Luckily the control algorithm is not hard.
Finally it gave me this drawing.
Compare with the drawing by Hugo's automaton.
It took smaller amount of time and effort than I had expected to finish this arm. That's 10 days of spare time and 3 days of full time.
There is indeed much room for improvement of accuracy. But then I am satisfied by how pieces of hardware and software work together to create the artistic outcome.
Appendix I - photo album
on google plus
Appendix II - presentation slides
Appendix III - demonstration video