Vision 350® & Vision 130® Pulse Train Outputs

Motion Control Made Easy

Download the Unitronics PTO Press Release here

The increasing drive for product quality requires more accurate and consistent movement from the components of modern day machines.  To move accurately and quickly requires the use of a servo or stepper motor, a device which needs to be told which direction to move in, at what speed and for precisely how far.  The requirement to be able to alter these parameters easily for different products puts a strain on traditonal PLC equipment which is not good at handling and processing large amounts of integer values.

Unitronics engineers have worked hard to reduce the pain involved in motion control by producing a set of function blocks that allow you to configure movement profiles using drop down boxes and multiple choice selection.  The net result is a neat little box in the middle of your program that outputs a pulse train to your motor control card.

There are six elements to the pulse train output (PTO) function block set

Available only on certain Unitronics Vision® models (those with high speed transistor outputs!) the Configuration function block is shown below.  This block defines the hardware system and converts pulses to engineering units, up to three channels may be used and there are three modes available

Having defined the physical system we now set up the move profile which consists of three stages, acceleration, steady speed and deceleration.  The Set Profile function block allows entry of start speed, stop speed, acceleration and deceleration times together with a 'jerk factor'.  There are six available jerk factors which specify whether the acceleration and deceleration profiles have straight line characteristics or use a smoother S Curve approach.

The parameters in a profile may be fixed numerical values or internal registers if the value needs to change under program or recipe control.  Unitronics Vision® OPLC's have internal data tables and can retrieve and save data onto an SD card which allows many different profiles to be accessed.

The last part of defining a move is the actual move itself, using the PTO Move function block the user specifies the direction (a positive value for one direction, a negative valur for the other direction), the speed and the target position. It is also possible to specify ABSOLUTE or RELATIVE movement, absolute movement being to a specific point and relative movement being another movement in the specified direction.

The last three elements of the function block set provide simple but convenient ways of implementing

Motion control programs written in a modern PLC often take up vast areas of code clogging up the memory and distracting from the original objective of controlling the machine.  Using a Unitronics function block not only makes the whole process simpler and easier to construct but it removes the clutter of incidental code leaving the control program nicely structured.