How does a servo motor work?

Have you ever considered how to control robotic vehicles with bomb retention devices that are usually used for military purposes, or how metal cutting and shaping machines provide precise motion for metal processing milling, lathes and bending, or how antenna positioning systems can control azimuth and altitude?

Servo motor applications are most commonly used in closed-loop systems. In closed-loop systems, precise position control is usually used in industrial and commercial applications. How does a servo motor work?

This passage is going to talk about the followings of servo motor:

(1) Basic knowledge of servo motor

(2) How to control servo motor?

(3) Application of servo motor

(1) Basic knowledge of servo motor

Let's start with the basics of servo motors. The servo motor is a part of the closed loop system and consists of several parts, namely the control circuit, the servo motor, the shaft, the potentiometer, the drive gear, the amplifier and the encoder or resolver.

Servo motor is an independent electrical device that can rotate machine parts efficiently and accurately. The output shaft of the motor can be moved to a specific angle, position and speed that conventional motors do not have. Servo motors use conventional motors and couple them with sensors to provide position feedback.

The controller is the most important part of the servo motor specially designed and used for this purpose. Servo motor is a closed-loop mechanism that incorporates position feedback to control rotational or linear speed and position. The motor is controlled by an analog or digital electrical signal, which determines the amount of movement that represents the final command position of the shaft. An encoder is used as a sensor that provides speed and position feedback. The circuit is built into the motor housing which is usually equipped with a gear system.

(2) How to control servo motor?

The servo motor is controlled by sending electric pulses of variable width or pulse width modulation (PWM) through the control line. There are minimum pulse, maximum pulse and repetition rate. Servo motors usually can only rotate 90° in either direction to achieve a total of 180° movement. The neutral position of the motor is defined as the position where the servo motor system has the same potential rotation in the clockwise or counterclockwise direction. The PWM sent to the motor determines the position of the shaft based on the duration of the pulse sent through the control line; the rotor will turn to the desired position. The servo motor expects to see a pulse every 20 milliseconds (ms), and the length of the pulse will determine how far the motor rotates. For example, a 1.5ms pulse will turn the motor to the 90° position. Shorter than 1.5 milliseconds will move it counterclockwise to the 0° position, longer than 1.5 milliseconds will move the servo motor clockwise to the 180° position.

The variable pulse width of the servo motor controls the servo motor position. When these servers are commanded to move, they will move to and maintain that position. If an external force presses on the server while the server maintains its position, the server will prevent it from moving out of that position. The maximum force the server can apply is called the torque level of the server. Servo motors does not maintain its position forever; the position pulse must be repeated to instruct the servo motor to stay in place.

(3) Application of servo motor

The application of servo motors has been applied to many industrial and commercial systems and products, such as robotics, where servo motors are used at each "joint" of the robot to perform its precise angle of motion.

Camera auto focus uses a servo motor built into the camera to accurately correct the position of the lens to sharpen out-of-focus images.

In antenna positioning systems, servo motors are used to locate the azimuth and elevation angles of antennas and telescopes, such as the positioning system used by the National Radio Astronomy Observatory in the United States.

At this point, the article is over, about what is a servo motor and its working principle. I hope this helps you understand the conditions required to create your own motion control project.