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?
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.
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!
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.
Jon
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