Servo (servomechanism)

A feedback control system that continuously measures a mechanism’s actual position, velocity, or other output, compares it against a target, and drives an actuator to correct the difference — the general mechanism behind everything from a ship’s autopilot to a camera autofocus motor. A governor is a simple servomechanism specialized to regulate speed alone; a PID controller is the standard formal algorithm used to compute a servo’s correction from present, accumulated, and changing error.