Re: Constant Velocity unwinder

Thanks Graham,
I have been going through this solution, I have built some op amp
circuits in the past, including P, I, D, as well as summing
amplificators, I even built a freq to voltage converter in college way
back.
I found this page, it pretty much sums up everything you and mariss said:
http://www.ecircuitcenter.com/Circuits/op_pid/op_pid.htm
Just Trying to figure out what value resistors and caps I need for my
application.
Best Regards
Fernando

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler" <eexgs@...>
wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Fernando" <fer_mayrl@> wrote:
> >
> > Thanks Mariss,
> > Not that proficient in electronics, but I will look into it.
> > I will let you know.
> > Regards and thanks a lot
> > Fernando.
>
> Mariss used the word node which makes it sound worse than it is :)
>
> "Form a summing node of the tach feedback (- voltage)
> with a velocity command (+ voltage)"
>
> just means stick the voltage from the tach and the voltage from a pot
> you will use to set the speed into a op-amp summing amplifier.
> Because the voltages are different signs the output of the op-amp will
> only be zero when they are both exactly the same otherwise it will be
> outputing a voltage to tell the VFD to do something. The P part is
> just the gain of that amplifier and the I and D are obtained by adding
> some capacitors etc, I gets rid of the steady state error and D
> responds to the dynamics (I doubt you need D).
>
> I have done something quite similar to this recently except it was PI
> not PID and I am trying to maintain tension in EDM wire rather than
> speed but the principle is the same. My circuit is breadboarded up
> and working, I can try and find the schematics if I produced any. It
> was driving a DC motor directly (well via a transister) but you could
> drive the 0-10v control on the VFD with no problems. You could also
> find a frequency to voltage converter circuit on the web to convert
> and encoder to a voltage if you fancied a non contact feedback method.
>
> Unlike a typical servo system you need no reversal of direction and as
> you seem to be countering the effects of spool size I suspect that the
> system does not need to have particularly good dynamic response etc so
> it should be fairly non critical.
>
> Graham
>