Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive...
Reexamination Certificate
2001-09-21
2004-06-08
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
C430S292000, C264S401000
Reexamination Certificate
active
06746814
ABSTRACT:
BACKGROUND
The present application relates to providing visual of a model produced by stereolithographic techniques such as providing gray-scale and/or color detail to the model.
The term rapid prototyping (RP) refers to a class of technologies that can automatically construct physical models from Computer-Aided Design (CAD) data. These “three dimensional printers” allow designers to quickly create tangible prototypes of their designs, rather than just two-dimensional pictures. Such models have numerous uses. They make excellent visual aids for communicating ideas with co-workers or customers. In addition, prototypes can be used for design testing. For example, an aerospace engineer might mount such a model airfoil in a wind tunnel to measure lift and drag forces.
In addition to prototypes, RP techniques can also be used to make tooling (referred to as rapid tooling) and even production-quality parts (rapid manufacturing). For small production runs and complicated objects, rapid prototyping is often the best manufacturing process available. Of course, “rapid” is a relative term. Most prototypes require from three to seventy-two hours to build, depending on the size and complexity of the object.
Because RP technologies are being increasingly used in non-prototyping applications, the techniques are often collectively referred to as “solid free-form fabrication”, “computer automated manufacturing”, or “layered manufacturing.” The latter term is particularly descriptive of the manufacturing process used in rapid prototyping commercial techniques, since a software package is used to “slice” the CAD model into a number of thin (e.g., approximately 0.1 mm to 0.7 mm) layers, which are then built up successively one on top of another. Thus, rapid prototyping is an “additive” process, combining layers of paper, wax, or plastic to create a solid object. In contrast, most machining processes (milling, drilling, grinding, etc.) are “subtractive” processes that remove material from a solid block. Accordingly, the additive nature of rapid prototyping allows the creation of objects with complicated internal features that cannot be manufactured by other means.
One of the most important rapid prototyping techniques is stereolithography (STL). In fact, stereolithography started the rapid prototyping revolution in the late 1980's. The STL technique builds three dimensional models from liquid photosensitive polymers that solidify when exposed to ultraviolet light. As illustrated in prior art
FIG. 1
, a model
20
is built upon a platform
22
situated just below the surface of a vat of, for example, liquid epoxy or acrylate resin. A low-power highly focused UV laser traces out the first layer, solidifying a cross section of the model while leaving the resin in a liquid state in those areas not identified as part of the “current” model cross section. As illustrated in
FIG. 1
, an elevator
24
incrementally lowers the platform
22
into the liquid polymer
26
. A sweeper
28
re-coats the solidified current model layer with liquid resin from the vat
30
, and the laser
32
(via lenses
34
and mirror
36
) traces each next layer atop the previous layer. This process is repeated until the prototype model
20
is complete. Afterwards, the solidified model
20
is removed from the vat
30
and rinsed clean of excess liquid resin. Subsequently, supports may be broken off the model and the model is then placed in an ultraviolet oven (not shown) for complete curing.
In detail, stereolithography, as well as other rapid prototyping techniques, all employ the same basic five-step process. The steps are:
Step 1 Create a CAD data model of the design;
Step 2 Convert the CAD data model to a standard stereolithographic (STL) data format;
Step 3 Manipulate the STL file so that the model to be generated is in a desired orientation and has a desire resolution by “slicing” the model represented by the STL file into thin cross-sectional layers;
Step 4 Construct the model one layer atop another using a STL device; and
Step 5 Clean and finish the model.
Thus, the object (i.e., model) to be built is first modeled (in Step 1) using a computer-aided design (CAD) software package. Solid modeling CAD systems tend to represent three dimensional objects more accurately than wire-frame modelers, and will therefore tend to yield better results (i.e., a more accurate model). However, regardless of the CAD packages used, to establish consistency, the STL rapid prototyping industry has adopted a standard data format for inputting data to stereolithographic model generating devices. Accordingly, in Step 2, the CAD file output in Step 1 is converted into STL format. This format represents a three dimensional surface as an assembly of planar triangles, like the facets of a cut jewel. Thus, the standardized STL output file contains the coordinates of the vertices and the direction of the outward normal of each triangle. Because STL files use planar elements, they cannot represent curved surfaces exactly.
In Step 3, a pre-processing program prepares the STL file for use by a STL device for generating the desired model. Several programs are available for this purpose, and most allow the user to adjust the size, location and orientation of the model to be built. Build orientation is important for several reasons. First, properties of rapid prototypes vary from one coordinate direction to another. For example, prototypes are usually weaker and less accurate in the z (vertical) direction than in the x-y plane. In addition, part orientation partially determines the amount of time required to build the model. Placing the shortest dimension in the z direction reduces the number of layers, thereby shortening build time. Additionally, all such pre-processing programs generate slices of the STL model into a number of layers from 0.01 millimeters (mm) to 0.7 mm thick (in the z direction), depending on the build technique and the resolution desired. The preprocessing program may also generate an auxiliary structure to support the model during the build. Supports are useful for delicate features, such as overhangs, internal cavities, and thin-walled sections.
In Step 4, the actual construction of the model is performed. Using one of several techniques RP machines build one layer at a time from polymers, paper, or powdered metal. Most machines are fairly autonomous, needing little human intervention. Subsequently, the built model may be cured so that further hardening occurs.
Finally, in Step 5, post-processing finishing is performed. This step involves removing the prototype from the machine and detaching any supports. Some photosensitive materials need to be fully cured before use. Prototypes may also require minor cleaning and surface treatment. Sanding, sealing, and/or painting the model will improve its appearance and durability.
However, in using stereolithographic techniques to build such models, the techniques for providing shading and/or color to such models have been performed by:
a. Introducing an additive into the resin such as the chemical compounds referred to in U.S. Pat. No. 5,514,519 to Neckers incorporated herein by reference. In particular, the following compounds have been added to such resins: carbon black, anthraquinone-based blue dyes, tetracyano uinodimethane, and photobleachable dyes such as: 1,3-dihydro-6′,8′-dichloro-1-hexyl-3,3-dimethyl spiro>2H-indole-2,2′->3H!benzopyran! (SP1) and 1,3-dihydro 6′-nitro-8′-bromo-1-hexyl, 3,3-dimethyl spiro>2H-indole-2,2′->3H!benzopyran!. Moreover, such additives may not provide visual details of the model. In particular, such prior art colorizing techniques can not easily provide multiple shades of any color. Thus, for example, visual details that could be represented by gray scale shading are typically unavailable. Accordingly, the gray scale or color representation of the bone structure in the model of a hand such as in
FIG. 2
has not been easily attained theretofore, or
b. The application of a tremendous amo
Hamilton Cynthia
Sierra Patent Group Ltd.
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