Bipolar stepper motor basics

SPMD250STP

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Bipolar stepper motor basics

Simplified to the bare essentials, a bipolar permanent magnet motor consists of a rotating-

permanent magnet surrounded by stator poles carrying the windings (Figure 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

commutating the voltage applied to the windings in sequence. For a motor of this type there

are three possible drive sequences.

5.1

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.

5.2

Two-phase-on or normal drive

This mode gives the highest torque since two windings are energized at any given time

according to the sequence (for clockwise rotation).

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

Figure 7 shows the sequence and the corresponding position of the rotor.