【Question 1】What is the step angle of a stepper motor?
【answer】
The step angle of a stepper motor represents the angle by which the motor rotates when the control system sends a pulse signal. In other words, the angle the motor rotor rotates for each input pulse signal is called the step angle, denoted by θ. Figure 1 shows a schematic diagram of a two-phase stepper motor with a step angle of 1.8°.
Figure 1. Step angle 1.8° (two-phase motor)
A stepper motor is characterized by rotating one step angle for every pulse received. Its angular or linear displacement is directly proportional to the number of electrical pulses; that is, the rotation distance of the stepper motor is proportional to the number of pulse signals applied to the driver . Based on this characteristic, the relationship between the number of pulses and the rotation angle shown in Figure 2 can be derived.
Figure 2 Relationship between pulse number and rotation angle
[Question 2] How to select a stepper motor?
【answer】
Generally, once the three main parameters of a stepper motor—step angle, static torque, and current—are determined, its model number is also determined. Currently, stepper motors on the market are classified by their frame size (motor outer diameter). Based on the frame size, they can be divided into international standards such as 42BYG (BYG is the code for inductor-type stepper motors), 57BYG, 86BYG, and 110BYG, while models like 70BYG, 90BYG, and 130BYG are domestic standards. Figure 3 shows the appearance of a 57BYG stepper motor and its wiring terminals.
Figure 357 shows the appearance of the stepper motor and its wiring terminals.
[Question 3] How is a stepper motor driver typically wired?
【answer】
Stepper motor control falls under the category of "open-loop" control and is used in applications requiring moderate positioning accuracy, such as machine tool feed and leadscrew positioning. Here is a brief introduction to the use of a stepper driver. Figure 4 shows the wiring diagram of a stepper motor driver, and its meanings are shown in Table 1.
Figure 4. Wiring diagram of stepper motor driver
[Question 4] What is the typical structure of a servo motor?
【answer】
In practical applications, the structure of a servo motor is usually as shown in Figure 5, which includes a motor stator, rotor, bearings, encoder, encoder connection cable, servo motor connection cable, etc.
Figure 5 General structure of servo motor
[Question 5] What are the different control modes of a servo driver?
【answer】
AC servo drives typically include position, speed, and torque loops. However, the drive, motor, and motion controller can be combined to create different operating modes to meet various application requirements. Servo drives mainly offer three modes: speed control, torque control, and position control.
(1) Speed control mode
The speed control of the servo drive is carried out in the same way as the frequency converter speed regulation, that is, the speed of the motor is adjusted by controlling the frequency of the output power supply. At this time, the servo motor operates in a speed control closed loop. The encoder detects and feeds back the speed signal to the servo drive, compares it with the set signal (such as multi-speed, potentiometer setting, etc.), and then performs speed PID control.
(2) Torque control mode
The servo driver torque control mode shown in Figure 6 controls the output torque of the servo motor through external analog input.
Figure 6 Torque control mode
(3) Position control mode
The driver position control mode can accept position command signals from motion controllers such as PLCs or positioning modules. Taking pulse and direction command signals as an example, the number of pulses determines the motor's position, the pulse frequency determines the motor's speed, and the level of the direction signal determines the servo motor's direction. This is similar to stepper motor control, but the pulse frequency is much higher to accommodate the high speed of the servo motor.
