On 06/30/2017 04:11 AM, Les Newell wrote:
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.
I can see the phase angle errors in halscope by looking at the
measured velocity at low speed. There is a regular 4 step cycle. I can
see the same effect on the other encoders, though it is not as
pronounced. All encoders have some phase angle error but I have to
admit this one is worse than I would like. The problem is compounded
by it being a fairly low resolution encoder. However this does not
explain the occasional big spikes, especially the example where I had
a spike of zero velocity for one count. The machine was moving at low
speed so I could see individual counts in Halscope. To read zero
velocity that count should have been MUCH wider than the others and it
was not. There has to be something wrong with the the way the velocity
is calculated.
Les
Years ago Jon Elson convinced me you almost could not too many counts/rev.
Going from 5000 c/in (glass scale) to 40K c/in made a huge difference in
how easy it was
to tune.
On my Z axis I mounted the encoder almost like an idler but on the cog
side of the belt.
Small timing pulley so I get upwards of 100K counts/in as opposed to
only 40K for X and Y.
Every bittle lit helps. :-)
Dave
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