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BIPOLAR STEPPER MOTOR BASICS

Simplified to the bare essentials, a bipolar perma-

nent magnet motor consists of a rotating-perma-

nent magnet surrounded by stator poles carrying

the windings (fig. 5).

Figure 5: Simplified Bipolar Two Phase Motor

Bidirectional drive current is imposed on windings

A-B and C-D and the motor is stepped by commu-

tating the voltage applied to the windings in se-

quence. For a motor of this type there are three

possible drive sequences.

Figure 6: One-Phase-on (Wave Mode) Drive

One-Phase-on or Wave Drive

Only one winding is energized at any given time

according to the sequence :

AB - CD - BA - DC

(BA means that the current is flowing from B to A).

Fig. 6 shows the sequence for a clockwise rotation

and the corresponding rotor position.

Two-Phase-on or Normal Drive

This mode gives the highest torque since two wind-

ings are energized at any given time according to

the sequence (for clockwise rotation).

AB & CD ; CD & BA ; BA & DC ; DC & AB

Fig. 7 shows the sequence and the corresponding

position of the rotor.

Half Step Drive

This sequence halves the effective step angle of

the motor but gives a less regular torque being one

winding or two windings alternatively energized.

Eight steps are required for a complete revolution

of the rotor.

The sequence is:

AB ; AB & CD ; CD ; CD & BA ; BA ; BA & DC ;

DC ; DC & AB

as shown in fig. 8.

By the configurations of fig. 6, 7, 8 the motor would

have a step angle of 90

° (or 45 ° in half step). Real

motors have multiple poles pairs to reduce the step

angle to a few degrees but the number of windings

(two) and the drive sequence are unchanged.

GS-D200/GS-D200S