COPYRIGHT NOTICE

[0001] A portion of the disclosure hereinbelow contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.

BACKGROUND

[0002] The disclosure is directed to devices, systems and methods for controlling the process of additive manufacturing. More specifically, the disclosure relates to devices, systems and methods for using a load cell in the measurement of viscous flow and viscous adhesion force for controlling printing parameters in stereolithographic (SLA) and/or digital light processing (DLP) 3D printers.

[0003] Vat polymerization technologies build parts by curing the resin into a solid layer-by- layer with a certain light source, therefore creating a three-dimensional structure. The two main vat polymerization technologies are: SLA (stereolithography) and DLP (Digital Light Processing).

[0004] 3D printer with SLA technology typically uses a platform immersed in a transparent tank that is filled with photopolymerizable resin. While the platform is immersed in the resin, the laser beam traces the build area and cures these areas according to the sliced STL template (or any other CAD/CAM format file). Following the layer formation, a platform is lowered or raised in the Z- direction, depending on whether the printer uses a top-down (e.g., a 355 nm laser beam projector placed above the vat and the exposure direction is from the top, and the platform is lowered) or bottom- up process (e.g., the laser beam projector placed beneath the transparent vat and the exposure direction is from the bottom, and the platform is raised), by a fixed distance equaling the height of a layer. The curing process is repeated layer-by-layer until the 3D model is completed. The height of a layer ranges typically from between about 12 to 150 pm. Likewise print speed of standard SLA printers is in the range of 10-20 mm/h, with the accuracy proportional to the diameter of the laser beam at the curing point, namely, the spot size of the curing laser.

[0005] Conversely, in DLP, the laser beam is replaced and the printer uses a projector to project the layer image of the cross section of an article, or a portion of the cross-section into the photopolymerizable resin. Typically, the printer uses optical semiconductor, or digital microscope device or DLP chip, capable of having about two million regular arrays of tiny interrelated microscopes. The DLP chip is operable to communicate with digital video or image signals, light sources (in other words, actinic radiation), and projection lenses, and project a full digital image onto the transparent vat base (on a bottom-up printer). Switching times of DLP chips can be, for example in the KHz range, producing high printing resolution which could print minimum size of between about 2 pm and about 75pm.

[0006] Both methods exhibit several shortcomings. For example, SLA has relatively low printing rate due to the curing rate depending on the moving of the laser beam. The larger size of the models, the slower the printing rate. In both printing methods, layer- shifting phenomena and strong detachment forces that badly effect the quality of the printed parts are regularly reported. The effect of those issues is often failed prints, waste and loss of resolution in printed parts. Moreover, strong detachment forces can break or damage delicate hardware features of the printer, and/or add to the wear and tear of equipment, shortening the life of the equipment. Additionally, during the printing process there is no real-time indication of the failure of the printing process.

[0007] There are several solutions, such as vat tilting, which is detrimental for accuracy, and optimization of part orientation to reduce the projected area for each layer, thus unfortunately limiting the variety of printable geometries.

[0008] These and other shortcomings are addressed by the following disclosure.

SUMMARY

[0009] Disclosed, in various exemplary implementation, are devices, systems and methods using a load cell in the measurement of viscous adhesion and viscous flow for controlling printing parameters in stereolithographic and/or digital light processing (DLP) 3D printers.

[00010] In an exemplary implementation provided herein is a load cell to measure at least one of: viscous adhesion, and viscous flow in the process of additive manufacturing, wherein the load cell is implemented in a system comprising: a vat having a transparent base: a build plate; an arm operable to be vertically translatable, the arm being coupled to the build plate; a projector module, operable to project actinic radiation to the vat for a predetermined period; and a photopolymerizable liquid resin disposed within the vat, wherein the load cell is coupled between the arm and the build plate.

[00011] In another embodiment, provided herein is a method of controlling additive manufacturing of an article of manufacture, implemented in a system comprising: a vat having a transparent base, a build plate, at least one of: an arm, and a pedestal, wherein each of the arm and the pedestal are operable to be vertically translatable, the arm being coupled to the build plate, a projector module, operable to project actinic radiation to the vat for a predetermined period, a photopolymerizable liquid resin disposed within the vat, and a load cell coupled between the arm and the build plate, the method comprising: using the load cell, measuring the at least one of: viscous adhesion, and viscous flow, each between the build plate and at least one of: the transparent vat base, and the polymerized resin; and based on the measurement of the at least one of: the viscous adhesion and the viscous flow each, varying at least one of: rate, degree of ascent or descent, and the residence time of the build plate above the at least one of the transparent vat base, and the polymerized resin.

[00012] These and other features of the methods, and systems for use of a load cell to measure at least one of: viscous adhesion, and viscous flow in the process of additive manufacturing, will become apparent from the following detailed description when read in conjunction with the figures and examples, which are exemplary, not limiting.

BRIEF DESCRIPTION OF THE FIGURES

[00013] For a better understanding of the devices, systems and methods using a load cell in the measurement of viscous adhesion and viscous flow for controlling printing parameters in SLA and/or DLP, with regard to the exemplary implementation thereof, reference is made to the accompanying examples and figures, in which:

[00014] FIG. 1A is a schematic illustrating the build plate orientation relative to the transparent vat base on first layer printing, with FIG. IB, illustrating the vat base orientation relative to the printed layer attached to the build plate;

[00015] FIG. 2 A, is a flow chart illustrating an exemplary implementation of using the feedback from the load cell to determine stabilizing time on descent following the printing of a single layer, with FIG. 2B, charting another exemplary implementation of using the feedback from the load cell to adjust build plate motion, and FIG. 2C, illustrating yet another exemplary implementation of using the feedback from the load cell to adjust build plate motion upon ascent;

[00016] FIG. 3, shows the correlation between printed area to detachment/engage forces as measured by the load cell;

[00017] FIG. 4, shows the feedback from the load cell in a failed printing; [00018] FIG. 5, illustrating an analysis of engagement/retraction cycle based on load cell feedback; and

[00019] FIG. 6, is a schematic illustration of an immersion model for both viscous flow and viscous adhesion models of liquid-mediated viscous adhesion over asperities.

DETAILED DESCRIPTION

[00020] Provided herein are exemplary implementations of systems and methods using a load cell to measure viscous adhesion and viscous flow for use in controlling printing parameters in SLA and/or DLP.

[00021] As indicated, SLA technology is typically implemented in a system comprising a vat (having a transparent base in a bottom-up configuration): a build platform operable to be vertically (e.g., in the Z-direction) translatable,; a projector module, operable to project actinic radiation to the vat as a laser beam; and a photopolymerizable liquid resin disposed within the vat, whereby the laser beam of a known spot diameter (determining dimensionality of the trace) traces the build area and cures these areas according to a rater representation of a 3D model file. Conversely, in DLP, the projector module is operable to project a layer image (or a section of the raster image) of the sliced cross section (raster) of the 3D-modeled article, or a portion of the cross-section into the photopolymerizable resin template. Following the first layer formation on the build plate, a platform is either lowered or raised in the Z-direction, depending on whether the printer uses a top-down (e.g., the laser beam/projector placed above the vat), and the platform is lowered, or bottom-up process (e.g., the laser beam/projector placed beneath a transparent vat base), and the exposure direction is from the bottom, and the platform is raised, by a fixed distance in the Z-direction equaling the height of a layer.

[00022] The curing process is will depend on many parameters, such as, for example, at least one of: laser intensity/ projection intensity, resin physico-chemical parameters, required article resolution, printing speed, projected area, layer height, resin rheology, excessive resin entrapment and the like. In addition, and in another exemplary implementation, following the accumulation of load cell force data, in combination with additional parameters disclosed herein, a database is assembled, and the parsed (raster) 3D visualization files, (whether or not sub-divided to projection portions), are used to pre-program the system according to the expected projection image.

[00023] Regardless of the printing method (e.g., SLA, DLP), when printing articles that are smaller than the depth of the vat, the liquid resin remains a medium between the build platform or the printed layer formed by the cured photopolymerizable resin and the vat base. In an exemplary implementation, the photopolymerizable resin composition used to form the article, part thereof, or mold, in the devices, systems and methods disclosed herein comprise: polyester (PES), polyethylene (PE), polyvinyl alcohol (PVOH), poly(vinylacetate) (PVA), poly-methyl methacrylate (PMMA), Poly(vinylpirrolidone), a multi-functional acrylate, or a combination comprising a mixture, a monomer of each of the foregoing photopolymerizable polymer, an oligomer of each of the foregoing photopolymerizable polymer, and a copolymer of one or more of the foregoing photopolymerizable polymers, each of which may further undergo cross-linking.

[00024] In this context, crosslinking refers to joining moieties from different polymer chains together by covalent bonding using a crosslinking agent, i.e., forming a linking group, or by radical polymerization of monomers such as, but not limited to methacrylates, methacrylamides, acrylates, or acrylamides. In some exemplary implementation, the linking groups are grown to the end of the polymer arms.

[00025] For example, the multi-functional acrylate is at least one of a monomer, oligomer, polymer, and copolymer of: 1 ,2-ethanediol diacrylate, 1,3-propanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, neopentyl glycol diacrylate, ethoxylated neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, tripropylene glycol diacrylate, bisphenol-A-diglycidyl ether diacrylate, hydroxypivalic acid neopentanediol diacrylate, ethoxylated bisphenol-A-diglycidyl ether diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, propoxylated glycerol triacrylate, tris(2-acryloyloxyethyl)isocyanurate, pentaerythritol triacrylate, ethoxylated pentaerythritol triacrylate, pentaerythritol tetraacrylate, ethoxylated pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate or a multifunctional acrylate composition comprising one or more of the foregoing. In an exemplary implementation, the term “copolymer” means a polymer derived from two or more monomers (including terpolymers, tetrapolymers, etc.), and the term “polymer” refers to any carbon-containing compound having repeat units from one or more different monomers.

[00026] In another exemplary implementation, the light projector is operable to emit electromagnetic actinic radiation (EMR) at a predetermined wavelength ( ) and be used to photopolymerize thus cure the resin, whether alone or in the presence of photoinitiator(s). For example, the EMR source is configured to emit coherent radiation (as a single beam, or a projected image) at a wavelength of between 190 nm and about 400nm, e.g. 355 nm, or 395 nm which in an exemplary implementation, can be used to accelerate and/or modulate and/or facilitate a photopolymerizable resin composition. Photoinitiators that can be used with the multifunctional acrylates described herein can be, for example radical photoinitiator. These radical photoinitiators can be, for example Irgacure® 500 fromCIBA SPECIALTY CHEMICAL and Darocur® 1173, Irgacure® 819, Irgacure® 184, TPO- L (ethyl(2,4,6, trimethyl benzoil) phenyl phosphinate) benzophenone and acetophenone compounds and the like. For example, the radical photoinitiator can be cationic photo-initiator, such as mixed triarylsulfonium hexafluoroantimonate salts. Another example of the radical photoinitiator used in the active continuous phase described herein, can be 2-ispropylthioxanthone.

[00027] In an exemplary implementation, the liquid photopolymerizable resin is a nonNewtonian viscoelastic fluid, that is typically exhibiting shear-thickening, or rheopectic rheological properties. In the context of the disclosure, the term “shear-thickening” means a liquid composition that demonstrates a large, sometimes discontinuous increase in viscosity with increasing shear stress. Shear thickening fluids can comprise one or more fillers that are functional in the shear thickening behavior of the fluid (e.g., silica nanoparticles, glass fibers, or graphene nanowires), in addition to other components to the extent that these other components do not materially interfere with the shear thickening response of the fluid to increasing stress. Moreover, the term “Rheopectic” or “rheopexy” as used herein refers to the property of the photopolymerizable liquid resin in which elastic modulus increases with time under shear, or suddenly applied force or stress. It is noted, that during the engagement of the build plate (or platform), in other words, when lowering the build plate to the predefined distance (XD, see e.g., FIG. 1A, IB), along the Z-axis, the platform creates shear stress that will depend on the rate of descent of the platform towards the vat base (See e.g., FIG. 1 A), or the top of the built, cured layer (See e.g., FIG. IB), staying

[00028] Moreover, while the built plate, or the cured build layer dwells at close proximity (between about 0.5 pm and about 75 pm) to the vat base, the photopolymerizable liquid resin, which is thermodynamically compatible with the built layer and possibly the vat base and/or the build plate, will wet (in other words, spread and have a contact angle t?<90°) at least one surface (namely the build plate and/or the cured build layer), promoting liquid-mediated adhesion. That liquid-mediated adhesion, formed of a rheopectic and/or shear-thickening material (the photopolymerizable liquid resin), requires a force to overcome. The photopolymerizable liquid resin-mediated adhesive forces can be divided into two components: a meniscus force - due to interfacial tension between the photopolymerizable liquid resin and the build plate, and/or the vat base, and/or the cured build layer; and a rate-dependent viscous force. These forces increase for smaller gaps (such a gaps in microfabricated articles), and smoother surfaces so that the adhesion of ultra-flat surfaces (such as the build platform, and/or the vat base), can be extremely strong (leading for example to defects such as detachment, and layer shifting). Not wishing to be bound by theory, but for SLA and DLP, following the curing of the first layer, the meniscus force is either negligible or non-existent, since the build plate is immersed in the photopolymerizable liquid resin (see e.g., FIG. 6), and only viscous forces exist, contributing to the viscous adhesion of the surfaces.

[00029] Conversely, on the ascent, the forces can be somewhat different. High viscous adhesion force during the separation of the build plate, and/or the cured build layer from the vat base, may cause high friction and viscous adhesion, and result in high local tensile stresses, which may be enough to cause a fracture, generate particles, delaminate, or partially delaminate contact surface. Viscous adhesion force increase with an increase in the residence time, making it advantageous to monitor the viscous adhesion forces. In the context of the disclosure, the term “viscous adhesion ” refers to the force in Newton per unit area (N/mm ² ) required to start movement of the build plate and/or the cured build layer away from the vat base, recorded at separation rate of between about 0.04 mm/second and about 2 mm- sec. ¹ . Moreover, during the ascent (apical Z-axis movement, or movement in the Z- direction causing separation between the build plate and the vat base), viscous adhesion or tension between the surfaces resist their separation. Then, as separation forces overcome the viscous adhesive forces, the surfaces separate rapidly, potentially creating a negative pressure. This negative pressure, combined with the speed with which the surfaces separate, can create a vapor cavity within fluid much like a solid that has been fractured, and upon collapse of the cavity, send shock waves through the liquid, again capable of causing fracture, generate particles, and either delamination, or partial delamination. Since the printing process is a typically a start-stop process, where residence time of the build plate over the cured layer vary (depending on the layer size), and viscous adhesion force increase with an increase in the residence time it will be advantageous to monitor the viscous adhesion forces both on the engagement (descent), and disengagement (ascent) stages.

[00030] Accordingly and in an exemplary implementation illustrated schematically in FIG.s 1 A, IB), provided herein is use of load cell 600, to measure viscous adhesion force in the process of additive manufacturing. In another exemplary implementation, load cell 600 is implemented in system 10 comprising: vat 100 having transparent base 1000 and a predetermined depth: build plate 200 (interchangeable with build platform); arm 300 operable to be vertically translatable, arm 300 being coupled to build plate 200; projector module 400, operable to project actinic radiation to vat 100 for a predetermined period; and photopolymerizable liquid resin 500, disposed within vat 100, wherein load cell 600 is coupled (sandwiched) between arm 300 and build plate 200.

[00031] Load cell 600 used in systems 10 and methods disclosed, is operable to provide the resolution to get a better understanding of the layer detachment process, enabling to spot small changes in the detachment force caused by small changes in the cured/projected area. The signal obtained from the load cell at a resolution of about no more than ±10 g, will in turn allow building a more accurate forces profile. Such profile will enable optimizing the layers detachment process (in other words, optimized layers detachment process is one the layer is pulled completely without damaging delicate features at a minimum time), by changing parameters such as: acceleration, velocity, (e.g., both affecting shear rate and shear stress) delays (e.g., residence time affecting viscous adhesion forces), temperature (e.g., affecting dynamic viscosity) and more.

[00032] The reaction time to the load cell signal, can be in an exemplary implementation, no more than 10 ms. in order to ensure “real time” response and close a loop on the Z-axis movement of the arm 300, while leveling the vat 100 on the glass at the beginning of each process. Accordingly, short reaction time will enable the system to react fast and stop at the specific location at a specific force applied on the glass, allowing a more repeatable printing process. Tn yet another exemplary implementation, the load cell is operable to measure the viscous adhesion force of between about -51 Kilogram force (Kgf, —500 Newton) and about 51 Kgf (500 N).

[00033] Projector module 400 further comprises: an X-Y stage 4000 capable of translation motion along X-axis direction and Y-axis direction orthogonal to each other, operable to translate a projector 4001 of the actinic radiation in a X-Y plane; and a second powertrain 4002 coupled to the X-Y stage, operable to translate stage 4000 along the X-axis direction and the Y-axis direction. Moreover, the predetermined period of actinic radiation projection is configured to polymerize the photopolymerizable liquid resin to a predetermined pattern forming layer 501i (see e.g., FIG. IB) having a predetermined layer-thickness. As further illustrated in FIG.s 1A, IB, system 10 further comprise: first powertrain 3000, coupled to arm 300; and central processing module (CPM) 700, in communication with first powertrain 3000, second powertrain 4002, load cell 600, vat 100, and projector module 400, CPM 700 further comprising at least one processor in communication with a non-transitory storage device, storing thereon a set of executable instructions, configured when executed to cause the at least one processor to: measure viscous adhesion force; and based on the measured viscous adhesion force, using the at least one of first powertrain 3000, and second powertrain 4002, vary at least one of: rate, degree of ascent or descent, and the residence time of build plate 200, the predetermined projection period of the actinic radiation, and rate and extent of motion of stage 4000 along the X-axis direction and the Y-axis direction, as well as vat 100 temperature. In an exemplary implementation vat 100 comprises transparent base 1000, and is operable to control the temperature of the photopolymerizable liquid resin 500. Control of the vat’s temperature, can be achieved by jacketing the vat, or incorporating heating elements into the vat walls and base. Sensors such as thermocouples on the vat walls, inside the resin, or using IR sensors above the resin can also be used.

[00034] In the context of the disclosure, the term “powertrain” encompasses a range of powertrain components including without limitation motor, gears, hubs, and poles stage 4000. Therefore, it should be understood that the term “powertrain” as used herein is inclusive of drivetrain components operable to effect the motion of stage 4000 in the X-Y axis direction.

[00035] In an exemplary implementation load cell 600 is operable to measure the viscous adhesion force FA (e.g., N/mm ² ) between build plate 200 and transparent base 1000 of vat 100, or in another example, measure the viscous adhesion force between the build plate and the polymerized resin layer.

[00036] In an exemplary implementation, the systems using the load cell to measure viscous adhesion forces used to implement the methods provided herein, can further comprises a computer aided manufacturing (“CAM”) module, the module comprising a central processing module (CPM) with at least one processor, a non-transitory memory device, storing thereon a set of executable instructions, which, when executed are configured to cause the at least one processor to: receive a 3D visualization file representing the printed article; generate a library of files, each file represents at least one, substantially 2D layer for printing, creating a substantially 2D representation image, wherein the CAM module and/or the CPM is operable to control each of the first and second powertrains, the vat temperature, and the projector module. Accordingly, the set of executable instructions are further configured, when executed to cause the processor to generate a library of a plurality of subsequent layers’ files from the 3D visualization file. Each subsequent file represents a substantially two dimensional (2D) subsequent layer for printing a subsequent portion of the printed article, wherein each subsequent layer file is indexed by at least, printing order. [00037] The 3D visualization file representing the printed article, can be, for example: an *.x_t an ODB, an ODB++, an. asm, an STL, an IGES, a STEP, a Catia, a SolidWorks, a Autocad, a Creo, a 3D Studio, a Gerber, a Rhino a Altium, an Oread, or a file comprising one or more of the foregoing; and wherein file that represents at least one, substantially 2D layer (and uploaded to the library) can be, for example, a JPEG, a GIF, a TIFF, a BMP, a PDF file, or a combination comprising one or more of the foregoing.

[00038] In addition, the computer program can comprise program code means for carrying out the steps of the methods described herein, as well as a computer program product comprising program code means stored on a medium that can be read by a computer. Non-transitory storage device(s) as used in the methods described herein can be any of various types of non-volatile memory devices or storage devices (in other words, memory devices that do not lose the information thereon in the absence of power). The term “memory device” is intended to encompass an installation medium, e.g., a CD-ROM, floppy disks, or tape device or a non-volatile memory such as a magnetic media, e.g., a hard drive, optical storage, or ROM, EPROM, FLASH, etc. The memory device may comprise other types of memory as well, or combinations thereof. In addition, the memory medium may be located in a first computer in which the programs are executed (e.g., the 3D DLP/STL printer provided), and/or may be located in a second different computer which connects to the first computer over a network, such as the Internet. In the latter instance, the second computer may further provide program instructions to the first computer for execution. The term “memory device” can also include two or more memory devices which may reside in different locations, e.g., in different computers that are connected over a network. Accordingly, for example, the bitmap library can reside on a memory device that is remote from the CAM module coupled to the 3D DLP/STL printer provided, and be accessible by the 3D DLP/STL printer provided (for example, by a wide area network).

[00039] The use of the term “module” does not imply that the components or functionality described or claimed as part of the module are all configured in a (single) common package. Indeed, any or all of the various components of a module, whether control logic or other components, can be combined in a single package or separately maintained and can further be distributed in multiple groupings or packages or across multiple (remote) locations and devices. Furthermore, in certain exemplary implementations, the term “module” refers to a monolithic or distributed hardware unit. [00040] Accordingly and in an exemplary implementation, the CPM is operable to receive input from load cell 600, and use the data to control the printer. An exemplary pseudocode is provided below:

A pseudocode of Control with integrated Load- Cell

Engage:

Define Float NewLayerPo sition = Num

Define Float StabilizingForceLimit = Num

S etZAxisTo(Ne w LayerPo sition)

Do:

LoadForce = LoadCell.ReadForce()

While (LoadForce > StabilizingForceLimit)

ProjcctNcxtLaycrWithDLPO

Retract:

Define Float MaxAcceleration = Num

Define Float LimitForce = Num

Define Float DeltaAcceleration = Num

Define float MaxForce = low Value

Define float MinForceToErrorlnRetract = Num

Image = GetLastPrintedSliceQ

Perimeter = GetPrintedAreaPrimeter(Image) Area = GetNumberOfPixlesInidePerimeter(image, Perimeter)

PrintedDots = GetNumberOfOnPixelsInsidePerimeter (Image, Perimeter)

DotsPerArea = PrintedDots/Area

WcightPcrimctcr = GctPcrimctcrWcight(Pcrimctcr)

WeightArea = GetAreaWeight(Area)

WeightPrintedDots = GetPrintedDotsWeight(PrintedDots)

WeightDotsPerArea = GetDotsPerAreaWeight(DotsPerArea)

TotalWeight = CalcultateTotalWeight(WeightPerimeter , WeightArea ,

WeightPrintedDots , WeightDotsPerArea)

If TotalWeight > 1

TotalWeight = 1

Initial Acceleration = Max Acceleration * (1 - TotalWeight)

SetAcceleration(InitialAcceleration)

CurrentAcceleration = InitialAcceleration

S tartRetract(ZT arget)

While(IsZMovingO)

CurrentLoadForce = LoadCell.ReadForce()

If(CurrentLoadForce > MaxForce)

MaxForce = CurrentLoadForce

If(CurrentLoadForce >= LimitForce)

CurrentAcceleration = CurrentAcceleration - DeltaAcceleration SetAcceleration(CurrentAcceleration )

If (MaxForce < MinForceToErrorlnRetract* TotalWeight) StopPrintingAndShowErrorQ

Automatic tray leveling - targeted force:

Define float StartZLocation = num

Define float TargctLoadForcc = num

Define float MovementDelta = num

NextLocation = StartZLocation

Do:

SetZAxisTo(NextLocation)

CurrentLoadForce = LoadCell.ReadForce()

NextLocation = NextLocation - MovementDelta

While(CurrentLoadForce > TargetLoadForce)

Automatic sensitive HW safety:

Define float MinAllowedForce = Num

CurrentLoadForce = LoadCell.ReadForce()

If(CurrentLoadForce < MinAllowedForce)

StopPrintingAndShowErrorQ

[00041] An even more complete understanding of the components, processes, assemblies, and devices disclosed herein can be obtained by reference to the accompanying drawings. These figures (also referred to herein as "FIG.") arc merely schematic representations (c.g., illustrations) based on convenience and the ease of demonstrating the present disclosure, and are, therefore, not intended to indicate relative size and dimensions of the devices or components thereof and/or to define or limit the scope of the exemplary implementation. Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the exemplary implementation selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure. In the drawings and the following description below, it is to be understood that like numeric designations refer to components of like function.

[00042] Turning now to FIG. 2A, a schematic flow chart of the use of load cell data in determining the viscous adhesion force to control the printer. As illustrated, upon movement 21 of build plate 200 to the next layer position (see e.g., XD, FIG. IB), real time feedback from load cell 600 is used 22 to determine the stabilization time of build plate (shear stress goes to 0), and projection module 400 is activated 23. Additionally, or alternatively as illustrated in FIG. 2B, descending build plate 200 is lowered 24 at a rate determined by the load cell measurement, whereby the rate is adjusted in real time 25 (e.g., to keep shear rate below elastic modulus, not to induce shear thickening), whereupon reaching the predetermined position, projection module 400 is activated 26. Using load cell 600 during retraction of build plate 200, is illustrated in FIG. 2C, where image processing, using an image module included with the system (not shown), in communication with the CPM, is used to determine the end of curing, obtain the next substantially 2D layer image for projection from the file library, and initiate retracting 27 build plate 200. Using load cell 600 measuring the viscous adhesion force, speed and acceleration is varied (adjusted) 28 to make sure the layer is detached without damage, and the build plate is then engaged 29, using e.g., the processes in FIG.s 2A, 2B. Accordingly, loadcell 600 will help optimizing the printing time by determine the minimum waiting times in the process, and by reducing the Z axis height movement when detaching layers (for example if a small area is cured, Z axis need to be moved less to detach the layer, when the pulling force=0 (in other words, viscous adhesion force is exceeded) the layer has detached), as well as whether the print has failed (see e.g., FIG. 4).

[00043] FIG. 3, illustrates the correlation between printed pyramid area to detachment/engage forces as measured by the load cell. As illustrated, the larger the printed area (bottom, base, left) the larger the viscous adhesion forces and the greater the viscous flow resistance in engaging the build plate (top).

[00044] Turning now to FIG. 5, illustrating an analysis of engagement/retraction cycle based on load cell feedback, attaching the physical processes to the measured signal from the load cell.

[00045] In an embodiment, the load cell used in the systems disclosed, is used to implement the methods described. Accordingly and in an exemplary implementation, provided herein is a method of controlling additive manufacturing of an article of manufacture, implemented in a system comprising: a vat having a transparent base, a build plate, at least one of: an arm, and a pedestal, wherein each of the arm and the pedestal are operable to be vertically translatable, the arm being coupled to the build plate, a projector module, operable to project actinic radiation to the vat for a predetermined period, a photopolymerizable liquid resin disposed within the vat, and a load cell coupled between the arm and the build plate, the method comprising: using the load cell, measuring viscous adhesion force between the build plate and at least one of: the transparent vat base, and the polymerized resin; and based on the measurement of the viscous adhesion force, varying at least one of: vat temperature, rate, degree of ascent or descent, and the residence time of the build plate above the at least one of the transparent vat base, and the polymerized resin.

[00046] The method further comprising measuring the viscous adhesion force between the build plate and the transparent base of the vat, and/or measuring the viscous adhesion force between the build plate and the formed resin layer. The methods disclosed can further comprise using the load sensor, measuring the load on the powertrain motor; and based on the measured first powertrain motor load, modifying the at least one of: the vat temperature, the rate, the degree of ascent or descent, and the residence time of the build plate above the at least one of: the transparent vat base, and the polymerized resin, the predetermined projection period of the actinic radiation, and the at least one of the rate and the extent of motion of the stage in the X-Y direction.

[00047] In the context of the disclosure, the term "operable" means the system and/or the device and/or the program, or a certain element or step is fully functional, sized, adapted and calibrated, comprises elements for, and meets applicable operability requirements to perform a recited function when activated, coupled, implemented, actuated, effected, realized, or when an executable program is executed by at least one processor associated with the system and/or the device. In relation to systems and circuits, the term "operable" means the system and/or the circuit is fully functional and calibrated, comprises logic for, having the hardware and firmware necessary, as well as the circuitry for, and meets applicable operability requirements to perform a recited function when executed by at least one processor.

[00048] Likewise, "transparent", as used herein, refers to a composition capable of at least 70% transmission of light. The light referred to can be, e.g., actinic light (e.g., from a laser), emitted light (e.g., from a an electromagnetic radiation source), or both, or transmittance of at least 80%, more preferably at least 85%, and even more preferably at least 90%, as measured spectrophotometrically using water as a standard (100% transmittance) at 690 nm. The term "transparent" as used herein would also refer to a composition that transmits at least 70% in the region ranging from 250 nm to 700 nm with a haze of less than 10%.

[00049] The term “load cell” may be used to mean any mechanism that translates/converts force into a signal such as an electrical or analog signal. Load cells/transducers are known in the art, and the description provided herein is intended to embrace all such mechanisms. Load cells in accordance with various exemplary implementations, may be coupled to a computing device by a physical connection such as a cable or a wire, and/or may be in wireless communication with a computing device and/or another load cell.

[00050] It is noted that the term “imaging module” as used herein means a unit that includes at least one built-in image and/or optic sensors and outputs electrical signals, which have been obtained through photoelectric conversion, as an image. The imaging modules described herein may communicate through a wired connection, for example, a hard-wired connection, a local area network, or the modules may communicate wirelessly. The imaging module may comprise charge coupled devices (CCDs), a complimentary metal-oxide semiconductor (CMOS) or a combination comprising one or more of the foregoing. If static images are required, the imaging module can comprise a digital frame camera, where the field of view (FOV) can be predetermined by, for example, the camera size and the distance from the layer/vat base/build plate. The cameras used in the imaging modules of the systems and methods disclosed, can be a digital camera. The term “digital camera” refers in an exemplary implementation to a digital still camera, a digital video recorder that can capture a still image of an object and the like. The digital camera can comprise an image capturing unit or module, a capture controlling module, a processing unit (which can be the same or separate from the central processing module)

[00051] The terms “first,” “second,” and the like, when used herein do not denote any order, quantity, or importance, but rather are used to denote one element from another. The terms “a”, “an” and “the” herein do not denote a limitation of quantity, and are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the channel(s) includes one or more channel). Reference throughout the specification to “one embodiment”, “another embodiment”, “an embodiment”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other exemplary implementation. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various exemplary implementation.

[00052] In addition, for the purposes of the present disclosure, directional or positional terms such as "top", “apical”, “basal”, “proximal”, “distal”, "bottom", "upper," "lower," "side," "front," "frontal," "forward," "rear," "rearward," "back," "trailing," "above," "below," "left," "right," "radial ," "vertical," "upward," "downward," "outer," "inner," "exterior," "interior," "intermediate," etc., are merely used for convenience in describing the various exemplary implementation of the present disclosure.

[00053] The term “coupled”, including its various forms such as “operably coupled”, "coupling" or "coupleable", refers to and comprises any direct or indirect, structural coupling, connection or attachment, or adaptation or capability for such a direct or indirect structural or operational coupling, connection or attachment, including integrally formed components and components which are coupled via or through another component or by the forming process (e.g., an electromagnetic field). Indirect coupling may involve coupling through an intermediary member or adhesive, or abutting and otherwise resting against, whether frictionally (e.g., against a wall) or by separate means without any physical connection.

[00054] Other sensors can be incorporated into the system, for example, image (visual) sensors (e.g., CMOS, CCD, for example to monitor resin color, projected image), microflow (or flow) sensors (e.g., EM based, Resonant feedback based, Pitot-based) viscosity sensors, timing sensors, conductivity sensors, or an array comprising one or more of the foregoing. The sensors, including the temperature sensors and/or humidity sensors can provide data to a processor comprising memory having thereon computer-readable media with a set of executable instruction enabling the processor, being in electronic communication with a driver or drivers, to automatically (in other words, without user intervention) change the position and rate of ascent and descent, relative to the cured layer, or the vat base.

[00055] The term "comprising" and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, "including", "having" and their derivatives. [00056] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other.

[00057] Likewise, the term "about" means that amounts, ranges, sizes, formulations, parameters, and other quantities and characteristics are not and do not need be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, ranges, size, formulation, parameter or other quantity or characteristic is "about" or "approximate" whether or not expressly stated to be such and is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, “about” can include a range of +/— 15% or 10%, or 5% of a given value.

[00058] Accordingly, provided herein is use of a load cell to measure at least one of: viscous adhesion force, and viscous flow in the process of additive manufacturing, wherein (i) the load cell is implemented in a system comprising: a vat having a transparent base: a build plate; an arm operable to be vertically translatable, the arm being coupled to the build plate; a projector module, operable to project actinic radiation to the vat for a predetermined period; and a photopolymerizable liquid resin disposed within the vat, wherein the load cell is coupled between the arm and the build plate, (ii) the projector module further comprises: an X-Y stage capable of translation motion along X-axis direction and Y-axis direction orthogonal to each other, operable to translate a projector of the actinic radiation in a X-Y plane; and a second powertrain coupled to the X-Y stage, operable to translate the stage along the X-axis direction and the Y-axis direction, wherein (iii) the predetermined period of actinic radiation projection is configured to polymerize the resin to a predetermined pattern forming a layer having a predetermined layer-thickness, wherein (iv) the load cell is operable to measure at least one of: the viscous adhesion force and the viscous flow between the build plate and the transparent base of the vat, and/or (v) between the polymerized resin layer and the transparent base of the vat, the system (vi) further comprise: a first powertrain , coupled to the arm; and a central processing module (CPM), in communication with the first powertrain , the second powertrain, the load cell, the vat, and the projector module, the CPM further comprising at least one processor in communication with a non-transitory storage device, storing thereon a set of executable instructions, configured when executed to cause the at least one processor to: measure at least one of: the viscous adhesion force and the viscous flow; and based on the measured at least one of: the viscous adhesion force and the viscous flow, using the at least one of: the vat, the first powertrain, and the second powertrain, vary at least one of: rate, degree of ascent or descent, and the residence time of the build plate, the predetermined projection period of the actinic radiation, rate and extent of motion of the stage along the X-axis direction and the Y-axis direction, and the vat temperature, wherein (vii) the first powertrain further comprises a motor and a sensor operable to measure motor load, wherein (viii) in measuring at least one of: the viscous adhesion force and the viscous flow, the set of executable instructions is further configured when executed to cause the at least one processor to: determine the load on the first powertrain motor, wherein (ix) the load cell is operable to measure at least one of: the viscous adhesion force and the viscous flow between about -51 Kilogram force (Kgf) and about 51 Kgf (in other words depending on engagement or disengagement, the sign ± will vary), and wherein (x) the load cell is operable to measure viscous adhesion force during an ascend or decent of at least one of the build plate, and the formed resin layer, from the transparent vat base.

[00059] In another exemplary implementation, provided herein is a method of controlling additive manufacturing of an article of manufacture, implemented in a system comprising: a vat having a transparent base, a build plate, at least one of: an arm, and a pedestal, wherein each of the arm and the pedestal are operable to be vertically translatable, the arm being coupled to the build plate, a projector module, operable to project actinic radiation to the vat for a predetermined period, a photopolymerizable liquid resin disposed within the vat, and a load cell coupled between the arm and the build plate, the method comprising: using the load cell, measuring at least one of: the viscous adhesion force and the viscous flow between the build plate, or the polymerized resin and the transparent vat base; and based on the measured viscous adhesion force, varying at least one of: vat temperature, rate, degree of ascent or descent, and the residence time of the build plate above the at least one of the transparent vat base, and the polymerized resin, wherein (xi) the projector module further comprises: an X-Y stage capable of translation motion along X-axis direction and Y-axis direction orthogonal to each other, operable to translate a projector of the actinic radiation in a X-Y plane; and a second powertrain coupled to the X-Y stage, operable to translate the stage along the X- axis direction and the Y-axis direction, (xii) the actinic radiation is configured to polymerize the resin to a predetermined pattern, the predetermined pattern forming a layer with a predetermined layer thickness, wherein the method (xiii) further comprising measuring at least one of: the viscous adhesion force and the viscous flow between the build plate, and the transparent vat base, and/or (xiv) between the polymerized resin and the transparent vat base, the system (xv) further comprise: a first powertrain , coupled to the arm; and a central processing module (CPM), in communication with the first powertrain, the second powertrain , the load cell, the vat, the arm, and the projector module, the CPM further comprising at least one processor in communication with a non-transitory storage device, storing thereon a set of executable instructions, configured when executed by the at least one processor, to cause the at least one processor to: using the load cell, measure the at least one of: the viscous adhesion force and the viscous flow between the build plate, or the polymerized resin, and the transparent vat base; and based on the measured viscous adhesion force, vary at least one of: vat temperature, rate, degree of ascent or descent, and the residence time of the build plate above the at least one of the transparent vat base, and the polymerized resin; and using the second powertrain , vary at least one of: rate and extent of motion of the stage along the X-axis direction and the Y-axis direction, wherein (xvi) the first powertrain further comprises a motor and a sensor operable to measure the motor load, the method further comprising: before, simultaneously with, or after the step of measuring at least one of: the viscous adhesion force and the viscous flow between the build plate, or the polymerized resin and the transparent vat base: using the load sensor, measuring the load on the powertrain motor; and based on the measured first powertrain motor load, modifying the at least one of: the vat temperature, the rate, the degree of ascent or descent, and the residence time of the build plate above the at least one of: the transparent vat base, and the polymerized resin, the predetermined projection period of the actinic radiation, and the at least one of the rate and the extent of motion of the stage in the X-Y direction, and wherein (xvii) the load cell is operable to measure at least one of: the viscous adhesion force and the viscous flow at between about -51 Kgf and about 51 Kgf.

[00060] While in the foregoing specification the systems and methods using a load cell in the measurement of viscous adhesion and viscous flow for controlling printing parameters in SLA and/or DLP, have been described in relation to certain preferred exemplary implementation, and many details are set forth for purpose of illustration, it will be apparent to those skilled in the art that the disclosure of the systems and methods using a load cell in the measurement of viscous adhesion and viscous flow for controlling printing parameters in SLA and/or DLP is susceptible to additional exemplary implementation and that certain of the details described in this specification and as are more fully delineated in the following claims can be varied considerably without departing from the basic principles of this disclosure.