Patent ID: 7318718

Claim:
An optical stereolithographic apparatus for performing optical stereolithography by preparing a mask for partially intercepting light on the basis of stereolithographic data for each photohardenable resin layer obtained by slicing a three dimensional object, exposing each unhardened resin layer of photohardenable resin to light through said mask, and repeating the exposure operation to stereolithographically form the three-dimensional object, characterized by including: a controller for outputting stereolithographic data of each layer on the basis of the data of the three-dimensional object; a mask forming unit for forming at least one mask having different mask patterns, wherein the exposure on each unhardened resin layer is divided into plural sub exposure steps so that the exposure is stepwise carried out by using each of said plural mask patterns one by one; a resin layer forming unit for forming each said unhardened resin layer of photohardenable resin, said resin layer forming unit being arranged so as to be spaced from said mask forming unit at a predetermined distance; a stroboscopic lamp configured to be an alternating source of light having an on-state and an off-state; the alternating source of light is directed towards an already formed unhardened resin layer, wherein the on-state causes the unhardened resin layer to harden, and the alternating source of light is in the off-state while a next one of the each unhardened resin layer is formed on the hardened resin layer; and a focusing unit disposed between each said unhardened resin layer and said mask forming unit for focusing the light passing through the mask onto each said unhardened resin layer.