On Tuesday 24 October 2017 08:47:02 John Kasunich wrote: > On Tue, Oct 24, 2017, at 08:14 AM, andy pugh wrote: > > On 24 October 2017 at 12:10, Gene Heskett <[email protected]> wrote: > > > Correct, except encoder.nn.velocity is fed thru a last 4 edges > > > averager to remove some of the noise in the encoders output. That > > > unforch also affects the spindle to Z phaseing in the G33.1 > > > backout. > > > > You might want to filter the velociity, but I see no point in > > filtering the position, which is what G33.1 uses > > > > You could also try using the DPLL timer to take jitter out of your > > encoder sampling. That's a pretty simple setting with the right > > firmware (one that ends in "D" for DPLL) > > I'm pretty sure Gene's "4 edge average" is dealing with mechanical > errors in his homebrew spindle encoder rather then sampling jitter. > The 4 edges mean that it averages over a full quadrature cycle and > thus deviations from proper 90 degree quadrature phasing are > masked. > > John Kasunich > [email protected]
Thats been my take on it too, John. The encoder wheel is mounted near the top of the spindle, on the sleeve the oem encoder for the oem crap controllers rpm indicator, and there is nothing there in that design to really make it truly concentric, plus at 268 edges, those slots are plenty fine, so a 1 thou error from backlash in the machine while carving the disk can easily be a 5 to 10 degree quad error. Note helped by the OD of the wheel as it has to clear the rest of the stuff under the drawbolt. 2.3" IIRC. I note that the average output still contains some of the 4 "pole" pattern, just reduced to 1/4 of its former peak to peak amplitude. Before the filter, the peak to peak is 50% of the average dc output, and that level of noise in the feedback hammers the motor around pretty bad since the Pico pwm-servo driver is a full 4 quadrant driver, taking up the backlash in the gears quite noisily. With the filter, its still noticeable at free spinning but quiets quite a bit under cutting loads. Add in the very poor quality of the bearings in the backgear, and you have a recipe for recommending the wearing of 30 db rated shooting ear muffs. Developing the clock for the fifo is done by looking for a diff across the first sample/hold, actually a mux2, and when there is a difference indicating an edge has passed, then the whole 4 stage fifo is clocked one step in the same servo-thread cycle. That of course is another source of timing error because the clocking is done at servo-thread intervals. All rigged for a gain of 1 thru the whole thing. Thanks John K. 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
