Apparatus and method for dispensing build material to make a three-dimensional article

A three-dimensional article making apparatus includes a build material dispenser positioned adjacent a platform for ejecting a plurality of droplets of build material; and dispenser positioners for relatively positioning the dispenser in five degrees of freedom with respect to the platform. Accordingly, the dispenser may be rotated and flipped to permit construction of a cantilevered portion of an article without requiring support material. The dispenser positioners include a Z-direction positioner for positioning the dispenser vertically relative to the platform, an X-Y positioner for positioning the dispenser in an X-Y planar direction relative to the platform, a flip angle positioner for rotatably positioning the dispenser relative to a generally horizontal axis, and a phi angle positioner for rotatably positioning the dispenser relative to a generally vertical axis. A processor is operatively connected to the dispenser and the dispenser positioners for advancing the dispenser along a predetermined path of travel while operating or firing the dispenser to construct the three-dimensional article in successive layers or portions based upon the article defining data. Method aspects of the invention are also disclosed.

FIELD OF THE INVENTION 
The invention relates to an apparatus and related methods for making a 
three-dimensional article, and more particularly, to an apparatus and 
methods for making an article based upon article defining data. 
BACKGROUND OF THE INVENTION 
In the design and manufacture of a three-dimensional article, it is common 
practice to first create an initial design of the article and then 
manually produce a custom prototype or model of the article based upon the 
initial design. After reviewing the initial design and prototype, design 
revisions are often made requiring the production of yet another 
prototype. This process of review and redesign may be repeated a number of 
times before finding the desired design thereby requiring that a number of 
preliminary designs and prototypes be produced for a single finished 
article. Accordingly, the process of designing and prototyping an article 
may involve considerable time, effort and expense. 
Computer aided design (CAD) is commonly used for automating the design 
process. With the aid of a computer, an operator is able to design a 
three-dimensional article and display the design on a two-dimensional 
medium, such as a display screen or paper. In addition, a computer aided 
milling machine, for example, may be coupled to a CAD system to produce a 
milled article in response to computer generated CAD data. Unfortunately a 
milling tool is typically large, expensive and may be limited in the 
article geometries that may be produced. 
Stereolithography is another technology for producing a prototype based 
upon computer generated coordinate data. An example of stereolithography 
is disclosed in U.S. Pat. No. 4,575,330 to Hull entitled "Apparatus for 
Production of Three-Dimensional Objects By Stereolithography." The patent 
discloses an apparatus producing an article by forming successive 
cross-sectional laminae of the article at the surface of a fluid medium. 
The fluid medium is capable of altering its physical state from a fluid to 
a solid in response to selective stimulation such as by UV radiation; 
particle bombardment, such as electron beams; chemical reaction; or 
impinging radiation other than UV radiation. The source of selective 
stimulation is controlled by a computer in response to computer generated 
coordinate data. 
Stereolithography, however, requires the use of more material than is 
actually incorporated in the article being produced, and also requires the 
exact placement of the article being constructed relative to the surface 
of the fluid medium. The fluids may be toxic and require special handling 
precautions. In addition, the depth of the layer created when the fluid 
surface is exposed to the stimulation may be difficult to control, and, 
accordingly, the resolution of surface features may be difficult to 
control. 
Another apparatus and method for forming three-dimensional articles from a 
material which is normally solid but flowable when heated is disclosed, 
for example, in U.S. Pat. No. 5,141,680 to Almquist et al. entitled 
"Thermal Stereolithography." The apparatus includes a nozzle for 
dispensing a stream of material which has been heated to the point that it 
flows. The material is dispensed through the nozzle by applying pressure, 
and the flow of material can be stopped by a slidable valve or by 
controlling the pressure. Precise control of the flow of material may be 
difficult to obtain. Moreover, unsupported portions of the article may be 
problematic and may collapse unless support is provided. Accordingly, a 
second support material is provided that must later be removed from the 
article. 
U.S. Pat. No. 5,121,329 to Crump discloses another apparatus wherein a flow 
of material through a nozzle is used to create a three-dimensional object. 
In this patent, the flow of material is determined by the size of the 
outlet orifice, a constant pressure, and the vertical height of the tip of 
the nozzle. In addition, a spring-loaded ball check valve may assist in 
metering the flow of material. Again, precise control of this flow may be 
difficult to obtain, and inaccuracies in the finished article may result. 
A significant advance in the art of three-dimensional modeling is disclosed 
in U.S. Pat. No. 4,665,492 to Masters entitled "Computer Automated 
Manufacturing Process and System." This patent discloses an apparatus 
including a repositionable ejection head for ballistically emitting small 
mass particles or droplets of particulate matter. A machine controller 
controls a positioner in response to a data file containing coordinate 
information representing the design of the article being produced. The 
mass particles are directed to the coordinates of a three-dimensional 
article as defined by the computer data file, wherein the starting 
coordinate reference position is described as an origination seed point. 
The mass particles may include plastic material, a slurry material having 
water content, charged particles which are electrically deflected, or 
other materials. 
Another method and apparatus for forming three-dimensional solid form 
objects is disclosed in U.S. Pat. No. 5,257,657 to Gore entitled "Method 
for Producing A Solid-Phase Object From A Material in the Liquid Phase." 
According to this patent, droplets of a liquid-phase material are ejected 
to form a spheroid. As noted in the patent, this method may not work well 
for glasses and plastics which do not have a set transition temperature at 
which they become rigid. 
Yet another method and apparatus for forming three-dimensional objects is 
disclosed in U.S. Pat. No. 5,136,515 to Helinski entitled "Method and 
Means for Constructing Three-Dimensional Articles by Particle Deposition." 
This patent discloses a device including two jetting heads, or alternately 
a single jetting head with two feeder lines. In both embodiments, the 
controller causes fabrication particle material to be ejected as droplets 
forming the three-dimensional object, while a complementary support 
structure is created by the ejection of support particles. While this 
scheme allows the fabrication of layers having various angles, the 
three-dimensional object must later be separated from the surrounding 
support material. Accordingly, this device requires the use of more 
material than is ultimately incorporated in the three-dimensional object. 
Moreover, two jets and two material supply systems are required, thereby 
increasing the cost and complexity of the apparatus. 
U.S. Pat. No. 5,260,009 to Penn entitled "System, Method, and Process for 
Making Three-Dimensional Objects" discloses yet another apparatus for 
forming three-dimensional articles wherein a second or support material is 
dispensed with each layer of the three-dimensional article as it is 
formed. 
The formation of three-dimensional articles by jetting a photosetting or 
thermosetting material is disclosed in U.S. Pat. No. 5,059,266 to Yamane 
et al. entitled "Apparatus and Method for Forming Three-Dimensional 
Article." A jet sequentially or intermittently jets the photosetting or 
thermosetting material in a droplet form along a flight path to a stage on 
which the article is constructed. An exposure unit is then used to cure 
the deposited material. If a photosetting material is used, the exposure 
unit is a source of light radiation. A mesh sheet may be required to form 
an article having a complicated shape. 
U.S. Pat. No. 5,140,937 also to Yamane et al. discloses an apparatus for 
forming a three-dimensional article having plural jets for jetting a 
thermosetting material and a heat supplying unit for curing the 
thermosetting material. U.S. Pat. No. 5,149,548, also to Yamane et al., 
discloses an apparatus for forming a three-dimensional article having a 
jet head for jetting a two part curable material including microcapsules. 
This apparatus also includes a microcapsule rupturing unit such as a 
source of heat, pressure or light radiation. Each of these Yamane et al. 
patents disclose an apparatus requiring a curing unit to solidify the 
deposited material. 
Other United States patents related to three-dimensional modeling are as 
follows: U.S. Pat. Nos. 5,207,371 to Prinz et al.; 5,301,415 to Prinz et 
al.; 5,301,863 to Prinz et al.; 5,204,124 to Secretan et al.; 4,749,347 to 
Valavaara; 5,303,141 to Batchelder et al.; 5,031,120 to Pomerantz et al.; 
and 5,287,435 to Cohen et al. Despite continuous development in the area 
of rapid prototype modelling, there is still a need for an apparatus and 
fabrication methods to quickly and inexpensively make arbitrary 
three-dimensional articles with a high degree of accuracy. 
SUMMARY OF THE INVENTION 
In view of the foregoing background, it is therefore an object of the 
invention to provide an apparatus and associated method to allow a 
designer to quickly and relatively inexpensively make an arbitrary 
three-dimensional article with high accuracy. 
It is another object of the present invention to provide an apparatus and 
associated method to permit making of a three-dimensional article 
including generally horizontally extending wall portions without requiring 
separate support material which surrounds the article and which must be 
later removed to free the finished article. 
These and other objects, features and advantages of the present invention 
are provided by an apparatus for making a three-dimensional article 
including a build material dispenser positioned adjacent a platform for 
dispensing a plurality of droplets of build material; and dispenser 
positioning means for relatively positioning the dispenser in five degrees 
of freedom with respect to the platform. Accordingly, the dispenser may be 
positioned and oriented to permit construction of a cantilevered portion 
of an article without requiring an additional support material surrounding 
the article. The dispenser is preferably a jet including means, such as a 
piezoelectric element or actuator, for ejecting a controlled volume or 
droplet of build material responsive to a corresponding firing signal from 
the processor. 
More particularly, the dispenser positioning means preferably includes 
Z-direction positioning means for positioning the dispenser vertically 
relative to the platform, X-Y positioning means for positioning the 
dispenser in an X-Y planar direction relative to the platform, flip angle 
positioning means for rotatably positioning the dispenser relative to a 
generally horizontal axis, and phi angle positioning means for rotatably 
positioning the dispenser relative to a generally vertical axis. In 
addition, a processor is preferably operatively connected to the dispenser 
and the dispenser positioning means for advancing the dispenser along a 
predetermined path of travel while operating or firing the dispenser to 
construct the three-dimensional article in successive layers or portions 
based upon the article defining data. 
The processor preferably controls the positioning means so that the 
dispenser is located a predetermined distance from respective intended or 
target landing positions of the droplets of build material as the 
dispenser is advanced along the predetermined path of travel. Accordingly, 
uniformity of construction and accuracy of the finished article are 
enhanced. 
The apparatus also preferably includes a supply of build material connected 
in fluid communication with the dispenser, and wherein the build material 
has predetermined characteristics for permitting successive dispensed 
droplets to adhere to and solidify upon previously dispensed and 
solidified build material. For example, the characteristics include 
melting temperature, viscosity, and surface tension. Moreover, the 
predetermined characteristics of the build material are desirably selected 
to permit successive droplets to adhere to and solidify upon previously 
dispensed and solidified build material defining a generally horizontal 
build direction. Thus, a horizontal unsupported or cantilevered portion of 
the article may be readily constructed according to the invention. 
The processor is preferably provided by a microprocessor operating under 
stored program control. The processor preferably positions the dispenser 
to dispense droplets at an angle of not greater than about 45.degree. from 
horizontal and, more preferably, not greater than 25.degree. from 
horizontal while constructing the cantilevered portion of the article in a 
generally horizontal build direction. The processor also preferably 
positions the dispenser to dispense droplets along an axis defined by a 
desired build direction when the desired build direction angle is greater 
than about 25.degree. from horizontal. Because of the adherence of the 
build material, the processor may also position the dispenser to dispense 
droplets vertically for a build direction angle of less than about 
45.degree. from vertical and, more preferably, less than about 25.degree. 
from vertical. 
To further facilitate construction of a horizontal portion of the article, 
the build material dispenser, in the form of a jet, preferably has a 
predetermined configuration so that a lowermost portion thereof, when 
positioned to eject droplets at an angle of not less than about than about 
5.degree. from horizontal, and, more preferably, not less than about 
20.degree. from horizontal, does not intersect an imaginary plane defined 
by a horizontal layer of the article being constructed. Accordingly, the 
jet may be readily positioned to fire at a relatively low angle without 
interference from previous constructed portions of the article. In one 
embodiment, the jet has a cylindrical body portion and a tip portion 
connected thereto, and wherein the tip portion is canted at a offset angle 
of at least about 5.degree. and, more preferably, at least 20.degree. from 
an axis defined by the cylindrical body portion. 
The apparatus also preferably includes a reservoir for containing the build 
material and connected in fluid communication with the dispenser, and a 
heater operatively connected to the reservoir for maintaining the build 
material in a liquid state. Moreover, the reservoir and the dispenser are 
preferably relatively positioned to form a negative meniscus of liquid 
build material at the orifice of the dispenser or jet. Thus, the quantity 
of build material dispensed responsive to control signals from the 
processor may be accurately controlled. In addition, problems associated 
with build material accumulating at the orifice may also be significantly 
reduced. 
A heated conduit is preferably connected in fluid communication between the 
reservoir and the dispenser. Accordingly, filling means is preferably 
provided for filling the conduit and the dispenser when the same are empty 
of build material. Emptying means are also preferably provided and 
connected to the reservoir for applying a vacuum to the reservoir for 
emptying liquid build material from the conduit and the dispenser. The 
emptying means may also be activated upon repowering of the apparatus if a 
complete power shutdown prevented earlier emptying. 
Another feature of the invention is that the processor may form a test 
pattern for adjusting one or more control parameters. Accordingly, the 
apparatus may preferably include test and compensation means operatively 
connected to the processor for sensing the test pattern of dispensed and 
solidified build material. The test and compensation means preferably 
includes an optical source and an optical detector both mounted adjacent 
the dispenser and operatively connected to the dispenser positioning 
means. 
Yet another aspect of the invention also leads to greater uniformity and 
accuracy in the article. The processor preferably further includes means 
for operating the dispenser and the dispenser positioning means to 
construct a layer of a wall portion of the article in a plurality of 
side-by-side segments of dispensed and solidified build material. The 
segments are formed in a sequence from a first side of the wall portion to 
a second side thereof. In addition, successive segments are preferably 
formed in alternating directions. Moreover, a next successive layer of the 
wall portion of the article may be formed in a plurality of side-by-side 
segments of ejected build material formed in an opposite sequence from the 
second side of the wall portion to the first side thereof. 
Yet an additional feature of the present invention is that the processor 
may also operate the dispenser and dispenser positioning means to 
construct a release portion of the article. The release portion preferably 
comprises ejected and solidified build material formed upon the platform 
and having reduced wall strength, for example, to thereby facilitate 
removal of the article from the platform. For example, the release wall 
may include openings, be of only a single segment of build material in 
thickness or have reduced contact points with the platform. To increase 
handling strength of the article, the processor also preferably includes 
means for operating the dispenser and dispenser positioning means to 
construct a base portion of the article, adjacent the release structure, 
and having a predetermined hatched wall pattern therein. 
A method aspect of the invention is for making a three-dimensional article 
based upon the article defining data. The method comprises the steps of: 
advancing a build material dispenser along a predetermined path of travel 
relative to a platform in three directions and rotatably positioning the 
dispenser about two axes thereby defining five degrees of freedom of 
movement for the dispenser relative to the platform, and while dispensing 
a plurality of droplets of build material from the dispenser to construct 
the three-dimensional article based upon the coordinate data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described more fully hereinafter with 
reference to the accompanying drawings, in which preferred embodiments of 
the invention are shown. This invention may, however, be embodied in many 
different forms and should not be construed as limited to the embodiments 
set forth herein. Rather, applicants provide these embodiments so that 
this disclosure will be thorough and complete, and will fully convey the 
scope of the invention to those skilled in the art. Like numbers refer to 
like elements throughout and prime notation is used to indicate similar 
elements in alternate embodiments. 
As illustrated in FIG. 1, the three-dimensional article manufacturing 
apparatus 30 according to the invention includes a generally rectangular 
housing 31. The housing includes an access opening 62 closed by a sliding 
door 63. A power port 49 facilitates electrical connection to an external 
power source such as from an AC outlet 65 shown in schematic form. A 
computer port 48 allows connection to an external computer 64 also shown 
in schematic form. An external computer 64, such as a work station or 
personal computer, is used to generate a digital data file containing the 
three-dimensional coordinate data defining an article or model to be 
built. For example, the data may be from an STL file which defines the 
article in triangular facets, as would be readily understood by those 
skilled in the art. 
In addition, it will be understood by those having skill in the art that 
the data file may be transferred to the apparatus by a transferable memory 
medium such as a magnetic disk or tape, or a microelectronic memory, not 
shown. Accordingly, the apparatus 30 may be adapted to receive coordinate 
data from any number of sources having the appropriate electronic data 
format. If data is transferred by a transferable memory medium, for 
example, the apparatus 30 may include a disk drive, a tape reader, or 
other means for reading electronic data from a transferrable memory 
medium. 
As illustrated in FIG. 2, the apparatus 30 includes a processor 33 which 
receives the digital data file and translates the coordinate data therein 
to control signals, as described further herein. The apparatus 30 also 
includes a power supply 29. 
The apparatus 30 includes a platform 32 on which the article 37 is built, 
and a ballistic jetting head 34 (FIGS. 5-7). Droplets of liquid build 
material are ballistically jetted from a piezoelectric jet 39 carried by 
jetting head 34 to the platform 32 in order to construct the article 37. 
The build material is normally solid when at the temperature of the 
interior of the apparatus. The build material is heated to maintain the 
build material in a liquid state. Accordingly, heated liquid droplets of 
build material are jetted from the jetting head 34 to an intended landing 
position on either the platform 32 or a portion of previously jetted build 
material. On contact with the platform or previously jetted build 
material, the heated liquid droplets cool and solidify. 
The piezoelectric jet 39 may also be positioned relatively close to the 
target position so that the build material may, in a sense, not be 
considered as traveling ballistically. Accordingly, the terms ejected and 
jetted are also used herein and describe a relatively small gap or no gap. 
The illustrated piezoelectric jet 39 is but one embodiment of a dispenser 
for dispensing build material in metered quantities and to precise target 
landing positions. It being readily understood by those of skill in the 
art, that other types of build material dispensers are also contemplated 
by the invention that can meter build material and accurately deliver it 
to a target position. Moreover, the term droplet as used herein is 
intended to cover individual or discrete volumes of build material that 
may be ejected, for example, by the piezoelectric jet 39. In addition, the 
term droplet is also intended to cover a volumetrically modulated stream 
of build material, wherein small quantities or volumes of build material 
may be connected to adjacent volumes without becoming discrete entities, 
such as because of a relatively small gap or because of the speed of 
dispensed build material, for example. 
In a preferred embodiment, the apparatus 30 includes positioning means for 
moving the ballistic droplet jetting head 34, including the piezoelectric 
jet 39 and the thermal normalization means, such as the illustrated heated 
body 87 in relation to the platform 32. Orthogonal drive shafts facilitate 
the movement of the jetting head 34 in the X- and Y-directions relative to 
the platform 32. As illustrated in FIGS. 2 and 3, a pair of X-axis drive 
shafts 44, which are driven by X-axis motor 69 and X-axis drive belt 68, 
facilitate movement of the jetting head 34 in the X-direction. Y-axis 
drive shaft 45, which is driven by Y-axis drive motor 71 and Y-axis drive 
belt 70 facilitates movement of the ballistic droplet jetting head 34 in 
the Y-direction. As will be understood by those having skill in the art, 
movement of the jetting head 34 in the X-Y planar direction may also be 
provided by an r/.theta. positioner including an arm adapted for radial 
movement at an angle .theta., and a positioner for positioning the jet at 
a radius, r, along the arm. 
In the illustrated embodiment, relative movement in the Z-direction is 
provided by a Z-axis positioner 43 which moves the platform 32 up and down 
in the Z-direction. The Z-axis positioner includes vertical drive shafts 
60 which engage the platform 32. The drive shafts 60 are driven by the 
vertical drive motor 61 and vertical drive belts 66 and 67. 
Referring more particularly to FIG. 2, liquid build material is supplied 
from a build material reservoir 78 to the jetting head 34 through the 
build material delivery hose or conduit 72. The build material reservoir 
78 and the delivery conduit 72 both include means for heating the build 
material so that it remains in a liquid state. In a preferred embodiment, 
both the build material reservoir 78 and the delivery conduit 72 include 
an electrical heating element. The build material reservoir 78 also 
includes a fill tube 79, and a connection to a pneumatic system for 
applying either vacuum or pressure to the liquid build material. The 
pneumatic system includes a pump 73, an accumulator 74, a pressure 
regulator 75, a purge valve 76, and a fill valve 77. 
A relatively constant level of liquid build material is maintained in the 
build material reservoir 78, so that the surface level of the liquid build 
material in the build material reservoir 78 is maintained at a relatively 
constant elevation with respect to the piezoelectric build material jet 
39. Dashed lines represent a nearly full liquid level 99 and a nearly 
empty liquid level 100 of build material in the build material reservoir 
78. In preferred embodiments, the jet 39 is situated above the surface 
level of the liquid build material, such as about 1 to 3 inches above the 
surface level of the liquid build material, to thereby maintain a negative 
meniscus, that is, having a concave shape at the orifice of the 
piezoelectric jet 39. Alternatively, a vacuum could be applied to the 
liquid build material, such as by coupling a vacuum source to the 
reservoir 78. The negative meniscus increases the accuracy and uniformity 
of successive ballistically jetted droplets and also reduces undesirable 
accumulation of build material adjacent the orifice of the jet 39. 
As illustrated perhaps best in FIGS. 5 and 6, the ballistic droplet jetting 
head 34 includes means for rotating the piezoelectric jet 39 and the 
heated body 87 about a horizontal axis or to a desired flip angle. The 
axis is defined by a horizontal shaft 85 which is driven by an associated 
motor 84 through drive gears 57 and 58. Accordingly, the firing direction 
41 may be adjusted from vertical, as shown in FIG. 5, to near horizontal 
as shown in FIG. 6. FIGS. 5 and 6 also further illustrate the positioning 
means which rotates the jetting head 34 about a vertical axis on shaft 83 
for rotation to a desired phi angle of rotation. This rotation is powered 
by vertical axis rotation motor 82 shown in schematic form. 
The jetting head 34 preferably carries both the piezoelectric jet 39 and 
the heated body 87. Both of these elements are heated to a temperature 
above the melting point of the build material. This heat may be generated 
by an electrical heating element. In a preferred embodiment, an electrical 
heater, such as a resistive wire 120, is operatively connected to the 
heated body 87. Accordingly, the jet 39 receives heated liquid build 
material from the delivery hose 72 and maintains the build material in a 
liquid state prior to jetting. As will be discussed in greater detail with 
regard to FIG. 15E, the heated body 87 is used to periodically normalize 
surface portions of a partially completed wall. 
Liquid build material is supplied to the jet 39 through the flexible build 
material delivery conduit 72. The conduit 72 is formed into a spiral coil 
86 within the vertical shaft 83 to enable rotation of the ballistic 
droplet jetting head 34 without restricting the flow of build material 
through the conduit and without requiring a rotatable joint and associated 
seal. FIG. 7 illustrates rotation of the ballistic droplet jetting head 34 
about the vertical shaft 83. The build material delivery conduit 72 enters 
the jetting head through the shaft 83. By rotating the shaft 83, the 
entire jetting head 34, including the jet 39 and the heated body 87, may 
be rotated 360 degrees about a vertical axis by the vertical axis motor 
82. 
The build material flows from the conduit 72 through a baffle 88 and a 
filter 89 to the jet 39, and out of the orifice 40 of the jet as shown in 
FIG. 8A. The heated liquid build material from hose 72 enters baffle 88 
before passing on to the jet 39. The baffle 88 provides two 90 degree 
bends in the path of the flow of build material. Accordingly, acoustic 
waves generated upstream from the baffle 88 are dissipated as they strike 
wall 105 of the baffle. In other words, the baffle 88 is beneficial to 
prevent movement of the head from breaking the negative meniscus at the 
orifice and also is useful during filling to prevent generation of air 
bubbles. The filter 89 prevents any contaminants from clogging the narrow 
passageway of the jet 39 and also provides a further reduction in the 
acoustic waves. The build material passes from the baffle 88 through the 
tubular connection 106 to the piezoelectric jet 39. 
A build material passage 104 within the piezoelectric jet 39 provides fluid 
communication between the baffle 88 and the orifice 40. As discussed 
above, a heating element, such as an electrical resistance wire, may be 
used to maintain the build material in a liquid state as it passes from 
the conduit 72 to the baffle 88, tubular connection 106, and jet 39. 
The orifice 40 of the jet 39 is maintained at a predetermined elevation 
above the surface level of liquid build material in the build material 
reservoir 78 in the illustrated embodiment. Accordingly, a predetermined 
negative pressure is exerted upon the liquid build material at the orifice 
40. As illustrated in FIG. 8B, orifice 40 has a predetermined diameter 
such that the liquid build material maintains a negative meniscus 103 at 
the orifice 40 under the influence of the negative pressure. Accordingly, 
the negative meniscus increases the accuracy and uniformity of successive 
ballistically jetted droplets and also reduces undesirable accumulation of 
build material adjacent the orifice 40 of the jet 39. 
The piezoelectric jet 39 includes a hollow body 102 including a plastic 
insert 102a defining a build material flow passage 104, and a containing a 
piezoelectric element 101, in turn, secured within the body by an epoxy 
101a. Upon application of an electric signal to the piezoelectric element 
101, the piezoelectric element either contracts or expands depending on 
the polarity of the signal. In response, an acoustic wave is generated in 
the liquid build material located in the build material flow passage 104. 
This acoustic wave is transmitted through the liquid build material to the 
negative meniscus 103 at the orifice 40. As a result of the acoustic wave, 
a droplet of heated liquid build material having a predetermined volume is 
jetted or ejected from the orifice 40 in firing direction 41 and at a 
predetermined velocity. The volume and velocity of the droplet are 
functions of the diameter of the orifice; the size of the piezoelectric 
element 101; the intensity and polarity of the electrical signal; and the 
temperature, surface tension and viscosity of the liquid build material. 
In preferred embodiments, it has been found that stable operation of the 
piezoelectric jet 39 can be sustained at frequencies of up to 12 KHz. 
Accordingly, the piezoelectric jet 39 is capable of firing 12,000 droplets 
per second wherein each droplet has a predetermined volume, velocity and 
firing direction. Other jetting means are also contemplated by the 
invention as would be readily understood by those skilled in the art. The 
jet 39 may also be operated to jet droplets in relatively quick 
succession, that is, in bursts of multiple droplets, so that the droplets 
in each burst collectively coalesce or solidify at an intended landing 
position as described in copending patent application Ser. No. 08/325,694 
and assigned to the present assignee, the entire disclosure of which is 
incorporated herein by reference. 
The build material typically melts at a temperature of from about 
50.degree. C. to 250.degree. C., cools quickly and adheres to itself, and 
has a low rate of shrinkage. Such a build material preferably comprises a 
solution of a resin having a hydroxyl number of from about 5 to 1000, and 
a molecular weight greater than about 500, dissolved in at least one 
primary aromatic sulfonamide preferably having a melting point greater 
than about 25.degree. C. The rheology of the build material is preferably 
such that a droplet remelts portions of deposited material so as to form a 
flowable bead. 
With respect to the resin portion of the build material, Applicants do not 
wish to be bound by any one theory, but believe that a resin having 
hydroxyl functionality, as defined by hydroxyl number, through hydrogen 
bonding, holds together the droplet after jetting through the jetting 
head. The upper limit of hydroxyl number (i.e., 1000) is important in that 
the higher the hydroxyl number, the higher the heat capacity of the resin, 
and the resin cools slower. Slower cooling is undesirable in that the 
build material tends to sag if it cools slowly as the article is being 
built. Exemplary resins include polyester resins, phenolic resins, 
polyamides, vinyl ester resins, polyurethanes, amino resins, melamine 
resins, urea resins, epoxy resins, and naturally-derived polymers such as 
coumarin-indene, shellac, protein and celluosics (e.g., ethyl cellulose, 
ethyl hydroxy ethyl cellulose, nitro cellulose, etc.), and mixtures 
thereof. 
Suitable polyester resins include practically any esterification product of 
a polybasic organic acid and a polyhydric alcohol. Polyester resins can 
also be derived from the esterification of a polycarboxylic acid or 
anhydride with a polyhydric alcohol. Suitable phenolic resins include 
practically any reaction product of an aromatic alcohol with an aldehyde. 
Particularly preferred, are the phenolic resins prepared by the reaction 
of phenol with formaldehyde. Suitable vinyl ester resins include 
practically any reaction product of an unsaturated polycarboxylic acid or 
anhydride with an epoxy resin. Exemplary epoxies include virtually any 
reaction product of a polyfunctional halohydrin, such as epichlorohydrin, 
with a phenol or polyhydric phenol. Specific resins include acrylics, 
styrene-acrylic copolymers and styrene-allyl alcohol copolymers. 
Typically, the build material includes about 1 to 50 percent of the resin, 
preferably about 5 to 30 percent, and more preferably about 5 to 15 
percent, by weight of the resin. 
With respect to the primary aromatic sulfonamide, it is believed that the 
primary aromatic sulfonamides provide the necessary self adhesion 
properties to the build material. Suitable aromatic sulfonamides are 
preferably primary C.sub.1 to C.sub.15 benzenesulfonamides, and most 
preferably the substitution is alkyl and is at the para position. 
Exemplary primary aromatic sulfonamides include 
p-n-ethylbenzenesulfonamide, p-toluenesulfonamide, 
p-methoxybenzenesulfonamide, p-n-nonylbenzenesulfonamide, 
p-n-butylbenzenesulfonamide, and mixtures thereof. Typically the build 
material includes about 1 to 50 percent, preferably about 70 to 90 
percent, and more preferably about 75 to 90 percent by weight of one or 
more of the aromatic sulfonamides. Particularly preferred is a 50/50 
mixture of p-toluenesulfonamide and p-n-ethylbenzenesulfonamide. 
The build material can include antioxidants (e.g., Ultranox 626 available 
from Borg Warner Chemicals, Inc.), flexibilizers, magnetic particles, 
pigments, and fluorescent agents, and other additives, the addition of 
which is within the skill of one in the art. Dyes can be added to the 
build material. Suitable dyes include FD & C Blue #1, Neozapon Red 492, 
Savinyl Black RLS and the like. Another additive could be a secondarily 
reactive organic compound such as one activated by exposure to UV light. 
These compounds can be used to provide an article which can be hardened so 
as to be unmeltable or machinable. Typically, the build material includes 
from about 1 to 10 percent by weight of the various additives. 
Suitable build materials are further described in commonly assigned 
copending U.S. patent application Ser. No. 08/326,004, the entire 
disclosure of which is incorporated herein by reference. In addition, 
other techniques for jetting or ejecting build material are further 
described in commonly assigned copending patent application Ser. No. 
08/326,004. 
An alternative embodiment of a jet 39' is shown in FIG. 9 having a firing 
direction 41' oriented at an offset angle relative to the jet axis 107 
defined by the cylindrical body 102'. This orientation is obtained by 
providing a tip 108 which is curved or canted at the angle offset from the 
body. The other elements are indicated by prime notation and are similar 
to those elements described in the first embodiment. This second 
embodiment has the advantage of allowing the firing direction 41' to be 
close to horizontal without interference with a layer of the article being 
constructed. The wider body 102 portion of the jet 39 containing the 
piezoelectric element 101 might otherwise come into contact with 
previously jetted layers of build material. In a preferred embodiment, the 
angle .alpha. is not less than 5.degree. or more preferably not less than 
20.degree. as illustrated. 
In FIGS. 10, 11 and 12 there are illustrated the formation of walls of an 
article oriented at various angles. In each of these figures, a 
cross-section of a wall is schematically illustrated and the wall is 3 
droplets thick, it being understood that the burst mode of operation may 
also be used in the present invention as described above in which case the 
wall is three bursts thick. In this preferred embodiment, the 3 droplet 
wall thickness provides a balance of strength, stability, and conservation 
of time and material. Now referring more particularly to FIG. 10, a 
vertical wall is being formed and the piezoelectric jet 39 is positioned 
directly above the wall. Upon application of an electrical pulse to the 
piezoelectric element, a heated liquid droplet of build material 35 is 
jetted from the orifice 40 in the firing direction 41. The liquid droplet 
35 will contact the wall at the intended landing point 36. Upon contact, 
the liquid droplet will bond with the previously solidified wall portion. 
Because the wall is 3 droplets wide, 3 droplets will be required to form a 
horizontal layer of the wall. Previously jetted pass or layer 38 is 
indicated by dashed lines schematically representing the droplets which 
formed the previous layer. In this illustration, the firing direction 41 
and the build direction 42 are aligned. 
Since the jet 39 may be accurately positioned and aligned with an intended 
landing point 36, the firing direction and build direction need not be 
aligned. Moreover, because of the adherence of the build material, it is 
possible to build walls having a build direction 42' as much as 
45.degree., and more preferably 25.degree. from vertical while maintaining 
the jet 39' and firing direction 41' in a vertical orientation as 
illustrated by the dashed lines of FIG. 10. 
FIG. 11 illustrates the formation of a wall having a non-vertical build 
direction wherein the build direction 42 and the axis of the jet 39, that 
is, its firing direction 41 are aligned. This arrangement may be preferred 
in the construction of walls having build directions 42 which are in the 
range of from vertical down to about 5.degree. from horizontal. 
FIG. 12 illustrates the formation of walls having a build direction 42 in 
the range of horizontal to about 45.degree. from horizontal. It is not 
desirable to bring the firing direction 41 of the jet 39 below 5.degree. 
and, more preferably 20.degree., from horizontal because the jet would 
contact previously jetted portions of the article. Accordingly, for 
horizontal walls, it is preferable to fire the piezoelectric jet 39 at 
orientations such that the firing direction 41 is at least 5.degree., and 
more preferably 20.degree., from horizontal as may be readily achieved 
with the embodiments of the jet 39 according to the invention. 
Accordingly, with the build material jet 39 and jetting head 34 
positionable in five degrees of freedom, horizontal walls can be produced 
without the need for separate support material. In certain article 
geometries, struts may be formed which can be later removed from the 
article as would be readily understood by those skilled in the art. 
In FIGS. 13A-13C, there is illustrated a preferred order of firing droplets 
of build material so as to minimize irregularities in the formation of a 
layer or pass on a wall. In FIG. 13A, a first linear segment or wall 
portion is formed by advancing the build material delivery jet along the 
first path 50 in a first direction 51. As the jet is advanced, ballistic 
droplets of build material are jetted to form the first segment on top of 
the existing wall. As shown in 13B, the build material delivery jet is 
then advanced along a second path 52 to construct a second segment 
side-by-side with the first segment and in a second direction 53 opposite 
the first direction 51. In FIG. 13C, the jet is advanced along a third 
path 54 side-by-side with the second path 52 in a direction 55 opposite 
the second direction 53. Accordingly, a third segment is formed 
side-by-side with the second segment. Although linear segments are 
illustrated, arcuate or curved segments may also be similarly formed 
according to the invention. 
FIG. 14 illustrates another aspect of the invention for enhancing build 
uniformity and accuracy in the article. In a next successive layer of the 
article, the respective segments 56b are laid down in an opposite order 
from the underlying segments 56a. 
In the formation of a wall portion or segment, irregularities may occur at 
the beginning and end of the segment. For example, the beginning of the 
segment may be relatively thick while the end may be relatively narrow. 
These differences in thickness may result from the acceleration and 
deceleration of the jet as it starts and stops movement or from surface 
tension effects of the build material. By altering the direction of 
advancement of the jet when forming side-by-side segments, these 
irregularities may be significantly reduced. 
In FIGS. 15A-L, there is illustrated the formation of a three-dimensional 
article 37' having unsupported features. As previously discussed, liquid 
build material is first jetted from the piezoelectric jet 39 to the 
platform 32 and then to previously jetted build material thereby forming 
successive layers. As illustrated in FIG. 15A, a release structure 109 may 
first be constructed to facilitate removal of the finished article from 
the platform 32. This structure 109 comprises a plurality of walls which 
have reduced thickness in the illustrated embodiment. In other 
embodiments, perforated wall portions may be formed, or a reduced number 
of contact points or piers may be formed supporting the article, for 
example, as would be readily appreciated by those skilled in the art. The 
release structure 109 also provides a starting structure upon which the 
three-dimensional article can be built and which is strong enough to 
provide a stable support during the construction of the article. As shown, 
the jet 39 moves along path 117 with a vertical firing direction 41 
pointed straight down towards the partially constructed release structure 
109. In a preferred embodiment, each successive pass or layer is jetted as 
the jet moves in an opposite direction. 
FIG. 15B illustrates the formation of a horizontal wall 110 which will form 
the bottom surface of the article. The horizontal wall 110 in this 
embodiment has a horizontal build direction and a three droplet or three 
segment thickness. Each linear segment is jetted as the jet 39 advances 
along a path 117 parallel to the edge of the wall with the firing 
direction 41 oriented at an angle of about 20 degrees from horizontal. As 
discussed with regard to FIGS. 13 and 14, each segment may be jetted as 
the jet moves in a direction opposite to the direction from which adjacent 
segments were jetted. In FIG. 15C, the completed horizontal wall 110 
extends across the top of the release structure 109. The dotted lines 
indicate the extent of the horizontal wall. 
As illustrated in FIG. 15D, vertical walls 111 may be formed upon the 
horizontal wall 110. These vertical walls 111, which are part of the model 
or article 37' being constructed, are three droplets or segments thick in 
the illustrated embodiment. This thickness for the structural parts of the 
article adds strength and stability to the finished article. An internal 
hatched wall pattern 112 provides added structural stability and strength 
to a base portion of the article. The hatching, if desired, may also be 
extended throughout the interior of the article being formed, thereby 
adding to the overall strength and stability of the article. To increase 
overall speed, the hatching may preferably be provided only in the base 
portion. 
The hatched wall pattern 112 may be made to any desired thickness. The 
hatched wall pattern 112 may be formed at the same vertical rate as the 
vertical walls 111. Accordingly, a pass or layer may be completed for the 
vertical walls 111 and the hatched wall pattern 112 before moving on to 
the next layer for the vertical walls or hatched wall pattern. 
FIG. 15E illustrates build rate normalization using a heated body 87. As 
previously discussed, the heated body or ironing pin 87 may be carried by 
the jetting head 34. Accordingly, after a predetermined number of passes 
or layers have been jetted, there may be a need to normalize the outer 
surface portions of the vertical walls. In a preferred embodiment, the 
process of build rate normalization occurs after 21 passes or layers of 
build material have been jetted. Accordingly, a balance is struck between 
the need for normalization and the time spent performing the operation. 
The heated body 87 may comprise aluminum with a Teflon.RTM. release coating 
thereon. The heated body 87 is brought into contact with the upper surface 
of walls 111 and advanced in a path 118 parallel to the outer surface. In 
a preferred embodiment, the path 118 is reversed each time the structure 
is normalized. The heated body 87 causes the build material to melt or 
reflow. Normalization may not be required for hidden internal structures, 
such as the hatched pattern of walls for strengthening the base portion of 
the article. The thermal normalization is further described in copending 
application Ser. No. 08/326,009 and assigned to the assignee of the 
present invention, the entire disclosure of which is incorporated herein 
by reference. 
FIG. 15F illustrates the continued building of vertical walls 111. FIG. 15F 
also illustrates the formation of a hatched structure 112 which fills only 
the bottom portion of the article. 
Now referring to FIG. 15G, a second horizontal wall 113 is being built over 
vertical walls 111. This structure is built using the same techniques 
described with regard to FIG. 15E. In FIG. 15H, there is illustrated the 
extension of wall 113 beyond vertical walls 111, creating a cantilevered 
or unsupported horizontal wall portion 114. This unsupported wall portion 
114 is created in the same manner as the previously formed supported 
portions. The jet 39 continues jetting passes or layers of build material 
on previous passes or layers. As before, the firing direction 41 is 
oriented at an angle near horizontal. FIG. 15I illustrates the completion 
of horizontal wall 113 with the unsupported wall portion 114. 
In FIG. 15J, vertical walls 115 are being formed on horizontal wall 113 
including unsupported horizontal portion 114. Vertical walls 115 are 
formed using the same sequence of operations discussed with regard to 
vertical walls 111 in FIGS. 15D-F. In FIG. 15K, vertical walls 115 have 
been completed, and the formation of horizontal wall 116 on vertical walls 
115 is shown. The formation of this horizontal wall follows the same 
sequence as discussed with regard to horizontal walls 113 and 110. In FIG. 
15L, horizontal wall 116 is complete, thereby completing this portion of 
the article 37'. 
As shown with regard to FIGS. 15A-L, a preferred embodiment of the present 
invention is capable of forming complex models having unsupported 
horizontal or cantilevered structures without the need for a surrounding 
support material. The completed model may be removed from the platform 32 
by breaking the release structure 109. The release structure 109 breaks 
away relatively easily from both the platform 32 and the horizontal wall 
110 forming the bottom of the model. Accordingly, the present invention 
provides a relatively simple and inexpensive way to produce a 
three-dimensional model or article of high accuracy. 
FIG. 16 illustrates the vacuum system used to empty and fill the delivery 
conduit 72 and jet 39. The vacuum system applies either a vacuum or a 
pressure to the build material reservoir 78 to either empty or fill the 
delivery hose 72, jetting head 34, and jet 39. When the system is powered 
down, it can be useful to empty the build material from the jetting head 
and delivery hose. Accordingly, fill valve 77 is closed and purge valve 76 
is opened. Then, pump 73 applies a vacuum through purge valve 76 to the 
build material reservoir 78. Accordingly, build material in the conduit 72 
and jet 39 is drawn back into the build material reservoir 78. This 
process allows the heaters in the jetting head 34 and conduit 72 to be 
turned off without having build material solidify in either the conduit or 
the jet. The build material reservoir 78 may then be cooled, allowing the 
build material therein to solidify without harm. 
When turning the system on, it is desirable to fill the conduit 72 and jet 
39. Accordingly, the purge valve 76 is closed and the fill valve 77 is 
opened. The pump 73 is then used to create a positive pressure in the 
accumulator bottle 74. Pressure regulator 75 is used to regulate the 
pressure that is applied to the build material reservoir 78 through the 
fill valve 77. After the build material in the reservoir 78 has been 
heated to form a liquid, and the conduit 72 and jet 39 have both been 
heated, a progressively increasing or rising pressure waveform is applied 
to the build material reservoir 78. Accordingly, the liquid build material 
flows with increasing velocity through the hose 72 towards the jetting 
head 34. The slowing increasing velocity of the material through the hose 
72 causes the leading edge of the build material to form a positive 
meniscus as it passes through the conduit. This positive or convex 
meniscus prevents the formation of bubbles in the conduit or jet which 
could interfere with operation of the piezoelectric jet. When the build 
material reaches the orifice 40 of the piezoelectric jet 39, the pressure 
is maintained for a short interval, allowing the build material to stream 
from the orifice. The pressure waveform then cuts off abruptly, allowing 
the formation of a negative meniscus at the orifice of the piezoelectric 
jet without causing an accumulation of build material adjacent the 
orifice. 
The operation of the pump 73, fill valve 77, purge valve 76, and pressure 
regulator 75 are controlled by the processor 33. Accordingly, emptying and 
filling operations may occur automatically in response to the power up and 
power down of the system. In addition, the processor may also determine 
whether the system is properly powered down or improperly shut off due to 
a power failure. If the system is properly shut down, the processor will 
send control signals to empty the conduit and jet. If there is a power 
failure, normal emptying may not be performed and build material may 
solidify in the jet and conduit. The processor then initiates emptying and 
filling prior to permitting normal operation of the jet. 
In FIG. 17A, there is illustrated a jetting head 34 having a heated body or 
ironing pin 87, a piezoelectric jet 39, and an optical detection unit 90. 
The optical detection unit 90 includes a light emitting diode (LED) 91 and 
an optical receiver 92. The LED 91 emits a beam 98 of light directed down 
to the surface being inspected. If the surface has certain reflective 
characteristics, the beam reflects back up toward the optical receiver 92. 
The LED 91 and receiver 92 are mounted such that the receiver detects the 
reflected light from a reflective surface. In this embodiment, the 
solidified build material has predetermined reflective characteristics 
such that the beam 98 may detect its presence. 
In one embodiment, the piezoelectric jet may jet a predetermined 
two-dimensional pattern 121 on the platform 32 of the system as 
illustrated in FIG. 17B. The optical detection unit 90 then scans the 
pattern 121 to determine the X- and Y-coordinates of each feature on the 
pattern. The measured coordinates can be compared to the known positions 
of the jet 39 when jetting the pattern and an analysis of the comparison 
used to determine X- and Y-axis offsets, for example. The jet 39 may also 
be used to jet a test pattern having a vertical component so that build 
rate may be determined or a Z-axis offset determined. 
In yet another embodiment, the optical detection unit 90 may be used to 
restart the build process in the event that the creation of the article is 
halted before completion. In this embodiment, the optical detection unit 
is used to determine the status of the build process at the time of the 
interruption. 
The optical detection unit 90 represents an embodiment of test and 
compensation means for permitting adjustment of a control parameter, such 
as firing frequency or carriage speed, as would be readily understood by 
those skilled in the art. In addition, mechanical, electrical or 
acoustical sensing means could be used to examine a test pattern and, 
hence, provide the test and compensation means according to the invention. 
FIG. 18 illustrates a cross-section of the build material conduit 72 which 
includes a flexible interior tubing 93, formed of a durable material such 
as VITON.TM.. The interior is surrounded by a thermally conductive 
material layer, such as a wire mesh braid 94. In a preferred embodiment, 
the conductive material is a copper braid. An insulated electrically 
resistive wire heating element 95 is wrapped around the wire mesh braid 94 
in a spiral fashion. The resistive wire may comprise a nichrome wire 
surrounded by an insulating material. The conduit 72 is thus uniformly 
heated by passing a current through the resistive wire. The braided layer 
94 and resistive wire heating element 95B are surrounded by an insulating 
material layer 96, such as fiberglass. The complete structure is then 
encased in heat-shrink tubing 97. In a preferred embodiment, this 
predetermined temperature is greater than the melting point of the build 
material. Accordingly, build material within the conduit 72 can be 
maintained as a liquid. 
Many modifications and other embodiments of the invention will come to the 
mind of one skilled in the art having the benefit of the teachings 
presented in the foregoing descriptions and the associated drawings. 
Therefore, it is to be understood that the invention is not to be limited 
to the specific embodiments disclosed, and that modifications and 
embodiments are intended to be included within the scope of the appended 
claims.