Types of Motor Drives

types of servo motors

Table of Contents

What Are Motor Drives?
What Are the Types of Motor Controllers and Drives?
DC Drive
Types of Motors That Rely on DC Drives and Their Applications
AC Drive
Types of Motors That Rely on AC Drives and Their Applications
Servo Motor Drives and Controllers
Servo Motor Applications
Stepper Applications
Need Your Motor Drives Repaired

Motor drives come in a wide variety of forms. These electronic or electrical devices are used to power a range of machines, robots, equipment and other applications. If you’re looking to purchase new motor drives or repair old ones, you’ll need to know what motor drives are, along with the different types of drives and how they are commonly used.

What Are Motor Drives?

Motor drives are electronic devices that control torque, position outputs and motor speed. As power goes into the motor, the drive modifies it so that your motor has the needed output. The terms “motor controllers” and “motor drives” are often used interchangeably since controller circuits are usually combined with drive circuits to produce a single unit.

What Are the Types of Motor Controllers and Drives?

There are a few different types of motors and motor drives that are common today. The four basic available motor drive types are stepper, AC, DC and servo. These motor drives each have input power types that are tailored to the output functions of their applications. Learn more about what the drives in these motors do and how they are commonly used below:

1. DC Drive

In its basic function, a DC drive converts alternating current (AC) into direct current (DC) to power a DC motor. DC drives are power modules that serve as the interface between a DC motor and a controller. Often, the motor comes with the controller integrated alongside the drive circuit, helping to power the control signals that communicate with the drive.

There a few different types of DC motor drives, with the most common type of drive coming with two SCRs (Silicon Controlled Rectifiers) that use a single-phase AC input to generate a half-cycle DC output. This type of power generation is referred to as a half-bridge method. More complex and powerful DC drives incorporate six SCRS to utilize a full-bridge method. When relying on a full-bridge method, the six SCRs will use a three-phase AC input to generate the DC output.

Occassionally, DC drives are referred to as variable speed drives. They have this name due to the way most types of DC drives adjust shaft speed. A DC Drive is typically characterized by its dependable speed regulation, broad speed range and how the drive transfers voltage to the motor.

Types of Motors That Rely on DC Drives and Their Applications

There are a variety of DC motors that rely on DC drives. All of these motors use the same operation to power them, with the motor rotation coming from the application of power through current-carrying conductors that are installed inside a magnetic field. The differences between DC motors arise when looking at how and where the electromagnetic fields are created. To give you an idea of where you might expect to use a DC motor, take a look at some of the main types below:

Linear Motors

Linear motors, like their name suggests, generate forces in only one direction. They create mechanical force though permanent rare-earth magnets that generate magnetic flux, which then interacts with the current in the conductors. Linear motors can accelerate quickly, position themselves with great precision and operate at fast speeds.

You can find linear motors in a variety of equipment types. Their ability to help with speed control makes them especially useful for applications where precise speeds are a priority. They are used in looms, sliding doors and baggage handling machines. Additionally, they are often installed in roller coasters to help with acceleration and speed control.

Brushed Motors

A brushed motor is a type of DC drive that uses physical touch to commutate and produce mechanical energy. The brushes in the motor are made with carbon or other types of material to be used as electrical contacts. While the shaft rotates, the spring-loaded brushes make contact with the commutator. In essence, the motor’s brushes help the DC power supply connect to the rotor assembly that contains the output shaft, commutator rings and armature.

These brushed motors have been around for more than a century, with companies and individuals still trusting them due to their significant ratio of torque to inertia. They are known for their reliability and affordability. You can often find brushed motors used in vehicles to control the power windows, windshield wipers and seat positioners. They also appear in battery-powered pumps, X-rays and welding equipment. In a more industrial setting, brushed motors are used in industrial equipment that requires quick bursts of power.

Brushless Motors

Unlike brushed motors, brushless motors don’t use physical touch to cause commutation to occur. As you might expect, they don’t use brushes to generate motion. Instead, they use magnets placed around the rotor that are then attracted to the stator’s powered coil windings. As a result of this design, the motor creates its torque with electromagnetism. The motor’s rotation speed can be adjusted by simply changing the direction and size of current contained in the stator coils.

Due to their efficiency and durability, brushless DC motors are best used in applications where a motor is going to need to be running for an extended period. Some examples of applications include hard drive disks, washing machines, computer fans and air conditioners.

2. AC Drive

An AC drive converts AC inputs to DC, much like the DC drive. However, after this first conversion is completed, the DC is converted back into AC that fuels the motor. Essentially, AC drives are frequency inverters or amplifiers that serve as an interface between an AC motor and controller. The drives make the voltage compatible with the motor by converting the controller’s step and direction inputs into the appropriate voltage.

Sometimes, AC drives are referred to as variable frequency drives, since the majority of AC motor drives adjust input frequency. Whatever name you refer to them as, the AC drive’s function stays the same, with the AC drive regulating a motor’s torque and output speed.

Types of Motors That Rely on AC Drives and Their Applications

There are a few different AC motors that rely on AC drives. Some of the main types of AC drives and the motors they power can be found below:

Synchronous Motors

If you want a reliable motor that keeps its speed consistent, synchronous motors are ideal. These motors and their AC drives can maintain a precise speed even with a full load. Since the stator’s rotating magnetic field maintains a speed that’s equal to the speed of the rotor, a synchronous motor doesn’t have any slip.

In practice, synchronous motors are used in machines that require exceptional accuracy. Some high-precision drill machines use them to ensure their drilling is as precise as possible. Other examples of machines that use synchronous motors include metering pumps, timers, clocks, speed controllers and electromechanical robots.

Induction Motors

Induction motors don’t use any kind of physical connection from stator windings to induce the current into the rotor windings. They are well known for their ability to generate a significant amount of power, their variable speed control capabilities and their adaptability to a broad variety of environments. Induction motors usually have some slip to them, where they lose their exact speed tracking.

Induction motors are the most used AC motors and drives in day-to-day processes. You’ll find induction motors in kitchen appliances, air conditioners, vehicles, industrial machines and water pumps. They are used in so many household devices due to their flexibility in meeting varying load demands from many electrical applications.

Sensorless Vector Drives

For greater speed control and torque output that’s low-speed, a sensorless vector drive takes sole control over the frequency and voltage that’s fed into the motor. This type of drive is the closest to DC motors in their effect. As their name suggests, they do not use any feedback sensors, such as resolvers or encoders.

Sensorless vector drives are used in several types of industrial applications. They’re often used in applications that have extremely high inertia or when an application needs a high level of steady-state speed accuracy.

3. Servo Motor Drives and Controllers

A servo motor is one of the most efficient motors that users can control easily to get the correct output. This type of motor relies on a servo drive that helps to generate precise movements to rotate or push the parts of your machine. A servo drive modifies the input power by taking the alternating or constant current source and turning it into a pulsed current output that ranges in pulse frequency and duration. These drives help to control positions, torques and motor speeds.

There are two primary sizes of servo motors — small and standard. As you might expect, the standard-sized motor offers greater speed and power than the motor system. Small servo motors are typically used by companies that have limited space and don’t need to have a huge amount of power. Large servos are constructed with metal parts to handle heavier work, while small servo motors are built with plastic parts.

Servo Motor Applications

Typically, Typically, servo motors and drives are used for motion control applications in the construction and manufacturing industries. Their main applications involve assisting a machine as it conducts a task that’s meant to be done frequently and in a particular way. In practice, they often help power spindle drive systems, conveyors, machine tools and robotics. To gain a broader understanding of servo motors, consider some of their applications below:

  • Robotics: Servo motors are often used in robotics. The small size of servo motors makes them perfect for use in many robots. Additionally, they provide the precision and force density that robots need to function correctly. Types of robots that rely on servo motors and drives include bomb detonation, robotic arms and remotely controlled firefighting crafts.
  • Industrial production: Companies in the manufacturing industry are always trying to produce robotic and automated processes that are more accurate and efficient. In manufacturing, servo motors are often used to power robotic arms that move materials. Additionally, servo drives are used in fabrication machines to help machines cut or bend metal sheets with greater precision and power. They are also used in conveyor systems to assist with their spinning elements.
  • Elevators: When a company creates elevator technology, safety is a primary concern. To help ensure that elevators transport passengers safely, companies use servo systems. This type of system helps make the ride as smooth as possible for riders through feedback and control processes.

4. Stepper

A stepper motor drive and controller modify alternating or constant current sources to a stepped current output that then adjusts the stepper motor’s input power. Due to their design, they also are called step amplifiers and pulse drives. Stepper motor drives monitor and adjust input power through permanent magnets. They also use carefully placed poles in both the stator and rotor that employ DC currents to help create stepwise rotation.

Since a stepper’s rotational output is not continuous, the input power has to be controlled in a way that helps the groups of stator poles either energize or de-energize. The stepper’s drives and controllers are crucial for the needed control that helps the stepper function properly. More specifically, the controller integrated with a stepper drive circuit sends the relevant control signals to the motor drive.

Stepper Applications

This type of motor is primarily used in industries like construction and manufacturing. They control torques, position and motor speeds of various types of machinery. They’re quite popular due to their open feedback design and precision. While they aren’t suited for high-speed applications, their precise, repeatable movements still work at a wide range of speeds. Stepper motors are known for how reliable, easy to use and reversible they are.

Steppers have several applications where they are commonly used. Companies regularly employ small-wattage steppers for micro-positioning, robots, machine tools, electric watch drives, medical equipment, printers, computer control systems and hard drive disks. Large-wattage steppers can be found in military equipment, conveyors, scientific exploration devices and machine tools.

Need Your Motor Drives Repaired?

With all of the information above, you should now have a basic understanding of the types of motor drives available to you, giving you a better idea of which motors drives are best for your needs. Whether you’re using DC motors, AC motors, servo motors or stepper motors, you’ll eventually have to perform some type of maintenance on them.

When you need motor drives repaired, you’ll want to reach out to an expert in the industry. Global Electronic Services offers comprehensive repair services and solutions that help your business continue to operate smoothly. Contact Global Electronic Services today with any questions you might have about motor drives or with inquiries about service.

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