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Counting process execution

Created by: Simon N at: 12/7/2011 6:50 PM (3 Replies)

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12/7/2011 6:50 PM	Rate (0)
Simon N Posts: 44 Rating: (0)	Hi All, Step 7 basic 1214c CPU I am struggling to find the best way of coding a sequence, let me desribe the issue I have a Air Ram, I want to apply ait to the air ram for (x) secound, release and then repeat this (y) times, this process will only continue while the safety circuit is acive So, User set up Press time - 5s Pressing times 5 The cycle would be press on (wait 5 secs) press of (2 secs) Press on (wait 5 secs) press of (2 secs) Press on (wait 5 secs) press of (2 secs) Press on (wait 5 secs) press of (2 secs) Press on (wait 5 secs) press of (2 secs) The time in the press of status relates to the time the press needs to raise to its start position. Could someone give me a small example of some code with the best way to achieve this process please. I am struggling getting the turning on / turing of sequencing right and the repetition. Thanks
Simon N Posts: 44 Rating: (0)
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12/7/2011 9:42 PM	Rate (1)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 3/24/2023 Posts: 13205 Rating: (2147)	The attached TIA Portal V11 SP1 Upd 2 program may get you thinking about a solution. This was loaded into a CPU-1214C DC/DC/RLY and tested. It ran as per your description using the online "Modify" option to set bits to 1 for E-Stop and Cycle Start. You'll have to write your specific abort, fault, cycle stop methods, but those are typically all the same - turn off the press, unless turning off the press actually creates a problem. Your application may have something that engages a holding mechanism, and turns off the press. Any number of variations. Anyhow, take a look. Nothing special about how it runs. A cyclic program runs a sequencer. Each time the sequencer runs, it enables a press cycle to run and keep running. Once it counts the proper number of complete cycles, it stops the cycle, then turns off the press, and turns on a 'press cycles complete' bit. The data for the cycle comes from a DB - for testing purposes those values are loaded on first scan with constant values - which could come from an HMI and user input. Probably simpler ways to handle it, but this does have the option to watch it run and it does not loop the PLC which is the computer programmer approach -- loops are bad in PLCs except in very special cases. Attachment Press_Cycle_Program.zip (111 Downloads)
	science guy
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12/8/2011 5:35 PM	Rate (0)
Simon N Posts: 44 Rating: (0)	Thanks, you have gone to a lot of trouble,. First thing I had to do is upgrade to the new service pack, this took all day !!! Thankyou for your time.
Simon N Posts: 44 Rating: (0)
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12/8/2011 5:51 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 3/24/2023 Posts: 13205 Rating: (2147)	Simon N Thanks, you have gone to a lot of trouble,. First thing I had to do is upgrade to the new service pack, this took all day !!! Thankyou for your time. After your system operates to satisfaction, please post your own method and how it works unless it's proprietary. My business isn't press cycles, but it once was and I saw several approaches. The easiest to understand is a simple sequencer with a couple counters all in one big FB/FC/OB. However, with the capabilities of modern PLC software, it makes sense to push the functionality to the lowest levels to make it easy to reuse the logic code and make it as generic as possible. The press on/off cycle could easily integrate a couple of prox or limit switch inputs or position feedback to determine when to start/stop and the timers set to prevent excessive burden. If it's crucial, you put in load cells to monitor force and turn off the press at the desired force. You can even do some calculus on the stroke to see when key events happen - local min/max, speeds, accels, etc. It all depends on what your process requires for proper quality control of the outcome. Having the latest software and firmware on these S7-1200 PLCs really makes a big difference. We're all beta testing as we go. I am running the latest software and yesterday after leaving it monitoring live online for 18 hours, TIA Portal crashed and required a restart. That's unsatisfactory for really useful software to monitor and watch things happen and help diagnose problems. Perhaps SP2 will fix that problem. SP1 fixed 50% of the crashes from the original problems with the portal. V11 fixed 95% of the crashes from V10.5 SP2. You would think Siemens could push their software harder than we users can! Have a wonderful day.
	science guy
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