Mobile Robot Exploration
by using Fused Data from Two Sensors.
Abstract
This research investigates the combined use of a sonar range finder and a
laser range finder (Biris) for exploring a structured indoor environment
(i.e. an art gallery). The environment of an art gallery is
particularly attractive for implementing a mapping since it is a generally
open space. It has a number of stationary objects and allows full
access to the space around them for the visitors, as well as for a
mobile robot of a size comparable to that of a human. The assumption is
that the floors are flat (except for some well defined places where stairs
exists) and smooth without any anomalies. Moreover the area is free from
moving objects (such as humans) for long periods of time.
This approach fuses the data acquired from two different kinds of sensors
in order to compensate for the unavoidable disadvantages any single kind of
sensor presents. The first sensor is a sonar range finder that is coarse,
but covers a longer range and it is relatively fast, and the second much
slower is a laser range finder that can be used to report precise
information about a small area. This combination of sensors is going
to be used by taking first a coarse estimation of the environment, and
then ``cleaning up'' the uncertainties with the laser sensor.
The main disadvantage of a sonar range finder is the possible false
estimate of distance caused from multiple bounces. Also, the way distance
is estimated by it leads to uncertainty at the boundaries of
objects. In order to enhance the performance of the sonar range finder and
to construct an accurate map, we combine it with the Biris laser range
finder, taking measures at the ends of the line segments to remove any
uncertainty. Also erroneous data from multiple bounces are going to be
eliminated by close examination with Biris.
The space exploration is based on two strategies. In the first, a rather
coarse map, clear enough (to allow secure navigation through the free
space) is constructed using the sonar range finder, and then the Biris
sensor is used in order to investigate uncertain areas that present a
threat of collision. In the second approach the objective is to accurately
map the environment, and the precision of the construction is going to take
precedence over the time spent in the task. In this case the sonar is used
to identify areas where could be an object, and then the robot approaches
and creates a detailed map using Biris.