Servo motors

Servo motors are closed-loop actuators: they use an integrated encoder (feedback device) and a controller to achieve and maintain extremely precise control over angular position, velocity, and acceleration.

A servomotor is a high-performance actuator (AC or DC) that excels at precision motion control, a critical difference from standard motors. The core mechanism is a closed-loop system: the motor is paired with an encoder or resolver that constantly reports the shaft's actual position. The dedicated controller compares this feedback to the commanded position, generating an error signal that instantly corrects the motor's power output. This continuous, real-time adjustment ensures high accuracy and repeatability, making servos indispensable for demanding applications like six-axis robotic arms, high-speed CNC machinery, and complex automated manufacturing processes.

https://en.wikipedia.org/wiki/Servomotor