EP3737832A1 - Optical sensing techniques for calibration of an additive fabrication device and related systems and methods - Google Patents
Optical sensing techniques for calibration of an additive fabrication device and related systems and methodsInfo
- Publication number
- EP3737832A1 EP3737832A1 EP18900224.9A EP18900224A EP3737832A1 EP 3737832 A1 EP3737832 A1 EP 3737832A1 EP 18900224 A EP18900224 A EP 18900224A EP 3737832 A1 EP3737832 A1 EP 3737832A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- additive fabrication
- fabrication device
- fiducial
- light
- calibration
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
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Classifications
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- B29C64/10—Processes of additive manufacturing
- B29C64/106—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material
- B29C64/124—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material using layers of liquid which are selectively solidified
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- B33Y99/00—Subject matter not provided for in other groups of this subclass
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Definitions
- the present invention relates generally to systems and methods for calibrating an additive fabrication device via optical sensing.
- Additive fabrication e.g., 3-dimensional (3D) printing
- additive fabrication techniques may include stereolithography, selective or fused deposition modeling, direct composite manufacturing, laminated object manufacturing, selective phase area deposition, multi-phase jet solidification, ballistic particle manufacturing, particle deposition, laser sintering or combinations thereof.
- solid objects are created by successively forming thin layers of a curable polymer resin, typically first onto a build surface and then one on top of another. Exposure to actinic radiation cures a thin layer of liquid resin, which causes it to harden and adhere to previously cured layers or the bottom surface of the build surface.
- an additive fabrication device configured to fabricate an object by forming layers of solid material on a build platform, the solid material being formed from one or more source materials, the additive fabrication device comprising at least one light source, at least one sensor, a dispenser configured to dispense the one or more source materials into a build region of the additive fabrication device, a first structure configured to contact the one or more source materials within the build region during said fabrication of the object, wherein a surface of the first structure includes at least a first calibration pattern, and at least one processor configured to direct the at least one light source to the first calibration pattern, measure, via the at least one sensor, an intensity of light scattered from the first calibration pattern, and determine a position of the first structure based at least in part on the measured intensity of light.
- a method of calibrating an additive fabrication device configured to fabricate an object by forming layers of solid material on a build platform, the solid material being formed from one or more source materials, the method comprising directing at least one light source of the additive fabrication device onto a first calibration pattern, wherein the additive fabrication device comprises a first structure configured to contact the one or more source materials within the build region during said fabrication of the object, and wherein the first calibration pattern is disposed on a surface of the first structure, measuring, via at least one sensor of the additive fabrication device, an intensity of light scattered from the first calibration pattern and originating from the at least one light source, and determining a position of the first structure based at least in part on the measured intensity of light.
- FIGs. 1A-1C illustrate a schematic view of a stereolithographic printer that forms a plurality of layers of a part, according to some embodiments
- FIGs. 2A-2B illustrate top and side views, respectively, of a container having a plurality of fiducial targets disposed on its surface, according to some embodiments;
- FIG. 2C illustrates illumination of fiducial targets of the container depicted in FIGs. 2A-2B and reception of light scattered from the fiducial targets, according to some embodiments;
- FIGs. 3A-3B depict illustrative calibration patterns suitable for application within a fiducial target, according to some embodiments.
- FIG. 4 illustrates a build platform in a stereolithographic printer having a plurality of fiducial targets disposed on its surface, according to some embodiments
- FIG. 5A depicts an illustrative selective laser sintering additive fabrication device, according to some embodiments.
- FIG. 5B illustrates a recoater within a selective laser sintering additive fabrication device having a plurality of fiducial targets disposed on its surface, according to some embodiments
- FIG. 6 is a block diagram of a system suitable for practicing aspects of the invention, according to some embodiments.
- Systems and methods for calibrating an additive fabrication device via optical sensing are provided.
- An additive fabrication device generally needs to be calibrated correctly to ensure that material is formed in the desired locations.
- an additive fabrication device that forms solid material by directing a laser beam (or other light source) onto source material is calibrated so that when the laser beam is directed in a particular manner, the light is incident upon a known location and, in some cases, at a known distance from the laser beam source.
- Such calibration may take the form of data stored or otherwise accessible to the additive fabrication device that can be referenced so that the system properly controls the laser beam to produce a desired result. If the calibration values are incorrect, the system will control the laser beam in a way that produces a result different from that which was intended.
- FIGs. 1A- C To illustrate one exemplary additive fabrication technique in which a part is formed on a build platform, an inverse stereolithographic printer is depicted in FIGs. 1A- C.
- Exemplary stereolithographic printer 100 forms a part in a downward facing direction on a build platform such that layers of the part are formed in contact with a surface of a container in addition to a previously cured layer or the build platform.
- stereolithographic printer 100 comprises build platform 104, container 106, axis 108 and liquid resin 110.
- a downward facing build platform 104 opposes the floor of container 106, which is filled with a liquid photopolymer 110.
- FIG. 1 A represents a configuration of stereolithographic printer 100 prior to formation of any layers of a part on build platform 104.
- a part 112 may be formed layerwise, with the initial layer attached to the build platform 104.
- the container’s floor may be transparent to actinic radiation, which can be targeted at portions of the thin layer of liquid
- photocurable resin resting on the floor of the container. Exposure to actinic radiation cures a thin layer of the liquid resin, which causes it to harden.
- the layer 114 is at least partially in contact with both a previously formed layer and the surface of the container 106 when it is formed.
- the top side of the cured resin layer typically bonds to either the bottom surface of the build platform 4 or with the previously cured resin layer in addition to the transparent floor of the container.
- any bonding that occurs between the transparent floor of the container and the layer must be broken. For example, one or more portions of the surface (or the entire surface) of layer 114 may adhere to the container such that the adhesion must be removed prior to formation of a subsequent layer.
- Techniques for reducing the strength of the bond between a part and a surface may include inhibiting the curing process or providing a highly smooth surface on the inside of a container. In many use cases, however, at least some force must be applied to remove a cured resin layer from the container.
- FIG. 1C illustrates the stereolithographic printer subsequent to the separation of the part 112 from the container 106 by application of force. The process shown in FIGs. 1A-1C may then repeat to form additional layers of the part until the desired part is produced.
- one common difficulty addressed by calibration stems from the need to determine various parameters needed to correctly form layers of solid material at any desired points within a spatial region of the device, referred to herein as the build region.
- Such parameters may take various forms, such as mappings of coordinates to various electrical properties, adjustments to paths and trajectories, and/or physical offsets between expected and actual exposure points.
- these parameters are fundamental to the operation of a system, such as a determination of voltages needed to cause a galvanometer-driven mirror to deflect the path of a laser beam the angle required to intersect the build region at a given point.
- parameters may be viewed as corrections to account for various physical imperfections or inaccuracies, such as might be caused by a misaligned exposure source.
- Various calibration steps may be taken as part of a manufacturing or dedicated calibration procedure in order to determine appropriate calibration parameters.
- a grid of optical sensors sometimes known as fiducial sensors or fiducials, are temporarily installed into the build region of an additive fabrication device at known locations.
- An exposure system potentially starting from a base or estimated set of parameters, may then be used to expose a point within the build region expected to correspond to a fiducial sensor.
- the fiducial sensor may confirm whether a given set of parameters results in the expected exposure point within the build platform.
- the absence of a detection may be used to provide feedback to a calibration process adjusting various parameters until the appropriate point within the build region is exposed.
- this may advantageously involve the use of multiple fiducial sensors at different known locations within the build region and repeated iterations of calibration and testing.
- Various approaches to such calibration may be applied, including forms of linear and nonlinear function fitting, lookup tables, and other algorithmic or heuristic techniques.
- fiducial sensors require space within the additive fabrication device that may cause the device to increase in size. In cases where a compact additive fabrication device is desirable, therefore, the use of fiducial sensors may tend to inhibit the production of a desired device.
- fiducial sensors can increase the cost and complexity of the additive fabrication device.
- Some additive fabrication devices include components intended to be used and replaced periodically. These devices in particular may suffer from increased cost where the disposable components include fiducial sensors, because the sensors must be re-installed and/or re purchased each time the component is replaced.
- an additive fabrication device may be calibrated via calibration patterns disposed onto suitable components of the device that are scanned by a suitable light source. By measuring the manner in which light scatters from one or more calibration patterns, a position of the calibration pattern may be determined.
- components of an additive fabrication device that, at some point in fabrication, come into contact with a source material from which the device forms parts may be especially suitable for the application of calibration patterns, since such components typically have a known and well-defined spatial relationship with the build region of the device.
- Embodiments of the present invention allow for determining the position of a component of an additive fabrication device without requiring the use of fiducial sensors or other active means associated with that position.
- One or more regions referred to herein as fiducial targets, may be provided at known locations within the additive fabrication device.
- a fiducial target may include any target that is recognizable via light scattered from its surface, such as a calibration pattern.
- fiducial targets may be incorporated into various components of an additive fabrication device, including removable components.
- the fiducial targets may, in some embodiments, diffusely emit or reflect energy received from a light source when the light source is incident on the pattern.
- One or more sensors may then be configured to detect and measure energy emitted or reflected from one or more fiducial targets.
- Such measurements may be utilized in various ways, and in some cases analyzed much as if the passive fiducial target were in fact an instrumented fiducial sensor. In some cases, whether a fiducial target has been exposed and/or to a position of the target may be determined based on the measurements.
- a fiducial target may be a calibration pattern with contrasting emission and/or reflection properties, such as a printed“bar code” or a similar distinctive pattern.
- a light source may be operated so that its emitted light travels over at least a portion of the fiducial target (e.g., by altering a direction in which the light source points, by moving the light source, by moving the fiducial target, or by some combination thereof). Movement of the illuminated areas between regions of the target with differing properties may then, in turn, create a distinctive pattern in the measurements taken by sensors measuring light scattering from the illuminated areas. These patterns may then be correlated, providing both additional spatial resolution for the location of the exposure point at a given time and increasing the reliability of the measurement, by allowing for detection of rising or falling signals, rather than against absolute values or thresholds.
- FIGs. 2A-2B illustrate top and side views, respectively, of a container having a plurality of fiducial targets disposed on its surface, according to some embodiments.
- a container 200 suitable for use in a stereolithographic printer is shown.
- Container 200 may be deployed, for example, as container 106 shown in FIGs. 1A-1C or in some other stereolithographic additive fabrication device.
- the container 200 includes a solid structure 202 on which a number of fiducial targets (including targets 223 and 224), shown in the figure as shaded circles, are disposed. At least region 221 of the solid structure is transparent; the remainder of structure 202 may, or may not be transparent, or may be transparent in a different manner to region 221 (e.g., transparent to different wavelengths of light).
- the region 220 is the build region for an additive fabrication device in which container 200 may be disposed - that is, the region 220 is the region in which solid material may be formed by the additive fabrication device.
- one technique by which solid material may be formed within a container such as container 200 is to direct actinic radiation through a transparent portion of the container, thereby photocuring a liquid photopolymer held within the container.
- fiducial targets 223 are included at comers of the container 200. While fiducial targets 223 are depicted in the example of FIGs. 2A-2B as being disposed in the interior of the container, they could alternatively be positioned on the opposite side of the base of the container.
- fiducial targets may be adhesive stickers or other conventionally printed material affixed to, or printed directly on, a known location of the container 200.
- the known locations of the fiducial target may be stored in a computer readable medium of the additive fabrication device and/or may be encoded within a pattern of a fiducial target, as described further below (e.g., a fiducial target coupled to a removable component), or otherwise accessible to a processor of the additive fabrication device.
- Various dimensions, including the size of a fiducial target and/or the size and shape of features of the fiducial target may also be stored in such ways and accessed to detect the fiducial target, as discussed further below.
- container 200 may be configured to be removably inserted into a stereolithographic additive fabrication device and configured to contain build material within the device to be exposed to actinic radiation.
- the container may be contained within an enclosure that substantially reduces the transmission of actinic radiation into the enclosure. In such instances, the principal source of actinic radiation within the system may originate within the enclosure.
- material within the build region 220 may be exposed by a laser emitting actinic radiation.
- This actinic radiation may be directed onto various points within the build region 220 by the use of galvanometer-driven mirrors, which rotate to deflect the path of a beam of radiation.
- actinic radiation may be transmitted through the actinically transparent region 221 before interacting with a curable material within the build region 220.
- a transparent region 221 may be the same size as the build region 220 or, as shown in the example of FIGs. 2A-2B, the build region 220 may lie within the transparent region 221 such that a peripheral area 222 exists where actinic radiation may be transmitted through an actinically transparent region 221, but where no formation of material is expected to occur.
- FIG. 2C illustrates illumination of fiducial targets of the container depicted in FIGs. 2A-2B and reception of light scattered from the fiducial targets, according to some embodiments.
- the example of FIG. 2C depicts one illustrative manner in which light may be produced by a light source 260, scattered from one or more fiducial targets, and the scattered light detected by a sensor 270.
- the light source and sensor may be positioned in any suitable locations with respect to the container 200, and that the light source and sensor shown in FIG. 2C are provided merely to illustrate the scattering of light from fiducial targets without wishing to be bound to any particular position of these elements.
- the light source 260 may be located below the container 200 (the light source 260 in FIG. 2C is shown located above the container).
- the senor and light source need not be positioned on the same side of the container with respect to one another, nor is system 250 limited to only a single light source and single sensor, but in general may include any number of such components.
- multiple sensors may increase the sensitivity of the system to detect light scattered from a fiducial target and/or may increase a coverage area in which such light may be detected.
- the light source 260 may also be a source of actinic radiation utilized to photocure a liquid photopolymer held in container 200.
- an additive fabrication device may include a single source of light (e.g., a laser beam) and that source of light may be directed to both scatter light from one or more fiducial targets, thereby calibrating the position of container 200, or may instead be directed to photocure liquid photopolymer in the container.
- the light source 260 may produce light of any wavelength, or combination of wavelengths, which may include visible as well as non-visible wavelengths (e.g., infrared, x-ray, ultraviolet, etc.).
- an additive fabrication device may include multiple light sources each configured to illuminate one or more fiducial targets within the device. In some cases, one of these light sources may also be controlled to form solid material (e.g., by photocuring a photopolymer, by consolidating powdered material, etc.).
- Multiple light sources may enable calibration based upon differences between the primary and alternative exposure source positioning or other properties.
- multiple light sources within an additive fabrication device may share components for directing light from the source to a target, such as lenses and/or mirrors.
- the light sources may use the same deflection or other guiding means (e.g., lenses and/or mirrors), allowing calibration information obtained through illumination of a fiducial target with one light source to directly indicate how the other light source would be expected to illuminate the same location.
- an embodiment utilizing a comparatively high-power infrared laser to expose a source material in an additive fabrication device may additionally include a comparatively low-power visible light laser diode.
- the beam produced by the low-power laser may be directed utilizing the same deflection or other guiding means used for the higher power laser (e.g., galvanometer-controller mirrors).
- fiducial targets may be illuminated using the lower power laser, as described above, and calibration parameters may be determined applicable to the direction of both high and lower power radiation sources.
- fiducial targets may be read using a calibration light source, such as a low-power laser, in order to determine the position of fiducial targets located on structures such as build platforms for fused filament fabrication systems or powder beds in binder-jetting powder systems.
- a calibration light source such as a low-power laser
- Such fiducial targets may then be used in a“reverse” direction, whereby an already-calibrated optical system may be operated to determine an unknown position for a fiducial target when performing additional calibration of the optical system.
- a known position of a fiducial target may then be used in order to confirm the presence and position of a movable or removable component, rather than for calibration of an optical system.
- fiducial targets may be used to measure translation and/or rotation of a target surface, such as a build platform or other component.
- the target surface may comprise one or more, and preferably at least three, fiducial targets on the surface, facing the exposure source of calibration exposure.
- the location in space of fiducial points may then be used to extrapolate the position of the target surface, including information regarding offsets and rotations. Techniques measuring the position and rotation of surfaces may be particularly useful in determining if two planes are parallel and, if not, introducing various compensations for the differences from parallel.
- sensor 270 may include one or more photodiodes and/or other photodetectors.
- Such sensors may, in some cases, be mounted behind wide angled diffusers, such as semi-opaque plastic domes and/or fitted with one or more optical filters.
- a filter fitted to sensor 270 may include a notch filters, a polarized filter, and/or other means of excluding light sources and/or frequencies.
- the light source 260 may be located beneath the container 200 and may direct light through the transparent portion 221 of the container such that the light may reach the fiducial targets 224 after passing through the transparent region 221. Scanning of fiducial targets 224 in this manner may provide a number of advantages. As one example, locating fiducial targets 224 substantially within the same plane as the build region 220 may improve calibrations performed using such targets 224 by accurately measuring any path length dependent shifts or errors to the fiducial targets, and thereby to the build region based on their relative spatial relationship. Moreover, certain types of materials comprising the transparent region 221 may influence the transmission of actinic radiation such that exposure is deflected or otherwise shifted.
- Placement of fiducial targets on the upper side of the transparent region 221 when the light source is located on the lower side of the container thus allows for such influences to potentially be measured and taken into consideration during a calibration process.
- the accuracy of fabrication, and thereby the quality of fabricated parts may be improved by directing light during fabrication according to the measured behavior of light through the container during calibration.
- This approach may be particularly beneficial, for example, where an optical window of a container has a thickness that varies across the window and/or where there are materials having different refractive indices within the window.
- the light source 260 may be located above the container 200 and may direct light onto fiducial targets 223 located on the upper side of the container.
- non-directional sensors may be oriented to face the fiducial targets and positioned in an area where scattered radiation from one or more fiducial targets is expected, such as below the mounted location of container 102 proximate to the exposure source.
- Such non-directional sensors may then be configured in order to measure the amount of actinic radiation impinging upon them, such as from a diffuse reflection source.
- Such non-directional sensors do not need to be placed within any particular optical path, so long as they are capable of detecting light diffusely reflected, or scattered, from the fiducial targets.
- the light source, sensor and/or fiducial target(s) may be moved to produce a scan of the fiducial target by adjusting the area of light exposed by the light source with respect to the fiducial target, and/or by adjusting the path that light takes from the light source to the sensor.
- the container 200 may be moved and/or the light source controlled to redirect the light in a different direction.
- the area of the container that the light source exposes will change, thereby potentially causing a change in light scattering behavior from one or more fiducial targets. This change may be measured by the sensor to determine information about the position of these targets.
- a calibration cycle may include one or more, though preferably a number of, exposures of fiducial targets 223 and/224 by light source 260 and corresponding detections of scattered light by sensor 270.
- the cycle may, in some cases, also include motion of the fiducial targets, light source and/or sensor as described above, in between or during exposures of the fiducial targets by the light source.
- a calibration cycle may be initiated by an additive fabrication device in response to a trigger event, such as insertion of a component of the additive fabrication device (e.g., insertion of container 200), as a step prior to fabrication of a part, and/or at intermediate stages during fabrication of a part.
- At least one processor coupled to the light source 260 and sensor 270 may be configured to operate the light source (e.g., turn the source on or off, adjust a direction of exposure, amount of exposure, and/or focal length) and to perform analysis of measurements produced by the sensor.
- the at least one processor may also be configured to move one or more components of the additive fabrication device on which one or more fiducial targets are disposed (e.g., container 200).
- the at least one processor may be configured to perform any of a number of fixed calibration cycles in which the light source and sensor are operated in a sequence to produce calibration data from fiducial targets within the additive fabrication device.
- such a sequence may include causing motion of one or more components of the additive fabrication device (e.g., container 200).
- the at least one processor may be configured with logic that determines operations of the light source 260 and/or sensor 270 to perform for further calibration in response to analysis of light received by the sensor 270.
- a fiducial target may be formed with a series of regions with increasing widths in an axis, such as lines of 50um through 200um, alternating with similar sized regions of contrasting optical properties (e.g., stripes). An exposure spot may then be moved across said alternating region in the direction of the axis and signals recorded at the non-directional sensor.
- Such recorded signals may then form a“sin” shaped wave, oscillating in amplitude based upon the motion of the exposure point across the alternating regions. Accordingly, the number of peaks and/or troughs of the signal may be used to determine the location of the exposure point within the sequence of alternating regions of known widths. This oscillation may then be used to determine the approximate full- width half-max of the exposure point.
- a measured amplitude of the indirect exposure signal may be at a maximum when the exposure point traverses a portion of the alternating region with stripes having widths approximately equal to the width of the exposure point.
- a circular exposure point having a radius of 250 pm may be partially scattered or reflected while passing over a fiducial target comprising alternating stripes having comparatively higher and lower scattering properties with 50 pm stripe widths.
- the amplitude of the oscillations measured in a signal scattering from the fiducial target may be comparatively low.
- the full width of the exposure point when passing over alternating stripes having 250 pm stripe width, the full width of the exposure point may be incident upon a region of comparatively higher or lower scattering, thus causing comparatively high amplitude oscillations in the indirect sensing signal compared with the amplitudes measured for 50 pm stripe widths.
- an approximate measurement of the full-width half-max dimension of the exposure point may be determined.
- an additive fabrication device may be configured to detect discontinuities in surface properties (e.g., diffusivity, reflectivity, etc.) of a fiducial target.
- the device may operate light source 260 and/or sensor 270 via the techniques described above such that the exposure path of the light source crosses a discontinuity in the surface properties of the fiducial target.
- a position of the discontinuity may be compared by at least one processor of the additive fabrication device to an expected position to determine whether there is a difference, and if so, to perform adjustments of the device to recalibrate. This process may be repeated until any difference between the expected and measured position falls below a desired threshold.
- FIG. 3A-3B illustrate two examples of suitable calibration patterns that may be used as fiducial targets, according to some embodiments.
- a fiducial target 301 is configured with areas of comparatively high reflectivity 302 and areas of comparatively low reflectivity 303 with respect to light emitted by a light source of an additive fabrication device.
- the type of pattern shown in FIG. 3A is sometimes referred to as a Secchi pattern, and may have a known radius R.
- a light source of an exposure system may be operated to scan the area of light exposure in a circle having radius R/2 and centered on the expected center of the fiducial target 301.
- a processor coupled to a sensor receiving scattered actinic radiation will typically detect four“edges” to the signal, corresponding to points at which the exposure path crosses from a sector with low reflectivity 303 into a sector with high reflectivity 302 and from high reflectivity 302 back into a low reflectivity 303 sector.
- the radius of the fiducial target 301 may be most advantageously selected to be larger than the maximum expected calibration error.
- the exposure path may be sufficiently out of calibration so as not to be contained within or intersect with the fiducial target.
- an approximate location of a fiducial target may be determined by scanning a wider area in order to identify regions with increased diffuse reflectivity, and attempting to calibrate using such a region as a probable target.
- the exposure point of a light source e.g., a laser
- the changing reflectivity, or other optical properties, from the fiducial targets within the grid may be detected by the non-directional sensor and an approximate location of each fiducial target within the grid determined. This process may be able to detect the location of multiple fiducial targets at different locations in a sequence. Such an approach may be particularly useful to detecting and correcting nonlinear distortions or fitting more accurate corrective calibrations onto exposure point targeting.
- the fiducial target may have properties that allow its spatial orientation to be determined by a processor analyzing light scattered from such a target, thus allowing for an overall orientation to be determined for a component bearing such fiducial targets.
- FIG. 3B depicts another illustrative calibration pattern 311, being a binary grid of contrasting regions, such as high 312 and low 313 reflectivity, similar to those used as data matrix,“QR”, or barcodes.
- a grid may be substantially or entirely antisymmetric, such that columns and/or rows are pairwise distinct.
- a calibration pattern like pattern 311 may provide for increased precision and faster calibration compared with a less complex pattern like patter 301 by allowing for more information to be gathered during a scan of an exposure point across the pattern.
- the sequence of signals recorded by a sensor receiving light scattered from a transit of a light exposure point across the grid may depend on both the particular matrix pattern on the fiducial target and the particular path taken by the exposure point during the transit.
- a specific path taken by an area of light exposure over the pattern 311 may be determined by comparing information about the known pattern with an observed sequence of signals produced by a sensor receiving light scattered from the pattern. The determined path may then be compared against a path implied by the current calibration of the additive fabrication device in order to determine one or more offsets used to refine the calibration.
- a sequence of signals produced by a sensor may be analyzed to determine the spacing between regions of contrasting optical properties on a fiducial target.
- a determined spacing may be compared to the known spacing between regions of the fiducial target in order to determine additional information about the position of the fiducial target.
- the distance of the fiducial target from the exposure source may be determined based on the ratio between the observed and expected spacing between regions. In many cases, this distance may provide a third, or “z”, dimension of position information.
- nonuniform changes in the observed spacing versus the actual spacing may indicate that the fiducial target is oriented at an angle to the exposure source, such that the distance changes over the field of the fiducial target.
- additional information may be encoded into a fiducial target such as matrix pattern 311 that is capable of being“read” (e.g., detected and decoded) via scanning with an exposure source either during a calibration procedure or during a separate step.
- a sequence of rising and falling signals detected by a sensor may be analyzed and converted into a digital code by a processor coupled to the sensor.
- Such matrix patterns may thus function as both a calibration source and a traditional barcode.
- information encoded into a fiducial target may identify a component of an additive fabrication device. For instance, such information may identify a model number of the component. In some cases, identification of a removable component, such as a container in a
- stereolithographic printer may be particularly beneficial.
- identification may uniquely identify the given instance of a component so that the additive fabrication device can track usage of the removable components and determine which component has been installed.
- Fiducial targets bearing encoded information may more readily provide a wide range of information storage attached to a removable component at low cost, including providing a unique identifier for a particular removable component or type of component, process parameter adjustments appropriate for a particular component or type of component, and/or various other types of information that may be useful for the operation, calibration, or maintenance of an additive manufacturing system.
- At least a portion of a calibration pattern may be formed from phase-change materials, such as GeSbTE (germanium- antimony- tellurium), capable of being both read and“written” to by an exposure source.
- phase-change materials such as GeSbTE (germanium- antimony- tellurium)
- information such as cycle counts, material usage, and other operating parameters changing over time, may be recorded and recovered from such fiducial targets.
- a fiducial target such as, but not limited to, calibration patterns 301 and 311 shown in FIGs. 3 A and 3B, may be removably attached to a component of an additive fabrication device. This may allow the fiducial target to be installed prior to manufacturing or some other step during the lifetime of the device, then subsequently removed once a desired calibration process has been performed.
- one or more fiducial targets may be formed onto a layer of adhesive material, forming a calibration“sticker,” and such a sticker may be placed on a desired component, such as the top surface of the bottom of a container (e.g., container 106, container 200) and/or the lower surface of a build platform.
- Fiducial targets present on the sticker, potentially identifying particular characteristics of said component, such as distortions or deflections, and accounting for such distortions in the calibration of the exposure source.
- the sticker may then be removed before normal operation of the system.
- embodiments using such as temporary attachment of fiducial targets may include fiducial targets essentially within the same area and plane of a planar build region and such fiducial targets may extend across the full build region during the calibration process, which may both account for the variances of the removable component and for any variances across the full range of the build region and any variation in the non-removable portion of the system.
- the fiducial targets may be detached and normal operation begun without the risk of obstruction by the fiducial targets or related material.
- FIG. 4 illustrates a build platform in a stereolithographic printer having a plurality of fiducial targets disposed on its surface, according to some embodiments.
- a build platform of an inverted stereolithographic printer such as that shown in FIGs. 1A-1C, is depicted in FIG. 4, although it will be appreciated that fiducial targets may be applied to any suitable build platform in any type of additive fabrication device.
- a build platform 404 has fiducial targets 424 and 422 disposed on its surface.
- the fiducial targets 422 are preferably located at comers of the build platform so as not to inhibit the formation of solid material on most of the surface of the build platform.
- build platform 404 may be calibrated by lowering the platform (i.e., moving it toward the container 406) to a location at or near the plane of the build region during normal operation. Preferably, this operation is performed without solid material present on the build platform, although this is not a requirement.
- the build platform may provide a calibration plate-like structure, potentially providing calibration data for the full range of the build region, while avoiding the need to insert a calibration plate and without obstructing the build region during normal operation. For example, by detecting a position of fiducial target 422 via techniques of illuminating and detecting scattered light as described above, a position of the lower face of the build platform may be determined. The position of the build region may optionally then be determined based on the known position of the build platform relative to the build region.
- Fiducial targets 424 may also be scanned to produce such a measurement by detecting the position of these targets via techniques of illuminating and detecting scattered light as described above and calculating the position of the build region based on knowledge of the spatial relationship between the top of the build platform and the build region (which in the example of FIG. 4 would include at least the thickness of the build platform).
- detecting a position of a fiducial target disposed on a build platform via techniques of illuminating and detecting scattered light as described above may enable detection and measurement of any x-y plane shift of the build platform.
- An x-y plane shift may occur in some cases when the build platform moves in one direction (a z-direction) and the mechanism that causes such motion can ‘wobble’ causing motion of the build platform in a direction perpendicular to the z- direction.
- any x-y shifts in the build platform produced as it moves in the z-direction may be identified and measured based on the received light scattered from the target.
- FIGs. 5A-5B describe application of these techniques in a selective laser sintering (SLS) additive fabrication device.
- SLS selective laser sintering
- SLS device 500 comprises a laser 510 paired with a computer-controlled scanner system 515 disposed to operatively aim the laser 510 at the fabrication bed 530 and move over the area corresponding to a given cross- sectional area of a computer aided design (CAD) model representing a desired part.
- Suitable scanning systems may include one or more mechanical gantries, linear scanning devices using polygonal mirrors, and/or galvanometer-based scanning devices.
- the material in the fabrication bed 530 is selectively heated by the laser in a manner that causes the powder material particles to fuse (sometimes also referred to as“sintering” or“consolidating”) such that a new layer of the object 540 is formed.
- SLS is suitable for use with many different powdered materials, including any of various forms of powdered nylon.
- areas around the fabrication bed e.g., the walls 532, the platform 531, etc.
- Such heaters may be used to preheat unconsolidated material, as discussed above, prior to consolidation via the laser.
- the build platform 531 may be lowered a predetermined distance by a motion system (not pictured in FIG. 5A). Once the build platform 531 has been lowered, the material deposition mechanism 525 may be moved across the fabrication bed 530, spreading a fresh layer of material across the fabrication bed 530 to be consolidated as described above.
- Mechanisms configured to apply a consistent layer of material onto the fabrication bed may include the use of wipers, rollers, blades, and/or other levelling mechanisms for moving material from a source of fresh material to a target location.
- the build platform 531 may be removable from the system 500.
- part cake since material in the powder bed 530 is typically only consolidated in certain locations by the laser, some material will generally remain within the bed in an unconsolidated state. This unconsolidated material is sometimes referred to as a“part cake.”
- the part cake may be used to physically support features such as overhangs and thin walls during the formation process, allowing for SLS systems to avoid the use of temporary mechanical support structures, such as may be used in other additive manufacturing techniques such as stereolithography. In addition, this may further allow parts with more complicated geometries, such as moveable joints or other isolated features, to be printed with interlocking but unconnected components.
- the object and the part cake may be cooled at a controlled rate so as to limit issues that may arise with fast cooling, such as warping or other distortion due to variable rate cooling.
- the object and part cake may be cooled while within the selective laser sintering apparatus, or removed from the apparatus after fabrication to continue cooling. Once fully cooled, the object can be separated from the part cake by a variety of methods.
- the unused material in the part cake may optionally be recycled for use in subsequent fabrication.
- FIG. 5B illustrates a recoater within a selective laser sintering additive fabrication device having a plurality of fiducial targets disposed on its surface, according to some embodiments.
- fiducial targets 527 are disposed onto a structure 526 that is mechanically coupled to the roller 525 (the structure 526 was omitted in FIG. 5A for clarity).
- the light source 560 is configured to illuminate the fiducial targets 527 as the roller is moved across the surface of the powder bed, as described above.
- the light scattered therefrom and detected by sensor 570 may provide positional information on the fiducial targets 527.
- such positional information may identify the distance from the light source to the fiducial targets 527, which in turn may provide for a determination of the height of the powder bed based on a known fixed distance between the top of the roller unit, where the fiducial sensors 527 are positioned, and the bottom of the roller, which contacts the surface of the powder bed.
- FIG. 6 is a block diagram of a system suitable for practicing aspects of the invention, according to some embodiments.
- System 600 illustrates a system suitable for generating instructions to control an additive fabrication device to perform calibration operations as described above in addition operation of the additive fabrication device to fabricate an object. For instance, instructions to operate one or more light sources, light directing components associated with such light sources (e.g., computer adjustable mirrors, such as mirror galvonometers), sensors, and/or one or more processors of the additive fabrication device may be generated. In some cases, the instructions may also, when executed by the additive fabrication device, cause the additive fabrication device to perform calibration operations discussed above, including to produce light, measure scattered light at a sensor, and calculate a position of a fiducial target based on the measured scattered light.
- computer system 610 may execute software that generates two-dimensional layers that may each comprise sections of the object. Instructions may then be generated from this layer data to be provided to an additive fabrication device, such as additive fabrication device 620, that, when executed by the device, fabricates the layers and thereby fabricates the object. Such instructions may be communicated via link 615, which may comprise any suitable wired and/or wireless communications connection.
- link 615 may comprise any suitable wired and/or wireless communications connection.
- a single housing holds the computing device 610 and additive fabrication device 620 such that the link 615 is an internal link connecting two modules within the housing of system 600.
- fiducial targets may alternatively, or additionally, exhibit other types of optical properties in order to provide fiducial targets capable of producing emissions for indirect sensing.
- fiducial sensors may comprise fluorescent or phosphorescent material such that energy absorbed from the exposure source with a given frequency may be reemitted at a different fluorescent frequency which may then be detected by a sensor.
- typical office paper may be treated with various whiteners or other compounds fluorescing strongly at 405 nm.
- Other compounds, such as fluorescein or 4,4’-Diamino-2,2’- stilbenedisulfonic acid may also be used.
- the senor may be masked or otherwise prevented from detecting energy other than at the frequency of the fluorescent emission, such as via a notch filter.
- a reverse-stokes-shift target material may be desirable for the forming of fiducial targets when the light source is, for example, an infrared laser.
- a fiducial target may comprise phosphors that re-emit energy from the exposure source when illuminated by, for example, an electron beam.
- exposure to radiation may cause regions of a fiducial target to heat at differential rates, thus emitting energy in infrared frequencies that may be indirectly measured.
- non-diffuse reflectivity may be utilized in order to scatter or deflect energy towards non-directional sensors expected to fall within the path of such scattered or deflected energy. In some embodiments, this may take the form of regions of retroreflectivity, capable of returning at least a portion of the energy incident onto the fiducial target region towards the exposure source.
- indirect sensing means may be configured within or proximate to the optical path of the exposure source, such that sensors may measure the amount of energy returned via retroreflection from the fiducial target.
- a sensing device with multiple points of resolution such as a digital camera sensor
- a sensing device with multiple points of resolution may be used to provide indirect sensing.
- Such a configuration may allow for the more rapid location of misaligned fiducial targets by providing additional visual information for aligning the exposure point with a fiducial target.
- such sensing devices may allow for the detection of exposure of multiple points of exposure, such as may be formed using a mask-type exposure system.
- the calibration techniques used in embodiments of the present invention may be particularly useful in providing for the calibration of systems using more than one exposure source, potentially with fields of exposure which may only partially, or may not, overlap within the field of the build region.
- characteristics of a variety of operations within a build region or larger build environment may be detected and measured.
- many materials undergo changes in color and/or reflectivity during a consolidation or curing.
- consolidated plastic powder may tend to scatter less energy than unconsolidated powder.
- the introduction of the second material typically a liquid, may also change the reflectivity of the combined material at various frequencies.
- the exposure source of the sintering device or, as described above, an alternative exposure source may be scanned across portions of the build region to determine sintered regions so as to adjust calibrations, detect failures, or otherwise make process decisions.
- the use of an non-directional sensor combined with a controlled energy source allows embodiments of the present inventions to infer various types of optical properties across a two dimensional plane or within a three-dimensional volume by varying the target of the controlled energy source in a time-dependent series, even when the only point of measurement is a fixed point source of measurements.
- processors When implemented in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers.
- processors may be implemented as integrated circuits, with one or more processors in an integrated circuit component, including commercially available integrated circuit components known in the art by names such as CPU chips, GPU chips, microprocessor, microcontroller, or co-processor.
- a processor may be implemented in custom circuitry, such as an ASIC, or semi-custom circuitry resulting from configuring a programmable logic device.
- a processor may be a portion of a larger circuit or semiconductor device, whether commercially available, semi-custom or custom.
- some commercially available microprocessors have multiple cores such that one or a subset of those cores may constitute a processor.
- a processor may be implemented using circuitry in any suitable format.
- the invention may be embodied as a method, of which an example has been provided.
- the acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.
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AU2003260938A1 (en) * | 2002-09-12 | 2004-04-30 | Objet Geometries Ltd. | Device, system and method for calibration in three-dimensional model printing |
US8040530B2 (en) * | 2007-08-23 | 2011-10-18 | 3D Systems, Inc. | Automatic geometric calibration using laser scanning reflectometry |
US10252466B2 (en) * | 2014-07-28 | 2019-04-09 | Massachusetts Institute Of Technology | Systems and methods of machine vision assisted additive fabrication |
DE102015226722A1 (en) * | 2015-12-23 | 2017-06-29 | Eos Gmbh Electro Optical Systems | Apparatus and method for calibrating a device for generatively producing a three-dimensional object |
US9919360B2 (en) * | 2016-02-18 | 2018-03-20 | Velo3D, Inc. | Accurate three-dimensional printing |
CN109416248B (en) * | 2016-06-27 | 2021-07-06 | 福姆实验室公司 | Position detection techniques for additive manufacturing and related systems and methods |
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2018
- 2018-01-09 WO PCT/US2018/012927 patent/WO2019139561A1/en unknown
- 2018-01-09 EP EP18900224.9A patent/EP3737832A4/en not_active Withdrawn
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EP3737832A4 (en) | 2021-08-11 |
WO2019139561A1 (en) | 2019-07-18 |
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