The mechanics of a stepper motor

1. Stepper Motor Classification

1.1. Reactive stepper motor (VR): The rotor is made of soft magnetic material, with simple structure, low cost, poor dynamic mechanical properties, and small step angle;

1.2, Permanent magnet stepper motor (PM): The rotor is made of permanent magnet material, with few rotor stages, large step angle, large torque and good dynamic performance;

1.3. Hybrid stepper motor (HB): It combines the advantages of VR and PM motors, has large output torque, small step angle, and good dynamic performance. It is currently the most widely used. The following is an introduction to this type of motor.

2. Two-phase hybrid stepper motor structure

2.1. The actual picture is shown below. It is mainly composed of stator, rotor and end cover.

2.2、The structural diagram is as follows

2.3. Sectional view analysis (section of the rotor S end)

The stator has 8 poles, as shown in the figure below. The green winding is phase A, and the magenta winding is phase B. The rotor has 50 teeth, evenly distributed. Each stator pole has 6 teeth, a total of 8*6=48 teeth. When a pair of pole teeth of the A-phase stator is completely aligned with the rotor teeth, the other pair of pole teeth of the A-phase stator must be completely misaligned with the rotor teeth. At this time, the B-phase stator teeth and the rotor teeth are half-aligned (or half-misaligned). Similarly, the state of the B-phase stator teeth when they are aligned with the rotor teeth can be judged.

2.4 Rotation Principle

①When A+ is connected to the positive pole of the power supply and A- is connected to the negative pole of the power supply, the A phase coil is turned on and a magnetic field is generated. As shown in the figure below, the blue N pole of the A phase and the S pole of the rotor attract each other and align, while the S pole of the A phase and the S pole of the rotor repel each other and stagger, and a stable state is reached at this time.

②When B+ is connected to the positive pole of the power supply and B- is connected to the negative pole of the power supply, phase B is turned on and the status is as follows:

③When A- is connected to the positive pole of the power supply and A+ is connected to the negative pole of the power supply, phase A is turned on and the status is as follows

④When B- is connected to the positive pole of the power supply and B+ is connected to the negative pole of the power supply, phase B is turned on and the status is as follows

⑤Then return to the state of Figure ①. After 4 steps, the rotor rotates one tooth. The angle corresponding to each tooth of the rotor is 360/50=7.2°. Therefore, in each step, the angle of the motor rotation is 7.2°/4=1.8°, which is the step angle of the stepper motor.

2.5. The complete painting is as follows

2.6. Rotor N-pole layout

The above explanation is about the force on the rotor S. The rotor N pole teeth and S pole teeth are completely staggered, as shown in the figure below. The force analysis is the same as that of the S pole.

3. Stepper Motor Demonstrator Function Introduction

In order to facilitate intuitive understanding of the motor rotation principle, a motor demonstrator was made, which can be operated manually or automatically, with 4-beat and 8-beat modes, and the speed can also be adjusted by yourself