Re: [CAD_CAM_EDM_DRO] Major encoder trouble, need advice.

Hi Jon, hi David,

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Ahh, that's very interesting, but I don't think speed has anything to do
with it. I think it is noise.
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You're probably right since it doesn't work properly even when running on
30VDC and turning at 20rpm.

I tried backdrivning it today, first with the motor disconnected from the
drive. I jogged it back and forth in short bursts as fast as my cordless
drill would go and in in slow bursts a couple of turns each way. There were
NO invalid transitions detected.

I then connected the motor to the drive and tried doing the same thing but
it didn't work out too well. Since the logic is powered I guess part of the
H-bridge conducts and it was hard(er) to turn the motor at any conciderable
speed, anyway, I moved it back and forth a bit - still NO invalid
transitions detected.

Then I mounted 10uF electrolytic cap right on the encoder and powered it all
up, jogged at 20 rpm for 10seconds and immediatly got invalid
counts...aaargh....

I took out and inspected all four brushes and they all look fine to me,
although I'm no expert.

To make absolutely sure and to proove to myself I wasn't getting insane I
removed the E7P encoder and mounted the AMT encoder instead. I cycled thru
my test program for ~10 minutes and there was zero, none, nada invalid
transitions detected. Same drive, same motor, same powersupply, same
computer - different encoder.

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>> USDigital recomends the 26C32 receiver while the HP-UHU has the
>> SN75115... big difference?

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VERY unlikely. An awfully complicated chip, with strobe, differential
output and response time control. Maybe there would be some benefit in
slowing it down with the response time control pin to filter out extremely
short pulses.
All my encoder counters have digital filtering in the FPGA to ignore
transient invalid transitions.
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Actually, the other "issue" with the drive that I mentioned had to with
these specific filter caps. If I have ANY caps mounted it will not work.
Other reports the same thing, after removing the caps it works just fine
(except with USDigital encoders). It's a strange thing since these caps are
supposed to be there and I HAVE tried adding them back when using the E7P
but it will not work. I've tried everything from 2.2pF to 10nF nothing works
- with ANY encoder.

I'll refrain from cutting the onboard GND-link as it sounds a bit
'dangerous'.


David,
See, that's ANOTHER good idea I haven't thought of despite working on this
for weeks. Thank you! I'll try powering the encoder separatly and if that
doesn't do it I'll see if I can find some ferrite beads to put on the
cables.

Thank you both, I was THIS close to just throw the damn encoder in the trash
but I REALLY need to get them working!

Best regards
/Henrik.