Monitoring of composite part manufacture

Abstract

A method and system for monitoring a manufacturing process for a composite part and a method of controlling the manufacturing process are disclosed. The composite part is made from layers of structural elements (220a, 220b, 220c) according to a lay-up definition, and the lay-up definition includes predefined relationships between respective sets of at least first, second and third structural elements. Placement of the second structural element of each set is dependent on placement of the first structural element of the set, but placement of at least the third structural element of the set is not dependent on placement of the first structural element. A plurality of structural elements (220a, 220b, 220c) are eligible for placement at the same time. The method includes: determining a set of structural elements previously placed; determining an eligible set of structural elements based on the predefined relationships; and outputting an indication of the eligible set of structural elements.

Description

[0001] 175001 / 01

[0002] Monitoring of Composite Part Manufacture

[0003] This invention relates to the monitoring of the manufacture of parts made from composite materials, such as fibre-reinforced composite materials.

[0004] It is known in the art that manufacture of parts made from composite material includes the lay-up of multiple sheets of ply typically within a mould, to shape and provide structural characteristics to the composite part. The sheets of ply are commonly sheets of woven or unidirectional fibres, such as fibre-glass or carbon- fibres. These can be pre-soaked in a resin material, or once placed into a mould, the resin material can be infused through the layers of ply to create a fibre- reinforced composite part. Techniques such as these are widely used in the manufacture of large-scale pieces, for example wind turbine blades, aircraft structures or parts for ships. In other applications the resin is pre-impregnated with the fibres before oven or autoclave curing.

[0005] When manufacturing small parts of composite material, each sheet of ply may be identical or easily distinguishable from each other, and there may be only a small number of sheets of ply in the whole part, making the layering of all the sheets of ply into a mould relatively simple. However, for large-scale parts, especially those with complex fibre directions and shape requirements, each sheet of ply must be laid into the mould in specific locations and in a specific stacking order to build up the required shape and carry the structural loads. Sheets of ply for different locations within the part may also be of different shapes and sizes.

[0006] The placement of each sheet of ply within a part is typically defined by a specialist during the design process for such composite parts. When designing large scale parts, different sections of the part are designed to have specific structural characteristics depending on the use of the part. Within such parts, it is common to have multiple sheets of ply in a single layer, each of which has to be individually positioned and checked relative to the design when placed. To aid with this process the design engineer will normally produce a list of the structural elements in a specific order, which is followed in a linear manner, placing each sheet of ply when indicated by the specified order. This means that the production of large parts from composite materials can be a laborious process requiring a highly skilled and experienced operatives. Across a single large part, multiple teams of operatives may progress through the placement of each sheet of ply in the part, but will each need to adhere to the instructions which determine the order for the sheets of ply to be laid and therefore will often need to wait until one team has finished a specific section before they can proceed further. The Applicant has recognised that this can be inefficient and can lead to confusion and errors as the different operatives follow their own method for speeding up the process which can lead to plies being placed out of order and / or in the wrong position.

[0007] According to a first aspect of the present invention there is provided a method of monitoring a process for manufacturing a composite part, the composite part comprising a plurality of layers of structural elements according to a lay-up definition, wherein the lay-up definition comprises a plurality of predefined relationships each between respective sets of at least first, second and third structural elements of said structural elements, whereby placement of the second structural element of each set is dependent on placement of the first structural element of the set, but placement of at least the third structural element of the set is not dependent on placement of the first structural element, such that a plurality of structural elements are eligible for placement at the same time during the manufacturing process; wherein the method comprises: determining a set of structural elements previously placed; determining an eligible set of structural elements from the previously placed set, wherein the eligible set of structural elements comprises structural elements which are eligible for placement in the lay-up definition based on the predefined relationships; and outputting an indication of the eligible set of structural elements.

[0008] When viewed from a further aspect the invention provides a computer software product and a non-transitory computer-readable medium comprising instructions that, when executed by a processor, cause the processor to carry out the method outlined above. According to another aspect of the present invention, there is provided a system for monitoring a process for manufacturing for monitoring a composite part, the composite part comprising a plurality of layers of structural elements according to a lay-up definition, wherein the lay-up definition comprises a plurality of predefined relationships each between respective sets of at least first, second and third structural elements of said structural elements, whereby placement of the second structural element of each set is dependent on placement of the first structural element of the set, but placement of at least the third structural element of the set is not dependent on placement of the first structural element, such that a plurality of structural elements are eligible for placement at the same time during the manufacturing process; wherein the system is configured to: determine a set of structural elements previously placed; determine an eligible set of structural elements from the previously placed set, wherein the eligible set of structural elements comprises structural elements which are eligible for placement in the lay-up definition based on the predefined relationships; and output an indication of the eligible set of structural elements.

[0009] According to a third aspect of the present invention, there is provided a method of controlling a manufacturing process for manufacturing a composite part, the composite part comprising a plurality of layers of structural elements according to a lay-up definition, wherein the lay-up definition comprises a plurality of predefined relationships each between respective sets of at least first, second and third structural elements of said structural elements, whereby placement of the second structural element of each set is dependent on placement of the first structural element of the set, but placement of at least the third structural element of the set is not dependent on placement of the first structural element, such that a plurality of structural elements are eligible for placement at the same time during the manufacturing process; wherein the method comprises: determining a set of structural elements previously placed; determining an eligible set of structural elements from the previously placed set, wherein the eligible set of structural elements comprises structural elements which are eligible for placement in the lay-up definition based on the predefined relationships; and outputting an indication of the eligible set of structural elements; placing structural elements from the indicated eligible sets of structural elements to form the composite part.

[0010] Thus, it will be seen by those skilled in the art that, in accordance with the present invention, the placement of structural elements during a lay-up process can be monitored and predefined relationships used to provide information as to which structural elements are eligible for placement next in the lay-up process. The Applicant has appreciated that by predefining the relationships between structural elements within a composite part, it is possible to exploit opportunities to place structural elements which don’t depend on each other whilst still ensuring accurate information is provided about which elements can be placed at any given time. This allows for more efficient placement of structural elements during the lay-up process by indicating all eligible structural elements based on the current state of manufacture so multiple elements may be placed in the lay-up at the same time e.g. by different teams where they are not dependent on one another.

[0011] After any structural element is placed, the newly eligible structural elements can be determined, so that no structural element is placed unless all required elements below it are already placed in the lay-up. By monitoring the lay-up process in accordance with the invention to ensure that structural elements are moved into position respecting the predefined relationships, correct layer structure can be achieved, avoiding the risk of failure of the parts made from incorrectly laid elements, whilst reducing the time taken to produce the part, as it becomes possible for multiple structural elements to be placed at the same time, but in different locations. For example, in a wind turbine blade, structural elements may be able to be placed in the root and tip of the blade at the same time if their placement is not interdependent.

[0012] Whilst parts made from an inconsistent lay-up process may be detected in product testing, by providing accurate and up-to date information during the manufacturing process, errors can be eliminated earlier, and overall product wastage can also be reduced. Reduction in possible variation between different parts in turn also helps improve overall product quality. By impacting the accuracy of the lay-up process, and by allowing more structural elements to be placed at the same time, the whole manufacturing process can be made more efficient. It can also relax the requirements for those operating the process to be highly trained.

[0013] It will be appreciated that a structural element may be any element used in the production of a part of composite material (i.e. a composite part). Typically, such structural elements would not perse have any structural rigidity. For example, the structural elements may be sheets of ply (e.g. a woven fibre sheet). Structural elements may be homogenous materials, metallic meshes or even core materials. In the manufacture of some parts, the lay-up process includes layering of elements already formed from multiple sheets of ply instead of, or in addition to the lay-up of single sheets of ply. Therefore, in some embodiments the structural element may be a prefabricated element (e.g. one made from multiple sheets of ply previously cured together) which may have some structural rigidity. In the production of a composite part a variety of different structural elements may be used. It is not essential for a given structural element to perform a critical structural function in the finished composite part. For example, it could provide useful thermal, electrical or even aesthetic properties.

[0014] The composite part may be any part made from a combination of different materials or layers. It will be appreciated that the composite part will typically comprise other elements or materials in addition to the structural elements (e.g. resin or powder) as will be known to those skilled in the art.

[0015] During manufacture, each structural element is placed so as to form the whole part as will be known by those skilled in the art. This placement may be into a mould, or placement may be relative to other parts (for example previously made composite parts, or other non-composite components. Each structural element may be a different shape and size, or some structural elements may be the same within the whole part. The whole part is typically designed with each structural element taking up a specific volume, with a certain position and orientation within the mould to create the whole composite part. The part will typically have a number of layers of structural elements which overlap each other in specific combinations as determined by the requirements for the part, whether structural or otherwise. Such parts are routinely designed using 3D computer models, which are then translated into manufacturing instructions by skilled engineers, however they may also be designed using scale physical models or other design documents.

[0016] In current arrangements manufacturing instructions are produced in the form of a linear order for the structural elements to be placed to create the part. The Applicant has appreciated that instead of the linear order being provided to the those laying up the structural elements, it is instead desirable to determine structural elements eligible for placement during manufacture by taking direct account of the predefined relationships between one structural element and another structural element.

[0017] The predetermined relationships between the sets of structural elements may be based on at least one of the volume of the structural elements, the perimeter of the structural elements, and / or the area of at least one surface of the structural elements. The predetermined relationships between structural elements can also include the location within the lay-up area where a structural element should be placed within the composite part.

[0018] It will be appreciated by the skilled person that correct placement of a structural element is one which reflects the predefined relationship which includes that structural element. The correct placement will typically be the placement which matches the designed structure of the part, for example that matches the 3D model. In the composite part, most structural elements in the lay-up will need to be laid on top of at least one other structural element, i.e. the placement of a structural element is dependent on the placement of another structural element. The exception for this will be the structural element (or structural elements) which is / are the first to be laid, e.g. in the bottom of a mould.

[0019] As mentioned above the Applicant has recognised that the structure of composite parts is often very complex, so there may at any given stage be a plurality of structural elements which can be placed on top of the set of structural elements which have already been placed, for example one may be able to be placed near the root of a turbine blade, and one may be able to be placed near the tip. In this way a plurality of structural elements are eligible for placement at the same time during the lay-up process. Looked at another way the manufacturing process may comprise a plurality of structural element dependency branches, wherein the placement of a first structural element in a first branch is not dependent on the placement of a second structural element in a second branch. The predetermined relationships between structural elements can therefore give rise to branches within the lay-up process, where multiple phases of the lay-up process may take place in each branch independently.

[0020] It will be appreciated that the steps of the method will typically be repeated many times during the manufacture in order to allow the lay-up process of the whole part to be monitored, and updated.

[0021] The previously placed set of structural elements may be one, or more, of the structural elements previously placed in the process, but not necessarily all of them. For example, the previously placed set of structural elements may include only structural elements previously placed which are not yet entirely covered by one or more other structural elements or may include only those previously placed structural elements which still have other structural elements directly dependent on them - i.e. those on branches which have not yet terminated.

[0022] The eligible set of structural elements may at any point in the manufacturing be one or more structural elements. Thus in some phases of the lay-up there may be only one structural element eligible for placement (for example when a structural element ends two branches, by overlapping with one structural element in the first branch and one structural element in the second branch). However in other phases there may be a plurality of structural elements which are eligible for placement in a phase (for example when a first structural element is eligible for placement in the first branch and a second structural element is eligible for placement in the second branch).

[0023] Once a structural element has been placed it will then belong to the set of previously placed structural elements. Determining the previously placed set of structural elements could be carried out in any suitable way. In a set of embodiments it is carried out deductively based on the previously indicated set of eligible structural elements and an input confirming that one or more of this set has been placed. In a set of embodiments such input is provided from a user interface. This allows a user to indicate that a structural element has been placed and / or indicating a location where the structural element has been placed. By providing a user input, a suitably skilled user can ensure proper progression of each stage during manufacture, enabling the next structural element(s) to be placed at the appropriate time.

[0024] Additionally or alternatively in a set of embodiments the determination is made independently - e.g. by a monitoring system which monitors the placement of structural elements. By monitoring the lay-up of structural elements, it can be ensured that only those structural elements actually placed are identified in the previously placed set, further improving the accuracy of the lay-up process by helping to ensure structural elements are not indicated as eligible for placement prematurely.

[0025] In a set of embodiments monitoring of placement of structural elements comprises visual monitoring using one or more image sensors. Image sensors may be configured to monitor a lay-up area. Image data may be acquired from a single sensor or from multiple sensors simultaneously. The image sensor(s) may be cameras. The image sensor(s) may be configured to monitor the whole of the layup area (e.g. the whole of a mould) or they may only need to be able to image the part of the mould into which structural elements will be laid (i.e. the lay-up area). Where multiple image sensors are provided they may each cover the whole of the monitored area or all or some may cover only part of the monitored area. Multiple image sensors located to view the lay-up area from different angles may be advantageous if one of the image sensors is blocked by other equipment, as another sensor can provide the data. - e.g. with one or more cameras.

[0026] Whilst in some embodiments it may be assumed that if a structural element is included in the set of previously placed element, it has been placed in the correct location (e.g. because a user has confirmed as such), in other embodiments determining the set of previously placed structural elements includes determining whether each structural element has been correctly placed - i.e. placed in the correct location and / or orientation. A subsequent structural element may only be eligible for placement if the structural elements in the previously placed set on which the structural element is dependent, based on the predetermined relationship, have been correctly placed. By confirming that those structural elements previously placed in the lay-up are correctly placed before an element dependent on it is placed, errors in the overall process can be minimised, further improving the efficiency of the lay-up process.

[0027] There are a variety of ways in which the placement of a structural element can be identified as correct. The image sensor(s) may provide data relating to the location of structural elements previously placed in the lay-up. The location of the structural elements previously placed in the lay-up may include data relating to at least one of: the top surface area of placed structural elements; and / or the perimeter of placed structural elements; and / or the volume of placed structural elements, the position of the placed structural element relative to other placed structural elements; the position of the placed structural elements relative to the geometry of the whole part (e.g. relative to a mould). The location of a placed structural element therefore indicates where structural elements are placed relative to each other so as to provide information needed to determine the eligible set.

[0028] In some embodiments, each of the structural elements has an identifier. In a subset of such embodiments each identifier comprises a plurality of symbols varying by shape and at least one of position and orientation on respective structural elements. Monitoring the placement of structural elements may include monitoring the expected locations for an identifier. The location of a structural element may be confirmed by the location of a correct identifier.

[0029] When each structural element has an identifier; it may be possible to determine from the image data whether the structural element in the mould is correct by detecting an identifier on the structural element from the image data, and comparing the detected identifier to an expected identifier from the set of eligible structural elements. Using specific identifiers may simplify the requirements of the image sensor(s) whilst maintaining the ability to accurately identify correct placement of structural elements within the lay-up.

[0030] The number of symbols in a given identifier can be chosen depending on the specific application, taking into account particularly the size of the structural elements and how many are required to manufacture a particular part. As will be appreciated, there may be good reasons to employ more symbols than is strictly required to differentiate the structural elements for a given part - e.g. to provide error detection or robustness against visual occlusion. It is not essential for each identifier in a predetermined set to have the same number of symbols but this is convenient,

[0031] The shapes used for the symbols are not essential but ideally they are simple and well defined with a small number of edges. For example, simple geometric shapes (e.g. squares, rectangles, circles, triangles) and familiar typographic symbols (e.g. +, x, <,>,!) or simple combinations thereof are used.

[0032] As the structure of the composite part is established before manufacturing begins, the respective set of identifiers used on the structural elements is also predetermined. This significantly simplifies the task of performing machine visual identification and in a set of embodiments the system may be arranged only to look for identifiers from the predetermined set of identifiers. An expected identifier may be determined from the eligible set of structural elements.

[0033] By outputting an indication of the eligible set of structural elements in accordance with the invention, those involved in the manufacturing process are able to have up to date information regarding which structural elements are eligible for placement. The indication of the eligible set of structural elements may include information about the identifier(s) relating to the eligible set of structural elements. The indication could be provided on a user interface such as a display screen (e.g. on a computer or mobile terminal) but in some (potentially overlapping) embodiments at least one projector projects an image relating to the eligible set of structural elements. Whilst other projector types could be used, conveniently the projector(s) is / are laser projector(s). The projected image may comprise an outline of each of the eligible set of structural elements and / or the identifier for each of the eligible set of structural elements. The projected images can thus be used to help place the correct structural element, improving the efficiency of the lay-up process.

[0034] Structural elements may be moved into place as a flat piece, for example via crane. However, in some manufacturing environments, or for some structural elements (especially those which are large), a structural element may be stored in a rolled or folded configuration, and then rolled out or unfolded into place in the desired location. In some embodiments the indication of the eligible set may include information regarding where in the lay-up area a rolled or folded structural element should be placed. This information may include the direction in which the structural element should be unrolled or unfolded. In some embodiments the projected image may include an indication providing this information.

[0035] It has been appreciated that when rolled of folded structural elements are placed in the lay-up, the complete placement of the structural element may take longer than simply placing a flat structural element, e.g. depending on the speed of unrolling / unfolding and the size of the structural element being placed. Furthermore it has been appreciated that where a subsequent structural element is dependent on a structural element which is initially rolled or folded, the overlap may be only partial and may affect only the first portion of the structural element to be unrolled or unfolded such that the subsequent structural element may become eligible for placement after a rolled or folded structural element has only partially been unrolled or unfolded.

[0036] In a set of embodiments therefore the predefined relationships comprise at least one predefined partial relationship between a set of at least fourth and fifth structural elements of said structural elements, whereby placement of the fifth structural element is dependent on partial placement of the fourth structural element and wherein the eligible set of structural elements further comprises the fifth structural element being eligible for placement in the lay-up definition based on the predefined partial relationship. The eligible set of structural elements may therefore include structural elements eligible for placement in the lay-up based on the predefined partial relationship between a structural element and another structural element which is only partially placed. It is therefore possible to begin the placement of a structural element dependent on another structural element when the overlapping section of the lower structural element has been unrolled or unfolded, instead of needing to wait until the whole of the lower structural element is placed. This can further help reduce the overall time taken for the whole lay-up process.

[0037] In a further set of such embodiments a plurality of subsequent structural elements are dependent on a structural element which is initially rolled or folded, the respective overlaps affecting respective portions of the structural element to be unrolled or unfolded such that the subsequent structural elements become eligible for placement after the rolled or folded structural element has been unrolled or unfolded to reveal the respective portions thereof.

[0038] Similarly, a rolled or folded structural element may be dependent on a plurality of previously placed structural elements. The rolled or folded structural element may have a first portion dependent on a first previously placed structural element and a second portion dependent on a second previously placed structural element, the first portion being an earlier part of the rolled structural element to be unrolled or unfolded than the second portion. In a set of embodiments therefore, the predefined relationships comprise at least one predefined multiple partial relationship between a set of at least sixth, seventh and eighth structural elements of said structural elements, whereby placement of a first portion of the eighth structural element is dependent on placement of the sixth structural element, placement of the second portion of the eighth structural element is dependent on placement of the seventh structural element and wherein the eligible set of structural elements further comprises the first and second portions of the eighth structural element respectively being eligible for placement in the lay-up definition based on the predefined multiple partial relationship.

[0039] This allows the first portion of a structural element (the eighth) to be placed (when the sixth element has been placed) and then the second portion of the eighth structural element may be unrolled or unfolded when the previously placed set of structural elements includes the seventh structural element on which the second portion is dependent. In this way waiting times before structural elements can be placed can be reduced, further increasing the efficiency of the lay up process. It will be appreciated that the terms rolled and unrolled can encompass both structural elements rolled around a roller, and structural elements which are simply rolled up. Similarly folded structural elements could be folded around a former or simply folded on themselves.

[0040] As discussed above, the predetermined relationships between the structural elements within the composite part may be determined in a number of ways. The designers of large composite parts may specify very large structural elements across some layers of the composite part, however manufacturing considerations may make such large structural elements impractical to produce or handle. In this situation the very large structural element is typically replaced with a plurality of structural elements which overlap a small amount at common borders instead. The plurality of structural elements together act in the same way as a single, very large structural element Whilst these elements have overlapping edges, they are not dependent on each other as a structural requirement in the same way as the dependent structural elements in the foregoing description. These structural elements can be defined as a group. Therefore, in a set of embodiments, the composite part comprises at least one group, wherein the group comprises a plurality of structural elements which have at least one mutually overlapping edge in the lay-up definition but where placement of any of the plurality of structural elements is not dependent on the previous placement of any other structural element in the group. The structural elements in the group can therefore become eligible for placement in different orders as determined by their predefined relationships to structural elements not in the group. It will be appreciated that structural elements in a group can be effectively treated as individual structural elements with predefined relationships with structural elements not in the group.

[0041] This allows for the lay-up process to progress more efficiently, instead of waiting for all structural elements in the group to be eligible at the same time, or in a specific order.

[0042] The skilled person will appreciate that the invention may be used in numerous applications, it is of particular benefit in large scale manufacture where multiple operators work on the lay-up process at the same time. The invention may be particularly useful in applications where increased efficiency in producing parts is important, especially when quality control between parts is also important, as variation in element orientation or presence within a part can cause significant problems when the whole engineered item is constructed. In some embodiments, the composite parts are wind turbine blades. The dimensions, and fibre orientation and distribution and thickness within a wind turbine blade is heavily engineered to ensure optimum transfer of energy through the rotation of the blades, whilst also ensuring that heavy winds do not cause damage to the whole wind turbine. It is therefore an application where part manufacture should be advantageously monitored. Similarly, the performance of parts in ships and aircraft is also critical.

[0043] Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0044] Figure 1 shows a manufacturing environment employing an embodiment of the present invention;

[0045] Figure 2 is a schematic diagram of the manufacturing monitoring system illustrated in Figure 1 ;

[0046] Figure 3 shows an example lay-up process from a top down perspective used in embodiments of the present invention;

[0047] Figure 4 shows a representation of predetermined relationships for the layup process of Figure 3;

[0048] Figures 5A, 5B, 5C and 5D show perspective views of phases of the lay-up process in accordance with another embodiment;

[0049] Figure 6 shows a perspective view of a phase of the lay-up process in accordance with further embodiment;

[0050] Figure 7 shows an example lay-up process from a top down perspective used in another embodiment of the present invention;

[0051] Figure 8 shows a representation of predetermined relationships for the layup process of Figure 7; and

[0052] Figure 9 is a flow diagram showing method steps for monitoring manufacture of composite parts according to embodiments of the present invention.

[0053] Figure 1 is a simplified diagram of the key parts of a manufacturing environment 200 for making parts of fibre reinforced composite material, during a lay-up process. Figure 1 shows sheets of ply 220a, 220b (i.e. structural elements) placed into a mould 210, and another sheet of ply 220c being lowered into the mould 210. A crane 250 is shown moving the sheet of ply 220c into the mould 210 from above. Each of the sheets of ply 220a, 220b, 220c has a respective identifier 224a, 224b, 224c comprising symbols in specific positions and orientations as will be described in more detail below. Above the crane 250 (e.g. attached to a ceiling or suspended from struts above the mould 210) are cameras 122 and projectors 130 which are part of a monitoring and indication system, as discussed below with reference to Figure 4.

[0054] In this embodiment, the part being manufactured is a wind turbine blade, although a person skilled in the art will appreciate that the manufacturing environment for other large-scale composite parts will be similar, and that the invention can be equally applied to various manufacturing environments.

[0055] The turbine blade is made from composite material that is manufactured by layering sheets of ply 220 into the mould 210 before the mould is filled with resin and the whole part is cured. This produces the specific shape required, with required complex fibre-orientation. The mould 210 may be around 90m in length, and the cameras 122 and projectors 130 are located at a distance of around 10m above the mould 210. Whilst only five cameras 122 are shown in this diagram for simplicity, to cover the area of the mould in practice many more (e.g. thirty) cameras 122 are evenly distributed above the mould 210. This diagram only shows a single crane 250 for simplicity, but it will be appreciated that multiple cranes, or other mechanical lifting means, may be used, and sheets of ply may also be placed in the lay-up using rollers or other known means.

[0056] Inside the mould 210 is a lay-up area into which sheets of ply 220 are layered. In a typical mould 210 of this size, the completed part will include two or three hundred individual sheets of ply, and each must be carefully moved into place. Of the two to three hundred separate sheets of ply 220, many will have the same profile (i.e. size and shape). For this exemplary turbine blade, fifteen different profiles of sheet of ply 220 are used, so there is a predefined set of fifteen different identifiers which uniquely identify each of the fifteen sheets of ply 220.

[0057] Depending on the required final shape and structural characteristics, some layers include multiple sheets of ply in different, separate locations as shown with sheets of ply 220a, 220b, and 220c in Figure 1 , whilst other layers may require only single sheets or sheets which overlap. Each sheet of ply 220 is specifically placed in the lay-up in a predetermined location but also in accordance with a predetermined relationship to other sheets of ply which have already been placed so as to respect the required order of the sheets in the stack specified in the design of the part. This provides the final part with a specific density profile which is based on where and in which order each sheet of ply is placed within the structure of the part. The manner in which sheets of ply 220 are placed into a mould 210 will vary depending on the size and type of part being produced and the design characteristics which have been specified, as will be appreciated by those skilled in the art.

[0058] The cameras 122 are located above the mould 210 to be able to view the area where the lay-up takes place, i.e. to view the inside of the mould 210. This allows the cameras to image each sheet of ply 220 as they are being laid in the mould 210 so it is possible to compile data relating to the locations of those sheets of ply 220 which have been placed in the lay-up.

[0059] In the embodiment of Figure 1 , each sheet of ply 220a, 220b, 220c has a respective identifier 224a, 224b, 224c which is used to identify the sheet of ply 220a, 220b, 220c where the combination of the shape, position and orientation of symbol(s) which create the identifiers 224a, 224b and 224c uniquely identify each sheet of ply 220a, 220b, 220c as having one of the specified sheet profiles used in this particular part. In general, within each manufacturing environment each sheet of ply 220 with a different profile is assigned a different identifier, which may be made up of one or more symbols (i.e. the symbols varying their positions and / or orientations and / or shapes for each different shape / size sheet of ply). The cameras 122 are located to produce image data which is processed in an imaging unit to identify the locations of placed sheets of ply 220a, 220b to create input data for a monitoring unit as discussed below with reference to Figure 3. Generally, a sheet of ply is identified as previously placed after it has been determined to have been placed in the correct location in the mould 210. Correct placement of a sheet of ply 220 can be determined by comparing the outline and / or identifier 224 against the sheets of ply 220 currently eligible for placement, i.e. against the expected locations for eligible sheets of ply within the mould 210. The monitoring unit can detect positions of the symbols of the identifiers 224a, 224b, 224c relative to the individual sheets of ply 220a, 220b, 220c themselves but also their positions relative to the mould 210. For sheets of ply 220 which are symmetric about one or more axes, the placement of the symbols within the identifier 224 can also be symmetric about the same axes, so that the sheet of ply 220 can be recognised as correct in in any correct orientation. It will be appreciated that whilst any shape of symbol could be used, the symbols should be easily identifiable from one another without the need for a high-resolution camera. The symbols are integrated with each sheet of ply 220 during the production of the individual sheets of ply 220 to ensure consistency of placement between production runs.

[0060] The projectors 130 are located so as to project images of identifiers 224 into the mould 210. The projectors 130 can project images of identifiers 224 into the mould 210 to indicate where a sheet of ply 220 should be placed. The projectors 130 are therefore placed above the mould 210 to be able to project images to any location within the mould 210 where an identifier 224 on any sheet of ply 210 during the layup procedure should be located when placed correctly. The projectors could also, or instead, project an outline of the eligible sheets.

[0061] Whilst in the example of Figure 1 each sheet of ply 220 is identifiable via an identifier 224, it will be appreciated that other imaging techniques may be used to determine the identify of a sheet of ply, and its location when placed. Equally, the identity and locations of sheets of ply 220 when placed in the mould may be determined by one or more other techniques, such as image recognition, QR codes or simply confirmation by a trained operator working in the manufacturing environment.

[0062] Figure 2 is a schematic diagram of the manufacturing monitoring system 100 employed in Figure 1. The monitoring system 100 includes an imaging unit 120 which has several image sensors in the form of the cameras 122 as shown in Figure 1 , which monitor the placement of sheets of ply, producing image data. The imaging unit 120 then processes the image data to determine which sheets of ply have been placed (correctly) in the lay-up. The imaging unit 120 then sends data to the monitoring unit 110 relating to the location of sheets of ply that have been placed into the lay-up. Data relating to the location of sheets of ply placed in the layup can also be provided to the monitoring unit 110 from the user interface 140. The monitoring unit 110 determines which sheets of ply are next eligible to be placed in the lay-up as will be further described below with reference to Figures 3 and 4.

[0063] The monitoring unit 110 provides outputs to the projector(s) 130 and the user interface 140 to provide indications as to which sheets of ply are eligible for placement in the lay-up based. The projector(s) 130 project images of the identifiers for eligible sheets of ply and outlines of the sheets of ply as will be described in more detail below with reference to Figures 5A to 5D. The monitoring unit 110 is computer implemented. The monitoring unit 110 includes a processor and a memory comprising computer-executable instructions that, when executed by the processor, cause the processor to perform the various steps outlined below. The monitoring unit could be provided on-site or off-site - e.g. as a cloud server. It could be a single computer or distributed across multiple processing resources.

[0064] The monitoring unit 110 has stored information in its memory regarding where each sheet of ply should be placed, and the predefined relationships between sheets of ply within a composite part, which is determined by whether the placement of a sheet of ply is dependent on the placement of any other sheets of ply which it overlaps. The relationships between sheets of ply in the part will be described in more detail below with reference to Figures 3 and 4.

[0065] When a part made of fibre-reinforced composite material is to be manufactured, details of the part are provided to the monitoring unit 110 - e.g. by downloading from a network (not shown). The details of the job include the relationships between sheets of ply, defined by the structure of the part. After the job is initiated by the operator, the monitoring unit 110 provides information about which sheet of should be initially placed in the lay-up to the operator via the user interface 140 and / or via information projected into the lay-up area by the projector(s) 130. The operator can then select the correct sheet of ply from a shelving area and move it into position in the mould.

[0066] Figure 3 shows, highly schematically, a series of layers in the lay-up process represented as top down views of sheets of ply A-J relative to the mould 210. Layer 1 includes sheets of ply A, B and C as previously represented in Figure 1. These sheets of ply A, B and C are the bottom layer in the mould 210 and they do not touch each other, therefore their placement does not depend on the placement of any previous sheets of ply. They can therefore be placed in the mould 210 independently of each other - potentially by multiple individuals or teams working in parallel.

[0067] The sheets of ply D-J placed in layers 2-5 all sit on top of the sheets of ply A, B and C in the bottom layer, so are dependent on the placement of at least one of the previous plies. In layer 2, sheet of ply D is located in the “root” of the blade, and only overlaps with ply A in the previous layer. However, sheet of ply E overlaps two plies, B and C in the layer underneath, so ply E is dependent on plies B and C. Moving on to layer 3, ply F is placed directly on top of ply D from layer 2, but ply G only overlaps with ply C from layer 1. As ply G is not dependent on any ply in layer 2, and only dependent on ply C in layer 1 , as soon as ply C has been placed it becomes eligible for placement, without needing to wait for layer 2 to be placed. This means that a team working at the tip of the blade can place sheet G whilst the team at the root of the blade are placing sheets D and E of layer 2. In layer 4, the single ply H overlaps with one ply F from layer 3, and one ply E from layer 2. This therefore only becomes eligible for placement once plies E and F have been placed. Both plies I and J in layer 5 overlap with sheet of ply H in layer 4, so are dependent on the previous placement of that sheet of ply. Ply J is of course also dependent in the previous placement of ply G, .

[0068] By evaluating the part as a whole, it is possible to determine whether the placement of any ply is dependent on the placement of any previous ply, which is then used to determine relationships between plies within the part. In this way, although shown in Fig. 3 for the purpose of illustration, the idea of individual layers of ply is in fact no longer required. The predetermined relationships take into account all those previously placed sheets of ply required to be placed ahead of another sheet of ply. By taking this approach, the lay-up process can be made significantly more efficient since plies are indicated as eligible for placement as soon as those on which they depend have been placed, which allows for a greater degree of parallel working than if a simple linear order is followed. The structure of the part outlined in Figure 3, can be represented by a network diagram as shown in Figure 4 which defines the relationships between sheets of ply, where dependencies between one ply and another ply are shown by arrows. The relationships between the plies are simplified to show only the relationship between one sheet of ply and those previous plies on which it is directly dependent. During manufacture of the composite part this network diagram is used to determine whether a given sheet of ply is eligible for placement. For this it is sufficient to know which sheets of ply have been correctly placed so far, and the next eligible plies can then be determined simply by following the arrows from those already placed.

[0069] Looking in more detail at Figure 4 it can be seen that the part of the lay-up process represented in the upper half of the diagram is split into two principal dependency branches (as shown by the dashed lines): one at the root of the blade and one at the tip. As shown in Figure 3, in the “root” branch, plies A, D and F are layered on top of each other. This is represented in the upper left part of the diagram of Figure 4, where it is clear from their linear relationship that F is only dependent on the placement of D, and D is dependent only on the placement of A. These plies are not dependent on any of the plies to be laid elsewhere in the mould.

[0070] A second dependency branch (the “tip” in this example) includes plies B, C, E and G, which are more interdependent on each other, but not dependent on the placement of any of the plies in the first “root” branch. The “root” and “tip” branches are joined with sheet H which is dependent on plies in both branches (plies F and E), and sheet of ply J which is dependent on both plies H and G. Whilst this example part finishes with plies I and J, it will be appreciated that in large parts, new dependency branches may be formed and reconnected throughout the process at different stages.

[0071] The branches depicted in the diagram are a representation of the dependencies defined by the designed structure of the part, and indicate the way in which the predetermined relationship between plies may mean multiple plies are eligible for placement at any one time. Individuals or teams placing plies into the mould as discussed above with reference to Figure 1, will naturally progress with the placement of plies at different speeds, depending on the size of the plies being placed, the ease of locating the next eligible ply, and whether plies are correctly placed in the lay-up quickly, or whether adjustment of their position is required. By providing details of the predefined relationships of plies, as represented by Figure 4, to the monitoring unit, all eligible plies can be identified so the placement of plies within independent branches can progress independently without the need to consider placement of other plies. After the identification of any placed ply, any newly eligible plies are identified and indicated to the manufacturing area through the projector(s) 130.

[0072] Figures 5A - 5D show a number of phases in the lay-up process which is a variant of the process outlined above. Here a first sheet of ply 320a is supplied as a roll 260. Referring to Figure 5A, a projected dashed line 132a is used to indicate that a first portion of the ply 320a is eligible for placement in the lay-up and where. A second dashed line 132b indicates that a further ply is also eligible but has not yet been placed. Figure 5A shows the ply 320a having been partially rolled out within the projected outline 132a, but instead of being fully placed, the projection includes a marker 136 indicating a staging point which indicates a location where the unrolling of the ply 320a should be paused while other plies are placed. In particular the ply indicated by the other projected outline 132b needs to be placed before the rest of the first ply 320a can be unrolled.

[0073] In Figure 5B a second ply 320b has been placed on top of the first, rolled out portion of the first ply 320a within a newly projected outline 132c which indicated that the second ply 320b was eligible in light of placement of the initial portion of the first ply 320a. The outline 132b and stop symbol 136 continue to be projected as the corresponding ply has not yet been placed.

[0074] In Figure 5C, a third ply 320c has been placed where indicated by the dashed line 132b. It will be appreciated though that this could have been placed earlier when the projection 132b was first made. In particular it could have been placed prior to the second ply 320b. This illustrates the flexibility provided by this embodiment in parallel placement of plies. As a result of the ply 320c being placed, in the final phase shown in Figure 5D, the projected outline 132d is provided, corresponding to the rest of the rolled first ply 320a which can now be fully placed, as further indicated by the arrow 137 which shows that the rolled ply 320a no longer needs to be held in that location. The final portion of the ply 320a is laid over the top of the third ply 320c, so this second portion of the first ply 320a was not eligible for placement before the third sheet of ply 320c was placed.

[0075] In large composite parts, with multiple dependency branches, as described above with reference to Figures 3 and 4, being able to place a first potion of a ply and defer the placement of the rest of it until a later stage gives greater flexibility when lower dependency branches are ready at different times. This means that one team working to place the sheets of ply can continue working without the need to wait for another team, reducing the overall time needed to place all the sheets of ply for the whole composite part.

[0076] Figure 6 shows another variant embodiment. This illustrates a phase in a lay-up for two sheets of ply 420a and 420b, with identifiers 424a and 424b, which are laid on top of each other, both plies being provided in a rolled configuration in a similar way to that discussed above with reference to Figures 5A-5D. A projected outline 432 is shown indicating where the lower sheet of ply 420a can be placed, as its projected identifier location 434a. Whilst this is depicted as a cross-hair to distinguish it from the symbol 424a itself, it would in practice have the same form as the identifying symbol.

[0077] As shown in Figure 6, after the first ply 420a has begun to be unrolled and has been identified by its identifier 224a, the second sheet of ply 420b, which is dependent on the first sheet of ply 420a can begin to be placed before the first sheet of ply 420a has been fully unrolled. Once the first ply’s identifier 424a has been detected, the monitoring unit determines that the second sheet of ply 420b is eligible for placement even though the first sheet of ply 420a is only partially unrolled (i.e. only a first portion of the first sheet of ply 420a has been placed). The projected identifier location 434b is then provided to indicate the eligibility of the second sheet of ply 420b for placement. Once the second sheet of ply 420b is partially unrolled, the second identifier 424b is detectable by the cameras in the correct location as shown by the second identifier 424b being overlapped by the second projected identifier location 434b (again depicted as a cross-hair for clarity). By considering a sheet of ply to be eligible for placement when the previous ply has been partially unrolled the overall time taken to lay the two sheets of ply is reduced. This stacking technique can also be used in combination with the staged placement of partially unrolled plies as discussed above with reference to Figures 5A-5D.

[0078] Figure 7 shows a feature of another variant embodiment of the invention comprising a group of plies. A series of layers in the lay-up process are represented as top down views of sheets of ply M-S relative to a mould 210, in a similar manner to Figure 3. In this embodiment, a single ply M is required in layer 1. Layer 2 would ideally have been a single ply which would have spanned the whole of the mould 210. However, with large parts like this turbine blade, it is not feasible to manufacture and place such very large sheets, so instead the notional ply was split into three sections N(i), N(ii) and N(iii), which have mutually overlapping edges as indicated by the dotted lines between each ply. In the basic approach outlined in respect of the first embodiment, three distinct but overlapping plies would have been identified as having dependencies on each other, for example requiring N(iii) to be placed before N(ii) is eligible for placement, which in turn should be placed before N(i) becomes eligible for placement. However in accordance with this embodiment, since the three plies N(i), N(ii) and N(iii) are structurally equivalent to a single, large one, they categorised as forming a group and so these dependencies are not applied, meaning that they are indeed effectively treated as a single ply when setting predetermined relationships as will be explained further below.

[0079] Layer 3 has a ply P which overlaps ply N(i) and a ply Q which overlaps both plies N(ii) and N(iii). Layer 4 has a ply R which overlaps ply P, as well as plies N(i) and N(ii) in layer 2, and a ply S overlaps with ply N(iii) from layer 2.

[0080] The structure of the part outlined in Figure 7, can be represented by a network diagram as shown in Figure 8, similar to the diagram of Figure 4, where dependencies between one ply and another ply, which define when plies become eligible for placement, are shown by the arrows. Plies N(i), N(ii) and N(iii) and shown together in a group 226. By grouping plies N(i), N(ii) and N(iii) the predetermined relationships between each ply in the group is changed so that these plies can be placed in any order with respect to each other, so long as their relationships with the other plies in the structure are maintained. This is further represented by the two-way dotted arrows between N(i), N(ii) and N(iii). The group of plies are therefore effectively treated as individual plies with no relationship between them. This means that whilst the part has four layers as shown in Figure 7, the predetermined relationships mean that fewer steps may be taken when manufacturing the part as ply N(i) can be placed at the same time as ply M, rather than needing to wait for plies N(ii) and N(iii) to be placed, and ply P is then eligible for placement at the same time as plies N(ii) and N(iii). Eligibility for placement of plies N(i), N(ii) and N(iii) therefore depends entirely on plies not in the group 226.

[0081] Any or all of the features described with reference to the embodiments of Figures 5 to 8 can be used in any combination with the first embodiment described or indeed with any other embodiments.

[0082] The various embodiments of the monitoring unit outlined above include steps carried out on a computing device. The monitoring unit is provided with data about the structure of the composite part, including the predetermined relationships between sheets of ply in the structure, and the locations for correct placement of all plies within the structure. The monitoring unit thus has the correct logical links between each sheet of ply so that phases are stepped through as each sheet of ply is correctly placed. The monitoring unit is therefore pre-programmed with information about the predetermined relationships.

[0083] The predetermined relationships can be taught to the monitoring unit via a test layup procedure, where for each step the correct sheet of ply is carefully positioned in place, before data is saved for the symbols in the detected positions based on provided image data (e.g. from the image sensors). Similarly, the imaging unit can also be trained to correctly identify plies from their shape and / or identifiers. When the system is trained via a test lay-up procedure, before data is recorded all obstructions should be removed from the lay-up area to ensure all plies are correctly identified, e.g. via their identifiers and / or perimeters in the lay-up area. The predetermined relationships can also be taught to the monitoring unit by inputting information directly from other computing systems. For example, if the geometry of a part is defined or aided by computer aided design (CAD) system, the CAD geometry can be used to determine the predetermined relationships. This may be via a full shell 3D calibration.

[0084] Whilst two distinct methods of teaching the predetermined sequence are outlined above, the skilled person will appreciate that a combination of both methods may be used to ensure any CAD input links to the reality of a calibration lay-up procedure. The programming of the locations of identifiers on plies may also be linked to the production of the sheets of ply themselves to ensure that once placed in the lay-up plies can be correctly identified as those expected by the imaging unit.

[0085] The finalised part structure may require altering after manufacture of multiple parts has begun. The monitoring system may include, for example as part of the user interface, a facility for a user to alter the structure and pre-defined relationships by e.g. by adding, deleting or moving sheets of ply in the structure, and altering their dependencies.

[0086] Figure 9 is a flow diagram 300 showing a method for monitoring composite part layup in accordance with the invention. It will be appreciated that the method is applicable to the specific examples of the monitoring system outlined above.

[0087] At step 310 image data is received from image sensors. As outlined above, the image data will be used to identify sheets of ply previously placed in the lay-up and / or identify the location of sheets of ply previously placed in the lay-up. The image data may relate to specific regions of the lay-up area, e.g. locations where previously eligible sheets of ply were indicated, or may be image data for the whole lay-up area. In some examples image data is acquired after a predetermined time has passed since a user input or previous cycle of the method. In some examples, the image data includes information relating to sheets of ply which have been partially placed, for example plies which have been held in a given location as discussed above with reference to Figures 5A-5D, or those still being laid, but whose first portion is detected as discussed above with reference to Figure 6. At step 320 the image data is processed to determine input data relating to the location of a first set of sheets of ply previously placed in the lay-up. Determining the input data can include comparing detected identifiers or outlines of plies with the plies identified as eligible for placement in a previous phase. In some examples the input data includes information relating to sheets of ply that have been identified as correctly placed. If a sheet of ply is not identified as correctly placed, information may be provided to the user via the user interface and / or projectors to aid with correcting the misplaced sheet of ply.

[0088] At step 330 the input data is received by the monitoring unit to be used in step 340 to determine a second set of sheets of ply which is those sheets of ply currently eligible for placement in the lay-up based on their predetermined relationships with the previously laid sheets of ply. The second set may also include sheets of ply where a first portion of the sheet of ply is eligible for placement as described above with reference to Figure 5A-5D and Figure 6 for example when a first sheet of ply is held at a staging point, or when a second sheet of ply can be stacked on top of the first sheet of ply. The predetermined relationships are determined based on the dependencies between the sheets of ply within the structure as discussed above with reference to Figures 3 and 4, and can include information regarding groups of plies as discussed above with relation to Figures 7 and 8.

[0089] At step 350 an indication of the eligible set of sheets of ply is output to a user, for example via the projectors and / or the user interface. The indication may include information relating to the identity of plies determined to be eligible for placement, and may also include information relating to the location where they should be placed, and whether placement should be held so a ply is only partially placed. The identity of an eligible sheet of ply may be provided as projections of their outline into the lay-up area and / or their identifier into the expected location in the lay-up area.

[0090] Once an indication of eligible plies has been provided, the method can return to evaluating image data to see if any new plies have been placed.

[0091] It will be appreciated by the skilled person that whilst the method steps are outlined in a particular order here, some of the steps may take place at different times within the process, or take place simultaneously with other steps. For example, there may be a continuous output in the form of projected images indicating eligible sheets of ply. The receipt of image data may also be continuous, or data may only be collected at predetermined intervals. It will therefore be appreciated that the outlined method is by way of example only, and that embodiments may include other steps to include those features outlined with reference to the system described above.

[0092] The examples of the invention illustrated above describe how sheets of ply are placed into a mould during manufacture and how these are monitored. It will be appreciated by those skilled in the art that the above examples equally apply to any individually laid structural element, of which a sheet of ply is just one example.

[0093] It will be appreciated by those skilled in the art that the invention has been illustrated by describing one or more specific aspects thereof, but is not limited to these aspects; many variations and modifications are possible, within the scope of the accompanying claims.

Claims

- 28 -Claims1. A method of monitoring a process for manufacturing a composite part, the composite part comprising a plurality of layers of structural elements according to a lay-up definition, wherein the lay-up definition comprises a plurality of predefined relationships each between respective sets of at least first, second and third structural elements of said structural elements, whereby placement of the second structural element of each set is dependent on placement of the first structural element of the set, but placement of at least the third structural element of the set is not dependent on placement of the first structural element, such that a plurality of structural elements are eligible for placement at the same time during the manufacturing process; wherein the method comprises: determining a set of structural elements previously placed; determining an eligible set of structural elements from the previously placed set, wherein the eligible set of structural elements comprises structural elements which are eligible for placement in the lay-up definition based on the predefined relationships; and outputting an indication of the eligible set of structural elements.

2. The method as claimed in claim 1, wherein the predetermined relationships between the sets of structural elements are based on at least one of: the volume of the structural elements, the perimeter of the structural elements, and / or the area of at least one surface of the structural elements.

3. The method as claimed in claim 1 or 2, wherein the predetermined relationships between structural elements include the location within a lay-up area where a structural element should be placed within the composite part.

4. The method as claimed in any of claims 1 to 3, wherein the previously placed set of structural elements consists of previously placed structural elements which still have other structural elements directly dependent on them in the lay-up definition.

5. The method as claimed in any preceding claim, wherein the predefined relationships comprise at least one predefined partial relationship between a set of at least fourth and fifth structural elements of said structural elements, whereby placement of the fifth structural element is dependent on partial placement of the fourth structural element and wherein the eligible set of structural elements further comprises the fifth structural element being eligible for placement in the lay-up definition based on the predefined partial relationship.

6. The method as claimed in any preceding claim, wherein the predefined relationships comprise at least one predefined multiple partial relationship between a set of at least sixth, seventh and eighth structural elements of said structural elements, whereby placement of a first portion of the eighth structural element is dependent on placement of the sixth structural element, placement of the second portion of the eighth structural element is dependent on placement of the seventh structural element and wherein the eligible set of structural elements further comprises the first and second portions of the eighth structural element respectively being eligible for placement in the lay-up definition based on the predefined multiple partial relationship.

7. The method as claimed in any preceding claim, wherein the composite part comprises at least one group, wherein the group comprises a plurality of structural elements which have at least one mutually overlapping edge in the lay-up definition but where placement of any of the plurality of structural elements is not dependent on the previous placement of any other structural element in the group, and wherein the structural elements in the group become eligible for placement in different orders as determined by their predefined relationships to structural elements not in the group.

8. The method as claimed in any preceding claim, wherein determining a set of structural elements previously placed is based on the previously indicated set of eligible structural elements and an input confirming that one or more of this set has been placed.

9. The method as claimed in claim 8, comprising receiving said the input is provided from a user interface.

10. The method as claimed in any preceding claim, wherein determining a set of structural elements previously placed comprises monitoring the placement of structural elements.

11. The method as claimed in claim 12, wherein monitoring the placement of structural elements comprises visual monitoring using one or more image sensors.

12. The method as claimed in claim 10 or 11 , wherein each of the structural elements has an identifier, and wherein monitoring the placement of structural elements includes monitoring the expected locations for the identifier of the respective structural element.

13. The method as claimed in claim 12, wherein the indication of the eligible set of structural elements comprises information about the identifier(s) relating to the eligible set of structural elements.

14. The method as claimed in any preceding claim, wherein determining the set of previously placed structural elements comprises determining whether each structural element in the set has been correctly placed.

15. The method as claimed in claim 14, wherein determining whether a structural element has been correctly placed comprises determining whether the structural element has been placed in a correct location and / or orientation.

16. The method as claimed in claim 14 or 15, wherein determining whether a structural element has been correctly placed comprises receiving data from a or the image sensor relating to the location of structural elements previously placed in the lay-up.

17. The method as claimed in any of claims 14 to 16, wherein each of the structural elements has an identifier, the method comprising determining that the location of a structural element is correct by determining the location of a correct identifier for said structural element.

18. The method as claimed in any preceding claim wherein the indication of the eligible set comprises information regarding where in the lay-up area a rolled or folded structural element should be placed.

19. The method as claimed in claim 18, wherein the indication of the eligible set comprises a direction in which the structural element should be unrolled or unfolded20. The method as claimed in any preceding claim, wherein the indication of the eligible set of structural elements is provided on a user interface and / or at least one projector configured to project an image relating to the eligible set of structural elements.

21. The method as claimed in claim 20 wherein the projected image comprises an outline of each of the eligible set of structural elements and / or the identifier for each of the eligible set of structural elements.

22. A computer software product or a non-transitory computer-readable medium comprising instructions that, when executed by a processor, cause the processor to carry out the method according to any preceding claim.

23. A system for monitoring a manufacturing process for manufacturing a composite part, the composite part comprising a plurality of layers of structural elements according to a lay-up definition, wherein the lay-up definition comprises a plurality of predefined relationships each between respective sets of at least first, second and third structural elements of said structural elements, whereby placement of the second structural element of each set is dependent on placement of the first structural element of the set, but placement of at least the third structural element of the set is not dependent on placement of the first structural element, such that a plurality of structural elements are eligible for placement at the same time during the manufacturing process; wherein the system is configured to: determine a set of structural elements previously placed; determine an eligible set of structural elements from the previously placed set, wherein the eligible set of structural elements comprises- 32 - structural elements which are eligible for placement in the lay-up definition based on the predefined relationships; and output an indication of the eligible set of structural elements.

24. A method of controlling a manufacturing process for manufacturing a composite part, the composite part comprising a plurality of layers of structural elements according to a lay-up definition, wherein the lay-up definition comprises a plurality of predefined relationships each between respective sets of at least first, second and third structural elements of said structural elements, whereby placement of the second structural element of each set is dependent on placement of the first structural element of the set, but placement of at least the third structural element of the set is not dependent on placement of the first structural element, such that a plurality of structural elements are eligible for placement at the same time during the manufacturing process; wherein the method comprises: determining a set of structural elements previously placed; determining an eligible set of structural elements from the previously placed set, wherein the eligible set of structural elements comprises structural elements which are eligible for placement in the lay-up definition based on the predefined relationships; and outputting an indication of the eligible set of structural elements; placing structural elements from the indicated eligible sets of structural elements to form the composite part.

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