The MakerLegoBot is a Lego Mindstorms-based 3D printer that turns software descriptions of Lego builds into completed Lego pieces, automatically, picking and snapping down pieces as it goes. Next step would be a MakerLegoBot that prints other MakerLegoBots, of course:
A Java Application that runs on the PC takes an .ldr MLCad file, determines a set of print instructions, and then sends the instructions via USB over to the MakerLegoBot for printing…
The core concept that makes 3D print of Legos possible is the sticky grab and axle release mechanism. The printer head selects from an array of Lego bricks, moves to the correct location, and then places each Lego in its determined spot…
It took many nights and many iterations to get the feed system working consistently. The current design works with 1×2, 2×2, 3×2, 4×2, and 8×2 Lego bricks. Once a brick is grabbed, the next brick in line falls into place.
MakerLegoBot: A Lego Mindstorms NXT 3D Lego Printer
(via Makerbot blog)