On Wednesday 08 November 2017 11:51:37 Jon Elson wrote: > On 11/07/2017 10:54 PM, Gene Heskett wrote: > > They are visible on my 100 mhz hitachi dual trace, but not to the > > extent shown by the pix I just sent, Jon. Quantization errors keep > > adding up. > > Well, this may actually be informative. What are the > voltage levels coming out of the encoder?
A few millivolts above ground to about 4.25, with 4.95 for a 5 volt buss, and thats buffered by a 74ls04. > Are they a good match for the logic thresholds of the Mesa > board? Maybe a pull-up or terminating resistor might help > clean up what the Mesa sees. If the A and B HAL signals are > AFTER the digital filter, then these width variations may be > caused by the Mesa board rejecting noise on the inputs. > I've seen a lot of problems with encoders where cable > capacitance causes both signals to transition at the same > time, and this illegal transition is rejected by the digital > filter. The transition is not recognized until the > crosstalk-caused transition corrects itself. With weak > pull-up, that can take some time. > > > I'm looking at the Omron 2500 line encoder for a touch over $40, and > > at least a month to get across the big pond. > > > > But while it looks to have ball bearings, they are probably vxd's. > > Shitly stuff thats not really fit for roller skate wheels. > > > > No clue how hard it might be to put decent bearings in it. > > Many encoders are not meant to be repaired. The glass disks > are plenty fragile, and getting the read head off and the > shaft pressed out without breaking them is quite tricky. > Even the ones with etched steel discs are fragile. > > > Can you pretend to advise? > > There are also "kit encoders" where you get a disk and read > head, and maybe an enclosure, and fit it to an existing > shaft. You could make up a bearing nest and shaft and fit > that to it. Avago, US Digital, Renco and others make these, > and they are not terribly expensive. You can get a wide > variety of the Avago (formerly HP HEDS-series) from Digi-Key > and Avnet. You should have no problem getting one of these > kits for $40, but of course that does NOT have the bearings > in it. I think US Digital has complete encoders close to > that price, with the etched steel disk. I have used the > Avago HEDS-type encoders to mount on motors with rear > shafts. Quite easy to do. So, if you can manage to fit a > rear shaft, that would be the best way to go. > Thats on the todo list, there is not a rear dust cover over the end of its shaft, so fitting a 6.35mm by 20mm extension isn't a major problem according to that voice I keep hearing. > I'm not sure a higher resolution encoder will really solve > your problem. As you raise encoder resolution, the timing > information you get from the edges gets smaller and smaller. > > > As in is the idea worth pursuing? Or should I > > make another of those disks, but first get my A axis moving, which > > should remove any variations in slot timing by elimination the xy > > backlash's incomplete compensations. But I'd still be stuck with a > > low slot count unless I can locate some mills with only 0.010 tip > > diameters. > > No, I would not try to do any big milling job with .010" end > mills. Got any hair? You won't after experiencing that! I lost some using a 0.028" mill. Veddy frajilly. > > IIRC I used several mills out of a ten pack of .028" diameter mills > > to make that one, and don't have any more of those left. > > > > That also begs the question about how small a slot is practical with > > these honeywell interrupters too. I should tour yard sales looking > > for dead $5 printers I suppose... They have very fine pitched wheels > > and matching encoders in /some/ of them. > > Well, I would not use slot-type sensors for an encoder. > There are sensors specifically made for encoder use. URL? Thanks Jon. 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
