AERIAL VEHICLE AND METHOD AND COMPUTER-AIDED SYSTEM FOR CONTROLLING AN AERIAL VEHICLE

Abstract

A method for controlling an aerial vehicle of a specific type, in particular a multirotor VTOL aerial vehicle with preferably electrically driven rotors, in which a) before a flight, a finite number of nominal trajectories (NT) for the aerial vehicle and a finite number of emergency trajectories (CT) arranged around the nominal trajectories (NT) are calculated and stored in a database available on board the aerial vehicle; b) before a flight, a finite number of type-specific admissible flying maneuvers of the aerial vehicle are pre-planned and stored in the database as a maneuver library; c) optionally before a flight, a number of discrete flight levels with different flight altitudes are defined and stored in the database; d) during a flight, the database is accessed by a computer-aided transition planning algorithm, in order, depending on a state of the aerial vehicle recorded by sensors, to change between the nominal trajectories (NT) and the emergency trajectories (CT) and also optionally between the defined flight levels by using the pre-planned flying maneuvers and to correspondingly activate a path-tracking controller and/or a flight control system of the aerial vehicle.

Claims

1. A method for controlling an aerial vehicle (1) of a specific type, the method comprising: a) before a flight, calculating and storing a finite number of nominal trajectories (NT) for the aerial vehicle (1) and a finite number of emergency trajectories (CT) arranged around the nominal trajectories (NT) in a database (2e) available on board the aerial vehicle (1); b) before the flight, pre-planning and storing a finite number of type-specific admissible flying maneuvers of the aerial vehicle (1) in the database as a maneuver library (2f); c) before the flight, defining and storing a number of discrete flight levels with different flight altitudes are defined and stored in the database (2e); d) during the flight, accessing the database (2e) within a real-time algorithm (2b) by a computer-aided transition planning algorithm (2h′), in order, depending on a state of the aerial vehicle (1) recorded by sensors (4), to change between the nominal trajectories (NT) and the emergency trajectories (CT) and also between the defined flight levels by using the pre-planned flying maneuvers and to correspondingly activate at least one of a path-tracking controller (2c) or a flight control system (2d) of the aerial vehicle (1).

2. The method as claimed in claim 1, wherein the emergency trajectories (CT) are arranged in at least one of a tree structure or at regular intervals.

3. The method as claimed in claim 2, wherein the path planning in step a) takes place by quasi-random algorithms for path planning, which process is repeated up to a desired degree of branching on the emergency trajectories (CT) generated in a previous step, so as to produce a tree-like flight path structure.

4. The method as claimed in claim 1, wherein the transition planning algorithm (2h′) has a restricted time horizon.

5. The method as claimed in claim 1, wherein steps a) to c) are performed on a ground-based computer and a result is subsequently transferred to the aerial vehicle (1) and is stored on board the aerial vehicle in the database (2e); or steps a) to c) are performed on an on-board computer of the aerial vehicle (1) and the result is stored on board the aerial vehicle (1) in the database (2e).

6. The method as claimed in claim 1, wherein, before the flight, entry and exit intervals (TI, EN, EX) are defined for each said trajectory and a change between the trajectories and the flight levels is only admissible within the entry and exit intervals (TI, EN, EX).

7. The method as claimed in claim 1, further comprising, in step d), determining by interaction of an emergency module (2g) and the transition planning algorithm (2h′) based on aerial-vehicle-specific parameters and environment variables whether a transition is required, and if so to which of the at least one of the trajectory or the flight level.

8. The method as claimed in claim 1, wherein, in step d), horizontal transitions between different ones of the trajectories are carried out completely decoupled from vertical transitions between different ones of the flight levels.

9. The method as claimed in claim 1, wherein, in step a), both a combination of individual trajectories and closed sets of reachable trajectories are calculated, said reachable trajectories are obtained from the pre-planned trajectories and transition intervals (TI) between the pre-planned trajectories.

10. The method as claimed in claim 1, wherein reachability sets (EM) are determined based on at least one of the following: i) disturbing effects during nominal operation including at least one of maximum wind and gust strength; ii) known flight performance parameters including at least one dynamics and kinematics of the aerial vehicle (1); or iii) model quality provided as a deviation between a physical model of the aerial vehicle (1), used as a basis at least for step a), and an observed or measured flying behavior.

11. The method as claimed in claim 10, wherein the reachability sets (EM) are used for the pre-planning of the flying maneuvers in step b).

12. The method as claimed in claim 1, further comprising providing at least one of landing site information, hazard potentials, or airspace structures in an expanded 3D map of a flying area, said map serving as a basis for the trajectory planning in step a).

13. The method as claimed in claim 1, further comprising, in step d), carrying out a time-incremental real-time planning of the actual flight path along one of the nominal trajectories (NT) and within the set of all of the emergency trajectories (CT) on board the aerial vehicle (1), including: i) updating a system state of the aerial vehicle (1); ii) derived from the updating of the system state, updating the trajectory and flight level to be flown; iii) updating a selected path from the previous time increment while taking into consideration an evaluation function and, if needed, a transition to a new path, using a model-based planning method with a restricted time horizon.

14. The method as claimed in claim 1, wherein the maneuver library (2f) comprises a discrete representation of a flight envelope of the aerial vehicle (1) taking into consideration various performance states of the aerial vehicle (1), such as a nominal state, failure scenarios or environmental conditions, and is stored in an optimized manner in a memory using symmetries and superposition.

15. The method as claimed in claim 1, wherein additionally parameterized trajectory segments are defined and stored in the database (2e), the trajectory segments being flight paths or partial flight paths that are locally performable, do not entail any change of a selected one of the trajectories but return to this trajectory once they have ended.

16. The method as claimed in claim 1, wherein each said trajectory is characterized based on properties stored in the database (2e), and the transition planning algorithm (2h′) makes decisions in step d) concerning the trajectory selection based on said properties.

17. The method as claimed in claim 1, wherein a change of the at least one of the flight level or trajectory takes place at a nearest branching point of a tree structure in which the emergency trajectories (CT) are arranged or by the transition planning algorithm (2h′) in a nearest one of an entry or an exit interval entry (TI, EN, EX) defined pre-flight for each said trajectory if no transition along the tree structure is possible.

18. The method as claimed in claim 1, wherein, as a mission increasingly progresses, the trajectories that cannot be reached any longer are removed and the set of trajectories taken into consideration is reduced to a set of the trajectories that are still reachable in a current flying state of the aerial vehicle (1).

19. A computer-aided system for controlling an aerial vehicle (1) of a specific type by the method according to claim 1, wherein the aerial vehicle is a multirotor VTOL aerial vehicle with electrically driven rotors (3b), with at least one computer, which is configured as at least one of a ground-based computer unit or as an on-board computer of the aerial vehicle (1), the at least one computer being configured for: A) performing a preplanning algorithm for carrying out method step a); B) providing the database (2e); C) performing the real-time algorithm (2b) which provides a decision module, an input of which is the state of the aerial vehicle (1) according to method step d) and an output of which is one of the trajectories that corresponds best to the current state of the aerial vehicle (1) from the finite number of nominal trajectories (NT) and the emergency trajectories (CT) in accordance with an evaluation metric; and D) performing the transition planning algorithm (2h′) according to method step d).

20. The system as claimed in claim 19, wherein the preplanning algorithm (6a) has: inputs for map data (6d) provided as popular map formats and for starting and target coordinates and outputs for geo-referenced, parameterized or non-parameterized trajectories with exit and entry intervals (EX, EN), and parameterized trajectory segments for changes of at least one of flight level or holding patterns, which are at least one of transferrable to the database (2e) or storable in the database (2e).

21. The system as claimed in claim 19, wherein the transition planning algorithm (2h′) has: inputs for a state vector consisting of a state estimation of the aerial vehicle (1) for exit and entry intervals (EX, EN) from the database (2e), for starting and target states from the database (2e), for the maneuver library (2f), for a target trajectory and target flight level and for a maneuver prioritization from the database (2e), and an output for a path vector (p, {dot over (p)}, {umlaut over (p)}, , ψ, {dot over (ψ)}, {umlaut over (ψ)}) for outputting to a position controller of the aerial vehicle (1) with a position specification p and temporal derivatives thereof, and a yaw angle Ψ and temporal derivatives thereof.

22. The system as claimed in claim 21, wherein the inputs for the state vector consisting of the state estimation of the aerial vehicle (1) are in the form of a sensor data fusion of different sensors (4).

23. The system as claimed in claim 19, wherein the real-time algorithm (2b) is configured to select at each time increment between a finite number of discrete ones of the trajectories that respectively corresponds to the nominal trajectory (NT), one of the emergency trajectories (CT), or a trajectory segment to be performed temporarily.

24. The system as claimed in claim 20, wherein the transition planning algorithm (2h′) is configured for instigating a change between the trajectories that are not replicated in a tree structure in which the emergency trajectories (CT) are arranged within the exit and entry intervals (EX, EN).

25. An aerial vehicle (1) comprising the system according to claim 19.

26. A method for controlling an aerial vehicle (1) of a specific type, the method comprising: before a flight, calculating and storing a finite number of nominal trajectories (NT) for the aerial vehicle (1) and a finite number of emergency trajectories (CT) arranged around the nominal trajectories (NT) in a database (2e) available on board the aerial vehicle (1); before the flight, pre-planning and storing a finite number of type-specific admissible flying maneuvers of the aerial vehicle (1) in the database as a maneuver library (2f); during the flight, accessing the database (2e) within a real-time algorithm (2b) by a computer-aided transition planning algorithm (2h′), in order, depending on a state of the aerial vehicle (1) recorded by sensors (4), to change between the nominal trajectories (NT) and the emergency trajectories (CT) and to correspondingly activate at least one of a path-tracking controller (2c) or a flight control system (2d) of the aerial vehicle (1).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0127] Further properties and advantages of the invention become apparent from the following description of specific exemplary embodiments with reference to the drawing.

[0128] FIG. 1 shows a possible configuration of the aerial vehicle according to the invention;

[0129] FIG. 2 schematically shows the reachable set EM of flight paths for an aerial vehicle;

[0130] FIG. 3 schematically shows a content of the maneuver library;

[0131] FIG. 4 shows a graphical representation of a mission planning for an aerial vehicle;

[0132] FIG. 5 shows nested contingency trajectories in a tree structure;

[0133] FIG. 6 shows an (online) transition, calculated in real time, between two precalculated trajectories; and

[0134] FIG. 7 shows a block diagram/flow diagram of the described path planning method with hardware allocation.

DETAILED DESCRIPTION

[0135] FIG. 1 shows a possible configuration of the aerial vehicle according to the invention as a multirotor eVTOL 1 with in the present case 18 drive units 3, only one of which is explicitly denoted in FIG. 1. According to the representation shown, each drive unit 3 comprises an electric motor 3a and a propeller 3b. According to the configuration of the aerial vehicle 1 in FIG. 1, the drive units, in particular the propellers 3b, are not pivotable. x, y and z denote distinguished axes of the aerial vehicle 1; L, M and N denote the associated (control) torques.

[0136] The aerial vehicle 1 has at reference sign 2 a flight control unit, which is described even more specifically further below on the basis of FIG. 7. The flight control unit 2 comprises in addition to a system monitor 2a also at reference sign 2b a real-time control unit, which is designed, preferably programmed, for (partially) carrying out the method according to the invention. Reference sign 4 denotes by way of example a sensor unit which is operatively connected to the system monitor 2a; the aerial vehicle 1 will generally comprise a multiplicity of such sensor units 4, which are in particular designed and suitable for determining an (overall) state of the aerial vehicle 1 (system state) and its environment. Represented at reference sign 5 is a pilot input unit, by way of which a human pilot (not shown) transmits its control requirements to the aerial vehicle 1, for example by way of a joystick or the like. However, within the scope of the invention, the aerial vehicle is in particular also capable of flying without human pilots, i.e. by an autopilot or the like. For determining the system state, the flight control device 2 may also use a physical model of the aerial vehicle 1, which is not represented any further in FIG. 4. The real-time control unit 2b interacts with the actual flight control system 2d or may comprise it (see FIG. 7), in order by suitable commanding of the drive units 3 to control the aerial vehicle 1 along a flight path that is precalculated and adapted in real time, as already described in detail.

[0137] Preferably, the flight control unit 2 determines by using the real-time control unit 2b the trajectory to be flown, as described in detail above, and correspondingly activates a path-tracking controller/the flight control system of the aerial vehicle 1 (cf. FIG. 7).

[0138] FIG. 2 schematically shows the reachable set EM of flight paths for an aerial vehicle 1, for example according to FIG. 1, in a (flight) level x-z, which contains obstacles HI, in particular in an urban environment. The reachable set EM describes the set of deviations, limited by the extreme case, occurring from a commanded path KB of the aerial vehicle 1. This extreme case takes into consideration maximum-possible deviations, in particular due to wind (gusts), controller deviations, model quality, measurement inaccuracies, etc. The path planning takes into consideration the reachable set EM, as explained above in detail, and in this way ensures that no collision with obstacles HI takes place, even in an extreme case.

[0139] FIG. 3 schematically shows a content of the maneuver library, as explained in detail further above. For the aerial vehicle 1, so-called maneuver libraries are calculated. These consist of maneuvers that are completely precalculated and kept in the database, one arbitrary one of which or the corresponding trajectory in a level x-y selected by way of example is denoted in FIG. 3 by the reference sign MT. In the calculation of these maneuvers, the reachability set EM (cf. FIG. 2) is taken into consideration in each case, as described further above. Instead of a series of states, maneuvers are stored in the (maneuver) library as executable controllers. These controllers are optimized to the extent that the set of states that can be reached by the execution of a controller with the assumption of a limited disturbing effect or the possible deviation from the target state becomes minimal. The information concerning this reachable set is ascribed to the maneuver/controller as an attribute. The maneuver library comprises a discrete representation of the flight envelope while taking into consideration various performance states of the aerial vehicle (for example nominal state, failure scenarios, environmental conditions) and is optimized in terms of memory by using symmetries and superposition.

[0140] FIG. 4 shows a graphical representation of a mission planning for an aerial vehicle with nominal starting and target sites NP with an associated nominal trajectory NT, which connects the mentioned starting and target sites NP. Also shown are emergency or contingency trajectories CT to alternate landing sites AP, only some of which contingency trajectories CT are denoted in FIG. 4. A number of parameterized holding patterns WS with transition points (“x”) on the landing trajectories can likewise be seen. Such landing trajectories may likewise be of a nominal nature here. The aim is that parameterized sections lead back to trajectories that lead to a landing site. This may be both the nominal trajectory and an emergency trajectory. Furthermore, potential transition paths TP and a two-dimensionally defined transition interval TI are represented by way of example in the left half of the image. The transition paths TP make possible a transition between various contingency trajectories CT. Such transitions are also possible within the transition interval TI (flexibly, after calculation by the real-time control unit, cf. FIGS. 1 and 7).

[0141] In FIG. 5, nested contingency trajectories, for example T.sub.1, T.sub.2, are shown in a tree structure, with a first contingency trajectory CT1, which branches off from the nominal trajectory NT, having further contingency trajectories of the first order (T.sub.1) or higher-order (T.sub.2) in turn branching off from it. The nominal trajectory NT, cf. FIG. 4, is represented at the bottom as a straight line.

[0142] In FIG. 6 it is shown how an (online) transition, calculated in real time, between two precalculated trajectories T.sub.1 and T.sub.2 (cf. for example FIG. 4 or 5) can take place. The transition starts in a so-called predefined exit zone EX on the trajectory T.sub.1 and runs to a so-called entry zone EN on the trajectory T.sub.2. It is algorithmically ensured by the real-time control unit (cf. FIGS. 1 and 7) that the transition runs within the specified intervals (TI, cf. FIG. 4). This scenario is not restricted to specific types of trajectories T.sub.1, T.sub.2 (cf. also FIG. 5).

[0143] FIG. 7 shows a block diagram of the described path planning method with hardware allocation. The degree of detail and extent of the preplanning is in this case variable, as already explained in detail above.

[0144] The aerial vehicle 1 according to the right part of FIG. 7 comprises in addition to the already mentioned system monitor 2a, which interacts with the sensors and further information sources (denoted together by reference sign 4; cf. FIG. 1) for determining a state of the aerial vehicle 1 and its environment, the already mentioned real-time control unit 2b with a path-tracking controller 2c. Reference sign 2d denotes the actual flight control system, which acts on the drive units of the aerial vehicle 1 (cf. FIG. 1), in order to influence the aerial vehicle in its movement. Reference sign 2e shows the already repeatedly mentioned database, in which the (precalculated) trajectories and maneuvers are stored. Reference sign 2f represents the maneuver library with performance guarantee and map and meta data. The maneuver library 2f and the database 2e may be stored in a common memory unit. Furthermore, FIG. 7 also shows an (emergency) decision module 2g in operative connection with the system monitor 2a and also a transition module 2h comprising a transition planning algorithm (transition planner) 2h′ and a transition controller 2h″ in operative connection at least with the maneuver library 2f.

[0145] The left part of FIG. 7 shows a preplanning unit 6, which is preferably installed or executed on a ground-based user PC. The result of the preplanning is stored in the database 2e, preferably before a flight of the aerial vehicle 1. The preplanning unit 6 comprises the actual preplanning algorithm 6a, which receives as input data mission data 6b, aerial vehicle parameters 6c and map/meta data 6d. The preplanning algorithm 6a comprises modules for nominal planning 6e (nominal trajectory/trajectories), contingency planning 6f (emergency trajectories) and planning of the transition intervals 6g, from the interaction of which in the sequence shown the entire mission preplanning 6h is obtained and is preferably buffer-stored in a buffer memory at reference sign 6i.

[0146] In the use of the configuration according to FIG. 7, the following sequence is obtained: after preplanning has taken place (on the ground), an inquiry takes place at reference sign S1 as to whether or not the mission preplanning 6h is being released. It is preferably provided that a so-called U-Space operator or air traffic control center evaluates and releases the mission planning If it does, the preplanning is transferred to the aerial vehicle 1 and is stored in the database 2e. If not, the procedure returns to 6e (nominal planning).

[0147] The planning data in the database 2e are then used by the aerial vehicle 1 or the real-time control unit 2b during the flight. They are for example available to the path-tracking controller 2c and/or the decision module 2g, the latter also receiving event data (“events”) from the system monitor 2a. “Events” stands here for events in the context of event-based automatic machines. An event may therefore be: “EPU xyz failed” or “rescue helicopter from the left”, etc.

[0148] The output of the decision module 2g is a trajectory for the aerial vehicle 1, which is preferably selected situation-dependently from pre-planned trajectories and segments according to the criteria described in detail above. This trajectory is checked at S2 by the real-time control unit 2b for whether (on the basis of the event data) a so-called online transition is required, i.e. a change, determined in real time, to another (emergency) trajectory and/or flight level. If not, the path-tracking controller 2c takes over the further control of the aerial vehicle 1 along the (original) trajectory (see the corresponding operative connection with the flight control system 2d for the transmission of suitable control commands SK). If it is, the transition planner 2h′ of the transition module 2h becomes active, determines a change in trajectory (transition) on the basis of the precalculated maneuver etc. in the maneuver library 2f and provides a correspondingly changed control of the aerial vehicle 1 by way of the transition controller 2h″ of the transition module 2h (see the corresponding operative connection with the flight control system 2d for the transmission of suitable control commands SK). Feedback in the form of a verification (at S3) as to whether the transition was successful takes place by way of the system monitor 2a. Discrete changes of the flight altitude can be implemented as and when required alone on the basis of a controller and without the need for a preceding planning algorithm. This takes place alone by the transition controller 2h″ of the transition module 2h.