CA2086157A1

CA2086157A1 - Stereolithographic apparatus and method of use

Info

Publication number: CA2086157A1
Application number: CA2086157A
Authority: CA
Inventors: Larry D. Mitcham; William E. Nelson
Original assignee: Individual
Current assignee: Texas Instruments Inc
Priority date: 1991-12-30
Filing date: 1992-12-23
Publication date: 1993-07-01
Also published as: EP0676275B1; EP0549993A1; DE69218572D1; DE69231229T2; JPH0639928A; EP0676275A1; KR100252458B1; TW214584B; US5247180A; DE69231229D1; EP0549993B1; DE69218572T2

Abstract

STEREOLITHOGRAPHIC
APPARATUS AND METHOD OF USE

ABSTRACT OF THE DISCLOSURE

A stereolithographic apparatus (10) is disclosed comprising a vat (12), a working surface in the vat (16), an elevating mechanism (18) for controlling the level of liquid (14) within the vat relative to the working surface (18), an illumination source for emitting radiation, and an area array deformable mirror device.
The illumination source emits radiation which is operable to harden a stereolithographic liquid (14), while the deformable mirror device is operable to reflect the incident radiation onto the surface of the liquid (14).
The deformable mirror device can harden an entire lamina of liquid in one brief exposure interval increasing throughout without sacrificing resolution.

Description

TI-16311 ~I~O L~1 ~ 7 PATENT APPLICATION
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STEREOLITHOGRAPHIC APPARATUS AND
METHOD OF USE

TEcXNICAL FIELD OF THE INV~NTION
This invention relates in general to electro-optical devices, and, more particularly, to a stereolithographic apparatus and method of use.

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BACKGROUN~ OF THE INVENTION
Stereolithography is a process by which three dimensional objects ar~ fabricated from thin layers of hardened or cured liquid polymers. The liquid polymers or resins are selectively hardened by an intense light source of suitable wave length. Typically, an ultraviolet (" W "), argon-ion, or other type of laser is used to harden the liquid polymer. The particular laser is directed to a thin film of the polymer by an x-y scanner interpreting, typically, computer-aided design ("CAD") data. The CAD data mathematically represents the shape of the object to be produced as a series of sequential thin layers of laminas, typically 1/lOOth of an inch in thickness. The object may thereby be produced by curing portions of a film of resin that correspond to the first layer of the object, by coating the hardened layer with a uniform thin liquid film, and by curing portions of the second film that correspond to the next lamina of the object. This process is repeated until each lamina of the model has been reproduced as a layer of hardened polymer. The model produced by ~tereolithography may be used for testing and evaluation of engin--ring designs, ~or tooling purposos and for low volume manufacturing application~.
Known stereolithographic process devices and methods are limited by at least two characteristics. First, the use of an x-y scanner limits the speed by which a laser beam may be scanned on to a film of liquid re in to approximately 55 inches per second. This speed, coupled with the high vertical resolution of the process, results in lengthy production time and low product output.
Second, the use of a partlcular laser as the illumination sourc~ limit~ the type of liquid resin that may be used in the system. Each resin has an individual reaction to various wavelengths of electromagnetic radiation.

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Typically, each resin may be hardened by only one t,vpe of laser. This results in little or no ability to change the resin composition without expensive hardware changes.
Also, not all wavelengths of radiation may be produced as laser light. This preclude~ the use of certain resins because no laser exists to cure them.
Therefore, a need has arisen for a stereolithographic apparatus which allows for high product output and which is compatible with a wider range stereolithographic resins.

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SUMMARY OF THE INVENTION
In accordanc~ with the present invention, a stereolithographic apparatus is provided which substantially eliminates or reduces disadvantages and problems associated with prior stereolithographic systems.
A stereolithographic apparatus is disclosed comprising a vat for receiving a stereolithographic liquid, a working surface within the vat, an elevating mechanism for controlling the level of the liquid in the vat, an illumination source for emitting radiation, and a deformable mirror device. The illumination source emits radiation which is operable to harden the liquid, while the deformable mirror device is operablé to reflect the incident radiation onto the surface of the liquid.
The first technical advantage of the disclosed invention is its speed. The plurality of mirrors which comprise the deformable mirror device allow an entire layer of resin to be hardened in one exposure interval.
Thi~ technique allows much greater throughput.
A second technical advantage o~ the device is its ~lexibility. Almost any illumination source may be used with the deformable mirror device. The illumination source can thare~ore be tailored to the particular resin so used and may, in ~act, be an inexpensive incandescent light bulb.
A third technical advantage of the disclosed invention is its cost. De~ormable mirror devices are currently available in mass produced quantities at costs ~ar below that o~ an x-y laser scanner.
Another technical advantage o~ the invention is its suitability to large model ~abrication. Multiple exposure heads may be combined to cure a large layer of a ~' liguid or a single exposure head may be positioned to :, . . . . . .

TI-16311 2 0 8 6 ~ 5 7 PATENT AppLIcATIoN

cure the same large area in a few exposure intervals.
Resolution will meanwhile remain high.

2086~57 BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which:
FIGUREs la through le illustrate one sequence of steps for producing a model using the stereolithographic process;
FIGURE 2 is a partially perspective, partially schematic illustration of an exposure head containing one embodiment of the disclosed invention for use in the process depicted in FIGUREs la through le:
FIGURE 3 depicts perspectively an area array deformable mirror device useful in the exposure head of FIGURE 2;
FIGURE 4 depicts schematically how the exposure head of FIGURE 2 may be combined with similar exposure heads to increase possible model size; and FIGURE 5 depicts perspectively how the exposure head of FIGURE 2 may be articulated to cure a larger film 9iZQ .

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DETAI~:D DESCRIPTION OF THE INVENTION
The preferred embodiment o~ the present invention and its advantages are best understood by referring to FIGUREs 1 through 4 of the drawings, like numerals being used for like and corresponding parts Or the various drawings FIGUREs la through le illustrate one sequence of steps for producing a model using the stereolithographic process (a) Stereolithographic apparatus ("SLA") 10 comprises vat 12 for receiving a stereolithographic liquid 14, a working sur~ace 16, an elevator 18 for controlling the level of the liguid relative to the work~ng surtace 16, and an exposure head 20 ror curing selected portions of the resin as will be described more ully below The stereolithographic liguid may be a - resin or a polymer, as is w ll known to those skilled in ~ the art SLA 10 may also comprise a liquid applicator 22 ''' rOr ensuring a unifor~ liguid thickness at each modeling , 20 stage In op-ration, a thin tilm ot liguid is applied to working ~urtac- 16 by, ~or instance, raising elevator 18 within vat 12 Elevator 18 will cause liquid 14 to rise through p-rrorations 24 to ~orm a thin ~ilm on working surtac- 16 Exposure head 20 then cures selected portion~ ot th- liguid rilm by directing electromagnetic radiation th-r-to Exposure head 20 is controlled by circuitry (shown in FIGURE 2) that interprets data Or the ob~oct to bQ so modeled The data represents the object a~ a ~eri-~ o thin sQguential layers or laminas which, wh-n stack d on top o~ each oth-r ~orm the complete ob~-ct Typically, computer-aided deQign (nCADn) data may b- most asily converted into sequential layers or ~, 3,'~ laminag 0~ th- model to b- produc-d ~,."
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(b) Elevator 18 again rises to cause liquid 14 to cover the previously cured layer 26 ("workpiece") resting on working surface 26 with a second film of liquid. ~his second layer of liquid will cover both the cured and uncured portions of the first layer. Applicator 22 may also spray a small amount of liquid onto workpiece 26 to ensure uniform film coverage of the workpiece 26. Each film is approximately one l/lOOth of an inch thick.
(c) Exposure head 26 cures the second layer of liquid applied in FIGURE lb as described in connection with FIGURE la.
(d) The steps in FIGUREs la through lc are then repeated until the entire part 28 has been produced.
(e) Complete part 28 may then be removed from SL~
10. Under certain conditions using certain liquids, it : may be necessary to cure part 28 in an oven (not shown) ; prior to its use.
An SLA, similar to that depicted in FIGUREs la through le, may be purchased from 3D Systems, Inc. of Valencia, California or ~rom Quadrax Laser Technologie~, Inc. of Portsmouth, Rhode Island. The 3D Systems' SLA
employs a HeCd laser with a wavelength of 325 nm. The 3D
Sy~tem differ~ from the process de~crib2d above. It ~ucce~sively lowers the working ~urface below the surface of liguid instead of raising the liquid relative to the working surface. There, the ~ormed object is slowly submerged as it is produced on the sur~ace of the liquid.
The Quadrax Laser Technologies' SLA uses an argon-ion visible light laser in the process described in connection with FIGUREs la-lc. Other SLA designers use ultraviolet (" W ") lasers to harden stereolithographic liguids.
FIGU~E 2 is a partially perspective, partially schematic illustration o~ an exposure head 20 containing one embodiment of the disclosed invention for use in the 20861~7 process depicted in FIGUREs la through le. The exposure head 20 comprises an illumination source 30 an area array deformable mirror device ("DMD") 32, two lenses 34 and 36, and control cir¢uitry 38. Illumination source 30 emits radiation that is operable to harden a particular SLA liquid. Lens 34 more uni~ormly illuminates DMD 32 than would otherwise occur without it. Lens 36 focuses and magnifies the light reflected of~ o~ DMD 32 onto the working surface 16 (shown in FIGUREs la-le). DMD 32 is an electro-optical device containing a regular n x m array of mirrors manufactured by Texas Instruments, Inc.
of Dallas, Texas. Each mirror may be electronically controlled to reflect incident radiation along one of a plurality o~ optical pathways. In the preferred embodiment, DMD 32 comprises a matrix o~ bistable mirrors, i.e., there are two optical pathways for each mirror. Illumination source 30, DMD 32, and lenses 34 and 36 are positioned such that light impinging upon DMD
32 from illumination source 30 may be focused onto a thin ~ilm o~ SLA reain ir, and only i~, one o~ the two optical pathways is selected. The optical pathway of radiation emitted ~rom illumination source 30 is depicted by the convsrging and diverging dashed lines. Each bistable mirror on DMD 32 is controlled by circuitry 38 which ; 25 interprets data rrOm a processor (not shown). Circuitry 38 may be located elsewhere or may be integrated completely with a standalone processor. Illumination source 30 may be tailored to the individual stereolithographic liquid used in the SLA process and might be an ordinary tungsten-halogen incandescent light bulb or any number o~ visible or non-visible light ; lasers.
FIGURE 3 depicts perspectively an area array de~ormable mirror device 32 illustratod in the exposure ~ 35 head 20 of FIGURE 2. DMD 32 comprises a body 40 having a :

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planar active surface 42 and a number of electrical pins 44. The active surface 42 of DMD 32 may contain an n x m matrix of individually addressable bistable mirrors. Each mirror is tvpically a square or diamond having sides of 12 to 20 microns. This small size allows a sinqle DMD having a footprint of approximately 2 square inches to have over 2 million individually addressable ; mirrors in, for instance, a 1920 x 1080 matrix. This small mirror size allows exposure head 20 (shown in FIGURE 2) to cure a 4 x 8 square inch area in a single exposure interval with the same resolution as achieved by prior x-y scanner/laser exposure head combinations.
Typically, these prior exposure heads achieve resolutions of + 0.005 inches. In such a case, lens 36 of FIGU~E 2 would also magnify the image of DMD 32 by a factor of 4x-6x.
FIGURE 4 depicts how multiple exposure heads 20 may be combined or "tiled" to cover an area of, for instance, 8 x 16 square inch. This allows the user to maintain the same high degrea o~ resolution descr$bed in connection with FIGURE 3. In such a tiled con~iguration, each exposure head 20 cures one quadrant o~ the film resin.
;ach guadrant exposes a 4 x 8 square inch area. Any number o~ exposure heads 20 can be combined to increase maximum model size.
FIGURE S depicts how a singlQ exposure head 20 may be mounted on a positioning device 46 with freedom of movement in two dimension~. The single exposure head 20 may thereby be made to cure a lamina o~ resin larger in size than the pro~ected image Or DMD 32 (FIGUREs 2 and 3). This allow~ the user to maintain the same high degree o~ resolution described in connection with FIGURE
3. Positioning devices used in lithographic processes are known in the art to have resolutions comparable with the SLA process. These positioning devices are used to .. ,., ~ .

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align photomasks with silicon wafers in the production of devices such as integrated circuits.
Although the present invention has been described in detail, it should be understood tbat various changes, S substitutions and operations can be made hereto without departing from the spirit and scope of the invention as defined by tbe appended claims.

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Claims

WHAT IS CLAIMED IS:

1. A stereolithographic apparatus comprising:
a vat for receiving a stereolithographic liquid;
a working surface within the vat;
an elevating mechanism for controlling the level of the liquid in the vat relative to the working surface;
and at least one exposure head, each exposure head comprising an illumination source for emitting radiation, the radiation operable to harden the liquid, and an area array deformable mirror device responsive to applied signals for selectively reflecting the radiation to form an image on the surface of the liquid.

2. The stereolithographic apparatus of Claim 1 further comprising a lens for magnifying the image of the area array deformable mirror device.

3. The stereolithographic system of Claim 1 further comprising a positioner for moving the exposure head in two dimensions.

4. The stereolithographic apparatus of Claim 3 further comprising a lens for magnifying the image of the area array deformable mirror device.

5. The stereolithographic apparatus of Claim 1 wherein the elevator raises the liquid relative to the working surface.

6. The stereolithographic apparatus of Claim 1 wherein the elevator lowers the working surface into the liquid.

7. The stereolithographic apparatus of Claim 1 wherein the liquid is a resin containing a photoactive agent.

8. The stereolithographic exposure head of Claim 1 wherein the liquid is a polymer containing a photoactive agent.

9. A stereolithographic exposure head for use with a stereolithographic apparatus, the exposure head comprising:
a plurality of mirrors individually responsive to input signals, the mirrors operable to reflect incident radiation along a plurality of optical pathways, the mirrors forming a n x m matrix;
an illumination source for emitting radiation incident upon the mirrors, the radiation operable to harden a stereolithographic liquid; and control circuitry responsive to input data operable to select one of the plurality of pathways along which each of the mirrors will reflect incident radiation to form an image.

10. The stsreolithographic exposure head of Claim 9 wherein said plurality of pathways comprise two pathways.

11. The stereolithographic exposure head of Claim 9 further comprising a lens for magnifying the image of the plurality of mirrors.

12. The stereolithographic exposure head of Claim 9 further comprising a positioner for moving the head in two dimensions.

13. A method of forming a model of cured resin comprising the steps of:
applying a thin film of stereolithographic liquid to a surface:
illuminating a plurality of deformable mirrors with radiation operable to cure the liquid resin: and deflecting certain of the mirrors such that a portion of the radiation is directed to the film of liquid, the directed radiation curing a portion of the resin, the portion of the resin forming at least part of a lamina of the model.

14. The method of Claim 13 further comprising the step of sequentially repeating the applying, illuminating and deflecting steps until the sequence of laminas forms the model.

15. The method of Claim 13 further comprising the steps of:
moving the plurality of deformable mirrors with respect to the thin film; and curing the uncured portions of the lamina of the model.

16. The method of Claim 15 further comprising the step of sequentially repeating the applying, illuminating, deflecting, moving and curing steps until the sequence of lamines forms the model.