Source: http://www.docstoc.com/docs/51306906/Stereolithographic-Method-And-Apparatus-For-Production-Of-Three-Dimensional-Objects-Using-Multiple-Beams-Of-Different-Diameters---Patent-6406658
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Stereolithographic Method And Apparatus For Production Of Three Dimensional Objects Using Multiple Beams Of Different Diameters - Patent 6406658
United States Patent: 6406658
6,406,658
Stereolithographic method and apparatus for production of three dimensional
objects using multiple beams of different diameters
A rapid prototyping and manufacturing (e.g. stereolithography) method and
apparatus for making three-dimensional objects on a layer by layer basis
by selectively exposing layers of material to prescribed stimulation,
using a beam having a first smaller diameter and a beam having a second
larger diameter, to form laminae of the object. The power of the smaller
beam is typically lower than the power of the larger beam. Object
formation is controlled by data representing portions of the layers to be
exposed with the larger beam (large spot portions) and those portions to
be exposed with the smaller beam (small spot portions). In a preferred
embodiment, portions exposed with the larger beam are formed first, for a
given layer. Portions are exposed with the small beam next. Thereafter the
entire perimeter of the laminae is traced using the small beam. Data
manipulation techniques are used to identify which portions may be formed
with the large beam to decrease exposure time and which should be formed
with the small beam to maintain accuracy of the lamina being formed. More
than two beam diameters may be used.
Manners; Chris R. (Moorpark, CA), Guertin; Michelle D. (Valencia, CA), Nguyen; Hop D. (Quartz Hill, CA), Partanen; Jouni P. (Los Angeles, CA), Tang; Nansheng (Valencia, CA), Everett; Michael A. (Saugus, CA)
264/401  ; 425/174.4; 425/375; 700/120
B29C 67/00&amp;nbsp(20060101); B29C 035/08&amp;nbsp(); B29C 041/02&amp;nbsp(); B29C 017/50&amp;nbsp(); B29C 019/00&amp;nbsp(); G06F 017/50&amp;nbsp(); G06F 019/00&amp;nbsp()
264/401 425/174.4,375 700/120
2000-313067
95/18009
96/12607
96/12608
96/12609
96/12610
Jacobs, Paul F., Stereolithography and Other RP&amp;M Technologies From Rapid Prototyping to Rapid Tooling, Society of Manufacturing Engineers,
Jacobs, Paul F. Rapid Prototyping &amp; Manufacturing Fundamentals of yStereolithography, Society of Manufacturing Engineers, 1992.
U.S. Patent application No. 08/722,335, filed Sep. 27, 1996, by Leyden et al. (now abandoned).
U.S. Patent application No. 09/061,796, filed Apr. 16, 1998, by Wu et al. (pending).
U.S. Patent application No. 09/154,967, filed Sep. 17, 1998, by Nguyen et al. (now abandoned).
U.S. Patent application No. 09/246,416, filed Feb. 8, 1999, by Bishop et al. (pending).
U.S. Patent application No. 09/246,504, filed Feb. 8, 1999, by Guertin et al. (pending).
U.S. Patent application No. 09/247,113, filed Feb. 8, 1999, by Chari et al. (pending).
U.S. Patent application No. 09/247,119, filed Feb. 8, 1999, by Kulkarni et al. (pending).
U.S. Patent application No. 09/247,120, filed Feb. 8,1999 by Everett et al. (pending).
U.S. Patent application No. 09/484,984, filed Jan. 1, 2000, by Earl et al. (pending)..
1.  A 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 data representing a three-dimensional object;
providing a first beam of prescribed stimulation having a first dimension;
providing a second beam of prescribed stimulation having a second dimension that is larger than the first dimension, the first beam aid second beam being produced by the same laser light source and having an aspect ratio of between approximately
0.9 and 1.1;
manipulating the data to form modified object data for forming the three-dimensional object, the modified data including data indicative of cross-sectional portions to be formed using the beam having the second dimension and indicative of
cross-sectional portions to be formed using the beam having the first dimension;
exposing the material to the first beam and/or the second beam in accordance with the modified data to form a successive lamina of the object;  and
2.  The method of claim 1 wherein the data manipulation includes use of an erosion routine in determining which portions of a lamina are to be formed using the second beam.
3.  The method of claim 2 wherein the data manipulation includes a Boolean intersection operation in determining which portions of a lamina are to be formed using the second beam.
4.  The method of claim 3 wherein the data manipulation includes an inverse erosion routine applied to the portion that will be exposed using the second beam in the process of determining which portions of the lamina will be formed using the
5.  The method of claim 4 wherein the data manipulation includes a differencing operation in determining which portions of a lamina are to be formed using the first beam.
6.  The method of claim 5 wherein the data manipulation excludes features smaller than a preset limit during the process of determining which portions of a lamina are to be formed using the first beam.
7.  The method of claim 1 wherein the portions to be exposed with the second beam are determined prior to determining the portions to be formed using the first beam.
8.  The method of claim 1 wherein determination of a first portion to expose using the first beam and a second portion to expose using the second beam are based on a region that does not include the entire cross-sectional area of the lamina.
9.  The method of claim 8 wherein the region includes one of an up-facing region, a down-facing region, or a continuing region.
10.  The method of claim 1 wherein the laser light source is made to produce more optical power when the second beam is exposing the material than when the first beam is exposing the material.
11.  The method of claim 1 wherein the second dimension is 1.5 or more times larger than the first dimension.
12.  The method of claim 1 wherein the first beam is substantially focused onto the material and the second beam exposes the material outside a beam waist.
13.  The method of claim 1 wherein the first beam is substantially focused onto the material and the second beam is substantially focused on the material.
14.  The method of claim 1 wherein during formation of a single lamina, the second beam is utilized prior to utilization of the first beam.
15.  The method of claim 1 wherein the second beam is used to form at least two of boundaries, hatch, and fill for regions of the lamina.
16.  An 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:
means for receiving data representing a three-dimensional object;
means for providing a first beam of prescribed stimulation having a first dimension and means for providing a second beam of prescribed stimulation having a second dimension that is larger than the first dimension, and the first dimension and the
second dimension have an aspect ratio of between approximately 0.9 and 1.1;
means for manipulating the data to form modified object data for forming the three-dimensional object, the modified data including data indicative of cross-sectional portions to be formed using the beam having the second dimension and indicative
of cross-sectional portions to be formed using the beam having the first dimension;
means for exposing the material to the first beam and/or the second beam in accordance with the modified data to form a successive lamina of the object;  and
means for operating the means for forming and the means for in order to form the object from a plurality of adhered laminae.
17.  An 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 memory for receiving data representing a three-dimensional object;
one source for providing a first beam of prescribed stimulation having a first dimension and a second beam of prescribed stimulation having a second dimension that is larger than the first dimension, the first dimension and the second dimension
having an aspect ratio of between approximately 0.9 and 1.1;
a computer programmed to manipulate the data to form modified object data for forming the three-dimensional object, the modified data including data indicative of cross-sectional portions to be formed using the beam having the second dimension
and indicative of cross-sectional portions to be formed using the beam having the first dimension;
an exposure system for exposing the material to the first beam and/or the second beam in accordance with the modified data to form a successive lamina of the object;  and
a computer programmed to operate the means for forming and the means for exposing in order to form the object from a plurality of adhered laminae.
18.  The method of claim 1 wherein the first beam is used to form at least two of (1) boundaries, (2) hatch and (3) fill for regions of the lamina which are different from the regions formed with the second beam.
19.  The method of claim 1 wherein the second dimension and the first dimension have a ratio in the range of 1.5-5.
20.  The method of claim 19 wherein the ration is 2.5-4.  Description
This invention relates to the formation of three-dimensional objects using a Rapid Prototyping and Manufacturing (RP&amp;M) technique.  The invention more particularly relates to the stereolithographic formation of three-dimensional objects using a
plurality of different dimensioned beams of radiation.
Rapid Prototyping and Manufacturing (RP&amp;M) is the name given to a field of technologies that can be used to form three-dimensional objects rapidly and automatically from three-dimensional computer data representing the objects.  RP&amp;M can be
considered to include three classes of technologies: (1) Stereolithography, (2) Selective Deposition Modeling, and (3) Laminated Object Manufacturing.
The stereolithography class of technologies creates three-dimensional objects based on the successive formation of layers of a fluid-like material adjacent to previously formed layers of material and the selective solidification of those layers
according to cross-sectional data representing successive slices of the three-dimensional object in order to form and adhere laminae (i.e. solidified layers).  One specific stereolithography technology is known simply as stereolithography and uses a
liquid material that is selectively solidified by exposing it to prescribed stimulation.  The liquid material is typically a photopolymer and the prescribed stimulation is typically visible or ultraviolet electromagnetic radiation.  The radiation is
typically produced by a laser though other sources of radiation are possible such as arc lamps, resistive lamps, and the like.  Exposure may occur by scanning a beam or by controlling a flood exposure by use of a light valve that selectively transmits or
reflects the radiation.  Liquid-based stereolithography is disclosed in various patents, applications, and publications of which a number are briefly described in the Related Applications section hereafter.
Another stereolithography technology is known as Selective Laser Sintering (SLS).  SLS is based on the selective solidification of layers of a powdered material by exposing the layers to infrared electromagnetic radiation to sinter or fuse the
powder particles.  SLS is described in U.S.  Pat.  No. 4,863,538, issued Sep. 5, 1989, to Deckard.  A third technology is known as Three Dimensional Printing (3DP).  3DP is based on the selective solidification of layers of a powdered material which are
solidified by the selective deposition of a binder thereon.  3DP is described in U.S.  Pat.  No. 5,204,055, issued Apr.  20, 1993, to Sachs.
The present invention is primarily directed to stereolithography using liquid-based building materials (i.e. medium).  It is believed, however, that the techniques of the present invention may have application in the other stereolithography
technologies in order to achieve faster object formation times and/or higher object resolution.
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.  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 issued Aug.  24, 1999 to Earl et al. and U.S.
patent application Ser.  No. 08/722,335, filed Sep. 27, 1996, by Leyden et al., now abandoned.
Though, as noted above, the techniques of the instant invention are directed primarily to liquid-based stereolithography object formation, it is believed that the techniques may have application in the SDM technologies to enhance object
resolution and/or to decrease object formation times.
Laminated Object Manufacturing, LOM, techniques involve the formation of three-dimensional objects by the stacking, adhering, and selective cutting of sheets of material, in a selected order, according to the cross-sectional data representing the
three-dimensional object to be formed.  LOM is described in U.S.  Pat.  No. 4,752,352, issued Jun.  21, 1988, to Feygin, U.S.  Pat.  No. 5,015,312, issued May 14, 1991, to Kinzie, and U.S.  Pat.  No. 5,192,559, issued Mar.  9, 1993, to Hull et al.; and
in PCT Publication No. WO 95-18009, published Jul.  6, 1995, by Morita.
It is believed that the techniques of the present invention may have application in the LOM technologies to enhance object resolution when using a laser beam or mechanical cutting tool to cutout cross-sections and dissecting or sublimating the
non-cross-section regions.
Various techniques for enhancing object formation speed have been described previously.  In particular various techniques have been described in U.S.  Pat.  No. 5,089,185, issued Feb.  18, 1992 to Hirano.  This patent describes the use of a large
diameter light flux for a section having a thickness larger than the diameter of the light flux and using a small diameter light flux for sections having a thickness smaller than the diameter of the light flux having the large diameter.  This patent
indicates, inter alia, that the light flux having the small diameter is connected to a low power laser source while the light flux having the large diameter is connected to a high power laser source.
Though this patent teaches the desire to use a large diameter light flux and a small diameter light flux, it fails to provide any teachings concerning how to manipulate object data to distinguish regions requiring the small diameter light flux
and those capable of being formed using the large diameter light flux.  This reference further fails to teach the desirability of distinguishing cross-sectional regions from one another when determining where to apply the large diameter and small
diameter light fluxes.
2.  Other Related Patents and Applications
The patents, applications, and publications mentioned above and hereafter are all incorporated by reference herein as if set forth in full.  Table 1 provides a listing of patents and applications co-owned by the assignee of the instant
application.  A brief description of subject matter found in each patent and application is included in the table to aid the reader in finding specific types of teachings.  It is not intended that the incorporation of subject matter be limited to those
topics specifically indicated, but instead the incorporation is to include all subject matter found in these applications and patents.  The teachings in these incorporated references can be combined with the teachings of the instant application in many
ways.  For example, the references directed to various data manipulation techniques may be combined with the teachings herein to derive even more useful, modified object data that can be used to more accurately and/or efficiently form objects.  As
another example, the various apparatus configurations disclosed in these references may be used in conjunction with the novel features of the instant invention.
TABLE 1  Related Patents and Applications  Patent No.  Issue Date  Application  No.  Filing Date Inventor Subject  4,575,330 Hull Discloses fundamental elements of  Mar 11, 1986 stereolithography.  06/638,905  Aug 8, 1984  4,999,143 Hull, et al.
Discloses various removable support  Mar 12, 1991 structures applicable to  07/182,801 stereolithography.  Apr 18, 1988  5,058,988 Spence Discloses the application of beam  Oct 22, 1991 profiling techniques useful in stereo-  07/268,816 lithography for
determining cure depth  Nov 8, 1988 and scanning velocity, etc.  5,059,021 Spence, et al. Discloses the utilization of drift  Oct 22, 1991 correction techniques for eliminating  07/268,907 errors in beam positioning resulting  Nov 8, 1988 from
instabilities in the beam scanning  system  5,076,974 Modrek, et al. Discloses techniques for post processing  Dec 31, 1991 objects formed by stereolithography.  07/268,429 In particular exposure techniques are  Nov 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 type  07/339,246 distortion, in objects being formed by  Apr 17, 1989 stereolithography.  5,123,734 Spence, et al. Discloses techniques for calibrating a  Jun 23, 1992 scanning system. In particular tech-  07/268,837 niques for mapping
from rotational  Nov 8, 1988 mirror coordinates to planar target  surface coordinates are disclosed  5,133,987 Spence, et al. Discloses the use of a stationary mirror  Jul 28, 1992 located on an optical path between the  07/427,885 scanning mirrors and
the target surface  Oct 27, 1989 to fold the optical path in a  stereolithography system.  5,141,680 Almquist, et al. Discloses various techniques for  Aug 25, 1992 selectively dispensing a material to  07/592,559 build up three-dimensional objects.  Oct
4, 1990  5,143,663 Leyden, et al. Discloses a combined stereolithography  Sep 1, 1992 system for building and cleaning  07/365,444 objects.  Jun 12, 1989  5,174,931 Almquist, et al. Discloses various doctor blade config-  Dec 29, 1992 urations for use in
forming coatings of  07/515,479 medium adjacent to previously  Apr 27, 1990 solidified laminae.  5,182,056 Spence, et al. Discloses the use of multiple wave-  Jan 26, 1993 lengths in the exposure of a stereo-  07/429,911 lithographic medium.  Oct 27,
1989  5,182,715 Vorgitch, et al. Discloses various elements of a large  Jan 26, 1993 stereolithographic system.  07/824,819  Jan 22, 1992  5,184,307 Hull, et al. Discloses a program called Slice and  Feb 2, 1993 various techniques for converting three-
07/331,644 dimensional object data into data  Mar 31, 1989 descriptive of cross-sections. Disclosed  techniques include line width compen-  sation techniques (erosion routines),  and object sizing techniques. The  application giving rise to this patent
included a number of appendices that  provide further details regarding stereo-  lithography methods and systems.  5,192,469 Hull et al. Discloses various techniques for form-  Mar 9, 1993 ing three-dimensional object from sheet  07/606,802 material by
selectively cutting out and  Oct 30, 1990 adhering laminae.  5,209,878 Smalley, et al. Discloses various techniques for reduc-  May 11, 1993 ing surface discontinuities between suc-  07/605,979 cessive cross-sections resulting from a  Oct 30, 1990
layer-by-layer building technique.  Disclosed techniques include use of  fill layers and meniscus smoothing.  5,234,636 Hull, et al. Discloses techniques for reducing sur-  Aug 10, 1993 face discontinuities by coating a formed  07/929,463 object with a
material, heating the mate-  Aug 13, 1992 rial 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 minimizing  Aug 24, 1993 curl distortion by
balancing upward curl  07/939,549 to downward curl.  Mar 31, 1992  5,256,340 Allison, et al. Discloses various build/exposure styles  Oct 26, 1993 for forming objects including various  07/906,207 techniques for reducing object distor-  Jun 25, 1992
tion. Disclosed techniques include: (1)  and building hollow, partially hollow, and  08/766,956 solid objects, (2) achieving more uni-  Dec 16, 1996 form cure depth, (3) exposing layers as  a series of separated tiles or bullets, (4)  using alternate
sequencing exposure pat-  terns from layer to layer, (5) using stag-  gered or offset vectors from layer to  layer, and (6) using one or more over-  lapping exposure patterns per layer.  5,321,622 Snead, et al. Discloses a computer program known as  Jun
14, 1994 CSlice which is used to convert three-  07/606,191 dimensional object data into cross-  Oct 30, 1990 sectional data. Disclosed techniques  include the use of various Boolean  operations in stereolithography.  5,597,520 Smalley, et al. Discloses
various exposure techniques  Jan 28, 1997 for enhancing object formation accu-  08/233,027 racy. Disclosed techniques address  Apr 25, 1994 formation of high resolution objects  and from building materials that have a  08/428,951 Minimum Solidification
Depth greater  Apr 25, 1995 than one layer thickness and/or a Min-  imum Recoating Depth greater than the  desired object resolution.  08/722,335 Leyden, et al. Discloses build and support styles for  Sep 27, 1996 use in a Multi-Jet Modeling selective
now deposition modeling system.  abandoned  5,943,235 Earl et al. Discloses data manipulation and system  Aug 24, 1999 control techniques for use in a Multi-Jet  08/722,326 Modeling selective deposition modeling  Sep 27, 1996 system.  5,902,537 Almquist,
et al. Discloses various recoating techniques  May 11, 1999 for use in stereolithography. Disclosed  08/790,005 techniques include 1) an ink jet dispens-  Jan 28, 1997 ing 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-state  Nov 24, 1998 lasers to stereolithography. Discloses  08/792,347 the use of a pulsed radiation source
for  Jan 31, 1997 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 stereolithographic form-
Dec 14, 1999 ation of objects using a pulsed radiation  08/847,855 source where pulsing occurs at selected  Apr 28, 1997 positions on the surface of a building  material.  6,084,980 Nguyen, et al. Discloses techniques for interpolating  Jul 4 2000
originally supplied cross-sectional data  08/855,125 descriptive of a three-dimensional  May 13, 1997 object to produce modified data descrip-  tive of the three-dimensional object  including data descriptive of inter-  mediate regions between the
originally  supplied cross-sections of data.  5,945,058 Manners, et al. Discloses techniques for identifying  Aug 31, 1999 features of partially formed objects.  08/854,950 Identifiable features include trapped  May 13, 1997 volumes, effective trapped
volumes, and  solid features of a specified size. The  identified regions can be used in auto-  matically specifying recoating para-  meters and or exposure parameters  5,902,538 Kruger, et al. Discloses simplified techniques for  May 11, 1999 making
high-resolution objects utilizing  08/920,428 low-resolution materials that are limited  Aug 29, 1997 by their inability to reliably form coat-  ings of a desired thickness due to a  Minimum Recoating Depth (MRD)  limitation. Data manipulation tech-
niques 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.  6,157,663 Wu, et al. Discloses use of frequency converted
Dec 5, 2000 solid state lasers in stereolithography.  09/061,796  Apr 16, 1998  09/154,967 Nguyen, et al. Discloses techniques for stereo-  Sep 17, 1998 lithographic recoating using a sweeping  now recoating device that pause and/or slows  abandoned down
over laminae that are being coated  over.  09/484,984 Earl, et al. Entitled &quot;Method and Apparatus for  Jan 18, 2000 Forming Three Dimensional Objects  Using Line Width Compensation with  Small Feature Retention.&quot; 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 &quot;Method and Apparatus for  Feb 8, 1999 Stereolithographically Forming Three  Dimensional Objects With
Reduced  Distortion.&quot; 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 &quot;Stereolithographic Method and  Feb 8, 1999 Apparatus
for Production of Three  Dimensional Objects Using Recoating  Parameters for Groups of Layers.&quot;  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.  6,261,077 Bishop, et al. Entitled &quot;Rapid Prototyping Apparatus  Jul 17, 2001 with Enhanced Thermal and Vibrational
09/246,416 Stability for Production of Three  Feb 8, 1999 Dimensional Objects.&quot; Discloses an  improved Stereolithographic apparatus  structure for isolating vibration and/or  extraneous heat producing components  from other thermal and vibration sen-
sitive components.  6,153,142 Chari, et al. Entitled &quot;Stereolithographic Method and  Nov 28, 2000 Apparatus for production of Three  09/247,113 Dimensional Objects with Enhanced  Feb 8, 1999 thermal Control of the Build environ-  ment. Discloses improved
stereolitho-  graphic techniques for maintaining build  chamber temperature at a desired level.  The techniques include varying heat  production based on the difference be-  tween a detected temperature and the  desired temperature.  6,241,934 B1
Everett, et al. Entitled &quot;Stereolithographic Method and  Jun 5, 2001 Apparatus for production of Three  09/247,120 Dimensional Objects Including En-  Feb 8, 1999 hanced Control of Prescribed Stimu-  lation Production.&quot; Discloses techniques  forming
objects using varying produc-  tion of prescribed stimulation (e.g. UV  radiation)and enhanced scanning con-  trol. Production is reduced or eliminated  during non-exposure periods (e.g.  recoating, z-wait, and pre-dip delay).  Production is set to a
based on the type of exposure that is  desired. Scanning speed is set based on  a number of criteria. Transition between  successive exposure vectors may be  made with multiple intervening non-  exposure vectors. The laser power is set  using an
AOM in combination with a  temporary detection of beam power.  6,159,411 Kulkarni, et al. Entitled &quot;Stereolithographic Method  Dec 12, 2000 and Apparatus for Production of Three  09/247,119 Dimensional Objects Including  Feb 8, 1999 Simplified Build
Preparation.&quot; Dis-  closes techniques for forming objects  using a simplified data preparation  process. Selection of the various para-  meter styles needed to form an object is  reduced to answering several questions  from lists of possible choices.
The following two books are also incorporated by reference herein as if set forth in full: (1) Rapid Prototyping and Manufacturing: Fundamentals of Stereolithography, by Paul F. Jacobs; published by the Society of Manufacturing Engineers,
Dearborn Mich.; 1992; and (2) Stereolithography and other RP&amp;M Technologies: from Rapid Prototyping to Rapid Tooling; by Paul F. Jacobs; published by the Society of Manufacturing Engineers, Dearborn Mich.; 1996.
It is a first object of the invention to provide enhanced techniques for forming three-dimensional objects using RP&amp;M technologies.
A first aspect of the invention is to provide a 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 data
representing a three-dimensional object; (2) providing a first beam of prescribed stimulation having a first dimension; (3) providing a second beam of prescribed stimulation having a second dimension larger than the first dimension; (4) manipulating the
data to form modified object data for forming the three-dimensional object, the modified data including data indicative of cross-sectional portions to be formed using the beam having the second.  dimension and indicative of cross-sectional portions to be
formed using the beam having the first dimension; (5) forming a layer of material adjacent to any last formed layer of material in preparation for forming a subsequent lamina of the object; (6) exposing the material to the first beam and/or the second
beam in accordance with the modified data to form a successive lamina of the object; and (7) repeating the acts of forming and exposing a plurality of times in order to form the object from a plurality of adhered laminae.
A second aspect of the invention is to provide an 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) means for
receiving data representing a three-dimensional object; (2) means for providing a first beam of prescribed stimulation having a first dimension; (3) means for providing a second beam of prescribed stimulation having a second dimension larger than the
first dimension; (4) means for manipulating the data to form modified object data for forming the three-dimensional object, the modified data including data indicative of cross-sectional portions to be formed using the beam having the second dimension
and indicative of cross-sectional portions to be formed using the beam having the first dimension; (5) means for forming a layer of material adjacent to any last formed layer of material in preparation for forming a subsequent lamina of the object; (6)
means for exposing the material to the first beam and/or the second beam in accordance with the modified data to form a successive lamina of the object; and (7) means for operating the means for forming and the means for exposing to form the object from
a plurality of adhered laminae.
A third aspect of the invention is to provide an 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 memory for
receiving data representing a three-dimensional object; (2) a source of a first beam of prescribed stimulation, the first beam having a first dimension; (3) a source of a second beam of prescribed stimulation, the second beam having a second dimension
larger than the first dimension; (4) a computer programmed to manipulate the data to form modified object data for forming the three-dimensional object, the modified data including data indicative of cross-sectional portions to be formed using the beam
having the second dimension and indicative of cross-sectional portions to be formed using the beam having the first dimension; (5) a recoating system for forming a layer of material adjacent to any last formed layer of material in preparation for forming
a subsequent lamina of the object; (6) a scanning system for exposing the material to the first beam and/or the second beam in accordance with the modified data to form a successive lamina of the object; and (7) a control system for operating the
recoating system and the scanning system to form the object from a plurality of adhered laminae.
Additional objects and aspects of the invention will be clear from the embodiments and their alternatives described below in conjunction with the FIGS. associated therewith.  Further aspects of invention involve the practice of the above referred
to aspects of the invention in combination with one another.
FIG. 5a depicts a top view of cross-section 106 of FIG. 2b.
FIG. 5b depicts a top view of cross-section 106 of FIG. 2b wherein the cross-section has been divided into large spot and small spot regions.
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.RTM.  system are described in U.S.  Pat.  Nos.  4,575,330; 5,184,307; and
5,182,715 as referenced above.  The preferred SLA.RTM.  system 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. 1a 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 applications 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. 09/248,352.  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 at a desired 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 67 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 80 be controlled to produce two or more beam diameters for
forming object laminae.  The AOM 72 is preferably controlled to adjust beam power based 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&#39;, 86&quot;, or 86&#39;&quot; as examples of the different directions in which the bear 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. 0.sup.th and 2.sup.nd) 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 5.
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 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&#39;.  From mirror 79&#39; 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&quot;, then a third focusing mirror 79&#39;&quot;,
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&#39; and 81&quot;.  The cylindrical lenses are used to remove astigmatism and in 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&#39; 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 a lenses 83&#39; and 83&quot; in the beam focusing module 80.  After passing through lens 83&quot; the beam direction is
reoriented by two folding mirrors 78.
The beam then reenters the focusing module and passes through movable lens 83&#39;&quot;.  The position of lens 83&#39;&quot; is controlled by stepper motor 87, moveable mount 88, and dive 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.
It is preferred that the focus system be precalibrated so that adjustment from one beam size to another may be accomplished without delay.  In this regard it is preferred that an encoder provide stepper motor position and that the computer
contain a table of encoder positions corresponding to different desired beam sizes.  Based on values in the look up table the stepper motor can be commanded to move to a new position based on a difference between present position and desired position.
Once the new position is reached, if desired, the actual beam diameter may be checked using a beam profiling system as described in previously referenced U.S.  Pat.  No. 5,058,988.  Various alternative approaches to setting beam size will be apparent to
The beam then proceeds to folding mirror 78 and out exit window 90 where after the beam encounters the scanning mirrors or other optical components.  The beam produced by this laser head is pulsed at a useable frequency (e.g. 22.5-40 KHz or
more).  The laser head is preferably water cooled by passing water in through the base plate that supports the components depicted in FIG. 1d.  The water preferably enters the plate through orifice 91 proceeds along a winding flow path and then exits the
plate at orifice 92.
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, (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.
The water passing through the base plate is also preferably used to cool the IR laser diodes 71.  It is preferred that the water pass through the base plate prior to passing on to the laser diodes 71.  The water may be recirculated through an
enclosed cooling system or other recirculating or non-recirculating system.  Various alternatives to water cooling are possible and will be apparent to those of skill in the art.
Preferred control and data manipulation systems and software are described in a number of the patents referenced above, including U.S.  Pat.  Nos.  5,184,307; 5,321,622; and 5,597,520.
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.
Other components of a preferred SLA.RTM.  system (not shown) may include a liquid level control system, a build chamber, an environmental control system including a temperature control system, safety interlocks, a viewing device, and the like.
SLA.RTM.  systems on which the instant invention can be utilized are available from 3D Systems, Inc.  of Valencia, Calif.  These SLA.RTM.  systems include the SLA-250 using a CW HeCd laser operating at 325 nm, the SLA-3500, SLA-5000, and the
SLA-7000 using a solid state lasers operating at 355 nm with a pulse repetition rates of 22.5 KHz, 40 Kz, 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.
The typical operation of an SLA.RTM.  system involves alternating formation of coatings of material (i.e. layers of material) and the selective solidification of those coatings to form an object from a plurality of adhered laminae.  The process
may conceptually be viewed as beginning with the elevator platform 9 immersed one layer thickness below the upper surface 20 of the photopolymer 5.  The coating of photopolymer is selectively exposed to prescribed stimulation (e.g. a beam of UV
radiation) which cures the material to a desired depth to form an initial lamina of the object adhered to the elevator platform.  This initial lamina corresponds to an initial cross-section of the object to be formed or corresponds to an initial
cross-section of supports that may be used to adhere the object to the platform.  After formation of this initial lamina, the elevator platform and adhered initial lamina are lowered a net amount of one layer thickness into the material.
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.
After formation of this coating, the second layer is solidified by a second exposure of the material to prescribed stimulation according to data representing a second cross-section of the object.  This process of coating formation and
solidification is repeated over and over again until the object is formed from a plurality of adhered layers (21, 23, 25, 27, 29, 31, and 33).
In some building techniques, incomplete solidification of some or all object cross-sections may occur.  Alternatively, in some processes an object lamina associated with a given layer (i.e. a lamina whose location should be positioned, relative
to the rest of the object, at the level corresponding to that layer of material) may not be exposed or may be only partially exposed in association with that layer (i.e. when that layer is located at the surface of the liquid).  Instead, that lamina may
be formed in whole or in part in association with a subsequently formed layer wherein the exposure applied to this subsequent layer is such as to cause material transformation to such an extent as to cause solidification in the material at the level of
the associated cross-section.  In other words, the layer which is associated with a given lamina may not be the layer in association with which the lamina will be solidified.  It may be said that the layer in association with which a lamina or portion of
a lamina is formed, is that layer which is located at the surface of material at the time the lamina is solidified.  The layer with which a lamina is associated, is that layer which corresponds to the dimensionally correct location of the lamina relative
to the rest of the object.
FIG. 2a depicts a side view of an object 41 to be produced stereolithographically.  In terms of forming horizontal layers, this figure depicts the vertical axis (Z) and one of the horizontal axes (X).  This object will be used to illustrate some
aspects of a preferred embodiment and alternative embodiment of the instant invention.  This object includes two horizontal (i.e. flat) down-facing features: one at the bottom 43 of the object and the other at the upper edge 45 of the hole 47 through the
middle of the object.  Similarly, this object includes two horizontal (i.e. flat) up-facing features: one at the top 49 of the object and the other at the lower edge 51 of the hole 47 through the middle of the object.  This object includes two vertical
walls 53 and 55 located on either side of hole 47.  This object also includes two non-horizontal (sometimes called, near flat) up-facing regions 57 and 59 located on either side of the object and two non-horizontal down-facing regions 61 and 63 located
on either side of the object.
FIG. 2b illustrates the object as it might be formed with a desired resolution using stereolithography wherein the minimum solidification depth, MSD, and minimum recoating depth, MRD, (discussed in U.S.  Pat.  Nos.  5,597,520 and 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 typically 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 quality 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.
FIG. 2c depicts the object as produced in FIG. 2b but with various regions of the object and object laminae distinguished.  In one classification scheme (as described in U.S.  Pat.  No. 5,321,622) each lamina of the object can be made up of one,
two or three different regions: (1) down-facing regions; (2) up-facing regions, and (3) continuing regions (i.e. regions that are neither down-facing nor up-facing).  In this scheme, the following eight vector types might be utilized though others may be
defined and used:
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.
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 ensue adhesion to a lower lamina.
TABLE 2  Object Regions Existing on Each Lamina of FIG. 2c  Up-Facing Continuing  Lamina &amp; Layer Down-Facing Region(s) Region(s) Region(s)  101, 201 231  102, 202 232 272  103, 203 233 273  104, 204 234 274  105, 205 235 275  106, 206 236 256
276  107, 207 237 277  108, 208 238 278  109, 209 259 279  110, 210 260 280  111, 211 241 261 281  112, 212 262 282  113, 213 263 283  114, 214 264 284  115, 215 265 285  116, 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; 5,943,235; 5,902,538 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.
The starting point for implementation of the instant invention need not be the data associated with a strict layer-by-layer building process as illustrated in FIG. 2b and 2c.  The starting point may be initial or modified three-dimensional object
data that has not yet been converted to cross-sectional data.  Furthermore, it may be modified cross-sectional data descriptive of laminae that will not be formed on a strict layer-by-layer basis.  For example, the starting point may be surface or
cross-sectional data that has been modified to accommodate for an MSD and/or an MRD that is greater than one layer thickness.
A first preferred embodiment of the instant invention involves the formation of three-dimensional objects using a first beam having a first diameter and a second beam having a second diameter that is larger than the diameter of the first beam.
The smaller of the beams is referred to herein as the &quot;small spot&quot;, while the larger of the beams is referred to herein as the &quot;large spot&quot;.  This first embodiment involves a data manipulation technique for determining which portions of each
cross-section should be formed with each beam.  FIG. 3 depicts a flow chart illustrating the preferred data manipulation process for the first embodiment.
In this embodiment support data is considered to always be formed using the smaller spot as the preferred support structures are typically of narrow dimension.  These support structures are further described in U.S.  Pat.  No. 4,999,143.  This
assumption about the support structure is advantageous in that it reduces data manipulation time with little or no impact on the beam size use conclusions.
The process begins with the initial data and parameters set forth in elements 300, 302, and 304.  Element 300 calls for supplying data representing the object or objects to be formed.  Element 302 sets a looping parameter for variable &quot;N&quot; equal
to one.  The variable &quot;N&quot; is used to designate the cross-section for which large spot and small spot data is being derived.  Since the process begins with N=1, the process starts with the first cross-section of object data.  Element 304 calls for
providing all necessary parameters for use in deriving cross-sectional data.
These parameters include but may not be limited to specification of large spot compensation information (LSCI) and small spot compensation information (SSCI).  This information may be obtained in a number of ways.  Several examples include: (1)
obtaining it from a storage location on already existing in the process computer or other computer, (2) it may be automatically derived from beam profile detection and evaluation, (3) it may be input by an operator.  The compensation information may be
in the form of beam diameter or radius, full or half line width associated with a line of desired cure depth formed by the beam, or the like.
Element 306 makes use of the data and parameters supplied by elements 300, 302, and 304.  Element 306 calls for the derivation of initial cross-section boundaries (ICSB) for cross-sections N-1, N, and N+1.  These cross-sections are preferably
compensated for the estimated line width associated with use of the smaller beam.  These initial cross-section boundaries are labeled as ICSB(N-1), ICSB(N), and ICSB(N+1), respectively.  The procedure used by this element may be that described in U.S.
Pat.  No. 5,321,622.
Element 308 calls for the setting of a variable &quot;I&quot; to a value of 1.  This variable is used as a marker for designating which cross-sectional region is being operated upon.  Element 310 calls for derivation of a cross-sectional region RB(I)
corresponding variable &quot;I&quot; based on ICSB(N).  Variable &quot;I&quot; can take on values from 1 to 3, each corresponding to one of (1) down-facing regions, (2) up-facing regions, or (3) continuing regions.
Element 312 calls for deriving initial large spot data, ILSD(I), by performing an erosion routine on RB(I) using large spot compensation information, LSCI.  This LSCI is preferably equal to one half the line width associated with the using the
large spot.  Techniques for performing erosion operations (e.g. line width compensations) are provided in previously referenced U.S.  Pat.  Nos.  5,321,622; 5,184,307; and 5,965,079 and U.S.  patent application Ser.  No. 09/484,984.  This element is used
to ensure that formation of the large spot region will not adversely impact the XY dimensions of the region.
Element 314 calls for deriving final large spot data FLSD(I).  This derivation occurs based on taking the Boolean intersection of the areas occupied by the initial large spot data for region (I) and the boundary for region (I).  This element is
used to ensure that the derivation of the ILSD(I) did not inadvertently result a region or regions of excess size.  The operation may be expressed as,
Element 316 calls for deriving expanded large spot data, ELSD(I), by performing an inverse erosion (i.e. an expansion) using LSCI.  The amount of inverse erosion is preferably equivalent to the original erosion amount used in element 312.  With
the exception of portions of the region that collapsed in response to the erosion of element 312, the reverse erosion of element 316 brings the expanded large spot data ELSD(I) boundary back to approximately the position of the original region data
RB(I).
Element 318 calls for deriving initial small spot data ISSD(I) by taking the Boolean difference between the area of original region data RB(I) and the area of the expanded large spot data, ELSD(I).  This may be expressed as,
Element 320 calls for deriving first modified small spot data, FMSSD(I), by performing an erosion routine based on small feature compensation information, SFCI.  The amount of the erosion is set based on a desire to remove small features of a
certain size.  These small features may inadvertently result from the prior operations or may simply be small features that may be ignored when determining which areas to expose with the small spot.  The erosion amount may be set at or above one half the
desired feature size that is to be removed.  The erosion amount may be set equal to the one half the line width obtained when using the small spot.
Element 322 calls for deriving second modified small spot data, SMSSD(I) by performing an inverse erosion routine based SFCI.  The amount of the inverse erosion is preferably identical to the amount used in step 320.  Element 320 and 322 provide
a second way of reducing unnecessary small spot exposures that may otherwise be called for.
Element 324 calls for deriving the final small spot data, FSSD(I).  This operation is preferably performed by taking the intersection of the second modified small spot data, SMSSD(I), with the original region data, RB(I).  This element is
provided in order to ensure that the derivations leading up to the SMSSD(I) have not produced a region of excess size.  The derivation of this element may be expressed as,
Element 326 makes the enquiry as to whether the value of &quot;I&quot; equals three.  As noted previously, in this embodiment the maximum value of &quot;I&quot; is three.  The first pass through sets 310-324 is used to produce large spot data and small spot data for
one of the possible cross-section regions.  This region may be, for example, the down-facing region for cross-section N. If the value of I, is the equal to three, element 326 causes the process to proceed to element 330 which increments the value of &quot;I&quot;
by one.  The process then repeats elements 310 to 324 for a next cross-sectional region to derive a large and small spot data for this next region (e.g. up-facing regions or continuing regions).  This looping through elements 310 to 324 is continued
until large spot and small spot data is generated for each of the applicable regions.
Once large and small spot data is derived for all three regions, the process proceeds to element 328.  Element 328 calls for saving the final large spot data for each of the three regions (for exposure using the large spot), the final small spot
data for each of the three regions (for exposure using the small spot), and saving the initial cross-section boundary for cross-section N (for exposure using the small spot).  The utilization of a complete trace of the overall cross-sectional perimeter
(ICSB) perimeter(s) by the small spot may perform one or more of several functions: (1) it may help to tie together the independent formed regions, (2) it may help to give the outer surface a smoother appearance, and/or (3) it may help increase the
accuracy of the perimeter region.
Though not explicitly indicated in the flow chart, if there is no data for a particular region, the execution of elements 310-324 for that region may be skipped such that the process jumps to element 326.  If no region data RB(I) exists for
particular region type, the process will simply produce no large or small spot data for that region of the cross-section.
Next, element 332 inquires as to whether N equals the maximum value of N. If the answer in element 332 is &quot;no&quot;, N is incremented by one, per element 338, and the process loops back through steps 306-330.  If the answer in 332 is &quot;yes&quot;, element
334 calls for the saving of all data in the proper order for object formation.  Once the data is saved, element 336 indicates that the process is complete.
The application of this process to an object cross-section is illustrated with the aid of FIGS. 4a and 4b.  FIG. 4a depicts a top view of lamina/cross-section 106 of FIG. 2c.  This lamina/cross-section is indicated in FIG. 2c and 4a as containing
five distinct regions.  FIG. 2c labels these regions from left to right as 236, 276, 256, 276, and 236, while FIG. 4a labels these regions as 400&#39;, 410&#39;, 420, 410&quot;, and 400&quot;, respectively.  Regions 400&#39; and 400&quot; are down-facing regions.  Regions 410&#39; and
410&quot; are continuing regions, and region 420 is an up-facing region.  According to this first preferred embodiment each of these regions will be independently supplied with large spot portions (to the extent possible) and small spot portions.
FIG. 4b illustrates that regions 410&#39;, 420, and 410&quot; are of sufficient size to allow large spot boundaries to be identified respectively as 412&#39;, 422, and 412&quot;, while regions 400&#39; and 400&quot; are too small to have any portion of them formed using
the large spot (based on the assumed line widths used).  The region between lines 414&#39; and 416&#39; will be formed upon tracing the boundary 412&#39; with the large spot beam.  Line 414&#39; may be very close to boundary 410&#39; depending on whether elements 312 and
316 of FIG. 3 were performed using identical or substantially identical compensation amounts.  The region 418&#39; interior to the loop formed by line 416&#39; will be filled in, as desired, by the large spot beam tracing hatch vectors.  The same respective
situation holds for elements 414&quot;, 416&quot;, and 418&quot;.  The situation is also analogous for elements 424, 426, and 428.  The loop formed by line 430 indicates the widening of the cross-sectional dimensions as the outer perimeter of the cross-section (which
corresponds to ICSB(N)) is traced with the small spot beam.  This inherent widening illustrates impetus for having the ICSB(N) initially compensated inward by one half the line width associated with the small spot.
In this first preferred embodiment the small spot is preferably about 10 mils in diameter while the larger spot is about 30 mils in diameters.  As the small beam will be used in the formation of the external boundaries of a cross-section, it is
preferred that the small spot beam be focused at or near the working surface such that the beam remains substantially in focus over the entire working surface of the building material.  In other words, to ensure minimal change in beam size, while using
the small spot with rotational scanning mirrors, it is desired that small spot exposure occur using the beam waist.  The large beam may be used in an off focus state as slight size variations in the beam at different locations on the working surface will
have little or no impact on the accuracy of the objects formed.  However, for optimal performance, it is preferred to have both bees focused on the surface of the material (i.e. beam waist at surface of the material).  Placing the beam waist of the
second beam at the material surface may occur in many ways.  As a single example, a moving carriage could translate lenses 83&#39; and 83&quot; as lens 83&#39;&quot; is moved to obtain a different spot size on the material while maintaining the beam waist at the material
Many alternatives of the techniques of the first embodiment are possible.  Examples of some alternatives are provided below.  These examples are only intended to be illustrative and not a complete listing.  Numerous other alternatives will be
apparent to those of skill in the art upon reviewing the disclosure herein.
Instead of basing the derivation of large spot and small spot regions on boundary data as preferred in the first embodiment, the derivation may be based on pixel data, voxel data, run length encoded data, or other data types.  Boolean operations,
erosion operations, and/or other operations may be performed using bit maps, or the like.
Element 306 may use boundaries that are not compensated for line width wherein required compensation could be performed at a later stage of processing.  As a further alternative the compensation may not be performed at all especially if a final
spot boundary is not intended to trace the entire cross-sectional perimeter.
Elements 306 and/or 310 may be performed in a modified manner if it is desired to compensate for a minimum solidification depth, MSD, that is greater than one layer thickness.  Similarly, elements 306 and/or 310 may be modified to account for
build process changes that deal with minimum recoating depth, MRD issues.  Procedures for deriving data that accommodates for MSD and/or MRD values greater than one layer thickness may be found in U.S.  Pat.  Nos.  5,999,184 and 5,902,538.
Element 312 may use an erosion amount different from one half the line width.  It may, for example use an amount that is larger than one half the line width.  It may be as small as the one half the difference between the large spot line width and
the small spot line width.  This is most particularly a possibility when the original ICSB is initially compensated inward by the one half the small spot line width.  If this limited amount of compensation is used, the external edges of the large spot
solidified region will approximately match the external edges of the small spot solidified regions with the exception of possibly some external corner regions wherein the large spot may be pulled inward from the desired boundary.  If this limited amount
of compensation is used the exposure of a small spot cross-sectional perimeter may become unnecessary in some circumstances.
Element 314 may be eliminated.  This will result in reduced processing time and for a given situation may result in little or no loss in part quality.
Element 316 may use a compensation amount different from that originally used.  For example, the compensation amount may be smaller than that originally used.  If a smaller amount of compensation is used, element 318 will produce a larger region
for small spot exposure.  The expanded portion of the small spot region may result in excess exposure of a portion of the regions exposed by the large spot.  If this extra exposure is limited to a small region (e.g. from a mil or two up to 10 mils or
so), it may not result in too much excess cure depth and may have the advantage of ensuring better more reliable exposure of the boundary portion between the large and small spot exposure zones.  The compensation amount may be larger than that used in
step 312, for example by 1-3 mils, to minimize unnecessary small spot exposures that might result from rounding errors and other imperfection in the operations.
Element 316 may be completely eliminated wherein element 318 would utilize the difference between the RB(I) and either the FLSD(I) or the ILSD(I).  Elements 320 and 322 may both be eliminated.  Alternatively, different compensation amounts may be
used in each element.  In particular the compensation of the inverse erosion of Element 322 may be based on a smaller compensation amount that was used in Element 320.  This smaller amount (e.g. one-quarter to three-quarters as much) could be used to
keep a portion of the FMSSD(I) from being excessively exposed during the final perimeter tracing.  This might even result in a better surface perimeter surface that for some objects than would result from the techniques of the first embodiment.
Element 324 calls for the maximum value of &quot;I&quot; to be three.  In other embodiments, smaller numbers of cross-sectional regions may be used.  In still further embodiments larger number of cross-sectional regions may be used.  For example, the
maximum value of &quot;I&quot; may be one, in which case RB(I)=RB(1)=ICSB(N).  As a second example, the maximum value of &quot;I&quot; may be two, wherein the cross-section may be divided into continuing regions and outward facing regions (i.e. a combination of up-facing
and down-facing regions).  Alternatively, the cross-section may be divided into down-facing regions and non-down-facing regions.  As a third example, the maximum value of &quot;I&quot; may be five, wherein the cross-section may be divided into flat down-facing,
near-flat down-facing, flat up-facing, near-flat up-facing, and continuing regions.  Of course many other values of &quot;I&quot; are possible along with designation of many different region types.
FIGS. 5a and 5b illustrate large and small spot regions where &quot;I&quot; is set equal to one.  FIG. 5a depicts a top view of the boundary 450 for cross-section 106 of FIG. 2b where the cross-section is not divided into separate regions.  FIG. 5b depicts
a large spot boundary 452 offset from boundary 450 by a desired amount.  Line loops 454 and 456 depict the region that will be exposed when tracing the large spot boundary 452.  Area 418 will be exposed by tracing the large spot to form hatch or fill.
Line loop 460 depicts the widening of the cross-sectional dimension when boundary 450 is traced using the small spot beam.
While the preferred source of both large and small spot prescribed stimulation is a beam produced by a single laser, other options exist: (1) two or more lasers may be used, or (2) one or more non-laser sources may be used.  The present invention
uses a pulsed laser source but it is also possible to use a continuous wave CW source as well.
When forming a single lamina, it may be desirable to minimize the number of transitions between large spot and small spot drawing.  As such it may be advantageous to draw all large spot vectors first, followed by all small spot vectors.
A single transition can still occur during the formation of each lamina, if a portion of the small spot or large spot regions are exposed first, followed by the formation of all portions using the opposite sized beam, and then completing the
lamina formation with original sized beam.  This alternative has the disadvantageous of changing the spot size during what could otherwise be an exposure time.
As it may take a second or two to change the spot size it is preferred that this be done during a period when exposure can not occur, such as for example, during recoating, z-wait, pre-dip delay, even during mid-exposure delays, such as an
inter-hatch delay or a hatch-to-boundary delay periods.  These mid-exposure delays are described in U.S.  patent application Ser.  No. 09/246,504.
It is believed that the last drawn vectors will hold their X and Y positions better, as such it is preferred that the small spot perimeter be formed last.  It is presently preferred that Large spot vectors be drawn (i.e. exposed) first on a given
layer, followed by small spot object exposure, and finally followed by support structure exposure.
Small spot power and large spot power may take on any appropriate values.  The actual power applied in each spot may be determined based on one or more parameters: (1) vector type, (2) region, and (3) desired cure depth to be achieved by a single
line of exposure or by a series of overlapping exposures.  Desired cure depth in turn may be based on a variety of parameters, including layer thickness, vector type, MSD and MRD issues, etc. It is possible that the power of both beams could be the same
or even more power could be used in the small spot.  Typically, however, the small spot beam will have smaller power.
More information about beam power and modifying it is supplied in U.S.  Pat.  No. 6,241,934 B1.  In particular the power in the small spot may be less than or equal to that used by the large spot.  In particular as the small spot is more
susceptible to scanning speed limitations based on pulse repetition rate, increasing the pulse repetition may allow higher scanning speeds to be obtained.
As noted above the AOM may be used to control beam power to a desired level.  Other techniques for controlling laser power include: (1) a mechanism for variably supplying electric power to a laser diode source that supplies pumping energy to the
laser source, (2) a mechanism for variably controlling operation of a Q-switch in the laser source, (3) an electro-optic modulator, (4) a mechanism for variably controlling a pulse repetition rate of the power in the beam, (5) a mechanism for controlling
the temperature of a laser diode source that supplies pumping energy to the laser source, (6) a mechanism for controlling a temperature of a frequency conversion crystal through which the beam from the laser source passes, and (7) a computer controlled
Depending on the detailed resolution of the objects to be formed, small spot diameters may range, from less than 3 mils to more than 50 mils while large spot diameters may range from less than 7 mils to more than 200 mils.  The smallest useful
beam size depends on the energy pulse, the required overlap per pulse and the net exposure required.  It is preferable that the large spot diameter be in the range of 1.5 to 5 times the diameter of the small spot and more preferably about 2.5 to 4 times
the size of the small spot.  If the disparity in size becomes too large, it may be advantageous to use one or more additional intermediate sized beams.
In forming lamina using the large spot, use of boundary exposures is optional.  When forming objects using a QUICKCAST build style (as described in U.S.  Pat.  Nos.  5,855,718 and 5,965,079), it is preferred that all hatch vectors be formed using
the smaller spot and that use of large spot be limited to skin regions when their size make the large spot applicable.
In an alterative embodiment, the decision to use large spot in favor of small spot may not be solely based on a large spot area existing, it may also be based on a comparison of time to change the spot size versus the savings in exposure time
that will be obtained as a result of using the large beam size.
An example preferred implementation using a dual sized beam system is presented herein next.  The beam size for the larger beam is preferably about 30 mils and the associated beam power is preferably about 800 mW (for example, 400 mW or greater),
the spacing between successive hatch lines is preferably about 15 mils (for example, between 25 and 125% of the beam diameter, and the scanning speed is preferably about 300 ips (for example, 100 ips or greater).  The smaller beam preferably has a
diameter of approximately 10 mils.
The object is to be formed using a building technique there only portions of some layers are solidified in association with those layers, wherein the remaining portions of the layers are formed in association with subsequent layers.  Such
techniques are described in U.S.  Pat.  Nos.  5,902,538, 5,597,520; and 5,209,878.  In particular, the object will be formed using two secondary layers located intermediate to successive primary layers (such techniques are described in the &#39;428
application noted above.  The separation between each layer (i.e. layer thickness) is 3 mils.
On a first secondary layer, only an outer boundary region is formed using the smaller beam.  Up-facing and down-facing regions may also be formed if they exist.  The exposure applied to these boundaries preferably results in a cure depth of
approximately 15 mils.  This boundary is preferably line width compensated by about 5 mils.
On a second secondary layer it is again preferred that only outer boundary regions be formed using the smaller beam.  Up-facing and down-facing regions may also be formed in association with this layer if they exist.  This boundary is also
preferably given a cure depth of approximately 15 mils and is line width compensated by about 5 mils.  In an alternative implementation, the boundaries formed in association this layer may be given a cure depth of less than 15 mils.  The cure depth used
may be dependent on the depth of liquid existing prior to exposure of these boundary regions.  For instance, depending on whether or not the outer boundary region of the second secondary layer overlays the boundary formed of the first secondary layer,
the depth of liquid prior to exposure may be equal to 3 mils or 6 mils.  Thus as the depth of liquid prior to exposure varies it may be preferable to adjust the cure depth associated with these outer boundary regions.
The primary layer above the second secondary layer is preferably formed using the following procedure.  First, an inwardly offset boundary is formed using the large beam.  This boundary is preferably offset inward from the line width compensated
outer boundary position by about 15 mils.  The beam preferably provides an exposure such that the large boundary does not adhere to the layer below.  This exposure preferably results in a cure depth of 8.
Second, a first pass of hatch is preferably formed within the bounds of the solidified large spot boundary region.  This hatch is preferably supplied with an exposure that yields a cure depth of approximately 8 mils.  This hatch may also be
retracted slightly from the solidified boundary so that no adhesion to the boundary occurs, or alternatively, it may adhere to the boundary.  This adhesion to the boundary may occur at all locations along the boundary or at only a portion of the
Third, a delay period of, for example, 15 seconds preferably occurs.  This delay time may be occupied by drawing other object regions or simply may be a wait period.
Fourth, a second exposure of hatch is preferably applied.  This hatch is preferably oriented in a direction perpendicular to the direction of the first pass of hatch.  The quantity of exposure applied on the second pass preferably yields a cure
depth of 10 mils.  As with the first exposure of hatch, it is preferred that the spacing between each hatch line be such that an overlapping exposure occurs so that a continuously solidified region is formed.  Any retraction associated with the second
pass of hatch is preferably similar to that used on the first pass, for example, 3 mils.
The fifth step involves the use of the small spot to expose an outer boundary for the cross-sectional region.  This exposure preferably results in a cure depth of approximately 15 mils.  Depending on whether or not this boundary overlays the
boundary on the previously formed secondary layers, the depth of liquid prior to exposure may be equal to approximately 3 mils to 9 mils.  For a shallower depth of liquid prior to exposure, it may be preferable to decrease the cure depth for the outer
boundary region.  This outer boundary may be line width compensated by approximately 5 mils.
With the execution of the fifth step, the exposure of the primary layer is completed.  In alternative implementations, additional exposure of hatch, and/or skin fill, and/or supports using the small spot may occur prior to or after the exposure
of the small spot outer boundary.  In addition, there may be exposure of skin fill using the large spot before or after the second pass of hatch with the large spot, but preferably before the exposure of the outer boundary with the small beam.
Once exposure of the primary lamina is accomplished, object formation continues with the repeated formation and exposure of groups of primary and secondary layers until the object is completed.  Further appreciation of object formation using
secondary layers and primary layers may be gathered from a review of U.S.  Pat.  No. 5,902,538.  The procedure described above is summarized in Table 3.  The parameters used for the formation and exposure of the three layers of the set are provided in
TABLE 3  Formation of a Set of Primary and Secondary Layers.  Action  Form first secondary layer  Draw boundary region of first secondary layer  Form second secondary layer  Draw boundary region of second secondary layer  Form primary layer
Draw inner boundary of primary layer using larger beam  Draw first pass of hatch of primary layer using larger beam  Delay occurs between the two passes of hatch of the primary layer  Draw second pass of hatch of primary layer using larger beam  Draw
outer boundary of primary layer using smaller beam
Apparatus may be formed by implementing the methods described herein by using a computer memory to receive and store data and processor circuitry to manipulate the data.  The memory and processor may be part of an SLA control computer.  The
processor may be controlled by software or hard coding.  Alternatively, implementation may occur without modifying some of the data, but instead by programming the SLA to modify the way the system interprets existing data.
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&amp;M
technologies to more rapidly form objects.
Though particular embodiments have been described and illustrated and many alternatives proposed, many additional embodiments and alternatives will be apparent to those of skill in the art upon review of the teachings herein.  As such, these
embodiments are not intended to limit the scope of the invention, but instead to be exemplary in nature.
Stereolithographic method and apparatus for production of three dimensional objects using multiple beams of different diameters, Manners, et al., Chris R. Manners, Michelle D. Guertin, Hop D. Nguyen, Jouni P. Partanen, Nansheng Tang, Michael A. Everett, Application number 09 248-352, Plastic And Nonmetallic Article Shaping Or Treating: Processes, Plastic Article Or Earthenware Shaping Or Treating: Apparatus, Data Processing:Generic Control Systems Or Specific Applications, three-dimensional ob
This invention relates to the formation of three-dimensional objects using a Rapid Prototyping and Manufacturing (RP&M) technique. The invention more particularly relates to the stereolithographic formation of three-dimensional objects using aplurality of different dimensioned beams of radiation.BACKGROUND OF THE INVENTION1. Related ArtRapid Prototyping and Manufacturing (RP&M) is the name given to a field of technologies that can be used to form three-dimensional objects rapidly and automatically from three-dimensional computer data representing the objects. RP&M can beconsidered to include three classes of technologies: (1) Stereolithography, (2) Selective Deposition Modeling, and (3) Laminated Object Manufacturing.The stereolithography class of technologies creates three-dimensional objects based on the successive formation of layers of a fluid-like material adjacent to previously formed layers of material and the selective solidification of those layersaccording to cross-sectional data representing successive slices of the three-dimensional object in order to form and adhere laminae (i.e. solidified layers). One specific stereolithography technology is known simply as stereolithography and uses aliquid material that is selectively solidified by exposing it to prescribed stimulation. The liquid material is typically a photopolymer and the prescribed stimulation is typically visible or ultraviolet electromagnetic radiation. The radiation istypically produced by a laser though other sources of radiation are possible such as arc lamps, resistive lamps, and the like. Exposure may occur by scanning a beam or by controlling a flood exposure by use of a light valve that selectively transmits orreflects the radiation. Liquid-based stereolithography is disclosed in various patents, applications, and publications of which a number are briefly described in the Related Applications section hereafter.Another stereolithography technology is known as Selective Laser Sin
Three-dimensional Carbon Fibers And Method And Apparatus For Their Production - Patent 8119198