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6.1 Overview 6 Common Sensing Techniques for Reactive Robots
To review Ch. 3, perception in a reactive robot system has two roles: to re-
lease a behavior,and to support or guide the actions of the behavior. All sensing
is behavior-specific, where behaviors may tap into the same sensors, but use
the data independently of each other. Also, the connotation of reactive robots
is that behaviors are most often stimulus-response, relying on direct percep-
tion rather than require memory. Recognition is not compatible with reactiv-
ity. In order for a reactive robot to be successful in theory, it must have reli-
able perception since perception and action are tightly coupled. For it to be
successful in practice, a robot has to have perceptual hardware and software
which updates quickly. This chapter covers the most common sensing tech-
niques for reactive robots. The sensors and sensing techniques described in
this chapter also apply to robot architectures in the Hybrid paradigm, since
Hybrid architectures use reactive behaviors.
Regardless of sensor hardware or application, sensing and sensors can be
thought of interacting with the world and robots as shown in Fig. 6.1. The
SENSOR sensor is a device that measures some attribute of the world. The term trans-
TRANSDUCER ducer is often used interchangeably with sensor. A transducer is the mech-
anism, or element, of the sensor that transforms the energy associated with
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what is being measured into another form of energy. A sensor receives en-
ergy and transmits a signal to a display or a computer. Sensors use transduc-
ers to change the input signal (sound, light, pressure, temperature, etc.) into
an analog or digital form capable of being used by a robot. In a reactive robot,
the sensor observation is intercepted by a perceptual schema which extracts
the relevant percept of the environment for the behavior. This percept is then
used by the motor schema, which leads to an action.
PASSIVE SENSOR A sensor is often classified as being either passive sensor or active sensor.
ACTIVE SENSOR Passive sensors rely on the environment to provide the medium for observa-
tion, e.g., a camera requires a certain amount of ambient light to produce a
usable picture. Active sensors put out energy in the environment to either
change the energy or enhance it. A sonar sends out sound, receives the echo,
and measures the time of flight. An X-ray machine emits X-rays and mea-
sures the amount blocked by various types of tissue. Although a camera is a
passive device, a camera with a flash is active. The term active sensor is not
ACTIVE SENSING the same as active sensing. Active sensing connotes the system for using an
effector to dynamically position a sensor for a “better look.” A camera with
a flash is an active sensor; a camera on a pan/tilt head with algorithms to
direct the camera to turn to get a better view is using active sensing.