programming

cueball

Guest
C
Heres a problem! I've got 7 pistons (A-G) and need a ladder diagram for the programe. The sequence is quite difficult for me to figure out. The sequence is:

A+ B+ A- C+ A+ B- A- C- D+ E+ E- D- F+ F-

this is to repeat 5 times before G+ G-

then the whole thing repeats again

it does not matter which plc is used
can anyone help me please??
 
The sequence shouldn't be a problem for you - you state exactly what's supposed to happen, and in what order.

The ladder could be fairly straight-forward, if you can answer one question - what are the transition conditions to go from one step to another?

That's the key, you see. It's like life:

To know where you are, you have to know how you got there.

Which university gives this problem out (I'm trying to keep track) ?

I'll give them credit, though - they change the sequence every term, so that the students can't just copy the answer.
 
Doesnt seem too difficult, is there a time they need to stay extended or retracted? This is nothing but a sequence type program with some minor modifications.

Here is how this site works. IF you want/need someone to do this there are many qualified and willing but they DO NOT work for free.

What you can get for free is help. If you are a student then you should be at a point where you can apply some form of logic and show it here, then others can assist. I suspect you are a student and need this as an assignment/homework, make an effort than come back and post it.

If you arent a student and this is needed for a company project or machine modification then you will need to give full details of the machine and what is to be accomplished.

Be prepared for some form of derision or ridicule.

Try to be nice guys, dont want Father Phil angry this close to xmas.
 
This question, or one strikingly similar has been posted here in the past. I assume its an exercise for a PLC programming class, although probably not for the HNC exam in Great Britain.

You have to create a sequence of 16 steps. Having a cylinder reach it's appropriate end-of-travel switch will be the event that triggers the transition from from one step to the next. Use a counter to keep track of the number of times you've gone through the repeatable section. At the conclusion of step 14, if the count is less than 5, the next step after 14 will be step 1. If the counter is at 5, the next step after 14 will be step 15. Reset the counter in step 15 or 16.

Some brands of PLC have functions that can reduce the amount of ladder logic required to program a sequence like this.

This is an excellent example of a system that could benefit from being programmed in SFC (Sequential Function Chart) instead of RLL (Relay Ladder Logic).

Start by programming a sequence that controls extending a piston until it reaches it's "Extended" limit switch, then retracting until it reaches it's "Retracted" limit switch, and then repeating the cycle. Once you have a program that works, it should be easy to expand your logic to handle a longer sequence.

Your program should also include some logic to reset the system to it's rest state in the event of an abnormal or aborted sequence.
 
What these guys are telling you is.... You will have to get the answer yourself, or at least try. There are many guys here that can figure it out for you. But, that is not why we are here. We have all been in your position at least a few times. Just the fact that you found this place filled with old farts, like us, is an accomphishment. I pride myself more on what I have done for the "youngsters" in my life, than what I have done professionally, which has been full filling. Phil has an excellent job here and I would hate to disappoint him by giving you the answer. It is there... go get it!
 
I received this personal message from cueball.

thanks very much for your posting relating to the problem i posted. i am in college and this problem is part of my project. the thing is we do not have a class teaching us how to write programs like this. i cant understand how they expect us to do it when we know nothing about it. do you know where i might get information on how to write programs. i do not want the solution to the problem, i just need to know where i can learn how to solve the problem myself. i need a push in the right direction!! can you help?? remember i dont want the solution just a little guidance

Well cueball, I thought that by suggesting you tackle a simpler problem with an eye toward extending your solution to your more complicated task, I was giving you a nudge in the right direction.

Here's another nudge. Have you done any programming in any other languages? You might try writing a program in a language that you are more comfortable in, and converting it to ladder logic. Consider the following ladder logic rung.

Input_1 Input_2 Output_1
--| |-------|/|--------( )--



It might be rendered in BASIC as

Def Input1 as Boolean, Input_2 as Boolean, Output_1 as Boolean
Def PLC_Run_State as Boolean

While PLC_Run_State = True

GoSub Read_Inputs

Output_1 = Input_1 AND NOT(Input_2)

GoSub Update_Outputs

Wend
 
Do what most of us do. Have a look in your PLC manual and find a function that will make your life easy. A piece of code for that problem would take most of us "old pfhaarts" a couple of minutes but we all had to learn to use our PLC manuals and grey matter. Think outside the square but do not complicate things. Apply the KISS principle wherever possible.
Here is another nudge/option - think about transitional shift - and differentiated inputs.
Remember, there are no problems only solutions.
Oh well, back to my next problem ..... err ..... solution!!!!!
Is the beer cold yet?????
beerchug
 
Last edited:

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