Laser jumping on the Y axis randomly...

[David Borneman]

Hi Guys,

First off let me say I am new here - and new to lasers in general. I have only owned one since January, and while I have hundreds upon hundreds of hours of cut time since then, in many ways I am still a noob and I know for sure there are very very simple things that I do not know yet (and should!)... so please keep that in mind if you see the issue but it seems to simple an answer to mention (lol).

As a preface, let me give you just a little background on the laser. Its a bogong 1325 - 100W CO2 machine with a 2500x1300 bed. It has the RD6445G-LM(EC) controller, and uses YKD3505M-DK-B1 stepper drivers to run KDE brand 57-H350C motors. To complicate issues, the Y axis uses 2 drivers and 2 motors to drive the gantry.

Now, have have several issues with this laser, but the one I am addressing here is a seemingly random jumping in the Y axis. I can cut entire sheets without the issue happening at all... and then sometimes it happens multiple times in short order. I have not yet caught it on video (I am working on that) due to its randomness, but I have the after pics

First off, here is a pic of a "single" cut (2 rows of product) with no spacing between:

20210711_051447.jpg

That cut went perfect. no slippage anywhere. I know it appears to not be cut thru, but it is. One little tap and it all falls apart

Now, here is a closeup of where the first of 2 slippages in this run happened:

20210711_022801.jpg

now, when that happens on a "no waste" cut (e.g. there are no spaces between one row and the next), this happens:

20210711_022811.jpg

That results in a loss of that entire row.

Now, I can "prevent" this by spacing rows with 2mm+ of acrylic between rows, which works if the slippage happens in the right direction (or if the slippage is less than 2mm)... but results in a lot of waste material, especially when we are talking about dozens of 2451x1231 sheets.

So... now you know what it's doing... what I have done to investigate this is: cleaned the entire machine. Re-oiled/greased as needed. Checked all the belts and made sure they are tight and not missing any teeth, and the motors are not missing any notches and no obvious wearing on either. Honestly besides all that I have no idea what the next step should be.

As I understand it (and I am very much a beginner, so I might well be overlooking something simple), the problem almost surely resides in either a motor that is malfunctioning or the associated stepper driver messing up. Since this is happening on the Y axis (it may have also happened in the X axis in the past, but if so I do not have photos), it could also be a sync issue between the paired motors. none of that helps me figure out which it is tho... or what to do about it.

Now... I know these parts are cheap chinese made things.... and I am not opposed to replacing them with better, higher quality, parts. Just have no idea where to start

So... let the flaming begin!

[Jeffrey Aley]

Interesting problem. How often does it happen (one in ten times, one in a hundred...) ? You'll want to have this info to determine if the problem is improving or getting worse when you make analog changes.

You have a large (and presumably heavy) gantry. So my hypothesis is that the programmed acceleration is a bit too high. Try reducing it a bit and see what happens. Reduce both the Idle Acc and the Max Acc. You may wish to also reduce the Idle Speed. These are all accessed in the upper-right corner of RDWorks under the USER tab, and the Processing radio button.

Remember to first READ the values from the laser, then SAVE the original values to a file. Make your experimental changes, and then WRITE the values back to the laser. By the way, on my screen, the OPEN, SAVE, READ, ... buttons were not visible. There's a boundary between the USER area and the Laser Work area below it. I had to move the boundary down in order to see the buttons.

Screen pics are available upon request.

Regards,

-Jeff

[Dave Vigness]

My first question is are the two sides of your Y axis physically linked. If not, you are asking for trouble. On a bed that large, the Y axis should be on a solid drive.

My next is wondering why two drivers for one axis? Or are the drivers not strong enough to handle two motors? If so, poor design.

I want to hazard a guess in that it's missed steps, but with your set up, if you do indeed have separate drive on each side, could be very complicated to diagnose.

How was your skew test on that big bed?

[Gene Uselman]

Have you tightened the 'grub' screws [set screws in the US]- sometimes the chicoms put in two screws in the same bore so pay attention to how deep your wrench goes into the gear/pulley. It looks like you do not recut lines that overlap which saves time but if the problem persists you might be able to salvage more of the pieces without that feature?

[David Borneman]

Interesting problem. How often does it happen (one in ten times, one in a hundred...) ? You'll want to have this info to determine if the problem is improving or getting worse when you make analog changes.

You have a large (and presumably heavy) gantry. So my hypothesis is that the programmed acceleration is a bit too high. Try reducing it a bit and see what happens. Reduce both the Idle Acc and the Max Acc. You may wish to also reduce the Idle Speed. These are all accessed in the upper-right corner of RDWorks under the USER tab, and the Processing radio button.

Remember to first READ the values from the laser, then SAVE the original values to a file. Make your experimental changes, and then WRITE the values back to the laser. By the way, on my screen, the OPEN, SAVE, READ, ... buttons were not visible. There's a boundary between the USER area and the Laser Work area below it. I had to move the boundary down in order to see the buttons.

Screen pics are available upon request.

Regards,

-Jeff

Not sure how to quantify how often it happens. Enough to cause me problems lol... but not on every sheet I cut. Once every 8 hours of operation maybe? Main problem is if it happens near the end of a row, nobody would even notice until we are doing QA on the parts, and then the bad parts are just discarded... our production schedule is so heavy right now that looking at every single part of each cut is just not feasable (while its still on the bed). Part of the problem is mine - lack of time. I have simply not had time to deal with it, so I have been ignoring it and moving on... until now. I have just now set up a gopro to record every cut for the next couple days so i can see and hear whats happening when these slips happen... perhaps that will give a clue, and I can record when they happen to get a better idea of how often they happen.

For the Acc numbers, we are using default values set by the seller. We actually did tinker with these way back in Feb, but doing so broke something (lol) so we had them connect and reset everything to their defaults. And to be honest I have no idea what all those values do... which is another reason I have not touched them. (I do have a lot to learn!)

My first question is are the two sides of your Y axis physically linked. If not, you are asking for trouble. On a bed that large, the Y axis should be on a solid drive.

My next is wondering why two drivers for one axis? Or are the drivers not strong enough to handle two motors? If so, poor design.

I want to hazard a guess in that it's missed steps, but with your set up, if you do indeed have separate drive on each side, could be very complicated to diagnose.

How was your skew test on that big bed?

Not sure exactly what you mean... ill include pics of my laser and the associated hardware here:

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20210711_232046.jpg

20210711_232051.jpg

20210711_232058.jpg

20210711_232104.jpg

20210711_232117.jpg

20210711_052510.jpg

20210711_202010.jpg

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Keep in mind I am very VERY new to this... so I said it has 2 drivers for the Y, but that was an assumption I made based on the pic of the drivers above.

And... I have decided to enter the "stupidest question of the day" pool with: What is a skew test? (be gentle!)

Have you tightened the 'grub' screws [set screws in the US]- sometimes the chicoms put in two screws in the same bore so pay attention to how deep your wrench goes into the gear/pulley. It looks like you do not recut lines that overlap which saves time but if the problem persists you might be able to salvage more of the pieces without that feature?

Set screws in what exactly? for the belts? Yes. We did tighten the belts... but my knowledge on this stuff and its terminology is very limited (sorry about that!).

current laser user settings.RDUSet

There are my current user settings... in case that is helpful.

[Dave Vigness]

Nice machine!

Can't quite tell from the pics. Is there a shaft connecting the two Y drive motors in any way? If not, you can loose a step on one and not the other and actually create a skew problem. Not sure if that relates directly to your current problem, but certainly something to take a closer look at. Not sure from the original pics, but it looks like the problem gets worse as you go across.

[Gene Uselman]

As to the grub screws- yes each motor and cross shaft and the gearing will have a pulley [for toothed belt] and each of those will be fastened to it's shaft [or motor] with a grub/locking screw. It appears that for the Y axis you have a hefty cross shaft from end to end of the gantry- which probably drives a toothbelt to power the gantry back and forth. My caution is sometimes they put a second grub screw behind the first on to lock it in place.

I took a screenshot of your picture with the step errors and... I am assuming that that was all in one messed up cut? Again, I am assuming it is cutting from left to right and top to bottom? The translucent yellow is the first step error which on my screen is .1, the second step error is .3 [green translucent]?

How far off am I in my assumptions? Not the actual .1 dimension, but the cut pattern and all being one cut job.

.

David cut issue.jpg

[David Borneman]

Nice machine!

Can't quite tell from the pics. Is there a shaft connecting the two Y drive motors in any way? If not, you can loose a step on one and not the other and actually create a skew problem. Not sure if that relates directly to your current problem, but certainly something to take a closer look at. Not sure from the original pics, but it looks like the problem gets worse as you go across.

No, there is no shaft connecting the 2 sides. Each appears to be independently driven... but the way the gantry is connected to the base (ill get pics later) is via a very secure looking rail system that would not take well to the gantry being even a micron out of alignment (I would guess). I am cutting now, but will get pics of the rails it sits on after its done.

As to the grub screws- yes each motor and cross shaft and the gearing will have a pulley [for toothed belt] and each of those will be fastened to it's shaft [or motor] with a grub/locking screw. It appears that for the Y axis you have a hefty cross shaft from end to end of the gantry- which probably drives a toothbelt to power the gantry back and forth. My caution is sometimes they put a second grub screw behind the first on to lock it in place.

I took a screenshot of your picture with the step errors and... I am assuming that that was all in one messed up cut? Again, I am assuming it is cutting from left to right and top to bottom? The translucent yellow is the first step error which on my screen is .1, the second step error is .3 [green translucent]?

How far off am I in my assumptions? Not the actual .1 dimension, but the cut pattern and all being one cut job.

.David cut issue.jpg

ok, so - in that pic you see the 2 rows of product, with the top row having a upper and lower bound cut, but the bottom row having only a lower bound cut with the top cut missing - because it is supposed to be a shared cut line with the top row of product. The top row cuts left to right, then the next row cuts right to left - like this:

Capture.PNG

There were multiple slips on that run. I counted 2.... but there may have been a 3rd. I may well have missed it. And if so, then it would mean we are slipping .1 per slip. If there were only 2, then it means the slippage amount is also not static... not sure what that would mean honestly lol. Looing at mypics, I only took closeups of the messed up cut. In future ill snap the entire cut as well so I can go back and go over it better.

[Gene Uselman]

What I found odd was the step error on the upper right cut does not seem to have been passed on to the next row- that one is even all the way across- it also has a step error but it is different from the row above. You have a very unusual problem there my good sir. I am going home now- talk tomorrow.

So you did not set up this file? I understood you were originating these parts. The machine is new to you but the cut file was from something else. Just trying to understand all the possible issues. I talk to a lot of people on the forum and sometimes have trouble keeping all the details straight.

[David Borneman]

I did set it up. My methodology for doing so is based on a number of lessons learned from this laser.... with the biggest one being that sometimes a cut piece will not fall thru, but rather be stuck between one of the slats that the sheet sits on and one of the crossbars that support the slats, resulting in a piece that starts to fall, but is caught... and if its caught at just the wrong angle, the other side can pop up above the plane of the material to the point where if the laser head crosses that position again it will get caught and can potentially drag the piece (and the entire sheet of material) out of position, or even catch up the head so that the machine loses steps and forgets where its at (x,y), causing all sorts of problems. My "fix" for this is to manually create each cut file so that each piece is cut individually (engraving, then cutouts, then border) and then the laser moves to the next item... at the end of the row the laser moves down before starting cutting the next row of items, so it never traverses over previously cut pieces until the entire cut file is complete - when it will move back to origin (no way to stop that I have found).

I am working on that particular problem by having a custom bed made for the laser that will hopefully prevent it from happening... but we are having some technical issues with it, so its not done yet

And yes... creating a cut file manually piece by piece is a right pain in the bum. I do have some sortcuts... for instance, those 2 rows I pictured above... I created another exact duplicate of that excepting that the top bound cut line is removed, so I can drop that in and just duplicate it x number of times until the sheet is full. Even so, it takes hours to create the files (and we have thousands of parts that need cut like that lol).