Patent Publication Number: US-2023150205-A1

Title: Scalable and fast three dimensional printing system

Description:
FIELD OF THE INVENTION 
     The present disclosure concerns an apparatus and method for the digital fabrication of three dimensional articles of manufacture through the solidification of liquid photon-curable (photocure) resins. More particularly, the present disclosure concerns an advantageous method of controlling a light engine that is scalable from one to multiple light engines in a three dimensional printing system. 
     BACKGROUND 
     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 one layer at a time. In some embodiments the light engine includes a light source that illuminates a spatial light modulator. 
     Some of these light engines originate from projectors that are used for displaying images and video. When these light engines are used for three dimensional printers, certain inefficiencies result because these light engines have electronics optimized for the display of full motion video. There is a need to redesign the electronics to be optimal for three dimensional printing. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is a schematic block diagram of a three dimensional printing system. 
         FIG.  2    is a diagram representing a build plane for a single light engine. 
         FIG.  3    is an electrical block diagram of an exemplary light engine. 
         FIG.  4    is a timing diagram of an exemplary sequence of bit planes for one image frame. 
         FIG.  5    is a flowchart of an exemplary method for operating a three dimensional printing system. 
         FIG.  6    is a timing diagram to illustrate an exemplary operational sequence for a three dimensional printing system. 
         FIG.  7    is a schematic block diagram of a three dimensional printing system having two or more light engines. 
         FIG.  8    is a diagram representing a composite build plane that is a composite of four partially overlapping build fields of four light engines. 
         FIG.  9    is an electrical block diagram depicting four exemplary light engines. 
         FIG.  10    is a flowchart of an exemplary method for operating a three dimensional printing system having more than one light engine. 
     
    
    
     SUMMARY 
     In a first aspect of the invention, a three dimensional printing system includes a vessel for containing photocure resin, a fixture for supporting a three dimensional article of manufacture, a movement mechanism for incrementally displacing the fixture, a light engine, and a controller that is electrically or wirelessly coupled to the movement mechanism and the light engine. The vessel includes a lower surface having a transparent sheet in contact with the photocure resin. The three dimensional article of manufacture has a lower face that is in facing relation with the transparent sheet. The light engine is configured to apply pixelated light through the sheet and to the lower face in order to solidify thin slices of the photocure resin proximate to a build plane. The build plane defines a lateral area that the light engine is capable of curing. The controller activates the light engine to perform the following steps: (a) receive a first incoming slice energy data array; (b) process the first incoming slice energy data array to define a first image frame; (c) receive an on signal; (d) activate the first light source in response to the on signal; (e) repeatedly send the first defined image frame to the first spatial light modulator during a defined cure time for a layer of the resin; (f) receive an off signal; (g) deactivate the first light source in response to the off signal; and (h) repeat steps (a) - (g) until the three dimensional article of manufacture is formed. 
     In one implementation the light engine includes a system processor coupled to a digital mirror device module and a light source module. In one embodiment the digital mirror device module includes an image scaler, a digital mirror device formatter, and a digital mirror device. The image scaler processes the received first slice image to do one or more of correction, calibration, scaling, and stitching and to provide a scaled energy data array. The digital mirror device formatter converts the scaled energy data array into an image frame compatible with the digital mirror device. The digital mirror device includes a digital mirror array which includes at least one million individually addressable mirror elements. The light source module includes a light source driver coupled to a light source. 
     In another implementation the first image frame defines a sequence of bit planes for individual pixel elements of the first spatial light modulator. An energy value delivered for each pixel element is determined by which bit planes are in an “on” state. Thus, the first image frame is an array of binary numbers with bit positions in a binary number corresponding with a bit plane. 
     In yet another implementation the first light source is activated simultaneously with a “temporal leading edge” of one of the defined image frames. The temporal leading edge of an image frame is the left hand side of an image frame in a time domain - it is when the image frame begins to affect operation of the spatial light modulator. Thus the first light source is turned on simultaneously with the activation of the first spatial light modulator with one of the defined image frames. 
     In a further implementation an integer number of the defined image frames are received by the first spatial light modulator between the activation and the deactivation of the light source. 
     In a yet further implementation a non-integer number of the defined image frames are received by the spatial light modulator between the activation and the deactivation of the light source. 
     In another implementation the three dimensional printing system includes a second light engine including a second light source that illuminates a second spatial light modulator, the second light engine configured to: (a) receive a second incoming slice energy data array, the second incoming slice energy data array is complementary with the first incoming slice energy data array to allow the first and second light engines to have different but partially overlapping build fields; (b) process the incoming slice energy data array to define a second image frame; (c) receive the on signal from the first light engine; (d) activate the second light source in response to the on signal; (e) repeatedly send the second defined image frame to the second spatial light modulator during the defined cure time; (f) receive the off signal from the first light engine; (g) deactivate the second light source in response to the off signal; and (h) repeat steps (a) - (g) until the three dimensional article of manufacture is formed. 
     In yet another implementation the first light engine sends the incoming slice energy data array along a first data path to a digital mirror device module and sends the on and off signals along a second data path to a first light source module. 
     In a second aspect of the invention, a three dimensional printing system includes a vessel for containing photocure resin, a fixture for supporting a three dimensional article of manufacture, a movement mechanism for incrementally displacing the fixture, a light engine, and a controller that is electrically or wirelessly coupled to the movement mechanism and the light engine. The vessel includes a lower surface having a transparent sheet in contact with the photocure resin. The three dimensional article of manufacture has a lower face that is in facing relation with the transparent sheet. The light engine is configured to apply pixelated light through the sheet and to the lower face in order to solidify thin slices of the photocure resin proximate to a build plane. The build plane defines an area that the light engine is capable of curing. The light engine includes a light source, a spatial light modulator that is illuminated by the light source, a system processor for receiving an incoming slice energy data array and light source switching signals; an image scaler that receives and processes the incoming slice energy data array and outputs a scaled energy data array after one or more of correcting, calibrating, scaling, and stitching of the incoming slice energy data array; a digital mirror device formatter that receives and converts the scaled energy data into an image frame and repeatedly sends the image frame to the spatial light modulator; and a light source driver that receives the light source switching signals and turns the light source on for a cure time duration that overlaps with the repeated image frame. In a first embodiment turning the light source on is synchronized with the start of one of the image frames. In a second embodiment an integer number of the image frames are received by the spatial light modulator while the light source is on. In a third embodiment a non-integer number of the image frames are received by the spatial light modulator while the light source is on. 
     In one implementation the light engine is a plurality of light engines configured to cooperatively generate a composite build plane, the plurality of light engines receiving different but complementary incoming slice energy data arrays. The plurality of light engines includes a master light engine and at least one subsidiary light engine, the master light engine receives the switching signals and routes them to the at least one subsidiary light engine. 
     In a third aspect of the invention a three dimensional printing system includes a vessel for containing photocure resin, a fixture for supporting a three dimensional article of manufacture, a movement mechanism for incrementally displacing the fixture, a plurality of light engines, and a controller that is electrically or wirelessly coupled to the movement mechanism and the plurality of light engines. The vessel includes a lower surface having a transparent sheet in contact with the photocure resin. The three dimensional article of manufacture has a lower face that is in facing relation with the transparent sheet. The light engines are configured to apply pixelated light through the sheet and to the lower face in order to solidify thin slices of the photocure resin proximate to a composite build plane. The composite build plane defines an area that the light engine is capable of curing. The plurality of light engines include a master light engine and at least one subsidiary light engine. The master light engine includes a system processor that is configured to: (a) receive an incoming slice energy data array specific to the master light engine; (b) receive light source switching signals; (c) route the incoming slice energy data array specific to the master light engine to a digital mirror device module that is within the master light engine; (d) apply the switching signals to a light source module that is within the master light engine; and (e) route the switching signals to the at least one subsidiary light engine. 
     In one implementation the composite build plane is defined by a plurality of partially overlapping build fields. Each build field is individually formed by one of the plurality of light engines. 
     In another implementation the digital mirror device module includes an image scaler, a digital mirror device formatter, and a digital mirror device. The image scaler processes the incoming slice energy data array to define a scaled energy data array and the digital mirror device formatter processes the scaled energy data array to define an image frame. The switching signals include an on signal and an off signal. A cure time is defined by a time duration between the on signal and the off signal. The digital mirror device formatter is configured to sequentially send an integer number of image frames to the digital mirror device during the cure time. 
     In yet another implementation the digital mirror device module includes an image scaler, a digital mirror device formatter, and a digital mirror device. The image scaler processes the incoming slice energy data array to define a scaled energy data array and the digital mirror device formatter processes the scaled energy data array to define an image frame. The switching signals include an on signal and an off signal. A cure time is defined by a time duration between the on signal and the off signal. The digital mirror device formatter is configured to sequentially send a non-integer number of image frames to the digital mirror device during the cure time. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG.  1    is a schematic block diagram of an exemplary three dimensional printing system  2 . In describing this 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  2  includes a vessel  4  containing photocurable resin  6 . Vessel  4  includes a transparent sheet  8  that defines at least a portion of a lower surface  9  of vessel  4 . A light engine  10  is disposed to project light up through the transparent sheet  8  to solidify the photocure resin  6  and to thereby form the three dimensional article of manufacture  12 . The three dimensional article of manufacture  12  is attached to a fixture  14 . A movement mechanism  16  is coupled to fixture  14  for translating the fixture  14  along the vertical axis Z. 
     A controller  18  is electrically or wirelessly coupled to the light engine  10  and the movement mechanism  16 . Controller  18  includes a processor (not shown) coupled to an information storage device (not shown). The information storage device includes a non-transient or non-volatile storage device (not shown) that stores instructions that, when executed by the controller  18  can be contained in a single IC (integrated circuit) or multiple ICs. Controller  18  can be at one location or distributed among multiple locations in three dimensional printing system  2 . Processor controls the light engine  10  and the movement mechanism  16 . 
     The three dimensional article of manufacture  12  has a lower face  20  that faces the transparent sheet  8 . Between the lower face  20  and the transparent sheet  8  is a thin layer of resin  22 . As light engine  10  applies light energy through the transparent sheet  8  it polymerizes resin proximate to a “build plane”  24  which can be coincident or proximate to the lower face  20 . 
     The light engine  10  includes a light source  26 , a spatial light modulator  28 , and other devices (see  FIG.  3   ). Light source  26  illuminates spatial light modulator  28  which generates a pixelated image that is projected up through the transparent film  8 . In an exemplary embodiment, light source  26  includes one or more light emitting diodes and/or lasers. The light source  26  can generate blue or ultraviolet light for curing layers of resin  6 . In an exemplary embodiment, the spatial light modulator  28  is a digital mirror device  28  that can include one million or more controllable mirror elements. Each mirror element (not shown) has at least two positions including an “on” position and an “off” position. In the “on” position it transmits light to illuminate a “pixel element”  25  of the build plane  24 . In an “off” position it leaves that pixel  25  element dark. ( FIG.  2    illustrates the build plane  24 ). 
     Controller  18  controls the light engine  10  to selectively harden a new layer of resin onto the lower face  20 . After each layer of resin is hardened, controller  18  controls movement mechanism  16  to raise the three dimensional article of manufacture  12  to allow for replenishment of the thin layer of resin  22 . 
       FIG.  2    depicts the lateral build plane  24  for a fixed value of Z. The lateral build plane  24  is defined a lateral extent of the light engine in X and Y for the fixed value of Z. The lateral build plane  24  has a center  30  and lateral edges  32 . Lateral edges  32  define the lateral extent of the lateral build plane  24 . While the lateral build plane  24  is shown as rectangular it is to be understood that distortions and other artifacts may render the lateral build plane  24  to have nonlinear lateral edges  32  and/or a non-rectangular shape. 
     Within the lateral build plane  24  are pixel elements  25 . Each pixel element  25  is defined by the spatial light modulator  28 . In an exemplary embodiment, each pixel element  25  corresponds to a mirror element of the spatial light modulator  28 .  FIG.  2    depicts build plane  20  as having far fewer pixel elements  25  than a real system for illustrative simplicity. In practice, build plane  20  can have one million or more individual pixel elements  25 . 
       FIG.  3    is an electrical block diagram depicting light engine  10  which includes system processor  34  that is coupled to information storage device  36 , light source module  35 , and digital mirror device module  37 . Light source module  35  includes light source driver  42  and light source  26 . Digital mirror device module  37  includes image scaler  38 , digital mirror device formatter  40 , and digital mirror device  28 . 
     System processor  34  orchestrates most or all of the major functions of the light engine  10 . System processor  34  is configured to receive an incoming slice energy data array from controller  18  that defines at least a portion of a new layer of the article of manufacture  12 . 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 spacing of the energy values in X and Y may or may not correspond to the pixel array on the spatial light modulator  28 . The system processor  34  transmits the incoming slice energy data array to the image scaler  38  of the digital mirror device module  37 . 
     Information storage device  36  can include one or more memory devices that store incoming or processed data for the system processor  34 . Such data can include the incoming slice energy data array. 
     Image scaler  38  processes the incoming image slice data to provide one or more of correction, calibration, scaling, and stitching. Correction includes de-warping, and corrections for distortions such as barrel distortion and the keystone effect. Calibration can include compensation for light source  26  output and variation in an optical path length from the light engine  10  to the build plane  24 . Scaling can include remapping and frame rescaling. Remapping is the conversion of the incoming data array spacing of energy values to the spacing of the pixel array of the spatial light modulator  28 . Frame rescaling is the scaling of the energy values from a total energy per pixel element  25  to an energy value per pixel element for one frame. For example, if it takes  10  frames to provide a required cure time with light source  26 , then the energy values would be reduced by 90% for each frame. Finally, stitching adjustments are performed when more than one light engine is used to define a build plane  24 . In some alternative embodiments, part of the correction, calibration, scaling, and stitching can be performed by the controller before the data is passed to the digital mirror device module  37  or by the digital mirror device formatter  40 . Then the image scaler  38  may not need to perform all of these functions. After these functions are performed, the image scaler  38  passes resultant scaled energy data array to the spatial light modulator formatter  40 . 
     Digital mirror device formatter  40  formats the scaled energy data array to a format compatible with the digital mirror device  28 . The scaled energy data array has a scaled (for the frame period) energy value for each pixel. The digital mirror device formatter  40  converts each scaled energy value into a binary number corresponding to a sequence of bit planes. A sequence of bit planes is depicted in  FIG.  4   . Each bit plane is a time duration during which a pixel element is either on or off. When a binary value of 1 is sent for a given bit plane, the pixel element is then turned on during the bit plane time duration. When a binary value of 0 is sent for a given bit plane, the pixel element is turned off for the bit plane time duration.  FIG.  4    illustrates a 6 bit image frame. The bit planes include a least significant bit (LSB) or bit zero that is the narrowest time duration defined for a mirror element to be on or off. The next most significant bit (bit one) has twice the time duration of bit zero. This repeats up to the most significant bit (MSB). While  FIG.  4    depicts a six bit frame for simplicity, other systems may utilize 8 bit frames or more or less bits. A binary number of 101010 would have bit zero turned on, bit two turned off, but three turned on, and so on for a six bit frame. The binary number thus defines the frame data for a given pixel element. The digital mirror device formatter  40  sends the image frame data for the build plane  24  to the digital mirror device  28  which sequentially activates and deactivates the individual mirror elements accordingly. 
     The system processor  34  is configured to receive switching signals from controller  18  and to pass the switching signals to the light source driver  42  of the light source module  35 . For embodiments having more than one light engine  10 , the system processor  34  can also send the switching signals to other light engines  10 . The light source driver  42  provides power to the light source  26 . In an exemplary embodiment light source  26  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  26  and an “off” signal that deactivates (turns off) the light source  26 . In other embodiments the light source  26  includes one or more of a laser and a blue light emitter. 
     Also depicted in  FIG.  3    is the transmission of light (thicker gray arrows  44  and  46 ) through the three dimensional printing system  2 . Element  44  depicts the “raw” or unprocessed light emitted by the light source  26 . Element  46  depicts the pixelated light that is reflected by the digital mirror device  28  and to optics that in turn deliver the pixelated light to the build plane  24 . 
       FIG.  5    is a flowchart and  FIG.  6    is a timing diagram depicting an exemplary method  48  of operation for the three dimensional printing system  2 . According to step  50 , the system processor  34  receives incoming slice N energy data array (from controller  18 ) to solidify an N th  layer of the three dimensional article of manufacture  12 . System processor  34  delivers the incoming slice N energy data array to the image scaler  38 . Step  50  is depicted as the top graph in  FIG.  6   . Receipt of slice N and slice N+1 image data is represented as the up arrows. 
     According to step  52  the image scaler  38  processes the slice N image data to provide one or more of correction, calibration, scaling, and stitching. As an alternative, one or more of these functions can occur in controller  18  or in the digital mirror device formatter  40 . One advantage over performing such functions in controller  18  is speed because the components of the digital mirror device module  37  has dedicated hardware that can perform these functions very rapidly. The image scaler  38  then delivers a scaled energy data array to digital mirror device formatter  40 . 
     According to step  54  the digital mirror device formatter  40  converts the scaled energy data array to an image frame having representation of bit planes (as depicted in  FIG.  4    for one image frame). According to step  56  the formatted image frame data is repeatedly sent to the digital mirror device  28 . The middle graph of  FIG.  6    depicts six image frames being sent to the digital mirror device  28  during a time duration that contains slice N. In general M frames are contained within a slice time duration and can vary from one frame to any number that are sufficient to properly solidify a layer of resin  6 . 
     In some embodiments each frame has a time duration of 1/30 th  of a second. A total cure time can be one or two seconds. A one second cure time would require 30 of such image frames. A two second cure time would require 60 image frames. In this exemplary embodiment one image frame may contain 8 bit planes. In other embodiments one image frame can contain 12, 16, 24, or more bit planes depending upon a desired energy resolution. 
     Other cure times are possible depending on the cure speed of the resin  6  being used. Other frame time durations are possible such as 1/50 th  of a second, 1/60 th  of a second, and so on. The number of bit planes during a frame can also vary depending upon the desired resolution. 
     Concurrent to the repeated sending of frames (step  56 ) steps  58  to  62  are performed. According to step  58  the system processor  34  receives an “on” switching signal from controller  18 . As part of step  58  system processor  34  delivers the on signal to the light source driver  42  which then activates or turns on the light source  26 . 
     According to step  60  the light source remains on during a cure time. During step  60  the digital mirror device formatter  40  continues to send image frames to the digital mirror device  28 . 
     According to step  62  the system processor receives an “off” switching signal. As part of step  62  the system processor delivers the off signal to the light source driver  42  which then deactivates or turns off the light source  26 . 
     In some embodiments the on and off signals are sent by the system processor to one or more subsidiary light engines  10 . A subsidiary light engine  10  would have an architecture similar to that of discussed with respect to  FIG.  3   . Such an arrangement will be discussed with respect to  FIGS.  7 - 10   . 
     The lower timing diagram of  FIG.  6    depicts steps  58 - 62 . Arrows up indicate the light source  26  being turned on and the arrows down indicate the light source  26  being turned off. The horizontal axes of  FIG.  6    indicate exemplary relative timing of receiving slice data, delivery of frames, and activation and deactivation of the light source  26 . Various embodiments are possible. 
     In some embodiments activation of the light source  26  can be synchronized with the beginning of a frame. In other embodiments they are not synchronized but the light source on and off occurs sometime during the delivery of the frames. 
     In some embodiments an integer number of frames are delivered by the digital mirror device formatter  40  to the digital mirror device  28  during the cure time of step  60 . In other embodiments a non-integer number of frames are delivered by the digital mirror device formatter  40  to the digital mirror device  28  during the cure time of step  60 . 
     According to step  64  controller  18  activates movement mechanism  16  to incrementally move the 3D article of manufacture  12  upward. According to step  66  the value of N increments to N + 1 so that the N+1 slice image data can be received by the system processor  34 . The sequence  48  repeats until the 3D article of manufacture  12  is fully formed. 
       FIG.  7    is a schematic block diagram of an exemplary three dimensional printing system  2  which is similar to that depicted in  FIG.  1    except for the use of more than one light engine  10 . This enables the imaging of laterally larger 3D articles of manufacturing  12  without a reduction in resolution. Otherwise like element numbers indicate like or similar elements. 
     The light engines  10  (light engine A and light engine B) have a zone of overlap  68  over which both light engines  10  provide energy to the same portion of the build plane  24 . While two light engines  10  are shown, it is to be understood that the three dimensional printing system  2  can include one or more light engines  10  and can include any number of light engines  10 . 
       FIG.  8    depicts a composite build plane  24  that is formed by a composite of four light engines A, B, C, and D. The different types of dashed outlines indicate overlapping build fields within the composite build plane  24  that are addressed by the light engines  10 . For example, the upper left build field that is bounded by the dotted rectangle A is the field of build plane  24  that is addressed by light engine A. Each of the build fields has a non-overlapping field portion and an overlapping field portion. The overlapping field portion overlaps with one or more of the other build fields. The indicated field portion  68  is an area of build plane  24  over which build field A overlaps with build field field B. Indicated build field portion  70  is an area of build plane  24  over which all four build fields A, B, C, and D overlap. The composite build plane  24  has an outer boundary  32  that is substantially rectangular but may have a different shape due to various distortions such as a keystone effect and/or barrel distortion. Also, each of build fields A, B, C, and D may be likewise distorted in shape. 
       FIG.  9    is an electrical block diagram depicting four exemplary light engines  10  according to capital letters A, B, C, and D. Refer to  FIG.  3    to see additional details applicable to these light engines  10 . The light engines  10  includes a master light engine A and three subsidiary light engines B, C, and D. The distinction between master and subsidiary light engines  10  is related to the routing of signals and controlling and timing of a cure cycle. The master light engine A delivers the switching signals to the subsidiary light engines B, C, and D whereby a cure cycle for all four light engines  10  can be simultaneous. 
     A light engine  10  includes a system processor  34  coupled to a light source module  35  and a digital mirror device module  37  (see  FIG.  3    for more details). The system processor  34  is configured to receive data from controller  18  for each new layer of photocure resin to be selectively cured onto the article of manufacture  12 . Data transmitted from controller  18  to light engines  10  includes incoming slice energy data arrays and switching signals. 
     The incoming slice energy data arrays are indicated in  FIG.  9    by “A DATA”, “B DATA”, “C DATA”, and “D DATA” for light engines A, B, C, and D respectively. The four data arrays define a slice for the composite build plane  24  illustrated in  FIG.  8   . As can be seen, the controller  18  provides incoming slice energy data arrays directly to the individual light engines  10 . The data arrays are complementary and they individually include a non-overlapping array and an overlapping data array for a particular build field. 
     The switching signals are indicated by “SWITCH” in  FIG.  9   . The switching signals are received by the system processor  34  of master light engine A which delivers the switching signals the light source module  35  within master light engine A. System processor  34  of master light engine A also delivers the switching signals to the subsidiary light engines B, C, and D. The system processor within a subsidiary light engine  10  then sends the switching signals to the light source module  35  which operates in the same way as the light source module  35  of the master light engine  10 . Having one master system processor  34  to receive and deliver the switching signals to subsidiary system processors  34  allows for synchronized and simultaneous operation of the light engines  10  which increases the speed of a three dimensional printing system  2  having multiple light engines  10 . 
       FIG.  10    is a flowchart depicting a method  78  of operation of a three dimensional printing system  2  having more than one light engine  10 . According to step  80  the controller  18  sends a slice N energy data array to each of light engines A, B, C, and D. Slice N data refers to data that defines an N th  layer of a three dimensional article of manufacture  12 . The data received by a particular light engine  10  (A, B, C, or D) is different than the other light engines since it defines one build field which has a portion that overlaps the three other build fields and a non-overlapping portion that is unique to that light engine. 
     According to step  82  the individual light engines  10  separately process the incoming slice N energy data arrays using image scaler  38 . Step  82  is similar to step  52  of  FIG.  5    except that step  82  includes separate processing for the light engines  10 . According to step  84  the data from step  82  is formatted for the individual spatial light modulators  28 . According to step  86  image frames are repeatedly sent to light modulators  28 . For a given light engine  10 , this is the same as step  56  of  FIG.  5    and the middle graph of  FIG.  6   . 
     According to step  88  the controller  18  sends an on pulse to the system processor  34  of master light engine A. According to step  90  the system processor  34  of master light engine A routes the on signal to the system processors  34  for the subsidiary light engines B, C, and D. Also as part of step  90  the system processors  34  activate the light sources  26  for all of the light engines A, B, C, and D simultaneously. According to step  92  the light sources  26  are on for a cure time for the layer N. According to step  94  the system processor  34  of master light engine A receives an “off” signal. According to step  96  the system processor  34  of light source A routes the off signal to the system processors  34  for the subsidiary light sources B, C, and D. Also as part of step  96  the system processors  34  deactivate the light sources  26  for all of the light engines A, B, C, and D simultaneously. 
     During the cure time  92  a plurality of the image frames are sent to the digital mirror devices  28  for the individual light engines  10 . The timing diagram depicted in  FIG.  6    depicts a similar sequence if  50  is replaced by step  80 , step  56  is replaced by step  86 , and steps  58 - 62  are replaced with steps  88 - 96 . As before the cure time  92  can contain an integer or non-integer number of image frames. The start of the cure time can be synchronized or not synchronized to the start of an image frame. 
     According to step  98  the movement mechanism  16  moves the three dimensionally article of manufacture  12  incrementally upward. According to step 100 the N increments to N+1 for the next slice image data to be delivered from controller  18  to the light engines  10 . Steps  80  to  100  can be repeated until the three dimensional article of manufacture  12  is completed. 
     The specific embodiments and applications thereof described above are for illustrative purposes only and do not preclude modifications and variations encompassed by the scope of the following claims. For example, while  FIGS.  8 - 10    are described for four light engines  10 , the technique of the disclosure can be applied to any number of light engines  10 .