THREE DIMENSIONAL PRINTING SYSTEM THAT AUTOMATICALLY REMOVES PARTICLES FROM BUILD PLANE

Abstract

A three dimensional printing system includes a print engine, a fixture, and a controller. The print engine further includes a vessel, a light engine, and a movement mechanism. The vessel is for containing a photocurable resin and has a lower portion with a transparent sheet defining a lower surface of the vessel. The light engine is configured to project radiation up through the transparent sheet over a lateral build plane which defines a maximum addressable lateral range of the light engine. The fixture has a lower face that faces downwardly. The controller is configured to: (1) position the lower face of the fixture at the build plane, and (2) operate the light engine and movement mechanism to solidify a particle trapping sheet proximate to the transparent sheet and substantially spanning the build plane and to thereby trap particles that are present along the build plane.

Description

FIELD OF THE INVENTION

The present disclosure concerns an apparatus and method for fabrication of solid three dimensional (3D) articles of manufacture from radiation curable (photocurable) resins. More particularly, the present disclosure improves the quality of a three dimensional (3D) article of manufacture through the automated removal of particles from a build plane at which a photocurable resin is being selectively solidified during fabrication.

BACKGROUND

Three dimensional (3D) printers are in rapidly increasing use. One class of 3D printers includes stereolithography printers having a general principle of operation including the selective curing and hardening of radiation curable (photocurable) liquid resins. A typical stereolithography system includes a containment vessel holding the photocurable resin, a movement mechanism coupled to a support surface, and a controllable light engine. The stereolithography system forms a three dimensional (3D) article of manufacture by selectively curing layers of the photocurable resin.

In one system embodiment the vessel includes a transparent sheet that forms part of a lower surface of the vessel. The support surface is positioned above and in facing relation with the transparent sheet. The following steps take place: (1) The movement mechanism positions the support surface whereby a thin layer of the photocurable resin resides between the support surface and the transparent sheet. (2) The light engine transmits pixelated light up through the transparent sheet to selectively cure a layer of the photocurable resin proximate to and onto the support surface. The focus of the pixelated light curing is referred to a “build plane.” (3) The movement mechanism then incrementally raises the support surface. Steps (2) and (3) are repeated to form a three dimensional (3D) article of manufacture having a lower face in facing relation with the transparent sheet.

One difficulty is an accumulation of particles on the transparent sheet and/or within the photocurable resin. The particles are formed from the photocurable resin and are the result of portions of a fabricated article that may break off and settle into the resin. A required gap between the build plane and the transparent sheet is very small. The lower face of the support surface or three dimensional article of manufacture must therefore be positioned very close (a small fraction of a millimeter typically) to the transparent sheet in order to perform step (2) above. During this positioning, the accumulated particles can become compressed between the transparent sheet and the lower face. These particles can be compressed and can damage the transparent sheet and become embedded in the three dimensional article of manufacture, possibly creating a defect. Damage to the transparent sheet will affect its light transmissive properties and therefore impact the quality of all subsequent fabrication. The transparent sheet is also expensive and disruptive to replace. What is needed is a system and method to prevent the particle accumulation and facilitate their automated removal.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram schematic of an exemplary embodiment of a three dimensional printing system for forming a three dimensional article of manufacture.

FIG. 2A is a block diagram schematic depicting a print engine and a first embodiment of a configuration whereby the print engine traps deleterious particles.

FIG. 2B is a block diagram schematic depicting a print engine and a second embodiment of a configuration whereby the print engine traps deleterious particles.

FIG. 2C is a block diagram schematic depicting a print engine and a third embodiment of a configuration whereby the print engine traps deleterious particles.

FIG. 3 is a plan view schematic of an exemplary fixture for supporting a particle trapping sheet.

FIG. 4 is a sectional view taken from AA′ of FIG. 3 with an exemplary particle trapping sheet included.

FIG. 5 is a schematic plan view of an exemplary particle trapping sheet.

FIG. 5A is a cross sectional view of an exemplary particle trapping sheet taken through BB′ of FIG. 5. This particle trapping sheet embodiment corresponds to FIG. 2A.

FIG. 5B is a cross sectional view of an exemplary particle trapping sheet taken through BB′ of FIG. 5. This particle trapping sheet embodiment corresponds to FIG. 2B.

FIG. 6A is a flowchart depicting a first embodiment of a process for operating printing system 2 which corresponds to FIG. 2A.

FIG. 6B is a flowchart depicting a second embodiment of a process for operating printing system 2 which corresponds to FIG. 2B.

FIG. 6C is a flowchart depicting a third embodiment of a process for operating printing system 2 which corresponds to FIG. 2C.

SUMMARY

In a first aspect of the disclosure, a three dimensional printing system includes a print engine, a fixture, and a controller. The print engine further includes a vessel, a light engine, and a movement mechanism. The vessel is for containing a photocurable resin and has a lower portion with a transparent sheet defining at least part of a lower surface of the vessel. The light engine is configured to project radiation up through the transparent sheet over a lateral build plane which defines a maximum addressable lateral range of the light engine. The fixture has a lower face that faces downwardly. The controller is configured to: (1) position the lower face of the fixture at the build plane which is at an operating distance from the transparent sheet, and (2) operate the light engine and movement mechanism to solidify a particle trapping sheet proximate to the transparent sheet and substantially spanning the build plane and to thereby trap particles that are present along the build plane.

In one implementation the controller includes a processor coupled to an information storage device. The information storage device includes a non-transient or non-volatile storage device storing instructions that, when executed by the processor, control the light engine and the movement mechanism. The controller can be at one location or distributed among a plurality of locations in the printing system. In a first embodiment the controller is entirely within the print engine which operates as a standalone three dimensional printer. In a second embodiment the controller includes a control server that controls the overall printing system and a print engine controller that is located within the print engine. In the second embodiment the three dimensional printing system includes various modules including one or more of a fixture cassette, a post processing station, an inspection station, and a robotic transport mechanism for transporting the fixture between the modules.

In another implementation the fixture has a lower end defining a recessed surface from which a plurality of projections extend downwardly from the recessed surface to distal tips. The particle trapping sheet defines an upper surface coupled to the distal tips and an opposed lower surface. The opposed lower surface further defines a plurality of tapering features. The controller is further configured to operate the light engine and the movement mechanism to form a three dimensional article of manufacture that is coupled to the tapering features. The tapering features minimize a surface area of connection between the three dimensional article of manufacture and the particle trapping sheet in order to facilitate the later physical separation of the particle trapping sheet from the three dimensional article of manufacture.

In yet another implementation the printing system includes a transport mechanism and the controller is further configured to: (3) unload the fixture from the print engine, (4) load a new fixture into the printing system, and (5) operate the light engine and the movement mechanism to form a three dimensional article of manufacture. The fixture used in steps (1) and (2) is a disposable fixture that is used exclusively for forming the particle trapping sheet and removing particles. The disposable fixture has a lower end defining a recessed surface from which a plurality of projections extend downwardly from the recessed surface to distal tips. An upper surface of the particle trapping sheet is formed onto the distal tips. The fixture used in steps (3) to (5) is a reusable fixture that is used entirely for forming three dimensional articles of manufacture.

In a further implementation the controller is configured to operate the light engine and the movement mechanism to form a three dimensional article of manufacture onto the fixture before forming the particle trapping sheet. The particle trapping sheet includes a plurality of upwardly extending extensions that form a framework for supporting the particle trapping sheet onto the three dimensional article of manufacture.

In a yet further implementation the particle trapping sheet has an upper surface and an opposed lower surface. The particle trapping sheet defines at least one opening passing from the upper surface to the opposed lower surface to provide flow of photocurable resin therethrough when the movement mechanism is raising or lowering the fixture. Preferably the at least one opening includes an array or plurality of openings that are laterally distributed across the particle trapping sheet.

In another implementation the particle trapping sheet includes a thin parallelepiped portion covering most or essentially all of the lateral area of the build plane. The thickness is minimized so as to minimize a required amount of resin for fabricating the particle trapping sheet. The particle trapping sheet also includes a framework of ribs or thickened portions to provide mechanical support for the thin parallelepiped portion. In some embodiments the particle trapping sheet includes tapering features and/or extensions for coupling to a three dimensional article of manufacture. The coupling occurs at a narrowed distal tip. The tapering features and/or extensions can be laterally aligned with the ribs so as to improve structural integrity. The thin parallelepiped portion can define openings therethrough to allow a flow of photocurable resin therethrough to facilitate vertical movement of the fixture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram schematic of an exemplary embodiment of a three dimensional printing system 2 for forming three dimensional articles of manufacture. Three dimensional printing system 2 includes fixture cassettes 4, print engines 6, post-processing stations 8, inspection stations 10, a transport mechanism 12, and a control server 14.

A fixture cassette 4 stores a stack of fixtures that are utilized in print engine 6, post-process stations 8, and inspection station 10. In some embodiments there are different fixtures stored in different fixture cassettes 4. One stack of fixtures can be disposable and utilized for a particle removal process. Another stack of fixtures can be reusable and utilized for the formation and transport of a three dimensional article of manufacture.

An embodiment of print engine 6 will be described in further detail with respect to FIGS. 2A, 2B, and 2C. Post process stations 8 are for added processes for a three dimensional article of manufacture after it is formed. Post processing stations can include rinsing and cleaning stations, drying stations, and curing stations, to name some examples. Inspection stations 10 can be utilized to inspect for defects and/or to measure critical dimensions for a three dimensional article of manufacture after fabrication and post processing is complete.

Transport mechanism 12 is configured to pick up a fixture from a fixture cassette 4 and to transfer it to a print engine 6. Transport mechanism 12 also transfers the fixture to the post process stations 8 and to the inspection stations 10. In one embodiment, the transport mechanism includes a robotic gripper that can move in three axes.

FIG. 2A is a schematic block diagram depicting print engine 6 and a first embodiment through which print engine 6 removes deleterious particles. In this and other 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.

Print engine 6 includes a vessel 16 containing photocurable resin 18. Vessel 16 includes a transparent sheet 20 that defines at least a portion of a lower surface 22 of vessel 16. A light engine 24 is disposed to project light up through the transparent sheet 20 to selectively cure the photocurable resin 18 during formation of a three dimensional article of manufacture 26. Light engine 24 includes light source 28 and spatial light modulator 30.

Between a lower face 32 of the three dimensional article of manufacture 26 and the transparent sheet 20 is a thin layer 34 of photocurable resin 18. As the light engine 24 operates, a portion of the thin layer 34 of photocurable resin 18 is cured and solidified at and proximate to a build plane 36. Build plane 36 defines a lateral extent (along X and Y) of a layer of photocure resin that the light engine 24 is capable of curing when forming the three dimensional article of manufacture 26.

Print engine 6 also includes a vertical movement mechanism 38 coupled to a fixture 40. Fixture 40 is for supporting the three dimensional article of manufacture 26. Fixture 40 includes a lower end 42 having an upwardly recessed surface 44 and projections 46 that extend downwardly from the recessed surface 44.

Print engine 6 includes print engine controller 48 that is under control of control server 14 and is coupled to light engine 24 and to vertical movement mechanism 38. In the illustrated embodiment, the print engine controller 48 controls the light engine 24 and the movement mechanism 38 to form a particle trapping sheet 50 before forming the three dimensional article of manufacture 26. The particle trapping sheet 50 is first formed at and proximate to the build plane 36 and just above the transparent sheet 20. During formation of the particle trapping sheet 50 the deleterious particulates are “bound up” in the particle trapping sheet 50 so that they are removed from the vicinity of the transparent sheet 20 to prevent build-up of particles and subsequent damage. The lateral extent of the particle trapping sheet 50 is preferably substantially the entire build plane 36.

The particle trapping sheet 50 includes tapering features 52 that taper between the particle trapping sheet 50 and the three dimensional article of manufacture 26. These tapering feature 52 facilitate removal of the particle trapping sheet 50 from the three dimensional article of manufacture 26 after processing is complete.

FIG. 2B is a schematic block diagram depicting print engine 6 and a second embodiment through which print engine 6 removes deleterious particles. In comparing FIGS. 2A and 2B, like reference numerals indicate like elements. The discussion for FIG. 2B will be limited to those features that necessarily make it different than FIG. 2A.

In the illustrated embodiment of FIG. 2B, the print engine controller 48 controls the light engine 24 and the movement mechanism 38 to form a three dimensional article of manufacture 26 before forming a particle trapping sheet 50. The particle trapping sheet 50 includes extensions 54 that form a framework for coupling the particle trapping sheet 50 to the three dimensional article of manufacture 26. As with FIG. 2A, the particle trapping sheet 50 preferably covers the entire build plane 36 of light engine 24.

FIG. 2C is a schematic block diagram depicting print engine 6 and a third embodiment through which print engine 6 removes deleterious particles. In comparing FIGS. 2A, 2B, and 2C, like reference numerals indicate like elements. The discussion for FIG. 2C will be limited to those features that necessarily make it different than FIGS. 2A and 2C.

In the illustrated embodiment of FIG. 2C, the fixture 40 is a disposable fixture 40 that is used entirely for forming the particle trapping sheet 50 to remove the deleterious particles. Other than being disposable, the fixture 40 is similar to the fixture 40 illustrated with respect to FIG. 2A and includes the upwardly recessed surface 44 from which the projections 46 extend downwardly.

FIG. 3 is a plan view schematic of fixture 40 looking upwardly in the +Z direction. The fixture 40 is shown having a recessed surface 44 from which projections 46 extend in the downward −Z direction. While the illustrated embodiment depicts nine projections 46 it is to be understood that any number of projections 46 can be employed. The use of closely spaced projections 46 can allow a reduction in the thickness and rigidity of the particle trapping sheet 50 because an unsupported distance is thereby reduced. The fixture 40 also includes openings 56 for allowing the photocurable resin 18 to pass through the fixture 40 as it is raised and lowered in the vessel 16.

FIG. 4 is a cross-sectional view of fixture 40 taken through AA′ of FIG. 3. FIG. 4 also includes the particle trapping sheet 50 which has been formed onto the projections 46 of the fixture 40. The projections 46 taper in downward −Z direction toward a distal end 58. Having a distal end 58 with a smaller cross sectional area reduces the impact of the projections 46 upon particles that are proximate to the transparent sheet 20.

FIG. 5 is a schematic plan view of an exemplary particle trapping sheet 50. FIG. 5A is a cross section of a first embodiment of the particle trapping sheet 50 that corresponds to the embodiment depicted in FIG. 2A. The particle trapping sheet 50 includes a thin parallelepiped portion 60 covering most or essentially all of a lateral area of the build plane 36. Minimizing the thickness of the thin parallelepiped portion 60 minimizes an amount of photocurable resin required to fabricate the particle trapping sheet 50. The particle trapping sheet 50 also includes thicker sections or ribs 62 that form a frame for supporting the thin parallelepiped portion 60. The particle trapping sheet 50 also includes tapering features 52 for attachment to the three dimensional article of manufacture 26. The tapering geometry of the tapering features 52 minimizes a lateral area of contact between the particle trapping sheet 50 and the three dimensional article of manufacture 26 to facilitate their later separation. The tapering features 52 are preferably laterally aligned with ribs 62 to improve structural integrity. The thin parallelepiped portion 60 also defines openings 64 that allow the flow of the photocurable resin 18 as the particle trapping sheet 50 is raised or lowered in the vessel 16. In this embodiment the particle trapping sheet 50 is attached to the fixture 40 at an upper side and to the three dimensional article of manufacture at a lower side defined by the tapering features 52 as in FIG. 2A.

While only a few openings 64 are shown, it is to be understood that a large number of such openings 64 can be defined. The openings can be angled or stepped whereby particles are trapped at the lateral positions of the openings 64. With a large number of openings 64, they can have a relatively small lateral dimensions to further enhance particle trapping in their vicinity.

FIG. 5B is a cross section of a second embodiment of the particle trapping sheet 50 that corresponds to the embodiment depicted in FIG. 2B. In comparing the embodiment of FIGS. 5A and 5B, like element numbers corresponding to like features. Therefore this discussion will focus on differences. The illustrated particle trapping sheet 50 includes extensions 54 for coupling the particle trapping sheet 50 to a lower side of the three dimensional article of manufacture 26. The extensions 54 may vary greatly in a vertical extent in Z according to a geometry of the three dimensional article of manufacture 26. Distal ends 66 of the extensions 54 are of a minimal cross sectional area to facilitate the separation of the particle trapping sheet 50 from the three dimensional article of manufacture 26. Preferably the extensions 54 are laterally aligned with ribs 62 to improve structural integrity.

FIG. 6A is a flowchart depicting a process 70 for operating printing system 2 to fabricate a three dimensional article of manufacture 26. All steps of this process are executed by control server 14 and print engine controller 48 that control portions of printing system 2 and print engine 6. Process 70 corresponds to the description of FIG. 2A.

According to step 72, the transport mechanism 12 retrieves a fixture 40 from a fixture cassette 4 and loads it into a print engine 6. The fixture 40 is an embodiment similar to that discussed with respect to FIG. 2A, FIG. 3, and/or FIG. 4. Upon loading the fixture 40 into print engine 6, the movement mechanism 38 can engage and vertically position the fixture 40.

According to step 74, the movement mechanism 38 lowers and positions the fixture 40 whereby the distal ends 58 of projections 46 are positioned at build plane 36. Build plane 36 is at an operating distance from the transparent sheet 20.

According to step 76, the print engine controller 48 operates the light engine 24 and the vertical movement mechanism 38 to form a particle trapping sheet 50 as is illustrated in FIG. 2A, FIG. 4, or FIG. 5A. The particle trapping sheet 50 preferably spans essentially the entire build plane 36 and is coupled to all of the projections 46. Formation of the particle trapping sheet traps loose particles that are primarily solidified photocurable resin. Also as part of step 76, the connecting features 52 are formed that taper downwardly.

According to step 78, the print engine controller 48 operates the light engine 24 and the vertical movement mechanism 38 to form a three dimensional article of manufacture 26 that couples to the connecting features 52. A lateral cross sectional area over which the connecting features 52 couple to the three dimensional article of manufacture 26 is preferably minimized to facilitate later separation.

According to step 79, the transport mechanism unloads the fixture 40 from the print engine 6 and additional processes are performed. These additional processes can include post processing, inspection, and removal of the particle trapping sheet 50 from the three dimensional article of manufacture 26. In one embodiment the transport mechanism 12 sequentially transfers the fixture 40 to different post process stations 8 and inspection stations 10. When the particle trapping sheet 50 is removed it separates along the lateral area between the connecting features 52 and the three dimensional article of manufacture 26.

In an alternative embodiment the print engine 6 is a standalone unit and steps 72 and 79 are performed manually. This includes manual loading and unloading of fixture 40 as well as cleaning, drying, UV curing, inspection, and removal of the particle trapping sheet 50.

FIG. 6B is a flowchart depicting a process 80 for operating printing system 2 to fabricate a three dimensional article of manufacture 26. All steps of this process are executed by control server 14 and print engine controller 48 that control portions of printing system 2 and print engine 6. Process 80 corresponds to the description of FIG. 2B.

According to step 82, the transport mechanism 12 retrieves a fixture 40 from a fixture cassette 4 and loads it into a print engine 6. The fixture 40 has a lower face 45 that faces downwardly.

According to step 84, the movement mechanism lowers and positions the lower face 45 of fixture 40 at the build plane 36. The build plane 36 is at an operating distance from the transparent sheet 20. According to step 86, the print engine controller 48 operates the light engine 24 and the vertical movement mechanism 38 to form a three dimensional article of manufacture 26.

According to step 88, the print engine controller 48 operates the light engine 24 and the vertical movement mechanism 38 to form a particle trapping sheet 50 as is illustrated in FIG. 2B or FIG. 5B. The particle trapping sheet 50 preferably spans the entire build plane 36. The particle trapping sheet 50 is coupled to the three dimensional article of manufacture 26 via extensions 54. The extensions 54 form a framework for properly supporting the particle trapping sheet 50 in the vessel 24.

According to step 89, the transport mechanism unloads the fixture 40 from the print engine 6 and additional processes are performed. These additional processes can include post processing, inspection, and removal of the particle trapping sheet 50 from the three dimensional article of manufacture 26. In one embodiment the transport mechanism 12 sequentially transfers the fixture 40 to different post process stations 8 and inspection stations 10. When the particle trapping sheet 50 is removed it separates along an interface between the distal ends 66 of extensions 54 and the three dimensional article of manufacture 26.

In an alternative embodiment the print engine 6 is a standalone unit and steps 82 and 89 are performed manually. This includes manual loading and unloading of fixture 40 as well as cleaning, drying, UV curing, inspection, and removal of the particle trapping sheet 50.

FIG. 6C is a flowchart depicting a process 90 for operating printing system 2 to fabricate a three dimensional article of manufacture 26. All steps of this process are executed by control server 14 and print engine controller 48 that control portions of printing system 2 and print engine 6. Process 90 corresponds to the description of FIG. 2C.

According to step 92, the transport mechanism 12 retrieves a disposable fixture 40 from a fixture cassette and loads it into a print engine 6. The fixture can be an embodiment that is similar to that discussed with respect to FIG. 2C, FIG. 3, or FIG. 4. Upon loading the fixture 40 into print engine 6, the movement mechanism 38 can engage and vertically position the fixture 40.

According to step 94, the movement mechanism 38 lowers and positions the fixture 40 whereby the distal ends 58 of projections 46 are positioned at build plane 36. Build plane 36 is at an operating distance from the transparent sheet 20.

According to step 96, the print engine controller 48 operates the light engine 24 and the vertical movement mechanism 38 to form a particle trapping sheet 50 as is illustrated in FIG. 2C. The particle trapping sheet 50 preferably spans essentially the entire build plane 36 and is coupled to all of the projections 46. Formation of the particle trapping sheet traps loose particles that are primarily solidified photocurable resin.

According to step 98, the transport mechanism unloads the disposable fixture 40 from the print engine 6. According to step 100, the transport mechanism loads a new fixture 40 into the print engine 6. According to step 102, the print engine controller 48 operates the light engine 24 and the vertical movement mechanism 38 to form a three dimensional article of manufacture 26.

According to step 104, the transport mechanism unloads the fixture 40 from the print engine 6 and additional processes are performed. These additional processes can include post processing, and inspection. In one embodiment the transport mechanism 12 sequentially transfers the fixture 40 to different post process stations 8 and inspection stations 10.

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.

Claims

1. A three dimensional printing system comprising: a print engine including: a vessel for containing a photocurable resin and having a lower portion with a transparent sheet;a light engine configured to project radiation up through the transparent sheet over a build plane defining a maximum addressable lateral range of the light engine; anda movement mechanism; anda fixture coupled to the movement mechanism with a lower face; anda controller configured to: (1) position the lower face of the fixture at an operating distance from the transparent sheet; and(2) operate the light engine and movement mechanism to solidify a particle trapping sheet proximate to the transparent sheet and substantially spanning the build plane and to thereby trap particles that are present along the build plane.

2. The three dimensional printing system of claim 1 wherein a lower end of the fixture defines a recessed surface and a plurality of projections extending downwardly from the recessed surface to distal tips, the particle trapping sheet is formed onto the distal tips.

3. The three dimensional printing system of claim 2 wherein the particle trapping sheet includes an upper surface coupled to the distal tips and an opposed lower surface, the controller is further configured to operate the light engine and movement mechanism to form a three dimensional article of manufacture onto the opposed lower surface.

4. The three dimensional printing system of claim 3 wherein the opposed lower surface includes a plurality of tapering features that couple the three dimensional article of manufacture to the opposed lower surface whereby the three dimensional article of manufacture can be separated from the tapering features along a minimal surface area.

5. The three dimensional printing system of claim 2 wherein the printing system includes a transport mechanism and the controller is further configured to: (3) unload the fixture from the print engine; (4) load a new fixture into the printing system; and (5) operate the light engine and the movement mechanism to form a three dimensional article of manufacture.

6. The three dimensional printing system of claim 1 wherein the controller is configured to operate the light engine and the movement mechanism to form a three dimensional article of manufacture between step (1) and step (2).

7. The three dimensional printing system of claim 6 wherein the particle trapping sheet includes a plurality of upwardly extending extensions that form a framework for supporting the particle trapping sheet onto the three dimensional article of manufacture.

8. The three dimensional printing system of claim 1 wherein the particle trapping sheet includes at least one opening passing from an upper surface to an opposed lower surface to provide flow of photocurable resin therethrough when the movement mechanism is raising or lowering the fixture.

9. The three dimensional printing system of claim 1 wherein the particle trapping sheet includes a thin parallelepiped portion covering most of the lateral area of the build plane, the particle trapping sheet includes a framework of ribs that provide mechanical support for the thinner portion.

10. A method of operating a three dimensional printing system for forming a three dimensional article of manufacture, the three dimensional printing system including a resin vessel containing photocurable resin and having a lower portion with a transparent sheet, a light engine configured to project radiation up through the transparent sheet over a build plane defining a maximum addressable lateral range of the light engine, a movement mechanism, a fixture coupled to the movement mechanism with a lower face, and a controller, the method including: (1) positioning the lower face of the fixture at an operating distance from the transparent sheet; and(2) operating the light engine and movement mechanism to solidify a particle trapping sheet proximate to the transparent sheet and substantially spanning the build plane to thereby trap particles that are present along the build plane.

11. The method of claim 10 wherein a lower end of the fixture defines a recessed surface and a plurality of projections extending downwardly from the recessed surface to distal tips and the particle trapping sheet is formed onto the distal tips.

12. The method of claim 11 wherein the particle trapping sheet includes an upper surface coupled to the distal tips and an opposed lower surface, the method further comprising operating the light engine and movement mechanism to form a three dimensional article of manufacture onto the opposed lower surface.

13. The method of claim 12 wherein the opposed lower surface includes a plurality of tapering features that couple the three dimensional article of manufacture to the opposed lower surface whereby the three dimensional article of manufacture can be separated from the tapering features along a minimal surface area.

14. The method of claim 11 wherein the printing system includes a transport mechanism and the method further comprises: (3) unload the fixture from the print engine; (4) load a new fixture into the printing system; and (5) operate the light engine and the movement mechanism to form a three dimensional article of manufacture.

15. The method of claim 10 further comprising operating the light engine and the movement mechanism to form a three dimensional article of manufacture between step (1) and step (2).

16. The method of claim 15 wherein the particle trapping sheet includes a plurality of upwardly extending extensions that form a framework for supporting the particle trapping sheet onto the three dimensional article of manufacture.

17. The method of claim 10 wherein the particle trapping sheet includes at least one opening passing from an upper surface to an opposed lower surface to provide flow of photocurable resin therethrough when the movement mechanism is raising or lowering the fixture.

18. The method of claim 10 wherein the particle trapping sheet includes a thin parallelepiped portion covering most of the lateral area of the build plane, the particle trapping sheet includes a framework of ribs that provide mechanical support for the thinner portion.