Hardware Reference
In-Depth Information
Actuator
Sensory input
Actuator
Real-Time
ENVIRONMENT
System
User input
Actuator
Figure 11.3
General structure of an open-loop control system.
Input
Controller
Plant
Actuators
ENVIRONMENT
Sensors
feedback
System
Figure 11.4
General structure of a feedback control system.
Feedback control systems (or closed-loop control systems) are systems that have fre-
quent interactions with the environment in both directions; that is, the actions produced
by the actuators strictly depend on the current sensory information. In these systems,
sensing and control are tied together, and one or more feedback paths exist from the
sensory subsystem to the controller. Sensors are often mounted on actuators and are
used to probe the environment and continuously correct the actions based on actual
data (see Figure 11.4).
Human beings are perhaps the most sophisticated examples of feedback control sys-
tems. When we explore an unknown object, we do not just see it, but we look at it
actively, and, in the course of looking, our pupils adjust to the level of illumination,
our eyes bring the object into sharp focus, our eyes converge or diverge, we move our
head or change our position to get a better view of it, and we use our hands to perceive
and enhance tactile information.
Modern “fly-by-wire” aircrafts are also good examples of feedback control systems.
In these aircrafts, the basic maneuvering commands given by the pilot are converted
into a series of inputs to a computer, which calculates how the physical flight controls
shall be displaced to achieve a maneuver, in the context of the current flight conditions.
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