Structure of Stepping Motors

In this new section on “Stepping Motors”, we will explain the structure, principles of operation, characteristics, and driving methods of stepping motors.

About Stepping Motors

These are motors that can accurately control the rotation angle and rotation speed in sync with a pulse signal, and are also called pulse motors. They use open-loop control to achieve accurate positioning without relying on a position sensor, and so these motors are widely used in devices and systems where positioning is necessary.

Structure of Stepping Motor (Two-phase bipolar)

The images below illustrate, from the left, examples of the outer appearance of stepping motors, structural diagrams of the interiors, and schematic diagrams of the motor structures.

In the outer appearance examples, HB (hybrid) type and PM (permanent magnet) type stepping motors are shown. The structure diagrams in the center similarly show HB type and PM type motors.

In a stepping motor, coils are fixed in place and a permanent magnet is able to rotate. The internal structural diagram on the right side is an example of a PM motor using two-phase (two sets of) coils. In the example of the basic structure, the coils are positioned on the outside and the permanent magnet is on the inside. In addition to two-phase coils, there are also tree-phase, five-phase, and other types with many phases.

There exist stepping motors with other structures as well, but for the purpose of explaining the principles of operation (in the next article), we have presented the basic motor structure. It is important to understand that in this structure, in essence, the coils are fixed in place and the permanent magnet can rotate.

※Image sources
Photo_1： https://www.monotaro.com/ Monotaro, stepping motor
Photo_2： Asakusagiken, servo actuator
Fig_1： Commercialization of a compact, high-resolution, high-rigidity hybrid type stepping motor (external dimensions 25×25 mm, step angle 1.8°)
Fig_2： https://www.nidec.com/ 2-4-2 claw pole type PM motor