WO2018215642A1

WO2018215642A1 - Method for approaching a base station, associated computer program and underwater drone

Info

Publication number: WO2018215642A1
Application number: PCT/EP2018/063767
Authority: WO
Inventors: Marc RICHARD; Jérôme TISSERAT; Raphaël BOURDON
Original assignee: Naval Group
Priority date: 2017-05-26
Filing date: 2018-05-25
Publication date: 2018-11-29
Also published as: FR3066828A1; FR3066828B1

Abstract

The invention relates to a method for approaching a base station carried out by an autonomous underwater drone, the method comprising at least the following three consecutive phases (100, 110, 120): - an adjustment phase (100), in which the underwater drone, located in a first adjustment position, determines (140) a first movement path and (150) along said first path; - a phase of starting (110) to approach the base station, in which the underwater drone determines (170) a second path for moving from a second position to a third position and moves (180) along said second path; and a final approach phase (120), in which the underwater drone determines (190) a third path of movement from the third position to a docking position and moves (200) along said third path.

Description

Method of approaching a base station, computer program and associated underwater drone

The present invention relates to a method of approaching a base station implemented by an autonomous underwater drone, able to move relative to the base station.

The invention also relates to a computer program comprising software instructions which, when executed by a computer, implement such an approach method.

The invention also relates to an underwater drone adapted to move relative to a base station.

The invention relates to the field of submarine navigation, for example for underwater activities of the offshore marine industry such as oil, gas, submarine mines, renewable energies, scientific activities such as the monitoring of marine life. environment or underwater sampling, as well as monitoring or intelligence-gathering activities associated with underwater exploration.

There are at least two types of underwater drones, or UUVs, of the English "Unmanned Underwater Vehicles" without a "human" pilot on board. A first type of submarine drone, called the ROV of the English "Remotely Operated Underwater Vehicle", is remotely controlled, for example by a control station via a cable, said leash. A second type of submarine drone, called AUV, of the English "Autonomous Underwater Vehicle", is able to move autonomously (ie without remote human control) by determining itself all the movements to be made. .

Subsequently, "underwater drone" means an AUV autonomous underwater mobile device that is able to auto-pilot itself automatically thanks to its onboard autopilot system.

To self-pilot, such an AUV autonomous underwater drone uses the principle of dead reckoning in relation to a reference position (usually its point of departure). and from measurements from its on-board navigation instruments (eg inertial unit, immersion sensor, compass etc.).

However, such self-esteem navigation, subject to strong drift, is insufficient and dangerous for an AUV autonomous underwater drone when it comes to approaching a base station to fix it.

A method of approaching a base station is known, for example from US 008600592 B2, which is based on sending an acoustic signal from a stationary transmitter to a receiver of a submarine drone. The underwater drone is configured to receive the acoustic signal and determine therefrom the direction to be followed to the base station.

However, according to this solution, the approach path of the submarine drone is not optimal and does not guarantee the securing safety of the drone as the base station during this stowage.

The object of the invention is then to provide an approach method, and an underwater drone, for optimizing the navigation safety of the drone when approaching the underwater drone to the base station.

To this end, the object of the invention is a method of approaching a stationary base station of the aforementioned type, implemented by an underwater drone, capable of moving relative to the base station, the method comprising at least the following three successive phases implemented by the underwater drone:

a registration phase, in which the underwater drone, located at a first registration position:

o determines actual coordinates of the reset position relative to the position of the base station, and determines a first path of movement of the registration position to a second predetermined approach release position, and

o moves according to said first trajectory,

an approaching triggering phase of the base station, in which the underwater drone, located in the second position:

o receives an approach command issued by the base station,

o determines a second path of displacement of the second position to a third predetermined final approach start position, and

o moves according to said second trajectory,

a final approach phase, in which the underwater drone, located in the third position, determines a third trajectory of displacement of the third position at a docking position at the base station, and moves in substantially following this third trajectory.

According to the method of approach of the invention a three-phase approach strategy is implemented to optimize obstacle avoidance when approaching the underwater drone with respect to the base station, and / or collision at the time of stowage at the base station.

The safety of the drone, like that of the base station, are thus guaranteed during the crucial approach and docking phase of the drone at the base station. In in other words, by applying the method according to the present invention, the drone applies a secure approach strategy by optimizing, as and when the three phases of the process, its trajectory.

The first recalibration phase makes it possible to cancel the drift effect due to the dead reckoning implemented by the drone prior to its arrival at the registration position.

The second phase allows an intermediate approach to reach a predetermined final approach point which allows the drone, according to the third phase to refine its trajectory to arrive without damage to the underwater drone, as the base station , at the stowage point at the base station.

According to other advantageous aspects of the invention, the approach method comprises one or more of the following characteristics, taken separately or in any technically possible combination:

the third trajectory is also used after unstacking the underwater drone of the base station;

the third trajectory is a line segment whose ends are respectively the third position and the stowed position;

the base station comprises a conical housing for receiving a submarine drone, and in which the third final approach starting position is located, on the outside, and on the axis of revolution, of the conical housing of home of underwater drone;

- The registration position is previously estimated by navigation instruments of the submarine drone;

the method comprises, at its execution, at least one bidirectional exchange of information (s) between the underwater drone and the base station;

during a rallying of the underwater drone to at least one of the positions of the group of positions comprising the resetting position, the second position or the third position, the underwater drone carries out a predetermined waiting trajectory; and

the waiting trajectory is repeated until the submarine drone receives information emitted within an acoustic signal by the base station.

The invention also relates to a computer program comprising software instructions which, when executed by a computer, implement a method as defined above.

The invention also relates to a submarine drone adapted to move relative to a base station, the underwater drone comprising: a registration module, configured for, when the underwater drone is located at a first registration position, to determine actual coordinates of the registration position relative to the position of the base station, and a first movement trajectory from the reset position to a second predetermined approach release position, and

a maneuverability module configured to move the underwater drone along said first trajectory,

a base station approach trigger module, configured for, when the underwater drone is located in the second position:

o receive an approach order issued by the base station,

o determining a second path of displacement of the second position to a third predetermined final approach starting position,

the maneuverability module being furthermore configured to move the underwater drone along said second trajectory,

a final approach module configured for, when the underwater drone is located in the third position, determining a third trajectory of displacement of the third position at a docking position at the base station,

- The maneuverability module being further configured to move the underwater drone substantially along said third path.

These features and advantages of the invention will appear more clearly on reading the description which follows, given solely by way of nonlimiting example, and with reference to the appended drawings, in which:

FIG. 1 is a diagrammatic sectional representation of a bidirectional underwater navigation system according to the invention,

FIG. 2 is a schematic representation of a processing unit of an acoustic signal,

FIG. 3 is a schematic representation of the principle of triangulation; FIG. 4 is a flowchart of a method of approaching a base station;

FIG. 5 is a schematic representation of an example approach of the base station.

In the remainder of the description, the expression "substantially" will express a relationship of equality at plus or minus 10%.

In FIG. 1, a bidirectional underwater navigation system 1 comprises an underwater drone 2 and a base station 4 in an underwater environment. delimited by the surface of the water S. The underwater drone 2 is able to move relative to the base station 4.

By the term "bidirectional" is meant the exchange (ie communication) of acoustic signals in two directions F namely on the one hand from the base station 4 to the underwater drone 2 and on the other hand from the sub-drone. 2 to the base station 4, to determine the position of the underwater drone 2 relative to the base station 4 and also exchange information by means of acoustic signals propagated in the water. The acoustic signals are for example transmitted at a fixed rate.

In other words, "bidirectional navigation system" means a two-way navigation and communication system.

By the term "maneuverability" is meant both the propulsion of the submarine drone 2 and the control of his or her governor (s).

An acoustic signal emitted by the base station 4 and received by the underwater drone 2 is called "first acoustic signal" thereafter.

The first acoustic signal comprises at least a first piece of information, determined by the base station 4. The first item of information is representative of a piloting order and / or a position of the underwater drone 2.

The piloting order is a predetermined order. By "predetermined order" is meant that a list of orders is known and defined beforehand for both the underwater drone 2 and the base station 4. The piloting order is for example an order of going back to the surface, an approach order (ie to trigger the approach phase) of the base station 4, an order to cancel the approach towards the base station 4, a stop command of urgency, a stowage order, a change order or mission start, a waiting order (ie including a waiting path T _A ) or an order to follow a waiting path T _A. Optionally, the first information is representative of a plurality of orders as mentioned above.

Optionally, the first information is representative of the absolute position of the base station 4 so that the underwater drone 2 can exploit it and determine its own absolute position.

The first acoustic signal makes it possible on the one hand to transmit the first information and on the other hand to determine the position of the underwater drone 2 relative to the base station 4 by the underwater drone 2 itself, by means of of a triangulation described below. Optionally, the first information comprising a position of the underwater drone 2 is fused, once received by the underwater drone 2, with data from the unrepresented instruments of the underwater drone 2 for better navigation accuracy. An acoustic signal emitted by the underwater drone 2 and received by the base station 4 is called "second acoustic signal" thereafter.

The second acoustic signal comprises at least a second piece of information. This second piece of information is information determined by the submarine drone 2 and is representative of a status and / or position of the underwater drone 2. The status of the submarine drone 2 is a predetermined status.

By "predetermined status" is meant that a list of statuses is known and defined beforehand for both the underwater drone 2 and the base station 4. The status of the underwater drone 2 is for example a positive or negative response to a pilot command issued in advance by the base station 4, a status of the submarine UAV 2 propulsion system, a status of the navigation system of the UAV 2, a status of the piloting of the submarine drone 2, a status of the maneuverability system (30) (for example concerning the control surfaces), a status of the energy system (for example concerning the batteries), a status of a sensor of the sub-drone. 2, a status of an actuator of the underwater drone 2 or a seabed registration data. Optionally, the second information is representative of a plurality of statuses. The second acoustic signal allows the base station 4 to transmit the second information and to determine the position of the underwater drone 2 relative to the base station 4 by means of a triangulation described below.

In relation with FIG. 1, the underwater drone 2 comprises a transceiver 10A connected by a link 11A to an acoustic signal processing unit 12A. Alternatively, the underwater drone 2 comprises a plurality of other transceivers not shown, each respectively connected to another acoustic signal processing unit, not shown. A data processing unit 14A is connected by a link 15A to the signal processing unit 12A. The data processing unit 14A is for example formed of a memory 16A associated with a processor 18A.

The underwater drone 2 is configured to receive the first acoustic signals from the base station 4 and to transmit second acoustic signals to the base station 4, in order to determine its position and exchange first and second information defined above. . Using the first acoustic signals, the underwater drone 2 is configured to navigate in a "remote control" mode, in which an operator of the base station 4 transmits guidance instructions, and configured to navigate in a "autoguiding" mode. , in which the underwater drone 2 itself defines movement instructions without using the first acoustic signals. Upon receipt of the first acoustic signals, the transceiver 10A embedded in the underwater drone 2 is configured to transform the first acoustic signals into an electrical signal. The signal processing unit 12A is configured to receive this electrical signal from the transceiver 10A by the link 11A, process this signal and transmit it through the link 15A to the data processing unit 14A.

The data processing unit 14A in the underwater drone 2 is configured to process the electrical signal received from the signal processing unit 12A through the input 15A. The data processing unit 14A in the underwater drone 2 is, for example, configured to process the first piece of information and / or generate a setpoint for moving the underwater drone 2.

To transmit the second acoustic signal of the underwater drone 2, the data processing unit 14A is configured to generate an electrical signal comprising at least a second piece of information and send it to the signal processing unit 12A via the link 15A. The signal processing unit 12A is configured to process the electrical signal and transmit it over the link 11A to the transceiver 10A. The transceiver 10A, embedded in the underwater drone 2, is then configured to emit the second acoustic signal.

In the memory 16A embedded in the underwater drone 2, data is stored such that the arrangement of the transceivers 10B, 10C, 10D, 10E of the base station 4 relatively to each other and the statuses such as the predetermined orders described above. The architecture of the signal processing unit 12A will be described in more detail below in connection with FIG. 2.

The underwater drone 2 further comprises a maneuverability system 30 connected to the data processing unit 14A by a link 32. In accordance with a setpoint issued by the data processing unit 14A, the maneuverability system 30 is in particular configured to move the underwater drone 2. The maneuverability system 30 comprises for example a not shown propeller, a jet propellant, not shown, or any other means of propulsion in water, not shown, as well as control surfaces , not shown, and a ballast, not shown.

Optionally, the underwater drone 2 comprises a navigation system (not shown), a control system (not shown), one or more sensors (not shown) and one or more actuators (not shown). .

The base station 4, also called "docking station" (docking station), is stationary relative to the seabed 5 to which it is attached according to the example of Figure 1. Alternatively, the base station 4 is mobile. By for example, the base station 4 is connected to a platform, a submarine or a boat, not shown, able to move.

In the example of FIG. 1, the base station 4 comprises four transceivers 10B, 10C, 10D, 10E of acoustic signals each connected, via a link 11B, to a unit 12B, 12C, 12D, 12E of acoustic signal processing. Preferably, the four transceivers 10B, 10C, 10D, 10E, placed orthogonally with respect to each other, form a tetrahedron not shown. The greater the distance between two transceivers 10B, 10C, 10D, 10E, the better the positioning accuracy by triangulation. For example, the distance between each transceiver 10B, 10C, 10D, 10E is obtained as a function of the size of the base station 4 itself dependent on that of the underwater drone 2. For example, for a drone under -marine 2 in cylindrical shape with a diameter of 600 mm, a distance is between one and two meters.

Alternatively, not shown, the base station 4 comprises three transceivers. In another variant, the base station 4 comprises N transceivers, N being an integer between 5 and 7.

To perform the triangulation, as described below, at least three transceivers 10B, 10C, 10D are required. The fourth transceiver 10E of the example of FIG. 1 brings additional precision and robustness to the bidirectional navigation system 1.

The base station 4 further comprises a data processing unit 14B, formed of a memory 16B associated with a processor 18B and connected by a link 15B to the signal processing units 12B, 12C, 12D, 12E respectively associated with the transmitters transceivers 10B, 10C, 10D, 10E.

The base station 4 is configured to determine the position of the underwater drone 2 by triangulation of the second acoustic signal transmitted by the transceiver 10A of the underwater drone 2 and received by the plurality of transceivers 10B, 10C , Base station 4 is also configured to transmit first acoustic signals including the first information.

To emit first acoustic signals, the data processing unit

14B in the base station 4 is configured to generate an electrical signal corresponding to the first information, from the predetermined orders stored in the memory 16B as well as the statuses previously described. The signal processing units 12B, 12C, 12D, 12E are configured to process the electrical signal and send it to their respective transceiver 10B, 10C, 10D, 10E configured to transmit the same same acoustic signal. Upon receipt of a second acoustic signal, the transceivers 10B, 10C, 10D, 10E are configured to receive the second acoustic signal and transmit it, via the signal processing units 12B, 12C, 12D, 12E to which they are each associated with the data processing unit 14B. The data processing unit 14B is configured to reproduce the second piece of information, transmitted and determined by the underwater drone 2 and representative of a status and / or position of the underwater drone 2, to an operator. Optionally, the data processing unit 14B is configured to generate an alert when the underwater drone 2 enters or leaves a predetermined area around the base station 4 defining the range of the bidirectional communication.

The base station 4 further comprises a housing 20, configured to accommodate the underwater drone 2, and adapted to the shape of the underwater drone 2. For example, for a cylindrical submarine drone 2, the housing 20 is delimited by walls forming a convergent cone having an axis of rotation R.

In a particular aspect, the transceivers 10A, 10E are acoustic transducers (not shown) configured to convert acoustic signals into electrical signals or vice versa. An acoustic transducer is both a hydrophone, i.e., a submarine microphone, (not shown) configured to transform acoustic signals (in the form of sound vibrations) into electrical signals and a speaker ( not shown) configured to transform electrical signals into acoustic signals.

Each first and second transmitted acoustic signal comprises an identifier of the transceiver 10A, ... 10E with which it is associated.

The communication rate, that is to say the number of first and second information exchanged per second between the underwater drone 2 and the base station 4 depends on the transceiver characteristics of the transceivers 10B, 10C , 10D, 10E of the base station 4 and the transceiver 10A of the underwater drone 2.

The frequency of each acoustic signal is chosen taking into account one or more aspects, such as:

- damping (absorption) of sound which increases with frequency;

- the size of the sources which is important for low frequencies;

the distance between two contiguous points, called spatial resolution, linked to the wavelength, which becomes better with a high frequency;

- the possible response of the target, which has its own frequency; and or

- environmental impacts, especially for fixed or scientific systems. The range of the acoustic signal transmitted in the underwater environment 6 depends on its frequency and the power of the transceivers 10B, 10C, 10D, 10E of the base station 4 and the transceiver 10A of the drone under For example, the frequency of each acoustic signal transmitted by the base station 4 or transmitted by the underwater drone 2 is between 30 Hz and 1.5 MHz and preferably between 10 kHz and 100 kHz for a maximum range of the acoustic signal of several kilometers, for example substantially equal to 2 km.

The location accuracy by triangulation is variable according to the technology used, in particular according to the number of transceivers 10B, 10C, 10D, 10E used, as described above. An increase of the acoustic frequency generally allows a better precision (according to the conditions of environment), to the detriment of the range decreasing with the increase of the frequency. The frequency between 10 kHz and 30 kHz allows an accuracy of the order of a centimeter, for example a precision between 1 and 15 cm. In the example of FIG. 1, the data processing unit 14A and the data processing unit 14B are of different types with respect to one another. For example, the data processing unit 14A in the underwater drone 2 is adapted to fulfill integration requirements on board the underwater drone 2, such as size, power consumption or robustness against vibrations. As a variant, the data processing unit, not shown, is of the same type in the base station and in the underwater drone.

In connection with FIG. 2, the signal processing unit 12A is described in more detail. The signal processing unit 12A comprises a signal transmission chain 50 and a signal receiving chain 52. The other signal processing units 12B, 12C, ... 12E comprise the same architecture.

The signal transmission chain 50 comprises, connected in series, at least one encoder 54, an interleaver 56, a mapping module 58, a time multiplexer 60 using frequencies or pilot signals 62, a modulator 64 and an amplifier 66. The signal transmission chain 50 is configured to receive the electrical signal from the data processing unit 14A, 14B respectively via the link 15A, 15B, and to provide, via the link 1 1 A, 1 1 B, a electrical signal amplified by the amplifier 66. Optionally, the signal transmission chain 50 comprises an encryption module (or encryption), not shown, and configured to encrypt or encrypt the first or second information.

The signal receiving chain 52 comprises, connected in series, at least one demodulator 70, a baseband filter module 72, a frequency detection module or pilot signal 74, a Doppler effect correction module 76 , a demapping module 78, for example for an MFSK modulation, a deinterleaver 80 and a decoder 82. The signal receiving chain 52 is configured to receive an electrical signal through the transceiver link 1 1 A, 1 1 B 10A, and to provide, via the link 15A, 15B, the electrical signal.

Optionally, the signal receiving chain 52 also comprises a decryption module (or decryption), not shown, and configured to decrypt or decrypt the first or second information, if it has been encrypted on transmission. The signal transmission chain 50 and the signal receiving chain 52 are known per se and will therefore not be described in more detail here.

In connection with FIG. 3, triangulation is the principle for determining the position of an object with respect to a plurality of reference positions by measuring the angles between the position of the object and the known reference positions. To determine the position of the object, in a (2D) plane, at least two reference positions are needed. In three dimensions (3D), a position includes three degrees of freedom. Thus, in a 3D coordinate system, at least three reference positions (not shown) are required.

In Fig. 3 (a), triangulation in a (2D) plane is shown and in Fig. 3 (b) 3D triangulation is shown.

FIG. 3 (a) shows the transceiver 10A of the underwater drone 2 and two transceivers 10B, 10C of the base station 4 in a reference frame comprising x 'and y' axes. For example, an acoustic signal emitted by the underwater drone 2 propagates from the transceiver 10A. The distance between the transceiver 10A and the transceivers 10B, 10C being different, the signal is not received at the same time by the two transceivers 10B, 10C. By calculating the difference in the time of reception of the acoustic signal between the two transceivers 10B, 10C, and from the knowledge of the speed of sound in the water, an angle α and the distance D between the emitter receiver 10A and the center of the reference x ', y' are determined.

In another example, also with reference to FIG. 3 (a), acoustic signals are transmitted simultaneously by the transceivers 10B, 10C and received by the transceiver 10A. Since the arrangement of the transceivers 10B, 10C relatively to each other is known to the submarine drone 2, the difference in times of reception of the acoustic signals by the transceiver 10A makes it possible to determine the angle a between the transceiver 10A and the transceivers 10B, 10C.

The principle of three-dimensional triangulation is represented in FIG. 3 (b) showing a reference xyz (direction east-direction north-depth) comprising a plane P. The plane P comprises the x'-y 'axes of FIG. 3 (a), and the transceivers 10A, 10B, 10C.

More specifically, from an acoustic signal transmitted by the transceiver 10A as a signal source, each transceiver 10B, 10C (and 10D, 10E not shown in FIG. 3 (b)) identifies and then receives the acoustic signal emitted by the source. The difference in arrival of the acoustic signal between two transceivers respectively 10B, 10C (and 10D, 10E not shown in FIG. 3 (b)) transmitted by the transceiver 10A makes it possible to determine the angle between the two transmitters receivers 10B, 10C, 10D, 10E considered and the transceiver 10A. The combination of the angles in the different planes (composed of the transceiver 10A as the source and two transceivers 10B, 10C, 10D, 10E) then makes it possible to determine the elevation β and the azimuth γ of the transmitter transceiver 10A of the underwater drone 2 in a x, y, z coordinate system adapted and centered on the base station 4. The position of the underwater drone 2 is thus determined.

In particular, the distance is determined from the knowledge of the speed of sound in the water, substantially between 1450 and 1550 m / s, and from the measurement of the duration put by the acoustic wave to traverse the drone distance under -marine 2 - base station 4. To do this, the clocks of the base station 4 and the underwater drone 2 are synchronized by a method, not shown, for example when stopping the underwater drone 2 in base station 4 between two missions. The clocks are in particular stable enough to allow a location by calculation of the propagation time during the mission.

Alternatively, the clocks are synchronized during the mission, by bidirectional exchange of acoustic signals to remove the drift of a clock and synchronize clocks again. To do this, the first or second acoustic signal comprises an acoustic synchronization frame of the clocks of the base station 4 and the underwater drone 2.

With the principle described above, the relative position of the underwater drone 2 with respect to the base station 4 can be determined. The absolute position of the underwater drone 2 is defined when the absolute position of the base station 4 is known, whether it is implemented by an operator before the launching of the underwater drone 2 or communicated within a transmitted signal. .

The bidirectional navigation system 1 and submarine communication makes it possible to exchange information during the mission of the underwater drone 2 and in particular during the approach of the base station 4, as described in more detail below. In other words, according to the present invention the navigation of the underwater drone 2 is optimized thanks to the implementation of a bidirectional communication system between the underwater drone 2 and the base station 4.

In Figure 4, a method of approaching the base station 4 ("Homing" in English) is shown. During the execution of the approach method of the base station 4, several bidirectional exchanges of information between the underwater drone 2 and the base station 4 are performed. The bidirectional navigation system 1 underwater is used to refine the trajectory of the underwater drone 2.

The method successively comprises a resetting phase 100, an approach initiation phase 110 and a final approach phase 120.

At the end of the operational mission, the submarine drone 2 begins its approach by indicating to the base station 4 its desire to dock when it enters the predetermined zone around the base station 4 delimiting the bidirectional communication range according to the invention.

During the initial step 130 at the start of the resetting phase 100, the underwater drone 2 moves, autonomously, towards a first registration position P1 which it considers, erroneously, to be a second predetermined position P2 of approach trigger. The second position P2 is for example filled before the operational mission and stored in the memory of the submarine drone 2, or communicated during the mission. Having sailed during his mission thanks to his own instruments, subject to drift, the actual P1 registration position of the underwater drone 2 does not correspond, in fact, to the second predetermined position P2.

The underwater drone 2 determines the real coordinates of its current P1 registration position by triangulation of the acoustic signals emitted and received by the underwater drone 2 and the base station 4, as described above.

Optionally, the registration phase 100 begins with a waiting step, not shown. In the waiting step, not shown, the underwater drone 2 and the base station 4 are detected before the triangulation of the acoustic signals.

In other words, during the rallying of the submarine drone 2 to the registration position P1, the underwater drone 2 performs a predetermined waiting path T _A , defined beforehand. In other words, as long as the underwater drone 2 does not receive acoustic signals transmitted by the base station 4, it carries out the waiting trajectory T _A. The shape of the waiting trajectory T _A is, for example, a circle or an oval geometry centered on the registration position P1. Optionally, the waiting trajectory T _A is repeated until reception by the underwater drone 2 of information transmitted within an acoustic signal by the base station 4. Optionally, the waiting path T _A is predefined by waypoints ("waypoints" in English) or instructions of course, immersion or speed. As an alternative, the waiting path T _A is optionally a constrained path. For example, the constrained trajectory comprises geometrical boundaries of which the underwater drone 2 must not leave. For example, geometric boundaries are defined by a radius of gyration or a conical shape.

In the next step 140, the underwater drone 2, knowing its real position, determines a first trajectory ΤΊ of displacement of the reset position P1 to the "real" second predetermined position P2 approach initiation.

In the next step 150, the underwater drone 2 moves according to the first trajectory T _1; thanks to its maneuverability system 30, in order to join the second position P2.

Optionally, when joining the second position P2, the underwater drone 2 performs the waiting trajectory T _A of the type as described above.

At the end of the resetting phase (100), the drift of the position of the underwater drone 2 is canceled.

In the next step 160, starting the approach initiation phase 1 10 of the base station 4, the underwater drone 2 receives an order of approach within the first acoustic signal transmitted by the base station 4 .

In the next step 170, the underwater drone 2 determines a second path T ₂ for moving the second position P2 to a third predetermined position P3 final approach start. The third final approach starting position P3 is preferably located on the axis of revolution R of the cone of the housing 20 of the base station 4.

In the next step 180, the underwater drone 2 moves along the second trajectory T ₂ , thanks to its maneuverability system 30, in order to join the third position P3. The displacement along the second trajectory T ₂ is carried out instantaneously or almost instantaneously after receiving 160 of the approach order and the determination 170 of the second trajectory T ₂ .

Optionally, when joining the third position P3, the submarine drone

2 performs the waiting path T _A of the type as described above.

In the next step 190, beginning the final approach phase 120, the underwater drone 2 determines a third trajectory T ₃ for moving the third position P3 to a docking position PA in the station housing 20. basic 4.

Such a trajectory T ₃ is optionally also predefined by waypoints ("waypoints" in English) or instructions of course, immersion or speed. As an alternative, the waiting trajectory T ₃ is optionally a constrained trajectory corresponding to geometrical boundaries of which the underwater drone 2 must not go out, for example defined by a radius of gyration or a conical shape, so aligning the longitudinal axis of the underwater drone 2 with the docking axis of the base station 4.

During the final step 200, the underwater drone 2 moves substantially along this third trajectory T ₃ , until the arrival at the docking position PA in the base station 4, in which the drone under -marine 2 is for example maintained and prepared for another mission. The third trajectory T ₃ is for example substantially a line segment whose ends are respectively the third position P3 and the docking position PA. Such a trajectory facilitates and secures the docking of the underwater drone 2 to the base station 4.

During the process according to the invention, a continuous, almost continuous, or periodic periodic rate exchange of acoustic signals between the base station 4 and the underwater drone 2 is carried out, to determine the position of the sub-drone. 2 and for the exchange of information.

For example, during the final step 200, the base station 4 issues a cancel command of the approach of the base station 4 to avoid a collision. The underwater drone 2 then cancels the approach and moves for example to the second position P2 where it will wait for a new order from the base station. More generally, such an issue of cancellation order of the approach is able to be issued at any time by the base station 4 as soon as it estimates or the operator who has control believes that it is necessary .

In another example, the underwater drone 2 being equipped with an obstacle avoidance system, not shown, deactivates this obstacle avoidance system, so as not to detect the base station 4 as an obstacle during the final step 200.

At the end of the final step 200, the emission of the acoustic signals of the base station 4 and the underwater drone 2 is stopped. By the method described above, the underwater drone thus applies a secure approach strategy.

Optionally, the third trajectory T ₃ is also used after unstaging the underwater drone 2 of the base station 4, to leave the base station 4 before the start of an operational mission. In other words, the third trajectory T ₃ is also used for launching the underwater drone 2 from the base station 2.

As an alternative, when unstacking (ie restarting) the underwater drone 2 does not necessarily achieve the same trajectory T ₃ . For example, the underwater drone 2 adopts a "free" trajectory in full autonomy, then its propulsion is activated (by the drone itself or by a remote operator) once the underwater drone 2 is sufficiently distant, beyond a predetermined distance, from the base station 4.

For example, in the absence of propulsion activated during the recovery of the UAV 2, the UAV 2 is for example pushed out of the base station 4, which gives it momentum, then if the drone has a positive buoyancy, the ascent of the underwater drone 2 operates quietly.

Optionally, each reset phase 100, trigger 1 10, or final approach 120 is adapted to be validated or stopped by an operator.

Alternatively, another trajectory, not shown, is used for launching the underwater drone 2 from the base station 2.

In Figure 5, an example of the approach method of the base station 4 is shown. At the end of its operational mission, the submarine drone 2 approaches the registration position P1 in order to begin the approach method described above. The overall trajectory of the underwater drone 2 in the example successively comprises the registration position P1, the waiting trajectory T _A , the first trajectory T _1; the second position P2, the waiting trajectory T _A , the second trajectory T ₂ , the third position P3, the third trajectory T ₃ and the docking position PA. The waiting trajectory T _A of FIG. 5 is of oval shape near the reset position P1 or the second position P2 respectively.

The distance between the third position P3 and the base station 4 depends on the size and capacity of the underwater vehicle 2. The distance between the registration position P1 and the base station 4 is for example substantially equal to 2 km. which corresponds to the range of the bidirectional system according to the invention and the distance between the third position P3 and the base station 4 is substantially equal to 500 m.

Advantageously, in the example of FIG. 5, the third position P3 is located on the axis of rotation R of the cone to allow the docking of the underwater drone 2 in the housing 20 corresponding to the shape of the underwater drone. 2. Alternatively, not shown, the housing comprises an opening wider than the dimensions of the underwater drone, allowing the docking of the underwater drone while the third position P3 is not localized on the axis of rotation R, but located, outside the housing, in a volume extending the housing cone (not shown).

It is conceivable that with such a method of approaching the base station 4 in the bidirectional navigation system 1 underwater, the navigation safety of the drone is optimized so as to protect the underwater drone 2, as the station of base 4, damage during the approach and docking of the underwater drone 2 to the base station 4.

Claims

1. Method of approaching a base station (4) implemented by an autonomous underwater drone (2) capable of moving relative to the base station (4), the method comprising at least the three phases (100, 1 10, 120) successive following implemented by the underwater drone (2):

a registration phase (100), in which the underwater drone (2), located at a first registration position (P1):

o determines (130) real coordinates of the resetting position (P1) with respect to the position of the base station (4), and determines (140) a first path (ΤΊ) of displacement of the resetting position (P1) ) at a second predetermined approach position (P2), and

o moves (150) along said first path (ΤΊ),

a triggering phase (1 10) approaching the base station (4), in which the underwater drone (2) located in the second position (P2):

o receives (160) an approach command issued by the base station (4), o determines (170) a second trajectory (T ₂ ) for moving the second position (P2) to a third predetermined position (P3) of final approach start, and

o moves (180) along said second trajectory (T ₂ ),

a final approach phase (120), in which the underwater drone (2), located in the third position (P3), determines (190) a third trajectory (T ₃ ) of displacement of the third position (P3 ) at a stowage position (PA) at the base station (4), and moves (200) substantially following this third path (T ₃ ).

2. A method of approaching a base station (4) according to claim 1, wherein the third trajectory (T ₃ ) is also used after unsetting of the underwater drone (2) of the base station (4). .

Method for approaching a base station (4) according to claim 1 or 2, wherein the third trajectory (T ₃ ) is a line segment whose ends are respectively the third position (P 3) and the position lashing (PA).

A method of approaching a base station (4) according to any one of the preceding claims, wherein the base station (4) comprises a subsea drone receiving housing (20) (2). ), and wherein the third final approach starting position (P3) is located, on the outside, and on the axis of revolution (R), of the underwater drone receiving housing (20). (2).

5. Method of approaching a base station (4) according to any one of the preceding claims, wherein the registration position (P1) is previously estimated by navigation instruments of the underwater drone (2).

6. Method of approaching a base station (4) according to claim 1, comprising, during its execution, at least one bidirectional exchange of information (s) between the underwater drone (2) and the station basic (4).

7. Method of approaching a base station (4) according to any one of the preceding claims, wherein, during a rallying of the underwater drone (2) to at least one of the positions of the group of positions comprising the reset position (P1), the second position (P2) or the third position (P3), the underwater drone (2) performs a predetermined waiting trajectory (T _A ).

8. A method of approaching a base station (4) according to claim 7, wherein the waiting trajectory (T _A ) is repeated until receipt by the submarine drone (2) information transmitted within an acoustic signal by the base station (4).

A computer program comprising software instructions which, when executed by a computer, implement an approach method according to any one of the preceding claims.

10. Underwater drone (2) adapted to move relative to a base station (4), the underwater drone (2) comprising:

- a registration module, configured for, when the underwater drone (2) is located at a first registration position (P1), to determine actual coordinates of the registration position (P1) with respect to the position of the station base (4), and a first path (ΤΊ) of displacement of the reset position (P1) to a second predetermined approach release position (P2), and a maneuverability module (30) configured to move the underwater drone (2) along said first trajectory (ΤΊ),

an approach trigger module of the base station (4), configured for, when the underwater drone (2) is located at the second position (P2):

o receive an approach command issued by the base station (4),

o determining a second trajectory (T ₂ ) for moving the second position (P2) to a third predetermined final approach starting position (P3),

the maneuverability module (30) being furthermore configured to move the underwater drone (2) along said second trajectory (T ₂ ),

a final approach module configured for, when the underwater drone (2) is located at the third position (P3), determining a third trajectory (T ₃ ) of displacement of the third position (P3) at a position d stowage (PA) at the base station (4),

- The maneuverability module (30) is further configured to move the underwater drone (2) substantially along said third path (T ₃ ).