The team modified a Soliodoodle 3D printer to scan its printing bed, assess the height and shape of the objects there and print on top of them. It sounds like a complicated task, but the hardware used to accomplish it is pretty simple. A $26 laser, attached to the Soliodoole's print head, draws a horizontal line across the printing surface, distorting slightly as it passes over objects that raise above the flat base. A nearby $30 webcam measures the changes in the line and feeds that data to a PC, which can use it (and subsequent laser repositioning) to create a model of the objects below. The team was able to use this method to print a cube on top of an already half-printed pyramid, completing an print job that was aborted earlier.

Unfortunately, modifying the printer was little more than a class project -- the team doesn't have any immediate plans to develop the low-cost scanner any further. Still, similar features could be a boon to the next generation of 3D printers, allowing the machines to resume interrupted print jobs or even detected a botched print before wasting precious materials. Want to see it in action? The video below awaits.