Smart machines/PLC overlap?

by Adi
(Pune, Maharashtra, India)

During my tour at a oilfield pipe making facility I noticed that the PLCs ran the show, but werent just telling dumb motors to energize or reading dumb encoders and switches etc.

There was some fairly smart equipment there as well. For example the saw (picture a chop saw but with a 3 ft blade) had a big console with a touch screen display and must of had some circuit boards and brains all its own inside. The maint guy was pointing out a schematic he had pulled out that the italian nomenclature was different for circuit symbols on this italian made behemoth.

The console was remotely mounted about 10 feet from the buisness end of the saw which was completley enclosed (I could imagine the noise)in a booth with a circulating cutting fluid system.

So I m wondering, the saw is smart and can be commanded by the operator but a whole cabinet of brand new PLCs was installed right behind the saw.

There was also a high tech smart welder with its touch screen on the line too along with some inspection equipment that I didnt get to see close up.

My question is if PLCs call the shots but are simple I/O boards that cant talk to computers thru their simple inputs how do they command a smart machine, does the saw just take a order from the PLC, "Cut pipe until further notice" and the saw takes it from there cutting 40 foot joints with it own optical encoder and controlling its own functions and then just set an output that indicates a cut is complete and the PLC then tells a motor to pull the new pipe away?

Why would you need a whole cabinet full of PLCs? All that happens after the saw is the pipes are moved down racks to be blown out with air and inspected, simple hydraulic arms halt and then let pipes roll with gravity once past the saw.

Do the PLCs stick their nose into every aspect of the saws operation? Where do smart machines and PLCs functions meet? can they talk to each other on the rs-232 bus? Are they made to work with plcs? Is there ever any conflict or safety concern if the smart machine has issues and "lies" to the PLC?