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Offline mhdale

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Losing Position
« on: June 01, 2006, 04:28:46 PM »
Hello Everyone I have an issue I am trying to fix. I have a system which appears to be working well but during a large job it lost position on the Y axis by .2108 Inches. WHich by My Stardards is Waaaaay Out there. I have been trying to trouble shoot where exactly it lost position and what may have caused it. To date I havent noticed any other jobs losing position by that much so I am baffled why it would do so now. I am running some tests trying to re-create the problem so I know If got it.... I dont feel like risking another $500 chunk of aluminium to cross my fingers. But It seems that sometimes My Verify Does not function like it normally does. Worse case I want to be able to verify I am not out of position by pausing and verifying my position.but sometimes... not allways when I hit Verify it travels up to top of Z and then just goes back down and I dont get any Relavent feedback.... I havent noticed a pattern as to why or when this occurs so I am really at a loss... Anyone out there with any suggestions?

Mike
Re: Losing Position
« Reply #1 on: June 01, 2006, 06:12:16 PM »
What do you have for a drive system (drives, motors, type of drive)? This will start to tell us where we should be looking for the missed steps...
Fixing problems one post at a time ;)

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Offline mhdale

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Re: Losing Position
« Reply #2 on: June 02, 2006, 01:10:15 PM »
Brian,
 I am running a Custom Built Stepper system running Pacific Science stepper drives & Motors with Mach 3 running on a P4 2.4G with 512 Ram and nothing else. I did have the screensaver on (Dont know why).
My big concern is that I have been unable to duplicate the problem, I.E. I have run a condensed version of the same program with less depth cuts and at a much faster feedrate to try and see if there was a motor setting or something and I cannot get it to lose position....also I cannot see any part of what it did machine where it might have gotten caught up .. everything looks perfect except that it gradually lost position on the Y axis....
Can you shed any light on the verify position behavior? If I can count on the verify position I can step through the job one section at a time.... painfull but at least I can get it done.
Thanks in advance
Mike
Re: Losing Position
« Reply #3 on: June 02, 2006, 04:01:49 PM »
What do you have for a pulsewidth under the motor settings? You may need to send a longer setp pulse for the drives...
Fixing problems one post at a time ;)

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www.machsupport.com

Offline mhdale

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Re: Losing Position
« Reply #4 on: June 02, 2006, 06:42:38 PM »
Pulse width is set to 4. But would that not show up all the time? What sort of symptoms would having a pulse width to short have on the overall accuracy of the system? This one has me stumped and very nervous about doing large jobs.....
I do appreciate your assistance and insight and anything I mean anything you can think of which might explain why it would lose position over a long job as opposed to same job cutting air with much higher feeds rates and less depth cuts...which I would think would tend to exacerbate the loss of position.. but did not.

Cheers

Mike

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Offline mhdale

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Re: Losing Position
« Reply #5 on: June 02, 2006, 09:17:02 PM »
Brian,
 If you Interrupt a program can you do a verify position without screwing anything up? Is that possibly whay it seems to not want to run the verify?
Mike

Offline ART

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Re: Losing Position
« Reply #6 on: June 02, 2006, 11:11:33 PM »
Hi:
 The only condition I can think of where verify will lift and immediately drop again, is when the system senses that there was home ref done since turnon.
The Z lifts to prepare fo rthe move to home. If it then senses no legal home position has been set, then it will simply dop again. Is it possibel that the homing was not done in that session, perhaps the program was started up and zeroed to the work for a run, but hjoming to the switches was not done?


  I agree with the position being way to far off, .2 inches is way to far in anyones books. :) , but looking in the code, the only possability woudl seem to be that the homing was determined to be not sone prior to verify, or the home switches sensed as inactive.

  If in you rposition, Id run some tests to see if I could track it down. First, single axis tests.. 100 rep's of G0X10, G0x0 and makie sure it returns to zero. Repeat on each axis. Then I do 100 rep's of G12I10 with the tool zeroed in the center of the table. Does it come back to perfect zero?

 These tests usually help track this type of error down.  Let me know how you do.

  If the program senses it woudl be wrong to do a verify, you wont get the Z lift in preperation, so I think your in an OK condition when your trying to do it.

Thanks
Art

Offline Chip

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Re: Losing Position
« Reply #7 on: June 03, 2006, 02:44:48 PM »
Hi, Mike

You mentioned that, " I did have the screensaver on (Dont know why)" this has cause problems for me in the past, Turn it off.

If it goes to sleep the wake up can cause lost steps.

Thank's, Chip
Re: Losing Position
« Reply #8 on: June 04, 2006, 12:51:26 PM »
Hi, How about stepper resonance problems at certain feedrates?

Kind Regards
CJ

Offline mhdale

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Re: Losing Position
« Reply #9 on: March 12, 2007, 08:26:24 PM »
CJ Note sure I know exactly how to tell if it is a stepper resonance problem....

Just an update on this problem I think my problem went away for a while, or I just havent had time to really delve into things, because of issues with the cnc we have not been using it as much as I would like.... However I have had some projects recently which have forced me to re-examine things again, so Im back at it and I have noticed the machine losing position a tad, I am just running a pretty long file and I will check at the end to see what I have lost. Now I am pushing my machine and I am sure I can slow everything down so that I never have to worry, but whats the fun in THAT!? There is NO reason I should need to run my system super slow... is there? In response to the inevitable question what type of machine it is a modified Red/Cam gantry CNC with Pacific Scientific nema 34 Steppers and drives the CNC 4PC breakout baords and a P4 2.8 G with 1 Gig of ram running mach .. spindle is a columbo 5hp ATC I am runing the MACH QUANTUM and I am loving the cutting speeds I can get with it. I am just concerned by the system seeming to loose position. I have double and triple checked motor settings and tried varous kernel settings. I seem to loose more steps with the kernel running at 45K as opposed to 35K without changing any settings. And when I try doing tests as ART suggests i cant seem to get it to lose position unless I ask it to do crazy things which will stall the motors..... is it possible its a PC problem?
 

Cheers
Mike