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Control System Design  Index  Book Contents 
Chapter 1
 Section 1.3
1. The Excitement of Control Engineering
1.3 Historical Periods of Control Theory
We have seen above that control engineering has taken several
major steps forward at crucial events in history (e.g., the
industrial revolution, the Second World War, the push into space,
economic globalization, and shareholdervalue thinking). Each of
these steps has been matched by a corresponding burst of
development in the underlying theory of control.
Early on, when the compelling concept of feedback was applied,
engineers sometimes encountered unexpected results. These then
became catalysts for rigorous analysis. For example, if we go back
to Watt's flyball governor, it was found that, under certain
circumstances, these systems could produce selfsustaining
oscillations. Toward the end of the 19th century, several
researchers (including Maxwell) showed how these oscillations
could be described via the properties of ordinary differential
equations.
The developments around the period of the Second World War were
also matched by significant developments in Control Theory. For
example, the pioneering work of Bode, Nyquist, Nichols, Evans, and
others appeared at this time. This resulted in simple graphical
means for analyzing singleinput, singleoutput feedback control
problems. These methods are now generally known by the generic
term Classical Control Theory.
The 1960's saw the development of an alternative state
space approach to control. This followed the publication of work
by Wiener, Kalman (and others) on optimal estimation and control.
This work allowed multivariable problems to be treated in a
unified fashion. This had been difficult, if not impossible, in
the classical framework. This set of developments is loosely
termed Modern Control Theory.
By the 1980's, these various approaches to control had reached a
sophisticated level, and emphasis then shifted to other related
issues, including the effect of model error on the performance of
feedback controllers. This can be classified as the period of
Robust Control Theory.
In parallel, there has been substantial work on nonlinear control
problems. This has been motivated by the fact that many realworld
control problems involve nonlinear effects.
There have been numerous other developments, including adaptive
control, autotuning, and intelligent control. These are too
numerous to detail here. Anyway, our purpose is not to give a
comprehensive history but simply to give a flavor for the
evolution of the field.
At the time of writing this book, control has become a mature
discipline. It is thus possible to give a treatment of control
which takes account of many different viewpoints and to unify
these in a common framework. This is the approach we will adopt
here.
