1. Field of the Invention
The present invention relates to three-dimensional printing apparatuses.
2. Description of the Related Art
A known three-dimensional printing apparatus applies light to liquid photo-curable resin stored in a tank so as to cure the photo-curable resin, thus printing a three-dimensional object.
For example, JP 2003-39564 A discloses a three-dimensional printing apparatus including a table provided with an opening; a tank that is placed on the table and stores photo-curable resin; a raisable and lowerable holder disposed above the tank; and a projecting device disposed below the table. The projecting device projects a cross-sectional image representing a cross-sectional shape of a three-dimensional object to be printed. The cross-sectional image, which has been projected from the projecting device, is reflected by a mirror and thus projected onto the photo-curable resin in the tank through the opening of the table. A portion of the photo-curable resin stored in the tank and corresponding to the cross-sectional shape represented by the cross-sectional image is cured so as to form a resin layer conforming to the cross-sectional shape. A region of the tank onto which a cross-sectional image is to be projected is a printing region.
A change in the cross-sectional shape represented by a cross-sectional image to be projected allows curing of an appropriate portion of the photo-curable resin stored in the tank. This enables formation of a resin layer having a desired cross-sectional shape. Sequential raising of the holder causes resin layers each having a desired cross-sectional shape to be formed continuously downward. Thus, a desired three-dimensional object is printed.
Although the three-dimensional printing apparatus disclosed in JP 2003-39564 A prints a three-dimensional object using the projecting device provided with a single projector, another known technique is to utilize a plurality of projectors so as to print a three-dimensional object using a larger printing region. This technique causes cross-sectional images projected from the projectors to overlap with each other in the printing region so that no gap exists between the cross-sectional images projected from the projectors.
Unfortunately, when cross-sectional images projected from projectors overlap with each other in a printing region, the total amount of optical energy applied to an area where the cross-sectional images overlap with each other is larger than the total amount of optical energy applied to an area where the cross-sectional images do not overlap with each other. This results in variations in the degree of curing of photo-curable resin stored in a tank. In other words, a portion of the photo-curable resin where the total amount of optical energy is larger may be cured to an excessive degree. To cope with this problem, JP 2014-37148 A discloses a technique by which the total amount of optical energy to be applied to an area where cross-sectional images overlap with each other is reduced in accordance with the total amount of optical energy to be applied to an area where cross-sectional images do not overlap with each other.
The technique disclosed in JP 2014-37148 A adjusts the total amount of optical energy to be applied to an area where cross-sectional images overlap with each other. There is, however, the need for a technique to reduce or eliminate variations in the degree of curing of photo-curable resin more easily without adjusting the total amount of optical energy.