Advanced Control. Off topic poll.

On my home planet this was standard High School curriculum.

But I skipped that day, so I am only vaguely familiar with them.

IMPO this is something required to keep a number of college professors employed, thinking back to all the 'critically needed' information taught this is only 1 of many things that are never used after graduation.
 
Good question

I'm curious about the reason for the original question.

I visit Chinese hydraulic servo forum a lot. Actually, I am the servo control section moderator. This is because we are trying to sell our products in China. I want to educate people on the difference in the ability to control hydraulic systems with different control algorithms like P only, PI, PD, PID, PID2 with or without feed forwards. I am trying to convince people that P only control has a poor ( slow ) response because it is limited by the time constant which is a function of the natural frequency and damping factor.

The problem is that no one seems to understand Laplace transforms. Not even the professors. I don't think they teach Laplace transforms to those getting a degree in hydraulics in China. In short, no one knows what I am talking about even if I explain in Chinese.

What I would like to do is find one or two people that understand Laplace transforms well enough to discuss a simple but real example of a proportional only control for a hydraulic cylinder. I don't know if I should do it here ( this isn't the right forum for this topic ) , on eng-tips.com or my own forum.deltamotion.com

What I need is to have an intelligent conversation about these different control methods for hydraulic cylinders. I would then go to the Chinese website and post links to our discussion. We all have computer translators now that can do a half way decent version.

BTW, we have a person in the EU now. Sometimes he finds people there that don't much beyond P or PI control. It is like trying to sell an Audi over a VW. They both have an engine, four wheels, and an engine so what is the difference? In the eyes of the unknowning, none.

Anyway, I want to know if there is someone that understands this:
http://deltamotion.com/peter/Mathcad/Mathcad - T1C1 P Only Laplace.pdf

The first page shows how Laplace transforms can be used to model a closed loop system and determine the actual and desired characteristic equation.
 
Most people aren't interested in the cumbersome maths associated with control theory, no matter how relevant or what result it may have on equipment. You want to sell PI over P? Don't even show them modelled step responses. Build a demo, put them side by side and trend all the system variables. Show them the difference.

Like most people have said, I studied this stuff in Uni. Most of the intricacies have long gone, but I KNOW at least the type of characteristics offered by P, PI and PID control. The only time I ever use this stuff is when my mechanical guys use a servo motor that's too small, hasn't got enough inertia, or modify the assembly so much that the latter become horrendously mismatched. Everything else works straight out of the box.


And if you really want to sell something, put blue LEDs in it :ROFLMAO:
 
And if you really want to sell something, put blue LEDs in it :ROFLMAO:


gwpZYOI.png
 
If this pretty enough? Green on blue? People tend to like green for good and red for bad. Bugs might like that blue light.


Seriously, someone must know this stuff to provide the tools that all of you use.

Look at the video. This system is designed this way on purpose. It is meant to be impossible to tune using a P, PI, PID or even a HYD02, M02AS or RMC100. The last 3 use PIDs with velocity and acceleration feed forwards.
Norm can tell you that a system with a 6.5Hz natural frequency and a damping factor of 0.15 is close to controlling a slinky.
http://deltamotion.com/peter/Videos/NF-FOA.mp4
Notice that I can tune this system up in a minute or two.

I am stuck, not because I don't know but because no one knows if I am right or wrong. I was hoping there would be one person here that knows the difference.


I can't get the image to show :(
 
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I like this video. I have seen the Slinky oscillating like that many times. Sometimes I say it’s like playing billiards with a rope.

The green trace is the signal to the valve. Looking at what the valve is doing when controlled by the 2nd order controller is what Peter means when he says the valve is really working. You need a fast valve to make this work.
 
As to your original question, I understand Laplace transforms.
You've stated your goals as:
we are trying to sell our products in China.
I want to educate people on the difference in the ability to control hydraulic systems with different control algorithms like P only, PI, PD, PID, PID2 with or without feed forwards.
I am trying to convince people that P only control has a poor ( slow ) response because it is limited by the time constant which is a function of the natural frequency and damping factor.
Based on your past posts and youtube videos, you seem personally interested in educating people. However, if your company's goal is to sell controllers, you need to take your engineer hat off, and put on your salesman hat. You need to sell the features of controller and what is does, and what it does better than other controllers. Explain how customers can design less expensive systems by using smaller hydraulic system that are controllable by your controller. Controls should be given in more layman's terms. Talk about how the hydraulics acts like a very stiff spring, but less stiff as hydraulic shafts are smaller, rather than time constants. Your demo video in the previous post is good, but needs to have the rough edges and aside comments removed if used for a sales video.

Remember, you are one of the exceptions. Most 'engineers' do not use higher math. Many didn't really understand it when they took the classes, and the soon forget it after graduation. You are not selling to engineers like yourself, you are selling to project managers, that may or may not have a engineering degrees. There are few people that do 'real engineering' that appreciate the math behind your controller. I concur with your conclusion.
The problem is that no one seems to understand Laplace transforms.
Most don't even want to understand.
 
It was taught in one of the required course in our Chem E program. I re-learned it when I studied for the PE exam. Now I lost it again... along with most of my mind.
 
Never formally learned them... Hell, I've only self-studied calculus. But I've glossed over the subject and seen it. I only have Associate Degrees. Working on the 4 year right now. I actually have to take calc 1 this spring. Looks interesting though.
 
I'm another person who was exposed to Laplace Transforms in college but never had the need to apply them in my subsequent career.
I remember Laplace transforms described as a tool to make it easier to solve differential equations by transforming them to an algebraic form. Similar to the use of logarithms to transform the process of raising to a power to one of multiplication and transforming the process of taking a root to one of division.
The availability of inexpensive calculators has rendered the logarithmic tables obsolete at least as far as for calculating powers and roots. Have subsequent techniques in digital technology done the same for Laplace transforms as a tool for solving differential equations?
 
As to your original question, I understand Laplace transforms.
You've stated your goals as:

Based on your past posts and youtube videos, you seem personally interested in educating people. However, if your company's goal is to sell controllers, you need to take your engineer hat off, and put on your salesman hat. You need to sell the features of controller and what is does, and what it does better than other controllers. Explain how customers can design less expensive systems by using smaller hydraulic system that are controllable by your controller. Controls should be given in more layman's terms. Talk about how the hydraulics acts like a very stiff spring, but less stiff as hydraulic shafts are smaller, rather than time constants. Your demo video in the previous post is good, but needs to have the rough edges and aside comments removed if used for a sales video.

Remember, you are one of the exceptions. Most 'engineers' do not use higher math. Many didn't really understand it when they took the classes, and the soon forget it after graduation. You are not selling to engineers like yourself, you are selling to project managers, that may or may not have a engineering degrees. There are few people that do 'real engineering' that appreciate the math behind your controller. I concur with your conclusion.

Most don't even want to understand.


I agree with everything that proof said, except that I'm part of the masses that learned and then forgot. I'd like to believe that I understood Laplace at the time, but it just hasn't been necessary at any point in my career.
 
I understand them a nice bit. I just got my first introduction to control theory. Now I want to begin self studying as I won't take that class for another year and a half.
 
As to your original question, I understand Laplace transforms.
You've stated your goals as:

Based on your past posts and youtube videos, you seem personally interested in educating people.
However, if your company's goal is to sell controllers, you need to take your engineer hat off, and put on your salesman hat. You need to sell the features of controller and what is does, and what it does better than other controllers.
This is why I need to find someone that can verify the calculations in the pdf I posted above. Salesmen lie whenever their mouth is moving. Especially in China. I can provide irrefutable proof but no one understands it.

Do you understand what is in my pdf? ALl the math is there. No steps are skipped.

BTW, the valve I use in the video is a fairly good Bosch valve. 4WRPEH6. Norm sells these. Also, many of you have been to our training classes. The system in the video is now part of our advanced training class.
 
Looking at this and making sense of it, the first thing I ask myself is this:

What is Kp, what is Gc(s) and Ga(s) .

What is ζ⋅

I guess what I'm looking at, not being familiar with these exact equations, is what are these variables representing so that I can start making sense of the relationships between the numbers. They may be standard, but it could be useful to include them at the beginning of this document.
 
Kp is the proportional gain
Gc(s) is the Laplace formula for the controller which consists only of the proportional gain.
Ga(s) is the Laplace transform for the open loop transfer function for the hydraulic actuator. This is fairly standard way of approximating a hydraulic actuator with a Laplace transform.
ζ is the damping factor.
Gc(s) and Ga(s) must be combined to get the closed loop transfer function that will determine what the response changes in position setpoints will be.
 
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