What are servo motors and how do they work?

Servo motors, or simply "servos," are precision instruments in the world of motors. In essence, it's a motor with a built-in ability to rotate very accurately. The key feature that sets it apart is its control circuit, which constantly monitors and adjusts the motor's position. This feedback allows servo motors to perform incredibly precise movements. For example, if you need to rotate an object to a specific angle or distance, you use a servo motor.

A servo motor is, at its core, a basic motor driven by a servomechanism. A servomechanism is a closed-loop system composed of four essential parts: a controlled device, a controller, an output sensor, and a feedback system. Servomechanisms are often used in situations where the exact control of position and speed is essential. In the industrial world, there are two main types of servos used: DC servo motors (powered by a direct current source) and AC servo motors (running on alternating current).

A DC servo motor is typically used for smaller projects that prioritize simplicity and cost-effectiveness. They're affordable, efficient, and straightforward. In contrast, an AC servo motor is the most popular in the industry. They provide the muscle needed for more demanding applications while also delivering precise control and minimal maintenance needs.

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Servo motor working principle

Servo motors are among the most efficient motors used across various industries. They allow the precise control of an object's angular or linear position, speed, and acceleration. This makes them indispensable for tasks that other motors struggle to perform, such as automation in factories and robotics. Servo motors operate on a unique working principle and come in various types and capabilities. To truly understand how a servo motor works, we need to take a look under the hood.

The motor is part of a closed-loop system comprising:

1. A motor - Either a DC or AC motor depending on the power source and specific application needs.
2. A gear system
3. A position sensor - Typically a potentiometer, but could also be an encoder, a resolver, or another position-sensing device.
4. A control circuit - Either an analog or digital circuit.

The motor is connected to the gear system, which serves to reduce motor speed, increase torque, and provide feedback to the potentiometer. This feedback is then converted into an electrical signal by the potentiometer and sent to the control circuit. The control circuit decodes the signal, compares it to the desired position, and then adjusts the motor's rotation to reach that position.

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Applications of servo motors

When asking "What is a servo motor used for?" You'll find that it's used in everything from remote-controlled toy cars and automatic doors to more important jobs in manufacturing, robots, pharmaceuticals, and food services. Some of the most common servo motor applications include:

1. Robotics: Servo motors are used to power robotic arms and grippers, ensuring the arms and joints move precisely to achieve the desired angles.
2. Robotic vehicles: Robotic vehicles, especially those used in industrial applications, use servo motors to control their wheels, providing the necessary torque for movement, starting, stopping, and speed control.
3. CNC machining: Servo motors accurately control the speed and position of cutting tools in CNC machines. You'll also find them offering exact motion control in milling machines.
4. Conveyors: A servo motor keeps things running smoothly in conveyor systems. It makes sure products start and stop exactly when they should - crucial for jobs like product labeling, bottling, and packaging.
5. Hobbyist projects: Hobbyists often use servo motors for projects like robots and model airplanes.

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Benefits of servo motors

Accurate and fast

Servo motors excel in precision, making them ideal for applications in industrial automation. Their high accuracy allows for easy adjustments to suit specific tasks while ensuring precise results. They also have strong motor output power to provide quick and precise movements while easily adjusting to changing needs.

Affordable

While servo motors were once considered expensive, their cost has dropped significantly in recent years. They may still be pricier than some motors, but the price difference is narrowing. Both companies and hobbyists are turning to servo motors for their affordability.

Readily available

Servo motors are easily accessible, and you can find them from many retailers that specialize in industrial parts. This availability is a big plus for businesses because they won't struggle to find replacement parts.

How to choose the right servo motor

Choosing the right machine for your application involves a process known as "motor sizing." This simply means figuring out the size and strength of the servo system you need based on how fast it should go and how strong it must be.

1. Speed and torque requirements: The speed and torque required for your application are key factors. You want to match the torque and speed needs of your application to the motor's speed and torque rating to prevent overheating, stalling, or loss of accuracy.
2. Gear ratio: Some servos use gears to boost their torque. The gear ratio tells you how much the motor's power is amplified.
3. Size and weight: Opt for a servo motor size and weight that aligns with the application's needs. Larger, heavier motors suit high-torque applications, while smaller, lighter ones are ideal for speed and high-precision tasks.
4. Accuracy: A servo motor's accuracy largely depends on its feedback system. Again, you want to make sure it matches your application's needs.
5. Environment: Environmental factors like ambient temperature, contamination, and vibration can affect performance. Consider where the motor will work and choose one that is designed for extreme environments.

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Servo motors in robotics

Servo motors almost always come up when discussing robotics and automation. Thanks to their precision, power, and torque capabilities, these motors play a crucial role in various automation applications. No matter the task at hand, there's a servo motor for it. Servos come in various sizes and strengths, making them versatile for a wide range of applications in robotics.

Cost control is incredibly important in industrial processes. Consider robotic arms, a common sight in many applications. A single robotic arm typically requires at least five servo motors to achieve the desired range of motion. This can be costly, but thankfully, servo motors fit the bill - in all senses.

Simplicity is another important part of industrial settings. Whether it's building robotic arms or similar systems, a straightforward approach is essential. Servo motors are simple, requiring only a voltage and pulse-width modulation (PWM) for control. They eliminate the need for motor controllers and are rapidly replacing stepper motors in the industry.

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Troubleshooting common servo motor problems

Servo motors are essential tools used across various industries, but like any equipment, they are not foolproof and can face issues that affect performance and safety. Knowing how to troubleshoot common issues is essential to ensure you get the best performance from these motors.

1. Contamination

One leading cause of servo motor failure is contamination. Oil, coolant, and debris can infiltrate servo motors and cause damage to critical components like bearings and windings, for example. You can fend off contamination by inspecting and cleaning your servo motors regularly. You could also consider sealing motor windings and using fully enclosed motor systems.

2. Bearing issues

If you hear growling or shrieking noises when your motor operates at high speeds, it's a sign of bearing failure. This can be brought on by various factors, including typical wear and tear, and improper installation or reinstallation. Regularly inspecting and replacing bearings can prevent these failures and help extend your servo motor's lifespan.

3. Overheating

Few servo motors escape the issue of overheating. High temperatures can cause damage to the internal components or connected systems, leading to costly downtime. Motor blockages, high ambient temperatures, and long operating hours are all common causes of overheating. Thankfully, many servo motors feature fail-safes that shut down the motor when things get too hot. Whenever possible, place your servo motor in a temperature-controlled environment with proper airflow.

4. Brake failure

While motor brakes play a critical role in stabilizing loads when your motor stops or powers down, these brakes are not designed for continuous and frequent use. To avoid brake failure, always engage the brake when the motor is at rest, allowing it to take a breather. If your application needs frequent stops or dynamic braking, look at brakes designed for that purpose.

5. Bad windings and cable issues

Winding and cable issues are also common problems in servo motors. Contaminants, such as water exposure, or the motor's natural vibrations, can harm the copper coils inside. As time goes on, power and control cables can wear down and potentially cause motor failure or voltage spikes. To tackle winding problems, regular maintenance tasks like rewinding damaged coils can help. You should also choose top-notch feedback cables.

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FAQs

What is the difference between DC and AC servo motors?

First, let's look at the main difference between DC motors and AC motors. While an AC motor relies on an AC power source, a DC motor relies on DC power, such as batteries. AC servo motors are considered the better option compared to DC motors, as they have higher torque, greater efficiency and reliability, and less radio frequency noise.

Which is better, a servo motor or a stepper motor?

Both servo motors and stepper motors have the same goal of providing precise speed control and positioning, but they differ in design and performance.

Servo motors are the ideal choice for high-speed, high-torque applications, while stepper motors are best for slower-speed, highly accurate applications. And, with just three wires to connect to the power supply compared to the six required for stepper motors, servo motors work faster, offering a straightforward solution.

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Conclusion

Servo motors are quite the unsung heroes of technology, quietly powering precision in various applications. They can move and hold positions with pinpoint accuracy and control torque and speed in the blink of an eye. This makes them perfect for handling complex tasks, including tricky manufacturing processes, which is why they're a go-to choice for robotics and automation.

With many companies using them for their reliability, precision, and efficiency, you'll likely keep seeing these devices in use for years to come.