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Old February 9th, 2019, 12:05 AM   #16
Peter Nachtwey
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NO,NO,NO!!!!!
Ethernet encoders should not be used for any demanding motion control. This application seems to be like a flying shear where one actuator must accelerate to match the speed of a master actuator/encoder. The master encoder should have very fine resolution and be deterministic. Ethernet is not deterministic nor does this encoder seem to have enough encoder counts per revolution. This makes it difficult to computer an accurate master speed. The master speed must be accurate because it is used as the target speed for the slave axis. If the master speed is not accurate then it is impossible to use the derivative gain on the slave axis. It is also impossible to compute a good feed forward for the slave or acceleration feed forward.

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After a few days I finally figured out that the feed forwards in the axis setup were at 100%
The velocity feed forward should be about 100% on Rockwell motion controllers. I know, remember I wrote the code for the HYD02 and M02AS. The problem is what I described above. The master velocity is for the velocity feed forward for the slave. If the master velocity resolution is as coarse as shown above then the slave velocity feed forward will be just as coarse.
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Old February 10th, 2019, 11:38 PM   #17
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The resolution on the encoder is terrible. Crank it to 4x quadrature if not using it already.
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Old February 11th, 2019, 12:25 AM   #18
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The resolution on the encoder is terrible. Crank it to 4x quadrature if not using it already.
One should always be mindful of how many counts they get per cycle. If there are 100 counts +/- 1 that is not a big problem whereas 2 counts +/- 1 is a 50% change. Even so, how much jitter will be caused by the Ethernet?

I always tell our customers to push our encoder inputs to the limit. We can easily handle 8 million counts or more. That means if the same time is 1 millisecond there are 8000 counts per millisecond on the average. The sampling should result in 8000 counts +/- 1 which is pretty good.

However, all this can be ruined if the master encoder is connected to feed chain driven by a sprocket. Sprockets to not pull a consistent rate so they will also cause sample jitter.
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Old February 11th, 2019, 02:12 AM   #19
Geoff White
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I believe the OP is using an incremental encoder plugged into an aux port on a drive.
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Old February 11th, 2019, 06:59 AM   #20
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All evidence (and Peter) point to the encoder. Depending on your application, you might be able to fudge it, but a sinusoidal encoder would fix it right.
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