In many contemporary automation systems, robotics, CNC equipment, and precision applications, servo motors are crucial parts. Position, speed, and torque may all be controlled with extreme precision because of their design and manufacture.

Understanding the inner workings of a servo motor is key to selecting the right motor for specific applications, and in this article, we will take an in-depth look at servo motor construction, its components, and their functions.

What is a Servo Motor?

An electromechanical device known as a servo motor offers precise control over torque, speed, and angular position. It is frequently utilized in robotics, CNC machines, automation systems, and applications needing high-performance motion control. Unlike standard motors, servo motors are typically integrated with a feedback system (such as an encoder) to continuously monitor and adjust performance, ensuring that the motor behaves according to the control commands.

Key Components of Servo Motors

The construction of a servo motor is relatively complex, involving several critical components that work together to achieve precise control. These components are:

  • Stator
  • Rotor
  • Feedback System (Encoder or Resolver)
  • Controller
  • Power Supply

Let’s explore each component in detail:

Stator

The servo motor’s stator is its stationary component. It consists of laminated steel plates wound with copper coils, which are connected to the AC or DC power supply. As electricity flows through these windings, a magnetic field is produced that interacts with the rotor to produce motion.

  • Function: In the case of an AC servo motor, this magnetic field is created by alternating current, while in a DC servo motor, the magnetic field is generated by the direct current supplied to the motor windings.
  • Construction: The stator is typically made from thin sheets of electrical steel (laminations) that reduce energy loss due to eddy currents.Copper or aluminum windings can be used to maximize electrical conductivity.

Diagram of Stator Construction

Rotor

The rotor consists of permanent magnets (in the case of permanent magnet servo motors) or an electromagnet (in the case of induction-type servo motors). The mechanical output is transferred to the load via the shaft that the rotor is mounted on.

  • Function: The rotor’s job is to turn electrical energy into mechanical energy by rotating inside the stator’s magnetic field. The rotor’s motion is precisely controlled through feedback systems and controllers to ensure accurate performance.
  • Construction: In brushless DC (BLDC) motors, the rotor is also equipped with permanent magnets, but in a slightly different configuration. For AC induction motors, the rotor may consist of laminated iron cores.

Diagram of Rotor Construction

Feedback System (Encoder or Resolver)

One essential part of the servo motor is the feedback system. It is made up of an encoder or resolver that continuously tracks the position, speed, and occasionally the rotational direction of the motor. The controller receives this feedback and uses it to instantly modify the motor’s behavior.

  • Function: The primary function of the feedback system is to ensure precise control by providing information about the motor’s actual performance. If the motor deviates from the desired position or speed, the controller uses this feedback to make adjustments, bringing the motor back to the desired setpoint.
  • Types of Feedback Systems:
    Encoders: These are optical or magnetic devices that measure the rotor’s position and speed. They might be absolute, giving a constant position value, or incremental, giving increases in relative position.
    Resolvers: These are electromechanical devices used in high-precision applications to provide continuous feedback about the rotor’s position.

Feedback System Diagram (Encoder vs Resolver)

Controller

The controller is the servo motor system’s brain. It is in charge of processing control signals, which are usually received from a computer, motion controller, or PLC, and then transmitting commands to the motor. To get the desired output, the controller modifies the duty cycle and input power.

  • Function: After interpreting the encoder or resolver’s feedback, the controller compares it to the intended setpoint. Using this information, it sends commands to the motor, adjusting the voltage or current to control speed, position, and torque.
  • Construction: The controller usually consists of a microprocessor or digital signal processor (DSP) that can handle complex control algorithms (such as PID control) to ensure high performance.

Power Supply

In AC servo motors, this is usually an AC power source, while in DC servo motors, a DC power source is used. The power supply must be capable of delivering high power with minimal voltage or current fluctuations, as servo motors demand high levels of precision and reliability.

  • Function: The power supply is made to give the motor and controller the voltage and current they require, guaranteeing steady operation and economical energy utilization.

Power Supply Circuit Diagram

Working Principle of Servo Motors

The following procedures can be used to comprehend how a servo motor operates:

  1. Input Signal: The controller receives an input signal, typically representing the desired position, speed, or torque.
  2. Feedback Monitoring: The feedback system (encoder or resolver) continuously monitors the actual position of the rotor.
  3. Error Calculation: To determine the required position or speed, the controller compares the input signal with the encoder or resolver’s actual position (feedback).
  4. Correction: The controller modifies the power supplied to the stator windings to rectify the rotor’s position if there is a discrepancy between the intended and actual locations.
  5. Continuous Monitoring: The controller continuously adjusts the motor to maintain accuracy, ensuring the motor reaches and holds the required setpoint.

Servo Motor Feedback Loop Diagram

Types of Servo Motors

Servo motors are classified into a variety of types based on their design and intended use. The most common types include:

AC Servo Motors:

  • Use alternating current (AC) to operate.
  • Separated into synchronous AC motors and permanent magnet (PM) AC motors and more.
  • Robotics, CNC machines, and industrial automation frequently use it.

DC Servo Motors:

  • Operate on direct current (DC) and provide smooth, precise motion.
  • Commonly used in applications that require low to medium torque and speed.

Brushless DC (BLDC) Servo Motors:

  • BLDC motor subtype that does not employ brushes.
  • Higher efficiency, less maintenance, and longer lifespan.
  • Used in applications where long operational life and high torque are required.
Feature AC Servo Motor DC Servo Motor BLDC Servo Motor
Power Source Alternating Current Direct Current Direct Current
Efficiency High Moderate Very High
Speed Control Precise with feedback systems Easy with voltage variation Precise and smooth
Torque Moderate to high Moderate High
Durability Highly durable and robust Requires more maintenance Highly durable and low maintenance
Cost Moderately expensive Cost-effective Expensive
Application Industrial automation, robotics Small appliances, toys, low-power tasks Electric vehicles, drones, medical equipment

Advantages of Servo Motors

  • Precision Control: Applications where accuracy and precision are essential are the focus of servo motor design. Feedback systems allow for continuous adjustment, ensuring that the motor stays on course.
  • High Efficiency: Servo motors are typically more efficient than regular motors, as they adjust the power input based on demand, avoiding unnecessary energy consumption.
  • High Torque and Speed Control: They offer superior torque control at different speeds, making them suitable for variable load applications.
  • Long Lifespan: Because servo motors (especially brushless types) have fewer moving parts subject to wear, they often last longer than regular motors.

Choosing the appropriate servo motor for a given application requires an understanding of the motor’s structure. A servo motor manufacturer designs these highly complex devices, which rely on several components working together to provide precise control over position, speed, and torque. By understanding how these components—such as the stator, rotor, feedback system, controller, and power supply—interact, engineers and technicians can better assess the motor’s capabilities and optimize its use in a wide variety of industries. Servo motors will become increasingly important in attaining accuracy and efficiency as automation and robotics continue to advance.