Method and system for recoating surfaces during additive manufacturing in a vat

Abstract

An additive manufacturing system comprises a vat (114) filled with a liquid (116) curable by radiation, a platform (120) immersed in the liquid, a wave generator (144) configured to generate a wave (146) over a surface (118) of the liquid, a radiation system (134) configured for applying radiation to the surface of the liquid, and a computerized controller (136) configured to control the radiation system to form on the surface of the liquid patterns defining a layer of an object (112).

Description

[0001] METHOD AND SYSTEM FOR RECOATING SURFACES DURING ADDITIVE

[0002] MANUFACTURING IN A VAT

[0003] RELATED APPLICATION

[0004] This application claims the benefit of priority of U.S. Provisional Patent Application No. 63 / 572,294 filed on 31 March 2024, the contents of which are incorporated herein by reference in their entirety.

[0005] FIELD AND BACKGROUND OF THE INVENTION

[0006] The present invention, in some embodiments thereof, relates to and, more particularly, but not exclusively, to a method and a system for recoating surfaces in vat based additive manufacturing technologies.

[0007] 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 rapid manufacturing (RM), and design related fields for purposes of visualization, demonstration and mechanical prototyping. 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.

[0008] In vat-based AM technologies, the manufacturing of an object is performed in a vat of a viscous and optically responsive liquid resin. One type of vat-based AM is stereolithography. In stereolithography, a build platform is lowered into a vat of a viscous, optically responsive, liquid resin. After the build platform is lowered, the resin is applied to the platform by means of a recoater device which moves over the surface of the platform to ensure an even spread of the viscous resin thereover. A precision-controlled laser, directed by a computer, scans the newly applied resin to trace a layer of the 3D object according to the respective two-dimensional position data that was generated by a slicing operation and that describe the layer. During the scan, the laser selectively solidifies the optically responsive resin, providing solidified building materials that form the layer. The newly formed layer is then lowered into the vat, the recoater device re-applies the resin over and around the newly formed layer, and the laser scans the resin to trace a subsequent layer. This process is executed repeatedly, building an object layer by layer from bottom to top. SUMMARY OF THE INVENTION

[0009] According to an aspect of some embodiments of the present invention there is provided an additive manufacturing system. The system comprises a vat filled with a liquid curable by radiation, a platform immersed in the liquid, a radiation system configured for applying radiation to a surface of the liquid, a computerized controller having a circuit configured to control the radiation system to form on the surface above the platform patterns defining a layer of an object, and a wave generator configured to generate a wave over the surface, wherein a motion of the wave generator is restricted to regions of the surface that are laterally separated from a region occupied by the layer.

[0010] According to an aspect of some embodiments of the present invention there is provided a method of fabricating an object by additive manufacturing. The method comprises immersing a platform in a liquid curable by radiation, applying radiation to a surface of the liquid above the platform to form patterns defining a layer of the object, and generating a wave over the surface by wave generator, wherein a motion of the wave generator is restricted to regions of the surface that are laterally separated from a region occupied by the layer.

[0011] According to some embodiments of the invention the wave generator is configured to vibrate vertically relative to the surface.

[0012] According to some embodiments of the invention the wave generator is configured to vibrate horizontally relative to the surface.

[0013] According to some embodiments of the invention vibration amplitude of the wave generator is selected to ensure that an amplitude of the wave is more than a thickness of the layer.

[0014] According to some embodiments of the invention a vibration amplitude of the wave generator is selected to ensure that an amplitude of the wave is less than three times a thickness of the layer.

[0015] According to some embodiments of the invention the wave generator is configured to perform a single motion period to form the wave.

[0016] According to some embodiments of the invention a duration of a single motion period of the wave generator is less than 2 seconds.

[0017] According to some embodiments of the invention the liquid is a photocurable liquid and the radiation is an optical radiation.

[0018] According to some embodiments of the invention the computerized controller is configured to initiate the control of the radiation system less than t seconds after an operation of the wave generator is ceased. According to some embodiments of the invention t equals 10. 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.

[0019] 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.

[0020] 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.

[0021] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0022] 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.

[0023] In the drawings:

[0024] FIG. 1 is a schematic illustration of a stereolithography system which includes a recoater;

[0025] FIG. 2 is a schematic illustration of an additive manufacturing system according to some embodiments of the present invention; FIG. 3 is a schematic illustration showing a top view of an example layer of an object, according to some embodiments of the present invention; and

[0026] FIG. 4 is a flowchart diagram of a method suitable for fabricating an object by additive manufacturing, according to some embodiments of the present invention.

[0027] DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0028] The present invention, in some embodiments thereof, relates to and, more particularly, but not exclusively, to a method and a system for recoating surfaces in vat based additive manufacturing technologies.

[0029] For purposes of better understanding some embodiments of the present invention, as illustrated in FIGs. 2-4 of the drawings, reference is first made to the construction and operation of a stereolithography system as illustrated in FIG. 1.

[0030] FIG. 1 is a schematic illustration of a stereolithography system 10 forming a layered object 12. System 10 includes a vat 14 filled with a liquid material 16, the upper surface of which is shown at 18. Liquid material 16 is typically of relatively high viscosity (e.g., hundreds of mPa-s). System 10 also comprises platform 20 on which object 12 is formed. By means of a vertical motion mechanism 22, platform 20 is movable along a vertical direction z, as shown by double arrow 24. To form a particular layer of object 12, a laser system 34 scans the surface 18 of liquid 16 according to two-dimensional position data that were generated by the slicing operation and that describe the layer. The laser beam from system 34 selectively solidifies liquid 16 at two-dimensional coordinates of points defined by the slicing operation thus forming the layer. FIG. 1 illustrates a state at which a plurality of layers 26 of object 12 has been formed, where the newest formed layer is layer 28. Layer 28 is an intermediate layer of object 12, and therefore at least one additional layer is to be formed by system 10 above layer 28.

[0031] Prior to the formation of a layer on top of layer 28, platform 20 is lowered (along the -z direction) into vat 14. The extent of lowering equals at least the thickness of a single layer of object 12. Oftentimes, platform 20 is lowered by more than the thickness of a single layer. The reason is the relatively high viscosity liquid material 16, which slows the flow of material 16 over the upper surface of layer 28. Immediately following the lowering of platform 20, the thickness of liquid 16 is not uniform and may potentially include imperfections such as bulges, depressions, and holes, which if not reduced or eliminated, could create inaccuracies in the next layer. A recoater 30, which typically has a shape of a blade or a roller, is applied to straighten the upper surface 18 of liquid 16. The straightening is performed by moving the recoater 30 horizontally so as to evenly spread the liquid 16. To further facilitate the recoating of layer 28 by liquid, a liquid delivery duct 32 may transfer an amount of liquid from a location at a periphery of the vat 14 to the region of surface 18 that is being straightened by recoater 30.

[0032] Thus, the stereolithographic fabrication process executed by system 10 is composed of three types of motions: a vertical motion of platform 20, a horizontal motion of recoater 30, and a scanning motion of the laser beam generated by system 34. The Inventors found that since the scanning motion of the laser beam is relatively fast, and since the vertical motion of the platform 20 is over a very short distance (approximately the thickness of one layer), a considerable amount of the total stereolithographic fabrication time is taken by the motion of recoater 30, which moves slower than the laser beam and over a much greater distance than the vertical motion of platform 20.

[0033] 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.

[0034] FIG. 2 is a schematic illustration of an AM system 100 according to some embodiments of the present invention. System 100 is capable of forming a layered three-dimensional object 112. FIG. 2 illustrates a state at which a plurality of layers 126 of object 112 has been formed, where the most newly formed layer is layer 128.

[0035] While the embodiments below are described with a particular emphasis to stereolithographic technology, it is to be understood that the present embodiments contemplate also other vat-based AM technologies. System 100 can employ any type of vat-based AM technology in which the upper surface of a liquid material in a vat is irradiated from above.

[0036] System 100 comprises a computerized controller 136 having a circuit 137 configured to control various elements of system 100 to execute various operations as described herein in order to fabricate object 112. Controller 136 can communicate with a host computer 162 which transmits to controller 136 digital data pertaining to fabrication instructions based on computer object data, e.g., in a form of a Standard Tessellation Eanguage (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). For clarity of presentation, communication lines between controller 136 and elements of system 100 other than host computer 162 are not shown in FIG. 2. System 100 comprise a vat 114 filled with a liquid material 116, the upper surface of which is shown at 118. Liquid material 116 is curable by radiation. Typically, liquid material 116 is a formulation comprising one or more polymerizable components. Such a formulation optionally and preferably comprises an initiator that initiates or catalyzes a chemical reaction upon exposure to the radiation. The formulation can also comprise additives such as, but not limited to, a photoinitiator, a thermal initiator, a polymerization catalyst, a surfactant, a dispersant, a viscosity modifier, a pigment, a dye, a surface active compound, a filler, particles, binders, or any combination thereof. The viscosity of liquid material 116 at room temperature (e.g., 25 °C) is typically from about 100 mPa-s to about 3500 mPa-s, e.g., about 800 mPa-s. The temperature of liquid material 116 during the operation of system 100 can be from about 20 °C to about 60 °C, e.g., about 25 °C or about 35 °C or about 45 °C.

[0037] In some embodiments of the present invention liquid material 116 is photocurable in which case it is curable by optical radiation. In this case, the formulation can comprise one or more photopolymerizable components, and a photoinitiator that initiates or catalyzes a photochemical reaction upon exposure to light. For example, liquid material 116 can be a UV-curable material, in which case it is curable by ultraviolet light. Other types of photocurable materials are also contemplated.

[0038] Representative examples of polymerizable components suitable for the present embodiments include, without limitation, a methacrylate monomer, an acrylate monomer, a thiol monomer, an allyl ether monomer, a vinyl acetate derivative monomer, a styrene monomer, a vinyl ether monomer, a vinyl chloride monomer, an acrylonitrile monomer, a vinyl silane monomer, a butadiene monomer, a norbornene, a maleate monomer, a fumarate monomer, an epoxide monomer, an anhydride monomer, a hydroxyl monomer, and any combinations thereof.

[0039] System 100 also comprises a solid platform 120 having a surface 121 on which object 112 is formed. Surface 121 is preferably horizontal with respect to the direction of gravity. The bottommost layer of object 112 can be formed on the surface 121 of platform 120, and other layers can be formed one on top of the other, as illustrated in FIG. 2. Platform 120 is immersed in liquid 116. The vertical distance between the surface 121 of platform 120 and the surface 118 of liquid 116 is controlled, preferably by computerized controller 136. The vertical distance between surfaces 121 and surface 118, can be increased by lowering platform 120 while keeping vat 114 at a fixed height above ground, and / or by elevating vat 114 while keeping platform 120 at a fixed height above ground, and / or by increasing the amount of liquid 116 in vat 114. In the representative illustration of FIG. 2, which is not to be considered as limiting, platform 120 is movable in the vertical direction z by means of a vertical motion mechanism 122, as shown by arrow 124. Controller 136 is preferably configured to ensure that the vertical distance between the surface 118 of liquid 116 and the top surface of layer 128 is at least the thickness of a single layer of object 112 (e.g., the thickness of layer 128). In some embodiments of the present invention the vertical distance between surface 118 of liquid 116 and the top surface of layer 128 is more than the thickness of a single layer (e.g., more than the thickness of layer 128).

[0040] A radiation system 134 is positioned above vat 114 in a manner that allows it to apply radiation 138 to surface 118 of liquid 116. The type of radiation applied by radiation system 134 is selected based on the type of liquid 116 in vat 114. For example, when liquid 116 is a photocurable liquid, radiation 138 is optical radiation. The wavelength of the radiation preferably matches the wavelength that induces curing of liquid 116. For example, when liquid 116 is a UV- curable liquid, the wavelength of the radiation is in the ultraviolet or visible range (e.g., from about 100 nm to about 450 nm). In an example embodiment, radiation system 134 is provided in the form of an array of light emitting diodes. In an example embodiment, radiation system 134 produces a coherent beam of light. For example, radiation system 134 can be a laser system in which case radiation 138 is in the form of a laser beam. In an example embodiment, radiation system 134 comprises a digital light processing (DLP) projector.

[0041] Radiation system 134 is equipped with a light handling mechanism 140 which controls radiation 138 before it interacts with liquid 116. In some embodiments of the present invention light handling mechanism 140 comprises a scanning mechanism which is capable of scanning surface 118 with a beam of radiation 138. In some embodiments of the present invention, light handling mechanism 140 comprises a DLP projector which applies digital processing to modulate radiation 138. Typically, projection is faster but with lower resolution than scanning. The use of scanning mechanism is therefore advantageous from the standpoint of higher resolution and the use of a DLP projector is advantageous from the standpoint of additive manufacturing speed. Also contemplated, are embodiments in which light handling mechanism 140 comprises both a scanning mechanism and a DLP projector, allowing to enjoy both the higher speed of the projection (e.g., at the inner parts of the object which are typically not visible), and the higher resolution of the scanning (e.g., at outer parts of the object which are typically visible).

[0042] When a scanning mechanism is employed, the scanning can be achieved by varying the direction of the beam, as illustrated by arrow 142. Also contemplated, are embodiments in which the scanning mechanism performs the scanning by laterally shifting the beam parallel to itself without changing the beam's direction. Further contemplated, are embodiments in which the scanning includes both direction variation and lateral shifting of the beam. The scanning mechanism can be an optical mechanism, e.g., an arrangement of rotating mirrors, and / or a mechanical mechanism, e.g., a robotic arm that moves the beam's source along a horizontal direction.

[0043] Radiation system 134 is part of system 100 and is preferably controlled by controller 136. In embodiments in which radiation system 134 comprises a scanning mechanism, the circuit 137 of controller 136 controls radiation system 134 to scan surface 118 above surface 121 of platform 120 along patterns which define a layer of object 112. In embodiments in which radiation system 134 comprises a DLP projector, the circuit 137 of controller 136 controls radiation system 134 to project patterns which define a layer of object 112 onto surface 118 above surface 121 of platform 120. In embodiments in which radiation system 134 comprises both a scanning mechanism and a DLP projector, some of the patterns that define the layer are projected by the DLP projector and other patterns that define the layer are scanned by means of the scanning mechanism. For example, the DLP projector can be used to form patterns at the inner part of the layer and the scanning mechanism can be used to form patterns at the peripheral part of the layer.

[0044] The patterns that are formed on surface 118 are described by data including two- dimensional coordinates of points along the patterns. FIG. 3 is a schematic illustration showing a top view of an example layer 128 of object 112, wherein layer 128 is defined by patterns 160. While the patterns in FIG. 3 are shown as straight linear patterns, this need not necessarily be the case, since, for some applications, it may be desired to define curved patterns (either by scanning or by projection). Further, the present embodiments contemplate defining a layer by patterns that include both curved patterns and straight patterns. For example, straight linear patterns can be applied by controlling system 134 to execute raster scanning, and curved patterns can be applied by controlling system 134 to execute vector scanning. Raster scanning is characterized by a motion of the beam over surface 118 along a fixed direction and switching off radiation 138 at points along the direction which are not to be part of the desired shape of the layer. Vector scanning is characterized by a motion of beam along a path selected based on locations over surface 118 at which the shape of the layer requires curing of material 116.

[0045] It may be favorable to control various characteristics of the radiation, such as spot size and / or cross-sectional shape (e.g., a focal plane) of the beam on surface 118, for example, by focusing the projected pattern on surface 118, so that the characteristics are as consistent as possible across the surface 118. Any one or more lenses may be employed to direct and / or control characteristics of the beam to achieve such consistency, such as but not limited to, one or more aspheric lenses, spherical lenses, concave lenses, convex lenses, F theta lenses, telecentric lenses, flat field lenses, curved field lenses, a Gradient Index Lens (GRIN Lens), or combinations thereof. It will be appreciated that, in practice, any “lens” referred to herein may be implemented as multiple discrete components and as such any disclosure relating to a “lens” should not be construed as being limited to a single optical component. Other light control elements such as, but not limited to, shutter, a spatial modulator, a reflator, can also be used, if desired.

[0046] Referring still to FIG. 2, system 100 further comprises a wave generator 144 configured to generate one or more waves 146 over surface 118. Wave generator 144 is controlled by controller 136. Wave 146 can be a capillary wave or a gravity wave. Capillary waves and gravity waves are waves that occur in fluid systems.

[0047] A capillary wave is a type of wave that occurs at the surface of a liquid as a result of the combined effects of gravity and surface tension. Surface tension is a cohesive force between liquid molecules at the surface of the liquid (surface 118 in FIG. 2). The formation of a capillary wave can be understood through a balance of gravity, which tends to pull the liquid downward, and surface tension, which tends to pull the wave upward. At sufficiently small wavelengths (e.g., a few millimeters to several centimeters), the surface tension dominates the gravity, resulting in a capillary wave. At wavelengths that are sufficiently large for the gravity to dominate the surface tension, the wave is a gravity wave. Wave 146 is typically manifested as one or more wrinkles propagating on surface 118. The propagation direction of wave 146 is shown at 150.

[0048] Wave generator 144 optionally and preferably replaces the conventional recoater 30 (see FIG. 1) that is employed in conventional stereolithography systems. Thus, in various exemplary embodiments of the invention system 100 is devoid of a recoater that moves above the entire area of the previously formed layer and spreads the liquid to recoat that layer. Preferably, the motion of wave generator 144 is restricted to regions 148 of surface 118 that are laterally separated from a region 152 of surface 118, wherein region 152 is the entire region of surface 118 that is above one or more of the layers of object 112 in their entirety, e.g., above the entire layer that is to be formed on top of the newest formed layer 128, and / or above the newest formed layer 128 in its entirety, and / or above all the layers 126 of object 112 that were already formed, in their entirety, and / or above all the layers of object 112 in their entirety. In some embodiments of the present invention region 152 of surface 118 is the entire region of surface 118 that is above surface 121 of platform 120.

[0049] In some embodiments of the present invention controller 136 is configured to control at least one parameter of wave 146 (such as, but not limited to, amplitude, frequency, and shape). This can be achieved in some embodiments of the present invention by selecting the pattern of the control signal that is transmitted from controller to wave generator 144. In some embodiments of the present invention, such a selection of parameter(s) is based on user input received by means of a user interface, such as, but not limited to, a user interface 164 controlling computer 162. For example, the user can select the parameter(s) of wave 146 based on the type of liquid that is loaded to vat 114 and / or the property and / or condition of the liquid (e.g., viscosity, temperature, pressure). The selection can be by means of a lookup table or other list of criteria for selecting wave parameters based on type and / or condition of the liquid. The parameters can alternatively or additionally be selected automatically by the system. For example, system 100 can comprise one or more sensors 166 that sense the property and / or condition of the liquid. Controller 136 can receive from sensor 166 signals that describe the liquid (e.g., viscosity, temperature, pressure) and select the wave parameters responsively to these signals, by mean of a digital lookup table or any other list of criteria.

[0050] In some embodiments of the present invention system 100 comprises a wave absorber 168 configured for absorbing the wave, in a manner that reduces or eliminate reflection of wave 146 from one or more of the walls of vat 114. Wave absorber 168 can be of any type known in the art. For example, wave absorber 168 can be made of a compliant material having a stiffness that is less than a stiffness of the walls of vat 114. Also contemplated, are embodiments in which wave absorber 168 is an active absorber that reduces the reflection by generating another wave that destructively interfere with wave 146.

[0051] In use of system 100, controller 136 controls radiation system 134 to apply radiation 138 to surface 118 to form patterns 160 (see FIG. 3), so as to solidify the liquid along these patterns and form a solidified building material that forms one layer of object 112. Typically, controller 136 deactivates system 134 after the layer is formed. Controller 136 then increases the distance between surface 121 of platform 120 and surface 118 of liquid 116 as further detailed hereinabove. Consider now the state shown in FIG. 2, namely after a plurality of layers 126 of object 112 has already been formed, where the topmost layer of layers 126 is the most recently formed layer 128. Due to the viscosity of liquid 116, when the distance between surfaces 121 and 118 is increased, surface 118 becomes non-planar, and the thickness of liquid 116 above the topmost layer 128 is nonuniform. At this stage, controller 136 temporarily activates wave generator 144. During the operation of generator 144, one or more of waves 146 is generated. When the operation of generator 144 is ceased, no wave is generated, but wave 146, which was generated during the period at which generator 144 was operative, may continue to exist on surface 118.

[0052] As wave(s) 146 propagates across surface 118, the height of liquid 116 increases locally at regions defined by the maxima of wave 146 at or behind its wavefront. In particular, during the motion of wave 146 above layer 128, the height of liquid 116 above layer 128 temporarily increases according to the amplitude of wave 146. By the force of gravity and dispersive forces, this temporal increment gradually decays behind the wavefront of wave 146 as it continues to propagate over surface 118. Wave 146 may reach the other end of vat 114 and experience a reflection off the wall of vat 114. The reflected wave moves at the opposite direction and may potentially pass again over layer 128, temporarily increasing the height of liquid 116 above layer 128. As a result of the viscosity of liquid 116, the amplitude of the reflected wave is substantially smaller than the original amplitude, and so the wave typically completes less than a single return pass over surface 118, and in any event does not perform an end-to-end pass within vat 114 more than a few times. Thus, eventually, wave 146 decays completely and surface 118 becomes planar, allowing controller to reactivate system 134 in order to begin forming the next layer. In some embodiments of the present invention, controller 136 initiates the application of radiation 138 in order to form the next layer less than t seconds after the operation of wave generator 146 is ceased. Representative examples for values of t suitable according to some embodiments of the present invention including, without limitation, 10, 8, 6, 4, and 2.

[0053] The time by which wave 146 completes its pass over surface 118 depends on the group velocity of wave 146, which depends on the properties of liquid 116 (e.g., surface tension, density) and of the air above surface 118 (typically the density). Typically, the group velocity of wave 146 is more that a few centimeters per seconds, e.g., 10, 12, 14, 16, 18, 20 cm / s or more. This group velocity is more than one or two orders of magnitude faster than the typical speed of a conventional recoater such as recoater 30. This is because the group velocity is the velocity at which a perturbation in surface 118 propagates, and is therefore significantly higher than a velocity that can be achieved by a mechanical locomotion system. In some embodiments of the present invention the phase velocity of wave(s) 146 is selected to ensure that wave 146 does not dispersed completely before propagating throughout the vat one or more times.

[0054] Since the group velocity of wave 146 is 1-2 orders of magnitude higher than the speed of a conventional recoater, the time by which wave 146 completes its passes over surface 118 is significantly shorter than the time required for the conventional recoater to operate, even if several passes of wave 146 are required until its complete decay. Thus, the system of the present embodiments reduces the recoating time of the newly formed layer 128. As the fabrication time of a layer of object 112 is oftentimes dominated by this recoating time, the system of the present embodiments has a higher throughput compared to system 10, and is therefore advantageous.

[0055] Wave generator 144 can be of any type that is capable of creating a perturbation at the surface 118 of liquid 116. FIG. 2 illustrates an embodiment in which the perturbation is created by a wave generating element in the form of a solid object that vibrates at the upper region of liquid 116. Also contemplated are embodiments in which the wave generating element is an acoustic wave generating element (e.g., a loudspeaker) that generates an acoustic wave directed towards surface 118, wherein the pressure applied by the acoustic wave creates a perturbation in surface 118. Further contemplated are embodiments in which the wave generating element wave is a gas pulse generator (e.g., an air pulse generator) that generates one or more pulses of gas moving towards surface 118, wherein the impact applied by gas pulse upon arrival to surface 118 creates a perturbation in surface 118. The shape of the wave generating element of wave generator 144 (e.g., the solid object or the loudspeaker or the air pulse generator) is preferably selected such that the wavefront of wave 146 is linear and straight. The advantage of this embodiment is that it reduces the likelihood of uncontrolled interferences between multiple propagation directions of wave 146. It is appreciated that even in the case of a straight linear wavefront, wave 146 can propagate along more than one direction. For example, part of wave 146 can propagate along direction 150 and another part of wave 146 can propagate at the opposite direction. Yet, it was found by the inventors that in such cases the interferences are negligible.

[0056] In some embodiments of the present invention wave generator 144 is configured to vibrate vertically relative to surface 118, as shown by arrow 154, in some embodiments of the present invention wave generator 144 is configured to vibrate horizontally relative to surface 118, as shown by arrow 156, and in some embodiments of the present invention wave generator 144 is configured to vibrate both vertically 154 and horizontally 156 in a combined motion (e.g., diagonal, circular, elliptic, etc.) relative to surface 118. When wave generator 144 vibrates horizontally, the amplitude of the vibration is at most the largest dimension of region 148 of surface 118.

[0057] The inventors found that it is sufficient to operate the wave generating element of wave generator 144 to perform a single motion period. For example, when the wave generating element vibrates vertically, controller 136 can control it to perform a single downstroke followed by a single upstroke or vice versa, and when the wave generating element vibrates horizontally, controller 136 can control it to perform a single rightstroke followed by a single leftstroke or vice versa. Immediately following the single motion period, controller 136 can deactivate wave generator 144. Alternatively, controller 136 can control wave generator 144 to perform more than one motion period (e.g. , 1.5 motion periods or 2 motion periods or more). A typical duration of a single motion period of wave generator 144 is less than 2 seconds (corresponding to vibration frequency of 0.5 Hz), or less than 1.5 seconds (corresponding to vibration frequency of about 0.67 Hz), or less than 1 second (corresponding to vibration frequency of 1 Hz), or less than 0.5 seconds (corresponding to vibration frequency of 2 Hz), or less.

[0058] The vibration amplitude of wave generator 144 is preferably selected to ensure that the amplitude of wave 146 is more than a thickness of a single layer of object 112, e.g., the thickness of the layer to be formed after wave 146 decays or the thickness of the top most layer 128 that was already formed. In some embodiments of the present invention the vibration amplitude of wave generator 144 is selected to ensure that the amplitude of wave 146 is less than three times the thickness of one such layer of object 112. A typical thickness of a layer is from about 20 microns to about 200 microns.

[0059] FIG. 4 is a flowchart diagram of a method suitable for fabricating an object (e.g., object 112) by additive manufacturing, according to various exemplary embodiments of the present invention. At least a portion of the operations of the method can be executed by system 100 described above.

[0060] 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 below 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.

[0061] The method begins at 400 and continues to 401 at which computer object data that collectively pertain to a shape of the object are received. For example, the computer (e.g., host computer 162) can access a computer-readable storage medium and retrieve the data from the medium. The computer can also generate the data, or a portion thereof, instead of, or in addition to, retrieving data from the storage medium, for example, by means of computer aided design (CAD) software or computer aided manufacturing (CAM) software. The computer object data can include a plurality of graphic elements (e.g., a mesh of polygons, non-uniform rational basis splines, etc.) defining a surface of the object. In some embodiments of the present invention the graphic elements are transformed to a grid of voxels defining the shape of the object, for example, using a slicing procedure that forms a plurality of slices, each comprising a plurality of two- dimensional coordinates of points along the patterns that form one layer of the object. Alternatively, the method can receive sliced computer object data from an external source, e.g., a computer-readable medium, in which case it is not necessary to execute the slicing operation. The data can be in any data format known in the art, including, any of the aforementioned computer object data formats.

[0062] The computer communicates with the controller of the system (e.g., controller 136 of system 100), to allow the computer to transfer the data to the controller. The computer can be configured to transfer all the data to the controller before the additive manufacturing process begins, or to initially transfer only a portion of the data, and continue transferring during the additive manufacturing process, e.g., upon a request from the controller. For example, the computer can be configured to transmit the data on a slice-by-slice basis, or in batches of two or more slices at a time.

[0063] The method proceeds to 402 at which a platform (e.g. , platform 120) is immersed in a liquid that is curable by radiation (e.g., liquid 116). Preferably, the platform is immersed in a manner that the vertical distance between the liquid surface and the top surface of the planform (when no layer was yet to be formed on the platform) or the most newly formed layer (when at least one layer was formed on the platform) is at least the thickness of a single layer of object (e.g., the thickness of the most newly formed layer). In some embodiments of the present invention, operation 402 is executed to ensure that the vertical distance between the surface of the liquid and the top surface of the planform or the top surface of the most newly formed layer is more than the thickness of a single layer (e.g., more than the thickness of the most newly formed layer).

[0064] The method continues to 403 at which a wave is generated over the surface. The wave is generated by a wave generator (e.g., wave generator 144), and can be a capillary wave or a gravity wave as further detailed hereinabove. Preferably, the motion of the wave generator is restricted to regions of the liquid's surface (e.g., region 148), that are laterally separated from a region occupied by one or more layers of the object (e.g., region 152) as further detailed hereinabove.

[0065] Optionally, the method proceeds to 404 at which the vertical distance between the liquid surface and the top surface of the planform or the most newly formed layer is adjusted. For example, when the vertical distance is more than the thickness of a single layer, the method can reduce the distance to ensure that the vertical distance is approximately (e.g., with tolerance of 10% or less or 5% or less or 1% or less) the thickness of a single layer, (e.g., the thickness of the most newly formed layer).

[0066] The method continues to 405 at which radiation is applied to the surface of the liquid above the platform to form solidified patterns defining a layer of the object, as further detailed hereinabove. The method can then loop to 401 for receiving computer object data of another layer of the object. When the data of the next layer of the object are already loaded, the method can loop to 402 for forming the next layer.

[0067] The method ends at 406.

[0068] As used herein the term “about” refers to ± 10 %

[0069] The terms "comprises", "comprising", "includes", "including", “having” and their conjugates mean "including but not limited to".

[0070] The term “consisting of’ means “including and limited to”. 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 subcombination 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.

[0075] 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.

[0076] 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. An additive manufacturing system, comprising: a vat filled with a liquid curable by radiation; a platform immersed in said liquid; a radiation system configured for applying radiation to a surface of said liquid; a computerized controller having a circuit configured to control said radiation system to form on said surface above said platform patterns defining a layer of an object; a wave generator configured to generate a wave over said surface, wherein a motion of said wave generator is restricted to regions of said surface that are laterally separated from a region occupied by said layer.

2. The system according to claim 1, wherein said wave generator is configured to vibrate vertically relative to said surface.

3. The system according to any of claims 1 and 2, wherein said wave generator is configured to vibrate horizontally relative to said surface.

4. The system according to any of claims 2 and 3, wherein a vibration amplitude of said wave generator is selected to ensure that an amplitude of said wave is more than a thickness of said layer.

5. The system according to any of claims 2-4, wherein a vibration amplitude of said wave generator is selected to ensure that an amplitude of said wave is less than three times a thickness of said layer.

6. The system according to any of claims 1-5, wherein said wave generator is configured to perform a single motion period to form said wave.

7. The system according to any of claims 1-6, wherein a duration of a single motion period of said wave generator is less than 2 seconds.

8. The system according to any of claims 1-7, wherein said liquid is a photocurable liquid and said radiation is an optical radiation.

9. The system according to any of claims 1-7, wherein said computerized controller is configured to initiate said control of said radiation system less than t seconds after an operation of said wave generator is ceased.

10. The system according to claim 9, wherein said t equals 10.

11. A method of fabricating an object by additive manufacturing, the method comprising: immersing a platform in a liquid curable by radiation; applying radiation to a surface of said liquid above said platform to form patterns defining a layer of the object; and generating a wave over said surface by wave generator, wherein a motion of said wave generator is restricted to regions of said surface that are laterally separated from a region occupied by said layer.

12. The method according to claim 11, wherein said wave generator is configured to vibrate vertically relative to said surface.

13. The method according to any of claims 11 and 12, wherein said wave generator is configured to vibrate horizontally relative to said surface.

14. The method according to any of claims 12 and 13, wherein a vibration amplitude of said wave generator is selected to ensure that an amplitude of said wave is more than a thickness of said layer.

15. The method according to any of claims 12-14, wherein a vibration amplitude of said wave generator is selected to ensure that an amplitude of said wave is less than three times a thickness of said layer.

16. The method according to any of claims 11-15, wherein said generating said wave comprises performing a single motion period of said wave generator.

17. The method according to any of claims 11-16, wherein a duration of a single motion period of said wave generator is less than 2 seconds.

18. The method according to any of claims 11-17, wherein said liquid is a photocurable liquid and said radiation is an optical radiation.

19. The method according to any of claims 11-17, wherein said applying said radiation is initiated less than t seconds after an operation of said wave generator is ceased.

20. The method according to claim 19, wherein said t equals 10.

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