What Are The Types Of Stepper Motor

A stepper motor is an actuator that is controlled with electrical pulses and converts the electrical pulses (digital signals) into angular displacements. In recent years, the rapid development of microelectronics technology and drive technology has further promoted the development of stepper motors. This paper will provide an in-depth introduction to stepper motor types, and comprehensively categorize them according to the number of phases,  the structure of the rotor, and the drive mode.

 

1. Classification according to the number of stator phase

The number of phases refers to the number of winding inside the stepper motor. The stepper motors that people commonly use today are two-phase, three-phase, and five-phase stepper motors. According to different phases, they have different step angles. Generally, the step angle of the two-phase stepping motor is 0.9 ° / 1.8 °, the three-phase stepper motor is 1.2 ° and the five-phase stepping motor of 0.72 °.

 

1. 1Two-phase stepper motor

A two-phase stepper motor has two windings and its structure is relatively simple, which is suitable for some applications that have some limitations on cost but require high precision, In addition, it usually exhibits low vibration levels, so it is also suitable for vibration-sensitive applications.

1.2 Three-phase hybrid stepping motor

A three-phase stepping motor has three windings with more complex structure, suitable for applications that require high smoothness of motion and control stability, such as high-end CNC machine tools and precision instruments.

1.3 Five-phase hybrid stepping motor

The 5-phase stepping motor has five windings. Compared with two-phase and three-phase motors, they can provide higher stepping angle resolution, which helps to realize finer motion control, suitable for applications requiring very high control accuracy, such as laser cutting machines, precision positioning systems, and so on.

 

 

2. Classification according to the rotor structure

According to the rotor structure, the stepper motor can be classified into variable reluctance stepper motors, hybrid stepper motors,  and Permanent Magnet Stepper Motor

 

2.1 Variable Reluctance stepper motor.

The motor rotor is made of soft magnetic material without magnetic steel and there are many small teeth of the same size and pitch on the outer surface of the rotor pole and the inner surface of the stator pole. When the stator coil is energized, the stator pole magnetizes and attracts the rotor teeth, generating torque to move one step. Compared with permanent magnet motors that produce magnetic attraction torque and magnetic repulsion torque, variable reluctance stepper motor only produces attraction torque Its structure is simple, and it has a small step angle, up to 1.2 °. Compared to other types of stepper motors, it costs less. But at the same time, it has some shortcomings, such as poor dynamic performance, low efficiency, large heat generation, etc

 

2.2 hybrid stepper motor

A hybrid stepper motor combines the advantages of reactive and permanent magnet type, with multi-phase windings on the stator, permanent magnet material on the rotor, and multiple small teeth on both the rotor and stator to improve the step precision. It is characterized by large output torque, good dynamic performance, and small step angle, but the structure is complicated and the cost is relatively high.

 

2.3 Permanent Magnet Stepper Motor

The rotor of the permanent magnet stepping motor is made of permanent magnet material, and the number of poles of the rotor is the same as the number of poles of the stator. It is characterized by good dynamic performance and large output torque, but this type of motor has poor precision and a large step angle (generally 7.5° or 15°).

 

3. Classification according to drive method (bipolar drive/unipolar drive)

Steppe motors are also categorized into unipolar stepper motors and bipolar stepper motors according to the drive method. If the coil of a stepper motor can conduct electricity in both directions, then the stepper motor is bipolar, on the contrary, if the coil of the stepper motor is only allowed to conduct electricity in one direction, then the stepper motor is unipolar.

 

The coil in the figure below is able to conduct electricity in both directions, so it is a bipolar stepper motor.

 

The middle wire of the coil in the figure below is always connected to the positive terminal of the power supply or always connected to the negative terminal of the power supply, and it is a unipolar stepper motor.

 

Generally, bipolar drives are used for low-speed, high-torque loads, while unipolar drives are used for high-speed drives. This is because the output torque of the bipolar type is about 50% larger than that of the unipolar type at low speeds. At high speeds, the inductance of the bipolar type becomes large due to the large number of turns, which reduces the current and thus the torque. Therefore, it is necessary to reasonably select the unipolar or bipolar drive application for the size of the load, the speed of use, the acceleration time, etc.