Re: Homing with servos - Pulse timing?

[Steve White <steve.white-at-lomar.com>]

Hello,

    I hate to speculate, but you sound desperate.  Is it possible that the
index pulse from the encoder and the the home switch actuation are aligned
almost perfectly (by chance) causing them happen at almost the same
instant, thereby fouling the logic in EMC?  I'm not familiar enough with
the logic to know if this is possible, but perhaps EMC looks for a state
change of the index pulse input after the home switch input, but by the
time it's reversed direction and starts looking - it's already happened.  I
have seen CNC machines that will occasionally home to a position out of
"true" home by one turn of the lead screw for this same reason.
    To rule this out, you could rotate the encoder coupling or move the
switch a bit to change the phasing between them.  I realize this is a wild
guess, but it should be simple to rule out by this test.  I hope I'm too
late and you have already found and fixed it!


Regards,
Steve

klmartineau-at-shaw.ca wrote:

> Okay, now I really need some of your insight.  I can't figure out why
> my axis aren't homing.
>
> I tried motion at 6.0 IPM - Index pulse goes from 0 to 4.5v for about
> 1.0 msec
> I tried axis cycle time at 0.000500 sec
> I tried EMCMOT =        stg8mod.o,  stg2mod.o, stgmod.o - all of which
> seem to work the same.
> I tried EMCMOT =        stg_v2_8axis_mod.o - but my machine always came
> out of estop when emc was shut down.
> I know that the stg sees the index pulse once a rev. by the lstg
> demo/test program.
>
> I have a stg v2 8axis board.
>
> The home motion hits the limit and reverses...forever...
>
> what am I overlooking...where's the bug...
>
> If anyone can help, even off list - klmartineau-at-shaw.ca - I may have to
> offer a reward.
>
> Kurtis