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 which greatly enhanced the capacity to turn raw materials into products of benefit to society. However, 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.
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Figure 1.1. Watt’s fly ball governor
The World Wars also lead 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 70’s also depended on control devel- opments. These developments then flowed back into consumer goods, as well as commercial, environmental and medical applications. These applications of ad- vanced 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 due, in part, to enhanced control. For many companies these developments were not only central to increased profitability but also 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 1.2 on page 8 shows the process schematic of a Kellogg ammonia plant. There are about 400 of these plants around
Section 1.2. Motivation for Control Engineering 7 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 ex- ample, in the case of rolling mills (illustrated in Figure 1.3 on page 13), the control system involves forces of the order of 2,000 tonnes, speeds up to 120 km/hour and tolerances (in the aluminum industry) of 5 micrometers or 1/500th of the thick- ness 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 totalk to each other in a seemless fashion).
Thus control engineering is an exciting multidisciplinary subject with an enor- mously 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 due to the increasing globalization of markets and environmental concerns.
1.2.1 Market GlobalizationIssues
Market globalization is increasingly occurring and this means that, to stay in busi- ness, manufacturing industries are necessarily placing increasing emphasis on issues of quality and efficiency. Indeed, in today’s society, few if any companies can afford to be second best. In turn, this focuses attention on the development of improved control systems so that processes operate in the best possible way. In particular, improved control is a key enabling technology underpinning:
• enhanced product quality
• waste minimization
• environmental protection
• greater throughput for a given installed capacity
• greater yield
• deferring costly plant upgrades, and
• higher safety margins.
All of these issues are relevant to the control of an integrated plant such as that shown in Figure 1.2.
Figure 1.2. Process schematic of a Kellogg ammonia plant
1.2.2 Environmental Issues
All companies and governments are becoming increasingly aware of the need to achieve the benefits outlined above whilst respecting finite natural resources and preserving our fragile environment. Again, control engineering is a core enabling technology in reaching these goals. To quote one well known example, the changes in legislation covering emissions from automobiles in California have led car manu- facturers to significant changes in technology including enhanced control strategies for internal combustion engines.
Section 1.3. Historical Periods of Control Theory 9 Thus, we see that control engineering is driven by major economic, political, and environmental forces. The rewards for those who can get all the factors right can be enormous.