On Sat, 27 Oct 2018, Alan Condit wrote:
Date: Sat, 27 Oct 2018 18:46:59 -0700
From: Alan Condit <condit.a...@gmail.com>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: "Emc-users@lists.sourceforge.net" <emc-users@lists.sourceforge.net>
Subject: [Emc-users] 5I25-7i76 encoder output
I have a homemade encoder on my lathe spindle. I am feeding the encoder
outputs into the encoder spindle inputs on the 7I76. The reported rpm seems
to be fluctuating wildly. I want to look at the signals to see if the width
of the signals is about the same for the index on time and for channel A and
B on and off times. Is it possible to look at the encoder signals with hal
scope? Or do I need to drag my oscilloscope out to the shop. I don??t see
the pins in the hal file.
Am I even thinking about this correctly?
<Alan
Duty cycle (deviation from 50 %) and quadrature errors (deviations from 90
degree phase difference between A and B) on low resolution encoders will add
considerable noise to encoder velocity estimation.
This is because with a low resolution encoder you will typically have 0 to 1
counts occuring per servo thread. Velocity estimation is done by dividing the
counts per servo thread by the time between the counts, so any duty cycle
or quadrature error will cause a large error in the measured time between
pulses if you only have 1 count.
This is not a serious problem on high resolution encoders since they will
typically have many counts per servo thread period (and any individual
quadrature cycle timing errors get divided by the number of counts)
Because of this, its usually neccesary to low pass filter the velocity signals
from low resolution encoders
You can monitor the A,B signals with halscope but only at fairly low speeds
due to the low sample rate of the inputs
The signals to look at are:
hm2_XXXX.0.encoder.NN.input-a
hm2_XXXX.0.encoder.NN.input-b
hm2_XXXX.0.encoder.NN.input-index
Where XXXX is teh FOGA card name and NN is the encoder number
Peter Wallace
Mesa Electronics
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