In this post, we will discuss of stepper motor vs servo motor. before that, we need to understand the definition of both motors.
What is the stepper motor?
Stepper motor also called a step motor is a type of brushless, synchronous electromechanical device. its full rotation divided into equal parts.
What is the servo motor?
Servo motor is an electrical motor that has an inbuilt encoder for gets reading from output motion. Also, it is used for the precise control of speed, torque, and position.
Before we discuss the mechanism of stepper motor vs servo motor need to understand the open-loop and close-loop controller system.
Open-loop controller system
An open-loop controller system also called a non-feedback system, it is a type of continuous controller system. Also, it does not compare the output signal with the input signal.so this type of controller system has not any auto error correction methods.
Closed-loop controller system
This controller system gets feedback from the output signal and it compares with the input signal. If it has any problem in output signal this system automatically fixes that issue.
Now we discuss the mechanism of stepper motor vs servo motor.
Mechanism of the stepper motor.
This motor has not any sensor for gets signal from the output, so it can’t get any feedback signal from output. It also called an open-loop circuit and the motor can control without any feedback path. The Stepper motor stator field winding pole generates a rotating magnetic field. So that magnetic-field work on rotor permeate magnet and it helps rotate the motor.
Mechanism of the servo motor.
This motor has a close loop circuit so its position, speed, and acceleration control by using that feedback path and its controller circuit. Also, that feedback path can use for error detection of the output motion.
Construction of stepper motor
Stepper motor is the electromechanical device, it has rotor and stator like a normal motor. Also, this motor rotor made by using a permanent magnet or soft iron. Most Stepper motor has eight poles or more stator winding. Now we discuss eight poles motor. That poles are connected four couple of poles and each couple of pole work at a time. Also, those magnetic fields rotate through the rotor. That rotation magnetic field helps to the rotation of the motor.
Construction of servo motor
Servo motor contains a normal motor and an inbuilt sensor. This sensor design by using an encoder. This sensor can detect output motion.
Stepper motor types
- Permanent magnet stepper motor.
This motor rotor made by using a permanent magnet, the motor rotation start by attraction or repulsion between rotor permanent magnet and starter electromagnet.
- Variable reluctance stepper motor.
Variable reluctance stepper motor rotor design by using plain iron. The stator rotation magnetic field attraction helps to rotate the motor.
- Hybrid synchronous stepper motor.
Its rotor made by the combination of permanent magnet and plain iron. This motor rotor permanent magnet covers soft iron casing. That soft iron cylinder shape rotor cover has small poles and its attraction or repulsion between stator helps the motor rotation.
Servo motor type
Servo motor type based on the power supply
- AC servo motor.
AC servo motor is an AC motor. Most of the time it used squirrel cage induction motor. Two-phase squirrel cage induction motor used for small load application and 3 phase induction motor used for high power applications.
- DC servo motor.
This type of motor has two separate dc power supply for field winding and armature winding. Motor control archive by changing field current or armature current.
Servo motor types based on the type of motion
- Positional rotation servo.
This is the most common type of servo motor and its output shaft rotates only half of the cycle. That motor can rotate the shaft’s particular angle and speed.
- Continuous rotation servo.
Continuous rotation servo motor also likes positional rotation but the main difference is it can rotate full cycle. The motor control signal can change the speed and direction of the rotation.
- Linear servo.
Liner servo motor also likes the positional rotation servo motor but its use to additional gear to get circular rotation into linear motion. This motor not commonly used in industrial applications.
Speed torque performance stepper motor vs servo motor
Above the graph, stepper motor torque gets high value under 1000rpm. After increasing the speed than 1000rpm torque value goes down, but the servo motor gets constant torque value under high-speed conditions.
Compare the advantages and disadvantages of stepper motor vs servo motor
Now we discuss the Advantages of both motors
Advantages of stepper motor
- This motor hasn’t a feedback path, so this motor is simple to control than the servo motor.
- Also, the external closed-loop control system is expensive, but no need for this kind of expensive unit.
- The closed-loop control system is used advanced technology, so the skilled person needs to control that system, but no need for any person to operate stepper motor.
- Stepper motor less expensive than a servo motor that is the most important advantage of it.
- Compare with DC servo motor stepper motor is a brushless motor so it has more life and less maintains.
- It has an excellent response for starting, stopping, and reversing.
- Stepper motor speed is proportional to the input frequency of the input pulse, so it is easy to control the motion of the motor.
- Stepper motor has a large number of the electromagnetic pole, so it can get a specific stopping point for many applications.
- It is safer to use than servo motor because it takes some damage to the system motor automatically stop.
- This motor has very high torque under low speed, so it no needs any gearbox for high load.
- Stepper motor does not get damage for high load applications.
Advantages of servo motor
- Servo motor has high efficiency and less noise generation.
- Also, it has constant torque under high speed. Servo motor can get high rpm like 3000-800RPM easily with constant torque. (Modern servo motor)
- Servo motor can run smoothly than a stepper motor.
- This motor can rotate any particular angle, position, and velocity.
- It can get quickly and easily any torque for particular applications.
- Servo motor very accurate than a stepper motor, because it encoder gets feedback and error correct every time.
Now we discuss the Disadvantages of both motors
The disadvantage of stepper motor
- Under the high-speed conditions, the stepper motor gets less torque value.
- Stepper motor has less accuracy than the servo motor because it has not any error correction path, so take some time to identify an error in the system.
- Also stepper motor has less efficiency than servo motor, because, it needs a constant power supply to remember position information.
Disadvantages of servo motor
- Servo motor needs to high initial cost because its control system is more expensive. To compare with stepper need more initial cost to install the system.
- Expensive software needs to control the servo motor. Eg: PLC
- Tuning a control loop of servo motor very difficult process. It needs more time and skill person. Sometimes it will take 6 hours or more.
- Limited peak toque, a servo motor can be damaged with high load application so need to the protection circuit.
- Some times its needs gearbox for high load applications.
Applications of stepper motor vs servo motor
Applications of stepper motor
- Floppy disk driver.
- Flatbed scanner.
- Computer printers.
- Slot machine.
- Image scanner.
- Compact disk driver.
- Camera lenses.
- CNC machine.
- 3D printer.
Applications of servo motor
- CNC machine.
- Automated manufacturing industries.
- Laser cutting machine.
|Function||Stepper Motor||Servo Motor|
|Toque under low speed||high||Little bit low than stepper motor|
|Toque under high speed||low||high|
|Controller system||Open-loop||Close loop|
Comparing with both motors we can understand servo motor is more expensive and get high performance under high-speed condition than a stepper motor. But the stepper motor gets high torque under low-speed condition. Stepper motor has a self-protection method but servo motor not, so we need to understand the most suitable motor for our task. I think you can identify in our stepper motor vs servo motor tutorial.