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Control: a Perspective ? Control: A Perspective ? K. J. Astr¨om˚ aand P. R. Kumar b aDepartment of Automatic Control, Lund University, Lund, Sweden bDepartment of Electrical & Computer Engineering, Texas A&M University, College Station, USA 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. Key words: Feedback, control, computing, communication, theory, applications. 1 Introduction dividual components like sensors and actuators in large systems. Today control is ubiquitous in our homes, cars Nature discovered feedback long ago. It created mech- and infrastructure. In the modern post-genomic era, a anisms for and exploits feedback at all levels, which is key goal of researchers in systems biology is to under- central to homeostasis and life. As a technology, control stand how to disrupt the feedback of harmful biological dates back at least two millennia. There are many exam- pathways that cause disease. Theory and applications of ples of control from ancient times [460]. Ktesibios (285{ control are growing rapidly in all areas. 222 BC) developed a feedback mechanism to regulate flow to improve the accuracy of water clocks. In the mod- The evolution of control from an ancient technology to a ern era, James Watts's use of the centrifugal governor modern field is a fascinating microcosm of the growth of for the steam engine was fundamental to the industrial the modern technological society. In addition to being of revolution. Since then, automatic control has emerged intrinsic interest, its study also provides insight into the as a key enabler for the engineered systems of the 19th nuances of how theories, technologies and applications and 20th centuries: generation and distribution of elec- can interact in the development of a discipline. This pa- tricity, telecommunication, process control, steering of per provides a perspective on the development of con- ships, control of vehicles and airplanes, operation of pro- trol, how it emerged and developed. It is by no means duction and inventory systems, and regulation of packet encyclopedic. To describe the field, we have, somewhat flows in the Internet. It is routinely employed with in- arbitrarily, chosen the years 1940, 1960 and 2000 as sepa- rators of four periods, which are covered in sections with the titles; Tasting the Power of Feedback Control: before ? This paper was not presented at any IFAC meeting. Cor- 1940, The Field Emerges: 1940{1960, The Golden Age: responding author K. J. Astr¨om.Tel.˚ +46 46 222 8781. Fax 1960{2000, and Systems of the Future: after 2000. We +46 46 138118. provide a reflection on the complexity of the interplay of This paper is partially based on work supported by the theory and applications in a subsequent section. Swedish Research Foundation LCCC Linneaus Center, the ELLIIT Excellence Center, the NSF under the Science and Technology Center Grant CCF-0939370 and Contract Nos. It was only in the mid 20th century that automatic con- CNS-1232602, CNS-1302182, and CPS-1239116, and the trol emerged as a separate, though multidisciplinary, AFOSR under contract No. FA 9550-13-1-0008. discipline. The International Federation of Automatic Email addresses: [email protected] (K. J. Astr¨om),˚ Control (IFAC) was formed in 1956 [513,443,354], the [email protected] (P. R. Kumar). first IFAC World Congress was held in Moscow in 1960, Preprint submitted to Automatica 17 October 2013 and the journal Automatica appeared in 1962 [42,149]. XX-th Century in January 2007, in which researchers By 2000 IFAC had grown to 66 Technical Committees. reflected on their view of its development [82]. A spe- As a key enabler of several technological fields, con- cial issue on the history of control systems engineering trol is quintessentially multidisciplinary. This is clearly [43] was published in 1984 at the centennial of IEEE. reflected in the diverse organizations, AIAA, AIChE, The IEEE Control Systems Society organized a work- ASCE, ASME, IEEE, ISA, SCS and SIAM that are shop on the Impact of Control: Past, Present and Future included in the American Automatic Control Council in Berchtesgaden, Germany, in 2009. Material from the (AACC) and IFAC. workshop was combined with an extensive collection of success stories and grand challenges in a comprehensive There is yet another sense in which control has been report [576]. The National Academy of Engineering pub- multidisciplinary { in its search for theories and princi- lished two studies about the future of engineering at the ples physicists, engineers, mathematicians, economists, turn of the century [488,489]. They point out the grow- and others have all contributed to its development. The ing importance of systems and the role of modeling and physicist Maxwell laid the theoretical foundation for simulation for computer based design and engineering. governors [456]. Later, one of the first books [343] was The US Air Force Office of Scientific Research (AFOSR) written by a physicist, a mathematician and an engineer. sponsored a panel to study future directions in control, The mathematicians Richard Bellman [59], Solomon Lef- dynamics and systems, which resulted in a comprehen- schetz [269], and L. S. Pontryagin [534] contributed to sive report [485], summarized in [486]. the early development of modern control theory. Indeed, respect for mathematical rigor has been a hallmark of The field of control is even attracting the attention of his- control systems research, perhaps an inheritance from torians, perhaps an indication that it has had a complex circuit theory [272,95]. development process that needs to be brought to light. There are books on the history of control [65,66,80], on Control theory, like many other branches of engineer- individual researchers [318], and on organizations and ing science, has developed in the same pattern as nat- projects [448,472,471]. There are sessions on the history ural sciences. Although there are strong similarities be- of the field at many control conferences. tween natural and engineering science, there are how- ever also some fundamental differences. The goal of nat- Paradoxically, in spite of its widespread use, control is ural science is to understand phenomena in nature. A not very much talked about outside a group of special- central goal has been to find natural laws, success be- ists; in fact it is sometimes called the \hidden technol- ing rewarded by fame and Nobel prizes. There has been ogy" [30]. One reason could be its very success which a strong emphasis on reductionism, requiring isolation makes it invisible so that all the attention is riveted to of specific phenomena, an extreme case being particle the end product device. It is more difficult to talk about physics. The goal of engineering science, on the other ideas like feedback than to talk about devices. Another hand, is to understand, invent, design and maintain man- reason is that control scientists have not paid enough made engineered systems. A primary challenge is to find attention to popular writing; a notable exception is the system principles that make it it possible to effectively 1952 issue of Scientific American which was devoted to understand and design complex physical systems. Feed- Automatic Control [657,122]. back, which is at the core of control, is such a principle. While pure reductionism has been tremendously suc- By 1940 control was used extensively for electrical sys- cessful in natural science, control is more complex since tems, process control, telecommunication and ship steer- interaction is a key element of engineered systems. ing. Thousands of governors, controllers for process con- trol, gyro-compasses and gyro-pilots were manufactured. Many overviews of control have been presented in con- Controllers were implemented as special purpose analog nection with various anniversaries. IFAC held a work- devices based on mechanical, hydraulic, pneumatic and shop in Heidelberg in September 2006 to celebrate its electric technology. Feedback was used extensively to ob- 50th anniversary [324]. Automatica celebrates its 50th tain robust linear behavior from nonlinear components. anniversary in 2014 [149]. A comprehensive overview of Electronic analog computing was emerging; it had orig- sensors and industrial controllers was published on the inally been invented to simulate control systems [307]. 50th anniversary of the International Society of Automa- Communication was driven by the need for centralized tion (ISA) [632]. The American Society of Mechanical control rooms in process control and fire control systems. Engineers (ASME) published a series of papers on the The benefits derived from the power of control were the history of control in connection with the 50th anniver- driving force. sary of the Journal Dynamic Systems, Measurement, and Control in 1993 [552]. The IEEE Control Systems Although the principles were very similar in the diverse Society sponsored the reprint of 25 seminal papers on industries, the commonality of the systems was not control theory, selected by an editorial board [50]. The widely understood. A striking illustration is that fea- European Journal of Control published a special issue: tures like integral and derivative action were reinvented On the Dawn and Development of Control Science in the and patented many times in different application fields.
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