The structure and basic working principle of stepper motor

A stepper motor is a motor that can accurately control the rotation angle and speed in synchronization with a pulse signal. It is also called a "pulse motor". Since stepper motors can achieve accurate positioning through open-loop control without the use of position sensors, they are widely used in equipment that requires positioning.

Structure of stepper motor (two-phase bipolar)

The following figures, from left to right, are an example of the appearance of a stepper motor, a simplified diagram of its internal structure, and a simplified diagram of its structural concept.

The appearance examples show the appearance of HB (hybrid) and PM (permanent magnet) stepper motors. The structure diagram in the middle also shows the structure of HB and PM.

The stepping motor has a structure where the coil is fixed and the permanent magnet rotates. The conceptual diagram of the internal structure of a stepping motor on the right is an example of a PM motor using two-phase (two sets) coils. In the basic structure example of a stepping motor, the coil is placed on the outside and the permanent magnet is placed on the inside. In addition to two-phase coils, there are also types with more phases such as three-phase and five-phase.

Some stepper motors have different structures, but in order to introduce its working principle, the basic structure of the stepper motor is given in this article. Through this article, we hope to understand that the stepper motor basically adopts the structure of fixed coil and rotating permanent magnet.

Basic working principle of stepper motor (single-phase excitation)

The following figure is used to explain the basic working principle of the stepper motor. This is an example of the excitation of each phase (a set of coils) of the two-phase bipolar coil above. The premise of this figure is that the state changes from ① to ④. The coils are composed of coil 1 and coil 2 respectively. In addition, the current arrow indicates the direction of current flow.

①

・Make the current flow into the left side of coil 1 and out from the right side of coil 1.

・Do not allow current to flow through Coil 2.

・At this time, the inside of the left coil 1 becomes N, and the inside of the right coil 1 becomes S.

・Therefore, the permanent magnet in the middle is attracted by the magnetic field of coil 1, changes to the state of S on the left and N on the right, and stops.

②

・Stop the current in Coil 1 and make the current flow into Coil 2 from the upper side and out from the lower side.

・The inner side of the upper coil 2 becomes N, and the inner side of the lower coil 2 becomes S.

・The permanent magnet is attracted by its magnetic field and stops after rotating 90° clockwise.

③

・Stop the current in Coil 2 and let the current flow into Coil 1 from the right side and out of Coil 1 from the left side.

・The inside of the left coil 1 becomes S, and the inside of the right coil 1 becomes N.

・The permanent magnet is attracted by its magnetic field and rotates another 90° clockwise and stops.

④

・Stop the current in coil 1 and make the current flow into coil 2 from the bottom and out from the top.

・The inner side of the upper coil 2 becomes S, and the inner side of the lower coil 2 becomes N.

・The permanent magnet is attracted by its magnetic field and rotates another 90° clockwise and stops.

By switching the current flowing through the coils in the order of ① to ④ above through an electronic circuit, the stepper motor can be rotated. In this example, each switching action causes the stepper motor to rotate 90°. In addition, by continuously flowing current through a certain coil, the stepper motor can be kept in a stopped state and have a holding torque. By the way, if the order of the current flowing through the coils is reversed, the stepper motor can be rotated in the reverse direction.