Technical field

The disclosure relates to the field of maintenance of fish pens.

Background

[0001] Biofouling of fish pens is a major issue in the fish farming industry. Algae and other biological compounds contaminate the nets of fish pens, which inter alia causes reduced health for the fish, reduced oxygen supply to the fish pen, and increased difficulty in inspecting wear of the fish pen. Several approaches have been employed to address biofouling related issues, including hoisting and pressure cleaning the nets, as well as the employment of separate underwater remotely operated vehicles (ROVs) that clean the net while submerged.

[0002] Underwater ROVs for cleaning of submerged nets of fish pens include ROVs operated via an umbilical, as well as disconnected ROVs. Umbilical operated ROVs suffer inter alia from issues that relate to the umbilical entangling with the net to be cleaned, difficulties of making the ROV stay in contact with the net to be cleaned, as well as issues with cleaning parts of the net in the vicinity of ropes and rope joints. All present ROVs suffer generally from issues related to making the ROV stay in contact with the net to be cleaned, especially while the ROV moves or are being moved across the net.

[0003] NO 20161708 describes an assembly for carrying out a cleaning operation on a net, where the assembly comprises a first unit, and a second unit configured to be positioned on opposite sides of the net to be cleaned. The first and second units of NO 20161708 adhere to one another and to the net to be cleaned by magnetic attraction and moves across the net using belts. A problem however, with the assembly of NO 20161708 is that the belt configuration used therein is not suitable for traversing obstacles of a net of a fish pen, such as ropes or rope nots projecting outwards from the net. Each belt assembly of NO 20161708 contains one track and two wheels, which means that the tracks of the assembly will be separated from one another when the assembly traverses an obstacle such as a rope. The latter separation causes a significant reduction in magnetic attraction between the first and second unit, thereby significantly increasing the risk of the assembly falling off the net. The reduction in magnetic attraction will further also reduce the grip between the belts of the cleaning unit and the net, increasing the likelihood of the cleaning unit getting stuck. The assembly of NO 20161708 is thus largely limited to only being able to clean obstacle free areas of a net of a fish pen.

[0004] It is an aim of the present invention to provide a cleaning device for cleaning an underwater net, which may move across said net while cleaning it, and which may safely traverse obstacles such as ropes and rope knots.

Summary of the invention

[0005] A first aspect of the present invention provides a cleaning device for cleaning a submerged net, the cleaning device comprising a first cleaning unit for being positioned on a first side of the net, the first cleaning unit comprising cleaning means for cleaning the net and two parallelly oriented belt assemblies, and a second cleaning unit for being positioned on a second side of the net opposite to the first cleaning unit, the second cleaning unit comprising two parallelly oriented belt assemblies, where each belt assembly comprises a track, a rear road wheel, a middle road wheel and a front road wheel, where each road wheel is provided with a suspension, where each track is provided with magnets for generating an attractive force between the belt assemblies of the first cleaning unit and the belt assemblies of the second cleaning unit such that the cleaning device adhere to the net and where the middle road wheel of each belt assembly is provided with wheel magnets or a magnetic component for causing an attractive force between the middle road wheel and the track of each belt assembly.

[0006] In an embodiment of the invention each belt assembly further comprises a damper wheel, and where each damper wheel is provided with a suspension for shifting the position of said damper wheel to compensate for a shift in position of a road wheel.

[0007] In another embodiment of the invention the track of each belt assembly forms a leading edge and/or trailing edge that forms a non-zero angle with a driving direction of said belt assembly.

[0008] In yet another embodiment of the invention the road wheels of each individual belt assembly are separated by a distance of at least 3 centimetres.

[0009] In yet another embodiment of the invention the track of each belt assembly is provided with a plurality of studs evenly positioned along the longitudinal direction of the track, and where the wheels of each belt assembly are provided with corresponding recesses for receiving the studs of the track.

[0010] In another embodiment of the invention each stud comprises a magnet. [0011] In yet another embodiment of the invention the track of each belt assembly is provided with an even number of studs and where the polarity of the magnet of any two adjacent studs are opposite to each other.

[0012] In yet another embodiment of the invention the track of each belt assembly comprises a plurality of rigid track elements connected together by flexible joints, and where each stud is provided on a rigid track element at a non-zero distance from any of the flexible joints.

[0013] In yet another embodiment of the invention the track of each belt assembly is made at least in part from rubber, plastic or silicone.

[0014] In yet another embodiment of the invention the track of each belt assembly is provided with friction studs on the side of the track facing away from the road wheels, where each friction stud protrudes up to 1 mm from the track.

[0015] In yet another embodiment of the invention any one or more of the rear road wheel, the front road wheel and/or the damper wheel of each belt assembly is/are provided with wheel magnets or a magnetic component for causing an attractive force between any one or more of the rear road wheel, the front road wheel and/or the damper wheel and the track of each belt assembly.

[0016] In yet another embodiment of the invention each belt assembly further comprises any number of drive wheels, damping wheels, road wheels, idlers and/or tightener wheels.

[0017] In yet another embodiment of the invention any one or more of said drive wheels, damping wheels, road wheels, idlers and/or tightener wheels is/are provided with wheel magnets or a magnetic component for causing an attractive force between any one or more of said drive wheels, damping wheels, road wheels, idlers and/or tightener wheels and the track of each belt assembly.

[0018] In yet another embodiment of the invention each wheel of each belt assembly has a diameter in the range of 60 mm to 120 mm.

[0019] In yet another embodiment of the invention the extension of the cleaning device is less than 150 cm.

[0020] A second aspect of the present invention provides use of a cleaning device according to the first aspect of the invention for cleaning a net or sheet of a fish pen.

[0021] Other advantageous features will be apparent from the accompanying claims. Brief description of the drawings

[0022] In order to make the invention more readily understandable, the description that follows will refer to accompanying drawings, in which:

[0023] Figure la is a schematic representation of a cleaning device where the first cleaning unit and the second cleaning unit may be seen as positioned on opposite sides of a net,

[0024] Figure lb is a schematic representation of the cleaning device where one cleaning unit is illustrated as transparent to visualise belt assemblies of the two cleaning units adjoining each other,

[0025] Figure 2a is a schematic representation of a belt assembly comprising a rear road wheel, a middle road wheel, a front road wheel and a track,

[0026] Figure 2b is a schematic representation of a belt assembly comprising a rear road wheel, a middle road wheel, a front road wheel, a damper wheel and a track,

[0027] Figure 3 is a schematic representation of a belt assembly that simultaneously visualizes several embodiments of the invention,

[0028] Figure 4 is a schematic representation of a track comprising friction studs, and [0029] Figure 5 is a schematic representation of a belt assembly where each road wheel and at least one damper wheel are provided with suspension.

Detailed description of the invention

[0030] In the following, general embodiments as well as particular exemplary embodiments of the invention will be described. References will be made to the accompanying drawings. It shall be noted, however, that the drawings are exemplary embodiments only, and that other features and embodiments may well be within the scope of the invention as claimed.

[0031] Unless otherwise defined, all terms of art, notations and other scientific terms or terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains. Certain terms of art, notations, and other scientific terms or terminology may, however, find a definition in the field of continuous propulsion systems, or they may be defined specifically as indicated below.

[0032] The present invention provides a cleaning device 100 for cleaning a submerged net 130, e.g. that of a fish pen. The cleaning device 100 according to the invention comprises a first cleaning unit 110 for being positioned on a first side of the net 130 and a second cleaning unit 120 for being positioned on a second side of the net 130, opposite to the first cleaning unit 110. The first cleaning unit 110 and second cleaning 120 unit are, as illustrated in figure la and lb, each provided with two parallelly oriented belt assemblies 150. Each belt assembly 150 comprises a rear road wheel 170, a middle road wheel 180, a front road wheel 190 and a track 160. The terms "front", "middle" and "rear" are here defined relative to the driving direction 230 of the cleaning device 100. However, as the driving direction 230 may be reversed, said terms are largely used herein to refer to the relative position of the road wheels 170,180,190, meaning in practice that the middle road wheel 180 is placed between the front road wheel 190 and the rear road wheel 170. A belt assembly 150 may in the context of the present invention be understood by a person skilled in the art as the collection of wheels, track 160, bearings, supports, etc. for enabling continuous track propulsion of the cleaning units 110,120, and hence the cleaning device 100.

[0033] Each belt assembly 150 of the cleaning units 110,120 may, as illustrated in figure la and lb, be arranged such that the ground pad 165 of the track 160 protrudes a non-zero distance from the underside of a cleaning unit 110,120. The ground pad 165 of each belt assembly 150 of the first cleaning unit may thus in other words be said to protrude a nonzero distance from the underside of the first cleaning unit 110, while the ground pad 165 of each belt assembly 150 of the second cleaning unit 120 may be said to protrude a nonzero distance from the underside of the second cleaning unit 120. A person skilled in the art will appreciate that the ground pad 165 of any belt assembly 150 may be interpreted as the part of a track 160 that lies between any two road wheels. A ground pad 165 may thus be considered as a part of a track 160. The ground pad 165 of any track 160 may according to the invention be considered as planar, or at least essentially planar, where "essentially planar" may be interpreted as meaning for example that the ground pad 165 of any belt assembly 150 occasionally may be tilted by a few degrees, or become at least in part wavy, e.g. due to the track 160 not being completely tight.

[0034] The first cleaning unit 110 and second cleaning unit 120 may, as illustrated in figure la, be arranged on opposite sides of the net 130 to be cleaned. The first cleaning unit 110 and second cleaning unit 120 may be aligned relative to one another such that the two belt assemblies 150 of the first cleaning 110 unit are aligned with and adjoins separate belt assemblies 150 of the second cleaning unit 120. The ground pad 165 of each respective track 160 of each belt assembly 150 of the first cleaning unit 110 may, as illustrated in figure lb, be positioned such that each ground pad 165 adjoins the ground pad 165 of the track 130 of separate belt assemblies 150 of the second cleaning unit 120. Note that in figure lb one of the cleaning units of the cleaning device is schematically illustrated as transparent for illustrative purposes. A person skilled in the art with knowledge of the present invention will appreciate that a net 130 to be cleaned may be present between any two ground pads 165 described as adjoining in the above context. Figure la and lb illustrates an example where the first cleaning unit 110 and second cleaning unit 120 are positioned on opposite sides of a net 130 to be cleaned such that the ground pad 165 of the track 160 of each belt assembly 150 of the first cleaning 110 unit adjoins, via the net 130 to be cleaned, a ground pad 165 of the track 160 of a belt assembly 150 of the second cleaning unit 120.

[0035] The track 160 of each belt assembly 150 is, as illustrated in figure lb, provided with magnets 210. The magnets 210 are provided in order to generate an attractive force between the belt assemblies 150 of the first cleaning unit 110 and the belt assemblies 150 of the second cleaning unit 120 such that the cleaning device 100 may adhere to a net 130 to be cleaned. A track 160 of a belt assembly 150 of the first cleaning unit 110 may as a way of example comprise magnets 210 with a first polarity, while a track 160 of a belt assembly 150 of the second cleaning unit 120 may comprise magnets 210 with a second polarity, opposite to the first polarity. When the tracks 160 of said two belt assemblies 150 are positioned such that they adjoin, an attractive force will occur between them such that a frictional force will be obtained between each cleaning unit 110,120 and the net 130 to be cleaned. The cleaning device 100 will thus, due to this attractive force and resulting frictional force, adhere to the net 130 to be cleaned such that the two cleaning units 110,120 may maintain a position on the net 130 relative to one another. A person skilled in the art will appreciate that there are numerous degrees of freedom in the configuration of the magnets 210 in each track 160. The magnets 210 in two adjoining tracks 160 may as a way of example be such that all the magnets 210 of a first track 160 have the same polarity, while all the magnets 210 in a second track 160, adjoining the first track 160, have the opposite polarity. Another example is that the magnets 210 in two adjoining tracks 160 may be such that any two adjacent magnets 210 in any one track 160 have opposite polarity, but where the tracks 160 of the two cleaning units are adjoining with a shift such that magnets 210 of opposite polarity are adjoining/attracting one another.

[0036] The cleaning device may according to the invention move across a net to be cleaned by means of the belt assemblies of the first and second cleaning unit. The adhesion to the net obtained by the magnetic attraction between adjoining tracks of the two cleaning units will result in a grip for the cleaning device such that movement is enabled. Said grip may thus be termed a magnetic induced grip. A person skilled in the art with knowledge of the present invention will appreciate that each belt assembly of the cleaning device may operate as a continuous track vehicle propulsion system that is configured to operate under water, i.e. where each belt assembly is provided with one or more of an engine, gear system, watertight gaskets, power supply, etc. The cleaning units may generally be provided with other parts necessary for allowing the cleaning device to move across a net to be cleaned. A person skilled in the art with knowledge of the present invention will appreciate that such parts may comprise e.g. watertight housing, transmitter, receiver, lighting device, battery, etc.

[0037] The middle road wheel 180 of each belt assembly 150 may as schematically illustrated in figure 1, 3 and 5 be provided with wheel magnets 215. The wheel magnets 215 may be provided in order to generate/ cause an attractive force between the middle road wheel 180 and the track 160 of each belt assembly 150 such that the track 160 is kept in contact with the middle road wheel 180 during operation of the cleaning device. The latter may for example contribute to a smoother moment of the cleaning device 100, reducing wobbling of the track 160, but also contribute to reducing the risk of the net being cleaned to be stuck between the middle road wheel 180 and the track 160. The attractive force may occur between the magnets 210 of the track 160 and the wheel magnets 215 of the middle road wheel 180. Alternatively, the track 160 may be provided with separate magnets that interact with the wheel magnets 215 of the middle road wheel 180 to generate said attractive force. A person skilled in the art with knowledge of the present invention will appreciate that the configuration of wheel magnets 215 in the middle road wheel 180 may vary and that many configurations are possible. One example is that all the magnets 210 in the track 160 are arranged with one polarity and that all the wheel magnets 215 of the middle road wheel 180 are arranged with the opposite polarity to generate an attraction with the magnets 210 of the track 160. Another example is that the magnets 210 in the track 160 are arranged with alternating polarity and that all the wheel magnets 215 of the middle road wheel 180 also are arranged with an alternating polarity. The distance between two adjacent wheel magnets 215 in the middle road wheel 180 may for example be the same as the distance between two adjacent magnets 210 in the track 160, and the middle road wheel 180 may further be synchronised with the track 160 such that each wheel magnet 215 of the middle road wheel 180 always are aligned with a magnet 210 of the track 160.

[0038] The middle road wheel 180 of each belt assembly 150 may, as an alternative to being provided with wheel magnets 215, be provided with a magnetic component. The magnetic component may thus interact with the magnets 210 in the track 160 to cause an attractive force to occur between the middle road wheel 180 and the track 160. The magnets 210 of the track 160 will in other words attract the magnetic component and hence the middle road wheel 180. The magnetic component may for example be a magnetic ring, such as an iron ring. The middle road wheel 180 of each belt assembly 150 may further be provided with a plurality of magnetic components, such as a plurality of iron pellets or similar. The middle road wheel 180 of each belt assembly 150 may alternatively in itself be magnetic, i.e., said magnetic component may be interpreted as a metallic element at least in part constituting the middle road wheel 180.

[0039] The cleaning device may according to the invention be dimensioned according to the net to be cleaned. A typical extension of the cleaning device is between 80 cm and 200 cm. The extension of the cleaning device is according to a specific embodiment of the invention less than 150 cm.

[0040] Each road wheel 170,180,190 is, as schematically illustrated in figure 5, provided with a suspension 200. The suspension 200 for each road wheel 170,180,190 may be configured for shifting the position of said road wheel 170,180,190 in a direction at least in part perpendicular to a driving direction 230 of the cleaning device. An example of such a distance is less than 10 centimetres, or more specifically a distance of between 3 and 5 centimetres. The suspension 200 of the road wheels 170,180,190 aims inter alia to enable the cleaning device to traverse obstacles of the net to be cleaned, such as ropes, knots or similar. The combination of the road wheel suspension 200 and the presence of three road wheels 170,180,190 means that any two adjoining tracks 160 may retain magnetic attraction even when the cleaning device is traversing an obstacle. As a way of example one can assume a cleaning device according to the invention traversing a rope of the net to be cleaned. As the cleaning device drives across the rope, the front road wheels 190 of each pair of adjoining tracks 160 will be displaced away from one another and the magnetic attraction between the part of the ground pad 165 between the front road wheel 190 and middle road wheel having only two road wheels would in such an instance likely lose its magnet- induced grip on the net to be cleaned and consequently fall of the net. The cleaning device according to the present invention would on the contrary maintain its magnet induced grip on the net, as the part of the ground pad 165 between the middle road wheel 180 and read road wheel 170 would still be adjoining, such that sufficient magnetic attraction may be maintained. Following the same example, the cleaning device will upon continuing its traversing of said rope move relative to the rope such that the front road wheels 190 once again are brought in contact with each other, but where the middle road wheels 180 subsequently are displaced from their default position using their respective suspension 200. At such a position the cleaning device according to the invention may maintain its adhesion to the net to be cleaned due to the magnet attraction between the ground pad 165 around the front road wheels 190 and the rear road wheels 170. The cleaning device will upon continuing its traversing of said rope, move relative to the rope such that the middle road wheels 180 once again are brought in contact with each other, but where the rear road wheels 170 subsequently are displaced from their default position using their respective suspension 200. The latter situation is equivalent to the situation where the front road wheels 190 were displaced.

[0041] Figure 2b, 3 and 5 illustrates an embodiment of the invention where each belt assembly 150 further comprises a damper wheel 220. Said damper wheel 220 may typically be positioned at a non-zero distance from the ground pad 165 of the belt assembly 150 to which it belongs. The latter location may here be in a direction perpendicular to the driving direction 230 of said belt assembly 150. A damper wheel 220 may be utilized to compensate for any strain in a track 160 caused when the cleaning device traverses an obstacle that causes one of its road wheels 170,180,190 to be displaced from their non-damped position. A road wheel 170,180,190 being displaced because the cleaning device traversing an obstacle will result in the relevant track 160 having to conform to the shape of the traversed object. Instead of the track 160 becoming strained due to the displacement of a road wheel 170,180,190, the damper wheel 220 may instead compensate for the shift in position of the road wheel 170,180,190, i.e. compensate for the resulting strain in the track 160, by being itself displaced. Each damper wheel 220 may thus in other words be provided with a suspension 200 for shifting the position of said damper wheel 220 to compensate for a shift in position of a road wheel 170,180,190. As a way of example, if a road wheel 170,180,190 of a belt assembly 150 is displaced in a direction perpendicular to the driving direction 230 of said belt assembly 150, a damper wheel 220 of that belt assembly may be displaced in the opposite direction of the displaced road wheel 170,180,190 in order to compensate for the increased length requirement on the track 160 due to the belt having to conform to the shape of the object that is being traversed. A typical object that needs to be traversed may as previously mentioned be a rope or a knot, which for example could have a diameter or extension of 3-5 centimetres. Each road wheel 170,180,190 may thus be provided with a suspension 200 for shifting the position of said road wheel 170,180,190 a distance of at least 3-5 centimetres in a direction at least in part perpendicular to a driving direction 230 of the cleaning device. Each damper wheel 220 may consequently be provided with a suspension 200 for shifting the position of said damper wheel 220 a distance of 3-5 centimetres. In general, any road wheel 170,180,190 may be provided with a suspension 200 for shifting the position of said road wheel 170,180,190 a distance up to 10 centimetres in a direction at least in part perpendicular to a driving direction 230 of the cleaning device. A suspension 200 may generally be any suitable suspension 200.

Examples of suitable suspensions 200 are spring-based suspension and hydraulic suspension.

[0042] According to an embodiment of the invention any one or more of the rear road wheel 170, the front road wheel 190 and/or the damper wheel 220 of each belt assembly 150 may be provided with wheel magnets 215. The wheel magnets 215 may be provided to generate an attractive force between any one or more of the rear road wheel 170, the front road wheel 190 and/or the damper wheel 220 and the track 160 of each belt assembly 150. The configuration of the wheel magnets 215 may be the same as described for the middle road wheel 180. Figure 1 schematically illustrates a cleaning device where any one or more of the rear road wheel 170, the front road wheel 190 and/or the damper wheel 220 of each belt assembly 150 is/are provided with wheel magnets 215. Any one or more of the rear road wheel 170, the front road wheel 190 and/or the damper wheel 220 of each belt assembly 150 may, as an alternative to being provided with wheel magnets 215, be provided with a magnetic component. The magnetic component may here be provided as described for the middle road wheel 180.

[0043] The cleaning device 100 may, as illustrated in figure la and lb be provided with cleaning means 140 for cleaning a submerged net 130. Both or either of the first cleaning unit 110 and second cleaning unit 120 may be provided with cleaning means 140. Cleaning means 140 may according to the invention be any suitable means for cleaning a net 130. As a way of example, the cleaning device 100 may be provided with one or more brushes, e.g. a rotating brush. The one or more brushes may be provided on only one of the cleaning units 110,120 or alternatively be distributed between the two cleaning units 110,120. A brush may upon rotation move across the net to clean the net of unwanted substances such a biofouling. In another example the cleaning means may comprise a waterbased cleaning device, such as a pressure cleaner. In yet another example the cleaning means may comprise one or more friction surfaces, such as a scrub or stationary brush, suitable for cleaning a net by being moved across the net 130.

[0044] The cleaning device may according to any embodiment of the invention be configured to traverse obstacles of a given size. As a way of example, the cleaning device may be configured to traverse an obstacle such as a rope or a rope knot. In order for the cleaning device to not loose adhesion to the net to be cleaned upon traversing an obstacle, the road wheels of each belt assembly may be spaced apart depending on the dimension of the obstacle to be traversed. In one embodiment of the invention the road wheels of each individual belt assembly may be separated by a distance of at least 3-5 centimetres. The latter distance is here measured between the surface of two adjacent road wheels. The road wheels of each individual belt assembly may generally be separated by a distance longer than 5 centimetres. It will be appreciated by a person skilled in the art that the upper limit for the spacing between two adjacent road wheels of the same belt assembly is determined by for example the obstacle that it is desirable to traverse, and/or for example the dimension and weight of the cleaning device. A distance between two adjacent road wheels of at least 3-5 centimetres, alternatively 5 - 10 centimetres, is considered adequate for most fish pen. Such a distance will allow the cleaning device to traverse ropes and rope knots without having two adjacent road wheels of the same belt assembly being displaced by the rope.

[0045] Any belt assembly may, as illustrated in figure 3 and 5, further comprise any number of drive wheels 320, damping wheels 220, road wheels, idlers 330 and/or tightener wheels 340. As a way of example, any belt assembly may be provided by a driving wheel 320, i.e. a wheel that supplies driving power to the track 160. Any road wheel or damper wheel 220 may in any relevant embodiments of the invention be a driving wheel 320. A person skilled in the art would appreciate that the cleaning device according to the present invention may comprise any number of additional wheels, e.g. dependent on the exact size and shape of the belt assemblies 150. A tightener wheel 340 may for example be provided to form the previously described driving edge 230 or trailing edge 250. In a particular embodiment of the invention, each belt assembly 150 may further comprise an additional middle road wheel 180. An additional middle road wheel 180 may contribute to increase the attraction between two adjoining belt assemblies 150 when the cleaning device traverses an obstacle. An additional middle road wheel 180 may contribute to ensuring a plane surface of the ground pad 165 of two adjoining tracks 160 being in contact during the traversing of said obstacle.

[0046] According to an embodiment of the invention, any one or more of said any number of drive wheels 320, damping wheels 220, road wheels, idlers 330 and/or tightener wheels 340 may be provided with wheel magnets 215. Said wheel magnets 215 may here be used to generate an attractive force between any one or more of said any number of drive wheels 320, damping wheels 220, road wheels, idlers 330 and/or tightener wheels 340 and the track 160 of each belt assembly 150. The configuration of the wheel magnets 215 in this embodiment may be the same as described for the middle road wheel 180. Figure 5 schematically illustrates a belt assembly where any one or more of said drive wheels 320, damping wheels 220, road wheels, idlers 330 and/or tightener wheels 340 is/are provided with wheel magnets 215. Any one or more of said any number of drive wheels 320, damping wheels 220, road wheels, idlers 330 and/or tightener wheels 340 of each belt assembly 150 may, as an alternative to being provided with wheel magnets 215, be provided with a magnetic component. The magnetic component may here be provided as described for the middle road wheel 180.

[0047] It will be appreciated by a person skilled in the art with knowledge of the present invention that the cleaning device will function without any of the wheels of the cleaning device being provided with wheel magnets or a magnetic component. Wheel magnets and a magnetic component may thus, in any embodiment of the invention, be omitted.

[0048] Each belt assembly 150 may, as illustrated in figure 3, be arranged such that the track 160 of each belt assembly 150 forms a leading edge 240 and/or trailing edge 250. Any leading edge 240 and/or trailing edge 250 may thus form a nonzero angle with a driving direction 230 of said belt assembly 150. A non-zero leading edge 240 may lead to eased traversing of obstacles, as such a leading edge 240 will reduce the angle with which the track 160 engages a given obstacle to be traversed. Said angle may sometimes be defined as an engagement angle or alternatively as an angle of attack. A further non-zero trailing edge 250 is optional and will have the same technical effect as the leading edge 240 in the event of the cleaning device reversing across an obstacle. A trailing edge 250 may additionally or alternatively be utilized in order to ease disengagement between magnets 210 of two adjoining tracks 160 as the cleaning device moves forward. A track 160 of a first cleaning unit adjoining a track 160 of a second cleaning unit will, due to the presence of magnets 210 in each track 160, experience a magnetic attraction towards each other. As the cleaning device moves forwards, magnets 210 of two adjoining tracks 160 will continuously engage in the front of the ground pad 165 and disengage at the trail of the ground pad 165. The magnets 210 disengaging at the trail of the ground pad 165 will have to be separated by a force greater than the attractive force caused by the magnets 210. Two tracks 160 forming a trailing edge 250 will cause a reduction of the required force for pulling apart magnets 210 of adjoining tracks 160, as the presence of a trailing edge 250 will allow for more of a pealing motion to be performed. Here the magnetic attraction between two engaged magnets 210 may be overcome more gradually than what would have been the case without a trailing edge 250. Any leading edge 240 and/or trailing edge 250 may, as illustrated in figure 3 be formed between a road wheel and an additional wheel, where the additional wheel is positioned a non-zero distance in a direction perpendicular to the driving direction. Said additional wheel may for example be a driving wheel 320.

[0049] The size of each wheel of the cleaning device will generally depend on the size of each cleaning unit. The size of each wheel may typically be dimensioned according to the type of track used, for example such that the track may run across the wheels without experiencing too great a curvature. In a particular embodiment of the invention each wheel of each belt assembly has a diameter in the range of 60 mm to 120 mm. Such a diameter has been found to be preferable when the track is made from silicone, rubber or plastic. Any wheel of a belt assembly that is positioned farthest to the front or back along the driving direction of a belt assembly will typically inflict the largest curvature on the track. These farthermost wheels may thus have a diameter that is larger than that of any road wheels appurtenant to the same belt assembly, e.g. in the range from 10% - 250% larger, in particularly in the range from 50% - 100 % larger. Any one or both of the farthermost wheels may for example be a driving wheel 320. [0050] The track 160 of each belt assembly 150 may as illustrated in figure 3 of the invention be provided with a plurality of studs 270, while each wheel of each belt assembly 150 may be provided with corresponding recesses 280 for receiving the studs 270 of the track 160. The studs 270 may provide an engagement between the wheels of a belt assembly 150 and the track 160 of the same belt assembly 150 such that grip is provided between the wheels and the track 160. The studs 270 may for example be used in order for a drive wheel 320 to provide propulsion to a track 160. The studs 270 may generally be evenly positioned along the longitudinal direction of the track, but any configuration is in principle possible.

[0051] Figure 3 illustrates a cleaning device where each track 160 is provided with studs 270 and where each stud 270 of each track 160 of the cleaning device comprises a magnet 210. The number of studs 270 comprising a magnet 210 may alternatively be lower than the total number of studs 270 per track. The latter configuration may for example be used to optimize the magnetic attraction between the first cleaning unit and the second cleaning unit. In a particular example, the track 160 of each belt assembly 150 may be provided with an even number of studs 270, where the polarity of the magnets 210 of any two adjacent studs 270 are opposite to each other. Two adjoining tracks 160 will thus experience an attractive force to one another between pairs of magnets 210 comprising studs 270 with opposite polarity. The latter configuration may be beneficial to avoid the tracks 160 skidding, as the alternating polarity of the magnets 210 will create a force between two adjoining tracks 160 at least in part parallel with the driving direction 230 of the cleaning device.

[0052] Figure 3 illustrates a particular embodiment of the invention where each track 160 of the cleaning device is provided with studs 270. Here, each track 160 comprises a plurality of rigid track elements 290 connected together by flexible joints 300, where each track element 290 is provided by at least one stud 270. Each stud 270 is in this example placed a non-zero distance from any of the flexible joints 300 connecting the track-elements 290, which inter alia prevents the studs 270 from being bent when the track 160 is moving. The latter can contribute to reducing wear on the belt assembly. A flexible joint 300 may generally be considered as any suitable joint that is flexible, such as a hinge or an elastic material connecting two adjacent rigid track elements 290. [0053] The track of any belt assembly of the cleaning device may according to any embodiment of the invention be made at least in part from rubber, plastic or silicone. A person skilled in the art will appreciate that the track may be made from other materials than those listed explicitly herein. The track may for example be made from a combination of materials, e.g. a combination of those mentioned above.

[0054] Figure 4 illustrates a track 160 of a belt assembly of the cleaning device where the track 160 is provided with friction studs 310. The friction studs 310 are here provided on the side of the track 160 that is configured to face away from any road wheels. The friction studs 310 are provided in order to improve the grip between two adjoining tracks, and also between the track 160 and the net to be cleaned. The friction studs 310 may according to an embodiment of the invention protrude up to 1 mm from the track, or alternatively up to 2 mm. Such a protrusion distance has been found to be preferred, as larger protrusion distances may contribute to unwanted wear on the net to be cleaned.

[0055] It will be appreciated that the cleaning device according to any embodiment of the invention is not limited to cleaning a net. The cleaning device may according to any embodiment of the invention alternatively be used to clean a seine, net cage, a water permeable sheet, water impermeable sheet or similar. Other examples are watertight tarpaulin, perforated tarpaulin, or similar.

[0056] A cleaning device according to any embodiment of the first aspect of the invention may thus in a second aspect of the invention be used for cleaning a net or sheet of a fish pen.

[0057] Other advantageous features will be apparent from the accompanying claims.