General Motors project requirement interpretation

[rootboy]

Cool. So what are they trying to say?
And I agree the OP is much better off talking directly with his GM contact.

Keith

Simply put, he has to if he wants to have any chance of being anywhere near compliant.

What I forgot to mention is that he will also want to get his GM contact to get him an account on Supply Power. This is where he will be able to download the resources that he will need to do the job.

The first one can be very, very, hard on the contractor. But from then on it should get easier than a normal project would be.

As for how we program things, it's ladder logic, that follows a "sequencer like" (in the case of process equipment, conveyors is different) format. In both cases the program is broken up into sub-programs for each device. A device being defined (but not limited to) as a stop, a VFD, an ASH house, a robot cell, etc.

Equipment like process equipment (ASH houses, RTOs, Carrier Cleaners, etc) will start and stop using a sequencer.

And keep in mind what may apply to one GM site might not apply to another. This is mostly due to when the equipment was installed (which would define which version of the specs were used). Some of our very old conveyors have no resemblance to our modern ones from a hardware or software perspective.

He will have to follow the blockpoint for the plant, this sets what versions of software, etc that will need to be followed.

So if the OP is adding on to an existing piece of equipment, then it might be best to follow the local requirements (the best advice is to follow the direction of the guy who holds the purse strings ;> )

Powertrain does things differently, including using Siemens PLCs. I've got no idea as to how those are programmed.

 

[kamenges]

Thanks, rootboy. I am currently in an industry segment that doesn't directly interface with the auto industry but that doesn't mean at some point I won't run across this stuff.

[RANT]
So I ask again, why would they use an acronym like SFC in their spec if they don't want an upper level graphical control construct? While "SFC" is not a strictly defined language and can certainly be used as a concept only, its reference would certainly would be interpreted as the graphical representation by the majority of individuals looking at the spec. They would be far better off referencing their own internal specs than something that could be confused as what it isn't. [/RANT]

Keith

 

[danatomega]

If you looked at the site I referenced:

You would have read:

This part of IEC 61131 specifies the syntax and semantics of a unified suite of programming languages for programmable controllers (PCs). These consist of two textual languages, IL (Instruction List) and ST (Structured Text), and two graphical languages, LD (Ladder Diagram) and FBD (Function Block Diagram). Sequential Function Chart (SFC) elements are defined for structuring the internal organization of programmable controller programs and function blocks.
​

And you would have noticed some semantic issues such as their reference to a 'PC'. Since 1984, a PC generally indicated a Personal Computer - a Programmable Logic Controller was a PLC. So, yes, they were taking some liberties with their terminology where they sort of mention SPC as an aside.

 

[flash053069]

Question for Steve

Write ladder logic for a simple sequence according to your interpretation of the spec and submit it to the person who will have to sign off on your program. Get that person to acknowledge that your sample would be in compliance. Any of the LogixPro exercises that pop up here from time to time would probably be good examples.

Steve,
I know I'm a little late for this discussion. However, reading through it sparked my interest in your statement. I am not familiar with SFC with me being relatively new to programming. It sounds like SFC was a program that simply says do this next. Would the elevator simulation where you use the JSR's sequentially be the same thing as SFC just in Ladder logic form?
Jim

 

[Steve Bailey]

My comment was intended as generic advice. When confronted with a spec that involves programming style, submit a sample of code that you think complies with the spec and get the customer to agree up front that your submission is in compliance.

 

[Zes]

I think they mean using LAD for state machine programming. If you have the CX-Programmer software I can upload project I've made for Nissan (NMGR) some time ago. It was not "Logic shall be developed in SFC fashion" requirement for software but it's "Poka Yoke" system and it has few sequenced stages for parts checking, so I think this method was suitable for the task. Actually the code quality not so good cause I was finishing project in rush but you'll can get the idea conception.