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GoTo Z fails if hit 2nd time
« on: December 03, 2006, 04:39:33 PM »
Hi All,

Working through some tuning and cutting issues that have been lingering for a while, and have one that I'm shaking my head at. It's probably due to ignorance on my part.

When I fire up the machine, Ref All Home (all axis go to machine zero just fine), then select my appropriate offset (say G56) and then hit GoTo Z, the machine rapids to the correct location determined by G56 (Say X6.0, Y2.0, -Z8.5). Cool.

Now, if I do a cycle start or simply jog X or Y away from G56 and hit GoTo Z, the machine does just that. However, if I do not Cycle Start or jog an axis, and Hit GoTo Z, the machine begins the GoTo Z process by going to Machine Z0, but once it arrives, it simply stops there (hitting the limit switch) and the Z DRO keeps counting to Zero where upon the machine stops totally (triggering a Reset I think). The X and Y never budge toward their G56 zeds.

I know how to avoid this by not hitting GoTo Z twice, but this can't be right. Anyone have any ideas what I'm doing wrong? Or do I possibly have the machine setup incorrectly? It certainly seems to operate as desired in other respects.

Thanks for your thoughts!!

David

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Re: GoTo Z fails if hit 2nd time
« Reply #1 on: December 03, 2006, 06:32:29 PM »
David:

 What do you have selected in the config/Safe_z dialog..?

Art
Re: GoTo Z fails if hit 2nd time
« Reply #2 on: December 05, 2006, 07:54:13 PM »
Hi Art,

Sorry not to have gotten back to you sooner. Life has a way...

In Config/Safe Z Setup, I have Allow Safe-Z Moves checked and the SafeZ DRO is in Machine Coordinates. Safe_Z is at it's deafult 0, and Goto SafeZ when Stop is Hit is unchecked.

I do have Auto Limit Overide checked, but nothing else that should effect the Z moves that I'm aware of.

Thanks a bunch for your attention.

David

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Re: GoTo Z fails if hit 2nd time
« Reply #3 on: December 05, 2006, 07:56:49 PM »
Ahh, OK, one final question, how are you selectin gyour G56, MDI Gcode or a button?

Thanks
Art
Re: GoTo Z fails if hit 2nd time
« Reply #4 on: December 05, 2006, 08:28:13 PM »
I have been going to the offsets page, clicking "Fixture 3" (for G56), then then returning to Program Run page. If I need to tune the offset, I go to Config/Fixture. If need a different offset for a different setup, I'll go back to the Offsets page and select G57 or whatever.

Am I abusing the concept offsets??

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Re: GoTo Z fails if hit 2nd time
« Reply #5 on: December 05, 2006, 08:55:41 PM »
Nope, I just needed to know where I forgot the sysnc.. Ill fix it up..

Thanks
Art

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Re: GoTo Z fails if hit 2nd time
« Reply #6 on: December 05, 2006, 09:04:23 PM »
Hi:

 Nope, still cant repeat this one.. DO me a favour and switch to machine coordinates , where does it go to? Does it count to zero (at which point it hits the switch? What ahppens if Safe_z is set to .25 or something (which woudl set it .25 down from the switch..?

Thanks
Art
Re: GoTo Z fails if hit 2nd time
« Reply #7 on: December 05, 2006, 09:15:57 PM »
OK. I'll need to go to the shop and test this one, so it'll be tomorrow midday before I have an answer. I'll get back to you then.

Thanks again Art!!

David
Re: GoTo Z fails if hit 2nd time
« Reply #8 on: December 08, 2006, 07:11:38 PM »
Art,

This has turned out to be a bit more detailed than I first thought. What's the old saw about devil and details...

Anyway, I will try to closely describe the behavior:

I find that a jog of more +/-.01" or more off of a chosen offset (say g58) in X or Y will allow a correct GoTo Z.  A movement of .001" is NOT enough to allow a successful GoTo Z. A movement in Z ONLY of any amount (.001" - 6.000"+) will not allow a successful GoTO Z. Obviously, the only way to recover is to do a Ref All.

Machine coordinates or Offset coordinates, the behavior is the same.

When a GoTo Z succeeds, the Z rises to machine Zero (moving from say -4.321 up to 0.000), the DRO stops at 000, all Z servo rotation stops, the X & Y go directly to their respective Offset zeros, then Z goes to its offset zero. Success.

When a GoTo Z fails, the Z approaches machine Zero, (moving from -4.321 toward 0.000) but the DRO does not stop at 000 (I can't actually detect it--too quick). Rather it immediately tries to return to Offset Z zero (which it shlould) but machine does not move. Rather the servo continues to "click" moving the belt about 1/2", then snapping back. It does this about every 1/2 second or so. Is the Z up against the stop? NO. I can move the Z past machine Zero another 0.018" before triggering a Reset, and still be off of the hard-stop.

To continue the story from the first Z servo "click", the Z will continue its click and short movement until the Z DRO returns to its selected offset Zero. Once the DRO does agree with offset zero, MACH is happy, but of course, the machine is totally out of sync with where Mach thinks it is.

Its like the Z must pause some minimal amount of time (e.g., enough time to move the X 0.010") so the Z knows how to continue, or the servo can pause long enough to reverse or... I know that makes no sense (the Z serve reverses direction in every other situtation. Indeed, I've run the system through many minutes of X, Y & Z and it returns to a known zero dead-on).

As per your request, I entered -0.25 in the Safe_Z field. Restarted Mach, Ref All, Goto Z, and then Goto Z again. The machine goes to about 1/4" shy of the limit switch and stops. But the Z DRO counts back toward Offset Zero and the servo is clicking every 1/2 second. And BTW, I get an error message "Safe_Z ignored, Z already higher than Safe_Z setting" with the -.25 in the Safe_Z field. It does not throw this error with 0 in this field.

Anyway, this is what I think I know at this point in time. I hope I have explained in sufficient detail that you can grok what I am seeing here. FYI, I'm running 2.020.

Thanks Art!!

David
Re: GoTo Z fails if hit 2nd time
« Reply #9 on: December 12, 2006, 08:27:18 PM »
Art,

Any further thoughts on the described condition?

Could I have a subtle motor/gecko tuning issue that would show up in this fashion?

Thanks for your energy on this!!

David