Abstract :
Classical control revisited? Why focus on something that is so familiar and unchanging? Is there anything new at all in such a mature and perhaps aged topic? Our response is that, while the tools of classical control, such as Bode plots, transfer functions, Nyquist theory, root locus plots, the Routh-Hurwitz stability test, PID controllers, and lead and lag compensators, may be familiar, aspects of each are not widely appreciated. Each article in this special issue presents a new facet of classical control, either clarifying a cloudy issue or exploring a new twist on a classical tool. The first article concerns Laplace transforms. Next, consider the classical root locus tool. The third article focuses on classical lead and lag compensation. The fourth article deals with controller architecture, an issue that is important as soon as we move beyond the traditional one-degree-of-freedom unity-feedback control loop. The final article is concerned with setpoint tracking while rejecting unknown constant disturbances and sensor biases
