Technical field

The present invention relates to an underwater drone placeable in water in a cage for aquaculture. The present invention also relates to a method for operating such an underwater drone.

Background

In aquaculture, fish are kept in cages in the sea for food production.

For various reasons, it may be desired to take pictures of the fish and/or of the cage itself. NO20140331 (A1) discloses a probe for monitoring fish, cages, and water quality in cages for aquaculture. The probe in NO20140331 (A1) comprises a waterproof container, which in turn comprises a first part and a second part, which are telescopically displaceable relative to each other to change the volume of a buoyancy chamber located within the two parts. The probe in NO20140331 (A1 ) becomes lighter than water when the parts of the container are pushed apart and will thus float to the surface. Similarly, probe becomes heavier than water when the parts are pulled together and will then sink to the bottom of the cage. Furthermore, the probe in NO20140331 (A1) comprises a camera for taking pictures of fish. The camera can also be used to take pictures of the cage itself.

Despite the above-mentioned probe of NO20140331 (A1), there is still room for an improved underwater drone.

US9381987 B1 discloses an air-based-deployment-compatible underwater vehicle that may be configured to perform vertical profiling is described. The vehicle may be configured, during information transmission, to perform motion stabilization at a water surface. A body of the vehicle may have a cylindrical shape. Buoyancy control components of the vehicle may be disposed within the body. The buoyancy control components may be configured to adjust a volume and/or buoyancy of the vehicle to facilitate vertical profiling. Fins may be hingedly disposed on the body at one or more locations on the vehicle. The fins may be movable between a first configuration and a second configuration. The fins, in the first configuration, may be positioned substantially flat against the body. The fins, in the second configuration, may extend radially outward to slow descent and to provide motion stabilization. The fins may be pitched to rotate the vehicle about a longitudinal axis during vertical profiling.

US2015284064 A1 FIGS. 9A, 9 B, and 9 C disclose a vehicle in a spin configuration. The spin configuration may be characterized by the working portions of lateral control surfaces being disposed proximal to the same end of vehicle with a first control surface and a second control surface being canted in equal amounts but in opposite directions. The spin configuration may facilitate measuring vertical currents by spinning vehicle during ascent where one revolution may be associated with a known static vertical displacement. Decrease or increase of vertical currents may result in more or less spin during ascent or descent compared to still water.

EP3654069 A1 discloses is directed to a system for acquiring seismic data from a seabed. The system includes a case having a cylindrical portion. The system can include one or more fins that can be configured to control rotation of the case through an aqueous medium, dampen rotation, or otherwise exert force or create force to manipulate the dynamics of the case.

US4007505 A discloses a stabilizing drag and spin inducing device is described for an instrumented underwater vehicle. A flexible plastic disc having a central aperture and segmented into angularly offset vanes is pressed onto the vehicle probe section with resulting distortion causing the disc to assume a conical configuration. The vanes flex to increase drag on descent and decrease drag on ascent, while also assuming spin inducing pitch.

W002084217 A2 relates to a method and a system for underwater surveillance and monitoring by means of using an autonomous underwater vehicle (AUV), such as inspection of fish farming pens. By using a plurality of external acoustic transmitters the position of the AUV can be determined by using a predefined reference system or dead reckoning. Summary of the invention

It is an object of the present invention to provide an improved underwater drone. According to a first aspect of the present invention, this and other objects are achieved by an underwater drone placeable in water in a cage for aquaculture, the underwater drone comprising: a longitudinal axis; a device or system adapted to cause the underwater drone to rise from a submerged position towards a surface of the water substantially in the direction of the longitudinal axis; at least one directional sensor aimed in a direction not coinciding with the direction of the longitudinal axis; and at least one (non- adjustable) fin adapted to cause the underwater drone to (automatically) rotate about its longitudinal axis as the underwater drone rises from the submerged position towards the surface of the water (by actuation of said device or system).

The present invention is based on the understanding that by adding at least one fin to the underwater drone, the underwater drone may conveniently be caused to rotate when it rises towards the water surface, without the need for more complicated and/or expensive rotation means, such as an underwater thruster or the like. Furthermore, with the rotation, the at least one sensor, for example a side-facing camera, can become pointed in all directions (360 degrees) during an ascent, which in turn means that such a camera can take images of the complete cage. The present invention is (also) an improvement over any solution wherein a camera is fixedly mounted in one direction in the cage, or any solution that uses some motorized means to aim a sensor in different directions.

The present invention can for example be used to capture images of many/several fishes for estimating biomass and/or lice counting. The present invention can also be used to scan the net wall of the cage for fouling, hole(s), or damage.

‘Substantially’ as in “substantially in the direction of the longitudinal axis” may be construed as +/- 15 degrees. Although the longitudinal axis typically is vertically oriented and the underwater drone rises vertically, it can be that the drone (while oriented vertically) drifts slightly sideways as it rises towards the water surface.

Furthermore, ‘directional’ as in “at least one directional sensor” may be construed as the sensor having an axis (direction) where it is most sensitive and/or has a limited angle of view or similar as opposed to an omnidirectional sensor.

‘Non-adjustable’ may be construed as the at least one fin cannot be adjusted, such as folded in/out, vary the pitch, etc.

The at least one fin may comprise at least two radiating fins curved or twisted so that each forms part of a helical surface. That is, the at least one fin may be or at least resemble at least two propeller blades. Such fins/blades may provide for a stable ascent with sufficient rotation of the underwater drone.

The underwater drone may have a substantially cylindrical hull, wherein the at least one fin consists of two (curved/twisted) fins arranged at substantially opposite positions on a circumference of the substantially cylindrical hull. This makes the underwater drone resemble a propeller with a(n elongated) hub, which may ensure the desired rotation as the underwater drone rises through the water.

In another embodiment, the at least one fin is a single flat fin, which fin is inclined relative to said longitudinal axis and extends about (only) a portion of the circumference of the substantially cylindrical hull. A flat fin, a fin that is in one plane, may have the ability to bend if needed. For example, if other heavy equipment in the cage would push on it. This could also avoid damages to the net of the cage.

In yet another embodiment, the at least one fin is two flat fins, wherein each flat fin is inclined relative to said longitudinal axis and extends about (only) a portion of the circumference of the substantially cylindrical hull of the underwater drone. The two flat fins may be arranged at substantially opposite positions on the circumference of the substantially cylindrical hull. The at least one fin may be designed so that the underwater drone rotates N turns (revolutions) per meter the underwater drone rises, wherein N is selected from the range of 0.2-1. In other words, one revolution every 1-5 meters, for example one revolution every 3 meters. The desired rotation may for example be achieved by appropriately selecting the pitch of the at least one fin.

The at least one directional sensor may be aimed in a direction substantially perpendicular to the longitudinal axis. In other words, the at least one directional sensor may be side-facing. In this way, because of the aforementioned rotation of the underwater drone, the complete cage (360°) can be sensed.

Each of the at least one directional sensor may be arranged in a fixed direction with respect to the underwater drone. That is, no dedicated means for aiming a sensor in different directions with respect to the underwater drone are needed, which may reduce manufacturing cost and maintenance. Instead, as mentioned above, the whole underwater drone may be rotated simply by the fin(s).

As also mentioned above, the at least one directional sensor may be a camera. The camera may be a digital camera. The camera may be adapted to capture images and/or video. The camera may be aimed such that its optical axis is substantially perpendicular to the longitudinal axis. The camera may be a side-facing camera.

The device or system adapted to cause the underwater drone to rise from a submerged position towards a surface of the water substantially in the direction of the longitudinal axis may also be adapted to cause the underwater drone to (vertically) descend/move down in the water.

Furthermore, the device or system adapted to cause the underwater drone to rise from a submerged position towards a surface of the water substantially in the direction of the longitudinal axis may be self-contained and independent of any external equipment, such as a lifting line.

Said device or system may for example comprise a watertight container comprising a first part and a second part telescopically displaceable in relation to each other to change the volume of a buoyancy chamber inside the two parts. Said device or system may further comprise a motor arranged in the first part and a threaded screw spindle, wherein the threaded screw spindle is received in a threaded counterpart of the second part, such that rotation of the motor in one direction causes the two parts to be brought closer together and such that rotation of the motor in the other direction causes the two parts to be brought away from each other. An O-ring may be arranged between the two parts, to prevent ingress of water. Furthermore, the watertight container may be sized such that when the two parts are brought completely together the underwater drone has a buoyancy causing the underwater drone to sink to the bottom of the cage.

Said device or system may be of the type disclosed in NO20140331 (A1), the content of which herein is incorporated by reference.

Alternatively said device or system could include equipment adapted to drop a ballast causing the underwater drone to rise, at least one underwater thruster, etc. Another alternative system may include an internal balloon, an external balloon, and a pump adapted to pump fluid between the balloons to adjust the buoyancy of the underwater drone.

The underwater drone may further comprise a control unit adapted to: actuate said device or system such that the underwater drone rotationally rises from the submerged position, for example from the bottom of the cage, towards the surface of the water; and actuate the at least one directional sensor to make readings while the underwater drone rotationally rises, for example capturing images/video of fish in the cage and/or images/video of a net wall of the cage with a camera.

According to a second aspect of the present invention, there is provided a method for operating an underwater drone, wherein the method comprises: causing an underwater drone according to the first aspect placed in water in a cage for aquaculture to substantially vertically rise from a submerged position towards a surface of the water (by actuation of said device or system), whereby the underwater drone automatically rotates about its longitudinal axis when the underwater drone rises from the submerged position towards the surface of the water; and making readings, by the at least one directional sensor, while the underwater drone rotationally rises.

This aspect may exhibit the same or similar features and technical effects as the first aspect, and vice versa. Furthermore, “substantially vertically” may here be construed as +/- 15 degrees to the (truly) vertical direction.

Each of the at least one directional sensor may get pointed at least 360 degrees (i.e. in all directions) with respect to the longitudinal axis of the underwater drone while the underwater drone rotationally rises from the submerged position to the surface of the water. In this way, readings/images of the complete cage can be taken.

Brief description of the drawings

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention.

Fig. 1a is a schematic side view of an underwater drone according to an embodiment of the present invention.

Fig. 1 b is a schematic top view of the underwater drone of fig. 1 a.

Figures 2a-b are side views of an underwater drone according to another embodiment of the present invention.

Fig. 2c is a top view of the underwater drone of figures 2a-b.

Figures 3a-b are schematic side views of an exemplary system for causing the underwater drone to rise from a submerged position towards the water surface.

Figures 4a-b illustrate a method for operation of an underwater drone.

Fig. 5a is a side view of an underwater drone according to yet another embodiment of the present invention.

Fig. 5b is a top view of the underwater drone of fig. 5a.

Detailed description of the invention Figures 1a-b show an underwater drone 10 according to an embodiment of the present invention.

The underwater drone 10 is intended to be placed and operate in water 12 in a cage 14 for aquaculture (aquaculture cage), see further figures 4a-b. Aquaculture refers to the cultivation of aquatic organisms (such as fish 16 or shellfish), especially for food. The underwater drone 10 is uncrewed. The underwater drone 10 is typically at least partly controlled by an onboard control unit 17.

The underwater drone 10 may have an elongated and substantially cylindrical hull 18. A longitudinal axis 20 of the underwater drone 10 may extend centrally and lengthwise (“nose through tail”) of the underwater drone 10/hull 18. In the water 12, the underwater drone 10/longitudinal axis 20 is typically vertically oriented.

The underwater drone 10 further comprises a device or system 22 adapted to cause the underwater drone 10 to rise from a submerged position 24 towards a surface 26 of the water 12 substantially in the direction of the longitudinal axis 20, as indicated by arrow 27. The underwater drone 10 typically rises vertically from the submerged position 24 towards the surface 26 of the water 12.

An exemplary system 22 is shown in figures 3a-b, wherein said system 22 comprises a watertight container comprising a first part 28 and a second part 30 telescopically displaceable in relation to each other to change the volume of a buoyancy chamber 32 inside the two parts. The two parts 28, 30 may form part of the aforementioned hull 18. The system 22 further comprises a motor 34 arranged in the first part 28 and a threaded screw spindle 36 connected to the motor 34, wherein the threaded screw spindle 36 is received in a threaded counterpart 38 of the second part 30, such that rotation of the motor 34 in one direction causes the two parts 28, 30 to be brought closer together and such that rotation of the motor 34 in the other direction causes the two parts 28, 30 to be brought away from each other.

The motor 34 may be powered by a battery (not shown) of the underwater drone 10. An O-ring 40 may be arranged between the two parts 28, 30 to prevent ingress of water. Furthermore, the watertight container may be sized such that when the two parts 28, 30 are brought completely together the underwater drone 10 has a buoyancy causing the underwater drone 10 to sink to the bottom of the cage 14. On the other hand, when the two parts 28, 30 are brought away from each other, the underwater drone 10 will float to the surface 26. The system 22, or rather the motor 34, may be connected to the aforementioned control unit 17, for actuation. It is appreciated that the system 22 may be completely self-contained and independent of any equipment external of the underwater drone 10.

Returning to figures 1a-b, the underwater drone 10 further comprises at least one directional sensor, for example a camera 42. The camera 42 may for example be mounted near the top of the underwater drone 10. The camera 42 is aimed in a direction not coinciding with the direction of the longitudinal axis 20 of the underwater drone 10. In figures to figures 1 a-b, the camera 42 is side-facing and aimed such that its optical axis 44 is perpendicular to the longitudinal axis 20. The camera 42 is also arranged in a fixed direction with respect to the underwater drone 10, but may nevertheless be capable to make readings/capture images/video in 360 degrees, as will be explained further below. The camera 42 may be connected to the control unit 17 for activation.

In accordance with the present invention, the underwater drone 10 further comprises at least one (exterior) fin 46a-b or 46c. The at least one fin 46a-b or 46c is adapted to cause the underwater drone 10 to automatically rotate about its longitudinal axis 20 as/when the underwater drone 10 (vertically) rises from the submerged position 24 towards the surface 26 of the water 12 in the direction of the longitudinal axis 20. The rotation is illustrated by arrow 47. In this way, the underwater drone 10 may conveniently be caused to rotate when it rises towards the surface 26, without the need for more complicated and/or expensive rotation means, such as an underwater thruster or the like. Furthermore, with the rotation, the camera 42 can become pointed in all directions (360 degrees) during an ascent, which allows the camera 42 to take images of the complete cage 14. That is, the at least one directional sensor/camera 42 is capable to make readings in 360 degrees while the underwater drone 10 rotationally rises. The at least one fin 46a-b or 46c may be designed so that the underwater drone 10 rotates approximately N turns (revolutions) per meter the underwater drone 10 rises in the water 12, wherein N is selected from the range of 0.2-1 (one revolution every 1-5 meters).

The at least one fin 46a-b or 46c may be attached to, and/or project from, the outside of the hull 18. The at least one fin 46a-b or 46c may be fixed (non-adjustable). The at least one fin 46a-b or 46c may be made of a semi rigid material. The at least one fin 46a-b or 46c may for example be made of plastic, such as (5 mm thick) HDPE (High Density Polyethylene). HDPE is light (nearly the same buoyancy as water) and flexible enough to avoid damages to the cage 14. It will also return to its original shape if bent.

In figures 1a-b, the at least one fin consists of two radiating fins 46a-b curved or twisted so that each forms part of a helical surface, like two propeller blades. The fins 46a-b are arranged at substantially opposite positions on a circumference 48 of the hull 18, preferably at the lower/rear end of the hull 18.

In another embodiment shown in figures 2a-c, the at least one fin is a single fin 46c. The fin 46c is inclined with respect to the longitudinal axis 20 by an angle a, wherein a may be in the range of 10-45 degrees or in the range of 10-30 degrees, such as (about) 20 degrees. Furthermore, the fin 46c may extend about approximately half the circumference 48 of the substantially cylindrical hull 18, as seen in particular in fig. 2c. In other words, an inner edge 52a of the fin 46c may helically wrap around the hull 18 for approximately (no more than) half a turn. Lengthwise, the fin 46c may extend along at least the lower/rear half of the hull 18. Furthermore, the fin 46c is preferably flat, having a flat surface 50. Furthermore, the fin 46c may have an at least partly curved outer contour 52b.

The center position s of the fin 46c differs from the geometric center of the fin area, being closer to the fin’s attacking edge, in this case during ascent. It is typically estimated to be where ½ of the fin’s area from the leading edge ahead is of it and equal areas to either side.

The fin 46c may be designed so that the center position s is perpendicular from the center line/longitudinal axis 20 at the center of moment with a distance r from the centerline/longitudinal axis 20 along the fin’s plane for stability to avoid wobble during ascent. During descent some wobble will be expected due to the attacking edge being on the opposite end and the corresponding shift in the fin’s center position, but wobble is less of a concern during the descent.

As indicated above, the pitch angle a of the fin 46c is the angle between the fin’s plane and centerline/longitudinal axis 20 and is for these purposes considered for low speeds and relatively shallow pitch angles.

The rotation speed, inverted as the distance per full revolution d can be expressed approximately, independent of the speed of ascent v as a function of r and a as d = 2TTG · tan(Tr/2 - a)

Specific rotation speed w be expressed as a function of ascension speed v: w = 2Trv/d = v / (r · tan(Tr/2-a))

Typically for fin 46c the pitch angle is a = 20° ( 0.35 rad ) and center position s a distance r = 0.175 m results in a rotation speed d « 3 m/revolution. For a typical speed of ascent for this design of v = 0.3 m/s specific rotation speed would be w « 0.6 rad/s.

The underwater drone 10 could alternatively have two fins 46c’ and 46c” of the type disclosed in (relation to) figures 2a-c, as illustrated in figures 5a-b. The two fins 46c’ and 46c” may be arranged at substantially opposite positions on the circumference 48 of the hull 18. The two fins 46c’ and 46c” may prevent the drone 10 from entering lift-up systems such as a pump for sludge and dead fish at the bottom 54 of the cage 14. The two fins 46c’ and 46c” may also allow the drone 10 not to go below the bottom 54 of the cage 14 so that the drone 10 then can stand.

Turning to figures 4a-b, these figures illustrate a method for operating an underwater drone like underwater drone 10.

The underwater drone 10 may initially be placed in the water 12 in the cage 14 at S1. System 22 may be actuated by the control unit 17, such that the two parts 28, 30 are brought close together, whereby the underwater drone 10 sinks (S2) to the bottom 54 of the cage 14, see S3. Here the underwater drone 10 may rest in a passive mode.

At a predetermined point in time (or after a predetermined period of time), the underwater drone 10 may switch to an active mode, wherein the control unit 17 actuates the system 22, such that that the two parts 28, 30 are brought away from each other, whereby the underwater drone 10 vertically rises at S4-S6 from the submerged position 24 at the bottom 54 of the cage 14 towards the surface 26. Because of the two fins 46a-b (or the fin 46c or the fins 46c’ and 46c”), the underwater drone 10 (automatically) rotates about its longitudinal axis 20 when the underwater drone rises 10 from the submerged position 24 towards the surface 26.

The control unit 17 may further actuate the camera 42 to make readings (i.e. capture images/video) at different depths while the underwater drone 10 rotationally rises during at least some of the ascent from the bottom 54 of the cage 14 to the surface 26. The camera 42 may for example capture images/video of fish 16 in the cage 14 and/or images/video of a net wall 56 of the cage 14. The readings/images/video may be stored on a computer memory or storage of the underwater drone 10. At S5, the underwater drone 10 and hence the camera 42 has rotated ½ revolution over the deeper position S4, and at the further decreased depth S6 the underwater drone 10/camera 42 has completed a full revolution (360 degrees). Hence, the camera 42 may become pointed at least 360 degrees (i.e. in all directions) about the longitudinal axis 20 of the underwater drone 10 while the underwater drone 10 rotationally rises from the submerged position 24 to(wards) the surface 26. In this way, readings/images can conveniently be taken of the complete cage 14.

The underwater drone 10 can also have a depth gauge (pressure sensor; not shown) so that it can determine (and record) at what depth(s) various readings/images/video are captured.

Once the underwater drone 10 has reached the surface 26 at S7, the readings/images/video (stored on the computer memory or storage) may be transmitted, preferably via wireless communication means 58 of the underwater drone 10, to a remote facility. Captured images/video of many/several fishes 16 may for example be used for estimating biomass and/or lice counting. Captured images/video of the cage 14 could be used to scan the net wall 56 for fouling, hole(s), and/or damage.

Steps S2-S7 may then be repeated, or the underwater drone 10 may be taken out of the water 12, for example for recharging or battery replacement or some other maintenance.

The person skilled in the art realizes that the present invention by no means is limited to the embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

For example, the at least one directional sensor could in addition to, or instead of, the camera 42 include at least one of an acoustic transmitter and receiver (0-20kHz) for an improved sampling in the cage 14, an echosounder for detecting the distribution of fish 16 in the cage 14 in different directions or find the actual shape of the net 56 as deformed by currents and mooring, a light sensor for registering the placement and brightness of light sources placed in the cage 14, etc.