Lattice structure and method and system for fabricating the same

Abstract

A printed structure comprises (400) a first lattice (430) of multipods (432) and a second lattice (440) of multipods (442) forming a superlattice (404). The first and the second lattices are interlaced along a lateral direction perpendicular to a build direction of the printed structure, wherein multipods (442) of the second lattice (440) are inverted along the build direction with respect to multipods (432) of the first lattice (430) and are arranged in a manner that vertices (446) of multipods of the second lattice are connected to feet (434) of multipods of the first lattice.

Description

[0001] LATTICE STRUCTURE AND METHOD AND SYSTEM FOR FABRICATING THE SAME

[0002] RELATED APPLICATION / S

[0003] This application claims the benefit of priority of U.S. Provisional Patent Application No. 63 / 706,819 filed on October 14, 2025, the contents of which are incorporated herein by reference in their entirety.

[0004] FIELD AND BACKGROUND OF THE INVENTION

[0005] The present invention, in some embodiments thereof, relates to additive manufacturing and, more particularly, but not exclusively, to a lattice structure and to a method and a system for fabricating a lattice structure by additive manufacturing.

[0006] Additive manufacturing (AM) is generally a process in which a three-dimensional (3D) object is manufactured utilizing a computer model of the objects. Such a process is used in various fields, such as design related fields for purposes of visualization, demonstration and mechanical prototyping, as well as for rapid manufacturing (RM). The basic operation of any AM system consists of slicing a three-dimensional computer model into thin cross sections, translating the result into two-dimensional position data and feeding the data to control equipment which manufacture a three-dimensional structure in a layerwise manner.

[0007] One type of AM is three-dimensional inkjet printing processes. In this process, a building material is dispensed from a dispensing head having a set of nozzles to deposit layers on a supporting structure. Depending on the building material, the layers may then be cured or solidified using a suitable device.

[0008] Various three-dimensional inkjet printing techniques exist and are disclosed in, e.g., U.S. Patent Nos. 6,259,962, 6,569,373, 6,658,314, 6,850,334, 7,183,335, 7,209,797, 7,225,045, 7,300,619, 7,479,510, 7,500,846, 7,962,237, and International Publication No. WO2020 / 194318, the contents of which are hereby incorporated by reference.

[0009] SUMMARY OF THE INVENTION

[0010] According to some embodiments of the present invention there is provided a printed structure. The printed structure comprises a first lattice of multipods and a second lattice of multipods forming a superlattice, the first and the second lattices being interlaced along a lateral direction perpendicular to a build direction of the printed structure, wherein multipods of the second lattice are inverted along the build direction with respect to multipods of the first lattice and are arranged in a manner that vertices of multipods of the second lattice are connected to feet of multipods of the first lattice.

[0011] According to some embodiments of the invention multipods of the second lattice are rotated about the build direction with respect to multipods of the first lattice.

[0012] According to some embodiments of the invention all feet of at least one of the multipods of the first lattice are coplanar with a vertex of at least one of the multipods of the second lattice.

[0013] According to some embodiments of the invention a vertex of at least one of the multipods of the first lattice is coplanar with all feet of at least one of the multipods of the second lattice

[0014] According to some embodiments of the invention for at least one of the multipods of the first lattice all feet of the multipod of the first lattice are coplanar, and wherein for at least one of the multipods of the second lattice, a vertex of the multipod of the second lattice is offset from a plane defined by the feet of the multipod of the first lattice.

[0015] According to some embodiments of the invention for at least one of the multipods of the second lattice, all feet of the multipod of the second lattice are coplanar defining a plane, and wherein for at least one of the multipods of the first lattice, a vertex of the multipod of the first lattice is offset from a plane defined by the feet of the multipod of the second lattice.

[0016] According to some embodiments of the invention all feet of multipods of the first lattice are coplanar with vertices of multipods of the second lattice, and wherein all vertices of multipods of the first lattice are coplanar with all feet of multipods of the second lattice.

[0017] According to some embodiments of the invention the structure comprises a third lattice of multipods arranged to support multipods of the first and / or second lattices. According to some embodiments of the invention multipods of the third lattice are inverted along the build direction with respect to multipods of the first lattice and are arranged in a manner that vertices of multipods of the first lattice are aligned along the build direction with multipods of the third lattice.

[0018] According to some embodiments of the invention the structure comprises a bilayer superlattice formed of a sequence of alternating lattices of multipods aligned along the build direction, wherein for any pair of adjacent lattices in the bilayer superlattice, multipods of one lattice of the pair are inverted along the build direction with respect to multipods of another lattice of the pair.

[0019] According to some embodiments of the invention the superlattice comprises a lattice of pillars oriented along the build direction, each pillar being connected to a connection point between a foot of a multipod of the second lattice and a vertex of a multipod of the first lattice.

[0020] According to some embodiments of the invention all uppermost points of multipods of the first lattice with respect to the build direction, all uppermost points of multipods of the second lattice with respect to the build direction, and all uppermost points of the pillars with respect to the build direction are coplanar.

[0021] According to some embodiments of the invention all uppermost points of multipods of the first lattice with respect to the build direction, all uppermost points of multipods of the second lattice with respect to the build direction, and all uppermost points of the pillars with respect to the build direction define a multiplicity of non-coplanar planes.

[0022] According to some embodiments of the invention the structure comprises an arrangement of frusta, each frustum being oriented in a manner that a truncated base of the frustum is connected to the superlattice and a non-truncated base of the frustum is away from the superlattice along the build direction.

[0023] According to some embodiments of the invention the structure comprises an arrangement of right solid shapes, each connected to a non-truncated base of one frustum.

[0024] According to an aspect of some embodiments of the present invention there is provided a printed structure comprises a bilayer superlattice formed of a sequence of alternating lattices of multipods aligned along a build direction of the printed structure, wherein for any pair of adjacent lattices in the bilayer superlattice, multipods of one lattice of the pair are inverted along the build direction with respect to multipods of another lattice of the pair.

[0025] According to some embodiments the structure is a sacrificial support structure supporting at least a portion of a three-dimensional object.

[0026] According to some embodiments the structure is an internal structure completely surrounded by external surfaces of a three-dimensional object.

[0027] According to an aspect of some embodiments of the present invention there is provided a three-dimensional object. The three-dimensional object comprises external surfaces, an internal support structure supporting the external surfaces from inside, and a sacrificial outer support structure supporting the external surfaces from outside, wherein at least one of the internal support structure and the sacrificial outer support structure comprises the structure as delineated above and optionally and preferably as further detailed below.

[0028] According to an aspect of some embodiments of the present invention there is provided a method of additive manufacturing. The method comprises: receiving computer object data describing slices of the structure as delineated above and optionally and preferably as further detailed below, wherein the slices are perpendicular to the build direction. The method further comprises transmitting the computer object data to a controller of an additive manufacturing system for additive manufacturing of layers in configured patterns respectively corresponding to the slices. According to an aspect of some embodiments of the present invention there is provided a system for additive manufacturing. The system comprises: a dispensing head for dispensing a building material; and a computerized controller configured for receiving computer object data describing slices of the structure as delineated above and optionally and preferably as further detailed below, wherein the slices are perpendicular to the build direction. The computerized controller is also configured for operating the dispensing head to dispense a building material in layers in configured patterns respectively corresponding to the slices.

[0029] According to an aspect of some embodiments of the present invention there is provided a method of fabricating a three-dimensional object. The method comprises: dispensing at least one building material in layers stacked along a build direction to form a lower superlattice comprising interconnected voids. The lower superlattice is optionally and preferably a bilayer superlattice formed of a sequence of alternating lattices of multipods aligned along the build direction, wherein for any pair of adjacent lattices in the bilayer superlattice, multipods of one lattice of the pair are inverted along the build direction with respect to multipods of another lattice of the pair. The method also comprises dispensing at least one building material in layers stacked along the build direction to form an upper superlattice on the lower superlattice comprising interconnected voids. The upper superlattice optionally and preferably comprises a first lattice of multipods interlaced with a second lattice of multipods along a lateral direction perpendicular to the build direction, wherein multipods of the second lattice are inverted along the build direction with respect to multipods of the first lattice and are arranged in a manner that vertices of multipods of the second lattice are connected to feet of multipods of the first lattice.

[0030] According to some embodiments of the invention the method comprises, for each layer, dispensing at least one building material to form a continuous periphery to the layer.

[0031] According to some embodiments of the invention the method comprises dispensing at least one building material to form a continuous base of the three-dimensional object, wherein the lower superlattice is formed on the continuous base.

[0032] According to some embodiments of the invention multipods of the second lattice are rotated about the build direction with respect to multipods of the first lattice.

[0033] According to some embodiments of the invention the upper superlattice comprises a lattice of pillars oriented along the build direction, each pillar being connected to a connection point between a foot of a multipod of the second lattice and a vertex of a multipod of the first lattice.

[0034] According to some embodiments of the invention the method comprises dispensing at least one building material in layers to form an arrangement of frusta, each frustum being oriented in a manner that a truncated base of the frustum is connected to the upper superlattice and a nontruncated base of the frustum is away from the superlattice along the build direction.

[0035] According to some embodiments of the invention the method comprises dispensing a right solid shape on each frustum, thereby forming an arrangement of right solid shapes on the arrangement of frusta.

[0036] According to some embodiments of the invention at least two of the right solid shapes have different lengths along the build direction.

[0037] According to an aspect of some embodiments of the present invention there is provided a method of fabricating a three-dimensional object. The method comprises: receiving computer object data describing the three-dimensional object, and selecting at least one region of the three- dimensional object, based on the computer object data. The method also comprises selecting parameters defining a support structure based on a geometry of the at least one region, wherein the support structure has a lower superlattice and an upper superlattice, each superlattice comprising interconnected voids. The method also comprises constructing, based on the parameters, computer object data describing the support structure, combining the computer object data describing the support structure with the computer object data describing the three-dimensional object to provide a combined computer object dataset describing an object assembly having at least one outer surface supported by the support structure. The method further comprises slicing the combined computer object dataset into a plurality of slices, each defined over a plurality of voxels, and dispensing at least one building material to form a plurality of layers stacked along a build direction and respectively corresponding to the plurality of slices. According to some embodiments of the present invention wherein the lower superlattice is a bilayer superlattice formed of a sequence of alternating lattices of multipods aligned along a build direction, wherein for any pair of adjacent lattices in the bilayer superlattice, multipods of one lattice of the pair are inverted along the build direction with respect to multipods of another lattice of the pair. According to some embodiments of the present invention the upper superlattice comprises a first lattice of multipods interlaced with a second lattice of multipods along a lateral direction perpendicular to the build direction, wherein multipods of the second lattice are inverted along the build direction with respect to multipods of the first lattice and are arranged in a manner that vertices of multipods of the second lattice are connected to feet of multipods of the first lattice.

[0038] According to some embodiments of the invention the object assembly represents an embedding of the support structure in the three-dimensional object.

[0039] According to some embodiments of the invention the object assembly represents a contiguous external contact between the support structure and the three-dimensional object. According to some embodiments of the invention multipods of the second lattice are rotated about the build direction with respect to multipods of the first lattice.

[0040] According to some embodiments of the invention the upper superlattice comprises a lattice of pillars oriented along the build direction, each pillar being connected to a connection point between a foot of a multipod of the second lattice and a vertex of a multipod of the first lattice.

[0041] According to some embodiments of the invention the support structure comprises an arrangement of frusta, each frustum being oriented in a manner that a truncated base of the frustum is connected to the upper superlattice and a non-truncated base of the frustum is away from the superlattice along the build direction.

[0042] According to some embodiments of the invention for any group of three or more adjacent frusta, there is a lateral overlap among non-truncated bases of all frusta in the group.

[0043] According to an aspect of some embodiments of the present invention there is provided a system for additive manufacturing. The system comprises: a dispensing head for dispensing a building material; and a computerized controller configured for executing the method as delineated above and optionally and preferably as further detailed below.

[0044] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

[0045] Implementation of the method and / or system of embodiments of the invention can involve performing or completing selected tasks manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of embodiments of the method and / or system of the invention, several selected tasks could be implemented by hardware, by software or by firmware or by a combination thereof using an operating system.

[0046] For example, hardware for performing selected tasks according to embodiments of the invention could be implemented as a chip or a circuit. As software, selected tasks according to embodiments of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In an exemplary embodiment of the invention, one or more tasks according to exemplary embodiments of method and / or system as described herein are performed by a data processor, such as a computing platform for executing a plurality of instructions. Optionally, the data processor includes a volatile memory for storing instructions and / or data and / or a non-volatile storage, for example, a magnetic hard-disk and / or removable media, for storing instructions and / or data. Optionally, a network connection is provided as well. A display and / or a user input device such as a keyboard or mouse are optionally provided as well.

[0047] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0048] Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

[0049] In the drawings:

[0050] FIGs. 1A-D are schematic illustrations of additive manufacturing systems according to some embodiments of the invention;

[0051] FIGs. 2A-2C are schematic illustrations of printing heads according to some embodiments of the present invention;

[0052] FIGs. 3A and 3B are schematic illustrations demonstrating coordinate transformations according to some embodiments of the present invention;

[0053] FIG. 4 is a schematic illustration of a three-dimensional printed structure, according to some embodiments of the present invention;

[0054] FIG. 5 is a schematic illustration of a three-dimensional printed structure, according to embodiments of the invention in which the shape of the printed structure is not cuboidal;

[0055] FIGs. 6A-G are schematic illustrations of one superlattice of the three-dimensional printed structure according to some embodiments of the present invention;

[0056] FIGs. 7A-C are schematic illustrations of another superlattice of the three-dimensional printed structure according to some embodiments of the present invention;

[0057] FIGs. 8A-E are schematic illustrations which exemplify lattices that can form the superlattice shown in FIGs. 7A-C according to some embodiments of the present invention;

[0058] FIG. 9 is a schematic illustration of a top section of the three-dimensional printed structure according to some embodiments of the present invention;

[0059] FIG. 10 is a schematic illustration of a frustum and a right solid shape of the top section shown in FIG. 9, according to some embodiments of the present invention; FIGs. 11A and 11B are schematic illustrations showing a relation between the superlattice shown in FIGs. 7A-C and the elements of the section shown in FIG. 9, according to some embodiments of the present invention;

[0060] FIG. 12 is a schematic illustration demonstrating overlaps among adjacent frusta in the section shown in FIG. 9, according to some embodiments of the present invention;

[0061] FIG. 13 is a flowchart diagram of a method suitable for encoding data for additive manufacturing, according to some embodiments of the present invention;

[0062] FIG. 14 is a flowchart diagram of a method suitable for fabricating a three-dimensional object, according to some embodiments of the present invention;

[0063] FIGs. 15A-D are schematic illustrations showing graphical user interface (GUI) screens that can be used according to some embodiments of the present invention to receive input for the construction of computer object data describing the three-dimensional structure shown in FIG. 4;

[0064] FIG. 16 is a flowchart diagram of another method suitable for additive manufacturing, according to various exemplary embodiments of the present invention;

[0065] FIGs. 17A-C are schematic illustrations of an object which is defined as an assembly of two shells, according to some embodiments of the present invention; and

[0066] FIGs. 18A-C are schematic illustrations of a three-dimensional object assembly 113, according to some embodiments of the present invention.

[0067] DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0068] The present invention, in some embodiments thereof, relates to additive manufacturing and, more particularly, but not exclusively, to a lattice structure and to a method and a system for fabricating a lattice structure by additive manufacturing.

[0069] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and / or methods set forth in the following description and / or illustrated in the drawings and / or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

[0070] The method and system of the present embodiments manufacture three-dimensional objects based on computer object data in a layerwise manner by forming a plurality of layers in a configured pattern corresponding to the shape of the objects. The formation of the layers is optionally and preferably by printing, more preferably by inkjet printing. The computer object data can be in any known format, including, without limitation, a Standard Tessellation Language (STL) or a StereoLithography Contour (SLC) format, an OBJ File format (OBJ), a 3D Manufacturing Format (3MF), Virtual Reality Modeling Language (VRML), Additive Manufacturing File (AMF) format, Drawing Exchange Format (DXF), Polygon File Format (PLY), or any other format suitable for Computer-Aided Design (CAD). The computer object data may also be in a format generated by a 3D printer software, viewer, or slicer (e.g., PNG, BMP, GCVF).

[0071] Typically, the outer shape of the object to be manufactured is selected by means of appropriate software, e.g., CAD software or the like. The software typically generates computer object data in the form of graphic elements (e.g., a mesh of polygons, non-uniform rational basis splines, etc.) defining a surface of the object. The graphic elements are processed by a computer which employs software known as "a slicer" that transforms the graphic elements to a grid of voxels that define the internal shape of the object, and that are arranged as a plurality of slices, each comprising a plurality of voxels describing a layer of the 3D object.

[0072] Each layer of the object can be formed by an AM apparatus which scans a two-dimensional surface and patterns it. While scanning, the apparatus visits a plurality of target locations on the two-dimensional layer or surface, and decides, for each target location or a group of target locations, whether or not the target location or group of target locations is to be occupied by building material formulation, and which type of building material formulation is to be delivered thereto. The decision is made according to a computer image of the surface.

[0073] In preferred embodiments of the present invention the AM comprises three-dimensional printing, more preferably three-dimensional inkjet printing. In these embodiments a building material is dispensed from a printing head having one or more arrays of nozzles to deposit building material in layers on a supporting structure. The AM apparatus thus dispenses building material in target locations which are to be occupied and leaves other target locations void. The apparatus typically includes a plurality of arrays of nozzles, each of which can be configured to dispense a different building material. This is typically achieved by providing the printing head with a plurality of fluid channels separated from each other, wherein each channel receives a different building material through a separate inlet and conveys it to a different array of nozzles.

[0074] Thus, different target locations can be occupied by different building material formulations. The types of building material formulations can be categorized into two major categories: modeling material formulation and support material formulation. The support material formulation serves as a supporting matrix or construction for supporting the object or object parts during the fabrication process and / or other purposes, e.g., providing hollow or porous objects. Support constructions may additionally include modeling material formulation elements, e.g. for further support strength. The modeling material formulation is generally a composition which is formulated for use in additive manufacturing and which is able to form a three-dimensional object on its own, without having to be mixed or combined with any other substance.

[0075] The final three-dimensional object is made of the modeling material formulation or a combination of modeling material formulations or modeling and support material formulations or modification thereof (e.g., following curing). All these operations are well-known to those skilled in the art of solid freeform fabrication.

[0076] In some exemplary embodiments of the invention an object is manufactured by dispensing two or more different modeling material formulations, each material formulation from a different array of nozzles (belonging to the same or different printing heads) of the AM apparatus. In some embodiments, two or more such arrays of nozzles that dispense different modeling material formulations are both located in the same printing head of the AM apparatus. In some embodiments, arrays of nozzles that dispense different modeling material formulations are located in separate printing heads, for example, a first array of nozzles dispensing a first modeling material formulation is located in a first printing head, and a second array of nozzles dispensing a second modeling material formulation is located in a second printing head.

[0077] In some embodiments, an array of nozzles that dispense a modeling material formulation and an array of nozzles that dispense a support material formulation are both located in the same printing head. In some embodiments, an array of nozzles that dispense a modeling material formulation and an array of nozzles that dispense a support material formulation are located in separate printing heads.

[0078] A representative and non-limiting example of a system 110 suitable for AM of an object 112 according to some embodiments of the present invention is illustrated in FIG. 1A. System 110 comprises an additive manufacturing apparatus 114 having a dispensing unit 16 which comprises a plurality of printing heads. Each head preferably comprises one or more arrays of nozzles 122, typically mounted on an orifice plate 121, as illustrated in FIGs. 2A-C described below, through which a liquid building material formulation 124 is dispensed.

[0079] Preferably, but not obligatorily, apparatus 114 is a three-dimensional printing apparatus, in which case the printing heads are printing heads, and the building material formulation is dispensed via inkjet technology. This need not necessarily be the case, since, for some applications, it may not be necessary for the additive manufacturing apparatus to employ three-dimensional printing techniques. Representative examples of additive manufacturing apparatus contemplated according to various exemplary embodiments of the present invention include, without limitation, fused deposition modeling apparatus and fused material formulation deposition apparatus. Each printing head is optionally and preferably fed via one or more building material formulation reservoirs which may optionally include a temperature control unit (e.g. , a temperature sensor and / or a heating device), and a material formulation level sensor. To dispense the building material formulation, a voltage signal is applied to the printing heads to selectively deposit droplets of material formulation via the printing head nozzles, for example, as in piezoelectric inkjet printing technology. Another example includes thermal inkjet printing heads. In these types of heads, there are heater elements in thermal contact with the building material formulation, for heating the building material formulation to form gas bubbles therein, upon activation of the heater elements by a voltage signal. The gas bubbles generate pressures in the building material formulation, causing droplets of building material formulation to be ejected through the nozzles. Piezoelectric and thermal printing heads are known to those skilled in the art of solid freeform fabrication. For any types of inkjet printing heads, the dispensing rate of the head depends on the number of nozzles, the type of nozzles and the applied voltage signal rate (frequency).

[0080] Optionally, the overall number of dispensing nozzles or nozzle arrays is selected such that half of the dispensing nozzles are designated to dispense support material formulation and half of the dispensing nozzles are designated to dispense modeling material formulation, i.e. the number of nozzles jetting modeling material formulations is the same as the number of nozzles jetting support material formulation. In the representative example of FIG. 1A, four printing heads 16a, 16b, 16c and 16d are illustrated. Each of heads 16a, 16b, 16c and 16d has a nozzle array. In this Example, heads 16a and 16b can be designated for modeling material formulation / s and heads 16c and 16d can be designated for support material formulation. Thus, head 16a can dispense one modeling material formulation, head 16b can dispense another modeling material formulation and heads 16c and 16d can both dispense support material formulation. In an alternative embodiment, heads 16c and 16d, for example, may be combined in a single head having two nozzle arrays for depositing support material formulation. In a further alternative embodiment any one or more of the printing heads may have more than one nozzle arrays for depositing more than one material formulation, e.g. two nozzle arrays for depositing two different modeling material formulations or a modeling material formulation and a support material formulation, each formulation via a different array or number of nozzles.

[0081] Yet it is to be understood that it is not intended to limit the scope of the present invention and that the number of modeling material formulation printing heads (modeling heads) and the number of support material formulation printing heads (support heads) may differ. In some embodiments, the number of arrays of nozzles that dispense modeling material formulation, the number of arrays of nozzles that dispense support material formulation, and the number of nozzles in each respective array are selected such as to provide a predetermined ratio, a, between the maximal dispensing rate of the support material formulation and the maximal dispensing rate of modeling material formulation. The value of the predetermined ratio, a, is preferably selected to ensure that in each formed layer, the height of modeling material formulation equals the height of support material formulation. Typical values for a are from about 0.6 to about 1.5.

[0082] As used herein throughout the term “about” refers to ± 10 %.

[0083] For example, for a = 1, the overall dispensing rate of support material formulation is generally the same as the overall dispensing rate of the modeling material formulation when all the arrays of nozzles operate.

[0084] Apparatus 114 can comprise, for example, M modeling heads each having m arrays of p nozzles, and S support heads each having s arrays of q nozzles such that Mxmxp = Sxsxq. Each of the Mxm modeling arrays and Sxs support arrays can be manufactured as a separate physical unit, which can be assembled and disassembled from the group of arrays. In this embodiment, each such array optionally and preferably comprises a temperature control unit and a material formulation level sensor of its own, and receives an individually controlled voltage for its operation.

[0085] Apparatus 114 can further comprise a solidifying device 324 which can include any device configured to emit light, heat or the like that may cause the deposited material formulation to harden. For example, solidifying device 324 can comprise one or more radiation sources, which can be, for example, an ultraviolet or visible or infrared lamp, or other sources of electromagnetic radiation, or electron beam source, depending on the modeling material formulation being used. In some embodiments of the present invention, solidifying device 324 serves for curing or solidifying the modeling material formulation.

[0086] In addition to solidifying device 324, apparatus 114 optionally and preferably comprises an additional radiation source 328 for solvent evaporation. Radiation source 328 optionally and preferably generates infrared radiation. In various exemplary embodiments of the invention solidifying device 324 comprises a radiation source generating ultraviolet radiation, and radiation source 328 generates infrared radiation.

[0087] In some embodiments of the present invention apparatus 114 comprises cooling system 134 such as one or more fans or the like

[0088] The printing head(s) and radiation source are preferably mounted in a frame or block 128 which is preferably operative to reciprocally move over a tray 360, which serves as the working surface. In some embodiments of the present invention the radiation sources are mounted in the block such that they follow in the wake of the printing heads to at least partially cure or solidify the material formulations just dispensed by the printing heads. Tray 360 is positioned horizontally. According to the common conventions an X-Y-Z Cartesian coordinate system is selected such that the X-Y plane is parallel to tray 360. Tray 360 is preferably configured to move vertically (along the Z direction), typically downward. In various exemplary embodiments of the invention, apparatus 114 further comprises one or more leveling devices 32, e.g. a roller 326. Leveling device 326 serves to straighten, level and / or establish a thickness of the newly formed layer prior to the formation of the successive layer thereon. Leveling device 32 preferably comprises a waste collection device 136 for collecting the excess material formulation generated during leveling. Waste collection device 136 may comprise any mechanism that delivers the material formulation to a waste tank or waste cartridge.

[0089] In use, the printing heads of unit 16 move in a scanning direction, which is referred to herein as the X direction, and selectively dispense building material formulation in a predetermined configuration in the course of their passage over tray 360. The building material formulation typically comprises one or more types of support material formulation and one or more types of modeling material formulation. The passage of the printing heads of unit 16 is followed by the curing of the modeling material formulation(s) by radiation source 126. In the reverse passage of the heads, back to their starting point for the layer just deposited, an additional dispensing of building material formulation may be carried out, according to predetermined configuration. In the forward and / or reverse passages of the printing heads, the layer thus formed may be straightened by leveling device 32, which preferably follows the path of the printing heads in their forward and / or reverse movement. Once the printing heads return to their starting point along the X direction, they may move to another position along an indexing direction, referred to herein as the Y direction, and continue to build the same layer by reciprocal movement along the X direction. Alternately, the printing heads may move in the Y direction between forward and reverse movements or after more than one forward-reverse movement. The series of scans performed by the printing heads to complete a single layer is referred to herein as a single scan cycle.

[0090] Once the layer is completed, tray 360 is lowered in the Z direction to a predetermined Z level, according to the desired thickness of the layer subsequently to be printed. The procedure is repeated to form three-dimensional object 112 in a layerwise manner.

[0091] In another embodiment, tray 360 may be displaced in the Z direction between forward and reverse passages of the printing head of unit 16, within the layer. Such Z displacement is carried out in order to cause contact of the leveling device with the surface in one direction and prevent contact in the other direction. The present embodiments contemplate use of a liquid material formulation supply system 330, which comprises one or more liquid material containers or cartridges 431, and which supplies the liquid material(s) to printing heads. Supply system 330 can be used in an AM system such as system 110, in which case the liquid material in each container is a building material.

[0092] A controller 20 controls fabrication apparatus 114 and optionally and preferably also supply system 330. Controller 20 typically includes an electronic circuit configured to perform the controlling operations. Controller 20 preferably communicates with a computer 24 which transmits digital data pertaining to fabrication instructions based on computer object data, e.g., a CAD configuration represented on a computer readable medium in a form of a Standard Tessellation Language (STL) format or the like. Typically, controller 20 controls the voltage applied to each printing head or each nozzle array and the temperature of the building material formulation in the respective printing head or respective nozzle array.

[0093] Once the manufacturing data is loaded to controller 20 it can operate without user intervention. In some embodiments, controller 20 receives additional input from the operator, e.g., using computer 24 or using a user interface 116 communicating with controller 20. User interface 116 can be of any type known in the art, such as, but not limited to, a keyboard, a touch screen and the like. For example, controller 20 can receive, as additional input, one or more building material formulation types and / or attributes, such as, but not limited to, color, characteristic distortion and / or transition temperature, viscosity, electrical property, magnetic property. Other attributes and groups of attributes are also contemplated.

[0094] Another representative and non-limiting example of a system 10 suitable for AM of an object according to some embodiments of the present invention is illustrated in FIGs. 1B-D. FIGs. 1B-D illustrate a top view (FIG. IB), a side view (FIG. 1C) and an isometric view (FIG. ID) of system 10.

[0095] In the present embodiments, system 10 comprises a tray 12 and a plurality of inkjet printing heads 16, each having one or more arrays of nozzles with respective one or more pluralities of separated nozzles. The material used for the three-dimensional printing is supplied to heads 16 by building material supply system 330, with one or more liquid material containers or cartridges 431, as further detailed hereinabove. Tray 12 can have a shape of a disk or it can be annular. Non-round shapes are also contemplated, provided they can be rotated about a vertical axis.

[0096] Tray 12 and heads 16 are optionally and preferably mounted such as to allow a relative rotary motion between tray 12 and heads 16. This can be achieved by (i) configuring tray 12 to rotate about a vertical axis 14 relative to heads 16, (ii) configuring heads 16 to rotate about vertical axis 14 relative to tray 12, or (iii) configuring both tray 12 and heads 16 to rotate about vertical axis 14 but at different rotation velocities (e.g., rotation at opposite direction). While some embodiments of system 10 are described below with a particular emphasis to configuration (i) wherein the tray is a rotary tray that is configured to rotate about vertical axis 14 relative to heads 16, it is to be understood that the present application contemplates also configurations (ii) and (iii) for system 10. Any one of the embodiments of system 10 described herein can be adjusted to be applicable to any of configurations (ii) and (iii), and one of ordinary skills in the art, provided with the details described herein, would know how to make such adjustment.

[0097] In the following description, a direction parallel to tray 12 and pointing outwardly from axis 14 is referred to as the radial direction r, a direction parallel to tray 12 and perpendicular to the radial direction r is referred to herein as the azimuthal direction <p, and a direction perpendicular to tray 12 is referred to herein is the vertical or build direction z.

[0098] The radial direction r in system 10 enacts the indexing direction y in system 110, and the azimuthal direction cp enacts the scanning direction x in system 110. Therefore, the radial direction is interchangeably referred to herein as the indexing direction, and the azimuthal direction is interchangeably referred to herein as the scanning direction.

[0099] The term “radial position,” as used herein, refers to a position on or above tray 12 at a specific distance from axis 14. When the term is used in connection to a printing head, the term refers to a position of the head which is at specific distance from axis 14. When the term is used in connection to a point on tray 12, the term corresponds to any point that belongs to a locus of points that is a circle whose radius is the specific distance from axis 14 and whose center is at axis 14.

[0100] The term “azimuthal position,” as used herein, refers to a position on or above tray 12 at a specific azimuthal angle relative to a predetermined reference point. Thus, radial position refers to any point that belongs to a locus of points that is a straight line forming the specific azimuthal angle relative to the reference point.

[0101] The term “vertical position,” as used herein, refers to a position over a plane that intersect the vertical axis 14 at a specific point.

[0102] Tray 12 serves as a building platform for three-dimensional printing. The working area on which one or objects are printed is typically, but not necessarily, smaller than the total area of tray 12. In some embodiments of the present invention the working area is annular. The working area is shown at 26. In some embodiments of the present invention tray 12 rotates continuously in the same direction throughout the formation of object, and in some embodiments of the present invention tray reverses the direction of rotation at least once (e.g., in an oscillatory manner) during the formation of the object. Tray 12 is optionally and preferably removable. Removing tray 12 can be for maintenance of system 10, or, if desired, for replacing the tray before printing a new object. In some embodiments of the present invention system 10 is provided with one or more different replacement trays (e.g., a kit of replacement trays), wherein two or more trays are designated for different types of objects (e.g., different weights) different operation modes (e.g., different rotation speeds), etc. The replacement of tray 12 can be manual or automatic, as desired. When automatic replacement is employed, system 10 comprises a tray replacement device 36 configured for removing tray 12 from its position below heads 16 and replacing it by a replacement tray (not shown). In the representative illustration of FIG. IB tray replacement device 36 is illustrated as a drive 38 with a movable arm 40 configured to pull tray 12, but other types of tray replacement devices are also contemplated.

[0103] Exemplified embodiments for the printing head 16 are illustrated in FIGs. 2A-2C. These embodiments can be employed for any of the AM systems described above, including, without limitation, system 110 and system 10.

[0104] FIGs. 2A-B illustrate a printing head 16 with one (FIG. 2A) and two (FIG. 2B) nozzle arrays 22. The nozzles in the array are preferably aligned linearly, along a straight line. Printing head 16 is fed by a liquid material and dispenses it through the nozzle arrays 22, in response to a voltage signal applied thereto by the controller of the printing system. Head 16 is fed by a liquid material which is a building material formulation.

[0105] In embodiments in which a particular printing head has two or more linear nozzle arrays, the nozzle arrays are optionally and preferably can be parallel to each other. When a printing head has two or more arrays of nozzles (e.g., FIG. 2B) all arrays of the head can be fed with the same building material formulation, or at least two arrays of the same head can be fed with different building material formulations.

[0106] When a system similar to system 110 is employed, all printing heads 16 are optionally and preferably oriented along the indexing direction with their positions along the scanning direction being offset to one another.

[0107] When a system similar to system 10 is employed, all printing heads 16 are optionally and preferably oriented radially (parallel to the radial direction) with their azimuthal positions being offset to one another. Thus, in these embodiments, the nozzle arrays of different printing heads are not parallel to each other but are rather at an angle to each other, which angle being approximately equal to the azimuthal offset between the respective heads. For example, one head can be oriented radially and positioned at azimuthal position 91, and another head can be oriented radially and positioned at azimuthal position 92. In this example, the azimuthal offset between the two heads is 91-92, and the angle between the linear nozzle arrays of the two heads is also 91-92. In some embodiments, two or more printing heads can be assembled to a block of printing heads, in which case the printing heads of the block are typically parallel to each other. A block including several inkjet printing heads 16a, 16b, 16c is illustrated in FIG. 2C.

[0108] In some embodiments, system 10 comprises a stabilizing structure 30 positioned below heads 16 such that tray 12 is between stabilizing structure 30 and heads 16. Stabilizing structure 30 may serve for preventing or reducing vibrations of tray 12 that may occur while inkjet printing heads 16 operate. In configurations in which printing heads 16 rotate about axis 14, stabilizing structure 30 preferably also rotates such that stabilizing structure 30 is always directly below heads 16 (with tray 12 between heads 16 and tray 12).

[0109] Tray 12 and / or printing heads 16 is optionally and preferably configured to move along the vertical direction z, parallel to vertical axis 14 so as to vary the vertical distance between tray 12 and printing heads 16. In configurations in which the vertical distance is varied by moving tray 12 along the vertical direction, stabilizing structure 30 preferably also moves vertically together with tray 12. In configurations in which the vertical distance is varied by heads 16 along the vertical direction, while maintaining the vertical position of tray 12 fixed, stabilizing structure 30 is also maintained at a fixed vertical position.

[0110] The vertical motion can be established by a vertical drive 28. Once a layer is completed, the vertical distance between tray 12 and heads 16 can be increased (e.g., tray 12 is lowered relative to heads 16) by a predetermined vertical step, according to the desired thickness of the layer subsequently to be printed. The procedure is repeated to form a three-dimensional object in a layerwise manner.

[0111] The operation of inkjet printing heads 16 and optionally and preferably also of one or more other components of system 10, e.g., the motion of tray 12, are controlled by a controller 20. The controller can have an electronic circuit and a non-volatile memory medium readable by the circuit, wherein the memory medium stores program instructions which, when read by the circuit, cause the circuit to perform control operations as further detailed below.

[0112] Controller 20 can also communicate with a host computer 24 which transmits digital data pertaining to fabrication instructions based on computer object data which can be according to any format suitable for additive manufacturing, such as, but not limited to, one of the aforementioned formats.

[0113] The object data formats can be structured according to a Cartesian system of coordinates. In these cases, computer 24 preferably executes a procedure for transforming the coordinates of each slice in the computer object data from a Cartesian system of coordinates into a polar system of coordinates. Computer 24 optionally and preferably transmits the fabrication instructions in terms of the transformed system of coordinates. Alternatively, computer 24 can transmit the fabrication instructions in terms of the original system of coordinates as provided by the computer object data, in which case the transformation of coordinates is executed by the circuit of controller 20.

[0114] The transformation of coordinates allows three-dimensional printing over a rotating tray. In non-rotary systems with a stationary tray with the printing heads typically reciprocally move above the stationary tray along straight lines. In such systems, the printing resolution is the same at any point over the tray, provided the dispensing rates of the heads are uniform. In system 10, unlike non-rotary systems, not all the nozzles of the head points cover the same distance over tray 12 during at the same time. The transformation of coordinates is optionally and preferably executed so as to ensure equal amounts of excess material formulation at different radial positions. Representative examples of coordinate transformations according to some embodiments of the present invention are provided in FIGs. 3A-B, showing three slices of an object (each slice corresponds to fabrication instructions of a different layer of the objects), where FIG. 3A illustrates a slice in a Cartesian system of coordinates and FIG. 3B illustrates the same slice following an application of a transformation of coordinates procedure to the respective slice.

[0115] Typically, controller 20 controls the voltage applied to the respective component of the system 10 based on the fabrication instructions and based on the stored program instructions as described below.

[0116] Generally, controller 20 controls printing heads 16 to dispense, during the rotation of tray 12, droplets of building material formulation in layers, such as to print a three-dimensional object on tray 12.

[0117] System 10 optionally and preferably comprises one or more radiation sources 18, which can be, for example, an ultraviolet or visible or infrared lamp, or other sources of electromagnetic radiation, or electron beam source, depending on the modeling material formulation being used. Radiation source can include any type of radiation emitting device, including, without limitation, light emitting diode (LED), digital light processing (DLP) system, resistive lamp and the like. Radiation source 18 serves for curing or solidifying the modeling material formulation. In various exemplary embodiments of the invention the operation of radiation source 18 is controlled by controller 20 which may activate and deactivate radiation source 18 and may optionally also control the amount of radiation generated by radiation source 18.

[0118] In some embodiments of the invention, system 10 further comprises one or more leveling devices 32 which can be manufactured as a roller 326 or a blade. Leveling device 32 serves to straighten the newly formed layer prior to the formation of the successive layer thereon. In some embodiments, leveling device 32 has the shape of a conical roller positioned such that its symmetry axis 34 is tilted relative to the surface of tray 12 and its surface is parallel to the surface of the tray. This embodiment is illustrated in the side view of system 10 (FIG. 1C).

[0119] The conical roller can have the shape of a cone or a conical frustum.

[0120] The opening angle of the conical roller is preferably selected such that there is a constant ratio between the radius of the cone at any location along its axis 34 and the distance between that location and axis 14. This embodiment allows roller 32 to efficiently level the layers, since while the roller rotates, any point p on the surface of the roller has a linear velocity which is proportional (e.g., the same) to the linear velocity of the tray at a point vertically beneath point p. In some embodiments, the roller has a shape of a conical frustum having a height h, a radius Ri at its closest distance from axis 14, and a radius R2 at its farthest distance from axis 14, wherein the parameters h, R\ and R satisfy the relation R\IRz={R-h)lh and wherein R is the farthest distance of the roller from axis 14 (for example, R can be the radius of tray 12).

[0121] The operation of leveling device 32 is optionally and preferably controlled by controller 20 which may activate and deactivate leveling device 32 and may optionally also control its position along a vertical direction (parallel to axis 14) and / or a radial direction (parallel to tray 12 and pointing toward or away from axis 14.

[0122] In some embodiments of the present invention printing heads 16 are configured to reciprocally move relative to tray along the radial direction r. These embodiments are useful when the lengths of the nozzle arrays 22 of heads 16 are shorter than the width along the radial direction of the working area 26 on tray 12. The motion of heads 16 along the radial direction is optionally and preferably controlled by controller 20.

[0123] Some embodiments contemplate the fabrication of an object by dispensing different material formulations from different arrays of nozzles (belonging to the same or different printing head). These embodiments provide, inter alia, the ability to select material formulations from a given number of material formulations and define desired combinations of the selected material formulations and their properties. According to the present embodiments, the spatial locations of the deposition of each material formulation with the layer is defined, either to effect occupation of different three-dimensional spatial locations by different material formulations, or to effect occupation of substantially the same three-dimensional location or adjacent three-dimensional locations by two or more different material formulations so as to allow post deposition spatial combination of the material formulations within the layer, thereby to form a composite material formulation at the respective location or locations. Any post deposition combination or mix of modeling material formulations is contemplated. For example, once a certain material formulation is dispensed it may preserve its original properties. However, when it is dispensed simultaneously with another modeling material formulation or other dispensed material formulations which are dispensed at the same or nearby locations, a composite material formulation having a different property or properties to the dispensed material formulations may be formed.

[0124] When the object is fabricated by dispensing more than one material formulation, the computer object data may optionally and preferably also comprise material assignment data, which assign a specific type of material formulation to each voxel or group of voxels, and therefore provide the controller with information regarding the type of material formulation to be dispensed at each voxel.

[0125] In some embodiments of the present invention the system dispenses digital material formulation for at least one of the layers.

[0126] The phrase “digital material formulations”, as used herein and in the art, describes a combination of two or more material formulations on a pixel level or voxel level such that pixels or voxels of different material formulations are interlaced with one another over a region. Such digital material formulations may exhibit new properties that are affected by the selection of types of material formulations and / or the ratio and relative spatial distribution of two or more material formulations.

[0127] As used herein, a "voxel" of a layer refers to a physical three-dimensional elementary volume within the layer that corresponds to a single pixel of a bitmap describing the layer. The size of a voxel is approximately the size of a region that is formed by a building material, once the building material is dispensed at a location corresponding to the respective pixel, leveled, and solidified. The building material dispensed to form a voxel comprises one or more drops of building material dispensed by at least one inkjet printhead.

[0128] In the context of a digital material, the interlacing can be either among single voxels, each containing a different building material, or among blocks of voxels wherein a block of voxels is defined as a continues region that is occupied by n voxels all containing the same building material, and wherein the border of this region is define as a collection of voxels that are adjacent to at least one voxel that contains a building material other than the building material contained in the voxels of the collection. In preferred embodiments, n is less than 1000, or less than 500, or less than 100, or less than 50, or less than 10.

[0129] In exemplary digital materials, the modeling material of each voxel or voxel block, obtained upon curing, is independent of the modeling material of a neighboring voxel or voxel block, obtained upon curing, such that each voxel or voxel block may result in a different model material and the new properties of the whole part are a result of a spatial combination, on the voxel level, of several different model materials.

[0130] The present embodiments thus enable the deposition of a broad range of material formulation combinations, and the fabrication of an object which may consist of multiple different combinations of material formulations, in different parts of the object, according to the properties desired to characterize each part of the object.

[0131] Further details on the principles and operations of an AM system suitable for the present embodiments are found in U.S. Patent No. 9,031,680, the contents of which are hereby incorporated by reference.

[0132] The present embodiments comprise a technique for fabricating a three-dimensional structure, which comprises structural elements and interconnected voids between the structural elements, by additive manufacturing, e.g., by means of system 10 or 110. The voids do not contain building material, but contain a non-solid substance, optionally and preferably a gas, such as, but not limited to, air. The advantage of fabricating a three-dimensional object with regions that do not contain building material is that the amount of building material that is required, and typically also the amount of produced waste and / or the associated fabrication cost, is reduced. Since the voids are made of a substance that is different from the building material building the structural elements, the mechanical properties (e.g., elasticity, compliance, density) and / or optical properties (e.g., optical density, transparency, opacity) of the fabricated structure are different from the mechanical properties of the structure, had it been fabricated without such voids, and so the amount, the size, and / or the distribution of the structural elements can be selected to provide the object with mechanical and / or optical properties that would not be obtainable had the object been a conventional solid object.

[0133] The three-dimensional structure according to some embodiments of the present invention typically serves as a support structure for a three-dimensional object which is also fabricated by additive manufacturing, wherein the three-dimensional structure and the three-dimensional object can be fabricated during the same additive manufacturing process. For example, a particular layer fabricated during the additive manufacturing process can include both regions belonging to the three-dimensional structure and regions belonging to other parts (e.g., external surfaces) of the object. When the three-dimensional structure serves as a support structure for a three-dimensional object, the support structure and the object supported by the support structure are referred to herein as a three-dimensional object assembly. The support structure of the three-dimensional object assembly can be internal and / or external with respect to an outer surface of the object, wherein when the support structure is internal with respect to an outer surface of the object, the object assembly is described geometrically as a partial embedding or more preferably a complete embedding of the support structure in the three- dimensional object, and when the support structure is external with respect to an outer surface of the object, the object assembly is described geometrically as an external contiguity between the support structure and the three-dimensional object.

[0134] FIGs. 18A-C are schematic illustrations of a three-dimensional object assembly 113, according to some embodiments of the present invention. FIG. 18A illustrates object assembly 113 in embodiments in which assembly 113 comprises object 112 and a support structure 400a, wherein there is a complete embedding of support structure 400a in object 112, in a manner that the outer walls 438 of object 112 surround structure 400a and are supported by structure 400a. An external support to the outer walls 438 of object 112 is provided by a continuous structure 480 that does not contain interconnected voids. FIG. 18B illustrates object assembly 113 in embodiments in which assembly 113 comprises object 112 and a support structure 400b, wherein there is external contiguity between support structure 400b and object 112 with no overlap between support structure 400b and object 112, so that structure 400b provides external support to the outer walls 438 of object 112. In FIG. 18B, an internal region of object 112 is filled with a continuous structure 482 that does not contain interconnected voids. FIG. 18C illustrates object assembly 113 in embodiments in which assembly 113 comprises object 112 and two support structures 400a, 400b, wherein there is a complete embedding of support structure 400a in object 112, and external contiguity between support structure 400b and object 112.

[0135] When the three-dimensional structure is internal, it occupies a three-dimensional region within the object that is closed from below and from above by one or more continuous layers of building material(s) and that is laterally surrounded by one or more continuous walls of building material(s). In this case, the three-dimensional structure supports the outer surface(s) of the object from inside the object, thereby preventing the outer surface(s) from collapsing inwardly.

[0136] When the support structure of the three-dimensional object assembly is internal, a set of parameters can be selected to define the wall thickness of the object that surrounds the structure. This can be done in more than one way. In some embodiments of the present invention a constant wall thickness throughout the object is applied. Typical such thickness can have a nominal value of from about 1 mm to about 3 mm, e.g., about 2mm). These embodiments are particularly useful for objects having a complex geometry. Alternatively, the wall thickness can vary. For example, different wall thicknesses can be defined for the side walls, the upper wall and the lower wall. These embodiments are particularly useful for objects having one or more generally planar outer surfaces.

[0137] When the three-dimensional structure is external, it is preferably, but not necessarily, sacrificial, and is fabricated to support one or more of the outer surface(s) of the object from outside the object, thereby preventing the outer surface(s) from collapsing outwardly.

[0138] The three-dimensional structure can be made of one or more building materials, e.g., a digital material. Typically, but not necessarily, when the three-dimensional structure is internal it comprises at least one modeling material, and when the three-dimensional structure is external it comprises at least one support material. In some embodiments of the present invention the three- dimensional structure is internal and is devoid of any support material. In some embodiments of the present invention the three-dimensional structure is external and is made only from a support material.

[0139] Since the three-dimensional structure of the present embodiments is manufactured by additive manufacturing, it comprises a plurality of layers stacked along the build direction z. During fabrication, the layers are horizontal (parallel to the tray of the AM system, e.g., tray 12 or 360), and the build direction z is vertical. Once an object, including the three-dimensional structure, is removed from the tray, the layers need not be horizontal, and the build direction need not be vertical. Yet, the layers remain perpendicular to the build direction z, and so the build direction can be readily identified by identifying the layers that form the object or three-dimensional structure, either by the naked eye or by means of optical instrumentation, and then inferring the build direction as the direction that is perpendicular to the identified layers.

[0140] In the following description of the three-dimensional structure of the present embodiments, any plane that is perpendicular to the build direction z (and that is therefore parallel to the layers of the printed three-dimensional structure) is referred to as a "lateral plane," and is symbolized by the Greek letter %. Any direction within a lateral plane % is referred to as a "lateral direction." During fabrication of the three-dimensional structure by a system employing a Cartesian system of coordinates (e.g., system 110) the X-Y plane is a lateral plane, and during fabrication of the three- dimensional structure by a system employing a polar system of coordinates (e.g., system 10) the r- tp plane is a lateral plane. Without loss of generality, the three-dimensional printed structure of the present embodiments is described below in terms of a Cartesian system of coordinates in which the lateral plane is spanned by the X and Y axes and the build direction is along the z axis. However, it is to be understood that the three-dimensional printed structure of the present embodiments can be fabricated by any AM system irrespectively of the system of coordinates employed by the system. FIG. 4 is a schematic illustration of a three-dimensional printed structure 400, according to some embodiments of the present invention. Structure 400 can be fabricated by additive manufacturing, e.g., by means of system 10 or 110. Structure 400 can serve as an internal and / or external support structure with respect to an outer surface of the object, and can therefore enact any of the support structures 400a and 400b shown in FIGs. 18A-C. For clarity of presentation FIG. 4 illustrates structure 400 in a generally cuboidal shape. However, it is to be understood that structure 400 can have any shape. Typically, the shape of structure 400 is selected based on the shape of the three-dimensional object that is to include structure 400. For example, computer software can define a virtual build space occupied by structure 400 of arbitrary shape, and thereafter carve the shape of structure 400 based on the shape of the object to be fabricated. As an example, the computer software can carve the shape of the interior of the object, or the shape of an external support structure that is required to support an object's part. A representative example of structure 400 in a case in which its shape is not cuboidal is illustrated in FIG. 5.

[0141] Shown in FIG. 4 is a three-dimensional printed structure 400, in embodiments in which it comprises a lower superlattice 402, an upper superlattice 404, and a top section 406. Each of these elements is described below. Before describing these elements in detail, it is to be understood that structure 400 can include any combinations of these elements. For example, in some embodiments of the present invention structure 400 comprises upper superlattice 404 but not lower superlattice 402 and not top section 406, in some embodiments of the present invention structure 400 comprises upper superlattice 404 and top section 406, but not lower superlattice 402, in some embodiments of the present invention structure 400 comprises lower superlattice 402, but not top section 406 and not upper superlattice 404, etc.

[0142] Also shown in FIG. 4 is base 408, which may or may not be part of structure 400. For example, base 408 can be one of the outer surfaces of an object that contains structure 400 in its interior. The lower part of structure 400, not including base 408 is designated by reference sign 405 and the upper part of structure 400, including top section 406 is designated by reference sign 407.

[0143] As used herein, "upper," "lower," and "top" refer to positions of the respective entities during the fabrication of structure 400. Thus, "upper" means farther than "lower" along the build direction z, and "top" means farthest among lattice 402, lattice 404, and section 406 along the build direction z.

[0144] As used herein, "superlattice" refers to a structure formed by a combination of two or more distinct lattices. Preferably, but not necessarily, each of the distinct lattices is periodic and so the superlattice is also periodic. FIGs. 6A-G illustrate lower superlattice 402 in greater detail. In various exemplary embodiments of the invention superlattice 402 is a bilayer superlattice.

[0145] As used herein "bilayer superlattice" refers to a structure consisting of two distinct layers, which are stacked on top of each other in a repeating pattern, wherein each layer is structured as a distinct lattice.

[0146] Bilayer superlattice 402 is formed of a sequence of alternating lattices 410, 412, of multipods 418, 420, where lattice 410 is formed of multipods 418, and lattice 412 is formed of multipods 420. Lattices 410 and 412 are aligned along the build direction z.

[0147] As used herein "multipod" refers to a structure that has multiple extensions (referred to as "pods") radiating from a base. The point where all pods converge is referred to as the vertex of the multipod, and the terminating end points of the pods (farthest points from the multipod's vertex) are referred to as the feet of the multipod.

[0148] For at least one of the multipods 418 of lattice 410, all feet of the multipod are preferable coplanar. For at least one of the multipods 420 of lattice 420, all feet of the multipod are preferable coplanar.

[0149] The pods of the multipod can have any cross-sectional shape, such as, but not limited to, a circular or polygonal cross-section. In some embodiments of the present invention the pods have a circular cross-section, and in some embodiments of the present invention the pods have a hexagonal cross-section.

[0150] Each multipod of the present embodiments can have three or more (e.g., 3, 4, 5, 6, etc.) pods. When the multipod includes three pods it is referred to as a tripod, when the multipod includes four pods it is referred to as a quadruped, when the multipod includes five pods it is referred to as a pentapod, when the multipod includes six pods it is referred to as a hexapod, etc.

[0151] In some embodiments of the present invention all the multipods of superlattice 402 are tripods, and in some embodiments of the present invention all the multipods of structure 400 are tripods.

[0152] A representative example of a single multipod 418 for the case in which the multipod is a tripod is illustrated in FIGs. 6B and 6C, showing a top view (FIG. 6B) and a side view (FIG. 6C) of multipod 418. The vertex of multipod 418 is shown at 424, and the feet are shown at 426. The azimuthal angle (measured within a lateral plane, perpendicularly to the build direction z) between adjacent pods is denoted 0. For example, for tripod, a typical value of 0 is from about 10° to about 60°. A single pod 422 of the of multipod 418 is illustrated in FIG. 6D. The length of pod 422 is denoted L, the inclination angle of pod 422 with respect to the build direction is denoted , and the diameter of the cross-section of pod 422 is denoted D. The length Hl of multipod 418 along the build direction is therefore Lxcos . The parameters L, <b, and D are selected such as to ensure that multipod 418 is self- supportive. Typical values for L are from about 12 to about 20 mm, e.g., about 16 mm, typical values for are from about 5° to about 10°, e.g., about 7°, and typical values for D are from about 1 mm to about 2 mm, e.g., about 1.5 mm. Other dimensions are also contemplated.

[0153] For any pair of adjacent lattices in bilayer superlattice 402, multipods of one lattice of the pair are inverted along the build direction z with respect to multipods of another lattice of the pair. Thus, multipods 420, which form lattice 412, are inverted along the build direction with respect to multipods 418, which form lattice 410. A representative illustration of the relative orientation between a single multipod 418 of lattice 410, and single multipod 420 of lattice 412 is illustrated in FIG. 6E, as shown the relative orientation of multipods 418 and 420 is that one multipod mirrors the other multipod across a lateral plane % perpendicular to the build direction z. In some embodiments of the present invention the vertices 424 and 428 of multipods 418 and 420, respectively, are aligned along the build direction z, as illustrated in FIG. 6E. Preferably, such a build direction alignment is repeated pairwise across lattices 410 and 412. Preferably, multipods 418 and 420 are congruent, namely they are identical in size and shape but assume different orientation.

[0154] Note that FIG. 6A shows two periods of superlattice 402, because each period includes both lattices 410 and 412, which are distinct from each other by virtue of the aforementioned inversion with respect to the build direction. Generally, superlattice 402 can have any number of periods, which is selected based on the parameters L and <b, and based on the desired height of superlattice 402.

[0155] A representative example of the lateral arrangement (perpendicularly to the build direction) of the multipods of superlattice 402 is illustrated in FIGs. 6F and 6G, where FIG. 6G is a zoom-in version of the lower left corner of FIG. 6F. The lateral distance between laterally adjacent multipods is selected based on the parameters L, and <b. A typical lateral distance between nearest- neighbor multipods is from about 2 mm to about 4 mm, e.g., about 3 mm. The angle between the lateral lattice vectors is selected based on the value of 0, and may, in some embodiments of the present invention be equal to 0. For example, in Cartesian coordinates, for a tripod with 0=60°, one lateral lattice vector can be oriented at angle of about 30° with respect to the x axis, and the other lateral lattice vector can be oriented along the y axis, forming an angle of 60° between the lattice vectors.

[0156] In some embodiments of the present invention, structure 400 comprises a third lattice 403 of multipods (FIG. 4), positioned between bilayer superlattice 402 and superlattice 404 along the build direction. Lattice 403 enacts a transitional structural element that addresses situations where the desired height for the part 405 of structure 400 that is below superlattice 404 does not correspond to an integer number of periods of bilayer superlattice 402. The multipods of lattice 403 can be similar to the multipods of bilayer superlattice 402. For example, the multipods of lattice 403 can be identical in structure to the multipods 418 of lattice 410 (FIGs. 6B-D) except that their height Hl and / or inclination angle may optionally and preferably be adjusted to provide the desired height for the part 405 of structure 400 that is below superlattice 404.

[0157] FIGs. 7A-C are schematic illustrations showing a side view (FIG. 7A) and top views (FIGs. 7B-C) of upper superlattice 404 according to some embodiments of the present invention, where FIG. 7B is a zoom-in view of a region in the lower-left corner of FIG. 7C. Upper superlattice 404 is formed of two or more lattices. FIGs. 8A-C exemplify lattices, two or more of which can form superlattice 404 according to some embodiments of the present invention.

[0158] For example, upper superlattice 404 can comprise a first lattice 430 of multipods 432 having feet 434 and vertices 436 (FIG. 8A), and a second lattice 440 of multipods 442 having feet 444 and vertices 446 (FIG. 8B). First 430 and second 440 lattices are interlaced along a direction in a lateral plane % perpendicular to the build direction z. The multipods 442 of second lattice 440 are inverted along the build direction z with respect to the multipods 432 of first lattice 430, and are arranged in a manner that the feet 444 of multipods 442 are connected to the vertices 436 of multipods 432. Preferably, multipods 432 and 442 are congruent, namely they are identical in size and shape but assume different orientation. Preferably, but not necessarily, all the feet 434 of multipods 432 of lattice 430 are coplanar with vertices 446 of multipods 442 of lattice 440, and all vertices 436 of multipods 432 of lattice 430 are coplanar with all feet 444 of multipods 442 of lattice 440, as illustrated in FIG. 7A. Alternatively, for one or more of the multipods of one of the lattices 430, 440, a vertex of that multipod is offset from a plane defined by the feet of the multipod of the other lattice.

[0159] In embodiments in which third lattice 403 is employed, its multipods are preferably arranged to support the multipods of one of the lattices 430 and 440 of superlattice 404. For example, the multipods of third lattice 403 can be inverted along the build direction z with respect to the multipods of the first lattice 430 and can be arranged in a manner that vertices of the multipods of the first lattice 430 are aligned along the build direction with vertices of the multipods of the third lattice 403.

[0160] As in the case of superlattice 402, each multipod of superlattice 404 can have three or more (e.g., 3, 4, 5, 6, etc.) pods. In some embodiments of the present invention all the multipods of superlattice 404 are tripods. In some embodiments of the present invention all multipods 432 of first lattice 430 have the same orientation within the lateral plane, and all multipods 442 of second lattice 440 have the same orientation within the lateral plane, as illustrated in FIGs. 8 A and 8B. Preferably, the orientation of multipods 442 differs from the orientation of multipods 432. For example, multipods 442 can be rotationally transformed versions of multipods 432. The relation between the orientation of a single multipod 432 and a single multipod 442 within the lateral plane according to some embodiments of the present invention is illustrated in FIG. 8D. The orientation in the lateral plane of one pod of multipod 432 is denoted 0(432 and the orientation in the lateral plane of one pod of multipod 442 is denoted 0(442. As shown, multipod 442 is rotated relative to multipod 432 at an angular amount of Aoc=oc442-oc432.

[0161] Superlattice 404 can, according to some embodiments of the present invention, comprise a lattice 450 of pillars 452 oriented along the build direction z. An illustration of a single pillar 452 of lattice 450 is provided in FIG. 8E. The length Hl along the build direction and cross-sectional diameter D of each pillar, is preferably the same as the length Hl along the build direction and cross-sectional diameter D of the multipods of superlattice 404. Each pillar 452 is connected to a connection point between a foot 444 of a multipod 442 of lattice 440 and a vertex 436 of a multipod 432 of lattice 430, as illustrated in FIGs. 7A and 7B. In some embodiments of the present invention all uppermost points of multipods 432, all uppermost points of multipods 442, and all uppermost points of pillars 452 are coplanar. In accordance with the above definition of "upper," the "uppermost points" are the farthest points of the respective entity (multipod, pillar) along the build direction z. Alternatively, all uppermost points of multipods 432, all uppermost points of multipods 442, and all uppermost points of pillars 452 define a multiplicity of non-coplanar planes, so that at least four of these uppermost points do not engage the same plane.

[0162] The azimuthal angle between adjacent pods, the length of each pod, the inclination angle of each pod, and the cross-sectional diameter of each pod of the multipods 432 and 442 (the aforementioned 0, L, <b, and D parameters) can be within the ranges defined above for the multipods 418 and 420 of superlattice 402. In some embodiments of the present invention, the value of the parameters 0, L, <b, and D parameters are the same for all the multipods of superlattices 402 and 404.

[0163] FIG. 9 illustrates top section 406 of structure 400 in greater detail. In various exemplary embodiments of the invention section 406 comprises an arrangement of frusta 462, each having a truncated base 464 and a non-truncated base 466 where base 466 is farther from lower 402 and / or upper 404 superlattice along the build direction z than base 464. Bases 464 and 466 are optionally and preferably parallel to each other. Without loss of generality, bases 464 of frusta 462 can be referred to as the bottom bases of the frusta, and bases 466 of frusta 462 can be referred to as the top bases of the frusta, because during the fabrication of a frustum by layerwise additive manufacturing its base 464 includes the bottommost layer of the frustum and its base 466 includes the topmost layer of the frustum.

[0164] Frusta 462 can be shaped as truncated cones (e.g., truncated right cones) or truncated pyramids (e.g., truncated right pyramids). Also contemplated are embodiments in which some frusta are truncated cones and some frusta are truncated pyramids. Preferably, but not necessarily, all the frusta have the same shape. Preferably, but not necessarily, all the frusta have the same shape and the same size.

[0165] Section 406 may optionally and preferably also comprise an arrangement of right solid shapes 472, each connected to a non-truncated base 466 of one frustum 462. The lateral crosssection of each solid shape 472 preferably has the same shape and size as lateral cross-section of the base 466 to which it is connected. For example, when a particular frustum is a cone having a circular cross-section, the solid shape 472 that is connected to this particular frustum can have the shape of a circular cylinder having a circular cross-section of the same size as the circular crosssection of base 466, and when a particular frustum is a pyramid having a polygonal cross-section, the solid shape 472 that is connected to this particular frustum can have the shape of a prism having a polygonal cross-section of the same type and size as the polygonal cross-section of base 466.

[0166] A single frustum 462 and a single right solid shape 472 is illustrated in FIG. 10, for the case in which frustum 462 is a circular cone and solid shape 472 is a circular cylinder. The (along the build direction z) and the cross-sectional diameter of the truncated base 464 of frustum 462 are denoted H2 and D2, respectively, and the (along the build direction z) and the cross-sectional diameter of right solid shape 472 are denoted H3 and D3, respectively. The apex angle of frustum 462 is denoted 0. Thus, in case of a frustum that has a shape of a circular cone, the cross-sectional diameter of the non-truncated base 466, and consequently also of right solid shape 472, is D3=D2+H2xtan(0 / 2). One of ordinarily skilled in the art would be able to find the relations among these parameters also for the case of other geometrical shapes. The parameters H2, D2, and 0, are selected so as to ensure that frustum 462 is self- supportive. Typical values for H2 are from about 3 mm to about 5 mm, e.g., about 4 mm, typical values for 0 are from about 5° to about 10°, e.g., about 7°, and typical values for D2 are from about 1 mm to about 2 mm, e.g., about 1.5 mm. Other dimensions are also contemplated. Preferably, but not necessarily, the parameters satisfy one or more of the relations: 0-0. D2~D, means equality with tolerance of ±10%. In some embodiments of the present invention at least two of right solid shapes 472 have different lengths H3 along the build direction z. In these embodiments, the surface of section 406 is non-planar, and the advantage of these embodiments is that they allow adapting the shape of the structure 400 to the shape of the layers of the object to be fabricated that are to be supported by structure 400.

[0167] Section 406 is typically connected to superlattice 404. This is illustrated in FIGs. 11A-B, showing a side view (FIG. 11 A) and a top view (FIG. 1 IB) of the relation between superlattice 404 and the elements of section 406. Each frustum 462 is oriented in a manner that its truncated base 464 is connected to superlattice 404 and its non-truncated top 466 is away from superlattice 404 along the build direction z. The bases 464 of frusta 462 can be connected to any of the elements of superlattice 404. For example, the bases 464 can be connected to the feet 434 of multipods 430. This embodiment is illustrated in FIG. 11B. Note that in the top view of FIG. 11B bottom bases 464 of frusta 462 are not shown as they are beneath top bases 466. Further, for clarity of presentation, only top bases 466 of two frusta 462 are illustrated in FIG. 1 IB.

[0168] In some embodiments of the present invention for any group of three or more adjacent frusta 462, there is a lateral overlap among the non-truncated tops 466 of all the frusta in the group. This embodiment is illustrated in FIG. 12, and is advantageous since it allows section 406 of structure 400 to fully support the liquid material that is dispensed over structure 400 to form an additional layer of the object.

[0169] Any of the structural elements of structure 400, specifically any of lower superlattice 402, upper superlattice 404, top section 406, and any component of these structural elements, including multipods 418, 420, 432, 442, pods 422, pillars 452, frusta 462, and right solid shapes 472, can be made of a single building material or a combination of building materials, e.g., a digital material as defined herein. Further, the structural elements of structure 400 can be made of the same building material or the same combination of building materials. Alternatively, two or more of the structural elements of structure 400 or the components of these structural elements, can be made of different building materials or different combinations of building materials.

[0170] Reference is now made to FIG. 13, which is a flowchart diagram of a method suitable for encoding data for additive manufacturing, according to various exemplary embodiments of the present invention.

[0171] It is to be understood that, unless otherwise defined, the operations described hereinbelow can be executed either contemporaneously or sequentially in many combinations or orders of execution. Specifically, the ordering of the flowchart diagrams is not to be considered as limiting. For example, two or more operations, appearing in the following description or in the flowchart diagrams in a particular order, can be executed in a different order (e.g., a reverse order) or substantially contemporaneously. Additionally, several operations described below are optional and may not be executed.

[0172] Computer programs implementing the method can commonly be distributed to users on a distribution medium such as, but not limited to, a flash memory, CD-ROM, or a remote medium communicating with a local computer over the internet. From the distribution medium, the computer programs can be copied to a hard disk or a similar intermediate storage medium. The computer programs can be run by loading the computer instructions either from their distribution medium or their intermediate storage medium into the execution memory of the computer, configuring the computer to act in accordance with the method. All these operations are well- known to those skilled in the art of computer systems.

[0173] The method can be embodied in many forms. For example, it can be embodied on a tangible medium such as a computer for performing the method steps. It can be embodied on a computer readable medium, comprising computer readable instructions for carrying out the method steps. In can also be embodied in an electronic device having digital computer capabilities arranged to run the computer program on the tangible medium or execute the instruction on a computer readable medium.

[0174] The method of the present embodiments can be executed by a data processor operating an AM system (e.g., computer 24). The computer object data processed by the method can be transmitted to the controller of the AM system (e.g., controller 20). The processed computer object data can be transmitted in its entirety before the AM process begins, or in batches (e.g., slice by slice) wherein the AM process begins after the first batch arrives but before receiving the last batch. The method of the present embodiments can alternatively be executed by the controller of the AM system (e.g., controller 20). In these embodiments, the controller receives input data and executes the method using these input data. The input data can be received by the controller before the AM process begins, or in batches, wherein the AM process begins after the first batch arrives but before receiving the last batch.

[0175] The method begins at 500 and optionally and preferably continues to 501 at which information pertaining to saving of building material is received, for example, via a user interface, such as, but not limited to, the user interface of computer 24. The information can be a percentage of the volume material to be reduced, a percentage of the weight of the final object to be reduced, and the like. In some embodiments of the present invention the information comprises a percentage of carbon footprint to be reduced. The method proceeds to 502 at which parameters describing the three-dimensional structure 400 are calculated based on the information received at 501. These parameters may include, for example, one or more of: the distances between the multipods of the structure 400, the sizes of the multipods, the number of pods of the multipods, the parameters of the individual multipods, the parameters of the individual pillars, frusta, and right solid shapes, and the like. The method proceeds to 503 at which the method constructs computer object data describing one or more of the superlattices and top section of structure 400 based on the parameters calculated at 502. At 504 computer object data of a three-dimensional object is received, and at 505 the computer object data received at 504 is combined with the computer object data constructed at 503.

[0176] At 506, a slicing operation is applied to the combined data to provide a plurality of slices. The slicing 506 can be done by the computer running slicer software to provide slice data describing a plurality of slices, each defined over a plurality of voxels, and describing one of the layers of the object to be manufactured. The slicing operation 506 may also assign to each voxel of each slice, a building material. In some embodiments of the present invention the method continues to 507 at which the slice data are transmitted to a controller of an AM system (e.g., controller 20) for additive manufacturing of a plurality of layers respectively corresponding to the plurality of slices.

[0177] The method ends at 508.

[0178] Reference is now made to FIG. 14, which is a flowchart diagram of a method suitable for fabricating a three-dimensional object, according to some embodiments of the present invention.

[0179] The method begins at 600 and optionally and preferably continues to 601 at which one or more building materials are dispensed in layers to form a continuous base of a three-dimensional object. The method proceeds to 602 at which one or more building materials are dispensed in layers to form a lower superlattice comprising interconnected voids, such as, but not limited to, superlattice 402. The method proceeds to 603 at which one or more building materials are dispensed in layers to form an upper superlattice comprising interconnected voids, such as, but not limited to, superlattice 404. The method optionally and preferably proceeds to 604 at which one or more building material are dispensed in layers to form a top section comprising frusta, such as, but not limited to, top section 406. The method optionally and preferably continues to 605 at which one or more building materials are dispensed in layers to form a continuous top section of the three- dimensional object.

[0180] For one or more of the layers that are formed during operations 602, 603, and 604, the method optionally and preferably dispenses one or more building materials to form a continuous periphery to the respective layer. A stack of all the continuous peripheries forms outer surfaces of the object that surround the support structure.

[0181] The method ends at 606.

[0182] In method 600, one or more of the parameters describing structure 400 can be calculated automatically by the method, for example, based on information pertaining to saving of building material is received, as further detailed hereinabove. Alternatively, or additionally, the parameters can be received from the user by means of a user interface, such as, but not limited to, the user interface of computer 24. Also contemplated are embodiments in which some of the parameters are received as user input and some parameters are automatically calculated, and embodiments in which some of the parameters are received as user input and some parameters are predetermined. Representative examples of parameters that can be received as user input include, without limitation, <b, D, 0, Hl, and the cross-sectional shape of the pods. Representative examples of parameters that can be predetermined include, without limitation, L, H2, and H3.

[0183] FIGs. 15A-D are schematic illustrations of graphical user interface (GUI) screens that can be used according to some embodiments of the present invention to receive parameters for the construction of the computer object data of structure 400. FIG. 15A shows a GUI screen that allows the user to select the type of lattices of structure 400, where all the parameters of the lattices are either predetermined or calculated automatically. FIG. 15B shows a GUI screen that allows the user to select various geometrical parameters for the multipods as well as different wall thicknesses to different outer surfaces of the object.

[0184] FIG. 15C shows a GUI screen that allows the user to select one or more building materials or building material combinations for the structural elements of structure 400 and optionally also one or more of their components. The GUI screen comprises a material selection control 822 for allowing the end-user to select the building materials (modeling and / or support) from which structure 400 is to be formed by the AM system. Control 822 can be in the form of one or more dropdown menus allowing to select the material from a predefined list of materials. Preferably, the GUI screen comprises a material information area 824 that displays the types of building materials that are currently loaded to the system. This can be achieved by transmitting an interrogating signal to the AM system (e.g., to controller 20), and responsively receiving a signal pertaining to the types of building materials that are currently loaded to the AM system. Typically, the interrogating signal is transmitted automatically by the computer immediately after the loading of GUI screen. The GUI screen can also comprise a material selection control 822 configured to allow selection only among the types of building materials that are currently loaded to the system. For example, materials that are not currently loaded into the AM system can be grayed out in the dropdown menu of control 822. Material selection control 822 is optionally and preferably configured to allow selecting one or more building materials for any of the structural elements and / or components of structural elements of structure 400. For example, material selection control 822 can include a material addition activation button 822a, so that upon activation of button 822a the number of dropdown menus in control 822 is increased by one menu allowing to select another material for the respective structural element and / or component. FIG. 15C illustrates a case in which material addition activation button 822a has been activated twice, resulting in two additional material selection dropdown menus.

[0185] In some embodiments of the present invention material selection control 822 comprises a material distribution rule control 828 for allowing the end-user to select, in cases in which two or more building materials are assigned to a respective structural element or component, the rule according to which the materials are distributed among the voxels of the structural element or component. The control 828 is optionally and preferably displayed only when two or more material selection dropdown menus are displayed. The material distribution rule control 828 is preferably in the form of a dropdown menu and may also include a graphical area displaying an illustration of the expected distribution for the selected rule.

[0186] The list of rules from which the end-user selects the material distribution rule optionally and preferably comprises a plurality of functions, wherein each function, once employed by the slicer software, receives input parameters describing the location of a voxel within the contour, and provides an output value, which is then used by the slicer software to probabilistically select the material for the respective voxel, thereby constructing a digital material. The functions in the list can be noise functions, such as, but not limited to, a simplex noise function, an open simplex noise function, a Worley noise function, a Perlin noise function, a sphere scattered noise function, a wavelet noise function, a value noise function, or the like.

[0187] Reference is now made to FIG. 16, which is a flowchart diagram of a method suitable for additive manufacturing, according to various exemplary embodiments of the present invention.

[0188] The method begins at 700 and optionally and preferably continues to 701 at which computer object data describing a three-dimensional object are received. The computer object data can be in any of the aforementioned data formats. The method proceeds to 702 at which one or more regions of the three-dimensional object are selected. Each selected region can be either a region of an external support structure of the object or an internal region of the object. The selected regions are regions that are to be occupied by the three-dimensional printed structure described herein.

[0189] Operation 702 can be executed automatically by computer software, either based on preprogramed set of criteria or based on user input. Also contemplated are embodiments in which part of operation 702 is executed based on pre-programed set of criteria and another part of operation 702 is based on user input.

[0190] Selection of regions can be executed at a level of the graphic elements defining a surface of the object, or at a level of the grid of voxels that define the internal shape of the object.

[0191] A typical situation for a selection based on pre-programed criteria is when the computer object data are structured in a manner that allows extracting a separate geometrical definition for each of a plurality of object parts, where the extracted geometrical definition defines the outer surface of the respective object part and may optionally and preferably also define an internal structure of the respective object part. An object part for which the computer object data allows extracting a separate geometrical definition of that object part is referred to herein as "a shell," and the computer object data that describe only the shell form a dataset referred to herein as computer object shell dataset. The computer object data of the entire object can thus be structured to include a collection of two or more computer object shell datasets which collectively describe the object as an assembly of shells. Such an object is referred to herein as an object assembly. Each shell of an object assembly can be an internal object part, an external object part, or a partially external, partially internal object part. All the computer object data in a collection of two or more computer object shell datasets that describes an object assembly form a dataset which is referred to herein as a combined computer object dataset, or briefly a combined dataset.

[0192] A representative example of an object assembly which is defined as an assembly of two shells is illustrated in FIG. 17A, and the two individual shells are illustrated in FIGs. 17B and 17C.

[0193] In situations in which the method receives a combined computer object dataset, operation 702 can be executed by selecting computer object shell dataset describing an internal object part or a subset of that dataset.

[0194] When operation 702 is based on user input, a GUI screen is optionally and preferably presented to the user. A representative example of a GUI screen 800 suitable for the present embodiments is illustrated in FIG. 15D. GUI screen 800 comprises a display area 802 on which an object 112 to be manufactured is displayed. Preferably, display area 802 displays, in addition to the object, or instead of the object, a cross section of object 112. GUI screen 800 also comprises one or more GUI controls 804 allowing the user to select a region 808 of object 112 over the display. For example, GUI controls 804 can provide the functionality of painting a portion of the displayed object or cross section thereof, thereby selecting the region.

[0195] The method optionally and preferably continues to 703 at which one or more wall thicknesses are selected for one or more outer surfaces of the object that are to surrounded the three-dimensional printed structure. The wall thicknesses can be selected based on a pre-programed set of criteria (e.g., a fixed predetermined wall thicknesses, a wall thicknesses that depends on the size and / or orientation of the outer surface relative to the build direction, etc.). The wall thicknesses can alternatively be selected based on user input, received, for example, by means of a GUI screen, such as, but not limited to, the GUI screen shown in FIG. 15B.

[0196] The method can then continue to 704 at which other parameters describing the three- dimensional structure 400 are selected. These parameters preferably comprise geometrical parameters, such as, but not limited to, one or more of: the distances between the multipods of the structure 400, the sizes of the multipods, the number of pods of the multipods, the parameters of the individual multipods, the parameters of the individual pillars, frusta, and right solid shapes, and the like. The parameters can also comprise one or more building materials or building material combinations for the structural elements of structure 400 and optionally also one or more of their components. The parameters can be pre-programed parameters and / or selected by the user, by means of one or more GUI screens, such as, but not limited to, the GUI screens shown in FIGs. 15A-C, as further detailed hereinabove. One or more of the parameters can be calculated based on the volume and / or shape defined by the geometry of the region selected at 702. Such calculation can be based on a dedicated algorithm executable by the computer software, which algorithm can be rule-based, in which case the parameters are calculated by means of a set of predefined rules, or data-driven, in which case a trained machine learning model is applied to the volume and / or shape of the selected region, and provides the calculated parameters as an output.

[0197] In some embodiments of the present invention the method proceeds to 705 at which computer object data describing one or more of the superlattices and top section of structure 400 are constructed based on the parameters selected at 704.

[0198] At 706 at which an amount of saving of building material is calculated. The saving can be calculated by subtracting the amount of building material expected to be used for printing structure 400 to form the region(s) selected at 702 from the amount of building material expected to be used for printing these regions as regions that are completely filled with building material without voids. The amount can be calculated either based on the computer object data generated at 705, or based on the parameters selected at 704, without using the generated computer object data. The calculated amount can be displayed on a GUI, e.g., at an information section 810 of GUI screen 800. Preferably, but not necessarily, the amount is displayed as percentage of the volume of material to be reduced. Also contemplated are embodiments in which the amount is displayed as a percentage of the weight of the final object to be reduced, and embodiments in which the amount is displayed as a percentage of carbon footprint to be reduced. The method optionally and preferably proceeds to decision 707 at which the method determines whether the amount of saving calculated at 706 satisfies a predetermined criterion or set of criteria. For example, the method can compare the expected percentage of the volume of material to be saved to a predetermined threshold. Operation 707 can be executed automatically without user intervention. Alternatively, operation 707 can be done by the user, based on the calculated amount that is displayed at an information section 810 of GUI screen 800. When the criterion or set of criteria is not met, the method loops back 708 to one of operations 702-704 to select a different region to be occupied by structure 400, and / or to re-design structure 400 using a different set of parameters. The loop back 708 can optionally and preferably be conditional to approval by the user, e.g., by means of GUI screen 800. When the criterion or set of criteria is met, the method proceeds to 505 at which the computer object data received at 701 is combined with the computer object data constructed at 705. It some embodiments, operation 705 is executed after decision 707 and before operation 505. The method can then proceed to 506, at which a slicing operation is applied to the combined data, and to 507 at which the slice data are transmitted to a controller of an AM system as further detailed hereinabove.

[0199] The method ends at 709.

[0200] As used herein the term “about” refers to ± 10 %.

[0201] The terms "comprises", "comprising", "includes", "including", “having” and their conjugates mean "including but not limited to".

[0202] The term “consisting of’ means “including and limited to”.

[0203] The term "consisting essentially of" means that the composition, method or structure may include additional ingredients, steps and / or parts, but only if the additional ingredients, steps and / or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

[0204] As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" may include a plurality of compounds, including mixtures thereof.

[0205] Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0206] Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases “ranging / ranges between” a first indicate number and a second indicate number and “ranging / ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

[0207] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0208] Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples.

[0209] EXAMPLES

[0210] Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non limiting fashion.

[0211] The three-dimensional printed structure 400 of the present embodiments was fabricated as an internal support structure in two objects. One object had a shape of an egg and the other object had a shape of a cube. For comparison, the same objects were also fabricated with their interior completely filled with the same building material that was used to fabricate structure 400, except without any voids. A reduction of about 46.5% and 67% in weight was measured for the egg and the cube, respectively.

[0212] All multipods of the support structure were realized as tripods. The values of the parameters 0, L, <b, D, and Hl were, respectively, about 60°, about 16 mm, about 7°, about 1.5 mm, and about 15 mm. The values of the parameters H2, 0, and D2, were, respectively, about 4 mm, about 7°, and about 1.5 mm. For the cube, the value of H3 was about 2 mm. For the egg, the value of H3 was varied according to the shape of the upper surface of the egg. The distances between nearest- neighbor tripods were about 3.15 mm. Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. It is the intent of the applicant(s) that all publications, patents and patent applications referred to in this specification are to be incorporated in their entirety by reference into the specification, as if each individual publication, patent or patent application was specifically and individually noted when referenced that it is to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting. In addition, any priority document(s) of this application is / are hereby incorporated herein by reference in its / their entirety.

Claims

WHAT IS CLAIMED IS:

1. A printed structure comprising a first lattice of multipods and a second lattice of multipods forming a superlattice, said first and said second lattices being interlaced along a lateral direction perpendicular to a build direction of the printed structure, wherein multipods of said second lattice are inverted along said build direction with respect to multipods of said first lattice and are arranged in a manner that vertices of multipods of said second lattice are connected to feet of multipods of said first lattice.

2. The structure according to claim 1, wherein multipods of said second lattice are rotated about said build direction with respect to multipods of said first lattice.

3. The structure according to claim 1, wherein all feet of at least one of said multipods of said first lattice are coplanar with a vertex of at least one of said multipods of said second lattice.

4. The structure according to claim 3, wherein a vertex of at least one of said multipods of said first lattice is coplanar with all feet of at least one of said multipods of said second lattice.

5. The structure according to any of claims 1-4, wherein for at least one of said multipods of said first lattice all feet of said multipod of said first lattice are coplanar, and wherein for at least one of said multipods of said second lattice, a vertex of said multipod of said second lattice is offset from a plane defined by said feet of said multipod of said first lattice.

6. The structure according to any of claims 1-5, wherein for at least one of said multipods of said second lattice, all feet of said multipod of said second lattice are coplanar defining a plane, and wherein for at least one of said multipods of said first lattice, a vertex of said multipod of said first lattice is offset from a plane defined by said feet of said multipod of said second lattice.

7. The structure according to claim 1, wherein all feet of multipods of said first lattice are coplanar with vertices of multipods of said second lattice, and wherein all vertices of multipods of said first lattice are coplanar with all feet of multipods of said second lattice.

8. The structure according to any of claims 1-7, comprising a third lattice of multipods, wherein multipods of said third lattice are inverted along said build direction with respect tomultipods of said first lattice and are arranged in a manner that vertices of multipods of said first lattice are aligned along said build direction with multipods of said third lattice.

9. The structure according to any of claims 1-8, comprising a bilayer superlattice formed of a sequence of alternating lattices of multipods aligned along said build direction, wherein for any pair of adjacent lattices in said bilayer superlattice, multipods of one lattice of said pair are inverted along said build direction with respect to multipods of another lattice of said pair.

10. The structure according to any of claims 1-4, wherein said superlattice comprises a lattice of pillars oriented along said build direction, each pillar being connected to a connection point between a foot of a multipod of said second lattice and a vertex of a multipod of said first lattice.

11. The structure according to claim 10, wherein all uppermost points of multipods of said first lattice with respect to said build direction, all uppermost points of multipods of said second lattice with respect to said build direction, and all uppermost points of said pillars with respect to said build direction are coplanar.

12. The structure according to claim 10, wherein all uppermost points of multipods of said first lattice with respect to said build direction, all uppermost points of multipods of said second lattice with respect to said build direction, and all uppermost points of said pillars with respect to said build direction define a multiplicity of non-coplanar planes.

13. The structure according to any of claims 5-9, wherein said superlattice comprises a lattice of pillars oriented along said build direction, each pillar being connected to a connection point between a foot of a multipod of said second lattice and a vertex of a multipod of said first lattice.

14. The structure according to any of claims 1-13, comprising an arrangement of frusta, each frustum being oriented in a manner that a truncated base of said frustum is connected to said superlattice and a non-truncated base of said frustum is away from said superlattice along said build direction.

15. The structure according to claim 14, wherein for any group of three or more adjacent frusta, there is a lateral overlap among non-truncated bases of all frusta in the group.

16. The structure according to any of claims 14 and 15, comprising an arrangement of right solid shapes, each connected to a non-truncated base of one frustum.

17. The structure according to claim 16, wherein at least two of said right solid shapes have different lengths along said build direction.

18. A printed structure comprising a bilayer superlattice formed of a sequence of alternating lattices of multipods aligned along a build direction of the printed structure, wherein for any pair of adjacent lattices in said bilayer superlattice, multipods of one lattice of said pair are inverted along said build direction with respect to multipods of another lattice of said pair.

19. The structure according to any of claims 1-18, being a sacrificial support structure supporting at least a portion of a three-dimensional object.

20. The structure according to any of claims 1-19, being an internal structure completely surrounded by external surfaces of a three-dimensional object.

21. A three-dimensional object, comprising external surfaces, an internal support structure supporting said external surfaces from inside, and a sacrificial outer support structure supporting said external surfaces from outside, wherein at least one of said internal support structure and said sacrificial outer support structure comprises the structure according to any of claims 1-18.

22. A method of additive manufacturing, comprising: receiving computer object data describing slices of the structure according to any of claims 1-20, said slices being perpendicular to said build direction; and transmitting said computer object data to a controller of an additive manufacturing system for additive manufacturing of layers in configured patterns respectively corresponding to said slices.

23. A system for additive manufacturing, comprising:a dispensing head for dispensing a building material; and a computerized controller configured for receiving computer object data describing slices of the structure according to any of claims 1-20, said slices being perpendicular to said build direction, and for operating said dispensing head to dispense a building material in layers in configured patterns respectively corresponding to said slices.

24. A method of fabricating a three-dimensional object, comprising: dispensing at least one building material in layers stacked along a build direction to form a lower superlattice comprising interconnected voids; and dispensing at least one building material in layers stacked along said build direction to form an upper superlattice on said lower superlattice comprising interconnected voids; wherein said lower superlattice is a bilayer superlattice formed of a sequence of alternating lattices of multipods aligned along said build direction, wherein for any pair of adjacent lattices in said bilayer superlattice, multipods of one lattice of said pair are inverted along said build direction with respect to multipods of another lattice of said pair; and wherein said upper superlattice comprises a first lattice of multipods interlaced with a second lattice of multipods along a lateral direction perpendicular to said build direction, wherein multipods of said second lattice are inverted along said build direction with respect to multipods of said first lattice and are arranged in a manner that vertices of multipods of said second lattice are connected to feet of multipods of said first lattice.

25. The method according to claim 24, comprising, for each layer, dispensing at least one building material to form a continuous periphery to said layer.

26. The method according to any of claims 24-25, comprising dispensing at least one building material to form a continuous base of the three-dimensional object, wherein said lower superlattice is formed on said continuous base.

27. The method according to any of claims 24-26, wherein multipods of said second lattice are rotated about said build direction with respect to multipods of said first lattice.

28. The method according to any of claims 24-27, wherein said upper superlattice comprises a lattice of pillars oriented along said build direction, each pillar being connected to aconnection point between a foot of a multiped of said second lattice and a vertex of a multipod of said first lattice.

29. The method according to any of claims 24-28, comprising dispensing at least one building material in layers to form an arrangement of frusta, each frustum being oriented in a manner that a truncated base of said frustum is connected to said upper superlattice and a nontruncated base of said frustum is away from said superlattice along said build direction.

30. The method according to claim 29, wherein for any group of three or more adjacent frusta, there is a lateral overlap among non-truncated bases of all frusta in the group.

31. The method according to any of claims 29 and 30, comprising dispensing a right solid shape on each frustum, thereby forming an arrangement of right solid shapes on said arrangement of frusta.

32. The method according to claim 31, wherein at least two of said right solid shapes have different lengths along said build direction.

33. A method of fabricating a three-dimensional object, comprising: receiving computer object data describing the three-dimensional object; selecting at least one region of the three-dimensional object, based on said computer object data; based on a geometry of said at least one region, selecting parameters defining a support structure having a lower superlattice and an upper superlattice, each superlattice comprising interconnected voids; constructing computer object data describing said support structure, based on said parameters; combining said computer object data describing said support structure with said computer object data describing the three-dimensional object to provide a combined computer object dataset describing an object assembly having at least one outer surface supported by said support structure; slicing said combined computer object dataset into a plurality of slices, each defined over a plurality of voxels; and dispensing at least one building material to form a plurality of layers stacked along a build direction and respectively corresponding to said plurality of slices;wherein said lower superlattice is a bilayer superlattice formed of a sequence of alternating lattices of multipods aligned along a build direction, wherein for any pair of adjacent lattices in said bilayer superlattice, multipods of one lattice of said pair are inverted along said build direction with respect to multipods of another lattice of said pair; and wherein said upper superlattice comprises a first lattice of multipods interlaced with a second lattice of multipods along a lateral direction perpendicular to said build direction, wherein multipods of said second lattice are inverted along said build direction with respect to multipods of said first lattice and are arranged in a manner that vertices of multipods of said second lattice are connected to feet of multipods of said first lattice.

34. The method according to claim 33, wherein said object assembly represents an embedding of said support structure in the three-dimensional object.

35. The method according to any of claims 33 and 34, wherein said object assembly represents a contiguous external contact between said support structure and the three-dimensional object.

36. The method according to any of claims 33-35, wherein multipods of said second lattice are rotated about said build direction with respect to multipods of said first lattice.

37. The method according to any of claims 33-36, wherein said upper superlattice comprises a lattice of pillars oriented along said build direction, each pillar being connected to a connection point between a foot of a multipod of said second lattice and a vertex of a multipod of said first lattice.

38. The method according to any of claims 33-37, wherein said support structure comprises an arrangement of frusta, each frustum being oriented in a manner that a truncated base of said frustum is connected to said upper superlattice and a non-truncated base of said frustum is away from said superlattice along said build direction.

39. The method according to claim 38, wherein for any group of three or more adjacent frusta, there is a lateral overlap among non-truncated bases of all frusta in the group.

40. A system for additive manufacturing, comprising:a dispensing head for dispensing a building material; and a computerized controller configured for executing the method according to any of claims-39.

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