Adjusting the suspension of a main branch of a greenhouse plant from an overhead wire in a greenhouse

Abstract

In a greenhouse for greenhouse plants, where one or more overhead wires are present and the plants are suspended from them by means of suspension hooks and wires, it is generally desirable to regularly adjust the suspension of a main branch of a greenhouse plant from an overhead wire. For this purpose, a device with a detection system and a hook gripper is provided The detection system takes an image and detects at least one suspension hook in the image The hook gripper then removes the suspension hook from the overhead wire, moves it around the main branch, and places it back on the overhead wire. Optionally, before or after moving the suspension hook around the main branch with the hook gripper, the hook gripper is used to move the suspension hook to unwind the suspension wire over at least one loop of the suspension hook.

Description

[0001] Adjusting the suspension of a main branch of a greenhouse plant from an overhead wire in a greenhouse

[0002] The invention relates to a method for adjusting the suspension of a main branch of a greenhouse plant from an overhead wire in a greenhouse using a suspension hook and a suspension wire partially wound around the suspension hook. The invention also relates to a device for use with this method. Examples of greenhouse plants in this context include a tomato plant, a cucumber plant, and a bell pepper plant.

[0003] In the context of the professional cultivation of greenhouse plants, the so- called high wire cultivation is known. This form of cultivation inter alia allows the greenhouse plants to grow much taller than the maximum height of the greenhouse, resulting in a higher yield per plant. It uses overhead wires stretched high in the greenhouse, with one overhead wire per row of greenhouse plants. The overhead wires can be, for example, iron wires. A greenhouse plant hangs from an overhead wire by means of a suspension hook, with a suspension wire that is partially wrapped around the suspension hook and partially wrapped around a main branch of the greenhouse plant, with clips, for example, used to secure the suspension wire to the main branch.

[0004] Initially, when the greenhouse plant is still lower than the overhead wire, the greenhouse plant is able to grow upwards along the suspension wire. Optionally, the suspension wire can be repeatedly wrapped around newly grown sections of the main branch. This is done by manipulating the greenhouse plant or by removing the suspension hook from the overhead wire and then winding the suspension wire at least one additional time around the main branch. Once the greenhouse plant has approximately reached the overhead wire, it can be ensured that the growth of the greenhouse plant can continue favourably. To do this, the greenhouse plant is lowered relative to the overhead wire by removing the suspension hook from the overhead wire, winding the suspension wire at least one additional time around the main branch, and then, before or after this, unwinding the suspension wire over at least one winding from the suspension hook before replacing the suspension hook on the overhead wire.

[0005] High wire cultivation not only results in a higher yield per greenhouse plant by allowing the plants to grow longer in the greenhouse, but also by ensuring that an upper part of the plants receive optimal light. This upper part of the plants is where the young leaves are and where the fruit develops best.

[0006] A disadvantage of high-wire cultivation is that handling the suspension hooks is a labour-intensive, manual process, the costs of which account for a significant portion of the total costs associated with vegetable cultivation. It is an object of the invention to provide a way to transition from manual to mechanical gripping and manipulation of the suspension hooks. To this end, the invention provides a method and a device for use in the method, with the invention specifically aimed at adjusting the suspension of a main branch of a greenhouse plant from an overhead wire in a greenhouse using a suspension hook and a suspension wire partially wrapped around the suspension hook.

[0007] Within the scope of the invention, a device comprising a detection system and a hook gripper for gripping and manipulating the suspension hook is used for the aforementioned adjustment of the suspension of a main branch of a greenhouse plant from an overhead wire in a greenhouse. The method comprises the following:

[0008] - capturing an image with the detection system and detecting at least one suspension hook in the image,

[0009] - grasping a detected suspension hook with the hook gripper,

[0010] - removing the suspension hook from the overhead wire using the hook gripper,

[0011] - using the hook gripper to move the suspension hook away from the overhead wire over a limited distance in a downward direction until an area of the main branch is reached where an upper turn of the suspension wire around the main branch is located,

[0012] - making at least one further turn of the suspension wire around the main branch by moving the suspension hook completely around the main branch using the hook gripper,

[0013] - placing the suspension hook back on the overhead wire using the hook gripper, and

[0014] - releasing the suspension hook.

[0015] Consequently, the device according to the invention can be defined as a device for use in the method, comprising a detection system configured to generate an image of the space and to recognize objects in the image using image processing, a hook gripper configured for gripping and manipulating a suspension hook from which a main branch of a greenhouse plant hangs, and a control system that is connected to the detection system and the hook gripper, and that is configured to successively:

[0016] - capture an image with the detection system and detect at least one suspension hook in the image,

[0017] - grasp a detected suspension hook with the hook gripper,

[0018] - use the hook gripper to remove the suspension hook from the overhead wire,

[0019] - use the hook gripper to move the suspension hook away from the overhead wire, over a limited distance in a downward direction until an area of the main branch is reached where an upper turn of the suspension wire around the main branch is located, - using the hook gripper, let the suspension wire make at least one further turn around the main branch by moving the suspension hook completely around the main branch,

[0020] - use the hook gripper to place the hanging hook back on the overhead wire, and

[0021] - release the suspension hook.

[0022] From the foregoing, it follows that the invention provides for the use of a device with a detection system and a hook gripper, whereby the hook gripper is controlled to engage a suspension hook and subsequently effect a specific movement of the suspension hook. The movement of the suspension hook comprises several phases: first, the suspension hook is removed from the overhead wire, then the suspension hook is moved away from the overhead wire and brought to an area of the main branch where at least one new wrap of the suspension wire must be made around the main branch, then the suspension hook is moved around the main branch to effect this at least one new wrap of the suspension rope, and finally, the suspension hook is placed back on the overhead wire and released. In this way, the device achieves a desired adjustment of the suspension of a main branch from an overhead wire.

[0023] Taking the suspension hook off the overhead wire may be accomplished by moving the suspension hook upwards for a limited distance and / or by locally pressing the overhead wire downwards for a limited distance. Placing the suspension hook back on the overhead wire can typically involve moving the suspension hook upwards.

[0024] Within the scope of the invention, it is a realistic option to move the suspension wire around the main branch before or after the hook gripper is used to make at least one subsequent turn around the main branch, in order to unwind the suspension wire over at least one winding of the hook. As explained above in connection with the prior art, this is a way to lower the greenhouse plant relative to the overhead wire. The extent to which the greenhouse plant is lowered may be selected based on the amount of fruit in a lower portion of the greenhouse plant. The detection system may be used to obtain this information, and also to determine a suitable location on the greenhouse plant and a suitable number for the new turns of the suspension wire around the main branch.

[0025] In a practical embodiment of the device, the hook gripper is tiltable between a horizontal position for positioning the suspension hook in a substantially horizontal orientation and a vertical position for positioning the suspension hook in a substantially vertical orientation. The hook gripper can then be moved to the vertical position for both removing the suspension hook from the overhead wire and replacing the suspension hook on the overhead wire, and it can also be moved to the horizontal position for looping the suspension wire around the main branch. The suspension hook is usually elongate. According to an insight of the invention, this fact can be advantageously used in the design of the hook gripper. For example, the invention provides the possibility of a hook gripper design in which the hook gripper comprises two clamping units that are configured to clamp onto the suspension hook at a distance from each other. In that case, the suspension wire can wrap around the main branch, comprising successive sub steps of

[0026] - positioning the suspension hook in a substantially horizontal orientation in front of the main branch using the hook gripper,

[0027] - making a first of the clamping units release the suspension hook and moving a second of the clamping units to position the suspension hook along a first side of the main branch,

[0028] - moving the hook gripper towards the main branch and moving the second of the clamping units to position the suspension hook behind the main branch and also to bring the suspension hook within reach of the first of the clamping units,

[0029] - causing the first of the clamping units to securely clamp onto the suspension hook,

[0030] - allowing the second of the clamping units to release the suspension hook and moving the first of the clamping units to position the suspension hook along a second side of the main branch,

[0031] - moving the hook gripper away from the main branch and moving the first of the clamping units to position the suspension hook in front of the main branch and also to bring the suspension hook into range of the second of the clamping units, and

[0032] -clamping the second of the clamping units onto the suspension hook.

[0033] Various options are conceivable for the design of the hook gripper and its clamping units. For example, the hook gripper may comprise a carrier section, with the clamping units are arranged on the carrier section so as to be rotatable independently from each other. Furthermore, each of the clamping units may comprise an arm with a clamp at one end that can be opened and closed.

[0034] A further practical possibility within the scope of the invention is that the device also comprise a plant gripper for gripping and holding at least the main branch. Such an additional gripper may be deployed in various ways, for example, by gripping the main branch before removing the suspension hook from the overhead wire with the hook gripper, and then, while removing the suspension hook from the upper wire with the hook gripper, moving the main branch upward in a similar manner to the suspension hook with the hook gripper. This way, the weight of the greenhouse plant can be relieved from the suspension hook, making it easier to move. A suitable moment for releasing the main branch is when the suspension hook has been replaced on the overhead wire with the hook gripper.

[0035] To prevent damage to the main branch, it is beneficial if at least parts of the plant gripper that are intended to come into contact with the main branch are provided with a coating.

[0036] In a practical embodiment, the device comprises a standing support mast, with the hook gripper and the plant gripper mounted on the support mast and movable along the mast. The support mast can be mounted, for example, on a trolley which is able to travel autonomously over rails typically found in greenhouses and which may also be part of a heating system. The control system may be configured to adjust the positions of the hook gripper and the plant gripper by setting an appropriate height for the hook gripper and the plant gripper on the support mast. The assembly of support mast, hook gripper, and plant gripper may optionally be designed such that the hook gripper and the plant gripper can pass each other on the support mast.

[0037] The device may be configured to perform more functions than simply adjusting the suspension of a main branch of a greenhouse plant from an overhead wire in a greenhouse. For example, the device may also be applicable for a method for removing a sucker from a greenhouse plant. In such a case, it is practical if the detection system is also configured to capture an image of a section of the greenhouse plant and detect at least a sucker and the course of a main branch on which the sucker is located, and if a sucker gripper is provided that is configured to engage the sucker, to detach the latter from the main branch. For the sake of completeness, it should be noted that a sucker is a new shoot that develops into a new branch with leaves, flowers, and fruit without further intervention. Removing a sucker is done, for example, to prevent the sucker from consuming energy and nutrients, thereby negatively affecting the development of the fruit on the main branch on which the sucker is located.

[0038] Alternatively, the device may include a pruning unit which is configured to perform a cutting action. The plant gripper may be used to move and temporarily hold a branch or leaves out of the way of another component, such as a pruning gripper or a pruning unit. When the aforementioned support mast is used, additional components, such as the pruning gripper and the pruning unit, can be movably mounted along the support mast. The detection system may be suitably expanded to generate an image that can be used as a basis for effectively moving and positioning additional components.

[0039] The detection system of the device can be configured in any suitable manner and may, for example, comprise at least one stereo vision camera. As is known per se, such a camera can be used to simulate human visual perception and is therefore suitable for obtaining a three-dimensional image with depth. It is practical if the detection system further comprises a suitable processor for processing input from the camera or cameras.

[0040] The invention will be explained below with reference to the figures, which are generally schematic in design and relate to a non-limiting exemplary embodiment of a device for use in a greenhouse with tomato plants, which is designed, among other things, for adjusting the suspension of a main branch of a tomato plant from an overhead wire, whereby like reference numerals indicate like or comparable parts, and in which: Figure 1 shows a schematic view of the device as well as a section of a pipe rail and a network of overhead wires in the greenhouse,

[0041] Figure 2 shows a schematic of the device, showing a control system of the device and components of the device with which the control system interacts during operation of the device, and

[0042] Figures 3-13 illustrate how a hook gripper of the device is used to grasp a suspension hook, remove it from an overhead wire, move it around a main branch of a tomato plant, and place it back on the overhead wire.

[0043] Figure 1 schematically shows a multifunctional device 100 for use in a greenhouse with tomato plants, as an example of a device according to the invention and a context in which the invention is applicable. Figure 1 also schematically shows a section of a pipe rail 1 and a network of overhead wires 2 in the greenhouse. The overhead wires 2 are used to hang the tomato plants from. In Figure 1 , this is illustrated for a single tomato plant, of which the upper portion of a main branch 3 is schematically shown. The main branch 3 hangs from an overhead wire 2 by means of a combination of a suspension hook 4 and a suspension wire 5, which is wrapped around the suspension hook 4 on one side and around the main branch 3 on the other.

[0044] The device 100 can be used for various purposes, including adjusting the suspension of the main branch 3 to the overhead wire 2. In particular, the device 100 can be used for

[0045] - gripping the suspension hook 4, removing the suspension hook 4 from the overhead wire 2, moving the suspension hook 4 around the main branch 3, and replacing the suspension hook 4 on the overhead wire 2, as will be explained in more detail with reference to figures 3-13,

[0046] - removing a sucker from the tomato plant, and - pruning the tomato plant by cutting portions from the tomato plant.

[0047] The device 100 comprises a hook gripper 10 for gripping and manipulating the suspension hook, a sucker gripper 20 for breaking off a sucker from the tomato plant, and a pruning unit 30 for pruning the tomato plant. The device 100 is also provided with a plant gripper 40 for holding and possibly moving a portion of the tomato plant during one or more of the possible actions, so that the action in question proceeds optimally without hindrance from, for example, the presence and / or weight of a portion of the tomato plant. The device 100 is generally designed as a vehicle 101 that can travel on the pipe rail 1 present in the greenhouse, with a vertical support mast 102 on which the hook gripper 10, the sucker gripper 20, the pruning unit 30, and the plant gripper 40 are mounted and along which the hook gripper 10, the sucker gripper 20, the pruning unit 30, and the plant gripper 40 are movable, both in a vertical direction and in a direction around the support mast 102. The support mast 102 is movable vertically. This allows the hook gripper 10, the sucker gripper 20, the pruning unit 30, and the plant gripper 40 to be positioned at any desired angle relative to the tomato plant. It is also possible that the hook gripper 10, the sucker gripper 20, the pruning unit 30 and the plant gripper 40 can pass each other on the support mast 102.

[0048] Referring to Figure 2, it is noted that the device 100 includes a detection system 50 for generating an image of the space and for recognising objects in the image using image processing. The detection system 50 may, for example, comprise a plurality of cameras, with at least one camera being disposed at a strategic position at each of the hook gripper 10, the sucker gripper 20, the pruning unit 30, and the plant gripper 40. For controlling the detection system 50, adjusting the position of the support mast 102, and controlling the movements and operation of the hook gripper 10, the sucker gripper 20, the pruning unit 30, and the plant gripper 40, the device 100 according to the invention comprises a control system 60. In Figure 2, the interaction of the control system 60 with various parts of the device 100 according to the invention is shown schematically, in particular the hook gripper 10, the sucker gripper 20, the pruning unit 30, the plant gripper 40, the detection system 50, and the support mast 102.

[0049] Referring to Figures 3-13, steps in an application of the hook gripper 10 are described below. As can be seen in these figures, the hook gripper 10 comprises a first clamping unit 11 and a second clamping unit 12, and each of the clamping units 11 , 12 comprises an arm 13 with a clamp 14 at one end thereof. Each of the clamping units 11 , 12 is rotatably mounted via the arm 13 on a carrier part 15 of the hook gripper 10. For the sake of completeness, it should be noted that for the sake of clarity, the suspension wire 5 is not shown in Figures 3-13.

[0050] Initially, the detection system 50 determines where a suspension hook 4 is located that is to be gripped and manipulated by the hook gripper 10, and the hook gripper 10 is moved towards this suspension hook 4 and positioned relative to this suspension hook 4 in such a way that the hook gripper 10 is able to engage with the latter using of both clamping units 11 , 12. Figure 3 illustrates how the hook gripper 10 is positioned relative to the suspension hook 4, in a vertical position and with the clamps 14 in an open position, and Figure 4 illustrates engagement of the hook gripper 10 with the suspension hook 4, still in a vertical position and with the clamps 14 in a closed position.

[0051] After the hook gripper 10 has engaged the suspension hook 4, the hook gripper 10 is moved upward a limited distance so that the suspension hook 4 can disengage from the overhead wire 2. From here, the hook gripper 10, containing the suspension hook 4, is moved downward and positioned in front of the main branch 3, to which the suspension hook 4 is connected by means of the suspension wire 5. The hook gripper 10 is also brought into a horizontal position so that a horizontal orientation of the suspension hook 4 is obtained. Figure 5 illustrates the situation thus obtained. From this situation, the clamp 14 of the first clamping unit 11 is moved from the closed position to the open position, and the second clamping unit 12 is rotated so that the suspension hook 4 is positioned along a first side of the main branch 4, as illustrated in Figure 6. Next, the hook gripper 10 is moved towards the main branch 3, so that it is possible to position the suspension hook 4 behind the main branch 4, as illustrated in Figures 7 and 8. For this purpose, the second clamping unit 12 is rotated back so that the first clamping unit 11 can again engage the suspension hook 4.

[0052] From its position behind the main branch 3, the suspension hook 4 is positioned along a second side of the main branch 3, as illustrated in Figure 9. To this end, the clamp 14 of the second clamping unit 12 is moved into the open position, and the first clamping unit 11 is rotated. Next, the hook gripper 10 is moved away from the main branch 3, so that it is possible to position the suspension hook 4 in front of the main branch 3 again, as illustrated in Figures 10 and 11. To this end, the first clamping unit 11 is rotated back so that the second clamping unit 12 can again engage the suspension hook 4.

[0053] As a result of the movement of the suspension hook 4 around the main branch 3, a new wrap of the suspension wire 5 around the main branch 4 is created. The suspension hook 4 can then be moved to the overhead wire 2 and replaced on the overhead wire 2, optionally after moving the hook gripper 10 such that the suspension wire 5 is unwound over at least one wrap of the suspension hook 4. This latter can also be done earlier, specifically between removing the suspension hook 4 from the overhead wire 2 and moving the suspension hook 4 around the main branch 3.

[0054] Figures 12 and 13 illustrate that in order to replace the suspension hook 4 on the overhead wire 2, the hook gripper 10 is returned to the vertical position so that the original vertical orientation of the suspension hook 4 is obtained, with Figure 13 in particular illustrating that the clamps 14 of the clamping units 11 , 12 are brought into the open position and that the hook gripper 10 is moved away from the suspension hook 4 when the suspension hook 4 is back in position on the overhead wire 2.

[0055] While the hook gripper 10 is used in the manner described above, it is advantageous when the plant gripper 40 is deployed to hold the main branch 3 and move it in such a way in correspondence with the suspension hook 4 that there is little or no downward force acting on the suspension hook 4.

[0056] During the various steps described above, the detection system 50 is used to monitor the various positions of the suspension hook 4 relative to the overhead wire 2 and the main branch 3, respectively, with image recording and processing. The device 100 is preferably designed to function completely autonomously, i.e. , to move autonomously on the pipe rail 1 and to perform all possible functions autonomously, so that manual intervention by one or more people is not required.

[0057] It will be clear to a person skilled in the art that the scope of the invention is not limited to the examples discussed above, but that various changes and modifications thereof are possible without departing from the scope of the invention as defined in the appended claims.

[0058] The invention can be summarized as follows. In the context of a tomato plant greenhouse in which one or more overhead wires 2 are present and the tomato plants are suspended from them by means of suspension hooks 4 and suspension wires 5, it is generally desirable to regularly adjust the suspension of a main branch 3 of a tomato plant from an overhead wire 2. To this end, a device 100 with a detection system 50 and a hook gripper 10 is provided. An image is captured with the detection system 50 and at least one suspension hook 4 is detected in the image. The hook gripper 10 then removes the suspension hook 4 from the overhead wire 2, moves it around the main branch 3, and places it back on the overhead wire 2. If necessary, before or after moving the suspension hook 4 around the main branch 3 with the hook gripper 10, the suspension hook 4 is moved with the hook gripper 10 in order to unwind the suspension wire 5 over at least one turn of the suspension hook 4.

Claims

CLAIMS1 . Method for adjusting the suspension of a main branch (3) of a greenhouse plant from an overhead wire (2) in a greenhouse with a suspension hook (4) and a suspension wire (5) which is partially wrapped around the suspension hook (4), by means of a device (100) comprising a detection system (50) and a hook gripper (10) for gripping and manipulating the suspension hook (4), the method comprising the following consecutive steps:- capturing an image with the detection system (50) and detecting at least one suspension hook (4) in the image,- grasping a detected suspension hook (4) with the hook gripper (10),- using the hook gripper (10) to remove the suspension hook (4) from the overhead wire (2),- using the hook gripper (10) move the suspension hook (4) away from the overhead wire (2) over a limited distance in a downward direction until an area of the main branch (3) is reached where an upper turn of the suspension wire (5) around the main branch (3) is located,- using the hook gripper (10) to make at least one further turn of the suspension wire (5) around the main branch (3) by moving the suspension hook (4) completely around the main branch (3),- placing the suspension hook (4) back on the overhead wire (2) using the hook gripper (10), and- releasing the suspension hook (4).

2. Method according to Claim 1 , wherein before or after making the suspension wire (5) make at least one further turn around the main branch (3) with the hook gripper (10), the suspension hook (4) is moved with the hook gripper (10) in order to unwind the suspension wire (5) over at least one turn of the suspension hook (4).

3. Method according to claim 1 or 2, wherein the hook gripper (10) is tiltable between a horizontal position for positioning the suspension hook (4) in a substantially horizontal orientation and a vertical position for positioning the suspension hook (4) in a substantially vertical orientation, wherein the hook gripper (10) is brought into the vertical position for the purpose of both removing the suspension hook (4) from the overhead wire (2) and placing the suspension hook (4) back onto the overhead wire (2), and wherein the hook gripper (10) is brought into the horizontal position for the purpose of causing the suspension wire (5) to make a turn around the main branch (3).

4. Method according to any of claims 1 to 3, wherein the hook gripper (10) comprises two clamping units (11 , 12) which are arranged to clamp onto the suspension hook (4) at a distance from each other, and wherein making the suspension wire (5) make a turn around the main branch (3) comprises successive sub-steps of- using the hook gripper (10) to position the suspension hook (4) in a substantially horizontal orientation in front of the main branch (3),- making a first of the clamping units (11 , 12) release the suspension hook (4) and moving a second of the clamping units (11 , 12) to position the suspension hook (4) along a first side of the main branch (3),- moving the hook gripper (10) towards the main branch (3) and moving the second of the clamping units (11 , 12) to position the suspension hook (4) behind the main branch (3) and also bring the suspension hook (4) within range of the first of the clamping units (11 , 12),- causing the first of the clamping units (11 , 12) to securely clamp onto the suspension hook (4),- allowing the second of the clamping units (11 , 12) to release the suspension hook (4) and moving the first of the clamping units (11 , 12) to position the suspension hook (4) along a second side of the main branch (3),- moving the hook gripper (10) away from the main branch (3) and moving the first of the clamping units (11 , 12) to position the suspension hook (4) in front of the main branch (3) and also to bring the suspension hook (4) into range of the second of the clamping units (11 , 12), and- causing the second of the clamping units (11 , 12) to securely clamp onto the suspension hook (4).

5. Method according to any of claims 1 to 4, wherein the device (100) also comprises a plant gripper (40) for gripping and holding at least the main branch (3), and wherein:- before removing the suspension hook (4) from the overhead wire (2) with the hook gripper (10), the main branch (3) is grasped with the plant gripper (40),- while removing the suspension hook (4) from the overhead wire (2) with the hook gripper (10), move the main branch (3) with the plant gripper (40) in a similar manner as the suspension hook (4) is moved upwards with the hook gripper (10), and- after placing the suspension hook (4) back on the overhead wire (2) with the hook gripper (10), the main branch (3) is released.

6. Device (100) for use in the method according to any of claims 1 to 5,comprising a detection system (50) adapted to generate an image of the space and to recognise objects in the image using image processing, a hook gripper (10) adapted to grip and manipulate a suspension hook (4) from which a main branch (3) of a greenhouse plant hangs, and a control system (60) which is connected to the detection system (50) and the hook gripper (10), and which is configured to successively:- capture an image with the detection system (50) and detect at least one suspension hook (4) in the image,- grab a detected suspension hook (4) with the hook gripper (10),- use the hook gripper (10) to remove the suspension hook (4) from the overhead wire (2),- use the hook gripper (10) to move the suspension hook (4) away from the overhead wire (2) over a limited distance in a downward direction until an area of the main branch (3) is reached where an upper turn of the suspension wire (5) around the main branch (3) is located,- use the hook gripper (10) to make at least one further turn of the suspension wire (5) around the main branch (3) by moving the suspension hook (4) completely around the main branch (3),- use the hook gripper (10) to place the suspension hook (4) back onto the overhead wire (2), and- release the suspension hook (4).

7. Device (100) according to claim 6, wherein the control system (60) is also configured to cause the suspension wire (5) to make at least one subsequent turn around the main branch (3) with the hook gripper (10) before or after moving the suspension hook (4) with the hook gripper (10) to unwind the suspension wire (5) over at least one turn of the suspension hook (4).

8. Device (100) according to claim 6 or 7, wherein the hook gripper (10) is tiltable between a horizontal position for positioning the suspension hook (4) in a substantially horizontal orientation and a vertical position for positioning the suspension hook (4) in a substantially vertical orientation.

9. Device (100) according to claim 8, wherein the control system (60) is configured to remove the hook gripper (10) from the overhead wire (2) for the purpose of both removing the suspension hook (4) from the overhead wire (2) and placing the suspension hook (4) back onto the overhead wire (2) in the vertical position, and to make the hook gripper (10) make a movement around the main branch (3) to bring in the horizontal position for the suspension wire (5).

10. Device (100) according to any of claims 6 to 9, wherein the hook gripper(10) comprises two clamping units (11 , 12) which are adapted to clamp onto the suspension hook (4) at a distance from each other.

11. Device (100) according to claim 10, wherein the control system (60) is configured to cause the suspension wire (5) to make a turn around the main branch (3) in succession:- use the hook gripper (10) to position the suspension hook (4) in a substantially horizontal orientation in front of the main branch (3),- make a first of the clamping units (11 , 12) release the suspension hook (4) and move a second of the clamping units (11 , 12) to position the suspension hook (4) along a first side of the main branch (3),- move the hook gripper (10) towards the main branch (3) and move the second of the clamping units (11 , 12) to position the suspension hook (4) behind the main branch (3) and also to bring the suspension hook (4) within reach of the first of the clamping units (11 , 12),- cause the first of the clamping units (11 , 12) to securely clamp onto the suspension hook (4),- allow the second of the clamping units (11 , 12) to release the suspension hook (4) and move the first of the clamping units (11 , 12) to position the suspension hook (4) along a second side of the main branch (3),- move the hook gripper (10) away from the main branch (3) and move the first of the clamping units (11 , 12) to position the suspension hook (4) in front of the main branch (3) and also to bring the suspension hook (4) into range of the second of the clamping units (11 , 12), and- cause the second of the clamping units (11 , 12) to securely clamp onto the suspension hook (4).

12. Device (100) according to claim 10 or 11 , wherein the hook gripper (10) comprises a carrier part (15), and wherein the clamping units (11 , 12) are arranged on the carrier part (15) so as to be rotatable independently from each other.

13. Device (100) according to any of claims 6 to 12, further comprising a plant gripper (40) for gripping and holding at least the main branch (3), wherein the control system (60) is configured to:- before removing the suspension hook (4) from the overhead wire (2) with the hook gripper (10), grasp the main branch (3) with the plant gripper (40),- while removing the suspension hook (4) from the overhead wire (2) with the hook gripper(10), move the main branch (3) upwards with the plant gripper (40) in a similar way as the suspension hook (4) with the hook gripper (10), and- after placing the suspension hook (4) back on the overhead wire (2) with the hook gripper (10) release the main branch (3).

14. Device (100) according to claim 13, comprising a standing support mast(102), wherein the hook gripper (10) and the plant gripper (40) are mounted on the support mast (102) and are movable along the support mast (102).

15. Device (100) according to claim 13 or 14, also for use in a method for removing a sucker from a greenhouse plant, wherein the detection system (50) is also configured to capture an image of a portion of the greenhouse plant and to detect in the image at least one sucker and the course of a main branch (3) on which the sucker is located, and wherein a sucker gripper (20) is provided which is configured to engage the sucker in order to detach it from the main branch (3).

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