Servo motor, how it works?

A servo motor is a general term used for a specific kind of linear or rotary actuators. Basically, the name servo motor is related to the term servomechanism, which means that the motor is constantly monitored to control its motion.  In principle, a servo motor uses a sensor, feedback encoder and controller to create a  closed-loop feedback system, allowing accurate control of its speed, torque, acceleration and position.

Types of motors used in a servo motor

The type of motor used in a servo motor depends largely on the application the servo motor is intended to be used for. For heavy-duty industrial applications, large AC induction motors are used connected to a VSD to control its RPM. Servo motors based upon  EC brushless motors are often used for smaller industrial applications. Moreover, for very simple applications brushed DC motors can be used. Generally Servomotors based upon earlier mentioned technologies utilize gearboxes to reduce speed and increase torque. However the best performing servomotors use direct drive torque motors, brushless AC PM motors. These torque motors create, in a compact and efficient servomotor design, a wide torque and speed range.

Servo motor on white background

Servo motors and stepper motors

Servo motors are often compared to stepper motors since both motors have common NEMA style mounting method. In general, servo motors are used in higher demanding applications compared to stepper motors. One of the main differences is that the servo motor uses closed-loop position control and the stepper motor (mostly) open-loop position control. As a result, the position accuracy of the stepper motor is limited. In case the performance requirements of the application are less high, the stepper motor is usually a more cost-effective solution. As the lack of an encoder and a lower cost controller reduces the cost of the total solution.

In summary, the type of servomotor best used for a specific application depends greatly on all the criteria. In addition, if the performance requirements are low a stepper motor might be a more cost-effective solution compared to a servomotor.