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Stepper Motors or Step Motors

Written By: 

Nikhil Agnihotri
 
What is a stepper motor?
A Stepper Motor or a step motor is a brushless, synchronous motor which divides a full rotation into a number of steps. Unlike a brushless DC motor which rotates continuously when a fixed DC voltage is applied to it, a step motor rotates in discrete step angles. The Stepper Motors therefore are manufactured with steps per revolution of 12, 24, 72, 144, 180, and 200, resulting in stepping angles of 30, 15, 5, 2.5, 2, and 1.8 degrees per step. The stepper motor can be controlled with or without feedback.

Stepper or Step Motors

 

Fig. 1: An Image Of Commonly Used Brushless DC Stepper Motor

 
How a stepper motor works?
Stepper motors work on the principle of electromagnetism. There is a soft iron or magnetic rotor shaft surrounded by the electromagnetic stators. The rotor and stator have poles which may be teethed or not depending upon the type of stepper. When the stators are energized the rotor moves to align itself along with the stator (in case of a permanent magnet type stepper) or moves to have a minimum gap with the stator (in case of a variable reluctance stepper). This way the stators are energized in a sequence to rotate the stepper motor. Get more information about working of stepper motors through interesting images at the stepper motor Insight.
 
How Stepper Motor works
 
Fig. 2: General Overview Of Internal Structure And Working Of Typical Stepper Motor
 
Types of Stepper Motor
By construction the step motors come into three broad classes:
1.      Permanent Magnet Stepper
2.      Variable Reluctance Stepper
3.      Hybrid Step Motor
These three types have been explained in detail in the following sections.
 
 

Type1: Permanent Magnet

1.    Permanent Magnet Stepper :
The rotor and stator poles of a permanent magnet stepper are not teethed. Instead the rotor have alternative north and south poles parallel to the axis of the rotor shaft.
Permanent Magnet Stepper Motor
 
Fig. 3: Crossectional Diagram Of Two Phase Permanent Stepper Motor
 
When a stator is energized, it develops electromagnetic poles. The magnetic rotor aligns along the magnetic field of the stator. The other stator is then energized in the sequence so that the rotor moves and aligns itself to the new magnetic field. This way energizing the stators in a fixed sequence rotates the stepper motor by fixed angles.
 
Working of Permanent Magnet Stepper Motor
 
Fig. 4: Diagram Explaining Working Of Permanent Magnet Stepper Motor
 
The resolution of a permanent magnet stepper can be increased by increasing number of poles in the rotor or increasing the number of phases.
Increase Resolution of Permanent Magnet Stepper Motor
 
Fig. 5: Figure Showing Ways To Increase Resolution Of Permanent Magnet Stepper Motor
 
 

Type2: Variable Reluctance

2.    Variable reluctance stepper  
The variable reluctance stepper has a toothed non-magnetic soft iron rotor. When the stator coil is energized the rotor moves to have a minimum gap between the stator and its teeth.
Two Phase Variable Reluctance Stepper Motor
 
Fig. 6: Basic Diagram Of Two-Phase Variable Reluctance Stepper Motor
 
The teeth of the rotor are designed so that when they are aligned with one stator they get misaligned with the next stator. Now when the next stator is energized, the rotor moves to align its teeth with the next stator. This way energizing stators in a fixed sequence completes the rotation of the step motor.
 
Working of Variable Reluctance Stepper Motor
 
Fig. 7: Diagram Explaining Working Of Variable Reluctance Stepper
 
The resolution of a variable reluctance stepper can be increased by increasing the number of teeth in the rotor and by increasing the number of phases.
 
Increase resolution of variable reluctance stepper motor
 
Fig. 8: Figure Showing Ways To Increase Resolution Of Variable Reluctance Stepper Motor
 
 

Type3: Hybrid

3.    Hybrid stepper :
A hybrid stepper is a combination of both permanent magnet and the variable reluctance. It has a magnetic teethed rotor which better guides magnetic flux to preferred location in the air gap.
Hybrid Stepper Motor
 
Fig. 9: Construction Of Two phase Hybrid Motor
 
The magnetic rotor has two cups. One for north poles and second for the south poles. The rotor cups are designed so that that the north and south poles arrange in alternative manner. Check out the insight of a Hybrid Stepper Motor.
Hybrid Stepper Motor Rotor
 
Fig. 10: Diagram Showing Internal Structure Of Magnetic Rotor In Hybrid Motor
 
The Hybrid motor rotates on same principle of energizing the stator coils in a sequence.
 
Working of a hybrid stepper motor
 
Fig. 11: Diagram Explaining Working Of Hybrid Stepper Motor
 
 
 

Types of Wiring

Types of Winding and Lead-out
The step motors are mostly two phase motors. These can be unipolar or bipolar. In unipolar step motor there are two winding per phase. The two winding to a pole may have one lead common i.e. centre tapped. The unipolar motor so, have five, six or eight leads. In the designs where the common of two poles are separate but centre tapped, motor have six leads. If the centre taps of the two poles are internally short, the motor has five leads. Eight lead unipolar facilitates both series and parallel connection whereas five lead and six lead motors have series connection of stator coils. The unipolar motor simplifies the operation because in operating them there is no need to reverse the current in the driving circuit. These are also called bifilar motors.
 
Unipolar Stepper Motor
 
Fig. 12: Wiring Diagram Of Unipolar Stepper Motor With Diffrent Leads
 
In bipolar stepper there is single winding per pole. The direction of current need to be changed by the driving circuit so the driving circuit of the bipolar stepper becomes complex. These are also called unifilar motors.
Bipolar Stepper Motor
 
Fig. 13: Wiring Diagram Of Bipolar Stepper Motor With Lead Outs
 
 

 

Stepping Modes

There are three stepping modes of a stepper motor. The stepping mode refers to the pattern of sequence in which stator coils are energized.
1.      Wave drive (One phase ON at a time)
2.      Full drive (Two phase ON at a time)
3.      Half drive (One and two phase ON at a time)
 
1.    Wave drive :
In wave drive stepping mode only one phase is energized at a time.
Stepper Motor Wave Drive
 
Fig. 14: Wave Drive Stepping Mode Pattern In Stepper Motor
2.    Full Drive :
In full drive, two phases are energized at a time.
Stepper Motor Full Drive
 
Fig. 15:Full Drive Stepping Mode pattern In Stepper Motor
 
3.    Half Drive :

In half drive, alternately one and two phases are energized. This increases the resolution of the motor.

Stepper Motor Half Drive

Fig. 16: Half Drive Stepping Mode Pattern In Stepper Motor

 

 

 

 

Comments

very nice information

 THIS INTERESTING

 

really gr8 one!!!

 

complicated a litte bit. 

well explained.. nice!

 informative knowledge

stepper motor is a lead part of engineering..

thanks for information about it.

i got a problem with my stepper...its not rotating but able to see some movement inside!can any 1 help meout?

 

nice piece of info........

 

Really goood!! Worth reading!!yes

very nice tutorial .very few one who give such a information.

                                                                                               v thanks

thanx for giving such a brief discruption..

super explanation. thank u so much......

Unipolar motors have single winding per phase

Bipolar has two windings per phase

Nice !!! Really its a Gorgeous Answer !!!!

large information in small space

 

its too good answer 

 

THNX 4 THE VALUABLE INFO

i saw first time this type of great explaination.

 

very good information for freshers

 

nice explanation

Its very useful for beginners as well as experts each and every information of programing as well as interfacing techniques u can learn without any doubts ..........hats of EG its one of my favorite site for controller 

easily understandable one

help me plz!!

what binary should be applied across the leads to stop stepper motor in wave drive stepping mode???

very good infor, it help me alot

 

Very nice information.

 

Thanx engineersgarage.com

It's a better explanation of stepper motor
why are the comments same on your links???

by this information i came to no what is stepper motor &types 

verynice information

good information

Can anyone suggest me with a stepper motor with 72 steps per revolution