PLC's and industrial automation

Doug Harrison wrote:

> Doug Fortune wrote:
>
> > glass cutters to pcb millers to woodworkers and even 'industrial
> automation' applications where they had been previously been quoted prices
> too high to be feasible. One guy in particular had an automated 'roughing
> cutoff' application where he employs someone all day to advance material a
> certain amount (from long stock) to +/- 1/4" and hits a button -
> whereupon the saw cuts the material, turns off, and retracts. He'd just
> need 1 stepper with a rubber wheel, 1 solenoid, and a simple DOS program to
> read a file and advance the stepper appropriately.
> >
>
> We built a machine to do this very thing about two years ago. It used a
> $149 PLC to control the whole process. It would punch and cut a piece every
> four seconds until it ran out of stock. The amazing thing is that it
> required less than 20 lines of code.

The wrinkle is that the size of each of the custom pieces was known
only shortly before, by a process futher down the line. Therefore, the
requirements were to be (dynamically) sent via ethernet to the pc
doing the cutting. I presume an advanced PLC could do this (read
from an ethernet, and change its behaviour appropriately), but I
don't have any experience with PLC's.

OK - lets hear from the PLC experts (maybe a short tutorial).
What is all this 'ladder logic' stuff? Is it programmed serially
into a static memory? ... or ?

Doug Fortune
http://www.cncKITS.com