Cartesian-XY-head 3D Printers
The first RepRap 3D printer, the Darwin, was based on the Cartesian-XY-head arrangement. The extruder head moves over the X and Y axis and the bed over the Z. Z axis movement on a 3D printer with the Cartesian-XY-head arrangement is very precise and requires very low accelerations, but the bed needs to be lightweight in order to maintain accuracy. Compare 3D Printers with a Cartesian-XY-head configuration below.