PLC and Stepper Driver Control Principle

PLC and Stepper Driver Control Principle

Control Principle

Stepper motors are commonly used for positioning control. They can be controlled by the number of pulses output by a PLC to determine the rotation angle (and thus the distance), with the pulse frequency regulating the motor's speed. Stepper motor systems are simple, cost - effective, and easy to control, making them suitable for applications where control precision is not extremely critical. For high - precision control scenarios, servo control systems are typically required.

A stepper system comprises a stepper driver and a stepper motor. The stepper motor is driven by the stepper driver, which acts as a power source. The driver is controlled by external pulse and direction signals (in this example, pulses from a Siemens PLC), thereby regulating the motor's rotation angle and speed.

Key Definitions

1. Driver: The intermediary between the PLC and stepper motor. It amplifies the pulse signals from the PLC and transmits them to the stepper motor, enabling the motor to operate according to the parameters set by the PLC and driver.

2. Step Angle: The angle by which the stepper motor rotates with each pulse. A common step angle is 1.8°, which is typically not adjustable.

Example: How many pulses does the PLC need to output to rotate a stepper motor with a step angle of 1.8° through one full revolution (360°) without microstepping?

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

3. Microstepping: In practical applications, a large step angle can cause significant vibration and increase control errors. Microstepping divides the step angle into smaller segments using the driver's DIP switches, resulting in smoother motor operation.

Example: If the step angle is 1.8° and microstepping is set to 10, how many pulses are required for the motor to complete one full revolution?

Answer: 360° / X = (1.8° / 10) / 1 ⇒ X = 2000 pulses.

Summary: A larger step angle requires fewer pulses, while a smaller step angle requires more pulses.

Stepper System Hardware (Using Phidgets Stepper Motor as Example)

1. Stepper Driver

Pulse + Direction Control: When a pulse is generated at PUL, the motor rotates, with the direction determined by DIR.

Forward Pulse + Reverse Pulse Control: Pulses at PUL make the motor rotate forward, while pulses at DIR make it rotate reverse. PUL and DIR should not generate pulses simultaneously.

2. Stepper Motor

When the A and B phase windings are swapped, the motor rotates in the opposite direction.

The signal voltage of the stepper motor is 5 V, while the Siemens PLC operates at 24 V. A 1.2 K, 1/4 W resistor must be connected in series when connecting to the driver, as shown in the red part of the diagram.

The Siemens PLC (CPU222) supports two types of high - speed pulse outputs:

PTO (Pulse Train Output) : 50% duty cycle.

PWM (Pulse - Width Modulation) : Adjustable duty cycle.

These high - speed pulse outputs can be used to control stepper driver and the movement and speed of specific equipment.