On Friday 30 June 2017 07:11:09 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 > I agree Les, and I've made a filter out of some hal components that sends as output, the sum of the last 4 velocity samples to the spindles PID as the usual feedback. This reduces that noise to about 25% of its raw value, and for the spindle of the G0704, allowed me to raise the P quite a bit. When there is a 5% timing error in the quadrature, it slams the PID output, sometimes from rail to rail, making Pgains above 1 unusable. With the filtering, a Pgain of 1.75 is still slaming the gearing backlash in the head unless its heavily loaded. But the noise isn't a bit rythmic, so I am thinking a head teardown and replacement of the roller skate quality bearings in it with decent bearings is in my future. From the .ini:
[SPINDLE_9] P = 1.75 I = 0.05 D = 0.002 FF0 = 1.00 FF1 = 0.085 FF2 = 0.00025 No clue if its correct, but its usable, and its quite stiff loading wise. Makes lot of racket and is beating the cheap head bearings to smithereens. This is an optical encoder with 268 edges. On an external scope it looks pretty good, but the 5i25's encoder velocity output is horrible. A similar encoder on TLM, I even went to the trouble of making a per opto-interrupter led dimmer so I could fine tune the duty cycle to minimize the amplitude velocity variation and the 4 cycle noise, but it cannot be equalized to a smooth line. So thats the first of my machines to get that averaging filter. That allows a Pgain of 3, and its quite stiff in terms of load vs speed. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ 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
