Page 31 - Modern Control Systems

Section 1.2 Brief History of Automatic Control 5
1.2 BRIEF HISTORY OF AUTOMATIC CONTROL

The use of feedback to control a system has a fascinating history. The first applications of
feedback control appeared in the development of float regulator mechanisms in Greece
in the period 300 to 1 B.C. [1, 2.31 The water clock of Ktesibios used a float regulator
(refer to Problem PI.11). An oil lamp devised by Philon in approximately 250 B.C. used
a float regulator in an oil lamp for maintaining a constant level of fuel oil. Heron of
Alexandria, who lived in the first century A.D., published a book entitled Pneumatics,
which outlined several forms of water-level mechanisms using float regulators [1].
The first feedback system to be invented in modern Europe was the tempera-
ture regulator of Cornelis Drebbel (1572-1633) of Holland [1]. Dennis Papin
(1647-1712) invented the first pressure regulator for steam boilers in 1681. Papin's
pressure regulator was a form of safety regulator similar to a pressure-cooker valve.
The first automatic feedback controller used in an industrial process is generally
agreed to be James Watt's flyball governor, developed in 1769 for controlling the
speed of a steam engine [1.2]. The all-mechanical device, shown in Figure 1.7, mea-
sured the speed of the output shaft and utilized the movement of the flyball to con-
trol the steam valve and therefore the amount of steam entering the engine. As
depicted in Figure 1.7, the governor shaft axis is connected via mechanical linkages
and beveled gears to the output shaft of the steam engine. As the steam engine out-
put shaft speed increases, the ball weights rise and move away from the shaft axis
and through mechanical linkages the steam valve closes and the engine slows down.
The first historical feedback system, claimed by Russia, is the water-level float
regulator said to have been invented by I. Polzunov in 1765 [4]. The level regulator
system is shown in Figure l.S.The float detects the water level and controls the valve
that covers the water inlet in the boiler.
The next century was characterized by the development of automatic control
systems through intuition and invention. Efforts to increase the accuracy of the

Shaft axis Measured Boiler
Mewl
ball

Output
shaft
Engine

FIGURE 1.7
Watt's flyball
governor.