Drone self-guided by a dual-purpose optronic distance measuring device.

Abstract

An aerial drone (1) comprising a fixed structure (2), a motorized drone propulsion and orientation assembly (3), an optronic rangefinder (6), and an electronic guidance unit (5) connected to the motorized assembly (3) and the optronic rangefinder (6) to control the motorized assembly (3) based on signals emitted by the optronic rangefinder (6). The device (6) includes an optical system (6.1) and an optronic sensor (6.2) that are fixed in orientation relative to the fixed structure (2). The electronic guidance unit (5) is arranged to control the motorized assembly (3) to move the drone over an exploration area by having the optronic sensor (6.2) scan the exploration area until it detects electromagnetic radiation emitted by a target, and then to guide the drone to the target using rangefinders. (Figure from the summary: Fig. 1)

Description

Title of the invention: Drone self-guided by dual-purpose optronic deviation measuring device.

[0001] 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.

[0002] BACKGROUND OF THE INVENTION

[0003] When it is not possible to use a remotely controlled drone, for example because radio communications with the drone are impossible, it is known to resort to a self-guided drone.

[0004] A drone of this type generally includes an autoguidance system that controls the drone's steering mechanisms to guide it from a pre-programmed starting point to a pre-programmed destination. The autoguidance system most often comprises a receiver of satellite positioning signals (or GNSS) from satellites in a constellation of satellites (GPS, GALILEO, GLONASS, BEIDU, etc.) orbiting the Earth, and an electronic navigation unit connected to the satellite receiver to calculate satellite navigation. Satellite navigation is very precise over the long term, but receiving satellite signals is not always possible, for example, due to terrain or the presence of jamming devices that interfere with satellite signals.

[0005] Some drones are also equipped with an inertial navigation system connected to the electronic navigation unit, which is then configured to calculate hybrid satellite / inertial navigation. This hybrid navigation has the advantage of providing reliable and more robust navigation in the event of satellite signal unavailability. However, when satellite signals are unavailable for a relatively long period, hybrid navigation drifts and becomes unusable unless higher-precision inertial navigation systems are used, the cost, size, weight, and energy consumption of which are generally incompatible with use on a drone.

[0006] There are also drones equipped with a mobile platform carrying optronic sensors sensitive in the visible and / or infrared range. Images of the drone's environment can then be used to allow it to orient itself and establish navigation, but using images for navigation requires significant computing resources. Furthermore, the environment must include previously known and identifiable landmarks.

[0007] It is also known to guide missiles towards a bright spot projected onto an object by a laser. The missile is equipped with a homing system including an optronic rangefinder device comprising an optical system with an optical axis on which an optronic sensor is mounted. The optronic sensor has four photodiodes that provide a signal proportional to the amount of light energy received and whose fields combine to form the sensor's field. A distinction is made between the total sensor field, 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 portion of the total field in which several photodiodes observe the light spot, thus enabling a range measurement. To facilitate the detection of the light spot and the range measurement, it is known to arrange the optical system to defocus the spot on the sensor.

[0008] The device is associated with a calculation circuit arranged to perform a deviation measurement, that is, to determine the position of the light spot located in the linear field of the sensor by calculating a centroid of the light spot in the linear field of the sensor from the energies detected by the photodiodes. Indeed:

[0009] - when the light spot is at the center of the sensor's field of view, the four pho The two diodes will measure the same light energy so that they provide signals of the same value, within measurement noise. The calculated center of gravity is therefore also located at the center of the linear field;

[0010] - if the light spot is shifted towards one of the photodiodes, said photodiode will provide a stronger signal than the other photodiodes and the calculated center of gravity of the detected spot will be shifted towards said photodiode.

[0011] After defocusing the spot on the sensor, the flux distribution in the image spot is representative of the incident flux distribution in the entrance pupil of the optical channel. However, the total field of view of the sensor is relatively narrow, and it is necessary to point the missile sensor in the direction of the targeted object in order for it to lock onto the target designated by the laser beam.

[0012] It could be considered to use a distance measuring 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 sensor's limited overall field of view. However, this would result in an increase in the drone's mass and size, thereby limiting the drone's payload and its stealth capabilities for applications where discretion is essential.

[0013] SUBJECT OF THE INVENTION

[0014] The invention is notably intended to enable guidance in an environment prohibiting the use of a satellite positioning receiver or radio communications. Summary of the invention

[0015] To this end, the invention provides an aerial drone comprising a fixed structure, a motorized propulsion and orientation system, an optronic rangefinder, and an electronic guidance unit connected to the motorized system and the optronic rangefinder for piloting the motorized system based on signals emitted by the optronic rangefinder. The optronic rangefinder comprises an optical system and an optronic sensor whose orientation is fixed relative to the fixed structure. The electronic guidance unit is arranged to pilot the motorized system to move the drone over an exploration area by having the optronic sensor scan the exploration area until it detects electromagnetic radiation emitted by a target, and then to guide the drone to the target by means of rangefinders.

[0016] The term "fixed structure" refers to all the fixed parts of the drone, such as the fuselage, fixed wings, and fixed tail surfaces. Thus, in the invention, an optronic beamforming device is used to detect electromagnetic radiation, compensating for its limited field of view and the absence of a platform that can be oriented by the drone's scanning movements.

[0017] According to optional features, used individually or in whole or in part in combination: - the electronic guidance unit controls a circular scan of the exploration area; - the electronic guidance unit controls a transverse scan relative to a substantially straight direction of movement of the drone above the exploration area; - the drone includes a self-destruct device linked to the electronic guidance unit, the electronic guidance unit being arranged to activate the self-destruct device in the event of detection of at least one predetermined event advantageously corresponding to an exceeding of a predetermined time to detect the target or to a predetermined characteristic of the electromagnetic radiation emitted by the target; - the drone includes an inertial navigation system connected to the electronic guidance unit, the electronic guidance unit being arranged to bring the drone to the exploration area from signals from the inertial navigation system; - electromagnetic radiation is emitted with a half-angle at the apex between + / - 85° and + / - 45° around an axis substantially normal locally to the ground; - Electromagnetic radiation is emitted by a laser emitter associated with a diverging optical system; - electromagnetic radiation is obtained by reflection on a surface at least partially reflective of a laser beam from a laser designator associated with a diverging optical system; - the target is a beacon containing a laser emitter that emits electromagnetic radiation.

[0018] Other features and advantages of the invention will become apparent from the following description of particular, non-limiting embodiments of the invention. Brief description of the drawings

[0019] Reference will be made to the attached drawings, among which:

[0020] [Fig-1] [Fig.1] is a schematic perspective view of a drone according to the invention;

[0021] [Fig.2] [Fig.2] is a schematic view from below of the drone according to the invention;

[0022] [Fig.3] [Fig.3] is a schematic perspective view showing a drone according to the invention searching for a target according to a first embodiment;

[0023] [Fig.4] [Fig.4] is a schematic top view of an area in progress exploration according to a first mode of exploration;

[0024] [Fig. 5] [Fig. 5] is a schematic top view of an area in progress exploration according to a second mode of exploration;

[0025] [Fig.6] [Fig.6] is a schematic perspective view showing the formation of a guidance target according to a second embodiment;

[0026] [Fig.7] [Fig.7] is a flowchart illustrating the drone guidance process. DETAILED DESCRIPTION OF THE INVENTION

[0027] With reference to Figures 1 and 2, the invention is described herein in application to an aerial drone, generally designated as 1, here of the quadcopter type, comprising a structure 2 and motorized propellers 3 forming a motorized assembly for propulsion and orientation of the drone. The motorization of the motorized propellers 3 is here an electric motor powered by a battery (not shown) carried within the structure 2. The structure 2 comprises a body 2.1 from which arms 2.2 extend, and each of the motorized propellers 3 is mounted at a free end of one of the arms 2.2. The body 2.1 includes a compartment 4, which opens here on the top of the body 1. The body 2.1 further forms a sealed enclosure containing an electronic guidance unit, generally designated as 5, powered by the battery and connected to the motorized propellers 3 to orient and steer the drone 1.The electronic guidance unit 5 includes, for example, at least one processor and a memory containing computer programs executable by the processor. The construction and function... The operation of these elements is known in itself and will not be described further here.

[0028] The electronic guidance unit 5 is also connected to an optronic deviation measuring device, generally designated as 6, comprising: - an optical system, generally designated in 6.1, having an optical axis, - an optronic sensor 6.2 positioned on the optical axis behind the system 6.1 optical, and - an electronic weighing circuit 6.3 connected to the optronic sensor 6.2.

[0029] The optical system 6.1 comprises one or more lenses for shaping electromagnetic light radiation, in the form of an incident light beam, entering the optical separation 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 having, in a manner known per se, four adjacent photodiodes arranged in quadrants and each associated with an optical group having a field that combines with that of the optical groups of the other photodiodes to define the field of the detector and thus of the optronic sensor 6.2. The photodiodes here are single-photodiodes that together define 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 device with deviation measurement 6 which has a field of view (or FoV) between + / - 5° and + / - 40° and a pupil with a diameter between 5 mm and 40 mm.

[0030] The weighing electronic circuit 6.3 comprises an electronic board having, 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 weighing electronic circuit 6.3 with a signal proportional to a quantity of light energy from the incident light beam having at least one wavelength of interest (for simplification; it 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 weighing electronic circuit 6.3 is arranged to perform a measurement of deviation known per se from the signals from the optronic sensor 6.2 and to send to the electronic guidance unit 5 signals representative of a deviation between the spot and the center of the optronic sensor 6.2, this gap being representative of a gap between the direction of the incident light beam and the direction in which the gap measuring device 6 points. The gap 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, i.e. without the possibility of motorized orientation of them 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.

[0031] The electronic guidance unit 5 is further connected to an inertial measurement unit 7 and to a communication device 8.

[0032] The inertial measurement 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 gyroscopes, arranged to measure the orientations of the measurement frame relative to an inertial frame. The inertial measurement unit 7 provides the electronic guidance unit 5 with signals representative of the movements of the drone 1.

[0033] The communication device 8 can be wired or wireless (for example, short-range radio such as the NFC system) and allows an operator with a suitable computer terminal (a computer, a smartphone, or a dedicated terminal) or an appropriate 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).

[0034] The electronic guidance unit 5 is arranged, in a manner known per se, to control the rotation of the motorized propulsion 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.

[0035] The electronic guidance unit 5 is more particularly arranged, in the guidance method preferably implemented by the invention, to implement three guidance modes.

[0036] According to a first guidance mode, or approach guidance, the electronic guidance unit 5 is configured to move the drone 1 from a starting position to an intermediate position. The first guidance mode is used here to move the drone 1 to an area to be explored using signals provided by the inertial measurement unit 7. The intermediate position is located in the center of the area to be explored and / or on a boundary of the area to be explored. The intermediate position and the boundaries of the area to be explored are programmed into the electronic guidance unit 5 via the communication device 8.

[0037] According to a second guidance mode, more particularly illustrated in Figures 3 to 5, or exploration guidance, the electronic guidance unit 5 is arranged to scan the exploration zone ZE with the observation field of the optronic assembly formed by the combination of the optronic sensor 6.2 and the optical system 6.1 until a predetermined electromagnetic radiation is detected. The electronic guidance unit 5 controls the drone 1 solely based on signals from the inertial measurement unit 7 so as to act on the roll, pitch, and yaw of the drone 1 in such a way 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 path TB. In [Fig. 4], the electronic guidance unit 5 commands a transverse scan relative to a substantially rectilinear direction of movement of the drone 1 above the exploration zone ZE. The scan width and length are stored in the electronic guidance unit 5. In [Fig. 5], the electronic guidance unit 5 commands a concentric, here circular, scan of the exploration zone ZE. It is understood that, in this latter case, the intermediate starting position of the scan can be located at the boundary of the exploration zone ZE (scanning from the periphery to the center) or at the center of the exploration zone ZE (scanning from the center to the periphery). The scan radii are stored in the electronic guidance unit 5.

[0038] 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.

[0039] According to a third guidance mode, or terminal guidance which takes over from exploration guidance, the electronic guidance unit 5 pilots the drone 1 from the deviation signals transmitted by the optronic deviation device 6 to reduce the gap 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 between the drone 1 and the target decreases (the spot growing larger when the drone 1 approaches the target).

[0040] As previously stated, the predetermined electromagnetic radiation originates from a target. Several methods are possible for creating the target.

[0041] In a first embodiment shown in [Fig. 3], the target is represented by a beacon 10 comprising a laser emitter arranged to emit a laser beam in a direction substantially normal locally to the ground, here vertical, corresponding to the beam emission axis AE. The laser emitter is associated with a diverging optical system such that the electromagnetic radiation is emitted in a cone with a half-angle at the apex α between + / - 85° and + / - 45° around the axis AE.

[0042] In a second embodiment shown in [Fig. 6], the target is materialized by a reflective sheet 11 (such as a simple white sheet or a sheet metallic), extended on the ground S, towards which a laser emitter 12, such as a tripod-mounted laser designator, associated with a diverging optical system 13, projects a laser beam such that the beam is reflected by the reflective fabric 11 substantially vertically in the form of electromagnetic radiation having a half-angle at the apex of between + / - 85° and + / - 45° around the principal direction of reflection. Alternatively, the reflective fabric 11 can be replaced by any reflective screen, rigid or not, rough or smooth, or even omitted if the ground (or a surrounding element such as a rock, building, or other) is sufficiently reflective. Preferably, the spot formed by the beam on the fabric will have a radius of approximately 1 meter, the reflective fabric being of substantially the same size.Preferably, the diverging optical system 13 will filter the laser beam to avoid speckle or scintillation effects.

[0043] 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 emitter is configured to produce sequences of pulses from a laser beam having 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 configure a single sequence to include pulses of different durations.

[0044] In a preferred embodiment of the invention, the drone 1 comprises a self-destruct device 9, here a pyrotechnic charge, connected to the electronic guidance unit 5, and the laser pulses are emitted at at least two selectable useful frequencies Futl and Fut2. Each frequency Futl and Fut2 is associated with an action to be performed by the drone 1, here: - nominal landing for Futl, and - self-destruct for Fut2.

[0045] 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 an area where radio communications and the reception of satellite positioning signals are impossible. The delivery must be made at a time and at an arrival position of the drone 1 agreed upon in advance by the two operators, it being understood that the second operator may be located within a radius of a few hundred meters of the agreed arrival position.

[0046] During an initial step, at the starting position, the first operator places the electronic data storage device in the hold 4 and stores in the electronic control unit 5 the starting position and the arrival position of the drone 1 agreed upon in prior to with the second operator using a computer terminal connected to the communication device 8.

[0047] For his part, at the arrival position (or in the vicinity thereof), the second operator activates the laser emitter to emit electromagnetic radiation at the useful frequency Futl to enable the terminal guidance of the drone 1.

[0048] The electronic guidance unit 5 commands 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, using the signals provided by the inertial measurement unit 7, the distance separating it from the intermediate position (step 101) until it has reached this position (check 102).

[0049] 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 (check 104).

[0050] Once the predetermined electromagnetic radiation is detected, the electronic guidance unit 5 begins terminal guidance (step 105) while continuously monitoring that the pulse frequency is indeed the Futl frequency (step 106).

[0051] 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 retrieve the electronic data storage device. The second operator can then command the electronic guidance unit 5 to return the drone 1 to its starting position (empty or with an electronic data storage device in the cargo bay 4) or keep the drone 1 for later reuse.

[0052] If the pulse frequency becomes equal to the Fut2 frequency (check 107), the electronic guidance unit 5 interrupts the terminal guidance and activates the self-destruct device 9 (step 109) which destroys the drone 1. It can be provided that the electronic guidance unit 5 commands a maneuver to move away from the drone 1 before activating the self-destruct device 9 in order to limit the risk of the drone 1 exploding in the vicinity of the second operator.

[0053] In parallel, when the electronic guidance unit 5 begins exploration guidance (step 103), it also starts a backup process by counting the exploration time (step 110) and verifying that the exploration time is less than a predetermined maximum threshold (verification 111). If the predetermined maximum threshold is reached, the electronic guidance unit 5 activates the self-destruct mechanism 9 (step 109), which destroys the drone 1.

[0054] Alternatively, if the drone 1 must be returned to its starting position in all cases, the maximum exploration time threshold can be determined in real time by the electronic guidance unit 5 based on the remaining autonomy of the drone 1 and the The distance between the current position of drone 1 and its starting position is such that drone 1 has sufficient range to return to its starting position once the exploration time reaches the maximum threshold. At this point, the electronic guidance unit 5 interrupts exploration guidance to return to its starting position using approach guidance.

[0055] It is understood that exploration guidance also makes it possible to overcome the lack of precision of the inertial navigation system; the lower this precision, the larger the exploration area will need to be.

[0056] 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.

[0057] In particular, the drone may have a different structure from that described and include, for example, a fixed wing, a different number of propellers, a tail assembly, control surfaces, and / or a different engine, for example, a thermal engine; and / or be devoid of a self-destruct mechanism...

[0058] 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: 1. The predetermined electromagnetic radiation is not detected; or 2. The maximum exploration time threshold is not reached, with self-destruction or a return to the starting position being commanded once the maximum threshold is reached.

[0059] The number of useful frequencies may be less than or greater than two. Thus, it is possible to predict: - a useful frequency commanding the nominal landing, and optionally - a useful frequency commanding an emergency landing and / or - a useful frequency commanding the interruption of the initial mission and the return to the starting position, and / or - a useful frequency commanding a diversion to another arrival position, and / or - a useful frequency triggering self-destruction...

[0060] The predetermined event to trigger 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 code type...).

[0061] 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 on part of the drone's route.

[0062] 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 assumption that radio waves are available without interference on part of the drone's path.

[0063] The exploration guidance can scan the exploration area from one end to the other, from the center to the periphery or vice versa, regardless of the shape of the area.

Claims

Demands

1. Aerial drone (1) comprising a fixed structure (2), a motorized drone propulsion and orientation assembly (3), an optronic deviation measuring device (6), and an electronic guidance unit (5) connected to the motorized assembly (3) and the optronic deviation measuring device (6) to pilot the motorized assembly (3) according to signals emitted by the optronic deviation measuring device (6), characterized in that the optronic deviation measuring 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 pilot the motorized assembly (3) to move the drone over an exploration area by having the optronic sensor (6.2) scan the exploration area until it detects electromagnetic radiation emitted by a target and then to bring the drone to the target by deviation measuring.

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

3. Drone (1) according to claim 1 or 2, wherein the electronic guidance unit (5) commands a transverse scan with respect to a substantially rectilinear direction of movement of the drone over the exploration area.

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

5. Drone (1) according to claim 4, wherein the predetermined event corresponds to exceeding a predetermined time to detect the target.

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

7. A drone according to any one of the preceding claims, wherein the electromagnetic radiation is emitted with a half-angle at the apex of between + / - 85° and + / - 45° about a sen- possibly normal locally on the ground.

8. Drone according to claim 7, wherein the electromagnetic radiation is emitted by a laser emitter (12) associated with a diverging optical system (13).

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

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