Servomechanism

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In mechanical and control engineering, a servomechanism (also called servo system, or simply servo) is a control system for the position and its time derivatives, such as velocity, of a mechanical system. It often includes a servomotor, and uses closed-loop control to reduce steady-state error and improve dynamic response.^[1] In closed-loop control, error-sensing negative feedback is used to correct the action of the mechanism.^[2] In displacement-controlled applications, it usually includes a built-in encoder or other position feedback mechanism to ensure the output is achieving the desired effect.^[3] Following a specified motion trajectory is called servoing,^[4] where "servo" is used as a verb. The servo prefix originates from the Latin word servus meaning slave.^[1]

The term correctly applies only to systems where the feedback or error-correction signals help control mechanical position, speed, attitude or any other measurable variables.^[5] For example, an automotive power window control is not a servomechanism, as there is no automatic feedback that controls position—the operator does this by observation. By contrast a car's cruise control uses closed-loop feedback, which classifies it as a servomechanism.