Page 104 - Introduction to Autonomous Mobile Robots

4 Perception

One of the most important tasks of an autonomous system of any kind is to acquire knowl-
edge about its environment. This is done by taking measurements using various sensors and
then extracting meaningful information from those measurements.
In this chapter we present the most common sensors used in mobile robots and then dis-
cuss strategies for extracting information from the sensors. For more detailed information
about many of the sensors used on mobile robots, refer to the comprehensive book Sensors
for Mobile Robots by H.R. Everett [15].

4.1 Sensors for Mobile Robots

There are a wide variety of sensors used in mobile robots (figure 4.1). Some sensors are
used to measure simple values like the internal temperature of a robot’s electronics or the
rotational speed of the motors. Other, more sophisticated sensors can be used to acquire
information about the robot’s environment or even to directly measure a robot’s global
position. In this chapter we focus primarily on sensors used to extract information about the
robot’s environment. Because a mobile robot moves around, it will frequently encounter
unforeseen environmental characteristics, and therefore such sensing is particularly critical.
We begin with a functional classification of sensors. Then, after presenting basic tools for
describing a sensor’s performance, we proceed to describe selected sensors in detail.

4.1.1 Sensor classification
We classify sensors using two important functional axes: proprioceptive/exteroceptive and
passive/active.
Proprioceptive sensors measure values internal to the system (robot); for example,
motor speed, wheel load, robot arm joint angles, battery voltage.
Exteroceptive sensors acquire information from the robot’s environment; for example,
distance measurements, light intensity, sound amplitude. Hence exteroceptive sensor mea-
surements are interpreted by the robot in order to extract meaningful environmental fea-
tures.