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

Jon Elson,

Thanks for clarifying yesterday's email. So the tach is the real missing
link.

Understanding what you do about this situation and the Gecko drives, do you
think Mariss could add tach feedback to his amps also? If he, say for
example, added DC tach feedback from the motor to the G340 amp, would we
then be able to say we have true velocity control? Would this configuration
completely bridge the gap?

It seems I remember Mariss saying something about making a velocity drive
sometime in the future. I wonder if this is what he is thinking of. I am
going to do a search on his emails to see if my memory is showing its
weakness again.

I was under the impression that the multiplier on the G340 drives only
allowed one to use the higher count encoders found in retrofit situations.
It does not do anything for us in the way of smoothing out the motion does
it?

Thanks again for your valuable help, Jon.

Tom Eldredge

----- Original Message -----
From: Jon Elson <jmelson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, March 20, 2001 2:36 PM
Subject: Re: [CAD_CAM_EDM_DRO] Re: Re: Re: GeckoDrives.. Can anyone Help?


>
>
> Tom Eldredge wrote:
>
> > As I understand it, the Gecko drives partially bridge the gap between
> > step/dir and servos, but do not give the velocity control that true
servo
> > systems provide.
> >
> > It seems as though in order to get true velocity control, the encoder
> > feedback needs to reach the control earlier in the processing stage.
>
> No, the encoder is not enough. As I gave in an example yesterday,
> I have 20000 encoder counts/inch, and can go down to .01 IPM
> before the stick-slip friction becomes dominant. This is only 3.3 encoder
> counts/second. That is not enough to give reliable velocity info to
> whatever is controlling the motors. In my case, a DC tach gives feedback
> to the servo amp up to a several KHz bandwidth no matter what the
> velocity is. The servo amp then generates armature current to keep the
> velocity constant.
>
> > Are people using 320/340 gecko drives with EMC and DeskNCrt? How are
they
> > typically hooking up the encoders--to the drives and the control with
the
> > camtronics board?
>
> I believe people are using the Gecko 320/340 with the encoders feeding
> back ONLY to the Gecko drives, not an encoder counter for the CPU.
>
> > Is DeskNCrt just as good or complete as the Lunix based EMC?
>
> I can't answer that. I can make some comments about the interrupt
response
> time under RT-Linux, with EMC. I get less than 10 uS interrupt response
jitter
> on a 266 MHz Pentium-II. The CPU time required to complete 4 axes of
> servo computations is about 50 uS on that CPU, indicating that you could
> run a servo update rate of 10 KHz without killing the CPU.
>
> I understand that DeskNCrt uses the standard character screen, which is
> a limitation. EMC uses a 'GUI' interface to the screen, that is
user-configurable,
> in color, has defined fields for various parts of the display. Ie. the
position
> display is in larger characters, and change color when the axis is at the
limit
> position or has been homed. There are other blocks that display state
with
> color or reversed video. There are slider bars to display feedrate
override.
> You can select files to run from a 'browser' type menu. There is an
> additional script that can be loaded into the GUI to preview the toolpath.
> This avoids the situation where a program contains an error that will stop
> the run in the middle. Since ALL interpreter functions are actually used
during
> the preview, if it runs in preview, it WILL run when motion is enabled.
> (This is called the 'backplot' option.)
> The advantage of being able to hop into the text editor, get files through
the
> network, use a calculator program, etc. while EMC is running is a great
advantage.
>
> Jon
>
>
>
>
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