This invention relates to the formation of three-dimensional objects using a Rapid Prototyping and Manufacturing (RPandM) technique (e.g. stereolithography). The invention more particularly relates to the formation of three-dimensional objects using data that has been modified to account for the line width induced in the building material (e.g. photopolymer) by a formation tool (e.g. a laser beam).
1. Related Art
Rapid Prototyping and Manufacturing (RPandM) 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. RPandM 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 create three-dimensional objects based on the successive formation of layers of a fluid-like medium adjacent to previously formed layers of medium 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. solidifed layers). One specific stereolithography technology is known simply as stereolithography and uses a liquid medium which is selectively solidified by exposing it to prescribed stimulation. The liquid medium is typically a photopolymer and the prescribed stimulation is typically visible or ultraviolet electromagnetic radiation. The radiation is typically produced by a laser. 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 medium by exposing the layers to infrared electromagnetic radiation to sinter or fuse the particles. SLS is described in U.S. Pat. No. 4,863,538 to Deckard. A third technology is known as Three Dimensional Printing (3DP). 3DP is based on the selective solidification of layers of a powdered medium which are solidified by the selective deposition of a binder thereon. 3DP is described in U.S. Pat. No. 5,204,055 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 for the purposes of enhancing resolution while maintaining aesthetic appeal of the objects being formed.
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 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; WO 96-12608; WO 96-12609; and WO 96-12610, all assigned to BPM Technology, Inc. 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 to Earl et al. and U.S. patent application Ser. No. 08/722,335 (both assigned to 3D Systems, Inc. as is the instant application).
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 for a given droplet or stream size while still maintaining aesthetic appeal of the objects being formed.
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. Nos. 4,752,352 to Feygin; and 5,015,312 to Kinzie, and in PCT Publication No. WO 95-18009 to Morita. It is believed that the techniques may have application in the LOM technologies to enhance object resolution when using laser beam or mechanical cutting tool to cutout cross-sections while still maintaining aesthetic appeals of the objects being formed.
Various techniques for compensating for the width of solidification induced by a beam when forming objects using stereolithography have been described previously. In particular various techniques have been described in (1) U.S. Pat. No. 5,184,307 to Hull et al., and 2) U.S. Pat. No. 5,321,622 to Snead et al.
The ""307 patent describes techniques for transforming three-dimensional object data into cross-sectional data for use in stereolithographic production of the objects. The derived cross-sectional data is typically divided into one or more groups of vectors. These groups of vectors typically include one or more boundary types (vectors that surround a given portion of a cross-section), one or more fill types that fall within selected boundary regions (sets of vectors that are typically parallel and closely spaced so that upon exposure the entire region is solidified), and one or more hatch types that fall within selected boundary regions (sets of vectors that are typically parallel but may be widely spaced so that some unsolidified material remains between the individually exposed lines). Prior to creating the fill and hatch, this reference teaches that selected boundaries should be offset inward (i.e. toward the object region as opposed to toward a non-object region) by an appropriate amount to account for the solidification width induced by the beam that is used to solidify the material. The offset amount is typically equal to about one half the width of solidification induced by the beam of radiation used to induce solidification.
One technique disclosed in the ""307 patent compensates boundaries by:
(1) Forming boundary vectors into loops;
(2) Offsetting each vector into the object by the half a line width; and
(3) Recalculating the endpoints and remove vectors that change orientation.
A second technique disclosed in the ""307 patent compensates boundaries by:
(1) Forming boundary vectors into loops,
(2) Deriving a displacement vector for each vertex of the boundary loop. The displacement vector should bisect the angle formed by the two boundary vectors that form the vertex. The displacement vector generally has a length equal to D/[(1xe2x88x92cos xcex8)/2)]{fraction (1/12)}, where D=about xc2xd the line width, and
where xcex8=angle between the two vectors. This offset amount is used unless the length is greater than a preset maximum amount (e.g. 2*LWC) in which case the length is limited to that preset maximum amount. Furthermore the length of the offset vector was limited to so that it would not extend beyond the midpoint of each of the two boundary vectors giving rise to it as dictated by a perpendicular bisector extending to those each of the two boundary vectors.
A third technique combines benefits of the first two techniques. The boundary vectors are moved inward by the desired amount as in the first technique. If this offset results in a vertex moving in by more than a desired amount an additional vector is added to the compensated boundary. This additional vector extends from (1) the intersection point of the two offset vectors to (2) a point that is a desired distance from the original vertex point.
A fourth technique adds an additional feature to the above techniques by determining whether the offset vectors cross-over one another or over the original vectors. If such a cross-over is determined to exist the offset vertices are backed up to a point where no cross-over occurs or alternatively the region of cross-over may be eliminated. Features can disappear in the three-dimensional object being formed when cross-over occurs.
The ""662 patent, as with the ""307 patent, is directed to techniques for producing cross-sectional data from three-dimensional object data for use in stereolithography. As with the ""307 patent, the ""662 patent provides techniques for deriving a plurality of different types of boundaries, hatch, and fill vectors. This patent also teaches various techniques for modifying selected boundary types to produce offset boundaries that are compensated for anticipated width of solidification that will occur during object formation.
A first technique taught in the ""662 patent teaches the boundary offsetting by migrating the boundary vertices along angle bisectors by an extent that the shortest distance between the migrated point and the original boundary are equal to the radius of the beam trace. The direction and magnitude of the migration is dictated by a displacement vector.
Excess migration is avoided by several adjustments: (1) Migration is limited to a value equal to two times the radius. (2) The possibility of cross-over is minimized by performing a test compensation equal to twice the desired compensation where a test is performed to see if any original segment has been crossed. If a cross-over is determined, the extent of migration is backed up to a point where the doubled displacement vector just touches the boundary segment. (3) A third test checks for cross-over of displacement vectors and if it occurs, each displacement vector is backed up to the cross-over point. (4) A fourth test determines whether a displacement vector crosses over a compensated boundary segment. If a cross-over is detected, the compensated boundary is moved back toward its original uncompensated segment to such an extent that the cross-over is removed. Alternatively, the displacement vector may also be shortened.
The ""662 patent teaches a preferred technique of performing compensation on cross-sectional boundaries prior to dividing the cross-sectional region into down-facing, up-facing, and continuing regions and deriving associated boundaries. It is further taught that alternatives may compensate for solidification width by compensating the region boundaries instead of the original cross-section boundaries. Alternatively, the net compensation of the regions may result from an original compensation of the initial cross-section boundaries plus negative or positive subsequent compensations.
In association with retracting hatch and fill vectors from compensated boundaries, the ""662 patent teaches the use of further boundary compensations including the formation of clipping vectors that connect compensated boundary vectors.
Even in view of the teachings of the above noted references, a need remains in the art for improved line width compensation techniques that provide high accuracy boundary placement in combination with retention of small cross-sectional features in the three-dimensional objects being formed from the modified data in an RPandM technique. The retention of small features is desired to enhance the aesthetic appeal and accuracy of the objects formed.
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 table 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.
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 RPandM Technologies: from Rapid Prototyping to Rapid Tooling; by Paul F. Jacobs; published by the Society of Manufacturing Engineers, Dearborn Mich.; 1996.
It is an object of the present invention to provide enhanced techniques (methods and apparatus) for forming three-dimensional using data that has been modified to at least partially account for width of solidification of a beam used in forming laminae of the object.
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 medium to a beam of prescribed stimulation, including: (A) providing data representing a three-dimensional object; (B) manipulating the data to form modified object data for forming the three-dimensional object, including offsetting data associated with at one cross-sectional boundary to derive a desired compensated boundary that at least partially compensates for the width of solidification induced by the beam, wherein the compensated boundary is derived from at least a first offset value and a second offset value; (C) forming a layer of material adjacent to any last formed layer of material in preparation for forming a subsequent lamina of the object; (D) exposing the material to the beam of prescribed stimulation to form a successive lamina of the object; and (E) 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 a method of forming a three-dimensional object from a plurality of adhered laminae by exposing successive layers of a medium to a beam of prescribed stimulation, including (A) providing data representing a three-dimensional object; (B) manipulating the data to form modified object data for forming the three-dimensional object, including offsetting data associated with at least some boundaries, to at least partially account for the width of solidification induced by the beam, by moving vertices of adjoining segments that form the boundaries inward by an amount dictated by a combination of (1) an angle formed by pairs of adjoining segments, and (2) a variable offset criteria that is based on at least two ranges of angles or is based on a variable offset criteria for at least one range of angles and two constant offset criteria for at least two ranges of angles; (C) forming a layer of material adjacent to any last formed layer of material in preparation for forming a subsequent lamina of the object; (D) exposing the material to the beam of prescribed stimulation to form a successive lamina of the object; and (E) repeating the acts of forming and exposing a plurality of times in order to form the object from a plurality of adhered laminae.
A third 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 medium to a beam of prescribed stimulation, including (A) providing data representing a three-dimensional object; (B) manipulating the data to form modified object data for forming the three-dimensional object, which includes (B1)offsetting data associated with at least some boundaries, to at least partially account for the width of solidification induced by the beam, by moving vertices of adjoining segments that form the boundaries inward by an amount dictated by a combination of (1) an angle formed by pairs of adjoining segments, and (2) a predetermined offset criteria; and (B2) converting at least one original boundary segment into at least first and second offset boundary segments, when at least one of the vertices of the original boundary segment is not offset by an amount that maintains a proposed offset segment parallel to the original segment, such that the first offset segment remains parallel to the original segment and the second offset segment is not parallel to the original segment; (C) forming a layer of material adjacent to any last formed layer of material in preparation for forming a subsequent lamina of the object; (D) exposing the material to the beam of prescribed stimulation to form a successive lamina of the object; and (E) repeating the acts of forming and exposing a plurality of times in order to form the object from a plurality of adhered laminae.
Other aspects of the invention supply apparatus for implementing the method aspects of the invention noted above and provide computer programmed media containing instructions for manipulating the data as noted in the first through third aspects of the invention.
It is a feature of the present invention that vertices are moved by the data manipulation to compensate for calculated vertices"" positions, instead of moving segments that form object boundaries, to prevent segments from crossing over each other.
It is another feature of the present invention that the vertices forming the object boundaries are moved one at a time and after each move, a check is made to ensure the topology of the object being formed has not changed and if so, the original vertex is not moved to the position of the new compensated or calculated vertex.
It is an advantage of the present invention that object features do not disappear in the three-dimensional object being formed by the data manipulation.
Additional aspects, features and advantages of the invention will be clear from the embodiments of the invention described below in conjunction with the Figures associated therewith. Further aspects of invention involve the practice of the above referred to aspects of the invention in various combinations with one another.