A method for manufacturing a (semi-)unique three-dimensional structure

Abstract

A method for manufacturing a (semi-)unique three-dimensional structure, comprising: - based on a computer representation: generating a weld plan comprising a first set of welding actions and a second set of welding actions; - welding profiles to a base plate according to the first set of welding actions; - placing verticals on the base plate, in a direction transverse to the profiles, thereby forming a plurality of cells; - wherein the welding robot is a portable welding robot; - for at least a portion of the cells: applying a cell identifier; - by a human operator: carrying the portable welding robot into a cell and placing said portable welding robot in a pre-determined position in said cell; - providing the cell identifier to the robot; - transferring the welding actions of the second set associated with the cell identifier to the robot; - based on said welding actions: from the pre-determined position inside said cell, said portable welding robot welding the verticals of the respective cell to the profiles and / or the base plate.

Description

[0001] Title: A method for manufacturing a (semi-)unique three-dimensional structure

[0002] BACKGROUND

[0003] The present invention relates to a method for manufacturing, e.g. by welding, a unique or semi-unique three-dimensional structure.

[0004] For the purpose of manufacturing, e.g. by welding, products in series, automation has become a huge factor in the last couple of decades - up to the point where car manufacturing factories hardly employ personnel and virtually all manufacturing steps are carried out by robots. This typically concerns series manufacturing only, though. For series manufacturing, repetitive steps can be taken and a factory layout can be designed in which a row of robots carries out a sequence of tasks that lead to the creation of the product. Each robot carries out the same task over and over, without much variation. Supplied goods must have low tolerances to make this possible, and product quality can be guaranteed.

[0005] For the manufacture of unique or semi-unique (i.e. non-repetitive) constructions, manned labour is still required to a much larger degree. For a unique construction, e.g. a cruise vessel, a yacht, an oil drilling rack, a bridge or other such constructions, the work required to automate the manufacturing process does not outweigh the manual work that is saved by manufacturing the construction using robots. With semi-unique it is meant that typically only one of these structures is built, although is sometimes happens that two, three or another small number of structures is built to the same specifications. In other words: the manufacturing process of these structures is non-repetitive. Manual welding is still very common on such construction sites. On top of that, tolerances of supplied goods may be much more lenient compared to tolerances of supplied goods for series production - making automation even more difficult.

[0006] Nonetheless, the use of robots for the production of such unique structures is considered - partly driven by the fact that skilled workers are more and more rare, working conditions for these workers can be very harsh, and the desire to perform better on aspects such as health and safety for the workers.

[0007] One option that is explored by some companies is the use of so-called “cobots”. A collaborative robot is understood to be a small robot that can be trained by a human to carry out a certain uncomplicated task repetitively. A human operator physically holds the cobot, guides it along a desired trajectory to do a certain task, after which the cobot can fulfil this precise task without the further involvement of the human operator. On the one hand, this opens the possibility to use robots even when the operator does not have the programming skills that are typically required to employ a typical industrial robot in a production process. On the other hand, this does not allow for much variation in tasks employed by the robot.

[0008] One example in which a “cobot” is used for the manufacturing of (semi- )unique three-dimensional structures is a brochure by Hyundai Welding, entitled “cobot solution for the shipbuilding industry”. This brochure generally mentions that cobots may be used to weld inside blocks of a structure - although very little information is provided on how the process actually works and how the cobots are trained. According to the brochure, “Arc Seam Tracking” and “Touch Sensing capability” seem to be one of the factors in operating the cobots.

[0009] Another prior art welding robot is the co-called Inrotech-Classic developed by the company Inrotech. It is intended for welding of webs and bulkheads in the shipbuilding industry, and comprises sensors that allow this mobile welding robot to identify structures and welds automatically. Although it is a bulky and heavy robot, it is made mobile by arranging it on a rail system, allowing it to move along an object for welding operations. However, due to its arrangement on the rail, the flexibility of the welding robot is limited to welding operations that are accessible by an articulated arm of said robot from its position on the rail. For example, this prior art welding robot cannot be used for welding operations inside cells that need to be accessed via a manhole, etc.

[0010] United States Patent US 9,937,577 B2 is acknowledged as further prior art, disclosing the use of identifiers, such as RFID tags, to allow a welding robot to select a welding sequence to drive a welding procedure with a workpiece.

[0011] It is an objective of the present disclosure to provide a workable solution to employ portable welding robots in the manufacturing of (semi-)unique three- dimensional structures. SUMMARY OF THE DISCLOSURE

[0012] Accordingly, the present disclosure relates to a method for manufacturing a (semi-)unique three-dimensional structure, wherein use is made of a base plate, a plurality of profiles and one or more verticals, a computer representation of the structure to be manufactured and one or more portable welding robots, the method comprising the steps of: based on the computer representation: generating a weld plan, the weld plan comprising a first set of welding actions for welding the profiles to the base plate, as well as a second set of welding actions for welding the verticals to the base plate and / or the profiles and form the three-dimensional structure;

[0013] - welding the profiles to the base plate according to the first set of welding actions, e.g. using an automated welding robot; placing the verticals on the base plate, in a direction transverse to the profiles, thereby forming a plurality of cells; for at least a portion of the plurality of cells: applying a cell identifier in the cell; by a human operator: carrying the portable welding robot into a cell, and placing said portable welding robot in a pre-determined position in said cell; providing the cell identifier to the portable welding robot; transferring the welding actions of the second set of welding actions that are associated with the cell identifier to the portable welding robot; and based on the welding actions associated with the cell identifier: from the pre-determined position inside said cell, said portable welding robot welding the verticals of the respective cell to the profiles and / or the base plate.

[0014] It is noted that the various steps of the method may be carried out in a different order than mentioned in the above. For example, the cell identifier may be applied before the profiles are welded on the base plate. As a further example, the welding actions may be transferred to the portable welding robot before it is placed in a cell. It is further noted that the method may not lead to a fully finished product. In accordance with the present disclosure, it may be sufficient to obtain a (semi-)unique three dimensional structure comprising a base plate, a plurality of profiles and one or more verticals.

[0015] Advantageously, when using a portable welding robot that can be carried by a human operator welding actions may be carried out by a welding robot even in areas of the structure-to-be-manufactured in which larger robots cannot carry out their work because they cannot reach the area where the weld is to be made. In this way, a portable welding robot offers significant advantages relative to a prior art mobile welding robot that may be placed on rails alongside a workpiece. More in particular, such a prior art mobile welding robot is limited to welding operations that are accessible by an articulated arm of said robot from its position on the rail. In contrast to such rail mounted mobile welding robots, the portable welding robot according to the invention can also be used for welding operations inside cells that would not be directly accessible by the articulated arm of a robot placed on a rail outside the cell. More in particular, the present invention allows the portable welding robot itself to be placed inside a cell, and even inside a cell that needs to be accessed via a manhole, etc.

[0016] According to a preferred embodiment of the method, the step of “by a human operator: carrying the portable welding robot into a cell, and placing said portable welding robot in a pre-determined position in said cell”, comprises said human operator carrying the portable welding robot through a manhole to enter the cell.

[0017] Advantageously, by generating in advance the set of welding actions required to weld the vertical(s) to the base plate and / or the profiles, the optimal position for the placement of the portable welding robot in each cell can be computed.

[0018] Advantageously, by generating in advance the set of welding actions required to weld the vertical(s) to the base plate and / or the profiles, all or a selected portion of the welding actions can be transferred to the portable welding robot, the portable welding robot carrying out the welding actions required at the position it is placed. Hence, no training is needed and the set of welding actions that may be carried out by the portable welding robot is virtually unlimited. This omits the need for extensive training of the portable welding robot and, more importantly, guarantees that the designer of the structure is unlimited in terms of manufacturability of the structure that is being designed. This in comparison to other solutions, where only a select set of options may be available for welding the vertical(s) to the base plate and / or the profiles, and where the designer of the structure is thus limited in his / her options for the design. This is deemed undesirable.

[0019] Advantageously, a robot carries out the welding tasks for welding the vertical(s) to the base plate and / or the profiles, with a human operator only being required to position the robot in the pre-determined position. This means that also less-skilled workers can be involved in the manufacture of the unique three-dimensional structure, which may decrease manufacturing time and / or manufacturing costs. On top of that, it is expected that a (skilled) operator working with one or more portable welding robots may ensure a larger number of welds than when the welding would be performed manually per a given time frame (e.g. per hour or per one day of work).

[0020] According to the present disclosure, a semi-unique three dimensional structure is manufactured. As used herein, semi-unique refers to a one-off or a small series of products. Typically, the maximum number of the same products produced with the method as disclosed herein is below ten and typically three at most. When more products are desired, more advanced automation techniques may be applied.

[0021] According to the present disclosure, a three-dimensional structure having profiles and verticals is manufactured. As used herein, both the profiles and the verticals may protrude in the vertical direction compared to the base plate. From a technical perspective, the profiles may act as skin stiffeners for the base plate, having a height of e.g. 5 cm - 70 cm. The verticals will typically be arranged transverse (e.g. perpendicular) to the profiles, and have a significantly larger height than the profiles. For example, the verticals may connect the base plate to another base plate, and act as ribs for the three-dimensional structure. The verticals are in principle unlimited in height, and will typically be at least the height of a person, e.g. at least 1.70 m. As long as the welding of the profiles to the base plate is concerned, gantry beams with welding robots mounted thereto can be used as the entire structure can be reached relatively easily in that stage of the manufacturing.

[0022] When the profiles are welded to the first base plate and the verticals are placed on the base plate, a welding robot attached to a gantry beam may no longer be able to reach the desired welding locations - especially not when the vertical is attached to a further base plate at its “top” side, so that a double-walled structure is formed. It is at this state of the manufacturing where the portable welding robot comes into play (as described in more detail in the below).

[0023] According to the present disclosure, a computer representation of the structure to be manufactured is available. Based on this computer representation, a weld plan is generated. For example, the RinasWeld program, proprietary software of the present applicant, can be used for this. It is however not excluded that the generation of a weld plan based on a computer representation of the structure to be welded is possible with other software packages.

[0024] According to the present disclosure, the weld plan comprises two sets of welding actions. One set for welding the profiles to the base plate, and a second set for welding the verticals to the base plate and / or the profiles. Welding of the profiles to the first base plate can, according to the present disclosure, be done in any way - e.g. using hand welding or automated welding robots. Several solutions are readily available for this purpose in the market - especially as long as the profiles can be accessed from the top. Once the profiles are mounted to the base plate and the verticals are placed on the base plate, cells or blocks are formed. Sticking to the nomenclature used in the art, an area of the base plate delimited by a pair of profiles and one or two verticals is called a cell or block. Cells or blocks of varying magnitude may be present on the base plate. The profiles may be of varying height, and may be of varying types - including I-beams, L-beams, T-beams, plates, Holland profiles and other known profiles. The profiles may have interruptions for such as rat holes, rounded edges etc.. The same goes for the verticals, which may also have interruptions such as rat holes, rounded edges, etc.. Moreover, the verticals may have man-holes to allow persons to access cells inside the outer layer of the three- dimensional structure.

[0025] According to the present disclosure, a portable welding robot is used to weld the verticals to the base plate and / or the profiles. For this purpose, the portable welding robot must know in which cell or block it is, and which welding actions are to be carried out in that cell. As such, a cell identifier is applied in each cell, the cell identifier being associated with a certain number of welding actions at a software level of the robot. Once the cell identifier is provided to the portable welding robot, it can carry out the required welding actions. It is highly advantageous if the portable welding robot has a dimension small enough for it to be carried, by the operator, through manholes arranged in verticals of the three-dimensional structure, to penetrate the structure and perform welding actions in the inner perimeter of the three-dimensional structure.

[0026] Depending on where the portable welding robot is positioned in the cell, it can reach more or fewer places where a welding action is to be carried out. As such, in generating the weld plan a position for the portable welding robot is determined as well. This position can physically be marked in the cell, or it can be provided to the operator in a different way (e.g. on a tablet in terms of relative position compared to a certain profile). The pre-determined position may be a dynamic position, with the start position inside the cell being marked or provided or stored in the robot. When the predetermined position is dynamic, the portable welding robot may move inside the cell, optionally on its own, to obtain the optimal welding position.

[0027] Once the portable welding robot is placed on the correct position and knows in which cell it is, it can carry out the welding actions and weld the vertical to the base plate and / or the profiles of the respective cells.

[0028] It should be noted that, whereas currently known solutions refer to the use of “cobots” to carry out welding actions, the core functionality of a “cobot”, the option to train the robot by a human operator, may not be required when the method according to the present disclosure is followed. Instead, the method as disclosed herein relies on the portable aspect of the welding robot, and transfers the set of welding actions from a data carrier to the portable welding robot - e.g. through a dedicated software interface. This ensures that a great number of different welding actions can be carried out by the portable welding robot - without the use for extensive training in advance.

[0029] It should be noted that, although the use of a portable welding robot has been disclosed in the above exclusively for welding verticals to a base plate and / or a profile, other accessories can of course be welded to components of a three-dimensional structure as well - including lifting eyes and the like.

[0030] In an embodiment of the present disclosure, the number of portable welding robots exceeds the number of human operators. For example, when one portable welding robot is carrying out the welding actions associated with the cell it is placed in, the operator may remove another portable welding robot from a cell in which it has carried out its desired welding actions and place it in a new cell. In this way, the use of human resources may be optimized. It may however be the case that some end users prohibit the use of more than one robot per human operator. Also in that case it is expected that with the method as presented herein construction of the (semi-)unique three dimensional structure is made more efficient. First of all, the human operator will fatigue less than when they are carrying out the welding tasks themselves, so that the margin of error is reduced. Second of all, the human operator may step outside of the cell where welding actions are being carried out by the portable welding robot (e.g. to a neighbouring cell with the portable welding robot in visual range) so that working conditions are more safe and sustainable to the human operator.

[0031] In an embodiment of the present disclosure, the pre-determined position in a respective cell is determined based on the range of motion of the portable welding robot. In particular, it may be desirable that the areas unreachable to the portable welding robot are minimized. To achieve this, in determining the weld plan an optimization may be carried out regarding said pre-determined position. For example, the pre-determined position may be physically visualized, i.e. marked, in each respective cell, e.g. using a paint marking, a printed marking or another visible marking. Alternatively, the pre-determined position may be listed on a cell basis in some kind of catalogue and be accessible to the human operator positioning the portable welding robot in the cells. For example, the list of pre-determined positions per cell may be on a paper catalogue, or in a digital catalogue, e.g. on an app accessible via a mobile device, such as a phone or tablet. Further alternatively, the portable welding robot could be intelligent enough to find its own pre-determined position after the cell identifier of the cell in which the robot is placed has been provided. For example, the robot could include some sensor which indicates the predetermined position in the cell, after which the robot can manoeuvre to the desired position based on the feedback from the sensor. It should explicitly be noted that the pre-determined position is not necessarily in the centre of the cell, but may be arranged off-centre I eccentrically with respect to the profiles forming the cell. It should further be explicitly noted that the best position to place the portable welding robot may be on the base plate, but alternatively also on one of the profiles that form the cell and / or on a vertical that forms the cell and / or on a further base plate that forms a roof of the cell.

[0032] In an embodiment of the present disclosure, the pre-determined position in a respective cell is determined based on the welding actions that are to be carried out by the portable welding robot. Like described in the above, an optimization algorithm may be run when generating the second set of welding actions to minimize the number of positions that cannot be reached by the portable welding robot - so that as little repositioning inside a cell as possible is needed. It should however not be excluded that for one or more of the cells, a portable robot must be placed on more than one position to reach each spot in which a weld is to be made. Depending on certain factors, it may be possible that it is accepted that the portable welding robot cannot carry out each weld by itself, and that some human involvement remains required.

[0033] In an embodiment of the present disclosure, wherein the three-dimensional structure is a part of a floating object, a bridge or another enclosed beam structure. However, besides these objects more unique structures can be designed; the method being applicable irrespective of the end product that is made therewith.

[0034] In an embodiment of the present disclosure, the weld plan is generated by computer software, the computer running the computer software being arranged in communication with the portable welding robot. As already hinted at in the above, to carry out the method as described herein it may be required to implement an additional interface layer for controlling the portable welding robot based on the generated weld plan - depending on whether such an interface already exists yes or no.

[0035] In an embodiment of the present disclosure, use is made of more than one portable welding robot. In such an embodiment, optionally each portable welding robot receives all welding actions of the second set of welding actions, e.g. in between the steps of generating the weld plan and placing the portable welding robot in a cell. This makes each portable welding robot ready to go irrespective of its location. Especially if the three-dimensional structure to be manufactured is relatively dense, wireless signals may not be received when the portable welding robot is positioned inside the structure. For that reason, it is convenient when all welding tasks are uploaded to the robots before they are deployed.

[0036] In an embodiment of the present disclosure, a welding action of the second set of welding actions is transferred to the portable welding robot after said cell identifier has been provided to the portable welding robot. This solution is for example possible when the welding robot is in wired or wireless connection with a database containing all welding actions. This solution may be favoured when capital expenditures are to be minimized and the portable welding robot is to be kept as simple as possible, with relatively low memory and operating requirements.

[0037] In an embodiment of the present disclosure, each cell has a unique cell identifier. In an embodiment, the welding actions to be carried out are unique for each cell. In that case, unique cell identifiers certainly are favoured. However, also when the welding actions to be carried out in two cells are the same, it may be advantageous to associate each cell with a unique identifier - if only because this makes tracking and logistics for the operator more convenient.

[0038] In an embodiment of the present disclosure, the cell identifier is manually entered into the portable welding robot by the human operator, or e.g. into an application, e.g. stored on a phone, tablet, controller or similar device that is associated with the portable welding robot. In an alternative embodiment, the portable welding robot may contain vision recognition software that is able to determine by itself in which cell the robot is positioned.

[0039] In an embodiment of the present disclosure, the portable welding robot is configured to generate a signal when it has carried out all welding actions in a respective cell. For example, this signal can be fed to a device associated with the operator, so that the operator may in return go to the cell where the portable robot was placed. Once there, the operator may visually inspect the welds and, if deemed of sufficient quality, relocate the portable welding robot. Relocation may be within the same cell to a second pre-determined position, or outside of the cell to a subsequent one. Based on the signals generated by the portable welding robot, progress of structure manufacturing may be effected, e.g. at a central location of the workshop.

[0040] In an embodiment of the present disclosure, the portable welding robot has a weight of at most 15 kg. This is deemed a weight that can be conveniently carried by one operator.

[0041] In an embodiment of the present disclosure, the step of generating a weld plan includes determining the position markers for each of the cells, taking into account the range of motion of the portable welding robot, wherein the weld plan is optimized by minimizing the number and / or total length of areas that are out of reach for the portable welding robot. BRIEF DESCRIPTION OF THE FIGURES

[0042] These and other aspects of the present disclosure are further elucidated in the below with reference to the attached figures. In these figures:

[0043] Figure 1 schematically shows a detailed overview of one cell C of an exemplary and non-limiting three-dimensional structure that may be manufactured with the method as disclosed herein;

[0044] Figure 2 schematically shows an overview of a row of cells C of an exemplary and non-limiting three-dimensional structure that may be manufactured with the method as disclosed herein;

[0045] Figure 3 schematically shows an isometric view of an exemplary and nonlimiting three-dimensional structure that may be manufactured with the method as disclosed herein;

[0046] Figure 4 schematically shows in an isometric view one exemplary and nonlimiting example of a portable welding robot.

[0047] DETAILED DESCRIPTION OF THE FIGURES

[0048] In the detailed description of the figures, Figures 1 , 2, 3 and 4 will be discussed in conjunction.

[0049] The method disclosed herein relates to the manufacturing of (semi-)unique three dimensional structures - and in particular three dimensional structures having a closed structure including a “bottom” plate and a “roof” plate. Such structures, when unique, have historically been manufactured mainly using skilled workers which weld together different components to a unique, bespoke, construction. In contrast to objects that are produced in series, automation for such structures is up to the present day highly limited, and skilled welders are employed to make these structures. Traditionally, a unique structure such as a cruise vessel or other like structures (including all sorts of unique floating structures for marine applications, but also all sorts of unique non-floating structures, e.g. bridges) are built up in layers, wherein reinforcing profiles are welded to base plates, after which the base plates are stacked and compartments are formed. The base plates are reinforced with profiles in one direction, and with higher vertical plates in another direction. For example, the profiles and verticals may be arranged perpendicular to each other, although another angular orientation is also possible. Some automation has been successfully implemented by several companies for the welding of the profiles to the base plate. For such (semi-)automated processes a gantry beam with a welding robot attached thereto is used. The base plate and profiles are accessible from the top, and the welding robot has sufficient room to carry out its work. When a three- dimensional structure having a “roof” I “ceiling” is to be made, there are two base plates to which the respective profiles can be welded with the gantry beam. To one base plate, the verticals can sometimes also already be welded with the gantry beam. When referring to Figure 3, it is in particular when the two base plates are to be welded to each other (after one base plate has been “flipped”) where the automated processes currently reach their limits. To obtain the structure shown in Figure 3, the verticals 3 attached to base plate 100 must be welded to base plate 1 and profiles 2 of the base plate 1 to have a rigid three-dimensional structure.

[0050] However, the welding robot attached to a gantry beam cannot reach the desired weld locations, so that presently a lot of hand welding is required at this stage of the manufacturing process.

[0051] The inventive concept underlying the present disclosure is that also in this last stage, automation by using portable welding robots can be applied - provided that the portable welding robot is pre-programmed to carry out a certain task, knows which task to fulfil and is positioned accurately.

[0052] To that end, according to the present disclosure all desired welding actions for obtaining the three-dimensional structure are predetermined using a weld plan. The weld plan is based on a computer representation of the structure to be manufactured. Known software can be used for this purpose, e.g. the commercially available RinasWeld program, proprietary to the present applicant. The weld plan distinguishes between two sets of welds - a first set that are to be carried out for welding the profiles 2 to the base plate 1 , and a second set of welding actions that are to be carried for welding the verticals 3 to the base plate 1 and / or to the profiles 2. Once all welding actions are carried out, the components of the three-dimensional structure are attached to each other and the structure is formed. Preferably, in generating the second set of welding actions, an optimal position for the welding robot 4 is already determined. In particular, by taking into account the precise types of welds that are to be carried out in a particular cell C of the structure and / or the range of motion possible for the portable welding robot 4, the weld plan generating software can optimize the optimal position for the welding robot 4 so that for example the welding robot 4 can be used most effectively - in the sense that it can weld as much of the desired welds as possible. Another parameter in finding the optimal position for the welding robot 4 to be placed may be the angle between the welding torch of the robot 4 and the sections to be welded. Only for a certain range of angles, a weld of sufficient quality can be guaranteed.

[0053] In that respect, it is noted that the optimal position may not always be in the middle of a cell.

[0054] In a first step, the profiles 2 are welded to the base plate 1 according to the first set of welding actions. For this step, various known solutions exist, and the disclosure is not limited in any kind to the type of solution chosen for this first step.

[0055] When a relatively uncomplicated three-dimensional structure is to be manufactured, e.g. the structures shown in Figures 1 and 2, the first step may constitute only the step of welding the profiles 2 to the base plate 1. However, when a more complicated structure is to be manufactured, in particular one with a first base plate 1 and a second base plate 100 topping the first base plate 1 , the first step may further include welding the profiles 200 associated with a second base plate 100 to the second base plate 100, as well as, optionally, welding the vertical sections 3 to the second base plate 100.

[0056] As should be clear from Figure 3, when the profiles 2 have been welded to the base plate 1 , rows 6 can be identified on the base plate 1. As it is known in advance what the structure 10 should look like in the end, as a computer representation is available, it is also already known at this stage where the verticals 3 will be arranged and, so, where the cells C will be positioned. After welding the profiles 2 to the base plate 1 , or before welding the profiles 2 to the base plate 1 , each cell may be marked with a cell identifier 7, such as shown in Figure 2. Preferably, the cell identifier 7 is a unique identifier for each cell C. In Figure 2, the cells C are marked A1 - A4 respectively.

[0057] Optionally, when the cells C are marked a position marker 8 can be applied. One example of a position marker 8 is indicated in cell A2 in Figure 2. The portable welding robot 4 is typically a robot weighing not more than 15 kg so that it can be carried (through a manhole) by a single human operator. The portable welding robot 4, of which an example is shown in Figure 4, may typically be mounted on a (not shown) base section having a predefined shape - e.g. rectangular. When the corners of the position where the base section of the robot 4 is to be placed are marked, the operator can conveniently place the robot 4 on the correct position in the cell C. As an alternative to physically marking the robot position, the operator may carry instructions regarding the desired position for the robot 4 in each cell - e.g. in the form of distances with respect to a certain reference. In any case, the optimal position for the robot is preferably determined while generating the weld plan, catalogued, and available to the operator that is to place the robot 4 in the cell C.

[0058] After the profiles 2 have been welded to the base plate 1 , the verticals 3 must be welded to the base plate 1 and / or the profiles 2. As shown in Figures 1 , 2 and 3, the verticals 3 are typically arranged transverse to the profiles 2, e.g. in a perpendicular orientation. Once the verticals 3 are positions, the cells C are physically formed - although it was of course previously known where the cells C would be located. The welding actions needed for this step have been generated already, as part of the weld plan, and are preferably grouped per cell C. As the area in which the welds are to be performed may no longer be accessible to an overhead welding gantry after the verticals 3 are placed - especially not when the verticals 3 are attached to another base plate 100 as in Figure 3 - portable welding robots 4 are used in this step.

[0059] The portable welding robots 4 are carried by (non-shown) human operators, who position them in the cells C. One can imagine that for the three-dimensional structure 10 shown in Figure 3 it is relatively easy to carry the robot 4 from one cell 4 to an adjacent one. However, when the three-dimensional structure to be manufactured is more of a closed box type, wherein roof and floor are parallel to each other, this may involve carrying the robot 4 through manholes and the like.

[0060] Once the portable welding robot 4 is placed in the cell C, in the predetermined position, the cell identifier 7 is to be provided to the robot 4. For example, the human operator may enter the cell identifier 7 into a software application associated with the robot 4. For example, the software application is stored on controller 5. Based on the cell identifier 7 / the cell C the robot 4 is positioned in, a certain number of welding actions has been pre-defined as part of the weld plan. These welding actions, for the particular cell C, are then transferred to the portable robot 4 and the welding actions needed in the cell C are carried out by the robot 4. In particular, with reference to Figure 1 , the welding actions carried out by the robot 4 may include welding the vertical 3 to the base plate 1 ; welding the vertical 3 to the profile 2 and welding a collar plate 32 to the vertical 3 and / or the profile 2 to close hole 31. As is visible from Figure 2, the precise type and number of welding actions to be carried out in each cell C may significantly differ. This is one of the reasons that the position at which the robot 4 is to be positioned may differ per cell C, and why the welding actions for the portable welding robot 4 are predetermined as part of the weld plan.

[0061] To transfer the welding actions for a particular cell C to the portable welding robot 4, preferably a communication interface is established between the computer generating the weld plan and the portable welding robot 4. Optionally, each welding robot 4 is pre-loaded with all welding actions and the welding actions for a particular cell C is activated once a certain cell identifier 7 is provided to the robot 4. Alternatively, the welding actions associated with a cell C are only provided to the portable welding robot 4 after the cell identifier 7 has been provided to the robot 4.

[0062] It is an option that the human operator manually overrides the welding actions determined for a particular cell C. In particular, when two components (e.g. a vertical 3 and a profile 2) do not align, e.g. due to manufacturing tolerances being higher than desired, and the gap in between the components is larger than it should be, automatic welding with a welding robot 4 may not result in the desired outcome. For example in such a case, the welding program for the cell C may be overridden. Optionally, in such cases a human operator is sent to the cell C after the robot 4 has finished its (adapted) program, to manually effect the desired weld.

[0063] As shown in Figure 3, multiple portable welding robots 4 may work on the three-dimensional structure at once. Each portable welding robot 4 may be operated by a single human operator, or one human operator may operate more than one portable welding robots 4 at the same time. As shown in Figure 3, each portable welding robot 4 may be associated with a dedicated controller 5. For example, the controller 5 may contain some of the intelligence of the robot 4 - to keep the robot 4 itself, which is to be carried by the human operator, as small as possible. In particular when a single human operator operates more than one portable welding robot 4, the robot 4 may be configured to generate a signal when it has carried out all welding actions in a respective cell. After the signal has reached the operator, he or she may go to the portable welding robot 4, optionally perform a visual inspection of the welding carried out by the robot 4, and place the robot 4 on its next position in accordance with the weld plan. The next position may be in the same cell C to carry out further welding actions that could not be carried out on the original position, or the next position may be in a further cell. When the next position for the robot 4 is in the same cell C, the robot 4 may optionally be raised on a platform, expand its reach to above the profile 2 (e.g. to weld a further bracket to the vertical 3 and the profile 2, at a position above the base plate 1).

[0064] When the portable welding robot 4 is configured to generate a signal once the welding actions in a certain cell C have been carried out, progress of the manufacturing status for the entire structure may be available at a system level.

[0065] The above described embodiment is intended only to illustrate the invention and not to limit in any way the scope of the invention. Accordingly, it should be understood that where features mentioned in the appended claims are followed by reference signs, such signs are included solely for the purpose of enhancing the intelligibility of the claims and are in no way limiting on the scope of the claims. The scope of protection is defined solely by the following claims.

Claims

CLAIMS1. A method for manufacturing a (semi-)unique three-dimensional structure, wherein use is made of a base plate, a plurality of profiles and one or more verticals, a computer representation of the structure to be manufactured and one or more welding robots, the method comprising the steps of:- based on the computer representation: generating a weld plan, the weld plan comprising a first set of welding actions for welding the profiles to the base plate, as well as a second set of welding actions for welding the verticals to the base plate and / or the profiles and form the three-dimensional structure;- welding the profiles to the base plate according to the first set of welding actions, e.g. using an automated welding robot;- placing the verticals on the base plate, in a direction transverse to the profiles, thereby forming a plurality of cells; characterized in that the welding robot is a portable welding robot, and the method further comprises the steps of:- for at least a portion of the plurality of cells: applying a cell identifier in the cell;- by a human operator: carrying the portable welding robot into a cell, and placing said portable welding robot in a pre-determined position in said cell;- providing the cell identifier to the portable welding robot;- transferring the welding actions of the second set of welding actions that are associated with the cell identifier to the portable welding robot; and- based on the welding actions associated with the cell identifier: from the predetermined position inside said cell, said portable welding robot welding the verticals of the respective cell to the profiles and / or the base plate.

2. The method according to claim 1 , wherein the number of portable welding robots exceeds the number of human operators.

3. The method according to any one of the preceding claims, wherein the predetermined position in a respective cell is determined based on the range of motion of the portable welding robot.

4. The method according to any one of the preceding claims, wherein the predetermined position in a respective cell is determined based on the welding actions that are to be carried out by the portable welding robot.

5. The method according to any one of the preceding claims, wherein the three- dimensional structure is a part of a floating object or a bridge.

6. The method according to any one of the preceding claims, wherein the weld plan is generated by computer software, the computer running the computer software being arranged in communication with the portable welding robot.

7. The method according to any one of the preceding claims, wherein use is made of more than one portable welding robot and wherein each portable welding robot receives all welding actions of the second set of welding actions, e.g. in between the steps of generating the weld plan and placing the portable welding robot in a cell.

8. The method according to any one of the preceding claims, wherein a welding action of the second set of welding actions is transferred to the portable welding robot after said cell identifier has been provided to the portable welding robot.

9. The method according to any one of the preceding claims, wherein each cell has a unique cell identifier.

10. The method according to any one of the preceding claims, wherein the cell identifier is manually entered into the portable welding robot by the human operator.

11. The method according to any one of the preceding claims, wherein the portable welding robot is configured to generate a signal when it has carried out all welding actions in a respective cell.

12. The method according to any one of the preceding claims, wherein the portable welding robot has a weight of at most 15 kg.

13. The method according to any one of the preceding claims, wherein the step of generating a weld plan includes determining the position markers for each of the cells, taking into account the range of motion of the portable welding robot, wherein the weld plan is optimized by minimizing the number and / or total length of areas that are out of reach for the portable welding robot.

14. The method according to any of the preceding claims, wherein the step of:- by a human operator: carrying the portable welding robot into a cell, and placing said portable welding robot in a pre-determined position in said cell, comprises said human operator carrying the portable welding robot through a manhole to enter the cell.

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