On Thursday 22 July 2021 01:02:26 dave engvall wrote: > "The solution is to either add more counts per revolution or use a ten > timesmore complex control algorithm." > > IIUC then the real problem here is statistical. That is the sample > size is too small to be significant. Maybe an over-simplification of > the issue but: > > I think there are a couple of ways to approach this. (1) time stamp > the index pulse. > (2) use a high count encoder and scale as necessary. > This is clearly limited by the response of the optics for the > disc. 100 - 200 KHz for the inexpensive stuff. > I don't think there is a one size fits all solution. In electronic > terms lathe spindles are pretty slow and have a lot of angular > momentum. Most lathe spindle > rpm range is not a lot over 5-6 binary bits. > I've actually considered putting a disc brake on the spindle. Not > exactly joking.
Needless mechanical complexity if you use a vfd to drive the lathe spindle. vfd's do not come programmed out of the box. Properly programmed, and despite the mass of an 8" 4 jaw mounted, I can rigid tap on that lathe at slower speeds. I've carved up some hal code driving a pyvcp display that displays the overtravel of the spindle after motion has issued the reversal at the bottom of a g33.1 move, actually anytime the spindle is reversed, and with proper programming of the vfd, I get at 100 rpms, an overshoot of .247 turns. It gets much worse at higher spindle speeds since nothing can repeal the stored energy represented by e=mv2. At 500 revs, its several turns and the belts are complaining. But the vfd is not complaining. its simply doing what it was told to do. An m5 from the keyboard stops the spindle dead in about a turn. vfd's, Ditto an error from one of the 3 phase stepper-servo's now moving it. Properly programmed, vfd's are indeed full 4 quadrant controllers. They can stop just as quick as they can start. But they don't come tuned like that out of the box. Thats a travesty out of the box. > Just late evening rattling the cage. > > Dave > > >>>> Could you solve the noise issue with a phase-locked loop? > >>> > >>> Yes, this would be a far better solution. But I didn't want to > >>> re-write the encoder counter from scratch. > >>> > >>> Ideally you would use two PLLs, one for the pulses and one for the > >>> index, to predict the pulse gap and extrapolate through it. > >>> > >>> -- > >>> atp > >>> "A motorcycle is a bicycle with a pandemonium attachment and is > >>> designed for the especial use of mechanical geniuses, daredevils > >>> and lunatics." > >>> � George Fitch, Atlanta Constitution Newspaper, 1912 > >>> > >>> _______________________________________________Emc-users mailing > >>> list Emc-users@lists.sourceforge.net > >>> https://lists.sourceforge.net/lists/listinfo/emc-users > >> > >> _______________________________________________ > >> Emc-users mailing list > >> Emc-users@lists.sourceforge.net > >> https://lists.sourceforge.net/lists/listinfo/emc-users > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
