Image Processing Reference
spot on the sensor. The task of the control system is to minimize the value of this er-
ror term; that is, keep the spot at the desired location. The performance of the con-
troller is evaluated in terms of the average value of the error, how long it takes the
system to reach the desired position, and whether it is stable. The PID system
optimizes these three performance features. It should be noted that in the PID con-
troller, a subset of the processing activities can be used. For example, a PD or even,
as shown earlier, a P controller can be constructed.
An alternative is the fuzzy-logic controller (FLC). This operates in a fashion
similar to the way a person would control a system. It can be highly advantageous
when a robust control system is required and not all of the details of the system can
be provided. Additionally, a fuzzy system has the advantage of requiring less com-
putational overhead than a PID system, so it can execute much more quickly and re-
quires less memory space. FLCs enable a system to soften its response to a given
change while still working with specific numbers.
Control schemes are a topic unto themselves, and a number of authoritative
topics are available, such as Valvano (2000) and Krstic et al. (1995).