Re: Freqmod test result & Q

[rehenry-at-up.net]

Chris

Hey thanks for the scope report.  This kind of stuff is great info. You
might build a little r/c network to connect to the step or clock pin and
you could get a curve trace of voltage based on the frequency.  This
would give you some sort of parallel graph with the stuff you can graph
from within the PC.

Now you did it.  I wrote the pantograph example as a thought experiment
or explanation and you want to prove it can't be done.  Any electrical
system will fall a bit short of the mechanical.  My last exposure to the
calculus was in the 60's so you are without a doubt way ahead of me with
the maths behind these things.  When you get if figured out, you can
explain to me how this stuff like ff0 works.  Gain of 0 may be a problem
but you might try what you are with a gain of 1.  Otherwise my thoughts
are below.

High gain. 1000 as shipped may be okay but you could up it some.

High acceleration.  I sent off an ini for a rotary axis the other day
with accel set to 150 and it seems to work okay.  You will need to set
deadband even with nothing out there so you don't get hunting between
adjacent steps.  Give yourself a bit more than half the distance between
steps for this and you should be fine.

When you get to the amps and motors for this, you will need to oversize
these components so that you get the quick response from motors driving
a mass.

Hope this helps.  Get back with your results.

Ray
 
> Greetings,
> 
> I'm running a test setup (o'scope on the port pins) on a SuSE8.0 base
> system with rtai-24.1.9 and freqmod.  I'm working to get an open-loop
> (no encoders for now) stepper configuration running. (If I get a good
> setup I'll do a fresh install and post the proceedure)
> 
> I see two primary types of "jitter" on the step clocks. 1) The time
> quantization for the [task] section "period" variable.  This is an
> expected effect in a digital timing generator.  2) Some jitter about
> the task_period, presumably due to interrupt latency variation.  I have
> not run motors yet, so I'm just commenting about what I see on the
> scope.  Both of these effects should also be present to some degree in a
> steppermod configuration.
> 
> Since I have no encoders, I want the control-loops to run like the
> pantograph example in the handbook. I sort-of expected to get this
> behavior in freqmod by setting P=I=D=Zero, Position-FF gain=1, other
> FF's zero. As others have reported to the list, emc does not seem to
> like P=0.
> 
> My question, ideally should P=I=D=0, PosFF=1,VelFF=AccFF=0
> provide the pantograph-like behavior?
> 
> -- 
> Recreational Calculus - Just For Fun!
> 
> Chris Wagner
> clwagner-at-eecs.wsu.edu
> 
> 


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