On Wed, 11 Jan 2017, Jon Elson wrote: > Date: Wed, 11 Jan 2017 10:36:18 -0600 > From: Jon Elson <el...@pico-systems.com> > Reply-To: "Enhanced Machine Controller (EMC)" > <emc-users@lists.sourceforge.net> > To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> > Subject: Re: [Emc-users] Two questions. > > On 01/10/2017 10:45 PM, Gene Heskett wrote: >> On Tuesday 10 January 2017 23:02:28 Jon Elson wrote: >> >>> On 01/10/2017 08:39 PM, Gene Heskett wrote: >>>> But if I hook up the halscope, the apparent quadrature error is >>>> worthless due to the 1KHz servo-loop timing limiting the bandwidth. >>> Well, that's why we use hardware encoder counters, as >>> sampling the quadrature at 1 KHz just isn't fast enough. >>> >>> Jon >> Plz elucidate Jon. Something has got to be better than this. See the pix >> I posted with the last reply to Peter & the list. The top, white trace >> in the halscope screen is the quadrature noise, easily 10x the timing >> wibbles I see on the hitachi's screen. >> >> > If you are looking at the quadrature signals at a 1 KHz > sampling rate, then unless the encoder is moving quite > slowly, the sampling will be too coarse. That screen shot > is kind of small (you can take just a single window as the > screenshot, by the way) but it looks like the duty cycle of > the encoders is not 50%. That may well be aliasing, as the > quadrature signals seem to be moving much too close to 1000 > Hz. You'd get much better results below 100 Hz. Or, with > Mesa hardware, you can sample these with the base thread. > > I can't comment on the velocity output from the Mesa, as I > don't know their gear (or driver). But, the scale is 2/div, > meaning the scaled velocity output is jumping around 2 user > units up and down at a KHz rate. Clearly, not good. > > Jon
The velocity output is calculated by using the number of counts divided by the time between the counts (time measured via a 1 MHz timestamp). If you have less than 2 counts per servo period the velocity estimation accuracy depends heavily the quadrature phase/symmetry since the edge spacing entirely determines the estimated velocity at this speed range. I suspect what Genes plot shows is that he has significant quadrature phase/symmetry errors at the FPGA inputs. Again here is a velocity plot of a accurate 100 Hz quadrature signal: http://freeby.mesanet.com/100_Hz_quadrature_velocity.png > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Developer Access Program for Intel Xeon Phi Processors Access to Intel Xeon Phi processor-based developer platforms. With one year of Intel Parallel Studio XE. Training and support from Colfax. Order your platform today. http://sdm.link/xeonphi _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
