1. Stepper motor
A stepper motor is a special electrical machine which rotates in discrete angular steps in response to a programmed sequence of input electrical pulses.
Working Principle
A magnetic interaction takes place between the rotor and the stator, which make rotor move.

2. Construction
The stator has windings
The rotor is of salient structure without any windings, and it may or may not have permanent magnets
Application
Application of stepper motor in diverse areas ranging from a small wrist watch to artificial satellites.
Power range 1W to 2.5KW
Torque range 1µN to 40 Nm

3. Stepper motor Variable reluctance (2) Permanent magnet Hybrid stepper
motor (HSM)
(4) Other type
(1.2) Multi stack VR
Stepping motor
(1.1) Single stack VR Stepper
Motor

4. 1. Variable reluctance motor
Variable reluctance stepper motor works on the principle that a magnetic material placed in magnetic field experience a force to align minimum reluctance path
Variable reluctance motor
(1.1) Single stack VR
Stepper Motor
(1.2) Multi stack VR
reluctance Stepping motor

5. Stator 1.1 Single stack VR Stepper Motor Construction Rotor
The stator made up of silicon steel stampings.
It has projecting poles, usually even no of poles.
The pole carry concentric windings
Rotor
Usually made up of silicon steel.
Solid silicon steel also used for core of rotor.
The rotor has projecting teeth on its outer periphery.
The no of rotor teeth and stator pole should not be equal. this make
motor self starting

6. Working
Rotor teeth can assume any position until the stator winding energized. For a four phase (eight pole) single stack VR stepper motor the angle rotated by the rotor (Φ) is given by
Φ=360/MxNr degree
Where
M = the number of stator phase
Nr= the number of rotor phase
In the present case M=4, Nr=6
Φ=360/4x6 degree = 15 degree

7. Switching Circuit

8. Modes of Excitation 1 Phase ON or full step mode
Phase ON (Half Stepping)
Two phase ON mode
Micro-stepping

9. 1 Phase ON (Full Stepping)

10. Rotor position for phase excitation

11. 2-1-2-1-Phase ON (Half Stepping)

12. Two phase ON mode