Stepper Motors

Stepper Motors

The stepper motor is a variation of the DC motor.

The stator of the stepper motor consists of many separate windings called poles arranged on teeth which are equally spaced around the body of the motor.

The rotor of the stepper motor is a permanent magnet.

Fig. 24 The rotor in a stepper motor can line up with any of the stator poles

When one of the stator coils is energized, the magnetic fields of the rotor and stator interact and the rotor lines up with that stator coil. If the next stator coil is energized and the first coil is de-energized then the rotor will rotate by an amount equal to the spacing of the stator teeth. The number of fixed positions the rotor can maintain is governed by the number of poles in the stator. The more poles the stator has, the more accurately the rotor may be positioned.

Fig. 25 As each stator pole is energised in turn, the rotor rotates.

The control circuit for a stepper motor determines the speed and sequence in which each stator coil is energized.

Stepper motors are limited to about one horsepower and 2000 rpm.