Function of Stepper Motor

General
Stepper motors are motors which, like most electric motors consist of a fixed stator and a moving rotor. The rotory motion does not take place continuously, but the rotor turns in steps through a particular angle of rotation, 90 ° for example.

Design
The illustration shows the principle design of a stepper motor with pole pair number 1 and a winding phase 2. The stator consists of soft magnetic iron and supports the windings. Opposite windings belong together, they form a winding phase (a and b in this case). The rotor consists of a permanent magnet. In the illustration it has the pole pair number 1.

Function
A rotation of the rotor is achieved if a current is allowed to flow through the winding phases a or b (refer to illustration).

The magnetic conditions in the stator change depending on the polarity (I) of the winding phases. The rotor will turn so that its south pole (S) is located at the north pole (N) of the stator and its north pole (N) at the south pole (S) of the stator.
One complete revolution of the rotor is shown in the illustrations. The rotor moves back to its initial position via the positions 1 to 4 in 90 steps.
In contrast to normal electric motors the motor can therefore stop in each of these positions with a particular holding torque. As a result this motor is particularly suitable as an actuator motor for accurate positioning.
The width of the step can be significantly reduced by increasing the pole pair numbers and winding phase numbers.
In addition by means of a complicated electronic actuation of the winding phases (sine/cosine actuation) it is theoretically possible to reduce the width of the step arbitrarily with small pole pair numbers and winding phase numbers.

Stepper motors (mit Sinus-Cosinusansteuerung) are used for the pointer instruments of the instrument cluster (A1) for example.