On Mon, 2008-08-04 at 13:58 -0700, Kirk Wallace wrote: > On Mon, 2008-08-04 at 14:54 -0500, Ray Henry wrote: > > > I'm curious though why you would not want to run ladder? It has obvious > > advantages. > > > > Ray > > Only if you know ladder and are tied to it somehow. I think writing > components in C is much more direct. I have very limited experience with > ladder (and C actually), which I believe is much more prevalent in > larger or more complex machines, but I wonder if that is still true with > today's machines? Anyone have a brand new Haas or Mori Seiki I can take > apart?
There are a few advantages to our ladder programming system. The first is that it mimics contacts, timers, counters, and coils and shows their status is a fairly easily readable display. A PLC based logical system also applies a predictable environment. It reads all the input signals (sense) then applies all of the logic to that state (model) and then sets the computed state of all of the outputs (act) at the same time. Now you can do that with a C program but you are not constrained to do so. As the model part of a hand written system becomes more complex it is more and more likely you will have unintended consequences for some action you took just a few lines up in the code. It's possible to create a race condition with PLC systems but it is less likely and rather easy to see happening in the display. And as a added benefit you need not shut down the machine to develop test and edit your machine logic. I'd push the estop button before I pressed ladder edit rung but if you've written the estop feed to the ladder loop correctly it should assert an estop whenever you edit the logic. And for a more recent machine tool, you would not need to take them apart, simply press the maintenance button and look for ladder. Or easier yet, look for the machine logic in the manuals. HTH Rayh ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
