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BClemens

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Missing steps in Y axis only
« on: February 21, 2009, 11:07:08 AM »
 I seem to have developed the same problem but only on Y axis - oval circle and the next Z step down is totally misplaced.
 
I'll start another thread....

This is a new problem because it was doing fine. I have removed the motor, checked backlash and gib tightness, checked the wiring, re-tuned the G320, and all I can think of. A repeating/revolving Y axis MDI will run as if it is OK then will miss an entire group of steps, then begins to work again - intermittent. Also when holding the Y axis mouse for constant jog it will miss for a group of steps and then begin to move - the DRO has counted all the while. These servo motors more than adequate. I'm still searching and I guess next step will be to make sure that the encoder is receiving constant voltage from the G320. Maybe try more of the computer unplug and replug trick...?

Thanks,
BC
Re: Missing steps in Y axis only
« Reply #1 on: February 21, 2009, 11:52:46 AM »
BC,  You didn't say what machine you were using, but I had the same thing happen to my "Y" axis. It ended up being a coolant leak getting into the encoder housing and the lines of encoder were being damaged ! After all they are printed on with either bug spit or berry juice !  I replaced the encoder three times before I found the wiley leak, but all is well now.
CRUISER
  Don

BClemens

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Re: Missing steps in Y axis only
« Reply #2 on: February 21, 2009, 12:01:21 PM »
Thanks Cruiser,

I checked the encoder when the motor was off. I checked the brushes too and broke one of the phenolic brush holders by tightening brush retainer plug too much....(Thanks for JB Weld!) The only thing I saw was a little piece of something on the encoder disc but brushed that away with a small soft paint brush and the motor brushes have very little wear at all. While the motor was off, I ran it for a while one way then the other.

Still searching....

Thanks very much,

Bill C.

Oh yes....this is a knee mill that I converted over a few years with ball screws and etc. It uses servo motors. The machine has been doing great, then begins to miss steps in Y - can't see the solution!
« Last Edit: February 21, 2009, 12:03:58 PM by BClemens »
Re: Missing steps in Y axis only
« Reply #3 on: February 21, 2009, 01:54:06 PM »
  Also when holding the Y axis mouse for constant jog it will miss for a group of steps and then begin to move

Hi, I had a similar problem when I first got my servo mill up and running, One of the drives kept moving or not moving according to some unknown problem. It was only when I was moving the mouse cursor across the screen I found the problem. A quick change of mouse and I was away, problem gone.
Dont ask me how or why cause it was a while back, all I know it had me confounded for ages.

Hope this helps
John

BClemens

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Re: Missing steps in Y axis only
« Reply #4 on: February 21, 2009, 02:29:19 PM »
This is a Microsoft mouse - couldn't possibly be faulty!!! (yea right!) Thanks for that input. Actually I believe this mouse is doing some funny stuff. I will change that too.

An oscilloscope on the encoder input to the G320, the 'A' signal quits at the same time the fault LED lights and the Y axis motor stops - but the DRO count keeps going.... Could this be a bad encoder? It is brand new (almost) and hasn't but just a few hours on it. I've taken the servo motor back off again to take a closer look at the encoder wheel. Cruiser may have hit on something here with what we're seeing on the scope - and intermittent as well. I'll be back....

Thanks again,

Bill C.

In the opening slot where the wheel is - in the encoder, should the disc be closer to one side of the slot? I cannot find any info on this from US Digital (E2)

BClemens

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Re: Missing steps in Y axis only
« Reply #5 on: February 21, 2009, 04:50:16 PM »
It's getting better! Now the motor continues to run even with the encoder disconnected from the G320 and no signal coming from Mach3. It will change direction by mousing the continuous jog but it appears that the signal from Mach3 disappears after a short run. The other axis are totally normal and will function even with the Y axis motor running away (I took the belt off after it slammed the limit switch). Now I'm totally baffled. I don't know what to replace; the encoder or the G320 or both. Replacing them both may become a 'political' problem. I'm getting a charge out of setting this machine up, but this is getting down right ridiculous. Cut about a foot of material then replace something on the operating system....

I'm still not sure where the encoder optic wheel goes in the slot in the encoder optics. I must have damaged it when attempting to clean up some dust out of it somehow. I was thinking when this mill was first being set-up that the motors would not even run unless the encoder was input into the G320, that is a note that I forgot to take...

Bill C.

Offline Chip

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Re: Missing steps in Y axis only
« Reply #6 on: February 21, 2009, 05:19:26 PM »
Hi, Bill

Sounds like your encoder is bad, Swap your Y Gecko to one of the axises that's working, The terminal strips will un-plug.

A Gecko without a encoder will run off in one direction on re-set looking for encoder pulses.

Mach will continue to count if your axis trips unless you've wired the err/trip signal to Mach to halt it.

Chip

BClemens

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Re: Missing steps in Y axis only
« Reply #7 on: February 21, 2009, 05:34:50 PM »
Thanks Chip, actually that is good news... With the system in reset, plugging in the Y motor and encoder, it just runs away when the reset is engaged without any input to the Y axis. That's why I was concerned that the G320 may have fried, but then it does respond when an input is given in Mach3. So by 'cleaning it' I basically finished it off!

I'll shift a G320 to another axis as you suggest and see what happens. I'm glad I'm not getting paid for this; I would have starved by now! But I work very cheaply for myself.

Thanks,
Bill C.

BClemens

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Re: Missing steps in Y axis only
« Reply #8 on: February 21, 2009, 06:40:21 PM »
OK, got it from another person who knows: the encoder is the culprit. "The Gecko G320 has no safety built-in to stop the motor if it loses feedback from the encoder." Although that doesn't seem right, it is proved by shifting the motor leads to another axis and G320 - does the same thing - runs away. Tried the Y G320 on a known good axis - all good. Mach3 axis super quick shutdown (reset) via the limit switches saved a massive amount of damage in this situation.

So; why did a US Digital E2 encoder fail? Are these encoders worthy of purchasing a replacement or should these be changed to something better - another brand?  Or should I just go ahead and buy enough of them to replace them all as they fail? (that's a silly question right there)

Thanks, keeping the 'stimulus plan' working from this end,

Bill C.

Offline Chip

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Re: Missing steps in Y axis only
« Reply #9 on: February 21, 2009, 07:29:51 PM »
Hi, Bill

Glad you got it sorted out, Hard to say on the encoder, Defective, Damaged on install, Just try to keep them shielded and clean.

Gecko's do have some safeguards, If it see's more than 128 inputs pulses with no encoder movement thy err/trip out, But on re-set it's not seeing any input pulses, So it has no way to know, That's why you have that big red E-stop Button.

Chip