Stepper motors Tutorial (figures) 2

To increase the precision we can employ a sequence as shown which is known as half stepping. In this before we de-energize the first coil we energize the second coil. So the rotor finds itself being pulled by two forces and it settles in between the two positions


A B A` B`
1 0 0 0
1 0 0 1
0 0 0 1
0 0 1 1
0 0 1 0
0 1 1 0
0 1 0 0
1 1 0 0

For bipolar motors we need to reverse the direction of the current flowing through the coil. So we apply the following sequence.

A B A` B`
0 0 1 1
0 1 1 0
1 1 0 0
1 0 0 1

Similar to unipolar we can also apply the half stepping sequence
Bipolar v/s Unipolar

Unipolar
Simple driving circuit because no current reversal
Size comparatively larger for same specification as bipolar

Bipolar
Smaller size
Higher torque
Complex driving circuit because current has to be reversed.

Drivers for stepper motors:
For unipolar motors we can use darlington pair array ICs like the ULN200x series since we don’t have to reverse the current.


But for bipolar motors we need to use an h-bridge which can source as well as sink current.