Common methods of stepper motor positioning control

Stepper motors are often used for positioning control. The number of pulses output by the PLC can control the angle of rotation (relatively speaking, it can be the distance), and the frequency of the pulses controls the speed of the stepper motor. However, it is simple, economical, and easy to control when used in situations where the control accuracy is not very high; for situations where the control accuracy is very high, a servo control system must be used.

Stepper system = stepper driver + stepper motor. The stepper motor is driven by the stepper driver, which is equivalent to the driving power supply, and it is controlled by external pulse signals and direction signals (the example here is the Siemens PLC output pulse), thereby controlling the rotation angle and speed of the stepper motor.

Stepper driver + stepper motor + Siemens PLC (CPU 222 CN)

Related definitions

1. Driver: The medium used for PLC to control the stepper motor. It is responsible for amplifying the pulse signal given by the PLC and transmitting it to the stepper motor, so that the motor runs according to the parameters given by the PLC and the driver.

Control Process

2. Step angle: The angle that each pulse causes the stepper motor to rotate. The most common angle is 1.8°, which generally cannot be changed.

For example: Without setting the subdivision, how many pulses does the PLC need to send to control a stepper motor with a step angle of 1.8° to rotate one circle (360°)?

Answer: 360°/X=1.8°/1, so X=200 pulses.

3. Subdivision: In actual applications, it is found that if the step angle is large, the angle of each rotation will be large, which will cause vibration and the corresponding control error will also become larger. Therefore, the subdivision function is introduced. That is, the step angle is divided into several more points through the DIP switch of the driver to make the motor rotate more smoothly.

For example: if the step angle is 1.8° and is set to 10 subdivisions, then each time the PLC sends a pulse, the motor only rotates 0.18°. How many pulses does the PLC need to send for the stepper motor to rotate one circle (360°)?

Answer: 360°/X=0.18°/1, so X=2000 pulses.

Summary: The larger the step angle, the fewer pulses; the smaller the step angle, the more pulses.

Introduction to stepper system hardware (taking the PFEID stepper motor as an example)

1. Stepper driver

PFEID Driver Description

There are generally two types of direction control for stepper motors:

A) Pulse + Direction: When a pulse is generated by PUL, the motor will rotate, and the direction is determined by DIR.

B) Forward pulse + reverse pulse: When PUL generates a pulse, it rotates forward; when DIR generates a pulse, it rotates reversely. However, PUL and DIR cannot generate pulses at the same time.

2. Stepper motor

When the AB two-phase windings are swapped, the motor can run in the reverse direction.

Stepper motor parameters

Wiring diagram with PLC

The signal voltage of the stepper motor is 5V, and the voltage used by Siemens PLC is 24V, so to connect to the driver, a 1.2K, 1/4W resistor needs to be connected in series, as shown in the red part of the figure.

Siemens PLC (CPU222) can output two types of high-speed pulses:

1. PTO (duty cycle 50%)

2. PWM (duty cycle can be changed)

The above two high-speed pulse output instructions can be used to control the stepper driver, and then control the stepper motor, and then control the movement and speed of some specific equipment.