According to cybernetician Ashby (1956), mathematicians and theorists interested in the principles of feedback mechanisms prefer the definition of "circularity of action", which keeps the theory simple and consistent. Over the years there has been some dispute as to the best definition of feedback. The development of cybernetics from the 1940s onwards was centred around the study of circular causal feedback mechanisms. This action of feeding back of the signal from output to input gave rise to the use of the term "feedback" as a distinct word by 1920. īy the end of 1912, researchers using early electronic amplifiers ( audions) had discovered that deliberately coupling part of the output signal back to the input circuit would boost the amplification (through regeneration), but would also cause the audion to howl or sing. The verb phrase to feed back, in the sense of returning to an earlier position in a mechanical process, was in use in the US by the 1860s, and in 1909, Nobel laureate Karl Ferdinand Braun used the term "feed-back" as a noun to refer to (undesired) coupling between components of an electronic circuit. This was a landmark paper on control theory and the mathematics of feedback. In 1868, James Clerk Maxwell wrote a famous paper, "On governors", that is widely considered a classic in feedback control theory. Early steam engines employed a purely reciprocating motion, and were used for pumping water – an application that could tolerate variations in the working speed, but the use of steam engines for other applications called for more precise control of the speed. In 1788, James Watt designed his first centrifugal governor following a suggestion from his business partner Matthew Boulton, for use in the steam engines of their production. Ĭentrifugal governors were used to regulate the distance and pressure between millstones in windmills since the 17th century. This then reoccurs in a circular fashion as the water level fluctuates. This device illustrated the principle of feedback: a low water level opens the valve, the rising water then provides feedback into the system, closing the valve when the required level is reached. The first ever known artificial feedback device was a float valve, for maintaining water at a constant level, invented in 270 BC in Alexandria, Egypt. Self-regulating mechanisms have existed since antiquity, and the idea of feedback had started to enter economic theory in Britain by the 18th century, but it was not at that time recognized as a universal abstraction and so did not have a name. Karl Johan Åström and Richard M.Murray, Feedback Systems: An Introduction for Scientists and Engineers History
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