Editing Servomechanism (section)

==History==
[[File:Scross helmsman.jpg|thumb|Power-assisted ship steering systems were early users of servomechanisms to ensure the rudder moved to the desired position.]]
[[James Watt]]'s [[steam engine]] [[Governor (device)|governor]] is generally considered the first powered feedback system. The [[windmill fantail]] is an earlier example of automatic control, but since it does not have an [[amplifier]] or [[Gain (electronics)|gain]], it is not usually considered a servomechanism.

The first feedback position control device was the ship [[steering engine]], used to position the rudder of large ships based on the position of the ship's wheel. 
[[John McFarlane Gray]] was a pioneer. His patented design was used on the [[SS Great Eastern]] in 1866.
[[Joseph Farcot]] may deserve equal credit for the feedback concept, with several patents between 1862 and 1868.<ref name="Bennett1986">{{cite book|last=Bennett|first=Stuart|title=A History of Control Engineering, 1800–1930|url=https://books.google.com/books?id=1gfKkqB_fTcC&pg=PA98|date=1986-01-01|publisher=IET|isbn=978-0-86341-047-5|pages=98–100}}</ref>

The telemotor was invented around 1872 by [[Andrew Betts Brown]], allowing elaborate mechanisms between the control room and the engine to be greatly simplified.<ref>[http://www.gracesguide.co.uk/Andrew_Betts_Brown Andrew Betts Brown<!-- Bot generated title -->]</ref> Steam steering engines had the characteristics of a modern servomechanism: an input, an output, an error signal, and a means for amplifying the error signal used for negative feedback to drive the error towards zero. The Ragonnet [[power reverse]] mechanism was a general purpose air or steam-powered servo amplifier for linear motion patented in 1909.<ref>Eugine L. Ragonnet, Controlling Mechanism for Locomotives, [https://patents.google.com/patent/US930225 U.S. Patent 930,225], Aug. 9, 1909.</ref>

Electrical servomechanisms were used as early as 1888 in [[Elisha Gray]]'s [[Telautograph]].

Electrical servomechanisms require a power amplifier. [[World War II]] saw the development of electrical [[fire-control]] servomechanisms, using an [[amplidyne]] as the power amplifier. [[Vacuum tube]] amplifiers were used in the [[UNISERVO]] tape drive for the [[UNIVAC I]] computer. The Royal Navy began experimenting with Remote Power Control ([[List of British ordnance terms#RPC|RPC]]) on [[HMS Champion (1915)|HMS Champion]] in 1928 and began using RPC to control searchlights in the early 1930s. During WW2 RPC was used to control gun mounts and gun directors.

Modern servomechanisms use solid state power amplifiers, usually built from [[MOSFET]] or [[thyristor]] devices. Small servos may use power [[transistor]]s.

The origin of the word is believed to come from the French "''Le Servomoteur''" or the slavemotor, first used by J. J. L. Farcot in 1868 to describe hydraulic and steam engines for use in ship steering.<ref name="origin">IEEE Industry Applications Magazine March/April 1996, pg 74</ref>

The simplest kind of servos use [[bang–bang control]]. More complex control systems use proportional control, [[PID control]], and state space control, which are studied in [[modern control theory]].