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In-Depth Information
Table 10.1 The mobile platform commands
Move the robot forward for “dist” millimetres on a straight path
MOVEFW [dist]
Move the robot backwards for “dist” millimetres on a straight path
MOVEBW [dist]
Rotate the robot counterclockwise for “deg” degrees
Rotate the robot clockwise for “deg” degrees
we consider a robot equipped with a telemeter device and a ring of ultrasonic
A telemeter device is composed of a laser range finder and a tower that
rotates the laser around a vertical axis. Each telemetric reading measures
the distance to the nearest obstacle in front of the telemeter device (see
Figure 10.2). The laser range finder is highly precise (let's say a precision of
1 millimetre) but the perception range is usually short (e.g. 1 metre).
Similarly, the rotary tower is highly precise (one-tenth of a degree) but
usually slow (10 degrees per second).
Combining the orientation of the rotary tower with the distance to the
obstacle in front of the laser it is possible to calculate the Cartesian coordi-
nates of a 2D point belonging to the obstacle surface. These point coordi-
nates are related to the robot reference frame (see Figure 10.2). A sequence
of consecutive measures acquired while the tower is rotating allows the
robot to track the edges of the obstacles that fall within the laser's range of
The onboard computer supports the high-level commands listed in
Table 10.2.
A sonar device is a sensor that emits ultrasonic signals and listens to their
echo. The distance to the obstacle that reflects the signal is proportional to
the signal flight time. Sensor devices are quite cheap and thus it is common
to equip a robot with a ring of twelve, sixteen or twenty-four sonars that
cover the entire working area around the mobile platform (see Figure 10.3).
Sonar measures have a very poor accuracy: the sonar beam propagates from
the device as a cone whose width is usually 30 degrees. If the sonar measures
a distance equal to 1 metre, the front of the sonar beam is approximately
equal to half a metre. This means that the position of the detected obstacle
Figure 10.2 The telemeter device installed on the mobile platform and its
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