Re: [CAD_CAM_EDM_DRO] Re: Re: Re: GeckoDrives.. Can anyone Help?

Jon,

I am using the 320'a and 340's. My application does do very slight tapers,
and when I had it set up for 2 steps /thousanth of an inch, you could see
when the moves were being made. So, I re-wrote the control to make 10 steps
/thousanth of an inch, and then you could not see the steps with your eyes
enough to be a problem. Of course, this slowed the whole thing down quite a
bit, and I had to optomise other things to get the speed back up some.
Tom Eldredge, Trustee

----- Original Message -----
From: Jon Elson <jmelson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, March 19, 2001 4:21 PM
Subject: Re: [CAD_CAM_EDM_DRO] Re: Re: Re: GeckoDrives.. Can anyone Help?


>
>
> Tom Eldredge wrote:
>
> > Gentlemen,
> >
> > Could we step/direction guys bridge this gap with Marris' help? Let me
make
> > a suggestion:
> >
> > Could we not make a hardware (IC based) adapter which included an
enocder
> > driven counter, a hardware comparator, and another hardware counter
driven
> > by our step /direction signals, and then a D/A converter driven by the
> > hardware comparator,
>
> As far as I know, this is exactly what the Gecko Drive G320 and G340 do.
>
> > which would then drive one of Marris' upcoming +_
> > servo amps? Would we not be thus able to provide the P, and he provide
the
> > I, D, and the actual amplifier to drive the servo motor?
> >
> > I have already emailed Marris with this idea. I suppose I should have
put
> > the whole thing on this forum rather than bother him, but after I
emailed
> > him, I thought others might have some good ideas related to this.
> >
> > It does not seem as though the hardware for the P of the PID would be
much
> > to come up with, and maybe it would provide another compromise helping
us to
> > get closer to the true velocity control desired in some applications.
>
> I can't see why you would not use the G320 or G340 for your application.
>
> > I probably do not see the big picture, but I thought I'd ask.
>
> OK, I guess the big picture is that as long as step pulses are coming out
of
> the computer, then the motion is in the form of discrete positions. If
you make
> the resolution of these discrete positions extremely small, then the
quantization
> should be small enough for any particular application, but then the
computer
> has to output step pulses at an incredible rate to get a decent rapid feed
rate.
> The advantage to a true velocity servo, straight from the computer, is
that
> the VELOCITY is not quantized by the resolution. So, at very slow speeds,
> the motion remains smooth. My velocity servo remains smooth down to .01
> IPM, at which point the stick slip friction takes over. This is at a rate
of
> 3.3 encoder counts/second on my system (20,000 counts/inch). With a
> pseudo-servo system, step pulses would come out at a rate of 3.3 per
second,
> and the machine would most likely move in discrete steps.
>
> This becomes most important in things like cutting very slight tapers on
> a lathe, or cutting angles that are very nearly parallel to a machine axis
on
> the milling machine. It also shows up in interpolating circles,
especially of
> larger diameter. 4 times in the full circle, one axis slows down to zero
speed
> and then reverses, moving very slowly at first.
>
> Jon
>
>
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