WO 2006/033903 PCT/US2005/032645
APPARATUS AND METHODS FOR SERVICING 3D PRINTERS
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent Application Serial No.
60/612,068, filed on September 21, 2004, and U.S. Patent Application Serial No. 10/999,847,
filed on November 30, 2004, the disclosures of which are incorporated herein by reference in
5 their entirety. This application also incorporates herein by reference a U.S. patent application
filed on November 30, 2004 and identified by U.S. Patent Application Serial No. 11/000,100.
FIELD OF THE INVENTION
[0002] The present invention relates to apparatus and methods for servicing 3D printers, for
example, for cleaning and aligning the printheads used in the 3D printers.
10 BACKGROUND
[0003] Generally, 3D printing involves the use of an inkjet type printhead to deliver a liquid
or colloidal binder material to layers of a powdered build material. The printing technique
involves applying a layer of a powdered build material to a surface typically using a roller. After
the build material is applied to the surface, the printhead delivers the liquid binder to
15 predetermined areas of the layer of material. The binder infiltrates the material and reacts with
the powder, causing the layer to solidify in the printed areas by, for example, activating an
adhesive in the powder. The binder also penetrates into the underlying layers, producing
interlayer bonding. After the first cross-sectional portion is formed, the previous steps are
repeated, building successive cross-sectional portions until the final object is formed. See, for
20 example, U.S. Patent Nos. 6,375,874 and 6,416,850, the disclosures of which are incorporated
herein by reference in their entireties.

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[0004] 3D printers produce colored parts by using colored binder materials to solidify the
powder. Clear binder is used to produce white part surfaces, and three primary colors are used in
varying proportions to produce a gamut of colors. The printer must apply the variously colored
binder droplets at precise locations to render the part surfaces in accurate color. 3D printers use
5 a separate printhead to apply each binder color. In general, non-uniformity in printheads and
mechanical variations in printhead mounting features produce inaccuracies in the positioning of
binder droplets that must be characterized and corrected.
[0005] Additionally, apparatus for carrying out 3D printing typically generates dust, which
can detrimentally effect the operation of the printheads. For example, the dust can clog the jet
10 nozzles that dispense the binder material, which can result in no binder material being dispensed
or the binder material being dispensed inaccurately.
[0006] It is, therefore, an object of the present invention to provide apparatus and methods
for continuously and efficiently servicing 3D printers.
SUMMARY
15 [0007] Generally, the invention relates to apparatus and methods for producing three-
dimensional objects, such as casting cores, toys, bottles, cans, architectural models, automotive
parts, molecular models, models of body parts, cell phone housings, and footwear, more rapidly
and efficiently than heretofore achievable. Additionally, the invention relates to systems and
methods for maintaining and operating the aforementioned apparatus.
20 [0008] More specifically, the invention relates to apparatus and methods for aligning
multiple printheads and apparatus and methods for cleaning the printheads. In one example, the
alignment method is an automatic method of determining droplet-positioning errors that is
particularly suited to 3D printing. In one example, a test pattern is printed with the printheads to
be aligned, assuming that they are perfectly positioned. The resulting image is then scanned to

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determine the deviation of the images printed from perfect position. The information thus gained
is then available to correct the identified errors. The present approach differs from the prior art
in at least its use of the harmonic content of the signal obtained from scanning an alignment
pattern to characterize misalignment. A scan traverses a multiplicity of nominally identical bar
5 pairs, averaging out the irregularities inherent in an image printed in powder. Imaging optics are
unnecessary since no edge detection is involved.
[0009] In one aspect, the invention relates to a method of creating a test pattern with a
plurality of printheads of a three-dimensional printer. The method includes the steps of defining
an area on a build surface for receiving the test pattern, selecting a reference printhead capable of
10 printing with a high contrast, printing a reference line with the reference printhead, and printing a
test line proximate to the reference line with at least one of the remaining printheads.
[0010] In various embodiments, the step of defining an area includes producing a contrast-
enhancing sublayer on the build surface. The contrast-enhancing sublayer can be produced by
printing the area in a solid, high contrast color using at least one of the printhead and overlaying
15 the printed area with at least one unprinted layer of build material. In one embodiment, the area
is printed with all of the available printheads at a maximum discharge level to saturate the area.
[0011] The step of selecting a printhead includes the steps of printing a target above the
contrast-enhancing sublayer with each of the printheads, comparing the targets to identify which
target has a highest contrast relative to an unprinted area, and selecting a printhead associated
20 with the highest contrast target. Further, the method can include the step of depositing a layer of
a build material on the build surface prior to each printing step. The printing steps can include
depositing a liquid binder in a predetermined pattern on the build material. The printheads, in
one embodiment, print with a liquid binder having a color selected from the group consisting of

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magenta, yellow, cyan, clear and black. Other colors and combinations of colors are
contemplated and within the scope of the invention.
[0012] Additionally, the step of printing a test line can include printing alternating bars of
color with at least two of the remaining printheads. The steps of printing a reference line and
5 printing a test line can include printing a plurality of reference lines and printing a corre ponding
plurality of test lines. In one embodiment, the reference lines and the test lines can be printed in
multiple passes. The step of printing a plurality of lines can include printing a plurality of
horizontal lines and a plurality of vertical lines. Also, the step of printing a reference line can
include printing ten horizontal reference lines and printing ten vertical reference lines proximate
10 thereto, and the step of printing a test line can include printing ten corresponding horizontal test
lines and printing ten corresponding vertical test lines. In some embodiments, two re ference
lines may be printed. In other embodiments, 20 reference lines may be printed.
[0013] In a particular embodiment of the method, the steps of printing a reference line and
printing a test line include printing a plurality of nominally identical line pairs parallel to a fast-
15 axis travel of the printheads, each line pair comprising one reference line and one test line, and
printing a plurality of nominally identical line pairs perpendicular to the fast-axis travel of the
printheads, each line pair comprising one reference line and one test line. In one embodiment,
each plurality of line pairs is arranged as an equally spaced linear array. Each test line can
include a series of test bars, where each of the remaining printheads prints a central test bar that
20 is nominally located at a distance from a corresponding reference line equal to 1/2 of a nominal
array spacing of the reference lines. In one embodiment, each remaining printhead prints a
plurality of additional test bars that are incrementally displaced about the central test bar.
[0014] In another aspect, the invention relates to a test pattern for aligning a plurality of
printheads in a three-dimensional printer. The test pattern includes a plurality of substantially

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evenly spaced solid reference lines and a plurality of test lines disposed in an alternating pattern
with the plurality of reference lines, wherein each of the test lines comprises at least one bar of a
non-reference color. In one embodiment, the colors are printed in an alternating pattern. In
various embodiments, the plurality of lines is oriented substantially vertically, or in a particular
5 embodiment, parallel to a fast-axis printhead travel. Further, the test pattern can include a
second test pattern disposed proximate the first test pattern. The second test pattern includes a
second plurality of substantially evenly spaced solid reference lines and a second plurality of test
lines disposed in an alternating pattern with the second plurality of reference lines. Each of the
test lines comprises at least one bar of a non-reference color, and the second plurality of lines can
10 be oriented substantially perpendicular to the fast-axis printhead travel.
[0015] In another aspect, the invention relates to a method of determining a correction
factor(s) for aligning a plurality of printheads. The printheads need to operate in concert to
produce colored images. Due to printhead and mounting variations, the relative positions of the
printheads need to be measured, and corrections need to be applied to the printhead drive signals
15 to cause the various colors to be printed in the proper registration. Generally, a test pattern is
printed with the printheads to be aligned, assuming that they are perfectly positioned. The
resulting image is then scanned to determine the deviation of the images printed from their
perfect position. The information thus gained is then available to correct the identified errors.
The present approach differs from the prior art in at least its use of the harmonic content of the
20 signal obtained from scanning the test pattern to characterize misalignment. A scan traverses a
plurality of nominally identical line pairs, averaging out the irregularities inherent in an image
printed in powder. Imaging optics are unnecessary, since no edge detection is involved.
[0016] Specifically, the method includes the steps of printing a test pattern on a build
surface, generating a set of electrical signals representative of the test pattern, analyzing the

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electrical signals to determine their harmonic content at at least one frequency, and determining a
correction factor(s) based on the harmonic content of the electrical signals. The test pattern can
include a line pair array. In one embodiment, the method includes generating a plurality of
electrical signals for analysis and determining a plurality of correction factors based on the
5 harmonic content of the plurality of electrical signals.
[0017] In various embodiments, the method includes generating the electrical signal by
illuminating the test pattern and measuring reflectance of the test pattern at predetermined
locations. In one embodiment, the step of analyzing the electrical signal includes applying an
analog filter (e.g., using op-amps) to the signal. In another embodiment, the step of analyzing
10 the electrical signal includes digitizing the signal and applying a digital filter (e.g., a Fast Fourier
Transform) to the signal. In one embodiment, the correction factor can be determined from a set
of third harmonic values. In another embodiment, the correction factor can be determined from a
set of first harmonic values. The correction factor can be near a nominal test bar displacement
for which a lowest value of the selected harmonic is determined. The correction factors can be
15 determined by locating a minimum value of an analytical curve that has been fitted to, or
representative of the set of third harmonic values. One embodiment of the method includes the
steps of extracting third harmonic values from the signals acquired by scanning the sensor across
the array, comparing the set of third harmonic values obtained for each color, and determining
the correction factors based on the minimum third harmonic values.
20 [0018] In another aspect, the invention relates to the servicing of a plurality of printheads in
a three-dimensional printer. In general, quality of the parts produced in the 3-D printing process
depends upon the reliable and accurate delivery of droplets of binder liquid from the nozzle
arrays located on the faces of the printheads. To maintain high performance standards, the
printheads must be serviced frequently during the 3-D printing process. The impact of droplets

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of binder liquid on the surface of the powder bed causes powder particles to be ejected from the
surface of the bed. Some of the ejected material collects on the faces of the printheads,
interfering with the delivery of binder liquid droplets. A principal purpose of the printhead
servicing is to remove this accumulated debris from the printhead faces.
5 [0019] One aspect of printhead servicing is a service station, which includes a cleaning
station, a discharge station, and a capping station. In one embodiment, the printheads are
disposable within a carriage capable of moving in at least two directions relative to the service
station. Another aspect of printhead servicing is a software algorithm that specifies when each
printhead needs to be serviced. In one embodiment, the printheads are disposable within a
10 carriage capable moving in at least two directions relative to the service station.
[0020] Various embodiments of the cleaning station include at least one receptacle for
receiving a printhead, at least one nozzle for spraying a cleaning fluid towards a printhead face
(or printing surface) of the printhead, and a wiper disposable in close proximity to the printhead
face for removing excess cleaning fluid, in some cases without contacting the printhead face.
15 The cleaning station can further include a splash guard for isolating the printhead face and
preventing the cleaning fluid from migrating beyond the printhead face. The splash guard
includes an open position and a sealed position, where the splash guard is biased open and is
actuated from the open position to the sealed position by contact with a printhead. The splash
guard can include a sealing lip that circumscribes the printhead face when in the sealed position.
20 In one embodiment, the sealing lip is generally rectangular in shape. The wiper can be formed
by one side of the sealing lip and can include a notched portion configured and located to
correspond to a location of a jet nozzle array on the printhead face to prevent the wiper from
contacting the jet nozzle array. The wiper is capable of movement relative to a printhead.

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[0021] Further, the cleaning station can include a fluid source for providing the cleaning
fluid to the at least one nozzle under pressure. The cleaning fluid can be provided to the at least
one nozzle via a manifold. In one embodiment, the at least one nozzle includes an array of
nozzles. The at least one nozzle can be positioned to spray the cleaning fluid across the
5 printhead face. In one embodiment, the printheads are disposed within a carriage capable of
movement in two directions with respect to the service station.
[0022] Various embodiments of the discharge station include a receptacle defining an
opening that generally corresponds to a printhead face of a printhead. The receptacle defines a
plurality of corresponding openings in one embodiment. The receptacle can include a tray for
10 capturing and/or directing discharged fluids. In one embodiment, the discharge from the
printheads is directed into a standing pool of waste liquid.
[0023] Various embodiments of the capping station include a printhead cap carrier and at
least one printhead cap disposed on the carrier for sealing a printhead face of a printhead. The
cap is moved between an off position and a capped position by the printhead contacting the
15 carrier. The capping station can include a plurality of caps disposed on the carrier. In one
embodiment, the carrier is biased to maintain the at least one cap in an off position. The
discharge station and the capping station can be a combined station. In such an embodiment, the
discharge from the printheads can be constrained in a cavity defined by a printhead face, a
printhead cap, and the standing pool of waste liquid.
20 [0024] In another aspect, the invention relates to an apparatus for cleaning a printhead. The
apparatus includes at least one nozzle for spraying a cleaning fluid towards a printhead face of
the printhead and a wiper disposable in close proximity to the printhead face for removing excess
cleaning fluid from the printhead face.

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[0025] In one embodiment, the apparatus includes a splash guard for isolating a printhead
face and preventing cleaning fluid from migrating beyond the printhead face. The splash guard
can include an open position and a sealed position, where the splash guard is actuated from the
open position to the sealed position by contact with a printhead. In addition, the splash guard
5 can include a sealing lip that circumscribes the printhead face when in the sealed position. The
sealing lip is generally rectangular in shape. In one embodiment, the wiper is formed by one side
of the sealing lip. The wiper can include a notched portion configured and located to correspond
to a location of a jet nozzle array on the printhead face to prevent the wiper from contacting the
jet nozzle array. The wiper is capable of movement relative to a printhead. Additionally, the
10 apparatus can include a fluid source for providing cleaning fluid to the at least one nozzle under
pressure. The at least one nozzle can an array of nozzles and can be positioned to spray the
cleaning fluid across a printhead face.
[0026] In another aspect, the invention relates to a method of cleaning a printhead. The
method includes the steps of positioning a printhead face of the printhead relative to at least one
15 nozzle, operating the at least one nozzle to spray cleaning fluid towards the printhead face, and
causing relative movement between a wiper and the printhead to pass the wiper in close
proximity to the printhead face to remove excess cleaning fluid. The wiper can include a notch
configured and located on the wiper to correspond to a jet nozzle array on the printhead face to
prevent the wiper from contacting the jet nozzle array.
20 [0027] In various embodiments, the step of positioning the printhead face includes sealing
the printhead face to prevent the cleaning fluid from migrating beyond the printhead face. The
operating step can include spraying the cleaning fluid across the printhead face. In addition, the
printhead can be operated to discharge any cleaning fluid ingested by the printhead during
cleaning. In one embodiment, the at least one nozzle comprises an array of nozzles.

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[0028] In another aspect, the invention relates to an apparatus for cleaning a printhead used
in a three-dimensional printer. The apparatus includes a sealing cap defining a cavity and
capable of engagement with a printhead face of the printhead, a cleaning fluid source in
communication with the cap for cleaning the printhead face, and a vacuum source in
5 communication with the cap for removing used cleaning fluid and debris. In operation, the
vacuum source creates a negative pressure within the cavity, the negative pressure preventing the
cleaning fluid from entering a jet nozzle, drawing the cleaning fluid into the cavity from the
cleaning fluid source, and/or drawing at least one of a binder fluid and debris from the jet nozzle.
The apparatus may further include a wiper disposed proximate the cap, the wiper positioned to
10 engage the printhead face as the printhead disengages from the cap.
[0029] In another aspect, the invention relates to a method of cleaning a printhead used in a
three-dimensional printer. The method includes the steps of engaging a printhead face of the
printhead with a sealing cap defining a cavity, drawing a vacuum in the cavity, and introducing a
cleaning fluid into the cavity and into contact with the printhead face. The method may further
15 include the step of removing the cleaning fluid from the cavity. In one embodiment, the method
includes the steps of disengaging the cap from the printhead face and wiping the printhead face
with a wiper. The step of drawing a vacuum creates a negative pressure within the cavity, the
negative pressure drawing the cleaning fluid into the cavity, preventing the cleaning fluid from
entering a jet nozzle and/or drawing at least one of a binder fluid and debris from the jet nozzle.
20 [0030] In still other embodiments, the invention can include alternative methods and
apparatus for cleaning the printheads apparatus. Methods of cleaning the printhead can include
wiping the printhead with a roller including a cleaning fluid, drawing a vibrating member across
the printhead, drawing a cleaning fluid across the printhead by capillary action through a wick,
and/or combinations thereof. In addition, the methods can include optionally the step of

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applying a vacuum to the printhead to remove debris. The apparatus for cleaning a printhead
used in a 3D printer can include a wick disposed adjacent the printhead for drawing a cleaning
fluid across the printhead.
[0031] In another aspect, the invention relates to an apparatus for cleaning a printhead used
5 in a 3D printer. The pressure in the interior of a printhead is typically lower than atmospheric
pressure. This negative pressure is balanced by the surface tension of the meniscuses that form
over the outlets of the printhead nozzles. It is desirable to flush the accumulated powder off the
face of the printhead with a clean wash solution without allowing the solution to be drawn into
the printhead when the meniscuses are destroyed. This goal is achieved in this apparatus by
10 maintaining an environment outside the printhead in which the pressure is lower than the
pressure inside the head. In addition, this induced pressure differential causes binder to flow out
of the heads through the nozzles, flushing out any powder that may have lodged in the nozzle
passageways. The apparatus includes a base, a cam track disposed within the base, a cap carrier
slidably engaged with the cam track, and a sealing cap defining a cavity and disposed on the
15 carrier. The cap being transportable into engagement with the face of the printhead by the
carrier. In various embodiments, the apparatus includes a cleaning fluid source in
communication with the cap for cleaning the printhead face and a vacuum source in
communication with the cap for removing used wash fluid and debris.
[0032] In further embodiments, the apparatus can also include a spring coupled to the carrier
20 and the base to bias the carrier into a receiving position for receiving the printhead. In one
embodiment, the carrier includes a stop disposed on a distal end of the carrier for engaging the
printhead as the printhead enters the apparatus. The printhead slides the carrier rearward along
the cam track after engaging the stop and until the printhead face and cap sealably engage. In a
further embodiment, the apparatus includes a latch pawl coupled to the base for engaging with

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the carrier to prevent forward movement of the carrier and a wiper disposed on a proximal end of
the carrier. The wiper is positioned to engage the printhead face as the printhead exits the
apparatus.
[0033] In still another aspect, the invention relates to a method of cleaning a printhead used
5 in a 3D printer. The method includes the step of receiving the printhead within an apparatus that
includes a base, a cam track disposed within the base, a cap carrier slidably engaged with the
cam track, and a sealing cap defining a cavity and disposed on the carrier. Additional steps
include engaging the face of the printhead with the cap, drawing a vacuum on the cavity, and
introducing a cleaning fluid into the cavity and into contact with the printhead face. In one
10 embodiment, the method includes the step of removing the cleaning fluid from the cavity. The
method can further include disengaging the cap from the printing surface and wiping the printing
surface with a wiper as the printhead is withdrawn from the apparatus.
[0034] In another aspect, the invention relates to an apparatus for cleaning or reconditioning
a printhead. The apparatus includes a nozzle array for spraying a washing solution towards a
15 face of a printhead and a wicking member disposed in proximity to the printhead face for
removing excess washing solution from the printhead face.
[0035] In various embodiments, the nozzle array includes one or more individual nozzles.
The wicking member and the printhead are capable of relative movement. A fluid source can
also be included in the apparatus for providing washing solution to the nozzle array under
20 pressure. In another embodiment, the wicking member includes at least one of a permeable
material and an impermeable material.
[0036] The nozzle array can be positioned to spray the washing solution at an angle with
respect to the printhead face. In another embodiment, the wicking member is disposed in close
proximity to the printhead face, without contacting print nozzles located on the printhead face.

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The spacing between the wicking member and the print nozzles can be automatically maintained.
In one embodiment, the spacing is maintained by causing a portion of the wicking member to
bear on the printhead face in a location removed from the print nozzles. The apparatus can also
include a basin for collecting washing solution and debris.
5 [0037] In another aspect, the invention relates to a method of cleaning or reconditioning a
printhead. The method includes the steps of positioning a face of the printhead relative to at
least one nozzle and operating the at least one nozzle to spray washing solution towards the
printhead face. Excess washing solution is then removed from the printhead face by passing a
wicking member in close proximity to the printhead face, without contacting the printhead face.
10 [0038] In one embodiment, the step of operating the at least one nozzle includes spraying the
washing solution at an angle to the printhead face. In another embodiment, the method can
include the step of operating the printhead to expel washing solution ingested by the printhead
during cleaning. The method can include automatically maintaining a space between the
wicking member and print nozzles located on the printhead face by, for example, causing a
15 portion of the wicking member to bear on the printhead face in a location removed from the print
nozzles.
[0039] In another aspect, the invention relates to a method of determining when a printhead
needs to be serviced. Servicing is needed to maintain adequate printhead performance.
Servicing is a time-consuming activity, however, and some aspects of the servicing process are
20 damaging to the printhead. It is therefore desirable to service a printhead on a schedule that
balances the positive and negative impacts of the process.
[0040] One approach to identifying a printhead in need of service is to infer the state of the
printhead indirectly from the information available about the ongoing printing process. It is
common, for example, to perform printhead servicing at intervals based on the time elapsed

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since last service, the number of droplets dispensed since last service, and the number of layers
printed since last service. Printhead service is performed when one or another of these indicative
factors reaches a predetermined trigger value. Alternatively, service-triggering variables may be
defined that are weighted functions of two or more indicative factors. In one implementation,
5 the trigger values for one or more of the indicative factors are adjusted to match the
characteristics of the powder and binder liquid materials in use. The specific factors and
corresponding trigger values may be selected to suit a particular application, environment, and/or
printhead.
[0041] It is particularly desirable to identify characteristics of the images being printed that
10 can be related quantitatively to the need for printhead service. One such factor is based on the
observation that the impact of droplets printed on the powder bed ejects less debris when the
underlying previous layer was printed. The binder printed on the previous layer tends to bind the
powder in the fresh layer, resulting in less debris being ejected, and correspondingly less debris
accumulating on the printhead face. Accordingly, in one implementation, printhead servicing is
15 performed when the number of droplets printed over previously unprinted powder reaches a
predetermined trigger value. Alternatively, a service interval based on the number of droplets
dispensed since the last service may be modified to take into account the proportion of the
droplets that were printed over previously unprinted powder. In another implementation, the
underlying layer is considered to be unprinted if the pixel immediately underneath or any of its
20 near neighbors are unprinted.
[0042] In another aspect, the invention relates to a method of determining a condition of a
printhead in use in a three-dimensional printer. The method includes the steps of acquiring a
data value for at least one operational parameter of the printhead and comparing the data value to
a threshold value, the relationship of the data value to the threshold value indicative of the

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condition of the printhead. In one embodiment, the method includes the step of initiating a
service routine on the printhead if the data value exceeds the threshold value. The operational
parameter can be selected from the group consisting of time elapsed, number of droplets
dispensed by the printhead, number of layers printed, droplets dispensed over previously printed
5 powder, droplets dispensed over previously unprinted powder, and combinations thereof.
Additionally, the data value can be compensated during acquisition to account for an operational
environmental factor of the three-dimensional printer, such as, for example, temperature,
humidity, binder material, and/or build material.
[0043] In another aspect, the invention relates to a method of determining a condition of a
10 printhead in use in a three-dimensional printer. The method includes the steps of counting
droplets dispensed by the printhead and determining a percentage of the droplets that were
dispensed over previously unprinted pixels. The method can include the step of initiating a
service routine on the printhead if the percentage exceeds a threshold value.
[0044] These and other objects, along with advantages and features of the present invention
15 herein disclosed, will become apparent through reference to the following description, the
accompanying drawings, and the claims. Furthermore, it is to be understood that the features of
the various embodiments described herein are not mutually exclusive and can exist in various
combinations and permutations.
BRIEF DESCRIPTION OF THE DRAWINGS
20 [0045] In the drawings, like reference characters generally refer to the same parts throughout
the different views. In addition, the drawings are not necessarily to scale, emphasis instead
generally being placed upon illustrating the principles of the invention. In the following
description, various embodiments of the present invention are described with reference to the
following drawings, in which:

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[0046] FIG. 1 is a schematic perspective view of a three dimensional printer in accordance
with one embodiment of the invention;
[0047] FIG. 2 is a schematic perspective view of a printhead carriage in accordance with one
embodiment of the invention;
5 [0048] FIGS. 3A and 3B are a schematic perspective view and a schematic plan view,
respectively, of a service station in accordance with one embodiment of the invention;
[0049] FIG. 4 is a schematic representation of the interaction between the carriage and the
service station during performance of a discharge function in accordance with one embodiment
of the invention;
10 [0050] FIGS. 5A-5D are schematic representations of one embodiment of a printhead
capping operation in accordance with one embodiment of the invention;
[0051] FIGS. 6A-6D are schematic representations of a printhead discharge and capping
operation in accordance with an alternative embodiment of the invention;
[0052] FIGS. 7A-7D are schematic representations of a printhead cleaning station in
15 accordance with one embodiment of the invention;
[0053] FIGS. 8A-8H are schematic representations of an alternative embodiment of a
printhead cleaning station in accordance with the invention;
[0054] FIGS. 9A and 9B are schematic representations of another alternative embodiment of
a printhead cleaning station in accordance with the invention;
20 [0055] FIGS. 10A-10D are schematic representations of yet another alternative embodiment
of a printhead cleaning station in accordance with the invention;
[0056] FIGS. 11 A-l 1J are schematic representations of one embodiment of an apparatus and
method for cleaning a printhead in accordance with the invention;

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[0057] FIG. 12 is a schematic representation of a step of the method of cleaning a printhead
in accordance with the embodiment of the invention depicted in FIGS. 11A-11J;
[0058] FIG. 13 is a schematic perspective view of a printing operation in accordance with
one embodiment of the invention;
5 [0059] FIGS. 14A and 14B are schematic representations of the impact of a liquid binder
droplet on a build surface;
[0060] FIG. 15 is a schematic perspective view of a printhead alignment process in
accordance with one embodiment of the invention;
[0061] FIGS. 16A and 16B are schematic representations of a contrast test target and test
10 pattern alignment method in accordance with one embodiment of the invention;
[0062] FIGS. 17A-17D are schematic representations of an alignment sensor system and
associated electronics in accordance with one embodiment of the invention;
[0063] FIG. 18 is a schematic representation of one step in a method of aligning color
printheads in accordance with one embodiment of the invention;
15 [0064] FIGS. 19A and 19B are detailed schematic representations of a test pattern in
accordance with one embodiment of the invention;
[0065] FIGS. 20A-20D are detailed schematic representations of the horizontal alignment
process in accordance with one embodiment of the invention; and
[0066] FIGS. 21A and 21B are detailed schematic representations of the vertical alignment
20 process in accordance with one embodiment of the invention.
DETAILED DESCRIPTION
[0067] Embodiments of the present invention are described below. It is, however, expressly
noted that the present invention is not limited to these embodiments, but rather the intention is

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that variations, modifications, and equivalents that are apparent to the person skilled in the art are
also included.
[0068] In brief overview, FIG. 1 is a schematic representation of a 3D printer 10 for creating
an object in accordance with one embodiment of the invention. The printer 10 produces three-
5 dimensional objects by depositing alternating layers of build material and binder liquid on a
build surface 165 or in a container to print multiple layers that ultimately form the three-
dimensional object. In some embodiments, the build material may include a powder and the
binder liquid may be incorporated into the build material. In some embodiments, the printer 10
may be used to create physical prototypes for viewing and design review. In other embodiments,
10 the printer 10 may be used to create molds for casting operations, or prototypes that may be used
to collect market feedback on a potential product.
[0069] The printer 10 shown includes a gantry 12, a carriage 14, a service station assembly
16, and a test pattern 18. Typically, the gantry 12 is actuatable along the X-axis to manufacture
the object layer by layer. In some embodiments a motor may be coupled to the gantry 12. In
15 other embodiments, the gantry 12 may be coupled to a screw, such that rotation of the screw
moves the gantry 12 along the X-axis. In some embodiments, the gantry 12 may be actuatable
along the vertical Z-axis. Other positioning systems may be employed, as desired.
[0070] The carriage 14 typically includes printheads 20 capable of dispensing binder
materials necessary for creating an object (see FIG. 2). In some embodiments, as the gantry 12
20 moves along the X-axis, the carriage 14 moves back and forth along the Y-axis. The carriage 14
is coupled to the gantry 12. Thus, as the carriage 14 moves along with the gantry 12 across the
printer 10, binder material may be deposited in a two dimensional pattern during travel across
the surface of the printer 10 along the X-axis and the Y-axis. Then, typically, the next pass
across the printer 10 will be at a different plane in the Z-axis, and material deposited in that z-

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plane on the Z-axis will bind with previously deposited material as part of the formation of the
desired object. In one embodiment, a stepping-motor-driven piston underneath the build table
provides Z-axis motion.
[0071] To further improve performance, the printer 10 also includes the service station 16.
5 In some embodiments, the service station 16 is located at a fixed point on the printer 10.
Generally, the service station 16 services the printheads 20 carried by the carriage 14. The
service station 16 is generally the physical location where debris or excess materials that are on
or about the printheads 20 are removed. In some embodiments, excess binder material is
removed or discharged from the carriage 14. Generally, the carriage 14 is actuated into the
10 service station 16 for maintenance, storage, or preservation from damage. Typically, the service
station 16 may be located at any point on the printer 10 where it is possible for the carriage 14 to
be actuated to engage the service station 16. Also included in the printer 10 is a test pattern 18.
In some embodiments, the test pattern 18 is a test area passed over by the printhead 20 to refine
alignment of the carriage 14 in creation of an object.
15 [0072] In some embodiments, the carriage 14 can be moved for diagnostic or service
purposes. Moving the carriage 14 provides the user with access to the printheads 20 for
maintenance purposes, such as cleaning or replacement. Printhead cleaning is described in detail
with respect to FIGS. 6A-6D, 7A-7D, 8A-8J, 9A-9B, 10A-10D, 11A-11J, and 12. In some
embodiments, the printheads 20 may be actuated to run a diagnostic routine of the printheads 20.
20 In an alternative embodiment, the carriage 14 can be raised from the printer 10 for service
purposes.
[0073] In one embodiment, the printer 10 includes an enclosure cover to contain any dust or
other debris generated during a printing operation. The enclosed area can be heated to facilitate
better reactions between the build material and the binder materials. Better reactions include, for

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example, faster reaction times and improved bonding. In one embodiment, the heating is
accomplished by introducing warm air at a low velocity to the enclosed area. The flow of air is
typically not directed at the build surface to prevent disturbing the build material after spreading.
In one example, the enclosure temperature is maintained from about 90 degrees F to about 150
5 degrees F, preferably from about 110 degrees F to about 135 degrees F, and more preferably
about 125 degrees F.
[0074] FIG. 2 depicts one embodiment of the carriage 14 in more detail. The carriage 14
generally includes one or more printheads 20. Typically, a printhead 20 is the apparatus through
which binder liquid is ejected during the creation of an object. FIG. 2 shows four printheads 20;
10 however, in other embodiments there may be more or fewer printheads 20. In some
embodiments, the printheads 20 may be inserted into the carriage 14 such that they are offset
from one another along the X-axis. In some embodiments, this offset is by substantially the
same distance along the X-axis. In other embodiments, the printheads 20 may be staggered
within the carriage 14 such that the distances between the printheads 20 vary.
15 [0075] FIGS. 3A and 3B depict one embodiment of the service station 16 in greater detail.
The service station 16 typically includes a discharge station 22, a printhead capping station 24,
and a printhead cleaning station 29. In various embodiments, the carriage 14 may engage the
discharge station 22, the printhead capping station 24, and the printhead cleaning station 29 in
any order, and any number of times. In some embodiments, the carriage 14 may engage the
20 same station, for example the discharge station 22, multiple times consecutively. In other
embodiments, the carriage 14 can alternate repeatedly between any of the discharge station 22,
the printhead capping station 24, and the printhead cleaning station 29 in any order, any number
of times. In some embodiments, the printheads 20 of the carriage 14 engage the service station
16 in order to perform maintenance upon the printheads 20 during creation of an object.

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[0076] Generally, the discharge station 22 includes discharge openings 28 through which the ,
printheads 20 may discharge debris, such as, for example, contaminated binder. The number of
the discharge openings 28 may vary. The discharge station 22 is typically an area where the
printheads 20 may expel such material, thus preventing excess buildup of contaminants in the
5 printheads 20 that could effect printing quality. Typically, debris entering the discharge station
is contained so that it does not contaminate the printheads 20, the carriage 14, the service station
16, or any other component of the printer 10.
[0077] In some embodiments, the printheads 20 may be actuated to a point immediately
above the discharge openings 28, where the printheads 20 discharge excess binding material or
10 other waste through the discharge openings 28. Generally, this waste is collected in a receptacle
47 (see FIG. 4.) In some embodiments, the carriage 14 is actuated into a position immediately
above the service station 16 and the printheads 20 are positioned above the discharge openings
28 at the surface of the service station 16. In some embodiments, the bottom surfaces of the
printheads 20 may extend below the plane of the surface of the discharge openings 28, where the
15 printheads 20 may discharge material in order to rid the printheads 20 of contamination or excess
building materials. This material then enters the receptacle 47. In one embodiment, the
discharge openings 28 are located above the receptacle 47. Generally, the receptacle 47 is a
location below the discharge openings 28 where the printheads 20 discharge their material. In
some embodiments, the receptacle 47 may include a reservoir for containing the discharged
20 material.
[0078] Generally, the printhead capping station 24 is the area where the printheads 20 are
capped by the printhead caps 26. In one embodiment, there is one printhead cap 26 for each
printhead 20. Generally, as a result of the carrier 14 engaging the printhead capping station 24,
the printhead caps 26 are actuated into a position circumscribing the printheads 20, such that the

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printhead caps 26 form a seal around the printhead face 54 (see FIG. 5D). The printhead caps 26
protect the printheads 20 against contamination, debris, and physical damage resulting from
contact with the printheads 20, deterioration, and the elements in general. Generally, the
printhead capping station 24 may cap printheads 20 at any point in time relative to the printheads
5 20 engaging the discharge station 22 or the printhead cleaning station 29. Generally, the
printhead caps 26 enclose the printheads 20 in order to form a seal to prevent damage, such as
drying out, from occurring to the printheads 20. In some embodiments, maintenance may
include cleaning on or about the printheads 20. Only a single service station 16 is shown for
descriptive purposes; however, multiple stations 16 may exist. Alternatively, a single service
10 station 16 may service multiple printheads 20 by, for example, successively positioning the
printheads 20 relative to the service station 16.
[0079] The printhead cleaning station 29 generally includes the area where the printheads 20
may be cleaned. In one embodiment, the printheads 20 may be cleaned with a pressurized
washing solution 92 (see FIG. 8E). In some embodiments, the printheads 20 enter the printhead
15 cleaning station 29 after the printheads 20 discharge material into the receptacle 47. In other
embodiments, the printheads 20 may enter the printhead cleaning station 29 without first
discharging material into the receptacle 47. In further embodiments, the printheads 20 may enter
both the printhead cleaning station 29 and the discharge station 22 repeatedly and in any order.
Typically, the cleaning station 29 cleans the printheads 20 by washing them in such a manner
20 that any debris is removed from the printheads 20 and the pressurized washing solution 92 itself
is contained so it does not contaminate the printheads 20, or any other part of the printer 10. For
example, in one embodiment, the printheads 20 are cleaned in a sealed environment to contain
any debris and cleaning materials. In another embodiment, the printheads 20 are protected
during cleaning so that there is no excess debris or cleaning materials left on the printheads 20

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that may later drip onto any component of the printer 10, for example, the build surface 165. In
one embodiment, the printheads 20 are cleaned one at a time. In another embodiment, the
printheads 20 may be cleaned simultaneously. In other embodiments, the printhead(s) 20 may be
cleaned repeatedly, in any order, and at any time relative to engagement of the carrier 14 with
5 any other components of the service station 16. In one embodiment, the printer 10 includes logic
for determining when to clean the printheads 20, as discussed in greater detail hereinbelow.
[0080] FIG. 3B is a plan view of the service station 16 of FIG. 3A. From this perspective,
the carriage 14 is actuated along the X-axis such that the printheads 20 are aligned with the
discharge openings 28. In one embodiment, upon completion of this alignment, the printheads
10 20 discharge residual or waste material through the discharge openings 28. In some
embodiments, the discharge may include binder material or other building material. In some
embodiments, after discharge, the printheads 20 are further actuated along the X-axis to the
printhead capping station 24, where the printhead caps 26 form a seal around the printheads 20.
The seal formed by the printhead caps 26 around the printheads 20 generally protects the
15 printheads 20 from the elements, contamination from debris or left over binding material, and
prevents the printheads 20 from drying out.
[0081] FIG. 4 is a graphical representation of the discharge function of an embodiment of the
invention, whereby binder material and debris 41 is discharged from the printhead 20. In some
embodiments, the binder debris 41 may include excess building material. In some embodiments,
20 this discharge function is performed after every pass of the carriage 14 across the build surface
165. In other embodiments, the discharge function may be performed periodically after any
given number of passes of the carriage 14. In still other embodiments, this function may be
performed at fixed time intervals. In this illustrative embodiment, the carriage 14 is positioned
above the service station 16 such that the printhead 20 is lined up over a spatial gap in between

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the aperture plates 40. In some embodiments, the aperture plates 40 include the solid surface
surrounding the discharge openings 28 (see FIG. 3B). After proper positioning of the carriage
14, the printhead 20 discharges the debris 41 or other waste. Generally, this debris 41 includes
contaminants, such as, for example, excess binder material left in the printhead 20. In one
5 embodiment, the debris 41 joins the waste liquid 42 in the waste liquid catch tray 43. In some
embodiments, the waste liquid 42 may include discharge from past discharges of the printheads
20Upon discharge, the droplets of binder liquid 41 impinge upon the surface of the standing
pool of waste liquid 42, minimizing splash and the consequent generation of undesirable waste
liquid aerosols. A spillway 44 is located at a distance above the bottom of receptacle 47
10 sufficient to maintain the standing pool of waste liquid 42. Generally, the waste liquid 42 then
proceeds down the spillway 44 where it eventually exits the service station 16 via a drain 45. In
some embodiments, any overflowing waste liquid 46 also exits the waste liquid catch tray 43 via
the drain 45, thus preventing contamination to the service station 16.
[0082] FIG. 5A illustrates one embodiment of the capping function of the invention,
15 whereby each printhead 20 is sealed by a cap. In some embodiments, this capping function may
be performed after any given number of passes across the printer 10. In still other embodiments,
this function may be performed at a fixed time interval or after completion of printing. In FIG.
5B, the carriage 14 is actuated along the X-axis and positioned over the service station 16. In
this illustrative embodiment, there is a spatial gap between the printhead 20 and the printhead
20 cap 26. At this point, the printhead cap 26 has not yet capped the printhead 20. Generally, the
printhead cap 26 remains stationary until the printhead cap actuator 50 engages the printhead cap
carrier 52. In some embodiments, the carriage 14 has already moved beyond the aperture plate
40 and the discharge openings 28 and, thus, in some embodiments, the printhead 20 may have
already expelled debris 41 into the waste liquid catch tray 43. In some embodiments, the

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carriage 14 may have already actuated over the printhead cleaning station 29. In some
embodiments, as the carriage 14 continues actuation along the X-axis, the printhead cap actuator
50 engages the printhead cap carrier 52. Generally, the printhead cap actuator 50 may include
metal, plastic, or rubber appendages of sufficient rigidity to move the printhead cap carrier 52
5 along the X-axis along with the carriage 14.
[0083] FIGS. 5C-5D illustrate the completion of the capping function. Typically, the
printhead cap carrier 52 is a metal or other solid material fixed to the service station 16 and
including a spring coefficient, such that movement of the carriage 14 and the printhead cap
actuator 50 along the X-axis causes the printhead cap carrier 52 to move along the X-axis in this
10 same direction. In some embodiments, this X-axis movement of the printhead cap carrier 52
then causes the printhead caps 26 to move along the Z-axis where they eventually cap the
printheads 20. In other embodiments, the carriage 14, including the printhead cap actuators 50,
and the printhead cap carrier 52 cease movement in the direction of carriage motion 53, and the
printheads 20 are capped.
15 [0084] Generally, the printhead cap actuator 50 engages the printhead cap carrier 52, causing
the printhead cap carrier 52 to move in the direction of the printhead cap actuator 50 motion. In
some embodiments, the printhead cap carrier 52 includes a spring element 601, whereby the
printhead cap carrier will pivot relative to the outer wall of the service station 16 when the spring
601 element is compressed. This pivot results in an uneven actuation of the printhead cap 26
20 towards the printhead 20. As a result, the edge of the printhead cap 26 farthest from the
printhead cap actuator 50 will initiate contact with the printhead 20. In other embodiments, it is
the edge of the printhead cap 26 located closest to the printhead cap actuator 50 that initially
contacts the printhead 20 first. In either of the above illustrative embodiments, the printhead cap
26 continues actuation towards the printhead 20 until the printhead cap 26 levels off and

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circumscribes the printheads 20. In some embodiments, the printhead cap 26 forms a seal
around the printheads 20. In one embodiment, one printhead 20 is capped by one printhead cap
26. In one embodiment multiple printhead caps 26 cap multiple printheads 20. Generally, there
is one printhead cap 26 used each printhead 20. Generally, the printheads 20 may be capped by
5 the printhead caps 26 any number of times and in any order relative to engagement of the
carriage 14 with any other component of the printer 10.
[0085] As shown in FIGS. 5C and 5D, the printhead cap carrier 52 includes an arm 600, a
spring element 601, and a plate 602. Generally, the arm 600 is engaged by the printhead cap
actuator 50 and is moved in the direction of the printhead cap actuator 53 motion. This
10 movement causes the spring element 601 to compress, resulting in a pivoting motion. This
pivoting motion causes the plate 602 to move towards the printhead 20. The printhead cap 26 is
typically disposed on a top surface of the plate 602. In one embodiment, the plate 602 is rigid
and, thus, the printhead cap 26 approaches the printhead 20 on a skew, such that one edge of the
printhead cap 26 engages the printhead 20 before any of the other edges of the printhead cap 26
15 engage the printhead 20. In various embodiments, any edge of the printhead cap 26 may first
engage the printhead 20. Typically, after the first engagement between any edge of the printhead
cap 26 and the printhead 20 the plate 602 continues its motion until the printhead cap 26
circumscribes the printhead 20. Specifically, the plate 602 may bend or flex in response to the
actuation force of the carriage 14 until the plate 602 adopts a substantially horizontal orientation.
20 [0086] FIG. 5C includes a cutaway cross-sectional view of the service station 16 and the
carriage 14. In this illustrative embodiment, the carriage 14 is actuated along the X-axis in the
indicated direction of carriage motion (arrow 53). The printhead cap actuator 50 will come into
contact with the printhead cap carrier 52 and both the printhead cap actuator 50 and the printhead
cap carrier 52 will move in the direction of carriage motion 53. In this illustrative embodiment,

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the printhead cap 26 is located upon the printhead cap carrier 52. Thus, movement of the
printhead cap carrier 52 in the direction of carriage motion 53 causes the printhead cap 26 to
move along the Z-axis. FIG. 5C includes a cut-away graphical representation of the carriage 14
and the service station 16. FIG. 5C illustrates the point of contact between the printhead cap
5 actuator 50 and the printhead cap carrier 52 as the carriage 14 moves in the direction of carriage
motion 53. In this embodiment, at this point, there is a spatial gap between the printhead 20 and
the printhead cap 26 and therefore the printhead cap 26 has not sealed the printhead 20.
[0087] FIG. 5D is a graphical representation of the carriage 14 and the service station 16 at a
point forward in time from that of FIG. 5C, such that the printhead cap 26 has capped the
10 printhead face 54 of the printhead 20. Typically, the printhead face 54 includes the bottom face
of the printhead 20 including and surrounding the point where the binder material is expelled
from the printhead 20. In this illustrative embodiment, the carriage motion 53 has caused the
printhead cap actuator 50 to engage and move the printhead cap carrier 52 in the direction of
carriage motion 53. In this embodiment, the printhead face 54 has a protective seal formed
15 around it by the printhead cap 26. Generally, the cap or seal is sufficient to protect the printhead
face 54 from damage or contamination. In some embodiments, the seal formed by the printhead
cap may be airtight.
[0088] FIG. 6A is a partial cross sectional side view of an alternative embodiment of a
service station 16 including a combined discharge and capping station. In this illustrative
20 embodiment, the carriage 14 is actuated in the direction of carriage motion 53, (along the X-axis)
and positions itself over the service station 16. In some embodiments, this actuation of the
carriage 14 may be in preparation for discharge from the printhead 20. In this illustrative
embodiment, the waste liquid catch tray 43 includes waste liquid 42. Generally, this waste liquid
42 was produced by previous discharges from past passes of the printhead 20 over the service

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station 16. In some embodiments, the lower edge of the printhead cap 60 may extend into the
area defined by the waste liquid catch tray 43, but generally the lower edge of printhead cap 60
does not contact the bottom surface of the waste liquid catch tray 43 and, thus, waste liquid 42
flows freely and collects in waste liquid catch tray 43 until the waste liquid surface 61 rises to
5 the top of spillway 44. At this point, the waste liquid 42 then enters the waste liquid overflow
tube 63 via overflow slot 62. Generally, waste liquid overflow tube 63 carries the waste liquid
42 out of the service station 16.
[0089] FIGS. 6B through 6D depict the capping and the discharge functions in greater detail.
The carriage 14 is moving in the direction of carnage motion 53, and is being positioned over the
10 service station 16. FIG. 6B illustrates an embodiment where contact has been made between the
printhead cap actuator 50 and the printhead cap carrier 52, but where the printhead cap carrier
has not yet moved far enough in the direction of carriage motion 53 to lift the printhead cap 26 to
a position where it caps the printhead 20. FIG. 6C illustrates an embodiment of a point further in
time from that of FIG. 6B. As shown in FIG. 6C, the printhead cap carrier 52 has moved the
15 necessary distance in the direction of the carriage motion 53 to lift the printhead cap 26 to a point
where it has formed a seal around the printhead 20. The capping function is substantially similar
to that described with respect to FIGS. 5A-5D. In some embodiments, the printhead cap 26
includes a discharge column 67 that defines a cavity 64. The printhead 20 discharges to the
waste liquid catch tray 43 through the discharge column. As shown in FIG. 6C, the printhead 20
20 expels debris 41 into the waste liquid catch tray 43, where it mixes with any existing waste liquid
42. In some embodiments, the collection of the waste liquid 42 will cross the spillway 44 and
proceed to travel through the overflow slot 62 and down waste liquid overflow tube 63 as
overflowing waste liquid 65, where it is eventually expelled from service station 16. Generally,
this discharge procedure ensures a clean and clog free printhead 20 and printhead face 54 to

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maintain the highest possible quality three dimensional printing. In some embodiments, multiple
printheads 20 may discharge material at substantially the same time.
[0090] Referring again to FIG. 6C, in some embodiments, a seal may be formed in the area
defined by the discharge cavity 64. Generally, the cavity 64 is bounded on the top by the
5 printhead 20 and the printhead cap 26, on the bottom by the waste liquid surface 61, and on the
sides by the discharge column 67. In one embodiment, the level of the surface of the waste
liquid 61 in the waste liquid catch tray 43 is sufficiently high to submerge a bottom portion of
the discharge column 67. The bottom portion of the discharge column 67 has a lowest point
below the lowest point of the spillway 44, which prevents the waste liquid 42 from dropping
10 below the lowest portion of the discharge column. In such a case, and where the printhead cap
26 is sealed against the printhead face 54 of the printhead 20, the cavity 64 is airtight, thereby
preventing the printhead face 54 from drying out. In this embodiment, the discharge 41 is
prevented from escaping the cavity 64 in any direction other than through the waste liquid
overflow tube 63, where it harmlessly exits the service station 16. This exemplary embodiment
15 minimizes the risk of contamination by the discharge 41 to any components of the printer 10.
[0091] FIGS. 7A-7D depict one embodiment of a printhead cleaning station 500 in
accordance with the invention. The printhead cleaning station 500 may also be mounted in the
service station 16. The printhead cleaning station 500 includes a reservoir 542 that holds a
washing solution 543 and a pump 545 that delivers the washing solution 543 under pressure to at
20 least one nozzle 540 and preferably an array of nozzles 540. The nozzles 540 are capable of
producing a high velocity stream of washing solution 543. In operation, the nozzles 540 are
directed to the printhead face 577 of the printhead 520. When directed onto the printhead face
577, the washing solution 543 loosens and removes contaminants, such as build material and
binding material, from the printhead face 577. The orientation of the nozzles 540 may be angled

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with respect to the printhead face 577, such that a fluid flow is induced across a plane of the
printhead face 577. For example, the washing solution can contact the printhead 520 at the side
nearest the nozzles 540 and drain from the side of the printhead 520 furthest from the nozzles
540. This approach improves the efficacy of the stream of washing solution 543 by reducing the
5 accumulation of washing solution on the printhead face 577, as well as the amount of washing
solution 543 and debris that would otherwise drain near and interfere with the nozzles 540. A
splash guard may also be included in the printhead cleaning station 500 to contain splashing
resulting from the streams of liquid washing solution 543.
[0092] It is desirable to remove a large portion of the washing solution 543 that remains on
10 the printhead face 577 after the operation of the nozzles 540 is complete. This is conventionally
accomplished by drawing a wiping element across the printhead face 577. A disadvantage of
this approach is that contact between the wiping element and the printhead face 577 may degrade
the performance of the printhead 520 by, for example, damaging the edges of the inkjet nozzle
orifices. Accordingly, it is an object of this invention to provide a means of removing
15 accumulated washing solution from the printhead face 577, without contacting the delicate
region around the inkjet nozzles. In one embodiment, a wicking member 544 may be disposed
such that the printhead face 577 may pass one or more times over its upper surface 546 in close
proximity, without contact, allowing capillary forces to draw accumulated washing solution 543
away from the printhead face 577. The wicking member 544 may be made from rigid, semi-
20 rigid, or compliant materials, and can be of an absorbent or impermeable nature, or any
combination thereof.
[0093] For the wicking member 544 to effectively remove accumulated washing solution
543 from the printhead face 577, the gap between the upper surface 546 of the wicking member
544 and the printhead face 577 must be small, a desirable range being between about 0 inches to

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about 0.03 inches. A further object of this invention is to provide a means for maintaining the
gap in this range without resort to precise, rigid, and costly components.
[0094] In another embodiment, the wicking member 544 may consist of a compliant rubber
sheet oriented approximately orthogonal to the direction of relative motion 547 between the
5 wicking member 544 and the printhead 520 and with a portion of its upper surface 546 disposed
so that it lightly contacts or interferes with the printhead face 577 only in non-critical areas away
from the printhead nozzle orifices. The upper surface 546 of the wicking member 544 may
include one or more notches 548 at locations where the wicking member 544 might otherwise
contact delicate components of the printhead face 577. System dimensions are selected so that
10 the wicking member 544 always contacts the printhead face 577, and is deflected as the
printhead 520 passes over it, independent of expected variations in the relative positions of the
printhead 520 and the printhead cleaning station 500. The upper surface 546 accordingly follows
the position of the printhead face 577, maintaining by extension a substantially constant space
between the printhead face 577 and the relieved surface notch 548. To further prolong the life of
15 the printhead 520, a bending zone of the wicking member 544 can be of reduced cross-section to
provide reliable bending behavior with little deformation of the upper surface 546 of the wicking
member 544.
[0095] FIGS. 7B-7D illustrate a reconditioning cycle in accordance with the invention. FIG.
7B shows the printhead 520 approaching the printhead cleaning station 500 along a path
20 designated by arrow 547. When the printheads 520 lightly contact the wicking member 544, as
shown in FIG. 7C, motion stops along the path 547 and the washing solution 543 is directed at
the printhead face 577 by the nozzle array 540. When the spraying operation is complete, the
printhead 520 continues to travel along the path 547, as shown in FIG. 7D. The wicking member
544 is further deflected to allow passage of the printhead 520, and the accumulated washing

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solution 543 is wicked away from the printhead face 577. After being sprayed and wiped, in
some embodiments the printhead 520 may print a plurality of droplets to eject any washing
solution that may have been ingested during the reconditioning process.
[0096] Additional cleaning methods are contemplated, such as wiping the printhead face 577
5 with a cylindrical "paint roller" that cleans and moistens itself by rolling in a reservoir of wash
fluid. In another embodiment, a cleaning system could include a continuous filament that carries
wash fluid up to printhead face 577 and carries debris away to a sump. The system may include
a small scraper that can be run over the filament to remove built up debris.
[0097] FIG. 8A depicts an alternative embodiment of cleaning a station 529 in accordance
10 with the invention. Generally, the printer 10 is capable of determining when to clean the
printheads 20 via the service station 16, as will be described in greater detail hereinbelow. In
some embodiments, only a single printhead 20 is cleaned by the service station 16. In other
embodiments, multiple printheads 20 are cleaned. In some embodiments, the service station 16
includes a nozzle manifold 80. Generally, the nozzle manifold 80 includes at least one nozzle
15 540 and preferably and array of nozzles 540. In some embodiments, the service station 16
includes a splash guard 81. Generally, the splash guard 81 is included in the printhead cleaning
station 529 to contain splashing resulting from the streams of the washing solution 543.
Typically, the splash guard 81 prevents contamination of powder or binding material by
containing the washing solution 543. Generally, the cleaning station 529 operates the same as
20 the cleaning station 500 described with respect to FIGS. 7A-7D, except for the addition of the
manifold 80 and the splash guard 81.
[0098] FIG. 8B is a graphical representation of the splash guard 81 that is located in the
printhead cleaning station 529. The splash guard 81 generally includes a notch 82, a drain
aperture 83, an actuation face 89, a flexure point 85, and a sealing lip 86. FIGS. 8C-8H depict

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the operation of the cleaning station 529. Typically, the printhead 20 is actuated such that the
printhead face 54 passes immediately over the notch 82 without contacting the surface of the
notch 82. Typically, avoiding contact between the printhead face 54 and notch 82 prevents
damaging or altering the trajectory of jet nozzles on the printhead face 54. In one embodiment,
5 the sealing lip 86 may act as a wiper, contacting the printhead 20 adjacent to the printhead face
54 without contacting the printhead face 54 itself. Once the printheads 20 have cleared the notch
82, they enter the space immediately above the drain aperture 83. Generally, the drain aperture
83 is for passing the washing solution 543. Once the printhead 20 is positioned roughly over the
drain aperture 83, the printhead 20 engages the actuation face 89. Typically, the printhead 20
10 engages the actuation face 89 in such a way as to cause the splash guard 81 to flex along the
flexure point 85. In some embodiments, the flexure point 85 includes a pivot point allowing at
least the portion of the splash guard 81 including the notch 82, the drain aperture 83, the
actuation face 89, and the sealing lip 86 to pivot in the direction of actuation of the printhead 20.
Generally, this pivot at the flexure point 85 raises the drain aperture 83 to the printhead 20 such
15 that the sealing lip 86 contacts the printhead 20. Generally, the sealing lip 86 is actuated into a
position where it forms a seal around the printhead face 54. Typically, the seal formed by the
sealing lip 86 is watertight, thus preventing the washing solution 543 from contaminating the
printer 10. Generally, the only available outlet for used washing solution 543 is through the
drain aperture 83.
20 [0099] FIG. 8C includes another perspective of the printhead 20 as it approaches the service
station 16. FIG. 8C generally represents the starting position of the cleaning operation
performed by the service station 16. In this illustrative embodiment, the printhead 20 is actuated
in the direction of the printhead motion 87 such that the printhead face 54 is brought above the
service station 16. As the printhead 20 is being actuated, the printhead side 88 will engage the

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actuation face 89 of the splashguard 81. After this engagement, the printhead 20 moves the
actuation face 89 such that the sealing lip 86 forms a seal around the printhead face 54 (see FIG.
8D). In some embodiments, the actuation face 89 pivots at the flexure point 85. In some
embodiments, the flexure joint 85 may include a spring element. Generally, this procedure
5 results in the forming of a watertight seal by the splash guard 81 around the underside of the
printhead 20 adjacent to the printhead face 54.
[0100] FIG. 8D depicts the printhead 20 moved into its desired position over the service
station 16. Generally, this is the point at which the service station 16 will clean the printhead 20.
As illustrated in FIG. 8D, the actuation face 89 seals the printhead 20 around part of the
10 printhead face 54. The seal is completed around the printhead face 54 by the splash guard lip 86.
Generally, the splash guard lip 86 is part of the splash guard 81. In one embodiment, as the
printhead 20 is actuating the splash guard 81 via its contact with the actuation face 89, the
resulting movement of the splash guard 81 also moves the sealing lips 86 into a position against
the bottom of the printhead 20 and along the printhead face 54. In some embodiments, the
15 sealing lips 86 come to rest against the underside of the printhead 20 against the printhead face
54. Generally, forming a seal around the printhead 54 on the underside of the printhead 20, as
opposed to along the printhead side 88, is desired as it prevents contamination of the printhead
side 88, or any other side of the printhead 20. For example, washing solution left on the
printhead 20 can drip off during printing, thereby effecting print quality.
20 [0101] FIG. 8E is a partially sectioned side view of the service station 16 during cleaning of
the printhead 20 by the service station 16 in accordance with one embodiment of the invention.
Subsequent to the forming of a seal around the printhead face 54, the nozzle manifold 80 sprays
the washing solution streams 91. Generally, the nozzle manifold 80 includes the pressurized
washing solution 92. In one embodiment, the pressurized washing solution 92 is sprayed onto

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the printhead face 54 in a single stream 91. In other embodiments, there are multiple streams 91
of the pressurized washing solution 92. In operation, the washing solution streams 91 are
directed at the printhead face 54 of the printhead 20. When directed onto the printhead face 54,
the washing solution streams 91 loosen and remove contaminants, such as binder material, from
5 the printhead face 54. The orientation of the washing solution streams 91 may be angled with
respect to the printhead face 54, such that a fluid flow is induced across a plane of the printhead
face 54. For example, in one embodiment, the washing solution stream 91 may contact the
printhead 20 at the side nearest the nozzle manifold 80 and drain from the side of the printhead
20furthest from the nozzle manifold 80. This approach improves the effectiveness of the
10 washing solution streams 91 by reducing the accumulation of the washing solution 92 on the
printhead face 54, as well as the amount of the pressurized washing solution 92 and debris that
would otherwise drain near and interfere with the nozzle manifold 80. FIG. 8F is another
partially sectioned view of the invention illustrated in FIG. 8E. The printhead face 54 is in
proper position for cleaning. The sealing lips 86 have formed a seal around the printhead face 54
15 thus protecting the remainder of the printhead 20 from contamination.
[0102] FIG. 8G illustrates the movement of the printhead 20 out of the service station 16
after a cleaning operation has been performed. The printhead 20 now moves in the direction of
printhead motion 93 away from the service station 16. This is generally the same as the direction
of carriage motion 53 that was used to enter the service station 16. As the printhead 20 is
20 actuating out of the service station 16, the printhead face 54 is carried over the sealing lip 86 and
the notch 82. In some embodiments, the sealing lip 86 may act as a wiper and remove debris and
washing solution 92 from the area on the bottom of the printhead 20 adjacent to the printhead
face 54; however, the notch 82 prevents contact between the sealing lip 86 and printhead face 54
in an area corresponding to the location of the jet nozzles. Contact between the sealing lip 86

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and the printhead face 54 may degrade the performance of the printhead 20 by, for example,
damaging the edges of the inkjet nozzle orifices on the printhead face 54. However, it is still
desirable to remove a large portion of the washing solution 92 that remains on the printhead face
54 after the operation of the nozzle manifold 80 is complete. Accordingly, it is an object of this
5 invention to provide a means of removing accumulated washing solution from the printhead face
54, without contacting the delicate region around the jet nozzles on the printhead face 54.
Because the notch 82 prevents direct contact between the sealing lip 86 and the printhead face
54, in one embodiment, a wicking member 544 (as described above) may be disposed such that
the printhead face 54 may pass one or more times over the wicking member 544 in close
10 proximity, without contact, allowing capillary forces to draw the accumulated pressurized
washing solution 92 away from the printhead face 54. FIG. 8H illustrates a partially sectioned
bottom perspective view of the service station 16 of FIG. 8A. Here it can be seen that the
sensitive portion of the printhead face 54 passes over the notch 82 as the printhead 20 is actuated
away from the service station 16 after a cleaning. Generally, the sensitive portion of the
15 printhead face 54 includes the printhead jet nozzle array.
[0103] FIGS. 9A and 9B illustrate an alternative embodiment of the splash guard 81 of FIG.
8B. In this embodiment, the splash guard 81 includes tapered sealing surfaces 94. Generally,
the tapered sealing surfaces 94 are shaped so that they will form a seal around the corners formed
by the printhead edges 95. Thus, the seal in this embodiment is formed by the tapered sealing
20 surfaces 94 contacting both the printhead face 54, and the printhead side 88 of the printhead 20.
Thus, the seal formed by this embodiment wraps around the edges of the printhead 20 to contain
the washing solution 92 during the cleaning operation. The operation of the alternative splash
guard 81 of FIGS. 9A and 9B and the associated cleaning components is substantially similar
that described hereinabove.

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[0104] [0100] FIGS. 10A-10D illustrate another alternative embodiment of the splash
guard 81 of FIG. 8B. In this embodiment, the splash guard 81 again forms a seal with the splash
guard sealing lips 86; however, in this embodiment, the splash guard 81 is actuated into its
sealed position around the printhead face 54 by a splashguard support spring 102. This
5 procedure is analogous to the procedure used to cap the printhead 20 in the capping operation.
Generally, the printhead 20 is carried over the service station 16 in the direction of a first
printhead motion (arrow 100). Once roughly positioned over the drain aperture 83, the direction
of the printhead motion changes direction to a substantially perpendicular printhead motion
(arrow 101). In some embodiments, the direction of the printhead motion 101 is orthogonal to
10 the previous direction of printhead motion 100. The printhead 20 now proceeds in the second
direction of the printhead motion 101 until the printhead side 88 engages the splash guard
support spring 102. (See FIG. 10B) As FIG. 10C illustrates, the splash guard support spring 102
moves in the direction of the second printhead motion 101. This moveinent engages the splash
guard 81 with the printhead face 54.
15 [0105] Once the cleaning operation is performed as described above, the printhead 20 moves
in a third direction of printhead motion (arrow 103) away from the service station 16. Generally,
the third direction of printhead motion 103 is opposite the first direction of printhead motion
100, as the printhead 20 disengages from the service station 16. This disengagement breaks the
seal formed by the splash guard sealing lip 86, and the printhead face 54 is carried over the
20 sealing lip 86 where a wiper operation may be performed to remove debris or the washing
solution 92 from the printhead face 54. As described above, a wicking operation may also be
performed.
[0106] FIGS. 11A-11J illustrate an alternative system 146 for cleaning the printhead 20. The
system 146 is located in the service station 16 (FIG. 1). In one embodiment, the system 146

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includes a cleaning station 148 made up generally of a latch pawl 152, a spring 154, a wiper 156,
a printhead cap 158, a cap carrier 192, a second spring 162, and a cam track 164. Only a single
cleaning station 148 is shown for descriptive purposes; however, multiple stations 148 may be
disposed in the service station 16. Alternatively, a single cleaning station 148 may service
5 multiple printheads 20 by, for example, successively positioning the printheads 20 relative to the
cleaning station 148.
[0107] FIG. 11A represents a starting position of the cleaning system 146. As sho-wn in FIG.
11B, the printhead 20 approaches the cleaning station 148 and engages the latch pawl 152. The
latch pawl 152 is actuated as the printhead 20 passes over the latch pawl 152. The printhead 20
10 continues to move past the latch pawl 152 and engages the wiper 156 (FIG. 11C). The printhead
20 passes over a wiper 156. As shown in FIG. 11D, the printhead 20 contacts the cap carrier
192, which is driven along the cam track 164 and compresses the spring 162. The printhead cap
26 is positioned against a printhead face 54 (FIGS. 11E and 11F). As shown in FIG. 1 1F, the
printhead cap 26 seals against the printhead face 54 while the face 54 is rinsed with washing
15 solution 92 (see FIG. 11F).
[0108] After the printhead face 54 is cleaned, the printhead 20 begins to move out of the
service station 16 (FIG. 11G). The latch pawl 152 engages the cap carrier 192, halting its
movement. As shown in FIG. 11H, the printhead 20 engages the wiper 156, which wipes the
printhead face 54. In an alternative embodiment, the wiper 156 vibrates to further clean the
20 printhead face 54. In an alternative embodiment, the wiper 156 may be notched in an area
corresponding to the location of the jet nozzles, thereby preventing contact between tine wiper
15 6 and the printhead face 54. The printhead 20 continues its forward movement, actuating the
latch pawl 152 (FIG. 11I), which, in turn, releases the cap carrier 192 (FIG. 11J). The cap carrier
192 snaps back to the start position. After the printhead face 54 is cleaned, the printhead 20

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begins to move out of service station 16 (FIG. 11G). The system 146 is now ready to clean
another printhead 20.
[0109] FIG. 12 depicts the system 146 for cleaning a printhead 20. (FIG. 12 also depicts
FIG. 11F in greater detail) The printhead 20 is positioned with the printhead face 54 against the
5 printhead cap 26, which in this embodiment is made of rubber. The cap includes a seal lip 172
for sealing about the printhead face 54. The service station 16 is coupled to a wash fluid supply
container 182 via a supply duct 184 and a wash fluid return container 186 via a return duct 188.
The wash fluid return container 186 is in communication with a vacuum source 180, in this case
a vacuum pump, via a vacuum duct 190. Additionally, a valve 178 is located in the return duct
10 188. The valve 178 may be manually or automatically actuated.
[0110] In operation, the vacuum source 180 creates a vacuum within a cavity 174 in the
printhead cap 54. The vacuum pulls wash fluid from the supply container 182 through the
supply duct 184. The wash fluid enters the cavity 174 as a spray 176 against the printhead face
54. The spray 176 washes debris, such as excess build material and dried binder, off the
15 printhead face 54. The used wash fluid and debris are drawn out of the cavity 174 by the
vacuum source 180 and into the return container 186 via the return duct 188. Additionally, the
negative pressure created in the cavity 174 by the vacuum source 180 prevents the wash fluid
from entering the jet nozzles and, in fact, may cause a small amount of binder to flow out of the
nozzles to flush any powdered build material out of the nozzles. Blockages or obstructions in the
20 jet nozzles can cause the jets to fire in the wrong direction. Once the operation is complete, the
system 146 moves onto the step depicted in FIG. 11G. In an alternative embodiment,
printhead(s) 20 are disposed above the service station 16. The sealing lip 86 is actuated into
alignment with the printheads 20, and the printheads 20 are wiped and lubricated from beneath to
remove any accumulated grit and to improve the flow of binding material out of the printheads

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20. Specifically, a lubricator applies a lubricant to the printhead face 20 to moisten any debris on
the printhead face 54. Then, the printhead 20 is moved to pass the printhead face 54 over sealing
lips 86, which act as a wiper and wipes the printhead face 54 clean.
[0111] FIG. 13 depicts a typical printing operation with a 3D printer in accordance with the
5 invention. Only one printhead 220 is shown for clarity. The printhead 220 moves over a powder
bed 200 that has been spread over a build surface of the 3D printer (se, for example, FIG. 1). As
previously described, the printhead 220 can move along an X-axis and a Y-axis. In the operation
depicted, the printhead 220 is moving in a single direction (arrow 202). As the printhead 220
travels above the powder bed 200, the printhead 220 performs a printing operation by depositing
10 droplets 212 of liquid binder on to the powder bed 200 in a predetermined manner, thereby
resulting in printed sections 204 and unprinted sections 206 in the powder bed 200.
[0112] After printing on the powder bed 200, a new layer of powder is spread over the
powder bed 200 in preparation for receiving the new printing 218. As the printhead 220 deposits
the droplets 212 onto the powder bed 200, particles 210 of the powder are ejected by the impact
15 of the droplets 212 on the powder bed 200 (see FIGS. 14A and 14B). These particles 210 may
eventually contact and adhere to the printhead 220. The resulting debris 216 degrades the
quality of printing by, for example, interfering with a printhead nozzle 208. The amount of
particles 210 ejected will depend, in part, on whether the powder is "wet" or "dry." The powder
is wet if the underlying layer was previously printed (see FIG. 14B). The powder is dry if the
20 underlying layer was previously unprinted (see FIG. 14A).
[0113] As shown in FIG. 14A, the printhead 220 is depositing droplets 212 on to a dry
powder bed 200. As the droplets 212 impact the powder bed 200, a relatively large volume of
particles 210 are displaced and a crater 214 is created in the powder bed 200. The particles 210

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are ejected upwardly towards the printhead 220, where they may collect as debris 216 on a face
of the printhead 220.
[0114] As shown in FIG. 14B, the printhead 220 is depositing droplets 212 on to a wet
powder bed 200. As the droplets 212 impact the powder bed 200, a relatively small volume of
5 particles 210 are displaced and a relatively small crater 214 is created in the powder bed 200.
The binder printed on the previous layer tends to bind the powder in the fresh layer, thereby
resulting in fewer particles being ejected, and correspondingly less debris accumulating on the
printhead face.
[0115] The 3D printer includes logic for monitoring the condition of the printhead 220 based
10 on, at least in part, the number of droplets printed over previously printed and/or unprinted
powder, since the last cleaning. Other factors include; for example, time in use, number of
droplets dispensed, and number of layers printed. The 3D printer can determine the frequency
and duration of any necessary cleaning routine, based on any one of the aforementioned factors
or combination of factors reaching a set threshold value. For example, the printhead 220 may be
15 cleaned after every five minutes of continuous use. The threshold values of any particular factor
can be varied depending on the types of liquid binder and powder materials used and other
operational environmental factors, such as temperature and humidity, that can affect printhead
condition.
[0116] Additionally or alternatively, the 3D printer can utilize other systems and methods
20 for monitoring and maintaining the cleanliness of the printhead 220. For example, in one
embodiment, the 3D printer could include an imaging system for viewing the printhead face. A
user could either manually determine that the printhead 220 requires cleaning or the 3D printer
could include the imaging system for automatically determining the need for cleaning. In a
manual system, an image of the printhead face is displayed to the user, for example on a video

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monitor, and the user can initiate a cleaning routine if deemed necessary. In one example of an
automatic system, the actual image of the face of the printhead in service is sent to a processor
for comparison to an image of a clean printhead face, (i.e., a test image). In one embodiment,
the printhead face is dark and the powder is relatively light in color. If a significant portion of
5 the printhead face is covered with debris, there will be a difference in contrast between the actual
image and the test image. If the difference in contrast reaches a predetermined threshold, the
system initiates the cleaning routine.
[0117] In some embodiments, the cleanliness of the printhead face can be maintained by the
use of an air curtain or an electro-static charge. The system can supply a low pressure curtain of
10 air across the printhead face that would reduce or prevent debris from collecting on the printhead
face. Alternatively, the printhead face could have an electro-static charged placed thereon that is
the same charge that is applied to the powder, thereby resulting in the powder particles being
repelled from the printhead face.
[0118] FIG. 15 is a schematic representation of a printhead alignment process in accordance
15 with one embodiment of the invention. Specifically, the printhead carriage 14 described
hereinabove is depicted in relation to an alignment test pattern 129. The test pattern 129 is
printed on the build surface 165 of the three-dimensional printing system 10 (see FIG. 1). The
test pattern 129 includes a contrast-enhancing sublayer 130 that defines an area upon which an
X-axis alignment pattern 133 and a Y-axis alignment pattern 134 are printed. The X and Y-axis
20 alignment patterns 133, 134 are line pair arrays made up of alternating reference lines 135 and
test lines 136. Also included on the sublayer 130 is a contrast optimization pattern 131, which is
described in greater detail with respect to FIGS. 16A and 16B. The carriage 14 includes an
alignment sensor system 132 that is used to scan the test pattern 129. The system 132 is
described in greater detail with respect to FIGS. 17A-17D.

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[0119] The pattern 129 is created by first spreading a layer of build material on the build
surface 165. The printheads 20 are then used to print the contrast-enhancing sublayer 130 on the
layer of build material powder. Generally, the contrast-enhancing sublayer 130 provides a
background reference to create a contrast between a printed layer and its surroundings.
5 Generally, it is desirable to perform the alignment process (e.g., creating the test pattern 129)
using the same binder solutions that will later be used to print the three-dimensional parts. Clear
binder can present a particular problem, in that an image printed on powder with clear binder is
difficult to distinguish from its unprinted surroundings. This problem can be solved by printing
the contrast-enhancing sublayer 130, though it is not required.
10 [0120] The contrast-enhancing sublayer 130 is printed on the build surface 165 of
dimensions sufficient to underlie the whole array of alignment pattern objects (e.g., the X-axis
alignment pattern 133, the Y-axis alignment pattern 134, and the contrast optimization pattern
131). In some embodiments, a dark color such as magenta or cyan may be used. The area may
be printed more than once to increase the darkness of the color. A layer of fresh powder is then
15 spread over this sublayer 130, obscuring the dark color. When an image is then printed on the
fresh layer with clear binder, the powder is wetted in the printed areas and becomes somewhat
transparent, revealing the dark color of the sublayer 130. In some embodiments, the contrast-
enhancing sublayer 130 and the powder spread over it may collectively be referred to as the
contrast-enhancing sublayer 130. The printed area then contrasts more clearly with its
20 surroundings to be detected more readily by the alignment sensor system.
[0121] Next, the contrast optimization pattern 131 is printed on the contrast-enhancing
sublayer 130. In some embodiments, the contrast optimization pattern 131 includes a printed
area or target 143-146 (see FIG. 16A) from each of the printheads 20. The alignment sensor
system 132 then determines the area of highest contrast between the printed targets 143-146 that

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collectively form the contrast optimization pattern 131 with contrast-enhancing sublayer 130 to
determine which target 143-146 of the contrast optimization pattern 131 (and its corresponding
printhead 20) has the greatest contrast relative to an unprinted area 141 (see FIG. 16A) of the
contrast-enhancing sublayer 130.
5 [0122] The general procedure is to adopt one of four colors as a reference standard and to
characterize the positional errors of the other colors with respect to the reference color. In one
embodiment, the four colors include clear (printed area 143), yellow (printed area 144), magenta
(printed area 145), and cyan (printed area 146). It may be desirable to adopt as a reference the
color that contrasts most with the unprinted background. To this end, a target is printed in each
10 color and then examined with the alignment sensor system 132. The color that produces the least
photo sensor output may be selected.
[0123] FIGS. 16A and 16B further detail the contrast optimization pattern 131. FIG. 16A is
a graphical representation of the contrast optimization pattern 131 including the aforementioned
targets 142-146. FIG. 16B shows the relationship between light source current and photo sensor
15 output (e.g., alignment sensor current). As the light impinging on a photo sensor increases, it
will eventually reach a level where the sensor output approaches a maximum and becomes
insensitive to further increases in light input. This state of insensitivity is commonly called
saturation, and is indicated by the saturated region 147 in FIG. 16B. The proportional region of
the sensor output is indicated by the proportional region 148 in FIG. 16B. To maximize the
20 information content of the sensor output signal, it is desirable to avoid saturating the sensor
under normal operating conditions. The powders used in 3D printing may vary widely in
reflectivity, resulting in large variations in maximum sensor illumination. To compensate for
this effect, the alignment sensor assembly is positioned over an unprinted area 142 above the
build surface and senses unprinted area 142 (see FIG. 16A). The input current through the light

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source is gradually increased until diminishing sensor output indicates saturation. The light
source current is then reduced to provide a safe operating margin within the proportional region
148. Alternatively, the light source current can be gradually increased until a predetermined safe
photo sensor output is reached.
5 [0124] Referring back to FIG. 15, two substantially identical arrays of line pairs disposed
substantially at right angles to each other make up the X-axis alignment test pattern 133 and the
Y-axis alignment test pattern 134. In one embodiment, one of the test patterns represents a slow
axis printing and the other test pattern represents a fast axis printing of the three-dimensional
printer 10. Generally, the X-axis alignment test pattern 133 and Y-axis alignment test pattern
10 134 are processed in sequence, and the processes are identical. Generally, both the X-axis
alignment pattern 133 and the Y-axis alignment pattern 134 include the reference line 135 and
the test line 136. In one embodiment, the reference line 135 is created by the printhead 20 that
was determined to have the greatest contrast relative to the contrast-enhancing sublayer 130.
The line pairs are discussed in greater detail hereinbelow with respect to FIGS. 18,19A, 19B,
15 and 21A.
[0125] In some embodiments, to determine the highest contrast between the contrast
optimization pattern 131 and the contrast-enhancing sublayer 130, the carriage 14 may include a
light source 137, for example a light emitting diode (LED), which produces a cone of light 138.
Alternatively, the light sources could be a laser or a lamp, and multiple light sources could be
20 utilized. The LED light source 137 illuminates the general area under examination. In some
embodiments, the LED light source 137 is a blue-green color to produce a high level of contrast
between printed and unprinted areas. An optical filter passes light only in a narrow wavelength
window that includes the LED output. Ambient room light contains relatively little light of the
wavelength passed by the filter, so that the great majority of the light that reaches the photo

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sensor originates from the light source. As a result, the system is relatively insensitive to
ambient room light variations.
[0126] In another embodiment, ambient light insensitivity is achieved by modulating the
light source 137 output at a frequency much higher than the signal of interest. The photo sensor
5 output is filtered electronically to pass only the frequency of the modulated light. This increases
the sensitivity of the system to low light levels. An optional lens can increase the sensitivity of
the system to low light levels.
[0127] FIGS. 17A-17D depict the alignment sensor system 132 in greater detail. The system
132 is typically part of the printhead carriage 14. In a particular embodiment, the system 132 is
10 mounted on a printed circuit board 160 that includes, for example, the logic for directing the
carriage 14, firing the printheads 20, and operating the alignment sensor system 132. The system
132 generally includes the light source 137, an optical filter 161, a light entrance 162, a photo
sensor 163, and an optional lens 164. The light source 137 is used to illuminate a spot on the test
pattern 129 that is about the same diameter as the width of the colored lines being scanned. The
15 light source 137 and the photo sensor 163 could each be focused or unfocused. FIGS. 17C-17D
depict different operational states of the alignment sensor system 132. FIG. 17C illustrates the
illumination of an illuminated area 166 on the build surface by the light cone 138. In one
embodiment, the light source floods the area of interest with light. In FIG. 17D, a sensed area
142 on the illuminated build surface 165 reflects light back to the photo sensor 163. Typically,
20 the sensed area 142 corresponds to a print target 142-146 or a portion of the reference line 135 or
test line 136 and is smaller in area than the illuminated area 166. The tubular light entrance
channel 162 restricts the field of vieAV of the photo sensor to a spot small relative to the
illuminated area. In some embodiments, the photo sensor 163 may include the capability of
detecting a surface photovoltage from the illuminated area 166 of the printing surface. In other

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embodiments, the system 132 may include an optional lens 164 to focus the reflected light on the
sensor 163.
[0128] FIG. 18 depicts the X-axis alignment pattern 133 of FIG. 15. The X-axis alignment
pattern 133 and the Y-axis alignment pattern 134 are substantially identical, with the exception
5 that the line pairs are oriented substantially perpendicularly, although alternative configurations
are contemplated and considered within the scope of the invention. As previously described, the
X-axis alignment pattern 133 includes a series of reference lines 135 and test lines 136.
Generally, each reference line 135 is printed by the printhead 20 with the highest contrast
relative to the contrast-enhancing sublayer 130, and each test line 136 is printed in an alternating
10 pattern by at least one of the three remaining printheads 20 with lesser relative contrasts. As the
number of printheads may vary in different embodiments, the number of corresponding color
bars in each test line 136 also may vary. In one exemplary embodiment, the reference line 135
may be made of clear deposited material, and test line 136 may be sequentially repeating yellow,
magenta, and cyan color deposits. Typically, the test pattern 129 is printed by the printheads 20
15 in order to determine if the printheads 20 are properly aligned. The test pattern 129 is printed
assuming the printheads 20 are perfectly positioned. Once the test pattern 129 has been printed,
the carriage 14 is actuated over the surface of the test pattern 129 and the alignment sensor
system 132 scans at least a portion of test pattern 129 to determine the deviation of the test line
136 from the perfect position. The scanned results are then used to correct any identified errors.
20 [0129] FIGS. 19A-19B illustrate the scan spot travel paths 171 across a test pattern. FIG.
19A illustrates a nominal X-axis alignment pattern 170. As the sensed area 142 passes over the
printed lines in the direction of line pair replication direction 173, the photo sensor 163 receives
reflected light that originated from the light source 137. The reflectances of the color bars differ
from the unprinted background (in one example, the unprinted background is white), and the

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reflectances of the colors vary amongst themselves. As illustrated by FIG. 19B, the basic unit of
the target is a line pair, such as line pair 174, which comprises a solid reference line 135 and a
test line 136 including an array 181 of systematically varying short bars 191 including a first
color bar 176, a second color bar 177, and a third color bar 178. Alternative embodiments may
5 have more or fewer color bars. Collectively, the color bars 176, 177, 178, are components of the
test line 136. This line pair 174 is periodically repeated in the direction shown with a constant
pitch ("P") 197 between successive reference lines, for exampl, reference lines 135. In the
illustrative embodiment of FIG. 19B, the line pair 174 is repeated 11 times; however, the number
of line pairs will vary to suit a particular application and/or desired level of accuracy.
10 [0130] In one embodiment, the scan spot traverses the array of line pairs 174 along travel
paths perpendicular to the reference line 135. In the embodiment illustrated by FIG. 19B,
complete examination of the target requires 33 scan spot passes. Three typical scan path travel
paths 171 are indicated (see FIG. 19A). In one embodiment, the width of the color bars 176,
177, 178, the minimum anticipated space between the bars, and the size of the scan spot should
15 be substantially equal. The color bars 176,177,178 shown in FIG. 19B vary systematically
around a spacing equal to about one half of the reference line pitch P 197. An exemplary short
bar is identified as short bar 191. In one embodiment, the increment of variation, ("5"), may
typically be 2 pixels at 300 dpi or 0.007 inches. The position of the uppermost group of three
short bars of the color bars 176,177,178 is nominally printed equidistant between two of the
20 reference lines 135. Progressing down the array, the groups of three color bars 176, 177,178
diverge from the central position by increasing amounts, for example +/- nδ, where "n" is an
integer (e.g., 1δ, 2δ, 3δ, etc.). The width and pitch of the reference lines 135 and test lines 136
are selected to optimize the signal contrast. The dimensions given herein axe for illustrative
purposes only and are in no way to be considered limiting.

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[0131] FIGS. 20A-20D illustrate one embodiment of the alignment process with respect to a
single scan spot travel path 171. FIGS. 20A and 20B illustrate the single scan spot pass travel
path 171 in the direction of carriage motion 193 across reference lines 135 and test lines 136. As
the scan spot passes over the printed color bars, the photo sensor receives reflected light that
5 originated from the light source 137. The reflectances of the color bars differ from the unprinted
background, and the reflectances of the colors vary amongst themselves. FIG. 20C illustrates the
sensor output signal, which represents strong periodicity related to the color bar spacing and
peak amplitude variations due to different color reflectances.
[0132] As shown in FIG. 20D, any signal can be represented as the sum of an arbitrarily
10 large number of sinusoids, each having a constant discrete frequency, a constant amplitude, and a
constant phase relationship to a fixed standard. The process of extracting the sinusoidal
constituents of a signal is called Fourier analysis. A common practical approach is to digitize the
signal and to then employ a computational algorithm, such as a Fast Fourier Transform ("FFT").
FIG. 20D shows the principle harmonic constituents of the signal shown in FIG. 20C. The
15 frequency of these constituents is fixed by the geometric constraints placed on the test pattern
129. The magnitude of the each constituent is affected by differences in color reflectivity and by
the displacement ("E") 183 (see FIG. 20B) of the adjustable color bar relative to its central
position. The magnitude of the harmonic component whose frequency is three times the
reference bar frequency increases with color test bar displacement from perfect alignment, and
20 can be used to determine the magnitude of the displacement. FIG. 20D is a graphical
representation of the sensor output indicating spatial frequency and a first harmonic peak 185, a
second harmonic peak 186, a third harmonic peak 187, and a fifth harmonic peak 188. The first
harmonic peak 185 may also be used as an indicator of misalignment.

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[0133] FIGS. 21A and 2IB illustrate an alignment pattern showing misalignment in one
embodiment of a test pattern in accordance with the invention. As discussed above, the
alignment pattern in FIG. 19A was shown as it would be printed by printheads 20 in perfect
alignment. FIG. 21A shows an alignment pattern printed by misaligned printheads 20. Each
5 adjustable color bar, including second color bar 192, is actually printed in a position displaced
from its nominal true position. To determine the positional error 183 of each color using this
alignment pattern, a total of eleven scans across this pattern are needed, as shown. Each scan
will produce a signal of the sort shown in FIG. 20C. For each of these signals, the magnitude of
the third harmonic can be extracted by digital FFT or analog filtering. Although the magnitude
10 of the third harmonic increases reliably with misalignment, the misalignment is only one
component of the magnitude of the harmonic. A portion of the peak is constant and depends on
the line width/space ratio. A portion of the peak is variable and depends on how well the color
bars are centered between the reference lines 135.
[0134] Determining at which nominal color bar displacement the magnitude of the third
15 harmonic is minimized can factor these other components out. The maximum value of the
harmonic of interest, for example the third harmonic, for each scan is collected. By fitting a
curve of these data points and determining the minimum point of this fitted curve (see FIG.
2 1B), it is possible to determine the misalignment to within a fraction of the alignment pattern
step resolution. If, for example, the printhead under examination were perfectly aligned, the
20 point of the fitted curve would coincide with a nominal color bar displacement 175 of
zero.
[0135] The location of the minimum yields an accurate correction factor. In one
embodiment, the correction factor is used to alter the timing of a firing signal to a printhead,
thereby altering the location of the printhead output. Specifically, this actual measured

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misalignment can be used as a corrective, geometric offset, causing the printhead 20 to "fire"
either early or late, so that the mechanical misalignment can be automatically compensated for
during printing. As a result, a very high level of printing accuracy can be achieved, resulting in
the production of dimensionally accurate three-dimensional articles, even when employing
5 multiple printheads. In one embodiment, the alignment process is carried out prior to printing
any three-dimensional parts and/or after a printhead is replaced.
[0136] Having described certain embodiments of the invention, it will be apparent to those of
ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may
be used without departing from the spirit and scope of the invention. The described
10 embodiments are to be considered in all respects as only illustrative and not restrictive.
[0137] What is claimed is:

1. A service station for maintaining a plurality of printheads in a three-dimensional printer,
the service station comprising:
a cleaning station;
a discharge station; and
a capping station.
2. The service station of claim 1, wherein either:
(a) the cleaning station comprises:
at least one receptacle for receiving a printhead;
at least one nozzle for spraying a cleaning fluid towards a printhead face of the
printhead; and
a wiper disposable in close proximity to the printhead face for removing excess
cleaning fluid; and optionally
i. the cleaning station further comprises a splash guard for isolating the printhead
face and preventing the cleaning fluid from migrating beyond the printhead face, and optionally
(a) the splash guard comprises an open position and a sealed position,
where the splash guard is biased open and is actuated from the open position to the sealed
position by contact with a printhead;
(b) the splash guard includes a sealing lip that circumscribes the printhead
face when in the sealed position;
(c) the sealing lip is generally rectangular in shape;
(d) the wiper is formed by one side of the sealing lip; or
(e) the wiper includes a notched portion configured and located to
correspond to a location of a jet nozzle array on the printhead face to prevent the wiper from
contacting the jet nozzle array;
ii. the wiper is capable of movement relative to a printhead;
iii. further comprises a fluid source for providing the cleaning fluid to the at least
one nozzle under pressure;
iv. the cleaning fluid is provided to the at least one nozzle via a manifold;
v. the at least one nozzle comprises an array of nozzles; or


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vi. the at least one nozzle is positionable to spray the cleaning fluid across the
printhead face;
(b) the printheads are disposable within a carriage capable of moving in at least two
directions relative to the service station;
(c) the discharge station comprises a receptacle defining an opening that generally
corresponds to a printhead face of a printhead, and optionally
i. the receptacle defines a plurality of corresponding openings;
ii. the receptacle comprises a tray for at least one of capturing and directing
discharged fluids; or
iii. the discharge from the printheads is directed into a standing pool of waste
liquid;
(d) the capping station comprises:
a printhead cap carrier; and
at least one printhead cap disposed on the carrier for sealing a printhead face of a
printhead, wherein the cap is moved between an off position and a capped position by the
printhead contacting the carrier; and optionally
i. the capping station comprises a plurality of caps disposed on the carrier; or
ii. the carrier is biased to maintain the at least one cap in an off position; or
(e) the discharge station and the capping station are combined, and optionally
i. the discharge from the printheads is directed into a standing pool of waste
liquid; or
ii. the discharge from the printheads is constrained in a cavity defined by a
printhead face, a printhead cap, and the standing pool of waste liquid.
3. An apparatus for cleaning a printhead, the apparatus comprising:
at least one nozzle for spraying a cleaning fluid towards a printhead face of the printhead;
and
a wiper disposable in close proximity to the printhead face for removing excess cleaning
fluid from the printhead face.

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4. The apparatus of claim 3, wherein either:
(a) the cleaning station further comprises a splash guard for isolating a printhead face and
preventing cleaning fluid from migrating beyond the printhead face; and optionally
i. the splash guard comprises an open position and a sealed position, and the
splash guard is actuated from the open position to the sealed position by contact with a printhead
ii. the splash guard includes a sealing lip that circumscribes the printhead face
when in the sealed position;
iii. the sealing lip is generally rectangular in shape; or
iv. the wiper is formed by one side of the sealing lip, the wiper including a
notched portion configured and located to correspond to a location of a jet nozzle array on the
printhead face to prevent the wiper from contacting the jet nozzle array;
(b) the wiper is capable of movement relative to a printhead;
(c) further comprises a fluid source for providing cleaning fluid to the at least one nozzle
under pressure;
(d) the at least one nozzle comprises an array of nozzles; or
(e) the at least one nozzle is positionable to spray the cleaning fluid across the printhead
face.
5. A method of cleaning a printhead, the method comprising the steps of:
positioning a printhead face of the printhead relative to at least one nozzle;
operating the at least one nozzle to spray cleaning fluid towards the printhead face; and
causing relative movement between a wiper and the printhead to pass the wiper in close
proximity to the printhead face to remove excess cleaning fluid, wherein the wiper defines a
notch configured and located on the wiper to correspond to a location of a jet nozzle array on the
printhead face to prevent the wiper from contacting the jet nozzle array.
6. The method of claim 5, wherein either:
(a) the step of positioning the printhead face comprises sealing the printhead face to
prevent the cleaning fluid from migrating beyond the printhead face;
(b) the operating step comprises spraying the cleaning fluid across the printhead face;


55
(c) further comprises the step of operating the printhead to discharge cleaning fluid
ingested by the printhead during cleaning; or
(d) the at least one nozzle comprises an array of nozzles.
7. An apparatus for cleaning a printhead used in a three-dimensional printer, the apparatus
comprising:
a sealing cap defining a cavity and capable of engagement with a printhead face of the
printhead;
a cleaning fluid source in communication with the cap for cleaning the printhead face;
and
a vacuum source in communication with the cap for removing used cleaning fluid and
debris.
8. The apparatus of claim 7, wherein either:
(a) the vacuum source creates a negative pressure within the cavity, the negative pressure
serving to at least one of:
draw the cleaning fluid into the cavity from the cleaning fluid source;
prevent the cleaning fluid from entering a jet nozzle; and
drawing at least one of a binder fluid and debris from the jet nozzle; or
(b) further comprises a wiper disposed proximate the cap, the wiper positioned to engage
the printhead face as the printhead disengages from the cap, and optionally
i. the wiper defines a notch configured and located on the wiper to correspond to a
location of a jet nozzle array on the printhead face to prevent the wiper from contacting the jet
nozzle array.
9. A method of cleaning a printhead used in a three-dimensional printer comprising the
steps of:
engaging a printhead face of the printhead with a sealing cap defining a cavity;
drawing a vacuum in the cavity; and
introducing a cleaning fluid into the cavity and into contact with the printhead face.


56
10. The method of claim 9, either:
(a) further comprising the step of removing the cleaning fluid from the cavity, and
optionally
i. further comprising the steps of:
disengaging the cap from the printhead face; and
removing excess cleaning fluid from the printhead face with a wiper; or
(b) the step of drawing a vacuum creates a negative pressure within the cavity, the
negative pressure serving to at least one of:
draw the cleaning fluid into the cavity;
prevent the cleaning fluid from entering a jet nozzle; and
drawing at least one of a binder fluid and debris from the jet nozzle.
11. A method of determining a condition of a printhead in use in a three-dimensional printer,
the method comprising the steps of:
acquiring a data value for at least one operational parameter of the printhead; and
comparing the data value to a threshold value, the relationship of the data value to the
threshold value indicative of the condition of the printhead.
12. The method of claim 11, either:
(a) further comprising the step of initiating a service routine on the printhead if the data
value exceeds the threshold value;
(b) the operational parameter is selected from the group consisting of time elapsed,
number of droplets dispensed by the printhead, number of layers printed, droplets dispensed over
previously printed powder, droplets dispensed over previously unprinted powder, and
combinations thereof; or
(c) the data value is compensated during acquisition to account for an operational
environmental factor of the three-dimensional printer, and optionally
i. the operational environmental factor is selected from the group consisting of
temperature, humidity, binder material, and build material.


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13. A method of determining a condition of a printhead in use in a three-dimensional printer,
the method comprising the steps of:
counting droplets dispensed by the printhead; and
determining a percentage of the droplets that were dispensed over previously unprinted
pixels.
14. The method of claim 13 further comprising the step of initiating a service routine on the
printhead if the percentage exceeds a threshold value.
LIBC/2943912.2

This invention relates
to apparatus and methods for producing
three-dimensional objects and auxiliary
systems used in conjunction with the
aforementioned apparatus and methods.
The apparatus and methods involve 3D
printing and servicing of the equipment
used in the associated 3D printer.
Provided is a service station (16) having a
discharge station (22), a cleaning station
(29) and a capping station (24). A wiper
(544, 81, 86) which may have a notch
(82), a washing solution (92) may spray
the nozzle plate, a splash guard (81),
a vacuum source, are also provided.
Methods of determining a condition of a
printhead are provided, eg acquiring an
operational parameter of the printhead,
or counting droplets.