On 06/29/2017 03:59 PM, Les Newell wrote:
Do you have and raw-write encoder filter tweaking stuff
in the hal file:
No. For testing purposes I am running the barest minimum
needed to achieve motion using a config generated by pncconf.
After spending a lot of time playing with halscope I have
some interesting findings. Most of what I thought was
noise is actually phase variation in the encoder counts.
There is a cycle that repeats every 4 counts. When zoomed
out of course it just looks like random hash. I checked by
monitoring the encoder counts and velocity at the same
time. I could clearly see the cycle repeating every 4
steps in the encoder count.
I think it is time to put a scope on the encoder. it sounds
like there may be a big duty cycle or phase angle error in
that encoder. In other words, at constant speed, the 4
quadrature transitions are not evenly spaced, but at least
one of them is out of time.
Now for the really weird bit. It didn't sink in before but
the spikes are always positive, no matter what direction I
am moving! in other words if I move in the positive
direction the spikes show increasing velocity. If I move
in the negative direction the spikes show decreasing
velocity. I have a log that shows one spike reaching zero
velocity for one encoder count. I have another log when
moving in the other direction where the spike is nearly
double velocity for one count. However in both cases the
width of the encoder count is pretty much the same as
nearby counts. I can't think of any way that electrical
noise could give this result. If anyone wants to see the
logs I'll upload them tomorrow.
Assuming the spikes happen fairly often, you should try
setting up Halscope to display velocity and trigger on
where you think a spike might reach, and then move the
axis by hand for a while and see if the scope triggers.
Not easy. The screw is difficult to get to and I can only
turn it about 1/4 turn at a time.
With a little hacking of Hal commands, you should be able to
set up a roughly constant speed on the motor, running open
loop. Or, even run closed loop and just hook the scope to
the encoder signals.
I can't see it being pickup in the encoder cable. It's
only about 18" long and doesn't run near any noisy wiring,
apart from a couple of inches near the 7i29. It is the
original screened cable fitted by the manufacturer of the
encoder. Apart from that I don't see how noise could
produce the results I am seeing.
OK, I did not know what your setup was there.
Jon
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