Advanced Motion & High-Speed Control
This lesson consolidates the fundamental concepts of motion control using Allen-Bradley Micro800 series PLCs using the PWM and PTO.
We will cover the mechanics of pulse and direction, the implementation of positioning instructions on the Micro850, and the specific application of the Pulse Train Output (PTO) on the Micro820.
Stepper Motor Motion Control: Pulse and Direction
Stepper motors and their associated drives provide precise positioning by interpreting pulse signals. The control signal is generally divided into two components:
Pulse: Each individual pulse represents a discrete step of the motor. By controlling the frequency of these pulses, you directly control the speed of the motor.
Direction: A separate digital signal defines whether the motor rotates clockwise or counter-clockwise.
This digital signaling allows the PLC to command exact distances and velocities without the need for complex feedback loops in many basic applications.
Micro850 Positioning Instructions
The Allen-Bradley Micro850 PLC utilizes specific motion function blocks to simplify complex positioning tasks. These instructions manage the acceleration, velocity, and target position parameters required to move an axis accurately. When programming these, ensure your configuration settings match your drive and mechanical requirements, specifically regarding units of measure and ramp times, to prevent mechanical shock or instability.
Micro820 Pulse Train Output (PTO)
While larger Micro800 controllers have specialized motion capabilities, the Micro820 (specifically the 2080-LC20-20QBB model) features a dedicated Pulse Train Output (PTO) on Output 6. This allows the smaller PLC to act as a motion controller for a single axis. By configuring this output, you can generate the high-frequency pulse trains necessary to drive stepper or servo hardware directly from the PLC, making it a compact solution for simple point-to-point motion tasks.