Note: Descriptions are shown in the official language in which they were submitted.
2fl~'~3~'~
PATENT
METHOD AND APPARATUS FOR THE COMfOTER-CONTROLLED
MANUFACTURE OF THREE-DIMENSIONAL OBJECTS FROM COMPUTER DATA
This application is a continuation-in-part of application S.N.
905,069, filed June 24, 1992, which is a continuation of
application S.N. 648,081, filed January 31, 1991, now abandoned.
BACKGROUND OF TAE INVENTION
Field of the Invention
Without limiting its scope, this invention relates to rapid
prototyping, and more particularly to a system, method, and process
for manufacture of three-dimensional objects from computer data
using computer-controlled dispensing of multiple media and
selective material subtraction.
Description of the Related Art
As complex designs increase the need for rapid prototype
fabrication, this need for immediate feedback requires model or
machine shops to fabricate complex parts in low volume with minimum
setup and run-time. Most fabrication methods, however, are slow,
complex, and expensive.
While manual machining and forming methods are often cheap and
effective for simple designs, the costs can be prohibitive for the
iterations required of complex parts and assemblies. Computer
Numerically Controlled (CNC) machines are widely used to automate
complex fabrication, but are costly to operate, maintain, and
program just for one-of-a-kind production.
The most widely known system in the field of rapid prototyping
is stereolithography. This system fabricates complex parts from
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computer data by employing a set of computer-controlled mirrors to
scan a laser beam across selected two-dimensional areas of liquid
photopolymer contained in a vat and thereby form a layer of solid
polymer. The cured layer, which is attached to a platform, is
lowered into the vat and new layers are generated one on top of the
previous layers to form a three-dimensional part.
When the part is complete, the excess resin is removed with
a solvent and the platform attachment as well as all overhang
supports are cut away from the desired object. Additional light
exposure is required to solidify any trapped liquid;
A major drawback to stereolithography and similar approaches
is that support structures must be designed to join the object to
the platform and attach any overhangs, large spans or disjoint
areas. The addition of these structures to the CAD model and
subsequent manual removal from the part during cleaning is labor
intensive and often requires special skills.
Another drawback is the additional occupational and
environmental safety measures required with the use of lasers or
resins. The chemicals used in this process and in cleanup require
special handling, ventilation, and storage to protect the operator
and the work place. High volumes of waste are generated in resin
removal and cleanup. The photopolymer is expensive and
nonrecyclable. All of this makes installation in common work areas
or offices impractical for size and environmental reasons.
Furthermore, because of the delicate nature of lasers and optics,
installation and calibration is very difficult. Maintenance is
expensive due to system complexity and laser costs.
Another lithographic fabrication method is selective laser
sintering. This method employs a heat laser to fuse (sinter)
selected areas of powdered material such as wax, plastic, or metal. -
In practice, a vat of powder is scanned by the laser thereby
melting individual particles which then stick to adjacent
particles. Layers of the fused powder axe processed sequentially
like photopolymer lithography. An advantage of the sintering
method is that the non-heated powder serves as a support for the
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part as it is formed. This means that the non-heated powder can
be shaken or dusted off the object.
Selective laser sintering, however, is also a complex,
expensive optical system. The resolution of the final part is
limited by the beam diameter, which is typically .Ol"-.02".
Furthermore, in an additional step, the powder is deposited and
levelled by a rolling brush which requires other electro-mechanical
components. Unfortunately, levelling fine powders with a rolling
brush often causes nonhomogeneous packing density. Additionally,
while power costs less (material & labor) than liquid photopolymer
systems, preparing a 30 micron layer is difficult. An object built
from this powder is of medium resolution, has a non-uniform surface
and, often, a non-homogeneous structure.
Research has been conducted at the Massachusetts Institute of
Technology in fabrication by three-dimensional printing. In this
research, ceramic powder is deposited using a wide feeder over a
vat or tray. A silica binder is then printed on selected areas of
the powder to form a solid cross-section. The process is repeated
to form a stack of cross-sections representing the final object.
This approach exhibits the same powder deposition problems as
selective laser sintering, along with the additional difficulty in
removing unbound powder from internal cavities. Furthermore,
objects generated by this system are not recyclable. The MIT
research is directed toward the production of ceramic molds. Metal
or other materials are then injected or poured into the mold which
is later broken away from the cast parts. Unfortunately, the
mold's internal cavities, which define the final parts, are not
easily inspected, which leads to an expensive trial and error
process to acquire accurate parts.
Additional problems found with the art have been an inability
to: provide for variable surface color or use more than one
material media in the fabrication of the desired object; remove the
media support for overhangs, large spans or disjoint areas
automatically; or provide an automated system for physically
reproducing three-dimensional computer designs and images. Systems
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currently available are expensive, the media they use cannot be
recycled, and they cannot provide for automated part handling after
fabrication due to their use of bulk powders and resins, which
require containers rather than conveyor platforms. Accordingly,
improvements which overcome any or all of these problems are
presently desirable.
By way of further background, U.S. Patent No. 4,665,492,
issued May 12, 1987 to Masters, describes a computer automated
process and system for fabricating a three-dimensional object. The
disclosed method requires the use of an origination seed at which
particles of the part-forming material are directed, and to which
the particles adhere to form the object. As such, it is believed
that the complexity of the shape of objects formed by the disclosed
method is limited, as only those objects which can be formed in a
unitary manner from the origination seed can be produced by this
method.
By way of still further background, U.S. Patent No. 4,961,154
issued October 2, 1990, and European Patent Office Publication No.
0 322 257 published June 6, 1989, disclose methods for producing
three-dimensional parts by the selective photoexposure of
photopolymers. Each of these references disclose a method and
apparatus by which a layer of photopolymer is dispensed and
selectively exposed to light, followed by development of the
exposed layer. These references further disclose that a different
support material may be substituted for the non-polymerized
photopolymer in each layer by removing the non-polymerized
photopolymer, and filling those portions of the layer from which
the non-polymerized polymer were removed with a different support
material, after which the next object layer is formed in a similar
manner. The methods disclosed in these references are limited to
photopolymer processing, and as such are useful to produce a part
from only a narrow set of materials. In addition, the machines fox
producing a part according to this method are necessarily quite
complex, considering that non-polymerized material must be removed
and disposed of during the processing of each layer, requiring the
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transport of the material being processed from station to station
in the machine.
SUMMARY OF TAE INVENTION
In view of the above problems associated with the related art,
it is an object of the present invention to provide a computer-
aided manufacturing system, apparatus and a method for fabricating
an object in more than one material media and/or in more than one
surface color.
It is another object of the present invention to provide an
automated system, apparatus and method for physically reproducing
three-dimensional computer designs and images, including automated
part handling after fabrication.
It is yet another object of the present invention to provide
a system, apparatus and method for automatically removing the media
support for overhangs, large spans, disjoint areas and the like
from the fabricated object.
It is a further object of the present invention to provide a
system, apparatus and method for fabrication of an object using
recyclable media.
It is a further object of the present invention to provide
such a system and method which utilizes an integrated head to
perform each of the process steps required in a part layer in a
single pass, thus simplifying the processing system required for
producing a part.
It is a further object of the present invention to further
improve such a method of producing a three-dimensional object, and
the reliability of the system for doing so, by forming objects as
filled shells from data bases specifying solid objects.
It is a further object of the present invention to further
improve such a method of producing a three-dimensional object, by
providing a method of dispensing and processing material only at
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those locations of each plane of the object being produced that are
necessary to support the next object layer.
These and other objects are accomplished in the system,
method, arid process of the present invention. zn preferred
embodiments, a method and process for computer-controlled
manufacturing of desired three-dimensional objects involves
dispensing a layer of liquid insoluble material onto a platform at
predetermined locations. This liquid media hardens once it
contacts the platform. Although using a water soluble platform is
preferable, the platform can be permanent without violating the
spirit of the invention.
A water soluble media is then sprayed to encapsulate the
hardened insoluble media. This water soluble media also hardens
on contact. The uppermost surface of this encapsulant is planed,
thereby removing a portion of the water soluble encapsulant to
expose the underlying insoluble material for new pattern
deposition. The resulting residue from such planning is removed
and another layer of liquid insoluble media is dispensed onto the
planed surface. These two-dimensional spray patterns are printed
sequentially or "stacked" to form a three-dimensional object
surrounded by a water soluble mold. This cycle of dispensing of
a liquid insoluble media layer and water soluble encapsulant layer,
followed by planing and removal of planing residue is known as a
print cycle and continues until the three-dimensional object is
completed. At this point, the object is immersed in water, thereby
dissolving the water soluble mold, leaving the three-dimensional
object intact.
According to another preferred embodiment a system for
manufacturing three-dimensional objects from computer data
comprises at least one object scanning and image capture device
used to generate and store specific data about a desired three-
dimensional object. This data is sent to a microprocessor control
system which processes the received data into sequential cross-
sections of the three-dimensional object to be physically rendered.
At least one dispensing device sprays a layer of at least one
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eutectic material in predetermined areas on a target surface and
at least one nozzle sprays water soluble material to encapsulate
the layer of eutectic material based on input from the
microprocessor control system. The exact positioning of the
sprayed materials is determined by not only the pattern received
from the CAD system, but also by a set of linear positioning
devices that move the at least one dispensing device, the at least
one nozzle or the target surface according to instructions received
from the microprocessor control system.
Once a layer of eutectic material is encapsulated with the
water soluble material, a microprocessor-controlled cutting device
planes the encapsulated material to expose the underlying eutectic
material, while a microprocessor-controlled vacuum fixture removes
the unwanted planed material. When all of the print cycles are
finished, the completed object and mold are immersed in a support
removal system employing water, thereby dissolving the water
soluble mold and leaving the three-dimensional object intact.
A major advantage to the system and process of the present
invention is that selected layers of liquid insoluble material, and
even selected locations within a layer, can be colored differently
than the remaining layers of liquid insoluble material, thereby
allowing for a full range of colors and everything from subtle
shading to abrupt changes of color within the same manufactured
object. This aspect makes it possible for quality, detailed
visualization models to be manufactured for a wide variety of uses
such as scientific, medical, and geological study, to name a few.
Furthermore, by using more than one type of insoluble material,
varying textures can be achieved as well. Also, by judicious
selection of the insoluble media, such as wax, thermoplastic, etc. ,
and the use of water soluble media for a mold, the mold media and
object itself is recyclable.
According to other embodiments of the invention, a single
integrated head is provided by which the prior layer is planarized,
and both the part layer and support material is dispensed, in a
single pass of the head over the target surface. Such construction
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provides for faster and simpler production of the part or object,
and a lower cost system for producing such parts and objects.
According to still another embodiment of the invention, the
system includes the capability of converting a computer data base
representation of a solid object into one representative of a
hollow object with a user-specified shell thickness. As a result,
the volume of part material required to form the part is reduced
to that of the shell alone, allowing for more of each layer to be
formed of support material rather than object material, such
support material being dispensed in a less precise manner. The
precision ink jet print head is also subject to less wear by this
method, improving system reliability.
According to still another embodiment of the invention, the
system includes the capability of determining, from the next and
later layers to be processed, if part material will be dispensed
thereover and, if not, ceasing the dispensing of support material
at such locations. Furthermore, this capability provides the
ability to only planarize the target surface at those locations at
which the next part layer will be dispensed, reducing the amount
of residue generated and the degree of processing beyond that
necessary.
These and other features and advantages of the invention will
be apparent to those skilled in the art from the following detailed
description of a preferred embodiment, taken together with the
accompanying drawings, in which:
DESCRIPTION OF THE DRAWINGS
FIG. is is a perspective drawing of an automated three-
dimensional object manufacturing station according to a preferred
embodiment of the present invention:
FIG. lb is a perspective drawing of an example three
dimensional object manufactured according to the present invention;
FIGs. 2a-c are front, top, and left side views of another
preferred embodiment of the rapid prototyping system of Figure la
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according to the present invention;
FIG. 3 is a perspective view of a microprocessor and water
rinse vat according to a preferred embodiment of the present
invention;
FIG. 4 is a process flow diagram depicting a process of
manufacturing a three-dimensional object according to a preferred
embodiment or the present invention;
FIG. 5 is a perspective view of a printhead inspection and
purging station according to a preferred embodiment of the present
invention;
FIGs. 6a-b are waveform diagrams reflecting detector output
according to a preferred embodiment of the present invention.
FIGS. 7a-c depict views of the resulting structure during
selected process steps for manufacture of a three-dimensional
object made of a low melting point material according to the
preferred embodiment of the present invention of FIG. 4; and
FIGS. 8a-c depict views of the resulting structure during
selected process steps for manufacture of a three-dimensional
object made of a high melting point or high viscosity material
according to a preferred embodiment of the present invention of
FIG. 4.
FIGs. 9a and 9b are elevation and plan views, respectively,
of an integrated dispensing and planarizing head according to an
alternative embodiment of the invention.
FIG. 10 is an elevation view of a planarizing blade according
to an alternative embodiment of the invention.
FIGS. lia and llb are elevation views of alternative
planarizing components according to alternative embodiments of the
invention.
FIG. 12 is an elevation view of an integrated dispensing and
planarizing head for producing a multilayer printed circuit board
according to an alternative embodiment of the invention.
FIG. 13 is a perspective cross-sectional view of a system for
producing a part according to an alternative embodiment of the
invention, in which the rinse tank is integrated with the object
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producing workstation.
FIGS. 14a and 14b are cross-sectional views of an example of
a three-dimensional object being produced according to another
alternative embodiment of the invention.
FIGs. 15a and 15b are a flow chart illustrating the operation
of an alternative method of producing the three-dimensional object
of FIGs. 14a and 14b.
FIGs. 16a through 16d illustrate volumes surrounding a voxel
being analyzed in the method of FIGs. 15a and 15b.
FIGS. 17a through 17d are cross-sectional views of an object
being formed according to another alternative embodiment of the
invention.
Corresponding numerals and symbols in the different figures
refer to corresponding parts unless otherwise indicated.
DETATLD DESCRIPTION OF THE PREFERRED ELKBO~DIl~NTS
The present invention fabricates exact copies of a CAD model
without tooling and can operate in an ordinary work environment
because it is environmentally safe.
Whenever CAD images are referred to herein, it should be
understood that images from other object scanning and image capture
devices can also be fabricated to scale using the present
invention. Without limiting the scope of the present invention,
examples of such devices commonly used include computer-aided
design (CAD), computer-aided manufacturing (CAM), computer-aided
engineering (CAE), computer tomography (CT), magnetic resonance
imaging (MRI), positronic emission tomography (PET), laser
profilers, confocal scanning microscopy (CMS), IR imagers, electron
microscopy, etc. In this fashion, an innumerable variety of
subjects, including models of living creatures or plants, and even
celestial bodies can also be objects reproduced in color with this
invention.
Figure la is a perspective drawing of an automated three-
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dimensional object manufacturing station according to a preferred
embodiment of the present invention. One or more microprocessor-
controlled dispensing or printing devices 10, which comprise
printhead 20, pump eutectic materials in liquid state, either as
droplets or narrow streams, toward a generally planar target
surface such as platform 15. Platform 15 serves as a base for the
first, ..and subsequent, printing and spraying operations.
Independent, computer-addressable dispensing devices 10 are
preferably inkjets, such as those on colored plotters or inkjet
page printers, adapted to spray melted wax, plastic, or other
material. Print devices 10 within printhead 20 are turned on or
off according to a two-dimensional data map stored and relayed by
a microprocessor.
"Microcomputer" in some contexts is used to mean that micro-
computer requires a memory and "microprocessor" does not. As used
herein these terms can also be synonymous and refer to equivalent
things. The phrase "processing circuitry" comprehends ASICs
(application specific integrated circuits) PAL (programmable array
logic, PLAs (programmable logic arrays), decoders, memories, non-
software based processors, or other circuitry, or digital computers
including microprocessors and microcomputers of any architecture,
or combinations thereof. Words of inclusion are to be interpreted
as nonexhaustive in considering the scope of the invention.
An injection mold tool (not shown) is used for fabricating
platform 15 from a water soluble material. The mold tool may have
pressure or vacuum ports as well as cooling/heating mechanisms to
accelerate the molding process. Additionally, the mold tool cavity
may be of varying cross-sectional thickness depending on the
geometry of the desired object. Platforms made of metal or other
non-soluble materials such as ceramics or special plastics are less
desirable than water soluble platforms because they diminish the
area exposed to solvent during the wash phase.
Returning to Figure la, one or more materials 25 are converted
by heat or other process to a liquid state, and then ejected by
printhead 20 to strike platform 15 where materials 25 rapidly
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solidify and adhere, thereby creating a two-dimensional pattern
layer of varying cross-section. Several such layers formed
sequentially on top of each other are known as a stack. It should
be realized that although object 55, comprising a stack of layers
of materials 25, 35 deposited in accordance with microprocessor
instruction, is portrayed in Figure la with visible layers, this
is done strictly for explanation and clarity. In practice, such
layers are preferably .005 inch in depth and are virtually
undetectable by the human eye.
one or more heated nozzles or guns 30 (seen better in the
embodiment of Figures 2a-c) spray a random coating, of preferably
water soluble material 35, thereby encapsulating previously printed
non-random, insoluble patterns. Material containment and delivery
system 40, discussed in more detail in connection with Figures 2a-
c, provides containers for each of materials 25, 35 to be deposited
according to the present invention. By using heated nozzles or
guns 30 for dispensing of water soluble material 35, printhead 20
life is extended because it is not utilized for any water soluble
material. Additionally, a significant reduction in computer data
volume and processing is realized due to the use of random spray
devices) 30, which do not require detailed instructions to direct
the sprayed particles to specific x, y points.
Water soluble material 35 is preferably solid at room
temperature, exhibits a melted viscosity which is compatible with
common paint spray type equipment, and has good machining
characteristics after deposition and hardening. Material 35
supports and encapsulates the desired insoluble three-dimensional
object during fabrication. As can be seen in Figure lb, the water
dispersion characteristics of material 35 assures a very clean
three-dimensional object 55, composed of any material 25, will
remain after immersion in a container of water.
A water soluble material is preferred over the support
materials used with other systems discussed previously, such as
powders (tend to leave a rough, flaking surface) or W-curable
resin (must be removed manually with a cutting tool or sander).
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Powder support methods also do not provide adequate holding force
against object warpage. The use of water soluble, or at least low
melting point, materials enables users of the present invention,
unlike other material deposition systems, to produce complex
features such as cantilevers, or suspended objects from ceilings
or walls, or even something, by way of example and not of
limitation, as intricate and complex as a ship in a bottle.
Additionally, water soluble materials are quite inexpensive and do
not necessarily need to be printed with printhead 20, but can be
quickly and cheaply sprayed on with nozzles 30.
Although using a water soluble material as a mold is preferred
overall, it should be understood that material 35 could be a low-
melting point material which would then be removed by exposure to
heat, or an alcohol-soluble material which would dissolve when
immersed in alcohol. In general, dissimilar properties of the mold
and object are exploited to remove the mold without affecting the
object. Thus, when the final layer is printed, the support is
melted or dissolved away, leaving the three-dimensional object
intact, an example of Which is seen in Figure 1b. These materials,
although frequently not as desirable as water soluble materials,
are preferred to the support materials discussed above in
connection with other material deposition systems, and use of such
falls within the scope of the present invention.
Positioning devices 45, arranged along the X,Y,Z axes of a
Cartesian coordinate system (and so labelled on Figure la), move
the printhead 20 and/or target surface 50 according to computer
instructions. Target surface 50 is platfona 15 far the initial
deposition layer, and the previous deposition layer for any
subsequent deposition layers. Specifically, positioning devices
45 can completely define any three-dimensional object, preferably
by moving target surface 50 horizontally (Y) or vertically (Z) , and
by moving printhead 20 horizontally (X) across target surface 30.
Positioning devices 45 employ circular motor 48 to move target
surface 50, sprayers 30, and printhead 20. It should be noted that
other motors, such as linear motors, could be used instead of
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circular motor 48.
It should be realized from the outset that positioning devices
45 could be a volumetric positioning device, or a planar
positioning device operating together with a linear positioning
device, or three linear positioning devices, etc., and such detail
should in no way limit the scope of the invention.
Figures 2a-c axe front, top, and left side views of another
preferred embodiment of the rapid prototyping system of Figure la
according to the present invention. The description of elements
shown in Figures 2a-c corresponding to those previously described
in connection with the embodiment of Figure la is hereby
incorporated. As can be seen by comparing Figures la and 2a-c, the
particular positioning of the elements of a system according to the
present invention is immaterial, except that printhead 20 and
sprayers) 30 are preferably positioned to dispense materials
perpendicularly onto target surface 50.
The prototyping system shown in Figures 2a-c rests on a
supporting table 56. Cantilever supports 58 strengthen supports
62 to fortify lintel support 64 from which printhead(s) 20,
sprayers) 30, etc. hang.
One or more cutting devices 60 (best seen in Figure 2a),
arranged so as to plane the uppermost surface of target surface 50
at specified intervals along the vertical axis of fabrication,
remove a portion of water soluble encapsulant 35 and expose
underlying insoluble material 25 for new pattern deposition.
Cutting devices) 60 also compensates for surface and height
variations caused by flow rate differences among multiple print
devices 10 on printhead 20. Warpage of the object is also reduced
because the planing action of cutting devices) 60 serves to
relieve stresses induced by material 25,35 cooling and shrinking.
Vacuum head and pumping system 65 (best seen in Figure 2c)
removes residue generated during the planing action of cutting
devices) 60. The residue can be recovered in a filtered canister
(not shown) for disposal or further recycling. Vacuum fixture 70
(best viewed in Figure 2a) holds building platform 15 to
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positioning devices 45 and permits simple, rapid removal and
replacement of platform 15 without risk of damage or deformation
to platform 15. Vacuum fixture 70 further enables a system
according to the present invention to provide an optional automated
object-in, object-out conveyor or rack 75 (shown in Figure la).
Work volume 78, outlined in dashed lines in Figure 2a,
indicates the maximum object envelope in which an object may be
situated as it is being printed. Because some material
combinations require printing at ambient temperatures above room
temperature (as with metals) or well below (as with water), an
environmentally-controlled chamber can be positioned within work
volume 78.
Bulk containers 80 (best seen in Figure 2c), paxt of material
containment and delivery system 40 of Figure ia, store dry, solid
volumes of process material 25,35 which are then conveyed and
metered by feed device 82 into corresponding smaller, heated
chambers 84 where melting and filtering occurs. Feed device 82
might be of an auger or screw feed device, although other feed
devices are possible, and is driven by motor 83. The ensuing
melted liquid media is pressurized by pressure devices 86, each of
which could be a pump or the like, prior to delivery via liquid
media feed lines 88 to printhead 20 or spray gun 30. Liquid media
feed Lines 88 are shown are shown with a break: this is for
clarity, as each of lines 88 continue from pressure'devices 86 to
either printhead 20 or sprayers) 30, depending upon the line. It
may be preferable, particularly where the distance between chambers
84 and printhead 20 or spray gun 30 is relatively long, to heat
media feed lines 88 in order to ensure that the medium remains in
its liquid phase prior to reaching printhead 20 or spray gun 30,
as the case may be.
Thus, in addition to shape-rendering, a system according to
the present invention uniquely enables an object to be fabricated
with high resolution color features. Beneficiaries of this unique
aspect include the medical, geological, architectural, and
engineering fields, as well as the arts, astronomy, and many other
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disciplines. Materials) 25 may be of different material colors
or color combinations, a well as different material composition.
To achieve any desired level of visual realism, the colors cyan,
magenta, yellow, black, and white are preferred since any
intermediate hue of the full color spectrum can be obtained by
material overlap or dithering.
Figure 3 is a perspective view of a microprocessor and a
support removal system according to a preferred embodiment of the
present invention. Microprocessor control system 90 and support
removal system 95 are shown at a work station. Although not shown,
such control and support removal systems could be arranged
differently and could be physically combined with the systems
depicted in Figures la or 2a-c to provide a fully-automated rapid
prototyping system.
A CAD system is used to generate and store specific data,
including dimensions, color, or other desired properties, which
simulate desired three-dimensional physical objects. This data is
sent to, stored, and processed by microprocessor control system
90. Microprocessor control system 90 contains, microprocessor
instructions, as well as image processing and data conversion code
to process the input data into sequential cross-sections of the
three-dimensional object to be physically rendered.
The system, method, and process for computer-controlled
manufacturing of desired three-dimensional objects involves
dispensing layers of liquid materials 25, 35 onto target surface
50 at predetermined locations. These predetermined locations are
established by microprocessor control system 90 based on the
processed slice data received from a computer image file in the CAD
system. Microprocessor control system 90 also controls the
sequence and timing of the system, method, and process operations
as well as the electro-mechanical components for material
conveyance, feedback sensors, and system processes.
It should be realized the microprocessor control system 90
could also encompass the CAD system, or any other desired object
scanning and image capture device, rather than having this function
TI-15114AA - 16 -
performed by separate systems.
Support removal system 95 consists of rinse vat 96 of
sufficient size to fully contain a volume of solvent and object 55
on which the solvent will act. Circulation pump or stirrer 98 may
be integrated to accelerate the dissolving process and carry away
residue. The solvent is water when the mold material 35 to be
removed is water soluble, etc.
Support removal system 95 could instead comprise temperature
chamber 96 into which object 55 is placed. Air circulator 98 may
be integrated in such chamber 96 to accelerate the dissolving
process. This latter system could be best employed when mold
material 35 melts at a lower temperature than object material 25.
This allows selective removal of the mold when exposed to a
temperature greater than the melting point of the mold and less
than the melding point of the object. A wide range of material
25,35 combinations are possible such as water and wax, wax and
plastic, plastic and metal, and so on. In the alternative, object
material 25 may be a photopolymer which is dispensed at selected
locations of the target surface and which is immediately cured upon
dispensation, such as by way of a flood W light or a fiber optic
directed at the dispensing location. In the case where object
material 25 is a cured photopolymer, a wax having a solubility
different than that of cured photopolymer may be used as support
material 35. In many cases mold and object materials 25,35 can be
recycled for repeated use, thereby reducing waste.
Figure 4 is a process flow diagram depicting a process of
manufacturing a three-dimensional object according to a preferred
embodiment of the present invention. Once the platform for the
object is positioned onto the vacuum fixture (Block 100), the
printhead jets are checked to see if they are all functioning.
This is accomplished by positioning printhead 20 so its output is
viewable to the optical inspection station (Block 100). The
printhead jets then print a pattern of short line segments (Block
120) which are scanned~to verify whether each of the jets are
functioning properly (Block 130). If all of the jets are
TI-15114AA - 17 -
~~~r~~ap~
determined to not be operating properly, printhead 20 is moved to
the purge and wipe station (Block 150) where the system is purged
to unblock the flow of the jets (Block 160). Printhead 20 is then
returned to the optical inspection station (Block 110), where the
jets are again checked (Blocks 120 and 130). Although it is not
shown in the process of Figure 4, it should be apparent that
printhead 20 could be checked as often as desired.
If all of the jets are operating properly (Block 140), the ink
supply is checked (Block 170). If the supply is found to be
inadequate, the melt canister is filled from the bulk canister
(Block 180). Once the ink supply is sufficient, the process
continues by loading the object's slice data (Block 190).
The object's slice data is generated from a three-dimensional
computer "object" image including color infonaation is converted
by application software to a vertical sequence of two-dimensional
patterns. Although a second image could be software generated in
the form of a negative volume around the first image, the "mold"
image converted to a set of two-dimensional slices and the slice
data of the object and mold then combined in sequential order, a
second image is not necessary or preferred. The global action of
sprayers 30 allow for accurate printing with only the object's
image.
Once the first slice data is loaded (Block 190), platform 15
is positioned so cutting devices) 60 can plan its upper surface
(Block 210) and platform 15 is lowered by one layer's thickness
(Block 220). Printhead 20 then scans and deposits the slice
pattern according to the slice data received (Block 230). The
first layer's slice data determines print head position above
platform 15 along with appropriate ejector function at that
location. Printhead 20 moves in a plane parallel to platform 15
until the layer is complete. Once the printing of the first
slice's pattern is completed, sprayers 30 spray the upper surface
of target surface 50 with a uniform layer of soluble support
material 35 (Block 240).
Although loading the next slice data is shown in the process
TI-15114AA - 18 -
c
flowchart before the planing step, it can occur after the planing
step or preferably, simultaneously with the planing step. In fact,
microprocessor control system 90 may load the next slice data at
any time during the print cycle when most expeditious.
If this is not the last layer to be printed (Block 250), the
ink supply is again checked (Block 170) and ink added if needed
(Block 180). The next slice data is loaded (Block 190) while
platform 15 is positioned so cutting devices) 60 can plane the
upper surface of target surface 50 (Block 210). Platform 15 is
then moved downward by one layer thickness (Block 220) and the next
layer printed (Blocks 230,240). If this is the last layer to be
printed (Block 250), the part is removed from the vacuum fixture
(Block 260) and immersed in a solvent, preferably water, to
dissolve the soluble support material (Block 270). This process
yields the completed three-dimensional object (Block 280).
In an example of preferred process according to the present
invention, liquid wax at 140 degF (material 25) is jet-printed in
sequential layers to form the object pattern. Simultaneously,
sequential layers of ice (material 35) are jet-printed around the
object pattern to fona a frozen mold. The combined solid mass of
materials 25, 35 is then heated to melt the mold portion only,
leaving a high resolution, recyclable casting pattern. Many other
materials 25,35 combinations are possible, limited only by the
imagination of those skilled in the art.
Figure 5 depicts a printhead inspection and purging station
according to a preferred embodiment of the present invention.
Printhead 20 receives melted media via media feeder tube 310 and
deposits drops 320 of such media onto conveyor belt 330 in the form
of short parallel lines 340. The surface of conveyor belt 330 is
preferably made of paper. Optical sensor 350 scans parallel lines
340 printed by simultaneous operation of all printing devices of
jets 10 (not visible from the drawing) of printhead 20. The
microprocessor responds to any output of optical sensor 350
indicating at least one malfunctioning print device by directing
printhead 20 away from conveyor belt 330 to complete a purge-and-
TI-15114AA - 19 -
2~9'~~~'~
wipe for expulsion of any foreign matter. Air is forced into
printhead 20 via purge valve-monitored air tube 360. This
effectively purges the foreign matter from any malfunctioning print
device 10 on printhead 20. Printhead 20 is then wiped off (not
shown) and repositioned over conveyor belt 330. Printhead 20 again
deposits fresh media drops 320 onto conveyor belt 330 in the form
of short parallel lines 340 which are scanned by optical sensor
350. This procedure repeats until all print devices 10 on
printhead 20 are properly functioning. Although an inspection
system employing an optical sensor is discussed as preferable,
various other inspection systems will occur to those skilled in the
art.
Figures 6a-b depict waveform diagrams reflecting the output
of optical sensor 350 according to a preferred embodiment of the
present invention. In these diagrams, square waveforms accurately
show the number of jets functioning. The lack of a square waveform
where there should be one indicates a malfunctioning jet. Figure
6a details the output from optical sensor 350 with all of the jets
functioning, while Figure 6b shows a waveform consonant with two
jets malfunctioning.
Figures 7a-c depict views of the resulting structure during
process steps 230, 240, and 210, respectively, for manufacture of
a three-dimensional object to be made of a low melting point
material such as wax, according to the preferred embodiment of the
present invention of Figure 4. Figure 7a shows printhead 20
depositing drops 420 of wax to form a wax layer 400 at specific
locations on soluble platform 15 as determined by the micro-
processor control system according to the CAD image. Such layer
400, regardless of composition, is known as the positive material
and, when all layers are completed, will form the desired three-
dimensional object.
In Figure 7b sprayer 30 sprays droplets 430 of water soluble
mold material 440 to encapsulate deposited wax layer 400 residing
on soluble platfona 410. Material 440, regardless of composition
is known as the negative materials and, when all layers are
TI-15114AA - 20 -
- . 2~~'~3~p1
completed, will form the mold. A unique feature of Figure 4 ~ s
process is seen in Figure 7b, namely that the sprayed negative
material 440 is random, such that spray particles are not directed
by computer to specific x,y points.
To prepare the surface for subsequent layers, a mill cutter
or other cutting devices) 60 removes some of the previous layer
thickness to expose the positive material 400. Figure 7c depicts
cutter 60 planing water soluble mold material 440 to expose
deposited was layer 400. This step also defines the thickness of
each layer and compensates for different inkjet dispensations.
After all layers are processed, negative material 440 is
selectively removed by solvent, not shown, leaving positive
material 400, wax in this case, intact.
Certain materials may be too viscous to be used in inkjet type
mechanisms. These materials may, however, exhibit desirable
properties such as durability, appearance, or solubility in water.
A desired use for such viscous material, intended only as an
example and not by way of limitation, might include circuit
assemblies manufactured from conductive media such as pastes and
epoxies.
To utilize high melting point or high viscosity materials,
atomizing nozzles and pressurized guns, such as those used for
painting, can be used as an alternative to inkjet type print-heads.
Such nozzles or guns can employ pressurized syringes or piston-type
action, and are available with various nozzle diameters.
Figures 8a-c depict views of the resulting structure during
process steps 230, 240, and 210, respectively for manufacture of
a three-dimensional object to be made of a high melting point or
high viscosity material, according to the preferred embodiment of
the present invention of Figure 4. It is understood that such high
melting point or high viscosity material can be metal, ceramic,
plastic, paste, epoxy, etc., as well as a combination or alloy of
such materials, such as tin-lead alloy as an example and not by way
of limitation.
Figure 8a shows inkjet printhead 20 depositing drops 520 of
TI-15114AA - 21 -
wax to form a wax layer 500 at specific locations on platform 15
as determined by the microprocessor control system according to the
CAD image. Such layer 500, regardless of composition, is the
negative material and, when all layers are completed, will form the
mold or support.
In Figure 8b sprayer nozzle or gun 30 sprays droplets 530 of
high melting point or high viscosity material 540 over the support
material 500 and any pattern cavities therein. Material 540,
regardless of composition is the positive material and, when
completed, will form the desired three-dimensional object. A
unique feature of Figure 4's process is seen in Figure 8b, namely
that the sprayed positive material 540 is random, such that spray
particles arc not directed by computer to specific x,y points.
To prepare the surface of subsequent layers, a mill cutter or
other device removes some of the previous layer thickness to expose
the positive material. Figure 8c depicts cutter 60 planing
positive material 540 to expose deposited wax layer 500. Each
layer is milled to a prescribed thickness which compensates for
different nozzle dispensations. After all layers are processed,
the final volume consists of a high melt-point or high viscosity
object with a low melt-point mold. The negative material 500 is
selectively removed by solvent or heat, not shown, leaving the high
melting point or high viscosity positive material 540 intact.
This approach is unique in that it enables objects to be made
of many more materials, such as nylon, PVC, or even metal alloys
to name a few, which could not be possible using inkjet printer
mechanisms alone. Furthermore, milling the upper surface of
deposited layers serves to relieve stress which, for other systems,
causes part warpage. Also, the number of inkjet printheads
required is reduced, since much of the material is sprayed randomly
while providing sufficient broad area coverage.
Referring now to Figures 9a and 9b, the construction and
operation of integrated printhead 600 according to an alternative
embodiment of the invention will now be described in detail.
Integrated printhead 600 includes the necessary apparatus for fully
TI-15114AA - 22 -
2U9'~v~~
producing a layer of object 55, including the dispensing of object
material 25 and support material 35, and the planarizing of the
surface for each layer, in a single pass over the target surface.
This single pass processing greatly speeds up the fabrication
process, and also reduces the complexity and cost of the system for
producing three-dimensional objects according to the present
invention.
Integrated printhead 600 includes mounting plate 604 to which
each of the components are mounted in a spaced apart relationship
thereto. Printhead 20 is mounted to plate 604, and is for
dispensing object material 25 from adjacent storage reservoir 620
responsive to signals provided on wires 602 connected thereto. As
illustrated in Figure 9b, nozzles 603 are staggered in a diagonal
fashion in the well-known manner for inkjet printheads. Located
behind printhead 20 (in the y-direction) and off'to one side
therefrom (in the x-direction) is dispenser 30 for dispensing
support material 35 from adjacent reservoir 630. For example,
dispenser 30 may be on the order of 0:1 inches (or greater) behind
printhead 20 in each of the x and y directions. Considering that
integrated printhead 600 will be traveling in the +y direction (as
indicated by the axis reference in Figures 9a and 9b), dispenser
30 will lag behind printhead 20 in the formation of the three-
dimensional object. In operation, dispenser 30 may be dispensing
support material 35 at a lagging location at the same time at which
printhead 20 is dispensing object material 25 in advance of
dispenser 30. As a result, a layer of a molded object may be
rapidly formed, without requiring multiple passes of the individual
printhead 20 and dispenser 30. In addition, the complexity of the
system is also much reduced, especially over the known systems
described in the above-cited U.S. Patent No. 4,961,154 and European
Patent Office Publication No. 0 322 257, each requiring
transporting the object among multiple process stations in order
to process a single layer.
Optionally, a heating element or duct for providing heated gas
(not shown) may be mounted to mounting plate 604 to locally heat
TI-15114AA - 23 -
the portion of target surface at which printhead 20 is to dispense
object material 25, particularly those locations at which object
material 25 is to be dispensed upon object material 25 in the prior
layer. Such local heating, whether effected by way of conduction,
convection or radiation, preferably raises the upper portion of
object material to a sufficient temperature so that it is in a
softened state, improving the adhesion of object material 25
dispensed in the current layer to object material 25 in the prior
layer. Furthermore, this local heating allows the thermal
contraction of object material 25 in the prior layer to match that
of object material 25 in the newly dispensed layer.
Integrated printhead 600 further includes knife 608 for
planarizing the target surface in advance of printhead 20 as
integrated printhead 200 travels in the y direction. In the single
pass processing enabled by integrated printhead 600, it is
preferable to planarize the target surface directly in advance of
dispensing object material 25 and support material 35, rather than
behind dispenser 30 and the dispensing of support material 35. By
planarizing in advance of printhead 20, object material 25 and
support material 35 have had a longer period of time in which to
solidify prior to planarizing than would be the case if knife 608
were located directly after dispenser 30. The planarization of the
more completely hardened material results in a more planar target
surface, and precludes the smearing of support material 35 between
successive layers of object material 25.
Surrounding knife 608 is vacuum pickup hood 610 for removing
the residue from the planarizing action of knife 608 on the target
surface; knife 608 is mounted within vacuum hood 610 by way of
mounting plate 606. Vacuum pickup hood 610 exhausts residue via
duct 612 to a recovery location away from the processing area. In
the alternative to vacuum pickup hood 610, a brush or air jet may
be provided to displace the residue from the target surface. Brush
shield 614, formed of bristles or other suitable construction, may
optionally be provided as shown in Figure 9a to prevent any residue
not picked up by vacuum hood 610 from affecting the selected
TI-15114AA - 24 -
2U~'~3~r~
locations at which printhead 20 dispenses object material 25, and
to protect the process mechanism at the selected dispensing
locations from other contaminants.
As illustrated in Figure 9a, knife 608 has a stepped cutting
edge, rather than a single cutting edge. It is believed that the
likelihood of chipping out a material when shaving its top surface
increases according to the ratio between the thickness being shaved
to the total thickness of the layer. Accordingly, a single cutting
blade of a single depth is believed to be quite likely to chip out
the surface, especially if the variation in surface topography
(peak-to-valley) is on the order of 30%, as is expected in this
method. According to this embodiment of the invention, the stepped
cutting blades of knife 608, each having a depth of on the order
of 0.001 inches, provide multiple shallow shaving steps in
succession. A flat region is provided at the very bottom surface
of the deepest blade to further smooth the target surface. As a
result, knife 608 greatly reduces the likelihood of chipping out
the target surface, as the thickness of material removed by each
incremental cutting surface, relative to the layer thickness, is
reduced.
Referring to Figure 10, knife 608' according to an alternative
construction is illustrated. Knife 608' includes a single sloped
blade with a trailing flat surface (when viewed in cross-section)
rather than multiple steps. As a result of this construction, each
incremental motion of blade 608' in the y direction will cause the
removal of an incremental amount of target surface, also avoiding
chipout of the target surface.
Also according to an alternative embodiment of the invention,
mounting plate 606' , to which knife 608' is mounted, is movable
under the control of solenoid 606 responsive to signals on wires
618. This construction allows for selective control of knife 608'
(or, alternatively, knife 608 with multiple shallow steps) , so that
the planarization is only performed at selected locations. For
example, at those locations of the target surface at which support
material 35 is to be next dispensed, no planarization is necessary
TI-15114AA - 25 -
~~9'~3~ ~l
due to the non-critical nature of the shape of the support material
35 in the object (as it will be removed anyway). In contrast, the
locations of the target surface at which object material 25 is to
be dispensed must be planarized to ensure that object material 25
adheres to that of the prior layer, and to provide proper
dimensional control in the formation of the object. Movable knife
608' can be controlled by way of solenoid 616 so that it contacts
the target surface only at those locations at which object material
25 is to be next dispensed: as a result, the amount of shaving and
planarizing residue generated is much reduced, as is the wear on
blade 608'.
Referring now to Figure 11a, integrated printhead 600'
according to an alternative construction, and utilizing an
alternative technique for planarization, is illustrated. According
to this example, roller 640 trails printhead 20 and dispenser 30
in integrated printhead 600', and smooths the surface of the
dispensed layer after dispensation of support material 35. It is
contemplated that cold rolling will suffice to smooth support
material 35 in many cases. Alternatively, roller 640 may be heated
to ensure proper smoothing of support material 35: in such a case,
it may be preferred to provide a non-stick coating, such as TEFLON
coating, on roller 640. In addition, to promote adhesion of the
next layer of object material 25 to the prior layer, roller 640 may
be provided With a knurled or otherwise rough surface to leave a
rough impression on the dispensed layer.
Referring now to Figure 11b, integrated printhead 600'~
according to still another alternative construction is illustrated
in an elevation view. Integrated printhead 600 " includes thermal
bar 642 which trails dispenser 30 at a height above the target
surface. Thermal bar 642 is energized to be heated, for example
by wires 644 in the example of a resistive element type, to reflow
support material 35 and object material 25, resulting in a smooth
target surface for the next layer.
Either of roller 640 or thermal bar 642 may be installed in
advance of printhead 20 rather than trailing as shown in Figures
TI-15114AA - 26 -
G t1
l0a and lOb, depending upon the characteristics of the materials
being used.
Further in the alternative, it is contemplated that object
material 25 and support material 35 may be dispensed in a layer in
such a manner as to have substantially a planar top surface,
without requiring additional planarizing and machining to form a
planar target surface for the next layer. This may be
accomplished, for example, by way of an inkjet printhead similar
to printhead 20, such that the dispensed volume of support material
35 is carefully controlled. In this case, integrated printheads
600, 600', 600 " described above would not include knife 608,
roller 640, thermal bar 642, or other means for planarizing the
target surface. Alternatively, by measuring the volume of support
material 35 dispensed in real time, the system can control the
volume of support material 35 dispensed by dispenser 30 so as to
match the thickness of the object material 25 dispensed by
printhead 20; printhead 2o may also be controlled so that the
volume of object material 25 it dispenses may be similarly adjusted
in real time. This measurement and control can additionally ensure
coplanarity of both object material 25 and support material 35
across the entire surface of the layer. Examples of real-time
measurement techniques contemplated to be useful in this method
include optical measurement such as an interferometer, mechanical
measurement such as a follower brush, and other known film
thickness measurement techniques.
Referring now to Figure 12, an application of the present
invention in producing a multilayer printed circuit board is
illustrated in cross-section. In this example, object material 25
comprises a conductive material such as aluminum, and support
material 35 comprises a dielectric material such as polycarbonate
plastic, a polymer resin, or other well known electrically
insulative materials. According to this embodiment of the
invention, support material 35 is not removed upon completion of
the formation of the object (which is a printed circuit board), but
instead remains as a unitary portion of the object formed.
TI-15114AA - 27 -
optionally, during its manufacture, selected locations of the
circuit board may receive soluble support material 35 to be removed
after formation of the object in the manner described above,
instead of support material 35 which is to remain in place, thus
enabling the fabrication of printed circuit boards of complex
shape.
As illustrated in Figure 12, integrated printhead 650 includes
printhead 20 for dispensing conductive object material 25, and
printhead 670 for dispensing insulative support material 35. In
contrast to dispenser 30 of printhead 600 described hereinabove,
printhead 670 preferably dispenses support material 35 with a
relatively high degree of precision. Construction of the printed
circuit board proceeds in similar manner as described hereinabove,
including the planarization of each layer s top surface by knife
660 (which trails printheads 20, 670 in this embodiment of the
invention).
In operation, the printed circuit board is constructed by
printhead 20 dispensing conductive object material 25 at those
locations at which printed conductor lines are to be located in
each layer. In the same single pass, printhead 670 dispenses
insulative support material 35 as required to fill the remainder
of the layer. Layers of the printed circuit board between those
with conductive lines receive, in this example, conductive object
material 25 at those locations where a vertical via 25V is to be
placed, connecting conductive lines of different layers; the
remainder of the layer containing conductive via 25V receives
support material 35.
As a result, the present invention allows for the formation
of a printed circuit board in a layerwise fashion, but without
requiring post-processing steps of forming holes through the board
and filling the holes with solder, as is required in conventional
printed circuit board manufacture. Furthermore, the present
invention enables the production of circuit boards with
significantly more complex shapes than available in conventional
circuit boards. For example, the present invention enables the
TI-15114AA - 28 -
~~g'~3a'~
formation of a unitary circuit board having locations with
different thicknesses and numbers of conductive layers. In
addition, it is contemplated that the present invention enables the
formation of a circuit board with walls, including walls that
contain conductive shielding for radio frequency interference
(RFI). The increased flexibility provided by the present invention
enables the formation of RFI shielding of differing thickness at
different locations of the printed circuit board (and walls),
depending upon the circuitry to be installed on the board.
Referring now to Figure 13, a system constructed according to
yet another embodiment of the present invention will now be
described. As is evident from the foregoing description, the
present invention is capable of building objects of quite large
size, for example on the order of one foot on a side. The weight
of an object so formed, in combination with the support material,
can be quite significant, such as on the order of 50 pounds. It
is therefore contemplated that it would be useful to provide a
system for removing support material 35 from object 55 in-situ with
the fabrication method, to reduce the effort required to transport
the molded object to a rinse station.
Figure I3 illustrates an example of a system for producing an
object according to the present invention, in which a wash tank is
integrated therewith. Cabinet 675 has integrated printhead 600 (or
such other printheads as desired) near its top surface, for forming
an object of object material 25 embedded in support material 35 and
overlying platform 15, as described hereinabove. In this
embodiment of the invention, platform 15 is mounted at the top of
telescoping actuator 680, which is controlled by a conventional
motor (not shown) so as to be able to lower platform 15 into the
interior of cabinet 675. Bellows 682 preferably surrounds actuator
680 to protect it from solvents to be introduced into cabinet 675,
as will be described hereinbelow. Cabinet 675 receives inlet hose
685 via which solvent fluid is communicated thereto by pump 684,
and presents outlet hoses 686, 687 to filter 688 so that dissolved
support material 35 is screened from the fluid received from
TI-15114AA - 29 -
cabinet 675, prior to its storage in tank 690 for re-introduction
by pump 684 into cabinet 675.
In operation, upon completion of an object, actuator 680
lowers platform 15 into the interior of cabinet 675. Pump 684 is
then energized so that solvent fluid, such as water or other
appropriate solvent used to selectively dissolve support material
35 relative to abject material 25, is pumped into the interior of
cabinet 675 via inlet hose 685, and recirculated therethrough via
outlet hoses 686, 687, filter 689 and tank 690. This solvent
dissolves support material 35 to yield object 55 formed of object
material 25, after which actuator 680 raises platform 15 to the top
surface of cabinet 675, allowing the operator to retrieve object
55 therefrom without the added weight of support material 35.
In addition, residue produced during the planarizing of a
layer by knife 608 described hereinabove may be simply be swept by
integrated printhead 600 off of the edge of the target surface into
the interior of cabinet 675, to dissolve the planed support
material 35 along with that surrounding object material 25.
The present invention as described hereinabove is thus very
effective in rapidly producing three-dimensional objects of complex
shape, directly from a CAD data base. It has been discovered,
however, that the efficiency in producing such objects can be still
further enhanced, and the life of the printhead mechanism
significantly lengthened, by producing objects according to an
alternative embodiment of the present invention which will now be
described hereinbelow relative to Figures 14a, 14b, 15a, 15b and
16a through 16e.
Referring first to Figures 14a and 14b, an object formed of
object material 25 surrounded by support material 35 is shown in
cross-section (in the y-z plane) , at a stage in its manufacture
prior to the dissolving of support material 35; it may be assumed
for purposes of this discussion that this y-z cross-section is
maintained for a sufficiently large range in the x-dimension. It
is evident from the view of Figure 14a that a large portion of the
object is formed of a solid block of object material 25. In the
TI-15114AA - 30 -
2~9'~~~w~
fabrication of this object, therefore, printhead 20 dispenses
object material 25 in a highly precise manner fox much of the
volume of the object, including the interior portion of the object,
and as such, the fabrication of the object of Figure 14 is quite
slow. Furthermore, it is well known that inkjet reliability is a
function of its time of use. Accordingly, it is preferred, not
only from a manufacturing throughput standpoint but also from a
system reliability standpoint, to minimize the time during which
the inkjet is in use.
Figure 14b illustrates, in the same y-z plane cross-section
as shown in Figure 14a, that the same object may alternatively be
formed of a shell of object material 25' of thickness t surrounding
filler support material 35'. The side walls (i.e., the x-dimension
limits) of the object of Figure 14b will also provide walls of
thickness t. So long as object material 25 is both insoluble in
the solvent used to dissolve support material 35 and also
impervious to filler support material 35', the dissolving of
support material 35 from outside of shell 25' will leave filler
support material 35' intact within shell 25'. Examples of
materials useful to form such a shell part include a water soluble
wax, such as polyethylene glycol, for support material 35 and
filler support material 35', and a water insoluble wax, such as
beeswax or carnauba wax, for shell object material 25'.
Since filler support material 35' may be dispensed with much
less precision than object material 25, such as by way of a spray
nozzle or dispenser nozzle, the fzequency of use of the inkjet
printhead to form the object of Figure 14b is much reduced from
that required to form the object of Figure 14a. As a result, the
object of Figure 14b may be formed in much less time than that of
Figure 14a, and with less wear of inkjet printhead 20 used to
dispense object material 25.
It is therefore contemplated that, by way of clever use of
conventional computer-aided-design programs, the designer of the
object to be formed may implement a shell design of a solid object
in the original description of the design in the data base.
TI-15114AA - 31 -
2~9'~J~~~
However, it is preferred that the computer control system far the
apparatus according to the present invention automatically generate
a shell part, such as that shown in Figure 14b, from the data base
for a solid part, such as that shown in Figure 14a, preferably with
a user-specified thickness t. This conversion from solid to shell
may be done off line, prior to initiation of the fabrication
process, so that the data base received by the fabrication system
is the shell data base; alternatively, conversion from solid to
shell may be done on a layer-by-layer basis by the fabrication
system itself, during the layerwise manufacture of the object. The
methods described hereinbelow for such conversion, including the
preferred method described relative to Figures 15a and 15b, are
suitable for use in either environment.
According to the preferred method for accomplishing such
conversion, each voxel (volume element) in the volume is
individually analyzed relative to its surrounding voxels to
determine if the voxel of interest is within the user-specified
thickness t of a voxel that is not part of the object. Referring
to Figure 16a, voxel of interest VOXEL is illustrated as the center
of cube V which is 2t in length in each dimension. As such, voxel
of interest VOXEL is the distance t away from each of the sides of
cube V. In the context of converting a solid object to a hollow
shell object, the present method determines if voxel of interest
VOXEL and each of the voxels surrounding it in cube V are to be
formed of object material 25: if so, voxel of interest VOXEL is at
least thickness t away from any edge of the object to be formed,
and thus may be formed of filler support material 35' rather than
of object material 25. Incrementing the voxels of interest
throughout the volume of the object to be formed will thus identify
which of those vaxels which previously were to be formed of object
material 25 may be formed of filler support material 35' to form
an object having walls no thinner than thickness t.
The analysis of a relatively large volume according to the
"brute force" technique of examining each voxel within a cube V
surrounding the voxel of interest VOXEL, while effective, is
TI-15114AA - 32 -
209'~~~'~
extremely cumbersome. Indeed, for a volume of n voxels, such a
method would require on the order of n" interrogations, resulting
in extremely long computing times. The method illustrated in the
flow charts of Figures 15a and 15b is intended to perform the data
conversion from solid to shell objects in significantly less time,
by analyzing only the surfaces of cube V in the manner described
hereinbelow. This method is suitable for operation on a modern
personal computer workstation or other data processing system of
similar computing power: it is further contemplated that one of
ordinary skill in the art can readily program such a computer to
perform this method, based on the following description.
This method is described hereinbelow relative to a slice of
the object volume in the x-y plane,, as suitable for use in a real-
time conversion during the layerwise formation of the object.
Alternatively, as noted above, if the conversion is performed off
line prior to object manufacture, this process will be performed
incrementally for a series of layers in the z-dimension.
Furthermore, it is assumed that the data base upon which the
conversion process of Figures 15a, 15b operates consists of memory
locations corresponding to a three-dimensional array of voxels,
each of which store a "hollow" or "solid" state, indicating that
it is not to receive object material 25, or is to receive object
material 25, respectively. According to this embodiment of the
invention, a third "marked" state is utilized, indicating for the
voxel that it is to receive filler support material 35'.
The conversion process according to this embodiment of the
invention begins with process 700, in which the user-specified
shell thickness t and the maximum x and y are set for a voxel in
an x-y slice of the object volume. In decision 701, the current
y value of the voxel of interest ("VOXEL") is interrogated to
determine if it is located within the shell thickness t from the
maximum y dimension ymax; if so, the conversion process ends, as
voxels in this y-dimension are necessarily either hollow or within
the shell of thickness t from a hollow voxel. If not, decision 703
is performed by which the x dimension of VOXEL is interrogated to
TI-15114AA - 33 -
~~~'~~~~~
see if it is within the shell thickness t of the maximum x
dimension xmax. If VOXEL is within distance t of xmax, a new VOXEL
is selected by incrementing the y value by two and returning
control to decision 701. It has been observed that incrementing
the x and y values of VOXEL by two will, of course, greatly speed
up the conversion process by reducing in half the number of VOXELs
interrogated; in addition, little resolution is lost by such
incrementing, as only the undesirable situation of a hollow area
of a single voxel's width is lost by incrementing by two.
If VOXEL is not within the shell thickness of the maximum
value xmax, decision 705 is performed by which the solid object
data base is interrogated to determine if VOXEL is solid. If not,
a new VOXEL is selected by incrementing by two in the x-dimension,
with control passing back to decision 703. If VOXEL is solid, it
may be a candidate for conversion to a hollow VOXEL (i.e., a
location to receive filler support material 35'), and the process
will continue with decision 707.
According to this embodiment of the invention, as indicated
hereinabove, the surfaces of cube V are interrogated to determine
if VOXEL may be marked. However, decision 707 begins a routine by
which analysis of the surfaces of cube V may be reduced, based upon
prior results. In decision 707, the prior vaxel in the same y-
dimension as VOXEL is interrogated to see if it has been "marked"
to be filled in by filler support material. If so, those voxels
at least t distance in the -x direction from VOXEL have already
been interrogated and are to be filled with filler support material
35', eliminating the need for the interrogation to be repeated in
the -x direction. An x-scan pointer is then set in process 708 so
that only the surfaces of cube V in the +x direction from VOXEL
need be interrogated to determine if VOXEL can be marked (i. e. , the -
portions of the surfaces of cube V having x greater than or equal
to t). The shaded surfaces illustrated in Figure 16b show those
portions which are to be analyzed if the result of decision 707 is
positive, including substitution of an internal surface of cube V
along the x=t plane in place of an external surface of cube V along
TI-15114AA - 34 -
2~~'~~~'~
the x=0 planar surface.
Referring back to Figure 15a, decision 709 is then performed
by which the voxel at the same x-dimension as VOXEL but at the
prior y scan line is interrogated to determine if it was marked to
become hollow. If so, the portions of those surfaces of cube V
having a y-dimension less than that of VOXEL need not be analyzed,
as prior analysis has found that the prior voxel in the y-dimension
could be safely marked, and a y-scan pointer is set to scan forward
only in the y-direction from VOXEL (process 710). Figure 16c
illustrates, by shading, the portions of the surfaces to be
analyzed if the result of decision 709 is positive (i.e., y greater
than or equal to VOXEL). An internal surface of cube V (along the
y=t plane) is also considered, in lieu of the y=0 surface.
Decision 711 is then performed by which the voxel directly
below VOXEL in the z-dimension is interrogated to determine if it
was marked to become hollow. If so, similarly as in the x and y
dimensions, a z-scan pointer is set in process 712 to scan forward
only in the z-dimension, analyzing the portions of the surfaces of
cube V having a z value greater than or equal to that of VOXEL.
The shaded surfaces of Figure 16d illustrate the portions of the
surfaces of cube V which are to be analyzed in this case.
It should be noted that any combination of positive results
may be returned from decisions 707, 709, 711, including the
combinations of no positive result and the combination of all
positive results. If all three voxels immediately adjacent to
VOXEL in all three of the x, y and z dimensions are marked as
hollow, only portions of the surfaces of cube V shown in Figure
16e need be analyzed, namely those locations having all three of
their x, y and z dimensions greater than that of VOXEL. Internal
surfaces of cube V along the x=t, y=t and z=t planes are also
included in the analysis. As a result, this portion of the method
can greatly decrease the amount of analysis required to determine
if VOXEL can be "marked".
Referring now to Figure 15b, once the extent of the surfaces
of cube V to be scanned has been determined, the analysis can
TI-15114AA - 35 -
2~~73~~
begin. Process 714 sets the z value to 2t, corresponding to the
top surface of cube V. Decision 715 then interrogates the voxel
at the initial x, y location (depending upon the results of
decisions 707, 709) of the top surface to determine if it is solid.
If not, meaning that this voxel on the top surface is outside of
the object region, VOXEL is necessarily within the distance t of
the outer edge of the object to be formed, the process ends for
VOXEL, and a new VOXEL is then interrogated after incrementing of
the x-value in process 706. If this voxel at the top surface is
solid, process 716 is performed by way of which the x and y values
are incremented over the z=2t surface (in this case, with the x-
axis being the fast axis). Decision 717 determines if the plane
is complete, and if not returns control to decision 715 to analyze
the next voxel.
rf no voxel at the top surface (z=2t) is hollow, the bottom
surface is analyzed by setting z to its lower limit in process 718
(to either 0 or t, according to the result of decision 711
described hereinabove). Decision 719 analyzes the state of each
voxel along this bottom surface, to the extent analyzed due to the
results of decisions 707, 709, and with decision 721 determining
when the bottom surface analysis is complete. If any of the voxels
of the bottom surface so analyzed are hollow, the process ends for
VOXEL as it cannot be made hollow, and the incrementing of the
voxel of interest is performed in process 706.
Upon completion of the bottom surface (assuming that no hollow
voxels were found), control passes to process 722 which sets the
x, y and z dimensions of the surface voxel to be analyzed to their
lower limits found in decisions 707, 709, 711, to begin analysis
of the side surfaces of cube V at the current z-value. Decision
723 determines if the z-value of the surface voxel has reached
beyond 2t (the top of cube V), and if so, passes control to process
736 described below. If not, decision 725 next determines if the
y value of the surface Voxel to be analyzed exceeds 2t, indicating
that a scan line is complete such that the z value must be
incremented in process 724, with control passed to decision 723.
TI-15114AA - 36 -
2~9'~~:~~1
If decision 725 indicates that the y value of the surface voxel has
not exceeded 2t, decision 727 is performed in which the surface
voxel y dimensions are examined to determine if it is resident on
either of the surfaces in the x-z planes ( i. e. , y=2t or y=lower
limit). If so, decision 729 is performed to analyze the surface
voxel along the x-z surface, incrementing the x-value in process
730 until the x-z surfaces are complete, for the current z-value,
as determined by decision 73i. Of course, if any surface voxel is
found to be hollow, VOXEL cannot be marked hollow and the next
VOXEL is then selected (process 706). Upon completion of the x-
dimension line in the x-z surface, the y value of the surface voxel
to be analyzed is incremented by one in process 732, and the y
value is tested in decisions 725 and 727 as before.
Upon decision 727 determining that the y value of the surface
voxel to be analyzed is not in one of the x-z surfaces to be
interrogated, only the x-limits (the x dimension lower scan limit
and x=2t) are tested in process 734. If both voxels are solid, the
y value is again incremented (process 732) and tested (decision
725, 727) , with the next y-dimension line extremes tested again
until y exceeds the 2t limit, in which case the z-value is
incremented (process 724) and the method repeated.
In this manner, each voxel in the side (or internal, as the
case may be) surfaces of cube V are analyzed slice-by-slice in the
z-dimension, until the z value of the surface voxels reaches the
terminal limit of 2t, at the top of cube V. If no voxel is found
to be hollow in this analysis, VOXEL may be marked to become hollow
in fabrication, as there is no voxel within distance t from VOXEL
that is not either solid or marked to become hollow. Process 736
is then performed, by which VOXEL and its surrounding voxels are
marked to become hollow when fabricated, by receiving filler
support material 35' thereat.
As a result of this method of Figures 15a and 15b, the data
base of the volume within which the object is to be formed may be
automatically converted from that for a solid object to that for
a shell object, such that filler support material 35' may be used
TI-15114AA - 37 -
in the interior portions of the object. This method thus improves
the life of inkjet printheads used to dispense object material 25,
and also greatly improves the rate at which objects may be
produced.
Further improvement in the rate at which objects may be
formed, as well as reduction in the amount of material used to form
a part, according to the present invention may also be obtained by
limiting the dispensing of support material 35. In particular,
those locations of the object over which object material 25 will
not be dispensed do not require the presence of support material
35 thereat. Referring now to Figures l7a through 17d, a process
for limiting the dispensation of support material 35 to only those
locations at which it is necessary to support object material 25
will now be described.
Figure 17a illustrates a cross-section along the y-z plane of
an object including object material 25 and support material 35.
As is evident from Figure 17a, overhang portion 250H of object
material 25 juts outwardly in the +y direction, and has a smaller
width (in the z-dimension) than the remainder of the object.
According to this alternative embodiment of the invention, region
355 above overhang 250H does not contain support material 35, as
it otherwise would if the object were formed without consideration
of whether object material 25 is present thereover.
The cross-sectional views of Figures 17b through 17d, taken
along the x-y plane, of the object of Figure 17a illustrate this
embodiment of the invention. This method of analysis of the object
to be forraed may be performed on a conventional personal computer
workstation or data processing system of similar computing power.
It is further contemplated that one of ordinary skill in the art,
having reference to this description in combination with
conventional computer-aided-design software, can readily practice
this embodiment of the invention.
Figure 17b illustrates a plan view of the object as it is
being formed at a relatively low layer, below the height (in the
z-direction) of overhang 250H; this layer will be formed, in the
TI-15114AA - 38 -
2D9"~3~'~
method described hereinabove, prior to the layers including
overhang 250H. According to this embodiment of the invention, the
computer workstation controlling the fabrication process analyzes
a shadow projection of the object material 25 portions of the
current layer being fabricated (shown by object material 25 in
Figure l7bj and all layers which are yet to be fabricated. As a
result, shadow 25S appears corresponding to overhang 25oH, even
though this layer of the object does not include overhang 250H.
As a result, support material will be provided as illustrated in
Figure 17b for this layer, including that amount of support
material necessary to support overhang 250H.
The fabrication method continues in a layerwise fashion,
proceeding in the +z direction, as described hereinabove. Figure
17c illustrates, in plan view, a layer of he object as it is being
formed at the height of overhang 250H: as such, object material 25
is dispensed as illustrated in Figure 17c, with support material
35 surrounding. In addition, since in this example no higher layer
of the object includes object material 25 outside of the bounds
shown in Figure 17c, no shadow is projected in this analysis.
Figure 17d illustrates a layer above the height of overhang
250H, again projecting a shadow view of its layer and all layers
thereabove. As indicated in Figure 17d, no shadow or actual
projection of overhang 250H is present, as overhang'250H is fully
below this level. In addition, no object material 25 will be
necessary above region 355 of Figure 17d, and thus dispenser 30
will be controlled so that no support material 35 is dispensed in
region 355. This volume of support material 35 is then saved, as
is the solvent and other processing necessary to deal therewith in
resolving the object so formed.
The simplicity of a system, method, and process according to
the present invention offers many advantages. The printheads are
small, inexpensive and can be configured to several scan methods,
including vector and raster. Ejector apertures are small, enabling
very high resolution. Furthermore, wide apertures or ejector
arrays can be utilized for high volume dispensing, as well as
TI-15114AA - 39 -
dispensing of high viscosity materials. Additionally, a system,
method, and process according to the present invention can be
tailored to various work environments and applications ranging from
foundries and machine shops to small desktop systems. Because the
media can be printed on any surface, automated conveyor and
material handling systems can be incorporated. This enables fast
and continuous throughput from multiple data sources. This
includes multiple computer-generated images, on at least one
computer, being rapidly prototyped by one or more systems built
according to the teachings of the present invention.
Some of the innumerable objects which can be produced by this
technique include prototypes, casting patterns, molds, sculptures,
and structural components. It will quickly be apparent to those
skilled in the art that this list is in no way exhaustive and that
numerous other uses of the present invention will occur to those
skilled in the art.
It should be understood that various embodiments of the
invention can employ or be embodied in hardware, software or
microcoded firmware. Process diagrams are also representative of
flow diagrams for microcoded and software based embodiments.
Further, while a specific embodiment of the invention has been
shown and described, various modifications and alternate
embodiments will occur to those skilled in the art. Accordingly,
it is intended that the invention be limited only in terms of the
appended claims.
TI-15114AA - 40 -
