As there is no commercial 3D laser range finder available that
could be used for mobile robots, it is common practice to
assemble 3D sensors out of a standard 2D scanner and an
additional servo drive [6,12]. The scanner
that is used for this experiment is based on a SICK LMS 291 in
combination with the RTS/ScanDrive developed at the University of
Hannover. Different orientations of the 2D scanner in combination
with different turning axes result in a number of possible
scanning patterns. The scanning pattern that is most suitable for
this rescue application is the yawing scan with a vertical 2D raw
scan and rotation around the upright axis (see Fig.
). The yawing scan pattern results in the maximal
possible field of view (360
horizontal and 180
vertical)
and an uniform distribution of scan points.
As 3D laser scanner for autonomous search and rescue applications
needs fast and accurate data acquisition in combination with low
power consumption, the RTS/ScanDrive incorporates a number of
improvements. One mechanical improvement is the ability to turn
continuously, which is implemented by using slip rings for power
and data connection to the 2D scanner. This leads to a
homogeneous distribution of scan points and saves the energy and
time that is needed for acceleration and deceleration of panning
scanners. Another improvement that becomes more important with
short scanning times of a few seconds is the compensation of
systematic measurement errors. In this case the compensation is
done by sensor analysis and hard real-time synchronization, using
a Linux/RTAI operation system. These optimizations lead to scan
times as short as 3.2s for a yawing scan with 1.5
horizontal and 1
vertical resolution (240x181 points).
For details on the RTS/ScanDrive see [17].