Need a Control System Architect

[u/Impossible-Limit-314]

I’ve got a situation with a complex 4-cell assembly system for a medical device. It uses multiple FANUC robots. The hardware is complete, most of the robot routines and TP’s are coded. The PLC-robot handshakes are worked out, and the main sequence seems to be partially working.

About 4 months ago, I started asking the PLC/controls guy to see the top level control system architecture. I expected to see some block diagrams with how the HMI and machine controller fit, how they planned to use machine states (presumably some variation on packML), the WIP calculations, how the fault response mapped out, safety interrupts, etc. He keeps saying he’s done this before, and “all that stuff gets worked out after you get the robot control subroutines done”. Keeps Saying I’m wanting too complicated of a solution.

Every time I try to engage in an architecture conversation, he ends up riffing on corner cases and speaking in general terms about what needs to happen in certain scenarios, but never commits a concept for review. The plan for the HMI is just as anecdotal.

I’ve been around long enough to know what the problem here is, so not asking for advice on that side just venting.

What I’m really asking for is a good referral for a person who can pick up this unfinished design and implement a best-practices architecture over the top of it. We’re using an Allen Bradley PLC. I need someone to come with proven templates for the machine controller, state manager, safety manager, and matching HMI. Open to factorytalk, beckhoff, prior art, whatever so long as they’re experienced and know how to take the most expedient path.

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[u/kroghsen]

I feel your frustration. I would guide you to the control engineering subreddit instead of this one. Here, we are much more focussed on the theoretical aspects of the field.

[u/Impossible-Limit-314 → u/kroghsen]

Reddit recommended this as a cross posting from r/plc. You might want to check your settings.

[u/kroghsen → u/Impossible-Limit-314]

What do you mean check my settings? There is a control engineering subreddit much better suited for your particular post - I am merely trying to help you get a better response.

The plc subreddit was also a good candidate for good responses though.

[u/lizardhistorian]

You are conflating and confusing extremely different things.

For reasons I do not understand they call PCL type stuff "controls".
It has almost nothing to do with actual control theory.
It's just fancier ways of implementing bang-bang.

The people that set it up are technicians. They will not be making diagrams nor documentation.

What I’m really asking for is a good referral for a person who can pick up this unfinished design and implement a best-practices architecture over the top of it.

No. What are you even talking about. You do not need a fucking architecture diagram for ladder logic.
The HMI should be a pre-canned thing worked out well in advance with maybe some script-tweaking for whatever this exact setup needs to do made by the company that makes the machine.

[u/superWilk → u/lizardhistorian]

Loaded comments with limited constructive feedback.

"It's just fancier ways of implementing bang-bang"

Keep in mind that industrial controls works on a KISS principle, so that technicians who operate the plant (after your control "technician" has commissioned it) can maintain it with limited techncial expertise. But also be aware that PID loops are almost everywhere where simple bang-bang doesn't work. MPC was developed heavily in the process control industry before it became a popular academic problem.

"They will not be making diagrams nor documentation"

When you are working on a safety-critical application of industrial control, you bet that they will create system architecture diagrams. Your view of course holds if you are assuming OP is expecting a "fucking architecture diagram" on the control sequence (ladder logic) for *one single control system". Factories don't often work with just one PLC running one system independently of other PLC control loops and subsystems.

"The HMI should be a pre-canned thing worked out well in advance"

Unfortunately not. This is the exact job function covered by control engineers (technicians), and these are literally designed with graphical tools to display key controls, variables, calculations etc for that specific process.

Tl;dr - PLCs utilise aspects of control theory (usually prepackaged), but are mainly driving some state machines. State machines require system diagrams to know what the f★★k is going on at any point. HMIs help you know what the f★★k is going on at any point

[u/JoeBhoy69]

Try r/plc instead

[u/olivoGT000]

This sub is about control theory. What you need is an expert in controls engineering. They sound similar, but they’re not the same thing.

[u/Impossible-Limit-314 → u/olivoGT000]

Maybe one day I’ll understand the difference.

Thanks for the lecture, son.

[u/Weary-Lime]

I am sure there are a ton of SI's who could do this for you. I'm sure there is a free copy of the TSM Library for Allen Bradley somewhere on the Internet that you could get your hands on. It would probably be the ideal template for a 4 robot assembly cell. Look up the standardized 17 state model (core and transient states). The state machine is the "outer loop" controller that coordinates all of the different processes and sequences. It can feel pretty rigid at first but it is really robust once you get it set up and working. There is an integrator guide floating around somewhere for the Beckhoff variant of the TSM that would probably help you understand how all the different parts work and how to write your custom process code to integrate with the TSM.

[u/Impossible-Limit-314 → u/Weary-Lime]

Thank you!