Plastic and nonmetallic article shaping or treating: processes – Stereolithographic shaping from liquid precursor
Patent
1996-04-29
1999-01-12
Tentoni, Leo B.
Plastic and nonmetallic article shaping or treating: processes
Stereolithographic shaping from liquid precursor
264 401, 264308, 36446827, 395119, 395120, 395141, 395142, 4251744, B29C 3508, B29C 4102
Patent
active
058582975
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to optical modeling method and apparatus of preparing a cubic resin model by curing ultraviolet-ray curable resin under irradiation of a laser beam and more particularly, to method and apparatus for providing an optical modeling product of high dimensional accuracy by correcting a superfluous curing thickness due to a transmitting laser beam.
2. Background Art
Conventionally, in connection with optical modeling method and apparatus, a method has been known in which three-dimensional shape model data is converted into contour line data and sectional shapes at respective contour lines are sequentially laminated to prepare a cubic model as described in "Optical Modeling Method" by Maruya et al, Nikkan Kogyo Shinbunsha.
Measures for improving accuracy are described in Japanese Patent Publication Nos. 4-79825, 4-79827, 5-33900 and 5-33901.
Also, "RP&M.cndot.SLA Special Seminar", sponsored by Japanese 3D System, Oct. 29-30, '92 describes that when a resin layer is subjected to laser irradiation by scanning a laser beam once or by intersecting laser beams, a curing depth at a laser beam intersecting portion is about 1.7 times as large as a curing depth at a scanned portion.
The aforementioned prior arts have failed to take into consideration correction of a superfluous curing thickness due to a transmitting laser beam at the bottom of an overhang portion. Consequently, at the bottom of that portion, fresh resin is cured by a transmitting laser beam and the thickness exceeds a design value, raising a problem that the dimensional accuracy is degraded.
Further, in order to match the dimension of a modeling product to a design value, a secondary working step such as shaving is needed but it is sometimes impossible for a narrow gap to be shaved and correction of a dimensional difference is needed.
A method of modifying the design dimension in three-dimensional CAD is also available as a method of correcting the dimensional difference but the dimensional modification in CAD is not easy and is time-consuming.
DISCLOSURE OF INVENTION
An object of the present invention is to solve the problems as above and to provide a method of automatically detecting the bottom of a modeling product or the bottom of an overhang portion and automatically correcting a dimensional difference inherent to (stereolithography).
To accomplish the above object, the dimensional difference is automatically corrected on surface shape data through a method in which vertex of polygonal patches constituting the surface shape data are replaced with nodes and nodes constituting a polygonal patch lying at the bottom of an overhang portion are moved to change the shape and position of that polygonal patch, and modeling is carried out based on those data.
To accomplish the above object, a superfluous curing thickness a at the bottom of an overhang portion is determined pursuant to the following equation (1), and the superfluous curing thickness .alpha. is precedently removed from a design value in a three-dimensional shape model and converted into contour line data.
Given that the number of laminated layers of modeling of an overhang portion is N, lamination pitch is P, light absorption coefficient of resin is k, wavelength of curing beam is .lambda. and the ratio of critical energy of resin curing to irradiation energy of a curing beam is Eo, a superfluous curing thickness .alpha. is determined for pre-correction of superfluous curing as below:
By removing and adding the superfluous curing thickness .alpha. determined form the above equation (1) from and to contour line data, an optical modeling product of high dimensional accuracy can be obtained.
How to determine the superfluous curing thickness a will be described with reference to FIG. 5, FIG. 11 (a) and FIG. 11(b). Given that lamination pitch is P, depth to the top of a first curing layer is D, the number of laminated layers is N and light absorption coefficient of resin is k, transmitting beam energy En(D,N) at the depth D upon laminat
REFERENCES:
patent: 5238639 (1993-08-01), Vinson et al.
Maruya et al. "Optical Modeling Method" Nikkan Kogyo Shinbunsha (1990), pp. 2-3.
"RP & M. SLA Special Seminar" Sponsored by 3D Systems Japan, Oct. 29-30, 1992 (no pages given).
Endoo Toshiroo
Goto Norio
Moritani Masumi
Ohkubo Masakatsu
Ozawa Masahiko
Hitachi , Ltd.
Tentoni Leo B.
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