Aj. Ijspeert et al., Collaboration through the exploitation of local interactions in autonomouscollective robotics: The stick pulling experiment, AUTON ROBOT, 11(2), 2001, pp. 149-171
This article presents an experiment which investigates how collaboration in
a group of simple reactive robots can be obtained through the exploitation
of local interactions. A test-bed experiment is proposed in which the task
of the robots is to pull sticks out of the ground-an action which requires
the collaboration of two robots to be successful. The experiment is implem
ented in a physical setup composed of groups of 2 to 6 Khepera robots, and
in Webots, a 3D simulator of Khepera robots.
The results using these two implementations are compared with the predictio
ns of a probabilistic modeling methodology (A. Martinoli, A. Ijspeert, and
F. Mondada, 1999, Robotics and Autonomous Systems, 29:51-63, 1999; A. Marti
noli, A. Ijspeert, and L. Gambardella, 1999, in Proceedings of Fifth Europe
an Conference on Artificial Life, ECAL99, Lecture Notes in Computer Science
, Springer Verlag: Berlin, pp. 575-584) which is here extended for the char
acterization and the prediction of a collaborative manipulation experiment.
Instead of computing trajectories and sensory information, the probabilist
ic model represents the collaboration dynamics as a set of stochastic event
s based on simple geometrical considerations. It is shown that the probabil
istic model qualitatively and quantitatively predicts the collaboration dyn
amics. It is significantly faster than a traditional sensor-based simulator
such as Webots, and its minimal set of parameters allows the experimenter
to better identify the effect of characteristics of individual robots on th
e team performance.
Using these three implementations (the real robots, Webots and the probabil
istic model), we make a quantitative investigation of the influence of the
number of workers (i.e., robots) and of the primary parameter of the robots
' controller-the gripping time parameter-on the collaboration rate, i.e., t
he number of sticks successfully taken out of the ground over time. It is f
ound that the experiment presents two significantly different dynamics depe
nding on the ratio between the amount of work (the number of sticks) and th
e number of robots, and that there is a super-linear increase of the collab
oration rate with the number of robots. Furthermore, we investigate the use
fulness of heterogeneity in the controllers' parameters and of a simple sig
nalling scheme among the robots. Results show that, compared to homogeneous
groups of robots without communication, heterogeneity and signalling can s
ignificantly increase the collaboration rate when there are fewer robots th
an sticks, while presenting a less noticeable or even negative effect other
wise.