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1. The Excitement of Control Engineering

1.2 Motivation for Control Engineering

Feedback control has a long history, which began with the early desire of humans to harness the materials and forces of nature to their advantage. Early examples of control devices include clock-regulating systems and mechanisms for keeping wind-mills pointed into the wind.

A key step forward in the development of control occurred during the industrial revolution. At that time, machines were developed that greatly enhanced the capacity to turn raw materials into products of benefit to society. The associated machines, specifically steam engines, involved large amounts of power, and it was soon realized that this power needed to be controlled in an organized fashion if the systems were to operate safely and efficiently. A major development at this time was Watt's fly-ball governor. This device regulated the speed of a steam engine by throttling the flow of steam; see Figure 1.1. These devices remain in service to this day.

Figure 1.1: Watt's fly-ball governor
Watt's fly-ball governor

The World Wars also led to many developments in control engineering. Some of these were associated with guidance systems whilst others were connected with the enhanced manufacturing requirements necessitated by the war effort.

The push into space in the 1960's and 1970's also depended on control developments. These developments then flowed back into consumer goods, as well as into commercial, environmental, and medical applications. These applications of advanced control have continued at a rapid pace. To quote just one example from the author's direct experience, centre-line thickness control in rolling mills has been a major success story for the application of advanced control ideas. Indeed, the accuracy of centre-line thickness control has improved by two orders of magnitude over the past 50 years, thanks, in part, to enhanced control. For many companies, these developments were central not merely to increased profitability but even to remaining in business.

By the end of the twentieth century, control has become a ubiquitous (but largely unseen) element of modern society. Virtually every system we come in contact with is underpinned by sophisticated control systems. Examples range from simple household products (temperature regulation in air-conditioners, thermostats in hot-water heaters, etc.), to more sophisticated systems, such as the family car (which has hundreds of control loops), to large-scale systems (such as chemical plants, aircraft, and manufacturing processes). For example, Figure fig:kellogg shows the process schematic of a Kellogg ammonia plant. There are about 400 of these plants around the world. An integrated chemical plant of the type shown in Figure 1.2 will typically have many hundreds of control loops. Indeed, for simplicity, we have not shown many of the utilities in Figure 1.2, yet these also have substantial numbers of control loops associated with them.

Many of these industrial controllers involve cutting edge technologies. For example, in the case of rolling mills (illustrated in Figure 1.3), the control system involves forces on the order of 2,000 tonnes, speeds up to 120 km/hour, and (in the aluminum industry) tolerances of 5 micrometers or 1/500th of the thickness of a human hair! All of this is achieved with precision hardware, advanced computational tools, and sophisticated control algorithms.

Beyond these industrial examples, feedback regulatory mechanisms are central to the operation of biological systems, communication networks, national economies, and even human interactions. Indeed, if one thinks carefully, control in one form or another can be found in every aspect of life.

In this context, control engineering is concerned with designing, implementing, and maintaining these systems. As we shall see later, this is one of the most challenging and interesting areas of modern engineering. Indeed, to carry out control successfully, one needs to combine many disciplines, including modeling (to capture the underlying physics and chemistry of the process), sensor technology (to measure the status of the system), actuators (to apply corrective action to the system), communications (to transmit data), computing (to perform the complex task of changing measured data into appropriate actuator actions), and interfacing (to allow the multitude of different components in a control system to talk to each other in a seamless fashion).

Thus, control engineering is an exciting multidisciplinary subject with an enormously large range of practical applications. Moreover, interest in control is unlikely to diminish in the foreseeable future. On the contrary, it is likely to become ever more important, because of the increasing globalization of markets and environmental concerns.