Optical: systems and elements – Lens – With support
Reexamination Certificate
2001-02-23
2002-07-30
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With support
C359S668000, C359S290000, C359S433000
Reexamination Certificate
active
06426840
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to beam conditioning in illumination systems and particularly to beam conditioning systems for use in stereolithography systems.
2. Discussion of the Related Art
In recent years, rapid prototyping and manufacturing (RP&M) techniques have been developed for industrial use in the fast production of three-dimensional models. In general, RP&M techniques build a three-dimensional object, layer-by-layer, from a working material utilizing a sliced data set representing cross-sections of the object to be formed. Typically an object representation is initially provided by a computer aided design (CAD) system and the representation is translated into a number of sliced data sets that are then transferred to the successive layers of the working material.
Stereolithography, the presently dominant RP&M technique, may be defined as a technique for automated fabrication of three-dimensional objects from a fluid-like material utilizing selective solidification of thin layers of the material at a working surface to form and adhere successive layers of the object (i.e., laminae). In stereolithography, data representing the three-dimensional object are input as, or converted into, two dimensional layer data representing cross-sections of the object to be formed. Thin layers of material are successively formed and selectively transformed (i.e., cured) into successive laminae according to the two-dimensional layer data. During transformation the successive laminae are bonded to previously formed laminae to allow integral formation of the three-dimensional object.
A preferred material used in a stereolithographic apparatus (SLA) is a liquid photopolymer resin. Typical resins are solidified by exposure to selected wavelengths of electromagnetic radiation (e.g. selected wavelengths of ultraviolet (UV) radiation or visible light). This radiation of selected wavelength may be termed “solidifying radiation.” The electromagnetic radiation is typically in the form of a laser beam that is directed to a target surface of the resin by two computer controlled scanning mirrors that scan the target surface along orthogonal directions. The scanning speed, pulse repetition frequency and spot size of the beam on the liquid surface are controlled to provide a desired exposure, depth of cure and solidification characteristics.
A more detailed description of stereolithography and the methods and apparatus for practicing photolithography are found in the following patents, which are hereby incorporated by reference:
U.S. Pat. No. 4,575,330 to Hull: Describes the fundamentals of stereolithography.
U.S. Pat. No. 5,058,988 to Spence, et al.: Describes the use of beam profiling techniques in stereolithography.
U.S. Pat. No. 5,059,021 to Spence, et al.: Describes the use of scanning system drift correction techniques for maintaining registration of exposure positions on the target surface.
U.S. Pat. No. 5,104,592 to Hull et al.: Describes the use of various scanning techniques for reducing curl-type distortion in objects that are being formed stereolithographically.
U.S. Pat. No. 5,123,734 to Spence, et al.: Describes a technique for calibrating a scanning system on a stereolithographic apparatus.
U.S. Pat. No. 5,133,987 to Spence, et al.: Describes the use of a large stationary mirror in the beam path between the scanning mirrors and a target surface.
U.S. Pat. No. 5,182,056 to Spence, et al.: Describes the simultaneous use of multiple wavelengths to expose the resin.
U.S. Pat. No. 5,184,307 to Hull, et al.: Describes the use of slicing techniques for converting three-dimensional CAD data into cross-sectional data for use in exposing the target surface to appropriate stimulation.
U.S. Pat. No. 5,321,622 to Snead, et al.: Describes the use of Boolean operations in deriving cross-sectional data from three-dimensional object data
U.S. Pat. No. 5,965,079, to Gigl, et al.: Describes various scanning techniques for use in stereolithography.
U.S. Pat. No. 5,999,184, to Smalley, et al.: Describes the use of solidification techniques to simultaneously cure multiple layers.
U.S. Pat. No. 6,129,884 to Beers, et al.: Describes the control of a pulsed illumination source to achieve desired solidification characteristics.
Commercially available photopolymer for use in stereolithography are typically of acrylate, epoxy or combined chemistry. Typically, resins contain a plurality of components. These components may include one or more photoinitiators, monomers, oligomers, inert absorbers, and other additives. The usefulness of resins for stereolithography is in part determined by the photospeed of the resin and the ability of the resin to form adequately cohesive laminae of appropriate thickness. It is desired that the photospeed be high enough to enable rapid solidification of cross-sections with available power levels of solidifying radiation. Further, since the depth of polymerization in the resin is linked to the locations at which photons are absorbed, absorption of photons by the resin should be sufficient to form adequately thin layers. Examples of preferred photopolymers include, but are not limited to, SL 7540, SL 7520, SL 7510, SL 5530, SL 5520, SL 5510 and SL 5195 (manufactured by Vantico, Inc. and as sold by 3D Systems, Inc. of Valencia, Calif.), SOMOS 9120, 9100, 8120, 8100, 7120 and 7120 (manufactured by DSM Somos of New Castle, Del.).
Photoinitiators are the component of the resin that determines the photosensitivity of the resin at a given wavelength. Radiation absorption by the photoinitiator leads to chemical changes in the photoinitiator that can cause polymerization of the monomers and oligomers. Thus, radiation of appropriate wavelengths to be absorbed by the photoinitiator is known as solidifying radiation. The monomers/oligomers can absorb certain wavelengths of electromagnetic radiation. As absorption by the monomers/oligomers typically does not yield an efficient polymerization reaction, absorption of solidifying radiation by the monomers/oligomers is typically undesired. Thus, the most effective wavelengths for use in stereolithography are those strongly absorbed by the photoinitiator (high coefficient of absorption) and only weakly absorbed by the monomers and oligomers (low coefficient of absorption). Examples of preferred photoinitiators include, but are no limited to, triarylsulfonium salts, mixtures of triarylsulfonium salts with phosphate salts or antimonate salts; 2,2-dimethoxy-2-phenyl acetophenone (BDK) C
16
H
16
O
16
; 2,4,6-trimethyl benzoyl diphenyl phosphine oxide (TPO); an 1-hydroxycyclohexyl phenyl ketone (HCPK) C
13
H
16
O
2
.
The useable wavelength range is bounded at the low wavelength end by monomer/oligomer absorption properties and at the upper wavelength end by photoinitiator absorption. As such, the reactive (i.e., actinic) spectral sensitivity of a photopolymer resin may be described as the product of the photoinitiator absorption spectrum and the monomer/oligomer transmission spectrum, as shown in FIG.
1
. Note that th
FIG. 1
illustration is for a particular photopolymer system. Other systems exist and will have different curves, providing different optimal illumination sources.
FIG. 1
depicts plots of photoinitiator absorption
11
, monomer/oligomer transmission
13
, and reactive sensitivity or reactive response
15
of the resin. The absorption and transmission coefficients not only depend or the specific chemical composition of each component, but also on the concentrations of each component within the resin. The absorption by the monomer/oligomer, which depends upon the wavelength of radiation, affects the activation of the photopolymers because the monomer/oligomer absorption sometimes competes with the photoinitiator absorption. Consequently, shifts in wavelength for peak reactive response may result due to changes in either composition or concentration. For a given resin composition this peak can be readily determined by one of skill in the art. Those of ordinary skill appreciate that differ
Partanen Jouni P.
Tang Nansheng
Wu Xingkun
3-D Systems, Inc.
D'Alessandro Ralph
Epps Georgia
Seyrah Saeed
Wright William H.
LandOfFree
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