Re: emc help

Hello
I guess having been an cnc enginneer for the last 10years,I tend to
assume people understand what i mean.
I all the thing you have said are on the surface correct but in
reality are completely wrong.

The servo update time which in emc's case is determined by the pc and
limited by the communication to the stg board,as well as the max
encoder input rates and maximum accurate control of the d/a converter.

So the realistic rate cannot be 999ipm ,especially with the
limit of .0001 resoulution or 10000 counts an inch.
At 400 ipm or 6.6666 ips is equal to 66khz of encoder,which makes
800ipm a max for a standard 150khz encoder(assuming a little head
room)


Then there is the case of how fast the processor can close the
servo loop,which become even harder with each additional axis.
Which is why i asked what the limit is when you make a multiple axis
translation.

Then we come to the case of point to point moves ,Or high speed
contouring,This is even a worse strain for the processor as you have
trajectory changes every few thousandths(determined by your step
distance and step over),All this will bring most cnc's to there knees
long before 400ipm(i have had fanuc's programmed at 999ipm with the
overide at 200% that couldnt go 50 ipm).
Not mention the accell/deaccell limits of the motors and drives.

So i ask yet again what is the max realistic feed rate that Emc will
support for the following:
1 a simple one axis move
2 a 3 axis move
3 a point to point contour move

Regards,
Greg

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> Greg wrote:
>
> >Hello,
> >I had already planned on settng an external plc to acount for
emc's
> >dismall i/o control.
> >My estop circuit is already integrated,thru a watchdog,drives,etc.
> >Having a 10 volt command while your computer is hung would be a
bad
> >situation.(can you say crash)
> >Since you seem to be knowledgable about emc
> >What is emc's top feed rate given a .0001 resoultion from the
encoders
> >(with a 2ghz computer)
> >
> Are we talking about an analog servo system? There is no top feed
rate,
> other than whatever velocity you have set 10 V equal to. There
probably
> are practical limits on the numbers you can enter for F, but I'll
bet it
> will take 999, probably 9999! In the ini file, you set a maximum
feedrate,
> and that is assumed to equal 10 V on the DAC. Assuming no position
> error is seen on the encoder, then if you have set the max feed
rate to
> 500 IPM (the number you would enter is inches/second or 8.3333),
> and you then command a feedrate of 250 IPM, EMC would output 5.0
> Volts on the DAC. If there is a position error, that would add to
or
> subtract
> from the 5.0 V.
>
> Most encoder counters can handle 300,000 to 1 million encoder
counts/second.
> So, that would be 30 to 100 inches a second, or 1800 to 6000 IPM.
Is that
> enough for you?
>
> The only downside to such huge numbers is the finite resolution of
the DAC
> voltage.
>
> >2 for a multiple axis interpolation
> >3 for a point to point traj
> >
> >
> These make no difference, the code is the same regardless.
>
> Jon