Types Of Stepper Motor:
Stepper Motors can be sperated into two groups:
1- Permanent-magnet (PM) stepper motor, this kind of motor creates rotation by using the forces between a permanent magnet and an electromagnet created by electrical current.An intersting characteristic of this motor is that even when it is unpowered, the motor exhbits some magnetic resistance to turning.
2-Variable - reluctance (VR) Stepper Motor,It creates rotaion entierly with electromagnetic forces electromagnets created by different coils.
Typical stepper motor has 4 wires coming out of it (i.e it has 2 coils so it divides the rotor rotation to 8 steps), some stepper motors can divide the full rotation into 200 step according to number of poles on both the stator and rotor
Lets consider a typical stepper motor with 2 coils (4 wires coming out of it , 2 wires for each coil )
Lets name these wires A , A' for the first coil and B , B' for the second coil
If you applied different logic voltages on the two ends of one coil (e.g A=0 A'=1 or A=1 A'=0) then this coil will be magnetaized and then you will have one pole inside the motor is north while the other is south.
If you applied the same logic voltages on the two ends of one coil (e.g A=0 A'=0 or A=1 A'=1)then this coil will not be magnetaized.
so according to the applied voltages on the four ends of the two coils, you can determine the position of the rotor.
so by applying the proper sequence of logic voltages on (a , a' , b , b' )the rotor will change its position from one samole to another.
Example: To rotate the motor one rotaion Clock wise:
then signals ( a , a' , b , b' ) will be :
1 0 0 1
0 0 0 1
0 1 0 1
0 1 0 0
0 1 1 0
0 0 1 0
1 0 1 0
1 0 0 0
To rotate it CCW:
1 0 0 1
1 0 0 0
1 0 1 0
0 0 1 0
0 1 1 0
0 1 0 1
0 0 0 1