On Wed, 1 Nov 2017, Eric H. Johnson wrote:
Date: Wed, 1 Nov 2017 19:25:36 -0400
From: Eric H. Johnson <ejohn...@camalytics.com>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: "'Enhanced Machine Controller (EMC)'" <emc-users@lists.sourceforge.net>
Subject: [Emc-users] Odd encoder problem
All,
A machine (table) that has been running for about three months has developed
an odd problem in the last couple weeks. Not sure if it has been getting
worse or if just the nature of the patterns being run has made the problem
more pronounced. The machine is an XYYA configuration with a pneumatic Z,
and using mainly Mesa boards. The problem is in the A axis. It seems to be
losing encoder counts at very low speed, but not otherwise. It took a bit to
track down because when I initially had it moving multiple rotations I could
not get any errors running A by itself. Running with a feed rate in excess
of 20000 (Degs per min), resulted in no errors. Slowing down to 10000
started to show a very small amount of error, and from 5000 on down the
error was very pronounced.
The hardware is a Mesa 7i43 FPGA, 7i33 quad analog servo card and YEnc line
drivers. The table is 15' x 30', thus requiring line drivers on X and A, but
for uniformity, were put on all four axes. The encoders are wired
differentially. The error is always in the same direction regardless of the
velocities used for the cw and ccw directions, thus would seem to be
dropping counts.
I would check that you get decent differential voltages across the 7I33 inputs
in both states of the inputs (no less than +-2.5 across the A,/A B,/B or Z,/Z
pairs in any state)
I did not have a scope with me to check the encoder signals. While a low
probablility, I do have spare YEnc modules, but ran out of time before
trying to swap it out. I don't really see how this type of problem
(electrical) can develop over time, but do not see how it can be anything
else.
Anyone seen anything like this when using that hardware?
Thanks,
Eric
------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users
Peter Wallace
Mesa Electronics
(\__/)
(='.'=) This is Bunny. Copy and paste bunny into your
(")_(") signature to help him gain world domination.
------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users
