The most interesting problem of the last two weeks

[Peter Nachtwey]

My intent is to present a Roll-yer-Own Controller that is based on simple Algebraic expressions and explanations.

That sounds interesting. What would you do differently from what is done already?

So far Peter, you have posted formulas that I had already developed. I told you at the beginning that my scheme was to be based on the isosceles triangle. You said that your scheme did so as well. So, we are going down the same path... but maybe, for different purposes.
So, again... I'm still working on it.

Terry, what would you use for the encoder input? An encoder or counter card? What do you do about the delay caused by the back plane? What about the analog output. What is the frequency response of the analog output card. What about the asynchronous sampling? How can you calculate speed when you don't have the I/O updated synchronously with the PLC scan? Keep working on it. I would not even attempt this stand control system using a PLC controlling just two stands.

So how do you tell if an application can be done? I have customers asking me this question all the time as if they want some guarantee the motion controller can cover for all their problems. My usual response is that the motion controller just moves electrons at close the speed of light. However, given proper design and sizing one should be able to predict how well the system will perform.

 

[Terry Woods]

Keith said...
"The original thread indicated 5 METERS between stands..."

If that is what it said in the orignal thread, not any posts in this thread, then, I don't recall seeing that spec.

You gotta know, don't cha(?), that it was truely hard to read that guy's posts. It was hard to glean any details at all while "listening" to all the weird-speak, and seeing the weird video inserts.

I mean, gee whiz... Phil deleted the thread! He didn't just LOCK it, he DELETED it! It was a literal assault on our sensibilities! Even Phil thought so!

So, my point is, I don't recall all of the details. I only know that there were few. And then, with that 100 meter-per-second thing... then I blew it off totally in terms of the particular poster.

But, in general, he did give me an interesting problem to use to explain Roll-yer-Own. And so, in as simplistic a way as I can develop, I'm going to use that problem to explain the general concept behind Roll-yer-Own.

Peter...
As I said, I'm going to use very modest constraints to ensure that there is no critical time limit situations relative to devices that monitor/control the process. Basically, and simply for the sake of describing the process necessary to control this situation, I'm going to push critial device timing issues aside by simply using very modest constraints.

And, by the way, in as much as you did the same, I already conceded that we are going down the same path. However, maybe for different purposes.

The idea is to present, for those that don't know, the Roll-yer-Own Method.

At this point, I'm only interested in presenting the basics of motion control without being subjected to the inherent limiting factors that become very apparent with some devices in time-critical problems.

That is... Here is a set of constraints. The constraints are well within the specs of the particular processor and subordinate devices. Here are the tools that you need to make this work!

Peter said...
"So how do you tell if an application can be done? I have customers asking me this question all the time as if they want some guarantee the motion controller can cover for all their problems."

First of all... those "customers" are poorly educated... whomever they are! I put the quotes around customers because... in too damned many cases... the "customers" are some management pukes that haven't got the slightest clue as to what is really necessary. Of course, those idiots tend to control the expenditures... but they are still idiots!

They are shooting from the hip, and they are shooting in the dark!

It is easy enough to prove, in terms of its' load, whether, or not, a particular PLC processor can handle the particular problem.

You, of course, are interested in selling your control modules. More power to you! However, customers must realize that YOU (Delta) would not be serving your own self-interest to show a potential customer that it is, infact, possible for his particular processor, under its' particular load, to handle a particular problem.

However, if it is proven that the PLC can not handle the problem, within the appropriate margins, then... your controller should be subjected to the same tests that excluded the PLC from being able to handle the problem. If your controller passes those tests, again within the appropriate margins, then you've got (or should have) a customer!

If your module doesn't pass the test, is the customer is asking for Pie-in-the-Sky? Or is that his request is reasonable and your product is simply not upto snuff (or would that be "s'nuff"?).

If the customer is going for Pie-in-the-Sky, then maybe he simply needs to be reined in and made aware of the Laws of Physics. If not, then your product needs to be updated.

That's simply the way it is - one way or the other. But then, in reality, if you find a customer asking for something within the Laws of Physics and yet beyond what your product can provide, your "canned answer" to that customer is... You are asking for Pie-in-the-Sky! Of course, at that point, the customer's expectation is Pie-in-the-Sky only with respect to your product.

If you are the absolute leader in that field then the customer is stuck.
If you are not... then the customer has options. Sure, there are cost issues for the customer... but then, that is for the customer to decide.

I can very easily see that it doesn't take much to prove whether or not your control module can work, or not. In the world of PLCs, it's all, and only, a matter of process, processor, and subordinate device, timing issues.

But then, in the final analysis... it all really depends on how your control module is programmed by... you, or the local-Rep, or the local Integrator (yuk*) or the local on-site guy!

(yuk*) The local Integrator is typically like a night-bomber... in-and-out... job done, gone and forgotten. I KNOW... I'VE DONE IT! And I've HATED MYSELF for doing so! So don't try to snow me on that ****.

The real key is the on-site guy. He is there, he has to live with it. He sees what is going on from day-to-day. What does he know? How capable is he in terms of your product? How capable is he in terms of... generally speaking, process control and process development?

If YOU (Peter, or one of your guys) doesn't do the right thing in terms of the real process issues (rather than that damned "good-enough" deal) then... how well is the customer and his problem really served?

Enough... I think I made my point... and then... more than enough!

 

[allscott]

"It is better to be thought an idiot than to open ones mouth and remove any doubt"

Author, anonymous

Terry, you should learn to keep your mouth shut when you don't know what you are talking about!!

I agree that the original post on this topic was obscene. I too was confused and disgusted with the path that thread went down.

TWcontrols, yes I have worked in steel and pipe mills for many years.

I understand that you may not remember the original post, but if you READ Peter's original post you would realize we are talking 5M not 36".

Terry, you should know the difference between a PLC and a dedicated motion controller. For those of you that don't know the main difference is;

In a PLC, the scan time is variable depending on the size of the program and the amount of I/O

In a motion controller the scan time is fixed. The amount of I/O and the size of the program is limited to the constraints that the processor has to update the I/O in the set amount of time.

I have personally used Peter's product on numerous applications. This product is not meant to be a substitute for a PLC. I have actually phoned Delta because I thought that their product was suitable for an application I was working on, only to be told "You would be better of doing this in your PLC", or "This is an application for a servo drive, here are some of the leaders in that field"

There are several way that you can use hydraulic motion control; You can go to Bosch/Rexroth, Vickers, or Parker. Terry, I can guarantee you that you will be Flippin mad if you ever had to deal with one of these systems. However, if the system was a Delta you would be right at home. I say this as a fellow "floor guy"

I met Peter at a training seminar. Other than that I have no affiliation with Delta Computer Sytems.

Back to the original thread, If anyone actually wants to know how the drive control works in a "real" steel or pipe mill, let me know and I will post.

 

[Peter Nachtwey]

Back to theo riginal question

Back to the original thread, If anyone actually wants to know how the drive control works in a "real" steel or pipe mill, let me know and I will post.

This would be good to know. It has been about since I was involved with anything that had to do with stands and maintaining the relative speeds. At that time PLCs where not used. Everything was controlled by specialized equipment. My part was very small in this area. I was only involved with what was called 'loopers' which were hydraulic actuators that pushed the hump or bow up. The hydraulic actuators feed their position back to the drives which used this information to tell if if the down stream stand had to go faster. One trick that has not been mentioned is that all the down stream stands had to be adjusted by the same amount.

Allscott, I would like to know how your mill controlled the speed between the stands. Speficially:
1. Was there a dedicated controller that controlled the relative speed.
2. How fast did it update?
3. How fast the material go and how big was the bow between the stand.
4. One installation started running steel before the loops were on-line. The steel must be able to tolerate a little stretching and bunching. Much more than the 4-5 mm I calculated.
5. What else do you think was important?
6. When did this happen. Technology changes.
7. Would you use a control logix WITHOUT motion controllers to control 5 to 7 stands?

 

[TimWilborne]

Ok I'm going to jump back on this thread for one more post to try to get this back to Peters origional question. Believe me or don't believe me, I don't care

Is the hump that critical? Not to the extent that it is being taken here but it never hurts to shoot for perfection
Will it be dependent on temperature? Yes
Can it be done with Controllogix? Yes
Has it been done with Controllogix? Yes
Can I give more information? Sorry but no

 

[allscott]

This would be good to know. It has been about since I was involved with anything that had to do with stands and maintaining the relative speeds. At that time PLCs where not used. Everything was controlled by specialized equipment. My part was very small in this area. I was only involved with what was called 'loopers' which were hydraulic actuators that pushed the hump or bow up. The hydraulic actuators feed their position back to the drives which used this information to tell if if the down stream stand had to go faster. One trick that has not been mentioned is that all the down stream stands had to be adjusted by the same amount.

Allscott, I would like to know how your mill controlled the speed between the stands. Speficially:
1. Was there a dedicated controller that controlled the relative speed.
2. How fast did it update?
3. How fast the material go and how big was the bow between the stand.
4. One installation started running steel before the loops were on-line. The steel must be able to tolerate a little stretching and bunching. Much more than the 4-5 mm I calculated.
5. What else do you think was important?
6. When did this happen. Technology changes.
7. Would you use a control logix WITHOUT motion controllers to control 5 to 7 stands?

I crafted what I thought was an intelligent response for this for 3 days.

When I was ready to post I realized that I had crossed the line of my confidentiality agreement. My previous employer is in the process of suing me, I don't need fuel for the fire.

Mr. Woods. I have rejoined the group but have decided to never post in the same topic that you have posted in for 2 reasons;

#1. I don't want to fight.

#2. I have spent many hours reading your previous posts. It is quite obvious that you are a talented (if somewhat mad) genious. I know that I could not offer any advice superior to what you have given on a particular subject. That's not a joke it's my honest opinion.

SO WHY DID I DECIDE TO REPLY TODAY OF ALL DAY'S;

I'm frustrated. I quit my job because of a safety concern out of a mechanical failure. 9000psi of water exploding out of a 7" piece of pipe sending steel through the roof of our facility was enough for me. Management didn't want to re-engineer the machine properly. I just happened to witness it. On my way home from the plant that day I told my wife "I'm done". I resigned the next day. I figured I was of better use to my family unemployed than dead.

Now everyone who has ever quit a job will tell you that you are supposed to find another job before quitting.

However, I live in ALBERTA CANADA, the land of endless opportunity.

For those of you that don't know. Alberta has the largest oil reserves in the world outside of Saudi Arabia. Canada, particularily Alberta, is seen as a "stable" country and is seen to the world as a reliable source of oil for the next century.

As a result, the economic activity in Alberta is ridiculous. I have lived in my home for exactly 1 year. The value of it has gone up by 40%.

So you would think that I wouldn't have any problem finding a job, me neither. The province is screaming for "qualified trades people" However as an Electrical Tecchnologist (not an electrician) I CAN'T FIND A JOB.

I am one of those Jack of all trades master of none. I come here becasue one of my "trades" is PLC programming. I'm pretty good at it but definately not a master, I learn a lot here.

I am also a "jack" at; control system design, motor controls, electronics, distribution design, control panel design and wiring, DCS, PC's, personnel management, running a backhoe/bobcat, driving a grain truck, parenting, wiring your house etc.......

DON'T CRY FOR ME ARGENTIA. I am sure that my biggest deficiency is effectively finding a job.

SO IF ANYONE IN CENTRAL ALBERTA IS LOOKING FOR SOMEONE LIKE ME PLEASE REPLY, if you know of any good lawyers close looking to fight "the man" let me know.