On 8/13/2012 5:23 PM, EBo wrote: > On Mon, 13 Aug 2012 16:48:33 -0400, Dave wrote: > >> On 8/13/2012 1:45 PM, EBo wrote: >> >>> On Mon, 13 Aug 2012 10:39:03 -0400, Dave wrote: >>> >>> >>>> ... >>>> >>>> On many hardware PLCs you can make programming changes on the fly >>>> without pausing the controller which means that you don't need to >>>> stop >>>> the machine >>>> to make program changes. Very important when it takes an hour or >>>> more >>>> to restart the machine after a shutdown. >>>> >>>> >>> a restart takes an hour or more after shutdown? Out of curiosity, >>> what >>> machine might that be, and why so long? >>> >>> >>> ------------------------------------------------------------------------------ >>> Live Security Virtual Conference >>> Exclusive live event will cover all the ways today's security and >>> threat landscape has changed and how IT managers can respond. >>> Discussions >>> will include endpoint security, mobile security and the latest in >>> malware >>> threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ >>> _______________________________________________ >>> Emc-developers mailing list >>> Emc-developers@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/emc-developers >>> >>> >>> >> >> That is common with a lot of process related equipment. Large >> extruder/molding systems, web processing machines are not usually as >> long but they can take a long time to restart, with a lot of people >> running around to get things going again. When the web is running a >> couple hundred feet per minutes in coordination with a number of >> other >> axes which are running applicators, cut offs, feeders,etc, you really >> don't want to shut it down to make a minor change. >> The machine cell I was working on two weeks ago took about 30 minutes >> to >> fully load with all of the parts in the queue - 5 machines with a >> robot >> in the center, and about 15 minutes to unload. If we had to shut >> down >> the system controller for each change, we would have to start all >> over >> again as machine and system state information would be lost Instead >> we >> made changes on the fly as much as possible to speed the debug >> process. >> >> Last year I was working on the controls for a refrigeration system >> for a >> plant that processed food. When we shut down the compressor system to >> make a change we would have to coordinate the shutdown with the rest >> of >> the plant so they would not require refrigeration for the duration of >> the process, it was a huge deal for the process people as the food >> has >> to be chilled at a certain rate during the process and the plant was >> large and was cooking multiple batches of food at various times. So >> all possible changes were made on the fly (very carefully). Once, >> when >> I had to shut it down for a couple of minutes (literally) to >> download a >> change that had to do with the controller hardware, they had 10+ >> people >> standing around with radios through out the plant all coordinated to >> tell me when I could put the controller in stop mode, download the >> change, and then put it back into run mode. That was not a fun >> situation. Part of that was a system design problem. The process >> engineer put all of the refrigerant compressors on one controller. >> :-( >> So while the change only took a couple of minutes, it took a while to >> restart all of the compressors and bring the system back up to >> pressure. When that plant loses power they throw out a lot of food. >> >> Power plant boiler controls are the same way. They take hours to >> shutdown and start up. >> >> Any company that runs a machine 24x7 usually has the same problem. >> Usually the reason they run it 24x7 is that the startup and shutdown >> process takes hours. >> > Dave, > > Thanks for the info. When I read the original post I was thinking that > these were machines controlled with EMC, and not full plant operations. > While I have never worked on equiptment like that, I remember reading > about industrial canning operations that had to be very carefully > controlled, and they lost something like $100,000 in product when one of > the lines went out... > > EBo -- > > >
Yes, I was actually referring to hardware based PLCs. But being able to implement changes quickly and visibly debug your code on the fly, without recompiling is a very nice feature of Classic Ladder also. You can't make changes without stopping the PLC scan, but Classic Ladder is a very nice addition to LinuxCNC. One of the Fanuc CNC systems I was working on earlier this year (I think it was an 18 IT?) had over 1000 rungs of ladder logic. Dave ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
