Finally figured out and did encoder shaft

Pictures and explanation are right there:
http://igor.chudov.com/projects/Bridgeport-Series-II-Interact-2-CNC-Mill/
I already wired it to the PPMC control box and I am able to read the readings (adjusted by diving by 4096 -- the pulse count) into EMC2.
What I would ilke to do is, somehow, make sure that encoder counts are not missed due to some mistake of mine such as bad wiring, misalignment, etc. I would like to count the index pulses separately and compare index count with the angular position oft he spindle. They should always stay within "1" of each other, if no counts are missed.
I have not yet figured out how to do it.
i
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Am I missing something, Ig?
How else would you determine the angular position of the spindle without the encoder? I thought that's what it _did_.(?)
(You do have a "zero index" on that encoder disk, right?) LLoyd
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On 2010-12-17, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

Well, the basic equation is that there is a full revolution of the encoder between the index pulses. If EMC2 sees a different number of pulses than 4096 (4096 pulses make a full revolution of the encoder), between two index pulses, thos would mean that pulses are missed. This is what I want to check somehow.
i

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Ignoramus6780 wrote:

Why not use the same method your other rotary axis does? You mentioned once you had a fourth axis installed.
--
John R. Carroll




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Mount a mirror on the shaft, shine a solidly-fixed laser pointer at it and mark the spot on a far wall. When you rotate the shaft so the spot comes back to the mark you have turned it exactly 1 revolution to an accuracy of about 1 milliradian or better.
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I was thinking something similar, but mechanical, but this optical approach is better.
But I would add one thing. The worry is mechanical slippage between hollow spindle and the little adapter plug iggy made, and slippage is greatest during rapid acceleration.
So, I would command the spindle into a long series starts, stops, reversals, and so on, that should leave the spindle in the same angular position as before the sequence. If no slippage, there will be little or no difference between where the spindle ended up (as indicated with the light beam) and the integral of the encoder output.
Joe Gwinn
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My bigger worry is missing pulses due to shaft misalignment.

What I did yesterday was to buy a digital "laser" tachometer that has a TOTAL function.
When it arrives, I will run the spindle for 3 minutes and look at spindle position number in EMC, and will compare it with the TOTAL number from the tach. They should differ by less than 1.0.
i
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I'd been wondering if an electronic counter would be a good solution, since there are numerous models with varying features made for all sorts of machine applications (counting/tachometer industrial applications). I thought someone more familiar with integrating them into computer applications might mention them as a good (but maybe not optimum) solution.
I have a couple of DPMs digital panel meters which are capable of reading several types of input devices, including optical TTL quadrature encoders. Other inputs are commonly used, from a fairly wide variety of signal sources.
Of course a DPM by itself often requires an enclosure (or approx. 2"x5" panel space) for mounting, but as far as a portable piece of test equipment, they can be very versatile for monitoring a wide variety of machine functions. The Totalize feature is common on most industrial DPM tach/counters, and other features are often fairly sophisticated specific programmable functions.
Quality counters are made to easily integrate into machine electrical systems, generally with output signal options that would likely be easily implemented as inputs for a PC CNC application (maybe with a simple isolation circuit).
--
WB
.........


"Ignoramus30138" <ignoramus30138@NOSPAM.30138.invalid> wrote in message
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Perhaps you could put the laser in the horizontal hole of a boring head.
jsw
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wrote:

Perhaps you could put the laser in the horizontal hole of a boring head.
jsw
--------------------------------------------------------------
That is probably more convenient, but a mirror makes it twice as accurate (1 deg of rotation = 2 deg. of beam deviation).
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Joseph Gwinn wrote:

It's not a servo spindle, so there is no way to perform such an exercise and return to the start position. What he could do is scribe a line across his adapter and the spindle, run a series of starts/stops/reverses and then visually inspect to see if the scribed line is still in alignment.
If he's worried that his adapter is slipping in the spindle bore, which it really shouldn't since it and the attached encoder wheel have little mass, he should just install the adapter with some Locktite removable threadlocker.
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On Thu, 16 Dec 2010 21:08:31 -0600, Ignoramus6780

I needed this on my lathe spindle. Turns out there was no way to do it in Galil/Camsoft (Let me know if EMC has a way)
Don Foreman came to the rescue. A small transistor amplified the index pulse to high speed opto 22 input. Allowed dead nuts accurate threading at 4000 RPM. He said duck soup easy, but total fricken mystery to me. Us MEs never quite trust those sparkEs.
Karl
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On 12/17/2010 04:00 AM, Karl Townsend wrote:

As far as I know, EMC2 requires a real encoder with index on the spindle, as it needs to accurately handle the reversal when doing rigid tapping. Yes, this really doesn't apply to a lathe threading cycle, but the EMC way is usually to go for mathematical purity and completeness.
Since most lathes have an extension at the rear of the spindle, it is usually possible to rig an encoder there somehow, often using a timing belt. I figured out how to do it on a Bridgeport 1J, where it is practically impossible to add a sprocket to the spindle. I think the same scheme could be used to put 3 sensors on a timing belt pulley or gear as would almost always be found on the threading gear train of any lathe that has a threading screw.
See http://pico-systems.com/bridge_spindle.html
Jon
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Jon, the reason why I could do it, relatively easily if you do not count two months of thinking and false starts, is that my mill does not use a drawbar and I could insert an adaptor into the top part of the spindle. With a 1J head, you do not have that luxury.
i
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On Fri, 17 Dec 2010 23:07:38 -0600, Ignoramus30138

You can't replace just the disc. The pickup has a mask in front of the sensors that matches the pitch of the lines on the disc. The sensor does not sense the passing of the individual lines on the disc -- it picks up light and dark transitions that result from the interference between the disc and mask.
--
Ned Simmons

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Thanks, I did not know this. In any case, I am not really in a big need of tapping at high speed above 500 RPM, for many reasons but one reason is that reversing of the spindle becomes harder.
i
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If your grating is misaligned with the two pickups, you'd likely get a skipped count on every revolution, at any speed.
Did you make the pickup head adjustable? Is the grating centered well on the shaft?
If the grating is centered and the head adjustable, you can do the "standard" limit-to-limit kind of adjustment on it, then split the difference, and you should be fine.
If not, spin the thing up to max (like you said you'd do), run it for a while, then stop it, index it, and tally up the counts.
My bet is, if it's working reliably at 500 rpm, it'll probably be fine at 4K.
LLoyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> fired this volley in

I should have added that back in my "robotics" days, I hand-built quite a number of quadrature encoders, with a few sporting 8K counts/rev, and never had any problems making them work. At the time, all I had was a fairly worn out Atlas 6x18 and a drill press.
I relied on a local photo-engraver to do reductions of my full-up 30"x30" drawings of the grating wheels. Inking the damned drawing on a 2K-spoke wheel was more work than any other part!
LLoyd
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On 2010-12-19, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

Lloyd, I will try to attach something to the spindle that can let me very accurately make exactly one revolution (by hand), and see if the number that EMC2 has, increases by exactly 1.000.
i
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On Dec 19, 3:05pm, Ignoramus12759 <ignoramus12...@NOSPAM. 12759.invalid> wrote:

Can you spin it up, and look at the signals with an oscilloscope? Any misalignment should show up as a variation of the quadrature relationship. The A vs B signals will have to be moving in relationship to each other in order to get a dropped count.
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