A Bit of Control Theory

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As every engineer knows, the essence of modern engineering is control theory. 

At the core of control theory is the concept of feedback loops. Without an understanding of how to use feedback loops to design systems, the marvels of the late Twentieth Century world would not have been possible. It is what separated the scattershot engineering of the pre-World War II era to precise engineering of the 1950s and beyond.

Engineers in almost all fields spend a lot of time mastering these concepts, because without them they could not design anything worthwhile.

A little bit of history is in order. 

Control theory dates from the 18th century work of James Watt, who invented the modern steam engine. The most common units of power, as that which is measured in a light bulb or a generator, are also named for Watt.

To invent a practical steam engine that was useful under varying loads, Watt needed also to invent a means by which the engine is regulated in a feedback, such that its operation stays within a certain range no matter what load is applied to it. 

Watt accomplished this by the invention of the governor, which is a spinning centrifuge, driven by the engine, that rotates to regulate the intake of fuel, by the same means that a figure skater has control his body's rate of rotation. In this way, the engine was safely operated in practical conditions without destroying itself.

Later advances in control theory relied heavily on mathematics to design feedback mechanisms. In the early 20th century it was discovered how to use mathematics to predict a feedback loop to keep ships on course while they are at sea (Minorsky, 1922). 

The great advances in control theory came when it was discovered to how to cope with arbitrary inputs in the system. For reasons that are quite lengthy, it turns out that the input of many systems, no matter type they are in the physical world, can often be described the sine wave that most people are familiar with. By the 1930s it was discovered mathematically now to predict certain feedback loops from these types of sine inputs for whole classes of systems.

In 1934, it was discovered by Hazen how to apply control theory to servomechanisms, which control  positioning of robots and other devices.

It the 1940s, it was discovered for certain systems how to use simple diagrams to make control theory predictions without the need to solve the mathematical differential equations. This is a tremendous advance that forms the basis of control theory education for engineers.

By the 1950s, the advances and simplifications in control theory were such that control theory was fully established in the driver's seat of engineering. The change can be described by Okata as causing a shift in the fundamental task of engineering.

Previously the task of engineering had been the design of a system that satisfied the requirements. After the 1950s, the task became one of the design of the optimal system that satisfied the requirements.