U.S. patent application number 12/273924 was filed with the patent office on 2009-04-30 for material delivery tension and tracking system for use in solid imaging.
This patent application is currently assigned to 3D Systems, Inc.. Invention is credited to Dennis F. McNamara, Suzanne M. Scott, Charles R. Sperry.
Application Number | 20090110763 12/273924 |
Document ID | / |
Family ID | 38421621 |
Filed Date | 2009-04-30 |
United States Patent
Application |
20090110763 |
Kind Code |
A1 |
Sperry; Charles R. ; et
al. |
April 30, 2009 |
Material Delivery Tension and Tracking System for Use in Solid
Imaging
Abstract
A solid imaging apparatus and method employing a radiation
transparent build material carrier and a build material dispensing
system that accurately controls the thickness of the transferred
layer of solidifiable liquid build material to the radiation
transparent build material carrier to achieve high resolution
imaging in three-dimensional objects built using an electro-optical
radiation source.
Inventors: |
Sperry; Charles R.;
(Florence, MA) ; McNamara; Dennis F.;
(Charlestown, NY) ; Scott; Suzanne M.;
(Springfield, VT) |
Correspondence
Address: |
3D Systems, Inc.;Attn: Keith A. Roberson
333 Three D Systems Circle
Rock Hill
SC
29730
US
|
Assignee: |
3D Systems, Inc.
|
Family ID: |
38421621 |
Appl. No.: |
12/273924 |
Filed: |
November 19, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11416812 |
May 3, 2006 |
7467939 |
|
|
12273924 |
|
|
|
|
Current U.S.
Class: |
425/174.4 |
Current CPC
Class: |
B29C 64/135 20170801;
B33Y 30/00 20141201; B33Y 10/00 20141201 |
Class at
Publication: |
425/174.4 |
International
Class: |
B29C 35/08 20060101
B29C035/08 |
Claims
1-11. (canceled)
12. A solid imaging system that layer-by-layer forms a
three-dimensional object with a solidifiable liquid build material
the system comprising: a solidifiable liquid build material
dispenser; a flexible build material carrier having a first side
and an opposing second sides the first side receiving liquid build
material from the build material dispenser; and a radiation source
to selectively solidify the liquid build material on the first side
of the flexible build material carrier; wherein the flexible build
material carrier comprises a reciprocating sheet of film.
13. A system according to claim 12, wherein the flexible build
material carrier comprises an endless flexible build material
carrier.
14. A system according to claim 12, wherein the dispenser comprises
a cartridge dispenser.
15. A system according to claim 14, wherein the cartridge dispenser
comprises a reservoir of solidifiable liquid build material within
the cartridge dispensers.
16. A system according to claim 14, wherein the cartridge dispenser
comprises a reservoir of solidifiable liquid build material remote
from the cartridge dispenser
17. A system according to claim 16, wherein the reservoir of
solidifiable liquid build material is in fluid communication with
the cartridge dispenser so that the reservoir can be replaced
separately from the cartridge dispenser.
18. A system according to claim 12, wherein the flexible build
material carrier comprises a radiation transparent carriers.
19. A system according to claim 12, wherein the radiation source
comprises a digital light projector.
20. A system according to claim 12, wherein the solidifiable liquid
build material comprises a photopolymer that is curable when
exposed to at least one of UV radiation and visible light.
21. A system according to claim 12 further comprising a gravure
wheel that applies the solidifiable liquid build material to the
first side of the flexible build material carrier.
22. A solid imaging system that layer-by-layer forms a
three-dimensional object with a solidifiable liquid build material,
the system comprising: a solidifiable liquid build material
dispenser; a flexible build material carrier having a first side
and an opposing second side, the first side receiving liquid build
material from the build material dispenser; a radiation source to
selectively solidify the liquid build material oil the first side
of the flexible build material carrier; and a gravure wheel that
applies the solidifiable liquid build material to the first side of
the flexible build material carrier.
23. A system according to claim 22, wherein the flexible build
material carrier comprises an endless flexible build material
carrier.
24. A system according to claim 22, wherein the dispenser comprises
a cartridge dispenser.
25. A system according to claim 24, wherein the cartridge dispenser
comprises a reservoir of solidifiable liquid build material within
the cartridge dispenser.
26. A system according to claim 24, wherein the cartridge dispenser
comprises a reservoir of solidifiable liquid build material remote
from the cartridge dispenser
27. A system according to claim 26, wherein the reservoir of
solidifiable liquid build material is in fluid communication with
the cartridge dispenser so that the reservoir can be replaced
separately from the cartridge dispenser.
28. A system according to claim 24, wherein the gravure wheel is
defined within the cartridge dispenser.
29. A system according to claim 22, wherein the flexible build
material carrier comprises a radiation transparent carrier.
30. A system according to claim 22, wherein the radiation source
comprises a digital light projector.
31. A system according to claim 22, wherein the solidifiable liquid
build material comprises a photopolymer that is curable when
exposed to at least one of UV radiation and visible light.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of copending U.S. patent
application Ser. No. 11/416,812, filed May 3, 2006, which is hereby
incorporated herein in its entirety by reference.
FIELD OF INVENTION
[0002] The present invention is directed to forming cross-sectional
layers with an image projection system using a solidifiable build
material in an apparatus for forming three-dimensional objects on a
layer-by-layer basis. More particularly, it is directed to an
apparatus and method for controlling the tension and tracking of an
endless belt used to deliver in a desired thickness the
solidifiable liquid build material used to form the
three-dimensional object being built in response to exposure by UV
or visible radiation.
BACKGROUND OF THE INVENTION
[0003] In recent years, many different techniques for the fast
production of three-dimensional models have been developed for
industrial use. These solid imaging techniques are sometimes
referred to as rapid prototyping and manufacturing ("RP&M")
techniques. In general, rapid prototyping and manufacturing
techniques build three-dimensional objects layer-by-layer from a
working medium utilizing a sliced data set representing
cross-sections of the object to be formed. Typically, an object
representation is initially provided by a Computer Aided Design
(CAD) system.
[0004] Stereolithography, presently the most common RP&M
technique, was the first commercially successful solid imaging
technique to create three-dimensional objects from CAD data.
Stereolithography may be defined as a technique for the automated
fabrication of three-dimensional objects from a fluid-like material
utilizing selective exposure of layers of the material at a working
surface to solidify and adhere successive layers of the object
(i.e. laminae). In stereolithography, data representing the
three-dimensional object is input as, or converted into,
two-dimensional layer data representing cross-sections of the
object. Layers of material are successively formed and selectively
transformed or solidified (i.e. cured) most often using a computer
controlled laser beam of ultraviolet (UV) radiation into successive
laminae according to the two-dimensional layer data. During
transformation, the successive laminae are bonded to previously
formed laminae to allow integral formation of the three-dimensional
object. This is an additive process. More recent designs have
employed the use of visible light to initiate the polymerization
reaction to cure the photopolymer build material that is commonly
referred to as resin.
[0005] Stereolithography represents an unprecedented way to quickly
make complex or simple parts without tooling. Since this technology
depends on using a computer to generate its cross-sectional
patterns, there is a natural data link to CAD/CAM. Such systems
have encountered and had to overcome difficulties relating to
shrinkage, curl and other distortions, as well as resolution,
accuracy, and difficulties in producing certain object shapes.
While stereolithography has shown itself to be an effective
technique for forming three-dimensional objects, other solid
imaging technologies have been developed over time to address the
difficulties inherent in stereolithography and to provide other
RP&M advantages.
[0006] These alternate technologies, along with stereolithography,
have collectively been referred to as solid freeform fabrication or
solid imaging techniques. They include laminated object
manufacturing (LOM), laser sintering, fused deposition modeling
(FDM), and various ink jet based systems to deliver either a liquid
binder to a powder material or a build material that solidifies by
temperature change or photocuring. Most recently a technology using
digital light processing technology has employed visible light to
initiate the photopolymerization reaction to cure a photopolymer
build material, commonly referred to as a resin. Each of these
additive technologies have brought various improvements in one or
more of accuracy, building speed, material properties, reduced
cost, and appearance of the build object.
[0007] All of the solid imaging or freeform fabrication techniques,
to be successful, must form objects that are near full density or
free of unintended voids or air pockets. Voids caused by air
pockets create discontinuities and weaknesses in the objects being
built, as well as not accurately reproducing the three-dimensional
aspect of the object being created from the CAD representation.
This problem is especially acute in technologies employing
solidifiable liquid resin that is placed down layer-by-layer
employing an intermediate transfer process. The use of an
intermediate transfer surface from which the solidifable liquid
resin is transferred to a support platform or an underlying layer
of material reduces the amount of excess resin that must be removed
from completed parts and eliminates the need to build in a vat or
large container of resin. This does eliminate the cost of
additional resin beyond what is necessary to build the then needed
parts. However, it increases the need for reliable and consistent
layer thickness in the transferred liquid resin and tracking and
tension of the endless belt used as the transfer surface as
cross-sections of material are formed.
[0008] Additionally, none of the prior solid freeform fabrication
approaches, while making substantial improvements, have yet to
achieve a truly low cost system that produces highly accurate and
visually appealing three-dimensional objects in a short build
time.
[0009] These problems are solved in the design of the present
invention by employing a material transfer technique and apparatus
in a low cost solid imaging technique in combination with the use
of digital imaging projection or laser scanning in a manner that
creates a three-dimensional object that accurately reflects the CAD
representation while consistently applying uniform thicknesses of
the solidifiable liquid resin used to form the three-dimensional
object.
SUMMARY OF THE INVENTION
[0010] It is an aspect of the present invention that a solid
imaging apparatus is provided that utilizes a radiation transparent
build material carrier and build material dispensing system that
accurately controls the thickness of the transferred layer of
solidifiable liquid build material to achieve high resolution
imaging in three-dimensional objects built using UV radiation or
visible light and a photopolymer build material.
[0011] It is a feature of the present invention that a radiation
transparent endless belt and belt tensioning system are employed to
control the thickness of the layer of solidifiable liquid build
material applied to the belt and transferred to a receiving
substrate layer by layer to create a three-dimensional part.
[0012] It is another feature of the present invention that the
solidifiable liquid build material is dispensed from a channel in a
dispensing cartridge to the endless belt by means of a fluid
wedge.
[0013] It is yet another feature of the present invention that a
belt tracking and alignment system is used to keep the endless belt
centered as it traverses its rotational path.
[0014] It is still another feature of the present invention that
the tension on the endless belt controls the thickness of the layer
of solidifiable build material applied to the endless belt, the
greater the tension the thinner the layer.
[0015] It is a further feature of the present invention that
optical sensors sense the presence of the endless belt at the edges
of the belt and signal for correction to the belt tracking when no
sensing is found at an edge.
[0016] It is an advantage of the present invention that a low cost
solid imaging device is obtained that provides accurate and
repeatable layers of build material during the building of
three-dimensional objects.
[0017] It is another advantage of the present invention that the
belt tensioning material dispensing design is simple and effective
in producing three-dimensional objects built layer-by-layer.
[0018] These and other aspects, features, and advantages are
obtained by the present invention through the use of a solid
imaging apparatus and method that employ an endless belt as a
radiation transparent build material carrier and a belt tensioning
system to control a fluid wedge formed at the dispenser to control
the thickness of the layer of solidifiable liquid build material
applied to the belt and transferred to a receiving substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] These and other aspects, features and advantages of the
invention will become apparent upon consideration of the following
detailed disclosure of the invention, especially when taken in
conjunction with the following drawings wherein:
[0020] FIG. 1 is a front perspective view of a flexible transport
solid imaging system utilizing a radiation transparent endless
flexible belt as the build material transfer means and a tracking
and tensioning apparatus:
[0021] FIG. 2 is a partially exploded front perspective view of a
flexible transport solid imaging system showing the radiation
transparent endless flexible belt and the tracking and tensioning
apparatus;
[0022] FIG. 3 is a rear perspective view of a flexible transport
solid imaging system showing the radiation transparent endless
flexible belt, light projector and build material feed
cartridge;
[0023] FIG. 4 is a front elevational view of a flexible transport
solid imaging system;
[0024] FIG. 5 is a front perspective view of an embodiment of a
flexible transport solid imaging system and one stepper motor used
to raise and lower the support platform to which solidifiable
liquid build material is transferred from the radiation transparent
endless flexible belt to form a three-dimensional object on the
support platform;
[0025] FIG. 6 is a diagrammatic illustration of a top plan view of
the endless flexible belt tracking and sensing system;
[0026] FIG. 7 is a diagrammatic illustration of a portion of the
endless flexible belt tracking system that controls the tracking of
the belt as it traverses its path about the flexible transport
solid imaging system; and
[0027] FIG. 8 is a diagrammatic illustration of a dispensing slit
or channel in the build material cartridge dispenser across which
the endless belt travels vertically downwardly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] Flexible transport solid imaging of the type disclosed
herein involves employing an appropriate electro-optical radiation
source in the layer-by-layer build-up of articles from a radiation
curable liquid photopolymer material that is delivered by the
flexible transport endless belt or reciprocatable sheet of film.
The radiation source can employ any wavelength of radiation
conducive to reflection from the electromagnetic spectrum, such as
light valve technology with electron or particle beams, but
preferably employs visible or UV radiation. Liquid photopolymer
material is applied to the endless flexible belt or reciprocatable
sheet of film from a cartridge employing an appropriate coating
device, such as a gravure wheel or fluid wedge, that transfers the
photopolymer build material to the flexible transport device to
provide fresh material to create new layers as the
three-dimensional object is built. The photopolymer build material
is transferred via transfer means to a receiving substrate without
entrapping air bubbles in the transferred layers. The photopolymer
build material is preferably imaged by radiation projected from
either a digital UV projector or a digital visible light projector
and solidified layer-by-layer. The projector includes a spatial
light modulator, such as a digital micro-mirror device ("DMD") that
selectively illuminates pixels for imaging. Visible light
projection is a preferred approach.
[0029] Solid imaged parts are preferably built on an elevator
platform that moves the build object or part up into contact with
the liquid photopolymer build material and, after exposure, down
and out of contact with the liquid photopolymer build material as
successive layers or laminae are formed during the building
process. The build object can be built on structures known as
supports rather than directly on the elevator platform. Supports
are used for more complex three-dimensional objects being built
that have unsupported or partially unsupported surfaces.
[0030] Commercially available digital light projectors, optionally
modified to have a shorter focal length, may be employed, such as
those available from InFocus Corporation of Wilsonville, Oreg. and
BenQ America Corp. of Irvine, Calif.
[0031] In one application of the present invention, the
photopolymer build material is delivered to the imaging area via a
radiation transparent flexible build material carrier film, such as
polypropylene or polycarbonate. The photopolymer build material is
applied in a thin layer to the flexible build material carrier or
transport film in the embodiment shown in FIG. 1.
[0032] As seen in FIG. 1, a flexible transport imaging system with
covers removed is indicated generally by the numeral 10. Flexible
transport imaging system 10 has a radiation transparent build
material carrier in the form of an endless belt 11 that is
positioned about a drive rollers 14 and 15 and follower or idler
rollers 19 and 20. A build material feed cartridge assembly is
indicated generally by the numeral 12. The cartridge assembly 12
and the idler rollers 14 and 15 are fixed in their relative
positions. Belt 11 is driven in the direction indicated by arrow 21
by electrical drive motors 22 and 24 that drive rollers 14 and 15,
respectively. The vertical distance between drive rollers 14 and 15
is fixed, but the horizontal distance between the drive rollers 14
and 15 and idler rollers 19 and 20 is variable to control the
tension in endless belt 11. Idler rollers 19 and 20, as seen in
FIG. 3, are rotatably mounted between vertical frame members 17 and
23.
[0033] A digital light projector is the radiation source 44, see
FIG. 3, that projects an image with selected pixels for
illumination onto a mirror system 41 below the upper run of endless
belt 11 in the exposure of a cross-section of a three-dimensional
object being formed on a support platform 53, best seen in FIG. 4.
As illustrated in the embodiment seen in FIG. 5, the support
platform 53 is raised and lowered by a stepper motor 58. In the
embodiment of FIGS. 1-4 a pair of stepper motors 58 is employed
that ride up a threaded lead screw 59 and guide rails 60 on
opposing sides of the imaging system 10. The guide rails 60 are
held in place by guide rail anchor plates 61 and 62 appropriately
fastened to the system frame. A support platform assembly bar 54 is
fastened to each stepper motor 58.
[0034] As best seen in FIGS. 1-4, support platform assembly bar 54
extends through slots 55 and 56 in frame end plates 35 and 40,
respectively. This enables the support platform assembly bar 54 to
move with the stepper motors 58 to raise and lower the support
platform 53. This brings the already formed cross-sectional layers
into contact with the layer of resin or solidifiable liquid build
material 47 that is deposited on endless belt 11 from the resin or
solidifiable liquid medium cartridge dispenser 13 that is a part of
build material feed cartridge assembly 12. Cartridge dispenser 13
includes a resin reservoir of solidifiable liquid medium and a
dispensing slit or channel 45, see briefly FIG. 8, through which
the solidifiable liquid build material is applied to belt 11.
[0035] FIGS. 1 and 2 show the drive roller carriage, indicated
generally by the numeral 27. Drive rollers 14 and 15 are rotatably
mounted between vertical frame members 16 and 18. Drive motors 22
and 24 are mounted to vertical frame member 18 and are drivingly
connected to drive rollers 14 and 15. Drive roller vertical frame
member 25 is attached to the end of the drive motors. Belt tracking
motor 26 controls the tracking of belt 11 as belt 11 rotates about
rollers 14, 15, 19 and 20 and faces in the opposite direction of
drive motors 22 and 24. Motor shaft 28, best seen in FIG. 2,
extends through frame member 25 from motor 26. A belt tracking
control arm 29 is attached to the end of shaft 28. A tracking
control arm frame member 30 connects frame members 16 and 18 and
includes a pivot attachment 31, see briefly FIGS. 4 and 6, that is
used to mount the drive roller carriage 27. Left edge belt tracking
optical sensor 33 and right edge belt tracking optical sensor 37
are mounted to frame member 30 as seen in FIGS. 1 and 2.
[0036] FIG. 6 is diagrammatical illustration of a top plan view of
the drive roller carriage 27. Drive roller 14, idler roller 19 and
endless belt 11 (in phantom lines) are shown, along with vertical
frame members 16, 18 and 25. Mounting arm 36 is attached between
pivot attachment 31 on the drive roller carriage and the pivot 39
on the frame end plate 35. The pivot point on pivot attachment 31
is offset a small distance from the center of attachment 31. An air
cylinder 32 mounts through end plate 35 so that cylinder plunger 34
contacts the back of pivot attachment 31 on the back of tracking
control arm frame member 30 of FIGS. 1 and 2. When air cylinder 32
of FIG. 6 is pressurized, the plunger 34 exerts a force on the
drive roller carriage via pivot attachment 31. The entire drive
roller carriage moves about pivot 39 which movement extends the
distance between drive rollers 14 and 15 and idler rollers 19 and
20, thereby putting tension on the endless belt 11 when the plunger
34 is extended or shortening the distance, thereby reducing
tension, when it is retracted. A desired tension can thus be
maintained on the endless belt 11.
[0037] The tension in the belt 11 controls the thickness of the
solidifiable liquid build material 47 applied to the endless belt
11 as the belt 11 travels vertically downwardly across the
dispensing slit or channel 45 in build material cartridge dispenser
13, as seen in FIG. 8. The dispensing slit or channel 45 supplies
build material from the reservoir (not shown) within cartridge
dispenser 13 to the surface 51 of the belt 11. The cartridge
dispenser 13 has a flat section above and below the channel 45,
indicated by the numerals 46 and 48, respectively, and an arcuate
section 49 with large radius at the bottom to provide clearance for
the build material 47 on the coated surface 51 of belt 11 as the
belt is driven in its path about rollers 14, 15, 19 and 20.
Alternatively, section 49 can be at an acute angle or a right angle
to provide the required clearance. As belt 11 moves past channel
45, a fluid wedge develops at the bottom edge 50 of the channel 45
that applies an even coating onto the belt 11 via the fluid wedge
effect so that the greater the tension, the thinner is the coating.
The cartridge dispenser 13 can have a reservoir of liquid build
material 47 integral with it or remotely from it. If positioned
remotely from dispenser 13, the reservoir is in fluid flow
communication with the dispenser 13 so that the reservoir can be
replaced separately from the cartridge dispenser 13.
[0038] The coating thickness is monitored by an appropriate sensor,
such as a pattern recognition device. If the coating thickness is
too thick, the cylinder plunger 34 will slowly be extended so as to
increase the belt 11 tension and decrease the fluid wedge, thereby
making the coating thinner until the correct thickness coating is
obtained. Alternately, if the coating is too thin, the plunger 34
will be retracted, decreasing the belt 11 tension and thereby
increasing the fluid wedge making the coating thicker until the
desired thickness is obtained. Coating thickness can be controlled
to 0.002 inches for faster imaging or to 0.001 inches for slower
imaging. The air cylinder 32 can exert between 10 to 20 pounds per
square inch against the belt 11 to ensure the belt is taut about
rollers 14, 15, 19 and 20. Any other effective device can be used
to exert pressure on the belt 11, such as a solenoid valve, spring
or other appropriate mechanical system. The fluid wedge can be
effectively created whether there is an angled bottom edge 50 or a
straight or rounded bottom surface to the channel 45. The
effectiveness of the fluid wedge is a function of a number of
factors including the viscosity of the solidifiable liquid build
material 47, the surface tension between the build material 47 and
the belt 11, the pressure head of liquid build material 47 in the
cartridge dispenser 13, the height of the opening of the dispensing
channel 45, the length of the flat sections 46 and 48, and the
speed and tension of the belt 11 as it traverses about rollers 14,
15, 19, and 20 and past channel 50.
[0039] Looking now at FIGS. 6 and 7, belt tracking motor 26 exerts
a rotational force on tracking control arm 29. The control arm 29
is attached to mounting arm 36 via any linkage suitable to pivot
the drive roller carriage 27, such as magnetic ball 38. Ball 38
rests in a slot in the control arm 29 and a countersink in mounting
arm 36. If motor 22 exerts a clockwise rotational force, the
control arm 29 pushes the magnetic ball 38 into the mounting arm
36, forcing the drive roller carriage 27 away from the mounting arm
36. Conversely, if the motor 22 exerts a counterclockwise
rotational force, the control arm 29 moves away from the mounting
arm 36 and the magnetic force pulls the carriage toward the
mounting arm 36. This rotates the drive roller carriage about pivot
point 31 of FIG. 6. Thus, the drive rollers 14 and 15 rotate to
steer the belt 11. As seen in FIGS. 1 and 2, if the drive roller
carriage 27 rotates clockwise, the belt 11 steers to the left, and
with a counter clockwise rotation, it steers to the right. Looking
again at FIG. 2, tracking sensors 33 and 37 are placed apart at a
distance so the width of the belt 11 just extends over the edges of
the sensors 33 and 37, respectively. Sensors 33 and 37 are optical
sensors that sense the presence of the belt 11. In operation, as
the belt 11 is being driven it will translate laterally until it
uncovers one of the sensors 33 or 37. The force on the tracking
motor 22 will then be reversed and the belt 11 will translate until
the other sensor is uncovered, and the process will reverse again.
In this manner, the belt 11 is constantly moving laterally back and
forth across a small distance.
[0040] An appropriate sub-pixel image displacement device, not
shown, is placed between the radiation light source 44 and the
target area on the belt 11 that is coated with the solidifiable
liquid build material 47. The exposure of the image cross-section
by illuminating selected pixels creates a solidified portion of the
cross-section of the three-dimensional object being formed. The
sub-pixel image displacement device alternatively can be a mirror
with the pixel shifting device being located outside of the runs of
the endless belt 11 or it could combine both a mirror and pixel
shifting device in a single element.
[0041] Any suitable fluid build material capable of solidification
in response to the application of an appropriate form of energy
stimulation may be employed in the practice of the present
invention. Many liquid state chemicals are known which can be
induced to change to solid state polymer plastic by irradiation
with UV radiation or visible light. A suitable visible light
curable photopolymer that may be employed in the practice of the
present invention is shown in Table I below. This formulation
exhibited excellent resolution and photospeed when utilized with a
BenQ PB7220 projector. The parts created displayed outstanding
green strength with balanced stiffness and toughness.
TABLE-US-00001 TABLE-1 Units of Weight Weight Percent Acrylate-24
(from Sartomer Company) % PRO 6817 (from Sartomer Company) 4.8
23.02 SR 833S (from Sartomer Company) 3.5 16.79 Ebecryl 83 (from
UCB Chemicals 2.4 11.51 Corp.) PRO 6169 (from Sartomer Company) 5.2
24.94 SR 531 (from Sartomer Company) 3.6 17.27 Irgacure I-907 (From
Ciba Specialty 0.75 3.60 Chemicals, Inc.) Irgacure I-819 (From Ciba
Specialty 0.6 2.88 Chemicals, Inc.) Total 20.85 100.00
Additives can be incorporated into the formulation to promote
release ability from the transparent transport means, such as
silicone acrylate materials.
[0042] In operation, data to build a three-dimensional object is
sent to the flexible transport solid imaging system from a CAD
station (not shown) that converts the CAD data to a suitable
digital layer data format and feeds it to a computer control system
(also not shown) where the object data is manipulated to optimize
the data via an algorithm to provide on/off instructions for the
digital light projector. The solid imaging layer data is attained
by the CAD data being processed by a slicing program to create
cross-sectional data. An algorithm is then applied to the
cross-sectional data by a suitable controller, such as a
microprocessor or computer, to create the instructions for the
digital light projector to illuminate selected pixels in the image
within the boundary of the three-dimensional object in the
cross-section being formed. An appropriate pixel shifting image
displacement device can be employed to increase the resolution and
edge smoothness of the cross-sections produced.
[0043] Upon completion of the imaging of a layer, the platform 53
is lowered. Since the cured image is now stuck to both the belt 11
and platform 53, the belt 11 is pulled downward with the platform
53 into a bow shape until the part layer peels from the belt 11.
The belt 11 then returns back into its straightened form. The
radiation transparent belt 11 carrying the build material 47 peels
away from the exposed and solidified layer of build material
forming the cross-section of the three-dimensional part being
formed with no horizontal motion therebetween. The flexibility of
the radiation transparent belt 11 enables the separation to occur
in a peeling type of action because the separation force is
proportional to the width of the exposed area of the build material
47 as opposed to the total area of the exposed build material, as
occurs in the case of an inflexible planar surface.
[0044] The substrate on which the part is built on the build
support platform 53 is chosen so that the part's bond to it is
stronger than its bond to the belt 11. The substrate material
should be pervious, flexible, and easily attachable to the build
support platform 53. It can be a fine sandpaper or similar material
to give grip, but more preferably is a porous material, such as
ground silicone, that allows any wet, uncured material to flow away
from the part to keep the part as dry as possible.
[0045] As the part grows, each new layer bonds to the cured build
material of the layer below it. Once the platform is in its lowest
position, the belt is driven in direction of travel 21 to re-coat
the belt 11 with the build material 47. The belt 11 will be driven
approximately 12'' to 18'' to establish a consistent layer
thickness of the build material. The platform 53 is then raised
into position. Since there is now a 0.001'' thick slice of the part
on the platform 53, the platform 53 is raised into a position
0.001'' lower than the previous one so that it is now the top of
the part that is in intimate contact with the coating of build
material 47 on the surface 51 of the belt 11. In practice, this
positioning is controlled by the stepper motors 58 that raise and
lower the platform 53 in a manner that is very accurate in its
movement and repeatable. If, for example, motors 58 move the
platform down 0.500'' after each exposure, but move up only
0.499'', they will always compensate for the 0.001'' buildup per
cycle. Now that the belt 11 has been re-coated and the platform 53
is in position, the next slice of the part is projected, and the
process continues until the part is complete.
[0046] While the invention has been described above with references
to specific embodiments thereof, it is apparent that many changes,
modifications and variations in the materials, arrangements of
parts and steps can be made without departing from the inventive
concept disclosed herein. For example, where a laser, laser
scanning mirrors and other related apparatus are employed in lieu
of digital image projection equipment, there is no sub-pixel image
placement device employed. Where supports are used in the build
process, either two separate materials or one material that is the
same for the build object and the supports are employed.
[0047] Accordingly, the spirit and broad scope of the appended
claims are intended to embrace all such changes, modifications and
variations that may occur to one of skill in the art upon a reading
of the disclosure. All patent applications, patents and other
publications cited herein are incorporated by reference in their
entirety.
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