To rotate this
motor continuously, we just apply power to the 3 windings in sequence.
Assuming positive logic, where a 1 means turning on the current through
a motor winding, the following control sequence will spin the motor illustrated
in Figure 1.1 clockwise 24 steps or 2 revolutions:
Winding 1
1001001001001001001001001
Winding 2 0100100100100100100100100
Winding 3 0010010010010010010010010
time --->
There are
also variable reluctance stepping motors with 4 and 5 windings, requiring
5 or 6 wires. The principle for driving these motors is the same as that
for the three winding variety, but it becomes important to work out the
correct order to energise the windings to make the motor step nicely.
The motor geometry
illustrated in Figure 1.1, giving 30 degrees per step, uses the fewest
number of rotor teeth and stator poles that performs satisfactorily. Using
more motor poles and more rotor teeth allows construction of motors with
smaller step angle. Toothed faces on each pole and a correspondingly finely
toothed rotor allows for step angles as small as a few degrees.
If
your motor has three windings, typically connected as shown in the schematic
diagram in Figure 1.1, with one terminal common to all windings, it is most
likely a variable reluctance stepping motor. In use, the common wire typically
goes to the positive supply and the windings are energized in sequence.
