Characteristics and classification of stepper motors

The stepper motor is an open-loop control motor that converts electrical pulse signals into angular displacement or linear displacement. In the case of non-overload, the motor's speed and stop position depend only on the frequency and number of pulses of the pulse signal, and are not affected by load changes. The rotation of the stepper motor runs step by step at a fixed angle. The angular displacement can be controlled by controlling the number of pulses to achieve accurate positioning. At the same time, the speed and acceleration of the motor can be controlled by controlling the pulse frequency to achieve speed regulation.

The position and speed signals of the stepper motor are not fed back to the control system during operation, so no feedback circuit is required, which makes the stepper motor control simple and accurate. When you want to drive the rotor to a specified position, the non-stepper motor needs to determine the position of the rotor based on the feedback circuit. However, the stepper motor does not need these feedbacks because it can simply perform multiple steps.

The advantages and disadvantages of stepper motors are very prominent compared with other motors. Specifically, the advantages of stepper motors include simple motor operation and easy control through pulse signal input to the motor; no feedback circuit is required to feedback the position and speed information of the rotating shaft (open-loop control); and higher reliability due to the lack of contact brushes. Of course, against the backdrop of many advantages, the disadvantages of stepper motors are also direct, such as the need for a pulse signal output circuit; when the control is not appropriate, synchronization loss may occur; and heat is generated due to the current still existing after the rotating shaft stops.

Classification of stepper motors

There are many classification standards for stepper motors. When classifying motors by output power, stepper motors are shown in the figure below. Stepper motors can achieve large output torque, so they can directly drive large loads and are suitable for some high-power control applications.

When classifying motors by power source, stepper motors are a special category of DC motors. Since stepper motors do not have commutation brushes and their rotation depends on the rotating magnetic field provided by the stepper drive, in theory stepper motors can also be considered a brushless DC motor.

Of course, in addition to power and power supply, there are other classification methods for motor systems based on motor structure and rotation principle. For example, there are two types of stepper motors, unipolar and bipolar. Under the conditions of the same current and the same torque output, unipolar stepper motors have twice as many coils as bipolar stepper motors, are more expensive, and have different control circuit structures. Most of the popular stepper motors on the market are bipolar stepper motors.

In addition, stepper motors are usually classified according to the characteristics of the rotor and the number of stator windings in terms of structure. For example, when classified by the number of stators, if there are two stators, it is called a "2-phase motor"; if there are three stators, it is called a "3-phase motor"; if there are five stators, it is called a "5-phase motor".

When stepper motors are classified by rotor type, they can be divided into rotors made of permanent magnets (PM type), gear-shaped rotors with rotor teeth (VR type), and gear-shaped rotors combined with permanent magnets (HB type).