XYZ Gantry Build with Rotary Axis

Didn’t realize it has so long since I’ve posted any updates. Project is still ongoing albeit with a few glitches and obstacles. It's been pretty hectic between a family crisis or two, a virus I caught and changing employers along the way.

When I last posted I thought I had found the last of the issues causing me to loose steps on the Z axis. Well I was wrong. I did get it down to where the lost steps didn’t show up until a job was run for a considerable length of time. I was rearranging the motor cables in the e-chain and noticed it affected the next run. Assuming it was noise being induced I pulled the cables and put shielding over them. I re-installed them and the problem was the same.

Oh, along the way I ordered an Ethernet Smooth Stepper and installed it. The ESS install was a breeze and appears to work great. I initially had some issues with zeroing but upgrading my Mach install and using the latest plugin for the ESS solved that issue.

So I ordered some IGUS motor cables and installed them. I ordered the PVC jacketed stuff as opposed to the TFE stuff on the recommendation of the IGUS Rep AND the fact that the price was almost half. The PVC stuff is a little larger in diameter and it just fit in the cable chain, AFTER I removed the power cable to the router. So I will have to make other arrangements for it.
Well, replacing the motor cables did NOT solve my problem either. After many, many test runs, tweaking settings and motor tuning I could not get good results. My Z usually ends up above zero after the job but at some motor tuning settings it wold occasionally be lower? I don't know if this clearly indicates a noise issue or something else?

Anyway, I decided I had wasted enough time messing around with trying to trace this down considering the control box was temporary. I decided to just go ahead and re-do the control box. Not planning on having to do this yet it kind of left me in a lurch as to what to use for a control box.

I knew I wanted to seperate the power stuff from the logic stuff. Long story short I picked up a couple of old computer cases.

So, the current plan is to join the two computer cases with the power supplies, contactor, etc mounted in one box and the logic boards and motor drives in the other box. Initially I am only going to install enough to get the 4 axis moving and 'hopefully' verify operation. No frills to get in the way (meters etc).

That's it for now, I'll post some pics when I get going.
BobL.

Bob,
So glad to hear you are still alive.
I was beginning to wonder. ;-)
Sounds like life has been keeping you busy.
Hopefully everything is back on a even keel now.
So how much Z variation are you seeing?
Any chance you have backlash issues?

I am looking forward to seeing some picture of you new arrangement.

Not much happening here. Can't get at router right now. Got a couple of things piled in front that I need to dispose of. Office is just getting back to normal after Spring Cleanse. Still have lots of boxes to unpack and finish negotiations with Insurance.


As Winston said. KBO..

Dave

Quote:

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Originally Posted by dfmiller

So how much Z variation are you seeing?
Any chance you have backlash issues?

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After an hour or so of running a job the Z would be about 1/4" above zero.

I hope it's not backlash, but now that you bring that up I started to think back.

I didn't feel any movent in the Z before I mounted it, seems like the backlash issues you and Will had were obvious in that manner.

I was going try to do some specific measurements to determine if it was backlash but thinking back I can't explicitly remembering getting valid info for that. By the time things settled down my ESS and cables were here and I set about getting them in, hoping it would help. Ran a few tests after that with no change.

Oh yeah, the PC PS I was using in the control box smoked and took out a couple of meters but fortunately nothing esle was damaged (as far as I can tell). Bottom line is I will take some measurements to try to see if backlash is the culprit.

I'll let you know what (if anything) I find out.

BobL.

Bob,
A quarter of an inch.
Crike.
That's 2500 steps lost.
You have a serious issue there.
Have you chatted with Steve at PMDX? I would be looking at setup of the Mach XML and hardware issues for sure.
That's not backlash for sure.

Dave

Well, that 1/4" was after a ton of Z movements.

My measurment tools consist of a handfull of dial indicators (0.001") and some digital calipers/depth gauge but the actual movement measured over 1 inch of travel is equal to the desired movement, at least as near as I can tell with these tools.

Still working on trying to get some coherent backlash measurements.

Right now I'm paying the price for throwing together that control box that I know was not optimum (to say the least). Hard to get too critical with all the potential issues in play. So I'll work on the control box.

Backlash is another problem entirely and I need to rule that out if possible. The thing that sticks in my craw is that with all times I altered the motor tuning settings I couldn't find any setting that was right on even when setting the velocity and acceleration very low. The ESS and good motor cables had no effect so I'm hoping it's in the box.

BobL.

Bob,
Got time for a phone discussion on this?

Is your number the same?

Dave

Yep, give me a call :)

It's not backlash. Backlash isn't cumulative, so even if you have 1/4" of backlash, it will still return to zero, provided you return there from the same direction that you used when you first measured.
By moving to a SmoothStepper, I would have though that any Mach3 issues would be eliminated.

What is your acceleration set for in the Z axis? Most of the time, the Z gaining position is due to the acceleration being too high.

Other than that, the only other culprit would be some electronic issues.

Ok, Dave and I just had a nice chat and at this point we do not believe backlash is the culprit.

This is good news to my ears.

So, I will continue with construction of the new box (as soon as I make room in the garage to work on it :) )

BobL.

Quote:

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Originally Posted by ger21

It's not backlash. Backlash isn't cumulative, so even if you have 1/4" of backlash, it will still return to zero, provided you return there from the same direction that you used when you first measured.
By moving to a SmoothStepper, I would have though that any Mach3 issues would be eliminated.

What is your acceleration set for in the Z axis? Most of the time, the Z gaining position is due to the acceleration being too high.

Other than that, the only other culprit would be some electronic issues.

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Gerry, I agree with everything you've said. My first though on the backlash was that it shouldn't be cululative but with the other guys problems in that area I wanted to confirm it myself.

As far as the Z acceleration I can't give you numbers but I can tell you I tried everying from V=100IPM / A= 15% down to 2 or three percent and then with V= 30IMP and acceleration set from 5 to even lower and lots of places in between. A points the Accel was so low it would drift to a stop. I know that not good/accurate info to go on, but through all of that the error was always similar (I say similar because I just eye-balled it after the run). I would think it should have changed in there somewhere, or at least it's a would be a big clue staring me in the face I don't recognize.

BobL.

Any chance the Z axis is binding, or the couplers are moving?

I don't think the Z is binding, plus I wouldn't think that would have the concistency displayed.

The coupler isn't moving. I marked it first off way back. It hasn't moved.

I started out with POS motor cables from the big box store. 18ga. with foil shield. Suspected them first off. Removed them, put braided sheilds on them, re-ran them, problem the same. I have replaced them with Igus 16ga. PVC jacketed motor cable at the reps recommendation. Problem exactly the same.

I started out with PP cables. Changed them. Have since replaced them with an Ethernet SmoothStepper. First had a cat5 unsheiled cable connecting them, then a nice sheilded cable. Same results both times.

I even wrapped all the ribbon cables in the control box with aluminum foil and grounded it. No change (since removed).

I have removed everyting in the control box except that needed for movement (the SuperPID is still in there). No change.

I've tried motor tuning, pulse stretching, Sherline mode, half stepped them, 10 micro-stepped them, verified motor wiring, verified pulse setting with the geko manual, swapped drives, and other stuff I'm sure.

I'm stumped. Please keep asking though as you never know which question will be the right one.

BobL.