Re: minferror parameter

[Fred Proctor <frederick.proctor-at-nist.gov>]

Till Franitza wrote:

>
Please add to your documentation what is the meaning of minferror in the
ini-files! What emcmot does here is quite difficult to understand and I
tend to say that it is a bit confusing. The "simple" ferror is - as I
understand it - somehow used as velocity-dependant while if this
boundary becomes smaller than minferror, minferror is used as boundary.
I found that out by looking into the source code.
<

In older versions of the EMC, [AXIS_#] FERROR was the value of the
following error, in user units, that if exceeded by the axis would cause
a motion abort.

In newer versions, [AXIS_#] MIN_FERROR modifies this behavior. If it's
present in the .ini file, velocity-dependent following errors are used.
The value of FERROR is scaled to be the ratio of the axis' current speed
to the [TRAJ] MAX_VELOCITY. So, for rapid moves, FERROR is used; at half
the rapid rate, half the FERROR will cause a motion abort.

MIN_FERROR is used to prevent very slow moves from having too small a
fatal following error. The following error has to be at least MIN_FERROR
to cause an abort.

If you leave MIN_FERROR out of the .ini file, it's set to be the same as
FERROR, which yields constant following error, as before.

The problem you may be having is that MIN_FERROR is present in the .ini
file, and it's set to 0.0. This makes any following error for axes that
aren't moving cause an abort. It should never be set to 0.0. In
generic.ini, FERROR defaults to 1.0, and MIN_FERROR defaults to 0.010.
These are probably bad values but you'll have to change these anyway for
your machine.

Another problem is that the scaling is done by dividing the actual axis
rate by the trajectory max rate. This isn't correct for robots or
hexapods, where the max trajectory and max axis rates aren't related
this simply. I didn't see any problems with this when I ran the
cable-based hexapod, but it should be fixed.

And:

>
The documentation emcsoft.html is not up to date in this case.
<

I'll add MIN_FERROR and update FERROR on the web page.

--Fred