These are master theses.
zova said:
May be it will be interesting for you.
zova, can you explain those pdf files to us?
They are pretty much worthless unless you just need a hint as to what is required to model the system. The are written by students to impress their professors and the professor know nothing more than the students. Most of you that have a winder know more practical information.
The pdf files didn't really get into how to compute the gains given the model. In the past we have done some pole placement where we calculate the gains as a function of the characteristic equation of the system. This can be done symbolically. That is how I do it. Then one has the formulas for changing the gains and feed forwards as the inertia of winder changes. This can be done every loop if necessary.
I like the way the through around terms like H infinity, ooh.
All that **** in the 3 pdf files an it doesn't say how to change the gains as a function of the radius. Purist would say that you really don't know the radius of the rolls. I say that all you need to do is get close enough and the PID can easily conver for errors in the model.
Back to this problem.
The problem with running in torque mode is that the derivative term must be very large relative to what it is in speed mode. This is because the PLC must now do the velocity stabilization which is normally done by the drive in speed mode. The problem is that PLCs are not very good at this relative to drives or motion controllers. The derivative term is basically multiplying the error in velocity between the target and the actual by a gain. We all know how difficult it is to calculate velocities on a PLC with the aid of special hardware. A PLC PID does not have that 'special hardware'. If accurate velocity errors can't be calculated then you can't increase the derivative gain or time constant up as high as required to stabilize the winder. This is the problem. I know this to be true because I got my master degree from the school of hard knocks.
I would get a real motion controller or a drive that has the winder algorithm built in. A PLC is not up to the job on this. PLCs can work in voltage mode when dancers or idle pulleys are used.
Perhaps calculating the gains as a function of radius is in order for a Friday night quiz. We can start from where one of Keith's Friday night quizzes left off. However, I fear there would only be Pandiani and Keith playing. We can use the example from the CTM PID site. It models a DC motor.
http://www.engin.umich.edu/group/ctm/PID/PID.html
And the forum goes OH NO not again!!!??