# stepper motor

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Related to stepper motor: Servo motor

## stepper motor

[′step·ər ‚mōd·ər]
(electricity)
A motor that rotates in short and essentially uniform angular movements rather than continuously; typical steps are 30, 45, and 90°; the angular steps are obtained electromagnetically rather than by the ratchet and pawl mechanisms of stepping relays. Also known as magnetic stepping motor; stepping motor; step-servo motor.

## Stepper Motor

(also magnetic stepping motor), a synchronous motor in which current pulses supplied to stator windings are converted into discrete angular motions, or steps, of a rotor. A stepper motor may be either a salient-pole motor or a non-salient-pole motor. The field windings are on the stator, and the rotor has no winding. In a variable-reluctance stepper motor, the rotor is made of a soft magnetic material. In a permanent-magnet stepper motor, the rotor is made of a hard magnetic material.

Figure 1. Cross section of a stepper motor: (a) at the initial moment, (b) at the moment the next set of stator windings is energized, (c) upon rotation through an angle θ; (1) stator, (2) rotor, (3) field windings

The current pulses are supplied from a power source to the field windings in sequence through a commutator. As a result, the direction of the magnetic flux in the space between the stator poles changes in discrete steps (Figure 1), causing the rotor to rotate through a certain angle θ. Each such rotation of the rotor is called a step.

The magnitude of a step depends on the number of field windings and either on the number of rotor projections (for a variable-reluctance stepper motor) or on the number of salient poles (for a permanent-magnet stepper motor). The step is usually 1.5°–3° for variable-reluctance motors or 15° for permanent-magnet stepper motors. A permanent-magnet stepper motor makes it possible to obtain a relatively high torque and ensures that the rotor does not move when the windings are not energized.

Stepper motors are used in electric stepping drives.

### REFERENCES

Ratmirov, V. A., and B. A. Ivobotenko. Shagovye dvigateli dlia sistern avtomaticheskogo upravleniia. Moscow-Leningrad, 1962.
Chechet, Iu. S. Elektricheskie mikromashiny avtomaticheskikh ustroistv, 2nd ed. Moscow, 1964.
Bruskin, D. E., A. E. Zorokhovich, and V. S. Khvostov. Elektricheskie mashiny i mikromashiny. Moscow, 1971.

M. D. NAKHODKIN

## stepper motor

(hardware)
An electric motor that rotates in small, fixed increments and is used, among other things, to control the radial position (seeking) of the heads on a disk drive.

## stepper motor

A motor that rotates in small, fixed increments and is used to control the movement of the access arm on a disk drive. Contrast with voice coil.
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