Layer thickness control for stereolithography utilizing variable liquid elevation and laser focal length

A method of fabricating an object comprising at least one layer using stereolithography, comprising:

• providing a vertically stationary, horizontal surface;
• raising a volume of curable liquid above the surface to a first selected depth approximating a thickness of a first layer of the object;
• selectively curing portions of the first selected depth of curable liquid above the surface to at least a semisolid state to define at least portions of the first layer;
• first determining a distance between the surface and a reference point above the surface before raising the volume of curable liquid thereabove;
• second determining a distance between a surface level of the curable liquid at the first selected depth and a reference point above the surface after raising the volume of curable liquid thereabove;
• and
• verifying that the depth of the curable liquid over the surface comprises the first selected depth from a difference between the first and second distance determinations.

An apparatus for forming a structure comprising a plurality of layers, comprising:

• a platform having a vertically fixed, horizontally oriented upper surface disposed in a reservoir for containing a curable liquid;
• a source of electromagnetic radiation for generating, focusing and traversing a beam of electromagnetic radiation effective to at least partially cure the curable liquid to at least a semisolid state;
• and
• a liquid displacement structure selectively movable into and out of a volume of the curable liquid in the reservoir to selectively vary a surface level of the curable liquid within the reservoir relative to the vertically fixed, horizontally oriented upper surface of the platform.

An apparatus for forming a structure comprising a plurality of layers, comprising:

• a platform having a vertically fixed, horizontally oriented upper surface disposed in a reservoir for containing a curable liquid;
• a source of electromagnetic radiation for generating, focusing and traversing a beam of electromagnetic radiation effective to at least partially cure the curable liquid to at least a semisolid state;
• and
• a portion of the reservoir configured to be movable with respect to the platform to selectively vary a surface level of the curable liquid within the reservoir relative to the vertically fixed, horizontally oriented upper surface of the platform.