WO2022093204A1

WO2022093204A1 - Spreader setting adjustments based on powder properties

Info

Publication number: WO2022093204A1
Application number: PCT/US2020/057610
Authority: WO
Inventors: David R. Otis, Jr.; Andreas H. Queisser; Daniel MOSHER; David A. Champion
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-10-28
Filing date: 2020-10-28
Publication date: 2022-05-05

Abstract

In some examples, a system determines, based on a captured image of a first layer of powder spread onto a target by a spreader, a physical property of the powder, and adjusts a setting associated with the spreader based on the determined physical property of the powder, where the adjustment produces an adjusted setting. The system causes spreading, by the spreader, of a second layer of powder using the adjusted setting.

Description

SPREADER SETTING ADJUSTMENTS BASED ON POWDER PROPERTIES

Background

[0001] Additive manufacturing machines produce three-dimensional (3D) objects by building up layers of build material, including a layer-by-layer accumulation and solidification of the build material patterned from computer aided design (CAD) models or other digital representations of physical 3D objects to be formed. A type of an additive manufacturing machine is referred to as a 3D printing system. Each layer of the build material is patterned into a corresponding part (or parts) of the 3D object.

Brief Description of the Drawings

[0002] Some implementations of the present disclosure are described with respect to the following figures.

[0003] Fig. 1 it is a schematic diagram of a portion of an additive manufacturing machine, according to some examples.

[0004] Fig. 2 is a flow diagram of an iterative closed-loop spreader setting adjustment process according to some examples.

[0005] Fig. 3 is a perspective view of a layer of powdered build material spread onto a build bed, according to some examples.

[0006] Fig. 4 is a flow diagram of an iterative closed-loop spreader setting adjustment process according to further examples.

[0007] Fig. 5 is a block diagram of a storage medium storing machine-readable instructions according to some examples.

[0008] Fig. 6 is a flow diagram of a process according to some examples.

[0009] Fig. 7 is a block diagram of a system according to some examples. [0010] Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. The figures are not necessarily to scale, and the size of some parts may be exaggerated to more clearly illustrate the example shown. Moreover, the drawings provide examples and/or implementations consistent with the description; however, the description is not limited to the examples and/or implementations provided in the drawings.

Detailed Description

[0011 ] In the present disclosure, use of the term "a," "an", or "the" is intended to include the plural forms as well, unless the context clearly indicates otherwise. Also, the term "includes," "including," "comprises," "comprising," "have," or "having" when used in this disclosure specifies the presence of the stated elements, but do not preclude the presence or addition of other elements.

[0012] In some examples, a build material used by an additive manufacturing machine such as a 3D printing system can include a powdered build material that is composed of particles in the form of fine powder or granules. The powdered build material can include metal particles, plastic particles, polymer particles, ceramic particles, glass particles, or particles of other powder-like materials.

[0013] In some examples of additive manufacturing machines, as part of the processing of each layer of build material, liquid agents can be dispensed by liquid agent dispensers (such as through a printhead or another fluid dispensing device) into a layer of build material. In examples where the build material is a non-metallic build material such as plastic or polymer, the applied liquid agents can include a fusing agent (which is a form of an energy absorbing agent) that absorbs heat energy emitted from an energy source used in the additive manufacturing process. For example, after a layer of build material is deposited onto a build platform (or onto a previously formed layer of build material) in the additive manufacturing machine, a fusing agent with a target pattern can be deposited on the layer of build material. The target pattern can be based on an object model (or more generally, a digital representation) of the physical 3D object that is to be built by the additive manufacturing machine. [0014] According to some examples, a fusing agent may be a liquid formulation that when deposited into portions of a build material layer absorbs radiated energy, including infrared and visible light energy. In further examples, a fusing agent may alternatively or additionally include an infrared light absorber, a near infrared light absorber, a visible light absorber, or an ultraviolet (UV) light absorber. After application of the fusing agent into portions of a non-metal build material layer, fusing energy is applied to heat up the build material layer portions for melting. The melted build material layer portions then coalesce and solidify, upon cooling.

[0015] If a powdered metal build material is used, then an additive manufacturing machine can apply a binder agent to layers of powdered metal build material such that the binder agent is applied to selected portions of each layer. In some examples, the binder agent can include a liquid functional agent (LFA), which is a water-based binder agent that includes latex, solvents, and surfactants.

Alternatively, the binder agent can include a pre-wetting liquid that can be applied to promote or inhibit infiltration of another binder agent. In addition, multiple types of binder agents can be used in some examples.

[0016] As each layer of the powdered metal build material is deposited, a binder agent can subsequently be dispensed by liquid agent dispensers (such as through a printhead or another fluid dispensing device) to the layer. Portions of the powdered metal build material where the binder agent is applied are bound together by the binder agent. The binder agent can include an ultraviolet-curable binder agent, heat- curable binder agent, and so forth. After the layers of powdered metal build material have been deposited and the binder agent has been applied to locations of each layer of the powdered metal build material, curing (e.g., based on application of heat or ultraviolet light in the additive manufacturing machine) of the binder agent in the layers of the powdered metal build material produces a so-called "green part." The green part is de-powdered to remove any external unbound build material powder. Afterwards, the green part can be transferred to an oven, where the binder agent can be decomposed using a thermal process, and where the bound build material powder (e.g., metal particles, etc.) are sintered together to form a highly dense 3D object. Sintering refers to coalescing powdered particles to form a solid mass with a higher density than the green part.

[0017] An additive manufacturing machine includes a spreader that is used to spread a powdered build material across a build bed. The spreader can include a roller, a blade, and so forth. The spreader is moveable in a spread direction (or multiple spread directions) to spread the powdered build material from a supply of the powdered build material across the build bed.

[0018] A layer of powdered build material that is spread across a build bed may have a physical property, such as a density or another physical property (e.g., thickness, particle size distribution such as distribution of fine particles and coarse particles, distribution of voids in the powdered build material, surface roughness or flatness of the layer, etc.) of the powder forming the powdered build material, that deviates from a target value of the physical property. The physical property of the spread layer of powdered build material can be a function of various factors, including properties of a supply of powdered build material (e.g., cohesion of particles of the powdered build material, an adhesion characteristic corresponding to an adhesion of particles of the powdered build material to a spreader, a distribution of particle sizes in the supply of powdered build material, etc.), environmental conditions (e.g., temperature, humidity, etc.), deviations in settings of a spreader from target values, and/or other factors.

[0019] Moreover, the layer of the powdered build material spread across the build bed may have a spread edge with a profile ("spread profile" of a layer of powdered build material) that does not meet a target profile, which can also be a function of some or a combination of the factors noted above. A "spread edge" can refer to the edge of the layer of the powdered build material that is most distal across the build bed from a supply region where the spreader initially started spreading the powdered build material.

[0020] In some examples, as properties of different supplies of powdered build material vary and/or as environmental conditions vary across different build operations performed by the additive manufacturing machine 100, the physical property (e.g., density, etc.) of layers of powdered build material and the spread profile of the layers of powdered build material can vary.

[0021] In accordance with some implementations of the present disclosure, a system determines, based on a captured image of a layer of powder spread onto a target by a spreader, a physical property of the powder, and causes adjustment of a setting associated with the spreader based on the determined physical property of the powder. The setting that can be modified can include any or some combination of the following: a setting relating to a vibration of the spreader, a translation or rotation speed of the spreader, a setting that adjusts a quantity of powdered build material that is spread (e.g., by adjusting an amount of movement of a supply of the powdered build material when supplying the quantity of the powdered build material for spreading), and so forth. Other settings associated with the spreader that can be modified include an environmental condition associated with spreading of the powdered build material by the spreader, such as a temperature, a humidity, and so forth.

[0022] Fig. 1 is a schematic view of a portion of additive manufacturing machine 100, such as a 3D printing system. Although specific example details of the additive manufacturing machine 100 are depicted in Fig. 1 , in other examples, an additive manufacturing machine can have a different arrangement of components.

[0023] The additive manufacturing machine 100 includes a build platform 102 on which 3D parts are to be formed by the additive manufacturing machine 100 on a layer-by-layer basis (i.e. successive layers of build material are added and processed). The 3D parts that are formed on a layer-by-layer basis produce a target 3D object (or multiple target 3D objects) that are to be built according to a digital representation(s) of the target 3D object(s). In other examples, the build platform can be part of an external build unit that is added to the additive manufacturing machine 100 during a build operation. [0024] The build platform 102 has an upper surface 104 on which successive layers 105 of powdered build material are spread, and then processed to form respective layers of 3D parts. The build platform 102 is movable along directions that are generally parallel to an axis 106, which in the example of Fig. 1 is a vertical axis. Thus, in the example of Fig. 1 , the build platform 102 is moveable upwardly and downwardly. During a build operation in which successive layers 105 of powdered build material are spread, the build platform 102 is incrementally moved downwardly along a direction 103. Each downward incremental movement is by a specified distance.

[0025] The additive manufacturing machine 100 also includes a build material reservoir 108 that contains a supply of powdered build material 110. The build material reservoir 108 is defined by walls 109 in some examples. The supply of powdered build material 110 is provided on a supply elevator 112 that is part of the build material reservoir 108. The supply elevator 112 is movable directions (e.g., upwardly and downwardly in the example of Fig. 1 ) generally parallel to the axis 106. The supply elevator 112 can refer to any structure that can move the supply of powdered build material 110 to provide a quantity of powdered build material to a supply region 114 from which a spreader 116 can spread a layer 118 of powdered build material onto a build bed.

[0026] Although Fig. 1 depicts an example mechanism for metering a quantity of powdered build material to the supply region 114, other mechanisms for metering a quantity of powdered build material to the supply region 114 can be used in other examples.

[0027] The spreader 116 can be in the form of a blade, a roller, or any other structure that is able to spread a layer of powdered build material across a build bed. The spreader 116 is moveable in a spread direction (along a spread axis 122) to spread powdered build material from the supply region 114 across the build bed. Note that the spreader 116 can move in each of the two opposite directions along the spread axis 122 when spreading a powdered build material. Fig. 1 shows a powdered build material mound 124 being spread by the movement of the spreader 116.

[0028] Initially, before a 3D build operation has started, a layer of build material is formed directly on the upper surface 104 of the build platform 102. Subsequently, a layer of build material is formed on a previously formed layer of build material. A build bed includes a combination of layers that has both solidified powder and nonsolidified powder.. More generally, a “build bed” refers to a structure onto which a build material layer can be spread for processing, where the structure can include just the upper surface of the build platform 102, or alternatively, can further include any previously formed part(s) of a 3D object.

[0029] In some examples, a fluid dispensing device 120 (e.g., a printhead) can be mounted to a moveable carriage (not shown) in the additive manufacturing machine 100. During a build operation, the carriage can move back and forth to move the fluid dispensing device 120 along a scan axis (or multiple scan axes), to dispense liquid agents to a layer of build material that was just spread by the spreader 116.

[0030] During a build operation, a controller 126 of the additive manufacturing machine 100 can control the operation of various components, including the build platform 102, the supply elevator 112, the spreader 116, the fluid dispensing device 120, and so forth.

[0031] As used here, a “controller” can refer to a hardware processing circuit, which can include any or some combination of a microprocessor, a core of a multicore microprocessor, a microcontroller, a programmable integrated circuit, a programmable gate array, a digital signal processor, or another hardware processing circuit. Alternatively, a “controller” can refer to a combination of a hardware processing circuit and machine-readable instructions (software and/or firmware) executable on the hardware processing circuit. [0032] The controller 126 includes a build platform control engine 128, a supply elevator control engine 130, a spreader control engine 132, and a spreader setting adjustment engine 136. An "engine" of the controller 126 can refer to a portion of the hardware processing circuit of the controller 126, or to machine-readable instructions executable by the controller 126. Note that the controller 126 can include other engines for performing other control tasks. Although depicted as separate engines, in further examples, some of the engines 128, 130, 132, and 136 may be combined. Moreover, although the engines 128, 130, 132, and 136 are depicted as being part of the same controller 126, some of the engines may be included in another controller(s), whether inside or outside of the additive manufacturing machine 100.

[0033] The build platform control engine 128 controls the up and down movement of the build platform 102, and the supply elevator control engine 130 controls the up and down movement of the supply elevator 112. In some examples, the supply elevator control engine 130 can cause the supply elevator 112 to move upwardly by a distance Az_su (in an upward direction 113 generally parallel to the axis 106). This upward movement of the supply elevator 112 is to cause a quantity of the supply of powdered build material 110 to be provided to the supply region 114.

[0034] The build platform control engine 128 causes the build platform 102 to be lowered in the downward direction 103 that is generally parallel to the axis 106 by a distance. Although not shown, the additive manufacturing machine 100 includes motors to cause the respective motions of the build platform 102 and the supply elevator 112, under control of the controller 126.

[0035] The controller 126 further includes a spreader control engine 132, which controls an operation of the spreader 116. For example, the spreader control engine 132 can control a motor (not shown) that moves the spreader 116 along the spread axis 122.

[0036] In some examples, the spreader 116 further includes a vibration transducer 134, which can be controlled by the spreader control engine 132. The vibration transducer 134 when activated can cause vibration of the spreader 116. In other examples, instead of using the vibration transducer 134, a motor or another vibration generator coupled to the spreader 116 can cause vibration of the spreader 116.

[0037] In accordance with some implementations of the present disclosure, the spreader setting adjustment engine 136 performs an iterative closed-loop spreader setting adjustment process that can adjust a setting of the spreader 116 for spreading layers of powdered building material.

[0038] Although Fig. 1 shows the spreader setting adjustment engine 136 as being part of the controller 126, it is noted that in other examples, the spreader setting adjustment engine 136 can be part of a separate controller in the additive manufacturing machine 100 or outside the additive manufacturing machine 100.

[0039] The additive manufacturing machine 100 includes a camera 142 (or alternatively, multiple cameras 142) to capture an image of the layer 118 of build material after a spreading operation of the spreader 116 has completed (e.g., after the spreader 134 has moved from an initial position at the supply region 114 to a target position along the spread direction of the spreader 116.

[0040] An image of the layer of build material captured by the camera(s) 142 is provided to the controller 126, such as over a communication channel.

[0041] In some examples, the iterative closed-loop spreader setting adjustment process performed by the spreader setting adjustment engine 136 can be part of a test operation in the additive manufacturing machine 100, or can be performed during an actual build operation in which a 3D object is being built by the additive manufacturing machine 100.

[0042] In some examples, for purposes of performing the iterative closed-loop spreader setting adjustment process, the supply elevator 112 can provide a partial supply of powder to the supply region 114 for spreading by the spreader 116. This partial supply is insufficient to provide a complete powder spread for a layer over the build bed. This is referred to as a "short spread." In other words, when the spreader 116 performs a short spread, the spreader 116 does not spread the layer 118 of powdered build material all the way to the most distal edge of the build platform, i.e. , the edge corresponding to the maximum extent of motion of the spreader 116 away from the supply region 114.

[0043] A short spread performed by the spreader 116 is contrasted to a "full spread," in which the spreader 116 spreads a layer of powdered build material from the initial position at the supply region 114 across the build platform to the a final position corresponding to the maximum extent of motion of the spreader 116 away from the supply region 114.

[0044] Performing a short spread in the iterative closed-loop spreader setting adjustment process allows for a relatively smaller quantity of powdered build material to be used to perform spreader setting adjustments. Since the iterative closed-loop spreader setting adjustment process is an iterative process that can perform multiple iterations, with each iteration including a spread of a layer of powdered built material, using a short spread in each iteration can conserve the powdered build material used (to avoid waste), and further, can reduce the amount of time in each iteration (since the spreader 116 does not have to continue to the end of the build platform to spread a layer of powdered build material across the entire build bed). Moreover, by performing a short spread, an image captured by the camera(s) 142 contains image data of a smaller area to be processed (as compared to image data of a larger area if a full spread were performed) by the spreader setting adjustment engine 136. This can allow the spreader setting adjustment engine 136 to perform its analysis more quickly.

[0045] Fig. 2 is a flow diagram an iterative closed-loop spreader setting adjustment process 200. The iterative closed-loop spreader setting adjustment process 200 can be performed during a test operation prior to initiating a build operation of the additive manufacturing machine 100. Alternatively, the iterative closed-loop spreader setting adjustment process 200 can be performed at intervals throughout the build operation (such as with layers that are not used to form 3D parts or with layers where 3D parts formed would not be adversely affected by short spreads). If the iterative closed-loop spreader setting adjustment process 200 is performed during the build operation, then a cover spread can be subsequently performed to cover up the layer formed by the short spread, such as by raising the supply elevator 112 by greater than the normal incremental distance to increase the volume of build material to be spread.

[0046] The process 200 is "closed-loop" in the sense that the process 200 iterates through multiple iterations with successive adjustments of spreader settings until a layer of build material formed using an adjusted spreader setting satisfies a criterion.

[0047] The spreader setting adjustment engine 136 causes (at 202) the spreader 116 to spread a layer of powdered build material onto a build bed. This spread can be a short spread or a full spread.

[0048] After the spread performed by the spreader 116, the spreader setting adjustment engine 136 triggers (at 204) the camera(s) 142 to capture an image of the layer of powdered of build material. For example, the spreader setting adjustment engine 136 can cause the controller 126 to send an indication (e.g., a signal, a command, etc.) to the camera(s) 142 to activate the camera(s) 142.

[0049] The spreader setting adjustment engine 136 analyzes (at 206) the captured image to identify a spread edge (shown in Fig. 3) of the layer of powdered build material as spread by the spreader 116, and to compute a physical property (e.g., density) and a spread profile of the layer of powdered build material.

Techniques to identify the spread edge and to compute the physical property and the spread profile are discussed further below in connection with Fig. 3.

[0050] The spreader setting adjustment engine 136 then determines (at 208), based on the analysis of the image, whether the physical property of the powdered build material spread by the spreader 116 and the spread profile of the layer of the powdered build material satisfies a criterion. If so, then that is an indication that a current setting (or current settings) of the spreader 116 is (are) acceptable, and the additive manufacturing machine can proceed (at 210) with a build operation to build a 3D object.

[0051] In some examples, the physical property and the spread profile satisfy the criterion if the physical property has a value (or values) within a specified range of values, and the spread profile has a similarity to a target profile to within a specified similarity tolerance.

[0052] However, if either or both of the physical property or the spread profile does not satisfy the criterion, then the spreader setting adjustment engine 136 modifies (at 214) a setting associated with the spreader 116. Modifying a setting associated with the spreader 116 can refer to modifying a single setting or modifying multiple settings associated with the spreader 116.

[0053] The settings that are modified can include any or some combination of the following: a setting relating to a vibration of the spreader 116, such as a frequency at which the spreader vibrates, the amplitude of vibration of the spreader 116, a sweep frequency range (which is the range of frequencies across which the vibration of the spreader 116 is to occur), a sweep time duration (which is a time duration along which the vibration frequency spreads across the sweep frequency range), and so forth. Another setting that can be modified is a translation speed of the spreader 116 along the scan axis 122. A further setting that can be modified includes a supply level rise (Az_su) of the supply elevator 112. In examples where the spreader 116 includes a roller, a setting that can be modified can include a speed of rotation or translation of the roller.

[0054] In other examples, other settings associated with the spreader 116 can be modified by the engine 136, such as an environmental condition (e.g., temperature, humidity, etc.) associated with the spreading of powdered build material by the spreader 116.

[0055] Another example of a setting associated with the spreader 116 that can be modified is the distance Az_su by which the supply elevator 112 (Fig. 1) is raised for the next layer of a build operation. The distance Az_su by which the supply elevator 112 is raised affects the quantity of powdered build material provided to the supply region 114, which affects a characteristic of the layer of powdered build material spread by the spreader 116.

[0056] After the setting associated with the spreader 116 is modified, a next iteration (212) of the iterative closed-loop spreader setting adjustment process 200 is initiated. Each iteration of the iterative closed-loop spreader setting adjustment process 200 includes tasks 202, 204, 206, 208, and 210. The iterative closed-loop spreader setting adjustment process 200 continues with successive iterations until the criterion is satisfied (as determined at 208).

[0057] In each successive iteration, the amount of the setting associated with the spreader 116 that is modified can include an incremental change in the setting, a random change in the setting, and so forth. As noted above, any of the foregoing modification of the setting associated with of the spreader 116 can refer to a modification of a single spreader setting or multiple spreader settings.

[0058] Fig. 3 is a perspective view of a layer 300 of powdered build material as spread by the spreader 116. The supply region 114 has a supply area represented as A_su. As noted above, the supply elevator 112 (Fig. 1) is raised by a distance Az_su to supply a quantity of powdered build material to the supply region 114.

[0059] The spreading performed by the spreader 116 starts from the supply region 114 and continues to a target position (for a short spread or a full spread), which results in spreading of the layer 300 of powdered build material. The spread layer of powdered build material has a spread edge 302, which as depicted in Fig. 3 has an irregular shape, i.e. , the spread edge 302 is not linear in some examples.

[0060] The layer 300 of powdered build material spread by the spreader 116 ends at the spread edge 302, such that a region 304 of the build bed that is past the spread edge 302 (more distal from the supply region 114 than the spread edge 302) does not include powdered build material that is spread by the spreader 116 in a current spreader operation. In other words, the layer 300 of powdered build material spread by a current spreader operation of the spreader 116 ends at the spread edge 302 and does not go past the spread edge 302. Note that some stray particles of the powdered build material may fall into the region 304, but the quantity of such stray particles is considered to be insignificant as compared to the quantity of powdered build material in the spread layer 300.

[0061 ] The spread area that ends at the spread edge 302 of the layer 300 of powdered build material is represented as A_sp.

[0062] The spreader setting adjustment engine 136 can compute a physical property, such as a density, of the powdered build material in the spread layer 300 according to the following:

where p_sp represents the density of the spread powdered build material, p_su represents a density of the supply of powdered build material 110 in the build material reservoir 108, A_su represents the supply area of the supply region 114, and Az_sp corresponds to the thickness of the spread layer of powdered build material.

[0063] In some examples, identifying the spread edge 302 can be based on use of thresholding in image processing of the image captured by the camera(s) 142 (Fig. 1). Thresholding refers to a process in which pixels of the image with image intensities that exceed a specified threshold are considered to be white pixels, and pixels of the image with image intensities that do not exceed the specified threshold are considered to be black pixels. For example, in Fig. 3, thresholding can identify the spread area that is covered by the spread layer of powdered build material as white pixels, and can identify the region 304 (that is not covered by the spread layer of powdered build material) as black pixels (or vice versa). [0064] In other examples, identifying the spread edge 302 can be based on use of canny edge detection in image processing of the image captured by the camera(s) 142 (Fig. 1 ).

[0065] In further examples, identifying the spread edge 302 can further employ additional techniques (such as based on use of pre-processing according to Fig. 4 below).

[0066] In some examples, the computation of the physical property in task 206 of Fig. 2 includes the computation of the density p_sp according to Eq. 1 above. To compute the density p_sp, the spread edge 302 is identified. Once the spread edge 302 is identified, the spread area A_sp can be computed. For example, the spread area A_sp by using numerical integration or summation of a position of the spread edge 302 (e.g., position along the y horizontal axis in Fig. 3) multiplied by a “bin width” (dx) along the x horizontal axis. The bin width (dx) depends on the resolution of a camera (e.g., 142) over the relevant range of the x axis. For example, the bin width (dx) may be the width of the whole build bed (along the x axis), or alternatively can be a width of a subset of the build bed.

[0067] Once the spread area A_sp is computed, and since Az_su, z_sp, p_su, and A_su are known or can be computed, the density p_sp of the spread layer of powdered build material can be computed according to Eq. 1 . For example, Az_su can be a configuration parameter set for the supply elevator control engine 130. Alternatively, Az_su can be computed by counting a number of cycles (e.g., number of encoder operations associated with the supply elevator control engine 130) used to raise the supply elevator 112.

[0068] The parameter Az_sp (thickness of the spread layer of powdered build material) can be determined by performing image processing of the spread layer of powdered build material, or alternatively, can be determined by counting a number of cycles (e.g., number of encoder operations associated with the build platform control engine 128) used to drop the build platform 102. In the latter example, the amount of drop of the build platform 102 can be used as an estimate of the thickness (Az_sp) of the spread layer of powdered build material.

[0069] Note that the layer of powdered build material can have varying intra-layer thickness (i.e. , the thickness across the layer is different at different locations). In further examples, image processing of the layer can be performed of the captured image of the layer (especially when the captured image is captured by multiple cameras calibrated with respect to one another and that are angled with respect to the layer) to determine variations in thickness across the layer.

[0070] Assuming two horizontal axes x and y as shown in Fig. 3, then the layer thickness as a function of an (x, y) coordinate can be represented as Az_sp (x,y).

[0071] Then, a volume

of the layer of powdered build material spread across the build bed can be computed as:

[0072] In the summation above, the origin of the spread area is roughly near a center of the spread area, and (-x, -y) represents a coordinate at the left, bottom corner of the spread area, and (x,y) represents a coordinate at the right, top corner of the spread area. This summation assumes a rectangular spread area — note that regions outside the spread area (in examples where the spread edge has an irregular shape as shown in Fig. 3, discussed below) have a zero thickness of the layer and so do not contribute to v_sp.

[0073] Once the volume

is computed, the value of Az_sp can be computed as ^sp^sp ■

[0074] In task 208 of Fig. 2, the computed density p_sp can be compared to a range of densities. If the computed density p_sp is within the range of densities, then a condition relating to density is satisfied. [0075] In some examples, the computation of the spread profile in task 206 of Fig. 2 includes the identification of the spread edge 302. The spread edge 302 represents the spread profile of the spread layer of powdered build material. The profile of the spread edge 302 can be compared to a target profile. If the shape of the profile of the spread edge 302 has a similarity to the target profile (based on comparison of curves corresponding to the spread edge 302 and the target profile) within a similarity threshold, then a condition relating to the spread profile is satisfied.

[0076] If both the condition relating to density and the condition relating to the spread profile are satisfied, then task 208 in Fig. 2 determines that the physical property and the spread profile satisfy the criterion of task 208. For example, if the target profile has a concave shape with a specified amount of curvature, and the spread profile of the spread edge 302 deviates from such concave shape by greater than a specified threshold, then that indicates that the spreader setting is to be adjusted to provide the target profile, such as by increasing or decreasing the amount of supply level rise, changing a frequency of vibration of the spreader, and so forth.

[0077] Fig. 4 is a flow diagram an iterative closed-loop spreader setting adjustment process 200A according to further examples. The iterative closed-loop spreader setting adjustment process 200A includes tasks that are similar to tasks of the process 200 shown in Fig. 2 (those tasks are labeled with the same reference numerals).

[0078] The iterative closed-loop spreader setting adjustment process 200A applies pre-processing to the image captured by the camera(s) 142 (Fig. 1 ). More specifically, the iterative closed-loop spreader setting adjustment process 200A applies (at 402) brightness gradient removal (BGR) to the captured image to produce a BGR-processed image.

[0079] BGR processing may be particularly useful in examples where a single camera 142 is used to capture an image of a layer of powdered build material spread (at 202). [0080] Brightness gradients in the captured image may result in inaccuracies in identifying the spread edge (e.g., 302 in Fig. 3) of the spread layer of powdered build material. A brightness gradient in the captured image can refer to a directional change in brightness along a direction across the captured image.

[0081] Brightness gradients can be approximated with best-fit polynomials (e.g., first order polynomials, second order polynomials, etc.), according to spatial intensity values within the image. For example, linear regression of the intensity values as a function of spatial location across the layer of powdered build material to one of the different order polynomials can be performed. A statistical measure is produced by each linear regression of the intensity values to a respective polynomial of a given order. This statistical measure is referred to as R-squared in some examples, where R-squared is a goodness-of-fit measure. The best-fit polynomial is the polynomial that has a best fit (e.g., the corresponding regression produces the lowest R-squared value).

[0082] The best-fit polynomial represents the brightness gradients in the captured image. In some examples, the best-fit polynomial can be calculated by a least-squares fit of pixel values at pixel locations in the captured image. The best-fit polynomial can then be used to remove the brightness gradients in the captured image to produce the BGR-processed image by, for example, subtracting a value of the best-fit polynomial returned when evaluated at each pixel location of the captured image.

[0083] Fig. 5 is a block diagram of a non-transitory machine-readable or computer-readable storage medium 500 storing machine-readable instructions that upon execution cause a system (e.g., the controller 126 of Fig. 1 ) to perform various tasks.

[0084] The machine-readable instructions include powder layer physical property determination instructions 502 to determine, based on a captured image of a first layer of powder spread onto a target (e.g., a build bed) by a spreader (e.g., 116 in Fig. 1 ), a physical property of the powder (a powdered build material). [0085] The machine-readable instructions include spreader setting adjustment instructions 504 to adjust a setting associated with the spreader based on the determined physical property of the powder, where the adjustment produces an adjusted spreader setting associated with the spreader. Adjusting the setting can refer to adjusting a single setting or adjusting multiple settings. Adjusting a setting can include modifying a parameter (stored in a memory, for example) that controls an operation of the spreader.

[0086] The machine-readable instructions include second layer spreading instructions 506 to cause spreading, by the spreader, of a second layer of powder using the adjusted spreader setting. For example, the machine-readable instructions can execute on the controller 126 that then controls the spreader to perform a spread operation using the adjusted spreader setting.

[0087] In some examples, the machine-readable instructions are executable to determine a spread area (e.g., A_sp in Eq. 1 ) of the first layer of the powder spread onto the target, where the determined physical property is further based on the determined spread area.

[0088] In some examples, the machine-readable instructions are executable to receive information of a density of a supply powder (e.g., p_su in Eq. 1 ) that is fed from a powder supply to a supply region, where the supply powder in the supply region is to be spread by the spreader as the first layer of the powder spread onto the target. The determined physical property is further based on the density of the supply powder.

[0089] In some examples, the machine-readable instructions are executable to receive information of a distance traveled by a supply powder elevator (e.g., Az_su in Eq. 1 ) to feed the supply powder to the supply region. The information of the distance traveled by the supply powder elevator can be a setting of the supply elevator control engine 130, or can be derived by counting the number of cycles performed by the supply elevator control engine 130 in raising the supply powder elevator. The determined physical property is further based on the distance traveled by the supply powder elevator.

[0090] In some examples, the machine-readable instructions are executable to determine a thickness (e.g., Az_sp in Eq. 1 ) of the first layer of the powder. The determined physical property is further based on the thickness.

[0091] In some examples, the setting associated with the spreader to be adjusted is selected from among a vibration characteristic of the spreader, a level rise of an elevator carrying a supply powder for spreading by the spreader, and a rotation characteristic of the spreader.

[0092] Fig. 6 is a flow diagram of a process 600 according to some examples.

[0093] The process 600 includes iteratively performing (at 602) a closed-loop spreader setting adjustment process (e.g., by the spreader setting adjustment engine 136) until a criterion is satisfied. The closed-loop spreader setting adjustment process includes receiving (at 604) an image of a layer of powder spread onto a target by a spreader, and determining (at 606), based on the image of the layer of the powder spread onto the target by the spreader, a physical property of the powder and a profile of a spread edge of the layer of the powder. The closed-loop spreader setting adjustment process includes further includes adjusting (at 608) a setting associated with the spreader based on the determined physical property of the powder and the determined profile.

[0094] The process 600 forms (at 610), using the spreader, a further layer of powder using an adjusted setting produced by the closed-loop spreader setting adjustment process.

[0095] Fig. 7 is a block diagram of a system 700 (e.g., a controller that can be part of or can be separate from an additive manufacturing machine for building a 3D object). The system 700 includes a hardware processor 702 (or multiple hardware processors). A hardware processor can include a microprocessor, a core of a multi- core microprocessor, a microcontroller, a programmable integrated circuit, a programmable gate array, or another hardware processing circuit.

[0096] The system 700 further includes a storage medium 704 storing machine- readable instructions executable on the hardware processor 702 to perform various tasks. Machine-readable instructions executable on a hardware processor can refer to the instructions executable on a single hardware processor or the instructions executable on multiple hardware processors.

[0097] The machine-readable instructions include density determination instructions 706 to determine, based on a captured image of a first layer of powder spread onto a target by a spreader, a density of the powder.

[0098] The machine-readable instructions include spreader setting adjustment instructions 708 to adjust a setting associated with the spreader based on the determined density of the powder, where the adjustment is to provide an adjusted spreader setting.

[0099] The machine-readable instructions include second layer spreading instructions 710 to cause spreading, by the spreader, of a second layer of powder using the adjusted spreader setting.

[00100] Using techniques according to some examples of the present disclosure, a spreader setting can be adjusted to achieve layers of build material used in an additive manufacturing machine with a physical property (e.g., density) that is within a target range. In this manner, uniformity in the physical property of the layers of build material is improved. Moreover, improving the uniformity in the physical property of the layers of build material allows a spreader to spread the layers with more uniform spread edges (e.g., spread edges with profiles that are closer to a target profile).

[00101] A storage medium (e.g., 500 in Fig. 5 or 704 in Fig. 7) can include any or some combination of the following: a semiconductor memory device such as a dynamic or static random access memory (a DRAM or SRAM), an erasable and programmable read-only memory (EPROM), an electrically erasable and programmable read-only memory (EEPROM) and flash memory or other type of nonvolatile memory device; a magnetic disk such as a fixed, floppy and removable disk; another magnetic medium including tape; an optical medium such as a compact disk (CD) or a digital video disk (DVD); or another type of storage device. Note that the instructions discussed above can be provided on one computer-readable or machine-readable storage medium, or alternatively, can be provided on multiple computer-readable or machine-readable storage media distributed in a large system having possibly plural nodes. Such computer-readable or machine-readable storage medium or media is (are) considered to be part of an article (or article of manufacture). An article or article of manufacture can refer to any manufactured single component or multiple components. The storage medium or media can be located either in the machine running the machine-readable instructions, or located at a remote site from which machine-readable instructions can be downloaded over a network for execution.

[00102] In the foregoing description, numerous details are set forth to provide an understanding of the subject disclosed herein. However, implementations may be practiced without some of these details. Other implementations may include modifications and variations from the details discussed above. It is intended that the appended claims cover such modifications and variations.

Claims

23 What is claimed is:

1 . A non-transitory machine-readable storage medium comprising instructions that upon execution cause a system to: determine, based on a captured image of a first layer of powder spread onto a target by a spreader of an additive manufacturing machine, a physical property of the powder; adjust a setting associated with the spreader based on the determined physical property of the powder, the adjustment to produce an adjusted setting; and cause spreading, by the spreader, of a second layer of powder using the adjusted setting.

2. The non-transitory machine-readable storage medium of claim 1 , wherein the determined physical property comprises a density of the powder in the first layer of powder.

3. The non-transitory machine-readable storage medium of claim 1 , wherein the instructions upon execution cause the system to: determine a spread area of the first layer of the powder spread onto the target, wherein the determined physical property is further based on the determined spread area.

4. The non-transitory machine-readable storage medium of claim 3, wherein the instructions upon execution cause the system to: receive information of a density of a supply powder that is fed from a powder supply to a supply region, the supply powder in the supply region to be spread by the spreader as the first layer of the powder spread onto the target, wherein the determined physical property is further based on the density of the supply powder.

5. The non-transitory machine-readable storage medium of claim 4, wherein the instructions upon execution cause the system to: receive information of a distance traveled by a supply powder elevator to feed the supply powder to the supply region, wherein the determined physical property is further based on the distance.

6. The non-transitory machine-readable storage medium of claim 3, wherein the instructions upon execution cause the system to: identify a spread edge of the first layer of the powder based on image processing of the captured image.

7. The non-transitory machine-readable storage medium of claim 6, wherein the identifying of the spread edge comprises: removing a brightness gradient from the captured image, to produce a processed image, wherein the determined physical property of the powder is based on the processed image.

8. The non-transitory machine-readable storage medium of claim 6, wherein the captured image is a first captured image obtained by a first camera, wherein the identifying of the spread edge is based on the first captured image and a second captured image obtained by a second camera of the first layer of the powder.

9. The non-transitory machine-readable storage medium of claim 6, wherein the instructions upon execution cause the system to: determine a profile of the spread edge, wherein the adjusting of the setting associated with the spreader is further based on a comparison of the determined profile to a target profile.

10. The non-transitory machine-readable storage medium of claim 1 , wherein the instructions upon execution cause the system to: determine a thickness of the first layer of the powder, wherein the determined physical property is further based on the thickness.

11 . The non-transitory machine-readable storage medium of claim 1 , wherein the setting associated with the spreader to be adjusted is selected from among a vibration characteristic of the spreader, a level rise of an elevator carrying a supply powder for spreading by the spreader, a translation characteristic of the spreader, and a rotation characteristic of the spreader.

12. A method performed by a system comprising a hardware processor, comprising: iteratively performing a closed-loop spreader setting adjustment process until a criterion is satisfied, the closed-loop spreader setting adjustment process comprising: receiving an image of a layer of powder spread onto a target by a spreader, determining, based on the image of the layer of the powder spread onto the target by the spreader, a physical property of the powder and a profile of a spread edge of the layer of the powder, and adjusting a setting associated with the spreader based on the determined physical property of the powder and the determined profile; and forming, using the spreader, a further layer of powder using an adjusted setting produced by the closed-loop spreader setting adjustment process.

13. The method of claim 12, wherein the criterion is satisfied responsive to a comparison of the determined physical property to a target range of values of the physical property, and a comparison of the determined profile to a target profile. 26

14. A system for an additive manufacturing machine for building a three- dimensional (3D) object, the system comprising: a processor; and a non-transitory machine-readable storage medium storing instructions executable on the processor to: determine, based on a captured image of a first layer of powder spread onto a target by a spreader, a density of the powder; adjust a setting associated with the spreader based on the determined density of the powder, wherein the adjustment is to provide an adjusted setting; and cause spreading, by the spreader, of a second layer of powder using the adjusted setting.

15. The system of claim 14, wherein the instructions are executable on the processor to: determine, based on the captured image of the first layer of the powder spread onto the target by the spreader, a profile of a spread edge of the first layer of the powder; and adjust the setting associated with the spreader further based on the determined profile.