Patent Description:
The present disclosure concerns a system for the digital fabrication of three dimensional articles of manufacture through the solidification of liquid photon-curable (photocure) resins using plural light engines. More particularly, the present disclosure concerns a system combining plural light engines that minimizes artifacts in a transition zone between the light engines.

Three dimensional printers are in widespread use. Examples of three dimensional printer technologies includes stereolithography, selective laser sintering, and fused deposition modeling to name a few. Stereolithography-based printers utilize a controllable light engine to selectively harden or solidify a liquid photocure resin in a layerwise manner until a three dimensional article of manufacture is formed. In some embodiments and according to the invention the light engine includes a light source that illuminates a spatial light modulator.

Document <CIT> discloses a method of forming a three-dimensional object which includes: providing a carrier and an optically transparent member having a build surface, the carrier and the build surface defining a build region therebetween; filling the build region with a polymerizable liquid, irradiating the build region with light through the optically transparent member to form a solid polymer from the polymerizable liquid, and advancing said carrier away from said build surface to form said three-dimensional object from said solid polymer. The irradiating step includes projecting focused light at the build region, and the advancing step is carried out at a rate that is dependent on an average light intensity of the focused light.

The spatial light modulator in combination with the light source illuminates a "build plane" within the photocure resin to selectively cure the resin. The build plane is divided into pixel elements that correspond to pixel elements of the spatial light modulator. A typical spatial light modulator has one million or more pixel elements. This may provide a high resolution for a relatively small article of manufacture. With larger articles of manufacture, the use of a single spatial light modulator causes critical dimensions to scale with size.

One way to provide larger sizes and smaller critical dimensions is to combine light engines to define the build plane. This has challenges, however. A "lateral seam" region in which one light engine ends and another begins will be utilized for fabricating important portions of a three dimensional article of manufacture. This can be problematic since light engines tend to have edge artifacts and defects that can adversely affect quality in the lateral seam region. There is a need to combine light engines while suppressing the effects of these artifacts and defects.

In a first aspect of the disclosure and according to claim <NUM>, a three dimensional printing system is configured to form a three dimensional article of manufacture through a layer-by-layer process. Layers are formed by selectively adding photocure resin onto a lower face of the three dimensional article of manufacture. Layers are formed by solidifying resin proximate to and on a "composite build plane" which is a two dimensional lateral area that is addressable by the three dimensional printing system. The three dimensional printing system includes a vessel, a plurality of light engines, and a controller. The vessel is for containing photocure resin. The plurality of light engines include at least a first light engine and a second light engine. The first light engine includes a first light modulator defining a first rectangular array of pixel elements that define a first build field and the second light engine includes a second light modulator defining a second rectangular array of pixel elements that define a second build field. The first build field and the second build field overlap along an overlap zone. The first light engine is configured to: (a) receive a first incoming slice energy data array corresponding to the first build field; (b) process the first incoming slice energy data array to provide a first scaled and corrected data array corresponding to the first rectangular array of pixel elements of the first light engine, the processing includes applying a first transparency mask to the first pixel elements within the overlap zone, the first transparency mask defines a transition zone between two extended threshold zones, the extended threshold zones include a first extended threshold zone that is proximate to an edge of the first build field, the first transparency mask has first transparency values that are below ten percent in the extended threshold region; and (c) deliver optical energy to the first build field based upon the first scaled and corrected data array to selectively cure the resin.

In one implementation the three dimensional printing system further includes a movement mechanism for translating the three dimensional article of manufacture in a vertical direction. The controller is electrically or wirelessly coupled to the plurality of light engines and to the movement mechanism. The three dimensional printing system includes a processor and an information storage device. The information storage device stores instructions, that when executed by the processor, control the plurality of light engines, the movement mechanism, and other devices within the three dimensional printing system. The processor and the information storage device can be located within the controller or distributed between the controller and the light engines. The processor and the information storage device can be integrated into one integrated circuit or can be distributed among multiple integrated circuits that can be co-located and/or distributed within the three dimensional printing system.

In another implementation the transparency threshold is less than six percent. In another embodiment the transparency threshold is less than four percent. In yet another embodiment the transparency threshold is less than or equal to two percent.

In yet another implementation the overlap zone is at least about <NUM> pixels wide in which the width defines a degree of overlap between build fields. In another embodiment the overlap zone is at least about <NUM> pixels wide. In yet another embodiment the overlap zone is at least about <NUM> pixels wide. In a further embodiment the overlap zone is <NUM> to <NUM> pixels wide. In a yet further embodiment the overlap zone is <NUM> to <NUM> pixels wide. In another embodiment the overlap zone is <NUM> to <NUM> pixels wide.

In a further implementation the extended threshold zone is at least <NUM> pixels wide. In another embodiment the extended threshold zone is at least <NUM> pixels wide. In yet another embodiment the extended threshold region is at least <NUM> pixels wide. A further embodiment the extended threshold region is at least <NUM> pixels wide.

In a yet further implementation a magnitude of an average gradient of the transparency in the transition zone is at least twice a magnitude of an average gradient of the transparency in the first extended threshold zone. The gradient in either the transition zone or the extended threshold zone is generally directed along a short axis of the overlap zone.

In another implementation the second light engine is configured to: (a) receive a second incoming slice energy data array corresponding to the second build field; (b) process the second incoming slice energy data array to provide a second scaled and corrected data array corresponding to the second rectangular array of pixel elements of the second light engine, the processing includes applying a second transparency mask to the second pixel elements within the overlap zone, the second transparency mask defines a second transition zone between two extended threshold zones, the extended threshold zones have include a second extended threshold zone that is proximate to an edge of the second build field, the second transparency mask has second transparency values that are below ten percent in the second extended threshold region; and (c) deliver optical energy to the second build field based upon the second scaled and corrected data array to selectively cure the resin. In one embodiment a sum of the first transparency values and the second transparency values is substantially equal to <NUM> percent in the overlap zone. In another embodiment the plurality of light engines includes a third light engine and a fourth light engine, the third light engine defining a third build field and the fourth light engine defining a fourth build field, the first, second, third, and fourth build fields overlap to define a four field overlap zone and wherein the first transparency mask further defines a four sided extended threshold zone which surrounds a transition zone, the first transparency values are below the threshold in the four sided extended threshold zone.

According to claim <NUM> the first light engine is further configured to format the first scaled and corrected data array to define an image frame and to deliver the image frame to a digital mirror device. Formatting the first scaled and corrected data array includes converting a pixel element energy value to a binary number that represents a sequence of bit planes.

In a second aspect of the disclosure, a three dimensional printing system is configured to form a three dimensional article of manufacture through a layer-by-layer process. Layers are formed by selectively adding photocure resin onto a lower face of the three dimensional article of manufacture. Layers are formed by solidifying resin proximate to and on a "composite build plane" which is a two dimensional lateral area that is addressable by the three dimensional printing system. The three dimensional printing system includes a vessel, a plurality of light engines, and a controller. The vessel is for containing photocure resin. The plurality of light engines define a corresponding plurality of build fields. The plurality of build fields collectively define a composite build plane. The plurality of build planes define one or more overlap zones, each overlap zone defined along lateral X and Y axes. The plurality of light engines are collectively configured to: (a) receive a plurality of incoming slice energy data arrays corresponding to the plurality of build fields; (b) process the plurality of incoming slice energy data arrays to provide a corresponding plurality of scaled and corrected data arrays, the processing includes applying a plurality of transparency masks to the one or more overlap zones, the plurality of transparency masks define transparency values for the light engines that vary along at least one lateral direction, the plurality of transparency masks define extended threshold zones that border transition zones, the transparency values within the extended threshold zones are less than six percent for light engines near their lateral limits; and (c) deliver optical energy to the composite build plane based upon the scaled and corrected data array to selectively cure the resin.

In one implementation the one or more overlap zones include a two field overlap zone over which two of the build fields overlap. The two field overlap zone has a major axis defined along axis X. A transparency value T(Y) for a given light engine within the two field overlap zone has a gradient GRADT(Y) along the axis Y. The two field overlap zone includes two extended threshold zones that are proximate to the edges of two build fields with a transition zone between them. In one embodiment a magnitude of GRADT(Y) within the transition zone of the two field overlap zone is at least twice a magnitude of GRADT(Y) in the extended threshold zone of the two field overlap zone. In another embodiment T(Y) is less than four percent in the extended threshold zone for one of the light engines. In yet another embodiment T(Y) is less than two percent in the extended threshold zone for one of the light engines.

In another implementation the one or more overlap zones includes a four field overlap zone over which four different build fields overlap. The four field overlap zone includes a four sided extended threshold zone that surrounds a transition zone. In one embodiment a transparency value T(X, Y) within the four field overlap zone has a gradient GRADT(X, Y) that varies in lateral axes X and Y. In another embodiment the four field overlap zone has a substantially square shape. The GRADT(X,Y) in the transition zone can have a magnitude that is at least twice the magnitude of GRADT(X,Y) in the extended threshold zone.

<FIG> is a schematic block diagram of an exemplary three dimensional printing system <NUM>. In describing the following figures, mutually perpendicular axes X, Y and Z will be used. Axes X and Y are lateral axes. In some embodiments X and Y are also horizontal axes. Axis Z is a central axis. In some embodiments Z is a vertical axis. In some embodiments the direction +Z is generally upward and the direction -Z is generally downward.

Three dimensional printing system <NUM> includes a vessel <NUM> containing photocurable resin <NUM>. Vessel <NUM> includes a transparent sheet <NUM> that defines at least a portion of a lower surface <NUM> of vessel <NUM>. A composite light engine <NUM> is disposed to project light up through the transparent sheet <NUM> to solidify the photocure resin <NUM> and to thereby form the three dimensional article of manufacture <NUM>. The three dimensional article of manufacture <NUM> is attached to a fixture <NUM>. A movement mechanism <NUM> is coupled to fixture <NUM> for translating the fixture <NUM> along the vertical axis Z.

A controller <NUM> is electrically or wirelessly coupled to the composite light engine <NUM> and the movement mechanism <NUM>. Controller <NUM> includes a processor <NUM> coupled to an information storage device <NUM>. The information storage device includes a non-transient or non-volatile storage device (not shown) that stores instructions that, when executed by the processor <NUM>, operate the movement mechanism <NUM> and/or the composite light engine <NUM>. Controller <NUM> can be contained in a single IC (integrated circuit) or multiple ICs. Controller <NUM> can be at one location or distributed among multiple locations in three dimensional printing system <NUM>. Processor <NUM> controls the composite light engine <NUM> and the movement mechanism <NUM>.

The three dimensional article of manufacture <NUM> has a lower face <NUM> that faces the transparent sheet <NUM>. Between the lower face <NUM> and the transparent sheet <NUM> is a thin layer of photocure resin <NUM>. As composite light engine <NUM> applies light energy through the transparent sheet <NUM> it polymerizes resin proximate to a "composite build plane" <NUM> which can be coincident or proximate to the lower face <NUM>.

The composite light engine <NUM> is formed from two or more individual light engines <NUM>. <FIG> depicts a composite light engine that is formed by the combination of two light engines 30A and 30B. The arrows shown illustrate that each light engine <NUM> illuminates a different portion of the build plane <NUM>. A portion of build plane <NUM> that is illuminated by one light engine <NUM> will be referred to as a "build field" <NUM> for the light engine <NUM>. According to the illustration, the build fields <NUM> for light engines 30A and 30B overlap over an "overlap zone" <NUM>.

In an exemplary embodiment the light engines <NUM> are positioned in close enough proximity whereby they are parallel to the same image plane. This allows pixel elements <NUM> (see <FIG>) generated by the two light engines <NUM> to have the same optimal lateral pitch P and lateral dimension S. In the illustrated embodiment of <FIG>, the pixel lateral dimension S is greater than the pitch P whereby pixel elements <NUM> overlap along the lateral dimensions.

The composite light engine <NUM> also includes a temperature control module <NUM>. The temperature control module <NUM> provides an optimal temperature in an environment surrounding the light engines <NUM>. The light engine <NUM> components and alignments are temperature sensitive and this is particularly important in the overlap zone <NUM>. Without the temperature regulation, the pixel sizes, alignment, and may not be uniform. In one embodiment the temperature control module <NUM> includes a temperature sensor and a heater to maintain a moderately elevated temperature environment for the light engines <NUM>.

In an alternative embodiment each of the light engines <NUM> have a separate temperature control module <NUM>. The separate temperature control modules <NUM> can be utilized to assure a consistent and optimal temperature for the light engines <NUM>.

In yet another embodiment the composite light engine <NUM> is located above the resin <NUM>. In this embodiment the fixture <NUM> would be a platform that raises and lowers within the resin <NUM>.

<FIG> depicts composite build plane <NUM> for the two light engines 30A and 30B. Light engine 30A defines build field 31A and light engine 30B defines build field 31B. Build fields 31A and 31B combine to define the composite build plane <NUM>. An overlap zone <NUM> is also shown over which build fields 31A and 31B overlap. The overlap zone <NUM> has a first edge 33A that is defined by a lateral limit of light engine 30A. The overlap zone <NUM> has a second edge 33B that is defined by a lateral limit of light engine 30B. As depicted, the edges 33A and 33B extend along axis X which is the long axis of the overlap zone <NUM>. Axis Y is perpendicular to the long axis of the overlap zone <NUM> and is a direction of overlap.

While composite build plane <NUM> and build fields 31A and 31B are shown as rectangular, in practice they may have distorted shapes. Defects introduced by imperfect optics of the light engines <NUM> may include various artifacts. Some of these are known as "barrel distortion" and "keystone effect" to name two examples. The edges 33A and 33B defined by light engines 30A and 30B may be wavy, distorted, or define an angle relative to the axis X.

Each of the build fields <NUM> define a rectangular array of pixel elements <NUM>. A single pixel element <NUM> is depicted in <FIG> as very large for illustrative purposes but it is to be understood that each build field <NUM> would have more than a million pixel elements <NUM>. The pixel elements are spaced along lateral axes X and Y by a pitch P. Each pixel element is substantially square shaped and has a lateral dimension of S. In a preferred embodiment, S > P so that pixel elements <NUM> overlap in the build fields <NUM> to some extent. This provides a smooth and uniform surface finish for three dimensional article of manufacture <NUM>. Thus, the pixel elements <NUM> are slightly out of focus. In an exemplary embodiment the pitch P is in a range of <NUM> to <NUM> microns or about <NUM> microns. The lateral pixel dimension S is in a range of about <NUM> to <NUM> microns or about <NUM> microns. Other overlapping configurations are possible with different dimensions. Also, rectangular pixels having different lengths and widths can be used. This overlapping configuration between pixel elements is beneficial for a smooth transition in the overlap zone <NUM>.

<FIG> depicts a close up view of a portion of the overlap zone <NUM> bounded by edges 33A and 33B. The overlap zone <NUM> is further divided into two extended threshold zones 34A and 34B and a transition zone <NUM>. The extended threshold zones <NUM> are defined by a worst case variations in Y of the actual edges defined by light modulators <NUM>. There is an inside boundary <NUM> of the extended threshold zone <NUM>. Between boundaries <NUM> and <NUM> is the extended threshold region width which contains all edge-related irregularities, artifacts, and variations produced by light engines <NUM>. The transition zone <NUM> is a zone over which the light engines <NUM> are ramped up and down to avoid any apparent seams in the overlap zone <NUM>.

Within the extended threshold zone 34A, the build field 31A is near the lateral limit of light engine 30A. Within the extended threshold zone 34B, the build field 31B is near the lateral limit of light engine 30B.

<FIG> is an electrical block diagram of an exemplary light engine <NUM>. Light engine <NUM> includes system processor <NUM> coupled to information storage device <NUM>, light source module <NUM>, and digital mirror device module <NUM>. The digital mirror device module <NUM> includes image scaler <NUM>, digital mirror device formatter <NUM>, and digital mirror device <NUM>. The light source module <NUM> includes light source driver <NUM> and light source <NUM>.

System processor <NUM> orchestrates operation of light engine <NUM>. System processor <NUM> is configured to receive an incoming slice energy data array that corresponds to a build field <NUM> that is illuminated by the light engine <NUM>. The incoming slice energy data array defines a two dimensional array of energy values that define optical cure energy to be applied versus position in X and Y. The pitch of the energy values in X and Y may or may not correspond to the pixel array on the spatial light modulator <NUM>. The system processor <NUM> transmits the incoming slice energy data array to the image scaler <NUM> of the digital mirror device module <NUM>.

Information storage device <NUM> can include one or more memory devices that store incoming or processed data for the system processor <NUM>. Such data can include the incoming slice energy data array.

Image scaler <NUM> processes the slice energy data array to provide one or more of correction, calibration, scaling, and transparency adjustment for the overlap zone <NUM>. Correction includes de-warping, and corrections for distortions such as barrel distortion and the keystone effect. Calibration can include compensation for light source <NUM> output and variation in an optical path length from the light engine <NUM> to the build plane <NUM>. Scaling can include remapping and frame rescaling. Remapping is the conversion of an incoming data array pitch to the pitch of a pixel array of the digital mirror device <NUM>. Frame rescaling is the scaling of the energy values from a total energy per pixel to an energy per pixel for one frame. Frame rescaling is needed if the frame period is different than a cure time. The transparency adjustment concerns energy modulation to provide correct energy values in the overlap zone <NUM>. In alternative embodiments one or more portions of correction, calibration, scaling, and transparency adjustment can be performed by controller <NUM> or in digital mirror device formatter <NUM>. Image scaler <NUM> outputs a scaled energy data array to the digital mirror device formatter <NUM>.

Digital mirror device formatter <NUM> converts the scaled energy data array to an image frame that is directly compatible with the digital mirror device <NUM>. The scaled energy data array has a scaled (for the frame period) energy value for each pixel. The digital mirror device formatter <NUM> converts each energy value into a binary number corresponding to a sequence of bit planes having a varying width or duration. The resultant data digital mirror device formatter <NUM> then sends one or more of the image frames to the digital mirror device <NUM>.

The system processor <NUM> is configured to receive switching signals from controller <NUM> and to pass the switching signals to the light source driver <NUM> of the light source module <NUM>. The light source driver <NUM> provides power to the light source <NUM>. In an exemplary embodiment light source <NUM> is a light emitting diode (LED) that emits ultraviolet (UV) light. The switching signals include an "on" signal that activates (turns on) the light source <NUM> and an "off" signal that deactivates (turns off) the light source <NUM>. In other embodiments the light source <NUM> includes one or more of a laser and a blue light emitter.

In an exemplary embodiment the light source <NUM> emits an optimal wavelength peak that is one or more of <NUM> nanometers (nm), <NUM>, about <NUM>, and/or <NUM>. These optimal wavelengths are readily absorbed by photoinitiators used in photocurable resin <NUM> thereby reducing an amount of photoinitiator required. This in turn improves polymerization efficiencies and thereby reduces blending discontinuities in the overlap zone <NUM>.

Also depicted in <FIG> is the transmission of light (thicker arrows <NUM> and <NUM>) through and from light engine <NUM>. Element <NUM> depicts the "raw" or unprocessed light emitted by the light source <NUM>. Element <NUM> depicts the pixelated light that is reflected by the digital mirror device <NUM> and to optics that in turn deliver the pixelated light to the build plane <NUM>.

Light engine <NUM> also includes an focus control system <NUM> for optimally focusing the pixel elements <NUM> on the build field <NUM>. In one embodiment the focus control system <NUM> includes a stepper motor for adjusting optics in light engine <NUM>. In a particular embodiment the focus control system <NUM> includes a sensor that senses the individual pixel element <NUM> dimension S.

<FIG> is a flowchart depicting an exemplary method <NUM> of operating a three dimensional printing system <NUM> having a plurality of light engines <NUM> that are assembled into a composite light engine <NUM>. Each light engine <NUM> illuminates a separate build field <NUM>. The build fields <NUM> partially overlap laterally in order to define the composite build field <NUM>. The lateral overlap between build fields <NUM> is an "overlap zone.

The method starts with beginning step <NUM> in which each light engine includes a transparency map. Exemplary transparency maps for the overlap of two light engines <NUM> are illustrated in <FIG>. The transparency map for a given light engine <NUM> can be stored in the light engine <NUM> or it can be stored in memory <NUM> of controller <NUM>. Steps <NUM>-<NUM> will be described for one light engine <NUM> but it is to be understanding that this process occurs in parallel for all of the light engines <NUM> that are being utilized to form an article of manufacture.

According to step <NUM>, the light engine <NUM> receives an incoming slice energy data array. According to step <NUM>, the light engine <NUM> processes the incoming slice energy data array to provide corrections, calibration, and scaling. According to step <NUM>, the light engine <NUM> processes the data array to apply a transparency map that reduces the energy values within the overlap zone. According to step <NUM> the light engine <NUM> formats the scaled energy data to provide an image frame that is compatible with the light engine. According to step <NUM> the light engine <NUM> activates the digital mirror device <NUM> with the frame data. The light engine <NUM> also activates the light source <NUM>. During step <NUM> a layer of resin <NUM> is selectively cured proximate to the build plane <NUM> and onto the lower face <NUM> of the three dimensional article of manufacture <NUM>. According to step <NUM>, the lower face is incrementally displaced upward. Steps <NUM>-<NUM> are repeated until the three dimensional article of manufacture <NUM> is fully formed.

<FIG> depicts a first embodiment of transparency maps for two overlapping light engines 30A and 30B. A transparency map plots transparency versus position along the Y axis which is approximately perpendicular to the long axis of the overlap zone <NUM>. For a given pixel element, the transparency is the percentage of the energy value to be utilized. Without a transparency map, the energy applied to the overlap zone <NUM> would be up to <NUM>% too high. Therefore the A and B maps are complementary - at a given Y value, the transparency of one is T(Y) and the other is <NUM>%-T(Y).

The overlap zone <NUM> is the region between Y-values of 33B and 33A. The edge of the build field 31B for light engine 30B is represented by the vertical line 33B. At edge 33B, the transparency TB(Y) for light engine 30B is <NUM> percent. In moving to the right, the value of TB(Y) increases and reaches <NUM>% at the edge 33A of light engine A. In moving between 33B to 33A, the sum TA(Y) + TB(Y) = <NUM>%.

The zone between 33B and 38B is called the "extended threshold zone" 34B. The extended threshold zone 34B zone receives light proximate to the edge of light engine 30B. In this extended threshold zone 34B there is a high likelihood of edge-related artifacts or geometric edge defects for light modulator 30B. For some light engines <NUM>, these defects or artifacts will substantially affect the cured thickness of a new resin layer. Therefore the transparency value TB for the edge of light modulator 30B is reduced to below a threshold value. In that vicinity, the complementary light modulator 30A does not have the edge defects and artifacts, so the accuracy of the composite cure in that zone will be much higher. According to claim <NUM>, the transparency TB in the extended threshold zone 34B proximate to the edge of a light modulator 30B is reduced to <NUM>% or less. In another embodiment it is reduced to <NUM>% or less. In yet another embodiment it is reduced to <NUM>% or less. In the illustrated embodiment of <FIG> the transparency TB is reduced by reducing a slope of TB(Y) versus Y in the extended threshold region 34B.

The zone between 38A and 33A is the extended threshold zone 34A. In extended threshold zone 34A the value of TA(Y) is reduced to below ten percent value for the same reasons as was discussed for extended threshold region 34B.

Between 38B and 38A is a "transition zone" <NUM> which is provided to provide a transition between the two light engines 38A and 38B. The slope of the transparency curves can be close to linear in much of the the transition zone <NUM>.

For T(Y) functions we can define the mathematical vector gradient of T(Y) as GRADT(Y). For the embodiment of <FIG>, and <FIG>, the gradient is substantially directed along the Y axis. The magnitude of GRADT(Y) is therefore the same as the slope of T versus Y. In an exemplary embodiment, an average magnitude of GRADT(Y) in the transition zone <NUM> will be at least twice the average magnitude of GRADT(Y) in the extended threshold zones <NUM>.

<FIG> depicts a second embodiment of transparency maps for light engines 30A and 30B. In the extended threshold zone 34B near the edge 33B of light engine 30B (between 33B and 38B on the graph), the transparency TB(Y) for modulator B is at a low fixed level. The value TB(Y) can be below <NUM>%, below <NUM>%, or below <NUM>% depending upon how much it is desired to reduce the edge artifacts or defects of light engine 30B. The transition from outside of the overlap region to the extended threshold zone is a step transition rather than a curve for edges 33A and 33B. Thus, at edge 33B, the curve of TA(Y) steps down by an amount by which the curve of TB(Y) steps down. Likewise, at edge 33A, the curve of TA(Y) steps down by an amount by which the curve of TB(Y) steps down.

At the extended threshold zone 34A near the edge 33A of light engine 30A (between 38A and 33A on the graph), the transparency TA(Y) for modulator B is at a low fixed level. Between the extended threshold zones 34A and 34B is the transition zone <NUM> (between 38B and 38A on the graph). In the transition zone, the plots of the transparency T are depicted as linearly varying.

Other possibilities can be considered. The extended threshold zones can be "stair stepped" upwardly from the edges <NUM> of the light modulators <NUM>. Smaller transparency values T can apply to Y locations that have the higher probability of a defect or artifact for a given light modulator <NUM>.

<FIG> depicts a composite build plane <NUM> for four light engines 30A, 30B, 30C, and 30D. Light engine 30A defines build field 31A, light engine 30B defines build field 31B, light engine 30C defines build field 31C, and light engine 30D defines build field 31D. As before there are overlap zones <NUM> between pairs of build fields <NUM> for respective pairs of light engines <NUM>. For the overlap of a pair of light engines, similar transparency maps as presented in <FIG> can apply.

However, with this arrangement there is a also a four field overlap zone <NUM> within which the build fields <NUM> for all four light engines <NUM> overlap. In the four field overlap zone <NUM> the transparency T(X, Y) for a given light engine <NUM> varies in along both lateral axis X and Y.

<FIG> is a more detailed view of an exemplary four field overlap zone <NUM>. The left edge of four field overlap zone <NUM> includes the edges 33B, 33D of light engines 30B and 30D. The other four edges of the four way overlap zone <NUM> indicate the respective edges <NUM> of the light engines <NUM>. The four field overlap zone <NUM> includes a four sided extended threshold zone <NUM> which surrounds a substantially square transition zone <NUM>. Edge defects and artifacts from the four light modulators <NUM> will generally be contained in the four sided extended threshold zone <NUM>.

For a given light engine <NUM>, the transparency along its edge would be reduced to at or below T(THRESHOLD). In the transition zone <NUM> the contributions of the light engines <NUM> would each vary approximately linearly away from their edges with the requirement being that for all locations, TA(X, Y) + TB(X, Y) + Tc(X, Y) + TB(X, Y) = <NUM>%. There are clearly many ways to do this, but the important aspect is to select a threshold transparency that is low enough such that the edge effects are acceptable.

This can be generalized to any number of overlapping light engines <NUM> to form a composite build plane <NUM>. For larger numbers of light engines <NUM> there will be two field overlap zones <NUM> and four field overlap zones <NUM> within which transparency mask functions T(X, Y) are used to transition between light engines <NUM> and to reduce the effects of edge artifacts and defects.

For T(X, Y) functions we can define the mathematical vector gradient of T(X, Y) as GRADT(X, Y). For a four field overlap zone the gradient is directed generally toward or away from a center <NUM> of the four field overlap zone. In an exemplary embodiment, an average magnitude of GRADT(X, Y) in the transition zone <NUM> will be at least twice the average magnitude of GRADT(X, Y) in the extended threshold zone <NUM>.

<FIG> is a flowchart depicting a startup procedure for the three dimensional printing system <NUM>. This startup procedure assures that discontinuities and artifacts will be minimized in the overlap zone <NUM>. The procedure starts with step <NUM> and the activation of the temperature control module <NUM>. The temperature control module <NUM> senses the temperature in the environment containing the light engines <NUM> and increases the temperature to an optimal level for the alignment of optics and operation of components within the composite light engine <NUM>.

According to step <NUM>, a wait time provided to give time for the composite light engine <NUM> to achieve thermal equilibrium at the optimal temperature. Optical adjustments are suspended during this wait time so that such adjustments are better maintained.

According to step <NUM> the focus control system <NUM> is operated to provide an optimal focus of the pixel elements <NUM>. In particular, the degree of focus of the pixel elements <NUM> for the different build fields is consistent across the composite build plane <NUM> so that the surface finish of the three dimensional article of manufacture <NUM> is consistent across the overlap zone <NUM>.

According to step <NUM>, a manufacturing operation begins. The method <NUM> of <FIG> includes steps that can be part of the manufacturing operation of step <NUM>.

Claim 1:
A three-dimensional printing system (<NUM>) which forms a three dimensional article of manufacture through a layer-by-layer process with layers formed by selectively curing photocure resin (<NUM>) onto a face of a three dimensional article of manufacture comprising:
a vessel (<NUM>) for containing the photocure resin (<NUM>); and
a plurality of light engines (<NUM>) including at least a first light engine (30A) and a second light engine (30B), the first light engine includes a first light modulator defining a first rectangular array of pixel elements (<NUM>) that define a first build field (31A), the second light engine (30B) includes a second light modulator defining a second rectangular array of pixel elements (<NUM>) that define a second build field (31B),
the first build field (31A) and the second build field (31B) overlap along an overlap zone (<NUM>), the first light engine (30A) is configured to:
(a) receive a first incoming slice energy data array corresponding to the first build field (31A);
(b) process the first incoming slice energy data array to provide a first scaled and corrected data array corresponding to the first rectangular array of pixel elements (<NUM>)of the first light engine (30A), the processing includes applying a first transparency mask to the first pixel elements (<NUM>) within the overlap zone (<NUM>), the first transparency mask defines a transition zone between two extended threshold zones (34A, 34B), the extended threshold zones (34A, 34B) include a first extended threshold zone (34A) that is proximate to an the edge of the first build field (31A), the first transparency mask has first transparency values that are below ten percent in the extended threshold region; and
(c) deliver optical energy to the first build field (31A) based upon the first scaled and corrected data array to selectively cure the resin,
wherein the first light engine is further configured to format the first scaled and corrected data array to define image frames and to deliver the image frames to a digital mirror device and wherein the formatting the first scaled and corrected data array includes converting a pixel element energy value to a binary number that represents a sequence of bit planes.