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Difference between AC Servo Motor and DC Servo Motor
A servo motor is a special type of electric motor which is used as a rotary or linear actuator for precise control of angular or linear position, velocity, acceleration and many other closed-loop position control applications.
Servo motors are designed with long rotor length and small diameter. Thus, due to low inertia, the servo motors have a high speed response. A typical servo motor consists of a motor, feedback system, controller, etc. Where, it uses the position feedback to control the speed and final position of the motor. The servo motor is equipped with an encoder or a speed sensor to provide speed and position feedback in the servo mechanism.
Depending on the power supply required for operation, servo motors are classified into two types -
- AC Servo Motor
- DC Servo Motor
In this article, we will highlight all the key differences between AC and DC servo motors, but let's start with some basics first.
What is an AC Servo Motor?
As its name implies, the type of servo motor which operates on alternating current supply is called an AC servo motor. Basically, it is a 2-phase squirrel cage induction motor. Although, these days, three-phase squirrel, cage induction motor is also used to implement the servo mechanism for high power applications.
AC servo motors are further classified into two types, based on their construction and operation, namely induction type AC servo motor and synchronous type AC servo motor.
AC servo motors are used in several applications where position control is required like robotics, machine tools, semiconductor devices, aircrafts, etc.
What is a DC Servo Motor?
A DC servo motor is a type of servo system which consists of a small DC motor, position sensing device and feedback circuit, gear system and a control circuit.
Just like any other electric motor, a DC servo motor also consists of two main parts namely stator and rotor. The stator of the servo motor consists of a cylindrical frame, inside which magnets are attached. The rotor consists of rotor shaft, a commutator and brushes.
The major applications of DC servo motors are in computers, prime movers, controlled machineries, etc.
Difference between AC Servo Motor and DC Servo Motor
Both AC and DC servo motors are actuators used in position control applications. However, there are many differences between them that are given in the following table −
| Basis of Difference | AC Servo Motor | DC Servo Motor |
|---|---|---|
| Definition | A servo mechanism in which a twophase or three-phase squirrel cage induction motor is used is known as AC servo motor. | A servo mechanism which consists of a DC motor is known as DC servo motor. |
| Power output | AC servo motor delivers low power output, usually about 0.5 W to 100 W | DC servo motor delivers relatively high power output. |
| Speed | AC servo motors are adaptable to high speed operating conditions. | DC servo motors are adaptable to the limited speed working conditions. |
| Torque | AC servo motors develop high torque. | DC servo motors develop a limited torque. |
| Operation | AC servo motors have smooth, stable and less noise operation. | DC servo motors have less stable and noisy operation. |
| Efficiency | AC servo motors are less efficient. Their efficiency is usually ranging from 5% to 20%. | DC servo motors have high efficiency. |
| Stability | The problem of stability associated with the AC servo motors is less. | DC servo motors have more problems of stability. |
| Electronic noise | In case of AC servo motors, there is no problem of electronic (radio frequency) noise. | In the DC servo motors, the presence of brushes cause electronic (radio frequency) noise. |
| Maintenance | AC servo motors require less maintenance. | AC servo motors require frequent maintenance due to presence of commutator and brushes. |
| Weight | AC servo motors are relatively light in weight. | DC servo motors are heavy. |
| Physical size | AC servo motors are small in size. | DC servo motors are large in size. |
| Suitability | AC servo motors are suitable for low power applications. | DC servo motors are suitable for high power applications. |
| Practical applications | The AC servo motors are used in applications like robotics, machine tools, semiconductor devices, aircrafts, etc. | The applications of DC servo motors are in computers, prime movers, controlled machineries, etc. |
Conclusion
In this post, we discussed all the major differences between AC servomotors and DC servomotors. Both AC and DC servomotors are used in several applications where precise position control is required like in robotics, computers, aircrafts, etc.
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