This robot is built using mostly EV3 Lego parts (see details below). It can draw any postscript formated image stored in the SD card. The program runs entirely inside the Lego brick. The robot uses a paint brush (pen-brush) and can control the thickness of the line by exercising different amounts of pressure on the brush.
Some pictures showing the Robot can be found next:
I use a couple of non-LEGO parts in this design in the mechanism that handles the brush. I use a bolt and large screw of an old BYGGA construction set that I had, I am pretty sure that similar mechanism can be created using LEGO parts.