WO2025048778A1

WO2025048778A1 - Flexible structures

Info

Publication number: WO2025048778A1
Application number: PCT/US2023/031275
Authority: WO
Inventors: Geoffrey Franklin SCHMID; James Andrew MCCUTCHEON; Randall Dean WEST
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2023-08-28
Filing date: 2023-08-28
Publication date: 2025-03-06
Anticipated expiration: 2026-02-28

Abstract

A flexible structure comprising a plurality of interlinked beams (102), wherein the beams (102) are curved and interlinked to define a plurality of concave rhombus forms (104) and wherein each rhombus form (104) is linked to at least two other rhombus forms (104).

Description

FLEXIBLE STRUCTURES

BACKGROUND

[0001] Flexible structures have many uses, for example in providing cushioning and support. Flexible structures may be incorporated into a number of objects, and may have properties tailored to a given purpose.

BRIEF DESCRIPTION OF DRAWINGS

[0002] Non-limiting examples will now be described with reference to the accompanying drawings, in which:

[0003] Fig. 1 is a perspective view of an example flexible structure.

[0004] Fig. 2A and 2B are schematic representations illustrating the behaviour of example flexible structures at rest and under stress respectively.

[0005] Fig. 3 is an example of part of a flexible structure.

[0006] Fig. 4 is an example of a flexible structure extending in a vertical plane.

[0007] Fig. 5 is an example of a flexible structure extending in a horizontal plane.

[0008] Fig. 6 is a graph illustrating how the stiffness of the beams of an example flexible structure varies with displacement.

[0009] Fig. 7 is a flowchart of an example method for determining an intended property for a flexible structure to be formed by additive manufacturing.

[0010] Fig. 8 is a flowchart of an example method of generating an object with a flexible structure.

[0011] Fig. 9 is an example of an object including a flexible structure as a portion thereof.

[0012] Fig. 10 is a simplified schematic drawing of an example machine readable medium associated with a processor. DETAILED DESCRIPTION

[0013] Flexible structures, in particular small-scale flexible structures, may have a number of uses. In some examples, such structures may be tailored to particular use cases. For example, such structures may be intended to provide a predetermined amount of cushioning, support or resilience.

[0014] Fig. 1 shows a perspective view of an example of a flexible structure, which structure may also be referred to as flexible fabric herein.

[0015] The flexible structure 100 is made up of a plurality of interlinked/adjoining beams 102, only some of which are labelled to avoid overcomplicating the figure. The beams 102 are curved and interlinked, linked or joined to define a plurality of concave rhombus forms 104. A rhombus form 104 is any form made up of four sides, which in examples herein are formed by the beams 102, i.e. each rhombus form 102 comprises four beams 102. In the example shown, there are eight such rhombus forms 104 shown (only three of which are labelled to avoid overcomplicating the figure). The form 104 may alternatively be described as a diamond shape or parallelogram shape with curved edges, or as a concave diamond form or a concave parallelogram form.

[0016] Each rhombus form 104 is linked or joined to (or interlinked with) at least two other rhombus forms 104. In some examples, each rhombus form 104 is linked to more than two other rhombus forms 104. In the example of Fig. 1 , there is a first set 106a of rhombus forms 104 linked or joined at a common intersection 108 which is stacked on top of a second set 106b of rhombus forms 104. Each rhombus form 104 of the second set 106b is linked or joined to two other rhombus forms 104 to form a ring. The rhombus forms 104 of the first set 106a are each linked/joined to the other rhombus forms 104 of that set, and the rhombus forms 104 of the second set 106b are each linked/joined to two other rhombus forms 104 of the second set 106b. In this example, a vertex of each rhombus form 104 of the first set 106a is linked or joined to a vertex of a rhombus form 104 of the second set 106b and the common intersection 108 is aligned with the centre of the ring. In this example, each rhombus form 104 of the first set 106a has a substantially orthogonal orientation with respect to the rhombus form 104 of the second set 106b to which it is linked. The structure 100 may be described as a lattice-like or mesh-like structure. [0017] In this example, each of the first set 106a and the second set 106b comprises four rhombus forms 104, although other arrangements may be provided. For example, each set 106a, 106b could comprise at least three rhombus forms 104. Rhombus forms 104 may also be referred to herein as rhombus bodies. A rhombus is a quadrilateral shape comprising side beams of equal length. While the term ‘rhombus’ has been used herein, the form/body could otherwise be, or be referred to as, a ‘diamond form/body’ or a ‘quadrilateral form/body.

[0018] The arrangement of rhombus forms 104 shown in Fig. 1 may provide a flexible structure unit, or a flexible structure cell, which may be joined to other such units/cells to provide a larger flexible structure or fabric. In other examples, the cell could be formed of a different arrangement of linked or joined rhombus forms 104.

[0019] As noted above, the beams 102 are curved. In examples, the beams have an arc-like form. While in the example of the figures, the curve is a smooth curve, in other examples, there may be one or more straight portions which are angled relative to one another. Moreover, the form 104 is concave. In other words, beams 102 are curved inwards towards the centre of the form 104 along their length. A concave curve means that, as the form 104 is compressed, stiffness is maintained, as will be discussed in greater detail below.

[0020] In some examples the curvature of a beam 102 may be substantially symmetrical about a mid-point thereof. In other examples the curvature of the beam 102 may be asymmetrical, such that a beam 102 has a ‘knee’ or ‘elbow’ which is closer to one end of the beam 102 than the other. In other examples, there may be more than one ‘knee’ or ‘elbow’ feature along the length of the beam 102. The radius of the curvature of a beam 102 at rest may be greater or less than that illustrated.

[0021] While in some examples, the cross section of the beams 102 may be substantially constant along their length, in other examples the cross section may vary.

[0022] The beams 102 may have an at least substantially rectangular cross section. The rectangular cross section may be a non-equilateral rectangle. While other shapes, such as square, circular or oval cross sections could be used in other examples, a rectangular cross-section provides multiple dimensions to adjust, which may assist in tailoring the structure to an intended purpose. For example, a height and width (or thickness) of the cross-section can be adjusted independently from one another. The dimensions of the cross section may be selected depending on intended properties such as the mass, durability, resilience or cushioning to be provided by the structure 100. For example thinner beams may be generally more flexible and light-weight than a comparable thicker beam but could provide less resilience (or ‘bounce’) and/or be weaker and therefore more liable to fail.

[0023] In the discussion that follows, two dimensions are discussed. First, a horizontal dimension H, as marked on one of the beams 102 of Figure 1 , is that which is intended to be perpendicular to the direction of compression in use of the structure 100. This horizontal dimension is parallel to an axis passing through the open centre of the rhombus form 104, and perpendicular to a face of the rhombus form 104 formed by the four beams 102. The ‘thickness’ of a beam 102, T, is perpendicular to this dimension in the beam 102, and can be thought of as the thickness of the solid material forming the solid perimeter of the face.

[0024] Changes in each dimension may impact the behaviour of the structure 100 differently. Increasing the horizontal dimension H linearly increases the stiffness as well as the mass. However, increasing the thickness T may increase the stiffness to the third power, so a small increase in the thickness of the beam 104 can result in a relatively large change in the stiffness. Moreover, increasing the thickness T also reduces the overall maximum travel distance for compression (as thicker beams will be brought into contact as result of a smaller compression displacement), and increases the peak stress. Thus, for example, a square cross section may present a good option for a stiffness to mass ratio, but a relatively flat rectangular dimension (i.e a greater horizontal dimension than thickness) may experience less stress and provide a greater travel, which may result in an increase in macro-strain to micro-strain ratio, in turn increasing durability.

[0025] To reduce the stress therefore, the cross section of the beam 104 may be longer in the horizontal dimension H than in thickness T.

[0026] It may also be noted that, when compared to beams with a circular cross section, rectangular cross sections may have a higher bending stiffness for a given mass in a material. Rectangular cross sections therefore in some examples reduce peak stress whilst providing the same stiffness as a circular cross section. In turn, a rectangular cross section may provide increased durability compared to a beam of circular cross section of a similar mass.

[0027] Moreover, when compressed, rectangular beams (including square beams) may collapse predictably onto one another. In some examples, the beams 102 of the rhombus forms 104 are arranged such that, when compressed, a flat surface of one beam 102 is urged into contact with a flat surface of another beam 102 (of that, or of a different rhombus form 104). In other words, at least one face, and in some examples opposing faces, of the beam 102 are oriented to extend in a plane which is parallel to an axis passing through the open centre of the rhombus form 104. A rectangular cross section therefore may provide a more stable form when in a compressed state for example when compared to a circular cross section, wherein beams may be more prone to shift relative to one another when compressed. Moreover, the rectangular cross section may provide more surface area of contact when the flexible structure compresses on itself.

[0028] In some examples, each rhombus form 104 and/or cell has a height and width, wherein the width is greater than the height. The width and the height may be defined relative to an intended direction of compression. In an example, it may be intended that, in use, the rhombus form 104 and/or cell is intended to be compressed vertically, i.e. to reduce the height dimension, in a direction perpendicular to the width dimension. Providing a rhombus form 104 or cell wherein the width is greater than the height may improve the durability of the structure as the structure is inherently more stress limiting (i.e. the beams 102 may at least partially contact each other relatively early in the compression operation). For example, the height dimension may be 70-80% of the width dimension. In other examples, the height dimension may be 70% to 90%, or 60% to 80%, or 60% to 90% of the width dimension.

[0029] The height and/or width of each rhombus form may be less than 2cm. The The flexible structure unit or cell comprising the two sets of rhombus forms 104 may for example have a height and width of less than 5cm, or less than 2cm. height and/or width of a cell such as that shown in Fig. 1 may be at least 6mm, at least 8mm, at least 10mm, at least 12mm or at least 15mm. In some examples, the width of the cell may be around 12mm and the height may be around 8mm. In some examples, the width of the cell may be around 15mm and the height of the cell may be around 12mm. Providing relatively small cells may allow a flexible structure to readily conform to the shape of an object compressing it, thus providing good support and/or cushioning. However, cells may be larger in other examples.

[0030] In some examples, each beam 102 comprises a wire-like element with a cross-sectional dimension of less than 2mm, less than 1.5mm or less than 1 mm. In some examples, the wire-like element may have a cross-sectional dimension of at least 0.8mm. Such wire-like elements may be flexible and/or relatively robust in use. Moreover, in some examples, dimensions in this range may be produced using additive manufacturing.

[0031] Figs. 2A and 2B illustrate a simplified line drawing of an example rhombus form 204 of an example flexible structure. The flexible structure may be compressed from the rest position shown in Fig. 2A to a compressed position shown in Fig. 2B. In this example, the rhombus form 204 is to be compressed by a distance X in the vertical direction. The axis of compression is aligned with the height of the rhombus form 204 in this example, and reduces the height from a first height Ht1 to a second height Ht2.

[0032] Figs. 2A and 2B show how the curvature of the beams allows the form 204 to collapse into itself. Straight beams may be more susceptible to buckling under compressive loads. Energy is consumed when the beams buckle and this may impact energy return. In other words, using curved beams means it is more likely that the structure will ‘bounce back’ after compression, and will behave in a predictable manner both during compression and return to its unstressed form (i.e. at rest, for example under gravity). Without being bound by theory, the curved beams may be less prone to buckle when the flexible structure 100 is compressed because the effective column length decreases as a function of the displacement of the compression. This may enable higher energy return under high displacement and/or reduce peak stress. Moreover, as can be seen in Fig. 2B, as the form 204 is compressed, upper and lower beams come into contact with one another in a contact region CR. As the curved beams may collapse on each other such that the contact region CR increases in length, this gradually reduces the length of the other portion of the beam, i.e. the portion of each beam which is free to deform as they come into contact. This increases the overall stiffness as a function of displacement, and may reduce a peak deceleration for a given impact against the flexible structure.

[0033] In summary then, by virtue of the concave beams, as the form 204 is compressed, the effective beam length decreases. In addition, the angle of the ‘remaining’ portion of the beam which is not constrained by contact with another beam relative to the axis of compression increases. This maintains the stiffness of the structure.

[0034] As will be appreciated, the position of a knee or inflection point, the radius of curvature and/or the dimensions of the beam can all influence the behaviour of a flexible structure as described herein. [0035] For the sake of comparison, it may be noted that if the curve were in the opposite direction (i.e., the form was concave), the structure would soften as it compressed.

[0036] Fig. 3 shows a front view of a face of a further example of a rhombus form 300 comprising four beams 302a-d, and which may form part of a flexible structure in some examples.

[0037] In this example, the rhombus form 300 comprises a height defined between a first pair of vertices 304a, b and a width defined between a second pair of vertices 306a, b. Each of the first pair of vertices 304a, b form a respective first joint. Each of the second set of vertices 306a, b form a respective second joint. The intended axis of compression is aligned with the height of the rhombus form 300. Therefore, compression tends to increase the interior angle of the first set of vertices 304a, b, and decrease the interior angle of the second set of vertices 306a, b.

[0038] The beams 302a-d comprise additional material 308a, b (also referred to herein as a thickening, a radius, a flare or a blend) at the first pair of vertices 304. The additional material 308a, b causes a thickening at these vertices. Put another way, the cross sectional area of the beam may comprise a flare at one end. Under compression, the first pair of vertices 304 are in tension. If a material failure is to occur, it is likely to be in the region of a vertex in tension. Therefore, the addition of material at these vertices reduces a stress concentration that could otherwise occur, and therefore serves to strengthen the structure as a whole. The amount of material added may be selected according to an intended behaviour of a structure in use. For example, the degree of thickening, and the length of the thickened portion may impact the response of the flexible structure under stress and/or the robustness of the structure to material failure.

[0039] The second pair of vertices 306 do not comprise such additional material. Rather, the second joint comprises a sharp angle. This acts as a hinge during compression, allowing the second joints to pinch close. In other words, each vertex of the second pair of vertices 306a, b can compress such that the beams 302 forming the vertex begin to come together to create a pinch. Adding extra material to the second pair of vertices would result in a region of high local stress which may result in damage to the structure.

[0040] Fig. 4 shows an example of a flexible structure 400 comprising a plurality of flexible structure units 402a, b, c (which may also be referred to as cells) arranged in a vertical lattice array. Each flexible structure unit 402a, b, c comprises a plurality of joined, linked or interlinked concave rhombus forms or bodies, which in this example are referred to as rhombus bodies. Each unit 402a, b, c comprises a first set of rhombus bodies joined, linked or interlinked at a common intersection and a second set of rhombus bodies each joined or linked to, or interlinked with, two other rhombus bodies to form a ring. The first and second set of rhombus bodies are stacked one on top of the other such that a vertex of each rhombus body of the first set is linked/joined to, or interlinked with, a vertex 408 of a rhombus body of the second set and the common intersection is aligned with the center of the ring. While in this example the vertical lattice array is shown as comprising a single column, in other examples a plurality of adjoining columns may be provided to provide a structure comprising a lattice array.

[0041] Fig. 5 shows another example of a flexible structure 500, in this example being arranged in a horizontally extending lattice array. In this example, the flexible structure unit or cell has a different formation, being formed of twelve sided polygons, or ‘dodecagons’, each comprising four concave rhombus forms forming a ring, with four inclined quadrilateral forms arranged above the ring and four inclined quadrilateral forms below the ring. In some examples, the beams forming the quadrilateral forms may be curved. The unit further comprises eight beams which extend from the polygon to link with an adjacent unit. In this example (and in other examples), the arrangement of the flexible structure (and or a cell or unit thereof) is such that it has “free arms” rather than drawing to a point (i.e., the vertices of Fig. 4). In some examples, the beams forming the free arms may be curved. In other words, rather than the edges forming a complete rhombus or other quadrilateral shape, an outside cell, unit or layer may be formed of a half rhombus form.

[0042] Considered another way, the flexible structure unit or cell comprises four rhombus forms taken from each of four adjoining second sets of rhombus forms described above with a horizontal slice of the first set of rhombus forms above it and a second horizontal slice of the first set of rhombus forms below it. The slice passes through the common intersection described above. In other words, while the appearance of the structures shown in Fig. 4 and Fig 5 is different, the underlying structure may be similar, albeit ‘sliced’ differently.

[0043] While in this example the horizontal lattice comprises one layer, in some examples a lattice array may comprise a plurality of layers and/or half-layers. Moreover, a similar horizontal lattice may be formed using the flexible structure unit or cell described above and shown in Fig. 1. [0044] Fig. 6 shows a graph illustrating the relationship between compressive force and compressive displacement for each of an example of a particular flexible structure having the general form described herein.

[0045] As the structure is compressed, the beams meet one another, meaning the effective beam length is shortened and, as can be seen from the figure, the stiffness rises. This is demonstrated by the non-linear force compression curve, shown relative to a dotted line indicative of a linear relationship. In addition, the physical limits of the beams touching means the structure is robust when stressed.

[0046] Moreover, the gradual change in stress means that the structure stores energy efficiently and may be suited to rebounding, and returning that energy. This may make the structure suitable for use in cushioning objects in motion, for shock absorption, or for providing an effective bounce back. For example, the structure may be used in shoes, such as athletics shoes, where it may return the energy of compression to the user thereof.

[0047] In some examples, it may be intended to provide a ‘travel’ distance, i.e. a compressive displacement) of around 35-55% of the height of the structure. For example, in a flexible structure with a height of material of 30mm, the maximum travel before the beams meet so as to prevent further compression may be around 50% or 15mm. In another example, there may be around 20mm of height of the flexible structure and around 40%, or 8mm, travel.

[0048] In particular examples now discussed with reference to Fig. 6, the flexible structure may be provided as part of footwear, for example in the midsole of a shoe. The shoe may for example be intended for use while standing, walking and running. In such cases, the thickness of the flexible structure may for example be between around 10mm (which may be a single layer, for example as shown in Fig. 5) to around 30mm. In some examples, a shorter travel distance may be appropriate in a first part of a shoe (e.g. a forefoot region) while a longer travel distance may be appropriate in a second part of the shoe, e.g. a midsole. This may be achieved by altering the design of the flexible structure, and/or the height, e.g. the number of layers.

[0049] If the graph of Fig. 6 represented the behaviour of a flexible structure in a running shoe having a maximum travel of 12mm, a first stress level, S1 , may be associated with a relatively small displacement, which may be the stress when a user is standing or walking. The stress at this point is proportional to the change in force over the change in distance. This may for example relate to a displacement of around 2-4mm at a load of between 200N and 400N, which varies with bodyweight. When running, a greater compression is caused and the impact stress S2 may be experienced by the structure.

[0050] The energy stored in the structure at the maximum compression D_max is indicated as the shaded region below the graph. In use of the shoe in running, this may be at least approximately proportional to bodyweight, and also to velocity squared. The energy input by the runner causes a displacement until the integral of the curve matches the input. The user feels the resultant force as a deceleration.

[0051] Thus, the structure may be designed to provide an appropriate response at S2, given an intended use case (for example, the expected, average or maximum bodyweight and/or running speeds of users). The structure may be designed to provide a stress S2 which is balanced between providing reasonable cushioning, and thus low deceleration (which may improve the experience of wearing the shoe) while also providing good cushioning at a relatively low stress level S1.

[0052] While the example of shoes has been used above, it will be appreciated that a similar performance may be useful in other scenarios. For example, packaging for delicate objects may provide an appropriate cushioning response under normal careful handling, but may also be intended to function well when a package is dropped.

[0053] In some examples, any of the flexible structures described herein may be generated using additive manufacturing. Additive manufacturing techniques may generate a three-dimensional object through the solidification of a build material, for example on a layer-by-layer basis. In some examples, the build material is a powder-like granular material, e.g. a plastic, ceramic or metal powder, and the properties of generated objects may depend on the type of build material and the type of solidification mechanism used. Build material may be deposited, for example on a print bed and processed layer by layer, for example within a fabrication chamber, and selectively solidified using data representing a slice of a three-dimensional object to be generated (which may for example be determined from structural design data). According to examples, a suitable build material may be a Nylon, such as PA12 or PA11 material, a Thermoplastic Polyurethane (TPU) material, Thermoplastic Polyamide material (TPA), Polypropylene (PP) and the like.

[0054] In some examples, selective solidification is achieved through directional application of energy, for example using a laser or electron beam which results in solidification of build material where the directional energy is applied. In other examples, at least one print agent may be selectively applied to the build material and may be liquid when applied. For example, a fusing agent may be selectively distributed onto portions of a layer of build material in a pattern derived from data representing a slice of a three- dimensional object (e.g. an object comprising a flexible structure) to be generated. The fusing agent may have a composition which absorbs energy such that, when energy (for example, heat) is applied to the layer, the build material to which it has been applied heats up, coalesces and solidifies, upon cooling, to form a slice of the three-dimensional object in accordance with the pattern. In other examples, a binding agent may be applied to build material to cause the selective binding thereof. In still other examples the build material may be a liquid build material which is selectively solidified by heating, cooling, curing or the like. Other additive manufacturing techniques may be used in other examples.

[0055] There may be a minimum feature size and/or separation which can be generated by a given additive manufacturing apparatus, for example a finite resolution in relation to the accuracy with which build material and/or print agents may be placed or with which additive manufacturing apparatus can be controlled. However, in practice, in some examples, the minimum ‘printable’ feature size may be determined not by the resolution of the object generation apparatus but by the temperature that such a feature can reach during the fusing process. The resolution may also vary with build material type, with some build materials (e.g., at the time of writing, TPU) being associated with a lower resolution than others (e.g. PA12 and PA11 ).

[0056] In some examples, elastomeric materials are used as build materials. PA11 may be particularly suited to use in generating small scale flexible structures because of the ability to form small features. However, elastomeric materials such as TPA and TPU may exhibit good properties of resilience and energy return which are suited to certain applications.

[0057] Fig. 7 illustrates a method 700 for determining a data model for a flexible structure to be formed by additive manufacturing. The method may comprise a computer implemented method for designing a flexible structure/flexible fabric such as those described above.

[0058] At block 702, an intended property for a flexible structure is determined. The flexible structure may comprise a flexible structre as described above, comprising a plurality of interlinked beams, wherein the beams are curved and are linked to define a plurality of concave rhombus forms, wherein each rhombus form is linked to at least two other rhombus forms. The intended property may for example comprise at least one of a flexibility of the structure, a durability of the structure, a volume (e.g., dimension(s) and the like, a number of layers and/or a number of columns) of the structure, a stiffness at at least one stress level, distance of travel under impact, resilience (or energy return), or the like. For example, determining the intended property may comprise receiving a specification of an intended property from a user or in design data.

[0059] At block 704, a physical attribute for the structure is determined based on the intended property. The physical attribute may for example comprise a geometrical parameter such as at least one of a size of a rhombus form (or of a unit), or a geometrical parameter of a beam. For example, the geometrical parameter may comprise a shape of a beam, a dimension of a beam (e.g. a cross sectional dimension of a beam, a length of a beam), a curvature of a beam, an amount of thickening or flaring at a vertex, or the like. For example, determining a cross sectional dimension of the beam may comprise determining the horizontal dimension and/or thickness of a rectangular cross-section. Determining the curvature of the beam may comprise determining at least one of the radius of the curvature, the point of inflection and/or whether the curvature is symmetrical.

[0060] For example, the cross-sectional dimension of a beam may be selected in order to provide an intended durability and/or resilience. In another example, the size of the flexible structure unit may be selected in order to allow the structure to fit within a predetermined volume.

[0061] In some examples, these may be associated with a selected material of manufacture, for example PA11 , PA12, TPU or the like. In some examples, the physical attribute may comprise a choice of a material of manufacture. In some examples, the physical attribute(s) of the structure or other parameters may be stored in a database, for example as flexible structure data models. For example, the dimensions of the beam may be selectable and/or the models may be scalable. In some examples, physical (e.g. geometrical) attributes such as structure geometries or other geometric parameters may be stored in association with data indicative of properties or property ranges of flexible structures having such properties. In such examples, a suitable unit design, or subset of designs/geometries may be selected automatically based on the intended property.

[0062] For example, in the case when the structure is to be incorporated in to a shoe, there may be a consideration of stiffness at a first, relatively low, stress level (i.e. how a shoe feels when a user is standing or walking), as well as consideration of stiffness at a second, higher or peak, stress level (i.e. the force felt on impact such as when running). Moreover, there may be consideration of displacement of the structure in use, e.g. how much linear travel should occur during impact. In addition, energy return may be considered. This may for example be maximised, so that the beams do not meet too early in an intended use. Similar considerations apply in other use cases.

[0063] In addition, the intended use may define other aspects of the structure such as the size of the structure. In the example of a shoe, the total stack height (i.e. how tall the structure can be) may be set in terms of what is practical for footwear. Similar considerations will apply in other examples.

[0064] Based on such criteria, at least one of the beam thickness, width, curvature and cell size can be determined for an intended use case.

[0065] Moreover, in some examples, determining a physical attribute of the structure may comprise specifying a regular grid layout for the units, and/or specifying the number of layers of units in the structure. For example, a regular grid layout may comprise a repeating pattern of a unit, or a group of units, as demonstrated by the lattices of Fig. 4 and Fig. 5.

[0066] At block 706, a flexible structure data model for use in generating the flexible structure having the physical attribute in additive manufacturing is determined. For example, this may comprise determining a mesh model, a vector model, a voxel model or some other model of the flexible structure. The flexible structure may be intended, when generated, to have the specified property.

[0067] The model may be provided as object model data which represents at least a portion of the structure to be generated by an additive manufacturing apparatus. Such object model data may for example comprise a Computer Aided Design (CAD) model, and/or may for example be a STereoLithographic (STL) data file, a 3D Manufacturing Format (3MF) file or the like. In some examples, the model may comprise a single unit, which may be replicated to form the flexible structure.

[0068] In some examples, blocks 702 and 704 may be combined and/or reversed in determining such models.

[0069] Fig. 8 is a flowchart of an example method for additive manufacturing comprising blocks 702, 704 and 706 described above. In addition, the method further comprises, in block 802, determining an object data model for generating an object having a flexible structure incorporated therein, the object model comprising the flexible structure. For example, this may comprise a data model of an object such as a sole of a shoe, or a part thereof, or a packaging container having the flexible structure forming part of a solid enclosure or the like.

[0070] The method 800 further comprises, in block 804, determining additive manufacturing instructions based on the object data model, which when executed by an additive manufacturing apparatus, cause the additive manufacturing apparatus to generate the object including, as at least a part thereof, the flexible structure. Determining the additive manufacturing instructions may comprise determining the instructions based on a predetermined mapping between the model data and print agents (e.g., print agent amounts), wherein the predetermined mapping for at least part of the model may be a mapping for generating flexible structures. In some examples, the mapping may be different for a solid region of the object model than for the region comprising the flexible structure.

[0071] For example, the mapping between the model data and print agents for the region corresponding to the flexible structure may be a specific mapping for generating flexible structures and/or for generating small scale structures. The mapping for generating other portions of the object may be a different mapping.

[0072] The flexibility of a feature may be affected by processing parameters used in the additive manufacturing process, such as temperature or the type and quantity of agents used. For example, applying a higher density of fusing agent to some features can increase rigidity and decrease flexibility. Conversely, a lower density ef fusing agent may result in a feature having a relatively high flexibility. Therefore, in some examples, a mapping for use in generating flexible structures may specify the application of a lower density of fusing agent to form some portions of the flexible structure than a mapping for generating other (e.g. substantially or relatively rigid) portions of the object. In some examples the density ef fusing agent may be referred to as an area coverage (for example, x drops per cm²).

[0073] Detailing or cooling agent which cools the build material may be used between regions to be solidified to control the extent of the fusing. In some examples, a mapping for use in generating flexible structures may specify the application of a higher density of detailing agent around the beams of the flexible structure than a mapping for generating other portions of the object (e.g. object portions having greater separations from adjacent portions). Such principles may also apply when generating instructions based on the model determined in the method of Fig. 7. [0074] The additive manufacturing instructions may comprise instructions to specify an amount of agent, such as print agent, fusing agent or detailing agent, to be applied to each of a plurality of locations on a layer of build material.

[0075] In some examples, other additive manufacturing parameters, such as any, or any combination of heating temperatures, build material choices, an intent of the print mode (e.g. prototype, or final product), and the like, may be specified in the instructions.

[0076] The method further comprises, in block 806, executing the instructions to generate the object. The object may be generated in a plurality of layers (which may correspond to respective slices of an object model) by selectively solidifying portions of layers of build material using additive manufacturing apparatus. For example, this may comprise forming a layer of build material, applying print agents, for example through use of ‘inkjet’ liquid distribution technologies in locations specified in object model data for an object model slice corresponding to that layer using at least one print agent applicator, and applying energy, for example heat, to the layer. A further layer of build material may then be formed, and the process repeated, for example with the object model data for the next slice.

[0077] Fig. 9 is an example of an object 900 including a flexible structure 902. Flexible structures may be used in any object where cushioning is required. For example, sporting goods, packaging, automotive uses and footwear may incorporate such structures. In this example, the object 900 comprising the flexible structure 902 is a sole of a shoe, which may be a sports shoe. The object 900 comprises a (relatively) rigid portion 904 and the flexible structure 902 arranged in a void in the rigid portion 904. The flexible structure 902 may have any of the features of the flexible structures 100, 400, 500 described in relation to Figs. 1 , 2, 3, 4 and 5 and/or be formed based on the method set out in Fig. 7 and/or Fig. 8. The object 900 may be formed in a layer-wise manner in a single build operation such that the rigid portion 904 and the flexible structure 902 may be formed at the same time, where these lie in a common slice of the object model, and therefore a common layer in an additive manufacturing process.

[0078] Fig. 10 shows a machine readable medium 1002 associated with a processor 1004. The machine readable medium 1002 comprises instructions 1006 which, when executed by the processor 1004, cause the processor 1004 to carry out tasks. [0079] The machine readable medium 1002 may include instructions which, when executed by the processor 1004, cause the processor 1004 to carry out any or any combination of the blocks of Fig. 7 or blocks 702-706, 802 and 804 of Fig. 8.

[0080] Examples in the present disclosure can be provided as methods, systems or machine-readable instructions, such as any combination of software, hardware, firmware or the like. Such machine-readable instructions may be included on a computer readable storage medium (including but not limited to disc storage, CD-ROM, optical storage, etc.) having computer readable program codes therein or thereon.

[0081] The present disclosure is described with reference to flow charts of the method, devices and systems according to examples of the present disclosure. Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in relation to one flow chart may be combined with those of another flow chart. It shall be understood that blocks in the flow charts, as well as combinations of the blocks in the flow charts can be realized by machine readable instructions controlling processing apparatus and/or other apparatus.

[0082] The machine-readable instructions may, for example, be executed by a general purpose computer, a special purpose computer, an embedded processor or processors of other programmable data processing devices to realize the functions described in the description and diagrams. In particular, a processor or processing apparatus may execute the machine-readable instructions. Thus, functional modules may be implemented by a processor executing machine readable instructions stored in a memory, or a processor operating in accordance with instructions embedded in logic circuitry. The term ‘processor’ is to be interpreted broadly to include a CPU, processing unit, ASIC, logic unit, or programmable gate array etc. The methods and functional modules may all be performed by a single processor or divided amongst several processors.

[0083] Such machine-readable instructions may also be stored in a computer readable storage that can guide the computer or other programmable data processing devices to operate in a specific mode.

[0084] Such machine-readable instructions may also be loaded onto a computer or other programmable data processing devices, so that the computer or other programmable data processing devices perform a series of operations to produce computer-implemented processing, thus the instructions executed on the computer or other programmable devices realize functions specified by block(s) in the flow charts.

[0085] Further, teachings herein may be implemented in the form of a computer software product, the computer software product being stored in a storage medium and comprising a plurality of instructions for making a computer device implement the methods recited in the examples of the present disclosure.

[0086] While the structures, method, apparatus and related aspects have been described with reference to certain examples, various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the present disclosure. It is intended, therefore, that the structures, method, apparatus and related aspects be limited only by the scope of the following claims and their equivalents. It should be noted that the above-mentioned examples illustrate rather than limit what is described herein, and that those skilled in the art will be able to design many alternative implementations without departing from the scope of the appended claims. [0087] The word “comprising” does not exclude the presence of elements other than those listed in a claim, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the claims.

[0088] The features of any dependent claim may be combined with the features of any of the independent claims or other dependent claims.

Claims

1. A flexible structure comprising a plurality of interlinked beams, wherein the beams are curved and are interlinked to define a plurality of concave rhombus forms, wherein each rhombus form is linked to at least two other rhombus forms.

2. The flexible structure of claim 1 , wherein the beams have a rectangular cross section.

3. The flexible structure of claim 1 , wherein each rhombus form comprises a height defined between a first pair of vertices and a width defined between a second pair of vertices, and wherein the beams comprise additional material at the first pair of vertices.

4. The flexible structure of claim 1 , which comprises at least one structural cell, each cell comprising a first set of rhombus forms linked at a common intersection and a second set of rhombus forms each linked to two other rhombus forms to form a ring, wherein the first and second set of rhombus forms are stacked such that a vertex of each rhombus form of the first set is linked to a vertex of a rhombus form of the second set and the common intersection is aligned with the center of the ring.

5. The flexible structure of claim 4 in which each cell has a height and width of less than 2 cm.

6. The flexible structure of claim 1 , which is formed by additive manufacturing.

7. The flexible structure of claim 1 in which each beam comprises a wire-like element with a cross-sectional dimension of less than 2mm.

8. The flexible structure of claim 1 in which each rhombus form has a height and width, wherein the width is greater than the height.

9. A flexible fabric, the fabric comprising a plurality of adjoining flexible structure units, each flexible structure unit comprising a plurality of interlinked concave rhombus bodies, wherein each unit comprises: a first set of rhombus bodies joined at a common intersection; and a second set of rhombus bodies each joined to two other rhombus bodies to form a ring, wherein the first and second set of rhombus bodies are stacked one on top of the other such that a vertex of each rhombus body of the first set is joined to a vertex of a rhombus body of the second set and the common intersection is aligned with the center of the ring.

10. The flexible fabric of claim 9, wherein each rhombus body is formed of beams having a rectangular cross section.

11. A method comprising, by processing circuitry: determining an intended property for a flexible structure to be formed by additive manufacturing, the flexible structure comprising a plurality of interlinked beams, wherein the beams are curved and are linked to define a plurality of concave rhombus forms, wherein each rhombus form is linked to at least two other rhombus forms, and the intended property comprises at least one of a volume of the structure, a flexibility of the structure, a resilience of the structure, a stiffness of the structure at at least one stress level, a distance of travel of the structure under impact and a durability of the structure; determining a physical attribute for the structure based on the intended property, the physical attribute comprising at least one of a size of the rhombus form and a geometrical parameter of a beam; and determining a flexible structure data model for use in generating the flexible structure having the physical attribute in additive manufacturing.

12. A method according to claim 11 wherein determining the physical attribute comprises determining a geometrical parameter comprising at least one of: a dimension of a cross section of a beam; a length of a beam; a flaring of a beam at a vertex between two beams; and a curvature of a beam.

13. A method according to claim 11 further comprising: determining an object data model for generating an object having a flexible structure incorporated therein, the object data model comprising the flexible structure data model.

14. A method according to claim 11 further comprising determining additive manufacturing instructions based on the data model, which when executed by an additive manufacturing apparatus, cause the additive manufacturing apparatus to generate the structure.

15. A method according to claim 14 further comprising executing the instructions to generate the object.