Is this really backlash ?

Discussions and help on this commercial controller.

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Re: Is this really backlash ?

Postby artofmystate » Thu Apr 19, 2012 4:49 am

Hey guys, I am going to reply back; I don't have the time this moment.
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Re: Is this really backlash ?

Postby Greolt » Thu Apr 19, 2012 5:16 am

Neil

I did a test which confirms that in my case there is no misalignment.

At least none that I can measure with the naked eye.

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Attachments
snake laser.jpg
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Re: Is this really backlash ?

Postby orcinus » Thu Apr 19, 2012 1:15 pm

Completely clueless about the subject (laser controllers), but considering the starts and ends of the cuts are *always* aligned, i see no way this could be backlash or missed steps.

If anything, it looks like a faulty look-ahead algorithm of some kind.

(DIsclaimer: clueless, as i've said, so take above with a grain of salt)
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Re: Is this really backlash ?

Postby iGull » Thu Apr 19, 2012 2:13 pm

Greolt wrote:Neil

I did a test which confirms that in my case there is no misalignment.

At least none that I can measure with the naked eye.

Greolt


Hi Greolt, no, as you say, your print looks fine. I'm assuming that you just rotated the piece of timber to take a pic - the cut was in Y yes? - and it started at the top left, went down to the bottom, across to the next snake and then up to the top again ?

The only thing different in your firmware is that you have an '8' as 8.12.04.01, mine is 7.12.04.01 - I bought it a few weeks ago - is yours recent ? I don't know what the significance of the 8 is - it would be good to know - Marco/Tim Wehr maybe ? Thanks for the trial.

@orcinus - yes, faulty algorithm, could be - how come it works in two other cases OK though ? But yes, I agree about it not being backlash. I just tried again the falling/rising edge setting for the stepper 'pulse' as requested by Marco (and Tim mentioned it earlier too) - just the same.

I'm working my way through the preferences, changing various things that may seem unimportant but might be :lol:

Be interested to hear from @artofmystate regarding his issues.

Cheers

Neil
EMOs are a sign of weakness ...
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Re: Is this really backlash ?

Postby iGull » Thu Apr 19, 2012 4:22 pm

Just a quick update, I rotated the snake pair 45deg and wrote it - perfect!
I then set up a file with four rotated snakes forming a diamond (I'll post pix later for those that are graphically challenged :-) along with a vertical and horizontal snake.
All four 45deg snakes are dead nuts on - width/height/diagonals/segments!
The vertical snake is off - segments mismatch and the length is 0.5mm short, the horizontal snake is also dead nuts on - this is all repeatable.

I put LaserCAD back to v5.88 and the firmware back to 120228V7.UG5 - with exactly the same results !

This cannot be backlash, is it something to do with v7 version of the board ???
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Re: Is this really backlash ?

Postby artofmystate » Thu Apr 19, 2012 8:08 pm

Here my hardware's information:

LaserCad v5.93
Main 7.12.04.01
LCD 5.11.12.06

Here's the results of the snake test using the original file with the exception of the power bumped to 20% to have the tube fire:

snake_test_2.jpg


I then ran the tests at various speeds and accelerations w/similar results: no massive backlash.

snake_test.jpg



I will work on a few other things shorty.
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Re: Is this really backlash ?

Postby artofmystate » Thu Apr 19, 2012 8:22 pm

Also, I ran another test using the same file I pictured earlier. Taking the advice to lower the accelerations, the results was the same: varying areas of backlash. (the areas of backlash matched the original pictured test)
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Re: Is this really backlash ?

Postby naPS » Thu Apr 19, 2012 8:30 pm

This sounds eerily similar to a problem I was experiencing about 6 months ago - and it actually did come down to backlash. From my post : (http://www.buildlog.net/forum/viewtopic ... 9&start=10)

"It looks like r691175002 was correct - it was *mostly* backlash! I'm shocked on this one!

The original pulley I had on there was out of round slightly, and replacing it made a pretty big difference in where the errors were occurring. But, even after replacing it, I was still getting some pretty decent wobble in my circles, and it was always flat spots on in the Y-direction, indicating problems with the X-axis not moving as much as it should.

I squared and re-squared. Checked and tightened everything. As a last resort, I said fuqit, and tightened the bejeezus out of the X-axis belt. I mean, it's so tight now I can almost pluck it like a guitar string. And guess what? No wobble whatsoever. My circles are perfect circles again, like they were before. I'm wondering if the belt that I have is past its useful life, and it's time to replace it, as I definitely didn't have to have it this tight before.

The other thing I did was flip which side of the carriage I was putting the belt through. Coming through on the top and folding it downwards allows the teeth to wrap-around the width of the carriage, and the connection there seems a lot more solid than it did before.

Thanks r691175002 - I'm glad I was wrong on this one!"
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Re: Is this really backlash ?

Postby iGull » Fri Apr 20, 2012 10:15 am

Tech_Marco wrote: If it worked out that way, that means something wrong with the machine itself, but not the DSP card (software and hardware). The making a 90 degree turn, the momentun from the motor is the greatest as it need to stop and lock itself quick then turn. The motor seems losing step and the only thing that it come to my mind is either the motor is bad or the current is low. Just my though
Marco


Hi All

Yes, I agree completely with you - the belts just need to be taut, not tight (if you get my drift :-))
I did some more testing late last night and changed the rectangular 'snake' for a snake made from arcs - problem showed up right away - at the start of a run - any direction, the arc was flat at the start - a sure sign of backlash.
I'm certain it's not mechanical backlash 'though, as my setup is extremely smooth and tight (I even tightened it up to 'naPS tight' LOL) - there is no problem in X - it uses a nema17 size motor for weight. I have a hi-torque nema23 in Y - however, the stepper drivers are keling 4020's - max 2A - I have the Y cranked up to max current, but perhaps I am asking too much of the wee 4020 and need something with a touch more 'beef'. The steppers are both brand new and seem to operate correctly, hold position well etc. They both run fairly warm as expected.
It has no problem moving the stage around. I wound all the speed an acceleration values right down to see if it would help, but it hasn't.
I'm going to order a new stepper driver with double the current and see where that leads ...

As an aside, artofmystate(Reuben) pm'd me his data - all cut perfectly (apart from my slight backlash issue) - nothing like his own results - hopefully he will get that sorted too.

I think I've convinced myself that it's not the LO controller, but I'm still going to swap it out for the lasersaur to try while waiting on the driver (painful :-))

Watch this space as they say.

Cheers

Neil
EMOs are a sign of weakness ...
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Re: Is this really backlash ?

Postby gavztheouch » Sat Apr 21, 2012 11:27 am

Image

Hi Neil,

My Lo DSP arrived yesterday and today I ran your test. I have a lot of backlash in my Y-axis around 0.4mm, which I measured with a dial test indicator. The test has shown up well over 1mm of offset in the snake which is over my measured backlash?
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