Page 20 - The Mechatronics Handbook

FIGURE 1.3 Watt’s flyball governor. (From Modern Control Systems, 9th ed., R. C. Dorf and R. H. Bishop, Prentice-
Hall, 2001. Used with permission.)

of a steam engine [10]. Employing a measurement of the speed of the output shaft and utilizing the
motion of the flyball to control the valve, the amount of steam entering the engine is controlled. As the
speed of the engine increases, the metal spheres on the governor apparatus rise and extend away from
the shaft axis, thereby closing the valve. This is an example of a feedback control system where the
feedback signal and the control actuation are completely coupled in the mechanical hardware.
These early successful automation developments were achieved through intuition, application of practical
skills, and persistence. The next step in the evolution of automation required a theory of automatic control.
The precursor to the numerically controlled (NC) machines for automated manufacturing (to be developed
in the 1950s and 60s at MIT) appeared in the early 1800s with the invention of feed-forward control of
weaving looms by Joseph Jacquard of France. In the late 1800s, the subject now known as control theory
was initiated by J. C. Maxwell through analysis of the set of differential equations describing the flyball
governor [11]. Maxwell investigated the effect various system parameters had on the system performance.
At about the same time, Vyshnegradskii formulated a mathematical theory of regulators [12]. In the 1830s,
Michael Faraday described the law of induction that would form the basis of the electric motor and the
electric dynamo. Subsequently, in the late 1880s, Nikola Tesla invented the alternating-current induction
motor. The basic idea of controlling a mechanical system automatically was firmly established by the end
of 1800s. The evolution of automation would accelerate significantly in the twentieth century.
The development of pneumatic control elements in the 1930s matured to a point of finding applications
in the process industries. However, prior to 1940, the design of control systems remained an art generally
characterized by trial-and-error methods. During the 1940s, continued advances in mathematical and
analytical methods solidified the notion of control engineering as an independent engineering discipline.
In the United States, the development of the telephone system and electronic feedback amplifiers spurred
the use of feedback by Bode, Nyquist, and Black at Bell Telephone Laboratories [13–17]. The operation
of the feedback amplifiers was described in the frequency domain and the ensuing design and analysis
practices are now generally classified as “classical control.” During the same time period, control theory
was also developing in Russia and eastern Europe. Mathematicians and applied mechanicians in the
former Soviet Union dominated the field of controls and concentrated on time domain formulations
and differential equation models of systems. Further developments of time domain formulations using
state variable system representations occurred in the 1960s and led to design and analysis practices now
generally classified as “modern control.”
The World War II war effort led to further advances in the theory and practice of automatic control
in an effort to design and construct automatic airplane pilots, gun-positioning systems, radar antenna
control systems, and other military systems. The complexity and expected performance of these military
systems necessitated an extension of the available control techniques and fostered interest in control
systems and the development of new insights and methods. Frequency domain techniques continued to
dominate the field of controls following World War II, with the increased use of the Laplace transform,
and the use of the so-called s-plane methods, such as designing control systems using root locus.

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