To understand the role of the servo drive in a servo system, you must first understand the other components the servo system depends on to make a movement.

Servo systems include four main parts; a controller, a drive, a motor, and a feedback device. The controller acts as the brain, or computer, sending out low voltage commands to the drive. The drive acts as a kind of middle man between the controller and the motor. It receives signals from the controller and sends an adequate amount of electrical energy to the motor to complete the required move.

What is a servo drive and how does it work?

Servo drives are also commonly referred to as amplifiers because it’s their job to receive low voltage signals from the controller and amplify the voltage to the level necessary to make a movement.

In a servo system, the drive or amplifier most commonly controls rotational force or turning effect, also known as torque; the rotational equivalent of linear force. It sometimes controls other parameters such as velocity and position.

What is a servo drive?

To fully understand the role of each component in a servo system, it helps to think about a servo system as a construction site.

The first component, the controller, is the engineer. It lays out original plans and makes necessary adjustments in response to information it receives from the feedback device. Then, it sends out orders to its workers in the form of low voltage signals.

Before the orders make it to the workers, however, they must go through the foreman. In the case of a servo system, this role is assumed by the servo drive. A foreman’s responsibilities on a job site include scheduling, coordinating, and supervising the efforts of the workers, ensuring all work is delivered safely, on time and within budget. Likewise, it’s the job of the servo drive to receive signals from the controller and supply the motor with the voltage necessary to complete the correct movement when prompted.

The motor is the team of construction workers. After receiving their orders from the controller, the servo drive supplies them with the energy and materials necessary to complete the job.

Servo drive basics

When used in various industries, servo drives are either digital or analog.

Digital servo drives

Digital servo drives have a microprocessor, which gives it the ability to multitask, analyzing incoming signals from the controller while controlling the mechanism. Speed is a major factor when considering a digital versus analog drive. A digital drive’s microprocessor allows the drive to be quickly self-adjusting, which is a valuable asset in many industrial environments that require machinery to quickly adapt to various conditions. For this reason, digital drives also typically require more power than their analog counterparts, making them more expensive.

Analog servo drives 

In an analog drive, the desired motor velocity is represented by an analog input voltage. The various adjustments necessary for tuning an analog servo drive are usually made with potentiometers. This process can take time, depending on the application of your analog servo drive, so many drives use what’s called a “personality card” that can be programmed with preset components.

The analog servo drive comes at a lower cost, but with the potential for high performance depending on the application. The digital servo drive is easier to set up and adjust, and it has a notable advantage over analog drives in situations where the load parameters are either unknown or difficult to measure.

What does a servo drive do?

The servo drive uses signals from the controller to determine the output voltage necessary to move a load.

Analog servo drives are sometimes called four-quadrant drives because they can produce acceleration and braking torque in both directions of rotation. A simpler, variable-speed drive that runs only in one direction without braking control is called a single-quadrant drive.

The microprocessor in the digital drive is programmed with code representing its equivalent analog system, so no potentiometer measurements are necessary. It also accounts for additional factors such as output velocity, the rate of change of the input, and the various tuning settings. When tuning a digital drive, all adjustments are performed using buttons or by sending data through a computer.

Servo drives usage examples

Servo motors and their components can be found in all kinds of electronics: from kids’ toys to your DVD player. They also play important roles on a much larger scale in cars, airplanes, and security systems. Hobbyists who collect radio-controlled cars, airplanes, and helicopters likely use servo motors every day. Here are some unique and unexpected places where servo motors are hard at work.


Servo drives are a popular choice in manufacturing robotics due to their wide range of motion as well as their ability to self-correct. These qualities and more make them a popular choice for assembly lines and robotic arms due to their efficiency.

Conveyor Belts

Stepper motors can produce high torque at a low speed while minimizing vibration. This makes them an ideal choice for quick positioning. Servo motors are easier to operate, however, allowing for smooth operation with large loads and belt mechanisms. In conveyors, servo motors are the best choice for positioning over long distances using a flat torque characteristic from low to high speeds.

Camera Auto Focus

Servo systems in camera lenses are very useful, especially for photographers attempting to produce images of wildlife photography or cover a live sporting event. The servo motor keeps your subject in focus as it moves, making it crucial for photographing events and concerts, where the subject is rarely standing still.

Automatic Doors

The servo drive in a motor for a set of automatic doors works similarly as it does in a conveyor belt. An advanced brushless AC motor features advantages like higher efficiency, larger torque, and a longer life span. The servo keeps motor noise at a minimum because of its precise manufacturing technology and direct driving design.

Industrial Machinery

Industrial Servo actuators and motors typically incorporate optical encoders within the body of the motor to increase reliability. This is especially important as these machines are capable of producing high forces with long strokes. Motion controllers help ensure accurate positioning.