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Control Station

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Automatica

Volume 50, Issue 1, January 2014, Pages 3-43

Survey Paper

Control: A perspective☆

Author links open overlay panelKarl J.A˚ströma1P.R.Kumarb

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https://doi.org/10.1016/j.automatica.2013.10.012Get rights and content

Abstract

Feedback is an ancient idea, but feedback control is a young field. Nature long ago discovered feedback since it is essential for homeostasis and life. It was the key for harnessing power in the industrial revolution and is today found everywhere around us. Its development as a field involved contributions from engineers, mathematicians, economists and physicists. It is the first systems discipline; it represented a paradigm shift because it cut across the traditional engineering disciplines of aeronautical, chemical, civil, electrical and mechanical engineering, as well as economics and operations research. The scope of control makes it the quintessential multidisciplinary field. Its complex story of evolution is fascinating, and a perspective on its growth is presented in this paper. The interplay of industry, applications, technology, theory and research is discussed.

Introduction

Nature discovered feedback long ago. It created feedback mechanisms and exploited them at all levels, that are central to homeostasis and life. As a technology, control dates back at least two millennia. There are many examples of control from ancient times (Mayr, 1969). Ktesibios (285–222 BC) developed a feedback mechanism to regulate flow to improve the accuracy of water clocks. In the modern era, James Watts' use of the centrifugal governor for the steam engine was fundamental to the industrial revolution. Since then, automatic control has emerged as a key enabler for the engineered systems of the 19th and 20th centuries: generation and distribution of electricity, telecommunication, process control, steering of ships, control of vehicles and airplanes, operation of production and inventory systems, and regulation of packet flows in the Internet. It is routinely employed with individual components like sensors and actuators in large systems. Today control is ubiquitous in our homes, cars and infrastructure. In the modern post-genomic era, a key goal of researchers in systems biology is to understand how to disrupt the feedback of harmful biological pathways that cause disease. Theory and applications of control are growing rapidly in all areas.

The evolution of control from an ancient technology to a modern field is a fascinating microcosm of the growth of the modern technological society. In addition to being of intrinsic interest, its study also provides insight into the nuances of how theories, technologies and applications can interact in the development of a discipline. This paper provides a perspective on the development of control, how it emerged and developed. It is by no means encyclopedic. To describe the field, we have, somewhat arbitrarily, chosen the years 1940, 1960 and 2000 as separators of four periods, which are covered in sections with the titles: Tasting the Power of Feedback Control: before 1940, The Field Emerges: 1940–1960, The Golden Age: 1960–2000, and Systems of the Future: after 2000. We provide a reflection on the complexity of the interplay of theory and applications in a subsequent section.

It was only in the mid 20th century that automatic control emerged as a separate, though multidisciplinary, discipline. The International Federation of Automatic Control (IFAC) was formed in 1956 (Kahne, 1996, Luoto, 1978, Oldenburger, 1969), the first IFAC World Congress was held in Moscow in 1960, and the journal Automatica appeared in 1962 (Axelby, 1969, Coales, 1969). By 2000 IFAC had grown to 66 Technical Committees. As a key enabler of several technological fields, control is quintessentially multidisciplinary. This is clearly reflected in the diverse organizations, AIAA, AIChE, ASCE, ASME, IEEE, ISA, SCS and SIAM that are included in the American Automatic Control Council (AACC) and IFAC.

There is yet another sense in which control has been multidisciplinary — in its search for theories and principles, physicists, engineers, mathematicians, economists, and others have all contributed to its development. The physicist Maxwell laid the theoretical foundation for governors (Maxwell, 1868). Later, one of the first books (James, Nichols, & Phillips, 1947) was written by a physicist, a mathematician and an engineer. The mathematicians Richard Bellman (Bellman, 1957b), Solomon Lefschetz (Grewal & Andrews, 2010), and L. S. Pontryagin (Pontryagin, Boltyanskii, Gamkrelidze, & Mischenko, 1962) contributed to the early development of modern control theory. Indeed, respect for mathematical rigor has been a hallmark of control systems research, perhaps an inheritance from circuit theory (Bode, 1960, Guillemin, 1940).

Control theory, like many other branches of engineering science, has developed in the same pattern as natural sciences. Although there are strong similarities between natural and engineering science, there are however also some fundamental differences. The goal of natural science is to understand phenomena in nature. A central goal has been to find natural laws, success being rewarded by fame and Nobel prizes. There has been a strong emphasis on reductionism, requiring isolation of specific phenomena, an extreme case being particle physics. The goal of engineering science, on the other hand, is to understand, invent, design and maintain man-made engineered systems. A primary challenge is to find system principles that make it possible to effectively understand and design complex physical systems. Feedback, which is at the core of control, is such a principle. While pure reductionism has been tremendously successful in natural science, it has been less effective in engineering science because interactions are essential for engineered systems.

Many overviews of control have been presented in connection with various anniversaries. IFAC held a workshop in Heidelberg in September 2006 to celebrate its 50th anniversary (IFAC, 2006). Automatica celebrates its 50th anniversary in 2014 (Coales, 1969). A comprehensive overview of sensors and industrial controllers was published on the 50th anniversary of the International Society of Automation (ISA) (Strothman, 1995). The American Society of Mechanical Engineers (ASME) published a series of papers on the history of control in connection with the 50th anniversary of the Journal Dynamic Systems, Measurement, and Control in 1993 (Rabins, 1993). The IEEE Control Systems Society sponsored the reprint of 25 seminal papers on control theory, selected by an editorial board (Başar, 2001). The European Journal of Control published a special issue: On the Dawn and Development of Control Science in the XX-th Century in January 2007, in which researchers reflected on their view of its development (Bittanti & Gevers, 2007). A special issue on the history of control systems engineering (Axelby, 1984) was published in 1984 at the centennial of IEEE. The IEEE Control Systems Society organized a workshop on the Impact of Control: Past, Present and Future in Berchtesgaden, Germany, in 2009. Material from the workshop was combined with an extensive collection of success stories and grand challenges in a comprehensive report (Samad & Annaswamy, 2011). The National Academy of Engineering published two studies about the future of engineering at the turn of the century (NAE, 2004, NAE, 2005). They point out the growing importance of systems and the role of modeling and simulation for computer based design and engineering. The US Air Force Office of Scientific Research (AFOSR) sponsored a panel to study future directions in control, dynamics and systems, which resulted in a comprehensive report (Murray, 2003), summarized in Murray, A˚ström, Boyd, Brockett, and Stein (2003).

The field of control is even attracting the attention of historians, perhaps an indication that it has had a complex development process that needs to be brought to light. There are books on the history of control (Bennett, 1979, Bennett, 1993, Bissell, 2009), on individual researchers (Hughes, 1993), and on organizations and projects (Mackenzie, 1990, Mindell, 2002, Mindell, 2008). There are sessions on the history of the field at many control conferences.

Paradoxically, in spite of its widespread use, control is not very much talked about outside a group of specialists; in fact it is sometimes called the "hidden technology" (A˚ström, 1999). One reason could be its very success which makes it invisible so that all the attention is riveted to the end product device. It is also more difficult to talk about ideas like feedback than to talk about devices. Another reason is that control scientists have not paid enough attention to popular writing; a notable exception is the 1952 issue of Scientific American which was devoted to Automatic Control (Brown and Campbell, 1952, Tustin, 1952).

By 1940 control was used extensively for electrical systems, process control, telecommunication and ship steering. Thousands of governors, controllers for process control, gyro-compasses and gyro-pilots were manufactured. Controllers were implemented as special purpose analog devices based on mechanical, hydraulic, pneumatic and electric technologies. Feedback was used extensively to obtain robust linear behavior from nonlinear components. Electronic analog computing was emerging; it had originally been invented to simulate control systems (Holst, 1982). Communication was driven by the need for centralized control rooms in process control and fire control systems. The benefits derived from the power of control were the driving force.

Although the principles were very similar in the diverse industries, the commonality of the systems was not widely understood. A striking illustration is that features like integral and derivative action were reinvented and patented many times in different application fields. The theoretical bases were linearized models and the Routh–Hurwitz stability criterion. A few textbooks were available (Joukowski, 1909, Tolle, 1905). Research and development were primarily conducted in industry.

Control was an established field by 1960 because of its development during the Second World War. Servomechanism theory was the theoretical foundation. Tools for modeling from data, using frequency response, together with methods for analysis and synthesis, were available. Analog computing was used both as a technology for implementation of controllers and as a tool for simulation. Much of the development had been driven by requirements from applications and practical needs. After a long and complex evolution there had finally emerged a holistic view of theory and applications, along with many applications in diverse fields. Control systems were mass produced, large companies had control departments, and there were companies which specialized in control. An international organization IFAC had been created, and its first World Congress was held in Moscow in 1960. Most of the research and development had been done in research institutes, and industries with collaborations with a few universities. By 1960 more than 60 books on control had been published.

However, many changes began occurring around 1960; the digital computer, dynamic programming (Bellman, 1957b), the state space approach to control (Kalman, 1961a), and the linear quadratic regulator (Kalman, 1960) had appeared, with the Kalman filter just around the corner (Kalman, 1961b). There commenced a very dynamic development of control, which we have dubbed the Golden Age. There were challenges from the space race and from introduction of computer control in the process industry as well as in many other applications such as automobiles and cellular telephones. There was a rapid growth of applications and a very dynamic development of theory, and many subspecialties were developed. University education expanded rapidly both at the undergraduate and the graduate levels. One consequence was that the parity that had been achieved between theory and practice after many decades was once again breached, this time in the reverse direction. Pure theory seized attention to a significant extent and there emerged a perception among some that there was a "gap" (Axelby, 1964), and that the holistic view had been lost (Bergbreiter, 2005).

It is of course difficult to have a good perspective on recent events but our opinion is that there are indications that yet another major development and spurt is now in progress. By around 2000, there had occurred a phase transition in technology, due to the emergence and proliferation of wireline and wireless networking, and the development of sensors, powerful computers, and complex software. At the turn of the century there were therefore new challenges; control of networks and control over networks, design of provably safe embedded systems, and autonomy and model based design of complex systems. The dramatic growth in technological capabilities thus provided many opportunities but also presented many challenges that require a tight integration of control with computer science and communication. This recognition led to the creation of many major research programs such as ARTIST2 (0000) and ArtistDesign (0000) focused on embedded systems in EU, and Cyber–Physical Systems in the US (Baheti & Gill, 2011).

Closer interaction with physics, biology and medicine is also occurring. Control is a key ingredient in devices such as adaptive optics and atomic force microscopes. Control of quantum and molecular systems is being explored. The need for and interest in using ideas from systems and control to obtain deeper insight into biological systems has increased. The field of systems biology has emerged and groups with control scientists and biologists have been created; noteworthy are the departments of bioengineering in engineering schools.

Section snippets

Tasting the power of feedback control

In order for the industrial revolution to occur, it required power, and control was essential to harness steam power. Therefore a major development of control coincided with the industrial revolution. Feedback control was a powerful tool. It made it possible to reduce the effect of disturbances and process variations, to make good systems from bad components, and to stabilize unstable systems. The major drawback was that feedback could cause instabilities. Recognition and solution of these

The field emerges

Control emerged as a discipline after the Second World War. Prior to the war it was realized that science could have a dramatic impact on the outcome of the war. Fire-control systems, gun-sights, autopilots for ships, airplanes, and torpedoes were developed. Significant progress was also made in process control. There was close collaboration between military agencies, industry, research labs, and university (Mindell, 2002, Oppelt, 1984). Engineers and researchers with experiences of control

The golden age

Any field would have been proud of the accomplishments that control had achieved by 1960, but more was to come. The space race and the use of digital computers to implement control systems triggered new developments. Servomechanism theory was not well suited for systems with many inputs and many outputs, performance had to be optimized, and computer control gave rise to new challenges. Modeling based on injection of sinusoidal signals was time consuming for process control. These challenges

Widening the horizon

Around 2000 there were indications that control was entering a new era. Traditional applications were exploding because of the shrinking cost of computing, while new applications were emerging. The applications ranged from micro- and nano-scale devices to large-scale systems such as smart national power-grids and global communication systems. The expansion of the Internet and the cellular networks were strong technology drivers, as was the desire for systems with increased autonomy. A sign of

The interplay of theory and applications

Feedback control is a key component of an amazingly broad range of applications, in fact touching upon almost everything in the modern world. The theory of control is a similarly deep field, drawing upon a broad range of mathematics, and sometimes even contributing to it. One can ask how such a broad range of applications and deep theory came to be. The answer is rich with texture, as expounded on in this paper.

Control systems need enabling technologies in order to be implementable. The

Concluding remarks

Control is a field with several unique characteristics. Its evolution is a veritable microcosm of the history of the modern technological world. It provides a fascinating interplay of people, projects, technology, and research.

Control transcends the boundaries of traditional engineering fields such as aeronautical, chemical, civil, electrical, industrial, mechanical and nuclear engineering. Its development was triggered not by a sole technological area but by several technological projects,

Acknowledgments

The authors are grateful to Leif Andersson, Karl-Erik A˚rzén, Tamer Basar, John Baillieul, Bo Bernhardsson, John Cassidy, Helen Gill, Aniruddha Datta, Johan Eker, Y. C. Ho, Charlotta Johnsson, David Mayne, Petar Kokotovic, Sanjoy Mitter, Richard Murray, Anders Rantzer, Pravin Varaiya, Eva Westin and the several anonymous reviewers for input and feedback on this paper.

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