U.S. patent application number 15/327855 was filed with the patent office on 2017-07-20 for gear-based liquefier assembly for additive manufacturing system, and methods of use thereof.
The applicant listed for this patent is Stratasys, Inc.. Invention is credited to James W. Comb, Dana R. Hansen, Jonathan B. Hedlund, Timothy A. Hjelsand.
Application Number | 20170203506 15/327855 |
Document ID | / |
Family ID | 53776996 |
Filed Date | 2017-07-20 |
United States Patent
Application |
20170203506 |
Kind Code |
A1 |
Hjelsand; Timothy A. ; et
al. |
July 20, 2017 |
GEAR-BASED LIQUEFIER ASSEMBLY FOR ADDITIVE MANUFACTURING SYSTEM,
AND METHODS OF USE THEREOF
Abstract
A liquefier assembly for use in an additive manufacturing system
to print three-dimensional parts, which includes an upstream
pressure-generating stage and downstream flow-regulating stage. The
upstream pressure-generating stage includes a drive mechanism, a
liquefier configured to melt a consumable material receive from the
drive mechanism to produce a molten material in a pressurized
state. The downstream flow-regulating stage includes a gear
assembly having a casing assembly and a pair of gears disposed
within the interior cavity and engaged with each other to regulate
a flow of the pressurized molten material through the gear assembly
for controlled extrusion.
Inventors: |
Hjelsand; Timothy A.;
(Waconia, MN) ; Hansen; Dana R.; (South Saint
Paul, MN) ; Comb; James W.; (Hamel, MN) ;
Hedlund; Jonathan B.; (Blaine, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Stratasys, Inc. |
Eden Prairie |
MN |
US |
|
|
Family ID: |
53776996 |
Appl. No.: |
15/327855 |
Filed: |
July 21, 2015 |
PCT Filed: |
July 21, 2015 |
PCT NO: |
PCT/US2015/041349 |
371 Date: |
January 20, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62027469 |
Jul 22, 2014 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 2948/9239 20190201;
B29C 2948/926 20190201; B29C 48/92 20190201; B29C 2948/92457
20190201; B33Y 40/00 20141201; B29C 48/05 20190201; B33Y 30/00
20141201; B29C 48/2886 20190201; B29C 64/118 20170801; B29C 48/2552
20190201; B29C 48/37 20190201; B29C 48/266 20190201; B29K 2105/0067
20130101; B29C 64/209 20170801; B33Y 10/00 20141201; B29C 48/02
20190201; B29C 2948/92952 20190201; B33Y 50/02 20141201; B29C
2948/92104 20190201; B29C 64/106 20170801; B29C 2948/92095
20190201; B29C 64/393 20170801 |
International
Class: |
B29C 67/00 20060101
B29C067/00; B33Y 40/00 20060101 B33Y040/00; B33Y 50/02 20060101
B33Y050/02; B33Y 10/00 20060101 B33Y010/00; B33Y 30/00 20060101
B33Y030/00 |
Claims
1. A liquefier assembly for use in an additive manufacturing system
to print three-dimensional parts, the liquefier assembly
comprising: a first drive mechanism configured to feed a consumable
material; a liquefier configured to receive the consumable material
fed from the first drive mechanism, to melt the received consumable
material to produce a molten material in a pressurized state; and a
gear assembly comprising: a casing assembly comprising; an inlet
opening configured to operably receive the pressurized molten
material from the liquefier; an interior cavity configured to
receive the pressurized molten material from the inlet opening; and
an outlet opening; a first gear disposed within the interior
cavity, and configured to rotate under motorized power; and a
second gear engaged with the first gear, and configured to counter
rotate with the rotation of the first gear, wherein the rotations
of the first gear and the second gear regulate a flow of the
pressurized molten material from the inlet opening to the outlet
opening.
2. The liquefier assembly of claim 1, wherein the liquefier
comprises: a tubular liquefier having a cylindrical or ribbon
geometry; and one or more heating assemblies configured to heat the
tubular liquefier.
3. The liquefier assembly of claim 1, wherein the consumable
material comprises a filament.
4. The liquefier assembly of claim 1, and further comprising a
nozzle operably connected to the casing assembly at the outlet
opening, wherein the nozzle is configured to extrude the regulated
flow of the molten material.
5. The liquefier assembly of claim 1, wherein the casing assembly
comprises: a first casing; and a second casing secured to the first
casing, and having the inlet opening, the interior cavity, and the
outlet opening.
6. The liquefier assembly of claim 1, and further comprising one or
more heater elements secured to the casing assembly, wherein the
one or more heater elements are configured to heat the casing
assembly.
7. The liquefier assembly of claim 1, and further comprising: a
second drive mechanism configured to feed a second consumable
material; a second liquefier configured to receive the second
consumable material fed from the second drive mechanism, to melt
the received second consumable material to produce a second molten
material in a pressurized state; wherein the inlet opening in the
casing assembly is also configured to operably receive the second
pressurized molten material from the second liquefier.
8. The liquefier assembly of claim 7, and further comprising a
manifold operably connected to the inlet opening of the casing
assembly, wherein the inlet opening is configured to operably
receive the pressurized molten materials from the first and second
liquefiers through the manifold.
9. The liquefier assembly of claim 1, and further comprising a
second drive mechanism configured to generate the motorized power
for rotating the first gear.
10. The liquefier assembly of claim 9, and further comprising one
or more communication lines configured to operably connect the
first drive mechanism and the second drive mechanism to a
controller assembly of the additive manufacturing system.
11. An additive manufacturing system for printing three-dimensional
parts, the additive manufacturing system comprising: an upstream
pressure-generating stage comprising: a first drive mechanism; a
liquefier; one or more heater assemblies configured to heat the
liquefier; a downstream flow-regulating stage comprising: a casing
assembly having an inlet opening operably connected to the
liquefier, an outlet opening, and an interior cavity
interconnecting the inlet and outlet openings; a pair of engaged
gears disposed within the interior cavity of the casing assembly;
and one or more heater elements configured to heat the casing
assembly; a second drive mechanism operably connected to at least
one gear of the pair of engaged gears; and a controller assembly
operably connected to the first and second drive mechanisms, and
configured to command the first drive mechanism to feed a
consumable material to the liquefier to produce a pressurized
molten material, and to command the second drive mechanism to
rotate the pair of engaged gears to regulate a flow of the
pressurized molten material.
12. The additive manufacturing system of claim 11, wherein the pair
of engaged gears comprises: a drive gear having a shaft that is
operably connected to the second drive mechanism; and an idler gear
engaged with the drive gear such that a rotation of the drive gear
counter rotates the idler gear.
13. The additive manufacturing system of claim 11, wherein the
liquefier comprises a tubular liquefier having a cylindrical or
ribbon geometry.
14. The additive manufacturing system of claim 11, and further
comprising a nozzle operably connected to the casing assembly at
the outlet opening, wherein the nozzle is configured to extrude the
regulated flow of the molten material.
15. The additive manufacturing system of claim 11, wherein the
casing assembly comprises: a first casing; and a second casing
secured to the first casing, and having the inlet opening, the
interior cavity, and the outlet opening.
16. A method for printing a three-dimensional part with an additive
manufacturing system, the method comprising: feeding a consumable
material to a liquefier retained by the additive manufacturing
system with a drive mechanism retained by the additive
manufacturing system; melting the fed consumable material in the
liquefier to produce a molten material; providing the molten
material in a pressurized state to a gear assembly retained by the
additive manufacturing system; and regulating a flow of the
pressurized molten material through the gear assembly to extrude
the molten material in a controlled manner.
17. The method of claim 16, wherein the gear assembly comprises a
pair of engaged gears, and wherein regulating the flow of the
pressurized molten material through the gear assembly comprises
counter rotating the engaged gears.
18. The method of claim 16, wherein the molten material is a first
molten material, and wherein the method further comprises: feeding
a second consumable material to a second liquefier retained by the
additive manufacturing system with a second drive mechanism
retained by the additive manufacturing system; melting the fed
second consumable material in the second liquefier to produce a
second molten material; providing the second molten material in a
pressurized state to the gear assembly with the first molten
material; and regulating the flow of the second pressurized molten
material through the gear assembly with the first pressurized
molten material to extrude the second molten material in a
controlled manner.
19. The method of claim 16, wherein regulating the flow of the
pressurized molten material through the gear assembly comprises
controllably applying an active torque on a drive gear of the gear
assembly to drive the pressurized molten material.
20. The method of claim 16, wherein regulating the pressurized
molten material through the gear assembly comprises controllably
releasing a resistive torque on a drive gear of the gear assembly
to drive the pressurized molten material.
Description
BACKGROUND
[0001] The present disclosure relates to additive manufacturing
systems for printing or otherwise producing three-dimensional (3D)
parts and support structures. In particular, the present disclosure
relates to print head extruders for printing 3D parts and support
structures in a layer-by-layer manner using an additive
manufacturing technique.
[0002] Additive manufacturing systems are used to print or
otherwise build 3D parts from digital representations of the 3D
parts (e.g., AMF and STL format files) using one or more additive
manufacturing techniques. Examples of commercially available
additive manufacturing techniques include extrusion-based
techniques, jetting, selective laser sintering, powder/binder
jetting, electron-beam melting, and stereolithographic processes.
For each of these techniques, the digital representation of the 3D
part is initially sliced into multiple horizontal layers. For each
sliced layer, a tool path is then generated, which provides
instructions for the particular additive manufacturing system to
print the given layer.
[0003] For example, in an extrusion-based additive manufacturing
system, a 3D part may be printed from a digital representation of
the 3D part in a layer-by-layer manner by extruding a flowable part
material. The part material is extruded through an extrusion tip
carried by a print head of the system, and is deposited as a
sequence of roads on a platen in planar layers. The extruded part
material fuses to previously deposited part material, and
solidifies upon a drop in temperature. The position of the print
head relative to the substrate is then incremented, and the process
is repeated to form a 3D part resembling the digital
representation.
[0004] In fabricating 3D parts by depositing layers of a part
material, supporting layers or structures are typically built
underneath overhanging portions or in cavities of 3D parts under
construction, which are not supported by the part material itself.
A support structure may be built utilizing the same deposition
techniques by which the part material is deposited. The host
computer generates additional geometry acting as a support
structure for the overhanging or free-space segments of the 3D part
being formed. Support material is then deposited pursuant to the
generated geometry during the printing process. The support
material adheres to the part material during fabrication, and is
removable from the completed 3D part when the printing process is
complete.
SUMMARY
[0005] An aspect of the present disclosure is directed to a
liquefier assembly for use in an additive manufacturing system to
print 3D parts. The liquefier assembly includes a drive mechanism
configured to feed a consumable material; a liquefier configured to
receive and melt the consumable material fed from the drive
mechanism to produce a molten material in a pressurized state, and
a gear assembly. The gear assembly includes a casing assembly that
has an inlet opening configured to operably receive the pressurized
molten material from the liquefier, an interior cavity configured
to receive the pressurized molten material from the inlet opening,
and an outlet opening. The gear assembly also includes a first gear
disposed within the interior cavity, and configured to rotate under
motorized power, and a second gear engaged with the first gear, and
configured to counter rotate with the rotation of the first gear,
where the rotations of the first and second gears regulate a flow
of the pressurized molten material from the inlet opening to the
outlet opening.
[0006] Another aspect of the present disclosure is directed to an
additive manufacturing system for printing 3D parts. The additive
manufacturing system includes an upstream pressure-generating stage
and a downstream flow-regulating stage. The upstream
pressure-generating stage includes a first drive mechanism, a
liquefier, and one or more heater assemblies configured to heat the
liquefier. The downstream flow-regulating stage includes a casing
assembly having an inlet opening operably connected to the upstream
liquefier, an outlet opening, and an interior cavity
interconnecting the inlet and outlet openings. The downstream
flow-regulating stage also includes a pair of engaged gears
disposed within the interior cavity of the casing assembly, one or
more heater elements configured to heat the casing assembly, and a
second drive mechanism operably connected to at least one gear of
the pair of engaged gears. The additive manufacturing system also
includes a controller assembly operably connected to the first and
second drive mechanisms, and configured to command the first drive
mechanism to feed a consumable material to the liquefier to produce
a pressurized molten material, and to command the second drive
mechanism to rotate the pair of engaged gears to regulate a flow of
the pressurized molten material.
[0007] Another aspect of the present disclosure is directed to a
method for printing a 3D part with an additive manufacturing
system. The method includes feeding a consumable material to a
liquefier retained by the additive manufacturing system with a
drive mechanism retained by the additive manufacturing system, and
melting the fed consumable material in the liquefier to produce a
molten material. The method also includes providing the molten
material in a pressurized state to a gear assembly retained by the
additive manufacturing system, and regulating a flow of the
pressurized molten material through the gear assembly to extrude
the molten material in a controlled manner.
Definitions
[0008] Unless otherwise specified, the following terms as used
herein have the meanings provided below:
[0009] The terms "axial" and "axially", such as with reference to
pressures applied to a liquefier having a longitudinal length,
refer to directions that are perpendicular to the longitudinal
length. These terms do not require a concentric axis, and also
apply to non-cylindrical liquefiers, such as rectangular
liquefiers, arcuate liquefiers, elliptical liquefiers, and the
like.
[0010] The term "operably connected", with reference to articles
being operably connected to each other, refers to direct
connections (physically in contact with each other) and indirect
connections (connected to each other with one or more additional
components, such as spacers, disposed between them).
[0011] The terms "command", "commanding", and the like, with
reference to a controller assembly commanding a device (e.g., a
drive mechanism, a heater assembly, and the like), refers to
directly and/or indirectly relaying control signals from the
controller assembly to the device such that the device operates in
conformance with the relayed signals. The signals may be relayed in
any form, such as communication signals to a microprocessor on the
device, applied electrical power to operate the device, and the
like.
[0012] The terms "preferred", "preferably", "example" and
"exemplary" refer to embodiments of the invention that may afford
certain benefits, under certain circumstances. However, other
embodiments may also be preferred or exemplary, under the same or
other circumstances. Furthermore, the recitation of one or more
preferred or exemplary embodiments does not imply that other
embodiments are not useful, and is not intended to exclude other
embodiments from the scope of the present disclosure.
[0013] Directional orientations such as "above", "below", "top",
"bottom", and the like are made with reference to a layer-printing
direction of a 3D part. In the embodiments shown below, the
layer-printing direction is the upward direction along the vertical
z-axis. In these embodiments, the terms "above", "below", "top",
"bottom", and the like are based on the vertical z-axis. However,
in embodiments in which the layers of 3D parts are printed along a
different axis, such as along a horizontal x-axis or y-axis, the
terms "above", "below", "top", "bottom", and the like are relative
to the given axis.
[0014] The term "providing", such as for "providing a material",
when recited in the claims, is not intended to require any
particular delivery or receipt of the provided item. Rather, the
term "providing" is merely used to recite items that will be
referred to in subsequent elements of the claim(s), for purposes of
clarity and ease of readability.
[0015] Unless otherwise specified, temperatures referred to herein
are based on atmospheric pressure (i.e. one atmosphere).
[0016] The terms "about" and "substantially" are used herein with
respect to measurable values and ranges due to expected variations
known to those skilled in the art (e.g., limitations and
variabilities in measurements).
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a front view of an additive manufacturing system
configured to print 3D parts and support structures with the use of
one or more extruders of the present disclosure.
[0018] FIG. 2 is a rear perspective view of a print head with an
extruder of the present disclosure, where the extruder includes an
upstream liquefier and a downstream gear assembly.
[0019] FIG. 3 is a front perspective view of the extruder.
[0020] FIG. 4 is an exploded front perspective view of the
extruder.
[0021] FIG. 5 is an exploded rear perspective view of casings of
the downstream gear assembly.
[0022] FIG. 6A is a side view of a drive gear of the downstream
gear assembly.
[0023] FIG. 6B is a front end view of the drive gear shown in FIG.
6A.
[0024] FIG. 7A is a side view of an idler gear of the downstream
gear assembly.
[0025] FIG. 7B is a front end view of the idler gear shown in FIG.
7A.
[0026] FIG. 8 is a top sectional view of the downstream gear
assembly, illustrating an engagement of the drive gear and the
idler gear.
[0027] FIG. 9 is a front schematic view of the extruder, further
illustrating the engagement of the drive gear and the idler
gear.
[0028] FIG. 10 is a schematic illustration of a controller assembly
of the additive manufacturing system in use with the print
head.
[0029] FIG. 11 is a front schematic view of an alternative extruder
of the present disclosure, which includes multiple upstream
liquefiers.
[0030] FIG. 12A is a front perspective view of the engaged drive
and idler gears, which illustrates flow profiles from the two
liquefiers around the drive and idler gears.
[0031] FIG. 12B is a front schematic view of the engaged drive and
idler gears and flow profiles shown in FIG. 12A.
[0032] FIG. 13A is a front perspective view of the engaged drive
and idler gears, which illustrates alternative flow profiles from
the two liquefiers around the idler and drive gears, where the two
liquefiers are oriented orthogonal to those shown in FIGS. 12A and
12B.
[0033] FIG. 13B is a top schematic view of the engaged drive and
idler gears and flow profiles shown in FIG. 13A.
[0034] FIG. 14 is a perspective view of a nozzle depositing molten
material with ripples in the bead width.
[0035] FIG. 15 is a perspective of a nozzle depositing molten
material while driving an extruder with a time-varying signal.
[0036] FIG. 16 is a graph of a command signal, a velocity component
of the command signal and a time-varying component of the command
signal.
[0037] FIG. 17 is an expanded block diagram of controller assembly
38.
[0038] FIG. 18 is a flow diagram of a method of generating a
time-varying signal to reduce ripples in a deposited molten
material.
DETAILED DESCRIPTION
[0039] The present disclosure is directed to a print head extruder
for use in an additive manufacturing system to print 3D parts and
support structures in a layer-by-layer manner using an additive
manufacturing technique. As discussed below, the extruder includes
one or more upstream liquefiers that function as a
pressure-generating stage, and a downstream gear assembly that
functions as a flow-regulating stage, where consumable materials
are fed to and melted in the one or more upstream liquefiers, and
the resulting molten material(s) are then provided to the
downstream gear assembly. At the downstream gear assembly, the
molten material(s) are controllably pumped, metered, or otherwise
provided to an extrusion nozzle, where they are extruded to produce
a series of roads of a 3D part or support structure.
[0040] The present disclosure is also directed to a controller
assembly of the additive manufacturing system, which is configured
to operate the downstream gear assembly in one of two modes,
depending on the feed and melting properties of the upstream
liquefier(s). In a first embodiment, the downstream gear assembly
functions as a downstream gear pump that preferably receives the
molten material(s) from the upstream liquefier(s) at lower positive
pressures. In this "gear pump" embodiment, the controller assembly
may command the downstream gear assembly to actively pump or
pressurize the molten materials for extrusion.
[0041] In a second embodiment, the downstream gear assembly
functions as a downstream gear brake that preferably receives the
molten material(s) from the upstream liquefier(s) at higher
positive pressures. In this "gear brake" embodiment, the controller
assembly may command the downstream gear assembly to controllably
limit or meter the flow of the pressurized molten materials for
extrusion.
[0042] In either embodiment, the upstream liquefier(s) preferably
generate a pressurized flow of the molten material(s) to the
downstream gear assembly, and the downstream gear assembly
preferably regulates the flow of the molten material(s) for
printing 3D parts and support structures. In particular, the
downstream gear assembly can potentially provide a faster and more
consistent transient response versus a conventional liquefier since
it does not have a moving meniscus, and has a smaller volume of
molten material that needs to be pressurized before flow out of a
nozzle, and does not experience a melt phase change and related
material expansion further complicating material metering. As such,
the downstream gear assembly has a small and consistent volume of
pressurized material between its gears and the nozzle.
[0043] The liquefier assembly of the present disclosure may be used
with any suitable extrusion-based additive manufacturing system.
For example, FIG. 1 shows system 10 in use with two consumable
assemblies 12, where each consumable assembly 12 is an easily
loadable, removable, and replaceable container device that retains
a supply of a consumable filament for printing with system 10.
Typically, one of the consumable assemblies 12 contains a part
material filament, and the other consumable assembly 12 contains a
support material filament. However, both consumable assemblies 12
may be identical in structure, and, in some cases, both consumable
assemblies 12 may contain part material filaments.
[0044] In the shown embodiment, each consumable assembly 12
includes container portion 14, guide tube 16, and print heads 18,
where each print head 18 preferably includes an extruder 20 of the
present disclosure. Container portion 14 may retain a spool, coil,
or other supply arrangement of a consumable filament, such as
discussed in Mannella et al., U.S. Publication Nos. 2013/0161432
and 2013/0161442; and in Batchelder et al., U.S. Publication No.
2014/0158802.
[0045] Guide tube 16 interconnects container portion 14 and print
head 18, where a drive mechanism of print head 18 (and/or of system
10) draws successive segments of the consumable filament from
container portion 14, through guide tube 16, to the extruder 20 of
the print head 18. In this embodiment, guide tube 16 and print head
18 are subcomponents of consumable assembly 12, and may be
interchanged to and from system 10 with each consumable assembly
12. Alternatively, as discussed below, guide tube 16 and/or print
head 18 (or parts thereof) may be components of system 10, rather
than subcomponents of consumable assemblies 12.
[0046] System 10 is an additive manufacturing system for printing
3D parts or models and corresponding support structures (e.g., 3D
part 22 and support structure 24) from the part and support
material filaments, respectively, of consumable assemblies 12,
using a layer-based, additive manufacturing technique. Suitable
additive manufacturing systems for system 10 include
extrusion-based systems developed by Stratasys, Inc., Eden Prairie,
Minn., such as fused deposition modeling systems under the
trademark "FDM".
[0047] As shown, system 10 includes system housing 26, chamber 28,
platen 30, platen gantry 32, head carriage 34, and head gantry 36.
System housing 26 is a structural component of system 10 and may
include multiple structural sub-components such as support frames,
housing walls, and the like. In some embodiments, system housing 26
may include container bays configured to receive container portions
14 of consumable assemblies 12. In alternative embodiments, the
container bays may be omitted to reduce the overall footprint of
system 10. In these embodiments, container portions 14 may stand
adjacent to system housing 26, while providing sufficient ranges of
movement for guide tubes 16 and print heads 18.
[0048] Chamber 28 is an enclosed environment that contains platen
30 for printing 3D part 22 and support structure 24. Chamber 28 may
be heated (e.g., with circulating heated air) to reduce the rate at
which the part and support materials solidify after being extruded
and deposited (e.g., to reduce distortions and curling). In
alternative embodiments, chamber 28 may be omitted and/or replaced
with different types of build environments. For example, 3D part 22
and support structure 24 may be built in a build environment that
is open to ambient conditions or may be enclosed with alternative
structures (e.g., flexible curtains).
[0049] Platen 30 is a platform on which 3D part 22 and support
structure 24 are printed in a layer-by-layer manner, and is
supported by platen gantry 32. In some embodiments, platen 30 may
engage and support a build substrate, which may be a tray substrate
as disclosed in Dunn et al., U.S. Pat. No. 7,127,309, fabricated
from plastic, corrugated cardboard, or other suitable material, and
may also include a flexible polymeric film or liner, painter's
tape, polyimide tape (e.g., under the trademark KAPTON from E.I. du
Pont de Nemours and Company, Wilmington, Del.), or other disposable
fabrication for adhering deposited material onto the platen 30 or
onto the build substrate. Platen gantry 32 is a gantry assembly
configured to move platen 30 along (or substantially along) the
vertical z-axis.
[0050] Head carriage 34 is a unit configured to receive one or more
removable print heads, such as print heads 18, and is supported by
head gantry 36. Examples of suitable devices for head carriage 34,
and techniques for retaining print heads 18 in head carriage 34,
include those disclosed in Swanson et al., U.S. Pat. Nos. 8,403,658
and 8,647,102. In some preferred embodiments, each print head 18 is
configured to engage with head carriage 34 to securely retain the
print head 18 in a manner that prevents or restricts movement of
the print head 18 relative to head carriage 34 in the x-y build
plane, but allows the print head 18 to be controllably moved out of
the x-y build plane (e.g., servoed, toggled, or otherwise switched
in a linear or pivoting manner).
[0051] Head gantry 36 is a belt-driven gantry assembly configured
to move head carriage 34 (and the retained print heads 18) in (or
substantially in) a horizontal x-y plane above chamber 28. Examples
of suitable gantry assemblies for head gantry 36 include those
disclosed in Comb et al., U.S. Publication No. 2013/0078073, where
head gantry 36 may also support deformable baffles (not shown) that
define a ceiling for chamber 28. In alternative embodiments, head
gantry 36 may utilize any suitable mechanism for moving head
carriage 34 (and the retained print heads 18), such as robotic
actuators, and the like.
[0052] In a further alternative embodiment, platen 30 may be
configured to move in the horizontal x-y plane within chamber 28,
and head carriage 34 (and print heads 18) may be configured to move
along the z-axis. Other similar arrangements may also be used such
that one or both of platen 30 and print heads 18 are movable
relative to each other. Platen 30 and head carriage 34 (and print
heads 18) may also be oriented along different axes. For example,
platen 30 may be oriented vertically and print heads 18 may print
3D part 22 and support structure 24 along the x-axis or the y-axis.
In another example, platen 30 and/or head carriage 34 (and print
heads 18) may be moved relative to each other in a non-Cartesian
coordinate system, such as in a polar coordinate system.
[0053] In the above-discussed embodiment, guide tube 16 and print
head 18 are subcomponents of consumable assembly 12. However, in
alternative embodiments, guide tube 16 and/or print head 18 may be
components of system 10, rather than subcomponents of consumable
assemblies 12. In these embodiments, additional examples of
suitable devices for print heads 18, and the connections between
print heads 18, head carriage 34, and head gantry 36 include those
disclosed in Crump et al., U.S. Pat. No. 5,503,785; Swanson et al.,
U.S. Pat. No. 6,004,124; LaBossiere, et al., U.S. Pat. Nos.
7,384,255 and 7,604,470; Batchelder et al., U.S. Pat. Nos.
7,896,209 and 7,897,074; and Comb et al., U.S. Pat. No. 8,153,182.
For instance, extruder 20 may optionally be retrofitted into an
existing additive manufacturing system.
[0054] In further alternative embodiments (e.g., as shown below in
FIG. 10), some parts of print head 18 and extruder 20 may be
subcomponents of system 10. In this case, other parts of print head
18 and extruder 20 may be subcomponents of the interchangeable
consumable assembly 12, which are engageable with (and removable
from) the parts that are subcomponents of system 10.
[0055] System 10 also includes controller assembly 38, which is one
or more computer-based systems configured to operate the components
of system 10. Controller assembly 38 may communicate over
communication line(s) 40 with the various components of system 10,
such as print heads 18 (including extruder 20), chamber 28 (e.g.,
with a heating unit for chamber 28), head carriage 34, motors for
platen gantry 32 and head gantry 36, and various sensors,
calibration devices, display devices, and/or user input devices. In
some embodiments, controller assembly 38 may also communicate with
one or more of platen 30, platen gantry 32, head gantry 36, and any
other suitable component of system 10.
[0056] Additionally, controller assembly 38 may also communicate
over communication line 42 with external devices, such as other
computers and servers over a network connection (e.g., a local area
network (LAN) connection, a universal serial bus (USB) connection,
or the like). While communication lines 40 and 42 are each
illustrated as a single signal line, they may each include one or
more electrical, optical, and/or wireless signal lines and
intermediate control circuits, where portions of communication
line(s) 40 may also be subcomponents of the removable print heads
18.
[0057] In some embodiments, the one or more computer-based systems
of controller assembly 38 are internal to system 10, allowing a
user to operate system 10 over a network communication line 42,
such as from an external computer in the same or similar manner as
a two-dimensional printer. Alternatively, controller assembly 38
may also include one or more external computer-based systems (e.g.,
desktop, laptop, server-based, cloud-based, tablet, mobile media
device, and the like) that may communicate with the internal
computer-based system(s) of controller assembly 38, as well as
communicating over a network via communication line 42.
[0058] In this alternative embodiment, the processing functions of
controller assembly 38 discussed below may be divided between the
internal and external computer-based systems. In yet another
alternative embodiment, the computer-based system(s) of controller
assembly 38 may all be located external to system 10 (e.g., one or
more external computers), and may communicate with system 10 over
communication line(s) 40.
[0059] During a printing operation, controller assembly 38 may
direct platen gantry 32 to move platen 30 to a predetermined height
within chamber 28. Controller assembly 38 may then direct head
gantry 36 to move head carriage 34 (and the retained print heads
18) around in the horizontal x-y plane above chamber 28. Controller
assembly 38 may also command print heads 18 to selectively draw
successive segments of the consumable filaments from container
portions 14 and through guide tubes 16, respectively.
[0060] The successive segments of each consumable filament are then
melted in the extruder 20 of the respective print head 18 to
produce a molten material, as discussed below. Upon exiting
extruder 20, the resulting extrudate may be deposited onto platen
30 as a series of roads for printing 3D part 22 or support
structure 24 in a layer-by-layer manner After the print operation
is complete, the resulting 3D part 22 and support structure 24 may
be removed from chamber 28, and support structure 24 may be removed
from 3D part 22. 3D part 22 may then undergo one or more additional
post-processing steps, as desired.
[0061] FIG. 2 is a rear perspective view of an example print head
18, which includes housing 44, drive mechanism 46, and an extruder
20 of the present disclosure, which are shown in use with filament
48. Examples of suitable components for housing 44 and drive
mechanism 46 include those discussed in LaBossiere et al., U.S.
Pat. No. 7,604,470; Batchelder et al., U.S. Pat. Nos. 7,896,209;
7,897,074; and 8,236,227; Swanson et al., U.S. Pat. No. 8,647,102;
Koop et al., U.S. Publication No. 2014/0159273; and Leavitt, U.S.
Publication No. 2014/0159284. However, extruder 20 may be
incorporated into any print head that is suitable for use with
system 10.
[0062] As shown, extruder 20 includes an upstream liquefier 50 and
a downstream gear assembly 52, where, as used herein, the terms
"upstream" and "downstream" are made with reference to a filament
feed direction, as illustrated by arrow 54. Liquefier 50 is an
example liquefier configured to receive and melt a consumable
material (e.g., filament 48), thereby generating a pressurized flow
of the molten material that is provided to gear assembly 52. In the
shown example, liquefier 50 is a rigid hollow tube fabricated from
one or more thermally-conductive materials (e.g., stainless steel),
with an inlet end 56a and an outlet end 56b offset from each other
along longitudinal axis 58.
[0063] Examples of suitable cylindrical geometries for liquefier 50
include those disclosed in Crump et al., U.S. Pat. No. 5,503,785;
Swanson et al., U.S. Pat. No. 6,004,124; LaBossiere, et al., U.S.
Pat. No. 7,604,470; Leavitt, U.S. Pat. No. 7,625,200; and
Batchelder et al., U.S. Pat. No. 8,439,665. As shown, liquefier 50
is thin walled, having an exemplary wall thickness ranging from
about 0.01 inches to about 0.03 inches. Exemplary inner diameters
for liquefier 50 range from about 0.05 inches to about 0.10 inches.
Exemplary lengths for liquefier 50 between inlet end 56a and outlet
end 56b include at least about 1.5 inches, and ranging to several
inches.
[0064] In alternative embodiments, liquefier 50 may have a ribbon
liquefier architecture for use with a ribbon filament. The term
"ribbon filament" as used herein refers to a filament (e.g.,
filament 48) having a substantially rectangular, arcuate, and/or an
elliptical cross-section along its longitudinal length, which may
optionally include one or more surface tracks for engaging with
drive mechanism 46, such as disclosed in Batchelder et al., U.S.
Pat. No. 8,236,227. Correspondingly, the term "ribbon liquefier" as
used herein refers to a hollow liquefier (e.g., liquefier 50)
having a substantially rectangular, arcuate, and/or an elliptical
inner-channel cross-section along its longitudinal length. Examples
of suitable ribbon filaments and ribbon liquefier architectures for
filament 48 and liquefier 50 include those discussed in Batchelder
et al., U.S. Pat. Nos. 8,221,669; 8,236,227; and 8,439,665.
[0065] Other suitable liquefiers include those disclosed in U.S.
Patent Publications Nos. 2015/0096717 and 2015/0097053.
[0066] Inlet end 56a of liquefier 50 is operably connected to
housing 44 such that liquefier 50 suspends below housing 44 when
installed to system 10. Gear assembly 52 is preferably connected to
outlet end 56b of liquefier 50 such that gear assembly 52 suspends
below housing 44 and liquefier 50 when installed to system 10. In
alternative embodiments, one or more portions of liquefier 50
and/or gear assembly 52 may be retained within housing 44, or one
or more additional components may operably connect outlet end 56b
of liquefier 50 to gear assembly 52. Furthermore, gear assembly 52
may also be operably connected to housing 44 in addition to the
connection to outlet end 56b of liquefier 50.
[0067] Drive mechanism 46 is a filament drive mechanism that is
configured to feed successive segments of filament 48 from guide
tube 16 to inlet end 56a of liquefier 50 under motorized power of
motor 60 (e.g., a step motor), based on commands from controller
assembly 38. Examples of suitable devices for drive mechanism 46
includes those disclosed in LaBossiere, et al., U.S. Pat. No.
7,384,255; and Batchelder et al., U.S. Pat. No. 7,896,209.
[0068] While drive mechanism 46 and motor 60 are preferably
positioned directly upstream from liquefier 50 (e.g., within
housing 44), as shown in FIG. 2, in alternative embodiments, one or
more drive mechanisms may be positioned at any suitable location(s)
along the pathway of filament 48 between (and including) container
14 and liquefier 50, such as at a fixed location within system 10.
In some embodiments, a spool drive mechanism (not shown) may be
used to engage with a spool in container 14, where the spool holds
a wound supply of filament 48. In this case, the spool drive
mechanism may rotate the spool to feed filament 48 through guide
tube 16 and into liquefier 50 (rather than directly engaging
filament 48). This reduces weight of print head 18. In addition,
the filament drive control can operate with less fidelity as it
only needs to supply pressure, and is not performing the tasks of
coordinating melt extrusion to gantry motion at high accelerations
and start/stops.
[0069] Furthermore, multiple drive mechanisms may be used together.
For instance, a first drive mechanism may be used to feed filament
48 from container 14 to print head 18. A second drive mechanism
(e.g., drive mechanism 46) retained by print head 18 may then
receive the fed filament 48 from the first drive mechanism, and
feed the received filament 48 into liquefier 50. As illustrated,
drive mechanism(s) 46 and motor(s) 60 are secured to housing 44 and
carried by head gantry 36 while printing 3D part 22. Alternatively,
drive mechanism(s) 46 and motor(s) 60 can be secured to system 10
at a location away from housing 44 to reduce the mass carried by
head gantry 36 while printing 3D part 22.
[0070] As further shown in FIG. 2, extruder 20 also includes an
upstream heater assembly 62, which is one or more heating elements
configured to transfer heat to at least a portion of the length of
liquefier 50. The transferred heat melts the received filament 48
within liquefier 50, thereby producing a molten material of
filament 48 for delivery to gear assembly 52. Examples of suitable
assemblies for heater assembly 62 includes those disclosed in Crump
et al., U.S. Pat. No. 5,503,785; Swanson et al., U.S. Pat. No.
6,004,124; LaBossiere, et al., U.S. Pat. No. 7,604,470; Leavitt,
U.S. Pat. No. 7,625,200; Batchelder et al., U.S. Pat. No.
8,439,665; and Swanson et al., U.S. Publication Nos. 2012/0018924
and 2012/0070523.
[0071] While illustrated with liquefier 50, extruder 20 may
alternatively include a variety of different upstream liquefiers to
generate the pressurized molten material, and provide the
pressurized molten material to gear assembly 52, such as without
limitation pellet and/or powder-fed screw-pumps, filament-fed
screw-pumps, slug-fed pumps, and the like. In a further embodiment,
liquefier 50 or its alternatives may be located even further
upstream from print head 18, such as at a fixed location. In this
embodiment, molten material may be fed to gear assembly 52 through
a heated conduit. This is beneficial for removing liquefier 50 from
print head 18, which can reduce consumable costs and print head
weight.
[0072] Furthermore, as discussed below, while illustrated with a
single liquefier 50, in alternative embodiments, extruder 20 may
include multiple upstream liquefiers to simultaneously feed
multiple consumable materials to gear assembly 52. This is
beneficial for increasing the flow rate of the molten materials to
gear assembly 52, such as doubling, tripling, or even quadrupling
the flow rate (or more). Additionally, the use of multiple upstream
liquefiers may also provide extrudates from gear assembly 52 having
unique cross sections and/or material properties, as also discussed
below. As illustrated, drive mechanism(s) 46 and motor(s) 60 are
secured to housing 44 and carried by head gantry 36 while printing
3D part 22. Alternatively, drive mechanism(s) 46 and motor(s) 60
can be secured to system 10 at a location away from housing 44 to
reduce the mass carried by head gantry 36 while printing 3D part
22.
[0073] As shown in FIGS. 2 and 3, gear assembly 52 is a downstream
gear-based assembly that includes base casing 64, gear casing 66,
and face casing 68, where gear casing 66 is secured between base
casing 64 and face casing 68 with bolts 70 (collectively referred
to as a casing assembly 71). While gear assembly 52 is illustrated
with a block-like geometry, in alternative embodiments, gear
assembly 52 may have any suitable configuration, such for reducing
weight and volumetric dimensions, and/or for aesthetic
qualities.
[0074] In the shown example, gear assembly 52 also includes heating
elements 72 extending through each of base casing 64, gear casing
66, and face casing 68. Heating elements 72 are a pair of electric
heating elements configured to heat and maintain base casing 64,
gear casing 66, and face casing 68 at an elevated temperature. This
prevents the received molten filament materials from cooling down
and/or solidifying within gear assembly 52 while print head 18 is
printing.
[0075] As further shown, gear assembly 52 also includes drive gear
74 and idler gear 76, which respectively extend into openings 78
and 80 of face casing 68. As discussed below, drive gear 74 and
idler gear 76 provide the flow-regulating functions (e.g., pumping
or metering functions) for gear assembly 52, and extend through
gear casing 66 and into base casing 64. In particular, drive gear
74 includes shaft 82 that extends beyond opening 78 of face casing
68 to operably connect with motor 84 (e.g., a step motor).
[0076] Drive gear 74 may be operably connected to motor 84 with a
variety of mechanisms. For instance, shaft 82 may directly insert
into the axis of motor 84, thereby allowing motor 84 to directly
rotate drive gear 74. Alternatively, one or more additional shafts
and/or gears may interconnect drive gear 74 and motor 84, such as
to position motor 84 at a remote location from gear assembly 52.
For example, motor 84 may also be located within housing 44 and
connected to drive gear 74 with one or more additional shafts
(e.g., parallel to axis 58) and gears, or other engagement
mechanisms that transfer the rotational power of motor 84 to drive
gear 74. This allows the drive motor 84 to be located at a distance
from the nozzle with a simple direct drive, and facilitates its use
in an heated environment which allows the nozzle to be positioned
in the heated zone (e.g., in chamber 28), while motor 84 is on the
cool side or unheated zone (e.g., outside of chamber 28).
[0077] Because the molten material is provided to gear assembly 52
under positive pressure, motor 84 may optionally be a low-torque
motor to perform the flow-regulating functions. This allows motor
84 to be smaller in size and lighter in weight, thereby allowing
print head 18 to be smaller and lighter. This can accordingly allow
head gantry 36 to move print head 18 more effectively. In this
low-torque motor 84 embodiment, controller assembly 38 commands
motors 60 and 84 in a partially or fully synchronized manner to
maintain suitable pressures for the molten material in gear
assembly 52.
[0078] In a further alternative embodiment, motors 60 and 84 may be
provided as a single motor that operates both drive mechanism 46
and drive gear 74. In this embodiment, controller assembly 38 may
command the single motor to operate drive mechanism 46 and drive
gear 74 in a synchronized manner.
[0079] Idler gear 76 is a second gear that is engaged with drive
gear 74, but is otherwise capable of freely rotating within gear
assembly 52. As such, the rotation of drive gear 74 counter rotates
idler gear 76 within gear casing 66. This generates the pumping
function for extruding the molten material in a controlled manner.
Alternatively, idler gear 76 may be replaced by a second drive gear
76 that is rotated with a separate motor (not shown) that is
commanded by controller assembly 38, preferably with synchronized
operation with motor 82. In this case, the second drive gear 76 may
also include a shaft that extends out of face casing 68, and
interconnects the second drive gear 76 to the separate motor.
[0080] As shown in FIG. 4, base casing 64, gear casing 66, and face
casing 68 respectively include lateral openings 86a, 86b, and 86c
for receiving heating elements 72. Heating elements 72 are
preferably received in lateral openings 86a, 86b, and 86c in a
secure manner (e.g., frictional fit and/or set screws) to prevent
heating elements 72 from dislodging or otherwise moving relative to
casings 64, 66, and 68.
[0081] Base casing 64, gear casing 66, and face casing 68 also
respectively include lateral openings 88a, 88b, and 88c for
receiving bolts 70 (not shown in FIG. 4). Lateral openings 88a in
base casing 64 are preferably threaded to threadedly engage with
bolts 70. This allows bolts 70 to securely hold casings 64, 66, and
68 together. Alternatively, gear assembly 52 may also include
external threaded nuts (not shown) to threadedly engage with bolts
70 outside of lateral openings 88a at base casing 64. In further
alternatives, bolts 70 may extend through lateral openings 88a,
88b, and 88c from the opposing direction, such that face casing 68
may be threaded to threadedly engage with bolts 70.
[0082] As further shown in FIG. 4, outlet end 56b of liquefier 50
is connected to a top or inlet opening 90 of gear casing 66.
Additionally, gear assembly 52 includes nozzle 92 connected to a
bottom or outlet opening 94 of gear casing 66 (as best shown below
in FIG. 9). Nozzle 92 is a small-diameter nozzle configured to
extrude the molten material at a desired road width. Exemplary
inner tip diameters for nozzle 92 include diameters ranging from
about 125 micrometers (about 0.005 inches) to about 760 micrometers
(about 0.030 inches). In some embodiments, nozzle 92 may include
one or more recessed grooves to produce roads having different road
widths, as disclosed in Swanson et al., U.S. Publication No.
2014/0048969, the contents of which are incorporated by
reference.
[0083] Nozzle 92 may also have an axial channel with any suitable
length-to-diameter ratio. For example, in some embodiments, nozzle
92 may have an axial channel with a length-to-diameter ratio to
generate high flow resistance, such as a ratio of about 2:1 to
about 5:1. In other embodiments, nozzle 92 may have an axial
channel with a length-to-diameter ratio to generate lower flow
resistance, such as ratios from about 2:1 to less than about 1:1.
Accordingly, suitable length-to-diameter ratios for the axial
channel of nozzle 92 may range from about 1:2 to about 5:1, where
in some low-flow resistance embodiments, ratios ranging from about
1:2 to about 1:1 may be preferred.
[0084] Preferably, inlet opening 90 and outlet opening 94 are
aligned with each other along longitudinal axis 58, and are in
fluid communication with each other at an interior cavity 96 in
gear casing 66. Interior cavity 96 is the region in which drive
gear 74 and idler gear 76 engage for driving the molten material of
filament 48 from liquefier 50 and inlet opening 90 to outlet
opening 94 and nozzle 92, as explained below.
[0085] In addition to shaft 82, drive gear 74 also includes hub 98
and gear 100, where gear 100 includes teeth 102, and resides
longitudinally between shaft 82 and hub 98. Similarly, idler gear
76 includes gear 104 having teeth 106, and resides longitudinally
between hubs 108 and 110. Drive gear 74 and idler gear 76 may each
be cast or machined from one or more metallic and/or polymeric
materials capable of withstanding the elevated temperatures within
gear assembly 52, such as stainless steel.
[0086] Face casing 68 also includes hub openings 112, which, in the
shown example, extend entirely through face casing 68.
Alternatively, the hub opening 112 for idler gear 76 may only
extend partially through face casing 68, such that the inserted
idler gear 76 is not externally visible from the closed gear
assembly 52. As shown in FIG. 5, base casing 64 also includes hub
openings 114, which, in the shown embodiment, do not extend
entirely through base casing 64. This can reduce any potential
leakage of the molten material through base casing 64. However, in
some alternative embodiments, hub openings 114 may extend entirely
through base casing 64 (e.g., for ease of manufacturing).
[0087] Base casing 64, gear casing 66, and face casing 68 may be
manufactured from one or more thermally-conductive, metallic
materials, such as stainless steel, bronze alloys, and the like.
Lateral openings 86a, 86b, 86c, 88a, 88b, and 88c, inlet opening
90, outlet opening 94, interior cavity 96, hub openings 112 and
114, and any other desired openings or features, may be produced
during the castings steps and/or maybe machined into casings 64,
66, and 68, as desired.
[0088] During assembly, gear shaft 82 of drive gear 74 may be
inserted through a first hub opening 112 of face casing 68, and hub
110 of idler gear 76 may be inserted into the other hub opening 112
of face casing 68. Gear casing 66 may be placed against face casing
68 such that drive gear 74 and idler gear 76 extend through
interior cavity 96. In particular, gears 100 and 104 are positioned
within interior cavity, preferably with a tight clearance with the
walls of interior cavity 96. Base casing 68 may then be placed
against the opposing side of gear casing 66 such that hubs 98 and
108 extend into hub openings 114.
[0089] Casings 64, 66, and 68 may then be secured together with
bolts 70 inserted through lateral openings 86a, 86b, 86c. Hub
openings 112 and 114 are preferably aligned with each other on
opposing sides of interior cavity 96 to allow drive gear 74 and
idler gear 76 to rotate relative to casings 64, 66, and 68 without
undue frictional resistance, but also with tight clearances to
minimize or eliminate any potential leakage of the molten material.
Outlet end 56b of liquefier 50 may also be secured to inlet opening
90 of gear casing 66, and nozzle 92 may be secured to outlet
opening 94 of gear casing 66. Heating elements 72 may also be
inserted into and securely retained within lateral openings 88a,
88b, and 88c.
[0090] FIGS. 6A and 6B further illustrate drive gear 74, and FIGS.
7A and 7B further illustrate idler gear 76, each of which may have
any suitable dimensions for use in gear assembly 52. In the shown
embodiment, drive gear 74 and idler gear 76 have the same or
substantially the same cross-sectional dimensions, with the only
difference being shaft 82 of drive gear 74, which is longer than
hub 110 of idler gear 76 for connection with motor 84.
[0091] FIGS. 6A and 6B show non-limiting examples of suitable
dimensions for drive gear 74. As shown, length 82L for shaft 82 may
range from about 0.3 inches to about 0.8 inches, length 98L for hub
98 may range from about 0.05 inches to about 0.2 inches, length
100L for gear 100 may range from about 0.1 inches to about 0.2
inches, and the overall length 74L for drive gear 74 is the sum of
the above lengths 82L, 98L, and 100L, such as from about 0.6 inches
to about 1.0 inch.
[0092] Similarly, outer diameters 82D and 98D respectively for
shaft 82 and hub 98 may each range from about 0.05 inches to about
0.2 inches, and outer diameter 100D at the periphery of teeth 100
may range from about 0.15 inches to about 0.2 inches. In the shown
embodiment, outer diameters 82D and 98D are the same or
substantially the same, where the outer diameters refer to the
maximum outer diameters, and exclude any chamfered or beveled
edges. In alternative embodiments, outer diameters 82D and 98D may
be different from each other.
[0093] FIGS. 7A and 7B correspondingly show non-limiting examples
of suitable dimensions for idler gear 76. As shown, length 104L for
gear 104 may range from about 0.1 inches to about 0.2 inches,
lengths 108L and 110L respectively for hubs 108 and 110 may each
range from about 0.05 inches to about 0.2 inches, and the overall
length 76L for idler gear 64 is the sum of the above lengths 104L,
108L, and 110L, such as from about 0.3 inches to about 0.5
inches.
[0094] Outer diameter 104D at the periphery of teeth 106 may range
from about 0.15 inches to about 0.2 inches, and outer diameters
108D and 110D respectively for hubs 108 and 110 may each range from
about 0.05 inches to about 0.2 inches. In the shown embodiment,
outer diameters 108D and 110D are the same or substantially the
same, where the outer diameters refer to the maximum outer
diameters, and exclude any chamfered or beveled edges.
[0095] In further embodiments, the dimensions of gears 100 and 104
are the same or substantially the same. In other words, in these
embodiments, lengths 100L and 104L are the same or substantially
the same, and outer diameters 100D and 104D are the same or
substantially the same. However, in alternative embodiments, outer
diameters 100D and 104D may be different from each other. In
additional embodiments, the dimensions of hubs 98 and 108 are the
same or substantially the same, such that lengths 98L and 108L are
the same or substantially the same, and outer diameters 98D and
108D are the same or substantially the same.
[0096] Additionally, FIG. 8 shows gears 100 and 104 of drive gear
74 and idler gear 76 engaged with each within interior cavity 96 of
gear casing 66. As shown, gear casing 66 preferably has a thickness
66T, at least at interior cavity 96, that is substantially the same
as lengths 100L and 104L of gears 100 and 104, or slightly larger,
to provide good lateral sealing properties between gears 100 and
104 and base casing 64 and face casing 68. Accordingly, examples of
suitable dimensions for thickness 66T of gear casing 66 may range
from about 0.1 inches to about 0.2 inches, and more preferably from
greater than about 100% to about 105% of lengths 100L and 104L.
[0097] Base casing 64 may have any suitable thickness 64T depending
on the desired dimensions of gear assembly 52, where thickness 54T
is preferably greater than a lengths 114L of hub openings 114. Hub
openings 114 are 64T sized to accommodate hubs 98 and 108 in a
manner that allows hubs 98 and 108 to rotate without undue
resistance, while also providing good sealing properties for
interior cavity 96, and positioning gears 100 and 104 close to each
other. Examples of suitable lengths 114L for hub openings 114 may
range from about 0.05 inches to about 0.2 inches, and more
preferably include those greater than 100% of lengths 98L and 108L.
Examples of suitable inner diameters 114D for hub openings 114 may
range from about 0.05 inches to about 0.2 inches, and more
preferably range from greater than about 100% to about 105% of
diameters 98D and 108D.
[0098] Correspondingly, face casing 68 may have any suitable
thickness 68T depending on the desired dimensions of gear assembly
52. Examples of suitable thickness 68T for face casing 68 may range
from about 0.05 inches to about 0.2 inches. Hub openings 112 are
preferably sized to accommodate shaft 82 and hub 110 in a manner
that allows shaft 82 and hub 110 to rotate without undue
resistance, while also providing good sealing properties for
interior cavity 96. Examples of suitable inner diameters 112D for
hub openings 112 may range from about 0.05 inches to about 0.2
inches, and more preferably range from greater than about 100% to
about 105% of diameters 82D and 110D.
[0099] FIG. 9 further illustrates the engagement of gears 100 and
104 in interior cavity 96 of gear casing 66. During a printing
operation, controller assembly 38 (shown in FIG. 1) commands drive
mechanism 46 (via motor 60) (shown in FIG. 2) to feed successive
segments of filament 48 into inlet end 56a of liquefier 50 (shown
in FIGS. 2-4). As filament 48 passes through liquefier 50 in the
direction of arrow 54, heater assembly 62 thermally melts the
received successive segments, where the molten portion of the
filament material forms a meniscus around the unmelted portion of
filament 48.
[0100] The downward movement of filament 48 functions as a
viscosity pump to pressurize the molten material and force it from
liquefier 50 into gear assembly 52. In particular, the pressurized
molten material flows from outlet end 56b of liquefier 50 into
inlet opening 90 of gear casing 66, as depicted by arrow 116. This
fills an upper region 118 of interior cavity 96 and inlet opening
90 with the pressurized molten material. The engaged teeth 102 and
106 of gears 100 and 104 prevent the received molten material from
flowing directly down between gears 100 and 104 into outlet opening
94, unless or until the gears are rotated.
[0101] Controller assembly 38 may direct motor 84 to rotate drive
gear 74 in the direction of arrow 120, which causes teeth 102 of
gear 100 to rotate in the same direction. The engagement between
teeth 102 and 106 accordingly counter rotates gear 104 (and idler
gear 76) in the direction of arrow 122. The molten material is then
carried around gears 100 and 104 in the interstitial spaces between
teeth 102 and 106 and the walls of interior cavity 96 (referred to
as interstitial spaces 123) to a lower region 124 of interior
cavity 96, as depicted by arrows 126 and 128. The continued driving
of the molten material around gears 100 and 104 in this manner
forces the molten material in lower region 124 downward through
outlet opening 94 and nozzle 92 to extrude the molten material in a
controlled manner, as depicted by arrow 130.
[0102] As can be appreciated, when printing 3D part 22 or support
structure 24, the extrudate flow from nozzle 92 is rarely held at a
constant, steady-state rate. Instead, the extrudate flow rate is
typically being changed repeatedly to accommodate a variety of
different tool path conditions, such as road start accelerations,
road stop decelerations, cornering decelerations and accelerations,
road width variations, and the like.
[0103] These flow rate changes are traditionally controlled by
adjusting the feed rate of filament 48 into liquefier 50 with drive
mechanism 46, based on drive commands from controller assembly 38.
This correspondingly adjusts the pressure generated by the
viscosity-pump action on the molten material. However, when
controller assembly 38 commands drive mechanism 46 to change the
feed rate of filament 48 into liquefier 50, there is a time
response delay between the signal command and when the extrusion
rate from nozzle 56 actually changes. This is due to response
limitations in the motor of drive mechanism 46 and the
viscosity-pump action in liquefier 50.
[0104] Gear assembly 52, however, does not directly rely on a
viscosity-pump action from filament 48 for regulating the flow of
the molten material. Instead, gear assembly 52 provides a
gear-based mechanism located close to nozzle 92 for regulating the
flow of the molten material in a highly-controlled manner In
particular, gears 100 and 104 can drive precise volumes of the
molten material in the interstitial spaces 123 between teeth 102
and 106 and the walls of interior cavity 96, based on the rotation
of gears 100 and 104. The small pressurized volumes of interstitial
spaces 123 can also decrease ooze and increase control of melt flow
from nozzle 92 because of the relative low volumes of the molten
material within each interstitial space 123, resulting in lower
levels of thermal expansion. These features can provide a high
level of dynamic control over the volumetric flow rates of the
molten material.
[0105] FIG. 10 illustrates an example architecture for controller
assembly 38 in use with extruder 20 and drive mechanism 46.
Controller assembly 38 may include any suitable computer-based
hardware, such as user interface 132, memory controller 134,
processor 136, storage media 138, input/output (I/O) controller
140, and communication adapter 142. Controller assembly 38 may also
include a variety of additional components that are contained in
conventional computers, servers, media devices, and/or printer
controllers.
[0106] User interface 132 is a user-operated interface (e.g.,
keyboards, touch pads, touch-screen displays, display monitors, and
other eye, voice, movement, or hand-operated controls) configured
to operate controller assembly 38. Memory controller 134 is a
circuit assembly that interfaces the components of controller
assembly 38 with one or more volatile random access memory (RAM)
modules of storage media 138. Processor 136 is one or more
computer-processing units configured to operate controller assembly
38, optionally with memory controller 134. For instance, processor
136 may include one or more microprocessor-based engine control
systems.
[0107] Storage media 138 is one or more internal and/or external
data storage devices, storage hardware or computer storage media
for controller assembly 38, such as volatile RAM modules, read-only
memory modules, optical media, magnetic media (e.g., hard disc
drives), solid-state media (e.g., FLASH memory and solid-state
drives), analog media, and the like. Storage media 138 may retain
an executable copy of processing program 144, a tool path generator
and other control software, and may retain one or more digital
models to be printed with system 10 and/or tool paths for printing
digital models, such as digital model 146. Controller assembly 38
may receive digital model 146 over communication line 42, where
digital model 146 may have any file format configured or
configurable by controller assembly 38 for 3D printing.
[0108] Controller assembly 38 may also use feedback to dynamically
control the print head, and the like. I/O controller 140 is a
circuit assembly that interfaces memory controller 134, processor
136, and storage media 138 with various input and output components
of controller assembly 38, including communication adapter 142.
Communication adapter 142 is one or more wired or wireless
transmitter/receiver adapters configured to communicate over
communication lines 40 and 42.
[0109] As briefly mentioned above, controller assembly 38 can use
gear assembly 52 in a variety of manners to controllably extrude
the molten material from nozzle 92. For instance, controller
assembly 38 may generate synchronized commands for motors 60 and 84
based on the desired tool path flow rates to be used. Similarly,
controller assembly 38 may generate the commands to heat assembly
62 and heating elements 72 depending on the particular thermal
profiles desired along liquefier 50 and gear assembly 52.
Controller assembly 38 may store these commands on storage media
138 as one or more data files (e.g., data files 148, 150, 152, and
154), and may use these data files 148, 150, 152, and/or 154 to
generate the tool path instructions for printing each sliced layer
with system 10.
[0110] Furthermore, the data files 148 and 150 may depend on how
gear assembly 52 is intended to operate. As discussed above, gear
assembly 52 may be operated as a "gear pump" and/or as a "gear
brake", and controller assembly 38 may optionally switch gear
assembly 52 back-and-forth between the operating states, if
desired.
[0111] In the gear pump embodiment, gear assembly 52 may receive
the pressurized molten material from liquefier 50 at a lower
positive pressure to prevent leakage from gear assembly 52. In this
case, motor 84 applies torque to rotate shaft 82 in the direction
of arrow 120 to drive the molten material to nozzle 92. The
viscosity-pumping action of liquefier 50 may provide the molten
material to gear assembly 52 with enough positive pressure to
prevent starvation of gear assembly 52. As mentioned above,
controller assembly 38 may command motors 60 and 84 to operate in
partially or fully synchronized manner to maintain sufficient
pressures of the molten material in gear assembly 52. In
comparison, gear assembly 52 itself preferably regulates the
extrusion of the molten material from nozzle 92 in a controlled
manner.
[0112] Alternatively, in the gear brake embodiment, gear assembly
52 can receive the molten material of filament 48 at a relatively
higher positive pressure, where motor 84 operably applies resistive
torque to shaft 82 to prevent shaft 82 from rotating under the
pressurized flow of the molten material. In this case, when
extrusion is desired, controller assembly 38 commands motor 84 to
controllably release the resistive torque on shaft 82, which allows
gears 100 and 104 to rotate and carry set volumes of the molten
material to nozzle 92.
[0113] In each of these embodiments, the flow of the molten
material to nozzle 92 is dictated by the rotations of gears 100 and
104, which regulate an accurate level of dynamic flow control over
the extrusion rates. Additionally, controller assembly 38 may
command gear assembly 52 (e.g., via motor 84) to perform particular
actions at acceleration and deceleration phases of a tool path. For
instance, controller assembly 38 may command motor 84 to reverse
the rotation on drive gear 74 at the end of a tool path to perform
a suck-back operation to reduce or eliminate oozing or melt flow
issues. In some embodiments, the oozing or melt flow issues can be
reduced or eliminated without cooling down gear assembly 52 or
nozzle 92. In some cases, liquefier assembly 20 can be operated
without requiring a purge or pre-condition operation between uses
(i.e., liquefier assembly 20 can be less dependent on its extrusion
history compared to standard liquefiers).
[0114] The downstream gear assembly 52 may also be used with
multiple upstream liquefiers. For example, as shown in FIG. 11,
gear assembly 52 may receive pressurized molten materials from a
pair of liquefiers 50, where each liquefier 50 may receive an
individual filament 48 from a dedicated drive mechanism 46 and
motor 60 (or from a single combined motor 60). In this embodiment,
controller assembly 38 may operate motors 60 together to feed a
pair of filaments 48 to the parallel liquefiers 50, as depicted by
arrows 156. This can be performed to effectively double the feed
rate of the consumable material.
[0115] Each filament 48 is melted in its respective liquefier 50
(e.g., via a heating assembly 62, not shown), and then driven under
the viscosity-pump action into a manifold 158, as depicted by
arrows 160. Controller assembly 38 may operate the separate motors
60 in a partially or fully synchronized manner, allowing the
pressurized flows to be the same or independently selected. For
example, controller assembly 38 may direct the pressurized flows of
the molten materials from each liquefier 50 to be the same or
substantially the same as each other (i.e., about a 1:1 volumetric
flow rate ratio), to be proportional but different from each other
(e.g., about a 2:1 volumetric flow rate ratio), and/or to vary
dynamically relative to each other, as desired.
[0116] Manifold 158 is an intermediate assembly configured to
direct the pressurized molten materials from each liquefier 50 into
inlet opening 90, as shown. As such, manifold includes two (or
more) inlet ports 162 for engagement with outlet ends 56b of
liquefiers 50, an outlet port 164 for engagement with inlet opening
90 of gear casing 66, and multiple merging conduits 166
interconnecting inlet ports 162 and outlet port 164.
[0117] The number of inlet ports 162 and conduits 166 may vary
depending on the desired number of liquefiers 50 to be used.
Examples of suitable numbers of inlet ports 162 and conduits 166
for manifold 158 range from two to ten, and in some embodiments,
from two to six, and in other embodiments, from two to four. In
some preferred embodiments, manifold 158 is also heated, such as
with a heater assembly 167 to assist in keeping the molten material
heated while flowing from liquefiers 50 to gear assembly 52.
[0118] If desired, manifold 158 may also include one or more mixing
units, such as an active or static mixer, to mix the received
molten materials before they are delivered to gear assembly 52.
However, when receiving the molten materials from multiple upstream
liquefiers 50, gear assembly 52 can generate extrudates from nozzle
92 that have unique cross sections. In particular, it has been
found that the molten material flows that enter inlet opening 90,
which are not pre-mixed, retain their unmixed cross sections after
passing around gears 100 and 104.
[0119] For example, as shown in FIGS. 12A and 12B, when an unmixed
inlet flow of a pair of molten materials 168 and 170 enter inlet
opening 90 and upper region 118 of interior cavity 96, the majority
of the material driven by gear 100 will be material 170, and the
majority of the material drive by gear 104 will be material 168.
When the driven materials 168 and 170 reconverge at lower region
124 of interior cavity 96, they will substantially retain their
separate volumes, subject to a small amount of mixing at their
interface 172. These separate volumes will then also continue
through the extrusion at nozzle 92, such that the deposited roads
also have the substantially separate cross sections.
[0120] This phenomenon is believed to be due to the low levels of
shear and turbulence that the molten materials are subjected to in
gear assembly 52. This can provide extrudates with unique
properties due to the substantial separation of materials. For
example, one side of a deposited road of the extrudate may have a
first color, and the other side of the deposited road may have a
second color. This can produce roads that are readily recognizable
due to their dual-color profiles. Further, because the amount of
material in gear assembly 52 is relatively small, the present
disclosure allows for a change in color of the extruded material
with a small transition time by changing the source of the extruded
material. Stated otherwise, the color of the extruded material can
be quickly changed by changing the source of the consumable
material.
[0121] This phenomenon can also be further used to tailor the
physical, chemical, and thermal properties of the deposited roads.
For instance, the deposited roads may be produced with pairs of
amorphous and semi-crystalline materials that retain substantially
separate cross sections. Other embodiments may incorporate pairs of
different soluble support materials having different strengths and
solubilities. Further embodiments may pair electrically-conductive
materials with electrically-insulating materials. A variety of
other material combinations may also be used.
[0122] FIGS. 13A and 13B illustrate a variation of the material
pairing with gears 100 and 104. It has also been found that when
the unmixed inlet flows are oriented orthogonal to those shown in
FIGS. 12A and 12B, such that flows 168 and 170 each pass around
each gear 100, and each pass around gear 104, when the driven
materials 168 and 170 reconverge at lower region 124 of interior
cavity 96, they will also substantially retain their separate
volumes, subject to a small amount of mixing at their interface
174. In this case, interface 174 is orthogonal to interface 172
(shown above in FIGS. 12A and 12B).
[0123] As can be appreciated, the results from FIGS. 12A, 12B, 13A,
and 13B can be also applied to a four-material arrangement. In this
case, the resulting extrudate will have cross-sectional quadrants
of the original materials, subject to small amounts of mixing at
their interfaces. As such, gear assembly 52 is capable of producing
extrudates with material unique properties that can be tailored to
a variety of individual needs.
[0124] Pumps and brakes sometimes suffer from variations or pulses
in the volume or flow of their output. Thus, the amount of material
output by the pump or brake increases and decreases over time even
when the pump or brake is operating at a constant speed. Within an
additive manufacturing system, such variations in the output of the
pump or brake result in bead width variations, also referred to as
"ripple", in the deposited material. For example, in the
perspective view of FIG. 14, nozzle 92 of gear assembly 52 deposits
a layer 1400 of molten material on a substrate consisting of a
previously deposited layer 1402, which in turn is deposited on a
second previously deposited layer 1404. As shown in exaggerated
form in FIG. 14, each of the deposited layers have a bead width
that ripples due to variations or pulsing in the output of the
material from nozzle 92. For example, layer 1400 includes a bead
width that varies from a wide width 1406 to a narrow width 1408 and
back to a wide width 1410. Wide widths 1406 and 1410 are formed
when the volume or flow of the material extruded by nozzle 92 is at
a higher value and narrow width 1408 is formed when the volume or
flow of the material extruded by nozzle 92 is at a lower value. As
shown in FIG. 14, the variations in the bead width for different
layers typically do not align with each other resulting in a rough
surface 1412.
[0125] In accordance with several embodiments, a method and system
are provided that reduce the variations in the bead width. In
particular, the method and system modify a command signal used to
control motor 84 of gear assembly 52 so as to compensate for
variations in the volume of material output by nozzle 92 that would
otherwise occur due to the mechanical features of extruder 20. In
particular, a time-varying signal is added to or incorporated in
the command signal so that nozzle 92 extrudes layers with reduced
bead-width ripple such as layers 1500, 1502 and 1504 shown in the
perspective view of FIG. 15. As shown in FIG. 15, each of the
layers has a substantially constant bead width such as
substantially constant bead width 1506 of layer 1500. Note that in
these embodiments, the different layers do not have to have the
same bead width but along sections of a single deposited layer, the
bead width is substantially uniform and does not vary as much as
when the time-varying signal is not incorporated in the command
signal.
[0126] In many embodiments, incorporating or adding the
time-varying signal to the command signal involves incorporating or
adding the time-varying signal to a velocity component of the
command signal. FIG. 16 provides a graph showing a velocity
component 1600 (dashed line) and a time-varying component 1602
(dotted line) of a motor command signal 1604 (solid line). Velocity
component 1600 changes the rate at which extruder 20 deposits
material through nozzle 92 based on the relative velocity and
acceleration between nozzle 92 and the surface area (such as a
substrate, previously deposited layer or tray) that is receiving
the deposited layer. This relative velocity and acceleration can be
due to movement of the component that deposits the material, such
as nozzle 92, and/or due to movement of the surface area
(substrate/existing layers/tray) that will receive the deposited
material.
[0127] Time-varying component 1602 changes the speed at which a
pump member or brake member, such as drive gear 74 and idler gear
76, move to reduce variations in the volume of material output by
the extruder. For example, in embodiments where the pump member or
brake member rotates, the time-varying component changes the rate
of rotation of the pump member or brake member. Time-varying
component 1602 has a frequency and an amplitude that both change
over time. In one embodiment, as velocity component 1600 increases,
both the amplitude and the frequency of time-varying component 1602
increase. For example, when velocity component 1600 is at a
relatively low level 1606, time-varying component 1602 has a
relatively small amplitude 1608 and a relatively low frequency as
indicated by a relatively long wavelength 1610 in FIG. 16. However,
when velocity component 1600 is at higher level 1612, time-varying
component 1602 has a relatively large amplitude 1614 and a
relatively high frequency as indicated by a relatively short
wavelength 1616 in FIG. 16.
[0128] In FIG. 16, velocity component 1600, time-varying component
1602, and motor command signal 1604 are depicted as continuous
signals. However, those skilled in the art will recognize that
velocity component 1600 and time-varying component 1602 can be
constructed of discrete values that are individually added together
to form discrete values for motor command signal 1604.
[0129] FIG. 17 provides an expanded block diagram of controller
assembly 38 showing the components used to generate a motor command
signal 1716 that incorporates both a velocity component, such as
velocity component 1600, and a time-varying component, such as
time-varying component 1602.
[0130] As shown in the block diagram of FIG. 17, velocity component
1750 of the motor command signal 1716 is formed by a velocity-based
pump/brake controller 1752 of processing program 144. Pump/brake
controller 1752 forms the velocity component based on a relative
nozzle velocity profile 1754 and a relative nozzle acceleration
profile 1756 found in tool path instructions 1758 stored on storage
media 138. Relative nozzle velocity profile 1754 describes the
relative velocity between nozzle 92 and the area (substrate,
previously deposited layers/tray) where the nozzle is depositing
material. This relative velocity can be due to movement of nozzle
92, movement of the area or a combination of both. Relative nozzle
acceleration profile 1756 describes the relative acceleration
between nozzle 92 and the area where the nozzle is depositing
material and can be due to the acceleration of nozzle 92, the
acceleration of the area or a combination of both.
[0131] Velocity profile 1754 and acceleration profile 1756 are
generated by tool path generation 1760 of processing program 144
based on a sliced part model 1762 that defines paths or roads where
material will be deposited for each layer of the part. In
accordance with one embodiment, the relative nozzle velocities
change at different portions of the part to allow for faster
building of the part. For example, the nozzle can be moved faster
along straight portions of the part but in general must be slowed
around curved portions of the part. As the relative nozzle velocity
changes, the rate of the flow of material must also change to
maintain the bead width. If the relative nozzle velocity increases
without the output flow rate of nozzle 92 increasing, the bead
width will thin. Similarly, if the relative nozzle velocity
decreases without the output flow rate of nozzle 92 decreasing, the
bead width will thicken.
[0132] Because there is a delay between when the motor command is
sent and when the flow rate of the material changes, the pump/brake
controller 1752 also takes into consideration relative nozzle
acceleration profile 1756, in some embodiments. Using the relative
nozzle acceleration profile, pump/brake controller 1752 is able to
adjust velocity component 1750 to account for the delay between the
motor command and the change in flow in the material.
[0133] Thus, pump/brake controller 1752 produces a velocity
component 1750 of the motor command that varies with changes in the
relative velocity and relative acceleration of the nozzle. As
described above, if the motor command only includes the velocity
component 1750, the resulting bead width of the material may vary
due to mechanical features of the pump/brake. To compensate for and
reduce this variation in the bead width, a ripple compensator 1708
of processing program 144 generates time-varying component 1712
that can be added to or incorporated with velocity component 1750
to form pump command 1716. In particular, time-varying component
1602 has its amplitude, phase, frequencies and shape set so as to
partially or fully cancel the variations in the flow that would
otherwise result from the mechanical features of the pump or brake
used to extrude the material.
[0134] FIG. 18 provides a flow diagram of a method in accordance
with one embodiment for generating and using time-varying component
1712 to reduce the ripple in the deposited material.
[0135] At step 1800 of FIG. 18, an input movement factor is set to
one or more of a measured speed of rotation of the pump or brake,
the velocity component 1750, and/or nozzle velocity and nozzle
acceleration profiles 1754 and 1756. The speed of rotation of the
pump or brake can be determined from a position encoder 1706 on the
motor or pump. When the input movement factor is set to the
measured speed of rotation of the pump or brake, the embodiment is
considered to use feedback to set time-varying component 1712. When
the input movement factor is set to velocity component 1750 or
nozzle velocity and acceleration profiles 1754 and 1756, the
embodiment is considered to use movement predictions or estimates
to set time-varying component 1712. Using such predictions or
estimates allows time-varying component 1712 to be created
deterministically.
[0136] At step 1801 of FIG. 18, a position or phase 1700 and a rate
of movement or speed of rotation 1702 of a pump/brake member or
motor 84 are received. These values can be received from position
encoder 1706 through an encoder interface 1704, which stores the
values in storage media 138. Position or phase 1700 and rate of
movement or speed of rotation 1702 represent the current state of
the pump/brake member and motor 84. Position encoder 1706 can
determine the phase/position and speed of rotation/movement of the
pump member or motor 84 using physical or optical markings on the
pump member or motor 84. The pump/brake member can be a gear such
as drive gear 74 and idler gear 76, or some other type of
pump/brake member such as a piston member, a roots member, or a
screw member. In some embodiments position encoder 1706 is located
on the motor opposite the connection to the pump while in other
embodiments, the position encoder is located on the shaft
connecting the motor to the pump. In embodiments in which the motor
includes one or more gears and position encoder 1706 is not located
on the shaft between the motor and the pump, position encoder 1706
and/or encoder interface 1704 scale the movement detected by
position encoder 1706 to account for the gear ratio between the
movement detected by position encoder 1706 and the movement of the
shaft connected to pump 1702.
[0137] At step 1802, a ripple compensator 1708 in processing
program 144 determines a relative phase angle for the time-varying
component of the pump command from a compensation map 1710 stored
on storage media 138 and/or based on the input movement factor. The
relative phase angle describes the phase difference between a
particular pump member/motor position 1700 (a state of the
pump/brake member) and a particular phase of the time-varying
component of the pump command that will be provided to motor 84 to
reduce the ripple in the bead width. In some embodiments, the
relative phase angle is stored in compensation map 1710 based on
tests performed on gear assembly 52 to identify the best relative
phase angle for gear assembly 52. Thus, different types of gear
assemblies can have different relative phase angles stored in
compensation map 1710. In other embodiments, the different relative
phase angles are used for different speeds of the pump. In such
embodiments, the input movement factor is used to determine a
current or predicted speed of the pump and this speed is used to
calculate the relative phase angle or is used to retrieve a
corresponding relative phase angle from compensation map 1710.
[0138] At step 1804, the relative phase angle from compensation map
1710 is used by ripple compensator 1708 to set an actual phase
angle for the time-varying component based on the position/phase of
the pump member/motor 1700. In one particular embodiment, the
actual phase angle is the sum of the relative phase angle from
compensation map 1710 and the current phase of the pump
member/motor 1700.
[0139] At step 1806, ripple compensator 1708 retrieves a
frequency-amplitude function from compensation map 1710. The
frequency-amplitude function describes the frequency and amplitude
for the time-varying component of the pump command as a function of
the predicted or actual frequency of rotation or speed of movement
of the pump member/motor 1702 as provided by the input movement
factor. At step 1808, ripple compensator 1708 uses the retrieved
frequency-amplitude function and the input movement factor to set
the frequency and amplitude for the time-varying component of the
pump command In general, the frequency and amplitude of the
time-varying component increase as the frequency or rotation or
speed of movement of the pump member/motor increases. Thus, in
general, the frequency and amplitude both increase with increases
in the input movement factor.
[0140] At step 1810, ripple compensator 1708 retrieves a shape for
the time-varying component from compensation map 1710. Possible
shapes for the time-varying component include sinusoidal, saw tooth
and square, for example. In accordance with one embodiment, the
shape of the time-varying is dependent on attributes of the gear
assembly. In other embodiments, the shape for time-varying
component 1712 is fixed in ripple compensator 1708 and does not
have to be retrieved.
[0141] At step 1814, ripple compensator 1708 uses the phase angle,
frequency, shape and amplitude of the time-varying component to
determine a current value for the time-varying component, which is
stored as time-varying component of pump command 1712.
[0142] At step 1816, an adder 1714 in processing program 144 adds
or combines the time-varying component of the pump command 1712
with the velocity component of the pump command 1750 to incorporate
the time-varying component into a pump command 1716 that is
provided to a motor interface 1718. Motor interface 1718 converts
the pump command 1716 into a motor driver signal that is provided
to motor 84 at step 1818. The ripple-compensated command is then
used by motor 84 to drive gear assembly 52 and deposit material
with reduced ripples as shown in FIG. 15.
[0143] Thus, during steps 1800-1818, controller 38 uses the state
of the pump member/rotor provided by the encoder signal of the
position encoder to modify the time-varying component.
[0144] Steps 1800-1818 are repeated to provide a series of pump
commands 1750 that together represent a pump command signal that
has a time-varying signal incorporated therein to reduce ripple in
the bead width of a deposited layer output by an extruder. Thus,
through steps 1800-1818, controller 38 applies a time-varying
signal to the extruder to compensate for time-varying changes in
the flow of material that would otherwise occur due to the
mechanical features of the extruder.
[0145] Although a molten material has been discussed in other parts
of the specification, the steps of FIG. 18 and the apparatus of
FIG. 17 may be used with other materials including materials that
are viscous or paste-like at room temperature and standard
pressures, for example.
[0146] Although the present disclosure has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the disclosure.
* * * * *