ABSTRACT
In the 1940s and 50s, several researchers proved that many dynamic systems can be mathematically modeled using differential equations. These previous works, in addition to the Transform theory, represent the foundation of the Control theory which provides an extremely powerful means of analyzing and designing control systems (Cordón et al. 2001). Many developments were achieved until the 70s, when the area was known as System Theory to indicate its defi nitiveness (Mamdani 1993). Its principles have been used to control a very large amount of systems using mathematics as the main tool, for several years. Unfortunately, in too many cases this approach could not
be sustained because many systems have unknown parameters or highly complex and nonlinear characteristics that make them not amenable to the full force of mathematical analysis as dictated by the Control Theory.
