System for managing the emergency landing trajectory of a drone or unmanned aircraft

Abstract

The invention relates to a system for managing the emergency landing trajectory of a drone (1), comprising: - a ground control station (2) comprising a first computer (3) provided with a module (4) for continuously determining a first emergency landing trajectory and a module (5) for verifying the first trajectory; and - a control unit (6) on board the drone comprising a second computer (7), comprising a module (8) for continuously determining a second landing trajectory, a module (9) for detecting a critical unknown involving a transition from a nominal mode to an emergency landing mode activating the operation of a module for selecting the first or second emergency landing trajectory; the selection module (10) being configured to select the first emergency landing trajectory created or the second emergency landing trajectory so as to select the first trajectory if the first trajectory takes into account the current value of the operating or environmental parameter(s) of the drone representative of the detected critical unknown, and to select the second trajectory if the first trajectory takes into account a last received value different from the current value of the operating or environmental parameter(s) of the drone representative of the detected critical unknown.

Description

DESCRIPTION Title of the invention: Emergency landing trajectory management system for a drone or unmanned aircraft.

[0001] The present invention relates to a system for managing the emergency landing trajectory of a drone or unmanned aircraft.

[0002] The invention relates to unmanned aircraft or drones. The invention relates to determining an emergency landing solution when a critical hazard occurs requiring rapid landing in an area that does not cause human loss. Hazards may be due to weather, a failure of an on-board system or a loss of location.

[0003] The invention aims to solve the problem of making the decision to interrupt a mission far from the operator who does not have a correct reconstruction of the environment, in particular in the event of delays in the transmission of information from the drone, due to its distance or even a loss of transmission.

[0004] Currently, the operator of the unmanned aircraft or drone is responsible for detecting when a hazard no longer allows the mission to continue. Their role is to use simple macro commands such as "Return Home" or to land the drone where it is, for example by spiraling down to the ground, based on their perception of a critical hazard.

[0005] These solutions work well when the drone is flying close to the operator and the operator has a good understanding of the drone's environment. This is not the case for missions lasting several hours. Therefore, the systems will need to provide automatic solutions to the operator.

[0006] Long-range drone operations, or in other words, those with a flight mission exceeding 10 km, must provide a solution to various critical hazards such as: a critical energy autonomy level: energy monitoring detects that the drone no longer has the capacity to reach the nearest predetermined landing zone; degradations in flight performance following an actuator failure, excessive wind or a structural problem following an impact with an external element, for which monitoring of the position of the drone in relation to the trajectory makes it possible to detect that the guidance and autopilot functions no longer allow the trajectory to be followed; or a critical divergence of the position in the case of a loss of the GNSS position, for which monitoring is put in place, and beyond a certain time, the growing uncertainty no longer allows the drone to be airworthy.

[0007] In these cases, an emergency mode is defined so that the drone responds to the critical hazard.

[0008] In the case of long-range operations, the classic solution known as the "Flight Termination System" (FTS), which consists of triggering the opening of a parachute or carrying out a spiral descent, is not viable because it is difficult for the operator to get a precise idea of ​​the situation, as the drone is several tens or even hundreds of kilometers from the operator.

[0009] Existing solutions for finding a path between two points while avoiding obstacles use path finding algorithms. However, in the context of drones, the low-cost on-board hardware solution does not offer the performance required for such algorithms.

[0010] Furthermore, development costs in the drone sector must be as low as possible for competitive reasons. Due to development costs related to the level of certification and performance, the path finding solution cannot be adopted.

[0011] An aim of the invention is to address the problems mentioned above, and to provide an emergency landing trajectory calculated by the drone system (ground / onboard) in the event of a critical hazard requiring the aircraft to land as quickly as possible, this trajectory having to bring the aircraft to an area without human activity while guaranteeing that prohibited zones or NFZ (No Fly Zone) are not flown over, taking into account the relief, as well as taking into account the presence of obstacles such as prohibited zones.

[0012] According to one aspect of the invention, there is provided a system for managing the emergency landing trajectory of a drone comprising: a ground control station comprising a first computer provided with: a module for continuously determining a first emergency landing trajectory taking into account the last value of at least one parameter representative of the operation or environment of the drone, received from the drone, and an emergency landing database, configured to calculate the first emergency landing trajectory from a path search type algorithm, the emergency landing database, and the last value received of the operating or environmental parameter(s) of the drone; and a module for verifying the first trajectory, from the emergency landing database;and a control unit on board the drone comprising a second calculator, comprising: a module for continuously determining a second emergency landing trajectory from the emergency landing database and the current value of at least one operating or environmental parameter of the drone, configured to calculate the second emergency landing trajectory by comprising, for each emergency landing point, a lateral trajectory calculation, a vertical trajectory calculation, and configured to verify that the emergency trajectory is safe in a safety corridor, from the emergency landing database, and the last value of the operating or environmental parameter(s) of the drone;a module for detecting a critical hazard involving a switch to an emergency landing mode activating the operation of a module for selecting the first or second emergency landing trajectory, a hazard being detected from the current value of at least one operating or environmental parameter of the drone; and the selection module being configured to select the first emergency landing trajectory developed or the second emergency landing trajectory so as to select the first trajectory if the first trajectory takes into account the current value of the parameter(s); operating or environmental parameters of the drone representative of the critical hazard detected, and to select the second trajectory if the first trajectory takes into account a last value received different from the current value of the operating or environmental parameter(s) of the drone representative of the critical hazard detected.

[0013] In one embodiment, the landing database includes polygonal landing zones, no-fly zones, and obstacles.

[0014] According to one embodiment, the touchdown database includes touchdown points with an associated final approach axis and an associated altitude, no-fly zones, and obstacles.

[0015] In one embodiment, the module for continuously determining a second emergency landing trajectory is configured to calculate emergency landing points by defining a landing point search sector, by identifying the segments of the polygons directly visible in a straight line, and for each landing point: determining a final approach axis for each landing point; and verifying compliance with a safety corridor of the trajectory avoiding no-fly zones and obstacles.

[0016] According to one embodiment, the module for continuously determining a second emergency landing trajectory is configured to evaluate the landing points, from closest to furthest, by calculating a lateral trajectory, a vertical emergency landing trajectory, and an associated safety corridor.

[0017] In one embodiment, the second computer has less computing power than the first computer.

[0018] The invention will be better understood by studying a few embodiments described as non-limiting examples and illustrated by the appended drawings in which:

[0019] [Fig.1] schematically illustrates a system for managing the emergency landing trajectory of a drone, according to one aspect of the invention; and

[0020] [Fig.2] schematically illustrates an emergency landing database, according to one aspect of the invention;

[0021] [Fig.3] schematically illustrates the identification on board the drone of landing zones in an emergency landing database, according to one aspect of the invention;

[0022] [Fig.4] schematically illustrates an on-board evaluation of the candidate landing points in the drone, along a lateral trajectory, according to one aspect of the invention; and

[0023] [Fig.5] schematically illustrates an evaluation on board the drone of the evolution of a candidate landing point, along a vertical trajectory, according to one aspect of the invention.

[0024] Throughout the figures, elements with identical references are similar.

[0025] [Fig.1] schematically illustrates a system for managing the emergency landing trajectory of a drone 1, according to one aspect of the invention. The system comprises a ground control station 2 comprising a first computer 3 provided with: a module 4 for continuously determining a first emergency landing trajectory taking into account the last value of at least one parameter representative of the operation or the environment of the drone, received from the drone, and a database of emergency landings; and a module 5 for verifying the first trajectory, from the database of emergency landings.

[0026] The sensors 14 of the drone 1 provide measurements to a transmitter / receiver module 11 of the drone 1 which transmits them to the first computer 3 of the ground control station 2. The sensors 14 of the drone 1 also provide these measurements to a flight tracking module 12 of the drone 1, making it possible, from these measurements of the sensors 14, to determine hazards, such as an inability to fly the end of the mission with the remaining energy capacities, an exceeding of the lateral and vertical deviations to the trajectory compared to predefined thresholds, or equipment failures.

[0027] The system also comprises a control unit 6 on board the drone comprising a second computer 7 having, for example, a computing power lower than that of the first computer 3, which comprises: a module 8 for continuously determining a second emergency landing trajectory from the emergency landing database and the current value of at least one operating or environmental parameter of the drone; a module 9 for detecting a critical hazard involving a switch to an emergency landing mode activating the operation of a module 10 for selecting the first or second emergency landing trajectory, a hazard being detected from the current value of at least one operating or environmental parameter of the drone;and the selection module 10 being configured to select the first emergency landing trajectory developed or the second emergency landing trajectory so as to select the first trajectory if the first trajectory takes into account the current value of the operating or environmental parameter(s) of the drone representative of the detected critical hazard, and to select the second trajectory if the first trajectory takes into account a last received value different from the current value of the operating or environmental parameter(s) of the drone representative of the detected critical hazard.;

[0028] The module 4 for continuously determining a first emergency landing trajectory is configured to calculate the first emergency landing trajectory from a path search type algorithm, the emergency landing database, and the last value received from the operating or environmental parameter(s) of the drone.

[0029] The module 8 for continuously determining a second emergency landing trajectory is configured to calculate the second emergency landing trajectory by comprising, for each emergency landing point, a lateral trajectory calculation, a vertical trajectory calculation, and configured to verify that the emergency trajectory is safe in a safety corridor, from the emergency landing database, and from the last value of the operating or environmental parameter(s) of the drone.

[0030] The landing database includes polygonal landing zones (LZ) and no-fly zones (NFZ).

[0031] The touchdown database includes touchdown points with an associated final approach axis and altitude, and no-fly zones.

[0032] Module 8 for continuously determining a second emergency landing trajectory is configured to calculate emergency landing points by defining a landing point search sector, and for each landing point: identify the segments of the polygons directly visible in a straight line; determine a final approach axis for each landing point; and verify compliance with a safety corridor of the trajectory avoiding no-fly zones.

[0033] Module 8 for continuously determining a second emergency landing trajectory is configured to evaluate the landing points, from closest to furthest, by calculating a lateral trajectory and a vertical emergency landing trajectory.

[0034] The basic idea of ​​the present invention is to use two separate emergency trajectory calculation algorithms on the two computers: to have a simple trajectory calculation on board the drone and a more elaborate solution in the ground control station.

[0035] An onboard trajectory selection algorithm allows the system to select the emergency trajectory to be flown when it enters emergency mode. The selected trajectory is then sent to the guidance / piloting module 13 for execution.

[0036] The determination module 8 of the second computer 7 on board calculates a second basic direct-to trajectory, or "Direct-To" in English, between the drone and a landing zone. The determination module 4 of the first computer 3, in the ground control station 2, calculates a second, more complex trajectory before being sent back to the drone.

[0037] The selection module 10 is configured to select the first emergency landing trajectory developed or the second emergency landing trajectory so as to select the first trajectory if the first trajectory takes into account the current value of the operating or environmental parameter(s) of the drone representative of a detected critical hazard, and to select the second trajectory if the first trajectory takes into account a last received value different from the current value of the operating or environmental parameter(s) of the drone representative of the detected critical hazard.

[0038] The flight monitoring module 12 of the drone 1 makes it possible to detect the inability to fly the end of the mission with the remaining energy capacities, the exceeding of the lateral and vertical deviations to the trajectory compared to predefined thresholds, and equipment failures. The result of this monitoring is transmitted to the module 9 for detecting a critical hazard which, in the event of detection of a critical hazard which no longer allows the continuation of the mission and requires an emergency landing (for example within 2 or 3 minutes), switches to an emergency landing mode. The ground operator also has the capacity to trigger an emergency landing if he considers that the situation requires it.

[0039] The present invention makes it possible: to have a reasonable computing load in the drone and to address low-capacity hardware; to generate a reasonable certification cost; to make it possible to simulate the algorithms on the ground in mission preparation in order to validate the landing solutions along the mission; and to avoid the need to store on board the drone a set of emergency solutions calculated on the ground to respond to a critical hazard in the event of loss of communication.

[0040] Upon detection of a critical hazard involving a transition to an emergency landing mode, the selection module 10 selects the trajectory, the first emergency landing trajectory developed or the second emergency landing trajectory so as to select the first trajectory if the first trajectory takes into account the current value of the operating or environmental parameter(s) of the drone representative of the detected critical hazard, and to select the second trajectory if the first trajectory takes into account a last received value different from the current value of the operating or environmental parameter(s) of the drone representative of the detected critical hazard.

[0041] Thus, on board the drone, when switching to emergency landing mode, there is potentially a choice between two solutions: the one coming from the ground and the one calculated on board. The selection function determines which of these two solutions is the most relevant.

[0042] Each emergency trajectory is associated with a set of data allowing the reasons for the emergency transition to be defined: low battery, loss of position, loss of equipment, etc. This data may have had an impact on the calculated emergency solution.

[0043] For example, constraints related to remaining autonomy can reduce the landing point search sector.

[0044] The module 10 selection mechanism works as follows: If the datasets associated with the first and second emergency trajectories are consistent: This means that ground control station 2 is well aware of the current constraints detected on board drone 1; - We then favor the first trajectory provided by ground control station 2, determined using more complex algorithms. Otherwise Ground control station 2 and the edge of drone 1 do not have the same information, due to transmission problems; The critical hazard detected on board drone 1 is considered more relevant; and We choose the trajectory calculated on board.

[0045] Prior to the mission, the emergency landing database is developed on the ground and loaded onto the aircraft at the start of the mission. [Fig.2] illustrates an example of a representative map of an emergency landing database

[0046] These landing zones, or LZs, correspond to areas identified as safe and are modeled using polygons. These polygons are generated using several data sources.

[0047] On the landing zones, a safety edge is subtracted, corresponding to the distance necessary for the drone to descend without touching an obstacle which would be at the edge of the landing zone, and taking into account an uncertainty (inaccuracy of terrain elevation, inaccuracy of altitude measurement, etc.). This safety edge depends on the type of drone (technical characteristics) and its capabilities (descent slope). Thus, any point in a landing zone is a valid landing point.

[0048] The emergency landing database also includes no-fly zones.

[0049] Alternatively, the touchdown database may include touchdown points with an associated final approach axis and an associated altitude.

[0050] Module 8 for continuously determining the second emergency landing trajectory from the emergency landing database and the current value of at least one operating or environmental parameter of the drone 1.

[0051] Module 8 for continuously determining the second emergency landing trajectory, on board the drone 1, comprises the following main steps: determination of candidate landing points, if necessary, i.e. if the landing database does not already contain them; for each landing point: calculation of the lateral trajectory; Calculation of the vertical trajectory; and Verification that the trajectory is safe (definition of a safety corridor and verification that it does not collide with a no-fly zone or an obstacle).

[0052] When the landing database does not directly contain landing points, but landing areas, the determination of candidate landing points is carried out as follows by module 8, as illustrated in [Fig.3].

[0053] A search area is determined in which a landing point is searched.

[0054] This sector is defined by an arc of a circle, or a circle, having as its center the position of the drone, extrapolated to X seconds ahead (X being the calculation frequency of this emergency solution of the second calculator 7) and the current heading of the drone 1. The length of the sector corresponds to the maximum distance traveled by the drone in emergency cases: for example 2 or 3 minutes in our case.

[0055] The angle of the search sector can be set based on the drone's performance or various external constraints.

[0056] Then, the polygons from the landing database previously loaded on board drone 1 are then evaluated with regard to this search sector. Only the polygon segments included in the search sector are considered. They are limited to the boundaries of the search sector if necessary.

[0057] A projection in polar coordinates is carried out, in order to be able to easily determine which areas are directly visible in a straight line from the center of the search sector, in which angular sector and at what distance.

[0058] The visible landing zones are then identified. The projections allow us to know which angular sectors allow a landing zone (LZ) to be reached, and at what distance. The fact that the edges of the landing zones (polygons) take into account a safety margin ensures that any point in the landing zone is eligible as a landing point.

[0059] This allows determining a set of candidate landing points to evaluate. For example, by aiming at the center of the visible LZ landing zone segments.

[0060] We may want to determine a particular landing axis in order to improve landing safety depending on the type of drone 1 or the flight conditions (such as wind).

[0061] In this case, from a candidate landing point, it is possible to restart a projection within the landing zone, in order to determine a landing axis (or several) which leaves enough distance to land within the zone.

[0062] It is possible to include consideration of other parameters such as wind direction.

[0063] It is then necessary, for both cases of the landing database, landing zones or landing points, to evaluate each landing point, with its associated final approach axis and its associated altitude.

[0064] Several evaluation strategies are possible, for example from closest to furthest, or from closest from the minimum distance to land to furthest.

[0065] Each landing point assessment performs the following steps.

[0066] First a lateral trajectory is calculated, as illustrated in [Fig.4]. The lateral trajectory calculation searches for the most direct joining trajectory from a given position and heading, to arrive at a given point with a given heading.

[0067] The starting point of the algorithm is the center of the search sector, and the current heading of the drone 1. The arrival point corresponds to the approach start point. It is placed along the landing axis, before the landing point. The approach segment (straight) is then added at the end of the trajectory.

[0068] Then, a vertical trajectory is calculated, as illustrated in 3D in [Fig.5], which takes into account the terrain elevations, available in a terrain database on board the drone 1, and the characteristics of the drone 1.

[0069] The trajectory must also meet terrain-following constraints to ensure that it remains flyable without risking collision with terrain. If this is not possible, the touchdown point is rejected or ignored.

[0070] Finally, the trajectory is checked to ensure that it does not collide with forbidden zones or obstacles (integrated as forbidden zones in the database). For this, a safety corridor around the trajectory is taken into account. If this is not possible, this landing point is ignored.

[0071] As soon as a candidate landing point has allowed the calculation of a safe trajectory, the calculation can stop: a valid solution has been found.

[0072] All these calculations are carried out continuously on board the drone 1 at a certain calculation frequency, limited by the capacities of the second computer 7. Thus, a posed solution is regularly updated based on the measured context.

[0073] In the event that an emergency trajectory is selected by the selection module 10 to be flown, new emergency trajectories are continually recalculated in order to propose an adequate solution to a change in critical hazards on board the drone 1.

[0074] The module 4 for continuously determining a first emergency landing trajectory firstly constructs a path which takes into account the no-fly zones NFZ. The computing capacity of the first computer 3 of the ground station 2 is generally greater than on board the drone 1 in the second computer 7, and allows the use of Path Finding type algorithms (Theta* or Field D*) or RRT type (rapid random tree) on the ground.

[0075] This path is then provided to a trajectory calculation algorithm to calculate the first 3D landing trajectory to take into account the terrain. The first trajectory is then provided to module 5 for verifying the first trajectory. Its role is to guarantee that a trajectory is flyable by proposing a DAL level, for "Design Assurance Levels" in English, equal to the algorithms on board the drone 1. The algorithm makes it possible to verify that the trajectory is flyable in terms of continuity and performance, that there is no conflict with the terrain, obstacles and No Fly Zones. The result of the verification and the trajectory are transmitted to the drone 1.

[0076] The trajectory thus produced is sent on board the drone, periodically or punctually, in order to be taken into account in the event of a critical hazard requiring switching to emergency mode.

[0077] Thus, the present invention makes it possible to guarantee that an emergency landing trajectory is always available throughout the mission, which responds to the nature of the critical hazard encountered.

[0078] Dynamically calculating a trajectory that takes into account the current context of drone 1 avoids pre-loading a large number of solutions on board. This reduces the memory capacity to be allocated to storing trajectories.

[0079] The solution continues to operate even if communication is lost between ground station 2 and drone 1.

[0080] The use of a simple algorithm on board drone 1 makes it possible to quickly simulate the flight sequence in mission preparation to identify sections not covered by an emergency solution.

Claims

CLAIMS 1. Emergency landing trajectory management system for a drone (1) comprising: a ground control station (2) comprising a first computer (3) provided with: a module (4) for continuously determining a first emergency landing trajectory taking into account the last value of at least one parameter representative of the operation or environment of the drone, received from the drone, and an emergency landing database, configured to calculate the first emergency landing trajectory from a path search type algorithm, the emergency landing database, and the last value received of the operating or environmental parameter(s) of the drone; and a module (5) for verifying the first trajectory, from the emergency landing database;and a control unit (6) on board the drone (1) comprising a second calculator (7), comprising: a module (8) for continuously determining a second emergency landing trajectory from the emergency landing database and the current value of at least one operating or environmental parameter of the drone, configured to calculate the second emergency landing trajectory by comprising, for each emergency landing point, a lateral trajectory calculation, a vertical trajectory calculation, and configured to verify that the emergency trajectory is safe in a safety corridor, from the emergency landing database, and the last value of the operating or environmental parameter(s) of the drone;a module (9) for detecting a critical hazard involving a switch to an emergency landing mode activating the operation of a module for selecting the first or second emergency landing trajectory, a hazard being detected from the current value of at least one operating or environmental parameter of the drone; and the selection module (10) being configured to select the first emergency landing trajectory developed or the second trajectory; emergency landing so as to select the first trajectory if the first trajectory takes into account the current value of the operating or environmental parameter(s) of the drone representative of the detected critical hazard, and to select the second trajectory if the first trajectory takes into account a last value received different from the current value of the operating or environmental parameter(s) of the drone representative of the detected critical hazard.

2. The system of claim 1, wherein the landing database comprises polygonal landing zones (LZ), no-fly zones (NFZ), and obstacles.

3. The system of claim 1, wherein the touchdown database includes touchdown points with an associated final approach axis and associated altitude, no-fly zones, and obstacles.

4. System according to claim 2, in which the module (8) for continuously determining a second emergency landing trajectory is configured to calculate emergency landing points by defining a landing point search sector, by identifying the segments of the polygons directly visible in a straight line, and for each landing point: determining a final approach axis for each landing point; and verifying compliance with a safety corridor of the trajectory avoiding no-fly zones and obstacles.

5. System according to claim 3 or 4, in which the module (8) for continuously determining a second emergency landing trajectory is configured to evaluate the landing points, from closest to furthest, by calculating a lateral trajectory, a vertical emergency landing trajectory, and an associated safety corridor.

6. System according to one of the preceding claims, in which the second computer (7) has a computing power lower than that of the first computer (3).

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