Introduction to stepper motor

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What is Stepper motor (step motor) ??

A stepper motor is a brush-less DC electric motor, it means that it converts electrical power into mechanical power.What make stepper motor different than other motor is the way it revolve.It rotate in steps unlike the other motors which rotates continuously, hence name given as stepper motor.Each step of motor is a fraction of full circle and its depends on hardware of motor and also driving method. Stepper motors are generally driven using pulses instead of AC or DC power supply that's why it called as Digital motor also. It convert each pulse into degree of rotation, e.g. 4 degree stepper motor, It converts each pulse arrival into rotate rotor shaft of motor through 4 degree.

Types of Stepper motor  

Permanent magnet stepper motor

The Permanent Magnet (PM)  motor is most basic type of stepper motor. Its rotor consist of a permanent magnet with 2 or more poles. The stator coils will attract or repulse the permanent magnet on the rotor  depending on pole generated on coil because of which  torque is generated.


Variable Reluctance (VR)  Stepper Motor 

This type of motor does not have a permanent magnet on the rotor. Here the rotor is made of soft iron. The stator consist of more than 4 coils. The coils are energized in opposite pairs, and will attract the rotor. The absence of a permanent magnet has some negative affect on the torque that is significantly decreased. But at the cost of reduced cost we can achieve zero detent torque . The detent torque, is the torque generated by the rotor permanent magnets that are magnetized to the stator's armature, when no current flows within the coils. You can get an idea what this torque is, suppose if you try to rotate an unconnected stepper motor by hand (not a VR stepper), you  will feel  the detent torque which pulls the magnets against the armature of the stator. 

Hybrid Stepper motor

Hybrid stepper motors are made of  combination of principle  PM and VR to achieve maximum power in a small package size.This type of motors have  hold and dynamic torque, and very small step angles, from 0.9 degree to 5 degree,and hence more accuracy. Their mechanical parts can rotate at high speeds relatively to the other stepper motor types. This is the type of motor used for high end CNC and robots. The major disadvantage is the cost.

Types of 2 phase Stepper motor:

Unipolar Stepper motor

It has five or six wires and four coils (here  two coils  divided by center connections on each coil). The center connections of the coils are tied together and used as the power connection. They are called unipolar steppers because power always comes in on this one pole.

Bipolar Stepper motor

This type of  Stepper motor usually has four wires coming out of it. Bipolar stepper motors have no common center connection. They have two separate coils.

Stay tuned for upcoming article '' Fundamentals of Stepper motor interfacing with microcontroller 8051."

 



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