May I opine that noise on one of the encoder lines may cause a zero speed estimation. If you get two of the same channel edges in a row the encoder logically must have reversed direction. It must go through zero speed to change direction. Since a third edge (one on the other channel) is not yet detected to know true speed in the other direction, zero is the best estimate. Not sure if LinuxCNC does it this way but you can indeed detect a 'zero' speed even without long pulses if purely looking at the information the edges are telling you. You might have noise?
On Fri, Jun 30, 2017 at 7:11 AM, Les Newell <les.new...@fastmail.co.uk> 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 > > > ------------------------------------------------------------ > ------------------ > 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 > ------------------------------------------------------------------------------ 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
