Drone self-guided by a dual-use optronic distance measurement device

Abstract

The invention relates to an aerial drone (1) including a fixed structure (2), a motor assembly (3) for propelling and orienting the drone, an optronic distance measurement device (6), and an electronic guidance unit (5) connected to the motor assembly (3) and to the optronic distance measurement device (6) in order to control the motor assembly (3) according to signals emitted by the optronic distance measurement device (6). The device (6) comprises an optical system (6.1) and an optronic sensor (6.2) which have a fixed orientation with respect to the fixed structure (2). The electronic guidance unit (5) is arranged to control the motor assembly (3) in order for the drone to move above an exploration area, scanning the exploration area by the optronic sensor (6.2) until detecting electromagnetic radiation emitted by a target, and then to guide the drone until the target by distance measurement.

Description

[0001] DRONE SELF-GUIDED BY DUAL-USE OPTRONIC DEPARTURE DEVICE

[0002] The present invention relates to the field of aerial drones, in particular transport and delivery drones, and more particularly any unmanned vehicle capable of traveling from one point to another autonomously.

[0003] BACKGROUND OF THE INVENTION

[0004] When it is not possible to use a remote-controlled drone, for example because radio communications with the drone are impossible, it is known to resort to a self-guided drone.

[0005] A drone of this type generally includes a self-guiding device that controls the drone's steering organs to bring the drone from a starting point to a destination point that have been pre-programmed. The self-guiding device most often includes a receiver of satellite positioning signals (or GNSS) coming from satellites in a constellation of satellites (GPS, GALILEO, GLONASS, BEIDU, etc.) in orbit around the Earth and an electronic navigation unit connected to the satellite receiver to calculate satellite navigation. Satellite navigation is very accurate in the long term, but reception of satellite signals is not always possible, for example, due to the relief or the presence of jamming devices interfering with the satellite signals.

[0006] Some drones are also equipped with an inertial unit connected to the electronic navigation unit which is then arranged to calculate a hybrid satellite / inertial navigation. This hybrid navigation has the advantage of providing reliable navigation that is more robust to the unavailability of satellite signals. On the other hand, when satellite signals are unavailable for a relatively long period, hybrid navigation drifts and is no longer usable unless higher precision inertial units are used, the cost, size, mass and energy consumption of which are generally incompatible with use on a drone.

[0007] There are also drones equipped with a mobile platform carrying optronic sensors sensitive to the visible and / or infrared range. Images of the drone's environment can then be used to allow it to locate itself and establish navigation, but using images for navigation requires significant computing resources. It is also necessary for the environment to include previously known and identifiable landmarks.

[0008] It is also known to guide missiles towards a light spot projected onto an object by a laser. The missile is equipped with a homing system comprising an optronic deviation measurement device which comprises an optical system having an optical axis on which an optronic sensor is arranged. The optronic sensor comprises four photodiodes which provide a signal proportional to a quantity of light energy received and which have fields combining to form the sensor field. A distinction will be made between the total field of the sensor which is the optical field in which a light spot can be detected by at least one of the photodiodes and the linear field which is the part of the total field in which several photodiodes observe the light spot thus allowing a deviation measurement. To facilitate the detection of the light spot and the deviation measurement, it is known to arrange the optical system to defocus the spot on the sensor.

[0009] The device is associated with a calculation circuit arranged to carry out a deviation measurement, that is to say to determine the position of the light spot located in the linear field of the sensor by calculating a barycenter of the light spot in the linear field of the sensor from the energies detected by the photodiodes. Indeed:

[0010] - when the light spot is in the center of the sensor field, the four photodiodes will measure the same light energy so that they provide signals of the same value, apart from measurement noise. The calculated barycenter is therefore also in the center of the linear field;

[0011] - if the light spot is shifted towards one of the photodiodes, said photodiode will provide a greater signal than the other photodiodes and the calculated barycenter of the detected spot will be shifted towards said photodiode.

[0012] After defocusing the spot on the sensor, the flux distribution in the image spot is representative of the distribution of the incident flux in the entrance pupil of the optical path. However, the total field of the sensor is relatively narrow and it is necessary to point the missile sensor in the direction of the target object so that it can lock onto the target designated by the laser beam.

[0013] It could be considered to use a deviation measurement device on a drone to guide it, but it would be necessary to mount the sensor on a steerable platform, of the same type as that of the image sensors mentioned above, to compensate for the weakness of the total field of the sensor. However, this would result in an increase in the mass and size of the drone, limiting the payload of the drone and its stealth for applications where discretion is mandatory.

[0014] SUBJECT OF THE INVENTION

[0015] The invention aims in particular to enable guidance in an environment prohibiting the use of a satellite positioning receiver or radio communications.

[0016] SUMMARY OF THE INVENTION

[0017] To this end, the invention provides an aerial drone comprising a fixed structure, a motorized assembly for propulsion and orientation of the drone, an optronic deviation measurement device, and an electronic guidance unit connected to the motorized assembly and to the optronic deviation measurement device to control the motorized assembly according to signals emitted by the optronic deviation measurement device. The optronic deviation measurement device comprises an optical system and an optronic sensor which are fixed in orientation relative to the fixed structure. The electronic guidance unit is arranged to control the motorized assembly to move the drone above an exploration zone by having the optronic sensor scan the exploration zone until electromagnetic radiation emitted by a target is detected and then to bring the drone to the target by deviation measurement.

[0018] Fixed structure means all the fixed parts of the drone such as the fuselage, a fixed wing, fixed planes of a tail. Thus, in the invention, the optronic deviation measurement device is used to detect electromagnetic radiation by compensating for the latter's small field of observation and the absence of a platform that can be oriented by the drone's scanning movements. According to optional characteristics, used individually or in whole or in part in combination:

[0019] - the electronic guidance unit controls a circular scan of the exploration area;

[0020] - the electronic guidance unit controls a transverse scan relative to a substantially rectilinear direction of movement of the drone above the exploration zone; - the drone comprises a self-destruction member connected to the electronic guidance unit, the electronic guidance unit being arranged to activate the self-destruction member in the event of detection of at least one predetermined event advantageously corresponding to an exceeding of a predetermined time for detecting the target or to a predetermined characteristic of the electromagnetic radiation emitted by the target;

[0021] - the drone comprises an inertial unit connected to the electronic guidance unit, the electronic guidance unit being arranged to bring the drone to the exploration zone using signals from the inertial unit;

[0022] - electromagnetic radiation is emitted with a half-angle at the apex between + / - 85° and + / - 45° around an axis substantially normal locally to the ground;

[0023] - electromagnetic radiation is emitted by a laser transmitter associated with a divergent optical system;

[0024] - the electromagnetic radiation is obtained by reflection on an at least partially reflecting surface of a laser beam from a laser designator associated with a diverging optical system;

[0025] - the target is a beacon comprising a laser transmitter emitting electromagnetic radiation.

[0026] Other characteristics and advantages of the invention will emerge from reading the following description of particular and non-limiting embodiments of the invention.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Reference will be made to the attached drawings, including:

[0029] [Fig. 1] Figure 1 is a schematic perspective view of a drone according to the invention; [Fig. 2] Figure 2 is a schematic bottom view of the drone according to the invention;

[0030] [Fig. 3] Figure 3 is a schematic perspective view showing a drone according to the invention searching for a target according to a first embodiment; [Fig. 4] Figure 4 is a schematic top view of an area being explored according to a first exploration mode;

[0031] [Fig. 5] Figure 5 is a schematic top view of an area being explored according to a second exploration mode;

[0032] [Fig. 6] Figure 6 is a schematic perspective view showing the formation of a guidance target according to a second embodiment;

[0033] [Fig. 7] Figure 7 is a flowchart illustrating the drone guidance process.

[0034] DETAILED DESCRIPTION OF THE INVENTION

[0035] With reference to Figures 1 and 2, the invention is described here in application to an aerial drone generally designated 1, here of the quadricopter type, comprising a structure 2 and motorized propulsive propellers 3 forming a motorized assembly for propulsion and orientation of the drone. The motorization of the motorized propulsive propellers 3 is here an electric motorization powered by a battery not shown embedded in the structure 2. The structure 2 comprises a body 2.1 from which arms 2.2 extend and each of the motorized propulsive propellers 3 is mounted at a free end of one of the arms 2.2. The body 2.1 comprises a hold 4, which here opens on the top of the body 1. The body 2.1 further forms a sealed enclosure containing an electronic guidance unit, generally designated 5, powered by the battery and connected to the motorized propulsive propellers 3 to orient and direct the drone 1.The electronic guidance unit 5 comprises, for example, at least one processor and a memory containing computer programs executable by the processor. The construction and operation of these elements are known per se and will not be described further here.

[0036] The electronic guidance unit 5 is also connected to an optronic deviation measurement device, generally designated 6, comprising:

[0037] - an optical system, generally designated in 6.1, having an optical axis,

[0038] - an optronic sensor 6.2 arranged on the optical axis behind the optical system 6.1, and

[0039] - an electronic weighing circuit 6.3 connected to the optronic sensor 6.2.

[0040] The optical system 6.1 comprises one or more lenses for shaping light electromagnetic radiation, having the shape of an incident light beam, entering the optronic deviation measurement device 6 to form an image spot on the sensitive surface of the optronic sensor 6.2. The optronic sensor 6.2 comprises a detector comprising, in a manner known per se, four adjacent photodiodes which are arranged in quadrants and which are each associated with an optical group having a field which combines with that of the optical groups of the other photodiodes to define the field of the detector and therefore of the optronic sensor 6.2. The photodiodes are here monophotodiodes defining together the sensitive surface of the optronic sensor 6.2. In the present case, by way of example, the combination of the optronic sensor 6.2 and the optical system 6.1 forms an optronic assembly of the optronic deviation measurement device 6 which has a field of observation (or FoV) of between + / - 5° and + / - 40° and a pupil having a diameter of between 5 mm and 40 mm.

[0041] The electronic weighing circuit 6.3 comprises an electronic card comprising, in a manner known per se, a processor and a memory containing an operating program for the optronic device 6. The four photodiodes provide the electronic weighing circuit 6.3 with a signal proportional to a quantity of light energy of the incident light beam having at least one wavelength of interest (for simplification; this is in fact a range of wavelengths which will preferably be narrow) to which the photodiodes are sensitive, forming the image spot on the optronic sensor 6.2. The electronic weighing circuit 6.3 is arranged to carry out a deviation measurement known per se from the signals coming from the optronic sensor 6.2 and to send to the electronic guidance unit 5 signals representative of a difference between the spot and the center of the optronic sensor 6.2, this deviation being representative of a deviation between the direction of the incident light beam and the direction in which the deviation measuring device 6 points. The deviation measuring device 6 is here mounted in a lower part of the body 2.1. More precisely, the optical system 6.1 and the sensor 6.2 are rigidly fixed to the body 2.1, that is to say without the possibility of motorized orientation of these relative to the body 2.1 (so-called strap-down mounting) and open onto a lower surface of the body 2.1 of the drone 1.

[0042] The electronic guidance unit 5 is further connected to an inertial unit 7 and to a communication unit 8.

[0043] The inertial unit 7 comprises, in a manner known per se, linear inertial sensors, such as accelerometers, arranged along the axes of a measurement frame to measure the components of a specific force vector and angular inertial sensors, such as gyrometers, arranged to measure the orientations of the measurement frame relative to an inertial frame. The inertial unit 7 provides the electronic guidance unit 5 with signals representative of the movements of the drone 1.

[0044] The communication device 8 may be of the wired type or of the wireless type (for example of the short-range radioelectric type such as the NFC system) and allows an operator having a suitable computer terminal (a computer, a smartphone, or a dedicated terminal) or a suitable interface device (a keyboard associated with a screen) to exchange data with the electronic guidance unit 5 and / or to modify operating control parameters of the drone 1).

[0045] The electronic guidance unit 5 is arranged, in a manner known per se, to control the rotation of the motorized propulsive propellers 3 to orient the drone 1 in roll, pitch and yaw and to move it along a trajectory while controlling the attitude of the drone 1.

[0046] The electronic guidance unit 5 is more particularly arranged, in the guidance method preferably implemented by the invention, to implement three guidance modes.

[0047] According to a first guidance mode, or approach guidance, the electronic guidance unit 5 is arranged to bring the drone 1 from a starting position to an intermediate position. The first guidance mode is used here to bring the drone 1 to an area to be explored using the signals provided by the inertial unit 7. The intermediate position is located at the center of the area to be explored and / or on a border of the area to be explored. The intermediate position and the limits of the area to be explored are programmed in the electronic guidance unit 5 via the communication member 8. According to a second guidance mode more particularly illustrated in FIGS. 3 to 5, or exploration guidance, the electronic guidance unit 5 is arranged to scan the exploration area ZE by the observation field of the optronic assembly formed by the combination of the optronic sensor 6.2 and the optical system 6.1 until the detection of a predetermined electromagnetic radiation. The electronic guidance unit 5 controls the drone 1 solely from the signals from the inertial unit 7 so as to act on the roll, pitch and yaw of the drone 1 in such a way that the optical axis of the optronic assembly formed by the combination of the optronic sensor 6.2 and the optical system 6.1 moves over the exploration zone ZE along a scanning trajectory TB. In Figure 4, the electronic guidance unit 5 controls a transverse scan relative to a substantially rectilinear direction of movement of the drone 1 above the exploration zone ZE. The scanning width and length are stored in the electronic guidance unit 5. In Figure 5, the electronic guidance unit 5 controls a concentric scan, here circular, of the exploration zone ZE.It is understood that, in the latter case, the intermediate scanning start position may be at the border of the scanning zone ZE (scanning from the periphery to the center) or at the center of the scanning zone ZE (scanning from the center to the periphery). The scanning rays are stored in the electronic guidance unit 5.

[0048] The electronic guidance unit 5 is arranged to interrupt the exploration guidance as soon as the predetermined electromagnetic radiation is detected by the optronic sensor 6.2 of the optronic deviation measuring device 6. The predetermined electromagnetic radiation comes from a target and here has the form of a series of laser beam pulses: the wavelength of the laser beam, the frequency and the duration of the pulses are predetermined and have been entered into the memory of the electronic guidance unit 5.

[0049] According to a third guidance mode, or terminal guidance which follows on from exploration guidance, the electronic guidance unit 5 pilots the drone 1 based on the deviation measurement signals transmitted by the optronic deviation measurement device 6 to reduce the distance between the spot and the center of the optronic sensor 6.2. The electronic guidance unit 5 has in memory a table relating the size of the spot and an approach speed so that the drone 1 is piloted to slow down as the distance separating the drone 1 from the target reduces (the spot growing larger when the drone 1 approaches the target).

[0050] As stated earlier, the predetermined electromagnetic radiation comes from a target. There are several ways to create the target.

[0051] In a first embodiment shown in Figure 3, the target is materialized by a beacon 10 comprising a laser transmitter arranged to emit a laser beam in a direction substantially normal locally to the ground, here vertical direction, corresponding to the emission axis of the beam AE. The laser transmitter is associated with a diverging optical system in such a way that the electromagnetic radiation is emitted in a cone with a half-angle at the apex a of between + / - 85° and + / - 45° around the axis AE.

[0052] In a second embodiment shown in Figure 6, the target is materialized by a reflective cloth 11 (such as a simple white cloth or a metallized cloth), spread on the ground S, towards which a laser transmitter 12, such as a tripod-mounted laser designator, associated with a diverging optical system 13, projects a laser beam in such a way that the beam is reflected by the reflective cloth 11 substantially vertically in the form of electromagnetic radiation having a half-angle at the vertex α of between + / - 85° and + / - 45° around the main direction of reflection. Alternatively, the reflective cloth 11 can be replaced by any reflective screen, rigid or not, rough or smooth, or can even be omitted if the ground (or a surrounding element such as a rock, a building or the like) is sufficiently reflective.Preferably, the spot formed by the beam on the canvas will have a radius of approximately 1 meter, the reflective canvas having a substantially identical size. More preferably, the divergent optical system 13 will ensure filtering of the laser beam to avoid speckle or scintillation effects.

[0053] In both embodiments, the electromagnetic radiation emitted by the target has predetermined characteristics. Indeed, if the electromagnetic radiation detected by the optronic sensor 6.2 does not have these characteristics, it is ignored. Thus, the laser transmitter is arranged to produce sequences of pulses of a laser beam having here a wavelength between 700 nm and 1650 nm. The pulses have a predetermined frequency and duration (here between 10 ns and 10 ms, and preferably between 10 and 100 ns). It is also possible to provide that the same sequence comprises pulses of different durations.

[0054] In a preferred implementation of the invention, the drone 1 comprises a self-destruction member 9, here a pyrotechnic charge, connected to the electronic guidance unit 5 and the laser pulses are emitted according to at least two useful frequencies Futl and Fut2 of your choice. Each frequency Futl and Fut2 is associated with an action to be carried out by the drone 1, here: nominal landing for Futl, and - self-destruction for Fut2.

[0055] An example of operation will now be described in detail for the accomplishment of a mission consisting of having a first operator transmit an electronic data medium to a second operator located in a territory in which radio communications and the reception of satellite positioning signals are impossible. The delivery must be carried out at a time and at an arrival position of the drone 1 agreed in advance between the two operators, it being understood that the second operator may be located within a radius of a few hundred meters in the vicinity of the agreed arrival position.

[0056] In an initial step, at the starting position, the first operator places the electronic data carrier in the hold 4 and stores in the electronic control unit 5 the starting position and the arrival position of the drone 1 agreed in advance with the second operator using a computer terminal connected to the communication device 8.

[0057] For his part, at the arrival position (or in the vicinity of it), the second operator activates the laser transmitter to emit the electromagnetic radiation at the useful frequency Futl to allow the terminal guidance of the drone 1.

[0058] The electronic guidance unit 5 controls the departure of the drone 1 towards the arrival position in approach guidance and calculates the intermediate position at a predetermined distance (here 2 kilometers) from the arrival position. The electronic guidance unit 5 continuously calculates, by exploiting the signals supplied by the inertial unit 7, the distance which separates it from the intermediate position (step 101) until it has reached this position (verification 102).

[0059] Once the intermediate position is reached, the electronic guidance unit 5 begins the exploration guidance (step 103) as long as the predetermined electromagnetic radiation is not detected (verification 104).

[0060] Once the predetermined electromagnetic radiation has been detected, the electronic guidance unit 5 begins terminal guidance (step 105) while continuously monitoring that the frequency of the pulses is indeed the Futl frequency (step 106).

[0061] If the pulse frequency remains equal to the Futl frequency (check 107), the electronic guidance unit 5 lands nominally (step 108) allowing the second operator to recover the electronic data medium. The second operator can then command the electronic guidance unit 5 to return the drone 1 to the starting position (empty or with an electronic data medium in the hold 4) or keep the drone 1 for later reuse.

[0062] If the frequency of the pulses becomes equal to the frequency Fut2 (verification 107), the electronic guidance unit 5 interrupts the terminal guidance and activates the self-destruction member 9 (step 109) which destroys the drone 1. It can be provided that the electronic guidance unit 5 commands a maneuver to move the drone 1 away before proceeding with the activation of the self-destruction member 9 so as to limit the risk of the drone 1 exploding near the second operator.

[0063] In parallel, when the electronic guidance unit 5 begins exploration guidance (step 103), it also starts a backup process by counting an exploration duration (step 110) and checks that the exploration duration is less than a predetermined maximum threshold (check 111). If the predetermined maximum threshold is reached, the electronic guidance unit 5 activates the self-destruction member 9 (step 109) which destroys the drone 1. Alternatively, if the drone 1 must be returned to its starting position in all cases, the maximum exploration duration threshold can be determined in real time by the electronic guidance unit 5 as a function of the remaining autonomy of the drone 1 and the distance separating the current position of the drone 1 and its starting position, so that the drone 1 has sufficient autonomy to reach its starting position once the exploration duration is equal to the maximum threshold.At this moment, the electronic guidance unit 5 interrupts the exploration guidance to return to its starting position using the approach guidance.

[0064] It is understood that exploration guidance also makes it possible to overcome the lack of precision of the inertial unit; the lower this precision, the more extensive the exploration zone will have to be.

[0065] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0066] In particular, the drone may have a structure different from that described and include, for example, a fixed wing, a different number of propulsive propellers, a tail, control surfaces, and / or a different motorization, for example thermal; and / or be devoid of a self-destruction device...

[0067] Other guidance modes are possible. For example, the intermediate position is the arrival position. Once the drone 1 is in the arrival position, the electronic guidance unit 5 begins exploration guidance by making concentric circles around the arrival position and widening these circles as long as:

[0068] 1. the predetermined electromagnetic radiation is not detected; or 2. the maximum exploration duration threshold is not reached, self-destruction or a return to the starting position being ordered once the maximum threshold is reached.

[0069] The number of useful frequencies can be less or more than two. We can thus provide:

[0070] - a useful frequency controlling the nominal landing, and optionally

[0071] - a useful frequency commanding an emergency landing and / or

[0072] - a useful frequency controlling the interruption of the initial mission and the return to the starting position, and / or

[0073] - a useful frequency ordering a diversion to another arrival position, and / or

[0074] - a useful frequency commanding self-destruction...

[0075] The predetermined event to trigger the self-destruction may correspond to exceeding a predetermined time to detect the target and / or to one or more predetermined characteristic(s) of the electromagnetic radiation emitted by the target (frequency of the laser beam, and / or duration of the pulses, and / or interval between the pulses, and / or organization of the series of pulses according to a Morse-type code, etc.).

[0076] The drone could carry a satellite positioning signal receiver used to bring the drone as close as possible to the exploration area in the event that satellite positioning signals are available along part of the drone's path.

[0077] The drone could carry a radio signal receiver to provide radio wave guidance of the drone to bring the drone as close as possible to the exploration area in the event that radio waves are available without interference over part of the drone's path.

[0078] The exploration guidance can scan the exploration area from one end to another, from the center to the periphery or vice versa, regardless of the shape of the area.

Claims

CLAIMS 1. Aerial drone (1) comprising a fixed structure (2), a motorized assembly for propulsion and orientation of the drone (3), an optronic deviation measurement device (6), and an electronic guidance unit (5) connected to the motorized assembly (3) and to the optronic deviation measurement device (6) to control the motorized assembly (3) according to signals emitted by the optronic deviation measurement device (6), characterized in that the optronic deviation measurement device (6) comprises an optical system (6.1) and an optronic sensor (6.2) which are fixed in orientation relative to the fixed structure (2), and in that the electronic guidance unit (5) is arranged to control the motorized assembly (3) to move the drone above an exploration zone by having the optronic sensor (6.2) scan the exploration zone until electromagnetic radiation emitted by a target is detected and then to bring the drone to the target by deviation measurement.

2. Drone (1) according to claim 1, wherein the electronic guidance unit (5) controls a circular scan of the exploration area.

3. Drone (1) according to claim 1 or 2, wherein the electronic guidance unit (5) controls a transverse scan relative to a substantially rectilinear direction of movement of the drone above the exploration zone.

4. Drone (1) according to any one of the preceding claims, comprising a self-destruction member (9) connected to the electronic guidance unit (5), the electronic guidance unit (5) being arranged to activate the member self-destruction (9) in the event of detection of at least one predetermined event.

5. Drone (1) according to claim 4, in which the predetermined event corresponds to exceeding a predetermined time for detecting the target.

6. Drone (1) according to any one of the preceding claims, comprising an inertial unit (7) connected to the electronic guidance unit (5), the electronic guidance unit (5) being arranged to bring the drone (1) to the exploration zone from signals from the inertial unit (7).

7. Drone according to any one of the preceding claims, in which the electromagnetic radiation is emitted with a half-angle at the apex of between + / - 85° and + / - 45° around an axis substantially normal locally to the ground.

8. Drone according to claim 7, in which the electromagnetic radiation is emitted by a laser transmitter (12) associated with a divergent optical system (13).

9. Drone according to claim 7 or 8, in which the electromagnetic radiation is obtained by reflection on an at least partially reflecting surface of a laser beam coming from a laser designator (12) associated with a divergent optical system (13).

10. Drone according to claim 7, in which the target is a beacon (10) comprising a laser transmitter emitting the electromagnetic radiation.

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