Servo Motors Types and Function

Servo motors are part of the important components in precise motion control systems, converting electrical signals into accurate mechanical movement. They are required especially for applications that require exact positioning, speed, and torque control. This article explains the different types of servo motors, their working principles, and how they compare to other motor types like stepper motors.

Catalog

Overview of Servo Motor

A servo motor is a specialized electric motor designed to precisely control the movement and positioning of mechanical components. It converts electrical signals, such as voltage, into motion, offering exact speed and position control. The motor's main feature is its ability to adjust speed and torque according to input signals, ensuring precise movement. Servo motors are classified into DC and AC types, each with distinct characteristics. They don't rotate with zero signal voltage, and their speed decreases as torque increases. In automated control systems, the servo motor acts as the actuator, offering low electromechanical time constants and high linearity.

Servo motors operate in a closed-loop system, continuously adjusting the motor's position based on feedback, ensuring exact movement as required by the system. These motors are commonly used in applications where precision is important, such as robotics, CNC machinery, and conveyor systems. They come in different types, including DC and AC servo motors, each with unique characteristics suited for various industrial and commercial uses.

How Servo Motors Operate?

Servo motors operate in a closed-loop system where the output’s position, orientation, and state are constantly adjusted based on input signals. They use pulses to control movement, with the motor rotating in response to each pulse. Feedback pulses ensure that the number of pulses sent and received match, allowing for precise positioning. This feedback system ensures fine displacements, sometimes as small as 0.001mm. DC servo motors can be brushed or brushless, typically used where cost is important. AC servo motors are usually brushless and come in synchronous or asynchronous designs, with synchronous motors favored for motion control due to their power capabilities and stable operation. It describes how servo motors adjust their position, speed, and torque in response to input signals. By using feedback pulses, the motor ensures precise movement, enabling highly accurate positioning, sometimes down to millimeters or even finer increments. The process is essential for applications that require high precision and reliable performance.

Different Types and Comparison of Servo Motors

It explores the various types of servo motors, highlighting their features and differences. It provides a comparison of AC and DC servo motors, as well as a detailed look at how different motor designs, such as permanent magnet AC and asynchronous motors, impact performance and suitability for specific applications.

AC Servo Motor

AC servo motors work similarly to capacitor split-phase single-phase asynchronous motors but feature rotor designs that ensure greater speed range and stable operation. The stator contains two windings with a 90° phase difference: a field winding and a control winding. The rotor, often made from squirrel cage material, minimizes inertia while ensuring a fast response. The rotor's rotation is influenced by the control voltage, with speed directly proportional to the voltage’s magnitude.

Permanent Magnet AC Servo Motor

Advancements in integrated circuits, power electronics, and AC drive technologies have greatly improved permanent magnet AC servo motors. These motors are compact, have low inertia, and provide high torque, making them ideal for high-speed and high-torque operations. They are replacing DC motors in many applications due to their reliability, low maintenance, and improved thermal performance.

Servo Motor vs. Single-Phase Asynchronous Motor

Though AC servo motors operate on a principle similar to split-phase asynchronous motors, they differ in rotor resistance. AC servo motors have higher resistance, offering benefits like higher starting torque and greater sensitivity. They also offer faster start-up times and greater control than asynchronous motors. However, AC servo motors typically have lower efficiency compared to DC motors, making them more suitable for smaller power control systems.

Servo Motor vs. Stepper Motor Performance Comparison

Stepper motors are commonly used in open-loop systems but have limitations compared to AC servo motors. While both use pulse-based control, stepper motors generally offer lower accuracy. For example, a stepper motor’s standard step angle is 1.8° or 0.9°, while AC servo motors with rotary encoders can achieve much finer control, down to 0.0027°. Additionally, stepper motors can experience vibrations and torque loss at high speeds, limiting their operational range. AC servo motors, however, maintain constant torque and operate smoothly, even at low speeds. Stepper motors also lack overload capacity and are prone to stalling under heavy load, while AC servo motors can handle overloads, providing higher reliability. AC servo motors also offer faster acceleration, reaching operational speed in milliseconds, whereas stepper motors require longer acceleration times.

Conclusion

AC servo motors outperform stepper motors in precision, performance, and reliability, especially in applications requiring high accuracy and response speed. However, stepper motors remain viable for cost-sensitive applications with less demanding requirements. The choice between these two motor types depends on the specific needs of the system, including control accuracy, load conditions, and speed response. Careful evaluation of these factors ensures the selection of the most appropriate motor for the task.

Frequently Asked Questions [FAQ]

1. What is a Servo Motor and How Does It Function?

A servo motor is a closed-loop system that uses positional feedback to regulate rotational or linear speed and position. Controlled by an electric signal, either analog or digital, the motor adjusts its movement to reach a specific position as commanded by the input signal.

2. What is the Purpose of a Servo Motor?

Servo motors, also known as servos, are electronic actuators used for precise control of machine parts. They operate in both angular and linear positions, providing specific control over velocity and acceleration for accurate motion.

3. What are the Different Types of Servo Motors?

A servo motor is a device that applies torque or force to a mechanical system, such as an actuator or brake, with power supplied by a servo amplifier. It operates within a closed-loop control system, ensuring precise movement.

4. Are Servo Motors AC or DC?

Servo motors come in two types: AC and DC. The main distinction is their power source—AC servo motors are powered by an electrical outlet, while DC servo motors rely on battery power.

5. How Can I Test if My Servo Motor is Functioning?

To check if your servo motor is working, use a multimeter to measure the ground resistance between the motor body and terminals, which should be around 100 kΩ or higher. Next, measure the winding resistance by connecting between the motor terminals.