Crash prediction sensor for 3D printing, devices including a crash prediction sensor, and method thereof

Abstract

The present teachings relates crash detection sensors and to devices and methods for producing three-dimensional printed parts in layers which identifies defects and / or prevents damage to one or more components of a 3D printer. The 3D printer includes a sensor (106) for identifying a defect (160) on a surface of the part being printed prior to a recoater (150) or printhead (116) passing over the surface. Without the sensor, the defect can immediately or eventually result in damage to the 3D printer. The teachings herein also relate to devices and methods for cleaning an optical sensor (138) or an optical source (136) used in manufacture of 3D components.

Description

[0001] Attorney Docket No.: 1156.091WO (VX121)

[0002] CRASH PREDICTION SENSOR FOR 3D PRINTING, DEVICES INCLUDING A CRASH PREDICTION SENSOR, AND METHOD THEREOF

[0003] FIELD

[0004]

[0001] The present teachings relates to crash prediction sensors and to devices and methods for producing three-dimensional printed parts in layers which identifies defects and / or prevents damage to one or more components of a 3D printer. The 3D printer includes a sensor for identifying a defect on a surface of the part being printed prior to a recoater or printhead passing over the surface. The present teaches devices and methods for cleaning an optical sensor or an optical source used in manufacture of 3D components.

[0005] BACKGROUND OF THE INVENTION

[0006]

[0002] Examples of 3D printing processes that include applying layers of particulate material are described for example in US Patent Number: 6,036,777 (filed on April 14, 1995 as US 08 / 422,384), US Patent Application Pre-Grant Publication Numbers: US 2004 / 0035542 A1 (filed on August 7, 2003 as US 10 / 381,550), US 2008 / 0001331 A1 (filed on June 25, 2007 as US 11 / 767,778), US 2010 / 0272519 A1 (filed on April 7, 2010 as US 12 / 681,961), US 2020 / 0130263 A1 (filed on January 7, 2020 as US 16 / 629,107) and US 2017 / 0355137 A1 (filed on June 20, 2017 as US 15 / 538,019), each incorporated herein by reference in its entirety.

[0007]

[0003] US 2017 / 0151727 A1 describes the use of sensors to measure an overfeed of a particulate material for detecting defects in a 3D printing process that relates to insufficient supply of the particulate material when applying a layer of the material to a surface. In such situations, the insufficient supply continues to propagate so that the defect can be identified by observing the status of the overfeed of particulate material at the end of a pass of the recoater. US 2017 / 0151727 A1 is incorporated herein by reference in its entirety.

[0008] SUMMARY

[0009]

[0004] During the layered production of 3D parts it has been determined that damage to a recoater and or a printhead can occur when there is a defect or object that protrudes above the expected height of a construction surface. This can be particularly problematic when using high travel speeds of the recoater and / or printhead. There is a need for devices and methods for preventing the recoater and / or the printhead from crashing into such protrusions.

[0010]

[0005] In some cases, a defect is small enough that it would not crash into the recoater or printhead. However, the defect may increase over time and / or be a sign of a part having insufficient quality. As such, there is also a need for devices and methods for detecting defects located between an expected height of the construction surface and a height of a recoater (e.g.,Attorney Docket No.: 1156.091WO (VX121)

[0011] a leveling surface of the recoater) or a printhead. When such a defect is identified, corrective action can be taken to prevent the defect from enlarging, to save material, to save machine time, or to continue a process with producing only a portion of the parts being built.

[0012]

[0006] Defects which may result in a protrusion include shrinkage and curling. This may be particularly problematic when producing large parts, when using large temperature gradients, or when there are gradients in density, or any combination thereof.

[0013]

[0007] In 3D printers that employ a recoater for providing layers of particulate material, over time, the particulate material can affect the amount of light (e.g., light flux) from a light source and / or the measured light (e.g., light flux). Accordingly, there is a need for monitoring the amount of light being received at the light sensor for gradual temporal changes and / or for cleaning a surface of a light source and / ora surface of a light sensor. Cleaning of the light source and / or the light sensor may be according to a schedule, preferably a predetermined scheduled. Cleaning of the light source and / or the light sensor may be initiated or scheduled based on a decrease in a light flux measurement (e.g., a decrease in a baseline light flux measurement).

[0014]

[0008] When a device, such as a sintering unit, a recoater or a printhead, impacts a part or object protruding from a construction surface, the impact can damage the part being build and / or the device.

[0015]

[0009] One or more of these problems can be reduced or eliminated using the teachings herein.

[0016]

[0010] An aspect of the teachings herein is directed to: a 3D printer for layered printing of molded articles comprising: a) a recoater device for applying particulate material in layers over a construction field while moving over the construction field, wherein the recoater device travels in an x-direction and has an elongated opening in the y-direction, and b) an optical sensor that moves over the construction field, wherein the optical sensor is arranged for measuring light that has traveled in a generally y-direction near or at the height of the construction field.

[0017]

[0011] Another aspect of the teachings herein is directed to a device fora 3D printer comprising: a recoater unit having an elongated container for holding a particulate material and an elongated opening for layer-wise depositing the particulate material onto a construction field of a 3D printer, wherein the recoater unit is configured for moving in a first direction and the elongated opening extends in a second direction generally perpendicular to the first direction, wherein the recoater unit includes a leveling means which defines the height of the layer being deposited; and a light sensor attached to the recoater unit, wherein the light sensor is arranged in advance of the recoater unit for measuring light traveling parallel to the second direction and having a vertical position (z-position) so that it can at least measure a portion of the light between the height of the previous layer and the height of the layer being deposited.Attorney Docket No.: 1156.091WO (VX121)

[0018]

[0012] Another aspect of the teachings herein is directed to a method comprising a step of i) detecting a defect in a construction field during the printing of one or more molded parts being printed in layers with a 3D printer while a recoater unit is approaching the defect; wherein the defect includes a build material or other object positioned above the height of the last complete layer that was deposited; and ii) controlling the process to prevent damage to the recoater unit or to another component in the 3D printer.

[0019]

[0013] Another aspect of the teachings herein is directed to a method comprising the steps of: printing of one or more molded parts with a 3D printer by including: repeatedly i) applying layers of particulate material on a surface; and ii) transmitting a light over the surface from a light source to a light sensor; wherein the method includes cleaning the light source and / or the light sensor.

[0020]

[0014] Another aspect of the teachings herein is directed to a device comprising: i) a recoater for applying a particulate material on a construction surface in layers; ii) a light source for transmitting a light over the applied layer of particulate material; and iii) a light sensor for measuring a flux of light; wherein the device includes a cleaning station for cleaning the light source and / or for cleaning the light sensor; wherein the device is for printing of one or more 3D parts.

[0021]

[0015] Any of these aspects may be characterized by one or more of the following: the optical sensor moves over the construction field in advance of the recoater device while the recoater device applies the particulate material; the recoater device has a leveling component having a leveling surface that defines a height of the particulate layer being deposited, wherein the optical sensor is characterized by a height equal to or greater than a height of the leveling surface, in a z-direction; the distance from the optical sensor to the leveling surface in the z-direction is about 50 mm or less, about 20 mm or less, about 10 mm or less, or about 5 mm or less; the distance from the optical sensor to the bottom surface of the recoater device in the z-direction is about 0 mm or more, about 1 mm or more, about 2 mm or more, or about 3 mm or more; the leveling component has a forward facing surface in the x-direction; a distance from the forward facing surface to the optical sensor in the x-direction is about 3 mm or more, about 5 mm or more, about 10 mm or more, or about 20 mm or more; a distance from the forward facing surface to the optical sensor in the x-direction is about 250 mm or less, about 100 mm or less, about 40 mm or less, or about 25 mm or less; the position of the optical sensor relative to the leveling component is adjustable in the x-direction and / or in the z-direction; the 3D printer includes a light source; the light source and the optical sensor are on opposing sides of the construction field (in the y-direction); the light from the light source is generally monochromatic; the optical sensor is tuned to one or more wavelengths of the light emitted from the light source; the optical sensor and the light source travel synchronously; the optical sensor and the recoater travel synchronously; theAttorney Docket No.: 1156.091WO (VX121)

[0022] optical sensor, light source and recoater travel synchronously; the optical sensor is attached to one side (in the y-direction) of the recoater; the optical sensor and the light source are attached to opposite sides of the recoater (in the y-direction); the light source includes an LED light; the light source is a single LED light; the light source employs light from a laser; the light is transmitted by means of fiber optics; the laser is remote from the construction field; the laser is outside a construction chamber of the 3D printer; the height (i.e . , Z-position) of the optical sensor and the light source are generally the same; the optical sensor and / or the light source move in front of a sintering unit; the optical sensor and / or the light source move in front of a print head; the device includes a controller for controlling a component of the 3D printer based on the amount of light measured by the light sensor; the controller stops a forward movement of the recoater in the x-direction, and / or stops a forward movement of a printhead in the x-direction, and / or stops the printhead from selectively printing a fluid for forming one molded article while allowing the printhead to continue to print a fluid for forming another molded article, and / or increases a temperature in a build chamber or a temperature of the construction field; the controller identifies an x-position of a defect, wherein the defect includes an object or a build material above an expected height of the last printed layer; the optical sensor is a first optical sensor and the 3D printer includes a second optical which is spaced apart from the first optical sensor in the x direction; the controller identifies an x-position and a y-position of a defect, wherein the defect includes an object or a build material above an expected height of the last printed layer; the height (i.e., z-position) of the first optical sensor and the second optical sensor are generally the same; the first optical sensor measures a first beam of light traveling in a first direction parallel to the surface of the construction field and the second optical sensor measures a second beam of light traveling in a second direction parallel to the surface of the construction field, wherein the first direction and the second direction form an angle greater than 0°; the device includes two optical sensors; the method employs two optical sensors; the two optical sensors are spaced apart in the X-direction; the two optical sensors measure light from the same light source; the two optical sensors measure light from different light sources; the optical sensor provides light measurement information to a controller; the defect is measured by an optical sensor arranged for measuring an intensity of a light that crosses a surface of the construction field; the defect includes a curling of a molded part; the defect includes an unexpected object on the construction field; the controller stops the recoater; the controller stops the print head; a surface temperature of the construction field is controlled by the controller, a surface temperature of the construction field is changed in one or more regions to reduce or eliminate a defect; the defect is detected without a laser in a print chamber of the 3D printer; the 3D printer is free of any lasers in the printing chamber; theAttorney Docket No.: 1156.091WO (VX121)

[0023] defect is detected by a change in light flux received by the light sensor prior; the 3D printer includes a cleaning station; the light sensor and / or light source is cleaned in a cleaning station after detecting a defect (e.g., after detecting a change in a light flux received by the light sensor); or the light source and / or print head is cleaned in a cleaning station between applying layers of a molded part.

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025]

[0016] FIG. 1 is a side view showing features of a 3D printer (X-Z plane) including an optical sensor.

[0026]

[0017] FIG. 2 is a cross-sectional view showing features of a 3D printer including an enclosure.

[0027]

[0018] FIG. 3 is a perspective view drawing of an illustrative device including a recoater, a light sensor and a light source.

[0028]

[0019] FIG. 4 is a side view drawing of the device of FIG. 3.

[0029]

[0020] FIG. 5 is a top view drawing showing a construction surface and illustrative locations on the construction surface used for statistical calculations of the light intensity, such as average, maximum, and minimum intensity. These may be used to set limits for identification of defects. These may be used for determining whether a surface of a light source or a surface of a light sensor needs to be cleaned (e.g., in a cleaning station).

[0030]

[0021] FIG. 6 is a graph showing a light intensity measurement at different positions during the travel of the recoater over the construction surface.

[0031] DETAILED DESCRIPTION

[0032]

[0022] The 3D printer is a printer that applies particulate material on a build surface in layers. The particulate material is preferably applied as a free-flowing solid material. The particulate material is selectively joined together to form a molded part. After printing one or more molded parts, the molded parts are typically surrounded or embedded in particulate material that has not been joined together. Any method may be used to join together the particulate material. For example, a binder may be used to bind together the surface of two or more adjacent particles. As another example, two or more adjacent particles may be joined together by sintering. In sintering, at least the surface of a particle is heated above its liquidus temperature (e.g., melting temperature). When adjacent surfaces of two contacting particles are heated above their liquidus temperature, the particles can fuse together. Then, upon cooling below the solidus temperature (e.g., crystallization temperature), the fused joint solidifies.

[0033]

[0023] The 3D printer includes a leveling component for providing the particulate to the build surface. The leveling component may be a part of a recoater device. The recoater preferably includes a reservoir for holding particulate material. The recoater may discharge the particulateAttorney Docket No.: 1156.091WO (VX121)

[0034] material onto the construction surface while the recoater traverses (e.g., in the X-direction) over the construction surface. The recoater preferably extends the length of the construction surface in the Y-direction (i.e., perpendicular to the travel direction of the recoater) so that a layer of particulate material can be applied to the construction surface in a single pass of the recoater. The recoater preferably only travels in the X-direction, forward and backwards over the construction space. The recoater may discharge particulate material and form a layer in only one direction (e.g., forward direction or reverse direction). The recoater may discharge particulate material on the construction surface and form layers in both the forward and reverse directions.

[0035]

[0024] The 3D printer may include a print head for selectively applying a liquid material over the particulate material. The liquid material is selectively applied so that the molded part is delineated from the particulate material which is not joined together. Typically, the regions printed with the liquid material become part of the molded part. However, negative printing process are also possible, where only the regions not printed with the liquid material become part of the molded part. Preferably, the liquid material liquid will penetrate the last layer of particulate material applied by the recoater.

[0036]

[0025] The feedstock of the particulate material includes the layers of particulate material that have been applied by the recoater.

[0037]

[0026] The 3D printer may include a build platform which supports the feedstock. After applying a layer of particulate material, the build platform may be lowered by a thickness of the layer, or the recoater and other components (e.g., light source, light sensor, or print head) may be raised by a thickness of the layer.

[0038]

[0027] Light source is a component from which light is projected over a construction surface.

[0039]

[0028] Light guide is a component which provides a light to the light source.

[0040]

[0029] Light generator is a component that produces light for the light source and / or light generator.

[0041]

[0030] The light preferably travels over the construction surface in a direction (i.e., light travel direction) parallel to a construction surface. The light preferably travels in a direction perpendicular to the vertical direction. The light from a light source preferably travels in a single direction over the construction surface to the optical sensor. The light may travel over the construction surface in a generally y-direction. For example, the light travel direction may be perpendicular to the direction of travel of the recoater. A single light source and a single optical sensor may be employed to identify an x-position of a defect or other protrusion.

[0042]

[0031] A defect detection device may be capable of determining both the x and y position of a defect or other protrusion. For example, both the x and y position may be determined using twoAttorney Docket No.: 1156.091WO (VX121)

[0043] light beams that travel in different angles. In particular a projection of the two light beams onto an x-y plane should form an obtuse angle, a, which is greater than 0 °. Preferably, both light beams travel on a common plane parallel to the construction surface. The y-position may be determined from the difference in the time between the detection of the defect with the two light beams.

[0044]

[0032] The light travel distance between the light source and the light sensor should be greater than the width of the construction surface (e.g., in the y-direction). Preferably the difference between the light travel distance and the width of the construction surface is about 5 mm or more, about 10 mm or more, or about 15 mm or more. Preferably the difference between the light travel distance and the width of the construction surface is about 400 mm or less, more preferably about 200 mm or less, even more preferably about 125 mm or less, and most preferably about 70 mm or less. Preferably, a ratio of the light travel distance to the width of the construction surface is about 1.20 or less, more preferably about 1.10 or less, even more preferably about 1.05 or less, even more preferably about 1.03 or less, and most preferably about 1.02 or less.

[0045]

[0033] The 3D parts may be constructed in a build container, preferably an exchangeable build container having side walls and bottom that moves in the z-direction relative to the side walls. The light travel distance between the light source and the light sensor typically is greater than the width of the build container (in the y-direction). Preferably the difference between the light travel distance and the width of the build container is about 5 mm or more, about 10 mm or more, or about 15 mm or more. Preferably the difference between the light travel distance and the width of the build container is about 400 mm or less, more preferably about 200 mm or less, even more preferably about 125 mm or less, and most preferably about 70 mm or less. Preferably, a ratio of the light travel distance to the width of the build container is about 1.20 or less, more preferably about 1.10 or less, even more preferably about 1.05 or less, even more preferably about 1.03 or less, and most preferably about 1.02 or less.

[0046]

[0034] An optical sensor may be positioned sufficiently in advance of the recoater ora component of the recoater so that a protrusion can be detected and the recoater stopped before it crashes into the defect. For example, the recoater may including a leveling component, such as a blade, and the optical sensor may help prevent a leading surface of the leveling component from crashing into the defect. The leveling component may have a leveling surface that defines the height of the particulate material being deposited by the recoater. Preferably, an optical sensor positioned in advance of the recoater and / or leveling component is attached to the recoater. The optical sensor may be directly attached to the recoater. The optical sensor may be attached to the recoater via a bracket or other device that allows for positioning of the optical sensor in the vertical direction and / or in a direction of travel of the recoater (i.e., x-direction). The difference in distanceAttorney Docket No.: 1156.091WO (VX121)

[0047] between the optical sensor and a leading surface (i.e., forward facing surface) of the leveling component preferably is about 3 mm or more, more preferably about 5 mm or more, even more preferably about 10 mm or more, and most preferably about 20 mm or more. The difference in distance between the optical sensor and a leading surface of the leveling component preferably is about 250 mm or less, more preferably about 100 mm or less, even more preferably about 40 mm or less, and most preferably about 25 mm or less. The height of the optical sensor may be about the same height as a leveling surface of the leveling component, higher than the leveling surface, or lower than the leveling surface. Preferably, the distance between the optical sensor and the leveling surface in the z-direction is about 50 mm or less, more preferably about 20 mm or less, even more preferably about 10 mm or less, and most preferably about 5 mm or less. Preferably, the distance between the optical sensor and the leveling surface in the z-direction is about 0 mm or more, more preferably about 1 mm or more, even more preferably about 2 mm or more, and most preferably about 5 mm or more.

[0048]

[0035] The light source and the optical sensors are preferably positioned on opposite sides of the recoater (in the y-direction). The positioning of the light source with respect to the leveling component may be the same as the positioning of the optical sensor, as described above. For example, the light source may be attached to the recoater, directly or via a bracket. The positioning of the light source relative to the leveling component may be adjustable in the z-direction and / or the x-direction. The difference in distance between the light source and a leading surface of the leveling component preferably is about 3 mm or more, more preferably about 5 mm or more, even more preferably about 10 mm or more, and most preferably about 20 mm or more. The difference in distance between the light source and a leading surface of the leveling component preferably is about 250 mm or less, more preferably about 100 mm or less, even more preferably about 40 mm or less, and most preferably about 25 mm or less. The height of the light source may be about the same height as a leveling surface of the leveling component, higher than the leveling surface, or lower than the leveling surface. Preferably, the distance between the light source and the leveling surface in the z-direction is about 50 mm or less, more preferably about 20 mm or less, even more preferably about 10 mm or less, and most preferably about 5 mm or less. Preferably, the distance between the light source and the leveling surface in the z-direction is about 0 mm or more, more preferably about 1 mm or more, even more preferably about 2 mm or more, and most preferably about 5 mm or more. Preferably the positioning of the light source and the optical sensor are the same, so that the light travels from the light source to the optical sensor in the y-direction (i.e., in a horizontal direction perpendicular to the direction of travel of the recoater).Attorney Docket No.: 1156.091WO (VX121)

[0049] Such a positioning of the light source and optical sensor makes it possible to identify the position of a defect in the x-direction with a single light source and a single optical sensor.

[0050]

[0036] The optical sensor and / or light source may be positioned sufficiently in advance of the printhead so that a protrusion can be detected and the printhead stopped before it crashes into the defect. The optical sensor and / or light source for preventing damage to the printhead are attached (directly or via a bracket) to the printhead, preferably on opposing sides of the printhead in the y-direction. The optical sensor and / or light source may be adjustable in the x-direction relative to a loading surface of the printhead and / or in the z-direction relative to a printing surface of the printhead.

[0051]

[0037] The optical sensor and / or light source may be positioned sufficiently in advance of a sintering unit so that a protrusion can be detected and the sintering unit stopped before it crashes into the defect. The optical sensor and / or light source for preventing damage to the sintering unit may be attached (directly or via a bracket) to the sintering unit, preferably on opposing sides of the sintering unit in the y-direction. The optical sensor and / or light source may be adjustable in the x-direction relative to a loading surface of the sintering unit and / or in the z-direction relative to a lower surface of the sintering unit.

[0052]

[0038] The controller may determine an initial baseline light intensity. For example, an initial baseline intensity may be an average intention during an initial pass of the optical sensor over a construction field. One or more control limits may be determined or set from the initial baseline intensity. For example, a control limit may be set for a corrective action in the build process. The corrective action may be aborting a build process to avoid damage to a recoater or a printhead. The corrective action may be an adjustment to the printing process that does not abort the entire build process. It will be appreciated that different control limits may result in different corrective actions.

[0053]

[0039] The controller may determine an adjusted baseline intensity (e.g., a temporal baseline intensity). By way of example, the adjusted baseline intensity may be the average light intensity measured from one, two, or more of the most recent passes of the recoater. The adjusted baseline intensity may be used to modify one or more control limits. For example, if the average light intensity decreases over time between cleanings of the light source and / or optical sensor, a control limit may be adjusted accordingly to compensate for the reduction in light intensity being detected. After cleaning of the light source and / or optical sensor, a new baseline intensity may be measured.

[0054]

[0040] The light source may generate a light or may be provided light, preferably from a stationary component. For example, the light may be generated by a light generator and provided to the lightAttorney Docket No.: 1156.091WO (VX121)

[0055] source by a light guide. Preferably, the construction space and recoater are positioned inside a build enclosure and the light generator is positioned outside the build enclosure. The light generator and / or light source preferably provide a highly focused light beam. The light beam may be monochromatic. For example, a light guide may be connected to a laser positioned outside of the build enclosure and transmit the light to the light source. The light generator may provide light to one or more, two or more, or three or more light sources. For example the light generator may provide for one or more light sources for preventing damage to a recoater, one or more light sources for preventing damage to a printhead, one or more light sources for preventing damage to a sintering unit, or any combination thereof.

[0056]

[0041] The optical sensor preferably has a sufficiently small opening angle so that errors from other light in the system is reduced, minimized or eliminated. Preferably, the opening angle of the optical sensor is about 15° or less, more preferably about 5° or less, even more preferably about 3° or less, and most preferably about 1 ° or less. The optical sensor may be tuned to one or more wavelengths, preferably one or more wavelengths of the light source. The optical sensor may include one or more filters and / or one a polarizers.

[0057]

[0042] When the measured light intensity drops below a process abort control limit, the controller may stop the recoater and I or the print head to avoid damage. It may be necessary to stop the recoater and / or the print head within seconds or even a fraction of a second after a reduction in the measured light intensity is detected.

[0058]

[0043] A controller may identify a defect being formed based on relatively small changes in the light intensity compared to the large changes in the light intensity that would require a process to be aborted due to a protrusion that could damage the recoater or printhead. For example, the processor may identify one or more locations on the build surface where the light intensity is repeatedly decreased (e.g., compared to a baseline or adjusted baseline value). The magnitude of the decrease may be monitored and the process may adjusted, without stopping the build process. For example, the process may be adjusted to eliminate the defect. As another example, the process may be adjusted to continue producing one part while stopping the production of another part. A defect may be eliminated by adjusting a temperature in a build chamber, adjusting a temperature of the construction field, adjusting a temperature of a sintering lamp, adjusting the amount or size of a liquid being printed from the printhead, adjusting a speed of the recoater, adjusting a speed of a printhead, adjusting a speed of a sintering lamp, or adjusting a dithering parameter of the printhead. The defect being formed may be a subcritical defect. A subcritical defect may be characterized as a defect which will not cause damage from an impact, a defect which will not materially affect the performance of the part, or a defect which can be corrected.Attorney Docket No.: 1156.091WO (VX121)

[0059] Upon identifying a subcritical defect, the controller may make one or more changes to the process, which may be temporary or permanent. A permanent change may be a change that is maintained until a part is completed, a build job is completed, or a job box is removed. For example, upon finding a subcritical defect, the controller may reduce the speed (e.g., traversing speed in the X-direction) of the recoater by about 10% or more, about 20% or more, about 30% or more, about 40% or more, about 60% or more, about 70% or more, or about 80% or more. Typically, the speed of the recoater is reduced by about 95% or less, about 85% or less, or about 75% or less. Upon determining that a defect has been partially reduced or completely eliminated, the controller may optionally make one or more additional changes to the process, typically returning a process condition towards its original condition (i.e. , before identifying the defect). For example, upon determining that a defect has been partially reduced or completely eliminated, the speed of the recoater may be increased back towards its original speed (i.e., a speed equal to or less than the original speed). The speed of a recoater may be increased in one or more steps. For example, the speed of the recoater may be increased towards its original speed in multiple passes of the coater, so that the controller can confirm that the defect does not appear again. After identifying a defect, the controller may change one or more process parameters for an entire pass of a recoater, a printhead or a sintering lamp, or may change the process parameter only in a region near the defect. For example, speed of a recoater, a printhead, or a sintering lamp, may be reduced in the region of the defect, while an original speed is used in one or more other regions away from the defect. As another example, a size of a liquid being printed from the printhead and / or a dithering pattern of a printhead may be adjusted in a region of the defect, while an original condition is employed in one or more other regions away from the defect.

[0060]

[0044] A controller may stop the printhead from selectively printing a fluid for forming one molded article while allowing the printhead to continue to print another molded article.

[0061]

[0045] A controller may calculate an average measured light intensity for each pass of the light beam and / or recoater over the construction field.

[0062]

[0046] A controller may calculate a minimum light intensity for each pass of the light beam and / or recoater over the construction field.

[0063]

[0047] A controller may record locations (e.g., in the x-direction and / or y-direction) of each instance that a light intensity below a warning limit is measured. Preferably, the warning limit is less than the average measured light intensity and / or below a baseline light intensity. Preferably, a ratio of the warning limit to the average measured light intensity is about 0.99 or less, 0.98 or less, about 0.97 or less, about 0.96 or less, about 0.95 or less, about 0.94 or less, about 093 or less, about 0.92 or less, about 0.91 or less, or about 0.90 or less.Attorney Docket No.: 1156.091WO (VX121)

[0064]

[0048] The 3D printer may include a cleaning station for cleaning a surface of a light source, a cleaning station for cleaning a surface of an optical sensor, or both. The cleaning station may remove particulate material or other material from the surface being cleaned. The cleaning station may use mechanical means to clean the surface. The cleaning station may use water, a solvent, a sponge, a swab, a cloth, a spray, or any combination thereof. The 3D printer may include one or more barriers for separating or partially separating the cleaning station from the construction field. A barrier may be removable for allowing the light source or optical sensor to enter the cleaning station.

[0065]

[0049] The 3D printer preferably is free of a laser that selectively melts or reacts a build material.

[0066]

[0050] The 3D printer preferably is free of an extruder that extrudes molten build material.

[0067]

[0051] The 3D printer preferably is free of a mirror or focusing system for controlling a laser beam positioned over the construction field that travels in a generally vertical direction.

[0068]

[0052] Unless otherwise stated, all ranges include both endpoints and all numbers between the endpoints. The use of "about" or "approximately" in connection with a range applies to both ends of the range. Thus, "about 20 to 30" is intended to cover "about 20 to about 30", inclusive of at least the specified endpoints.

[0069]

[0053] The disclosures of all articles and references, including patent applications and publications, are incorporated by reference for all purposes. The term "consisting essentially of' to describe a combination shall include the elements, ingredients, components or steps identified, and such other elements ingredients, components or steps that do not materially affect the basic and novel characteristics of the combination. The use of the terms "comprising" or "including" to describe combinations of elements, ingredients, components or steps herein also contemplates embodiments that consist essentially of the elements, ingredients, components or steps.

[0070]

[0054] Plural elements, ingredients, components or steps can be provided by a single integrated element, ingredient, component or step. Alternatively, a single integrated element, ingredient, component or step might be divided into separate plural elements, ingredients, components or steps. The disclosure of "a" or "one" to describe an element, ingredient, component or step is not intended to foreclose additional elements, ingredients, components or steps.

[0071]

[0055] It is understood that the above description is intended to be illustrative and not restrictive. Many embodiments as well as many applications besides the examples provided will be apparent to those of skill in the art upon reading the above description. The scope of the invention should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patentAttorney Docket No.: 1156.091WO (VX121)

[0072] applications and publications, are incorporated by reference for all purposes. The omission in the following claims of any aspect of subject matter that is disclosed herein is not a disclaimer of such subject matter, nor should it be regarded that the inventors did not consider such subject matter to be part of the disclosed inventive subject matter.

[0073] EXAMPLES

[0074]

[0056] An obstacle is placed at a location on a build surface. Light is transmitted over the build surface from a light source to a light sensor. The light source and light sensor are mounted on opposing ends of the recoater (i.e. , outside of the build space) and in front of a recoater. As the recoater traverses over the build surface, the light intensity is measured. The measured light intensity is shown in FIG. 6. When the light travel pass reaches the obstacle, the light intensity decreases.

[0075]

[0057] REFERENCE NUMBERS OF DRAWINGS

[0076]

[0058] 100 Cross-section schematic (xz plane) showing features of a 3D printer I construction process.

[0077]

[0059] 102 Feedstock of previously applied layers (n layers)

[0078]

[0060] 104 Construction surface

[0079]

[0061] 105 Expected height of the previously applied layer

[0080]

[0062] 106 Optical sensor

[0081]

[0063] 108 Center of optical sensor

[0082]

[0064] 110 Particulate material being applied

[0083]

[0065] 112 Leveling component of the recoater

[0084]

[0066] 114 Bottom surface of the leveling component

[0085]

[0067] 116 Print head

[0086]

[0068] 118 Height of the layer being applied (n+1 layer)

[0087]

[0069] 120 Cross-sectional view (xz plane) of a 3D printer including an enclosure and a light generator outside of the enclosure

[0088]

[0070] 122 Enclosure

[0089]

[0071] 124 Build space

[0090]

[0072] 126 Light guide

[0091]

[0073] 128 Light generator (e.g., laser)

[0092]

[0074] 132 Recoater (e.g., rerecoater)

[0093]

[0075] 133 Leveling component

[0094]

[0076] 134 Particulate material container

[0095]

[0077] 136 Light sourceAttorney Docket No.: 1156.091WO (VX121)

[0096]

[0078] 138 Light sensor

[0097]

[0079] 139 Light path between the light source and light sensor

[0098]

[0080] 150 Recoater

[0099]

[0081] 151 Ends of the recoater (e.g., outside of the construction surface)

[0082] 152 Light source

[0100]

[0083] 154 Light path

[0101]

[0084] 154 Light sensor

[0102]

[0085] 156 Boundary of the construction surface

[0103]

[0086] 157 Travel direction of the recoater and light sensor

[0104]

[0087] 158 Each dotted line represents a measurement of light at an X-location

[0088] 160 Obstacle on the construction site or other defect

[0105]

[0089] 162 Light intensity

[0106]

[0090] 164 Travel direction of the recoater and light sensor

[0107]

[0091] 166 Minimum intensity

[0108]

[0092] 167 Critical intensity

[0109]

[0093] 168 Measurements before the obstacle I defect

[0110]

[0094] 169 Measurements at I after the obstacle I defect

[0111]

[0095] 170 Powder roll

Claims

Attorney Docket No.: 1156.091WO (VX121)CLAIMSWhat is claimed is:Claim 1. A 3D printer for layered printing of molded articles comprising:a) a recoater device for applying particulate material in layers over a construction field while moving over the construction field, wherein the recoater device travels in an x-direction and has an elongated opening in the y-direction, andb) an optical sensorthat moves over the construction field, wherein the optical sensor is arranged for measuring light that has traveled in a generally y-direction near or at the height of the construction field.Claim 2. The 3D printer of claim 1 , wherein the optical sensor moves over the construction field in advance of the recoater device while the recoater device applies the particulate material. Claim 3. The 3D printer of claim 1, wherein the recoater device has a leveling component having a leveling surface that defines a height of the particulate layer being deposited, wherein the optical sensor is characterized by a height equal to or greater than a height of the leveling surface, in a z-direction;preferably wherein the distance from the optical sensor to the leveling surface in the z-direction is about 50 mm or less, more preferably about 20 mm or less, even more preferably about 10 mm or less, and most preferably about 5 mm or less;preferably wherein the distance from the optical sensor to the bottom surface of the recoater device in the z-direction is about 0 mm or more, more preferably about 1 mm or more, even more preferably about 2 mm or more, and most preferably about 3 mm or more.Claim 4. The 3D printer of claim 3, wherein the leveling component has a forward facing surface in the x-direction,wherein a distance from the forward facing surface to the optical sensor in the x-direction is about 3 mm or more, preferably about 5 mm or more, more preferably about 10 mm or more, and most preferably about 20 mm or more; and / ora distance from the forward facing surface to the optical sensor in the x-direction is about 250 mm or less, preferably about 100 mm or less, even more preferably 40 mm or less, and most preferably about 25 mm or less.Claim 5. The 3D printer of claim 3 or 4, wherein the position of the optical sensor relative to the leveling component is adjustable in the x-direction and / or in the z-direction.Claim 6. The 3D printer of any of claims 1 to 5, wherein the 3D printer includes a light source, wherein the light source and the optical sensor are on opposing sides of the construction field (in the y-direction).Attorney Docket No.: 1156.091WO (VX121)Claim 7. The 3D printer of claim 6, wherein the light of the light source is generally monochromatic. Claim 8. The 3D printer of claim 6 or 7, wherein the optical sensor is tuned to one or more wavelengths of the light emitted from the light source.Claim 9. The 3D printer of any of claims 6 through 8, wherein- the optical sensor and the light source travel synchronously; and / or- the optical sensor and the recoater travel synchronously.Claim 10. The 3D printer of any of claims 6 through 9, wherein the optical sensor is attached to one side (in the y-direction) of the recoater.Claim 11. The 3D printer of any of claims 6 through 10, wherein the optical sensor and the light source are attached to opposite sides of the recoater (in the y-direction).Claim 12. The 3D printer of any of claims 6 through 11, wherein the light source includes an LED light, preferably wherein the light source is a single LED light.Claim 13. The 3D printer of any of claims 6 to 12, wherein the light source employs light from a laser.Claim 14. The 3D printer of claim 13, wherein the light is transmitted by means of fiber optics, preferably wherein the laser is remote from the construction field and / or the laser is outside a construction chamber of the 3D printer.Claim 15. The 3D printer of any of claims 6 to 14, wherein the height of the optical sensor and the light source are generally the same.Claim 16. The 3D printer of any of claims 1 to 15, wherein the optical sensor and / or the light source move in front of a sintering unit.Claim 17. The 3D printer of any of claims 1 to 16, wherein the optical sensor and / or the light source move in front of a print head.Claim 18. The 3D printer of any of claims 1 to 17, wherein the device includes a controller for controlling a component of the 3D printer based on the amount of light measured by the light sensor.Claim 19. The 3D printer of claim 18, wherein the controller:stops a forward movement of the recoater in the x-direction, and / orstops a forward movement of a printhead in the x-direction, and / orstops the printhead from selectively printing a fluid for forming one molded article while allowing the printhead to continue to print another molded article, and / orincreases a temperature in a build chamber or a temperature of the construction field.Attorney Docket No.: 1156.091WO (VX121)Claim 20. The 3D printer of any of claims 18 or 19, wherein the controller identifies an x-position of a defect, wherein the defect includes an object or a build material above an expected height of the last printed layer.Claim 21. The 3D printer of any of claims 1 through 20, wherein the optical sensor is a first optical sensor and the 3D printer includes a second optical which is spaced apart from the first optical sensor in the x direction.Claim 22. The 3D printer of any of claims 1 through 21, wherein the controller identifies an x-position and a y-position of a defect, wherein the defect includes an object or a build material above an expected height of the last printed layer.Claim 23. The 3D printer of claim 21 or 22, wherein the height (i.e . , z-position) of the first optical sensor and the second optical sensor are generally the same.Claim 24. The 3D printer of any of claims 21 through 23, wherein the first optical sensor measures a first beam of light traveling in a first direction parallel to the surface of the construction field and the second optical sensor measures a second beam of light traveling in a second direction parallel to the surface of the construction field, wherein the first direction and the second direction form an angle greater than 0°.Claim 25. A device for a 3D printer comprising:a recoater unit having an elongated container for holding a particulate material and an elongated opening for layer-wise depositing the particulate material onto a construction field of a 3D printer, wherein the recoater unit is configured for moving in a first direction and the elongated opening extends in a second direction generally perpendicular to the first direction, wherein the recoater unit includes a leveling means which defines the height of the layer being deposited; and a light sensor attached to the recoater unit, wherein the light sensor is arranged in advance of the recoater unit for measuring light traveling parallel to the second direction and having a vertical position (z-position) so that it can at least measure a portion of the light between the height of the previous layer and the height of the layer being deposited.Claim 26. The device of claim 25, wherein the device includes a light source.Claim 27. The device of claim 26, wherein the device is characterized by one or any combination of:- the light source is generally monochromatic; or- the optical sensor is tuned to a wavelength of light of a light source; or- the light source and the optical sensor are attached to opposing ends of the recoater unit; orAttorney Docket No.: 1156.091WO (VX121)- a positioning of the light source is adjustable in the X-direction and / or a positioning of the optical sensor is adjustable in the X-direction; or- the device includes two optical sensors; or- the device includes two optical sensors spaced apart in the X-direction and measures light from the same light source or from different light sources; or- the optical sensor provides light measurement information to a controller.Claim 28. A method comprising a step ofi) detecting a defect in a construction field during the printing of one or more molded parts being printed in layers with a 3D printer while a recoater unit is approaching the defect; wherein the defect includes a build material or other object positioned above the height of the last complete layer that was deposited; andii) controlling the process to prevent damage to the recoater unit or to another component in the 3D printer.Claim 29. The method of claim 28, wherein the defect is measured by an optical sensor arranged for measuring an intensity of a light that crosses a surface of the construction field.Claim 30. The method of claim 28 or 29, wherein the defect includes a curling of a molded part. Claim 31. The method of any of claims 28 to 30, wherein the defect includes an unexpected object on the construction field.Claim 32. The method of any of claims 28 to 31 , wherein the step of controlling includes reducing a speed of or stopping the recoater and / or reducing a speed of or stopping a printhead.Claim 33. The method of any of claims 28 to 32, wherein the step of controlling includes increasing a temperature at a surface of the construction field.Claim 34. The method of any of claims 28 to 33, wherein the step of controlling includes stopping the printing of one molded part while continuing the printing of another molded part.Claim 35. The method of any of claims 28 to 34, wherein the method includes a step of shining a light over a surface of the construction field from a light source to an optical sensor, wherein the light source and optical sensors are on opposing sides of the construction field.Claim 36. The method of claim 35, wherein the light source includes or is a monochromatic light source.Claim 37. The method of claim 35 or 36, wherein the light source includes an LED light source. Claim 38. The method of any of claims 35 to 37, wherein the light source includes or is a laser light source, preferably using a fiber optic(s) to transfer a laser light from the laser to a periphery of the construction field.Attorney Docket No.: 1156.091WO (VX121)Claim 39. The method of any of claims 35 to 38, wherein the optic sensor is tuned to one or more wavelengths of the light source.Claim 40. The method of any of claims 28 to 39, wherein the step of detecting is performed without a laser in a printing chamber of the 3D printer.Claim 41. The method of any of claims 28 to 40, wherein the method reduces waste and / or increases efficiency.Claim 42. The method of any of claims 28 to 41, wherein the method includes the controller determining that the defect is reduced or eliminated.Claim 43. The method of claim 42, wherein a process parameter that was controlled by the controller is returned towards an original condition, in one or more steps.Claim 44. A method comprising the steps of:printing of one or more molded parts with a 3D printer by including:repeatedlyi) applying layers of particulate material on a surface; andii) transmitting a light over the surface from a light source to a light sensor; wherein the method includes cleaning the light source and / or the light sensor.Claim 45. The method of claim 44, wherein the method includes detecting a change in a light flux received by the light sensor prior to the step of cleaning.Claim 46. The method of claim 44 or 45, wherein the 3D printer has a cleaning station and the step of cleaning is performed at the cleaning station, optionally between applying layers of the one or more molded parts.Claim 47. A device comprising:i) a recoater for applying a particulate material on a construction surface in layers; ii) a light source for transmitting a light over the applied layer of particulate material; and iii) a light sensor for measuring a flux of light;wherein the device includes a cleaning station for cleaning the light source and / or for cleaning the light sensor;wherein the device is for printing of one or more 3D parts.Claim 48. The device of claim 46, wherein the recoater, the light source and the light sensor travel over the construction surface in a common direction.

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