U.S. patent application number 16/188443 was filed with the patent office on 2019-03-14 for fabrication of 3d objects via multiple build platforms.
This patent application is currently assigned to Xactiv, Inc.. The applicant listed for this patent is Xactiv, Inc.. Invention is credited to Dan A. HAYS, James MASON, Peter J. MASON.
Application Number | 20190077141 16/188443 |
Document ID | / |
Family ID | 56366907 |
Filed Date | 2019-03-14 |
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United States Patent
Application |
20190077141 |
Kind Code |
A1 |
HAYS; Dan A. ; et
al. |
March 14, 2019 |
FABRICATION OF 3D OBJECTS VIA MULTIPLE BUILD PLATFORMS
Abstract
A method is disclosed for improving the productivity of
digitally fabricated 3D objects with the same or different shape
and material composition. The improved productivity is enabled by
the incorporation of multiple build platforms and multiple objects
per build platform within a 3D object fabrication apparatus. Some
3D manufacturing processes such as those based on
electrophotography require a wait time to condition the build
object before the next layer of build and support material can be
applied. Under these fabrication conditions, the utilization of
multiple build platforms in the 3D object manufacturing process
effectively minimizes the wait time between layer deposition so
that the productivity for fabricating 3D objects is improved.
Furthermore, the incorporation of an additional adjacent set of
multiple platforms enables rapid changeover when the fabrication of
one set of 3D objects is completed on an adjacent set of build
platforms.
Inventors: |
HAYS; Dan A.; (Venice,
FL) ; MASON; Peter J.; (Fairport, NY) ; MASON;
James; (Victor, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xactiv, Inc. |
Fairport |
NY |
US |
|
|
Assignee: |
Xactiv, Inc.
Fairport
NY
|
Family ID: |
56366907 |
Appl. No.: |
16/188443 |
Filed: |
November 13, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14994180 |
Jan 13, 2016 |
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16188443 |
|
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62103269 |
Jan 14, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B33Y 30/00 20141201;
B29C 64/171 20170801; B29C 64/182 20170801; B29C 64/241 20170801;
G03G 15/1625 20130101; G03G 2215/1695 20130101; B29C 64/153
20170801; B29C 64/205 20170801; G03G 15/224 20130101; B33Y 10/00
20141201; B29C 64/236 20170801 |
International
Class: |
B33Y 30/00 20060101
B33Y030/00; G03G 15/16 20060101 G03G015/16; B33Y 10/00 20060101
B33Y010/00; G03G 15/22 20060101 G03G015/22; B29C 64/153 20060101
B29C064/153 |
Claims
1. A method of fabricating a plurality of objects, the method
comprising: a) depositing a first powder layer on a surface of a
first object substrate on a first build platform located at a
material transfer station; b) consolidating the first powder layer
on the first object substrate to form a first solid layer of a
first object on the first object substrate; c) locating a second
object substrate on a second build platform at the material
transfer station following removal of the first build platform with
the first object substrate from the material transfer station; d)
depositing a first powder layer on the surface of the second object
substrate; e) consolidating the first powder layer on the second
object substrate to form a first solid layer of a second object on
the second object substrate; and f) removing the second build
platform with the second object substrate from the material
transfer station.
2. The method of claim 1, wherein consolidating the first powder
layer on the first object substrate to form the first solid layer
of the first object on the first object substrate is performed
after the removing the first build platform with the first object
substrate from the material transfer station, and consolidating the
first powder layer on the second object substrate to form the first
solid layer of the second object on the second object substrate is
performed after removing the second build platform with the second
object substrate from the material transfer station.
3. The method of claim 1, wherein consolidating the first powder
layer on the first object substrate to form the first solid layer
of the first object on the first object substrate and consolidating
the first powder layer on the second object substrate to form the
first solid layer of the second object on the second object
substrate are performed at the material transfer station.
4. The method of claim 3, wherein consolidating the first powder
layer on the first object substrate is performed during depositing
the first powder layer on the surface of the first object
substrate, and consolidating the first powder layer on the second
object substrate is performed during depositing the first powder
layer on the surface of the second object substrate.
5. The method of claim 1, wherein consolidating the first powder
layer on the first object substrate and consolidating the first
powder layer on the second object substrate are performed after
depositing the first powder layer on the surface of the first
object substrate and depositing the first powder layer on the
surface of the second object substrate.
6. The method of claim 1, further comprising first depositing the
first powder layer deposited on the surface of the first object
substrate on a surface of an intermediate substrate, moving that
first powder layer on the surface of the first intermediate
substrate to the first build platform located at the material
transfer station prior to depositing the first powder layer on the
surface of the first object substrate; and first depositing the
first powder layer deposited on the surface of the second object
substrate on the surface of the intermediate substrate, moving that
first powder layer on the surface of the intermediate substrate to
the second build platform located at the material transfer station
prior to depositing that first powder layer on the surface of the
second object substrate.
7. The method of claim 6, wherein the intermediate substrate is a
belt substrate.
8. The method of claim 6, wherein the intermediate substrate is a
drum substrate.
9. The method of claim 6, wherein the first powder layer deposited
on the surface of the first object substrate and the first powder
layer deposited on the surface of the second object substrate are
first deposited on the surface of the intermediate substrate by an
electrophotographic process.
10. The method of claim 6, further comprising pre-conditioning, on
the surface of the intermediate substrate, the first powder layer
deposited on the surface of the first object substrate and the
first powder layer deposited on the surface of the second object
substrate prior to depositing the first powder layer on the surface
of the first object substrate and depositing the first powder layer
on the surface of the second object substrate.
11. The method of claim 1, further comprising post-conditioning the
first solid layer of the first object on the first object substrate
and the first solid layer of the second object on the second object
substrate.
12. The method of claim 1, further comprising pre-conditioning the
first solid layer of the first object on the first object substrate
and the first solid layer of the second object on the second object
substrate.
13. The method of claim 1, further comprising: a) moving the first
build platform with the first object substrate and first solid
layer of the first object to the material transfer station; b)
depositing a second powder layer on the first solid layer of the
first object; c) consolidating the second powder layer with the
first solid layer of the first object; d) locating the second build
platform with the second object substrate and first solid layer of
the second object at the material transfer station following
removal of the first build platform with the first object substrate
from the material transfer station; e) depositing a second powder
layer on the first solid layer of the second object; f)
consolidating the second powder layer deposited on the first solid
layer of the second object with the first solid layer of the second
object; and g) removing the second build platform with the second
object substrate from the material transfer station.
14. The method of claim 13, wherein the first object and second
object are each comprised of h consolidated layers, the method
further comprising repeating h-2 times: a) moving the first build
platform with the first object substrate and consolidated solid
layers of the first object to the material transfer station; b)
depositing an additional powder layer on the consolidated solid
layers of the first object; c) consolidating the additional powder
layer with the consolidated solid layers of the first object; d)
locating the second build platform with the second object substrate
and consolidated solid layers of the second object at the material
transfer station following removal of the first build platform with
the first object substrate and consolidated solid layers of the
first object from the material transfer station; e) depositing an
additional powder layer on the consolidated solid layers of the
second object; f) consolidating the additional powder layer with
the consolidated solid layers of the second object; and g) removing
the second build platform with the second object substrate from the
material transfer station.
15. The method of claim 13, wherein the movings and removings of
the first build platform to and from the material transfer station,
and movings and removings of the second build platform to and from
the material transfer station are performed using linear
pathways.
16. The method of claim 13 wherein the movings and removings of the
first build platform, and movings and removings of the second build
platform are performed along a first cyclic loop pathway in
communication with the material transfer station in a first loop
direction.
17. The method of claim 1, further comprising providing a third
build platform and a fourth build platform adjacent to the first
build platform and the second build platform, the third and fourth
build platforms movable relative to the material transfer station
along a second cyclic loop pathway.
18. The method of claim 17, wherein the second cyclic loop pathway
is in a second loop direction that is opposite the first loop
direction.
19. The method of claim 17, further comprising: a) disposing a
third object substrate on the third build platform; b) disposing a
fourth object substrate on the fourth build platform; c) moving the
first build platform and first object substrate and first solid
layer of the first object and the second build platform and second
object substrate and first solid layer of the second object
relative to the material transfer station to a distal location
wherein the first cyclic loop pathway is not in communication with
the material transfer station; d) moving the third build platform
and third object substrate and moving the fourth build platform and
fourth substrate relative to the material transfer station to a
proximal location wherein the second loop pathway is in
communication with the material transfer station; e) locating the
third build platform and third object substrate at the material
transfer station, depositing a first powder layer on the surface of
the third object substrate and consolidating the first powder layer
on the third object substrate to form a first solid layer of the
third object on the third object substrate; and f) locating the
fourth build platform and fourth object substrate at the material
transfer station following removal of the third build platform with
the third object substrate from the material transfer station,
depositing a first powder layer on the surface of the fourth object
substrate and consolidating the first powder layer on the fourth
object substrate to form a first solid layer of the fourth object
on the fourth object substrate.
20. The method of claim 1, wherein the first and second build
platforms are joined to an outer surface of a cylinder having an
axis of rotation equidistant from all points on the outer surface,
and the method further comprises rotating the cylinder about its
axis of rotation to cause the locating of the first build platform,
first object substrate and first powder layer of the first object
at the material transfer station, and to cause the removal of the
first build platform with the first object substrate and first
solid layer of the first object from the material transfer station,
and to cause the locating of the second build platform, second
object substrate and first powder layer of the second object at the
material transfer station, and to cause the removal of the second
build platform with the second object substrate and first solid
layer of the second object from the material transfer station.
21. The method of claim 20, wherein n build platforms are joined to
the surface of the cylinder, the method comprising: a) for each of
the n-2 additional object build platforms, rotating the cylinder
about its axis of rotation to cause the locating of the build
platform, the object substrate and the powder layer of the object
on that build platform at the material transfer station; b)
consolidating the powder layer on the object substrate to form a
first solid layer of the object on the object substrate on that
build platform; and c) rotating the cylinder about its axis of
rotation to cause the removal of that build platform with the
object substrate and solid layer of the object on that build
platform from the material transfer station.
22. The method of claim 1, wherein the number of object build
platforms is n, the method comprising for each of the n-2
additional object build platforms: a) depositing a powder layer on
a surface of an additional object substrate on an additional build
platform located at the material transfer station; b) consolidating
the powder layer on the additional object substrate to form a first
solid layer of the additional object on the additional object
substrate; and c) removing the additional build platform with the
additional object substrate from the material transfer station.
23. The method of claim 22, wherein the first object, the second
object, and the n-2 additional objects are each comprised of h
consolidated layers, the method further comprising, for each of the
first build platform, second build platform, and additional build
platforms, repeating h-1 times: a) selecting a chosen build
platform from one of the first build platform, second build
platform, and additional build platforms, and moving the chosen
build platform with object substrate and consolidated solid layers
of the object on the chosen build platform to the material transfer
station; b) depositing an additional powder layer on the
consolidated solid layers of the object on the chosen build
platform; c) consolidating the additional powder layer with the
consolidated solid layers of the object on the chosen build
platform; and d) removing the chosen build platform from the
material transfer station.
24. An apparatus for making a plurality of objects, the apparatus
comprising: a) a plurality of object substrates, each of the
substrates comprising a powder receiving surface; b) a plurality of
build platforms, each of the build platforms engageable with any
one of the object substrates; c) a material transfer station
comprised of a fixture engageable with any one of the build
platforms; d) a transporting device engaged with each of the build
platforms and operable to repeatedly transport each of the build
platforms to and from the material transfer station; and e) a
powder layering device operable to dispense a layer of powder onto
one of the powder receiving surface or a consolidated layer of
powder on the powder receiving surface of any one of the object
substrates when that object substrate is located at the material
transfer station.
25. The apparatus of claim 24, wherein the powder layering device
is comprised of a powder layer generating device operable to
dispense a powder layer onto a powder layer transfer device
comprising a transfer substrate having a surface movable between
the powder layer generating device and the material transfer
station.
26. The apparatus of claim 25, wherein the powder layer transfer
device substrate is comprised of a belt substrate.
27. The apparatus of claim 25, wherein the powder layer transfer
device substrate is a drum substrate.
28. The apparatus of claim 25, wherein the powder layer generating
device is an electrophotographic imaging engine.
29. The apparatus of claim 24, wherein the transporting device
transports the build platforms to and from the material transfer
station in linear pathways.
30. The apparatus of claim 24, wherein the transporting device
transports the build platforms to and from the material transfer
station in cyclic loop pathways.
31. The apparatus of claim 30, wherein the transporting device is
comprised of: a) a first conveyor engaged with a first portion of
the build platforms and operable to transport the first portion of
the build platforms to and from the material transfer station in a
first cyclic loop pathway; and b) a second conveyor adjacent to the
first conveyor and engaged with a second portion of the build
platforms and operable to transport the second portion of the build
platforms to and from the material transfer station in a second
cyclic loop pathway.
32. The apparatus of claim 24, wherein the transporting device is a
cylinder comprising an outer surface and having an axis of rotation
equidistant from all points on the outer surface, and each of the
build platforms are joined to the outer surface of the cylinder,
and wherein the cylinder is rotatable around its axis of rotation
to transport each of the build platforms to and from the material
transfer station.
33. The apparatus of claim 24, wherein: a) the transporting device
is comprised of a first cylinder and a second cylinder, each of the
first and second cylinders comprising an outer surface and having
an axis of rotation equidistant from all points on the outer
surface of that cylinder; b) a first portion of the build platforms
are joined to the outer surface of the first cylinder, and the
first cylinder is movable to a location proximate to the material
transfer station and rotatable around its axis of rotation to
transport each of the build platforms of the first portion of the
build platforms to and from the material transfer station; and c) a
second portion of the second cylinder is movable to the location
proximate to the material transfer station and rotatable around its
axis of rotation to transport each of the build platforms of the
second portion of the build platforms to and from the material
transfer station.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application is a continuation of copending U.S. patent
application Ser. No. 14/994,180, filed on Jan. 13, 2016, which
claims the benefit of U.S. Provisional Patent Application No.
62/103,269 filed Jan. 14, 2015, the disclosures of which are
incorporated herein by reference. The above benefit/priority claims
is/are being made in an Application Data Sheet submitted herewith
in accordance with 37 C.F.R. 1.76 (b)(5) and 37 C.F.R. 1.78.
BACKGROUND
Technical Field
[0002] Devices for digital fabrication of three-dimensional objects
by either selectively depositing or binding raw materials together
in layers.
Description of Related Art
[0003] This disclosure relates to the modification of a process and
apparatus for more efficiently manufacturing three-dimensional (3D)
objects using digital fabrication methods. The 3D manufacturing
process, also known as additive manufacturing, rapid prototyping,
or solid free form, uses digital files that describe cross sections
for building the desired part and support structure. Various 3D
manufacturing methods have been proposed for digitally fabricating
a uniquely shaped object on a single build platform. The build rate
of digitally produced 3D objects is inherently slow since 1) each
2D cross section is typically formed by a two-dimensional scanning
device and 2) many 2D layers (up to thousands in a high resolution
part) are required to produce an object. Furthermore, some
manufacturing methods require additional time to post-process a
layer before deposition of the next layer. Regardless of the method
for building the 3D object, there is a general need to implement
process improvements for reducing the time to build multiple,
uniquely shaped 3D objects.
[0004] Various additive manufacturing systems have been proposed to
produce three-dimensional objects by either selectively depositing,
binding or polymerizing raw materials together in layers. The
various methods include fused filament extrusion, ink jetting,
selective laser sintering, powder/binder jetting, electron beam
melting, stereolithography and electrophotography processes. In
general, the various methods tend to exhibit a slow build rate. For
example, many of the selective deposition methods have a slow build
rate since the deposition of the build and support materials is
generally provided by a scanning head for extruding or jetting the
material for each layer. To improve the build rate with a fused
filament extrusion method, a 3D printer from Cartesio called the
CartesioLDMP has multiple extruder heads for simultaneously
printing multiple similar shaped 3D objects on a single stationary
platform.
[0005] The 3D manufacturing method based on electrophotography has
the potential of improving the build rate since it is well known
from the electrophotographic industry that 2D layers of imaged
powder can be formed and deposited in a time less than about half
of a second. However, the 3D object build rate utilizing the
electrophotographic method is decreased if a wait time required
before depositing another layer is comparable to or greater than
the build time for each layer.
[0006] The electrophotographic process can enable high 2D layer
formation rates since the imaging of a uniformly charged
photoreceptor is provided by light exposure from either a scanning
laser beam or LED imaging bar. The deposition of powder material is
provided by a high process speed powder development system.
Typically, insulative powder is triboelectrically charged in a
development system. Electrostatic forces acting on the charged
powder are used to develop an electrostatic image formed by laser
or LED light exposure of a uniformly charged photoreceptor.
Likewise, electrostatic forces are used to transfer the charged
powder image on the photoreceptor to a medium such as paper or an
intermediate roll or belt. The electric field for electrostatic
transfer of the charged powder to the medium is typically provided
by either depositing gaseous ions on the backside of the medium or
applying an electrical bias to a stationary or roller electrode
behind a belt or roll comprised of a charge-relaxable material or
overcoating, respectively. In electrostatically transferring
charged powder to a medium such as paper or an intermediate roll or
belt, one can apply rather high electric fields (40 volts per
micrometer) for efficient powder transfer without air breakdown
limitations. The high transfer efficiency is not degraded in color
electrophotographic printers that require the electrostatic
transfer of several charged powder layers involving different
combinations of cyan, magenta, yellow and black toner layers.
[0007] Although it is recognized that the electrophotographic
process can enable rapid formation of 2D layers, a number of
researchers have reported problems in producing arbitrarily thick
3D objects when using conventional electrophotography to produce
charged powder depositions that are repeatedly electrostatically
transferred and heat fused to the object being built. For example,
a publication on "Transfer Methods toward Additive Manufacturing by
Electrophotography" by Jones et al. in the conference proceedings
of the Society for Imaging Science and Technology (IS&T),
NIP27: 2011 International Conference on Digital Printing
Technologies, pp. 180-184 reports the use of a conventional
monochrome printer with conventional toner for repeatedly
electrostatically transferring a uniformly deposited toner layer
onto a moving platform and heat fusing the layer before the next
deposition cycle. It was noted that after about 20 transfers, the
surface had many defects and irregularities that compromise the
quality of the object. It was remarked that every research group,
to the author's knowledge, encountered the same type of surface
defects when attempting to deposit non-conductive toner with stack
heights in excess of 1 mm.
[0008] In spite of the surface defects problem encountered after
many electrostatic transfers of charged powder to build an object,
the effectiveness of the conventional electrostatic transfer
process diminishes as thickness of the object increases. When the
electrostatic force for transferring charged powder is provided by
an electric field due to an electrical bias between the conducting
substrate of the build object and the ground plane of the
photoconductor, the applied electric field and correspondingly the
electrostatic force decreases with increasing thickness of the
object. Furthermore, the accumulation of charge on the object due
to the charge on the transferred powder creates an electric field
that suppresses powder transfer and therefore limits the thickness
of the build object and causes irregularities in the surface. To
suppress the build limitation due to charge accumulation on the
object, the feasibility of using a corona (gaseous ions) charging
device for charging the top layer of the object with a polarity
opposite to that of the toner has been reported in a publication by
A. Dutta on "Study and Enhancement of Electrophotographic Solid
Freeform Fabrication" as a Masters of Science thesis in the
Department of Mechanical and Aeronautical Engineering at University
of Florida, Gainesville, Fla. in 2002. (See
http://etd.fcla.edu/UF/UFE0000527/dutta_a.pdf.) The top charging
method doubled the thickness of the build object from 1 mm to 2 mm
before surface quality degradation was observed. Although objects
thicker than 2 mm could be produced, the surface defects became
exaggerated with each successive transfer. A publication by A.
Kumar Das on "An Investigation on the Printing of Metal and Polymer
Powders Using Electrophotographic Solid Freeform Fabrication" as a
Masters of Science thesis in the Department of Mechanical and
Aeronautical Engineering at University of Florida, Gainesville,
Fla. in 2004 (See http://etd.fcla.edu/UF/UFE0005385/das_a.pdf)
suggests that although the corona charging counteracted the powder
charge in the initial layers, its effectiveness was diminished for
a thicker object.
[0009] To circumvent the 3D object build thickness and surface
irregularity problems associated with electric field transfer of
charged powder from electrophotographic images to the build object,
an alternative approach of using of heat and pressure to transfer
the charged powder layers to a build object has been described by a
number of researchers. The first to disclose the utilization of
heat and pressure to build 3D objects from electrophotographic
produced powder layers was Bynum in U.S. Pat. No. 5,088,047 (1992).
This patent discloses the use of an electrophotographic print
engine to deposit layers of toner on a TEFLON.RTM.
(polytetrafluoroethylene) coated belt. Each layer on the belt was
made tacky by heating or exposure to solvent vapor before being
transferred to the build object with a combination of heat and
pressure. Other relevant patents include U.S. Pat. No. 5,593,531
issued to Penn, U.S. Pat. No. 6,066,285 issued to Kumar, U.S. Pat.
No. 6,780,368 issued to Liu and Jang, and U.S. Pat. No. 8,488,994
issued to Hanson et al. In these U.S. Patents, a transfer medium is
configured to receive and transfer imaged layers of a
thermoplastic-based powder from an electrophotographic imaging
engine. Before the imaged layer is transferred to the build object
or support material, a heater is used to heat the imaged layers on
the transfer medium to at least a fusing temperature of the
thermoplastic-based powder. The system also includes a layer
transfusion assembly comprising a build platform where the layer
transfusion assembly is configured to transfuse the heated layers
in a layer-by-layer manner onto the build platform to print the 3D
object. The system usually also includes a post-transfusing cooling
unit configured to actively cool the transfused layers to maintain
the printed 3D object at about an average temperature that is below
a deformation temperature for the 3D object. The utilization of
heating and cooling cycles of the transfer medium and 3D
part/support materials in the transfusion process builds in a wait
time that limits the overall speed of the electrophotographic
method for digitally producing 3D objects. The disclosures of these
U.S. Pat. No. 5,088,047 of Bynum; U.S. Pat. No. 5,593,531 of Penn;
U.S. Pat. No. 6,066,285 of Kumar; U.S. Pat. No. 6,780,368 of Liu et
al.; and U.S. Pat. No. 8,488,994 of Hanson et al. are incorporated
herein by reference.
[0010] Although there is no evidence from the Bynum patent that
this disclosure was reduced to practice, the publication by Jones
et al. on "Transfer Methods toward Additive Manufacturing by
Electrophotography" in the conference proceedings of the Society
for Imaging Science and Technology (IS&T), NIP27: 2011
International Conference on Digital Printing Technologies, pp.
180-184 indicates that other researchers have subsequently
developed hardware and published experimental results using some
combination of heat and pressure for transfer and fusing
electrophotographic produced powder layers to produce 3D objects.
For example, the Jones et al. 2011 publication describes the use of
an industrial laser (electrophotographic) printer and infrared
heaters to assess the maximum thickness one can achieve in building
a 3D object according to the Bynum transfer approach. It was
learned that stack heights are limited to about 1 mm to 2 mm before
quality issues due to surface irregularities prevent further build
thicknesses.
[0011] The fact that the quality of the 3D objects produced by the
heat and pressure transfer method is not substantially improved
over the quality of such objects produced by the electrostatic
transfer method (including an electrostatic conditioning of the
object during the building) has been discussed by Jones et al. in
the conference proceedings of the Society for Imaging Science and
Technology (IS&T), NIP28: 2012 International Conference on
Digital Printing Technologies, pp. 327-331. The implication is that
during the build of the 3D object, charge accumulation on the
object due to the charge of the transferred powder and possible
contact charging by the heated transfer roller is the cause of
non-uniform transfer and consequently unacceptable 3D object
quality when the build thickness is typically greater than about 1
to 2 mm. It was suggested that acceptable 3D object quality
produced by the electrophotographic method is reliant on managing
the residual charge on the build object.
[0012] From a review of the literature and patents, it is clear
that the build rate of digitally produced 3D objects based on the
electrophotographic process is limited by a wait time associated
with the transfer of each 2D layer to the build object. Heat is
typically employed to render the 2D layer sufficiently tacky during
a transfusion step that also uses pressure to adhere the layer to
the build object. Furthermore, the build object can be either
charged or neutralized with gaseous ions to improvement the quality
of the build object. Whenever heating is used such as in the
transfusion step, there is a wait time introduced in the process
that depends on heating rates, thermal conductivities, heat
capacities, and cooling rates. The productivity for digitally
building a 3D object on a build platform with the
electrophotographic process is compromised if the thermal wait time
for applying another layer exceeds the time that it takes to
produce a 2D layer by the electrophotographic process.
[0013] In summary, in the patents, published applications, and
literature known to the Applicants that describe various methods
including electrophotographic methods, for digitally fabricating 3D
objects, such methods are limited to a single build platform
architecture. If the lateral size of the 3D object is smaller than
the build platform size, it is possible to produce multiple 3D
objects on a single platform. However, the productivity for
producing 3D objects is not substantially improved for 3D
fabrication methods in which the layer formation is based on a
single 2D scanning system. After a 3D object is fabricated on any
single build platform using a particular process, the 3D object
must either be removed from the build platform, or the build
platform with the 3D object must be removed and replaced with
another build platform for fabricating another 3D object of the
same or different shape. Under such constraints, the rate for
producing multiple 3D objects is undesirably slow when using an
apparatus and process that is limited to a single build
platform.
[0014] Accordingly, there remains a need for a high build rate
method and apparatus, which can build a three-dimensional part.
SUMMARY
[0015] It is the purpose of the present disclosure to describe a
method for improving the productivity of digitally fabricated
multiple 3D objects of the same or different shape and material
composition. The improved productivity is obtained by incorporating
multiple build platforms within the 3D manufacturing apparatus. In
one aspect of the present disclosure, variants of the
electrophotographic process may be used for producing 3D objects.
For such 3D manufacturing processes based on electrophotography, a
wait time is typically required before another layer can be applied
on top of the build object. This wait time can substantially reduce
the build rate, particularly for those manufacturing processes in
which the deposition time for a layer is rather short. With
multiple build platforms, a layer can be rapidly applied to one
build object after another as long as the time between layer
depositions for a particular object is greater than the wait time
required before deposition of the next layer in the case of when
only a single platform is utilized. The time for when another layer
is applied to a particular build object depends on the process
speed and the number of build platforms in the system. Thus, the
overall productivity for manufacturing many objects by the use of
multiple build platforms is substantially improved over the
production of the same number of 3D objects with a manufacturing
process based on a single platform.
[0016] A number of architectures are envisioned for providing
multiple platforms for digitally fabricating 3D objects. For planar
build platforms, the multiple platforms can be shuttled back and
forth in linear translations, or incorporated in a circulating
racetrack configuration. If the build platforms are in the shape of
an arc segment of a right circular cylinder, such multiple build
platforms can be attached to the surface of a rotating cylindrical
drum of nominally the same radius of curvature as the platforms.
Regardless of the particular configuration of multiple platforms, a
duplicate set of multiple platforms can also be configured adjacent
to the other set. When a complete set of multiple objects is
produced, the adjacent set of multiple platforms can be
automatically moved to the build station to continuously fabricate
3D objects on a new set of multiple platforms. While the new set of
objects is being produced, the previous completed set of objects
can be removed and new build platforms installed. Thus, the 3D
object build rate, and consequently overall productivity, is
substantially improved through the utilization of two sets of
adjacent multiple platforms that essentially enable continuous
deposition of layers for the fabrication of 3D objects of similar
or different shapes.
[0017] In accordance with the present disclosure, a method of
fabricating a plurality of objects using multiple build platforms
is provided. The method comprises depositing a first powder layer
on a surface of a first object substrate on a first build platform
located at a material transfer station; consolidating the first
powder layer on the first object substrate to form a first solid
layer of a first object on the first object substrate; locating a
second object substrate on a second build platform at the material
transfer station following removal of the first build platform with
the first object substrate from the material transfer station;
depositing a first powder layer on the surface of the second object
substrate; consolidating the first powder layer on the second
object substrate to form a first solid layer of a second object on
the second object substrate; and removing the second build platform
with the second object substrate from the material transfer
station.
[0018] In certain embodiments, consolidating the first powder layer
into a solid layer of the first object on the first object
substrate may be performed after removing the first build platform
with the first object substrate from the material transfer station.
In like manner, consolidating the first powder layer on the second
object substrate to form the first solid layer of the second object
on the second object substrate may be performed after removing the
second build platform with the second object substrate from the
material transfer station. Consolidating a powder layer on an
object substrate, or on previously consolidated layers on the
substrate may be performed by applying at least one of heat and
pressure to the powder layer.
[0019] In other embodiments, consolidating the first powder layer
on the first object substrate to form the first solid layer of the
first object on the first object substrate and consolidating the
first powder layer on the second object substrate to form the first
solid layer of the second object on the second object may be
performed at the material transfer station. Consolidating the first
powder layer on the first object substrate may be performed during
depositing the first powder layer on the surface of the first
object substrate, and consolidating the first powder layer on the
second object substrate may be performed during depositing the
first powder layer on the surface of the second object substrate.
Alternatively, consolidating the first powder layer on the first
object substrate and consolidating the first powder layer on the
second object substrate may be performed after depositing the first
powder layer on the surface of the first object substrate and
depositing the first powder layer on the surface of the second
object substrate. The method may further include pre-conditioning
the first solid layer of the first object on the first object
substrate and the first solid layer of the second object on the
second object substrate.
[0020] In certain embodiments, the method may further comprise
first depositing the first powder layer deposited on the surface of
the first object substrate on a surface of an intermediate
substrate, moving that first powder layer on the surface of the
first intermediate substrate to the first build platform located at
the material transfer station prior to depositing the first powder
layer on the surface of the first object substrate; and depositing
the first powder layer deposited on the surface of the second
object substrate on the surface of the intermediate substrate,
moving that first powder layer on the surface of the intermediate
substrate to the second build platform located at the material
transfer station prior to depositing that first powder layer on the
surface of the second object substrate. The intermediate substrate
may be a belt substrate or a drum substrate. The depositing of
powder layers on the surface of the intermediate substrate may be
performed by an electrophotographic process. In certain
embodiments, the intermediate substrate may be a belt substrate. In
other embodiments, the intermediate substrate may be a drum
substrate.
[0021] The method may further comprise pre-conditioning the powder
layers on the surface of the intermediate substrate prior to
depositing the respective powder layers on the respective surfaces
of the object substrates, or the consolidated layers adhered
thereto. The method may further comprise post-conditioning the
respective first solid layers or consolidated solid layers on the
respective object substrates.
[0022] In instances in which the objects are comprised of two
layers, the method further comprises moving the first build
platform with the first object substrate and first solid layer of
the first object to the material transfer station; depositing a
second powder layer on the first solid layer of the first object;
consolidating the second powder layer with the first solid layer of
the first object; locating the second build platform with the
second object substrate and first solid layer of the second object
at the material transfer station following removal of the first
build platform with the first object substrate from the material
transfer station; depositing a second powder layer on the first
solid layer of the second object; consolidating the second powder
layer with the first solid layer of the second object; and removing
the second build platform with the second object substrate from the
material transfer station.
[0023] Objects comprised of many more layers may be fabricated.
Stated generally, for first and second objects comprised of h
consolidated layers, after the consolidation of the first two
layers of the first and second objects, the method comprises
repeating the following steps h-2 times: moving the first build
platform with the first object substrate and consolidated solid
layers of the first object to the material transfer station;
depositing an additional powder layer on the consolidated solid
layers of the first object; consolidating the additional powder
layer with the consolidated solid layers of the first object;
locating the second build platform with the second object substrate
and consolidated solid layers of the second object at the material
transfer station following removal of the first build platform with
the first object substrate and consolidated solid layers of the
first object from the material transfer station; depositing an
additional powder layer on the consolidated solid layers of the
second object; consolidating the additional powder layer with the
consolidated solid layers of the second object; and removing the
second build platform with the second object substrate from the
material transfer station.
[0024] In certain embodiments, the moving of the build platforms to
and from the material transfer station may be performed using
linear pathways. In other embodiments, the moving of the build
platforms may be performed using cyclic loop pathways. The cyclic
loop pathways may be rectangular or elliptical pathways, or
"racetrack" shaped having linear elongated sides and circular ends.
In embodiments in which the build platforms are joined to a
cylinder, the cyclic loop pathways are circular.
[0025] The method may be used to fabricate more than two objects.
Stated generally, in the fabrication of each additional object, for
the addition of another layer, the method comprises selecting a
chosen build platform from the set of build platforms that are
holding the objects, and moving the chosen build platform with
object substrate and consolidated solid layers of the object on the
chosen build platform to the material transfer station; depositing
an additional powder layer on a surface of the object substrate on
the consolidated solid layers of the object on the chosen build
platform; consolidating the additional powder layer with the
consolidated solid layers of the object on the chosen build
platform; and removing the chosen build platform from the material
transfer station. For each additional object, the powder layer
depositions and consolidations may be repeated as described above
to fabricate the objects with multiple layers.
[0026] In certain embodiments of methods for fabricating more than
two objects, the build platforms may be divided into two or more
groups that are movable by conveyors that are adjacent to each
other. Such embodiments are advantageous in that the cycle time for
fabricating an object is reduced, as will be described
subsequently. In one such embodiment, the method further comprises
providing a third build platform and a fourth build platform
adjacent to the first build platform and the second build platform,
the third and fourth build platforms movable relative to the
material transfer station along a second cyclic loop pathway;
disposing a third object substrate on the third build platform;
disposing a fourth object substrate on the fourth build platform;
moving the first build platform and first object substrate and
first solid layer of the first object and the second build platform
and second object substrate and first solid layer of the second
object relative to the material transfer station to a distal
location wherein the first cyclic loop pathway is not in
communication with the material transfer station; moving the third
build platform and third object substrate and the fourth build
platform and fourth substrate relative to the material transfer
station to a proximal location wherein the second loop pathway is
in communication with the material transfer station; locating the
third build platform and third object substrate at the material
transfer station, depositing a first powder layer on the surface of
the third object substrate and consolidating the first powder layer
on the third object substrate to form a first solid layer of the
third object on the third object substrate; and locating the fourth
build platform and fourth object substrate at the material transfer
station following removal of the third build platform with the
third object substrate from the material transfer station,
depositing a first powder layer on the surface of the fourth object
substrate and consolidating the first powder layer on the fourth
object substrate to form a first solid layer of the fourth object
on the fourth object substrate. The second cyclic loop pathway may
be in a direction that is opposite to the direction of the first
cyclic loop pathway.
[0027] In certain embodiments, the first and second build platforms
may be joined to an outer surface of a cylinder having an axis of
rotation equidistant from all points on the outer surface. The
first and second build platforms follow a loop pathway that is
circular. In such embodiments, the method further comprises
rotating the cylinder about its axis of rotation to cause the
locating of the first build platform, first object substrate and
first powder layer of the first object at the material transfer
station, and to cause the removal of the first build platform with
the first object substrate and first solid layer of the first
object from the material transfer station, and to cause the
locating of the second build platform, second object substrate and
first powder layer of the second object at the material transfer
station, and to cause the removal of the second build platform with
the second object substrate and first solid layer of the second
object from the material transfer station.
[0028] In certain embodiments for fabricating more than two
objects, wherein n build platforms are joined to the surface of the
cylinder, the method further comprises: for each of the n-2
additional object build platforms, rotating the cylinder about its
axis of rotation to cause the locating of the build platform, the
object substrate and the powder layer of the object on that build
platform at the material transfer station; consolidating the powder
layer on the object substrate to form a first solid layer of the
object on the object substrate on that build platform; and rotating
the cylinder about its axis of rotation to cause the removal of
that build platform with the object substrate and solid layer of
the object on that build platform from the material transfer
station.
[0029] In accordance with the present disclosure, an apparatus for
making a plurality of objects is also provided. The apparatus
comprises a plurality of object substrates, each of the substrates
comprising a powder receiving surface; a plurality of build
platforms, each of the build platforms engageable with any one of
the object substrates; a material transfer station comprised of a
fixture engageable with any one of the build platforms; a
transporting device engaged with each of the build platforms and
operable to repeatedly transport each of the build platforms to and
from the material transfer station; and a powder layering device
operable to dispense a layer of powder onto one of the powder
receiving surface or a consolidated layer of powder on the powder
receiving surface of any one of the object substrates when that
object substrate is located at the material transfer station.
[0030] In certain embodiments, the powder layering device may be
comprised of a powder layer generating device operable to dispense
a powder layer onto a powder layer transfer device comprising a
transfer substrate having a surface movable between the powder
layer generating device and the material transfer station. The
powder layer transfer device substrate may be a belt substrate or a
drum substrate. The powder layer generating device may be an
electrophotographic imaging engine. In certain embodiments, the
transporting device transports the build platforms to and from the
material transfer station in linear pathways.
[0031] In other embodiments, the transporting device transports the
build platforms to and from the material transfer station in cyclic
loop pathways. In one such embodiment, the transporting device of
the apparatus is comprised of a first conveyor engaged with a first
portion of the build platforms and operable to transport the first
portion of the build platforms to and from the material transfer
station in a first cyclic loop pathway; and a second conveyor
adjacent to the first conveyor and engaged with a second portion of
the build platforms and operable to transport the second portion of
the build platforms to and from the material transfer station in a
second cyclic loop pathway. In another embodiment, the transporting
device of the apparatus is a cylinder comprising an outer surface
and having an axis of rotation equidistant from all points on the
outer surface, and each of the build platforms are joined to the
outer surface of the cylinder, and wherein the cylinder is
rotatable around its axis of rotation to transport each of the
build platforms to and from the material transfer station.
[0032] In a further embodiment, multiple cylinders may be used to
transport the build platforms, each cylinder transporting a portion
of the build platforms joined thereto. In one such embodiment, the
transporting device of the apparatus is comprised of a first
cylinder and a second cylinder, each of the first and second
cylinders comprising an outer surface and having an axis of
rotation equidistant from all points on the outer surface of that
cylinder. A first portion of the build platforms are joined to the
outer surface of the first cylinder, and the first cylinder is
movable to a location proximate to the material transfer station
and rotatable around its axis of rotation to transport each of the
build platforms of the first portion of the build platforms to and
from the material transfer station. A second portion of the second
cylinder is movable to the location proximate to the material
transfer station and rotatable around its axis of rotation to
transport each of the build platforms of the second portion of the
build platforms to and from the material transfer station.
[0033] The use of multiple conveyors or multiple cylinders, each
moving a portion of the build platforms, is advantageous because it
reduces the cycle time to fabricate an object, as will be explained
subsequently.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] The present disclosure will be provided with reference to
the following drawings, in which like numerals refer to like
elements, and in which:
[0035] FIG. 1 is a schematic illustration of a conventional
electrophotographic printer;
[0036] FIG. 2 is a schematic illustration of two
electrophotographic printers for depositing different powder layers
onto a belt medium for transfer onto a 3D object on a moveable
planar build platform that enables post-transfer conditioning;
[0037] FIGS. 3A, 3B, and 3C are schematic plan views of an
apparatus for fabricating 3D objects comprised of multiple planar
build platforms being continuously translated past a layer
deposition apparatus, and optionally, one or more conditioning
stations;
[0038] FIG. 4 is a schematic illustration for transferring layers
to one or more 3D object build platforms, followed by one or more
stations for conditioning the layers;
[0039] FIG. 5A and 5B are schematic plan views of an apparatus for
fabricating 3D objects comprised of multiple planar build platforms
continuously translated past a layer deposition apparatus with a
transfer station and, optionally, one or more conditioning stations
in a "racetrack" configuration;
[0040] FIG. 6 is a schematic plan view of an apparatus for
fabricating 3D objects, which illustrates in the upper half of the
FIG. 6, multiple planar build platforms continuously translated
past a layer deposition apparatus in a racetrack configuration, and
in the lower half of the FIG. 6, a similar set of stationary
multiple planar platforms adjacently positioned for rapid switching
between the racetrack configurations relative to the layer
deposition apparatus in order to provide virtually continuous 3D
object building on multiple platforms;
[0041] FIG. 7 is a schematic plan view of an apparatus for
fabricating 3D objects similar to the apparatus of FIG. 6, except
both the upper and lower halves of multiple planar build platforms
have been shifted so that the layer deposition apparatus can begin
to build 3D objects on the lower half while the completed 3D build
objects on the upper half are removed and replaced with clean build
platforms;
[0042] FIG. 8 is a schematic side view of an apparatus for
fabricating 3D objects comprised of a rotating cylindrical drum
fitted with multiple build platforms in the shape of an arc segment
of a right circular cylinder, in which powder layers are
sequentially roller transferred to the cylindrical build platforms;
and
[0043] FIG. 9 is a schematic plan view of an apparatus for
fabricating 3D objects comprised of two adjacent rotating
cylindrical drums fitted with multiple build platforms in the shape
of an arc segment of a right circular cylinder, wherein the
adjacent drums can be shuttled back and forth under the roller
transfer station when one drum has completed building the 3D
objects.
DETAILED DESCRIPTION
[0044] For a general understanding of the present invention,
reference is made to the drawings. In the drawings, like reference
numerals have been used throughout to designate identical elements.
It is to be understood that the overall scale of the drawings and
the relative sizes of particular features are as shown for the sake
of clarity of illustration, and may vary from that shown.
Additionally, this disclosure may identify certain components with
adjectives such as "top," "upper," "bottom," "lower," "left,"
"right," etc. These adjectives are provided in the context of the
orientation of the drawings, which is not to be construed as
limiting the apparatus disclosed herein to use in a particular
spatial orientation.
[0045] It is also to be understood that any connection references
used herein (e.g., attached, coupled, connected, and joined) are to
be construed broadly and may include intermediate members between a
collection of elements and relative movement between elements
unless otherwise indicated. As such, connection references do not
necessarily imply that two elements are directly connected and in
fixed relation to each other.
[0046] To fully illustrate the benefit of utilizing multiple build
platforms for improving the productivity of digitally fabricated 3D
objects, a detailed description of certain preferred embodiments is
provided in connection with 3D manufacturing processes based on
electrophotography. This emphasis on electrophotographic processes
should not be interpreted to limit the utility of multiple build
platforms as being operable with only electrophotographic
processes. Rather, multiple build platforms can improve
productivity for a number of other 3D manufacturing processes for
which a post layer conditioning time is comparable to or greater
than the layer deposition time. The emphasis on electrophotographic
processes is due to the fact that the electrophotography printing
process can produce 2D powder layers of the size of paper documents
(21 cm by 28 cm) at rates up to approximately 180 prints per
minute. This is equivalent to a rate of about one layer every 1/3
of a second. If each powder layer is approximately 25 .mu.m thick,
at this rate a 7.5 cm high 3D object can be fabricated in an hour.
Accordingly, while the combination of an electrophotographic
process with multiple build platforms is one preferred embodiment
of an apparatus for and a method of making a three-dimensional
object, other additive manufacturing processes may also be used
with multiple build platforms to perform the 3D object fabrication,
such as those additive manufacturing processes that require coating
a powder layer on the 3D object and support material before the
next layer is subjected to ink jet or laser scanning.
[0047] For the purposes of understanding certain
electrophotographic embodiments of the apparatus and methods of the
present disclosure, a summary of the electrophotographic process
will first be presented. Referring to FIG. 1, system 10 is a
schematic illustration of a conventional electrophotographic
printer for producing black and white prints on a typical medium
such as paper. The printer contains a number of sub-systems
configured around a rotating grounded and conductive drum 12
overcoated with photoconductive material 14. The shaft 16 is
connected to a drive motor (not shown) for rotation of the drum 12
in the direction of the arrow 18. The photoconductive material 14
may be provided from a variety of materials such as amorphous
selenium and alloys, zinc oxide either alone or in combination with
organic materials, or organic materials alone that provide
photoinduced charge generation and transport. The photoconductive
material 14 is uniformly charged with a corona device 22 and then
exposed to light from a laser raster output scanner 24 comprised of
a modulated laser beam reflected off a rotating polygon mirror.
Alternatively, a LED image bar may be used to produce an
electrostatic latent image on the photoconductor. A development
system 26 containing typically insulative powder referred to as
toner is charged by triboelectricity in either single component
(illustrated in FIG. 1) or two-component (mixture of toner with
larger magnetic carrier beads) development systems. The
triboelectrically charged toner is used to develop either charged
or discharged areas of the electrostatic image on the
photoconductor; according to the charge polarity of the toner. The
toned region 28 of the photoconductor 14 is the region between
approximately the 3 o'clock and the 6 o'clock positions of the
photoconductor 14 in FIG. 1. A medium 32 such as paper is fed
between the toned photoconductor 14 and a corona ion transfer
device 34. The polarity of the ion charge applied to the medium 32
by the corona ion transfer device 34 is opposite to that of the
toner charge so that there is an electrostatic attraction of the
toner 28 to the medium 32. The toned medium passes through a fusing
system 36 that binds the toner 29 to the medium 32 by heat and
pressure. Any residual toner (not shown) on the photoconductor that
was not transferred to the medium 32 is removed by a cleaning
system 38 before repeating the printing cycle.
[0048] FIG. 2 illustrates an architecture for digitally fabricating
3D objects with the electrophotographic process. FIG. 2 depicts two
electrophotographic print engines, 20 and 30, for providing
triboelectric charged powder images for the 3D object and support
materials, for example. The images of charged powder are
electrostatically transferred to an intermediate transfer belt 42
with the aid of electrically biased transfer rollers 44. The powder
layer 46 can be quickly transferred to the build object 58. Under
these circumstances, a synchronous roller contact 88 between the
powder layer 46 on the transfer belt 42 and the translating build
object 58 is sufficient to enable the layer transfer. The build
platform 50 is attached to a moving carriage or conveyor 52 that
can be translated back and forth in the process direction 54, as
well as the vertical direction 56 through the use of motors and
drive apparatus. FIG. 2 illustrates the possibility of using
pre-transfer heating 48 and post-transfer conditioning with the
energy source 74, layer consolidation 72 by heat and pressure, and
a cooling device 64.
[0049] Although not shown in FIG. 2, it may also be desirable to
use one or more stations for pre-conditioning the build object 58
immediately before powder layer 46 is transferred to the build
object 58 at a material transfer station such as that formed by a
synchronous roller contact 88 between the powder layer 46 on the
transfer belt 42 and the translating build object 58. One example
of a pre-conditioning station is a means for applying an adhesive
to the build object 58 to facilitate the transfer of the powder
layer 46 to the build object.
[0050] As described previously herein, the patents, published
patent applications, and literature describing various methods for
digitally fabricating 3D objects are limited to those having a
single build platform architecture. In contrast, in accordance with
the present disclosure, methods and apparatus are provided that
incorporate multiple build platforms for improved 3D fabrication
productivity. Such methods and apparatus will now be described with
reference to FIGS. 3A-9.
[0051] First, with regard to terms used in the following
disclosure, the term "build platform" is meant to indicate a base
or substrate that receives sequentially deposited layers of
material that form a three-dimensional object. A first layer is
deposited directly onto the substrate, a second layer is deposited
onto the first layer, and so forth with subsequent layers deposited
in sequence so as to build the three-dimensional object layer by
layer upon the build platform. The layer deposition apparatus,
and/or any layer conditioning apparatus that operates immediately
before or after layer deposition, may include a layer transfusing
apparatus, such as a heated pressure roller transfuse apparatus, or
other conditioning apparatus such as those described subsequently
herein.
[0052] When the layer depositions are completed to form the 3D
object, the object is separated from the build platform. In certain
embodiments, the build platform may have a planar surface for
receiving the layers of material. The surface of the build platform
that receives the layers of material will preferably have only a
moderate degree of adhesion to the material being deposited. The
adhesion will be sufficient to enable the build platform to be
moved during layer depositing operations without the object
becoming detached from the platform, but low enough so that the
object can easily be separated from the build platform when the
object is complete.
[0053] As described previously, the process by which the layers are
deposited may include electrophotographic processes such as the
process described previously with reference to FIGS. 1 and 2, or
other additive manufacturing processes such as selective laser
sintering, ink jet binding and electron beam melting of powder
layers. The deposited layers may include more than one material.
For example, a layer or series of layers may include "build"
material, which is a material that will be included in the final 3D
object, and "support" material, which is a material that is
temporarily placed in a layer so as to support subsequent build
material that is deposited on top of it, and which will later be
removed from the 3D object by dissolution, breaking away, or other
suitable means.
[0054] FIGS. 3A-3C show schematic plan views in which a series of
three-dimensional objects are fabricated using multiple build
platforms arranged in a linear array. In reference to FIG. 3A, a
layer of build and support material is transferred in zone 77 to
the build object 58 on build platform 50. As the build platforms
50, 60, and 70 are linearly translated in the direction of arrow
84, the configuration shown in FIG. 3B is obtained whereby one or
more post-transfer stations 82 are used to condition the
transferred layer of object 58 on platform 50. At the same time, a
layer of build and support material is transferred in zone 77 to
the object 68 being built on build platform 60. Further linear
advancements of the build platforms 50, 60, 70, and the 3.sup.rd
through (n-1)th build platforms (not shown but indicated by
sequential dots) occurs such that the 3.sup.rd through (n-1)th
platforms receive layers from the layer deposition apparatus (not
shown).
[0055] Upon yet further linear advancement of the build platforms
50, 60 and 70, the configuration shown in FIG. 3C is obtained
whereby one or more post-transfer stations 82 are used to condition
the transferred layer of object 68 on platform 60 and a layer of
build and support material is transferred in zone 77 to the object
78 being built on build platform 70. It should be noted that the
post-transfer stations for conditioning the transferred layer can
include the steps of transfusing, heating, cooling, consolidating,
UV curing, coating powder for the next layer, etc. It should
further be noted that after a layer is transferred and conditioned
on the nth build platform, the whole array of the n build platforms
is stepped down and rapidly translated back in the direction of
arrow 86 of FIG. 3C, in a time period referred to subsequently
herein as the "fly back time". The height of the platforms is reset
each time for repeatedly transferring the next set of layers.
[0056] In general, there can be n number of build platforms in a
linear array as indicated in FIGS. 3A-3C. A practical number for n
depends on the time required for conditioning a build object such
as object 58 after the transfer step, in comparison to the transfer
time. To quantitatively understand the build rate benefit of using
a linear array of multiple platforms when post transfer
conditioning is required or desired, it is informative to
demonstrate the benefit with mathematical descriptions. Towards
that end, FIG. 4 defines various parameters used in the
calculations. Suppose that the width 40 of a build platform in the
process direction is W.sub.p, the gap 80 between build platforms is
W.sub.g and the process speed 54 for layer transfer is V.sub.p. The
time to build a single layer on a single build platform, T.sub.1p,
is
T 1 p = W p + W g V p . ( 1 ) ##EQU00001##
[0057] If conditioning of the transferred layer is desired before
another layer can be transferred to the 3D object, extra time is
required for moving the build platform 50 past various conditioning
stations such as 74, 72 and 64. Assume that the distance of the
m.sup.th conditioning station from the layer transfer zone is given
by C.sub.m, where m is equal to 1 to N with N corresponding to the
conditioning station that is at the maximum distance from the
transfer zone. The extra time for complete conditioning is
determined by the distance C.sub.N, which can also be expressed as
the product of f.sub.N times (W.sub.p+W.sub.g). It should also be
noted that if one or more pre-transfer conditioning stations are
used, the time for pre-transfer conditioning is likewise determined
by the greatest distance between a pre-transfer conditioning
station and the transfer zone. When both pre-transfer and
post-transfer conditioning stations are used, f.sub.n is calculated
according to the maximum difference in distance between any
pre-transfer and post-transfer conditioning stations.
[0058] The time to build a single layer on a single build platform
50 with conditioning, T.sub.1pc, is
T 1 pc = W p + W g V p + f N ( W p + W g ) V p = W p + W g V p ( 1
+ f N ) . ( 2 ) ##EQU00002##
The time to build a single layer on two build platforms 40 and 50
with conditioning, T.sub.2pc, is
T 2 pc = W p + W g V p ( 2 + f N ) . ( 3 ) ##EQU00003##
The time to build a single layer on a linear array of n build
platforms, T.sub.npc, with conditioning is
T npc = W p + W g V p ( n + f N ) . ( 4 ) ##EQU00004##
The average time to build a single layer on a single platform for a
linear array of n platforms with conditioning, aveT.sub.npc, is
aveT npc = W p + W g V p ( 1 + f N n ) . ( 5 ) ##EQU00005##
[0059] After a single layer is applied and conditioned on a linear
array of n multiple platforms at a process speed 54 of V.sub.p, the
array of n platforms is stepped down and returned to the beginning
at a fly back speed 76 of V.sub.fb. The fly back time for a linear
array of n platforms, T.sub.nfb, will equal the build time
T.sub.npc from Eq. 4 times the ratio of V.sub.p to V.sub.fb. Thus,
the total time to build a single layer on a linear array of n
platforms with conditioning and fly back, T.sub.n, is
T n = W p + W g V p ( n + f N ) ( 1 + V p V fb ) . ( 6 )
##EQU00006##
[0060] The average time to build a single layer on a single
platform for a linear array of n platforms with conditioning and
fly back, aveT.sub.n, is
aveT n = W p + W g V p ( 1 + f N n ) ( 1 + V p V fb ) . ( 7 )
##EQU00007##
[0061] Assume now that the 3D fabrication process uses
electrophotography to produce the layers that are roller 88
transferred to the 3D build object at the layer transfer zone. The
process speed 62 of electrophotography is typically in the range of
10 to 75 cm/s. For a process speed 54 of V.sub.p=30 cm/s and
platform plus gap width of (W.sub.p+W.sub.g)=15 cm, the time to
build a single layer (without any conditioning or fly back time) on
a single build platform, T.sub.1p, from Eq. 1 is 0.5 seconds. If
f.sub.N is 2 and the ratio of the fly back speed, V.sub.fb, to
process speed, V.sub.p, is 3, then from Eq. 7 for n=1 the time to
deposit one layer on a single platform is 2 seconds. For n=10, the
average time to build a single layer on a single platform according
to Eq. 7 is 0.8 seconds. In the limit of a large number of
platforms, the average time to produce a single layer (with
conditioning and fly back time) on a single platform approaches
0.67 seconds.
[0062] If the height of a transferred layer after conditioning is
H.sub.l and from Eq. 7 the average time to produce a single layer
on a single platform for a linear array of n platforms with
conditioning and fly back is aveT.sub.n, then the rate of building
a 3D object, R, in units of height per unit time is
R = H l aveT n = H l W p + W g V p ( 1 + f N n ) ( 1 + V p V fb ) .
( 8 ) ##EQU00008##
[0063] To build a 3D object of height H.sub.o, the 3D object
average build time, T.sub.o, is
T o = H o R = H o H l [ W p + W g V p ( 1 + f N n ) ( 1 + V p V fb
) ] . ( 9 ) ##EQU00009##
[0064] If f.sub.N is 2, the ratio of the fly back speed, V.sub.fb,
to process speed, V.sub.p, is 3 and H.sub.l is 25 .mu.m, the time
to build a 3D object to a height of 9 cm is 2 hours for a single
platform corresponding to n=1. For n=10, the average time to build
a 3D object to the same height of 9 cm is reduced to 48
minutes.
[0065] With a linear array of multiple build platforms for
digitally fabricating 3D objects, a fly back time is required
before the next set of layers can be transferred to the build
objects. To obviate the need for a fly back time that decreases the
rate of building a 3D object, the movement of a set of the multiple
build platforms can be configured such that the multiple platforms
are continuously circulated through the transfer station. One
configuration for the continual circulation of multiple platforms
61 is illustrated in FIGS. 5A and 5B. In FIG. 5A, half of a set of
build platforms 51 are moving in the direction of arrow 92 whereas
simultaneously, the other half of build platforms 50 are moving in
the opposite direction of arrow 88. The build platforms 50 and 51
may be moved by conveyors, such as conveyor 52 of the apparatus of
FIG. 4.
[0066] A build or support layer is transferred to the build object
58 at transfer station 82. The transferred layers pass under
different types of one or more conditioning stations such as 84 and
86. When each half set of respective build platforms 50 and 51
moving in opposite directions becomes positioned as shown in FIG.
5B, the respective leading build platforms 53 and 55 of each half
set are switched to the other set as indicated by the directional
arrows 96 and 98. The build platform switching reestablishes the
configuration shown in FIG. 5A. Thus, the build platforms 50 and 51
continually circulate without essentially a pause until the
fabrication of the 3D objects is completed. After each platform has
received a layer, the support structure is incrementally lowered to
accommodate the thickness of the next layer. It should be noted
that although FIGS. 5A and 5B depict a particular architecture for
circulating the build platforms, other architectures such as
racetrack or carousel configurations are also feasible.
[0067] When multiple build platforms are continuously circulated
through the transfer station as illustrated in FIGS. 5A and 5B, the
need for a fly back time is obviated in comparison to a linear
array of build platforms. With no fly back time, the average time
to build a single layer on a single platform for a circulating set
of n platforms with conditioning is given by Eq. 5.
[0068] When the fabrication of a set of 3D objects is completed on
a set of build platforms as illustrated in FIGS. 5A and 5B, the
fabrication system will need to be stopped so that the completed 3D
objects and platforms can be removed and new build platforms
installed. The need for a changeover time reduces the build
productivity, and thus there is a further opportunity for improving
throughput of the 3D object fabrication system. To reduce the
impact of the changeover time on productivity, FIG. 6 shows two
sets 61 and 71 of build platforms that are adjacent to each other
and movable by conveyors (not shown). The 3D objects are fabricated
on the circulating set 61 of build platforms on a first conveyor,
while the set 71 of build platforms are idled in an adjacent
position on a second conveyor. As illustrated in the apparatus 103
of FIG. 7, the multiple planar build platforms 61 and 71 have been
shifted in the direction of 102 perpendicular to the process
direction 88 so that the transfer station 82 and one or more
conditioning stations such as 84 and 86 can begin to build 3D
objects on the build platforms 71 while the completed 3D objects on
build platforms 61 are removed and replaced with clean build
platforms. It is noted that the multiple planar build platforms 61
and 71 are moved relative to the material transfer station 82,
i.e., the build platforms 61 and 71 may be moved with the material
transfer station 82 remaining fixed, or vice versa, or a
combination of motion of both.
[0069] When fabrication of the set of 3D objects on build platforms
71 is completed, both sets of build platforms are translated in the
direction of 107 perpendicular to the process direction 88 so that
another set of 3D objects can be fabricated on set 61. The
circulation of the completed set of 3D objects on circulating set
71 is now idled while the next set of objects on build platforms 61
is being fabricated. The idled set 71 enables removal of the
completed 3D objects and the reloading of new build platforms.
During 3D object fabrication, one set of build platforms rotates
counter-clockwise as illustrated by directional arrows 88 and 92 in
FIG. 6 whereas the other set rotates clockwise as illustrated by
directional arrows 94 and 104 in FIG. 7. When fabrication of any
set of 3D objects is completed, both sets are translated back and
forth to enable virtually continuous 3D object building.
[0070] During the fabrication of objects on the set of build
platforms 61, the build platforms 61 are moved along a first cyclic
loop pathway that is in communication with the material transfer
station 82 as illustrated in FIG. 6. As used in this instance, "in
communication" means that the first cyclic loop pathway is proximal
to the material transfer station 82 so that the build platforms 61
can each be moved to the material transfer station 82, and the
powder layers upon each of them can be consolidated by the material
transfer station 82. Subsequently, as illustrated in FIG. 7 the
build platforms are moved "out of the way," i.e. to a position such
that the first cyclic loop pathway is not in communication with the
material transfer station 82; and the set of build platforms 71 is
moved such that the second cyclic loop pathway of the build
platforms 71 is in communication with the material transfer station
82. The build platforms 71 are then each moved to the material
transfer station 82, and the powder layers upon each of them are
consolidated by the material transfer station 82. The second cyclic
loop pathway may be in a direction that is opposite the first loop
pathway, as depicted in FIGS. 6 and 7.
[0071] In the digital fabrication of 3D objects, the object is
typically fabricated on a planar build platform in a manner similar
to electrophotographic printing on a planar sheet of paper as shown
in FIG. 1 and described previously herein. Each layer of the build
material represents a planar cross-section of the 3D object. This
digital representation is appropriate for 3D objects with large
cross-sectional areas. However, an alternative architecture for
fabricating 3D objects with multiple platforms is feasible for 3D
objects with small cross-sectional areas. FIG. 8 shows a schematic
side view illustration of an apparatus 101 for fabricating 3D
objects that is comprised of multiple build platforms that are
non-planar and disposed on the outer wall of a cylindrical support
drum 106 that rotates about a shaft 108. On the surface of the
cylindrical drum 106, multiple build platforms 80 in the shape of
an arc segment of a right circular cylinder are attached to the
drum 106. Electrophotographic engines (not shown) produce powder
layers 46 on transfer belt 42. The powder layer 46 can optionally
be exposed to a heat source 114 prior to transfer to the build
object 112 at the transfer zone 116 defined by the roller 88. The
surface speed of the build object 112 is maintained synchronous
with the speed of the transfer belt 42. Various desired
post-transfer conditioning stations can be configured after the
transfer zone 116. Examples of such stations include a heat or UV
energy source 118, a compaction or fusing roll 122, a cooling
source 124 and an ion charging source 126. After a complete
revolution of drum 106, the rotating shaft 108 is incrementally
lowered as indicated by arrow 132 to accommodate the thickness of
the next layer to be transferred.
[0072] When the fabrication of a set of 3D objects 112 is completed
on a set of build platforms 80 on one drum 106 as illustrated in
FIG. 8, the fabrication system 101 will need to be stopped so that
the completed 3D objects 112 and platforms 80 can be removed and
new cylindrical build platforms 80 installed. As described
previously, the need for a changeover time reduces the 3D object
build productivity. To reduce the impact of the changeover time on
productivity, an apparatus for fabricating 3D objects is provided
as shown in FIG. 9. The apparatus 105 is comprised of two adjacent
cylindrical drums 106A and 106B with sets of cylindrical section
build platforms 80 that are adjacent to each other. At the point in
the process as depicted in FIG. 9, 3D objects are being fabricated
on the rotating set 90 of build platforms 80 on a cylindrical drum
106A. Successive layers of build and support material are
transferred to the build object 112 in the transfer zone 116.
During fabrication of the 3D objects on rotating set 90, the set
100 of build platforms are idled in an adjacent position. When
fabrication of the set 90 of 3D objects is completed, both sets are
translated as indicated by arrow 136 in the axial direction so that
another set of 3D objects can be fabricated on the set 100 of build
platforms. The completed set 90 of 3D objects is now idled while
the next set 100 of objects is being fabricated. The idled set 90
enables removal of the completed 3D objects and reloading of new
build platforms. When fabrication of any set of 3D objects is
completed, both sets are translated back and forth to enable
virtually continuous 3D object building.
[0073] In using a cylindrical drum architecture for building 3D
objects on multiple platforms as illustrated in FIGS. 8 and 9, it
is necessary to use both object and support materials if the base
of the 3D object to be fabricated is flat. If the flat base of the
3D object to be fabricated has a width of W.sub.b in the process
direction and the radius 128 of the cylinder (See FIG. 8) defined
by the outer surface of the cylindrical build platforms 80 is
R.sub.c, then the gap, G, between the outer edge of a flat base and
the build platform is given by the formula,
G= {square root over (R.sub.c.sup.2+(W.sub.b/2).sup.2)}-R.sub.c.
(10)
[0074] For W.sub.b=15 cm and R.sub.c=30 cm, G=9.2 mm. For the same
base width but a larger radius of R.sub.c=60 cm, G=4.7 mm. It
follows that at the outer edge of a flat base, the total thickness
of the support material must be equal to or greater than G to be
able to fabricate a flat base for a 3D object.
[0075] The 3D objects fabricated on a rotating drum must have
sufficient cohesion and adhesion to the cylindrical section
platform so as to not come off when the objects are oriented upside
down during drum rotation. A centrifugal force also acts on the 3D
object during drum rotation. It is of interest to compare the
centrifugal force to the gravitational force. If the surface speed
of the object is the speed 62 of the transfer belt V.sub.b, then
the centrifugal force, F.sub.c, is given by the equation
F c = m V b 2 R c , ( 11 ) ##EQU00010##
where m is the mass of the object. Since the gravitational force is
mg where g=9.8 m/s.sup.2 is the acceleration due to gravity, it is
of interest to calculate the centrifugal acceleration in comparison
to g for typical operating conditions. For V.sub.b=30 cm/s and
R.sub.c=30 cm, the centrifugal acceleration is 0.3 m/s.sup.2. For a
typical operating surface speed and drum radius, the centrifugal
force can be neglected.
[0076] When a set of multiple build platforms are configured with
an adjacent set such that the platforms are continuously circulated
through a transfer station as illustrated in FIGS. 6, 7 and 9, the
rate of producing layers on the build object does not depend on the
fly back time. Under these conditions, the rate for height per unit
time, for continuously building a 3D object becomes
R c = H l aveT n = H l W p + W g V p ( 1 + f N n ) . ( 12 )
##EQU00011##
[0077] To build a 3D object of height H.sub.o under the continuous
build conditions, the object average build time, T.sub.c, is
T c = H o R c = H o H l W p + W g V p ( 1 + f N n ) . ( 13 )
##EQU00012##
[0078] If the width of the build platform, W.sub.b, is decreased,
then the rate of building 3D objects is increased according to Eq.
12. The time to build 3D objects is decreased according to Eq. 13.
On the other hand, multiple 3D objects can be fabricated on a build
platform of any practical size. Multiple objects, M, can be arrayed
on a build platform in the process direction and/or perpendicular
to the process direction. The rate for fabricating 3D objects,
R.sub.N, will be greater by a factor of M according to the
equation
R M = M H l aveT n = M H l W p + W g V p ( 1 + f N n ) . ( 14 )
##EQU00013##
[0079] The time for fabricating a 3D object with M multiple objects
per platform, T.sub.M, is
T M = H o R m = H o M H l W p + W g V p ( 1 + f N n ) . ( 15 )
##EQU00014##
[0080] It is, therefore, apparent that there has been provided, in
accordance with the present invention, a method for improving the
productivity of digitally fabricating multiple 3D objects of the
same or different shape. The improved productivity is obtained by
incorporating multiple build platforms and multiple objects per
platform within the 3D manufacturing apparatus. The productivity
improvements are particularly significant for the 3D manufacturing
process based on electrophotography.
[0081] Having thus described the basic concept of the invention, it
will be rather apparent to those skilled in the art that the
foregoing detailed disclosure is intended to be presented by way of
example only, and is not limiting. Various alterations,
improvements, and modifications will occur to those skilled in the
art, though not expressly stated herein. These alterations,
improvements, and modifications are intended to be suggested
hereby, and are within the spirit and scope of the invention.
Additionally, the recited order of processing elements or
sequences, or the use of numbers, letters, or other designations
therefore, is not intended to limit the claimed processes to any
order except as may be expressly specified in the claims.
* * * * *
References