With the continuous development of the mechanization, electrification and automation of the production process, various types of special motors have emerged. The working principle of these motors is generally similar to the basic principles of ordinary asynchronous motors and DC motors, but they have their own particularities in performance, structure, and production process, and are often used in automatic control processes. In general, the power of these motors is small, only a fraction of a watt is small, and large is only a few tens of watts or several hundred watts, which belongs to the range of miniature motors.
There are many kinds of stepping motors, and they can be divided into two types: reactive and energetic; they can be divided into single-phase, two-phase and multi-phase according to the number of phases.
Fig.1 Structure of reactive stepper motor
Fig. 1 is a schematic diagram of a reactive stepping motor. Its stator has six magnetic poles evenly distributed, and windings are wound on the magnetic poles. The two opposing poles form a group, as shown in the figure. The following describes the basic principles of single-shot, six-shot, and double-three-shot energizing methods for a reactive stepper motor.
First, the basic principle of a single three-shot power
Let A phase be energized first (B and C two phases are not energized) to generate magnetic flux in the direction of axis A-A′ and form a closed loop through the rotor. At this time, the A and A' poles become the N and S poles of the electromagnet. Under the action of the magnetic field, the rotor is always trying to go to the position where the reluctance is the smallest, that is, to go to the position of the teeth of the rotor to align the A and A' poles (Fig. 2a); then the B-phase is energized (A and C phases are not Power on). Turn it clockwise to rotate 30°. Its teeth are aligned with the C and C' poles (Figure 2c). It is not difficult to understand that when the pulse signals are sent one by one, if the power is applied in the order of A→C→B→A→, the rotor of the motor rotates counterclockwise. This power-on mode is called single-shot mode.
Fig. 2 Rotor position in single three-shot energizing mode Basic principle of energizing mode in two and six shots
Let A phase be energized first and the rotor teeth align with the stators A and A' (Fig. 3a). Then, phase B is turned on while phase A continues to be energized. At this time, the stator B and B′ poles produce magnetic pull force on the rotor teeth 2 and 4, so that the rotor rotates clockwise, but the A and A′ poles continue to pull the teeth 1 and 3. Therefore, the rotor turns to the balance between the two magnetic tensions. . The position of the rotor at this time is shown in Fig. 3b, that is, the rotor rotates clockwise by 15° from the position of (a). Then phase A powers off and phase B continues to power up. At this time, the rotor teeth 2, 4 and the stators B, B' are pole-aligned (figure c), and the rotor is turned again by 15° from the position of the figure (b). Its location is shown in Figure 3d. In this way, if electricity flows in the order of A→A, B→B→B, C→C→C, A→A..., the rotor will rotate clockwise one by one, with a step angle of 15°. The current is switched six times, the magnetic field rotates one revolution, and the rotor advances a pitch angle. If the power is supplied in the order of A→A, C→C→C, B→B→B, A→A, the motor rotor rotates counterclockwise. This way of energizing is called six-shot mode.
Third, the basic principle of double three-shot power
If each time is a two-phase power, that is, press the A, B → B, C → C, A → A, B → ... order of power, it is called double three-shot mode, visible from Figure 3b, and Figure 3d step The angle is also 30°. Therefore, when using a single three-shot and double three-shot method, the rotor advances one pitch angle in three steps, and advances one third of the pitch angle each time. In the six-shot mode, the rotor moves six steps forward one tooth. From the horn, each step advances one-sixth of the pitch angle. Therefore, the step angle θ can be calculated by the following formula:
Zr is the number of rotor teeth; m is the number of running.
The most common step angle for a typical stepper motor is 3° or 1.5°. From the above equation, the rotor has more than 4 teeth (90° pitch angle) and 40 teeth (9° pitch angle). In order to align the rotor teeth with the stator teeth, the tooth width and pitch must be equal for both. Therefore, in addition to the six poles on the stator, there are five small teeth on each pole face that are the same as the rotor teeth. Stepper motor structure shown in Figure 4.
Figure 4 Three-phase reactive stepper motor structure diagram From the above description we can see, stepper motor has a simple structure, easy maintenance, high accuracy, sensitive start, stop and other accurate performance. In addition, the speed of the stepper motor is determined by the frequency of the electrical pulse and is synchronized with the frequency.
Fourth, stepping motor drive power
The stepping motor needs to be equipped with a dedicated power supply. The role of the power supply is to allow the motor's control windings to be energized in a specific order, ie controlled by the input electrical impulses. This dedicated power supply is called the drive power supply. The stepping motor and its driving power supply are an interconnected whole, and the running performance of the stepping motor is a combination of the motor and the driving power.
1, the basic requirements of the drive power
(1) The number of phases of the drive power supply, the power-on mode, and the voltage and current all meet the needs of the stepper motor;
(2) to meet the stepper motor starting frequency and operating frequency requirements;
(3) It can minimize the vibration of the stepper motor;
(4) Reliable work and strong anti-interference ability;
(5) Low cost, high efficiency, easy installation and maintenance