Re: What is wanted in a controller, was Re: Correct or Max voltage > for Bridgeport Nema 42? + more...

>    From: "audiomaker2000" <audiomaker@...>

> It was I to blame for that long rant.

<S>

> Perhaps adding this flexible I/O to some current software is a
> monumental task. I'm not a developer so I don't know.

You guessed it, Sean. The programmable logic controller (PLC) is the
hardest and most expensive part of the retrofit of many of these older
machines. In even the latest machines there is a separation of CNC
functions into motion control and PLC. Most all of what you describe in
this post is done by the PLC.

If you have the complete documentation for a machine it should include a
ladder list of the I/O and CNC related stuff that was built into the
original. For many machines these lists will run a hundred pages or more
of long paper. Granted they don't use the paper very efficiently but
there is a lot of logic that goes into even a rather plain machine.

More than just the size of the pile of logic, is the fact that the logic
is different for each machine. One shop I work with has four Mazak 414
mills. All have M32 controls. Now if you think that the logic of each
would be the same -- think again. Many of the parameters used to setup
logic conditions are numbered the same between mills but even some of
these will do different things on different machines. When I begin to
troubleshoot I make sure that I've got the correct ladder for the machine
I'm looking at.

We do need to improve the way that "hobby" level machines are programmed
for this logic. I am only acquainted with how the EMC does it and at
present it requires either C or Tcl/Tk programming ability to go beyond
the two major logic definitions included with the distribution. There
is an open source PLC project or two that are gaining momentum and are
nearing a first release. But even here with a working software PLC, you
would need to know how to program it and what logic is needed by the
specific machine that you want to run with it. I suspect that it will be
some time before a hobby level machine can probe the I/O and CNC
connected to it and intuit the logic that it needs.

The commercial retro CNC's often allow you to purchase an add in PLC.
The last I checked with one distributor it cost an extra $1k for this
"feature." The good thing was that they offered a free three day
programming course with it.

And then there is all of the govt mandated hardware and software logic
that varies from country to country and in some places from county to
county! If you expect someone to sell a R'fit kit they will have to take
account of this as well. And then there's product liability!

HTH

Ray