On Sunday 27 October 2013 05:45:34 Jon Elson did opine:
> andy pugh wrote:
> > On 26 October 2013 21:09, Jon Elson <[email protected]> wrote:
> >> The ABS encoders, if battery backup
> >> is provided, apparently put out a burst of quadrature pulses to
> >> revolve the apparent position to the offset from the index
> >> position, thereby eliminating the need to home the axis. But,
> >> I've never tried this with my PWM system.
> >
> > I can't see any reason for this not to "just work" if the power-up
> > sequence is correct.
>
> Yes, that's the trick. You'd have to wait for LinuxCNC to be fully up,
> AFTER
> it zeroes the encoder counters, and then power on the encoders so they
> send that quadrature pulse train. It may require some control signal
> to the encoder
> to make it do this. Fanuc, of course, doesn't have any documents on
> ANYTHING, they are more secret than the CIA. Then, you'd have to
> have LinuxCNC clear all offsets in the .var file, so that the initial
> value in the encoder position counts are taken as the machine position
> at startup. This is certainly not the usual way of using LinuxCNC, but
> it seems like it MIGHT work without any code changes. Clearing the
> offsets in the .var file might be handled by a startup script.
>
> Jon
Whoever writes that startup script gets my good housekeeping seal of
approval.
I don't know how many times I've had to stop linuxcnc on my lathe, delete
both the .var and position.txt files, and restart it before my homing
sequence works correctly. If at some point, I have used a touch-off to
adjust an error, its remembered forever till I stop, kill the files &
restart. Or if, in shutting down linuxcnc, it crashes the box, which seems
to be about a 1/100 occurrence, the .var file in particular will be
trashed, causing linuxcnc to do an error exit on the restart until the file
is nuked. IIRC this can be triggered for demo purposes by nuking the file,
then touching it, leaving an empty file.
Perhaps in addition to the current "linuxcnc -l" to load the last config,
maybe it could grow a -k option that deletes those files, truly starting
from scratch? Checking the current man page, it doesn't even document the
-l. Shouldn't that have been fixed when the -l was introduced? The man
page was last edited by Alex Joni in 2006.
Cheers, Gene
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Democracy means simply the bludgeoning of the people by the people for
the people.
-- Oscar Wilde
A pen in the hand of this president is far more
dangerous than 200 million guns in the hands of
law-abiding citizens.
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