The Development of Control Engineering in Britain and the Cambridge Contribution

Malcolm C. Smith

At Caius there are two Engineering Fellows who specialise in control engineering (GV and MCS). The latter was recently asked to prepare an article for the American Control Systems Society (IEEE) on educational practice in the Britain in the area of control, as part of a survey of several countries around the world. In fact the U.K. has been quite strong in this area historically, so it was quite nice for it to be represented in the survey. A few extracts from the article are sewn together below, specially abridged and prepared for the Caius Engineer at the request of the editor (Dr T.P. Bligh).

Historically, applications of feedback control date back to antiquity (e.g. Egyptian water clocks), though one of the most famous examples in technology is the centrifugal governor for steam engines invented by the Scottish engineer James Watt. It was this application that brought about the birth of control theory in a paper for the Royal Society of London by James Clerk Maxwell---a Scot, a Cambridge man, and perhaps most famous for his equations of electromagnetics. Another Cambridge man, who was contemporary with Maxwell, Edward J. Routh, was responsible for an important stability criterion which bears his name and which is taught in control courses all over the world to this day (see the end of the article for an anecdote on the Tripos performance of Maxwell and Routh). Routh was one of the most famous and successful coaches at Cambridge in the 19th century, being a private tutor to more than six hundred pupils between 1855 and 1888, and preparing the Senior Wrangler (top mathematics student) on 27 occasions---an unparalleled feat. Routh was himself Senior Wrangler in 1854.

It seems that the stability analysis of governors and related mechanisms was taught from this time at Cambridge, at first in the mathematical tripos and later on in mechanical sciences (after the beginning of this tripos in 1894). The question below is the last of 10 on the "Heat Engines and Dynamics of Machines'' examination paper in the Cambridge Mechanical Sciences Tripos part II of 1897 --- students were instructed to answer not more than eight (!) such questions in three hours:

"Investigate the equations of motion of the governing masses in some form of Watt's centrifugal governor, and find an expression for the period of the oscillations about the state of steady motion. Point out in what circumstances the oscillations will degenerate into hunting, and shew how this fault may be prevented.''

Questions related to regulation, control, and later feedback in amplifiers, continued to be set occasionally for Tripos exams on the initiative of individual lecturers. However, the treatment and appreciation of automatic control as a subject in its own right did not begin until after World War II.

The emergence of Control Engineering as a discipline, and the realisation that there were common techniques and methods which could be used in a wide variety of applications (ranging from control of power plants, chemical processes, to aircraft stability, engines, even applications in economics, biology), happened in the late 1930s and 1940s. A substantial part of what came to be called "classical control'' originated in the work on feedback amplifiers at the Bell Laboratories in America in the late 1920s and 1930s. Experience of engineers in Britain involved in key war-time applications (such as radar fire control) helped to establish a strong basis of expertise in the area. In 1942, a very influential committee was formed to coordinate work and to facilitate an exchange of information: the Interdepartmental Committee on Servomechanisms (the Servo Panel). Several members of this committee played an important role in disseminating control system design techniques after the war and in helping universities to establish courses. Due partly to the Servo Panel, Britain was the first country to hold a major international conference on automatic control (the Cranfield Conference of 1951).

An influential figure in Britain at this time was Arnold Tustin, who worked for Metropolitan Vickers until 1945 and became Professor at Birmingham University (1947) and later at Imperial College (1955). In a lecture to the Servo Panel in 1942, Tustin described the design methods developed at Metro-Vick for gun control, which used the frequency response locus. The connection with the Nyquist stability criterion and work going on in America was later drawn to Tustin's attention by P.J. Daniell of the Mathematics Department at the University of Sheffield. (Incidentally Daniell was one of several people to independently develop the describing function method in the 1940s---this is one of the topics taught in the I3 module in the fourth year of the Engineering Tripos). Another influential member of the Servo Panel was A.L. Whiteley who developed the use of inverse Nyquist diagrams for feedback design in 1943 at British Thomson-Houston Company (in parallel with H.T. Marcy in America). It seems that the experience gained by early British designers in the use of frequency response methods had a strong effect on the subsequent development of control in Britain. It is possible that this influence extends to later research on multivariable control design and H-infinity control.

Probably the first set of lectures on automatic control engineering (as a subject in its own right) at Cambridge were given by G.D.S. MacLellan (Pembroke) in 1946-7. By the late 1940s, the basic theory of closed loop systems was being given in a course on "mechanics of machines'', taken by all engineering undergraduates, and was treated as an extension of the elementary theory of engine governors. For those who went on to Part II of the mechanical sciences tripos (roughly the top 20% of students) there were more advanced lectures, for example, on the applications of control to the governing of prime movers (for mechanical engineers) and the theoretical background common to servo-mechanisms and feedback amplifiers (for electrical engineers). The principle of teaching the basics of classical control to all engineering undergraduates in their second year has continued until the present day, with the material being moved from the mechanics paper to a new information engineering paper in 1986. The teaching of control in the third year underwent a gradual unification (from separate mechanical/electrical treatments) which was fully achieved in 1987. This principle has continued after the introduction of the four-year M.Eng course in 1992.

The control research group at Cambridge was established in 1947 by R.H. Macmillan and was later expanded by J.F. Coales after 1952. A post-graduate course in control engineering was started in 1954 which was intended mainly for graduates who had spent some time in industry. This course continued until it was replaced by the M.Phil in control engineering and operational research in 1977, which itself continued until 1986. Research by the control group was carried out first in the areas of mechanical control systems, and later in nonlinear and optimal control with A.T. Fuller, and applications to industrial processes. After 1974, multivariable frequency response methods became a prominent research theme with the appointment of A.G.J. MacFarlane. From the mid 1980s the group was recognized for work in the major new approach of H-infinity control with the work of Professor K. Glover now the Deputy Head of Engineering (Research) at Cambridge. These techniques were recently implemented successfully on a Harrier aircraft at Bedford with the control systems design work being carried out at Cambridge by R. Hyde and K. Glover.

To conclude, here is the promised anecdote on Maxwell and Routh. It was already noted above that Routh was Senior Wrangler in 1854. In fact Maxwell sat for the mathematical tripos in the same year and was placed second. Apparently Maxwell was so confident of achieving first place himself that he did not trouble to rise early to hear the list of successful candidates read out in the Senate House, but sent his servant instead. (Interesting, isn't it, that undergraduates had servants in those days!) On his return, Maxwell is said to have enquired, "Well, tell me who's second!'', and was somewhat taken aback to receive the reply, "You are, sir''.