Graduate students at the Georgia Institute of Technology have built the first graffiti-painting
robot system that mimics the fluidity of human movement.
Aptly named GTGraffiti, the system uses motion capture technology to record human painting
motions and then composes and processes the gestures to program a cable-driven robot that
spray paints graffiti artwork.
For a robot to be able to paint in a human style, both the robot and the art must be
designed with the other in mind — at least for now.
The GTGraffiti system consists of three stages: artwork capture, robot hardware, and planning
and control.
First, the team uses motion capture technology to record human artists painting — a strategy
that allows for insight into the types of motions required to produce spray-painted
artwork.
For this study, the team invited two artists to paint the alphabet in a bubble letter graffiti
style.
As each artist painted, they recorded the motions of the artist’s hand across the
canvas, as well as the movements of the spray paint can itself.
Capturing hand and spray paint can trajectories is crucial for the robot to be able to paint
using similar layering, composition, and motion as those of a human artist.
The team then processed the data to analyze each motion for speed, acceleration, and size,
and used that information for the next stage — designing the robot.
Taking these data into consideration, as well as portability and accuracy required for the
artwork, they chose to use a cable-driven robot.
Cable-driven robots, like the Skycams used in sports stadiums for aerial camera shots,
are notable for being able to scale to large sizes.
The robot runs on a system of cables, motors, and pulleys.
The team’s robot is currently mounted on a 9 by 10-foot-tall steel frame, but it should
be possible to mount it directly onto a flat structure of almost any size, such as the
side of a building.
For the third stage, the artist’s composition is converted into electrical signals.
Taken together, the figures form a library of digital characters, which can be programmed
in any size, perspective, and combination to produce words for the robot to paint.
A human artist chooses shapes from the library and uses them to compose a piece of art.
For this study, the team chose to paint the letters “ATL.”
Once the team chooses a sequence and position of characters, they use mathematical equations
to generate trajectories for the robot to follow.
These algorithmically produced pathways ensure that the robot paints with the correct speed,
location, orientation, and perspective.
Finally, the pathways are converted into motor commands to be executed.
With all the computing and competing movements, the motors on the robot could potentially
work against each other, threatening to rip the robot apart.
To address this, the central robot controller is programmed to recalculate motor commands
1,000 times per second so that the robot can function safely and reliably.
Once assembled, the robot can then paint an artwork in the style of a human graffiti artist.
Some of the most typical industries for robotics applications include manufacturing, biomedicine,
automobiles, agriculture, and the military.
But the arts, it turns out, can showcase robotics in an especially powerful way.
The arts, especially painting or dancing, exemplify some of the most complex and nuanced
motions humans can make.
So if the researchers want to create robots that can do the highly technical things that
humans do, then creating robots that can dance or paint are great goals to shoot for.
These are the types of skills that demonstrate the extraordinary capabilities of robots and
can also be applied to a variety of other applications.
On a personal level, the researcher is motivated by his hope for people to perceive robots
as being helpful to humanity, rather than seeing them as job-stealers or entities that
cause feelings of fear, sadness, or doom as often depicted in film.
Presently, the team’s plans for the robot are centered around two main thrusts: preserving
and amplifying art.
To this end, they are currently experimenting with reproducing pre-recorded shapes at different
scales and testing the robot’s ability to paint larger surfaces.
These abilities would enable the robot to paint scaled up versions of original works
in different geographical locations and for artists physically unable to engage in onsite
spray painting.
In theory, an artist would be able to paint an artwork in one part of the world, and a
GTGraffiti bot could execute that artwork in another place.
The robot is not generating the art itself, but rather working together with the human
artist to enable them to achieve more than they could without the robot.
The researcher envisions that the robot system will eventually have capabilities that allow
for real-time artist-robot interaction.
He hopes to develop the technology that could enable an artist standing at the foot of a
building to spray paint graffiti in a small space while the cable-driven robot copies
the painting with giant strokes on the side of the building.