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Difference between Servo Motor and Stepper Motor
Both servo motor and stepper motor are special electrical machines that can satisfy the basic requirements of a positioning application. Servo motors and stepper motors convert the input electrical energy into angular velocity or movement of the motor shaft. However, there are quite different from each other in the way they operate.
In this article, we have highlighted all the differences between servo motor and stepper motor. But, before discussing the differences, let's have some basic information about the servo and stepper motors so that it becomes easier to understand the differences between them.
What is a Servo Motor?
A servo motor is an actuator (rotatory or linear) which allows the precise control of angular or linear position, velocity and acceleration. The working of a servo motor is based on the principle of servomechanism.
Servo motor involves a closed loop control system, i.e. a feedback mechanism which allows the angular precision so that it can produce desired rotation according to the applied electric signal. Basically, the servo motor consists of an electric motor coupled to a sensor for position feedback.
The applied electric signal to the servo motor can be either an analog signal or a digital signal. When the electric signal is input to the servo motor, it produces a movement required to position the shaft corresponding to the electric signal. Here, an encoder is used as a feedback unit that provides information about the speed and position to a controller. Thus, the speed of the servo motor changes in proportion to the applied electric signal.
What is a Stepper Motor?
A type of brushless DC electric motor which divides a full rotation of the shaft into a number of equal steps is known as stepper motor. The stepper motor uses open-loop control system, i.e. it does not have any feedback mechanism.
The rotor of a stepper motor is generally a permanent magnet rotor. When the stator winding of the stepper motor is energized from an external electric supply, it rotates the rotor discretely. This rotation of the rotor is due to magnetic interaction between the magnetic poles of the stator winding and the poles of the rotor.
Therefore, in case of a stepper motor, the electrical input to the stator winding of the motor produces an output in the form of a discrete angular rotation of the rotor. This discrete rotation is produced in a way that when the stator winding is energized, a step by step current flows through the winding sequentially, thereby magnetizing the stator. Consequently, the electromagnetic poles developed in the stator rotate the rotor in the steps.
Difference between Stepper Motor and Servo Motor
Both stepper and servo motors are used in the same applications, i.e. positioning. However, there are many differences between a servo motor and a stepper motor that are listed in the following table −
| Basis of Difference | Servo Motor | Stepper Motor |
|---|---|---|
| Definition | A type of electric motor whose operation is controlled with the help of servo mechanism is known as servo motor. | A type of brushless DC motor which divides the full rotation of shaft into a number of equal discrete steps is known as stepper motor. |
| Operation | The operation servo motor is continuous. | The operation of stepper motor is divided into discrete steps. |
| Control system configuration | Servo motor is configured in a closed loop control system. | Stepper motor has open loop control system |
| Feedback mechanism | The feedback mechanism exists in a servo motor. | There is no feedback mechanism in case of stepper motor. |
| Torque speed characteristics | Servo motor produces high torque at high speeds. | Stepper motors produce high torque at low speeds. |
| Suitability with fluctuating loads | Servo motors are not suitable for fluctuating loads. | Stepper motors can be used for fluctuating loads as well. |
| Suitability for low rigidity mechanism | Servo motors are not suitable for low rigidity mechanisms like belt and pulley mechanism. | Stepper motors are suitable for low rigidity mechanisms. |
| Hunting | In a servo motor, the hunting exists during stop position. | In a stepper motor, there is no hunting during stop position. |
| Design | Servo motors have relatively complex design. | The stepper motors are simpler in design. |
| Power consumption | Servo motors need relatively less power. | Stepper motors consume comparatively more power. |
| Efficiency | The efficiency of servo motor is comparatively high. | The stepper motors are relatively less efficient. |
| Noise | The noise in case of servo motor is comparatively less. | Stepper motors produce high noise. |
| Operating speed | Servo motors have high operating speed. | The operating speed for stepper motors is low. |
| Reliability | Servo motors are comparatively less reliable. | Stepper motors are more reliable than servo motors. |
| Tolerance towards moment of inertia | Servo motors have low tolerance towards moment of inertia. | Stepper motors have high tolerance towards moment of inertia. |
| Life span | Servo motors have short life span. | The life span of stepper motors is longer. |
| Prone to damages due to overload | The servo motors are more prone to get damaged due to overload. | Stepper motors are less prone to get damaged due to overload. |
| Responsiveness | Servo motors have low responsiveness. | The responsiveness for stepper motors is high. |
| Synchronous operation | The synchronous operation is relatively difficult in case of servo motors. | The synchronous operation is easier in case of stepper motors. |
| Need of tuning and gain adjustment | Servo motors require tuning and gain adjustment. | Stepper motors do not require tuning and gain adjustment. |
| Cost | The cost of servo motors is high. | The cost of stepper motors is comparatively less. |
| Applications | Servo motors are extensively used in remote controlled equipment, robots, antenna positioning systems, industrial automation, cameras, etc. | Stepper motors are used in 3D printers, welding machines, textile machines, medical equipment, etc. |
Conclusion
From the above comparison, it is clear that the operation of servo motors is more efficient than that of the stepper motors. It is because the servo motor uses closed loop control system configuration to improve its positioning accuracy and angular displacement.
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