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I am brand new to PLCs and Visilogic. I am looking to upgrade a punch press system to use a PLC and eventually add other aspects into the PLC control like low lube and part detection. This is my first attempt at using/programming a PLC so I want to start with the basics. I wanted to share my thought process and see if perhaps anyone might be able to give me encouragement or see an error in my thinking ;) I attended 2 days of a Unitronic seminar so I have a general understanding from the exercises but no real world experience with programming. So here is my situation....

I have a Vision 350. Once my system is started, the V350 is to signal my servo feed. The feed will take this signal, close a switch and it will cycle. It will send a 24 vdc signal as it is in motion which I want to send to the V350. Once the feed has stopped, the signal will drop to 0 and the V350 will then move to the next rung and signal the press. I do not have the particulars on what the press will send but I am assuming it is similar to the feed for now. Once the press has cycled, the signal will drop to 0 and the controller will start the process again.

Since each of my units have "brains" to determine their feed length and single stroke properties, I believe all I need is to set a direct contact on the ladder to send a momentary signal to start each unit. What I am unsure of is what element needs to be used when looking for the signal to drop to 0? Is this a negative transition or perhaps something that is directly related to the physical reading of the input...a comparison function?

Any thoughts are greatly appreciated.

Jeff

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  • MVP 2021

Jeff,

You are correct in picking the negative transition instruction to determine when the input goes to a logical zero. The output of the instruction will be on for one scan, which you can use to make another action.

On a larger scale, if you are new to PLC's I would highly recommend building a simulator with 24V lights and switches and wire it up to your PLC. I've used a cardboard box as the enclosure for this - you don't have to get fancy. Play with your program on the simulator before you hook the PLC to the actual press - this is not the type of machine to make programming mistakes on.

Also make sure you have an adequate safety system on this thing, and it should be totally outside the PLC. You can have an input the PLC reporting that the safety system is satisfied, and make sure any PLC outputs controlling moving parts that could hurt somebody run through a safety relay tied into the system. Depending on how old the punch press is, you may have to add considerable guarding, light curtains, door switches, etc. I have done a couple of press retrofits and the program is usually not complicated, but you need a healthy dose of CYA when you get involved with one of these.

Joe T.

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