What is a servo motor and how does it work?


There are many types of electric motors available on the market! They are basically separated into direct current (DC) and alternating current (AC) motors, and among them, we can mention the Servo motor. If you don’t know what a servo motor is, how a servo motor works and its main characteristics, rest assured! In this article, the World of Electrical answers these and other questions related to the Servo motor. So come on guys!

What is a servo motor?
Servo motors do not belong to a specific motor class, that is, they can be both AC and DC motors. Servos are actuators designed for applications where it is necessary to perform movement control with high precision positioning, fast reversal, and high performance. They are widely used in robotics, automated systems, CNC machines, and other diverse applications.

Servos have several differences from other types of motors! Among these differences, the main one is that the servos have incorporated an encoder and a controller in them. This encoder is actually a speed sensor that has the function of providing the speed and positioning of the motor.

To control the speed and the final position of the motor, the Servo works with a servomechanism that uses position feedback. Basically, a Servo motor internally combines a motor with a feedback circuit, a controller and other complementary circuits.

Types of Servo Motors
We can classify Servo motors in two ways, AC (alternating current) and DC (direct current) servo motors, that is, this will depend on the power supply required for its operation. DC servo motors are generally used for smaller projects, they are relatively low cost and efficient.

AC servo motors are normally used in industrial environments, as they are usually of high power, offer greater accuracy in their control and little maintenance. Now that we know a little about these two classifications of Servo Motors, let’s go deeper into the information about DC Servo Motors.

Direct Current (DC) servo motor
A DC Servo motor is basically formed by a small DC motor, a feedback pot, a gearbox, and an electronic circuit to start it, as shown in the image below.

Learn how a servo motor works.
The internal structure of a servo motor!

The servo is similar to a common direct current motor, where its stator consists of a cylindrical structure and a magnet coupled to the inside of its frame. In addition, the polarity of the control voltage is able to determine the direction of torque developed by the motor.

DC servo motor: working principle

A DC servo motor works as follows, a reference voltage is regulated to a value corresponding to the desired output. Depending on the control circuit, we can generate this voltage using a potentiometer, pulse width modulation (PWM) or through timers.

To control the Servo motor digitally, we can use a microcontroller to then produce control signals with greater precision and thus supply voltage pulses, which are obtained through the PWM technique.

To guarantee better performance in relation to its operation, the Servo motors need a feedback signal that corresponds to the current positioning of the servo, being obtained through a position sensor. This positioning sensor is actually an internal potentiometer that provides a voltage signal corresponding to the angle of the motor shaft.

This voltage signal related to the current position of the motor is compared with the desired voltage, that is, with the voltage that is obtained by the pulse width. Thus producing an error signal with positive or negative voltage.

If the error signal is positive, the voltage applied to the motor armature causes the rotor to rotate in one direction. However, if the error is negative, the armature voltage reverses and in this case, the motor rotor rotates in the opposite direction. As long as there is an error signal, the motor will continue to rotate, that is, the motor will rotate until the error signal is zero.