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Stepper motors are commonly used for positioning control, and they can control the rotation angle (which can be relative distance) through the number of pulses output by the PLC. The frequency of the pulses controls the speed of the stepper motor. For applications where high precision is not required, this method is simple, economical, and easy to control; however, for applications requiring high precision, a servo control system must be used.
The stepper system consists of a stepper driver and a stepper motor. The stepper motor is driven by the stepper driver, which acts as the power source and is controlled by external pulse signals and direction signals (for example, Siemens PLC output pulses), 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 control of stepper motors, responsible for amplifying the pulse signals from the PLC and sending them to the stepper motor, allowing the motor to operate according to the parameters set by the PLC and driver.
Control Process
2. Step Angle: The angle that the stepper motor rotates with each pulse, commonly 1.8°, which generally cannot be changed.
Example: Without setting subdivision, how many pulses does the PLC need to send to rotate a stepper motor with a step angle of 1.8° one full turn (360°)?
Answer: 360°/X=1.8°/1, so X=200 pulses.
3. Subdivision: In practical applications, it is found that if the step angle is large, the angle of each rotation is also large, which can cause vibration and increase corresponding control errors. Therefore, the subdivision function is introduced. This means dividing the step angle into several smaller parts through the DIP switch of the driver, allowing for smoother motor rotation.
Example: If the step angle is 1.8° and set to 10 subdivisions, then for each pulse sent by the PLC, the motor only rotates 0.18°, how many pulses does the PLC need to send to rotate the stepper motor one full turn (360°)?
Answer: 360°/X=0.18°/1, so X=2000 pulses.
Conclusion: The larger the step angle, the fewer the pulses; the smaller the step angle, the more the pulses.
Introduction to Stepper System Hardware (Using PEFED Stepper Motor as an Example)
1. Stepper Driver
PEFED Driver Description
There are generally two ways to control the direction of the stepper motor:
A) Pulse + Direction: When PUL has a pulse, the motor will rotate, and the direction is determined by DIR.
B) Forward Pulse + Reverse Pulse: When PUL has a pulse, it rotates forward; when DIR has a pulse, it rotates backward. However, PUL and DIR cannot have pulses at the same time.
2. Stepper Motor
Switching the A and B phase windings can reverse the motor direction.
Stepper Motor Parameters
Wiring Diagram with PLC
The signal voltage of this stepper motor is 5V, while the voltage used by the Siemens PLC is 24V, so a 1.2K, 1/4W resistor needs to be connected in series, as shown in the red part of the diagram.
Siemens PLC (CPU222) can output high-speed pulses in two ways:
1. PTO (50% duty cycle)
2. PWM (duty cycle can be changed)
Using these two types of high-speed pulse output instructions can control the stepper driver, and thus control the stepper motor, and subsequently control the movement and speed of specific equipment.
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