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titioned Surveillance System (PSS), is based on a mo-
dified artificial ants algorithm (Dorigo, 1992). The
logic presented differs from the traditional one, the
pheromone deposited by an agent has a repulsive pro-
perty. This way, the agents tend to disperse throug-
hout the environment, avoiding that two or more
agents perform the surveillance task in the same area
or in very close areas. Besides that, the strategy tends
to guide the robots into areas with no recent visitation,
due to the absence of the substance.
The strategy must partition the environment in
sectors that will be occupied by each one of the ro-
bots. The robots, individually, will be able to define
autonomously their sectors due to the adopted beha-
vior when the pheromone is detected. Hence, the
number of sectors in an environment is equal to the
number of robots. The environment’s partition favors
the surveillance task fulfillment more efficiently.
Each robot is equipped with two kinds of sensors:
one of them detects the pheromone released by the
robot itself; the second one detects the pheromone re-
leased by the other robots.
The coordination is not dependent of the parame-
ters that define an environment and no information
about the position and direction of the robots. Experi-
ments performed in different scenarios shows a gene-
ral behavior of the robots, consisting in two phases:
first, the robots develop a dispersion behavior, and
then, each agent defines a restrictive sector to cover
and sensor. Lastly, o system reaches a stability stage.
In this instant, the surveillance task is performed fol-
lowing the desired requirements: the environment is
totally and repeatedly sensed and virtually partitioned
into small disjointed sectors, which each one is moni-
tored by a robot.
The paper is structured as it follows. The proposed
strategy is described in Section 2 as well as the models
of the sensors used. In Section 3, the experiments and
discussion about the obtained results in simulations
are presented. Main contributions, relevant aspects
and future works are presented in Section 4.
2 PARTITIONED
SURVEILLANCE SYSTEM
The PSS strategy was developed to deal with explo-
ration and surveillance tasks of unknown environ-
ments, according to the principles of the ants algo-
rithm (Dorigo, 1992). Essentially, the system is based
on multiple mobile agents able to take decisions of
movement adjustment, individually, according to the
stimuli from the environment.
The mentioned tasks are performed due to the
robot’s ability to deposit a substance, named phero-
mone, on the environment, to mark the regions which
they visited (or monitored). This substance has a
repulsive feature, i.e, the robots tend to avoid areas
with pheromone concentration. That behavior cau-
ses the robots spreading out in the environment. Alt-
hough the robots deposit only one kind of pheromone,
each one is able to distinguish its pheromone, (own
pheromone) from the one deposited by the others (odd
pheromone).
The proposed strategy is distributed, reactive and
independent of the parameters usually considered in
multiple agent systems: environment structure and di-
mension, number of robots and robots’ position. The
robots play a sequence of actions (Figure 1) in order
to execute the surveillance task, they are: pheromone
dispersion, pheromone detection and direction adjus-
tment. That sequence determines an iteration to exe-
cute the surveillance task. For all actions of the se-
quence, the robots keep a constant speed. The robot’s
angular speed is changed according to the external sti-
muli detected by the sensors. Each action is described
in next sections.
Figure 1: Task diagram for one robot.
2.1 Robot and Sensors Models
The robots are equipped with two types of phero-
mone sensors. One of them allows the detection of its
own pheromone and the other detects only odd phero-
mone. Both of them has the same physical structure.
Consider the index s, s ∈ {own,odd}, refers to the
pheromone sensors, own and odd, respectively. The
sensor field is a sector of a circle C
s
defined accor-
ding to a radius R
s
centralized on the robot’s frontal
part. The sensors covers an area of β
s
degrees from
the left to β
s
degrees from the right of the robot’s mo-
vement direction, β
s
∈ [0
◦
,180
◦
] (Figure 2). The total
cover area of 2β
s
degrees is divided in identical circu-
lar sectors C
s
i
, each one measuring α
s
degrees.
Every iteration, the pheromone sensors detect a set
of stimuli from the environment at a specific and pa-
rameterizable distance. The detection only occurs at
the boundary of the sensors (detection limit).
The robots also possess a proximity sensor. Its
model is similar to the pheromone sensors. At each
iteration, this sensor detects, in each circular sector,
a set of stimuli corresponding to the distance of ob-
stacles. The amount of pheromone accumulated close
to obstacles generates not attractive areas for robots.
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