On 09/09/2020 12:16 PM, Gene Heskett wrote:
On Wednesday 09 September 2020 12:38:43 Jon Elson wrote:
On 09/09/2020 11:08 AM, Gene Heskett wrote:
Is it possible to get an enable signal, per axis, from the mesa
cards that would become true, hopefully a couple micky-secs ahead of
the first stepper pulse so no missed steps would normally occur,
losing its home, and go back false when the last step has been sent?
It maybe could be timed right if it actually steps on the trailing
edge of the pulse, and the enabling action was on the leading edge.
This is the TRICKY bit, knowing when an axis is SOON going
to start moving.
Jon
I'd be surprised if these things needed any lead time at all, Jon. The
hitachi docs on this chip do not mention any timing constraints in
regard to this. So its likely that it could be brought up to full song
with the leading edge of the pulse. If that triggered a retriggerable
oneshot that was then or'd with the pulse, and its output would be the
enable high current signal. Let the oneshot time out in 50 millisecs if
no pulse, putting it back in reduced current at the end of the move. If
the oneshot was in the mesa, would be ideal, and divorced from the
enable granularity of the 1khz servo thread. That granularity could
easily lose enough steps to destroy a home position, something I intend
to have with this BS-1 clone. A oneshot in the hal file would be a
disaster in that case because of the millisecond+ delay. A oneshot in
the cable to the driver would work, but if its in the mesa card, better
yet. :)
Certainly worth a try. One horrible possibility is that the
DIP switches are only read once at
power-up. The first couple steps should be spaced out as
the axis accelerates which should give the drive time to
ramp up the current.
Jon
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