Source: http://www.google.com/patents/US6126884?dq=6004266
Timestamp: 2017-10-17 02:21:58
Document Index: 662683061

Matched Legal Cases: ['application No. 08', 'application No. 08', 'application No. 09', 'application No. 09', 'application No. 09', 'application No. 09', 'application No. 09', 'application No. 09', 'application No. 09', 'application No. 09', 'application No. 09', 'application No. 09']

Patent US6126884 - Stereolithographic method and apparatus with enhanced control of prescribed ... - Google Patents
A rapid prototyping and manufacturing (e.g. stereolithography) method and apparatus for producing three-dimensional objects by selectively subjecting a liquid or other fluid-like material to a beam of prescribed stimulation. In a preferred embodiment a source of prescribed stimulation is controlled to...http://www.google.com/patents/US6126884?utm_source=gb-gplus-sharePatent US6126884 - Stereolithographic method and apparatus with enhanced control of prescribed stimulation production and application
Publication number US6126884 A
Application number US 09/248,353
Also published as DE60020895D1, DE60020895T2, EP1026564A2, EP1026564A3, EP1026564B1
Publication number 09248353, 248353, US 6126884 A, US 6126884A, US-A-6126884, US6126884 A, US6126884A
Inventors Thomas A. Kerekes, Ross D. Beers
Patent Citations (40), Non-Patent Citations (16), Referenced by (44), Classifications (16), Legal Events (4)
Stereolithographic method and apparatus with enhanced control of prescribed stimulation production and application
US 6126884 A
1. A stereolithographic method of forming a three-dimensional object from a plurality of adhered laminae by exposing successive layers of a material to a beam of prescribed stimulation, comprising:
providing a source of a beam of prescribed stimulation; forming a layer of material adjacent to any last formed layer of material in preparation for forming a subsequent lamina of the object;
exposing the material to the beam of prescribed stimulation to form the subsequent lamina of the object according to a plurality of exposure vectors representing the subsequent lamina; and
repeating the acts of forming and exposing a plurality of times in order to form the object from a plurality of adhered laminae,
wherein providing a plurality of non-exposure vectors between at least some pairs of successive exposure vectors, wherein the non-exposure vectors comprise a ramp vector and a jump vector.
2. The method of claim 1 wherein the ramp vector includes a first ramp vector and a second ramp vector with the jump vector occurring intermediate therebetween.
3. The method of claim 2 additionally comprising a non-exposure jump vector positioned intermediate to the first ramp vector and the second ramp vector.
4. The method of claim 2 wherein the first ramp vector is oriented in a direction parallel to a first direction.
5. The method of claim 3 wherein the first ramp vector is scanned so as to allow the scanning speed of the beam to change from a first speed to a speed that is substantially no more than a desired redirection speed.
6. The method of claim 5 wherein the time for scanning the first ramp vector is determined based on at least (1) a difference between the first scanning speed and the desired redirection speed, and (2) a maximum acceptable acceleration of the scanning system.
7. The method of claim 5 wherein the length of the first ramp vector is determined based on at least (1) a difference between the first scanning speed and the desired redirection speed, and (2) a maximum acceptable acceleration of the scanning system.
8. The method of claim 4 wherein the second ramp vector is oriented in a direction parallel to a second direction.
9. The method of claim 8 wherein the second ramp vector is scanned so as to allow the scanning speed of the beam to change to a second speed from an initial speed at the beginning of the second ramp vector.
10. The method of claim 9 wherein the time for scanning the second ramp vector is determined based on at least (1) a difference between the first scanning speed and the desired redirection speed, and (2) a maximum acceptable acceleration of the scanning system.
11. The method of claim 9 wherein the length of second ramp vector is determined based on at least (1) a difference between the first scanning speed and the desired redirection speed, and (2) a maximum acceptable acceleration of the scanning system.
12. The method of claim 3 wherein the non-exposure vector further comprises a transition vector between the first ramp vector and the jump vector.
13. A stereolithographic apparatus for forming a three-dimensional object from a plurality of adhered laminae by exposing successive layers of a material to a beam of prescribed stimulation, comprising:
a source of a beam of prescribed stimulation; a recoating system to form a layer of material adjacent to any last formed layer of material in preparation for forming a subsequent lamina of the object;
a scanning system to expose the material to the beam of prescribed stimulation to form the subsequent lamina of the object according to a plurality of exposure vectors representing the subsequent lamina; and
a computer programmed to operate the recoating system and the scanning system to form thc object from a plurality of adhered laminae,
wherein software is programmed or hardware is configured to provide a plurality of non-exposure vectors between at least some pairs of successive exposure vectors, wherein the non-exposure vectors comprise a first ramp vector and a jump vector.
14. The apparatus of claim 13 wherein the software is programmed or the hardware is configured to provide the first ramp vector and a second ramp vector with the jump vector occurring intermediate therebetween.
15. The apparatus of claim 13 wherein the software is programmed or hardware is configured to orient the first ramp vector in a direction parallel to a first direction.
16. The apparatus of claim 15 wherein the software is programmed or hardware is configured to scan the first ramp vector so as to allow the scanning speed of the beam to change from a first speed to a speed that is substantially no more than a desired redirection speed.
17. The apparatus of claim 16 wherein the software is programmed or hardware is configured to determine a time for scanning the first ramp vector based on at least (1) a difference between the first scanning speed and the desired redirection speed, and (2) a maximum acceptable acceleration of the scanning system.
18. The apparatus of claim 16 wherein the software is programmed or hardware is configured to set a length of the first ramp vector based on at least (1) a difference between the first scanning speed and the desired redirection speed, and (2) a maximum acceptable acceleration of the scanning system.
19. The apparatus of claim 17 wherein the software is programmed or hardware is configured to orient a second ramp vector in a direction parallel to a second direction.
20. The apparatus of claim 19 wherein the software is programmed or hardware is configured to scan the second ramp vector so as to allow the scanning speed of the beam to change to a second speed from an initial speed at the beginning of the ramp up vector.
21. The apparatus of claim 20 wherein the software is programmed or hardware is configured to determine a time for scanning the second ramp vector based on at least (1) a difference between the first scanning speed and the desired redirection speed, and (2) a maximum acceptable acceleration of the scanning system.
22. The apparatus of claim 21 wherein the software is programmed or hardware is configured to determine a length of the second ramp vector based on at least (1) a difference between the first scanning speed and the desired redirection speed, and (2) a maximum acceptable acceleration of the scanning system.
23. The apparatus of claim 14 wherein the software is programmed or hardware is configured to produce at least one additional non-exposing vector comprising a transition vector located at the end of the first ramp vector.
Selective Deposition Modeling, SDM, involves the build-up of three-dimensional objects by selectively depositing solidifiable material on a lamina-by-lamina basis according to cross-sectional data representing slices of the three-dimensional object. The material being dispensed may be solidified upon cooling, by heating, exposing to radiation, or upon application of a second physical material. A single material may be dispensed or multiple materials dispensed with each having different properties. One such technique is called Fused Deposition Modeling, FDM, and involves the extrusion of streams of heated, flowable material which solidify as they are dispensed onto the previously formed laminae of the object. FDM is described in U.S. Pat. No. 5,121,329, issued Jun. 9, 1992, to Crump. Another technique is called Ballistic Particle Manufacturing, BPM, which uses a 5-axis, ink-jet dispenser to direct particles of a material onto previously solidified layers of the object. BPM is described in PCT publication numbers WO 96-12607, published May 2, 1996, by Brown; WO 96-12608, published May 2, 1996, by Brown; WO 96-12609, published May 2, 1996, by Menhennett; and WO 96-12610, published May 2, 1996, by Menhennett. A third technique is called Multijet Modeling, MJM, and involves the selective deposition of droplets of material from multiple ink jet orifices to speed the building process. MJM is described in U.S. Pat. No. 5,943,235, filed Sep. 27, 1996, and issued Aug. 24, 1999 to Earl et al. and in U.S. Application Ser. No. 08/722,335, filed Sep. 27, 1996, by Leyden et al. now abandoned (both assigned to 3D Systems, Inc. as is the instant application).
TABLE 1______________________________________Related Patents and ApplicationsPat. No.Issue DateApplicationNo.Filing Date    Inventor   Subject______________________________________4,575,330    Hull       Discloses fundamental elements ofMar 11, 1986        stereolithography.06/638,905Aug 8, 19844,999,143    Hull, et al.               Discloses various removable supportMar 12, 1991        structures applicable to07/182,801          stereolithography.Apr 18, 19885,058,988    Spence     Discloses the application of beamOct 22, 1991        profiling techniques useful07/268,816          in stereolithography for determiningNov 8, 1988         cure depth and scanning velocity, etc.5,059,021    Spence, et al.               Discloses the utilization of driftOct 22, 1991        correction techniques for eliminating07/268,907          errors in beam positioning resultingNov 8, 1988         from instabilities in the beam               scanning system5,076,974    Modrek, et al.               Discloses techniques for post processingDec 31, 1991        objects formed by stereolithography.07/268,429          In particular exposure techniques areNov 8, 1988         described that complete the solidifi-               cation of the building material. Other               post processing steps are also disclosed               such as steps of filling in or sanding               off surface discontinuities.5,104,592    Hull       Discloses various techniques for reduc-Apr 14, 1992        ing distortion, and particularly curl type07/339,246          distortion, in objects being formed byApr 17, 1989        stereolithography.5,123,734    Spence, et al.               Discloses techniques for calibrating aJun 23, 1992        scanning system. In particular07/268,837          techniques for mapping from rotationalNov 8, 1988         mirror coordinates to planar target               surface coordinates are disclosed5,133,987    Spence, et al.               Discloses the use of a stationary mirrorJul 28, 1992        located on an optical path between the07/427,885          scanning mirrors and the target surfaceOct 27, 1989        to fold the optical path in a               stereolithography system.5,141,680    Almquist, et al.               Discloses various techniques forAug 25, 1992        selectively dispensing a material to07/592,559          build up three-dimensional objects.Oct 4, 19905,143,663    Leyden, et al.               Discloses a combined stereolithographySep 1, 1992         system for building and cleaning07/365,444          objects.Jun 12, 19895,174,931    Almquist, et al.               Discloses various doctor bladeDec 29, 1992        configurations for use in forming07/515,479          coatings of medium adjacent toApr 27, 1990        previously solidified laminae.5,182,056    Spence, et al.               Discloses the use of multiple wave-Jan 26, 1993        lengths in the exposure of a07/429,911          stereolithographic medium.Oct 27, 19895,182,715    Vorgitch, et al.               Discloses various elements of a largeJan 26, 1993        stereolithographic system.07/824,819Jan 22, 19925,184,307    Hull, et al.               Discloses a program called Slice andFeb 2, 1993         various techniques for converting07/331,644          three-dimensional object data into dataMar 31, 1989        descriptive of cross-sections. Disclosed               techniques include line width               compensation techniques (erosion               routines), and object sizing techniques.               The application giving rise to this               patent included a number of appendices               that provide further details regarding               stereolithography methods and systems.5,192,469    Hull, et al.               Discloses various techniques forMar 9, 1993         forming three-dimensional object from07/606,802          sheet material by selectively cuttingOct 30, 1990        out and adhering laminae.5,209,878    Smalley, et al.               Discloses various techniques for reduc-May 11, 1993        ing surface discontinuities between07/605,979          successive cross-sections resultingOct 30, 1990        from a layer-by-layer building               technique. Disclosed techniques include               use of fill layers and meniscus               smoothing.5,234,636    Hull, et al.               Discloses techniques for reducingAug 10, 1993        surface discontinuities by coating a07/929,463          formed object with a material, heatingAug 13, 1992        the material to cause it to become               flowable, and allowing surface tension               to smooth the coating over the object               surface.5,238,639    Vinson, et al.               Discloses a technique for minimizingAug 24, 1993        curl distortion by balancing upward07/939,549          curl to downward curl.Mar 31, 19925,256,340    Allison, et al.               Discloses various build/exposure stylesOct 26, 1993        for forming objects including various07/906,207          techniques for reducing objectJun 25, 1992        distortion. Disclosed techniques include:And                 (1) building hollow, partially hollow,5,965,079           and solid objects, (2) achieving moreOct 12, 1999        uniform cure depth, (3) exposing layers08/766,956          as a series of separated tiles or bullets,Dec 16, 1996        (4) using alternate sequencing exposure               patterns from layer to layer, (5) using               staggered or offset vectors from layer               to layer, and (6) using one or more               overlapping exposure patterns per layer.5,321,622    Snead, et al.               Discloses a computer program known asJun 14, 1994        CSlice which is used to convert07/606,191          three-dimensional object data intoOct 30, 1990        cross-sectional data. Disclosed               techniques include the use of various               Boolean operations in stereolithography.5,597,520    Smalley, et al.               Discloses various exposure techniquesJan 28, 1997        for enhancing object formation08/233,027          accuracy. Disclosed techniques addressApr 25, 1994        formation of high resolution objectsAnd                 from building materials that have a5,999,184           Minimum Solidification Depth greaterDec 7, 1999         than one layer thickness and/or a08/428,951          Minimum Recoating Depth greater thanApr 25, 1995        the desired object resolution.08/722,335    Thayer, et al.               Discloses build and support styles forSep 27, 1996        use in a Multi-Jet Modeling selectiveNow                 deposition modeling system.abandoned5,943,235    Earl, et al.               Discloses data manipulation and systemAug 24, 1999        control techniques for use in a08/722,326          Multi-Jet Modeling selective depositionSep 27, 1996        modeling system.5,902,537    Almquist, et al.               Discloses various recoating techniquesMay 11, 1999        for use in stereolithography. Disclosed08/790,005          techniques include 1) an inkjetJan 28, 1997        dispensing device, 2) a fling recoater,               3) a vacuum applicator, 4) a stream               recoater, 5) a counter rotating roller               recoater, and 6) a technique for deriving               sweep extents.5,840,239    Partanen, et al.               Discloses the application of solid-stateNov 24, 1998        lasers to stereolithography. Discloses08/792,347          the use of a pulsed radiation sourceJan 31, 1997        for solidifying layers of building               material and in particular the ability               to limit pulse firing locations to only               selected target locations on a surface               of the medium.6,001,297    Partanen, et al.               Discloses the stereolithographicDec 14, 1999        formation of objects using a pulsed08/847,855          radiation source where pulsing occursApr 28, 1997        at selected positions on the surface               of a building material.08/855,125    Nguyen, et al.               Discloses techniques for interpolatingMay 13, 1997        originally supplied cross-sectional               data descriptive of a three-dimensional               object to produce modified data               descriptive of the three-dimensional               object including data descriptive of               intermediate regions between the               originally supplied cross-sections               of data.5,945,058    Manners, et al.               Discloses techniques for identifyingAug 31, 1999        features of partially formed objects.08/854,950          Identifiable features include trappedMay 13, 1997        volumes, effective trapped volumes,               and solid features of a specified size.               The identified regions can be used in               automatically specifying recoating               parameters and or exposure parameters.5,902,538    Kruger, et al.               Discloses simplified techniques forMay 11, 1999        making high-resolution objects utilizing08/920,428          low-resolution materials that are limitedAug 29, 1997        by their inability to reliably form               coatings of a desired thickness due               to a Minimum Recoating Depth (MRD)               limitation. Data manipulation               techniques define layers as primary or               secondary. Recoating techniques are               described which can be used when the               thickness between consecutive layers               is less than a leading edge bulge               phenomena.09/061,796    Wu, et al. Discloses use of frequency convertedApr 16, 1998        solid state lasers in stereolithography.09/154,967    Nguyen, et al.               Discloses techniques for stereolitho-Sep 17, 1998        graphic recoating using a sweeping               recoating device that pause and/or slows               down over laminae that are being               coated over.09/484,984    Earl, et al.               Entitled "Method and Apparatus forJan 18, 2000        Forming Three-Dimensional Objects               Using Line Width Compensation with               Small Feature Retention." Discloses               techniques for forming objects while               compensating for solidification width               induced in a building material by a               beam of prescribed stimulation.09/246,504    Guertin, et al.               Entitled "Method and Apparatus forFeb 8, 1999         Stereolithographically Forming Three               Dimensional Objects With Reduced               Distortion." Discloses techniques               for forming objects wherein a delay is               made to occur between successive               exposures of a selected region of               a layer.09/248,352    Manners, et al.               Entitled Stereolithographic Method andFeb 8, 1999         Apparatus for Production of Three               Dimensional Object Using Multiple               Beams of Different Diameters"               Discloses stereolithographic               techniques for forming objects using               multiple sized beams including data               manipulation techniques for determining               which portions of lamina may be               formed with a larger beam and which               should be formed using a smaller beam.09/248,351    Nguyen, et al.               Entitled "Stereolithographic MethodFeb 8, 1999         and Apparatus for Production of Three               Dimensional Objects Using Recoating               Parameters for Groups of Layers."               Discloses improved techniques for               managing recoating parameters when               forming objects using layer thicknesses               smaller than a minimum recoating depth               (MRD) and treating some non-consecu-               tive layers as primary layers and treat-               ing intermediate layers there between as               secondary layers.09/246,416    Bishop, et al.               Entitled "Rapid Prototyping ApparatusFeb 8, 1999         with Enhanced Thermal and Vibrational               Stability for Production of Three               Dimensional Objects." Discloses an               improved Stereolithographic apparatus               structure for isolating vibration and/or               extraneous heat producing components               from other thermal and vibration               sensitive components.09/247,113    Chari, et al.               Entitled "Stereolithographic Method andFeb 8, 1999         Apparatus for production of Three               Dimensional Objects with Enhanced               thermal Control of the Build               environment. Discloses improved               stereolithographic techniques for               maintaining build chamber temperature               at a desired level. The techniques               include varying heat production based               on the difference between a detected               temperature and the desired               temperature.09/247,119    Kulkarni, et al.               Entitled "Stereolithographic MethodFeb 8, 1999         and Apparatus for Production of Three               Dimensional Objects Including               Simplified Build Preparation."               Discloses techniques for forming               objects using a simplified data               preparation process. Selection of the               various parameter styles needed to form               an object is reduced to answering               several questions from lists of               possible choices.______________________________________
It is an object of the invention to improve the quality of vector scanning in a stereolithography system.
It is a first aspect of the invention to provide a stereolithographic method of forming a three-dimensional object from a plurality of adhered laminae by exposing successive layers of a material to a beam of prescribed stimulation, including: (1) providing a source of a beam of prescribed stimulation; (2) forming a layer of material adjacent to any last formed layer of material in preparation for forming a subsequent lamina of the object; (3) exposing the material to the beam of prescribed stimulation to form the subsequent lamina of the object according to a plurality of exposure vectors representing the subsequent lamina; and (4) repeating the acts of forming and exposing a plurality of times in order to form the object from a plurality of adhered laminae. Providing a plurality of non-exposure vectors between at least some pairs of successive exposure vectors, wherein the non-exposure vectors comprise a ramp vector and a jump vector.
It is a second aspect of the invention to provide an stereolithographic apparatus for forming a three-dimensional object from a plurality of adhered laminae by exposing successive layers of a material to a beam of prescribed stimulation, including: (1) a source of a beam of prescribed stimulation; (2) a recoating system to form a layer of material adjacent to any last formed layer of material in preparation for forming a subsequent lamina of the object; (3) a scanning system to expose the material to the beam of prescribed stimulation to form the subsequent lamina of the object according to a plurality of exposure vectors representing the subsequent lamina; (4) and a computer programmed to operate the recoating system and the scanning system to form the object from a plurality of adhered laminae. Software is programmed or a hardware is configured to provide a plurality of non-exposure vectors between at least some pairs of successive exposure vectors, wherein the non-exposure vectors comprise a ramp vector and a jump vector.
FIG. 5 depicts a flow chart of a preferred embodiment.
FIGS. 1a and 1b depict schematic representations of a preferred stereolithography apparatus 1 (SLA) for use with the instant invention. The basic components of an SLA are described in U.S. Pat. Nos. 4,575,330; 5,184,307; and 5,182,715 as referenced above. The preferred SLA includes container 3 for holding building material 5 (e.g. photopolymer) from which object 15 will be formed, elevator 7 and driving means (not shown), elevator platform 9, exposure system 11, recoating bar 13 and driving means (not shown), at least one computer (not shown) for manipulating object data (as needed) and for controlling the exposure system, elevator, and recoating device.
FIG. 1a depicts the partially formed object as having its most recently formed lamina lowered to a position approximately one layer thickness below the desired level of the upper surface of the building material 5 (i.e. desired working surface). As the layer thickness is small and the building material very viscous, FIG. 1 a indicates that the material has not flowed significantly across the last formed lamina even after lowering the platform 9. FIG. 1b depicts the coating bar 13 as being swept part way across the previously formed lamina and that the next layer of building material has been partially formed.
A preferred exposure system is described in several of the patents and one application referenced above including U.S. Pat. Nos. 5,058,988; 5,059,021; 5,123,734; 5,133,987; 5,840,239; and Ser. No. 09/247,120. This preferred system includes a laser, a beam focusing system, and a pair of computer controlled XY rotatable scanning mirrors of either the motor driven or galvanometer type.
FIG. 1c provides a block diagram of selected elements of a preferred stereolithography system 1 wherein like elements are identified with like numerals. The exposure system includes an IR laser head 70, that produces a pulsed beam of radiation operating a desired repetition pulse repetition rate (e.g. 22.5-40 KHz). The exposure system further includes, an AOM 72, a first frequency conversion crystal 74, a second frequency conversion crystal 76, two folding mirrors 78, focusing optics 80, a pair of XY scanning mirrors 82, and a detector 84. A control computer 86 is provided to preferably control, among other things, the scanning mirrors 82, the AOM 72, the detector 84, and the focusing optics 80. The optical path is depicted with reference numeral 86. The computer preferably controls the above noted components based on object data that has been modified for stereolithographic formation. It is preferred that the focusing optics be controlled to produce two or more beam diameters for forming object laminae. The AOM is preferably controlled to adjust beam power base on a plurality of criteria including beam size.
The scanning mirrors are used to selectively direct the beam path to desired locations onto the surface of the building material 5 or onto other items such as detector 84. The optical path beyond the scanning mirrors is depicted with reference numerals 86', 86", or 86'" as examples of the different directions in which the beam may be directed. The AOM is used to set the beam power that is allowed to proceed from the IR laser head 70 to the first and second frequency conversion crystals. The beam that is allowed to proceed to the frequency conversion crystals is sent along a first order beam path from the AOM. The other beam path orders (e.g. 0th and 2nd) are inhibited from progressing to the frequency conversion crystals. The focusing optics are used to obtain a desired focus and/or beam diameter at the surface 20 of the building material
A more detailed depiction of the beam-generating portion of the exposure system is depicted in FIG. 1d wherein like numerals to those used in the other figures depict similar components. The radiation-generating portion of the exposure system comprises a laser head 68, IR generating laser diodes 71, and a fiber optic cable 69. The laser diodes produce approximately 808 nm radiation at approximately 18 watts. The fiber optic cable directs the output of the laser diodes 71 to an IR laser 70 inside the UV laser head, the radiation from the fiber optic is used to supply pumping radiation to the IR laser 70. The laser 70 produces 1.064 micron radiation that is directed to acousto-optic modulator (AOM) 72 that is used to control the beam power by deflecting varying amounts of the beam power along different optical paths. A zeroth order optical path directs the beam into a beam dump. For example, a trap formed by two triangular shaped elements 73. A first order optical path directs the beam through a half-wave plate 75 that rotates the polarization of the beam.
From the half wave plate 75 the beam enters a frequency conversion module 93 through an aperture 77. From aperture 77 the beam proceeds to focusing mirror 79'.
From mirror 79' the beam proceeds through a first frequency conversion crystal 74. This first crystal 74 converts a portion of the first beam into a beam that has double the frequency. The remaining portion of the original beam and the beam of doubled frequency proceed to second focusing mirror 79", then a third focusing mirror 79'", and then through a second frequency conversion crystal 76. The second crystal 76 generates a third beam of tripled frequency compared to the original beam that entered first crystal 74. A beam containing all three frequencies then proceeds out of the conversion module 93 through aperture 77. The mirrors 78 and other optical elements are wavelength selective and cause the remaining portions of the original and doubled frequency beams to attenuate. As such, only the tripled frequency portion of the beam proceeds along the rest of the beam path through laser head 68.
From aperture 77 the beam proceeds to folding mirror 78, and continues through cylindrical lens 81' and 81". The cylindrical lenses are used to remove astigmatism and excess ellipticity from the beam. Excess ellipticity is determined based on an aspect ratio of the beam that is defined as the ratio of minimum beam dimension at a focal plane and the maximum beam dimension at the focal plane. An aspect ratio of one implies the beam is circular while an aspect ratio of 1.1 or 0.9 implies that the width of the beam in one dimension is approximately 10% greater than or less than the width in the other dimension. Aspect ratios in excess of 1.1 or 0.9 are generally considered excessive though in some circumstances the beams may be useable.
From cylindrical lens 81"the beam proceeds to folding mirror 78. Most of the beam then proceeds through beam splitter 94, while a very small portion (e.g. around 1-4%) is reflected from the beam splitter back to detector 85 where a power measurement may be taken which can then be used in determining the overall power in the beam. The main portion of the beam moves through lenses 83' and 83" in the beam focusing module 80. After passing through lens 83" the beam direction is reoriented by two folding mirrors 78.
The beam then reenters the focusing module and passes through movable lens 83'". The position of lens 83'" is controlled by stepper motor 87, moveable mount 88, and lead screw 89. The motor is computer controlled so that the beam focal plane may be varied depending on the desired beam size at the surface of the building material.
A laser power supply may be used to control operation of the laser in several ways: (1) it supplies a desired amount of electric power to the laser diodes 71 to produce a desired optical output (e.g. about 18 watts), (2) it controls thermal electric heaters/coolers or other heaters/coolers to control the temperatures of the laser diodes, the IR laser, and/or the conversion crystals, (3) it may control the AOM Q-switch, (4) it may control the focusing system, (5) it may be used to control the detector and to interpret signals therefrom. Alternatively, or additionally, the process computer may be used to control one or more of the above noted elements. The process computer preferably is functionally connected to the laser power supply so that it may further control laser operation.
Referring now to FIGS. 1a and 1b, a preferred recoating device is described in U.S. Pat. No. 5,902,537 as referenced above and includes recoater bar 13, regulated vacuum pump 17, and vacuum line 19 connecting the bar 13 and the pump 17.
SLAs on which the instant invention can be utilized are available from 3D Systems, Inc. of Valencia, Calif. These SLAs include the SLA-250 system using a CW HeCd laser operating at 325 nm, the SLA-3500, SLA-5000, and the SLA-7000 systems using solid state lasers operating at 355 nm with a pulse repetition rates of 22.5 KHz, 40 KHz, and 25 KHz, respectively. Preferred building materials are photopolymers manufactured by CIBA Specialty Chemicals of Los Angeles, Calif., and are available from 3D Systems, Inc. These materials include SL 5170, SL 5190, and SL 5530HT.
Hereinafter, layer thickness and other units of distance may be expressed in any of three units: (1) inches, (2) milli-inches (i.e. mils), or (3) millimeters . As the material is typically very viscous and the thickness of each layer is very thin (e.g. 4 mils to 10 mils), the material may not readily form a coating over the last solidified lamina (as shown in FIG. 1a). In the case where a coating is not readily formed, a recoating device may be swept at or somewhat above the surface of the building material (e.g. liquid photopolymer) to aid in the formation of a fresh coating. The coating formation process may involve the sweeping of the recoating bar one or more times at a desired velocity.
FIG. 2b illustrates the object as it might be formed with a desired resolution using stereolithography wherein the MSD and MRD (discussed in U.S. Pat. Nos. 5,597,520 and U.S. Pat. No. 5,902,538) of the material are both less than or equal to the desired layer thickness (i.e. resolution). In this example, the thickness 220 of each layer is the same. As indicated, the object is formed from 16 adhered laminae 101-116 and 16 associated layers of material 201-216. As layers are typically solidified from their upper surface downward, it is typical to associate cross-sectional data, lamina and layer designations with the upper extent of their positions. To ensure adhesion between laminae, at least portions of each lamina are typically provided with a quantity of exposure that yields a cure depth of more than one layer thickness. In some circumstances use of cure depths greater than one layer thickness may not be necessary to attain adhesion. To optimize accuracy it is typical to manipulate the object data to account for an MSD greater than one layer thickness or to limit exposure of down-facing regions so that they are not cured to a depth of more than one layer thickness.
A comparison of FIG. 2a and 2b indicates that the object as reproduced in this example is oversized relative to its original design. Vertical and Horizontal features are positioned correctly; but those features which are sloped or near flat (neither horizontal nor vertical), have solidified layers whose minimal extent touches the envelope of the original design and whose maximum extent protrudes beyond the original design. Further discussion of data association, exposure, and sizing issues can be found in U.S. Pat. Nos. 5,184,307 and 5,321,622 as well as a number of other patents referenced above.
Down-facing boundaries--Boundaries that surround down-facing regions of the object.
Up-facing boundaries--Boundaries that surround up-facing regions of the object.
Continuing boundaries--Boundaries that surround regions of the object that are neither up-facing nor down-facing
Down-facing Hatch--Lines of exposure that are positioned within the down-facing boundaries. These lines may be closely or widely spaced from one another and they may extend in one or more directions.
Up-facing Hatch--Lines of exposure that are positioned within the up-facing boundaries. These lines may be closely or widely spaced from one another and they may extend in one or more directions.
Continuing Hatch--Lines of exposure that are positioned within continuing boundaries. These lines may be closely or widely spaced from one another and they may extend in one or more directions.
Down-facing Skin/Fill--Lines of exposure which are positioned within the down-facing boundaries and closely spaced so as to form a continuous region of solidified material.
Up-facing Skin/Fill--Lines of exposure which are positioned within the up-facing boundaries and closely spaced so as to form a continuous region of solidified material.
Taken together, the down-facing boundaries, down-facing hatch and down-facing fill define the down-facing regions of the object. The up-facing boundaries, up-facing hatch, and up-facing fill, define the up-facing regions of the object. The continuing boundaries and continuing hatch define the continuing regions of the object. As down-facing regions have nothing below them to which adhesion is desirably achieved (other than possibly supports), the quantity of exposure applied to these regions typically does not include an extra amount to cause adhesion to a lower lamina though extra exposure might be given to appropriately deal with any MSD issues that exist. As up-facing and continuing regions have solidified material located below them, the quantity of exposure applied to these regions typically includes an extra amount to ensure adhesion to a lower lamina.
TABLE 2______________________________________Object Regions Existing on Each Lamina of FIG. 2cLamina & Down-Facing   Up-Facing                           ContinuingLayer    Region(s)     Region(s)                           Region(s)______________________________________101,201  231102,202  232                    272103,203  233                    273104,204  234                    274105,205  235                    275106,206  236           256      276107,207  237                    277108,208  238                    278109,209                259      279110,210                260      280111,211  241           261      281112,212                262      282113,213                263      283114,214                264      284115,215                265      285116,216                266______________________________________
Other schemes for region identification and vector type creation are described in various patents and applications referenced above, including U.S. Pat. Nos. 5,184,307; 5,209,878; 5,238,639; 5,597,520; 5,902,538; 5,943,235 and, Application Ser. No. 08/855,125. Some schemes might involves the use of fewer designations such as: (1) defining only outward facing regions and continuing regions where down-facing and up-facing regions are combined to form the outward facing regions; (2) combining all fill types into a single designation; or (3) combining up-facing and continuing hatch into a single designation or even all three hatch types into a single designations. Other schemes might involve the use of more designations such as dividing one or both of the up-facing and down-facing regions into flat regions and near-flat regions.
Other region identifications might involve the identification of which portions of boundaries regions associated with each lamina are outward facing and/or interior to the lamina. Outward facing boundary regions are associated with the Initial Cross-Section Boundaries (ICSB). The ICSB may be considered the cross-sectional boundary regions existing prior to the cross-sections into the various desired regions.
ICSBs are described in U.S. Pat. Nos. 5,321,622 and 5,597,520. Interior boundaries are bounded on both sides by object portions of the lamina whereas outward boundaries are bounded on one side by an object portion of the lamina and on the other side by a non-object portion of the lamina.
An advantage to this technique is in extending the effective life of the laser system. In this context the term "effective life" refers to the number of hours of object formation that may be obtained from the laser between repairs. When a frequency converted laser is used in producing ultraviolet radiation, damage to the exiting surface of the frequency conversion crystal that is responsible for UV radiation production has been observed. This damage has been responsible for significantly shortening laser life. As the extent of damage to the UV radiation producing crystal appears to be directly related to the power produced by the crystal and the time of operation, the present embodiment lengthens the effective life of the laser by reducing the power exiting the crystal. A preferred laser for use in this embodiment is the laser illustrated in FIGS. 1c and 1d. As indicated, an AOM (i.e. acousto-optic modulator) 72 is located between IR laser head 70 and two frequency conversion crystals 74 and 76. The AOM is controlled by the system control computer (e.g. process computer) to inhibit the power from reaching the frequency conversion crystals when it is not needed for exposing the building material 5 at surface 20 or for some other purpose. As it is not uncommon for recoating time, and other periods of non-exposure to exceed over 50% of the actual time for forming an object, it is possible for this technique to double or even further extend laser life.
The result of this technique is illustrated in FIG. 4 where a plot of laser output power (output of prescribed stimulation is shown as a function of time). In this plot, the lapse of time covers the exposure of three layers and the formation of two layers.
Several layer formation events are depicted in the Figure: (1) PB=Beam profiling and analysis, (2) Expose=Exposure of a layer to form a lamina, (3) Pd=Predip delay, (4) Coat=time to form a layer over a previously formed lamina which is typically the time to sweep a recoating device over the previously formed lamina, and (5) Z-wait=delay time after sweeping before exposure begins.
Besides the periods of inhibition noted in FIG. 4, other periods may exist when inhibition can occur. One such time is known as interhatch delay and is described in U.S. patent application Ser. No. 09/246,504. Inhibition or reduction may occur during all of these periods, a portion of each period or even just a portion of one of these periods or during some other period.
The time period T1 may be based on several factors. For example, these factors may include (1) time to attenuate or inhibit the beam, and (2) time to reactivate the beam and stabilize it. The time period T2 may be based on several factors as well including (2) above and the period between recheck reevaluations. In an alternative, the decision to turn on the beam may be based on the lapse of a count down clock as opposed to looping through a comparison routine.
This embodiment provides a technique for effectively controlling vector exposure especially when high scan speeds are utilized. This technique links selected exposure vectors (i.e. vectors which are intended to expose building material) with one or more non-exposure vectors (i.e. vectors which are used to redirect the beam scanning direction and speed without significantly exposing the building material) so it is ensured that at the beginning of an exposure vector the scanning speed and direction of movement are appropriate for the vector to be traced. Likewise, at the end of an exposure vector it is ensured that the scanning speed remains appropriate for the vector.
A flowchart representing an implementation of this embodiment is provided as FIG. 5. FIG. 5 starts off with Element 400 which sets a variable "i" equal to one. This variable provides a designation for each exposure vector that is to be drawn. The next consecutive exposure vector is designated "i+1".
Element 402 calls for supplying data representing a first exposure vector, EVI, and a second exposure vectors, EVi+1. Some parameters for each vector include: (1) beginning X position for each vector, Xib, X(i+1)b ; (2) beginning Y position for each vector, Yib, Y(i+1)b ; (3) ending X position for each vector, Xie, X(i+1)e ; (4) ending Y position for each vector, Yie, Y(i+1)e ; (5) X component of scanning speed for each vector, SXi and SXi+1 ; and (6) ) Y component of scanning speed for each vector, SYi and SYi+1.
Element 404 calls for supplying values for four global control parameters: (1) HSBorder: Maximum per axis drawing speed for borders that do not require ramps=N1; (2) HSRamp: Speed change attainable when applying maximum acceleration=N2;
(3) HSRest: Speed at which change of direction transitions are allowed to occur=N3; and (4) FF: time period for applying feed forward commands to the ends of some vectors=N4. Some preferred values for these parameters include HSBorder=70 ips (i.e. inches/second), HSRamp=25 ips/tick, HSRest=70 ips, and FF=4 ticks. In a preferred system 1 tick=15 microseconds.
Element 406 calls for determining the difference in speed along each of the X and Y axes between the first and second vectors. This information along with the global parameters 406 are taken as input to Element 408.
Element 408 calls for an analysis of whether or not either of ΔSX or ΔSY is greater than N1. If this condition is met, it means that a transition between the two vectors cannot occur without the introduction of two or more non-exposure vectors. If the response is "yes", the process proceeds to element 410 where the process of generating non-exposure vectors begin. Alternatively, if the response is "no", the process proceeds to element 424 where another inquiry is made.
Element 410 calls for applying feed forward acceleration control at the end of the "i"th exposure vector EVi for a period of N4, blocking the beam when the end of the "i"th exposure vector EVi is reached, and inserting a first ramp vector RV1i parallel to the "i"th exposure vector EVi at the end of EVi. Feed forward is the concept of applying acceleration commands prior to the time that a change in direction or speed is to occur. The amount of acceleration force to apply and the time over which to apply it may be empirically determined based on optimizing the positioning and scanning speed at the end of the first vector and at the beginning of the second vector. It may be preferred to error on the side of rounding corners than overshooting them. This optimization may be based on minimizing the overall error in position and/or scanning speed that results when the transition is made. In a present preferred embodiment, scanning mirror commands are preferably updated every 15 microseconds. Each 15 microsecond period is considered one "tick". In a preferred system, the maximum acceleration has been set to approximately 25 inches/sec/tick. In this system, it has been empirically determined that use of a feed forward period of 4 ticks gives good results. Of course other values of N4 may be used in specifying the feed forward period depending on the system conditions and any desired positioning and speed tolerance criteria.
Element 412 calls for setting the time and/or length of the first ramp vector RV1 to a minimum amount necessary to allow both the X-scanner and the Y-scanner to reach a desired scanning speed when a desired maximum level of acceleration N2 is applied. The scanning time for the first ramp vector may be expressed mathematically as the greater of:
(SXi -N3-N4*N2)/N2
(SYi -N3-N4*N2)/N2.
Element 414 calls for Creating a transition vector TVi starting at end of the first ramp vector RV1i and extending in the same direction as the first ramp vector for a length of time equal to a normal feed forward amount N4. In this embodiment the entire length of the vector receives feed forward acceleration commands. The feed forward commands accelerate each scanner appropriately to transition to a jump vector that will be created in element 420. As such, at this point in the process the feed forward criteria can not be specifically set.
Element 416 calls for Inserting a second ramp vector RV2i parallel to the next exposure vector EV1+1 so that the second ramp vector RV21 ends at the beginning of EVi+1. The X and Y components of scanning speed at the end of the second ramp vector are equal to the desired values for the next exposure vector.
Element 418 calls for setting the time/length of the second ramp vector RV2i. The time/length is set to an amount greater than or equal to the minimum necessary to transition from a scanning speed N3 of the jump vector to the scanning speed of the next exposure vector. The time period for scanning the second ramp vector may be specified to be the equal to or greater than the larger of
(SXi+1 -N3)/N2,
(SYi+1 -N3)/N2.
Element 420 calls for inserting a jump vector JVi from the end of the first ramp vector RV1i to the beginning of the second ramp vector RV21. Feed forward acceleration commands are applied over the last N4 ticks of the jump vector JVi. At the end of the jump vector (i.e. beginning of the next exposure vector), the propagation of the beam is uninhibited so that it is allowed to progress through the optical system to the building material.
Element 424 is reached by conclusion in element 408 that the change in both the X and Y scanning speed components is less than an acceptable amount set by the HSBorder variable. Element 424 calls for an analysis of whether the ending point of the "i"th exposure vector EVi is coincident with the beginning point of the (i+1)th exposure vector EVi+1.
If the ending points are equivalent, then the process proceeds to Element 422. By failing the criterion of element 408 and passing the criterion of element 424, it may be concluded that a transition between the "i"th exposure vector and the (i+1)th exposure vector may be made with sufficient accuracy using only feed forward commands that will be applied at the end of the "i"th exposure vector.
If the criterion of element 424 is not met, the process proceeds to element 426 wherein a transition vector JVi is inserted between the "i"th and (i+1)th exposure vectors. This transition vector is used to bridge the gap between the two vectors.
Additional non-exposure vectors are not typically needed as it is possible to achieve the desired changes in direction and speed based on use of feed forward acceleration commands at the end of the "i"th transition vector and the end of jump vector JVi.
Element 428 inquiries as to whether EVi is the last vector to be formed. If it is not, variable "i" is incremented by one (element 432) and the process loops back through elements 402 to 428. If the "i"th exposure vector is the last vector, the process proceeds to element 430 where the beam is inhibited and the process ended.
Application of the procedure outlined in FIG. 5 is illustrated with the aid of FIGS. 6 and 7. FIG. 6 depicts a top view of a set of vectors for use in forming a hypothetical lamina. These vectors represent a cross-section of the object to be formed and are laid out in the X-Y plane. These vectors include a set of four boundary vectors 440, 442, 444, and 446. They also include a set of vectors 448, 450, and 452 internal to the boundary and parallel to the Y-axis (e.g. Y-hatch or Y-fill vectors). These cross-sectional vectors also include a set of vectors 454, 456, and 458 internal to the boundary and parallel to the Y-axis (e.g. Y-hatch or Y-fill vectors). Each of these groupings of vectors may utilize different quantities of exposure, may have different position tolerance criteria, and may be formed with different beam sizes. As such, the beam power used with each of these sets may be different.
The transition between two of the boundary vectors 444 and 446 is depicted in
FIG. 7. Even though the two boundary vectors have a coincident point, the combination of their respective scanning speeds and angle result in a transition which cannot be made with sufficient accuracy without using a series of non-exposure vectors. As such, FIG. 7 depicts a first ramp vector 460 beginning at the end of exposure vector 444, extending in a direction parallel to that of vector 444, and having a length necessary to transition the scanning speed of 444 down to a desired amount (i.e. HSRest). A transition vector begins at the end of ramp vector 460, extending in a direction parallel to that of the ramp vector, and having a length equal to the desired Feed forward amount (e.g. 4 ticks). The transition vector is followed by a jump vector that extends to the beginning of a second ramp vector 466. Feed forward commands are supplied at the end of jump vector 464 to make the transition to the direction of the second ramp vector without necessarily changing the net scanning speed. The second ramp vector 466 connects the jump vector 464 to the next exposure vector 446. The length of the ramp vector is sufficient to allow the scanning speed to attain the desired value of the next exposure vector.
FIG. 8 depicts three plots of values for scanning variables (i.e. IR power production, UV power reaching the vat, and scanning speed) versus the two exposure vectors bridged by the non-exposure vectors of FIG. 7. As indicated in the lower portion of the figure, the IR power production of the laser preferably remains the same. As indicated in the middle portion of the figure, it is preferred that UV power reaches the vat only during scanning of the two exposure vectors 444 and 446. It is preferred that UV power production cease during the scanning of the non-exposure vectors. With an AOM acting as the beam inhibitor, it is possible to shut down the beam and revive it within a few microseconds. The upper portion of the figure provides a plot of the net scanning speed resulting from the speed of scanning of the two substantially orthogonal is mirror scanners. As indicated, the exposure vector 444 is scanned with a large speed 470, the ramp vector 460 ramps the speed down to a desired lower amount, the transition vector 462 maintains the same net speed, the second ramp vector increases the scanning speed to a desired amount 472 for exposure vector 446.
The third preferred embodiment provides a technique for adjusting the power of the prescribed stimulation. Element 500 calls for setting a process control variable "i" equal to one. Element 502 calls for determining a desired laser power DLP based on desired exposure for each of the vectors making up an "i"th vector set VS(i). The vector set may be made up of various vectors. For example, VS may include all vectors of a single type on a given cross-section. VS may include all vectors of all types on a single cross-section or on a plurality of cross-sections. The individual vectors in VS may be given different exposures but a common laser power is used in drawing with the vectors.
ALP-DLP=ΔLP
Element 508 calls for determining whether the difference in laser power is within a desired tolerance band εLP,
ALP<δLP
The process then continues from either step 510 or 514, where an inquiry is made as to whether or not the VS(i) is the last vector set. If so, element 520 indicates that the process is complete. If not, the procedure moves to element 518 where "i" is incremented by one and the process loops back to element 500.
Element 600 of FIG. 10 calls for setting a process variable "i" equal to one. Element 602 calls for providing an "i"th vector set VS(i) where each vector in the set will be exposed with a beam having a single beam power.
ALP-HLP=ΔLP
ALP≧0+δLP?
If the response to the inquiry of element 614 is "yes," the process proceeds to Element 616 where the laser power is lowered from the ALP to HLP. Once the laser power is reset the process exposes the VS(I) using the HLP (Element 618)
If the response to the inquiry of element 614 was "no," the process moves forward to element 620 and 622. Element 620 calls for deriving the expose time, ETH (I), for the full set of vectors in VS(I) using the highest usable laser power HLP. Element 622 calls for deriving the expose time, ETA (I), for the full set of vectors in VS(I) using the actual laser power ALP.
ETA (I)-ETH (I)=ΔET
Is ΔET>δET?
If the inquiry produces a negative response, exposure occurs using the actual laser power (Element 628). If the inquiry produces a positive response, the laser power is increased to the highest useable power (Element 630). Whereafter Element 632 calls for exposing the vector set VS(i) using the highest usable laser power HLP.
Element 634 inquires as to whether the "i" th vector set VS(I) is the last vector set. If an affirmative response is obtained, the process proceeds to element 636 and determinates. If a negative response is obtained, the process proceeds to element 638 where the variable "i" is incremented by one, after which the process loops back to Element 602, where elements 602-634 are repeated until all the vector sets have been processed.
Various other alternatives and modifications to this fourth embodiment are possible. For example, the derivation of exposure time may be based on an estimate or on an exact calculation. The preset value δET may be a constant or a variable. It may take on one value if the change in power is to cause a dead time in exposure or it may be zero if the change in power has no impact on build time because the change will occur during a non-drawing period anyway. Some alternatives have been discussed herein above while others will be apparent to those of skill in the art.
In this embodiment a system user specifies a maximum draw speed by means of a graphical user interface. The maximum draw speed is specified for selected vectors. The selected vectors are those whose scan speeds are considered critical to the build process. Alternatively, the vectors for which maximum scan speed are specified may be those for which exposures are known to control the process based on their cure depths and the like, such that once they are specified, the specification of maximum speed for the other vector types would not change the process. Based on, inter alia, known material properties, desired cure depths, and maybe beam profile information, the beam power required to produce the maximum velocity is calculated for each of the vector types. For example, the vector type for which maximum scan speeds are specified may be one type of boundary and one type of hatch, alternatively boundary only or hatch only.
A top scanning speed is derived for each vector type. The top speed is based on the laser beam diameter, pulse repetition rate and an overlap criteria specified for each vector type. The overlap criterion specifies how close two consecutive pulses must be so that sufficient overlap is obtained. This overlap is usually considered in terms of percentage of beam diameter. A sample equation for top speed is,
Top Speed=Q*B*(1-OL)
Where Q is the pulse repetition rate in Hz, B is the beam diameter at the working surface in inches or mm, and OL is the minimum overlap criteria. The result of the computation is scanning speed in inches/second or mm/second. Overlap criteria may be empirically determined by building test objects with different overlap amounts and determining which overlap amounts produce objects with sufficient integrity, or other build property or build properties. Minimum overlap amounts on the order of 40%-60% of beam diameter have been found to be effective.
If a multiple beam diameter system and process is used, the small spot laser power is set to the lowest of:
Various further alternatives and modifications to this embodiment are possible. Some of these alternatives have been discussed herein above while others will be apparent to those of skill in the art.
Implementation of the methods described herein to form apparatus for forming objects according to the teachings herein can be implemented by programming an SLA control computer, or separate data processing computer, through software or hard coding. Methods and apparatus in any embodiment can be modified according to the alternative teachings explicitly described in association with one or more of the other embodiments. Furthermore, the methods and apparatus in these embodiments and their alternatives can be modified according to various teachings in the above incorporated patents and applications. It is believed that the teachings herein can be applied to other RP&M technologies.
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U.S. Classification 264/401, 425/135, 264/40.1, 425/174.4, 700/120, 425/375
International Classification G03F7/20, B29K105/32, B29C67/00
Cooperative Classification B29C64/135, B29C64/106, B33Y30/00, B29C2037/90, B33Y10/00
European Classification B29C67/00R2D2, B29C67/00R2
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:KEREKES, THOMAS;BEERS, ROSS D.;REEL/FRAME:009929/0110;SIGNING DATES FROM 19990413 TO 19990420