Peter Nachtwey
Member
This is meant for those that have been through college and know how to use Laplace transforms and differential equations.
I am making a series of YouTube videos. They will not be flashy but they will be very informative about closed loop control. The reason why I am making these videos is that I have many decades of experience at supporting customers with many different types of application. I am basically self taught. I had to learn because others wouldn't. I just wanted to sell motion controllers.
I have been very dissatisfied with books written by professors that repeat the same old examples using the same old techniques trying to do almost useless stuff like root locus and other things that prove a system is stable. In real life that isn't good enough. Customers want a system that just isn't stable, they want responses that are perfect. This means that about 90% of a control text book is useless.
The other part about control books that I don't like is that they involve a lot of matrix math. Matrix math is good in some places but it is generally USELESS in a motion controller because a motion controller must be doing motion control not indexing through arrays. The other thing I don't like about matrix math is that the parameters are generally put into the matrix math blender and just become a number in an element or two. This does not lead to understanding of what and how parameters affect the response. I prefer symbolic math. I can see what parameters affect the response and how. It is no wonder people graduate from college knowing only what the definition for P, I and D gains but NOT what they are really doing which is placing closed loop poles.
Basically, I have a extreme contempt for most universities and colleges. Most do not have professors that really know any more than what someone wrote in a book before them. They cheat their students by wasting their time on 90% of useless information that I have never used in all my 33+ years of doing motion control software. There are a few good professors out there but not enough.
Have you ever looked at a control book and noticed that there are a lot of problems where you are given Laplace transform transfer functions? Where do they come from? All that stuff you learn is useless UNTIL you can generate your own open loop transfer function. Mechanical engineers should be able to provide the transfer functions to the control engineer, if they really designed instead of evolved or kludge the design, but they don't so I had to learn myself.
In my NOT SO HUMBLE opinion there are two things that are important.
1 System identification. If you don't know what you are controlling you can only guess and tweak gains.
2. Pole placement. Giver the open loop transfer function from the system identification you can place the poles where you will get the desired response. The controller gains can then calculated from the desired closed loop pole locations and the open loop transfer function.
This is for very advanced control
3. Model based control. This is a more advanced topic and isn't available on PLCs but it can make a huge difference in performance.
All the rest except Bode and Pole Zero plots are just distractions.
If you have got this far and are still interested then go to YouTube and search for Peter Ponders PID or my name. I will add more videos. I plan to cover how to control many different type of plants and control methods, not just PID. If you go to my channel you will see the video with the most views is the Sliding Mode Control video with Smith Predictor for controlling a temperature system with a second order plus dead time plant.
Edit, a current thread is asking what is the affect of scan time. I will make a video on that too.
I am making a series of YouTube videos. They will not be flashy but they will be very informative about closed loop control. The reason why I am making these videos is that I have many decades of experience at supporting customers with many different types of application. I am basically self taught. I had to learn because others wouldn't. I just wanted to sell motion controllers.
I have been very dissatisfied with books written by professors that repeat the same old examples using the same old techniques trying to do almost useless stuff like root locus and other things that prove a system is stable. In real life that isn't good enough. Customers want a system that just isn't stable, they want responses that are perfect. This means that about 90% of a control text book is useless.
The other part about control books that I don't like is that they involve a lot of matrix math. Matrix math is good in some places but it is generally USELESS in a motion controller because a motion controller must be doing motion control not indexing through arrays. The other thing I don't like about matrix math is that the parameters are generally put into the matrix math blender and just become a number in an element or two. This does not lead to understanding of what and how parameters affect the response. I prefer symbolic math. I can see what parameters affect the response and how. It is no wonder people graduate from college knowing only what the definition for P, I and D gains but NOT what they are really doing which is placing closed loop poles.
Basically, I have a extreme contempt for most universities and colleges. Most do not have professors that really know any more than what someone wrote in a book before them. They cheat their students by wasting their time on 90% of useless information that I have never used in all my 33+ years of doing motion control software. There are a few good professors out there but not enough.
Have you ever looked at a control book and noticed that there are a lot of problems where you are given Laplace transform transfer functions? Where do they come from? All that stuff you learn is useless UNTIL you can generate your own open loop transfer function. Mechanical engineers should be able to provide the transfer functions to the control engineer, if they really designed instead of evolved or kludge the design, but they don't so I had to learn myself.
In my NOT SO HUMBLE opinion there are two things that are important.
1 System identification. If you don't know what you are controlling you can only guess and tweak gains.
2. Pole placement. Giver the open loop transfer function from the system identification you can place the poles where you will get the desired response. The controller gains can then calculated from the desired closed loop pole locations and the open loop transfer function.
This is for very advanced control
3. Model based control. This is a more advanced topic and isn't available on PLCs but it can make a huge difference in performance.
All the rest except Bode and Pole Zero plots are just distractions.
If you have got this far and are still interested then go to YouTube and search for Peter Ponders PID or my name. I will add more videos. I plan to cover how to control many different type of plants and control methods, not just PID. If you go to my channel you will see the video with the most views is the Sliding Mode Control video with Smith Predictor for controlling a temperature system with a second order plus dead time plant.
Edit, a current thread is asking what is the affect of scan time. I will make a video on that too.