Apparatus and method for production of three-dimensional models by spatial light modulator

• US 6,051,179 A
• Filed: 03/18/1998
• Issued: 04/18/2000
• Est. Priority Date: 03/19/1997
• Status: Expired due to Fees

• Current Assignee: Gulf Filtration Systems Inc. (Desktop Metal, Inc.), William R. Hagenau
• Original Assignee: Replicator Systems, Inc.
• Inventors: Hagenau, William R.
• Primary Examiner(s): DAVIS, ROBERT B
• Application Number:
  US09/040,829
• Time in Patent Office: 762 Days
• Field of Search: 264/401, 425/174.4
• US Class Current: 264/401
• CPC Class Codes: B29C 64/129 characterised by the energy source therefor, e.g. by global irradiation combined with a mask
• CPC Class Codes: B33Y 10/00 Processes of additive manufacturing
• CPC Class Codes: B33Y 30/00 Apparatus for additive manufacturing; Details thereof or accessories therefor
• CPC Class Codes: B33Y 50/02 for controlling or regulating additive manufacturing processes

Abstract

An apparatus and the method of its operation for rapid prototyping of a three-dimensional object which includes a radiant energy source of a wide beam of radiant energy of suitable intensity and wavelength for curing a layer of photo-curable resin contained in an open vat, a spatial light modulator (SLM) having an array of pixel elements which are individually digitally controllable by a computer, for modulating the radiant energy beam projected from the radiant energy source on a pixel by pixel basis, to form a series of time sequential images of the cross-sectional laminae of the object, an optical system for focusing each image formed by the SLM, one at a time, onto successive layers of photo-curable resin for predetermined exposure times to thereby form stacked laminae of cured resin, each lamina of cured resin being in the shape of a different one of the cross-sectional laminae, and a piston support for lowering each lamina of cured resin after it is formed by the SLM and for depositing a layer of resin corresponding to the thickness of one cross sectional lamina of the three-dimensional object before the step of projecting a new image by the SLM. The SLM, the piston support for lowering, and the optical system operate repeatedly and sequentially until a complete copy of the object is thereby produced.

Claims

1. An improved three-dimensional object producing apparatus of the type for irradiating a liquid surface of a vat of liquid photo-curable resin to form a succession of cured resin layers corresponding to successive cross-sectional laminae of a three-dimensional object, and incrementally lowering the cured resin layers below the liquid surface as they are formed to build up a three-dimensional copy of the object, wherein the improvement comprises:

a radiant energy source of a wide beam of radiant energy of suitable intensity and wavelength for curing a layer of the photo-curable resin;

a spatial light modulator (SLM) having an array of pixel elements which are individually controllable, for modulating the radiant energy beam projected from the radiant energy source on a pixel-by-pixel basis, to form a series of time sequential images of the cross-sectional laminae of the object;

optical means for focusing each image formed by the SLM, one at a time, onto successive layers of photo-curable resin for predetermined exposure times to thereby form stacked laminae of cured resin, each lamina of cured resin being in the shape of a different one of the cross-sectional laminae; and

means for positioning each lamina of cured resin after it is formed by the SLM below the liquid surface corresponding to the thickness of one cross-sectional lamina of the three-dimensional object before the projection of a new image by the SLM to thereby flow a layer of photo-curable liquid resin to cover the lamina of cured resin;

wherein the SLM, the means for lowering, and the optical means operate repeatedly and sequentially until a complete copy of the object is thereby produced; and

wherein certain pixels'"'"' states are repeatedly toggled ON and OFF during the exposure so that during a given exposure period the pixels are ON a predetermined percentage of the time and OFF the remaining percentage of the time.

2. A three-dimensional object producing apparatus according to claim 1, wherein the pixel elements are individually digitally addressable.

3. A three-dimensional object producing apparatus according to claim 1, wherein the SLM is comprised of an array of micromirrors on a semiconductor memory chip.

4. A three-dimensional object producing apparatus according to claim 3, wherein the array of micromirrors is 800×

600 micromirrors or larger.

5. A three-dimensional object producing apparatus according to claim 1, wherein the SLM is comprised of an array of micromirrors with reflective aluminum surfaces.

6. A three-dimensional object producing apparatus according to claim 1, wherein the optical means focusses radiant energy from each pixel of the SLM on a top layer of resin to create individual pixel resin segments, and some pixel resin segments are deliberately underexposed, leaving them in a partially uncured state that is not completely solidified, so that when a subsequent photo-curable resin layer is applied, the pixel resin segment aligned above a pixel resin segment which is in a partially uncured state is exposed for a longer period to expose the aligned pixel resin segments of both the current and previous resin layers until they are solidified, whereby a pixel resin segment that is exposed and solidified through a succeeding layer acts as a peg that binds two layers together, resulting in an interlocking of layers to avoid delaminating.

7. A three-dimensional object producing apparatus according to claim 1, wherein the optical means focusses radiant energy, and the focus is adjusted by means of a zoom motor.

8. A three-dimensional object producing apparatus according to claim 7, wherein the zoom motor is controlled by the computer to adjust the build area size and resolution.

9. A three-dimensional object producing apparatus according to claim 1, wherein the optical means filters light of wavelengths other than those required for photopolymerization.

10. A three-dimensional object producing apparatus according to claim 1, wherein the optical means collimates the radiation source.

11. A three-dimensional object producing apparatus according to claim 1, wherein the optical means polarizes the radiation source.

12. A three-dimensional object producing apparatus according to claim 1, further comprising:

control means for controlling the SLM, the optical means and the means for lowering, the control means including;

a three-dimensional shape information memory for storing at least part of three-dimensional shape data defining the three-dimensional object to be formed;

a computer for generating cross-sectional patterns and programmed with a computer aided design (CAD) software program, the computer analyzing the three-dimensional shape data stored in the shape information memory, and mathematically slicing the solid model into layers of programmed thickness of Z height, where Z is the direction of lowering, to thereby produce a series of cross-sectional images of laminae;

means for connecting the control means to the SLM, the optical means and the means for lowering.

22. A three-dimensional object producing apparatus according to claim 12, wherein the computer overlays a map of a pixel layout on the SLM and compares this overlay to the cross-sectional image of a lamina and determines which pixels must be turned ON and which pixels must be turned OFF in order to project the accurate cross-sectional image of the lamina.

23. A three-dimensional object producing apparatus according to claim 12, further comprising:

pixel toggle means controlled by the computer for repeatedly toggling ON and OFF certain pixels so that during a given exposure period for curing a lamina of resin, the pixels are ON a predetermined percentage of the time and OFF the remaining percentage of the time.

24. A three-dimensional object producing apparatus according to claim 23, wherein the pixel toggle means uses pulse width modulation (PWM) to achieve pixel toggling by supplying a square wave pulse input to the SRAM to produce a desired pulsing.

25. A three-dimensional object producing apparatus according to claim 12, wherein the computer calculates the exposure time (the ON time) for each pixel based on the resin properties, layer thickness required, and radiant energy intensity.

26. A three-dimensional object producing apparatus according to claim 25, wherein the radiant energy intensity is measured with sensors.

27. A three-dimensional object producing apparatus according to claim 25, herein the radiant energy intensity is estimated from the known properties of the radiation source.

28. A three-dimensional object producing apparatus according to claim 25, wherein the exposure time (t_ON(x, y)) of each pixel is a function as related by the working curve equation:

t_ON(x, y) =(E_c exp (C_d /D_p))/H.sub.(x, y), where

E_c --Critical Exposure, a resin property,

D_p --Penetration Depth, a resin property,

C_d --Layer Thickness, a programming parameter of the computer, and

H(x, y)--Radiant energy irradiance at a given pixel (x, y).

29. A three-dimensional object producing apparatus according to claim 12, wherein the SLM is comprised of an array of micromirrors on a static random access memory (SRAM) chip.

30. A three-dimensional object producing apparatus according to claim 29, wherein individual addressable locations of the SRAM can be electrically charged in either a high voltage state or a low voltage state to cause rotation of the micromirrors toward the SRAM locations.

31. A three-dimensional object producing apparatus according to claim 30, wherein each micromirror is constructed over two opposing SRAM locations allowing the micromirror to be biased toward either of two address locations so that two separate reflective states are achieved, which allows radiant energy to be reflected for each pixel onto or away from the liquid surface of the photo-curable resin.

32. A three-dimensional object producing apparatus according to claim 31, wherein the reflective surface of each micromirror is 0.017 mm square.

13. An improved three-dimensional object producing apparatus of the type for irradiating a liquid surface of a vat of liquid photo-curable resin to form a succession of cured resin layers corresponding to successive cross-sectional laminae of a three-dimensional object, and incrementally lowering the cured resin layers below the liquid surface as they are formed to build up a three-dimensional copy of the object, wherein the improvement comprises:

a radiant energy source of a wide beam of radiant energy of suitable intensity and wavelength for curing a layer of the photo-curable resin;

a spatial light modulator (SLM) having an array of pixel elements which are individually controllable, for modulating the radiant energy beam projected from the radiant energy source on a pixel-by-pixel basis, to form a series of time sequential images of the cross-sectional laminae of the object;

optical means for focusing each image formed by the SLM, one at a time, onto successive layers of photo-curable resin for predetermined exposure times to thereby form stacked laminae of cured resin, each lamina of cured resin being in the shape of a different one of the cross-sectional laminae;

means for positioning each lamina of cured resin after it is formed by the SLM below the liquid surface corresponding to the thickness of one cross-sectional lamina of the three-dimensional object before the projection of a new image by the SLM to thereby flow a layer of photo-curable liquid resin to cover the lamina of cured resin;

wherein the SLM, the means for lowering, and the optical means operate repeatedly and sequentially until a complete copy of the object is thereby produced;

control means for controlling the SLM, the optical means and the means for lowering, the control means including;

a three-dimensional shape information memory for storing at least part of three-dimensional shape data defining the three-dimensional object to be formed;

a computer for generating cross-sectional patterns and programmed with a computer aided design (CAD) software program, the computer analyzing the three-dimensional shape data stored in the shape information memory, and mathematically slicing the solid model into layers of programmed thickness of Z height, where Z is the direction of lowering, to thereby produce a series of cross-sectional images of laminae;

means for connecting the control means to the SLM, the optical means and the means for lowering; and

wherein;

the means for lowering includes a piston sealed to the sides of the vat to prevent the transfer of resin past the piston and means controlled by the computer for lowering and raising the piston;

the portion of the vat below the piston is filled with the resin, so that the portion of the vat below the piston will source the resin that is deposited on the build surface for the layer by layer build.

14. A three-dimensional object producing apparatus according to claim 13, wherein:

to prepare a resin layer, the means for lowering lowers the piston down a distance equal to a programmed layer thickness to displace an amount of resin required to form a layer.

15. A three-dimensional object producing apparatus according to claim 14, further comprising a transfer tube connected from the portion of the vat below the piston to a position above the surface of the resin in the vat, wherein resin is forced from the portion of the vat below the piston through the transfer tube and deposited onto the build surface when the piston is lowered by the means for lowering.

16. A three-dimensional object producing apparatus according to claim 15, further comprising means for heating the transfer tube to elevate the temperature of the resin within the transfer tube to a temperature to improve viscosity or rate of polymerization.

17. A three-dimensional object producing apparatus according to claim 15, further comprising means for positioning the transfer tube above the resin surface to more evenly or quickly distribute the resin layer.

18. A three-dimensional object producing apparatus according to claim 15, further comprising spray heads connected to the transfer tube that dispense the resin in an even layer over the top surface of the piston.

19. A three-dimensional object producing apparatus according to claim 13, further comprising:

a piston arm attached to a lower surface of the piston and connected to the lowering means for controlling movement of the piston; and

a volume compensator having the same shape and volume as the piston arm, and placed above the piston to equalize the cross-sectional area for purposes of resin replacement.

20. A three-dimensional object producing apparatus according to claim 19, further comprising:

a bladder or other means for adjusting the volume of the volume compensator.

21. A three-dimensional object producing apparatus according to claim 20, further comprising:

the volume compensator is adjusted by the computer to raise or lower the liquid level of the build surface most commonly to adjust for shrinkage of the hardened resin.

33. An improved three-dimensional object producing method of the type for irradiating a liquid surface of a vat of liquid photo-curable resin to form a succession of cured resin layers corresponding to successive cross-sectional laminae of a three-dimensional object and incrementally lowering the cured resin layers below the liquid surface as they are formed to build up a three-dimensional copy of the object, wherein the improvement comprises the steps of:

(a) generating computer aided design (CAD) digital data which define a plurality of two-dimensional graphical patterns that comprise laminae of a three-dimensional object to be formed and storing the CAD digital data in a memory;

(b) generating a wide beam of radiant energy of suitable intensity and wavelength for curing a layer of the photo-curable resin;

(c) reading out the CAD digital data and pixelating a graphical pattern to determine which pixels of a spatial light modulator (SLM) must be turned to an ON state in order to solidify corresponding individual pixel resin segments that, taken together, form a lamina of the photo-curable resin contained in a vat;

(d) modulating the wide beam of radiant energy by individually digitally controlling each pixel element of an array of pixel elements of the SLM to modulate the radiant energy beam on a pixel-by-pixel basis to form a series of time sequential images of the cross-sectional laminae of the object;

(e) focusing each image from the SLM, one at a time, onto successive layers of the photo-curable resin for predetermined exposure times to thereby form stacked laminae of cured resin, each lamina of cured resin being in the shape of a different one of the cross-sectional laminae;

(f) lowering each lamina of cured resin after it is formed;

(g) depositing a layer of resin corresponding to the thickness of one cross-sectional lamina of the three-dimensional object before the step of projecting a new image by the SLM; and

wherein the modulating step further comprises the step of repeatedly toggling ON and OFF certain pixels'"'"' states during the exposure period so that the certain pixels are ON a predetermined percentage of the time and OFF the remaining percentage of the time.

34. An improved three-dimensional object producing method according to claim 33, further comprising the step of determining which pixel resin segments to partially cure into a gel state in order to create layer binding.

35. An improved three-dimensional object producing method according to claim 33, further comprising the step of determining which pixel resin segments to partially cure in order to reduce curl.

38. A three-dimensional object producing method according to claim 33, wherein the modulating step and lowering step further comprise the steps of deliberately underexposing some pixel resin segments, leaving them in a partially uncured state that is not completely solidified, applying a subsequent photo-curable resin layer over the partially uncured pixel resin segments, and exposing pixel resin segments aligned above the partially uncured pixel resin segments for a longer period to expose the aligned pixel resin segments of both the current and previous resin layers until they are solidified, whereby a pixel resin segment that is exposed and solidified through a succeeding layer acts as a peg that binds two layers together, resulting in an interlocking of layers to avoid delaminating.

39. A three-dimensional object producing method according to claim 38, wherein exposure is delayed or adjusted so that more than two layers are interlocked.

40. A three-dimensional object producing method according to claim 33, wherein the exposure time (t_ON(x, y)) of each pixel is a function as related by the working curve equation:

t_ON(x, y) =(E_c exp (C_d /D_p))/H.sub.(x, y) where

E_c --Critical Exposure, a resin property,

D_p --Penetration Depth, a resin property,

C_d --Layer Thickness, a programming parameter of the computer, and

H.sub.(x, y) --Radiant energy irradiance at a given pixel (x, y).

41. A three-dimensional object producing method according to claim 33, wherein exposure is delayed or adjusted so that more than two layers are interlocked.

42. A three-dimensional object producing method according to claim 33, wherein the SLM is used for optically scanning the completed three-dimensional object.

43. A three-dimensional object producing method according to claim 39, wherein optical scan data is used to calibrate the apparatus.

36. An improved three-dimensional object producing method of the type for irradiating a liquid surface of a vat of liquid photo-curable resin to form a succession of cured resin layers corresponding to successive cross-sectional laminae of a three-dimensional object and incrementally lowering the cured resin layers below the liquid surface as they are formed to build up a three-dimensional copy of the object, wherein the improvement comprises the steps of:

(a) generating computer aided design (CAD) digital data which define a plurality of two-dimensional graphical patterns that comprise laminae of a three-dimensional object to be formed and storing the CAD digital data in a memory;

(b) generating a wide beam of radiant energy of suitable intensity and wavelength for curing a layer of the photo-curable resin;

(c) reading out the CAD digital data and pixelating a graphical pattern to determine which pixels of a spatial light modulator (SLM) must be turned to an ON state in order to solidify corresponding individual pixel resin segments that, taken together, form a lamina of the photo-curable resin contained in a vat;

(d) modulating the wide beam of radiant energy by individually digitally controlling each pixel element of an array of pixel elements of the SLM to modulate the radiant energy beam on a pixel-by-pixel basis to form a series of time sequential images of the cross-sectional laminae of the object;

(e) focusing each image from the SLM, one at a time, onto successive layers of the photo-curable resin for predetermined exposure times to thereby form stacked laminae of cured resin, each lamina of cured resin being in the shape of a different one of the cross-sectional laminae;

(f) lowering each lamina of cured resin after it is formed;

(g) depositing a layer of resin corresponding to the thickness of one cross-sectional lamina of the three-dimensional object before the step of projecting a new image by the SLM;

wherein the step of lowering includes lowering a piston within the vat, and filling the portion of the vat below the piston with the resin, so that the portion of the vat below the piston will source the resin that is deposited for the layer-by-layer build.

37. An improved three-dimensional object producing method according to claim 36, further comprising the step, after the step of lowering the piston, of recoating an upper surface of the piston by wiping away any excess liquid or bubbles to assure accuracy of the layer thickness.

44. An improved three-dimensional object producing apparatus of the type for irradiating a surface of a container of flowable medium capable of solidification when subjected to prescribed radiant energy to form a succession of hardened medium layers corresponding to successive cross-sectional laminae of a three-dimensional object, and incrementally lowering the hardened medium layers below the flowable surface of the medium as they are formed to build up a three-dimensional copy of the object, wherein the improvement comprises:

a radiant energy source of a wide beam of radiant energy of suitable intensity and wavelength for hardening a layer of the medium;

a spatial light modulator (SLM) having an array of pixel elements which are individually controllable, for modulating the radiant energy beam projected from the radiant energy source on a pixel-by-pixel basis, to form a series of time sequential images of the cross-sectional laminae of the object;

optical means for focusing each image formed by the SLM, one at a time, onto successive layers of the medium for predetermined exposure times to thereby form stacked laminae of hardened medium, each lamina of hardened medium being in the shape of a different one of the cross-sectional laminae;

means for positioning each lamina of hardened medium after it is formed by the SLM below the flowable surface of the medium corresponding to the thickness of one cross-sectional lamina of the three-dimensional object before the projection of a new image by the SLM to thereby flow a layer of the medium to cover the lamina of hardened medium;

wherein the SLM, the means for lowering, and the optical means operate repeatedly and sequentially until a complete copy of the object is thereby produced; and

wherein certain pixels'"'"' states are repeatedly toggled ON and OFF during the exposure so that during a given exposure period the pixels are ON a predetermined percentage of the time and OFF the remaining percentage of the time.

45. A three-dimensional object producing apparatus according to claim 44, wherein the pixel elements are individually digitally addressable.

46. A three-dimensional object producing apparatus according to claim 44, wherein the SLM is comprised of an array of micromirrors on a semiconductor memory chip.

47. A three-dimensional object producing apparatus according to claim 44, wherein the optical means focusses radiant energy from each pixel of the SLM on a top layer of medium to create individual pixel medium segments, and some pixel medium segments are deliberately underexposed, leaving them in a partially uncured state that is not completely solidified, so that when a subsequent flowable medium layer is applied, the pixel medium segment aligned above a pixel medium segment which is in a partially uncured state is exposed for a longer period to expose the aligned pixel medium segments of both the current and previous medium layers until they are solidified, whereby a pixel medium segment that is exposed and solidified through a succeeding layer acts as a peg that binds two layers together, resulting in an interlocking of layers to avoid delaminating.

48. A three-dimensional object producing apparatus according to claim 44, wherein the optical means filters light of wavelengths other than those required for photopolymerization.

49. A three-dimensional object producing apparatus according to claim 44, wherein the optical means collimates the radiation source.

50. A three-dimensional object producing apparatus according to claim 44, wherein the optical means polarizes the radiation source.

51. A three-dimensional object producing apparatus according to claim 44, further comprising:

control means for controlling the SLM, the optical means and the means for lowering, the control means including;

a three-dimensional shape information memory for storing at least part of three-dimensional shape data defining the three-dimensional object to be formed;

a computer for generating cross-sectional patterns and programmed with a computer aided design (CAD) software program, the computer analyzing the three-dimensional shape data stored in the shape information memory, and mathematically slicing the solid model into layers of programmed thickness of Z height, where Z is the direction of lowering, to thereby produce a series of cross-sectional images of laminae;

means for connecting the control means to the SLM, the optical means and the means for lowering.

52. A three-dimensional object producing apparatus according to claim 51, wherein the computer overlays a map of a pixel layout on the SLM and compares this overlay to the cross-sectional image of a lamina and determines which pixels must be turned ON and which pixels must be turned OFF in order to project the accurate cross-sectional image of the lamina.

53. A three-dimensional object producing apparatus according to claim 51, wherein the pixel toggle means uses pulse width modulation (PWM) to achieve pixel toggling by supplying a square wave pulse input to the SRAM to produce a desired pulsing.

54. A three-dimensional object producing apparatus according to claim 51, wherein the computer calculates the exposure time (the ON time) for each pixel based on the medium properties, layer thickness required, and radiant energy intensity.

55. A three-dimensional object producing apparatus according to claim 54, wherein the exposure time (t_ON(x, y)) of each pixel is a function as related by the working curve equation:

t_ON(x, y) =(E_c exp (C_d /D_p))/H.sub.(x, y), where

E_c --Critical Exposure, a medium property,

D_p --Penetration Depth, a medium property,

C_d --Layer Thickness, a programming parameter of the computer, and

H.sub.(x,y) --Radiant energy irradiance at a given pixel (x, y).