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Author Topic: Losing Steps?  (Read 4010 times)

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Losing Steps?
« on: September 16, 2010, 03:17:29 PM »
I have my small router up and running with a new computer.  My problem is that whenever I run something ( 5 minute program) and return the machine to zero, the gantry has moved about .003 " to the positive in x.  The larger the program, the more this shows up.  I intended the router to cut lithophanes, so you can see that a 6 hour program will probably add up to a great difference.  The odd thing is that it always moves towards positive x.

I have played with different setting, and the best scenario is Sherline1/2 pulse at 25,000 kernel speed with 1/32 microstepping.  Lowering the microstepping, raising the kernel speed, or using the standard pulse setting greatly exacerbates the problem (anywhere from 2-5 times the distance).  My machine is using Keling 4030 drivers and 36v supply with Keling 495oz Nema 23 steppers.  I guess it seems strange to me that it is never off the negative way.....it always misses steps in one direction? 

I'm not using shielded wire for the steppers.

My look ahead lines are set at 200, and my feed rate is at 50 with a rapid of 250.  My drive ratio is 1.19 inches per turn and steps per inch are 5368....velocity is 250 with acceleration of 20.  Changing acceleration doesnt change a thing......I went way slower and way faster. My cv setting is 1.

Any Ideas?
Re: Losing Steps?
« Reply #1 on: September 16, 2010, 03:32:04 PM »
Maybe you could try to increase the step and direction time in uS, try with 5uS.

Also is they're some number after 5368 steps per inch, try to put a couple of decimals after dot.

Jeff

Offline GeorgeRace

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Re: Losing Steps?
« Reply #2 on: September 16, 2010, 07:41:08 PM »
I am not sure but wonder if using non shielded wires is causing your problem.  I had a lot of similar problems when I first built my setup.  Using shielded wire solved all of my problems.  Sounds like increasing the pulse width increases the error distance, which could indicate that something is picking up a stray pulse causing an error to occur.
George
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Re: Losing Steps?
« Reply #3 on: September 16, 2010, 07:55:57 PM »
Increasing the time had no real effect.....I tried every number between 0-5. 

 I can't imagine how a finer number for steps per inch could affect anything, either.  Even if the calibration was way off, the motors still work in units, and 20 units out and 20 back still brings you home.  Am I missing something here?  Wouldn't surprise me too much if I was.....lol.

I  will give the shielding  a go......I actually have it on the machine, I just haven't connected the drain yet. John at Keling said I shouldn't need it, but I see no reason not to try it.

Offline Hood

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Re: Losing Steps?
« Reply #4 on: September 16, 2010, 08:05:46 PM »
Backlash?
Hood

Offline Dan13

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Re: Losing Steps?
« Reply #5 on: September 17, 2010, 05:34:06 AM »
Are you using a breakout board? If it has optos, they might be slow or have a bad timing for outputting the direction change pulse. Trying to connect the PP directly to the drives will show if the problem is in the breakout board.

Try checking the Active Low for the step pulse.

If it's a consistent lose of steps and only in one direction, then I'd doubt it has something to do with shielding.

Dan

Offline RICH

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Re: Losing Steps?
« Reply #6 on: September 17, 2010, 06:11:30 AM »
Suggest you swap the cables and see if the problem is duplicated on the y axis.

I get the feeling that it may be mechanicaly related to the x axis due to a combination of backlash, axis system , and infuenced by velocity.

RICH
Re: Losing Steps?
« Reply #7 on: September 17, 2010, 11:05:30 AM »
OK.....I'm trying to wrap my head around the logic for some of these suggestions.

If my problem is mechanical.....back lash, etc......why does the amount of disparity between the DRO's and actual measured home position change dramatically when going from sherline 1/2 pulse to standard pulse?  .002 in sherline mode......and .015 in standard.  If its mechanical, shouldn't it remain consistent since I'm not changing anything mechanical?

Dan13.......what is a PP, and how do I go about checking your suggestion?

I'll try the cable swap idea.

Offline RICH

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Re: Losing Steps?
« Reply #8 on: September 17, 2010, 03:12:10 PM »
If you swap the axis, and the problem  is not mechanical, then you will see the problem go to the Y axis.
Note that you have implied that there is no problem with the Y axis.

RICH
Re: Losing Steps?
« Reply #9 on: September 17, 2010, 03:49:45 PM »
I changed the Dir step pulse width to 0 in the Sherline mode (formerly 1) and now it is dead on.  I ran a 50,000 line program in the air to double check, and it ended up .001 off.  I'm ok with that.