I have came across this website for a drawing machine, Hektor.
"Hektor is a portable Spray-paint Output Device for laptop computers...Hektor’s light and fragile installation consists only of two motors, toothed belts and a can holder that handles regular spray cans. The can is moved along drawing paths just as the human hand or old plotters would. During operation, the mechanism sometimes trembles and wobbles, and the paint often drips. The contrasts between these low-tech aspects and the high-tech touch of the construction hold ambiguous and poetic qualities and make Hektor enjoyable to watch in action.
Hektor was created with a certain attitude towards design and the use of tools. Intuition played an important role in the search for a new output device that goes beyond the limitations of today's clean computer, screen and vector-graphic based design and conveys the abstract geometries contained in these graphics in a different way than normal printers do.
The aim was to make a statement about design by providing a new tool to other designers and artists to experiment with, a tool with an inherently particular and distinctive aesthetic."
The videos are really amazing.
There are also many other similar designs using pens.
http://www.as220.org/labs/blog/drawbot/
http://www.polargraph.co.uk/whats-a-polargraph/
http://web.me.com/sami6877/unanything/Site/Secret_Work/Entries/2010/6/1_Drawbot.html
http://vimeo.com/channels/drawingmachines#13233410
"The process is long, sometimes taking multiple weeks nonstop to finish a drawing. In a sense the machine is the artist, abiding to a specific set of rules as it decides how to draw."