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Old December 27th, 2008, 07:00 AM   #1
bara_hence
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Program design help and ideas

I am working on a complex process cell or what to call it.. It works like a line with a continuos flow where you fill molds with product and it goes through tempering zones and so on..

The thing I now want some advice on is the logic for start,stop,paus,BacktoBack recipe change and so on..

Me myself whas thinking of doing this with states.. First I have six states wich are really modes for the machine - Stopping-Stopped ShuttingDown-Shutdown Standbying-Standby the difference between these states is temp setpoints (Standby-Stopped) and the shutdown state means nothing is running. From the standby state one should be able to start the machinery (doh) and then we go to the starting state here we start all the equipment in an orderly fashion and when thats done we enter the production state.. From the production state the operator can choose to start the fill machines either one by one or all at once.. I was thinking of having some bit resetted or setted here.. When making product you have several stop situations 1. Production paus may be initiaded by some downstream condition and if this is the case the line should restart after this condition goes away. Therefore i have a restart state. Production stop, Controlled Stop i have them gathered in a contr.stopping state and i have a back to back state for product change and so on....

I can post a picture later it gets much more clearer then...


I have never done this type of machine and the question i have is there an easier way for me it seems it is getting really complex in the end..

Any words from you experts how do you design a "machine" like this??
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Old December 27th, 2008, 07:06 AM   #2
Thim
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Quote:
Originally Posted by bara_hence View Post
I am working on a complex process cell or what to call it.. It works like a line with a continuos flow where you fill molds with product and it goes through tempering zones and so on..

The thing I now want some advice on is the logic for start,stop,paus,BacktoBack recipe change and so on..

Me myself whas thinking of doing this with states.. First I have six states wich are really modes for the machine - Stopping-Stopped ShuttingDown-Shutdown Standbying-Standby the difference between these states is temp setpoints (Standby-Stopped) and the shutdown state means nothing is running. From the standby state one should be able to start the machinery (doh) and then we go to the starting state here we start all the equipment in an orderly fashion and when thats done we enter the production state.. From the production state the operator can choose to start the fill machines either one by one or all at once.. I was thinking of having some bit resetted or setted here.. When making product you have several stop situations 1. Production paus may be initiaded by some downstream condition and if this is the case the line should restart after this condition goes away. Therefore i have a restart state. Production stop, Controlled Stop i have them gathered in a contr.stopping state and i have a back to back state for product change and so on....

I can post a picture later it gets much more clearer then...


I have never done this type of machine and the question i have is there an easier way for me it seems it is getting really complex in the end..

Any words from you experts how do you design a "machine" like this??

Maybe this is helpfull ISA S88, it sort of describes how to do things like that
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Old December 27th, 2008, 03:55 PM   #3
gkelley@mcaps-inc.co
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Try breaking it down in small processes and tackling each process one at a time.
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Old December 27th, 2008, 06:10 PM   #4
bara_hence
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Yes I have been looking at isa s88 and also ns88 and omac and so on.. So Ive made up my state model but I get the feeling it may be to overcomplicate things.. But maybe this is the best way..

Like I said i have never worked on such a system andthats why im looking to you pros..

And yes I have divided the process in several units and the units have some equipment modules and so on.. But the hard thing to do for me is to handle all the possible states for the entire process cell.. Isnt there anyone with a good example maybe of a plc project programmed according to isa s88 with the state models and so on??
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Old December 28th, 2008, 03:20 AM   #5
Terry Woods
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In general, he's a rookie, inexperienced with proper problem description

Granted, English is not his first language. But logic IS universal... and this guy is not showing that he understands the basics.

First I have six states wich [sic] are really modes for the machine -

Stopping-Stopped
ShuttingDown-Shutdown
Standbying-Standby

How about a "Running Mode" and a "Fault Mode"?

Maybe, upon Initial PowerUp the primary scheme should look like...

Standby -> Start -> Starting -> Running -> Fault -> Stopping -> Stopped -> Fault Cleared -> Standby

After all, when you initially power up your machine it should go to the Standby positiion... shouldn't it?


Begin Gibberish

the difference between these states is temp setpoints (Standby-Stopped) and the shutdown state means nothing is running. From the standby state one should be able to start the machinery (doh) and then we go to the starting state here we start all the equipment in an orderly fashion and when thats done we enter the production state..

Gibberish done, I think...

From the production state the operator can choose to start the fill machines either one by one or all at once.. I was thinking of having some bit resetted or setted here..

When making product you have several stop situations I see only one described.

1. Production paus may be initiaded by some downstream condition and if this is the case the line should restart after this condition goes away.

If you are saying that the line should be ABLE to be REstarted, then that is OK.

If, on the other hand, you are saying that the line should restart automatically, BY ITSELF, after the fault is cleared... you are NUTS! That shoud NEVER, NEVER, NEVER, EVER be included in a process where humans are involved!

Can you not see that?


Therefore i have a restart state. Production stop, Controlled Stop i have them gathered in a contr.stopping state and i have a back to back state for product change and so on....

Obviously, we need more clarification as to the nature of your problem/concern.
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Old December 28th, 2008, 01:41 PM   #6
bara_hence
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Ok my bad English makes things unclear i shall try to explain better.

I am designing the program from a URS (User Requierement Specification) that the costumer has made.. In that they have specified three modes wich are:

1. Shutdown
2. Stopped
3. Standby
4. Producing

The shutdown mode is easy everything is off.

The Stopped mode is used when making a long stop for example a weekend in this mode certain zones of the machine is maintaining a temperature setpoint..

The standby mode is used for short stops for example lunch break or equal.. This mode is equialent to the stopped mode just other setpoints.. The use of the word standby is maybe wrong but this is what the costumer wants.. And yes this is the state that should be activated when the machine is powered up if a recipe is still in the memory the recipe is taken away from the memory when the operator chooses the shutdown mode for the machine..

The sequence of a start from the shutdown mode is:
1. Choose recipe
2. Confirm Recipe
3. Start machine (The machine shall start but not make product)
4. The operator can choose to manually start one by one of the "producing" units or choose to go to full production directly.

I was thinking solving the problem this way-->

Shutdown-Standby-Starting Machine-Machine Started

In the machine started state i would allow the operator to start the units manually or by pressing the full production button run a startup sequence in the same state.. Is this a good soulution in your eyes??

From all of the states one could always go to a E-stopping state or a Stopping state and from the costumers wishes when the e-stop or stopping is done the machine should go to the standby state wich means some heaters and fans would start..

About the restart what i meant was the downstream has a buffert wich can become full when that happens the machine should go to paus when the buffert isnt full anymore the machine should restart and of course only if it is in a safe condition to do so.. And thats not so hard becausse to acess the machine one must open a door (there are many) and then the machine would go to the e-stopping state..

I will make a picture to better explain how i was thinking becausse its hard for me describing the hole thing in English..
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Old December 28th, 2008, 02:22 PM   #7
bara_hence
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Ugly draft of a state model for this line..

The init state is the powerupstate and if there is a recipe in the memory the next state would be standby if not a recipe in memory shutdown state..

Maybe there is a few errors with this picture but i think you get the idea..

Any suggestions how to get this better??

Maybe i should add a production starting state and a production running state instead of dealing with this whitin the productionstate (as i stated before when the machine goes from machine starting to production it really doesnt produce product it just dry cykles the operator must choose full production or start the units one by one to produce...)

One of the more experienced programmers at my firm says dont do it with state machines keep it with simple logic.. Maybe this is the way to go Im asking you guys how you would tackle this kind of problem.. Me myself are thinking that it could get very hard to do this without thinking in states..
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File Type: pdf Diagram.pdf (114.9 KB, 35 views)
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Old December 28th, 2008, 08:29 PM   #8
Terry Woods
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Corrupted PDF?

My Adobe Reader 8 says the PDF file is corrupt...
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Old December 28th, 2008, 08:47 PM   #9
Mickey
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Quote:
Originally Posted by Terry Woods View Post
My Adobe Reader 8 says the PDF file is corrupt...
Same for Foxit reader Ver. 3.0
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Last edited by Mickey; December 28th, 2008 at 08:49 PM.
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Old December 29th, 2008, 01:47 AM   #10
ragu29
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star-delta starter

sir,
we are doing a project in plc.....so,if u could help us pls post us the ladder logic diagram for a star-delta starter
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Old December 29th, 2008, 03:25 AM   #11
bara_hence
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Hmm file corrupt thats strange ill try to make a new one later today.. For me the files work in okular a linux pdf viewer but when rebooting to windows i get the same error..
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Old December 29th, 2008, 03:36 AM   #12
bara_hence
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Found the error.. Dia made it an PS file so i converted it.. Now im ready to be yelled at
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