continues to operate in response to tracking instructions, which are generated within the sensing unit and are directed for tracking the locked object. The tracking instructions are generated in order to maintain the object in the center of the FOV of the sensing device, even while the object moves relative to the sensing unit.

GENERAL DESCRIPTION

According to an aspect of the presently disclosed subject matter there is provided A UAV control unit mountable on a UAV comprising: a sensing unit comprising a sensing device, the sensing unit is configured to execute tracking of an object of interest; the control unit further comprises a processing unit configured to autonomously determine, during tracking of the object of interest, a velocity of the object of interest; determine, based on at least the velocity of the object of interest and data indicative of a desired field of regard, UAV tracking velocity adapted for maintaining a distance between the UAV and the object of interest within a certain range to allow retaining the object of interest within the desired field of regard during tracking of the object.

In addition to the above features, the method according to this aspect of the presently disclosed subject matter can optionally comprise one or more of features (i) to (viii) below, in any desired combination or permutation:

(i) . wherein the processing unit is further configured to generate instructions for controlling various aerial control devices in order to control the UAV to fly in the determined UAV velocity.

(ii) . The control unit is further configured to determine the UAV tracking velocity based on velocity of the object of interest, wind speed and flight characteristics of a selected flight pattern.

(iii) . The control unit is further configured for selecting an appropriate flying pattern to: The control unit according to any one of the preceding claims is further configured for selecting an appropriate flying pattern to: calculate the relative UAV ground speed needed for tracking the target in a given flight pattern; determine whether the relative UAV ground speed is applicable or not; and accordingly determine which of the flight patterns are available; and generate instructions for controlling the UAV to fly in a flight pattern selected from the available flight patterns. (iv) . The control unit is further configured to determine a velocity of the UAV based on information indicative of the current mission type and adapt the velocity accordingly.

(v) . The control unit according is further configured to repeatedly determine the UAV tracking velocity, using, in each determination, updated velocity of the object of interest and updated flight parameters for adapting the UAV tracking velocity to changes.

(vi) . The control unit is further configured, responsive to information indicative of a flight constraint, to calculate a bank angle which allows the aircraft to continue and track the object of interest without violating the flight constraint; and generate instructions to aerial control devices for guiding the aircraft for tracking the object without violating the flight constraints.

(vii) . The control unit is configured to calculate an updated UAV velocity to enable tracking the object without violating the flight constrains.

(viii) . The control unit is configured to repeatedly calculate the bank angle during tracking of the object in order to adapt the bank angle to real-time changes in the flight constraint data.

(ix). wherein the flight constraint is any one of: no-flight zone constraint flight of the aircraft over a certain ground area; a LOS or BLOS communication link constraint requiring an open communication link between the aircraft and a communication satellite at all times; a camera LOS constraint requiring an open LOS between an onboard camera and one or more objects of interest at all times; avoiding the perpendicular of the camera gimbals; a topographical and/or land cover constraint.

According to another aspect of the presently disclosed subject matter there is provided a method of autonomously controlling a UAV during tracking of an object of interest, the UAV comprising a sensing unit configured to execute tracking of an object of interest; the method comprising: executing tracking of an object of interest; determining, during tracking of the object of interest, velocity of the object of interest; determining, based on at least the velocity of the object of interest and data indicative of a desired field of regard, UAV tracking velocity adapted for maintaining a distance between the UAV and the object of interest within a certain range to allow retaining the object of interest within a desired field of regard during tracking of the object.

According to another aspect of the presently disclosed subject matter there is provided a non-transitory program storage device readable by a computer, tangibly embodying a program of instructions executable by the computer to perform a method of a method of autonomously controlling a UAV during tracking of an object of interest, the UAV comprising a sensing unit configured to execute tracking of an object of interest; the method comprising: executing tracking of an object of interest; determining, during tracking of the object of interest, velocity of the object of interest; determining, based on at least the velocity of the object of interest and data indicative of a desired field of regard, UAV tracking velocity adapted for maintaining a distance between the UAV and the object of interest within a certain range to allow retaining the object of interest within a desired field of regard during tracking of the object.

According to another aspect of the presently disclosed subject matter there is provided an aircraft configured with an auto-pilot flight and object tracking capabilities; the aircraft comprising a control unit, comprising: a sensing unit comprising a sensing device, the sensing unit is configured to execute tracking of an object of interest; the control unit further comprises a processing unit configured to autonomously determine, during tracking of the object of interest, a velocity of the object of interest; determine, based on at least the velocity of the object of interest and data indicative of a desired field of regard, aircraft tracking velocity adapted for maintaining a distance between the aircraft and the object of interest within a certain range to allow retaining the object of interest within the desired field of regard during tracking of the object.

According to some examples, the aircraft is a UAV.

The method, the program storage device and UAV disclosed in accordance with the presently disclosed subject matter can optionally comprise one or more of features (i) to (ix) listed above with respect to the method, mutatis mutandis, in any desired combination or permutation.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the presently disclosed subject matter and to see how it may be carried out in practice, the subject matter will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:

Fig. 1 is a functional block diagram of a UAV communicating with a control unit, according to an example of the presently disclosed subject matter;

Fig. 2a is a schematic illustration in top view of a UAV tracking an object of interest while flying in spiral flight pattern according to an example of the presently disclosed subject matter;

Fig. 2b is a schematic illustration in top view of a UAV tracking an object of interest while flying in offset-spiral flight pattern according to an example of the presently disclosed subject matter;

Fig. 2c is a schematic illustration in top view of a UAV tracking an object of interest while flying in sector-spiral flight pattern according to an example of the presently disclosed subject matter; Fig. 2d is a schematic illustration in top view of a UAV tracking an object of interest while flying in serpentine flight pattern according to an example of the presently disclosed subject matter;

Fig. 3 is a flowchart showing an example of a sequence of operations which are carried out during tracking of an object of interest, in accordance with the presently disclosed subject matter;

Fig. 4 is a flowchart showing an example of a sequence of operations which are carried out during tracking of an object of interest, in accordance with the presently disclosed subject matter;

Fig. 5 is a flowchart showing an example of a sequence of operations which are carried out during tracking of an object interest, in accordance with the presently disclosed subject matter;

Fig. 6a is a schematic illustration exemplifying a flight constraint according to an example of the presently disclosed subject matter;

Fig. 6b is a schematic illustration exemplifying a flight constraint according to an example of the presently disclosed subject matter; and

Fig. 7 is a functional block diagram schematically illustrating an example of a flight control unit, in accordance with the presently disclosed subject matter.

DETAILED DESCRIPTION

In the drawings and descriptions set forth, identical reference numerals indicate those components that are common to different embodiments or configurations. Elements in the drawings are not necessarily drawn to scale.

Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "determining", "generating", "calculating" or the like, include action and/or processes of a computer that manipulate and/or transform data into other data, said data represented as physical quantities, e.g. such as electronic quantities, and/or said data representing the physical objects.

UAV onboard control unit 30 and control unit 110 can both be implemented as computerized devices comprising or otherwise operatively connected to at least one computer processing unit configured for executing various operations as described below. The terms "computerized device", "computer", "processing device", or variations thereof should be expansively construed to cover any kind of electronic device with data processing capabilities, including, by way of non-limiting example, a personal computer, a server, a computing system, a communication device, a processor (e.g. digital signal processor (DSP), a microcontroller, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), etc.), any other electronic computing device, and\or any combination thereof.

As used herein, the phrase "for example," "such as", "for instance" and variants thereof describe non-limiting embodiments of the presently disclosed subject matter. Reference in the specification to "one case", "some cases", "other cases" or variants thereof means that a particular feature, structure or characteristic described in connection with the embodiment(s) is included in at least one embodiment of the presently disclosed subject matter. Thus the appearance of the phrase "one case", "some cases", "other cases" or variants thereof does not necessarily refer to the same embodiment(s).

It is appreciated that certain features of the presently disclosed subject matter, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the presently disclosed subject matter, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. In embodiments of the presently disclosed subject matter, fewer, more and/or different stages than those shown in Figs. 3, 4 and 5 may be executed. In embodiments of the presently disclosed subject matter one or more stages illustrated Figs. 3, 4 and 5 may be executed in a different order and/or one or more groups of stages may be executed simultaneously. It should be understood that presently disclosed subject matter contemplates any combination of operations which are described separately with reference to any one of Fig. 3, Fig. 4 or Fig. 5 into a single process.

Figs. 1 and 7 illustrate a general schematic of the system architecture in accordance with an embodiment of the presently disclosed subject matter. Functional elements in Figs. 1 and 7 may be centralized in one location or dispersed over more than one location. In other embodiments of the presently disclosed subject matter, the system may comprise fewer, more, and/or different (e.g. distributed differently) functional elements than those shown in Figs. 1 and 7. For example, division in UAV 120 and control unit 110 into the specified functional elements is done for the sake of example only and should not be construed as limiting in any way. For example, functional elements drawn as nested within other functional elements may be otherwise designed as independent functional units. In a specific example, functional elements illustrated in Fig. 1 as nested within UAV onboard control unit 30 (for example sensing unit 10 and command processing module 12) may not be located within unit 30 but rather otherwise operatively connected to unit 30. Alternatively, onboard control unit 30 can be formed by the interconnection of different functional elements.

While the present description refers to a UAV, this is done by way of example only, and the same principles and similar functional elements described in relation to a UAV can be likewise applied to a piloted aircraft configured with an auto-pilot flight and object tracking functionality.

As explained in the background section, UAVs are sometimes used for the purpose of observing and tracking objects located in a surveyed scene. A UAV in observation mode surveys the area below and provides sensing-data of the surveyed area. A UAV in tracking mode strives to maintain a certain object of interest (i.e. the object being tracked, also referred to herein as "target") within the FOV of the sensing device, preferably in its center. To this end, tracking instructions are generated for directing the sensing device (e.g. camera) to point in the direction of the object and keep the object in the center of FOV. In case the object is moving, various methods, which are known per se, (e.g. implementing different contour-tracking algorithms), are used in order to maintain the moving object within the FOV of the sensing device.

Fig. 1 is a functional block diagram of a UAV operatively connected to a control unit, according to an example of the presently disclosed subject matter. Fig. 1 shows UAV 120 comprising UAV onboard control unit 30, communication unit 11 and UAV aerial control devices 15. UAV communication unit 11 is configured to provide B/LOS (beyond line of sight/line of sight) communication link with communication unit 41 of control unit 110. Communication between UAV 120 and control unit 110 can be realized by any suitable communication infrastructure and protocol known in the art. Communication unit 11 can comprise or be otherwise operatively connected to an aerial data terminal (B/LOS ADT) as known in the art. Likewise, communication unit 41 can comprise or be otherwise operatively connected to a ground data terminal (B/LOS GDT) as known in the art.

UAV onboard control unit 30 comprises (or is otherwise operatively connected to) sensing unit 10. The sensing unit can comprise one or more sensing devices. The sensing device can be for example, an electro-optic sensor which can provide for example, color optical images, black and white optical images, as well as an infra-red image sensor, or any other types of imaging device.

UAV onboard control unit 30 can further comprise a command processing module 12 configured to receive control-data and generate instructions for executing respective commands. For example, command processing module 12 can be configured to process any one of pointing, locking, and tracking commands directed for controlling the sensing device.

Turning to control unit 110 it comprises (in addition to communication unit 41) display unit 47, input device 49 and command generator 43.

Display unit 47 comprises one or more display devices (e.g. one or more LED screens) for displaying sensing-data received from UAV 120. Input device 49 is configured to enable an operator to interact with the control unit. Input device 49 includes for example, keyboard, joystick, computer mouse, touch pad, touch screen or any other device enabling operator-interaction with the control system.

Command generator 43 is configured to generate control-data responsive to instructions inputted to the control unit. For example, an operator may interact with the control unit for generating locking and tracking instructions directed for tracking an object of interest located in the surveyed scene. Command generator 43 is configured to generate a respective tracking command based on the received instructions. The command is then transmitted to the UAV for execution.

UAV flight control unit 14 is a computerized device configured to control aerial control devices for navigating the UAV to a desired position and/or along a certain flight path. UAV flight control unit 14 can comprise or be otherwise operatively connected to sensing unit 10.

In the event a lock and track command is received with respect to an object of interest (target) located in the surveyed scene, command processing module 12 can be configured to process the command and provide instructions to the sensing unit for locking and tracking the object. Similarly, an operator can provide direction commands in order to manually control the payload (sensing device) for tracking objects or surveying the ground.

During execution of the lock and track command or while manually operating the sensing device, if it is determined (e.g. by command processing module 12) that execution of a command requires the repositioning of the UAV, UAV flight control unit 14 can generate and provide instructions for controlling various UAV aerial control devices 15 in order to navigate the UAV for tracking the object of interest.

UAV aerial control devices include for example throttle, stabilizers, ailerons and rudders. UAV flight control unit 14 may include various control units, each dedicated for controlling the operation of a respective aerial control device. A more detailed example of UAV flight control unit 14 is provided below with reference to Fig. 7.

While in observation mode or tracking mode, UAV onboard flight control unit 30 can be configured to assume one of a number of possible flight patterns accommodated for observing an area or tracking a target. These flight patterns are used in order to allow the UAV to stay in an operational position from the object of interest.

An operational position is defined by at least a distance which enables to maintain an area of interest (e.g. in observation mode) or an object of interest (e.g. in tracking mode) within the field of regard of the sensing unit. The term "field of regard" refers to a range of the angle of the sensing device with respect to the body of the UAV (referred to herein as "lowering angle"). An object or an area which is within the field of regard of the sensing device can be viewed by the sensing device without being blocked by the UAV body or other payloads connected to the UAV body (e.g. a radar device). The field of regard depends on the position of sensing device on the UAV as well as the position of other devices attached to the UAV's body. Fig. 8 shows an example of a UAV carrying sensing unit 10 where the field of regard is indicated by two straight lines extending from the two side of sensing unit 10. Notably, the fuselage of the UAV on the left side of the sensing unit and the payload 8 on the right side of the sensing unit limit its field of regard. Thus, in order to maintain an object of interest within the field of regard of the sensing device, the distance between the UAV and the object of interest must be kept within a certain range defined as part of the operational position.

Furthermore, the closer the object to the UAV, the greater the lowering angle which is required in order to view the object, and vice versa, the further away the object from the UAV, the smaller the lowering angle which is required in order to view the object. In case the object of interest is at a distance from the UAV which is greater than a certain threshold distance, and the respective lowering angle of the camera is accordingly small, the resulting imaging information obtained by the sensing device may suffer from various problems such as small object size in the captured images, small FOV, problems resulting from topographical or land coverage elements blocking sight of the object, etc.

In addition, as explained below it is sometimes necessary to observe an area or observe/track an object of interest from a certain direction and distance, because of various constraints limiting the flight of the UAV. In such cases, the operational position of the UAV can be defined based on the position and attitude of the UAV which is prescribed in order to avoid violating the constraint.

A UAV, operating in either observation mode or tracking mode, can fly in various types of flight patterns. In one type of flight pattern (referred to herein as "spiral flight pattern") UAV flight control unit directs the UAV to advance in spiraling circles. In this type of flight pattern, an area of interest or target is maintained substantially at the central area of the circles. This flight pattern is schematically illustrated in fig. 2a showing in top view a UAV tracking a moving vehicle along a road in spiral flight maneuvers, where the UAV is located substantially above the target (a moving car) and the target is maintained substantially in the center of the spiraling circles. Spiral flight pattern can be likewise executed in observation mode while flying over an area of interest.

In another flight pattern (referred to herein as "offset-spiral flight pattern") UAV flight control unit directs the UAV to advance in spiraling circles, where the circles are located in an offset relative to the location of the object or area of interest. In this flight pattern the object or area of interest is maintained in a substantially constant offset with respect to the UAV while the UAV advances in spiraling circular maneuvers alongside the object. This flight pattern is schematically illustrated in fig. 2b showing a UAV in top view tracking a moving vehicle along a road in spiral flight maneuvers where the UAV is located in an offset with respect to the moving object. Offset-spiral flight pattern can be likewise executed in observation mode while flying over an area of interest.

In another flight pattern (referred to herein as "sector-spiral flight pattern") UAV flight control unit directs the UAV to fly along a specific part of the circle. According to this flight pattern, the object or area of interest is maintained substantially at the central area of the circle sector. The advantage of this flight pattern is that the UAV is always in a specific position relative to the LOS, whereas the distance from the LOS, or the lowering angle, remains the same during the majority of the time of the flight. This flight pattern is schematically illustrated in fig. 2c showing a UAV in top view tracking a moving vehicle along a road in sector-spiral flight pattern. Sector-spiral flight pattern can be likewise executed in observation mode while flying over an area of interest.

As demonstrated in fig. 2a, 2b and 2c in all three types of flight patterns mentioned above, the UAV advances along with the target by continuously spiraling in the direction of the object movement.

When operating in tracking mode, these flight patterns require that the UAV maintains a velocity which is greater than the velocity of the target. In order to keep the traget within the field of regard during tracking, the distance between the UAV and the object of interest is maintained within a certain range. To maintain this range, the velocity of the UAV must be adapted to the velocity of the object of interest, and to any changes in this velocity. Accordingly, the presently disclosed subject matter includes a UAV onboard control unit (as well as a flight control unit) and a corresponding method for automatically controlling UAV velocity during tracking of an object of interest. This enables a UAV to automatically adapt its flying velocity to the real-time conditions during the tracking of an object of interest and thus facilitate the tracking with a lesser degree of human intervention.

Fig. 3 is a flowchart illustrating operations carried out in accordance with an example of the presently disclosed subject matter. The operations described with reference to Fig. 3 (as well as to figs. 4 and 5 below) can be executed, for example, by a UAV onboard control unit 30.

At block 301 sensing unit (10) onboard a UAV locks on an object of interest. Locking can be executed responsive to a lock and track command received from a control unit. The lock and track command can be generated for example by a control unit operator which is viewing images which are continuously generated by the sensing unit (10) and transmitted from the sensing unit to the control unit.

After the sensing unit has locked onto the object of interest, the velocity of the object of interest is determined (block 303). The velocity of a moving object can be determined using any one of various known methods, including, for example, by calculating the inertial LOS ground positions at any calculations cycle, and then integrating and filtering these positions into the estimated LOS ground speed. Alternatively, this can be accomplished using a Video Motion Detection algorithm. To this end, sensing unit 10 can comprise an object velocity determination unit (e.g. implemented by a VMD module).

The velocity of the object of interest is monitored and the velocity of the UAV is adapted according to changes in the object's velocity (block 305). According to one example, UAV flight control unit 14 can be configured to determine, based on the determined velocity of the object and the current velocity of the UAV, whether a change to the velocity of the UAV is required in order to maintain the distance between the UAV and the object within a certain predefined range. The predefined range is selected in order to keep the object of interest within the field of regard, and to maintain the lowering angle of the camera within a desired range.

In addition to the velocity of the UAV and the velocity of the object of interest, various other flight parameters may be used for determining the appropriate velocity of the UAV, including for example, current air speed of UAV, current wind speed, flight pattern characteristics, etc. This allows continuously maintaining the object of interest within the field of regard notwithstanding changes in flight parameters (such as changes to wind speed and/or object velocity).

The flight pattern characteristics include for example, the specific characteristics of the maneuvers made by the UAV flying in a certain flight pattern. For example, if a UAV is flying in spiral flight pattern, the flight pattern characteristics include the turning radius of the aircraft while circling the object.

Information with respect to flight parameters (in addition to object velocity discussed above) can be obtained from various gauges and sensors onboard the UAV such as air speed detector 701, GPS 703, altimeter 705 etc.

Turning to fig. 4 showing another example of a sequence of operations which are performed during tracking of an object of interest, in accordance with the presently disclosed subject matter.

In process 400 it is determined which flight patterns are available for tracking the object of interest. The flying patterns which can be used while tracking an object of interest depend on the velocity of the object of interest and the performance limitation of the UAV.

For example, during this process the ability of a UAV to track the object while flying in spiral flight pattern or serpentine flight pattern can be determined. The term "serpentine flight pattern" refers to a flight pattern where the UAV positions itself at a certain distance behind the object of interest and tracks the object of interest from behind while making serpentine shaped maneuvers and striving to maintain a substantially constant distance from the object. Serpentine flight pattern is schematically illustrated in fig. 2d.

In serpentine flight pattern, the UAV can fly in a velocity which is closer to the velocity of the target and in general reduce the flight distance the UAV is required to travel while tracking. The UAV is characterized by a certain minimal velocity (herein "minimal UAV flight velocity") which is the lowest velocity in which the UAV can fly safely without stalling. Thus, a UAV can track an object of interest while flying in serpentine flight pattern if the velocity of the object of interest prescribes a respective UAV velocity which is equal or greater than the minimal UAV flight velocity.

Notably, in spiral flight pattern and spiral-offset flight pattern, due to the spiral movement of the UAV, it travels a greater distance than the object of interest. The UAV is therefore required to fly at a velocity (ground speed) which is greater than the velocity (ground speed) of the object of interest in order to be able to track the object. Thus, the UAV can assume this flight pattern only if the required ground speed is not greater than a maximal UAV ground speed.

Thus, it is determined which of the flight patterns can be used under the current conditions. The determination can include, for example executing the operations of process 400 for each of the optional flight patterns.

The first 2 blocks in fig. 4 correspond to identical operations as those described earlier with respect to fig. 3 and therefore are not described here in detail. At block 403 a relative UAV ground speed needed for tracking the target in each flight pattern is calculated. The relative UAV ground speed is dependent on the velocity of the target (determined at block 303 above) and the excess distance relative to the distance traveled by the object, which the UAV travels when flying in a certain flight pattern. Onboard flight control unit 30 can be configured to determine the needed relative velocity of the UAV based on the velocity of the target and the relevant flight pattern. At block 405 it is determined whether the needed ground speed is applicable or not. To this end the current maximal ground speed of the UAV can be calculated and compared to confirm that it is equal to or greater than the needed ground speed. The ground maximal speed is calculated by subtracting from the maximal air speed the wind speed. The wind speed component which is subtracted is the wind speed opposing the UAV along the progression vector of the target.

Furthermore, when determining whether serpentine flight pattern can be used, it is concluded whether the needed ground speed is equal to or greater than a minimal UAV flight ground speed.

Based on the above calculations it is determined which of the flight patterns can be used while tracking the respective target.

At block 407 a flight pattern is selected. If only one flight pattern is available that flight pattern is selected. If more than one flight pattern can be implemented, a desired flight pattern can be selected. Selection of a flight pattern can be done by an operator, or otherwise a flight pattern can be automatically selected by the onboard UAV control unit based on predefined rules (e.g. prioritizing a certain type of pattern over the other, or selecting a flight pattern based on some condition such as the velocity of the target).

Once a flight pattern is selected, the UAV is adapted to fly at the required velocity and is maneuvered for tracking the target according to the selected flight pattern (block 409). To this end UAV flight control unit 14 can generate instructions for controlling various aerial control devices (including for example controlling the throttle for changing UAV velocity) for facilitating flying in the selected flight pattern.

According to another example, if a specific flight pattern is requested, the process in Fig. 4 can start by determining whether the desired flight pattern is available, and then continue to check the availability of other flight patterns only if the desired flight pattern is unavailable. As indicated by the arrows connecting block 403 back to block 303, during tracking various flight parameters (e.g. the velocity of the object of interest, air speed, wind speed, desired flying pattern etc.) are repeatedly determined and the velocity, as well as flight pattern, can be accordingly adapted to any changes in these parameters. For example, in the event that a serpentine flight pattern is implemented and the object slows down to a velocity which prescribes a UAV velocity which is lower than the minimal UAV flight velocity, the UAV can automatically switch from serpentine flight pattern to a different flight pattern (e.g. spiral flight pattern) and adapt the velocity of the UAV accordingly.

According to some examples of the presently disclosed subject matter, UAV velocity can be adapted also based on the specific type of mission which is being executed. Usually, while not tracking an object (loitering) the aircraft strives to fly at an optimal speed in order to reduce consumption of resources and thus extend the available mission time. For example, as explained above, during tracking, the velocity of the UAV is adapted to the velocity of the target. However, during flight, while not in tracking mode (e.g. while switching from tracking one object to tracking another object) UAV onboard control unit 30 can be configured to adapt the velocity of the UAV to an optimal velocity (e.g. a velocity which is optimized to mitigate speed and fuel consumption) when traveling to the relevant destination (e.g. the location of the next object to be tracked).

Proceeding to fig. 5, it shows another example of a sequence of operations which are performed during sensing device driven UAV navigation, in accordance with the presently disclosed subject matter. The first 3 blocks in fig. 5 correspond to identical operations described earlier with respect to fig. 3 and therefore are not described in detail. The operations described with reference to fig. 5 are related to an autonomously controlled aircraft operating under flight constraints.

In different flight scenarios, progression of a UAV is restricted by various flight constraints. Flight constraints include for example: - No-flight zones (NFZ), which are areas over which aircraft are not permitted to fly. Similarly, restricted airspace is an area (volume) of airspace in which air traffic is restricted. Such constraints are commonly set up by authorities for military, security or safety reasons. For example, for national security reasons, aircraft are often allowed to cross borders between neighboring countries, only after being officially authorized to do so. In some cases, where the border delineates enemy territory, crossing of such a border may be altogether prohibited. Likewise, some aircraft (such as UAVs) are not allowed to fly over populated areas for human safety reasons.

- Flight restrictions related to topography and/or the land cover in urban areas. For example, flight routes can be restricted in the vicinity of tall mountains or buildings to avoid the risk of collision.

- Flight constraint can be related to line of sight (LOS) communication link with the UAV (e.g. when using high frequency transmission). In order to maintain LOS communication continuously available, it is imperative to maintain a clear line of site between the onboard communication antenna and a respective remote communication antenna. Accordingly, in order to avoid the violation of a communication loss restriction (requiring maintaining an open LOS communication link at all times) UAV control unit is configured to use information indicative of the remote antenna transmission angle and calculate a maximal bank angle which will not violate the communication loss restriction.

- Flight constraint related to beyond line of site (BLOS) communication link with the UAV. BLOS communication link is a satellite based communication link enabling to communicate with a UAV over greater distance than line of sight communication. In order to maintain BLOS communication continuously available it is imperative to maintain a clear line of site between the communication antenna and a respective communication satellite. However, as illustrated in fig. 6a while turning, banking of the wings may position the UAV (e.g. the UAV fuselage) between the antenna, located for example on the dorsal side of fuselage, and the direction of the satellite, thus blocking line of sight between the UAV and the satellite.

- Flight restriction related to the operation of an onboard sensing device such as a camera. In order to maintain the camera continuously operative, it is imperative to keep an open line of sight between the camera and the object(s) of interest (e.g. in the direction of the ground). However, as illustrated in fig. 6b while turning, banking of the wings may position the UAV fuselage between the camera (located for example on the ventral side of the fuselage) and the direction of the earth, thus blocking the line of sight between the camera and the object(s) which are being captured. Note that in the illustrated example, banking of the UAV directs the image sensor FOV away from the object of interest 610. Another flight restriction is related to interference to the LOS of the camera which may occur when the camera is brought close to the perpendicular of the camera gimbals, where it is difficult to handle and manage the camera. It is desired to avoid this "dead zone" of the camera as well.

In some cases, the flight path of the UAV prescribed by the flight pattern of the UAV while tracking an object of interest cannot be maintained without violating certain flight restrictions. According to the presently disclosed subject matter, during tracking of an object of interest, UAV onboard control unit 30 can be configured, while tracking an object of interest, to consider information related to one or more flight restrictions and adapt the flight path of the UAV in order to avoid violation of such restrictions. Once the flight restriction is no more relevant, flight control unit can direct the UAV to continue and fly according to the flight pattern.

During flight, while tracking an object of interest, onboard control unit 30 may receive flight constrained data indicative of a certain flight constraint (block 501). Responsive to the received data, the flight path of UAV, which is generated according to a certain flight pattern, is adapted in order to avoid violating the flight constraint. This can be executed by onboard control unit 30 e.g. with the help of a dedicated processing unit (flight path updating module, which can be for example part of navigation module 721 shown below) which is configured to provide flight instructions to UAV flight control unit 14.

According to the presently disclosed subject matter, this is accomplished for example by adapting the bank angle of the UAV for obtaining a respective flight path which does not violate the flight restriction. A fixed wing aircraft turns by banking the wings in the direction of the desired turn at a specific angle known as the bank angle (angle BA shown in figs. 6a and 6b). When the wings of an aircraft are banked, the force acting on the wings is divided into vertical and horizontal components. The horizontal component of the produced lift force turns the aircraft to the desired direction. By changing the bank angle when flying from one point to next, the UAV can avoid the violation of various flight constraints while maintaining the original flight route, thereby avoiding the need to calculate and/or use an alternative flight route.

According to examples of the presently disclosed subject matter, responsive to receiving flight constrained data indicative of a flight constraint, UAV onboard control unit is configured to determine whether the flight route of the UAV, generated for the purpose of tracking the object of interest, is in conflict with the specified flight restriction.

If so, UAV onboard control unit is further configured to limit the bank angle and/or to calculate a bank angle enabling the UAV to proceed along the flight route without violating the flight constraint (block 503). The flight control unit can then use the calculated bank angle for generating instructions to various aerial control devices in order to control the aircraft to turn in the desired bank angle (block 505). According to one example, the bank angle calculation is directed for maintaining the flight path of the UAV as short as possible.

Notably, changing the progression route of the aircraft in order to avoid the violation of a given constraint may consequently increase or decrease the distance which is travelled by the aircraft. Thus, according to the presently disclosed subject matter, control unit 30 can be configured, while in tracking mode, in addition to changing the course of the flight, to avoid constraint violation to also adapt the velocity of the aircraft in order to enable to continue and track the target (block 507). Specifically, the velocity of the aircraft is adapted in order maintain the target within the field of regard notwithstanding any changes made to the flight course due to one or more flight constraints.

Calculation of the bank angle is repeatedly performed (as long as the constraint is valid) in order to repeatedly determine a suitable bank angle according to the realtime conditions, which may be continuously changing. For example, during tracking of an object of interest, the turning radius of the UAV according to the flight pattern which is being used, can be changed (increased or decreased) in order to avoid violating a certain flight restriction.

Thus, the presently disclosed subject matter further includes an autonomous UAV onboard control unit (and respective method) which is configured to control an aircraft flying autonomously according to a certain flight pattern, and generates instructions for controlling the aircraft during tracking of an object of interest while taking into consideration flight constraints and avoiding the violation thereof.

For example, in order to avoid the violation of a communication loss restriction (e.g. which requires maintaining an open BLOS communication link at all times), UAV onboard control unit is configured to use information indicative of the satellite transmission angle and calculate a maximal bank angle which will not violate the communication loss restriction. To this end UAV onboard control unit is configured to calculate the earth angles of observation from the UAV to the satellite, and, based on this information, calculate a maximal bank angle that would result in the fuselage blocking BLOS communication. The flight route of the UAV for tracking the object of interest is adapted according to the limitations of the maximal bank angle which was calculated. Specifically, during tracking of an object of interest, the radius of the turns made according to a specific flight pattern which is being implemented, are adapted in order to avoid violating the flight restriction.

Notably, UAV onboard control unit can be configured to consider more than one constraint and provide a bank angle which does not violate any one of the constraints. Once a flight restriction is no more relevant, the UAV resumes to flying without considering the restriction.

Fig. 7 is a functional block diagram schematically illustrating a UAV flight control unit, according to an example of the presently disclosed subject matter. Functional elements in fig. 7 corresponding to functional elements described earlier with reference to fig. 1 are assigned with the same reference numbers.

Flight control unit 14 is suitably mounted on UAV 120 and is operatively connected to various devices and subsystems onboard the aircraft. Flight control unit 14 can be configured in general to control the UAV during flight and direct it to a desired destination. To this end control unit 14 is configured to receive flight instructions.

Control-data as well as flight constraints related data can be sent to the UAV via communication unit 11. Flight control unit 14 can also be configured to control or assist in other flight related operations which are not described here in detail (e.g. take-off, landing, emergency landing, shutting off, etc.). Flight control unit 14 may be fully automated, but in some implementations it may also react to commands issued by another system or a human operator.

Flight control unit 14 comprises or otherwise operatively connected to one or more processing units. Each processing unit comprises or is operatively connected to one or more computer processors and computer memory (transitory and/or non- transitory). While Fig. 7 shows only a single processing unit (720) it is noted that this is so for the sake of simplicity and clarity only and should not be construed as limiting. Processing unit 720 is connected to a number of input interfaces which provide information required for controlling the UAV. Input interfaces include for example: air speed input interface 701a configured to obtain data indicative of air speed of the UAV from one or more air speed detectors 701 (e.g. implemented as Pitot tubes); navigation system input interface 703a configured to obtain data indicative of UAV position and heading from a positioning utility such as GPS receiver 703 and INS (not shown); altitude input interface 705a configured to obtain data indicative of current altitude of the UAV from altimeter 705. Altimeter 705 can be implemented, for example, as a pressure altimeter, a sonic altimeter, a radar altimeter, a GPS based altimeter, and so forth.

It is noted that control unit 14 can be further configured to obtain additional information (including situation data of all kinds) indicative of flight and state of UAV 120. It is further noted that the list above is given by way of non-limiting example only and flight control unit 14 can be operatively connected to additional or different types of input interfaces and/or various devices to those specified above.

Processing unit 720 can comprise for example the following modules:

• Navigation module 721 configured to control the UVA flight in order to direct the UAV to a desired destination and maintain its course along a desired flight route. The flight route can be a predetermined path to a certain destination (e.g. pre- stored in data-repository 722 before takeoff) or can be a flight route provided in realtime after takeoff. During observation or tracking of an object of interest, navigation module 721 is configured to determine a flight path for enabling to track an object of interest. The flight path can be determined based on a selected flight pattern and the location and velocity of the object of interest.

• UAV velocity determination unit 722 is configured to determine an appropriate UAV velocity for tracking a given object of interest. As explained above, the velocity is determined based on various flight parameters e.g. the velocity (ground speed) of the object of interest, air speed, wind speed, desired flying pattern. • Pattern determination module is configured to automatically determine an appropriate flight pattern based on predefined rules as well available information with respect to the target and possible flight constrains. Flight pattern can be also determined based on control-data received from an operator or another remote control device.

• Flight constraint analysis module 723 configured to analyze information pertaining to a flight constraint (flight constraints related data) and determine a flight path which does not violate such restrictions.

During tracking of an object of interest, flight constraint analysis module 723 can make use for example of a bank angle calculation module 725 configured for calculating a bank angle which allows to proceed and track the object of interest without violating a given flight constraint. The bank angle can be used by navigation module 721 for controlling various aerial control devices and directing the UAV to continue and track the object.

As is well known in the art, calculation of the bank angle and respective flight radius is based on various parameters including: lift acting on the aircraft (L); the angle of bank of the aircraft (φ); the mass of the aircraft (m); and the ground speed of the aircraft which is composed of the aircraft true air speed and the wind speed (v). In straight level flight, lift (L) is equal to the aircraft weight. In turning flight the lift (L) exceeds the aircraft weight, and is equal to the weight of the aircraft (mg - g is the gravitational field strength) divided by the cosine of the angle of bank. Thus, given a certain bank angle, the respective flight radius can be determined and vice versa.

In order to allow the UAV to turn in an efficient and fully-coordinated manner, it is necessary to have various aerial control devices available. For example, ailerons (rectangular flaps at the back of the wing) are needed to bank and hence initiate the turn, elevator is needed to maintain UAV altitude during the turn, rudder is needed to coordinate the movement of the nose, and the throttle is needed to increase/decrease thrust while turning, thereby affecting the radius of the turn. • Elevators control module 727 is configured to control the elevators 745 located on the horizontal tail wing. Elevators enable the plane to go up and down through the air. The elevators change the horizontal stabilizer's angle of attack, and the resulting lift either raises the rear of the aircraft (pointing the nose down) or lowers it (pointing the nose skyward).

• Ailerons control module 727 is configured to control the ailerons 741 which are horizontal flaps located near the end of an airplane's wings. Ailerons allow one wing to generate more lift than the other, resulting in a rolling motion that allows the plane to bank left or right.

• Rudder control module 729 is configured to control a rudder 743 which is a flap located on the vertical tail wing. The rudder enables the plane to turn left or right.

• Throttle control module 733 is configured to control the throttle 749 which is configured in turn to increase/decrease thrust while turning. The throttle enables UAV flight control unit to control the speed of the aircraft (e.g. while adapting the UAV velocity to the velocity of an object of interest and a selected flight pattern).

According to an example of the presently disclosed subject matter, based on the bank angle and flight path which are determined by the navigation module 721, instructions are generated by each one of the above modules for controlling a respective control device to obtain the desired UAV maneuver.

It is to be understood that the system according to the presently disclosed subject matter may be a suitably programmed computer. Likewise, the presently disclosed subject matter contemplates a non-transitory computer program being readable by a computer for executing the method of the presently disclosed subject matter. The presently disclosed subject matter further contemplates a machine- readable memory (transitory and non-transitory) tangibly embodying a program of instructions executable by the machine for executing the method of the presently disclosed subject matter. It is also to be understood that the presently disclosed subject matter is not limited in its application to the details set forth in the description contained herein or illustrated in the drawings. The presently disclosed subject matter is capable of other embodiments and of being practiced and carried out in various ways. Hence, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for designing other structures, methods, and systems for carrying out the several purposes of the present presently disclosed subject matter.

Claims

Claims:

1. A UAV control unit mountable on a UAV comprising: a sensing unit comprising a sensing device, the sensing unit is configured to execute tracking of an object of interest; the control unit further comprises a processing unit configured to autonomously determine, during tracking of the object of interest, a velocity of the object of interest; determine, based on at least the velocity of the object of interest and data indicative of a desired field of regard, UAV tracking velocity adapted for maintaining a distance between the UAV and the object of interest within a certain range to allow retaining the object of interest within the desired field of regard during tracking of the object.

2. The control unit according to claim 1, wherein the processing unit is further configured to generate instructions for controlling various aerial control devices in order to control the UAV to fly at the determined UAV velocity.

3. The control unit according to any one of the preceding claims is configured to determine the UAV tracking velocity based on velocity of the object of interest, wind speed and flight characteristics of a selected flight pattern.

4. The control unit according to any one of the preceding claims is further configured for selecting an appropriate flying pattern to: calculate the relative UAV ground speed needed for tracking the target in a given flight pattern; determine whether the relative UAV ground speed is applicable or not; and accordingly determine which of the flight patterns are available; and generate instructions for controlling the UAV to fly in a flight pattern selected from the available flight patterns.

5. The control unit according to any one of the preceding claims is further configured to determine a velocity of the UAV based on information indicative of the current mission type and adapt the velocity accordingly.

6. The control unit according to any one of the preceding claims is configured to repeatedly determine the UAV tracking velocity, using, in each determination, updated velocity of the object of interest and updated flight parameters for adapting the UAV tracking velocity to changes.

7. The control unit according to any one of the preceding claims is further configured, responsive to information indicative of a flight constraint, calculate a bank angle which allows the UAV to continue and track the object of interest without violating the flight constraint; and generate instructions to aerial control devices for guiding the UAV for tracking the object without violating the flight constraints.

8. The control unit according to claim 7 is configured to calculate an updated UAV velocity to enable tracking the object without violating the flight constraints.

9. The control unit according to claim 7 is configured to repeatedly calculate the bank angle during tracking of the object in order to adapt the bank angle to real-time changes in the flight constraint data.

10. The control unit according to any one of claims 7 to 9 wherein the flight constraint is any one of: no-flight zone constraint flight of the UAV over a certain ground area; a LOS or BLOS communication link constraint requiring an open communication link between the UAV and a communication satellite at all times; a camera LOS constraint requiring an open LOS between an onboard camera and one or more objects of interest at all times; avoiding the perpendicular of camera gimbals; and a topographical and/or land cover constraint.

11. An aircraft configured with an auto-pilot flight and object tracking capabilities; the aircraft comprising a control unit, comprising: a sensing unit comprising a sensing device, the sensing unit is configured to execute tracking of an object of interest; the control unit further comprises a processing unit configured to autonomously determine, during tracking of the object of interest, a velocity of the object of interest; determine, based on at least the velocity of the object of interest and data indicative of a desired field of regard, aircraft tracking velocity adapted for maintaining a distance between the aircraft and the object of interest within a certain range to allow retaining the object of interest within the desired field of regard during tracking of the object.

12. The aircraft according to claim 11 is a UAV.

13. A method of autonomously controlling a UAV during tracking of an object of interest, the UAV comprising a sensing unit configured to execute tracking of an object of interest; the method comprising: executing tracking of an object of interest; determining, during tracking of the object of interest, velocity of the object of interest; determining, based on at least the velocity of the object of interest and data indicative of a desired field of regard, UAV tracking velocity adapted for maintaining a distance between the UAV and the object of interest within a certain range to allow retaining the object of interest within a desired field of regard during tracking of the object.

14. The method according to claim 13, further comprising: generating instructions for controlling various aerial control devices in order to control the UAV to fly at the determined UAV velocity.

15. The method according to any one of claims 13 to 14 further comprising: determining the UAV tracking velocity also based on wind speed and flight characteristics of a selected flight pattern.

16. The method according to any one of claims 13 to 15 further comprising: selecting an appropriate flying pattern comprising: calculating the relative UAV ground speed needed for tracking the target in a given flight pattern; determining whether the relative UAV ground speed is applicable or not; and accordingly determining which of the flight patterns are available; and generating instructions for controlling the UAV to fly in a flight pattern selected from the available flight patterns.

17. The method according to any one of claims 13 to 16 further comprising: determining a velocity of the UAV based on information indicative of the current mission type; and generating instructions for controlling the UAV to fly in a serpentine flight pattern.

18. The method according to any one of claims 13 to 17 further comprising: repeatedly determining the UAV tracking velocity, while using in each determination updated velocity of the object of interest and updated flight parameters for adapting the UAV tracking velocity to changes.

19. The method according to any one of claims 13 to 18 further comprising: responsive to information indicative of a flight constraint, calculating a bank angle which allows the UAV to continue and track the object of interest without violating the flight constraint; and generating instructions to aerial control devices for guiding the UAV for tracking the object without violating the flight constraints.

20. The method according to claim 19 comprising: calculating an updated UAV velocity to enable tracking the object without violating the flight constraints.

21. The method according to 19 further comprising: repeatedly calculating the bank angle during tracking of the object in order to adapt the bank angle to realtime changes in the flight constraint data.

22. The method according to any one of claims 19 to 21 wherein the flight constraint is any one of: no-flight zone constraint flight of the UAV over a certain ground area; a LOS or BLOS communication link constraint requiring an open communication link between the UAV and a communication satellite at all times; a camera LOS constraint requiring an open LOS between an onboard camera and one or more objects of interest at all times; avoiding the perpendicular of camera gimbals; and a topographical and/or land cover constraint.

23. A computer-readable non-transitory memory device tangibly embodying a program of instructions executable by the computer for executing a method of a method of autonomously controlling a UAV during tracking of an object of interest, the UAV comprising a sensing unit configured to execute tracking of an object of interest; the method comprising: executing tracking of an object of interest; determining, during tracking of the object of interest, velocity of the object of interest; determining, based on at least the velocity of the object of interest and data indicative of a desired field of regard, UAV tracking velocity adapted for maintaining a distance between the UAV and the object of interest within a certain range to allow retaining the object of interest within a desired field of regard during tracking of the object.