A servomechanism is a force amplifier mechanism where the output accurately follows the input but with greater power. Movement can be linear or rotary. if the output is controlled by the input only it is called an Open Loop system. If there is some form of feedback or follow-up the system is called a Closed-loop system using the servo-loop to provide part of the control. Most closed-loop systems use negative feedback where essentially the servomechanism constantly compares demand with output, any difference generating an error signal which drives the output in the required direction to reduce the error to zero.
Servomechanisms may be dc or ac operated.
Continuous operation is assured in a servomechanism because any variation in the output from that demanded by the input automatically produces a difference between output and input, and hence an error signal. The error signal again starts the correcting action.
A servomechanism has many applications, covering a wide range of power, position, Speed, and acceleration requirements.