Control Clasico

Reprinted by permission from Chapter 1: Introduction to Modern Control Theory, in:
F.L. Lewis, Applied Optimal Control and Estimation, Prentice-Hall, 1992.
A BRIEF HISTORY OF FEEDBACK CONTROL
Contents
• Outline
• A Brief History of Automatic Control
o Water Clocks of the Greeks and Arabs
o The Industrial Revolution
o The Millwrights
oTemperature Regulators
o Float Regulators
o Pressure Regulators
o Centrifugal Governors
o The Pendule Sympathique
o The Birth of Mathematical Control Theory
o Differential Equations
o Stability Theory
o System Theory
o Mass Communication and The Bell Telephone System
o Frequency-Domain Analysis
oThe World Wars and Classical Control
o Ship Control
o Weapons Development and Gun Pointing
o M.I.T. Radiation Laboratory
o Stochastic Analysis
o The Classical Period of Control Theory
o The Space/Computer Age and Modern Control
o Time-Domain Design For Nonlinear Systems
o Sputnik - 1957
o Navigationo Optimality In Natural Systems
o Optimal Control and Estimation Theory
o Nonlinear Control Theory
o Computers in Controls Design and Implementation
o The Development of Digital Computers
o Digital Control and Filtering Theory
o The Personal Computer
o The Union of Modern and Classical Control
• The Philosophy of ClassicalControl
• The Philosophy of Modern Control
• References

Outline

In this chapter we introduce modern control theory by two approaches. First, a short history of automatic control theory is provided. Then, we describe the philosophies of classical and modern control theory.
Feedback control is the basic mechanism by which systems, whether mechanical, electrical, or biological,maintain their equilibrium or homeostasis. In the higher life forms, the conditions under which life can continue are quite narrow. A change in body temperature of half a degree is generally a sign of illness. The homeostasis of the body is maintained through the use of feedback control [Wiener 1948]. A primary contribution of C.R. Darwin during the last century was the theory that feedback over longtime periods is responsible for the evolution of species. In 1931 V. Volterra explained the balance between two populations of fish in a closed pond using the theory of feedback.
Feedback control may be defined as the use of difference signals, determined by comparing the actual values of system variables to their desired values, as a means of controlling a system. An everyday example of afeedback control system is an automobile speed control, which uses the difference between the actual and the desired speed to vary the fuel flow rate. Since the system output is used to regulate its input, such a device is said to be a closed-loop control system.
In this book we shall show how to use modern control theory to design feedback control systems. Thus, we are concerned not with naturalcontrol systems, such as those that occur in living organisms or in society, but with man-made control systems such as those used to control aircraft, automobilies, satellites, robots, and industrial processes.
Realizing that the best way to understand an area is to examine its evolution and the reasons for its existence, we shall first provide a short history of automatic control theory. Then, we givea brief discussion of the philosophies of classical and modern control theory.
The references for Chapter 1 are at the end of this chapter. The references for the remainder of the book appear at the end of the book.

1.1 A BRIEF HISTORY OF AUTOMATIC CONTROL
There have been many developments in automatic control theory during recent years. It is difficult to provide an impartial analysis of...