Stereolithography apparatus for improving planarity of a transparent sheet

A three-dimensional (3D) printing system configured to manufacture a 3D article, the 3D printing system comprising:

• a machine chassis including a vessel support;
• a build vessel containing photocurable fluid and supported by the vessel support, the build vessel including:
• a vessel base having a downward extending tension ring;
• and
• a transparent sheet that is tensioned over the tension ring and laterally bounds a build plane defined along orthogonal lateral axes including an X-axis and a Y-axis of the 3D printing system, wherein a lower surface of the transparent sheet supported by the tension ring defines a datum plane;
• a carriage supporting a glass plate and a roller along a leading edge of the glass plate, wherein the roller extends laterally below two opposing sides of the tension ring, and the carriage is configured to press the roller against the two opposing sides of the tension ring so that an upper crest of the roller is pressed against the datum plane;
• an actuator coupled to the glass plate and configured to vertically position an upper surface of the glass plate in two positions including (U) an upper position at which the upper surface of the glass plate is coplanar with the datum plane and (L) a lower position in which the upper surface of the glass is spaced away from the datum plane;
• a build platform supported over a build area of the build plane, the build platform including a build plate having a lower surface for supporting the 3D article over the build area;
• and
• a light engine;
• the machine chassis having a non-build area laterally adjacent to the build area.