Re: [CAD_CAM_EDM_DRO] EMC problem/question

Hugh & Denise Currin wrote:

> Crew:
>
> I am having a problem with EMC and don't know where to go from here. I am
> hoping someone more familiar with EMC can direct me.
>
> I've noticed my mill doesn't come back to zero after a number of moves. If
> I repeat
>
> g01 x0.1 f10
> g01 x0.0
>
> twenty times in a program the zero is off by 0.010". If I change the
> distance moved from 0.1" to 0.2" I get the same error, .010. I can do the
> same with moves in the y direction. Double the moves (40) gives double the
> error 0.020". I changed the feed rate to F5 and the errors are the
> same. I changed the default and maximum accelerations in the .ini file
> from 10 to 5 with no effect. Finally I wrote a program with

I'll bet your step resolution is .0005", and you are losing exactly that much
every time the machine reverses. The first thing is to check the specs on
the Camtronics driver for the setup and hold time on the direction line
relative
to the step line. My guess is that the driver needs a certain time for the
direction
line to be stable either before the step pulse or after the step pulse. I
suspect
that EMC is violating this requirement in one direction, thereby causing a
step
to occur in the wrong direction.

One possible way to fix this might be to invert the sense of the step pulse.
This can't be changed in the .ini file, so your choices are to possibly
reverse
it by the way the connection is made at the driver, if it uses opto-isolators
at its
input. Otherwise, you can hack the software that drives the step/dir bits to
the parallel port or add an inverter chip at the output of the parallel port
(on the
step signals, only).

If this doesn't seem to be the problem, you should try steppermod (if you are
using freqmod) or vice versa. Steppermod is a simple step generating program
that has the disadvantage of generating somewhat rough step timing, but at
high rates. Freqmod generates much smoother step timing, but burns a lot
more CPU resources doing it.

One other possiblity is the backlash compensation. There was a problem
at one time, which could be in your version, where the extra steps added to
correct
for backlash were coming out too fast, causing lost steps. If you have a
nonzero
value there, try setting it to zero and see if the problem goes away.

Jon